Vagal nerve stimulation improves mitochondrial dynamics via an M3 receptor/CaMKKβ/AMPK pathway in isoproterenol‐induced myocardial ischaemia

Mitochondrial dynamics—fission and fusion—are associated with ischaemic heart disease (IHD). This study explored the protective effect of vagal nerve stimulation (VNS) against isoproterenol (ISO)‐induced myocardial ischaemia in a rat model and tested whether VNS plays a role in preventing disorders of mitochondrial dynamics and function. Isoproterenol not only caused cardiac injury but also increased the expression of mitochondrial fission proteins [dynamin‐related peptide1 (Drp1) and mitochondrial fission protein1 (Fis‐1)) and decreased the expression of fusion proteins (optic atrophy‐1 (OPA1) and mitofusins1/2 (Mfn1/2)], thereby disrupting mitochondrial dynamics and leading to increase in mitochondrial fragments. Interestingly, VNS restored mitochondrial dynamics through regulation of Drp1, Fis‐1, OPA1 and Mfn1/2; enhanced ATP content and mitochondrial membrane potential; reduced mitochondrial permeability transition pore (MPTP) opening; and improved mitochondrial ultrastructure and size. Furthermore, VNS reduced the size of the myocardial infarction and ameliorated cardiomyocyte apoptosis and cardiac dysfunction induced by ISO. Moreover, VNS activated AMP‐activated protein kinase (AMPK), which was accompanied by phosphorylation of Ca²⁺/calmodulin‐dependent protein kinase kinase β (CaMKKβ) during myocardial ischaemia. Treatment with subtype‐3 of muscarinic acetylcholine receptor (M₃R) antagonist 4‐diphenylacetoxy‐N‐methylpiperidine methiodide or AMPK inhibitor Compound C abolished the protective effects of VNS on mitochondrial dynamics and function, suggesting that M₃R/CaMKKβ/AMPK signalling are involved in mediating beneficial effects of VNS. This study demonstrates that VNS modulates mitochondrial dynamics and improves mitochondrial function, possibly through the M₃R/CaMKKβ/AMPK pathway, to attenuate ISO‐induced cardiac damage in rats. Targeting mitochondrial dynamics may provide a novel therapeutic strategy in IHD.     

Mitochondrial fission contributes to mitochondrial dysfunction and insulin resistance in skeletal muscle

Mitochondrial dysfunction in skeletal muscle has been implicated in the development of insulin resistance and type 2 diabetes. Considering the importance of mitochondrial dynamics in mitochondrial and cellular functions, we hypothesized that obesity and excess energy intake shift the balance of mitochondrial dynamics, further contributing to mitochondrial dysfunction and metabolic deterioration in skeletal muscle. First, we revealed that excess palmitate (PA), but not hyperglycemia, hyperinsulinemia, or elevated tumor necrosis factor alpha, induced mitochondrial fragmentation and increased mitochondrion-associated Drp1 and Fis1 in differentiated C2C12 muscle cells. This fragmentation was associated with increased oxidative stress, mitochondrial depolarization, loss of ATP production, and reduced insulin-stimulated glucose uptake. Both genetic and pharmacological inhibition of Drp1 attenuated PA-induced mitochondrial fragmentation, mitochondrial depolarization, and insulin resistance in C2C12 cells. Furthermore, we found smaller and shorter mitochondria and increased mitochondrial fission machinery in the skeletal muscle of mice with genetic obesity and those with diet-induced obesity. Inhibition of mitochondrial fission improved the muscle insulin signaling and systemic insulin sensitivity of obese mice. Our findings indicated that aberrant mitochondrial fission is causally associated with mitochondrial dysfunction and insulin resistance in skeletal muscle. Thus, disruption of mitochondrial dynamics may underlie the pathogenesis of muscle insulin resistance in obesity and type 2 diabetes.     

