bims-mikwok Biomed News
on Mitochondrial quality control
Issue of 2021‒07‒04
twenty-one papers selected by
Avinash N. Mukkala
University of Toronto

  1. Redox Biol. 2021 Jun 17. pii: S2213-2317(21)00206-8. [Epub ahead of print]45 102047
      The contribution of the Ubiquitin-Proteasome System (UPS) to mitophagy has been largely attributed to the E3 ubiquitin ligase Parkin. Here we show that in response to the oxidative stress associated with hypoxia or the hypoxia mimic CoCl2, the damaged and fragmented mitochondria are removed by Parkin-independent mitophagy. Mitochondria isolated from hypoxia or CoCl2-treated cells exhibited extensive ubiquitination, predominantly Lysine 48-linked and involves the degradation of key mitochondrial proteins such as the mitofusins MFN1/2, or the import channel component TOM20. Reflecting the critical role of mitochondrial protein degradation, proteasome inhibition blocked CoCl2-induced mitophagy. The five conserved ubiquitin-binding autophagy receptors (p62, NDP52, Optineurin, NBR1, TAX1BP1) were dispensable for the ensuing mitophagy, suggesting that the mitophagy step itself was independent of ubiquitination. Instead, the expression of two ubiquitin-independent mitophagy receptor proteins BNIP3 and NIX was induced by hypoxia or CoCl2-treatment followed by their recruitment to the oxidation-damaged mitochondria. By employing BNIP3/NIX double knockout and DRP1-null cell lines, we confirmed that mitochondrial clearance relies on DRP1-dependent mitochondrial fragmentation and BNIP3/NIX-mediated mitophagy. General antioxidants such as N-Acetyl Cysteine (NAC) or the mitochondria-specific Mitoquinone prevented HIF-1α stabilization, ameliorated hypoxia-related mitochondrial oxidative stress, and suppressed mitophagy. We conclude that the UPS and receptor-mediated autophagy converge to eliminate oxidation-damaged mitochondria.
    Keywords:  HIF-1α; Hypoxia; Mitochondria; Mitophagy; Oxidative stress; Proteasome; Ubiquitin
  2. Oxid Med Cell Longev. 2021 ;2021 5543452
      A healthy mitochondrial network produces a large amount of ATP and biosynthetic intermediates to provide sufficient energy for myocardium and maintain normal cell metabolism. Mitochondria form a dynamic and interconnected network involved in various cellular metabolic signaling pathways. As mitochondria are damaged, controlling mitochondrial quantity and quality is activated by changing their morphology and tube network structure, mitophagy, and biogenesis to replenish a healthy mitochondrial network to preserve cell function. There is no doubt that mitochondrial dysfunction has become a key factor in many diseases. Ischemia/reperfusion (IR) injury is a pathological manifestation of various heart diseases. Cardiac ischemia causes temporary tissue and organelle damage. Although reperfusion is essential to compensate for nutrient deficiency, blood flow restoration inconsequently further kills the previously ischemic cardiomyocytes. To date, dysfunctional mitochondria and disturbed mitochondrial quality control have been identified as critical IR injury mechanisms. Many researchers have detected abnormal mitochondrial morphology and mitophagy, as well as aberrant levels and activity of mitochondrial biogenesis factors in the IR injury model. Although mitochondrial damage is well-known in myocardial IR injury, the causal relationship between abnormal mitochondrial quality control and IR injury has not been established. This review briefly describes the molecular mechanisms of mitochondrial quality control, summarizes our current understanding of the complex role of mitochondrial quality control in IR injury, and finally speculates on the possibility of targeted control of mitochondria and the methods available to mitigate IR injury.
