Mitochondrial Fusion Genes Research Articles

A Common Missense Variant in OMA1 Associated with the Prognosis of Heart Failure.

Mitochondrial dysfunction plays a vital role in the pathophysiologic process of heart failure (HF). As a quality control system, mitochondrial fusion and fission are under control of mitochondrial fusion and fission-related proteins. The objective of this study was to investigate the effects of common variants in mitochondrial fusion and fission-related genes on the prognosis of HF. We performed whole exome sequencing (WES) with 1000 HF patients; the statistically significant variant was further genotyped in the replicated population with 2324 HF patients. A series of function analysis including western blot, cell proliferation assay, and in vitro OMA1 activity assay were conducted to illuminate the underlying mechanism. We identified a missense variant rs17117699 associated with the prognosis of HF in group without β-blocker use rather than with β-blocker use in two-stage population: adjusted P = 0.79, HR = 0.88 (0.36-2.13) in group with β-blocker use and adjusted P = 0.016, HR = 1.43 (1.07-1.91) in group without β-blocker in first-stage population; adjusted P = 0.42, HR = 0.85 (0.56-1.28) in group with β-blocker use and adjusted P = 0.015, HR = 1.39 (1.06-1.82) in group without β-blocker in replicated stage. Functional analysis indicated that rs17117699-G allele increased the activity of OMA1 assessed by the ratio of S-OPA1 to L-OPA1 and suppressed cells proliferation under ISO treatment when compared with rs17117699-T allele. Furthermore, OMA1 functioned downstream of β-adrenergic receptor signaling and ISO-induced OPA1 cleavage is dependent on OMA1. Our findings demonstrate that rs17117699T>G in OMA1 increases the risk of HF mortality via enhancing its OPA1 cleavage activity. It is a promising potential treatment target for HF. NCT03461107. https://www.clinicaltrials.gov/ct2/show/NCT03461107?term=03461107&cond=Heart+Failure&cntry=CN&rank=1.

Acetate and Butyrate Improve β-cell Metabolism and Mitochondrial Respiration under Oxidative Stress.

Islet dysfunction mediated by oxidative and mitochondrial stress contributes to the development of type 1 and 2 diabetes. Acetate and butyrate, produced by gut microbiota via fermentation, have been shown to protect against oxidative and mitochondrial stress in many cell types, but their effect on pancreatic β-cell metabolism has not been studied. Here, human islets and the mouse insulinoma cell line MIN6 were pre-incubated with 1, 2, and 4 mM of acetate or butyrate with and without exposure to the apoptosis inducer and metabolic stressor streptozotocin (STZ). Both short-chain fatty acids (SCFAs) enhanced the viability of islets and β-cells, but the beneficial effects were more pronounced in the presence of STZ. Both SCFAs prevented STZ-induced cell apoptosis, viability reduction, mitochondrial dysfunction, and the overproduction of reactive oxygen species (ROS) and nitric oxide (NO) at a concentration of 1 mM but not at higher concentrations. These rescue effects of SCFAs were accompanied by preventing reduction of the mitochondrial fusion genes MFN, MFN2, and OPA1. In addition, elevation of the fission genes DRP1 and FIS1 during STZ exposure was prevented. Acetate showed more efficiency in enhancing metabolism and inhibiting ROS, while butyrate had less effect but was stronger in inhibiting the SCFA receptor GPR41 and NO generation. Our data suggest that SCFAs play an essential role in supporting β-cell metabolism and promoting survival under stressful conditions. It therewith provides a novel mechanism by which enhanced dietary fiber intake contributes to the reduction of Western diseases such as diabetes.

Changes in the Expression of Mitochondrial Morphology-Related Genes during the Differentiation of Murine Embryonic Stem Cells.