Hydrogen Sulphide modulating mitochondrial morphology to promote mitophagy in endothelial cells under high‐glucose and high‐palmitate

Endothelial cell dysfunction is one of the main reasons for type II diabetes vascular complications. Hydrogen sulphide (H₂S) has antioxidative effect, but its regulation on mitochondrial dynamics and mitophagy in aortic endothelial cells under hyperglycaemia and hyperlipidaemia is unclear. Rat aortic endothelial cells (RAECs) were treated with 40 mM glucose and 200 μM palmitate to imitate endothelium under hyperglycaemia and hyperlipidaemia, and 100 μM NaHS was used as an exogenous H₂S donor. Firstly, we demonstrated that high glucose and palmitate decreased H₂S production and CSE expression in RAECs. Then, the antioxidative effect of H₂S was proved in RAECs under high glucose and palmitate to reduce mitochondrial ROS level. We also showed that exogenous H₂S inhibited mitochondrial apoptosis in RAECs under high glucose and palmitate. Using Mito Tracker and transmission electron microscopy assay, we revealed that exogenous H₂S decreased mitochondrial fragments and significantly reduced the expression of p‐Drp‐1/Drp‐1 and Fis1 compared to high‐glucose and high‐palmitate group, whereas it increased mitophagy by transmission electron microscopy assay. We demonstrated that exogenous H₂S facilitated Parkin recruited by PINK1 by immunoprecipitation and immunostaining assays and then ubiquitylated mitofusin 2 (Mfn2), which illuminated the mechanism of exogenous H₂S on mitophagy. Parkin siRNA suppressed the expression of Mfn2, Nix and LC3B, which revealed that it eliminated mitophagy. In summary, exogenous H₂S could protect RAECs against apoptosis under high glucose and palmitate by suppressing oxidative stress, decreasing mitochondrial fragments and promoting mitophagy. Based on these results, we proposed a new mechanism of H₂S on protecting endothelium, which might provide a new strategy for type II diabetes vascular complication.     

Rotaviral nonstructural protein 4 triggers dynamin‐related protein 1‐dependent mitochondrial fragmentation during infection

Dynamic equilibrium between mitochondrial fission and mitochondrial fusion serves as an important quality control system within cells ensuring cellular vitality and homeostasis. Viruses often target mitochondrial dynamics as a part of their obligatory cellular reprogramming. The present study was undertaken to assess the status and regulation of mitochondrial dynamics during rotavirus infection. Distinct fragmentation of mitochondrial syncytia was observed during late hours of RV (SA11, Wa, A5‐13) infection. RV nonstructural protein 4 (NSP4) was identified as the viral trigger for disrupted mitochondrial morphology. Severance of mitochondrial interconnections was found to be a dynamin‐related protein 1 (Drp1)‐dependent process resulting synergistically from augmented mitochondrial fission and attenuated mitochondrial fusion. Cyclin‐dependent kinase 1 was subsequently identified as the cellular kinase responsible for fission‐active Ser616 phosphorylation of Drp1. In addition to its positive role in mitochondrial fission, Drp1 also resulted in mitochondrial translocation of E3‐ubiquitin ligase Parkin leading to degradation of mitochondrial fusion protein Mitofusin 1. Interestingly, RV‐NSP4 was found to interact with and be involved in recruiting fission‐active pool of Serine 616 phosphoDrp1 (Ser616 pDrp1) to mitochondria independent of accessory adaptors Mitochondrial fission factor and Fission protein 1 (Fis1). Inhibition of either Drp1 or Ser616 pDrp1 resulted in significant decrease in RV‐NSP4‐induced intrinsic apoptotic pathway. Overall, this study underscores an efficient strategy utilised by RV to couple apoptosis to mitochondrial fission facilitating dissemination of viral progeny.     

Cadmium induced Drp1-dependent mitochondrial fragmentation by disturbing calcium homeostasis in its hepatotoxicity

