bims-mibica Biomed News
on Mitochondrial bioenergetics in cancer
Issue of 2021‒10‒03
fifty papers selected by
Kelsey Fisher-Wellman
East Carolina University

  1. EMBO Rep. 2021 Sep 30. e52727
      The classical view of oxidative phosphorylation is that a proton motive force (PMF) generated by the respiratory chain complexes fuels ATP synthesis via ATP synthase. Yet, under glycolytic conditions, ATP synthase in its reverse mode also can contribute to the PMF. Here, we dissected these two functions of ATP synthase and the role of its inhibitory factor 1 (IF1) under different metabolic conditions. pH profiles of mitochondrial sub-compartments were recorded with high spatial resolution in live mammalian cells by positioning a pH sensor directly at ATP synthase's F1 and FO subunits, complex IV and in the matrix. Our results clearly show that ATP synthase activity substantially controls the PMF and that IF1 is essential under OXPHOS conditions to prevent reverse ATP synthase activity due to an almost negligible ΔpH. In addition, we show how this changes lateral, transmembrane, and radial pH gradients in glycolytic and respiratory cells.
    Keywords:  IF1; Mitochondrial F1FO ATP synthase; local pH measurements; proton motive force; ΔpH
  2. Int J Mol Sci. 2021 Sep 17. pii: 10027. [Epub ahead of print]22(18):
      The Warburg effect is important for cancer cell proliferation. This phenomenon can be flexible by interaction between glycolysis and mitochondrial oxidation for energy production. We aimed to investigate the anticancer effects of the pyruvate dehydrogenase kinase inhibitor, dichloroacetate (DCA) and the mitochondrial respiratory complex I inhibitor metformin in liver cancer cells. The anticancer effect of DCA and/or metformin on HepG2, PLC/PRF5 human liver cancer cell lines, MH-134 murine hepatoma cell lines, and primary normal hepatocytes using MTT assay. Inhibition of lactate/ATP production and intracellular reactive oxygen species generation by DCA and metformin was investigated. Inhibition of PI3K/Akt/mTOR complex I was evaluated to see whether it occurred through AMPK signaling. Anticancer effects of a combination treatment of DCA and metformin were evaluated in HCC murine model. The results showed that metformin and DCA effectively induced apoptosis in liver cancer cells. A combination treatment of metformin and DCA did not affect viability of primary normal hepatocytes. Metformin upregulated glycolysis in liver cancer cells, thereby increasing sensitivity to the DCA treatment. Metformin and DCA inhibited mTOR complex I signaling through upregulated AMPK-independent REDD1. In addition, metformin and DCA increased reactive oxygen species levels in liver cancer cells, which induced apoptosis. A combination treatment of metformin and DCA significantly suppressed the tumor growth of liver cancer cells using in vivo xenograft model. Taken together, the combined treatment of metformin and DCA suppressed the growth of liver cancer cells. This strategy may be effective for patients with advanced liver cancer.
    Keywords:  REDD1; Warburg effect; liver cancer; mTOR complex I
  3. J Clin Invest. 2021 Sep 30. pii: e152911. [Epub ahead of print]
      Emerging evidence has shown that open reading frames inside lncRNA could encode micropeptides. However, their roles in cellular energy metabolism and tumor progression remain largely unknown. Here, we identified a 94-amino acid-length micropeptide encoded by lncRNA LINC00467 in colorectal cancer. We also characterized its conservation across higher mammals, localization to mitochondria, and the concerted local functions. This peptide enhanced the ATP synthase construction by interacting with the subunit α and γ (ATP5A and ATP5C), increased ATP synthase activity and mitochondrial oxygen consumption rate, and thereby promoted colorectal cancer cell proliferation. Hence, this micropeptide was termed as "ATP synthase associated peptide" (ASAP). Furthermore, loss of ASAP suppressed patient-derived xenograft growth with attenuated ATP synthase activity and mitochondrial ATP production. Clinically, high expression of ASAP and LINC00467 predicted poor prognosis of colorectal cancer patients. Taken together, our findings revealed a colorectal cancer-associated micropeptide as a vital player in mitochondrial metabolism and provided a therapeutic target for colorectal cancer.
    Keywords:  Colorectal cancer; Gastroenterology; Noncoding RNAs; Oncology
  4. J Cell Biol. 2021 Nov 01. pii: e202103122. [Epub ahead of print]220(11):
      Mitochondrial function is integrated with cellular status through the regulation of opposing mitochondrial fusion and division events. Here we uncover a link between mitochondrial dynamics and lipid metabolism by examining the cellular role of mitochondrial carrier homologue 2 (MTCH2). MTCH2 is a modified outer mitochondrial membrane carrier protein implicated in intrinsic cell death and in the in vivo regulation of fatty acid metabolism. Our data indicate that MTCH2 is a selective effector of starvation-induced mitochondrial hyperfusion, a cytoprotective response to nutrient deprivation. We find that MTCH2 stimulates mitochondrial fusion in a manner dependent on the bioactive lipogenesis intermediate lysophosphatidic acid. We propose that MTCH2 monitors flux through the lipogenesis pathway and transmits this information to the mitochondrial fusion machinery to promote mitochondrial elongation, enhanced energy production, and cellular survival under homeostatic and starvation conditions. These findings will help resolve the roles of MTCH2 and mitochondria in tissue-specific lipid metabolism in animals.
  5. Cell Commun Signal. 2021 Sep 25. 19(1): 98
      BACKGROUND: The calcium (Ca2+)/calmodulin (CAM)-activated kinase kinase 2 (CAMKK2)-signaling regulates several physiological processes, for example, glucose metabolism and energy homeostasis, underlying the pathogenesis of metabolic diseases. CAMKK2 exerts its biological function through several downstream kinases, therefore, it is expected that depending on the cell-type-specific kinome profile, the metabolic effects of CAMKK2 and its underlying mechanism may differ. Identification of the cell-type-specific differences in CAMKK2-mediated glucose metabolism will lead to unravelling the organ/tissue-specific role of CAMKK2 in energy metabolism. Therefore, the objective of this study was to understand the cell-type-specific regulation of glucose metabolism, specifically, respiration under CAMKK2 deleted conditions in transformed human embryonic kidney-derived HEK293 and hepatoma-derived HepG2 cells.METHODS: Cellular respiration was measured in terms of oxygen consumption rate (OCR). OCR and succinate dehydrogenase (SDH) enzyme activity were measured following the addition of substrates. In addition, transcription and proteomic and analyses of the electron transport system (ETS)-associated proteins, including mitochondrial SDH protein complex (complex-II: CII) subunits, specifically SDH subunit B (SDHB), were performed using standard molecular biology techniques. The metabolic effect of the altered SDHB protein content in the mitochondria was further evaluated by cell-type-specific knockdown or overexpression of SDHB.
    RESULTS: CAMKK2 deletion suppressed cellular respiration in both cell types, shifting metabolic phenotype to aerobic glycolysis causing the Warburg effect. However, isolated mitochondria exhibited a cell-type-specific enhancement or dampening of the respiratory kinetics under CAMKK2 deletion conditions. This was mediated in part by the cell-type-specific effect of CAMKK2 loss-of-function on transcription, translation, post-translational modification (PTM), and megacomplex assembly of nuclear-encoded mitochondrial SDH enzyme complex subunits, specifically SDHB. The cell-type-specific increase or decrease in SDHs protein levels, specifically SDHB, under CAMKK2 deletion condition resulted in an increased or decreased enzymatic activity and CII-mediated respiration. This metabolic phenotype was reversed by cell-type-specific knockdown or overexpression of SDHB in respective CAMKK2 deleted cell types. CAMKK2 loss-of-function also affected the overall assembly of mitochondrial supercomplex involving ETS-associated proteins in a cell-type-specific manner, which correlated with differences in mitochondrial bioenergetics.
    CONCLUSION: This study provided novel insight into CAMKK2-mediated cell-type-specific differential regulation of mitochondrial function, facilitated by the differential expression, PTMs, and assembly of SDHs into megacomplex structures. Video Abstract.
    Keywords:  CAMKK2; Oxidative phosphorylation; Respiration; Respiratory supercomplex; Succinate dehydrogenase
  6. Cells. 2021 Aug 31. pii: 2255. [Epub ahead of print]10(9):
      Mitochondrial disorders represent a large group of severe genetic disorders mainly impacting organ systems with high energy requirements. Leigh syndrome (LS) is a classic example of a mitochondrial disorder resulting from pathogenic mutations that disrupt oxidative phosphorylation capacities. Currently, evidence-based therapy directed towards treating LS is sparse. Recently, the cell-permeant substrates responsible for regulating the electron transport chain have gained attention as therapeutic agents for mitochondrial diseases. We explored the therapeutic effects of introducing tricarboxylic acid cycle (TCA) intermediate substrate, succinate, as a cell-permeable prodrug NV118, to alleviate some of the mitochondrial dysfunction in LS. The results suggest that a 24-hour treatment with prodrug NV118 elicited an upregulation of glycolysis and mitochondrial membrane potential while inhibiting intracellular reactive oxygen species in LS cells. The results from this study suggest an important role for TCA intermediates for treating mitochondrial dysfunction in LS. We show, here, that NV118 could serve as a therapeutic agent for LS resulting from mutations in mtDNA in complex I and complex V dysfunctions.