During embryonic development, cells undergo changes in gene expression, signaling pathway activation/inactivation, metabolism, and intracellular organelle structures, which are mediated by mitochondria. Mitochondria continuously switch their morphology between elongated tubular and fragmented globular via mitochondrial fusion and fission. Mitochondrial fusion is mediated by proteins encoded by Mfn1, Mfn2, and Opa1, whereas mitochondrial fission is mediated by proteins encoded by Fis1 and Dnm1L. Here, we investigated the expression patterns of mitochondria-related genes during the differentiation of mouse embryonic stem cells (ESCs). Pluripotent ESCs maintain stemness in the presence of leukemia inhibitory factor (LIF) via the JAK-STAT3 pathway but lose pluripotency and differentiate in response to the withdrawal of LIF. We analyzed the expression levels of mitochondrial fusion- and fission-related genes during the differentiation of ESCs. We hypothesized that mitochondrial fusion genes would be overexpressed while the fission genes would be downregulated during the differentiation of ESCs. Though the mitochondria exhibited an elongated morphology in ESCs differentiating in response to LIF withdrawal, only the expression of Mfn2 was increased and that of Dnm1L was decreased as expected, the other exceptions being Mfn1, Opa1, and Fis1. Next, by comparing gene expression and mitochondrial morphology, we proposed an index that could precisely represent mitochondrial changes during the differentiation of pluripotent stem cells by analyzing the expression ratios of three fusion- and two fission-related genes. Surprisingly, increased Mfn2/Dnm1L ratio was correlated with elongation of mitochondria during the differentiation of ESCs. Moreover, application of this index to other specialized cell types revealed that neural stems cells (NSCs) and mouse embryonic fibroblasts (MEFs) showed increased Mfn2/Dnm1L ratio compared to ESCs. Thus, we suggest that the Mfn2/Dnm1L ratio could reflect changes in mitochondrial morphology according to the extent of differentiation.

Apoptosis inducing factor: Cellular protective function in Dictyostelium discoideum

Apoptosis Inducing Factor (AIF), a nuclear encoded mitochondrial inter-membrane space flavoprotein with intrinsic NADH oxidase activity, plays an important role in inducing cell death mechanisms. In response to cell death signals, it undergoes mitochondrio-nuclear translocation leading to DNA fragmentation. In addition to its role in cell death, AIF has a pro-survival role, wherein it contributes to the maintenance of mitochondrial structure and function in a coordinated manner. However, its exact mechanism of controlling mitochondrial homeostasis is unclear. The current study aims to explore the protective functions of AIF by its downregulation and overexpression in Dictyostelium discoideum. Constitutive AIF downregulated (dR) cells exhibited compromised oxidative phosphorylation along with elevated levels of cellular ROS. Interestingly, constitutive AIF dR cells showed amelioration in the activity of the ETC complexes upon antioxidant treatment, strengthening AIF's role as an ROS regulator, by virtue of its oxidoreductase property. Also, constitutive AIF dR cells showed lower transcript levels of the various subunits of ETC. Moreover, loss of AIF affected mtDNA content and mitochondrial fusion-fission mechanism, which subsequently caused morphometric mitochondrial alterations. Constitutive AIF overexpressed (OE) cells also showed higher cellular ROS and mitochondrial fission genes transcript levels along with reduced mitochondrial fusion genes transcript levels and mtDNA content. Thus, the results of the current study provide a paradigm where AIF is implicated in cell survival by maintaining mitochondrial bioenergetics, morphology and fusion-fission mechanism in D. discoideum, an evolutionarily significant model organism for mitochondrial diseases.

Mitochondrial DNA Haplotypes Influence Energy Metabolism across Chicken Transmitochondrial Cybrids.

The association between mitochondrial DNA haplotype and productive performances has been widely reported in chicken breeds. However, there has not been physiological evidence of this seen previously. In this study, chicken transmitochondrial cells were generated using the nucleus of the DF-1 cell line and mitochondria of primary cell lines derived from two native chicken breeds, Tibetan chicken and Shouguang chicken. Generally, Tibetan chicken primary cells showed a stronger metabolic capacity than Shouguang chicken primary cells. However, the Tibetan chicken cybrids had a dramatic drop in relative mtDNA copies and oxygen consumption. Higher rates of oxygen consumption (OCR) and expression levels of mitochondrial biogenesis and fusion genes were observed in Shouguang chicken cybrids, potentially reflecting that the mitochondrial DNA haplotype of Shouguang chicken had better coordination with the DF-1 nucleus than others. Meanwhile, mitonuclear incompatibility occurred in Tibetan chicken cybrids. The results demonstrate functional differences among mitochondrial DNA haplotypes and may shed light on the interaction between the mitochondria and nucleus in Gallus gallus domesticus.