  3. Am J Physiol Cell Physiol. 2021 06 30.
      Mitochondrial Transplantation is emerging as a novel cellular biotherapy to alleviate mitochondrial damage and dysfunction. Mitochondria play a crucial role in establishing cellular homeostasis and providing cell with the energy necessary to accomplish its function. Owing to its endosymbiotic origin, mitochondria share many features with their bacterial ancestors. Unlike the nuclear DNA, which is packaged into nucleosomes and protected from adverse environmental effects; mitochondrial DNA are more prone to harsh environmental effects, in particular that of the reactive oxygen species (ROS). Mitochondrial damage and dysfunction are implicated in many diseases ranging from metabolic diseases to cardiovascular and neurodegenerative diseases, among others. While it was once thought that transplantation of mitochondria would not be possible due to its semi-autonomous nature and reliance on the nucleus, recent advances have shown that it is possible to transplant viable functional intact mitochondria from autologous, allogenic, and xenogeneic sources into different cell types. Moreover, current research suggests that the transplantation could positively modulate bioenergetics and improve disease outcome. Mitochondrial transplantation techniques and consequences of transplantation in cardiomyocytes are the theme of this review. First, we outline the different mitochondrial isolation and transfer techniques. Second, we detail the consequences of mitochondrial transplantation in the cardiovascular system, more specifically in the context of cardiomyopathies and ischemia. Lastly, we elaborate our vision on how mitochondrial transplantation may mitigate other cardiac conditions secondary to mitochondrial damage and dysfunction, such as atherosclerosis and ST-elevated myocardial infarction.
    Keywords:  Bioenergetics; Ischemia Reperfusion Injury; Mitochondiral transplantation; Mitochondrial Cardiomyopathy; Mitochondrial Transfer
  4. Biology (Basel). 2021 Jun 29. pii: 600. [Epub ahead of print]10(7):
      Mitochondria are double membrane-enclosed organelles performing important cellular and metabolic functions such as ATP generation, heme biogenesis, apoptosis, ROS production and calcium buffering. The mitochondrial inner membrane (IM) is folded into cristae membranes (CMs) of variable shapes using molecular players including the 'mitochondrial contact site and cristae organizing system' (MICOS) complex, the dynamin-like GTPase OPA1, the F1FO ATP synthase and cardiolipin. Aberrant cristae structures are associated with different disorders such as diabetes, neurodegeneration, cancer and hepato-encephalopathy. In this review, we provide an updated view on cristae biogenesis by focusing on novel roles of the MICOS complex in cristae dynamics and shaping of cristae. For over seven decades, cristae were considered as static structures. It was recently shown that cristae constantly undergo rapid dynamic remodeling events. Several studies have re-oriented our perception on the dynamic internal ambience of mitochondrial compartments. In addition, we discuss the recent literature which sheds light on the still poorly understood aspect of cristae biogenesis, focusing on the role of MICOS and its subunits. Overall, we provide an integrated and updated view on the relation between the biogenesis of cristae and the novel aspect of cristae dynamics.
    Keywords:  MICOS; cristae; cristae biogenesis; cristae dynamics; mitochondria
  5. Cell Death Dis. 2021 Jun 28. 12(7): 657
      Subcellular organelles communicate with each other to regulate function and coordinate responses to changing cellular conditions. The physical-functional coupling of the endoplasmic reticulum (ER) with mitochondria allows for the direct transfer of Ca2+ between organelles and is an important avenue for rapidly increasing mitochondrial metabolic activity. As such, increasing ER-mitochondrial coupling can boost the generation of ATP that is needed to restore homeostasis in the face of cellular stress. The mitochondrial unfolded protein response (mtUPR) is activated by the accumulation of unfolded proteins in mitochondria. Retrograde signaling from mitochondria to the nucleus promotes mtUPR transcriptional responses aimed at restoring protein homeostasis. It is currently unknown whether the changes in mitochondrial-ER coupling also play a role during mtUPR stress. We hypothesized that mitochondrial stress favors an expansion of functional contacts between mitochondria and ER, thereby increasing mitochondrial metabolism as part of a protective response. Hela cells were treated with doxycycline, an antibiotic that inhibits the translation of mitochondrial-encoded proteins to create protein disequilibrium. Treatment with doxycycline decreased the abundance of mitochondrial encoded proteins while increasing expression of CHOP, C/EBPβ, ClpP, and mtHsp60, markers of the mtUPR. There was no change in either mitophagic activity or cell viability. Furthermore, ER UPR was not activated, suggesting focused activation of the mtUPR. Within 2 h of doxycycline treatment, there was a significant increase in physical contacts between mitochondria and ER that was distributed throughout the cell, along with an increase in the kinetics of mitochondrial Ca2+ uptake. This was followed by the rise in the rate of oxygen consumption at 4 h, indicating a boost in mitochondrial metabolic activity. In conclusion, an early phase of the response to doxycycline-induced mitochondrial stress is an increase in mitochondrial-ER coupling that potentiates mitochondrial metabolic activity as a means to support subsequent steps in the mtUPR pathway and sustain cellular adaptation.