    Keywords:  TCA cycle; glycolysis; leigh syndrome; mitochondrial respiration; succinate prodrug
  7. Cell Death Discov. 2021 Oct 01. 7(1): 269
      Ferroptosis is an iron-dependent cell death characterized by the accumulation of hydroperoxided phospholipids. Here, we report that the NUPR1 inhibitor ZZW-115 induces ROS accumulation followed by a ferroptotic cell death, which could be prevented by ferrostatin-1 (Fer-1) and ROS-scavenging agents. The ferroptotic activity can be improved by inhibiting antioxidant factors in pancreatic ductal adenocarcinoma (PDAC)- and hepatocellular carcinoma (HCC)-derived cells. In addition, ZZW-115-treatment increases the accumulation of hydroperoxided lipids in these cells. We also found that a loss of activity and strong deregulation of key enzymes involved in the GSH- and GPX-dependent antioxidant systems upon ZZW-115 treatment. These results have been validated in xenografts induced with PDAC- and HCC-derived cells in nude mice during the treatment with ZZW-115. More importantly, we demonstrate that ZZW-115-induced mitochondrial morphological changes, compatible with the ferroptotic process, as well as mitochondrial network disorganization and strong mitochondrial metabolic dysfunction, which are rescued by both Fer-1 and N-acetylcysteine (NAC). Of note, the expression of TFAM, a key regulator of mitochondrial biogenesis, is downregulated by ZZW-115. Forced expression of TFAM is able to rescue morphological and functional mitochondrial alterations, ROS production, and cell death induced by ZZW-115 or genetic inhibition of NUPR1. Altogether, these results demonstrate that the mitochondrial cell death mediated by NUPR1 inhibitor ZZW-115 is fully rescued by Fer-1 but also via TFAM complementation. In conclusion, TFAM could be considered as an antagonist of the ferroptotic cell death.
  8. STAR Protoc. 2021 Dec 17. 2(4): 100843
      Investigating dynamic changes of mitochondrial ATP and cytosolic glucose levels of single living cells over time by genetically encoded biosensors provides an informative readout of their metabolic activities. Here, we describe how to monitor the metabolic K+-sensitivity of HEK293 cells exploiting ATP-, glucose-, and K+ probes. Fluorescence live-cell imaging of these Förster resonance energy transfer-based biosensors over time in response to gramicidin, an ionophoric peptide, indicated an absolute dependency of cellular ATP homeostasis on high intracellular K+ levels. For complete information on the generation and use of this protocol please refer to Bischof et al. (2021).
    Keywords:  Cancer; Cell Biology; Cell culture; Chemistry; Metabolism; Microscopy; Molecular Biology; Molecular/Chemical Probes
  9. Cell. 2021 Sep 21. pii: S0092-8674(21)01049-7. [Epub ahead of print]
      Although oxidative phosphorylation is best known for producing ATP, it also yields reactive oxygen species (ROS) as invariant byproducts. Depletion of ROS below their physiological levels, a phenomenon known as reductive stress, impedes cellular signaling and has been linked to cancer, diabetes, and cardiomyopathy. Cells alleviate reductive stress by ubiquitylating and degrading the mitochondrial gatekeeper FNIP1, yet it is unknown how the responsible E3 ligase CUL2FEM1B can bind its target based on redox state and how this is adjusted to changing cellular environments. Here, we show that CUL2FEM1B relies on zinc as a molecular glue to selectively recruit reduced FNIP1 during reductive stress. FNIP1 ubiquitylation is gated by pseudosubstrate inhibitors of the BEX family, which prevent premature FNIP1 degradation to protect cells from unwarranted ROS accumulation. FEM1B gain-of-function mutation and BEX deletion elicit similar developmental syndromes, showing that the zinc-dependent reductive stress response must be tightly regulated to maintain cellular and organismal homeostasis.
    Keywords:  BEX2; BEX3; CUL2; FEM1B; mitochondria; oxidative phosphorylation; reactive oxygen species; reductive stress; ubiquitin
  10. Metabolites. 2021 Aug 25. pii: 572. [Epub ahead of print]11(9):
      A theory that can best explain the facts of a phenomenon is more likely to advance knowledge than a theory that is less able to explain the facts. Cancer is generally considered a genetic disease based on the somatic mutation theory (SMT) where mutations in proto-oncogenes and tumor suppressor genes cause dysregulated cell growth. Evidence is reviewed showing that the mitochondrial metabolic theory (MMT) can better account for the hallmarks of cancer than can the SMT. Proliferating cancer cells cannot survive or grow without carbons and nitrogen for the synthesis of metabolites and ATP (Adenosine Triphosphate). Glucose carbons are essential for metabolite synthesis through the glycolysis and pentose phosphate pathways while glutamine nitrogen and carbons are essential for the synthesis of nitrogen-containing metabolites and ATP through the glutaminolysis pathway. Glutamine-dependent mitochondrial substrate level phosphorylation becomes essential for ATP synthesis in cancer cells that over-express the glycolytic pyruvate kinase M2 isoform (PKM2), that have deficient OxPhos, and that can grow in either hypoxia (0.1% oxygen) or in cyanide. The simultaneous targeting of glucose and glutamine, while elevating levels of non-fermentable ketone bodies, offers a simple and parsimonious therapeutic strategy for managing most cancers.
    Keywords:  IDH1; chimpanzees; evolution; fermentation; glutaminolysis; glycolysis; ketogenic metabolic therapy; metastasis; mitochondrial substrate level phosphorylation; mutations; oncogenes; respiration
  11. Metabolites. 2021 Sep 15. pii: 627. [Epub ahead of print]11(9):
      Mitochondria are dynamic organelles that constantly alter their shape through the recruitment of specialized proteins, like mitofusin-2 (Mfn2) and dynamin-related protein 1 (Drp1). Mfn2 induces the fusion of nearby mitochondria, while Drp1 mediates mitochondrial fission. We previously found that the genetic or pharmacological activation of mitochondrial fusion was tumor suppressive against pancreatic ductal adenocarcinoma (PDAC) in several model systems. The mechanisms of how these different inducers of mitochondrial fusion reduce pancreatic cancer growth are still unknown. Here, we characterized and compared the metabolic reprogramming of these three independent methods of inducing mitochondrial fusion in KPC cells: overexpression of Mfn2, genetic editing of Drp1, or treatment with leflunomide. We identified significantly altered metabolites via robust, orthogonal statistical analyses and found that mitochondrial fusion consistently produces alterations in the metabolism of amino acids. Our unbiased methodology revealed that metabolic perturbations were similar across all these methods of inducing mitochondrial fusion, proposing a common pathway for metabolic targeting with other drugs.
    Keywords:  fission; fusion; leflunomide; metabolomic reprogramming; metabolomics; mitochondrial morphology; mitofusin-2; pancreatic cancer
  12. Cancer Lett. 2021 Sep 25. pii: S0304-3835(21)00496-1. [Epub ahead of print]522 171-183
      The clinical efficacy of cisplatin in the treatment of esophageal squamous cell carcinoma (ESCC) is undesirable. Signal transducer and activator of transcription 3β (STAT3β), a splice variant of STAT3, restrains STAT3α activity and enhances chemosensitivity in ESCC. However, the underlying molecular mechanisms remain poorly understood. Here, we found that high expression of STAT3β contributes to cisplatin sensitivity and enhances Gasdermin E (GSDME) dependent pyroptosis in ESCC cells after exposure to cisplatin. Mechanistically, STAT3β was located into the mitochondria and its high expression disrupts the activity of the electron transport chain, resulting in an increase of ROS in cisplatin treatment cells. While high levels of ROS caused activation of caspase-3 and GSDME, and induced cell pyroptosis. STAT3β blocked the phosphorylation of STAT3α S727 in mitochondria by interacting with ERK1/2 following cisplatin treatment, disrupting electron transport chain and inducing activation of GSDME. Clinically, high expression of both STAT3β and GSDME was strongly associated with better overall survival and disease-free survival of ESCC patients. Overall, our study reveals that STAT3β sensitizes ESCC cells to cisplatin by disrupting mitochondrial electron transport chain and enhancing pyroptosis, which demonstrates the prognostic significance of STAT3β in ESCC therapy.