Mitochondria are critical targets in the hepatotoxicity of cadmium (Cd). Abnormal mitochondrial dynamics have been increasingly implicated in mitochondrial dysfunction in pathophysiological conditions. Therefore, our study aimed to investigate the effects and underlying mechanism of Cd on mitochondrial dynamics during hepatotoxicity. In the L02 liver cell lines, 12 μM cadmium chloride (CdCl₂) exposure induced excessive mitochondrial fragmentation as early as 3 h post-treatment with Cd, which preceded the mitochondrial dysfunction such as reactive oxygen species (ROS) overproduction, mitochondrial membrane potential (ΔΨm) loss and ATP reduction. Concurrent to mitochondrial fragmentation, CdCl₂ treatment increased the protein levels of dynamin-related protein (Drp1) and promoted the recruitment of Drp1 into mitochondria. Strikingly, mitochondrial fragmentation also occurred in the liver tissue of rats exposed to CdCl₂, accompanied by enhanced recruitment of Drp1 into mitochondria. Moreover, in L02 cells, Drp1 silencing could effectively reverse Cd-induced mitochondrial fragmentation and mitochondrial dysfunction. Furthermore, the increased expression and mitochondrial recruitment of Drp1 were tightly related to the disturbance of calcium homeostasis, which could be prevented by both chelating [Ca²⁺]_i and inhibiting [Ca²⁺]_m uptake. Overall, our study indicated that Cd induced Drp1-dependent mitochondrial fragmentation by disturbing calcium homeostasis to promote hepatotoxicity. Manipulation of Drp1 may be the potential avenue for developing novel strategies to protect against cadmium-induced hepatotoxicity.     

Dynamin‐related protein 1‐mediated mitochondrial fission contributes to IR‐783‐induced apoptosis in human breast cancer cells

IR‐783 is a kind of heptamethine cyanine dye that exhibits imaging, cancer targeting and anticancer properties. A previous study reported that its imaging and targeting properties were related to mitochondria. However, the molecular mechanism behind the anticancer activity of IR‐783 has not been well demonstrated. In this study, we showed that IR‐783 inhibits cell viability and induces mitochondrial apoptosis in human breast cancer cells. Exposure of MDA‐MB‐231 cells to IR‐783 resulted in the loss of mitochondrial membrane potential (MMP), adenosine triphosphate (ATP) depletion, mitochondrial permeability transition pore (mPTP) opening and cytochrome c (Cyto C) release. Furthermore, we found that IR‐783 induced dynamin‐related protein 1 (Drp1) translocation from the cytosol to the mitochondria, increased the expression of mitochondrial fission proteins mitochondrial fission factor (MFF) and fission‐1 (Fis1), and decreased the expression of mitochondrial fusion proteins mitofusin1 (Mfn1) and optic atrophy 1 (OPA1). Moreover, knockdown of Drp1 markedly blocked IR‐783‐mediated mitochondrial fission, loss of MMP, ATP depletion, mPTP opening and apoptosis. Our in vivo study confirmed that IR‐783 markedly inhibited tumour growth and induced apoptosis in an MDA‐MB‐231 xenograft model in association with the mitochondrial translocation of Drp1. Taken together, these findings suggest that IR‐783 induces apoptosis in human breast cancer cells by increasing Drp1‐mediated mitochondrial fission. Our study uncovered the molecular mechanism of the anti‐breast cancer effects of IR‐783 and provided novel perspectives for the application of IR‐783 in the treatment of breast cancer.     

RhoA/ROCK1 regulates the mitochondrial dysfunction through Drp1 induced by Porphyromonas gingivalis in endothelial cells

Porphyromonas gingivalis (P. gingivalis) is a pivotal pathogen of periodontitis. Our previous studies have confirmed that mitochondrial dysfunction in the endothelial cells caused by P. gingivalis was dependent on Drp1, which may be the mechanism of P. gingivalis causing endothelial dysfunction. Nevertheless, the signalling pathway induced the mitochondrial dysfunction remains unclear. The purpose of this study was to investigate the role of the RhoA/ROCK1 pathway in regulating mitochondrial dysfunction caused by P. gingivalis. P. gingivalis was used to infect EA.hy926 cells (endothelial cells). The expression and activation of RhoA and ROCK1 were assessed by western blotting and pull-down assay. The morphology of mitochondria was observed by mitochondrial staining and transmission electron microscopy. Mitochondrial function was measured by ATP content, mitochondrial DNA and mitochondrial permeability transition pore openness. The phosphorylation and translocation of Drp1 were evaluated using western blotting and immunofluorescence. The role of the RhoA/ROCK1 pathway in mitochondrial dysfunction was investigated using RhoA and ROCK1 inhibitors. The activation of RhoA/ROCK1 pathway and mitochondrial dysfunction were observed in P. gingivalis-infected endothelial cells. Furthermore, RhoA or ROCK1 inhibitors partly prevented mitochondrial dysfunction caused by P. gingivalis. The increased phosphorylation and mitochondrial translocation of Drp1 induced by P. gingivalis were both blocked by RhoA and ROCK1 inhibitors. In conclusion, we demonstrate that the RhoA/ROCK1 pathway was involved in mitochondrial dysfunction caused by P. gingivalis by regulating the phosphorylation and mitochondrial translocation of Drp1. Our research illuminated a possible new mechanism by which P. gingivalis promotes endothelial dysfunction.     