  6. Oxid Med Cell Longev. 2021 ;2021 3726885
      Myocardial infarction is associated with oxidative stress and mitochondrial damage. However, the regulatory mechanisms underlying cardiomyocyte oxidative stress during myocardial infarction are not fully understood. In the present study, we explored the cardioprotective action of optic atrophy 1- (Opa1-) mediated mitochondrial autophagy (mitophagy) in oxidative stress-challenged cardiomyocytes, with a focus on mitochondrial homeostasis and the MAPK/ERK pathway. Our results demonstrated that overexpression of Opa1 in cultured rat H9C2 cardiomyocytes, a procedure that stimulates mitophagy, attenuates oxidative stress and increases cellular antioxidant capacity. Activation of Opa1-mediated mitophagy suppressed cardiomyocyte apoptosis by downregulating Bax, caspase-9, and caspase-12 and upregulating Bcl-2 and c-IAP. Using mitochondrial tracker staining and a reactive oxygen species indicator, our assays showed that Opa1-mediated mitophagy attenuated mitochondrial fission and reduced ROS production in cardiomyocytes. In addition, we found that inhibition of the MAPK/ERK pathway abolished the antioxidant action of Opa1-mediated mitophagy in these cells. Taken together, our data demonstrate that Opa1-mediated mitophagy protects cardiomyocytes against oxidative stress damage through inhibition of mitochondrial fission and activation of MAPK/ERK signaling. These findings reveal a critical role for Opa1 in the modulation of cardiomyocyte redox balance and suggest a potential target for the treatment of myocardial infarction.
  7. Redox Biol. 2021 Jun 18. pii: S2213-2317(21)00208-1. [Epub ahead of print]45 102049
      Mitochondrial dysfunction is a fundamental challenge in septic cardiomyopathy. Mitophagy and the mitochondrial unfolded protein response (UPRmt) are the predominant stress-responsive and protective mechanisms involved in repairing damaged mitochondria. Although mitochondrial homeostasis requires the coordinated actions of mitophagy and UPRmt, their molecular basis and interactive actions are poorly understood in sepsis-induced myocardial injury. Our investigations showed that lipopolysaccharide (LPS)-induced sepsis contributed to cardiac dysfunction and mitochondrial damage. Although both mitophagy and UPRmt were slightly activated by LPS in cardiomyocytes, their endogenous activation failed to prevent sepsis-mediated myocardial injury. However, administration of urolithin A, an inducer of mitophagy, obviously reduced sepsis-mediated cardiac depression by normalizing mitochondrial function. Interestingly, this beneficial action was undetectable in cardiomyocyte-specific FUNDC1 knockout (FUNDC1CKO) mice. Notably, supplementation with a mitophagy inducer had no impact on UPRmt, whereas genetic ablation of FUNDC1 significantly upregulated the expression of genes related to UPRmt in LPS-treated hearts. In contrast, enhancement of endogenous UPRmt through oligomycin administration reduced sepsis-mediated mitochondrial injury and myocardial dysfunction; this cardioprotective effect was imperceptible in FUNDC1CKO mice. Lastly, once UPRmt was inhibited, mitophagy-mediated protection of mitochondria and cardiomyocytes was partly blunted. Taken together, it is plausible that endogenous UPRmt and mitophagy are slightly activated by myocardial stress and they work together to sustain mitochondrial performance and cardiac function. Endogenous UPRmt, a downstream signal of mitophagy, played a compensatory role in maintaining mitochondrial homeostasis in the case of mitophagy inhibition. Although UPRmt activation had no negative impact on mitophagy, UPRmt inhibition compromised the partial cardioprotective actions of mitophagy. This study shows how mitophagy modulates UPRmt to attenuate inflammation-related myocardial injury and suggests the potential application of mitophagy and UPRmt targeting in the treatment of myocardial stress.