    Keywords:  Chemosensitivity; Esophageal squamous cell carcinoma; Mitochondria; Pyroptosis; STAT3β
  13. Life (Basel). 2021 Sep 10. pii: 949. [Epub ahead of print]11(9):
      Mitochondrial bioenergetic function is a central component of cellular metabolism in health and disease. Mitochondrial oxidative phosphorylation is critical for maintaining energetic homeostasis, and impairment of mitochondrial function underlies the development and progression of metabolic diseases and aging. However, measurement of mitochondrial bioenergetic function can be challenging in human samples due to limitations in the size of the collected sample. Furthermore, the collection of samples from human cohorts is often spread over multiple days and locations, which makes immediate sample processing and bioenergetics analysis challenging. Therefore, sample selection and choice of tests should be carefully considered. Basic research, clinical trials, and mitochondrial disease diagnosis rely primarily on skeletal muscle samples. However, obtaining skeletal muscle biopsies requires an appropriate clinical setting and specialized personnel, making skeletal muscle a less suitable tissue for certain research studies. Circulating white blood cells and platelets offer a promising primary tissue alternative to biopsies for the study of mitochondrial bioenergetics. Recent advances in frozen respirometry protocols combined with the utilization of minimally invasive and non-invasive samples may provide promise for future mitochondrial research studies in humans. Here we review the human samples commonly used for the measurement of mitochondrial bioenergetics with a focus on the advantages and limitations of each sample.
    Keywords:  bioenergetics; fibroblasts; frozen tissue; leukocytes; mitochondria; oxygen consumption; platelets; respirometry; skeletal muscle
  14. Antioxidants (Basel). 2021 Aug 25. pii: 1349. [Epub ahead of print]10(9):
      Nucleotide pools need to be constantly replenished in cancer cells to support cell proliferation. The synthesis of nucleotides requires glutamine and 5-phosphoribosyl-1-pyrophosphate produced from ribose-5-phosphate via the oxidative branch of the pentose phosphate pathway (ox-PPP). Both PPP and glutamine also play a key role in maintaining the redox status of cancer cells. Enhanced glutamine metabolism and increased glucose 6-phosphate dehydrogenase (G6PD) expression have been related to a malignant phenotype in tumors. However, the association between G6PD overexpression and glutamine consumption in cancer cell proliferation is still incompletely understood. In this study, we demonstrated that both inhibition of G6PD and glutamine deprivation decrease the proliferation of colon cancer cells and induce cell cycle arrest and apoptosis. Moreover, we unveiled that glutamine deprivation induce an increase of G6PD expression that is mediated through the activation of the nuclear factor (erythroid-derived 2)-like 2 (NRF2). This crosstalk between G6PD and glutamine points out the potential of combined therapies targeting oxidative PPP enzymes and glutamine catabolism to combat colon cancer.
    Keywords:  cancer cell metabolism; colon cancer; glucose-6-phosphate dehydrogenase; oxidative stress; pentose phosphate pathway
  15. Genes (Basel). 2021 Aug 29. pii: 1348. [Epub ahead of print]12(9):
      Mitochondria are very important intracellular organelles because they have various functions. They produce ATP, are involved in cell signaling and cell death, and are a major source of reactive oxygen species (ROS). Mitochondria have their own DNA (mtDNA) and mutation of mtDNA or change the mtDNA copy numbers leads to disease, cancer chemo/radioresistance and aging including longevity. In this review, we discuss the mtDNA mutation, mitochondrial disease, longevity, and importance of mitochondrial dysfunction in cancer first. In the later part, we particularly focus on the role in cancer resistance and the mitochondrial condition such as mtDNA copy number, mitochondrial membrane potential, ROS levels, and ATP production. We suggest a therapeutic strategy employing mitochondrial transplantation (mtTP) for treatment-resistant cancer.
    Keywords:  cancer radioresistance; clinically relevant radioresistant (CRR) cells; mitochondria; mitochondrial DNA
  16. Anal Chem. 2021 Sep 28.
      Mitochondria, as energy factories, participate in many metabolic processes and play vital roles in cell life. Most human diseases are caused by mitochondrial dysfunction, and mitochondrial temperature is an important indicator of mitochondrial function. Despite the biological importance of mitochondria, there are few tools for detecting changes in mitochondrial temperature in living organisms. Here, we report on a thermosensitive rhodamine B (RhB)-derived fluorogenic probe (RhBIV) that enables fluorescent labeling of cell mitochondria at concentrations as low as 1 μM. We demonstrate that this probe exhibits a temperature-dependent response in cell mitochondria. Furthermore, in mice, it has a long half-life (t1/2) and is primarily enriched in the liver. This unique thermosensitive probe offers a simple, nondestructive method for longitudinal monitoring of mitochondrial temperature both in vitro and in vivo to elucidate fundamental physiological and pathological processes related to mitochondrial function.
  17. Free Radic Biol Med. 2021 Sep 28. pii: S0891-5849(21)00744-9. [Epub ahead of print]
      Mitochondria are the cytoplasmic organelles mostly known as the "electric engine" of the cells; however, they also play pivotal roles in different biological processes, such as cell growth/apoptosis, Ca2+ and redox homeostasis, and cell stemness. In cancer cells, mitochondria undergo peculiar functional and structural dynamics involved in the survival/death fate of the cell. Cancer cells use glycolysis to support macromolecular biosynthesis and energy production ("Warburg effect"); however, mitochondrial OXPHOS has been shown to be still active during carcinogenesis and even exacerbated in drug-resistant and stem cancer cells. This metabolic rewiring is associated with mutations in genes encoding mitochondrial metabolic enzymes ("oncometabolites"), alterations of ROS production and redox biology, and a fine-tuned balance between anti-/proapoptotic proteins. In cancer cells, mitochondria also experience dynamic alterations from the structural point of view undergoing coordinated cycles of biogenesis, fusion/fission and mitophagy, and physically communicating with the endoplasmic reticulum (ER), through the Ca2+ flux, at the MAM (mitochondria-associated membranes) levels. This review addresses the peculiar mitochondrial metabolic and structural dynamics occurring in cancer cells and their role in coordinating the balance between cell survival and death. The role of mitochondrial dynamics as effective biomarkers of tumor progression and promising targets for anticancer strategies is also discussed.
    Keywords:  Cancer; MAMs; Metabolic rewiring; Mitochondria; OXPHOS; ROS; Structural dynamics
  18. Redox Biol. 2021 Sep 14. pii: S2213-2317(21)00294-9. [Epub ahead of print]47 102135
      Metabolic conditions such as obesity, insulin resistance and glucose intolerance are frequently associated with impairments in skeletal muscle function and metabolism. This is often linked to dysregulation of homeostatic pathways including an increase in reactive oxygen species (ROS) and oxidative stress. One of the main sites of ROS production is the mitochondria, where the flux of substrates through the electron transport chain (ETC) can result in the generation of oxygen free radicals. Fortunately, several mechanisms exist to buffer bursts of intracellular ROS and peroxide production, including the enzymes Catalase, Glutathione Peroxidase and Superoxide Dismutase (SOD). Of the latter, there are two intracellular isoforms; SOD1 which is mostly cytoplasmic, and SOD2 which is found exclusively in the mitochondria. Developmental and chronic loss of these enzymes has been linked to disease in several studies, however the temporal effects of these disturbances remain largely unexplored. Here, we induced a post-developmental (8-week old mice) deletion of SOD2 in skeletal muscle (SOD2-iMKO) and demonstrate that 16 weeks of SOD2 deletion leads to no major impairment in whole body metabolism, despite these mice displaying alterations in aspects of mitochondrial abundance and voluntary ambulatory movement. This is likely partly explained by the suggestive data that a compensatory response may exist from other redox enzymes, including catalase and glutathione peroxidases. Nevertheless, we demonstrated that inducible SOD2 deletion impacts on specific aspects of muscle lipid metabolism, including the abundance of phospholipids and phosphatidic acid (PA), the latter being a key intermediate in several cellular signaling pathways. Thus, our findings suggest that post-developmental deletion of SOD2 induces a more subtle phenotype than previous embryonic models have shown, allowing us to highlight a previously unrecognized link between SOD2, mitochondrial function and bioactive lipid species including PA.
    Keywords:  Lipid metabolism; Mitochondria; ROS; Skeletal muscle; Superoxide
  19. Antioxidants (Basel). 2021 Aug 24. pii: 1336. [Epub ahead of print]10(9):
      Sorafenib and regorafenib, multikinase inhibitors (MKIs) used as standard chemotherapeutic agents for hepatocellular carcinoma (HCC), generate reactive oxygen species (ROS) during cancer treatment. Antioxidant supplements are becoming popular additions to our diet, particularly glutathione derivatives and mitochondrial-directed compounds. To address their possible interference during HCC chemotherapy, we analyzed the effect of common antioxidants using hepatoma cell lines and tumor spheroids. In liver cancer cell lines, sorafenib and regorafenib induced mitochondrial ROS production and potent cell death after glutathione depletion. In contrast, cabozantinib only exhibited oxidative cell death in specific HCC cell lines. After sorafenib and regorafenib administration, antioxidants such as glutathione methyl ester and the superoxide scavenger MnTBAP decreased cell death and ROS production, precluding the MKI activity against hepatoma cells. Interestingly, sorafenib-induced mitochondrial damage caused PINK/Parkin-dependent mitophagy stimulation, altered by increased ROS production. Finally, in sorafenib-treated tumor spheroids, while ROS induction reduced tumor growth, antioxidant treatments favored tumor development. In conclusion, the anti-tumor activity of specific MKIs, such as regorafenib and sorafenib, is altered by the cellular redox status, suggesting that uncontrolled antioxidant intake during HCC treatment should be avoided or only endorsed to diminish chemotherapy-induced side effects, always under medical scrutiny.