High Levels of Physical Activity in Later Life Are Associated With Enhanced Markers of Mitochondrial Metabolism.

The age-associated reduction in muscle mass is well characterized; however, less is known regarding the mechanisms responsible for the decline in oxidative capacity also observed with advancing age. The purpose of the current study was therefore to compare mitochondrial gene expression and protein content between young and old recreationally active, and older highly active individuals. Muscle biopsies were obtained from the vastus lateralis of young males (YG: 22 ± 3 years) and older (OG: 67 ± 2 years) males not previously engaged in formal exercise and older male master cyclists (OT: 65 ± 5 years) who had undertaken cycling exercise for 32 ± 17 years. Comparison of gene expression between YG, OG, and OT groups revealed greater expression of mitochondrial-related genes, namely, electron transport chain (ETC) complexes II, III, and IV (p < .05) in OT compared with YG and OG. Gene expression of mitofusion (MFN)-1/2, mitochondrial fusion genes, was greater in OT compared with OG (p < .05). Similarly, protein content of ETC complexes I, II, and IV was significantly greater in OT compared with both YG and OG (p < .001). Protein content of peroxisome proliferator-activated receptor gamma, coactivator 1 α (PGC-1α), was greater in OT compared with YG and OG (p < .001). Our results suggest that the aging process per se is not associated with a decline in gene expression and protein content of ETC complexes. Mitochondrial-related gene expression and protein content are substantially greater in OT, suggesting that exercise-mediated increases in mitochondrial content can be maintained into later life.

Glucocorticoid transiently upregulates mitochondrial biogenesis in the osteoblast.

Glucocorticoid (GC)-induced bone loss is the most prevalent form of secondary osteoporosis. Previous studies demonstrated that long-term incubation of dexamethasone (DEX) induced oxidative stress and mitochondrial dysfunctions, consequently leading to apoptosis of differentiated osteoblasts. This DEX-induced cell death might be the main causes of bone loss. We previously described that DEX induced biphasic mitochondrial alternations. As GC affects mitochondrial physiology through several different possible routes, the short-term and long-term effects of GC treatment on mitochondria in the osteoblast have not been carefully characterized. Here, we examined the expression levels of genes that are associated with mitochondrial functions at several different time points after incubation with DEX. Mitochondrial biogenesis-mediated genes nuclear respiratory factor 1 (Nrf1) and Nrf2 were upregulated after 4-h incubation, and then declined after 24-h incubation, suggesting that mitochondrial biogenesis were transiently upregulated by DEX. In contrast, mitochondrial fusion gene optic atrophy 1 (Opa1) and mitofusin 2 (Mfn2) started to be elevated as the biogenesis started to decrease. Finally, the mitochondrial fission increased and apoptosis becomes prominent. Agree with the mitochondrial biphasic alterations hypothesis, the results suggested an early increase of mitochondrial activities and biogenesis upon DEX stimulation to the osteoblasts. The oxidative phosphorylation and inducible nitric oxide synthase levels increased results in oxidative stress accumulation, leading to mitochondrial fusion, and subsequently fission and triggering the apoptosis. Our results indicated that the primary effects of GC on mitochondria are promoting their functions and biogenesis. Mitochondrial breakdown and the activation of the apoptotic pathways appeared to be the secondary effect after long-term treatment.

Organelle fusion in fertility

Reproduction The fertility of organisms as diverse as male fruit flies and mice requires a mitochondrial fusion gene. But what for? Mitochondria cluster and fuse during early sperm development with the help of guanosine triphosphatases called mitofusins. When mitochondrial fusion fails, oxidative phosphorylation decreases, and mitochondrial transport and degradation are also affected. Varuzhanyan et al. tested how reliant the success of male germ cell development in mice is on mitofusins. Mitofusins are needed to trigger a metabolic shift during meiosis. When mitofusins are eliminated, germ cells display damage to the cristae ultrastructure, increased apoptosis, reduced oxidative phosphorylation, and a loss of mitochondrial ribosomes. Thus, mitofusins are vital for maintaining translation of respiratory chain and mitochondrial proteins to enable male fertility. eLife 8 , e51601 (2019).

