bims-nenemi Biomed News
on Neuroinflammation, neurodegeneration and mitochondria
Issue of 2022‒02‒06
seventeen papers selected by
Marco Tigano
Thomas Jefferson University

  1. Mol Cell. 2022 Jan 28. pii: S1097-2765(22)00008-9. [Epub ahead of print]
      BAX and BAK are key apoptosis regulators that mediate the decisive step of mitochondrial outer membrane permeabilization. However, the mechanism by which they assemble the apoptotic pore remains obscure. Here, we report that BAX and BAK present distinct oligomerization properties, with BAK organizing into smaller structures with faster kinetics than BAX. BAK recruits and accelerates BAX assembly into oligomers that continue to grow during apoptosis. As a result, BAX and BAK regulate each other as they co-assemble into the same apoptotic pores, which we visualize. The relative availability of BAX and BAK molecules thereby determines the growth rate of the apoptotic pore and the relative kinetics by which mitochondrial contents, most notably mtDNA, are released. This feature of BAX and BAK results in distinct activation kinetics of the cGAS/STING pathway with implications for mtDNA-mediated paracrine inflammatory signaling.
    Keywords:  AFM; BAK; BAX; BCL-2; inflammatory cell death; membrane pore; mitochondria; pore-forming protein; single-molecule imaging; super-resolution microscopy
  2. Mol Cell Biochem. 2022 Jan 31.
      In the present study we have shown that treatment of SH-SY5Y cells with either thapsigargin or tunicamycin is associated with a significant decrease in ROUTINE and ATP-coupled mitochondrial respiration as well as a decrease in spare and maximal respiratory capacity. We have also shown that treating cells with either thapsigargin or tunicamycin is associated with significant changes in mitochondrial membrane potential (ΔΨm) generation, which is mainly associated with the reversal of the succinyl-CoA ligase reaction and a decreased activity of complex II. Despite the induction of endoplasmic reticulum (ER) specific unfolded protein response (UPR), as documented by increased expression of HRD1, ER stress did not induce mitochondrial UPR since the expression of both mitochondrial protease LONP1 and mitochondrial chaperone HSP60 was not significantly altered. Inhibition of IRE1α ribonuclease with STF-083010 did not protect the SH-SY5Y cells from ER stress-induced mitochondrial dysfunction. STF-083010 itself had significant impact on both mitochondrial respiration and generation of ΔΨm, which has mainly been associated with the uncoupling of respiratory chain from ATP synthesis.
    Keywords:  Endoplasmic reticulum stress; Mitochondrial dysfunction; Parkinson’s disease; Unfolded protein response
  3. Brain Res Bull. 2022 Jan 29. pii: S0361-9230(22)00017-X. [Epub ahead of print]181 97-108
      Subarachnoid hemorrhage (SAH) is a hemorrhagic stroke disease with high mortality and disability rates. Neurological recovery in early brain injury (EBI) after SAH is a crucial stage to reduce complications and improve the prognosis of patients. The mitochondrial unfolded protein response (UPRmt) is an essential mitochondrial damage repair process, that degrades aggresomes formed by misfolded proteins. UPRmt is a response to cellular stress and enhances mitochondrial homeostasis. GrpEL1 is a nucleotide exchange factor that assists mtHSP70 in nonnative folding proteins in mitochondria. However, the role of UPRmt and GrpEL1 after SAH is unclear. Western blot, Immunofluorescence, Aggresome staining, JC-1 staining were conducted to detect UPRmt after SAH in vivo and in vitro. The results showed that the UPRmt-related proteins HSP60 and mtHSP70 did not change in the EBI after SAH in vivo and in vitro but increased in the isolated mitochondria. In vitro primary neurons treated with oxyhemoglobin (OxyHb) achieved the same result as MG132 induction, increasing neuron protein aggresomes. The expression of GRPEL1 was unchanged in total protein and mitochondrial protein by Western blot. Co-immunoprecipitation (Co-IP) experiments showed that the GRPEL1-mtHSP70 complex decreased after OxyHb treatment. After GRPEL1 overexpression, the GRPEL1-mtHSP70 complex increased, while aggresome in neurons decreased. JC-1 showed an increased mitochondrial membrane potential, ATP content increased, and Western blot analysis revealed decreased cleaved-Caspase 9, suggesting improved mitochondrial function. In conclusion, the reduced GrpEL1-mtHSP70 complex is an essential factor affecting UPRmt in EBI after SAH. Increasing GrpEL1 promotes GrpEL1 and mtHSP70 binding, promoting the neuronal mitochondrial homeostasis, and might be an essential clinical intervention target for EBI after SAH.