    Keywords:  BCL-2; apoptosis; chemotherapy; glutathione; hepatocellular carcinoma; mitochondria; mitophagy; oxidative stress; superoxide; tumor spheroids
  20. FASEB J. 2021 Oct;35(10): e21891
      In humans, insulin resistance has been linked to an impaired metabolic transition from fasting to feeding (metabolic flexibility; MetFlex). Previous studies suggest that mitochondrial dynamics response is a putative determinant of MetFlex; however, this has not been studied in humans. Thus, the aim of this study was to investigate the mitochondrial dynamics response in the metabolic transition from fasting to feeding in human peripheral blood mononuclear cells (PBMCs). Six male subjects fasted for 16 h (fasting), immediately after which they consumed a 75-g oral glucose load (glucose). In both fasting and glucose conditions, blood samples were taken to obtain PBMCs. Mitochondrial dynamics were assessed by electron microscopy images. We exposed in vitro acetoacetate-treated PBMCs to the specific IP3R inhibitor Xestospongin B (XeB) to reduce IP3R-mediated mitochondrial Ca2+ accumulation. This allowed us to evaluate the role of ER-mitochondria Ca2+ exchange in the mitochondrial dynamic response to substrate availability. To determine whether PBMCs could be used in obesity context (low MetFlex), we measured mitochondrial dynamics in mouse spleen-derived lymphocytes from WT and ob/ob mice. We demonstrated that the transition from fasting to feeding reduces mitochondria-ER interactions, induces mitochondrial fission and reduces mitochondrial cristae density in human PBMCs. In addition, we demonstrated that IP3R activity is key in the mitochondrial dynamics response when PBMCs are treated with a fasting-substrate in vitro. In murine mononuclear-cells, we confirmed that mitochondria-ER interactions are regulated in the fasted-fed transition and we further highlight mitochondria-ER miscommunication in PBMCs of diabetic mice. In conclusion, our results demonstrate that the fasting/feeding transition reduces mitochondria-ER interactions, induces mitochondrial fission and reduces mitochondrial cristae density in human PBMCs, and that IP3R activity may potentially play a central role.
    Keywords:  fasting; mitochondria-ER interaction; mitochondrial cristae; mitochondrial fusion; mitochondrial morphology; obesity
  21. Proc Natl Acad Sci U S A. 2021 Oct 05. pii: e2110387118. [Epub ahead of print]118(40):
      Loss of metabolic homeostasis is a hallmark of aging and is characterized by dramatic metabolic reprogramming. To analyze how the fate of labeled methionine is altered during aging, we applied 13C5-Methionine labeling to Drosophila and demonstrated significant changes in the activity of different branches of the methionine metabolism as flies age. We further tested whether targeted degradation of methionine metabolism components would "reset" methionine metabolism flux and extend the fly lifespan. Specifically, we created transgenic flies with inducible expression of Methioninase, a bacterial enzyme capable of degrading methionine and revealed methionine requirements for normal maintenance of lifespan. We also demonstrated that microbiota-derived methionine is an alternative and important source in addition to food-derived methionine. In this genetic model of methionine restriction (MetR), we also demonstrate that either whole-body or tissue-specific Methioninase expression can dramatically extend Drosophila health- and lifespan and exerts physiological effects associated with MetR. Interestingly, while previous dietary MetR extended lifespan in flies only in low amino acid conditions, MetR from Methioninase expression extends lifespan independently of amino acid levels in the food. Finally, because impairment of the methionine metabolism has been previously associated with the development of Alzheimer's disease, we compared methionine metabolism reprogramming between aging flies and a Drosophila model relevant to Alzheimer's disease, and found that overexpression of human Tau caused methionine metabolism flux reprogramming similar to the changes found in aged flies. Altogether, our study highlights Methioninase as a potential agent for health- and lifespan extension.
    Keywords:  13C-Methionine labeling; Alzheimer’s disease; Methioninase; aging; methionine restriction
  22. Cancers (Basel). 2021 Sep 14. pii: 4609. [Epub ahead of print]13(18):
      The tumor's physiology emerges from the dynamic interplay of numerous cell types, such as cancer cells, immune cells and stromal cells, within the tumor microenvironment. Immune and cancer cells compete for nutrients within the tumor microenvironment, leading to a metabolic battle between these cell populations. Tumor cells can reprogram their metabolism to meet the high demand of building blocks and ATP for proliferation, and to gain an advantage over the action of immune cells. The study of the metabolic reprogramming mechanisms underlying cancer requires the quantification of metabolic fluxes which can be estimated at the genome-scale with constraint-based or kinetic modeling. Constraint-based models use a set of linear constraints to simulate steady-state metabolic fluxes, whereas kinetic models can simulate both the transient behavior and steady-state values of cellular fluxes and concentrations. The integration of cell- or tissue-specific data enables the construction of context-specific models that reflect cell-type- or tissue-specific metabolic properties. While the available modeling frameworks enable limited modeling of the metabolic crosstalk between tumor and immune cells in the tumor stroma, future developments will likely involve new hybrid kinetic/stoichiometric formulations.
    Keywords:  constraint-based modeling; genome-scale metabolic models; immune system; kinetic metabolic models; metabolic crosstalk; metabolic reprogramming in cancer; stoichiometric models
  23. Pharmacol Ther. 2021 Sep 27. pii: S0163-7258(21)00197-2. [Epub ahead of print] 107995
      The past thirty years have seen a surge in interest in pathophysiological roles of mitochondrial, and the accurate quantification of mitochondrial DNA copy number (mCN) in cells and tissue samples is a fundamental aspect of assessing changes in mitochondrial health and biogenesis. Quantification of mCN between studies is surprisingly variable due to a combination of physiological variability and diverse protocols being used to measure this endpoint. The advent of novel methods to quantify nucleic acids like digital polymerase chain reaction (dPCR) and high throughput sequencing offer the ability to measure absolute values of mCN. We conducted an in-depth survey of articles published between 1969 - 2020 to create an overview of mCN values, to assess consensus values of tissue-specific mCN, and to evaluate consistency between methods of assessing mCN. We identify best practices for methods used to assess mCN, and we address the impact of using specific loci on the mitochondrial genome to determine mCN. Current data suggest that clinical measurement of mCN can provide diagnostic and prognostic value in a range of diseases and health conditions, with emphasis on cancer and cardiovascular disease, and the advent of means to measure absolute mCN should future clinical applications of mCN measurements.
    Keywords:  Cancer; Cardiovascular disease; Digital PCR; High throughput sequencing; Mitochondria; Mitochondrial DNA
  24. Circulation. 2021 Sep 29.
      Background: The integrated stress response (ISR) is an evolutionarily conserved process to cope with intracellular and extracellular disturbances. Myocardial infarction is a leading cause of death worldwide. Coronary artery reperfusion is the most effective means to mitigate cardiac damage of myocardial infarction, which however causes additional reperfusion injury. This study aimed to investigate the role of the ISR in myocardial ischemia/reperfusion (I/R). Methods: Cardiac-specific gain- and loss-of-function approaches for the ISR were employed in vivo. Myocardial I/R was achieved by the ligation of the cardiac left anterior descending artery for 45 minutes, followed by reperfusion for different times. Cardiac function was assessed by echocardiography. Additionally, cultured H9c2 cells, primary rat cardiomyocytes, and mouse embryonic fibroblasts were used to dissect underlying molecular mechanisms. Moreover, tandem mass tag (TMT) labeling and mass spectrometry was conducted to identify protein targets of the ISR. Pharmacological means were tested to manipulate the ISR for therapeutic exploration. Results: We show that the PERK/eIF2α axis of the ISR is strongly induced by I/R in cardiomyocytes in vitro and in vivo. We further reveal a physiological role of PERK/eIF2α signaling by showing that acute activation of PERK in the heart confers robust cardioprotection against reperfusion injury. In contrast, cardiac-specific deletion of PERK aggravates cardiac responses to reperfusion. Mechanistically, the ISR directly targets mitochondrial complexes via translational suppression. We identify NDUFAF2, an assembly factor of mitochondrial complex I, as a selective target of PERK. Overexpression of PERK suppresses the protein expression of NDUFAF2 while PERK inhibition causes an increase of NDUFAF2. Silencing of NDUFAF2 significantly rescues cardiac cell survival from PERK knockdown under I/R. Further, we show that activation of PERK/eIF2α signaling reduces mitochondrial complex-derived reactive oxygen species and improves cardiac cell survival in response to I/R. Moreover, pharmacological stimulation of the ISR protects the heart against reperfusion damage, even after the restoration of occluded coronary artery, highlighting a clinical relevance for myocardial infarction treatment. Conclusions: These studies suggest that the ISR improves cell survival and mitigate reperfusion damage by selectively suppressing mitochondrial protein synthesis and reducing oxidative stress in the heart.