    Keywords:  FUN14 domain-containing 1; Inflammation; Mitochondrial unfolded protein response; Mitophagy; Septic cardiomyopathy
  8. Biology (Basel). 2021 Jun 23. pii: 572. [Epub ahead of print]10(7):
      Mitochondria are highly dynamic organelles that interchange their contents mediated by fission and fusion. However, it has previously been shown that the mitochondria of cultured human epithelial cells exhibit a gradient in the relative abundance of several proteins, with the perinuclear mitochondria generally exhibiting a higher protein abundance than the peripheral mitochondria. The molecular mechanisms that are required for the establishment and the maintenance of such inner-cellular mitochondrial protein abundance gradients are unknown. We verified the existence of inner-cellular gradients in the abundance of clusters of the mitochondrial outer membrane protein Tom20 in the mitochondria of kidney epithelial cells from an African green monkey (Vero cells) using STED nanoscopy and confocal microscopy. We found that the Tom20 gradients are established immediately after cell division and require the presence of microtubules. Furthermore, the gradients are abrogated in hyperfused mitochondrial networks. Our results suggest that inner-cellular protein abundance gradients from the perinuclear to the peripheral mitochondria are established by the trafficking of individual mitochondria to their respective cellular destination.
    Keywords:  image analysis; inner-cellular heterogeneity; nanoscopy; protein distribution; super-resolution microscopy
  9. Membranes (Basel). 2021 Jun 23. pii: 465. [Epub ahead of print]11(7):
      Mitochondria are known as the powerhouse of eukaryotic cells. Energy production occurs in specific dynamic membrane invaginations in the inner mitochondrial membrane called cristae. Although the integrity of these structures is recognized as a key point for proper mitochondrial function, less is known about the mechanisms at the origin of their plasticity and organization, and how they can influence mitochondria function. Here, we review the studies which question the role of lipid membrane composition based mainly on minimal model systems.
    Keywords:  cardiolipin; cone-shaped lipid asymmetry; cristae; curvature-based sorting; mitochondria; nonbilayer structures
  10. Metabolites. 2021 Jun 05. pii: 359. [Epub ahead of print]11(6):
      Myelin is a lipid-rich membrane that wraps around axons and facilitates rapid action potential propagation. In the brain, myelin is synthesized and maintained by oligodendrocytes. These cells have a high metabolic demand that requires mitochondrial ATP production during the process of myelination, but they rely less on mitochondrial respiration after myelination is complete. Mitochondria change in morphology and distribution during oligodendrocyte development. Furthermore, the morphology and dynamic properties of mitochondria in mature oligodendrocytes seem different from any other brain cell. Here, we first give a brief introduction to oligodendrocyte biology and function. We then review the current knowledge on oligodendrocyte metabolism and discuss how the available data on mitochondrial morphology and mobility as well as transcriptome and proteome studies can shed light on the metabolic properties of oligodendrocytes.
    Keywords:  ATP; glycolysis; metabolism; mitochondria; myelination; oligodendrocyte; oligodendrocyte precursor cell (OPC); oxidative phosphorylation; proteome; transcriptome
  11. Biol Open. 2021 Jun 15. pii: bio058553. [Epub ahead of print]10(6):
      Mitochondrial DNA (mtDNA) encodes gene products that are essential for oxidative phosphorylation. They organize as higher order nucleoid structures (mtNucleoids) that were shown to be critical for the maintenance of mtDNA stability and integrity. While mtNucleoid structures are associated with cellular health, how they change in situ under physiological maturation and aging requires further investigation. In this study, we investigated the mtNucleoid assembly at an ultrastructural level in situ using the TFAM-Apex2 Drosophila model. We found that smaller and more compact TFAM-nucleoids are populated in the mitochondria of indirect flight muscle of aged flies. Furthermore, mtDNA transcription and replication were cross-regulated in the mtTFB2-knockdown flies as in the mtRNAPol-knockdown flies that resulted in reductions in mtDNA copy numbers and nucleoid-associated TFAM. Overall, our study reveals that the modulation of TFAM-nucleoid structure under physiological aging, which is critically regulated by mtDNA content.