    Keywords:  Aggresome; GrpEL1; HSP60; MtHSP70; Subarachnoid hemorrhage; UPRmt
  4. Virus Genes. 2022 Feb 01.
      Mitochondrial virus-induced signal adaptor (MAVS), also known as VISA, IPS-1, and Cardif, is a crucial adaptor protein in the RIG-I-like receptor (RLR) signaling pathway. Upon viral infection, RIG-I recognizes viral dsRNA and further transfers it to mitochondria, where it binds to MAVS through its CARD domain, generating a series of signal cascades. Transduction through this signaling cascade leads to phosphorylation and nuclear translocation of interferon regulatory factor 3/7 (IRF3/IRF7) and activation of NF-κB, which ultimately produces type I interferon (IFN) and proinflammatory cytokines. Here, our experiments demonstrated that overexpression of SRY-related high-mobility group protein 9 (SOX9) significantly inhibited Sendai virus (SeV)-induced and MAVS-mediated activation of the IFN-β promoter and ISRE. However, knocking out the expression of SOX9 in cells promoted SeV-induced IFN-β promoter and ISRE activation. Further studies have shown that SOX9 interacts with MAVS and targets MAVS to inhibit the association of MAVS-TRAF2, thereby inhibiting MAVS-mediated TRAF2 ubiquitination. Taken together, these results indicate that SOX9 downregulates IFN-β expression and antiviral signal transduction by targeting MAVS.
    Keywords:  MAVS; RIG-I; RLR antiviral signaling; SOX9
  5. Ageing Res Rev. 2022 Jan 31. pii: S1568-1637(22)00020-4. [Epub ahead of print] 101578
      Maintenance of mitochondrial DNA (mtDNA) homeostasis includes a variety of processes, such as mtDNA replication, repair, and nucleotides synthesis, aimed at preserving the structural and functional integrity of mtDNA molecules. Mutations in several nuclear genes (i.e., POLG, POLG2, TWNK, OPA1, DGUOK, MPV17, TYMP) impair mtDNA maintenance, leading to clinical syndromes characterized by mtDNA depletion and/or deletions in affected tissues. In the past decades, studies have demonstrated a progressive accumulation of multiple mtDNA deletions in dopaminergic neurons of the substantia nigra in elderly population and, to a greater extent, in Parkinson's disease patients. Moreover, parkinsonism has been frequently described as a prominent clinical feature in mtDNA instability syndromes. Among Parkinson's disease-related genes with a significant role in mitochondrial biology, PARK2 and LRRK2 specifically take part in mtDNA maintenance. Moreover, a variety of murine models (i.e., "Mutator", "MitoPark", "PD-mitoPstI", "Deletor", "Twinkle-dup" and "TwinkPark") provided in vivo evidence that mtDNA stability is required to preserve nigrostriatal integrity. Here, we review and discuss the clinical, genetic, and pathological background underlining the link between impaired mtDNA homeostasis and dopaminergic degeneration.