  25. Cells. 2021 Sep 06. pii: 2334. [Epub ahead of print]10(9):
      The metabolic milieu of solid tumors provides a barrier to chimeric antigen receptor (CAR) T-cell therapies. Excessive lactate or hypoxia suppresses T-cell growth, through mechanisms including NADH buildup and the depletion of oxidized metabolites. NADH is converted into NAD+ by the enzyme Lactobacillus brevis NADH Oxidase (LbNOX), which mimics the oxidative function of the electron transport chain without generating ATP. Here we determine if LbNOX promotes human CAR T-cell metabolic activity and antitumor efficacy. CAR T-cells expressing LbNOX have enhanced oxygen as well as lactate consumption and increased pyruvate production. LbNOX renders CAR T-cells resilient to lactate dehydrogenase inhibition. But in vivo in a model of mesothelioma, CAR T-cell's expressing LbNOX showed no increased antitumor efficacy over control CAR T-cells. We hypothesize that T cells in hostile environments face dual metabolic stressors of excessive NADH and insufficient ATP production. Accordingly, futile T-cell NADH oxidation by LbNOX is insufficient to promote tumor clearance.
    Keywords:  LDHA; Lactobacillus brevis NADH oxidase; armor CAR T-cells
  26. Life Sci Alliance. 2021 Nov;pii: e202101093. [Epub ahead of print]4(11):
      Special AT-rich sequence binding protein-1 (SATB1) is localized to the nucleus and remodels chromatin structure in T cells. SATB1-deficient CD4 T cells cannot respond to TCR stimulation; however, the cause of this unresponsiveness is to be clarified. Here, we demonstrate that SATB1 is indispensable to proper mitochondrial functioning and necessary for the activation of signal cascades via the TCR in CD4 T cells. Naïve SATB1-deficient CD4 T cells contain fewer mitochondria than WT T cells, as the former do not express mitochondrial transcription factor A (TFAM). Impaired mitochondrial function in SATB1-deficient T cells subverts mitochondrial ROS production and SHP-1 inactivation by constitutive oxidization. Ectopic TFAM expression increases mitochondrial mass and mitochondrial ROS production and rescues defects in the antigen-specific response in the SATB1-deficient T cells. Thus, SATB1 is vital for maintaining mitochondrial mass and function by regulating TFAM expression, which is necessary for TCR signaling.
  27. Cell Death Dis. 2021 Sep 30. 12(10): 893
      Uncontrolled mitosis is one of the most important features of cancer, and mitotic kinases are thought to be ideal targets for anticancer therapeutics. However, despite numerous clinical attempts spanning decades, clinical trials for mitotic kinase-targeting agents have generally stalled in the late stages due to limited therapeutic effectiveness. Alisertib (MLN8237) is a promising oral mitotic aurora kinase A (AURKA, Aurora-A) selective inhibitor, which is currently under several clinical evaluations but has failed in its first Phase III trial due to inadequate efficacy. In this study, we performed genome-wide CRISPR/Cas9-based screening to identify vulnerable biological processes associated with alisertib in breast cancer MDA-MB-231 cells. The result indicated that alisertib treated cancer cells are more sensitive to the genetic perturbation of oxidative phosphorylation (OXPHOS). Mechanistic investigation indicated that alisertib treatment, as well as other mitotic kinase inhibitors, rapidly reduces the intracellular ATP level to generate a status that is highly addictive to OXPHOS. Furthermore, the combinational inhibition of mitotic kinase and OXPHOS by alisertib, and metformin respectively, generates severe energy exhaustion in mitotic cells that consequently triggers cell death. The combination regimen also enhanced tumor regression significantly in vivo. This suggests that targeting OXPHOS by metformin is a potential strategy for promoting the therapeutic effects of mitotic kinase inhibitors through the joint targeting of mitosis and cellular energy homeostasis.
  28. Chembiochem. 2021 Sep 27.
      Cellular senescence, a stable form of cell cycle arrest, facilitates protection from tumorigenesis and aids in tissue repair as they accumulate in the body at an early age. However, long-term retention of senescent cells causes inflammation, aging of the tissue, and progression of deadly diseases such as obesity, diabetes, and atherosclerosis. Various attempts have been made to achieve selective elimination of senescent cells from the body, yet little has been explored in designing the mitochondria-targeted senolytic agent. Many characteristics of senescence are associated with mitochondria. Here we have designed a library of alkyl-monoquaternary ammonium-triphenyl phosphine (TPP) and alkyl-diquaternary ammo-nium-TPP of varying alkyl chain lengths, which target the mitochondria; we also studied their senolytic properties. It was observed that the alkyl-diquaternary ammonium-TPP with the longest chain length induces apoptosis to senescent cells selectively via an increase of reactive oxygen species (ROS) and mitochondrial membrane disruption. This study demonstrated that mitochondria could be a potential target for designing new small molecules as senolytic agents for the treatment of a variety of dysfunctions associated with pathological aging.
    Keywords:  alkyl-quaternary ammonium-TPP * mitochondria * membrane disruption * senescence * Macula retina mouse model
  29. Am J Physiol Endocrinol Metab. 2021 09 27.
      Mitochondrial dysfunction is evident in diseases affecting cognition and metabolism such as Alzheimer's disease and type 2 diabetes. Human studies of brain mitochondrial function are limited to post-mortem tissue, preventing the assessment of bioenergetics by respirometry. Here, we investigated the effect of two diets on mitochondrial bioenergetics in three brain regions: the prefrontal cortex (PFC), the entorhinal cortex (ERC), and the cerebellum (CB), using middle-aged non-human primates. Eighteen female cynomolgus macaques aged 12.3 ± 0.7 years were fed either a Mediterranean diet that is associated with healthy outcomes or a Western diet that is associated with poor cognitive and metabolic outcomes. Average bioenergetic capacity within each brain region did not differ between diets. Distinct brain regions have different metabolic requirements related to their function and disease susceptibility. Therefore, we also examined differences in bioenergetic capacity between brain regions. Mitochondria isolated from animals fed a Mediterranean diet maintained distinct differences in mitochondrial bioenergetics between brain regions while animals fed the Western diet had diminished distinction in bioenergetics between brain regions. Notably, fatty acid β-oxidation was not affected between regions in animals fed a Western diet. Additionally, bioenergetics in animals fed a Western diet had positive associations with fasting blood glucose and insulin levels in PFC and ERC mitochondria, but not in CB mitochondria. Altogether, these data indicate that a Western diet disrupts bioenergetics across brain regions and that circulating blood glucose and insulin levels in Western diet fed animals influence bioenergetics in brain regions susceptible to Alzheimer's disease and type 2 diabetes.
    Keywords:  Bioenergetics; Glucose; Mediterranean Diet; Mitochondria; Western Diet
  30. Genes (Basel). 2021 Sep 21. pii: 1460. [Epub ahead of print]12(9):
      The modulation of dynamic histone acetylation states is key for organizing chromatin structure and modulating gene expression and is regulated by histone acetyltransferase (HAT) and histone deacetylase (HDAC) enzymes. The mammalian SIRT6 protein, a member of the Class III HDAC Sirtuin family of NAD+-dependent enzymes, plays pivotal roles in aging, metabolism, and cancer biology. Through its site-specific histone deacetylation activity, SIRT6 promotes chromatin silencing and transcriptional regulation of aging-associated, metabolic, and tumor suppressive gene expression programs. ATP citrate lyase (ACLY) is a nucleo-cytoplasmic enzyme that produces acetyl coenzyme A (acetyl-CoA), which is the required acetyl donor for lysine acetylation by HATs. In addition to playing a central role in generating cytosolic acetyl-CoA for de novo lipogenesis, a growing body of work indicates that ACLY also functions in the nucleus where it contributes to the nutrient-sensitive regulation of nuclear acetyl-CoA availability for histone acetylation in cancer cells. In this study, we have identified a novel function of SIRT6 in controlling nuclear levels of ACLY and ACLY-dependent tumor suppressive gene regulation. The inactivation of SIRT6 in cancer cells leads to the accumulation of nuclear ACLY protein and increases nuclear acetyl-CoA pools, which in turn drive locus-specific histone acetylation and the expression of cancer cell adhesion and migration genes that promote tumor invasiveness. Our findings uncover a novel mechanism of SIRT6 in suppressing invasive cancer cell phenotypes and identify acetyl-CoA responsive cell migration and adhesion genes as downstream targets of SIRT6.
