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Nonalcoholic fatty liver disease (NAFLD) encompasses a spectrum of pathologies, ranging from steatosis to nonalcoholic steatohepatitis (NASH). The factors promoting the progression of steatosis to NASH are still unclear. Recent studies suggest that mitochondrial lipid composition is critical in NASH development. Here, we showed that CDP-DAG synthase 2 (Cds2) was downregulated in genetic or diet-induced NAFLD mouse models. Liver-specific deficiency of Cds2 provoked hepatic steatosis, inflammation and fibrosis in five-week-old mice. CDS2 is enriched in mitochondria-associated membranes (MAMs), and hepatic Cds2 deficiency impaired mitochondrial function and decreased mitochondrial PE levels. Overexpression of phosphatidylserine decarboxylase (PISD) alleviated the NASH-like phenotype in Cds2f/f;AlbCre mice and abnormal mitochondrial morphology and function caused by CDS2 deficiency in hepatocytes. Additionally, dietary supplementation with an agonist of peroxisome proliferator-activated receptor alpha (PPARα) attenuated mitochondrial defects and ameliorated the NASH-like phenotype in Cds2f/f;AlbCre mice. Finally, Cds2 overexpression protected against high-fat diet-induced hepatic steatosis and obesity. Thus, Cds2 modulates mitochondrial function and NASH development.

The mitochondrial DNA m.3243A > G mutation is well-known to cause a variety of clinical phenotypes, including diabetes, deafness, and osteoporosis. Here, we report isolation and expansion of urine-derived stem cells (USCs) from patients carrying the m.3243A > G mutation, which demonstrate bimodal heteroplasmy. USCs with high levels of m.3243A > G mutation displayed abnormal mitochondrial morphology and function, as well as elevated ATF5-dependent mitochondrial unfolded protein response (UPRmt), together with reduced Wnt/β-catenin signaling and osteogenic potentials. Knockdown of ATF5 in mutant USCs suppressed UPRmt, improved mitochondrial function, restored expression of GSK3B and WNT7B, and rescued osteogenic potentials. These results suggest that ATF5-dependent UPRmt could be a core disease mechanism underlying mitochondrial dysfunction and osteoporosis related to the m.3243A > G mutation, and therefore could be a novel putative therapeutic target for this genetic disorder.

Abnormal mitochondrial function is a well-recognized feature of acute and chronic kidney diseases. To gain insight into the role of mitochondria in kidney homeostasis and pathogenesis, we targeted mitochondrial transcription factor A (TFAM), a protein required for mitochondrial DNA replication and transcription that plays a critical part in the maintenance of mitochondrial mass and function. To examine the consequences of disrupted mitochondrial function in kidney epithelial cells, we inactivated TFAM in sine oculis-related homeobox 2-expressing kidney progenitor cells. TFAM deficiency resulted in significantly decreased mitochondrial gene expression, mitochondrial depletion, inhibition of nephron maturation and the development of severe postnatal cystic disease, which resulted in premature death. This was associated with abnormal mitochondrial morphology, a reduction in oxygen consumption and increased glycolytic flux. Furthermore, we found that TFAM expression was reduced in murine and human polycystic kidneys, which was accompanied by mitochondrial depletion. Thus, our data suggest that dysregulation of TFAM expression and mitochondrial depletion are molecular features of kidney cystic disease that may contribute to its pathogenesis.

C-terminal fragments of Tar DNA-binding protein 43 (TDP-43) have been identified as the major pathological protein in several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). However, how they affect cellular toxicity and neurodegeneration, including the modulation process remains unknown. This study revealed that the C-terminal fragment of TDP-43 (TDP-25) was localized primarily to mitochondria and caused abnormal mitochondrial morphology, inducing Parkin-mediated mitophagy. Also, we discovered that the knockdown of selective autophagy receptors, such as TAX1BP, Optineurin, or NDP52 caused TDP-25 accumulation, indicating that TDP-25 was degraded by mitophagy. Interestingly, myosin IIB, a nonmuscle type of myosin and actin-based motor protein, is mostly colocalized to TDP-25 associated with abnormal mitochondria. In addition, myosin IIB inhibition by siRNA or blebbistatin induced mitochondrial accumulation of insoluble TDP-25 and Tom20, and reduced neuronal cell viability. Our results suggest a novel role of myosin IIB in mitochondrial degradation of toxic TDP-25. Therefore, we proposed that regulating myosin IIB activity might be a potential therapeutic target for neurodegenerative diseases associated with TDP-43 pathology.

Rett syndrome (RTT) is a pervasive neurodevelopmental disorder associated with mutation in MECP2 gene. Despite a well-defined genetic cause, there is a growing consensus that a metabolic component could play a pivotal role in RTT pathophysiology. Indeed, perturbed redox homeostasis and inflammation, i.e. oxinflammation, with mitochondria dysfunction as the central hub between the two phenomena, appear as possible key contributing factors to RTT pathogenesis and its clinical features. While these RTT-related changes have been widely documented by transcriptomic profiling, proteomics studies supporting these evidences are still limited. Here, using primary dermal fibroblasts from control and patients, we perform a large-scale proteomic analysis that, together with data mining approaches, allow us to carry out the first comprehensive characterization of RTT cellular proteome, showing mainly changes in expression of proteins involved in the mitochondrial network. These findings parallel with an altered expression of key mediators of mitochondrial dynamics and mitophagy associated with abnormal mitochondrial morphology. In conclusion, our proteomic analysis confirms the pathological relevance of mitochondrial dysfunction in RTT pathogenesis and progression.

Wound healing may be disrupted by lipopolysaccharide (LPS)-induced mitochondrial dysfunction, inflammation, and excessive oxidative stress, which can lead to undesirable consequences. The haematopoietic cell-specific protein 1-associated protein X-1 (HAX-1) is a mitochondrial matrix protein that regulates mitochondrial function. This study aimed to comprehensively identify the role of HAX-1 in the inhibition of LPS-induced mitochondrial dysfunction and apoptosis in human dermal fibroblasts (HDFs). HAX-1 expression was assessed in the HDF-a cell line using real-time polymerase chain reaction, western blotting, and immunohistochemical staining. The viability, migration, and apoptosis of HDF-a cells were evaluated using the water-soluble tetrazolium-1 assay, transwell assay, and flow cytometry analysis, respectively. Mitochondrial function was evaluated based on reactive oxygen species (ROS) generation and mitochondrial membrane potential (ΔΨm). Our results demonstrated that LPS stimulation markedly repressed HAX-1 expression in HDFs and silencing of HAX-1 led to mitochondrial ROS accumulation, ΔΨm disruption, and abnormal mitochondrial morphology. Accordingly, overexpression of HAX-1 or administration of metformin enhanced mitochondrial fusion and normalized mitochondrial dynamics, thereby reversing LPS-induced mitochondrial dysfunction, fibroblast apoptosis, and viability and migration inhibition in HDF-a cells. These data support a mechanism wherein HAX-1 plays a crucial role in LPS-induced fibroblast apoptosis in a mitochondria-dependent manner.

Hazy weather in China has recently become a major public health concern due to high levels of atmospheric fine particulate matter (PM2.5) with a large amount of polycyclic aromatic hydrocarbon (PAHs). In this study, the mass concentration of PAHs in hazy PM2.5 in urban Taiyuan city, China was determined and toxicities of different dosage of the hazy PM2.5 on rat alveolar macrophages (AMs) were examined. It was found that the hazy PM2.5, bounded with many species of PAHs (CHR, BbF, BaP, BaA, and etc.), significantly increased cellular malondialdehyde (MDA) content followed by the decreasing in superoxide (SOD) and glutathione peroxidase (GPx) in AMs. They induced mitochondrial changes in ultrastructure as evidenced by mitochondrial swelling and cristae disorganization, and a dose-dependent decrease in mitochondrial profile density. Also, the mRNA expression levels of mitochondrial fusion-related genes were modified. The Mfn1 and Mfn2 which are essential for mitochondrial fusion increased significantly in hazy PM2.5-treated group compared to the control in a dose-dependent manner, OPA1 was significantly increased at the highest PM2.5 dose delivered. These findings suggested that exposure to hazy PM2.5 could activate oxidative stress pathways in AMs, resulting in abnormal mitochondrial morphology and fusion/fission frequency. Possibly, the toxic effects were mostly attributed to the high burden of varied PAHs in hazy PM2.5.