线粒体动力学改变在神经变性疾病中的地位

线粒体是一种处于高度运动状态的细胞器,频繁地出现分裂和融合,线粒体分裂和融合的动态过程被称为线粒体动力学。对于神经元来说,线粒体的动力学过程具有十分重要的生物学意义。已知线粒体融合介导蛋白的功能缺失性突变可以导致常染色体显性遗传性视神经萎缩和Charcot-Marie-Tooth病等神经变性疾病。近来发现,在迟发性神经变性疾病中,线粒体动力学的改变也具有重要地位。本文将在线粒体动力学的分子调控以及与细胞死亡的关系、在神经变性疾病中的地位等方面综述这一领域的最新进展。     

Hormone‐induced mitochondrial fission is utilized by brown adipocytes as an amplification pathway for energy expenditure

Adrenergic stimulation of brown adipocytes (BA) induces mitochondrial uncoupling, thereby increasing energy expenditure by shifting nutrient oxidation towards thermogenesis. Here we describe that mitochondrial dynamics is a physiological regulator of adrenergically‐induced changes in energy expenditure. The sympathetic neurotransmitter Norepinephrine (NE) induced complete and rapid mitochondrial fragmentation in BA, characterized by Drp1 phosphorylation and Opa1 cleavage. Mechanistically, NE‐mediated Drp1 phosphorylation was dependent on Protein Kinase‐A (PKA) activity, whereas Opa1 cleavage required mitochondrial depolarization mediated by FFAs released as a result of lipolysis. This change in mitochondrial architecture was observed both in primary cultures and brown adipose tissue from cold‐exposed mice. Mitochondrial uncoupling induced by NE in brown adipocytes was reduced by inhibition of mitochondrial fission through transient Drp1 DN overexpression. Furthermore, forced mitochondrial fragmentation in BA through Mfn2 knock down increased the capacity of exogenous FFAs to increase energy expenditure. These results suggest that, in addition to its ability to stimulate lipolysis, NE induces energy expenditure in BA by promoting mitochondrial fragmentation. Together these data reveal that adrenergically‐induced changes to mitochondrial dynamics are required for BA thermogenic activation and for the control of energy expenditure.     

DLP1‐dependent mitochondrial fragmentation and redistribution mediate prion‐associated mitochondrial dysfunction and neuronal death

Mitochondrial malfunction is a universal and critical step in the pathogenesis of many neurodegenerative diseases including prion diseases. Dynamin‐like protein 1 (DLP1) is one of the key regulators of mitochondrial fission. In this study, we investigated the role of DLP1 in mitochondrial fragmentation and dysfunction in neurons using in vitro and in vivo prion disease models. Mitochondria became fragmented and redistributed from axons to soma, correlated with increased mitochondrial DLP1 expression in murine primary neurons (N2a cells) treated with the prion peptide PrP^106–126 in vitro as well as in prion strain‐infected hamster brain in vivo. Suppression of DLP1 expression by DPL1 RNAi inhibited prion‐induced mitochondrial fragmentation and dysfunction (measured by ADP/ATP ratio, mitochondrial membrane potential, and mitochondrial integrity). We also demonstrated that DLP1 RNAi is neuroprotective against prion peptide in N2a cells as shown by improved cell viability and decreased apoptosis markers, caspase 3 induced by PrP^106–126. On the contrary, overexpression of DLP1 exacerbated mitochondrial dysfunction and cell death. Moreover, inhibition of DLP1 expression ameliorated PrP^106–126‐induced neurite loss and synaptic abnormalities (i.e., loss of dendritic spine and PSD‐95, a postsynaptic scaffolding protein as a marker of synaptic plasticity) in primary neurons, suggesting that altered DLP1 expression and mitochondrial fragmentation are upstream events that mediate PrP^106–126‐induced neuron loss and degeneration. Our findings suggest that DLP1‐dependent mitochondrial fragmentation and redistribution plays a pivotal role in PrP^Sc‐associated mitochondria dysfunction and neuron apoptosis. Inhibition of DLP1 may be a novel and effective strategy in the prevention and treatment of prion diseases.     