    Keywords:  ACLY; SIRT6; Sirtuin; acetyl-CoA; cancer; chromatin; gene expression; histone acetylation
  31. Nat Commun. 2021 Sep 28. 12(1): 5680
      Existing preclinical methods for acquiring dissemination kinetics of rare circulating tumor cells (CTCs) en route to forming metastases have not been capable of providing a direct measure of CTC intravasation rate and subsequent half-life in the circulation. Here, we demonstrate an approach for measuring endogenous CTC kinetics by continuously exchanging CTC-containing blood over several hours between un-anesthetized, tumor-bearing mice and healthy, tumor-free counterparts. By tracking CTC transfer rates, we extrapolated half-life times in the circulation of between 40 and 260 s and intravasation rates between 60 and 107,000 CTCs/hour in mouse models of small-cell lung cancer (SCLC), pancreatic ductal adenocarcinoma (PDAC), and non-small cell lung cancer (NSCLC). Additionally, direct transfer of only 1-2% of daily-shed CTCs using our blood-exchange technique from late-stage, SCLC-bearing mice generated macrometastases in healthy recipient mice. We envision that our technique will help further elucidate the role of CTCs and the rate-limiting steps in metastasis.
  32. PLoS One. 2021 ;16(9): e0257403
      An important approach in tumor therapy is combining substances with different action mechanisms aiming to enhance the antineoplastic effect, decrease the therapeutic dosage, and avoid resistance mechanisms. Moreover, evaluating compounds already approved for the treatment of non-neoplastic diseases is promising for new antineoplastic therapies. Sodium dichloroacetate (DCA) reactivates oxidative phosphorylation in the cancer cell mitochondria, reducing apoptosis resistance in cancer cells. Furthermore, metformin inhibits the proliferation of tumor cells and CD133+ cancer -stem-like cells. In the present study, we evaluated the independent and synergistic effect of metformin and DCA on the metabolic activity, cell proliferation, and apoptosis of a canine prostate adenocarcinoma (Adcarc1258) and a transitional cell carcinoma cell line (TCC1506) in comparison to a primary canine fibroblast culture. Determining metformin uptake in tumor cells was performed by quantitative HPLC. Depending on the dosage, metformin as a single agent inhibited the metabolic activity and cell proliferation of the tumor cells, showing only minor effects on the fibroblasts. Furthermore, 1 mM metformin increased apoptosis over 96 h in the tumor cell lines but not in fibroblasts. Additionally, metformin uptake into the tumor cells in vitro was measurable by quantitative HPLC. Synergistic effects for the combination therapy were observed in both neoplastic cell lines as well as in the fibroblasts. Based on these results, metformin might be a promising therapeutic agent for canine urogenital tumors. Further studies on kinetics, toxicology, bioavailability, and application of metformin in dogs are necessary.
  33. J Mater Chem B. 2021 Sep 29.
      With the emergence and rapid development of super-resolution fluorescence microscopy, monitoring of mitochondrial morphological changes has aroused great interest for exploring the role of mitochondria in the process of cell metabolism. However, in the absence of water-soluble, photostable and low-toxicity fluorescent dyes, ultra-high-resolution mitochondrial imaging is still challenging. Herein, we designed two fluorescent BODIPY dyes, namely Mito-BDP 630 and Mito-BDP 760, for mitochondrial imaging. The results proved that Mito-BDP 760 underwent aggregation-caused quenching (ACQ) in the aqueous matrix owing to its hydrophobicity and was inaccessible to the cells, which restricted its applications in mitochondrial imaging. In stark contrast, water-soluble Mito-BDP 630 readily penetrated cellular and mitochondrial membranes for mitochondrial imaging with high dye densities under wash-free conditions as driven by membrane potential. As a comparison, Mito Tracker Red presented high photobleaching (the fluorescence intensity dropped by nearly 50%) and high phototoxicity after irradiation by a laser for 30 min. However, Mito-BDP 630 possessed excellent biocompatibility, photostability and chemical stability. Furthermore, clear and bright mitochondria distribution in living HeLa cells after incubation with Mito-BDP 630 could be observed by CLSM. Convincingly, the morphology and cristae of mitochondria could be visualized using an ultra-high-resolution microscope. In short, Mito-BDP 630 provided a powerful and convenient tool for monitoring mitochondrial morphologies in living cells. Given the facile synthesis, photobleaching resistance and low phototoxicity of Mito-BDP 630, it is an alternative to the commercial Mito Tracker Red.
  34. Sci Rep. 2021 Sep 30. 11(1): 19408
      DJ-1 is a ubiquitously expressed protein that protects cells from stress through its conversion into an active protease. Recent work found that the active form of DJ-1 was induced in the ischemic heart as an endogenous mechanism to attenuate glycative stress-the non-enzymatic glycosylation of proteins. However, specific proteins protected from glycative stress by DJ-1 are not known. Given that mitochondrial electron transport proteins have a propensity for being targets of glycative stress, we investigated if DJ-1 regulates the glycation of Complex I and Complex III after myocardial ischemia-reperfusion (I/R) injury. Initial studies found that DJ-1 localized to the mitochondria and increased its interaction with Complex I and Complex III 3 days after the onset of myocardial I/R injury. Next, we investigated the role DJ-1 plays in modulating glycative stress in the mitochondria. Analysis revealed that compared to wild-type control mice, mitochondria from DJ-1 deficient (DJ-1 KO) hearts showed increased levels of glycative stress following I/R. Additionally, Complex I and Complex III glycation were found to be at higher levels in DJ-1 KO hearts. This corresponded with reduced complex activities, as well as reduced mitochondrial oxygen consumption ant ATP synthesis in the presence of pyruvate and malate. To further determine if DJ-1 influenced the glycation of the complexes, an adenoviral approach was used to over-express the active form of DJ-1(AAV9-DJ1ΔC). Under I/R conditions, the glycation of Complex I and Complex III were attenuated in hearts treated with AAV9-DJ1ΔC. This was accompanied by improvements in complex activities, oxygen consumption, and ATP production. Together, this data suggests that cardiac DJ-1 maintains Complex I and Complex III efficiency and mitochondrial function during the recovery from I/R injury. In elucidating a specific mechanism for DJ-1's role in the post-ischemic heart, these data break new ground for potential therapeutic strategies using DJ-1 as a target.
  35. Front Oncol. 2021 ;11 713721
      Mitochondria participate in the progression of hepatocellular carcinoma (HCC) by modifying processes including but not limited to redox homeostasis, metabolism, and the cell death pathway. These processes depend on the health status of the mitochondria. Quality control processes in mitochondria can repair or eliminate "unhealthy mitochondria" at the molecular, organelle, or cellular level and form an efficient integrated network that plays an important role in HCC tumorigenesis, patient survival, and tumor progression. Here, we review the influence of mitochondria on the biological behavior of HCC. Based on this information, we further highlight the need for determining the role and mechanism of interaction between different levels of mitochondrial quality control in regulating HCC occurrence and progression as well as resistance development. This information may lead to the development of precision medicine approaches against targets involved in various mitochondrial quality control-related pathways.
    Keywords:  chemoresistance; hepatocellular carcinoma; mitochondrial quality control; tumor progression; tumorigenesis
  36. Structure. 2021 Sep 20. pii: S0969-2126(21)00333-6. [Epub ahead of print]
      Respiratory complex I drives proton translocation across energy-transducing membranes by NADH oxidation coupled with (ubi)quinone reduction. In humans, its dysfunction is associated with neurodegenerative diseases. The Escherichia coli complex represents the structural minimal form of an energy-converting NADH:ubiquinone oxidoreductase. Here, we report the structure of the peripheral arm of the E. coli complex I consisting of six subunits, the FMN cofactor, and nine iron-sulfur clusters at 2.7 Å resolution obtained by cryo electron microscopy. While the cofactors are in equivalent positions as in the complex from other species, individual subunits are adapted to the absence of supernumerary proteins to guarantee structural stability. The catalytically important subunits NuoC and D are fused resulting in a specific architecture of functional importance. Striking features of the E. coli complex are scrutinized by mutagenesis and biochemical characterization of the variants. Moreover, the arrangement of the subunits sheds light on the unknown assembly of the complex.
