bims-mibica Biomed News
on Mitochondrial bioenergetics in cancer
Issue of 2020‒02‒23
forty-nine papers selected by
Kelsey Fisher-Wellman
East Carolina University

  1. Genetics. 2020 Feb 19. pii: genetics.303029.2020. [Epub ahead of print]
      Complex I is the first enzyme involved in the mitochondrial electron transport chain. With more than 40 subunits of dual genetic origin, the biogenesis of complex I is highly intricate and poorly understood. We used Chlamydomonas reinhardtii as a model system to reveal factors involved in complex I biogenesis. Two insertional mutants, displaying a complex I assembly defect characterized by the accumulation of a 700 kDa subcomplex, were analyzed. Genetic analyses showed these mutations were allelic, with insertional mutations in the gene AMC1 (Cre16.g688900), encoding a low-complexity protein of unknown function. The complex I assembly and activity in the mutant was restored by complementation with the wild-type gene, confirming AMC1 is required for complex I biogenesis. The N-terminus of AMC1 targets a reporter protein to yeast mitochondria, implying that AMC1 resides and functions in the Chlamydomonas mitochondria. Accordingly, in both mutants, loss of AMC1 function results in decreased abundance of the mitochondrial nd4 transcript, which encodes the ND4 membrane subunit of complex I. Loss of ND4 in a mitochondrial nd4 mutant is characterized by a membrane arm assembly defect, similar to that exhibited by loss of AMC1. These results suggest AMC1 is required for the production of mitochondrially-encoded complex I subunits, specifically ND4. We discuss the possible modes of action of AMC1 in mitochondrial gene expression and complex I biogenesis.
    Keywords:  Chlamydomonas reinhardtii; energy transducing membranes; low-complexity protein; mitochondrial complex I assembly; mitochondrial gene expression; respiration
  2. EBioMedicine. 2020 Feb 12. pii: S2352-3964(20)30021-9. [Epub ahead of print]52 102646
      BACKGROUND: Previously, we found that amplification of chromosome 17q24.1-24.2 is associated with lymph node metastasis, tumour size, and lymphovascular invasion in invasive ductal carcinoma. A gene within this amplicon, CACNG4, an L-type voltage-gated calcium channel gamma subunit, is elevated in breast cancers with poor prognosis. Calcium homeostasis is achieved by maintaining low intracellular calcium levels. Altering calcium influx/efflux mechanisms allows tumour cells to maintain homeostasis despite high serum calcium levels often associated with advanced cancer (hypercalcemia) and aberrant calcium signaling.METHODS: In vitro 2-D and 3-D assays, and intracellular calcium influx assays were utilized to measure tumourigenic activity in response to altered CANCG4 levels and calcium channel blockers. A chick-CAM model and mouse model for metastasis confirmed these results in vivo.
    FINDINGS: CACNG4 alters cell motility in vitro, induces malignant transformation in 3-dimensional culture, and increases lung-specific metastasis in vivo. CACNG4 functions by closing the channel pore, inhibiting calcium influx, and altering calcium signaling events involving key survival and metastatic pathway genes (AKT2, HDAC3, RASA1 and PKCζ).
    INTERPRETATION: CACNG4 may promote homeostasis, thus increasing the survival and metastatic ability of tumour cells in breast cancer. Our findings suggest an underlying pathway for tumour growth and dissemination regulated by CACNG4 that is significant with respect to developing treatments that target these channels in tumours with aberrant calcium signaling.
    FUNDING: Canadian Breast Cancer Foundation, Ontario; Canadian Institutes of Health Research.
    Keywords:  Breast cancer metastasis; Gamma subunits; L-type channels; Voltage-gated calcium channels (VGCCs)
  3. Cancer Discov. 2020 Feb 21. pii: CD-19-1059. [Epub ahead of print]
      Disease recurrence causes significant mortality in B-progenitor acute lymphoblastic leukemia (B-ALL). Genomic analysis of matched diagnosis and relapse samples show relapse often arising from minor diagnosis subclones. However, why therapy eradicates some subclones while others survive and progress to relapse remains obscure. Elucidation of mechanisms underlying these differing fates requires functional analysis of isolated subclones. Here, large-scale limiting dilution xenografting of diagnosis and relapse samples, combined with targeted sequencing, identified and isolated minor diagnosis subclones that initiate evolutionary trajectory toward relapse (termed diagnosis Relapse Initiating clones, dRI). Compared to other diagnosis subclones, dRI were drug tolerant with distinct engraftment and metabolic properties. Transciptionally, dRI displayed enrichment for chromatin remodelling, mitochondrial metabolism, proteostasis programs and an increase in stemness pathways. The isolation and characterization of dRI subclones reveals new avenues for eradicating dRI cells by targeting their distinct metabolic and transcriptional pathways before further evolution renders them fully therapy resistant.
  4. Cancer Res. 2020 Feb 21. pii: canres.2991.2019. [Epub ahead of print]
      Pancreatic ductal adenocarcinoma (PDAC) is highly resistant to radiation therapy (RT), chemotherapy, or a combination of these modalities, and surgery remains the only curative intervention for localized disease. Although cancer-associated fibroblasts (CAFs) are abundant in PDAC tumors, the effects of RT on CAFs and the response of PDAC cells to RT are unknown. Using patient samples and orthotopic PDAC biological models we showed that RT increased inducible nitric oxide synthase (iNOS) in the tumor tissues. Mechanistic in vitro studies showed that, although undetectable in RT-activated tumor cells, iNOS expression and nitric oxide (NO) secretion were significantly increased in CAFs secretome following RT. Culture of PDAC cells with conditioned media from RT-activated CAFs increased iNOS/NO signaling in tumor cells through nuclear factor kappa B (NFĸB), which in turn elevated the release of inflammatory cytokines by the tumor cells. Increased NO after RT in PDAC contributed to an acidic microenvironment that was detectable using the radiolabeled pH (low) insertion peptide (pHLIP®). In murine orthotopic PDAC models, pancreatic tumor growth was delayed when iNOS inhibition was combined with RT. These data show the important role that iNOS/NO signaling plays in the effectiveness of RT to treat PDAC tumors.
  5. Oncogene. 2020 Feb 17.
      The Bcl-xL apoptosis inhibitor plays a major role in vertebrate development. In addition to its effect on apoptosis, Bcl-xL is also involved in cell migration and mitochondrial metabolism. These effects may favour the onset and dissemination of metastasis. However, the underlying molecular mechanisms remain to be fully understood. Here we focus on the control of cell migration by Bcl-xL in the context of breast cancer cells. We show that Bcl-xL silencing led to migration defects in Hs578T and MDA-MB231 cells. These defects were rescued by re-expressing mitochondria-addressed, but not endoplasmic reticulum-addressed, Bcl-xL. The use of BH3 mimetics, such as ABT-737 and WEHI-539 confirmed that the effect of Bcl-xL on migration did not depend on interactions with BH3-containing death accelerators such as Bax or BH3-only proteins. In contrast, the use of a BH4 peptide that disrupts the Bcl-xL/VDAC1 complex supports that Bcl-xL by acting on VDAC1 permeability contributes to cell migration through the promotion of reactive oxygen species production by the electron transport chain. Collectively our data highlight the key role of Bcl-xL at the interface between cell metabolism, cell death, and cell migration, thus exposing the VDAC1/Bcl-xL interaction as a promising target for anti-tumour therapy in the context of metastatic breast cancer.
  6. Genes Dev. 2020 Feb 20.
      Excessive reactive oxygen species (ROS) can cause oxidative stress and consequently cell injury contributing to a wide range of diseases. Addressing the critical gaps in our understanding of the adaptive molecular events downstream ROS provocation holds promise for the identification of druggable metabolic vulnerabilities. Here, we unveil a direct molecular link between the activity of two estrogen-related receptor (ERR) isoforms and the control of glutamine utilization and glutathione antioxidant production. ERRα down-regulation restricts glutamine entry into the TCA cycle, while ERRγ up-regulation promotes glutamine-driven glutathione production. Notably, we identify increased ERRγ expression/activation as a hallmark of oxidative stress triggered by mitochondrial disruption or chemotherapy. Enhanced tumor antioxidant capacity is an underlying feature of human breast cancer (BCa) patients that respond poorly to treatment. We demonstrate that pharmacological inhibition of ERRγ with the selective inverse agonist GSK5182 increases antitumor efficacy of the chemotherapeutic paclitaxel on poor outcome BCa tumor organoids. Our findings thus underscore the ERRs as novel redox sensors and effectors of a ROS defense program and highlight the potential therapeutic advantage of exploiting ERRγ inhibitors for the treatment of BCa and other diseases where oxidative stress plays a central role.