    Keywords:  Mitochondrial DNA; Mitochondrial RNA polymerase (mtRNAPol); Mitochondrial nucleoid; Mitochondrial transcription factor B2 (mtTFB2); Transcription factor A (TFAM)
  12. J Adv Res. 2021 Jul;31 35-47
      Introduction: Incidents of myocardial infarction and sudden cardiac arrest vary with time of the day, but the mechanism for this effect is not clear. We hypothesized that diurnal changes in the ability of cardiac mitochondria to control calcium homeostasis dictate vulnerability to cardiovascular events.Objectives: Here we investigate mitochondrial calcium dynamics, respiratory function, and reactive oxygen species (ROS) production in mouse heart during different phases of wake versus sleep periods.
    Methods: We assessed time-of-the-day dependence of calcium retention capacity of isolated heart mitochondria from young male C57BL6 mice. Rhythmicity of mitochondrial-dependent oxygen consumption, ROS production and transmembrane potential in homogenates were explored using the Oroboros O2k Station equipped with a fluorescence detection module. Changes in expression of essential clock and calcium dynamics genes/proteins were also determined at sleep versus wake time points.
    Results: Our results demonstrate that cardiac mitochondria exhibit higher calcium retention capacity and higher rates of calcium uptake during sleep period. This was associated with higher expression of clock gene Bmal1, lower expression of per2, greater expression of MICU1 gene (mitochondrial calcium uptake 1), and lower expression of the mitochondrial transition pore regulator gene cyclophilin D. Protein levels of mitochondrial calcium uniporter (MCU), MICU2, and sodium/calcium exchanger (NCLX) were also higher at sleep onset relative to wake period. While complex I and II-dependent oxygen utilization and transmembrane potential of cardiac mitochondria were lower during sleep, ROS production was increased presumably due to mitochondrial calcium sequestration.
    Conclusions: Taken together, our results indicate that retaining mitochondrial calcium in the heart during sleep dissipates membrane potential, slows respiratory activities, and increases ROS levels, which may contribute to increased vulnerability to cardiac stress during sleep-wake transition. This pronounced daily oscillations in mitochondrial functions pertaining to stress vulnerability may at least in part explain diurnal prevalence of cardiac pathologies.
    Keywords:  Calcium dynamics; Clock genes; Diurnal; Heart; Hydrogen peroxide; Mitochondria function
  13. Exp Ther Med. 2021 Aug;22(2): 863
      Hepatocytes from donors with preexisting hepatic steatosis exhibited increased sensitivity to ischemia-reperfusion injury (IRI) during liver transplantation. Augmenter of liver regeneration (ALR) protected the liver against IRI, but the mechanism was not clarified. Therefore, the hypothesis that ALR attenuated IRI in steatotic liver by inhibition of inflammation and downregulation of the Toll-like receptor 4 (TLR4)/nuclear factor-κB (NF-κB) pathway was examined. C57BL/6 mice were subjected to a methionine-choline-deficient (MCD) diet to induce liver steatosis. Mice were transfected with ALR-containing adenovirus 3 days prior to partial warm hepatic IRI. After 30 min of ischemia and 6 h of reperfusion injury, liver function, hepatic injury, the inflammatory response and TLR4/NF-κB signaling pathway activation were assessed. ALR maintained liver function and alleviated hepatic injury as indicated by the decreased levels of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST), preserved hepatic structure and reduced apoptosis. ALR also reduced the IRI-induced inflammatory response by suppressing Kupffer cell activation, inhibiting neutrophil chemotaxis and reducing inflammatory cytokine production. Further investigation using reverse transcription-quantitative PCR, western blotting and immunohistochemistry revealed that ALR reduced TLR4/NF-κB signaling pathway activation, which led to a decreased synthesis of inflammatory cytokines. ALR functioned as a regulator of the IRI-induced inflammatory response by suppressing the TLR4/NF-κB pathway, which supports the use of ALR in therapeutic applications for fatty liver transplantation.