    Keywords:  POLG1, Twinkle; Parkinsonism; Parkinson’s disease; mitochondrion; mtDNA homeostasis
  6. J Biol Chem. 2022 Jan 28. pii: S0021-9258(22)00092-8. [Epub ahead of print] 101652
      Mitochondrial dysfunction induces a strong adaptive retrograde signaling response; however, many of the down-stream effectors of this response remain to be discovered. Here, we studied the shared transcriptional responses to three different mitochondrial respiratory chain inhibitors in human primary skin fibroblasts using QuantSeq 3'-RNA-sequencing. We found that genes involved in the mevalonate pathway were concurrently downregulated, irrespective of the respiratory chain complex affected. Targeted metabolomics demonstrated that impaired mitochondrial respiration at any of the three affected complexes also had functional consequences on the mevalonate pathway, reducing levels of cholesterol precursor metabolites. A deeper study of complex I inhibition showed a reduced activity of ER-bound sterol-sensing enzymes through impaired processing of the transcription factor SREBP2 and accelerated degradation of the ER cholesterol-sensors SQLE and HMGCR. These adaptations of mevalonate pathway activity affected neither total intracellular cholesterol levels nor the cellular free (non-esterified) cholesterol pool. Finally, measurement of intracellular cholesterol using the fluorescent cholesterol binding dye filipin revealed that complex I inhibition elevated cholesterol on intracellular compartments. Taken together, our study shows that mitochondrial respiratory chain dysfunction elevates intracellular free cholesterol levels and therefore attenuates the expression of mevalonate pathway enzymes, which lowers endogenous cholesterol biosynthesis, disrupting the metabolic output of the mevalonate pathway. We conclude that intracellular disturbances in cholesterol homeostasis may alter systemic cholesterol management in diseases associated with declining mitochondrial function.
    Keywords:  Cholesterol; CoQ; HMGCR; SQLE; SREBP2; farnesyl pyrophosphate; geranyl pyrophosphate; mevalonate pathway; mitochondria; retrograde signaling; sterol; ubiquinol
  7. Free Radic Res. 2022 Jan 30. 1-16
      MutY homolog (MUTYH), an important protein in base excision repair (BER) system, excises adenine in the nascent strand opposite 8-oxoguanine in template DNA and restores G:C base-pair to maintain the fidelity of DNA replication. The loss of MUTYH causes oxidative stress and influences cardiac function, but the mechanism remains to be addressed. Here we demonstrate that Mutyh deficiency alters mitochondrial structure and impairs mitochondrial function through downregulation of mitochondrial fusion protein Mfn2 and alteration of the ratio of L-Opa1/S-Opa1 accompanied by reduction of α-ketoglutaric acid (α-KG) under oxidative stress condition. Further analysis reveals that the Mutyh deficiency may cause downregulation of histone demethylases and DNA demethylases and inhibition of the Mfn2 transcription. Oxidative stress associated with tert-butyl hydroperoxide (t-BHP) exposure results in the degradation of L-Opa1 and impairs the balance of L-Opa1/S-Opa1. Interestingly, α-KG supplementation alleviates the damage associated with Mutyh deficiency, restores the expression of Mfn2 and prevents degradation of L-Opa1. The current study demonstrates the relationship among Mutyh deficiency-coupled oxidative stress, the altered expressions of Mfn2 and Opa1, and the mitochondrial dysfunction, in which an intermediate in the tricarboxylic acid (TCA) cycle, α-KG has a key regulatory role.
    Keywords:  MUTYH; cardiac dysfunction; mitochondrial fusion; oxidative stress; α-KG
  8. Front Integr Neurosci. 2021 ;15 747901
      Neural mitochondrial dysfunction, neural oxidative stress, chronic neuroinflammation, toxic protein accumulation, and neural apoptosis are common causes of neurodegeneration. Elamipretide, a small mitochondrially-targeted tetrapeptide, exhibits therapeutic effects and safety in several mitochondria-related diseases. In neurodegeneration, extensive studies have shown that elamipretide enhanced mitochondrial respiration, activated neural mitochondrial biogenesis via mitochondrial biogenesis regulators (PCG-1α and TFAM) and the translocate factors (TOM-20), enhanced mitochondrial fusion (MNF-1, MNF-2, and OPA1), inhibited mitochondrial fission (Fis-1 and Drp-1), as well as increased mitophagy (autophagy of mitochondria). In addition, elamipretide has been shown to attenuate neural oxidative stress (hydrogen peroxide, lipid peroxidation, and ROS), neuroinflammation (TNF, IL-6, COX-2, iNOS, NLRP3, cleaved caspase-1, IL-1β, and IL-18), and toxic protein accumulation (Aβ). Consequently, elamipretide could prevent neural apoptosis (cytochrome c, Bax, caspase 9, and caspase 3) and enhance neural pro-survival (Bcl2, BDNF, and TrkB) in neurodegeneration. These findings suggest that elamipretide may prevent the progressive development of neurodegenerative diseases via enhancing mitochondrial respiration, mitochondrial biogenesis, mitochondrial fusion, and neural pro-survival pathway, as well as inhibiting mitochondrial fission, oxidative stress, neuroinflammation, toxic protein accumulation, and neural apoptosis. Elamipretide or mitochondrially-targeted peptide might be a targeted agent to attenuate neurodegenerative progression.