    Keywords:  breast cancer; chemotherapy; gene signature; glutamine; glutathione; metabolic flux; mitochondria; nuclear receptor; organoid; oxidative stress; taxane
  7. Oncotarget. 2020 Jan 28. 11(4): 452-461
      Exercise is associated with favorable changes in circulating immune cells and improved survival in early-stage breast cancer patients, but the mechansims remain to be fully elucidated. Preclinical studies indicate that physical activity started before tumor injection reduces tumor incidence and progression. Here we tested whether exercise has anti-tumor effects in mice with established 4T1 mammary carcinoma, a mouse model of triple negative breast cancer. Exercise slowed tumor progression and reduced the tumor-induced accumulation of myeloid-derived suppressor cells (MDSCs). The reduction in MDSCs was accompanied by a relative increase in natural killer and CD8 T cell activation, suggesting that exercise restores a favorable immune environment. Consistently, exercise improved responses to a combination of programmed cell death protein 1 (PD-1) blockade and focal radiotherapy. These data support further investigations of exercise in breast cancer patients treated with combinations of immunotherapy and cytotoxic agents to improve cancer outcomes.
    Keywords:  breast cancer; exercise training; immune cells; immunotherapy; myeloid-derived suppressor cells
  8. Lab Invest. 2020 Feb 17.
      In patients with breast cancer, primary chemotherapy often fails due to survival of chemoresistant breast cancer stem cells (BCSCs) which results in recurrence and metastasis of the tumor. However, the factors determining the chemoresistance of BCSCs have remained to be investigated. Here, we profiled a series of differentially expressed microRNAs (miRNAs) between parental adherent breast cancer cells and BCSC-mimicking mammosphere-derived cancer cells, and identified hsa-miR-27a as a negative regulator for survival and chemoresistance of BCSCs. In the mammosphere, we found that the expression of hsa-miR-27a was downregulated, and ectopic overexpression of hsa-miR-27a reduced both number and size of mammospheres. In addition, overexpression of hsa-miR-27a sensitized breast cancer cells to anticancer drugs by downregulation of genes essential for detoxification of reactive oxygen species (ROS) and impairment of autophagy. Therefore, enhancing the hsa-miR-27a signaling pathway can be a potential therapeutic modality for breast cancer.
  9. Arch Biochem Biophys. 2020 Feb 12. pii: S0003-9861(19)31131-2. [Epub ahead of print]683 108299
      BACKGROUND: ER (endoplasmic reticulum) stress leads to decreased complex I activity in cardiac mitochondria. The aim of the current study is to explore the potential mechanisms by which ER stress leads to the complex I defect. ER stress contributes to intracellular calcium overload and oxidative stress that are two key factors to induce mitochondrial dysfunction. Since oxidative stress is often accompanied by intracellular calcium overload during ER stress in vivo, the role of oxidative stress and calcium overload in mitochondrial dysfunction was studied using in vitro models. ER stress results in intracellular calcium overload that favors activation of calcium-dependent calpains. The contribution of mitochondrial calpain activation in ER stress-mediated complex I damage was studied.METHODS: Thapsigargin (THAP) was used to induce acute ER stress in H9c2 cells and C57BL/6 mice. Exogenous calcium (25 μM) and H2O2 (100 μM) were used to induce modest calcium overload and oxidative stress in isolated mitochondria. Calpain small subunit 1 (CAPNS1) is essential to maintain calpain 1 and calpain 2 (CPN1/2) activities. Deletion of CAPNS1 eliminates the activities of CPN1/2. Wild type and cardiac-specific CAPNS1 deletion mice were used to explore the role of CPN1/2 activation in calcium-induced mitochondrial damage.
    RESULTS: In isolated mitochondria, exogenous calcium but not H2O2 treatment led to decreased oxidative phosphorylation, supporting that calcium overload contributes a key role in the mitochondrial damage. THAP treatment of H9c2 cells decreased respiration selectively with complex I substrates. THAP treatment activated cytosolic and mitochondrial CPN1/2 in C57BL/6 mice and led to degradation of complex I subunits including NDUFS7. Calcium treatment decreased NDUFS7 content in wild type but not in CAPNS1 knockout mice.
    CONCLUSION: ER stress-mediated activation of mitochondria-localized CPN1/2 contributes to complex I damage by cleaving component subunits.
    Keywords:  CPNS1 knockout mice; Calpain; Electron transport chain
  10. Genes (Basel). 2020 Feb 18. pii: E212. [Epub ahead of print]11(2):
      Different mitochondrial DNA (mtDNA) mutations have been identified to cause mitochondrial encephalopathy, lactate acidosis and stroke-like episodes (MELAS). The underlying genetic cause leading to an enormous clinical heterogeneity associated with m.3243A>G-related mitochondrial diseases is still poorly understood. Genotype-phenotype correlation (heteroplasmy levels and clinical symptoms) was analysed in 16 patients (15 literature cases and one unreported case) harbouring the m.3243A>G mutation. mtDNA copy numbers were correlated to heteroplasmy levels in 30 different post-mortem tissue samples, including 14 brain samples of a 46-year-old female. In the central nervous system, higher levels of heteroplasmy correlated significantly with lower mtDNA copy numbers. Skeletal muscle levels of heteroplasmy correlated significantly with kidney and liver. There was no significant difference of heteroplasmy levels between clinically affected and unaffected patients. In the patient presented, we found >75% heteroplasmy levels in all central nervous system samples, without harbouring a MELAS phenotype. This underlines previous suggestions, that really high levels in tissues do not automatically lead to a specific phenotype. Missing significant differences of heteroplasmy levels between clinically affected and unaffected patients underline recent suggestions that there are additional factors such as mtDNA copy number and nuclear factors that may also influence disease severity.
    Keywords:  MELAS-syndrome; genotype–phenotype correlation; m.3243A>G; mtDNA heteroplasmy
  11. J Biol Chem. 2020 Feb 18. pii: jbc.RA120.012739. [Epub ahead of print]
      Heme (iron protoporphyrin IX) is a well-known prosthetic group for enzymes involved in metabolic pathways such as oxygen transport and electron transfer through the mitochondrial respiratory chain. However, heme has also been shown to be an important regulatory molecule (as "labile" heme) for diverse processes such as translation, kinase activity, and transcription in mammals, yeast, and bacteria. Taking advantage of a yeast strain deficient for heme production that enabled controlled modulation and monitoring of "labile" heme levels, here we investigated the role of "labile" heme in the regulation of mitochondrial biogenesis. This process is regulated by the HAP complex in yeast. Using several biochemical assays along with EM and epifluorescence microscopy, to the best of our knowledge, we show for the first time that cellular "labile" heme is critical for the post-translational regulation of HAP complex activity, most likely through the stability of the transcriptional co-activator Hap4p. Consequently, we found that "labile" heme regulates mitochondrial biogenesis and cell growth. The findings of our work highlight a new mechanism in the regulation of mitochondrial biogenesis by cellular metabolites.
    Keywords:  Hap4p; bioenergetics; heme; labile heme; mitochondria; mitochondrial biogenesis; oxidation-reduction (redox); oxidative phosphorylation (OXPHOS); transcription factor; yeast
  12. Int J Mol Sci. 2020 Feb 15. pii: E1317. [Epub ahead of print]21(4):
      Doxorubicin (DXR) is a drug widely used in chemotherapy. Its mode of action is based on its intercalation properties, involving the inhibition of topoisomerase II. However, few studies have reported the mitochondrial effects of DXR while investigating cardiac toxicity induced by the treatment, mostly in pediatric cases. Here, we demonstrate that DXR alters the mitochondrial membrane composition associated with bioenergetic impairment and cell death in human cancer cells. The remodeling of the mitochondrial membrane was explained by phosphatidylserine decarboxylase (PSD) inhibition by DXR. PSD catalyzes phosphatidylethanolamine (PE) synthesis from phosphatidylserine (PS), and DXR altered the PS/PE ratio in the mitochondrial membrane. Moreover, we observed that DXR localized to the mitochondrial compartment and drug uptake was rapid. Evaluation of other topoisomerase II inhibitors did not show any impact on the mitochondrial membrane composition, indicating that the DXR effect was specific. Therefore, our findings revealed a side molecular target for DXR and PSD, potentially involved in DXR anti-cancer properties and the associated toxicity.