    Keywords:  NF-κB; Toll-like receptor 4; augmenter of liver regeneration; fatty liver; ischemia-reperfusion injury
  14. Elife. 2021 Jun 30. pii: e65215. [Epub ahead of print]10
      The spatiotemporal distribution of mitochondria is crucial for precise ATP provision and calcium buffering required to support neuronal signaling. Fast-spiking GABAergic interneurons expressing parvalbumin (PV) have a high mitochondrial content reflecting their large energy utilization. The importance for correct trafficking and precise mitochondrial positioning remains poorly elucidated in inhibitory neurons. Miro1 is a Ca²⁺-sensing adaptor protein that links mitochondria to the trafficking apparatus, for their microtubule-dependent transport along axons and dendrites, in order to meet the metabolic and Ca2+-buffering requirements of the cell. Here, we explore the role of Miro1 in parvalbumin interneurons and how changes in mitochondrial trafficking could alter network activity in the mouse brain. By employing live and fixed imaging, we found that the impairments in Miro1-directed trafficking in PV+ interneurons altered their mitochondrial distribution and axonal arborization while PV+ interneuron mediated inhibition remained intact. These changes were accompanied by an increase in the ex vivo hippocampal γ-oscillation (30 - 80 Hz) frequency and promoted anxiolysis. Our findings show that precise regulation of mitochondrial dynamics in PV+ interneurons is crucial for proper neuronal signaling and network synchronization.
    Keywords:  cell biology; mouse; neuroscience
  15. Curr Biol. 2021 Jun 23. pii: S0960-9822(21)00821-6. [Epub ahead of print]
      The mitochondrion is an ancient endosymbiotic organelle that performs many essential functions in eukaryotic cells.1-3 Mitochondrial impairment often results in physiological defects or diseases.2-8 Since most mitochondrial genes have been copied into the nuclear genome during evolution,9 the regulatory and interaction mechanisms between the mitochondrial and nuclear genomes are very complex. Multiple mechanisms, including antioxidant, DNA repair, mitophagy, and mitochondrial biogenesis pathways, have been shown to monitor the quality and quantity of mitochondria.10-12 Nonetheless, it remains unclear if these pathways can be further modified to enhance mitochondrial stability. Previously, experimental evolution has been used to adapt cells to novel growth conditions. By analyzing the resulting evolved populations, insights have been gained into the underlying molecular mechanisms.13 Here, we experimentally evolved yeast cells under conditions that selected for efficient respiration while continuously assaulting the mitochondrial genome (mtDNA) with ethidium bromide (EtBr). We found that the ability to maintain functional mtDNA was enhanced in most of the evolved lines when challenged with mtDNA-damaging reagents. We identified mutations of the mitochondrial NADH dehydrogenase NDE1 in most of the evolved lines, but other pathways are also involved. Finally, we show that cells displaying enhanced mtDNA retention also exhibit a prolonged replicative lifespan. Our work reveals potential evolutionary trajectories by which cells can maintain functional mitochondria in response to mtDNA stress, as well as the physiological implications of such adaptations.
    Keywords:  experimental evolution; mitochondrial DNA; mitochondrial quality control; replicative lifespan; yeast genomics
  16. PLoS Genet. 2021 Jul 02. 17(7): e1009664
      Mitochondrial defects can cause a variety of human diseases and protective mechanisms exist to maintain mitochondrial functionality. Imbalances in mitochondrial proteostasis trigger a transcriptional program, termed mitochondrial unfolded protein response (mtUPR). However, the temporal sequence of events in mtUPR is unclear and the consequences on mitochondrial protein import are controversial. Here, we have quantitatively analyzed all main import pathways into mitochondria after different time spans of mtUPR induction. Kinetic analyses reveal that protein import into all mitochondrial subcompartments strongly increases early upon mtUPR and that this is accompanied by rapid remodelling of the mitochondrial signature lipid cardiolipin. Genetic inactivation of cardiolipin synthesis precluded stimulation of protein import and compromised cellular fitness. At late stages of mtUPR upon sustained stress, mitochondrial protein import efficiency declined. Our work clarifies the enigma of protein import upon mtUPR and identifies sequential mtUPR stages, in which an early increase in protein biogenesis to restore mitochondrial proteostasis is followed by late stages characterized by a decrease in import capacity upon prolonged stress induction.