Duchenne muscular dystrophy (DMD) is an X-linked neuromuscular disease caused by a pathogenic disruption of the DYSTROPHIN gene that results in non-functional dystrophin protein. DMD patients experience loss of ambulation, cardiac arrhythmia, metabolic syndrome, and respiratory failure. At the molecular level, the lack of dystrophin in the muscle results in myofiber death, fibrotic infiltration, and mitochondrial dysfunction. There is no cure for DMD, although dystrophin-replacement gene therapies and exon-skipping approaches are being pursued in clinical trials. Mitochondrial dysfunction is one of the first cellular changes seen in DMD myofibers, occurring prior to muscle disease onset and progresses with disease severity. This is seen by reduced mitochondrial function, abnormal mitochondrial morphology and impaired mitophagy (degradation of damaged mitochondria). Dysfunctional mitochondria release high levels of reactive oxygen species (ROS), which can activate pro-inflammatory pathways such as IL-1β and IL-6. Impaired mitophagy in DMD results in increased inflammation and further aggravates disease pathology, evidenced by increased muscle damage and increased fibrosis. This review will focus on the critical interplay between mitophagy and inflammation in Duchenne muscular dystrophy as a pathological mechanism, as well as describe both candidate and established therapeutic targets that regulate these pathways.

Mitochondria are highly dynamic organelles, constantly undergoing shape changes, which are controlled by mitochondrial movement, fusion, and fission. Mitochondria play a pivotal role in various cellular processes under physiological and pathological conditions, including metabolism, superoxide generation, calcium homeostasis, and apoptosis. Abnormal mitochondrial morphology and mitochondrial protein expression are always closely related to the health status of cells. Analysis of mitochondrial morphology and mitochondrial protein expression in situ is widely used to reflect the abnormality of cell function in the chemical fixed sample. Paraformaldehyde (PFA), the most commonly used fixative in cellular immunostaining, still has disadvantages, including loss of antigenicity and disruption of morphology during fixation. We tested the effect of ethanol (ETHO), PFA, and glutaraldehyde (GA) fixation on cellular mitochondria. The results showed that 3% PFA and 1.5% GA (PFA-GA) combination reserved mitochondrial morphology better than them alone in situ in cells. Mitochondrial network and protein antigenicity were well maintained, indicated by preserved MitoTracker and mitochondrial immunostaining after PFA-GA fixation. Our results suggest that the PFA-GA combination is a valuable fixative for the study of mitochondria in situ.

MicroRNA-125b, the first microRNA to be identified, is known to promote cardiomyocyte maturation from embryonic stem cells; however, its physiological role remains unclear. To investigate the role of miR-125b in cardiovascular biology, cardiac-specific miR-125b-1 knockout mice were generated. We found that cardiac-specific miR-125b-1 knockout mice displayed half the miR-125b expression of control mice resulting in a 60% perinatal death rate. However, the surviving mice developed hearts with cardiac hypertrophy. The cardiomyocytes in both neonatal and adult mice displayed abnormal mitochondrial morphology. In the deficient neonatal hearts, there was an increase in mitochondrial DNA, but total ATP production was reduced. In addition, both the respiratory complex proteins in mitochondria and mitochondrial transcription machinery were impaired. Mechanistically, using transcriptome and proteome analysis, we found that many proteins involved in fatty acid metabolism were significantly downregulated in miR-125b knockout mice which resulted in reduced fatty acid metabolism. Importantly, many of these proteins are expressed in the mitochondria. We conclude that miR-125b deficiency causes a high mortality rate in neonates and cardiac hypertrophy in adult mice. The dysregulation of fatty acid metabolism may be responsible for the cardiac defect in the miR-125b deficient mice.

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.

Assembly of the dimeric complex III (CIII2) in the mitochondrial inner membrane is an intricate process in which many factors are involved. Despite many studies this process is yet to be completely understood. Here we report the identification of human OCIAD2 (Ovarian Carcinoma Immunoreactive Antigen domain containing protein 2) protein as an assembly factor for CIII2. OCIAD2 was found deregulated in several carcinomas and in some neurodegenerative disorders; however its non-pathological role was not elucidated to date. We have shown that OCIAD2 localizes to mitochondria and interacts with electron transport chain (ETC) proteins. Complete loss of OCIAD2 using gene editing in HEK293 cells resulted in abnormal mitochondrial morphology, decrease assembly of both CIII2 and supercomplex III2+IV and decreased activities of complex I and III. Identification of OCIAD2 as a protein required for assembly of functional CIII2 provides a new insight into the biogenesis and architecture of the ETC. Elucidating the mechanism of OCIAD2 action is important both for the understanding of cellular metabolism and for understanding of its role in the malignant transformation.

Intrinsic apoptosis relies on the ability of the BCL-2 family to induce the formation of pores on the outer mitochondrial membrane. Previous studies have shown that both BAX and BAK are essential during murine embryogenesis, and reports in human cancer cell lines identified non-canonical roles for BAX and BAK in mitochondrial fission during apoptosis. BAX and BAK function in human brain development remains elusive due to the lack of appropriate model systems. Here, we generated BAX/BAK double knockout human-induced pluripotent stem cells (hiPSCs), hiPSC-derived neural progenitor cells (hNPCs), neural rosettes, and cerebral organoids to uncover the effects of BAX and BAK deletion in an in vitro model of early human brain development. We found that BAX and BAK-deficient cells have abnormal mitochondrial morphology and give rise to aberrant cortical structures. We suggest crucial functions for BAX and BAK during human development, including maintenance of homeostatic mitochondrial morphology, which is crucial for proper development of progenitors and neurons of the cortex. Human pluripotent stem cell-derived systems can be useful platforms to reveal novel functions of the apoptotic machinery in neural development.

Background Sepsis remains a major health issue without an effective therapy. Ferroptosis, an iron‐dependent programmed cell death, has been proposed to be related to the pathogenesis of sepsis. Irisin, a myokine released during exercise, improves mitochondrial function under various conditions. Ferroptosis is closely related to mitochondrial function. However, the role of irisin in sepsis‐induced ferroptosis and mitochondrial dysfunction in the liver remained unknown. Thus, we hypothesize that irisin treatment suppresses ferroptosis and improves mitochondrial function in sepsis. Methods To study this, we first explored the role of serum irisin levels in patients with sepsis, and then determined the effect of irisin administration on ferroptosis and mitochondrial function in the liver of septic mice. Results Serum irisin levels were decreased and negatively correlated with the APACHE II scores in patients with sepsis. In mice subjected to cecal ligation and puncture (CLP), exogenous irisin administration suppressed ferroptosis, inhibited inflammatory response, decreased reactive oxygen species (ROS) production, restored abnormal mitochondrial morphology, and increased mtDNA copy number and adenosine triphosphate (ATP) content. The effect of irisin on ferroptosis was confirmed in LPS‐treated hepatocytes and CLP‐induced septic mice. Inhibition of glutathione peroxidase 4 (GPX4), a central regulator of ferroptosis, reduced irisin's protective effects in LPS‐treated hepatocytes and CLP‐induced septic mice, while blocking the irisin receptor with RGD peptide or Echistain decreased irisin‐induced GPX4 expression. Conclusions Serum irisin levels are decreased and negatively correlated with disease severity in patients with sepsis, and irisin treatment suppresses ferroptosis and restores mitochondrial function in experimental sepsis. Irisin may offer therapeutic potential in the management of sepsis.

The understanding of the pathophysiology of bipolar disorder (BD) remains modest, despite recent advances in neurobiological research. The mitochondrial dysfunction hypothesis of bipolar disorder has been corroborated by several studies involving postmortem brain analysis, neuroimaging, and specific biomarkers in both rodent models and humans. Evidence suggests that BD might be related to abnormal mitochondrial morphology and dynamics, neuroimmune dysfunction, and atypical mitochondrial metabolism and oxidative stress pathways. Mitochondrial dysfunction in mood disorders is also associated with abnormal Ca2+ levels, glutamate excitotoxicity, an imbalance between pro- and antiapoptotic proteins towards apoptosis, abnormal gene expression of electron transport chain complexes, and decreased ATP synthesis. This paper aims to review and discuss the implications of mitochondrial dysfunction in BD etiology and to explore mitochondria as a potential target for novel therapeutic agents.