    Keywords:  bioenergetics; doxorubicin; phosphatidylethanolamine; phosphatidylserine decarboxylase
  13. Am J Physiol Lung Cell Mol Physiol. 2020 Feb 19.
      Primary graft dysfunction (PGD) is directly related to ischemia/reperfusion (I/R) injury and a major obstacle in lung transplantation (LTx). Nitrite (NO2-), which is reduced in vivo to form nitric oxide (NO) has recently emerged as an intrinsic signaling molecule with a prominent role in cytoprotection against I/R injury. Using a murine model, we provide the evidence that nitrite mitigated I/R-induced injury by diminishing infiltration of immune cells in the alveolar space, reducing pulmonary edema, and improving pulmonary function. Ultrastructural studies support severe mitochondrial impairment in the lung undergoing I/R injury which was significantly improved by nitrite treatment. Nitrite also abrogated the increased pulmonary vascular permeability caused by I/R. In-vitro, hypoxia-reoxygenation (H/R) exacerbated cell death in lung epithelial and microvascular endothelial cells. This contributed to mitochondrial dysfunction as characterized by diminished complex I activity and mitochondrial membrane potential, but increased mitochondrial reactive oxygen species (mtROS). Pretreatment of cells with nitrite robustly attenuated mtROS production through modulation of complex I activity. These findings illustrate a potential novel mechanism in which nitrite protects the lung against I/R injury by regulating mitochondrial bioenergetics and vascular permeability.
    Keywords:  Ischemia/reperfusion injury; Mitochondrial dysfunction; Nitrite; Primary Graft Dysfunction; Vascular permeability
  14. Antioxid Redox Signal. 2020 Feb 20.
      SIGNIFICANCE: Mitochondria represent a major source of intracellular reactive oxygen species (ROS) generation. This is often a consequence of oxidative phosphorylation (OXPHOS), which can produce ROS as a result of leakage from the electron transport chain (ETC). In addition, quality control mechanisms exist to protect cells at from cytotoxic ROS production. One such mechanism is selective autophagic degradation of ROS-producing mitochondria, termed mitophagy, that ultimately results in elimination of mitochondria in the lysosome. Recent Advances. However, while the relationship between mitophagy and ROS production are clearly interwoven, they have yet to be fully untangled. In some circumstances, mitochondrial ROS (mtROS) are elevated as as a consequence of mitophagy induction.CRITICAL ISSUES: In this review, we discuss mtROS generation and their detrimental effects on cellular viability. Additionally, we consider the cellular defense mechanisms that the eukaryotic cell employs to abrogate superfluous oxidative stress. In particular, we delve into the prominent mechanisms governing mitophagy induction that bear on oxidative stress.
    FUTURE DIRECTIONS: Finally, we examine the pathological conditions associated with defective mitophagy where additional research may help to facilitate understanding.
  15. J Diabetes Res. 2020 ;2020 2057187
      We report here the clinical, genetic, and molecular characteristics of type 2 diabetes in a Chinese family. There are differences in the severity and age of onset in diabetes among these families. By molecular analysis of the complete mitochondrial genome in this family, we identified the homoplasmic m.15897G>A mutation underwent sequence analysis of whole mitochondrial DNA genome, which localized at conventional position ten of tRNAThr, and distinct sets of mtDNA polymorphisms belonging to haplogroup D4b1. This mutation has been implicated to be important for tRNA identity and stability. Using cybrid cell models, the decreased efficiency of mitochondrial tRNAThr levels caused by the m.15897G>A mutation results in respiratory deficiency, protein synthesis and assembly, mitochondrial ATP synthesis, and mitochondrial membrane potential. These mitochondrial dysfunctions caused an increase in the production of reactive oxygen species in the mutant cell lines. These data provide a direct evidence that a novel tRNA mutation was associated with T2DM. Thus, our findings provide a new insight into the understanding of pathophysiology of maternally inherited diabetes.
  16. Biochim Biophys Acta Mol Basis Dis. 2020 Feb 13. pii: S0925-4439(20)30071-5. [Epub ahead of print] 165726
      Mitochondrial diseases are considered rare genetic disorders characterized by defects in oxidative phosphorylation (OXPHOS). They can be provoked by mutations in nuclear DNA (nDNA) or mitochondrial DNA (mtDNA). MERRF (Myoclonic Epilepsy with Ragged-Red Fibers) syndrome is one of the most frequent mitochondrial diseases, principally caused by the m.8344A>G mutation in mtDNA, which affects the translation of all mtDNA-encoded proteins and therefore impairs mitochondrial function. In the present work, we evaluated autophagy and mitophagy flux in transmitochondrial cybrids and fibroblasts derived from a MERRF patient, reporting that Parkin-mediated mitophagy is increased in MERRF cell cultures. Our results suggest that supplementation with coenzyme Q10 (CoQ), a component of the electron transport chain (ETC) and lipid antioxidant, prevents Parkin translocation to the mitochondria. In addition, CoQ acts as an enhancer of autophagy and mitophagy flux, which partially improves cell pathophysiology. The significance of Parkin-mediated mitophagy in cell survival was evaluated by silencing the expression of Parkin in MERRF cybrids. Our results show that mitophagy acts as a cell survival mechanism in mutant cells. To confirm these results in one of the main affected cell types in MERRF syndrome, mutant induced neurons (iNs) were generated by direct reprogramming of patients-derived skin fibroblasts. The treatment of MERRF iNs with Guttaquinon CoQ10 (GuttaQ), a water-soluble derivative of CoQ, revealed a significant improvement in cell bioenergetics. These results indicate that iNs, along with fibroblasts and cybrids, can be utilized as reliable cellular models to shed light on disease pathomechanisms as well as for drug screening.
    Keywords:  Autophagy; Coenzyme Q(10); Mitochondria; Mitochondrial diseases; Mitophagy
  17. Sci Rep. 2020 Feb 17. 10(1): 2766
      Recent studies associated certain type of cardiovascular disease (CVD) with specific mitochondrial DNA (mtDNA) defects, mainly driven by the central role of mitochondria in cellular metabolism. Considering the importance of the control region (CR) on the regulation of the mtDNA gene expression, the aim of the present study was to investigate the role of mtDNA CR mutations in two CVDs: stroke and myocardial infarction (MI). MtDNA CR mutations (both fixed and in heteroplasmy) were analysed in two demographically-matched case-control samples, using 154 stroke cases, 211 MI cases and their corresponding control individuals. Significant differences were found, reporting mutations m.16145 G > A and m.16311 T > C as potential genetic risk factors for stroke (conditional logistic regression: p = 0.038 and p = 0.018, respectively), whereas the m.72 T > C, m.73 A > G and m.16356 T > C mutations could act as possible beneficial genetic factors for MI (conditional logistic regression: p = 0.001, p = 0.009 and p = 0.016, respectively). Furthermore, our findings also showed a high percentage of point heteroplasmy in MI controls (logistic regression: p = 0.046; OR = 0.209, 95% CI [0.045-0.972]). These results demonstrate the possible role of mtDNA mutations in the CR on the pathogenesis of stroke and MI, and show the importance of including this regulatory region in genetic association studies.
  18. React Oxyg Species (Apex). 2020 Mar 01. 9(26): 95-108
      Shifted NAD(H) redox status and enhanced reactive oxygen species (ROS) scavenging systems have been observed in cancers. However, how such redox shift is related to the ROS level in cancer cells is less clear. Based on collecting the intrinsic fluorescence of oxidized flavoproteins (Fp containing flavin adenine dinucleotide) and reduced nicotinamide adenine dinucleotide (NADH), optical redox imaging (ORI) provides a quantitative measure of the mitochondrial redox state by the optical redox ratio, Fp/(NADH+Fp), a surrogate marker of the NAD+-coupled redox state NAD+/NADH. Our study aims to explore the relationship between NAD(H) redox status and ROS by imaging NADH, Fp, and ROS levels using cultured breast cancer cell models. By manipulating either ROS levels via application of exogenous H2O2 or redox status via metabolic perturbation compounds, we found that: (1) oxidation of NAD(H) redox status correlates with ROS levels at lower H2O2 concentrations (up to ~700 μM), but not necessarily at higher concentrations; (2) an elevated ROS level diminishes NADH and reduces redox ratio plasticity; (3) either more oxidized or more reduced status can correlate to an increased ROS level; and (4) sometimes, a more oxidized status can correlate to a decreased ROS level depending on cell lines. These observations indicated that cellular NAD(H) redox state and ROS are intricately related but can also change separately. This study can benefit cancer research as both NAD(H) redox status and ROS have been implicated in cancer transformation and progression.