Inhibition of mitochondrial fission protects podocytes from albumin-induced cell damage in diabetic kidney disease

AimsIdentifying the mechanisms that underlie progression from endothelial damage to podocyte damage, which leads to massive proteinuria, is an urgent issue that must be clarified to improve renal outcome in diabetic kidney disease (DKD). We aimed to examine the role of dynamin-related protein 1 (Drp1)-mediated regulation of mitochondrial fission in podocytes in the pathogenesis of massive proteinuria in DKD.MethodsDiabetes- or albuminuria-associated changes in mitochondrial morphology in podocytes were examined by electron microscopy. The effects of albumin and other diabetes-related stimuli, including high glucose (HG), on mitochondrial morphology were examined in cultured podocytes. The role of Drp1 in podocyte damage was examined using diabetic podocyte-specific Drp1-deficient mice treated with neuraminidase, which removes endothelial glycocalyx.ResultsNeuraminidase-induced removal of glomerular endothelial glycocalyx in nondiabetic mice led to microalbuminuria without podocyte damage, accompanied by reduced Drp1 expression and mitochondrial elongation in podocytes. In contrast, streptozotocin-induced diabetes significantly exacerbated neuraminidase-induced podocyte damage and albuminuria, and was accompanied by increased Drp1 expression and enhanced mitochondrial fission in podocytes. Cell culture experiments showed that albumin stimulation decreased Drp1 expression and elongated mitochondria, although HG inhibited albumin-associated changes in mitochondrial dynamics, resulting in apoptosis. Podocyte-specific Drp1-deficiency in mice prevented diabetes-related exacerbation of podocyte damage and neuraminidase-induced development of albuminuria. Endothelial dysfunction-induced albumin exposure is cytotoxic to podocytes. Inhibition of mitochondrial fission in podocytes is a cytoprotective mechanism against albumin stimulation, which is impaired under diabetic condition. Inhibition of mitochondrial fission in podocytes may represent a new therapeutic strategy for massive proteinuria in DKD.     

Parkinson's disease-associated DJ-1 mutations impair mitochondrial dynamics and cause mitochondrial dysfunction

Mitochondrial dysfunction represents a critical event during the pathogenesis of Parkinson's disease (PD) and expanding evidences demonstrate that an altered balance in mitochondrial fission/fusion is likely an important mechanism leading to mitochondrial and neuronal dysfunction/degeneration. In this study, we investigated whether DJ-1 is involved in the regulation of mitochondrial dynamics and function in neuronal cells. Confocal and electron microscopic analysis demonstrated that M17 human neuroblastoma cells over-expressing wild-type DJ-1 (WT DJ-1 cells) displayed elongated mitochondria while M17 cells over-expressing PD-associated DJ-1 mutants (R98Q, D149A and L166P) (mutant DJ-1 cells) showed significant increase of fragmented mitochondria. Similar mitochondrial fragmentation was also noted in primary hippocampal neurons over-expressing PD-associated mutant forms of DJ-1. Functional analysis revealed that over-expression of PD-associated DJ-1 mutants resulted in mitochondria dysfunction and increased neuronal vulnerability to oxidative stress (H(2) O(2)) or neurotoxin. Further immunoblot studies demonstrated that levels of dynamin-like protein (DLP1), also known as Drp1, a regulator of mitochondrial fission, was significantly decreased in WT DJ-1 cells but increased in mutant DJ-1 cells. Importantly, DLP1 knockdown in these mutant DJ-1 cells rescued the abnormal mitochondria morphology and all associated mitochondria/neuronal dysfunction. Taken together, these studies suggest that DJ-1 is involved in the regulation of mitochondrial dynamics through modulation of DLP1 expression and PD-associated DJ-1 mutations may cause PD by impairing mitochondrial dynamics and function.     