Mitochondrial dysfunction and impaired Ca2+ handling are involved in the development of diabetic cardiomyopathy (DCM). Dynamic relative protein 1 (Drp1) regulates mitochondrial fission by changing its level of phosphorylation, and the Orai1 (Ca2+ release-activated calcium channel protein 1) calcium channel is important for the increase in Ca2+ entry into cardiomyocytes. We aimed to explore the mechanism of Drp1 and Orai1 in cardiomyocyte hypertrophy caused by high glucose (HG). We found that Zucker diabetic fat rats induced by administration of a high-fat diet develop cardiac hypertrophy and impaired cardiac function, accompanied by the activation of mitochondrial dynamics and calcium handling pathway-related proteins. Moreover, HG induces cardiomyocyte hypertrophy, accompanied by abnormal mitochondrial morphology and function, and increased Orai1-mediated Ca2+ influx. Mechanistically, the Drp1 inhibitor mitochondrial division inhibitor 1 (Mdivi-1) prevents cardiomyocyte hypertrophy induced by HG by reducing phosphorylation of Drp1 at serine 616 (S616) and increasing phosphorylation at S637. Inhibition of Orai1 with single guide RNA (sgOrai1) or an inhibitor (BTP2) not only suppressed Drp1 activity and calmodulin-binding catalytic subunit A (CnA) and phosphorylated-extracellular signal-regulated kinase (p-ERK1/2) expression but also alleviated mitochondrial dysfunction and cardiomyocyte hypertrophy caused by HG. In addition, the CnA inhibitor cyclosporin A and p-ERK1/2 inhibitor U0126 improved HG-induced cardiomyocyte hypertrophy by promoting and inhibiting phosphorylation of Drp1 at S637 and S616, respectively. In summary, we identified Drp1 as a downstream target of Orai1-mediated Ca2+ entry, via activation by p-ERK1/2-mediated phosphorylation at S616 or CnA-mediated dephosphorylation at S637 in DCM. Thus, the Orai1–Drp1 axis is a novel target for treating DCM.

Metabolic plasticity is the ability of a biological system to adapt its metabolic phenotype to different environmental stressors. We used a whole-body and tissue-specific phenotypic, functional, metabolomic and transcriptomic approach to systematically assess metabolic plasticity in diet-induced obese mice after a combined nutritional and exercise intervention. Although most pathological features were successfully reverted, we observed a high degree of metabolic dysfunction irreversibility in visceral white adipose tissue, characterised by abnormal mitochondrial morphology and functionality. Despite two sequential therapeutic interventions and apparent global phenotypic recovery, obesity specifically triggered in visceral adipose a cascade of events progressing from mitochondrial metabolic and proteostatic defects to widespread cellular stress, which compromises its biosynthetic and recycling capacity. Our data indicate that obesity prompts a lasting metabolic fingerprint that leads to a progressive breakdown of metabolic plasticity in white adipose tissue, becoming a significant milestone in disease progression.

Mitochondrial morphology is dynamically changed in conjunction with spatiotemporal functionality. Although considerable efforts have been made to understand why abnormal mitochondrial morphology occurs in various diseases, the biological significance of mitochondrial morphology in states of health and disease remains to be elucidated owing to technical limitations. In the present study, we developed a novel method, termed inducible Counter Mitochondrial Morphology (iCMM), to purposely manipulate mitochondrial morphological patterns on a minutes timescale, using a chemically inducible dimerization system. Using iCMM, we showed that mitochondrial morphological changes rapidly lead to the characteristic reconstitution of various biological information, which is difficult to investigate by conventional genetic engineering. The manipulation of mitochondrial morphology using iCMM can improve our understanding of the interplay between mitochondrial morphology and cellular functions.Competing Interest StatementThe authors have declared no competing interest.View Full Text

Summary Leigh syndrome (LS) is a rare, inherited neuro-metabolic disorder that presents with bilateral brain lesions. This disease is caused by defects in the mitochondrial respiratory chain and associated nuclear-encoded proteins. We generated induced pluripotent stem cells (iPSCs) from three widely available LS fibroblast lines and identified, through whole exome and mitochondrial sequencing, unreported mutations in pyruvate dehydrogenase (GM0372, PDH; GM13411, MT-ATP6/PDH) and dihydrolipoyl dehydrogenase (GM01503, DLD). LS derived cell lines were viable and able to differentiate into key progenitor populations, but we identified several abnormalities in three-dimensional differentiation models of brain development. The DLD-mutant line showed decreased neural rosette (NR) formation, and there were differences in NR lumen area in all three LS lines compared to control. LS-derived cerebral organoids showed defects in neural epithelial bud generation and reduced size when grown for 100 days. Loss of cortical architecture and markers were detected at days 30 and 100. The MT-ATP6/PDH line produced organoid neural progenitor cells with an abnormal mitochondrial morphology characterized by fragmentation and disorganization, and demonstrated increased generation of astrocytes. These studies aim to provide a comprehensive phenotypic characterization of available patient-derived cell lines that could be used as LS model systems.

Tofogliflozin may prevent glomerular (enlarged mesangial area, foot process effacement, podocyte loss) and tubulointerstitial damage (increased expression of MCP‐1 and KIM‐1), partly by ameliorating hyperglycemia, renal inflammation, and abnormal mitochondrial morphology., Trials on cardiovascular and renal outcomes in patients with type 2 diabetes have consistently demonstrated that sodium–glucose cotransporter 2 (SGLT2) inhibitors reduce the risk of diabetic kidney disease (DKD) progression. However, their renal protective mechanisms have yet to be completely understood and the effect on albuminuria reduction in animal models is controversial. We investigated these issues using KK and KK‐Ay mice as a control (CTRL) and as a model for type 2 diabetes (DKD), respectively. KK‐Ay mice were treated with 0.015% tofogliflozin, which is an SGLT2 inhibitor, starting at seven weeks of age for eight weeks. Compared with the CTRL mice, the DKD mice had higher HbA1c levels and albuminuria. Although tofogliflozin treatment significantly lowered HbA1c levels, it did not reverse albuminuria. Tofogliflozin treatment enhanced damage in both the glomerular (i.e., enlarged mesangial area, increased foot process effacement rate, and decreased number of WT‐1‐positive cells) and tubulointerstitial (increased protein levels of KIM‐1 and MCP‐1, increased number of macrophages, and abnormal mitochondrial morphology) areas. Our results suggest that tofogliflozin may prevent glomerular and tubulointerstitial damage, partly by ameliorating hyperglycemia, renal inflammation, and abnormal mitochondrial morphology.

Advanced glycation end products (AGEs) can stimulate osteoblast apoptosis and have a critical role in the pathophysiology of diabetic osteoporosis. Mitochondrial abnormalities are closely related to osteoblast dysfunction. However, it remains unclear whether mitochondrial abnormalities are involved in AGE-induced osteoblastic cell apoptosis. Silibinin, a major flavonolignan compound of silimarin, has strong antioxidant and mitochondria-protective properties. In the present study, we explored the possible mitochondrial mechanisms underlying AGE-induced apoptosis of osteoblastic cells and the effect of silibinin on osteoblastic cell apoptosis. We demonstrated that mitochondrial abnormalities largely contributed to AGE-induced apoptosis of osteoblastic cells, as evidenced by enhanced mitochondrial oxidative stress, conspicuous reduction in mitochondrial membrane potential and adenosine triphosphate production, abnormal mitochondrial morphology, and altered mitochondrial dynamics. These AGE-induced mitochondrial abnormalities were mainly mediated by the receptor of AGEs (RAGE). In addition, we found that silibinin directly downregulated the expression of RAGE and modulated RAGE-mediated mitochondrial pathways, thereby preventing AGE-induced apoptosis of osteoblastic cells. This study not only provides a new insight into the mitochondrial mechanisms underlying AGE-induced osteoblastic cell apoptosis, but also lays a foundation for the clinical use of silibinin for the prevention or treatment of diabetic osteoporosis.