LOW GLUCOSE ENHANCES THE CYTOPROTECTIVE EFFECT OF METFORMIN AGAINST DOXORUBICIN-INDUCED CYTOTOXICITY

Metformin, an oral anti-diabetic drug, is currently being investigated for its anti-aging properties and has also been used as adjunct therapy in cancer. Cancer is a disease of aging. Type 2 diabetes is also prevalent in older adults. We wanted to test the hypothesis that metformin could protect normal cells during chemotherapy treatment under different glucose conditions. We used C2C12 myoblast cells to study cellular bioenergetics, variations in gene expressions, and biochemical alterations induced by metformin and pegylated liposomal doxorubicin (L-Doxo) under low glucose (2.7 mM or 50 mg/dL) and normal physiologic glucose (5.5 mM, or 100 mg/dL) conditions. Using confocal microscopy, we noted that treatment of C2C12 cells with 30 µg/mL L-Doxo under low glucose and normal physiologic glucose conditions induced cellular defects. Furthermore, L-Doxo treatment dysregulated the expression of mitochondrial fission and fusion genes, which may influence transformation of the network’s connectivity. L-Doxo treatment significantly reduced mitochondrial oxygen consumption rate (OCR) and extracellular acidification rate (ECAR). However, pre-treatment with 100 nM metformin provided protection against L-Doxo-induced damage and increased cell viability and ATP levels in cells even under low glucose conditions. Our data provide further evidence by which low dose metformin exerts protective effects against L-Doxo, a chemotherapeutic drug, under low glucose conditions. Metformin appears to act via AMPKα, Raptor, and SRF, and has significant cellular protective effects that may be useful in cancer and/or aging.

Increased Mitochondrial Mass Leads to Heightened Pyroptosis that Drives CD4+ T Cell Depletion in Patients with HIV-1 Infection

In HIV-1 infection, over 90% CD4+ T cells have died of caspase-1 mediated pyroptosis. What governs the increased susceptibility of CD4+ T cells to pyroptosis is poorly understood. Here, we examined the involvement of mitochondria in pyroptosis. Mitochondrial mass (MM) levels are significantly higher in CD4+ T cells from HIV-infected patients than that in healthy controls, and cells with the MMhigh phenotype manifest greater sensitivity to caspase-1 mediated pyroptosis. Moreover, the increased MM is more pronounced in the early differentiated and inactivated CD4+ T cells. However, higher MM is not intrinsically linked to T cell differentiation disorder or excessive activation of CD4+ T cells. Mechanistically, the increased MM is significantly correlated with an elevated expression of the mitochondrial fusion gene Mfn1. Additionally, MM increase in CD4+ T cells is associated with heightened sensitivity of these cells to pyroptosis in HIV-1 infected patients whom were either treated with antiretroviral drugs or not. These results reveal a previously unknown mechanism that links mitochondrial change to pyroptosis, and suggest that modulation of this interaction may help to prevent CD4+ T cell loss in HIV infection. Funding Statement: This work was funded in part by The National 13th Five-Year Plan’s Grand Program on Key Infectious Disease Control (2018ZX10302-102 to F.Z., 2018ZX10715-005 to H.Z.), the National Natural Science Foundation of China (NSFC81672000 to H.Z.), the Culture Project of Beijing Municipal Commission of Health and Family Planning (215-3-109 to L.W.), the Science and technology innovation service capacity building (1192070325 to F.Z.). Declaration of Interests: The authors have no conflicts of interest to declare. Ethics Approval Statement: Written informed consent was obtained from each subject. The local human research subject review board (RSRB) approved the study.

The mechanisms of PM2.5 and its main components penetrate into HUVEC cells and effects on cell organelles.