  17. Am J Physiol Cell Physiol. 2021 06 30.
      Impaired oxidative capacity and mitochondrial function contribute to the dystrophic pathology in muscles of Duchenne muscular dystrophy (DMD) patients and in relevant mouse models of the disease. Emerging evidence suggests an association between disrupted core clock expression and mitochondrial quality control, but this has not been established in muscles lacking dystrophin. We examined the diurnal regulation of muscle core clock and mitochondrial quality control expression in dystrophin-deficient C57BL/10ScSn-Dmdmdx (mdx) mice, an established model of DMD. Male C57BL/10 (BL/10; n=18) and mdx mice (n=18) were examined every 4 hours beginning at the dark cycle. Throughout the entire light-dark cycle, extensor digitorum longus (EDL) muscles from mdx mice had decreased core clock mRNA expression (Arntl, Cry1, Cry2, Nr1d2; p<0.05) and disrupted mitochondrial quality control mRNA expression related to biogenesis (decreased; Ppargc1a, Esrra; p<0.05), fission (increased; Dnm1l; p<0.01), fusion (decreased; Opa1, Mfn1; p<0.05) and autophagy/mitophagy (decreased: Bnip3; p<0.05; increased: Becn1; p<0.05). Cosinor analysis revealed a decrease in the rhythmicity parameters mesor and amplitude for Arntl, Cry1, Cry2, Per2, and Nr1d1 (p<0.001) in mdx mice. Diurnal oscillations in Esrra, Sirt1, Map1lc3b and Sqstm1 were absent in mdx mice, along with decreased mesor and amplitude of Ppargc1a mRNA expression (p<0.01). The expression of proteins involved in mitochondrial biogenesis (decreased: PPARGC1A, p<0.05) and autophagy/mitophagy (increased: MAP1LC3BII, SQSTM1, BNIP3; p<0.05) were also dysregulated in tibialis anterior muscles of mdx mice. These findings suggest that dystrophin deficiency in mdx mice impairs the regulation of the core clock and mitochondrial quality control, with relevance to DMD and related disorders.
    Keywords:  diurnal variation; dystrophin; mitochondria; muscular dystrophy
  18. J Neurochem. 2021 Jul 03.
      Protein arginine methyltransferases (PRMTs) are a family of enzymes involved in gene regulation and protein/histone modifications. PRMT8 is primarily expressed in the central nervous system, specifically within the cellular membrane and synaptic vesicles. Recently, PRMT8 has been described to play key roles in neuronal signaling such as a regulator of dendritic arborization, synaptic function and maturation, and neuronal differentiation and plasticity. Here, we examined the role of PRMT8 in response to hypoxia-induced stress in brain metabolism. Our results from liquid chromatography mass spectrometry, mitochondrial oxygen consumption rate (OCR), and protein analyses indicate that PRMT8(-/-) knockout mice presented with altered membrane phospholipid composition, decreased mitochondrial stress capacity, and increased neuroinflammatory markers, such as TNF-α and ionized calcium binding adaptor molecule 1 (Iba1, a specific marker for microglia/macrophage activation) after hypoxic stress. Furthermore, adenovirus-based overexpression of PRMT8 reversed the changes in membrane phospholipid composition, mitochondrial stress capacity, and neuroinflammatory markers. Together, our findings establish PRMT8 as an important regulatory component of membrane phospholipid composition, short-term memory function, mitochondrial function, and neuroinflammation in response to hypoxic stress.