    Keywords:  Breast cancer; Flavoproteins; Intrinsic fluorescence; NADH; Optical redox imaging; Reactive oxygen species; Redox ratio
  19. Biochim Biophys Acta Mol Basis Dis. 2020 Feb 15. pii: S0925-4439(20)30072-7. [Epub ahead of print] 165727
      Mitochondrial complex I (CI), the first multiprotein enzyme complex of the OXPHOS system, executes a major role in cellular ATP generation. Consequently, dysfunction of this complex has been linked to inherited metabolic disorders, including Leigh disease (LD), an often fatal disease in early life. Development of clinical effective treatments for LD remains challenging due to the complex pathophysiological nature. Treatment with the peroxisome proliferation-activated receptor (PPAR) agonist bezafibrate improved disease phenotype in several mitochondrial disease mouse models mediated via enhanced mitochondrial biogenesis and fatty acid β-oxidation. However, the therapeutic potential of this mixed PPAR (α, δ/β, γ) agonist is severely hampered by hepatotoxicity, which is possibly caused by activation of PPARγ. Here, we aimed to investigate the effects of the PPARα-specific fibrate clofibrate in mitochondrial CI-deficient (Ndufs4-/-) mice. Clofibrate increased lifespan and motor function of Ndufs4-/- mice, while only marginal hepatotoxic effects were observed. Due to the complex clinical and cellular phenotype of CI-deficiency, we also aimed to investigate the therapeutic potential of clofibrate combined with the redox modulator KH176. As described previously, single treatment with KH176 was beneficial, however, combining clofibrate with KH176 did not result in an additive effect on disease phenotype in Ndufs4-/- mice. Overall, both drugs have promising, but independent and nonadditive, properties for the pharmacological treatment of CI-deficiency-related mitochondrial diseases.
    Keywords:  Clofibrate; Hepatotoxicity; KH176; Mitochondrial complex I deficiency; Peroxisome proliferator activated receptor (PPAR); Redox modulator
  20. Annu Rev Biochem. 2020 Feb 19.
      Mitochondria are essential metabolic hubs that dynamically adapt to physiological demands. More than 40 proteases residing in different compartments of mitochondria, termed mitoproteases, preserve mitochondrial proteostasis and are emerging as central regulators of mitochondrial plasticity. These multifaceted enzymes limit the accumulation of short-lived, regulatory proteins within mitochondria, modulate the activity of mitochondrial proteins by protein processing, and mediate the degradation of damaged proteins. Various signaling cascades coordinate the activity of mitoproteases to preserve mitochondrial homeostasis and ensure cell survival. Loss of mitoproteases severely impairs the functional integrity of mitochondria, is associated with aging, and causes pleiotropic diseases. Understanding the dual function of mitoproteases as regulatory and quality control enzymes will help unravel the role of mitochondrial plasticity in aging and disease. Expected final online publication date for the Annual Review of Biochemistry, Volume 89 is June 22, 2020. Please see for revised estimates.
  21. Int J Biol Sci. 2020 ;16(5): 849-858
      Changes in mitochondrial structure and function are mostly responsible for aging and age-related features. Whether healthy mitochondria could prevent aging is, however, unclear. Here we intravenously injected the mitochondria isolated from young mice into aged mice and investigated the mitotherapy on biochemistry metabolism and animal behaviors. The results showed that heterozygous mitochondrial DNA (mtDNA) of both aged and young mouse coexisted in tissues of aged mice after mitochondrial administration, and meanwhile, ATP content in tissues increased while reactive oxygen species (ROS) level reduced. Besides, the mitotherapy significantly improved cognitive and motor performance of aged mice. Our study, at the first report in aged animals, not only provides a useful approach to study mitochondrial function associated with aging, but also a new insight into anti-aging through mitotherapy.
    Keywords:  bioenergy; learning and memory; mitochondria; motor
  22. Nat Rev Mol Cell Biol. 2020 Feb 18.
      Owing to their ability to efficiently generate ATP required to sustain normal cell function, mitochondria are often considered the 'powerhouses of the cell'. However, our understanding of the role of mitochondria in cell biology recently expanded when we recognized that they are key platforms for a plethora of cell signalling cascades. This functional versatility is tightly coupled to constant reshaping of the cellular mitochondrial network in a series of processes, collectively referred to as mitochondrial membrane dynamics and involving organelle fusion and fission (division) as well as ultrastructural remodelling of the membrane. Accordingly, mitochondrial dynamics influence and often orchestrate not only metabolism but also complex cell signalling events, such as those involved in regulating cell pluripotency, division, differentiation, senescence and death. Reciprocally, mitochondrial membrane dynamics are extensively regulated by post-translational modifications of its machinery and by the formation of membrane contact sites between mitochondria and other organelles, both of which have the capacity to integrate inputs from various pathways. Here, we discuss mitochondrial membrane dynamics and their regulation and describe how bioenergetics and cellular signalling are linked to these dynamic changes of mitochondrial morphology.
  23. Int J Neurosci. 2020 Feb 21. 1-16
      PURPOSE: Mitochondrial dysfunction is a prominent feature of Alzheimer's disease (AD). As vascular endothelial growth factor (VEGF) has been shown to be protective in AD, the aim of this study was to investigate the effects of VEGF on mitochondrial function in models of AD.MATERIALS AND METHODS: Adeno associated virus (AAV)-VEGF was injected into the hippocampus of APP/PS1 mice. Cognitive function was assessed in these mice with use of the Morris water maze (MWM) and β-amyloid (Aβ) levels in the hippocampus were also measured. Cell viability and reactive oxygen species (ROS) levels were determined in the SH-SY5Y cells treated with Aβ25-35 which served as a cell model of AD. Transmission electron microscopy (TEM) was used to evaluate structural changes in mitochondria and mitochondrial DNA (mtDNA) copy number and mitochondrial membrane potential (MMP) were also recorded. Finally, we investigated the effects of VEGF upon mitochondrial biogenesis, autophagy and mitochondrial autophagy (mitophagy) as determined both in vivo and in vitro with western blots.
    RESULTS: VEGF treated mice showed improvements in spatial learning and memory along with reduced Aβ levels. VEGF protected SH-SY5Y cells against Aβ25-35 induced neurotoxicity as demonstrated by increased cell viability and decreased ROS production.Associated with these effects were improvements in mitochondrial structure and function, and increased numbers of mitochondria resulting from stimulation of mitochondrial biogenesis.
    CONCLUSIONS: VEGF alleviates Aβ related patholoy in models of AD. In part, these beneficial effects of VEGF result from protection of mitochondria and stimulation of mitochondrial biogenesis.
    Keywords:  Alzheimer’s disease; adeno associated virus; mitochondrial biogenesis; mitochondrial structure and function; vascular endothelial growth factor
  24. Mol Cell Biochem. 2020 Feb 17.
      Arctigenin, a mitochondrial complex I inhibitor, has been identified as a potential anti-tumor agent, but the involved mechanism still remains elusive. Herein, we studied the underlying mechanism(s) of action of arctigenin on acidity-tolerant prostate cancer PC-3AcT cells in the lactic acid-containing medium. At concentration showing no toxicity on normal prostate epithelial RWPE-1 and HPrEC cells, arctigenin alone or in combination with docetaxel induced significant cytotoxicity in PC-3AcT cells compared to parental PC-3 cells. With arctigenin treatment, reactive oxygen species (ROS) levels, annexin V-PE positive fractions, sub-G0/G1 peak in cell cycle analysis, mitochondrial membrane depolarization, and cell communication network factor 1 (CCN1) levels were increased, while cellular ATP content and phospho (p)-Akt level were decreased. Pretreatment with ROS scavenger N-acetylcysteine effectively reversed the series of phenomena caused by arctigenin, suggesting that ROS served as upstream molecules of arctigenin-driven cytotoxicity. Meanwhile, arctigenin increased the levels of p-receptor-interacting serine/threonine-protein kinase 3 (p-RIP3) and p-mixed lineage kinase domain-like pseudokinase (p-MLKL) as necroptosis mediators, and pretreatment with necroptosis inhibitor necrostatin-1 restored their levels and cell viability. Treatment of spheroids with arctigenin resulted in necroptotic cell death, which was prevented by N-acetylcysteine. The siRNA-based knockdown of CCN1 suppressed the levels of MLKL, B-cell lymphoma 2 (Bcl-2), and induced myeloid leukemia cell differentiation (Mcl-1) with increased cleavage of Bcl-2-associated X (Bax) and caspase-3. Collectively, these results provide new insights into the molecular mechanisms underlying arctigenin-induced cytotoxicity, and support arctigenin as a potential therapeutic agent for targeting non-Warburg phenotype through induction of necroptosis via ROS-mediated mitochondrial damage and CCN1 upregulation.