    Keywords:  Escherichia coli; NADH dehydrogenase; assembly; bioenergetics; complex I; cryo electron microscopy; electron transfer; iron-sulfur clusters; membrane proteins; quinones
  37. ACS Sens. 2021 Sep 29.
      Mitochondria, as the center of energy production, play an important role in cell homeostasis by regulating the cellular metabolism and mediating the cellular response to stress. Epigenetic changes such as DNA and histone methylation have been increasingly recognized to play a significant role in homeostasis and stress response. The cross-talking between the metabolome and the epigenome has attracted significant attention in recent years but with a major focus on how metabolism contributes to epigenomic changes. Few studies have focused on how epigenetic modifications may alter the mitochondrial composition and activity. In this work, we designed a novel probe targeting methylated CpGs of mitochondrial DNA (mtDNA). We demonstrated the capability of our probe to reveal the spatial distribution of methylated mtDNA and capture the mtDNA methylation changes at a single-cell level. We were also able to track single-cell mtDNA and nDNA methylation simultaneously and discovered the unsynchronized dynamics of the nucleus and mitochondria. Our tool offers a unique opportunity to understand the epigenetic regulation of mtDNA and its dynamic response to the microenvironment and cellular changes.
    Keywords:  DNA CpG methylation; epigenetics; live-cell probe; mitochondria; super-resolution microscopy
  38. FASEB J. 2021 Nov;35(11): e21854
      Ammonia is one of the major metabolites produced by intestinal microorganisms; however, its role in intestinal homeostasis is poorly understood. The present study investigated the regulation of intestinal tight junction (TJ) proteins by ammonia and the underlying mechanisms in human intestinal Caco-2 cells. Ammonia (15, 30, and 60 mM) increased the permeability of the cells in a dose-dependent manner, as indicated by reduced transepithelial electrical resistance and increased dextran flux. Immunoblot and immunofluorescence analyses revealed that the ammonia-induced increase in TJ permeability reduced the membrane localization of TJ proteins such as zonula occludens (ZO)1, ZO2, occludin, claudin-1, and claudin-3. DNA microarray analysis identified a biological pathway "response to reactive oxygen species" enriched by ammonia treatment, indicating the induction of oxidative stress in the cells. Ammonia treatment also increased the malondialdehyde content and decreased the ratio of reduced to oxidized glutathione. Meanwhile, ammonia treatment-induced mitochondrial dysfunction, as indicated by the downregulation of genes associated with the electron transport chain, reduction of the cellular ATP, NADH, and tricarboxylic acid cycle intermediate content, and suppression of the mitochondrial membrane potential. In contrast, N-acetyl cysteine reversed the ammonia-induced impairment of TJ permeability and structure without affecting the mitochondrial parameters. Collectively, ammonia impaired the TJ barrier by increasing oxidative stress in Caco-2 cells. A mitochondrial dysfunction is possibly an event preceding ammonia-induced oxidative stress. The findings of this study could potentially improve our understanding of the interplay between intestinal microorganisms and their hosts.
    Keywords:  ammonia; intestine; mitochondria; oxidative stress; tight junction
  39. Cancer Res. 2021 Oct 01. 81(19): 4896-4898
      The Warburg effect, the propensity of some cells to metabolize glucose to lactate in the presence of oxygen (also known as aerobic glycolysis), has long been observed in cancer and other contexts of cell proliferation, but only in the past two decades have significant gains been made in understanding how and why this metabolic transformation occurs. In 2004, Cancer Research published a study by Elstrom and colleagues that provided one of the first connections between a specific oncogene and aerobic glycolysis. Studying hematopoietic and glioblastoma cell lines, they demonstrated that constitutive activation of AKT promotes an increased glycolytic rate without altering proliferation or oxygen consumption in culture. They proposed that it is this effect that allows constitutive AKT activation to transform cells and found that it sensitizes cells to glucose deprivation. In the years since, mechanistic understanding of oncogenic control of metabolism, and glycolysis specifically, has deepened substantially. Current work seeks to understand the benefits and liabilities associated with glycolytic metabolism and to identify inhibitors that might be of clinical benefit to target glycolytic cancer cells.See related article by Elstrom and colleagues, Cancer Res 2004;64:3892-9.
  40. Antioxidants (Basel). 2021 Sep 14. pii: 1458. [Epub ahead of print]10(9):
      Cancer cells preferentially accumulate iron (Fe) relative to non-malignant cells; however, the underlying rationale remains elusive. Iron-sulfur (Fe-S) clusters are critical cofactors that aid in a wide variety of cellular functions (e.g., DNA metabolism and electron transport). In this article, we theorize that a differential need for Fe-S biogenesis in tumor versus non-malignant cells underlies the Fe-dependent cell growth demand of cancer cells to promote cell division and survival by promoting genomic stability via Fe-S containing DNA metabolic enzymes. In this review, we outline the complex Fe-S biogenesis process and its potential upregulation in cancer. We also discuss three therapeutic strategies to target Fe-S biogenesis: (i) redox manipulation, (ii) Fe chelation, and (iii) Fe mimicry.
    Keywords:  cancer therapy; carcinogenesis; iron metabolism; iron–sulfur cluster biogenesis
  41. Cancer Res. 2021 Sep 30. pii: canres.0061.2021. [Epub ahead of print]
      Acute myeloid leukemia (AML) is an aggressive hematological malignancy, exhibiting high levels of reactive oxygen species (ROS). ROS levels have been suggested to drive leukemogenesis and is thus a potential novel target for treating AML. MTH1 prevents incorporation of oxidized nucleotides into the DNA to maintain genome integrity and is upregulated in many cancers. Here we demonstrate that hematological cancers are highly sensitive to MTH1 inhibitor TH1579 (karonudib). A functional precision medicine ex vivo screen in primary AML bone marrow samples demonstrated a broad response profile of TH1579, independent of the genomic alteration of AML, resembling the response profile of the standard-of-care treatments cytarabine and doxorubicin. Furthermore, TH1579 killed primary human AML blast cells (CD45+) as well as chemotherapy resistance leukemic stem cells (CD45+Lin-CD34+CD38-),which are often responsible for AML progression. TH1579 killed AML cells by causing mitotic arrest, elevating intracellular ROS levels, and enhancing oxidative DNA damage. TH1579 showed a significant therapeutic window, was well tolerated in animals, and could be combined with standard-of-care treatments to further improve efficacy. TH1579 significantly improved survival in two different AML disease models in vivo. In conclusion, the pre-clinical data presented here support that TH1579 is a promising novel anticancer agent for AML, providing a rational to investigate the clinical usefulness of TH1579 in AML in an on-going clinical phase 1 trial.
  42. Biophys Rep. 2021 Sep 08. 1(1): None
      Voltage-dependent anion-selective channel (VDAC) is one of the main proteins of the outer mitochondrial membrane of all eukaryotes, where it forms aqueous, voltage-sensitive, and ion-selective channels. Its electrophysiological properties have been thoroughly analyzed with the planar lipid bilayer technique. To date, however, available results are based on isolations of VDACs from tissue or from recombinant VDACs produced in bacterial systems. It is well known that the cytosolic overexpression of highly hydrophobic membrane proteins often results in the formation of inclusion bodies containing insoluble aggregates. Purification of properly folded proteins and restoration of their full biological activity requires several procedures that considerably lengthen experimental times. To overcome these restraints, we propose a one-step reaction that combines in vitro cell-free protein expression with nanodisc technology to obtain human VDAC isoforms directly integrated in a native-like lipid bilayer. Reconstitution assays into artificial membranes confirm the reliability of this new methodological approach and provide results comparable to those of VDACs prepared with traditional protein isolation and reconstitution protocols. The use of membrane-mimicking nanodisc systems represents a breakthrough in VDAC electrophysiology and may be adopted to further structural studies.
  43. Mater Sci Eng C Mater Biol Appl. 2021 Oct;pii: S0928-4931(21)00534-8. [Epub ahead of print]129 112394
      The ability of some tumours to impart radioresistance serves as a barrier in the cancer therapeutics. Mitochondrial metabolism significantly persuades this cancer cell survival, incursion and plays a crucial role in conferring radioresistance. It would be of great importance to target the active mitochondria to overcome this resistance and achieve tumoricidal efficacy. The current report investigates the improved radiosensitization effect (under Gamma irradiation) in hepatocellular carcinoma through active mitochondrial targeting of alpha-ketoglutarate decorated iron oxide-gold core-shell nanoparticles (GNP). The loading of a chemotherapeutic drug N-(4-hydroxyphenyl)retinamide in GNP allows adjuvant chemotherapy, which further sensitizes cancerous cells for radiotherapy. The GNP shows a drug loading efficiency of 8.5 wt% with a sustained drug release kinetics. The X-Ray diffraction (XRD) pattern and High-Resolution Transmission Electron microscopy (HRTEM) indicates the synthesis of core iron oxide nanoparticles with indications of a thin layer of gold shell on the surface with 1:7 ratios of Fe: Au. The GNP application significantly reduced per cent cell viability in Hepatocellular carcinoma cells through improved radiosensitization at 5 Gy gamma radiation dose. The molecular mechanism revealed a sharp increment in reactive oxygen species (ROS) generation and DNA fragmentation. The mitochondrial targeting probes confirm the presence of GNP in the mitochondria, which could be the possible reason for such improved cellular damage. In addition to the active mitochondrial targeting, the currently fabricated nanoparticles work as a potent Magnetic Resonance Imaging (MRI)/Computed Tomography (CT) contrast agent. This multifunctional therapeutic potential makes GNP as one of the most promising theragnostic molecules in cancer therapeutics.