    Keywords:  Bendavia; MTP-31; SS-31; brain; mitochondrial; neurodegeneration
  9. Aging Dis. 2022 Feb;13(1): 157-174
      Mitochondrial dysfunction may play a crucial role in various diseases due to its roles in the regulation of energy production and cellular metabolism. Serine/threonine kinase (AKT) is a highly recognized antioxidant, immunomodulatory, anti-proliferation, and endocrine modulatory molecule. Interestingly, increasing studies have revealed that AKT can modulate mitochondria-mediated apoptosis, redox states, dynamic balance, autophagy, and metabolism. AKT thus plays multifaceted roles in mitochondrial function and is involved in the modulation of mitochondria-related diseases. This paper reviews the protective effects of AKT and its potential mechanisms of action in relation to mitochondrial function in various diseases.
    Keywords:  AKT; disease; energy dynamics/metabolism; mitochondrial autophagy; pathway signaling
  10. Redox Biol. 2022 Jan 29. pii: S2213-2317(22)00024-6. [Epub ahead of print]50 102252
      Tumor suppressor p53 plays a pivotal role in orchestrating mitochondrial remodeling by regulating their content, fusion/fission processes, and intracellular signaling molecules that are associated with mitophagy and apoptosis pathways. In order to determine a molecular mechanism underlying flow-mediated mitochondrial remodeling in endothelial cells, we examined, herein, the role of p53 on mitochondrial adaptations to physiological flow and its relevance to vascular function using endothelial cell-specific p53 deficient mice. We observed no changes in aerobic capacity, basal blood pressure, or endothelial mitochondrial phenotypes in the endothelial p53 mull animals. However, after 7 weeks of voluntary wheel running exercise, blood pressure reduction and endothelial mitochondrial remodeling (biogenesis, elongation, and mtDNA replication) were substantially blunted in endothelial p53 null animals compared to the wild-type, subjected to angiotensin II-induced hypertension. In addition, endothelial mtDNA lesions were significantly reduced following voluntary running exercise in wild-type mice, but not in the endothelial p53 null mice. Moreover, in vitro studies demonstrated that unidirectional laminar flow exposure significantly increased key putative regulators for mitochondrial remodeling and reduced mitochondrial reactive oxygen species generation and mtDNA damage in a p53-dependent manner. Mechanistically, unidirectional laminar flow instigated translocalization of p53 into the mitochondrial matrix where it binds to mitochondrial transcription factor A, TFAM, resulting in improving mtDNA integrity. Taken together, our findings suggest that p53 plays an integral role in mitochondrial remodeling under physiological flow condition and the flow-induced p53-TFAM axis may be a novel molecular intersection for enhancing mitochondrial homeostasis in endothelial cells.
    Keywords:  Endothelial cell; Fluid shear stress; Mitochondria; TFAM; mtROS; p53
  11. iScience. 2022 Feb 18. 25(2): 103734
      The mitochondrial unfolded protein response (UPRmt) is a promising pharmacological target for aging and age-related diseases. However, the integrative analysis of the impact of UPRmt activation on different signaling layers in animals with different genetic backgrounds is lacking. Here, we applied systems approaches to investigate the effect of UPRmt induced by doxycycline (Dox) on transcriptome, proteome, and lipidome in two genetically divergent worm strains, named N2 and CB4856. From the integrated omics datasets, we found that Dox prolongs lifespan of both worm strains through shared and strain-specific mechanisms. Specifically, Dox strongly impacts mitochondria, upregulates defense response, and lipid metabolism, while decreasing triglycerides. We further validated that lipid genes acs-2/20 and fat-7/6 were required for Dox-induced UPRmt and longevity in N2 and CB4856 worms, respectively. Our data have translational value as they indicate that the beneficial effects of Dox-induced UPRmt on lifespan are consistent across different genetic backgrounds through different regulators.