Mff is an essential factor for mitochondrial recruitment of Drp1 during mitochondrial fission in mammalian cells

The cytoplasmic dynamin-related guanosine triphosphatase Drp1 is recruited to mitochondria and mediates mitochondrial fission. Although the mitochondrial outer membrane (MOM) protein Fis1 is thought to be a Drp1 receptor, this has not been confirmed. To analyze the mechanism of Drp1 recruitment, we manipulated the expression of mitochondrial fission and fusion proteins and demonstrated that (a) mitochondrial fission factor (Mff) knockdown released the Drp1 foci from the MOM accompanied by network extension, whereas Mff overexpression stimulated mitochondrial recruitment of Drp1 accompanied by mitochondrial fission; (b) Mff-dependent mitochondrial fission proceeded independent of Fis1; (c) a Mff mutant with the plasma membrane-targeted CAAX motif directed Drp1 to the target membrane; (d) Mff and Drp1 physically interacted in vitro and in vivo; (e) exogenous stimuli-induced mitochondrial fission and apoptosis were compromised by knockdown of Drp1 and Mff but not Fis1; and (f) conditional knockout of Fis1 in colon carcinoma cells revealed that it is dispensable for mitochondrial fission. Thus, Mff functions as an essential factor in mitochondrial recruitment of Drp1.     

Nutrient excess and altered mitochondrial proteome and function contribute to neurodegeneration in diabetes

Diabetic neuropathy is a major complication of diabetes that results in the progressive deterioration of the sensory nervous system. Mitochondrial dysfunction has been proposed to play an important role in the pathogenesis of the neurodegeneration observed in diabetic neuropathy. Our recent work has shown that mitochondrial dysfunction occurs in dorsal root ganglia (DRG) sensory neurons in streptozotocin (STZ) induced diabetic rodents. In neurons, the nutrient excess associated with prolonged diabetes may trigger a switching off of AMP kinase (AMPK) and/or silent information regulator T1 (SIRT1) signaling leading to impaired peroxisome proliferator-activated receptor γ coactivator-1 (PGC-1α) expression/activity and diminished mitochondrial activity. This review briefly summarizes the alterations of mitochondrial function and proteome in sensory neurons of STZ-diabetic rodents. We also discuss the possible involvement of AMPK/SIRT/PGC-1α pathway in other diabetic models and different tissues affected by diabetes.     

6-Hydroxydopamine (6-OHDA) induces Drp1-dependent mitochondrial fragmentation in SH-SY5Y cells

Mitochondrial alterations have been associated with the cytotoxic effect of 6-hydroxydopamine (6-OHDA), a widely used neurotoxin to study Parkinson's disease. Herein we studied the potential effects of 6-OHDA on mitochondrial morphology in SH-SY5Y neuroblastoma cells. By immunofluorescence and time-lapse fluorescence microscopy we demonstrated that 6-OHDA induced profound mitochondrial fragmentation in SH-SY5Y cells, an event that was similar to mitochondrial fission induced by overexpression of Fis1p, a membrane adaptor for the dynamin-related protein 1 (DLP1/Drp1). 6-OHDA failed to induce any changes in peroxisome morphology. Biochemical experiments revealed that 6-OHDA-induced mitochondrial fragmentation is an early event preceding the collapse of the mitochondrial membrane potential and cytochrome c release in SH-SY5Y cells. Silencing of DLP1/Drp1, which is involved in mitochondrial and peroxisomal fission, prevented 6-OHDA-induced fragmentation of mitochondria. Furthermore, in cells silenced for Drp1, 6-OHDA-induced cell death was reduced, indicating that a block in mitochondrial fission protects SH-SY5Y cells against 6-OHDA toxicity. Experiments in mouse embryonic fibroblasts deficient in Bax or p53 revealed that both proteins are not essential for 6-OHDA-induced mitochondrial fragmentation. Our data demonstrate for the first time an involvement of mitochondrial fragmentation and Drp1 function in 6-OHDA-induced apoptosis.     