Mechanisms by which long corticospinal axons degenerate in hereditary spastic paraplegia (HSP) are largely unknown. Here, we have generated induced pluripotent stem cells (iPSCs) from patients with two autosomal recessive forms of HSP, SPG15 and SPG48, which are caused by mutations in the ZFYVE26 and AP5Z1 genes encoding proteins in the same complex, the spastizin and AP5Z1 proteins, respectively. In patient iPSC-derived telencephalic glutamatergic and midbrain dopaminergic neurons, neurite number, length and branching are significantly reduced, recapitulating disease-specific phenotypes. We analyzed mitochondrial morphology and noted a significant reduction in both mitochondrial length and their densities within axons of these HSP neurons. Mitochondrial membrane potential was also decreased, confirming functional mitochondrial defects. Notably, mdivi-1, an inhibitor of the mitochondrial fission GTPase DRP1, rescues mitochondrial morphology defects and suppresses the impairment in neurite outgrowth and late-onset apoptosis in HSP neurons. Furthermore, knockdown of these HSP genes causes similar axonal defects, also mitigated by treatment with mdivi-1. Finally, neurite outgrowth defects in SPG15 and SPG48 cortical neurons can be rescued by knocking down DRP1 directly. Thus, abnormal mitochondrial morphology caused by an imbalance of mitochondrial fission and fusion underlies specific axonal defects and serves as a potential therapeutic target for SPG15 and SPG48.

Fe3O4 nanoparticles, one kind of magnetic nanomaterials (NMs), are widely used in drug delivery, biological imaging, sensors, catalysts and pollution management. However, its toxicity to biological systems and related toxicity mechanisms remain to be explored. In this study, we investigate the effect of as-synthesized Fe3O4 nanoparticles on growth of Saccharomyces cerevisiae, an important model fungus. Growth inhibition assays showed that Fe3O4 nanoparticles remarkably inhibited yeast growth. Interestingly, this inhibitory effect was not attributed to the well-known plasma membrane damage, cell wall damage and ROS accumulation. Further investigations revealed that the nanoparticles strongly impaired mitochondrial functions, resulting in abnormal mitochondrial morphology, decreased mitochondrial membrane potential (MMP) and attenuated ATP production. Most importantly, the respiratory chain complex Ⅳ, rather than other respiratory chain complexes and ATP synthases, was found to be the main target of the nanoparticles. This study uncovers a novel ROS-independent toxicity mechanism of Fe3O4 nanoparticles to eukaryotic cells.

Mitochondrial function requires coordinated activities of interacting proteins encoded in both the nuclear and mitochondrial genomes. Nuclear mutations cause human mitochondrial disorders that commonly exhibit unexplained clinical variability (e.g. age of onset and severity)... Proper mitochondrial activity depends upon proteins encoded by genes in the nuclear and mitochondrial genomes that must interact functionally and physically in a precisely coordinated manner. Consequently, mito-nuclear allelic interactions are thought to be of crucial importance on an evolutionary scale, as well as for manifestation of essential biological phenotypes, including those directly relevant to human disease. Nonetheless, detailed molecular understanding of mito-nuclear interactions is still lacking, and definitive examples of such interactions in vivo are sparse. Here we describe the characterization of a mutation in Drosophila ND23, a nuclear gene encoding a highly conserved subunit of mitochondrial complex 1. This characterization led to the discovery of a mito-nuclear interaction that affects the ND23 mutant phenotype. ND23 mutants exhibit reduced lifespan, neurodegeneration, abnormal mitochondrial morphology, and decreased ATP levels. These phenotypes are similar to those observed in patients with Leigh syndrome, which is caused by mutations in a number of nuclear genes that encode mitochondrial proteins, including the human ortholog of ND23. A key feature of Leigh syndrome, and other mitochondrial disorders, is unexpected and unexplained phenotypic variability. We discovered that the phenotypic severity of ND23 mutations varies depending on the maternally inherited mitochondrial background. Sequence analysis of the relevant mitochondrial genomes identified several variants that are likely candidates for the phenotypic interaction with mutant ND23, including a variant affecting a mitochondrially encoded component of complex I. Thus, our work provides an in vivo demonstration of the phenotypic importance of mito-nuclear interactions in the context of mitochondrial disease.

iPLA2γ, calcium-independent phospholipase A2γ, discerningly hydrolyses glycerophospholipids to liberate free fatty acids. iPLA2γ-deficiency has been associated with abnormal mitochondrial function. More importantly, the iPLA2 family is causative proteins in mitochondrial neurodegenerative disorders such as parkinsonian disorders. However, the mechanisms by which iPLA2γ affects Parkinson's disease (PD) remain unknown. Mitochondrion stress has a key part in rotenone-induced dopaminergic neuronal degeneration. The present evaluation revealed that lowered iPLA2γ function provokes the parkinsonian phenotype and leads to the reduction of dopamine and its metabolites, lowered survival, locomotor deficiencies, and organismal hypersensitivity to rotenone-induced oxidative stress. In addition, lowered iPLA2γ function escalated the amount of mitochondrial irregularities, including mitochondrial reactive oxygen species (ROS) regeneration, reduced ATP synthesis, reduced glutathione levels, and abnormal mitochondrial morphology. Further, lowered iPLA2γ function was tightly linked with strengthened lipid peroxidation and mitochondrial membrane flaws following rotenone treatment, which can cause cytochrome c release and eventually apoptosis. These results confirmed the important role of iPLA2γ, whereby decreasing iPLA2γ activity aggravates mitochondrial degeneration to induce neurodegenerative disorders in a rotenone rat model of Parkinson's disease. These findings may be useful in the design of rational approaches for the prevention and treatment of PD-associated symptoms.

Key points Abnormal mitochondrial morphology and function in cardiomyocytes are frequently observed under persistent Gq protein-coupled receptor (Gq PCR) stimulation. Cardiac signalling mechanisms for regulating mitochondrial morphology and function under pathophysiological conditions in the heart are still poorly understood. We demonstrate that a downstream kinase of Gq PCR, protein kinase D (PKD) induces mitochondrial fragmentation via phosphorylation of dynamin-like protein 1 (DLP1), a mitochondrial fission protein. The fragmented mitochondria enhance reactive oxygen species generation and permeability transition pore opening in mitochondria, which initiate apoptotic signalling activation. This study identifies a novel PKD-specific substrate in cardiac mitochondria and uncovers the role of PKD on cardiac mitochondria, with special emphasis on the molecular mechanism(s) underlying mitochondrial injury with abnormal mitochondrial morphology under persistent Gq PCR stimulation. These findings provide new insights into the molecular basis of cardiac mitochondrial physiology and pathophysiology, linking Gq PCR signalling with the regulation of mitochondrial morphology and function. Abstract Regulation of mitochondrial morphology is crucial for the maintenance of physiological functions in many cell types including cardiomyocytes. Small and fragmented mitochondria are frequently observed in pathological conditions, but it is still unclear which cardiac signalling pathway is responsible for regulating the abnormal mitochondrial morphology in cardiomyocytes. Here we demonstrate that a downstream kinase of Gq protein-coupled receptor (Gq PCR) signalling, protein kinase D (PKD), mediates pathophysiological modifications in mitochondrial morphology and function, which consequently contribute to the activation of apoptotic signalling. We show that Gq PCR stimulation induced by α1 -adrenergic stimulation mediates mitochondrial fragmentation in a fission- and PKD-dependent manner in H9c2 cardiac myoblasts and rat neonatal cardiomyocytes. Upon Gq PCR stimulation, PKD translocates from the cytoplasm to the outer mitochondrial membrane (OMM) and phosphorylates a mitochondrial fission protein, dynamin-like protein 1 (DLP1), at S637. PKD-dependent phosphorylation of DLP1 initiates DLP1 association with the OMM, which then enhances mitochondrial fragmentation, mitochondrial superoxide generation, mitochondrial permeability transition pore opening and apoptotic signalling. Finally, we demonstrate that DLP1 phosphorylation at S637 by PKD occurs in vivo using ventricular tissues from transgenic mice with cardiac-specific overexpression of constitutively active Gαq protein. In conclusion, Gq PCR-PKD signalling induces mitochondrial fragmentation and dysfunction via PKD-dependent DLP1 phosphorylation in cardiomyocytes. This study is the first to identify a novel PKD-specific substrate, DLP1 in mitochondria, as well as the functional role of PKD in cardiac mitochondria. Elucidation of these molecular mechanisms by which PKD-dependent enhanced fission mediates cardiac mitochondrial injury will provide novel insight into the relationship among mitochondrial form, function and Gq PCR signalling.