    Keywords:  Arctigenin; CCN1; Lactic acid; Necroptosis; Oxidative stress; Prostate cancer
  25. Nanomaterials (Basel). 2020 Feb 13. pii: E319. [Epub ahead of print]10(2):
      Conventional nanotoxicological assays are subjected to various interferences with nanoparticles and especially carbon nanotubes. A multiparametric flow cytometry (FCM) methodology was developed here as an alternative to quantify oxidative stress, mitochondrial impairment, and later cytotoxic and genotoxic events. The experiments were conducted on RAW264.7 macrophages, exposed for 90 min or 24 h-exposure with three types of multiwalled carbon nanotubes (MWCNTs): pristine (Nanocyl™ CNT), acid functionalized (CNTf), or annealed treatment (CNTa). An original combination of reactive oxygen species (ROS) probes allowed the simultaneous quantifications of broad-spectrum ROS, superoxide anion (O2•-), and hydroxyl radical (•OH). All MWCNTs types induced a slight increase of broad ROS levels regardless of earlier antioxidant catalase activity. CNTf strongly stimulated the O2•- production. The •OH production was downregulated for all MWCNTs due to their scavenging capacity. The latter was quantified in a cell-free system by electron paramagnetic resonance spectroscopy (EPR). Further FCM-based assessment revealed early biological damages with a mitochondrial membrane potential collapse, followed by late cytotoxicity with chromatin decondensation. The combined evaluation by FCM analysis and cell-free techniques led to a better understanding of the impacts of MWCNTs surface treatments on the oxidative stress and related biological response.
    Keywords:  acid functionalization; annealing treatment; carbon nanotubes; chromatin decondensation, scavenging capacity; cytotoxicity; flow cytometry and spin trapping in-cell free system; mitochondrial membrane potential collapse; oxidative stress
  26. Redox Biol. 2020 Feb 07. pii: S2213-2317(19)31353-9. [Epub ahead of print]32 101451
      Mitochondria are indispensable organelles that perform critical cellular functions, including energy metabolism, neurotransmission, and synaptic maintenance. Mitochondrial dysfunction and impairment in the organellar homeostasis are key hallmarks implicated in the progression of neurodegenerative disorders. The members of DJ-1/ThiJ/PfpI family are highly conserved, and loss of DJ-1 (PARK7) function in humans results in the impairment of mitochondrial homeostasis, which is one of the key cellular etiology implicated in the progression of Parkinson's Disease. However, the underlying molecular mechanism involved in mitochondrial maintenance and other cellular processes by DJ-1 paralogs is poorly understood. By utilizing genetic approaches from S. cerevisiae, we uncovered intricate mechanisms associated with the mitochondrial phenotypic variations regulated by DJ-1 paralogs. The deletion of DJ-1 paralogs led to respiratory incompetence and the accumulation of enhanced functional mitochondrial mass. The lack of DJ-1 paralogs also displayed enriched mitochondrial interconnectivity due to upregulation in the fusion-mediating proteins, facilitated by the elevation in the basal cellular ROS and oxidized glutathione levels. Intriguingly, these mitochondrial phenotypes variations cause cell size abnormalities, partially suppressed by reestablishing redox balance and upregulation of fission protein levels. Besides, in the absence of DJ-1 paralogs, cells exhibited a significant delay in the cell-cycle progression in the G2/M phase, attributed to mitochondrial hyperfusion and partial DNA damage. Additionally, the aberrations in mitochondrial dynamics and cell-cycle induce cell death mediated by apoptosis. Taken together, our findings first-time provide evidence to show how DJ-1 family members regulate mitochondrial homeostasis and other intricate cellular processes, including cell cycle and apoptosis.
    Keywords:  Apoptosis; DJ-1; Hsp31; Mitochondria; Parkinson disease
  27. Mol Cell Biochem. 2020 Feb 17.
      Circadian rhythms help organisms adapt to changes of external environment by regulating energy metabolism and remaining the balance of homeostasis. Numerous researches have proved that the physiological function of liver was precisely controlled by circadian rhythms. Clock, one of core circadian genes, has been demonstrated to regulate the oxidative phosphorylation process of mitochondrial, which provides energy for living cells and acts as one of the hub for apoptosis. However, whether Clock gene regulates mitochondrial apoptosis pathways in liver cells remains less explored. In the present study, we used lentiviral vector to establish a stable AML12 cell lines which were capable of expressing specific shRNA to interfere the expression of Clock gene and investigated the effect of Clock on mitochondrial apoptosis pathways. Herein, we found that the interference of Clock gene could significantly suppress mitochondrial apoptosis pathways by stabilizing mitochondrial membrane potential and inhibiting mitochondria out membrane permeablization, which might be a result of lower expression of BAD and BIM proteins. Moreover, the interference of Clock gene could downregulate the expression of mitochondrial apoptosis factors, i.e. AIF, CYCS, APAF-1 and SMAC, which will suppress the formation of apoptosome and the process of DNA degradation to further inhibit apoptosis process. This work provides an insight on the important role of Clock gene participating in mitochondrial apoptosis pathways of hepatocytes and unveils a probable pathogenesis of how circadian rhythm regulates liver diseases.
    Keywords:  Apoptosis; Bcl-2 family proteins; Clock; Hepatocytes; Mitochondria out membrane permeablization; Mitochondrial membrane potential
  28. Exp Gerontol. 2020 Feb 18. pii: S0531-5565(19)30673-4. [Epub ahead of print] 110882
      Impairment of mitochondrial biogenesis and mitochondrial dysfunction is a prominent feature of Alzheimer's disease (AD). However, the extent to which the impairment of mitochondrial biogenesis influences mitochondrial dysfunction at the onset and during progression of AD is still unclear. Our study demonstrated that the protein expression pattern of the transcription factor pCREB/CREB, together with the protein expression of PGC-1α, NRF1, and TFAM are all significantly reduced in early ages of 3xTg-AD mice. We also found reduced mRNA expression levels of PKAC-α, CREB, PGC-1α, NRF1, NRF2, and TFAM as early as 1 month-of-age, an age at which there was no significant Aβ oligomer deposition, suggesting that mitochondrial biogenesis is likely impaired in ages preceding the development of the AD pathology. In addition, there was a decrease in VDAC2 expression, which is related to mitochondrial content and mitochondrial function, as demonstrated by protein expression of complex IV, as well as complex II + III, and complex IV activities, at later ages in 3xTg-AD mice. These results suggest that the impairment in mitochondrial biogenesis signaling mediated by PGC-1α at early ages of the AD mice model likely resulted in mitochondrial dysfunction and manifestation of the AD pathology at later ages. Taken together, enhancing mitochondrial biogenesis may represent a potential pharmacological approach for the treatment of AD.
    Keywords:  3xTg-AD; Alzheimer's disease; Mitochondria dysfunction; Mitochondrial biogenesis; PGC-1α
  29. Exp Neurol. 2020 Feb 18. pii: S0014-4886(20)30079-0. [Epub ahead of print] 113248
      As components of the Mediterranean diet (MedDiet) olive polyphenols may play a crucial role for the prevention of Alzheimer's disease (AD). Since mitochondrial dysfunction is involved in both, brain ageing and early AD, effects of 10 different purified phenolic secoiridoids (hydroxytyrosol, tyrosol, oleacein, oleuroside, oleuroside aglycon, oleuropein, oleocanthal, ligstroside, ligstroside aglycone and ligustaloside B) and two metabolites (the plant metabolite elenolic acid and the mammalian metabolite homovanillic acid) were tested in very low doses on mitochondrial function in SH-SY5Y-APP695 cells - a cellular model of early AD. All tested secoiridoids significantly increased basal ATP levels in SY5Y-APP695 cells. Oleacein, oleuroside, oleocanthal and ligstroside showed the highest effect on ATP levels and were additionally tested on mitochondrial respiration. Only oleocanthal and ligstroside were able to enhance the capacity of respiratory chain complexes. To investigate their underlying molecular mechanism, the expression of genes associated with mitochondrial biogenesis, respiration and antioxidative capacity (PGC1-α, SIRT1, CREB1, NRF1, TFAM, complex I, IV and V, GPx1, SOD2, CAT) were determined using RT-PCR. Exclusively ligstroside increased mRNA expression of SIRT1, CREB1, complex I, and GPx1. Furthermore, oleocanthal but not ligstroside decreased Aβ 1-40 levels in SH-SY5Y-APP695 cells. To investigate the in vivo effects of purified secoiridoids, the two most promising compounds (oleocanthal and ligstroside) were tested in a mouse model of ageing. Female NMRI mice, aged 12 months, received a diet supplemented with 50 mg/kg diet oleocanthal or ligstroside for 6 months (equivalent to 6.25 mg/kg b.w.). Young (3 months) and aged (18 months) mice served as controls. Ligstroside fed mice showed improved spatial working memory. Furthermore, ligstroside restored brain ATP levels in aged mice and led to a significant life extension compared to aged control animals. Our findings indicate that purified ligstroside has outstanding performance on mitochondrial bioenergetics in models of early AD and brain ageing by mechanisms that may not interfere with Aβ production. Additionally, ligstroside expanded the lifespan in aged mice and enhanced cognitive function.