Atmospheric particulate matter (PM2.5) is associated with the morbidity and mortality of cardiovascular diseases. However, whether PM2.5 penetrates into the cells and the potential mechanisms are unknown. Hence, the study firstly indicated that PM2.5 could penetrate into the HUVEC cells, and phagocytosis, micropinocytosis, caveolin as well as clathrin mediated the internalization of PM2.5 into HUVEC cells. Particularly, the components of PM2.5-Metal, PAHs and WSC could enter into HUVEC cells mainly via the micropinocytosis, clathrin and caveolin mediated endocytosis, respectively. The current data of environmental assessments indicated that PM2.5-Metal were extremely harmful to the ecological environment and human health. Moreover, accompanying with mitochondrial fusion gene Mfn1 was increased and fission genes Opa1 and Drp1 were decreased, and the lysosome related genes LAMP2 and LAMP3 were decreased, the phenomenon that the morphology of mitochondrial and lysosome injured was observed in HUVEC cells treated with PM2.5 and/or PM2.5-Metal. These data suggest that PM2.5 and its main components depend on different endocytosis penetrate into HUVEC cells and cause the mitochondrial and lysosomal damages. Thereby, our study provides the potential mechanism of haze particles penetration into HUVEC cells and damage to organelles.

Pretreatment with vildagliptin boosts ischemic-postconditioning effects on cardioprotection and expression profile of genes regulating autophagy and mitochondrial fission/fusion in diabetic heart with reperfusion injury.

The burden of myocardial ischemia/reperfusion (IR) injury is 2-3-folds higher in diabetic patients, so protecting diabetic hearts is clinically important. Here, we investigated the effect of combinational therapy with vildagliptin and ischemic postconditioning (IPostC) on cardioprotection and the expression of genes regulating autophagy and mitochondrial function in diabetic hearts with IR injury. Type 2 diabetes was induced through high-fat diet and streptozotocin protocol in Wistar rats. Vildagliptin was orally administered to diabetic rats 5weeks before IR injury. Myocardial-IR injury was modeled by ligation of left the coronary artery for 30min followed by 60-min reperfusion, on a Langendorff-perfusion system. IPostC was applied at early reperfusion as 6 alternative cycles of 10-s reperfusion/ischemia. Creatine-kinase levels were measured spectrometrically, and infarct size was evaluated by TTC staining method. Left ventricles were harvested for assessing the expression levels of autophagy and mitochondrial-related genes using real-time PCR. Induction of diabetes significantly increased creatine-kinase release in comparison to healthy rats, and all treatments significantly reduced the release of enzyme toward control levels (P < 0.05). Only the combination therapy (IPostC + vildagliptin) could significantly reduce the infarct size of diabetic hearts as compared to untreated diabetic-IR group (P < 0.01). The levels of autophagy genes LC3 and p62 were significantly higher in diabetic groups than healthy ones. Induction of IR injury in diabetic hearts enhanced mitochondrial fission (drp-1) and reduced mitochondrial fusion (mfn1 and mfn2) genes. IPostC alone had no significant effect on the gene expression and vildagliptin alone could only affect LC3-II and mfn2 expressions. Nevertheless, administration of combination therapy significantly reduced the expression of both autophagy genes and increased both LC3-II/I and mfn2/1 ratios as compared with diabetic-IR hearts (P < 0.01-0.05). Application of this combination therapy could overcome the diabetes-induced failure of cardioprotection by individual treatments and improve mitochondrial dynamic and autophagy flux.