Summary: A subset of mitochondrial tRNAs (mt-tRNAs) contains taurine-derived modifications at 34U of the anticodon. Loss of taurine modification has been linked to the development of mitochondrial diseases, but the molecular mechanism is still unclear. Here, we showed that taurine modification is catalyzed by mitochondrial optimization 1 (Mto1) in mammals. Mto1 deficiency severely impaired mitochondrial translation and respiratory activity. Moreover, Mto1-deficient cells exhibited abnormal mitochondrial morphology owing to aberrant trafficking of nuclear DNA-encoded mitochondrial proteins, including Opa1. The mistargeted proteins were aggregated and misfolded in the cytoplasm, which induced cytotoxic unfolded protein response. Importantly, application of chemical chaperones successfully suppressed cytotoxicity by reducing protein misfolding and increasing functional mitochondrial proteins in Mto1-deficient cells and mice. Thus, our results demonstrate the essential role of taurine modification in mitochondrial translation and reveal an intrinsic protein homeostasis network between the mitochondria and cytosol, which has therapeutic potential for mitochondrial diseases. : Taurine modification of mitochondrial tRNA is associated with mitochondrial disease. Fakruddin et al. find that taurine modification is indispensable for mitochondrial protein translation. The authors also find that deficiency of taurine modification impairs a mitochondrial-cytosolic proteostatic network through an Opa1-dependent mechanism and demonstrate the therapeutic potential of chemical chaperones. Keywords: tRNA, modification, taurine, mitochondria, Opa1

The VPS13 proteins (VPS13A–D) are thought to mediate lipid transport between organelles and are linked to distinct neurological disorders in humans. Baldwin et al. found that, in addition to known involvement in mitochondrial morphology, VPS13D is essential for peroxisome biogenesis., The VPS13 gene family consists of VPS13A–D in mammals. Although all four genes have been linked to human diseases, their cellular functions are poorly understood, particularly those of VPS13D. We generated and characterized knockouts of each VPS13 gene in HeLa cells. Among the individual knockouts, only VPS13D-KO cells exhibit abnormal mitochondrial morphology. Additionally, VPS13D loss leads to either partial or complete peroxisome loss in several transformed cell lines and in fibroblasts derived from a VPS13D mutation–carrying patient with recessive spinocerebellar ataxia. Our data show that VPS13D regulates peroxisome biogenesis.

Altres ajuts:Fundació La Marató de TV3 (201437.10 to R.R.). Rio Hortega grant (CM17/00074) from "Acción Estratégica en Salud 2013-2016" Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease for which the pathophysiological mechanisms of motor neuron loss are not precisely clarified. Environmental and epigenetic mechanisms such as microRNAs (miRNAs) could have a role in disease progression. We studied the expression pattern of miRNAs in ALS serum from 60 patients and 29 healthy controls. We also analyzed how deregulated miRNAs found in serum affected cellular pathways such as apoptosis, autophagy and mitochondrial physiology in SH-SY5Y cells. We found that miR-335-5p was downregulated in ALS serum. SH-SY5Y cells were transfected with a specific inhibitor of miR-335-5p and showed abnormal mitochondrial morphology, with an increment of reactive species of oxygen and superoxide dismutase activity. Pro-apoptotic caspases-3 and 7 also showed an increased activity in transfected cells. The downregulation of miR-335-5p, which has an effect on mitophagy, autophagy and apoptosis in SH-SY5Y neuronal cells could have a role in the motor neuron loss observed in ALS.

Maintaining skeletal muscle mitochondrial quality is important not only for muscle activity but also for systemic metabolism. Exercise has long been recognized to have a positive impact on muscle mitochondrial quality. Although exercise triggers various changes in the mitochondrial dynamics, its molecular basis remains to be elucidated. We have previously reported that inactivation of the muscle-specific protein, zinc finger MYND domain-containing protein 17 (Zmynd17), results in mitochondrial abnormalities. To investigate the link between Zmynd17 activity and exercise-induced mitochondrial maintenance, we observed the effect of consecutive exercise on the mitochondrial quality in Zmynd17-deficient muscles. Zmynd17-deficient mice displayed abnormal mitochondrial morphology in limb muscles, which remarkably improved upon voluntary exercise. Interestingly, morphological abnormalities in mitochondria were even more apparent when PGC1α, a regulator of exercise-induced mitochondrial biogenesis, was overexpressed in Zmynd17-KO limb muscle. These abnormalities were also ameliorated by voluntary exercise. Our results show that neither the effect of consecutive exercise on mitochondrial quality nor PGC1α-induced mitochondrial biogenesis are mediated through Zmynd17 activity, thereby suggesting the existence of a complex mechanism of mitochondrial quality control in muscles., Frontiers in Cell and Developmental Biology, 7, art.no.330; 2019

As one of the best-studied RNA binding proteins in plant, pentatricopeptide repeats (PPRs) protein are mainly targeted to mitochondria and/or chloroplasts for RNA processing to regulate the biogenesis and function of the organelles, but its molecular mechanism and role in development remain to be further revealed. Here, we identified a mitochondria-localized P-type small PPR protein, MITOCHONDRION-MEDIATED GROWTH DEFECT 1 (MID1) that is crucial for Arabidopsis development. Mutation in MID1 causes retarded embryo development and stunted plant growth with defects in cell expansion and proliferation. Molecular experiments showed that MID1 is required for the splicing of the nad2 intron 1 in mitochondria. Consistently, mid1 plants display significant reduction in the abundance and activity of mitochondrial respiration complex I, accompanied by abnormal mitochondrial morphology and energy metabolism. Furthermore, MID1 is associated with other trans-factors involved in NICOTINAMIDE ADENINE DINUCLEOTIDE HYDROGEN (NADH) DEHYDROGENASE SUBUNIT 2 (nad2) intron 1 splicing, and interacts directly with itself and MITOCHONDRIAL STABILITY FACTOR 1 (MTSF1). This suggests that MID1 most likely functions as a dimer for nad2 intron 1 splicing. Together, we characterized a novel PPR protein MID1 for nad2 intron 1 splicing.

Neurons are particularly vulnerable to mitochondrial dysfunction due to high energy demand and an inability to proliferate. Therefore, dysfunctional mitochondria cause various neuropathologies. Mitochondrial damage induces maintenance pathways to repair or eliminate damaged organelles. This mitochondrial quality control (MQC) system maintains appropriate morphology, localization, and removal/replacement of mitochondria to sustain brain homeostasis and counter progression of neurological disorders. Glucocorticoid release is an essential response to stressors for adaptation; however, it often culminates in maladaptation if neurons are exposed to chronic and severe stress. Long-term exposure to high levels of glucocorticoids induces mitochondrial dysfunction via genomic and nongenomic mechanisms. Glucocorticoids induce abnormal mitochondrial morphology and dysregulate fusion and fission. Moreover, mitochondrial trafficking is arrested by glucocorticoids and dysfunctional mitochondria are subsequently accumulated around the soma. These alterations lead to energy deficiency, particularly for synaptic transmission that requires large amounts of energy. Glucocorticoids also impair mitochondrial clearance by preventing mitophagy of damaged organelle and suppress mitochondrial biogenesis, resulting in the reduced number of healthy mitochondria. Failure to maintain MQC degrades brain function and contributes to neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and Huntington's disease. However, mechanisms of glucocorticoid action on the regulation of MQC during chronic stress conditions are not well understood. The present review discusses pathways involved in the impairment of MQC and the clinical significance of high glucocorticoid blood levels for neurodegenerative diseases.