    Keywords:  Ageing; Mitochondrial dysfunction; Neurodegeneration; Olive secoiridoids
  30. DNA Cell Biol. 2020 Feb 20.
      Polycystic ovary syndrome (PCOS) is one of the most common female reproductive metabolisms. It is an endocrine disease that affects reproductive women and often exhibits with hyperandrogenemia, insulin resistance (IR), low inflammation, and an increased risk of type 2 diabetes mellitus, metabolic syndrome, and cardiovascular events such as hypertension and dyslipidemia in patients. However, the molecular mechanism of PCOS is still unclear. Recently, an increasing number of studies have shown that the oxidative stress induced by mitochondrial dysfunction has negative effects on IR, lipid metabolism, and follicular development, suggesting that mitochondrial dysfunction plays an essential role in the development of PCOS. Abnormal mitochondrial DNA copy number in patients with PCOS, and mitochondrial gene mutations, has been the focus of research in recent years, and functional mitochondrial diseases have been gradually accepted as a related factor in PCOS. This review is intended to summarize and discuss previous and recent studies and findings on the connections between mitochondrial dysfunction and PCOS.
    Keywords:  follicular development; mitochondrion; polycystic ovary syndrome; reproductive metabolism
  31. Diabetologia. 2020 Feb 19.
      AIMS/HYPOTHESIS: Diabetic cardiomyopathy, characterised by increased oxidative damage and mitochondrial dysfunction, contributes to the increased risk of heart failure in individuals with diabetes. Considering that A-kinase anchoring protein 121 (AKAP1) is localised in the mitochondrial outer membrane and plays key roles in the regulation of mitochondrial function, this study aimed to investigate the role of AKAP1 in diabetic cardiomyopathy and explore its underlying mechanisms.METHODS: Loss- and gain-of-function approaches were used to investigate the role of AKAP1 in diabetic cardiomyopathy. Streptozotocin (STZ) was injected into Akap1-knockout (Akap1-KO) mice and their wild-type (WT) littermates to induce diabetes. In addition, primary neonatal cardiomyocytes treated with high glucose were used as a cell model of diabetes. Cardiac function was assessed with echocardiography. Akap1 overexpression was conducted by injecting adeno-associated virus 9 carrying Akap1 (AAV9-Akap1). LC-MS/MS analysis and functional experiments were used to explore underlying molecular mechanisms.
    RESULTS: AKAP1 was downregulated in the hearts of STZ-induced diabetic mouse models. Akap1-KO significantly aggravated cardiac dysfunction in the STZ-treated diabetic mice when compared with WT diabetic littermates, as evidenced by the left ventricular ejection fraction (LVEF; STZ-treated WT mice [WT/STZ] vs STZ-treated Akap1-KO mice [KO/STZ], 51.6% vs 41.6%). Mechanistically, Akap1 deficiency impaired mitochondrial respiratory function characterised by reduced ATP production. Additionally, Akap1 deficiency increased cardiomyocyte apoptosis via enhanced mitochondrial reactive oxygen species (ROS) production. Furthermore, immunoprecipitation and mass spectrometry analysis indicated that AKAP1 interacted with the NADH-ubiquinone oxidoreductase 75 kDa subunit (NDUFS1). Specifically, Akap1 deficiency inhibited complex I activity by preventing translocation of NDUFS1 from the cytosol to mitochondria. Akap1 deficiency was also related to decreased ATP production and enhanced mitochondrial ROS-related apoptosis. In contrast, restoration of AKAP1 expression in the hearts of STZ-treated diabetic mice promoted translocation of NDUFS1 to mitochondria and alleviated diabetic cardiomyopathy in the LVEF (WT/STZ injected with adeno-associated virus carrying gfp [AAV9-gfp] vs WT/STZ AAV9-Akap1, 52.4% vs 59.6%; KO/STZ AAV9-gfp vs KO/STZ AAV9-Akap1, 42.2% vs 57.6%).
    CONCLUSIONS/INTERPRETATION: Our study provides the first evidence that Akap1 deficiency exacerbates diabetic cardiomyopathy by impeding mitochondrial translocation of NDUFS1 to induce mitochondrial dysfunction and cardiomyocyte apoptosis. Our findings suggest that Akap1 upregulation has therapeutic potential for myocardial injury in individuals with diabetes.
    Keywords:  AKAP1; Apoptosis; Diabetic cardiomyopathy; Mitochondrial dysfunction; NDUFS1
  32. Exp Gerontol. 2020 Feb 18. pii: S0531-5565(19)30856-3. [Epub ahead of print] 110883
      Aging is typically associated with a decline in whole animal performance that ultimately contributes to death. It is suspected that a decline in ATP production leads to dysfunction in cellular processes, contributing to the decline in performance. Birds require large amounts of ATP to support physiological process, especially flight, which is one of the most energetically expensive forms of locomotion in the animal kingdom to sustain. Since the bulk of ATP production is coordinated through mitochondrial activity, we set out to explore mitochondrial function in young (~8 months) and old (~73 months) zebra finches (Taeniopygia guttata). We exploited the fact that avian red blood cells (RBCs) are nucleated and have functional mitochondria to explore the phenomenon of age-related decline in mitochondrial function without the need for terminal sampling. We found that RBCs from old zebra finches have lower flux control ratios (mitochondrial O2 consumption attributed to ATP production; 0.29-0.36-fold), exhibit higher respiration (1.4-fold), and significantly higher citrate synthase activity (1.4-fold) than young birds. Respiration rates normalized to citrate synthase activity suggest that mitochondrial quality is changing, as leak state is significantly lower (0.39-fold) in old zebra finches in comparison to young animals. Overall, our findings indicate a possible change in the function of mitochondria in older zebra finches, which may be associated with a corresponding increase in mitochondrial quantity, possibly to offset a decline in mitochondrial quality.
    Keywords:  Aging; Birds; Citrate synthase; Mitochondrial dysfunction; Senescence
  33. Circ Res. 2020 Feb 06.
    Keywords:  Mitochondrial transplantation; calcium overload
  34. Front Oncol. 2020 ;10 31
      Bcl2-associated athanogene (BAG)2 as a co-chaperone has been demonstrated to be involved in tumor growth and metastasis, but its biological function in gastric cancer remains unknown. Here, we reported that BAG2 was highly expressed in gastric cancer cell lines and tissues, indicating poor prognosis. High expression of BAG2 was significantly associated with T stage and differentiation level of gastric cancer (P < 0.001). Functional experiments revealed that BAG2 knockdown in gastric cancer cells inhibited the proliferation, invasion and migration of cells through AKT/mTOR and extracellular regulated kinase (ERK) pathways. Proteomic analysis identified that BAG2 may be involved in the regulation of mitogen-activated protein kinase (MAPK) pathway. In addition, immunoprecipitation showed that BAG2 could bind to ERK1/2. Luciferase reporter assay and Western blot verified that BAG2 was down-regulated by miR186. Taken together, our findings may reveal the basic function of BAG2 and uncover a potential therapeutic target for gastric cancer.
    Keywords:  BAG2; gastric cancer; iTRAQ proteomics technology; miR186; therapeutic target
  35. Cells. 2020 Feb 14. pii: E443. [Epub ahead of print]9(2):
      Cytochrome c oxidase (COX) is regulated through tissue-, development- or environment-controlled expression of subunit isoforms. The COX4 subunit is thought to optimize respiratory chain function according to oxygen-controlled expression of its isoforms COX4i1 and COX4i2. However, biochemical mechanisms of regulation by the two variants are only partly understood. We created an HEK293-based knock-out cellular model devoid of both isoforms (COX4i1/2 KO). Subsequent knock-in of COX4i1 or COX4i2 generated cells with exclusive expression of respective isoform. Both isoforms complemented the respiratory defect of COX4i1/2 KO. The content, composition, and incorporation of COX into supercomplexes were comparable in COX4i1- and COX4i2-expressing cells. Also, COX activity, cytochrome c affinity, and respiratory rates were undistinguishable in cells expressing either isoform. Analysis of energy metabolism and the redox state in intact cells uncovered modestly increased preference for mitochondrial ATP production, consistent with the increased NADH pool oxidation and lower ROS in COX4i2-expressing cells in normoxia. Most remarkable changes were uncovered in COX oxygen kinetics. The p50 (partial pressure of oxygen at half-maximal respiration) was increased twofold in COX4i2 versus COX4i1 cells, indicating decreased oxygen affinity of the COX4i2-containing enzyme. Our finding supports the key role of the COX4i2-containing enzyme in hypoxia-sensing pathways of energy metabolism.