    Keywords:  Chronobiology; Proteomics; Transcriptomics
  12. J Cell Sci. 2022 Jan 31. pii: jcs.259194. [Epub ahead of print]
      To rapidly adapt to stresses such as infections, cells have evolved several mechanisms, which include the activation of stress response pathways and the innate immune response. These stress responses result in the rapid inhibition of translation and condensation of stalled mRNAs with RNA-binding proteins and signalling components into cytoplasmic biocondensates called stress granules (SGs). Increasing evidence suggests that SGs contribute to antiviral defence and thus viruses need to evade these responses to propagate. We previously showed that Feline Calicivirus (FCV) impairs SGs assembly by cleaving the scaffolding protein G3BP1. We also observed that uninfected bystander cells assembled G3BP1-positive granules, suggesting a paracrine response triggered by infection. We now present evidence that virus-free supernatant generated from infected cells can induce the formation of SG-like foci, that we named paracrine granules. They are linked to antiviral activity and exhibit specific kinetics of assembly-disassembly, and protein and RNA composition that are different from canonical SGs. We propose that this paracrine induction reflects a novel cellular defence mechanism to limit viral propagation and promote stress responses in bystander cells.
    Keywords:  G3BP1; Stress granules; Viruses
  13. Nat Commun. 2022 Feb 03. 13(1): 653
      Mitochondria are energy-generating organelles and mitochondrial biogenesis is stimulated to meet energy requirements in response to extracellular stimuli, including exercise. However, the mechanisms underlying mitochondrial biogenesis remain unknown. Here, we demonstrate that transcriptional coactivator with PDZ-binding motif (TAZ) stimulates mitochondrial biogenesis in skeletal muscle. In muscle-specific TAZ-knockout (mKO) mice, mitochondrial biogenesis, respiratory metabolism, and exercise ability were decreased compared to wild-type mice. Mechanistically, TAZ stimulates the translation of mitochondrial transcription factor A via Ras homolog enriched in brain (Rheb)/Rheb like 1 (Rhebl1)-mTOR axis. TAZ stimulates Rhebl1 expression via TEA domain family transcription factor. Rhebl1 introduction by adeno-associated virus or mTOR activation recovered mitochondrial biogenesis in mKO muscle. Physiologically, mKO mice did not stimulate exercise-induced mitochondrial biogenesis. Collectively, our results suggested that TAZ is a novel stimulator for mitochondrial biogenesis and exercise-induced muscle adaptation.
  14. Front Cell Infect Microbiol. 2021 ;11 784762
      The innate immune system represents a balanced first line of defense against infection. Type I interferons (IFNs) are key regulators of the response to viral infections with an essential early wave of IFN-β expression, which is conditional, time-restricted, and stochastic in its nature. The possibility to precisely monitor individual cells with active IFNB1 transcription during innate signaling requires a robust reporter system that mimics the endogenous IFN-β signal. Here, we present a reporter system based on expression of a destabilized version of eGFP (d2eGFP) from a stably integrated reporter cassette containing the IFNB1 promoter and 3'-untranslated region, enabling both spatial and temporal detection of regulated IFNB1 expression. Specifically, this reporter permits detection, quantification, and isolation of cells actively producing d2eGFP in a manner that fully mimics IFN-β production allowing tracking of IFNB1 gene activation and repression in monocytic cells and keratinocytes. Using induced d2eGFP expression as a readout for activated immune signaling at the single-cell level, we demonstrate the application of the reporter for FACS-based selection of cells with genotypes supporting cGAS-STING signaling. Our studies provide a novel approach for monitoring on/off-switching of innate immune signaling and form the basis for investigating genotypes affecting immune regulation at the single-cell level.