Polyglutamine (polyQ)-mediated mitochondria damage is one of the prime causes of polyQ toxicity, which leads to the loss of neurons and the injury of non-neuronal cells. With the discovery of the crucial role of the gut-brain axis and gut microbes in neurological diseases, the relationship between visceral damage and neurological disorders has also received extensive attention. This study successfully simulated the polyQ mitochondrial damage model by expressing 78 or 84 polyglutamine-containing Ataxin3 proteins in Drosophila intestinal enterocytes. In vivo, polyQ expression can reduce mitochondrial membrane potential, mitochondrial DNA damage, abnormal mitochondrial morphology, and loose mitochondrial cristae. Expression profiles evaluated by RNA-seq showed that mitochondrial structural genes and functional genes (oxidative phosphorylation and tricarboxylic acid cycle-related) were significantly down-regulated. More importantly, Bioinformatic analyses demonstrated that pathological polyQ expression induced vitamin B6 metabolic pathways abnormality. Active vitamin B6 participates in hundreds of enzymatic reactions and is very important for maintaining mitochondria's activities. In the SCA3 Drosophila model, Vitamin B6 supplementation significantly suppressed ECs mitochondria damage in guts and inhibited cellular polyQ aggregates in fat bodies, indicating a promising therapeutic strategy for the treatment of polyQ. Taken together, our results reveal a crucial role for the Vitamin B6-mediated mitochondrial protection in polyQ-induced cellular toxicity, which provides strong evidence for this process as a drug target in polyQ diseases treatment.

Cognitive impairment, termed chemobrain, is a common neurotoxicity associated with chemotherapy treatment, affecting an estimated 78% of patients. Prompted by the hypothesis that neuronal mitochondrial dysfunction underlies chemotherapy-induced cognitive impairment (CICI), we explored the efficacy of administering the small-molecule pifithrin (PFT)-μ, an inhibitor of mitochondrial p53 accumulation, in preventing CICI. Male C57BL/6J mice injected with cisplatin ± PFT-μ for two 5-day cycles were assessed for cognitive function using novel object/place recognition and alternation in a Y-maze. Cisplatin impaired performance in the novel object/place recognition and Y-maze tests. PFT-μ treatment prevented CICI and associated cisplatin-induced changes in coherency of myelin basic protein fibers in the cingular cortex and loss of doublecortin+ cells in the subventricular zone and hippocampal dentate gyrus. Mechanistically, cisplatin decreased spare respirator capacity of brain synaptosomes and caused abnormal mitochondrial morphology, which was counteracted by PFT-μ administration. Notably, increased mitochondrial p53 did not lead to cerebral caspase-3 activation or cytochrome-c release. Furthermore, PFT-μ administration did not impair the anticancer efficacy of cisplatin and radiotherapy in tumor-bearing mice. Our results supported the hypothesis that neuronal mitochondrial dysfunction induced by mitochondrial p53 accumulation is an underlying cause of CICI and that PFT-μ may offer a tractable therapeutic strategy to limit this common side-effect of many types of chemotherapy. Cancer Res; 77(3); 742–52. ©2016 AACR.

Elevated levels of DNA ligase IIIα (LigIIIα) have been identified as a biomarker of an alteration in DNA repair in cancer cells that confers hypersensitivity to a LigIIIα inhibitor, L67, in combination with a poly (ADP-ribose) polymerase inhibitor. Because LigIIIα functions in the nucleus and mitochondria, we examined the effect of L67 on these organelles. Here, we show that, although the DNA ligase inhibitor selectively targets mitochondria, cancer and nonmalignant cells respond differently to disruption of mitochondrial DNA metabolism. Inhibition of mitochondrial LigIIIα in cancer cells resulted in abnormal mitochondrial morphology, reduced levels of mitochondrial DNA, and increased levels of mitochondrially generated reactive oxygen species that caused nuclear DNA damage. In contrast, these effects did not occur in nonmalignant cells. Furthermore, inhibition of mitochondrial LigIIIα activated a caspase 1–dependent apoptotic pathway, which is known to be part of inflammatory responses induced by pathogenic microorganisms in cancer, but not nonmalignant cells. These results demonstrate that the disruption of mitochondrial DNA metabolism elicits different responses in nonmalignant and cancer cells and suggests that the abnormal response in cancer cells may be exploited in the development of novel therapeutic strategies that selectively target cancer cells. Cancer Res; 76(18); 5431–41. ©2016 AACR.

In humans, mitochondrial DNA (mtDNA) depletion syndromes are a group of genetically and clinically heterogeneous autosomal recessive disorders that arise as a consequence of defects in mtDNA replication or nucleotide synthesis. Clinical manifestations are variable and include myopathic, encephalomyopathic, neurogastrointestinal or hepatocerebral phenotypes. Through clinical exome sequencing, we identified a homozygous missense variant (c.533C>T; p.Pro178Leu) in mitochondrial transcription factor A (TFAM) segregating in a consanguineous kindred of Colombian-Basque descent in which two siblings presented with IUGR, elevated transaminases, conjugated hyperbilirubinemia and hypoglycemia with progression to liver failure and death in early infancy. Results of the liver biopsy in the proband revealed cirrhosis, micro- and macrovesicular steatosis, cholestasis and mitochondrial pleomorphism. Electron microscopy of muscle revealed abnormal mitochondrial morphology and distribution while enzyme histochemistry was underwhelming. Electron transport chain testing in muscle showed increased citrate synthase activity suggesting mitochondrial proliferation, while respiratory chain activities were at the lower end of normal. mtDNA content was reduced in liver and muscle (11% and 21% of normal controls respectively). While Tfam mRNA expression was upregulated in primary fibroblasts, Tfam protein level was significantly reduced. Furthermore, functional investigations of the mitochondria revealed reduced basal respiration and spare respiratory capacity, decreased mtDNA copy number and markedly reduced nucleoids. TFAM is essential for transcription, replication and packaging of mtDNA into nucleoids. Tfam knockout mice display embryonic lethality secondary to severe mtDNA depletion. In this report, for the first time, we associate a homozygous variant in TFAM with a novel mtDNA depletion syndrome.

Mitochondria maintain a distinct pool of ribosomal machinery, including tRNAs and tRNAs activating enzymes, such as mitochondrial tyrosyl-tRNA synthetase (YARS2). Mutations in YARS2, which typically lead to the impairment of mitochondrial protein synthesis, have been linked to an array of human diseases including optic neuropathy. However, the lack of YARS2 mutation animal model makes us difficult to elucidate the pathophysiology underlying YARS2 deficiency. To explore this system, we generated YARS2 knockout (KO) HeLa cells and zebrafish using CRISPR/Cas9 technology. We observed the aberrant tRNATyr aminoacylation overall and reductions in the levels in mitochondrion- and nucleus-encoding subunits of oxidative phosphorylation system (OXPHOS), which were especially pronounced effects in the subunits of complex I and complex IV. These deficiencies manifested the decreased levels of intact supercomplexes overall. Immunoprecipitation assays showed that YARS2 bound to specific subunits of complex I and complex IV, suggesting the posttranslational stabilization of OXPHOS. Furthermore, YARS2 ablation caused defects in the stability and activities of OXPHOS complexes. These biochemical defects could be rescued by the overexpression of YARS2 cDNA in the YARS2KO cells. In zebrafish, the yars2KO larva conferred deficient COX activities in the retina, abnormal mitochondrial morphology, and numbers in the photoreceptor and retinal ganglion cells. The zebrafish further exhibited the retinal defects affecting both rods and cones. Vision defects in yars2KO zebrafish recapitulated the clinical phenotypes in the optic neuropathy patients carrying the YARS2 mutations. Our findings highlighted the critical role of YARS2 in the stability and activity of OXPHOS and its pathological consequence in vision impairments.

Mitochondrial cristae are critical for efficient oxidative phosphorylation, however, how cristae architecture is precisely organized remains largely unknown. Here, we discovered that Mic19, a core component of MICOS (mitochondrial contact site and cristae organizing system) complex, can be cleaved at N-terminal by mitochondrial protease OMA1 under certain physiological stresses. Mic19 directly interacts with mitochondrial outer-membrane protein Sam50 (the key subunit of SAM complex) and inner-membrane protein Mic60 (the key component of MICOS complex) to form Sam50–Mic19–Mic60 axis, which dominantly connects SAM and MICOS complexes to assemble MIB (mitochondrial intermembrane space bridging) supercomplex for mediating mitochondrial outer- and inner-membrane contact. OMA1-mediated Mic19 cleavage causes Sam50–Mic19–Mic60 axis disruption, which separates SAM and MICOS and leads to MIB disassembly. Disrupted Sam50–Mic19–Mic60 axis, even in the presence of SAM and MICOS complexes, causes the abnormal mitochondrial morphology, loss of mitochondrial cristae junctions, abnormal cristae distribution and reduced ATP production. Importantly, Sam50 displays punctate distribution at mitochondrial outer membrane, and acts as an anchoring point to guide the formation of mitochondrial cristae junctions. Therefore, we propose that Sam50–Mic19–Mic60 axis-mediated SAM–MICOS complexes integration determines mitochondrial cristae architecture.