    Keywords:  mitochondria, OXPHOS, respiratory chain, cytochrome c oxidase, COX, COX4 isoforms, COX4i2, oxygen affinity, p50, oxygen sensing
  36. Antioxid Redox Signal. 2020 Feb 16.
      SIGNIFICANCE: Cancer is related to redox biology from many points of view, such as initiation and promotion, metabolism and growth, invasion and metastasis, vascularization or through the interaction with the immune system. In addition, this extremely complex relationship depends on the redox homeostasis of each cellular compartment, which might be used to fight cancer. Recent advances: New ways of modulating specific and little explored aspects of redox biology have been revealed, as well as new delivery methods or uses of previously known treatments against cancer. Here, we review the latest experimental evidence regarding redox biology in cancer treatment and analyze its potential impact in the development of improved and more effective antineoplastic therapies.CRITICAL ISSUES: A critical issue that deserves particular attention is the understanding that both extremes of redox biology (i.e. oxidative stress and reductive stress) might be useful or harmful in relation to cancer prevention and treatment.
    FUTURE DIRECTIONS: Additional research is needed to understand how to selectively induce reductive or oxidative stress adequately to avoid cancer proliferation or to induce cancer cell death.
  37. Cell Rep. 2020 Feb 18. pii: S2211-1247(20)30085-1. [Epub ahead of print]30(7): 2332-2348.e10
      Mitochondria are key organelles for brain health. Mitochondrial alterations have been reported in several neurodegenerative disorders, including Alzheimer's disease (AD), and the comprehension of the underlying mechanisms appears crucial to understand their relationship with the pathology. Using multiple genetic, pharmacological, imaging, and biochemical approaches, we demonstrate that, in different familial AD cell models, mitochondrial ATP synthesis is affected. The defect depends on reduced mitochondrial pyruvate oxidation, due to both lower Ca2+-mediated stimulation of the Krebs cycle and dampened mitochondrial pyruvate uptake. Importantly, this latter event is linked to glycogen-synthase-kinase-3β (GSK-3β) hyper-activation, leading, in turn, to impaired recruitment of hexokinase 1 (HK1) to mitochondria, destabilization of mitochondrial-pyruvate-carrier (MPC) complexes, and decreased MPC2 protein levels. Remarkably, pharmacological GSK-3β inhibition in AD cells rescues MPC2 expression and improves mitochondrial ATP synthesis and respiration. The defective mitochondrial bioenergetics influences glutamate-induced neuronal excitotoxicity, thus representing a possible target for future therapeutic interventions.
    Keywords:  Alzheimer’s disease; GSK-3b; bioenergetics; calcium homeostasis; hexokinase 1; mitochondrial metabolism; mitochondrial pyruvate carrier; presenilin; pyruvate
  38. Cancer Immunol Res. 2020 Feb 19. pii: canimm.0702.2019. [Epub ahead of print]
      The success of checkpoint inhibitors in cancer treatment is associated with the infiltration of tissue-resident memory T cells (Trm). In this study, we found that about 30% of tumor infiltrating lymphocytes (TILs) in TME of gastric adenocarcinoma (GAC) were CD69+CD103+ Trm cells. Trm cells were low in patients with metastasis and the presence of Trm cells was associated with better prognosis in GAC patients. Trm cells expressed high PD-1, TIGIT, and CD39 and represented tumor-reactive TILs. Instead of utilizing glucose, Trm cells relied on fatty acid oxidation for cell survival. Deprivation of fatty acid resulted in Trm cell death. In a tumor cell-T cell coculture system, GAC cancer cells outcompeted Trm cells for lipid uptake and induced Trm cell death. Targeting PD-L1 decreased fatty acid binding protein (Fabp) 4 and Fabp5 expression in tumor cells of GAC. In contrast, the blockade of PD-L1 increased Fabp4/5 expression in Trm cells, promoting lipid uptake by Trm cells and resulting in better survival of Trm cells in vitro and in vivo. PD-L1 blockade unleashed Trm cells specifically in the patient-derived xenograft (PDX) mice. PDX mice that did not response to PD-L1 blockade had less Trm cells than responders. Together, these data demonstrated that Trm cells represent a subset of TILs in the antitumor immune response and that metabolic reprogramming could be a promising way to prolong the longevity of Trm cells and enhance antitumor immunity in GAC.
  39. J Mol Biol. 2020 Feb 13. pii: S0022-2836(20)30102-9. [Epub ahead of print]
      The mitochondrial cytochrome c oxidase, the terminal enzyme of the respiratory chain, contains heme and copper centers for electron transfer. The conserved COX2 subunit contains the CuA site, a binuclear copper center. The copper chaperones SCO1, SCO2, and COA6 are required for CuA center formation. Loss of function of these chaperones and the concomitant cytochrome c oxidase deficiency cause severe human disorders. Here we analyzed the molecular function of COA6 and the consequences of COA6 deficiency for mitochondria. Our analyses show that loss of COA6 causes combined complex I and complex IV deficiency and impacts membrane potential driven protein transport across the inner membrane. We demonstrate that COA6 acts as a thiol-reductase to reduce disulphide bridges of critical cysteine residues in SCO1 and SCO2. Cysteines within the CX3CXNH domain of SCO2 mediate its interaction with COA6 but are dispensable for SCO2-SCO1 interaction. Our analyses define COA6 as thiol-reductase, which is essential for CuA biogenesis.
    Keywords:  COA6; Cu(A) center; copper metallochaperones; cytochrome c oxidase; mitochondria
  40. Biochim Biophys Acta Gen Subj. 2020 Feb 13. pii: S0304-4165(20)30046-5. [Epub ahead of print] 129556
      BACKGROUND: Multi-drug resistance (MDR) develops because cancer cells evade toxicity of several structurally unrelated drugs. Besides other mechanisms, MDR is linked to the overexpression of ATP Binding Cassette (ABC), transporters, among which ABCB1 is the best characterized one. Since overactivation of PI3K/Akt/mTOR plays a pivotal role in the growth of human cancers, we hypothesized whether dual PI3K and mTOR inhibitor, BEZ235 (BEZ, dactolisib) reverses resistance to doxorubicin (DOX).METHODS: Ovarian (A2780) and pancreatic (MiaPaca2) cancer cells were used to generate DOX-resistant clones by overexpressing ABCB1 or stepwise treatment of DOX. Intracellular accumulation of DOX was measured by flow cytometry after treatment with BEZ.
    RESULTS: BEZ treatment caused increase in intracellular levels of DOX which was almost identical to the naïve parental cell lines. BEZ was found to be weak substrate for ABCB1 as demonstrated by minimal increase in ATPase activity. BEZ treatment caused dose-dependent decrease in cell viability in combination with DOX which was associated with increase in cleaved PARP expression in the drug resistant clones.
    CONCLUSIONS: These results suggest that BEZ is a non-substrate inhibitor of ABCB1 and is able to effectively re-sensitize cells overexpressing ABCB1 to the effects of DOX.
    GENERAL SIGNIFICANCE: Dual PI3 Kinase/mTOR inhibitor, BEZ has the potential to reverse MDR in cancer patients.
    Keywords:  ABC transporters; Doxorubicin; Multidrug resistance; Ovarian cancer; PI3/mTOR signaling; Pancreatic cancer
  41. Mitochondrion. 2020 Feb 17. pii: S1567-7249(19)30287-9. [Epub ahead of print]
      Polycystic ovary syndrome (PCOS) is a common endocrine disorder characterized by irregular menstrual cycles, hyperandrogenism and subfertility. Due to its complex manifestation, the pathogenic mechanism of PCOS is not well defined. Cumulative effect of altered genetic and epigenetic factors along with environmental factors may play a role in the manifestation of PCOS leading to systemic malfunction. With failure of genome-wide association study (GWAS) and other studies performed on nuclear genome to provide any clue for precise mechanism of PCOS pathogenesis, attention has been diverted to mitochondria. Mitochondrion plays an important role in cellular metabolic functions and is linked to IR. Recently, increasing reports suggest that mitochondrial dysfunction may be a contributing factor in the pathogenesis of PCOS. Hence, in this review, we have discussed mitochondrial biology in brief and emphasizes on genetic and epigenetic aspects of mitochondrial dysfunction studied in PCOS women and PCOS-like animal models. We also highlight underlying mechanism behind mitochondrial dysfunction contributing to PCOS and its related complications such as obesity, diabetes, cardiovascular diseases, metabolic syndrome, non-alcoholic fatty liver disease (NAFLD) and cancer. Furthermore, contrasting remarks against involvement of mitochondrial dysfunction in PCOS pathophysiology have also been presented. This review enhances our understanding in relation to mitochondrial dysfunction in the etiology of PCOS and stimulates further research to explore a clear link between mitochondrial dysfunction and PCOS pathogenesis and progression. Understanding pathogenic mechanisms underlying PCOS will open new windows to develop promising therapeutic strategies against PCOS.