Effects of abnormal expression of fusion and fission genes on the morphology and function of lung macrophage mitochondria in SiO2-induced silicosis fibrosis in rats in vivo

Silicosis is a serious occupational disease affecting millions of related workers. Many studies showed lung macrophages play an important role in the disease. However, the changes of macrophages are not fully characterized and the mechanisms need further investigations. The objectives of this work were to evaluate the effects of abnormal expression of fusion and fission genes on the morphology and function of lung macrophage mitochondria in SiO2-induced silicosis fibrosis in rats. In this study, the rats were injected with 1 mL of SiO2 suspension (100 mg/mL) into the lungs to establish silicosis models, and killed after 30, 60, and 120 days. The rats which were injected with normal saline (1 mL) into lungs were used as control. The lungs of rats were taken for pathological observation. Lung macrophages were collected to measure the number, activity, level of MDA and SOD, and relative content of fusion (Mfn1, Mfn2) and fission (Fis, DRP) genes. Subsequently, mitochondria were extracted from the macrophages to measure the changes of function, including MDA, SOD, ATP, and ATPase. We found that silica dust inhalation led to the proliferation of collagen fibers in the lung tissue. During this process, the number and activity of macrophages increased, the degree of lipid peroxidation increased, and the expression of mitochondrial fusion and fission genes was abnormal. Moreover, the mitochondrial lipid peroxidation level in macrophages increased, the production of ATP and the activity of ATPase decreased, and the abnormal forms of mitochondria occurred. Our results indicated that the morphology and function of mitochondria in macrophages changed during the progress of silicosis, which were related to the abnormal expression of fusion and fission genes.

Simultaneous Measurements of RNA Molecules Transcribed from Mitochondrial Division or Fusion Genes in Single Cells

Simultaneous Measurements of RNA Molecules Transcribed from Mitochondrial Division or Fusion Genes in Single Cells

Simultaneous Single-Cell Measurements Demonstrate a Positive Correlation between RNA Copy Number for Mitochondrial Division and Fusion Genes and Mitochondrial Fragmentation

Simultaneous Single-Cell Measurements Demonstrate a Positive Correlation between RNA Copy Number for Mitochondrial Division and Fusion Genes and Mitochondrial Fragmentation

Oligonol Alleviates Sarcopenia by Regulation of Signaling Pathways Involved in Protein Turnover and Mitochondrial Quality.

Oligonol has been shown to moderate mitochondrial biogenesis, protein synthesis, and protein degradation in diabetic mice in a previous study. It is therefore hypothesized that oligonol alleviated sarcopenia by regulating pathways involved in protein turnover and mitochondrial quality. The 32-week-old senescence-accelerated mouse prone 8 (SAMP8) mice are fed with chow diet containing 200 mg kg-1 oligonol for 8 weeks. Oligonol supplementation increased skeletal muscle mass, cross-sectional areas, and grip strength in SAMP8 mice. Oligonol increased phosphorylation of AKT/mTOR/p70sk6, inhibited nuclear localization of FoxO3a and NFκB, and decreased transcription of MuRF-1 and MAFbx in skeletal muscle of SAMP8 mice. Downregulation of mitochondrial biogenesis genes (PGC-1α and Tfam) and mitochondrial fusion genes (Mfn2 and Opa1), loss of PINK1, overexpression of Atg13, LC3-II, and p62, and abundant accumulation of autophagosomes and lysosomes in skeletal muscle of SAMP8 mice are limited by oligonol. Furthermore, oligonol reduced expression of released cytochrome c and cleaved caspase-9 in skeletal muscle of SAMP8 mice. Regulating pathways involved in protein synthesis and degradation, mitochondrial biogenesis, mitochondrial fusion/fission, autophagy, and mitochondria-dependent apoptosis by oligonol contribute to positive protein turnover and mitochondrial quality, thus increasing muscle mass and strength in SAMP8 mice.

Morphological control of mitochondria as the novel mechanism of Gastrodia elata in attenuating mutant huntingtin-induced protein aggregations