    Keywords:  IFNB1 reporter; IFNB1 transcription; flow cytometry; innate immunity; single-cell
  15. Front Cell Dev Biol. 2021 ;9 788634
      Mitochondrial autophagy (or mitophagy) regulates the mitochondrial network and function to contribute to multiple cellular processes. The protective effect of homeostatic mitophagy in cardiovascular diseases (CVDs) has attracted increasing attention. FUN14 domain containing 1 (FUNDC1), an identified mitophagy receptor, plays an essential role in CVDs. Different expression levels of FUNDC1 and its phosphorylated state at different sites alleviate or exacerbate hypoxia and ischemia/reperfusion injury, cardiac hypertrophy, or metabolic damage through promotion or inhibition of mitophagy. In addition, FUNDC1 can be enriched at contact sites between mitochondria and the endoplasmic reticulum (ER), determining the formation of mitochondria-associated membranes (MAMs) that regulate cellular calcium (Ca2+) homeostasis and mitochondrial dynamics to prevent heart dysfunction. Moreover, FUNDC1 has also been involved in inflammatory cardiac diseases such as septic cardiomyopathy. In this review, we collect and summarize the evidence on the roles of FUNDC1 exclusively in various CVDs, describing its interactions with different cellular organelles, its involvement in multiple cellular processes, and its associated signaling pathways. FUNDC1 may become a promising therapeutic target for the prevention and management of various CVDs.
    Keywords:  FUNDC1; LC3; MAM; cardiovascular diseases; mitophagy
  16. J Exp Clin Cancer Res. 2022 Jan 29. 41(1): 43
      BACKGROUND: Targeting mitochondrial oncoproteins presents a new concept in the development of effective cancer therapeutics. ATAD3A is a nuclear-encoded mitochondrial enzyme contributing to mitochondrial dynamics, cholesterol metabolism, and signal transduction. However, its impact and underlying regulatory mechanisms in cancers remain ill-defined.METHODS: We used head and neck squamous cell carcinoma (HNSCC) as a research platform and achieved gene depletion by lentiviral shRNA and CRISPR/Cas9. Molecular alterations were examined by RNA-sequencing, phospho-kinase profiling, Western blotting, RT-qPCR, immunohistochemistry, and immunoprecipitation. Cancer cell growth was assessed by MTT, colony formation, soft agar, and 3D cultures. The therapeutic efficacy in tumor development was evaluated in orthotopic tongue tumor NSG mice.
    RESULTS: ATAD3A is highly expressed in HNSCC tissues and cell lines. Loss of ATAD3A expression suppresses HNSCC cell growth and elicits tumor regression in orthotopic tumor-bearing mice, whereas gain of ATAD3A expression produces the opposite effects. From a mechanistic perspective, the tumor suppression induced by the overexpression of the Walker A dead mutant of ATAD3A (K358) produces a potent dominant-negative effect due to defective ATP-binding. Moreover, ATAD3A binds to ERK1/2 in the mitochondria of HNSCC cells in the presence of VDAC1, and this interaction is essential for the activation of mitochondrial ERK1/2 signaling. Most importantly, the ATAD3A-ERK1/2 signaling axis drives HNSCC development in a RAS-independent fashion and, thus, tumor suppression is more effectively achieved when ATAD3A knockout is combined with RAS inhibitor treatment.
    CONCLUSIONS: These findings highlight the novel function of ATAD3A in regulating mitochondrial ERK1/2 activation that favors HNSCC development. Combined targeting of ATAD3A and RAS signaling may potentiate anticancer activity for HNSCC therapeutics.
    Keywords:  ATAD3A; HNSCC; Mitochondrial ERK1/2; RAS; VDAC1; WA dead mutant
  17. Nat Cancer. 2021 Nov;2(11): 1204-1223
      Therapy resistance represents a major clinical challenge in acute myeloid leukemia (AML). Here we define a 'MitoScore' signature, which identifies high mitochondrial oxidative phosphorylation in vivo and in patients with AML. Primary AML cells with cytarabine (AraC) resistance and a high MitoScore relied on mitochondrial Bcl2 and were highly sensitive to venetoclax (VEN) + AraC (but not to VEN + azacytidine). Single-cell transcriptomics of VEN + AraC-residual cell populations revealed adaptive resistance associated with changes in oxidative phosphorylation, electron transport chain complex and the TP53 pathway. Accordingly, treatment of VEN + AraC-resistant AML cells with electron transport chain complex inhibitors, pyruvate dehydrogenase inhibitors or mitochondrial ClpP protease agonists substantially delayed relapse following VEN + AraC. These findings highlight the central role of mitochondrial adaptation during AML therapy and provide a scientific rationale for alternating VEN + azacytidine with VEN + AraC in patients with a high MitoScore and to target mitochondrial metabolism to enhance the sensitivity of AML cells to currently approved therapies.