    Keywords:  Mitochondrion; Polycystic Ovary syndrome; mitochondrial dysfunction; oxidative stress; subfertility
  42. Aging (Albany NY). 2020 Feb 18. 12
      Metformin is one of the most commonly used first-line oral medications for type 2 diabetes mellitus. Multiple observational studies, reviewed in numerous systematic reviews, have shown that metformin treatment may not only reduce the risk of cancer but may also improve the efficacy of cancer treatment in diabetic patients. Recent studies have been conducted to determine whether a similar protective effect can be demonstrated in nondiabetic cancer patients. However, the results are controversial. The potential optimal dose, schedule, and duration of metformin treatment and the heterogeneity of histological subtypes and genotypes among cancer patients might contribute to the different clinical benefits. In addition, as the immune property of metformin was investigated, further studies of the immunomodulatory effect of metformin on cancer cells should also be taken into account to optimize its clinical use. In this review, we present and discuss the latest findings regarding the anticancer potential of metformin in nondiabetic patients with cancer.
    Keywords:  anticancer; cancer; metformin; nondiabetic patients; prevention
  43. Front Oncol. 2020 ;10 52
      Lung squamous cell carcinomas (SCCs) are highly aggressive tumors, and there is currently no effective targeted therapy owing to the lack of specific mutation targets. Compared with lung adenocarcinoma (ADCs), lung SCCs reportedly utilized higher levels of glucose metabolism to meet the anabolic and catabolic needs required to sustain rapid tumor growth. Hexokinase 2 (HK2) is an enzyme that catalyzes the rate-limit and first committed step in glucose metabolism. Here, we investigated the expression and effect of HK2 in lung SCCs. We found a significantly higher HK2 expression in lung SCCs, but not lung ADC or normal tissues. HK2 depletion or inhibition decreased the glycolysis and tumor growth via activating AMPK signaling pathway, which downregulated mTORC1 activity. Furthermore, we found an increased oxygen respiration rate compensating for HK2 depletion. Thus, metformin treatment showed combinatorial therapeutic value, which resulted in greater induction of lung SCC apoptosis in vitro and in vivo. Our study suggests that HK2 depletion in combination with metformin might be a novel effective strategy for lung SCCs therapy.
    Keywords:  apoptosis; glycolysis; hexokinase 2; lung squamous cell carcinoma; metformin
  44. Nat Commun. 2020 Feb 20. 11(1): 991
      Characterizing the complex composition of solid tumors is fundamental for understanding tumor initiation, progression and metastasis. While patient-derived samples provide valuable insight, they are heterogeneous on multiple molecular levels, and often originate from advanced tumor stages. Here, we use single-cell transcriptome and epitope profiling together with pathway and lineage analyses to study tumorigenesis from a developmental perspective in a mouse model of salivary gland squamous cell carcinoma. We provide a comprehensive cell atlas and characterize tumor-specific cells. We find that these cells are connected along a reproducible developmental trajectory: initiated in basal cells exhibiting an epithelial-to-mesenchymal transition signature, tumorigenesis proceeds through Wnt-differential cancer stem cell-like subpopulations before differentiating into luminal-like cells. Our work provides unbiased insights into tumor-specific cellular identities in a whole tissue environment, and emphasizes the power of using defined genetic model systems.
  45. Nat Commun. 2020 Feb 20. 11(1): 970
      Deregulation of mitochondrial network in terminally differentiated cells contributes to a broad spectrum of disorders. Methylmalonic acidemia (MMA) is one of the most common inherited metabolic disorders, due to deficiency of the mitochondrial methylmalonyl-coenzyme A mutase (MMUT). How MMUT deficiency triggers cell damage remains unknown, preventing the development of disease-modifying therapies. Here we combine genetic and pharmacological approaches to demonstrate that MMUT deficiency induces metabolic and mitochondrial alterations that are exacerbated by anomalies in PINK1/Parkin-mediated mitophagy, causing the accumulation of dysfunctional mitochondria that trigger epithelial stress and ultimately cell damage. Using drug-disease network perturbation modelling, we predict targetable pathways, whose modulation repairs mitochondrial dysfunctions in patient-derived cells and alleviate phenotype changes in mmut-deficient zebrafish. These results suggest a link between primary MMUT deficiency, diseased mitochondria, mitophagy dysfunction and epithelial stress, and provide potential therapeutic perspectives for MMA.
  46. J Pathol. 2020 Feb 19.
      Previously we reported that the microRNA miR-210 is aberrantly upregulated in clear cell renal cell carcinoma (ccRCC) via deregulation of the VHL-HIF pathway. In the present study, to investigate the biological impact of miR-210 in ccRCC tumorigenesis, we developed a transgenic mouse line expressing miR-210 in proximal tubule cells under control of the mouse SGLT2/Slc5a2 promoter. Light microscopy revealed desquamation of the tubule cells and regeneration of the proximal tubule, suggesting that miR-210 expression led to damage of the proximal tubule cells. Electron microscopy revealed alterations to the mitochondria in proximal tubule cells, with marked reduction of the mitochondrial inner membrane, which is the main site of ATP production via oxidative phosphorylation. An additional in vitro study revealed that this loss of the inner membrane was associated with downregulation of Iscu and Ndufa4, the target genes of miR-210, suggesting that the miR-210-ISCU/NDUFA4 axis may affect mitochondrial energy metabolism. Furthermore, metabolome analysis revealed activation of anaerobic glycolysis in miR-210-transfected cells, and consistent with this the secretion of lactate, the final metabolite of anaerobic glycolysis, was significantly increased. Lactate concentration was higher in the kidney cortex of transgenic mice relative to wild-type mice, although the difference was not significant (p = 0.070). On the basis of these findings, we propose that miR-210 may induce a shift of energy metabolism from oxidative phosphorylation to glycolysis by acting on the mitochondrial inner membrane. In addition to activation of glycolysis, we observed activation of the pentose phosphate pathway and an increase in the total amount of amino acids in miR-210 transfected cells. This may help cells synthesize nucleotides and proteins for building new cells. These results suggest that miR-210 may be involved in the metabolic changes in the early stage of ccRCC development, helping the cancer cells to acquire growth and survival advantages. This article is protected by copyright. All rights reserved.
    Keywords:  ISCU; NDUFA4; clear cell renal cell carcinoma; metabolome; miR-210; mitochondrial alteration; transgenic mouse
  47. Biochem Biophys Res Commun. 2020 Feb 13. pii: S0006-291X(20)30299-0. [Epub ahead of print]
      The hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are encoded by a family of four genes (HCN1-4). All isoforms are expressed in the heart, HCN4 being the most abundant in the sinoatrial node (SAN). HCN channels are responsible for the "funny" current (If) associated with the generation and autonomic control of the diastolic depolarization phase of cardiac action potential. In this work we performed a proteomic analysis of HCN4 transfected in HEK293 cells. Most of the identified proteins in the HCN4 network belonged to mitochondria. The subcellular localization of HCN channels was predicted in plasma membrane, mitochondria and nucleus. Experimentally, HCN2 (full-length, truncated), HCN3 (full-length, truncated) and HCN4 (truncated) were detected in rat heart mitochondria by immunoblotting. If sensitive to ZD7288, was recorded by patch-clamp in mitoplasts from cardiomyocytes. Mitochondrial membrane potential (ΔΨm) assessment in H9c2 cells revealed that ZD7288 induced almost 50% higher hyperpolarization respect to control at 30 min. Furthermore, ZD7288 reduced oxygen consumption attributed to ATP synthesis in H9c2 cells. In conclusion, we identify for the first time functional HCN channels in mammalian cardiac mitochondria and demonstrate their impact on ΔΨm and respiration.
    Keywords:  Cardiomyocyte; HCN channels; Ivabradine; Mitochondria; Potassium channels; ZD7288
  48. Trends Cancer. 2020 Feb;pii: S2405-8033(19)30261-4. [Epub ahead of print]6(2): 75-78
      Obesity and type 2 diabetes (T2D) increase the prevalence and worsen the prognosis of more than a dozen tumor types; however, the mechanism for this association remains hotly debated. Here we discuss a potential role for insulin as the key hormonal mediator of tumor metabolism and growth in obesity-associated insulin resistance.
    Keywords:  diabetes; insulin resistance; metabolism; obesity