BackgroundAccording to Compendium of Materia Medica, Gastrodia elata (GE) Blume as a top grade and frequently prescribed herbal medicine has been used in treating dizziness, headaches, and epilepsy, indicating a neuroprotective effect. Because GE is capable of suppressing a hyperactive liver and thus calming endogenous wind, and because Huntington's disease (HD) can be classified as a phenomenon of disturbed liver wind, it is suggested that GE might be beneficial in treating HD. However, although current studies support GE for the prevention of diverse neurodegenerations such as HD, its detailed mechanisms remain elusive. PurposeTo investigate the molecular mechanism of GE in preventing HD by focusing on mitochondrial morphology, which is highly associated with HD etiology and thus proposed as a therapeutic target of neurodegenerations. Study design/methodsThe overexpression of the mutant huntingtin (mHTT) gene in rat pheochromocytoma (PC12) cells was used as an in vitro cell model of HD. A filter retardation assay was applied to measure protein aggregations during HTT expression. Cotransfection with mitochondrial fusion and fission genes was used to test their relationships with HTT aggregates by monitoring with a confocal laser scanning microscope and filter retardation assay. Western blot analysis was used to estimate protein expression under different drug treatments or cotransfections with other related genes. ResultsThe overexpression of mutant but not normal HTT genes significantly resulted in protein aggregations in PC12 cells. GE dose-dependently attenuated mHTT-induced protein aggregations and free radical formations. GE significantly reversed mHTT-induced mitochondrial fragmentation and dysregulation of mitochondrial fusion and fission molecules. The overexpression of mitochondrial fusion genes attenuated mHTT-induced protein aggregations. Further, Mdivi-1, a DRP1 fission molecule inhibitor, significantly reversed mHTT-induced protein aggregations and mitochondrial fragmentation. ConclusionGE attenuated mHTT aggregations through the control of mitochondrial fusion and the fission pathway.

Dual roles of mitochondrial fusion gene FZO1 in yeast age asymmetry and in longevity mediated by a novel ATG32-dependent retrograde response.

The replicative lifespan of the yeast Saccharomyces cerevisiae models the aging of stem cells. Age asymmetry between the mother and daughter cells is established during each cell division, such that the daughter retains the capacity for self-renewal while this ability is diminished in the mother. The segregation of fully-functional mitochondria to daughter cells is one mechanism that underlies this age asymmetry. In this study, we have examined the role of mitochondrial dynamics in this phenomenon. Mitochondrial dynamics involve the processes of fission and fusion. Out of the three fusion and three fission genes tested, we have found that only FZO1 is required for the segregation of fully-functional mitochondria to daughter cells and in the maintenance of age asymmetry as manifested in the potential of daughters for a full replicative lifespan despite its deterioration in their mothers. The quality of mitochondria is determined by their turnover, and we have also discovered that deletion of FZO1 reduces mitophagy. Mitochondrial dysfunction elicits a compensatory retrograde response that extends replicative lifespan. Typically, the dysfunction that triggers this response encompasses energy production. The disruption of mitochondrial dynamics by deletion of FZO1 also activates the retrograde response to extend replicative lifespan. We call this novel pathway the mitochondrial dynamics-associated retrograde response (MDARR) because it is distinct in the signal proximal to the mitochondrion that initiates it. Furthermore, the MDARR engages the mitophagy receptor Atg32 on the mitochondrial surface, and we propose that this is due to the accumulation of Atg32-Atg11-Dnm1 complexes on the mitochondrion in the absence of Fzo1 activity. MDARR can be masked by the operation of the 'classic' retrograde response.

Effects of hypothermia on learning and memory ability and expression of fusion gene and fission gene mRNA of mitochondria in hippocampus of rats