    Keywords:  Alpha-ketoglutarate; Cancer; Magnetic Resonance Imaging; Mitochondrial targeting; Nanoparticles; Radiosensitization
  44. Front Genet. 2021 ;12 647152
      Colorectal cancer (CRC) is one of the most prevalent malignant tumors worldwide. Colon adenocarcinoma (COAD) is the most common pathological type of CRC and several biomarkers related to survival have been confirmed. Yet, the predictive effect of a single gene biomarker is not enough. The tricarboxylic acid (TCA) cycle and carbon metabolism play an important role in tumors. Thus, we aimed to identify new gene signatures from the TCA cycle and carbon metabolism to better predict the survival of COAD. This study performed mRNA expression profiling in large COAD cohorts (n = 417) from The Cancer Genome Atlas (TCGA) database. Univariate Cox regression and multivariate Cox regression analysis were performed, and receiver operating characteristic (ROC) curve was used to screen the variable combinations model which is most relevant to patient prognosis survival mostly. Univariable or multivariate analysis results showed that SUCLG2, SUCLG1, ACLY, SUCLG2P2, ATIC and ACO2 have associations with survival in COAD. Combined with clinical variables, we confirmed model 1 (AUC = 0.82505), most relevant to patient prognosis survival. Model 1 contains three genes: SUCLG2P2, SUCLG2 and ATIC, in which SUCLG2P2 and SUCLG2 were low-expressed in COAD, however, ATIC was highly expressed, and the expressions above are related to stages of CRC. Pearson analysis showed that SUCLG2P2, SUCLG2 and ATIC were correlated in normal COAD tissues, while only SUCLG2P2 and SUCLG2 were correlated in tumor tissues. Finally, we verified the expressions of these three genes in COAD samples. Our study revealed a possible connection between the TCA cycle and carbon metabolism and prognosis and showed a TCA cycle and carbon metabolism related gene signature which could better predict survival in COAD patients.
    Keywords:  TCA cycle; colon adenocarcinoma; one carbon metabolism; prognostic; signature
  45. Mol Cancer Ther. 2021 Sep 28. pii: molcanther.MCT-20-1095-A.2020. [Epub ahead of print]
      Cisplatin and tyrosine kinase inhibitors (TKIs) are recommended to treat non-small-cell lung cancer (NSCLC). However, ubiquitously acquired drug resistance in NSCLC patients diminishes their therapeutic efficacy. Strategies for overcoming cisplatin and TKI resistance are an unmet medical need. We previously described a group of near-infrared heptamethine carbocyanine fluorescent dyes, referred to as DZ, with tumor-homing properties via differentially expressed organic anion-transporting polypeptides on cancer cells. This group of organic dyes can deliver therapeutic payloads specifically to tumor cells in the form of a chemical conjugate. We synthesized DZ-SIMvastatin (DZ-SIM) initially to target cell membrane cholesterol biosynthesis in lung cancer cells. DZ-SIM induced apoptosis in both cisplatin-sensitive and resistant as well as EGFR TKI-sensitive and resistant lung cancer cells. This conjugate specifically accumulated in and effectively inhibited the growth of xenograft tumors formed by NSCLC cells resistant to first (H1650) and third (PC9AR) generation EGFR TKIs. DZ-SIM induced cell death by targeting mitochondrial structure and function. We concluded that DZ-SIM could be a promising novel therapy for overcoming drug resistance in NSCLC patients.
  46. Oncol Lett. 2021 Nov;22(5): 767
      Propofol is a commonly used intravenous anesthetic agent that can also suppress the proliferation of various human cancer types, including colorectal cancer (CRC). The present study aimed to investigate whether propofol could induce the ferroptosis of CRC cells by regulating signal transducer and activator of transcription 3 (STAT3). STAT3 expression in normal and CRC tissues was measured. Human normal colonic epithelial NCM460 cells and human CRC SW480 cells were exposed to different concentrations of propofol and then cell viability was detected. SW480 cells were transfected with a vector overexpressing STAT3 and treated with propofol, and the cell viability, colony formation, cell proliferation, iron level, ROS production and ferroptosis of these cells and control cells were evaluated. Overall, the results showed that STAT3 was highly expressed in CRC tissues. Propofol exerted no marked effect on NCM460 cell viability, but inhibited SW480 cell viability in a concentration-dependent manner. Meanwhile, STAT3 was downregulated by propofol in a concentration-dependent manner. Propofol also inhibited CRC cell proliferation and colony formation, and enhanced cellular iron and ROS levels. Additionally, the expression of proteins involved in ferroptosis was also altered by propofol, including the upregulation of CHAC1 and PTGS2 expression in CRC cells, and the inhibition of GPX4 expression. However, STAT3 overexpression blocked the effect of propofol on CRC cells. In conclusion, propofol may trigger the ferroptosis of CRC cells by downregulating STAT3 expression.
    Keywords:  colorectal cancer; ferroptosis; propofol; signal transducer and activator of transcription 3
  47. J Exp Biol. 2021 Sep 28. pii: jeb.242462. [Epub ahead of print]
      An unavoidable consequence of aerobic metabolism is the production of reactive oxygen species (ROS). Mitochondria have historically been considered the primary source of ROS, however, recent literature has highlighted the uncertainty in primary ROS production sites and it is unclear how variation in mitochondrial density influences ROS-induced damage and protein turnover. Fish skeletal muscle is comprised of distinct, highly aerobic red muscle and anaerobic white muscle, offering an excellent model system in which to evaluate the relationship of tissue aerobic capacity and ROS-induced damage under baseline conditions. The present study uses a suite of indices to better understand potential consequences of aerobic tissue capacity in red and white muscle of the pinfish, Lagodon rhomboides. Red muscle had a 7-fold greater mitochondrial volume density than white muscle, and more oxidative damage despite also having higher activities of the antioxidant enzymes superoxide dismutase and catalase. The dominant protein degradation system appears to be tissue dependent. Lysosomal degradation markers and autophagosome volume density were greater in white muscle, while ubiquitin expression and 20S proteasome activity were significantly greater in red muscle. However, ubiquitin ligase expression was significantly higher in white muscle. Red muscle had a more than two-fold greater rate of translation and total ATP turnover than white muscle, results that may be due in part to the higher mitochondrial density and the associated increase in oxidative damage. Together these results support the concept that an elevated aerobic capacity is associated with greater oxidative damage and higher costs of protein turnover.
    Keywords:  Autophagy; Oxidative stress; Protein turnover; Ubiquitin proteasome system
  48. Nature. 2021 Sep 29.
    Keywords:  Ageing; Metabolism; Nutrition; Physiology
  49. Aging (Albany NY). 2021 Sep 27. undefined(undefined):
    Keywords:  DNA repair; aging rate; base excision repair; longevity; mitochondria
  50. Cancer Med. 2021 Sep 26.
      BACKGROUND: The majority of patients with small-cell lung cancer (SCLC) show a good response in the early stages of treatment, but more than 90% of patients will develop drug resistance. Therefore, biomarkers are urgently needed to identify patients who can benefit from systemic treatment.METHODS: We prospectively enrolled 52 extensive-stage SCLC patients before treatment from a local hospital to identify mutations related to patient prognosis, and verified them in the published Jiang's cohort and George's cohort.
    RESULTS: We found that patients with high mutations (mut-high) in the fatty acid (FA) metabolism pathway had a longer progression-free survival (PFS) in the local hospital cohort (HR = 0.446, 95% CI, 0.207-0.959, p = 0.0387) and a longer overall survival (OS) in Jiang's cohort (HR = 0.549, 95% CI, 0.314-0.960, p = 0.0351) than patients with low mutations (mut-low). Multivariate analysis suggested that mut-high status was an independent prognostic factor in both cohorts. George's cohort verified that mut-high status was associated with a longer OS than mut-low status (HR = 0.730, 95% CI 0.440-1.220, p = 0.2277). The possible mechanisms were as follows: the frequency of mutated FA synthase (FASN) in the mut-high group was greater than that in the mut-low group, and pathways related to the cell cycle, DNA repair, and oxidative phosphorylation were enriched in the mut-high group.
    CONCLUSIONS: The prognosis of SCLC patients treated with chemotherapy was better among patients with more mutations in the FA metabolism pathway, and the underlying mechanisms could be found at the genome and transcriptome levels.
    Keywords:  biomarker; fatty acid metabolic pathway; prognosis; small-cell lung cancer (SCLC); whole exome sequencing (WES)