Mitochondria are organelles highly dynamic in most types of cells, constantly changing morphology and forming dynamically continuous networks. Defects of mitochondrial dynamics are associated with various human diseases including neurodegenerative diseases and cardiovascular diseases. In the heart, mitochondria are rigidly organized between myofilaments into a crystal-like lattice pattern, the apparently limited mitochondrial movement raises the question of whether mitochondria communicate with each other dynamically. A large body of evidence reveals abnormal mitochondrial morphology in cardiac diseases and that deficiencies of mitochondrial dynamic related proteins lead to cardiac dysfunctions, indicating an essential role of mitochondrial dynamics in regulating the cardiac function. Here we will review mitochondrial dynamics in the heart with the focus on recent findings of the direct inter-mitochondrial communication in adult cardiomyocytes, and will discuss the possible regulating mechanisms.

PARKIN (E3 ubiquitin ligase PARK2), PINK1 (PTEN induced kinase 1) and DJ-1 (PARK7) are proteins involved in autosomal recessive parkinsonism, and carcinogenic processes. In damaged mitochondria, PINK1’s importing into the inner mitochondrial membrane is prevented, PARKIN presents a partial mitochondrial localization at the outer mitochondrial membrane and DJ-1 relocates to mitochondria when oxidative stress increases. Depletion of these proteins result in abnormal mitochondrial morphology. PINK1, PARKIN, and DJ-1 participate in mitochondrial remodeling and actively regulate mitochondrial quality control. In this review, we highlight that PARKIN, PINK1, and DJ-1 should be regarded as having an important role in Cancer Biology. The STRING database and Gene Ontology (GO) enrichment analysis were performed to consolidate knowledge of well-known protein interactions for PINK1, PARKIN, and DJ-1 and envisage new ones. The enrichment analysis of KEGG pathways showed that the PINK1/PARKIN/DJ-1 network resulted in Parkinson disease as the main feature, while the protein DJ-1 showed enrichment in prostate cancer and p53 signaling pathway. Some predicted transcription factors regulating PINK1, PARK2 (PARKIN) and PARK7 (DJ-1) gene expression are related to cell cycle control. We can therefore suggest that the interplay among PINK1/PARKIN/DJ-1 network during mitochondrial quality control in cancer biology may occur at the transcriptional level. Further analysis, like a systems biology approach, will be helpful in the understanding of PINK1/PARKIN/DJ-1 network.

Schnyder corneal dystrophy (SCD) is a rare autosomal dominant disease in humans, characterized by abnormal deposition of cholesterol and phospholipids in cornea caused by mutations in the UbiA prenyltransferase domain containing 1 (UBIAD1) gene. In this study, we generated a mouse line carrying Ubiad1 N100S point mutation using the CRISPR/Cas9 technique to investigate the pathogenesis of SCD. In vivo confocal microscopy revealed hyper-reflective dot-like deposits in the anterior cornea in heterozygotes and homozygotes. No significant change was found in corneal epithelial barrier function or wound healing. Electron microscopy revealed abnormal mitochondrial morphology in corneal epithelial, stromal, and endothelial cells. Mitochondrial DNA copy number assay showed 1.27 ± 0.07 fold change in homozygotes versus 0.98 ± 0.05 variation in wild type mice (P Ubiad1N100S mouse provides a promising animal model of SCD revealing that mitochondrial dysfunction is a prominent component of the disease. The different phenotype in human and mouse may due to difference in cholesterol metabolism between species.

Mitochondrial cristae are critical for efficient oxidative phosphorylation, however, how cristae architecture is precisely organized remains largely unknown. Here, we discovered that Mic19, a core component of MICOS (mitochondrial contact site and cristae organizing system) complex, can be cleaved at N-terminal by mitochondrial protease OMA1. Mic19 directly interacts with mitochondrial outer-membrane protein Sam50 (the key subunit of SAM complex) and inner-membrane protein Mic60 (the key component of MICOS complex) to form Sam50-Mic19-Mic60 axis, which dominantly connects SAM and MICOS complexes to assemble MIB (mitochondrial intermembrane space bridging) supercomplex for mediating mitochondrial outer- and inner-membrane contact. OMA1-mediated Mic19 cleavage causes Sam50-Mic19-Mic60 axis disruption, which separates SAM and MICOS and leads to MIB disassembly. Disrupted Sam50-Mic19-Mic60 axis, even in the presence of SAM and MICOS complexes, causes the abnormal mitochondrial morphology, loss of mitochondrial cristae junctions, abnormal cristae distribution and reduced ATP production. Importantly, Sam50 displays punctate distribution at mitochondrial outer membrane, and acts as an anchoring point to guide the formation of mitochondrial cristae junctions. Therefore, we propose a model that Sam50-Mic19-Mic60 axis mediated SAM-MICOS complexes integration determines mitochondrial cristae architecture.

Skeletal muscle aging is associated with a progressive decline in muscle mass and strength, a process termed sarcopenia. Evidence suggests that accumulation of mitochondrial dysfunction plays a causal role in sarcopenia, which could be triggered by impaired mitophagy. Mitochondrial function, mitophagy and mitochondrial morphology are interconnected aspects of mitochondrial biology, and may coordinately be altered with aging. However, mitochondrial morphology has remained challenging to characterize in muscle, and whether sarcopenia is associated with abnormal mitochondrial morphology remains unknown. Therefore, we assessed the morphology of SubSarcolemmal (SS) and InterMyoFibrillar (IMF) mitochondria in skeletal muscle of young (8-12wk-old) and old (88-96wk-old) mice using a quantitative 2-dimensional transmission electron microscopy approach. We show that sarcopenia is associated with larger and less circular SS mitochondria. Likewise, aged IMF mitochondria were longer and more branched, suggesting increased fusion and/or decreased fission. Accordingly, although no difference in the content of proteins regulating mitochondrial dynamics (Mfn1, Mfn2, Opa1 and Drp1) was observed, a mitochondrial fusion index (Mfn2-to-Drp1 ratio) was significantly increased in aged muscles. Our results reveal that sarcopenia is associated with complex changes in mitochondrial morphology that could interfere with mitochondrial function and mitophagy, and thus contribute to aging-related accumulation of mitochondrial dysfunction and sarcopenia.

Recent studies have reported intrinsic metabolic reprogramming in Pkd1 knock-out cells, implicating dysregulated cellular metabolism in the pathogenesis of polycystic kidney disease. However, the exact nature of the metabolic changes and their underlying cause remains controversial. We show herein that Pkd1 k o /ko renal epithelial cells have impaired fatty acid utilization, abnormal mitochondrial morphology and function, and that mitochondria in kidneys of ADPKD patients have morphological alterations. We further show that a C-terminal cleavage product of polycystin-1 (CTT) translocates to the mitochondria matrix and that expression of CTT in Pkd1 ko/ko cells rescues some of the mitochondrial phenotypes. Using Drosophila to model in vivo effects, we find that transgenic expression of mouse CTT results in decreased viability and exercise endurance but increased CO2 production, consistent with altered mitochondrial function. Our results suggest that PC1 may play a direct role in regulating mitochondrial function and cellular metabolism and provide a framework to understand how impaired mitochondrial function could be linked to the regulation of tubular diameter in both physiological and pathological conditions.