Mitochondrial oxidative stress causes mitochondrial fragmentation via differential modulation of mitochondrial fission-fusion proteins

Mitochondria are dynamic organelles that undergo continual fusion and fission to maintain their morphology and functions, but the mechanism involved is still not clear. Here, we investigated the effect of mitochondrial oxidative stress triggered by high-fluence low-power laser irradiation (HF-LPLI) on mitochondrial dynamics in human lung adenocarcinoma cells (ASTC-a-1) and African green monkey SV40-transformed kidney fibroblast cells (COS-7). Upon HF-LPLI-triggered oxidative stress, mitochondria displayed a fragmented structure, which was abolished by exposure to dehydroascorbic acid, a reactive oxygen species scavenger, indicating that oxidative stress can induce mitochondrial fragmentation. Further study revealed that HF-LPLI caused mitochondrial fragmentation by inhibiting fusion and enhancing fission. Mitochondrial translocation of the profission protein dynamin-related protein 1 (Drp1) was observed following HF-LPLI, demonstrating apoptosis-related activation of Drp1. Notably, overexpression of Drp1 increased mitochondrial fragmentation and promoted HF-LPLI-induced apoptosis through promoting cytochrome c release and caspase-9 activation, whereas overexpression of mitofusin 2 (Mfn2), a profusion protein, caused the opposite effects. Also, neither Drp1 overexpression nor Mfn2 overexpression affected mitochondrial reactive oxygen species generation, mitochondrial depolarization, or Bax activation. We conclude that mitochondrial oxidative stress mediated through Drp1 and Mfn2 causes an imbalance in mitochondrial fission-fusion, resulting in mitochondrial fragmentation, which contributes to mitochondrial and cell dysfunction.     

Nitric oxide-induced mitochondrial fission is regulated by dynamin-related GTPases in neurons

Mitochondria are present as tubular organelles in neuronal projections. Here, we report that mitochondria undergo profound fission in response to nitric oxide (NO) in cortical neurons of primary cultures. Mitochondrial fission by NO occurs long before neurite injury and neuronal cell death. Furthermore, fission is accompanied by ultrastructural damage of mitochondria, autophagy, ATP decline and generation of free radicals. Fission is occasionally asymmetric and can be reversible. Strikingly, mitochondrial fission is also an early event in ischemic stroke in vivo. Mitofusin 1 (Mfn1) or dominant-negative Dynamin related protein 1 (Drp1(K38A)) inhibits mitochondrial fission induced by NO, rotenone and Amyloid-beta peptide. Conversely, overexpression of Drp1 or Fis1 elicits fission and increases neuronal loss. Importantly, NO-induced neuronal cell death was mitigated by Mfn1 and Drp1(K38A). Thus, persistent mitochondrial fission may play a causal role in NO-mediated neurotoxicity.     

Water-Soluble Coenzyme Q10 Reduces Rotenone-Induced Mitochondrial Fission

Parkinson’s disease is a neurodegenerative disorder characterized by mitochondrial dysfunction and oxidative stress. It is usually accompanied by an imbalance in mitochondrial dynamics and changes in mitochondrial morphology that are associated with impaired function. The objectives of this study were to identify the effects of rotenone, a drug known to mimic the pathophysiology of Parkinson’s disease, on mitochondrial dynamics. Additionally, this study explored the protective effects of water-soluble Coenzyme Q10 (CoQ10) against rotenone-induced cytotoxicity in murine neuronal HT22 cells. Our results demonstrate that rotenone elevates protein expression of mitochondrial fission markers, Drp1 and Fis1, and causes an increase in mitochondrial fragmentation as evidenced through mitochondrial staining and morphological analysis. Water-soluble CoQ10 prevented mitochondrial dynamic imbalance by reducing Drp1 and Fis1 protein expression to pre-rotenone levels, as well as reducing rotenone treatment-associated mitochondrial fragmentation. Hence, water-soluble CoQ10 may have therapeutic potential in treating patients with Parkinson’s disease.