    Keywords:  Protein arginine methyltransferase; hypoxic stress; mitochondrial function; neuroinflammation; phospholipids
  19. Cells. 2021 Jun 19. pii: 1554. [Epub ahead of print]10(6):
      Mitochondria play a fundamental role in the energetics of cardiac cells. Moreover, mitochondria are involved in cardiac ischemia/reperfusion injury by opening the mitochondrial permeability transition pore which is the major cause of cell death. The preservation of mitochondrial function is an essential component of the cardioprotective mechanism. The involvement of mitochondrial K+ transport in this complex phenomenon seems to be well established. Several mitochondrial K+ channels in the inner mitochondrial membrane, such as ATP-sensitive, voltage-regulated, calcium-activated and Na+-activated channels, have been discovered. This obliges us to ask the following question: why is the simple potassium ion influx process carried out by several different mitochondrial potassium channels? In this review, we summarize the current knowledge of both the properties of mitochondrial potassium channels in cardiac mitochondria and the current understanding of their multidimensional functional role. We also critically summarize the pharmacological modulation of these proteins within the context of cardiac ischemia/reperfusion injury and cardioprotection.
    Keywords:  cardiac tissue; cytoprotection; ischemia/reperfusion; mitochondria; mitochondrial potassium channels; potassium channel openers
  20. Biomolecules. 2021 Jun 30. pii: 968. [Epub ahead of print]11(7):
      Various environmental stimuli, including oxidative stress, could lead to granulosa cell (GC) death through mitophagy. Recently, it was reported that melatonin (MEL) has a significant effect on GC survival during oxidative damage. Here, we found that MEL inhibited oxidative stress-induced mitophagy to promote GC survival. The loss of cell viability upon H2O2 exposure was significantly restored after MEL treatment. Concomitantly, MEL inhibited the activation of mitophagy during oxidative stress. Notably, blocking mitophagy repressed GC death caused by oxidative stress. However, MEL cannot further restore viability of cells treated with mitophagy inhibitor. Moreover, PTEN-induced putative kinase 1 (PINK1), a mitochondrial serine/threonine-protein kinase, was inhibited by MEL during oxidative stress. As a result, the E3 ligase Parkin failed to translocate to mitochondria, leading to impaired mitochondria clearance. Using RNAi to knock down PINK1 expression, we further verified the role of the MEL-PINK1-Parkin (MPP) pathway in maintaining GC survival by suppressing mitophagy. Our findings not only clarify the protective mechanisms of MEL against oxidative damage in GCs, but also extend the understanding about how circadian rhythms might influence follicles development in the ovary. These findings reveal a new mechanism of melatonin in defense against oxidative damage to GCs by repressing mitophagy, which may be a potential therapeutic target for anovulatory disorders.
    Keywords:  PINK1-Parkin pathway; granulosa cells; melatonin; mitophagy; oxidative damage
  21. Anal Chem. 2021 Jun 28.
      Mitophagy is a vital biological process playing central roles in the regulation of metabolic activity and quality control of mitochondria. The presented dual-color fluorescent probes to directly monitor mitophagy were based on the optical response to pH change during mitophagy, but pH fluctuation may lead to interference. To overcome this, herein, two fluorescent probes (G-Mito, R-Lyso) were rationally designed to visualize mitophagy directly in a dual-color manner, relying on the Förster resonance energy transfer (FRET) process for the first time. Green emissive G-Mito targeted and anchored the mitochondria via reaction with protein thiols. Red-emissive R-Lyso exclusively targeted lysosomes. Live cells loaded with the two probes demonstrated strong fluorescence in only the green channel with excitation at 405 nm. After mitophagy, G-Mito in mitochondria was delivered into the lysosomes, and red fluorescence evidently increased due to the FRET process. With the probes, mitochondria, lysosomes, and autolysosomes could be discriminatively visualized in three different sets of signals. Mitophagy induced by starvation and in normal physiological status were successfully observed. The probes revealed that a certain amount of H2O2 could induce mitophagy. We expect that the two probes can serve as molecular tools for validation of mitophagy and promote the development of related areas.