X-linked Charcot-Marie-Tooth disease type 4 (CMTX4), caused by AIFM1 (Apoptosis-Inducing Factor, Mitochondrion associated 1) mutations and associated with deafness and cognitive impairment, is a rare subtype of Charcot-Marie-Tooth disease. Here, we report a novel missense variant of AIFM1 in a X-linked recessive Chinese family with childhood-onset, slowly progressive, isolated axonal motor and sensory neuropathy. Calf magnetic resonance imaging revealed fatty infiltration and atrophy severely involving the muscles of peroneal compartment. Pathologies exhibited abnormal mitochondrial morphology and accumulation in axoplasm of nerve fiber and subsarcolemmal area of muscle. A hemizygous variant (c.513G>A, p.Met171Ile) in the family was identified and was classified as likely pathogenic according to the standards and guidelines of the American College of Medical Genetics and Genomics. Our report expands the genetic spectrum of diseases related to AIFM1 mutations and indicates that fatty infiltration and atrophy of muscles in the peroneal compartment may be a feature of CMTX4 in early stage.

Background Dysfunction of mitochondria is involved in podocyte injury in some kidney diseases, but the relationship between abnormal mitochondrial morphology and podocyte injury as well as the underlying mechanism is still unclear. This study aims to investigate dynamic changes of mitochondrial morphology and the potential molecular events in an adriamycin (ADR)-induced podocyte injury model. Methods Podocyte apoptosis was evaluated by annexin V assay. Podocyte mitochondrial membrane potential (MMP) was measured with MitoCapture kit. Double staining was used to show the distribution changes of mitochondria and actin filament as well as mitofusin proteins and podocin. Mitochondrial shape descriptors were obtained using analySIS Image system. Effects of cyclosporine A (CsA) or minocycline (Mcy) on mitochondrial morphology were explored in ADR-induced nephropathy rats. Results ADR caused podocyte damage displaying as induction of cellular apoptosis and increase of activated caspase 3 and cytochrome c. The MMP level was decreased remarkably in ADR-treated podocytes. Mitochondrial morphological changes induced by ADR occurred rapidly from large and ellipsoid shape to the small, long and irregular. ADR significantly decreased surface area, perimeter and circularity, while increasing aspect ratio of mitochondria. In addition, mitochondria number transiently increased at 6 h following ADR application. Mitochondria intensity was increased along with punctate mitochondria formation, which co-localized with polymerized actin cytoskeleton in ADR podocytes. In ADR-induced nephropathy rats, 24-h proteinuria was decreased significantly by CsA or Mcy. ADR-induced abnormal changes of mitochondrial morphology were restored by CsA or Mcy. The induction of mitofusin proteins and the reduction of podocin in ADR rat glomeruli were rescued by CsA or Mcy. Conclusions Mitochondrial dysfunction may be an early event in ADR-induced podocyte damage, and the protective role of CsA or Mcy may be mediated partially by improving mitochondrial function through inhibiting the induction of mitofusin proteins.

Spermatids undergo the final steps of maturation during spermiogenesis, a process that necessitates extensive rearrangement of organelles such as the mitochondria. Male infertility has been linked to mitochondrial disorder, for example, hypospermatogenesis and asthenozoospermia. However, the mechanisms that regulate mitochondrial dynamics during spermiogenesis remain largely unknown. We found the glycerol kinase (Gyk)-like proteins glycerol kinase-like 1 (Gykl1) and glycerol kinase 2 (Gk2) were specifically localized to the mitochondria in spermatids. Male mice deficient in either Gykl1 or Gk2 were infertile due to dysfunctional spermatozoa, which exhibited unregulated ATP production, disordered mitochondrial sheath formation, abnormal mitochondrial morphology, and defective sperm tail. We demonstrated that the unique C-terminal sequences found in Gykl1 and Gk2 mediated their targeting to the mitochondrial outer membrane. Furthermore, both Gykl1 and Gk2 could interact with Pld6 (MitoPLD) and induce Pld6 and phosphatidic acid (PA)-dependent mitochondrial clustering in cells. Taken together, our study has revealed previously unsuspected functions of Gyk-like proteins in spermiogenesis, providing new insight into the potential mechanisms that lead to spermatozoa dysfunction and male infertility.

Chemotherapy-induced peripheral neuropathy (CIPN), a debilitating major side effect of cancer treatment, is characterized by pain and sensory loss in hand and feet. Platinum-based chemotherapeutics like cisplatin frequently induce CIPN. The molecular mechanism underlying these neurotoxic symptoms is incompletely understood and there are no preventive or curative interventions. We hypothesized that cisplatin acts as a cellular stressor that triggers p53 accumulation at mitochondria, leading to mitochondrial dysfunction and CIPN. To test this hypothesis, we examined the effect of the small molecule pifithrin-μ (PFT-μ), an inhibitor of p53 mitochondrial association on CIPN and the associated mitochondrial dysfunction. We show here for the first time that in vivo cisplatin rapidly increases mitochondrial accumulation of p53 in dorsal root ganglia (DRG), spinal cord, and peripheral nerve without evidence for apoptosis. Cisplatin-treatment also reduced mitochondrial membrane potential and lead to abnormal mitochondrial morphology and impaired mitochondrial function in DRG neurons. Pre-treatment with PFT-μ prevented the early cisplatin-induced increase in mitochondrial p53 and the reduction in mitochondrial membrane potential. Inhibition of the early mitochondrial p53 accumulation by PFT-μ also prevented the abnormalities in mitochondrial morphology and mitochondrial bioenergetics (reduced oxygen consumption rate, maximum respiratory capacity, and adenosine triphosphate synthesis) that develop in DRG and peripheral nerve after cisplatin-treatment. Functionally, inhibition of mitochondrial p53 accumulation prevented the hallmarks of CIPN including mechanical allodynia, peripheral sensory loss (numbness) as quantified by an adhesive-removal task, and loss of intra-epidermal nerve fibers. In conclusion, PFT-μ is a potential neuroprotective agent that prevents cisplatin-induced mitochondrial dysfunction in DRG and peripheral nerves thereby protecting against CIPN through blockade of the early cisplatin-induced increase in mitochondrial p53. Notably, there is accumulating evidence that PFT-μ has anti-tumor activities and could therefore be an attractive candidate to prevent CIPN while promoting tumor cell death.

Exercise limitation comes from a close interaction between cardiovascular and skeletal muscle impairments. To better understand the implication of possible peripheral oxidative metabolism dysfunction, we studied the proteomic signature of skeletal muscle in pulmonary arterial hypertension (PAH). Eight idiopathic PAH patients and eight matched healthy sedentary subjects were evaluated for exercise capacity, skeletal muscle proteomic profile, metabolism, and mitochondrial function. Skeletal muscle proteins were extracted, and fractioned peptides were tagged using an iTRAQ protocol. Proteomic analyses have documented a total of 9 downregulated proteins in PAH skeletal muscles and 10 upregulated proteins compared to healthy subjects. Most of the downregulated proteins were related to mitochondrial structure and function. Focusing on skeletal muscle metabolism and mitochondrial health, PAH patients presented a decreased expression of oxidative enzymes (pyruvate dehydrogenase, p

Mild cognitive impairment (MCI) occurs during the predementia stage of Alzheimer disease (AD) and is characterized by a decline in cognitive abilities that frequently represents a transition between normal cognition and AD dementia. Its pathogenesis is not well understood. Here, we demonstrate the direct consequences and potential mechanisms of oxidative stress and mitochondrial dynamic and functional defects in MCI-derived mitochondria. Using a cytoplasmic hybrid (cybrid) cell model in which mitochondria from MCI or age-matched non-MCI subjects were incorporated into a human neuronal cell line depleted of endogenous mitochondrial DNA, we evaluated the mitochondrial dynamics and functions, as well as the role of oxidative stress in the resultant cybrid lines. We demonstrated that increased expression levels of mitofusin 2 (Mfn2) are markedly induced by oxidative stress in MCI-derived mitochondria along with aberrant mitochondrial functions. Inhibition of oxidative stress rescues MCI-impaired mitochondrial fusion/fission balance as shown by the suppression of Mfn2 expression, attenuation of abnormal mitochondrial morphology and distribution, and improvement in mitochondrial function. Furthermore, blockade of MCI-related stress-mediated activation of extracellular signal-regulated kinase (ERK) signaling not only attenuates aberrant mitochondrial morphology and function but also restores mitochondrial fission and fusion balance, in particular inhibition of overexpressed Mfn2. Our results provide new insights into the role of the oxidative stress-ERK-Mfn2 signal axis in MCI-related mitochondrial abnormalities, indicating that the MCI phase may be targetable for the development of new therapeutic approaches that improve mitochondrial function in age-related neurodegeneration.