Objective To study the effects of hypothermia on learning and memory ability and mRNA expression of fusion gene and fission gene of mitochondria in hippocampus of rats. Methods 32 Wistar rats were randomly divided into 4 groups according to low-temperature exposure time in the test: high-exposure group(low-temperature exposure for 24 h/d), middle-exposure group(low-temperature exposure for 12 h/d), low-exposure group(low-temperature exposure for 6 h/d) and control group.The temperature of low-temperature exposure was 0-5 ℃.The total test time was 45 d. Morris water maze test was performed on each group from the fifth day before the end of the low-temperature test to the first day after the low-temperature test.After the water maze test, the mRNA expressions of mitochondrial fusion genes(Mfn1, Mfn2) and fission genes(Fis1, Drp1) in hippocampus were detected by RT-qPCR. Results Compared with the control group, the escaping latency of the high-exposure group and the middle-exposure group at the first day and the fifth day of water maze test were significantly longer than those in the control group, and the difference was statistically significant(P<0.05, P<0.01). The escaping latency of the sixth day and the number of platform crossings at the beginning of the water maze test were significantly different from those in the control group(P<0.05, P<0.01). Compared with the control group, the escaping latency of the high-exposure group and the middle-exposure group was significantly prolonged on the sixth day, and the number of the platform crossings decreased significantly.The difference was statistically significant(P<0.05, P<0.01). The high, middle and low-exposure group of mitochondrial fusion and fission genes mRNA expressions were as follows respectively: Mfn1: 4.05±0.21, 1.51±0.23, 1.17±0.83; Mfn2: 5.38±0.74, 0.84±0.53, 0.47±0.33; Fis1: 1.65±0.58, 0.49±0.42, 0.40±0.32; Drp1: 4.11±0.37, 0.99±0.82, 0.55±0.29.Compared with the control group, the mRNA expression of the fusion and the fission genes in the high-exposure group increased significantly(P<0.01). Conclusion The abnormalities of mitochondrial fusion and fission gen mRNA expression in the hippocampus may be one of the mechanisms of the decline of learning and memory functions caused by low temperature exposure. Key words: Low temperature; Learning and memory; Fusion gene; Fission gene; Mitochondrion; Hippocampus; Rat

Relationship between changes in mitochondrial function and hippocampal neuronal apoptosis after recurrent convulsion during developmental stage.

The aim of the present study was to establish a recurrent convulsion model during the developmental stage using inhalation of flurothyl, and to observe the relationship between the changes in mitochondrial function in hippocampal neurons and hippocampal neuronal apoptosis after recurrent convulsion. A total of 36 Sprague-Dawley male rats were selected and randomly divided into the control (NS) group and recurrent-seizure (RS) group for 0, 1.5, 3, 12 and 24 h. After the last seizure the rats were subdivided with 6 animals in each group. Rats in the seizure group inhaled flurothyl repeatedly to induce status convulsivus, 30 min once daily, for 7 consecutive days, while the same operation was conducted in the control group without inhalation of flurothyl. At each time-point after the last seizure, blood was taken from the heart, followed by decapitation and immediate removal of the brain. Half of the brain tissue was immediately fixed in 10% paraformaldehyde to prepare paraffin-embedded tissues for hematoxylin and eosin (H&E) histological staining. Hippocampus was taken from the other half of the brain and stored at −80°C. Changes in mitochondrial membrane potential (ΔΨm) in hippocampal neurons were detected by flow cytometer. Dynamic changes of mitochondrial fusion and division-related genes, mitochondrial fusion protein 2 (Mfn2) and dynamin-related protein 1 (Drp1), in the hippocampus after recurrent convulsion were observed using reverse transcription-polymerase chain reaction (RT-PCR)and western blot analysis. The expression of caspase-3 and cytochrome c (Cyt c) was determined by RT-PCR and western blot analysis. After successful establishment of the recurrent convulsion model in rats during developmental stage using flurothyl, H&E staining results exhibited that in the CA1 region of hippocampus in the NS group, karyopyknosis occurred in nucleus that was stained to be brown and yellow, and the expression peak of apoptotic cells mainly existed at 24 h after the last convulsion. RT-PCR and western analysis revealed that apoptosis-related gene caspase-3 expression in the RS group was elevated at 1.5 h after the last convulsion, and lasted 24 h after convulsion. Detection results of mitochondrial ΔΨm revealed a significant reduction 1.5, 3 and 12 h after convulsion in hippocampal neurons of experimental rats, which reached the trough at 12 h, and rapidly increased after 24 h. The expression of Mfn2 mRNA in the RS group was significantly lower than that in the control group, while the expression of Drp1 mRNA in RS group was distinctly higher than that in the control group. RT-PCR and western blot analysis revealed that, mitochondrial apoptosis-related gene Cyt c expression was increased at 3 h after the last convulsion, and lasted 24 h after convulsion. Correlation analysis showed that the changes in mitochondrial function were closely related to neuronal apoptosis. The results of the study show that apoptosis exists in the hippocampus of rats after recurrent convulsion, which is closely related to the changes in mitochondrial function.