Inhibition of Drp1-dependent mitochondrial fission by natural compounds as a therapeutic strategy for organ injuries.

Mitochondria are morphologically dynamic organelles frequently undergoing fission and fusion processes that regulate mitochondrial integrity and bioenergetics. These processes are considered critical for cell survival. The mitochondrial fission process regulates mitochondrial biogenesis and mitophagy. It is associated with apoptosis, while mitochondrial fusion controls the accurate distribution of mitochondrial DNA and metabolic substances across the mitochondria. Excessive mitochondrial fission results in mitochondrial structural changes, dysfunction, and cell damage. Accumulating evidence demonstrates that mitochondrial dynamics affect neurodegenerative and cardiovascular diseases along with several other diseases. Biological molecules regulating the process of mitochondrial fission are potential targets for developing therapeutic agents. Many natural products target the dynamin-related protein 1 (Drp1)-dependent mitochondrial fission pathway, and their inhibitory effects ameliorate mitochondrial fragmentation. In this article, we reviewed the research literature that describes Drp1-dependent inhibition as a mechanism for the protective effects of natural compounds.

Nodakenin attenuates cartilage degradation and inflammatory responses in a mice model of knee osteoarthritis by regulating mitochondrial Drp1/ROS/NLRP3 axis.

Osteoarthritis (OA) is a common degenerative disease with few treatments. In traditional Chinese medicine (TCM), Radix Angelicae biseratae (RAB) is commonly used to treat OA. Nodakenin (Nod) is one main coumarin active component in RAB and exhibits anti-inflammatory, anti-oxidative, and anti-apoptotic effects. Reactive oxygen species (ROS) produced by mitochondria play a vital role in the pathogenesis of OA. We hypothesized that Nod might ameliorate cartilage degradation and inflammatory responses by regulating the mitochondrial Drp1/ROS/NLRP3 axis. With this, the effects of Nod on a mouse model of knee OA and activated primary chondrocytes were assessed. The results showed that Nod intervention improved bone volume, lowered trabecular separation, and increased trabecular number in the subchondral bone. Nod decreased the Osteoarthritis Research Society International (OARSI) scores and increased collagen II-positive areas in the articular cartilage of the tibial plateau. Compared with OA mice, Nod-treated animals exhibited lower levels of inflammatory factors in the serum and synovitis of the knee joint. In vitro results indicated that Nod suppressed dynamin-related protein 1 (Drp1) phosphorylation and massive ROS production by Drp1-dependent mitochondrial fission in lipopolysaccharide-stimulated chondrocytes. Moreover, Nod inhibited the mRNA levels of inflammatory cytokines (COX 2, IL-1ß, and TNF-α), nod-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome, and matrix metalloproteinase 13 expression in activated chondrocytes. In conclusion, Nod attenuates cartilage degradation and inflammatory responses in mice with OA by regulating the mitochondrial Drp1/ROS/NLRP3 axis, suggesting its potential for OA therapy.

Mangiferin, a natural glucoxilxanthone, inhibits mitochondrial dynamin-related protein 1 and relieves aberrant mitophagic proteins in mice model of Parkinson's disease.

BACKGROUND: Parkinson's disease (PD) is the second most common neurodegenerative disease featured to mitochondrial dysfunction in neuronal cells. Dynamin-related protein 1 (Drp1) is an important regulator of mitochondrial fission and subsequent mitophagy. Mangiferin (MGF) is a glucosyl xanthone mainly derived from Mangifera indica L., possessing multifaceted properties, e.g., antioxidant, anti-inflammatory, and enhancement of cognitive ability. Besides, it can cross the blood-brain barrier, thereby exerting a neuroprotective effect. However, so far, MGF's effect in balancing mitochondrial homeostasis via regulation of Drp1 level and mitophagic pathway in PD remains rarely reported. PURPOSE: We aimed to investigate the neuroprotective effect of MGF against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD and examine the possible mechanisms. METHODS: We utilized C57BL/6 mice exposed to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP); Behavioral parameters, containing the open field test, balance beam, pole test, and rotarod test, assessed the locomotor activity; immunohistochemistry assessed the number of TH-positive neurons; transmission electron microscopy detected ultrastructural mitochondrial morphology in the dopaminergic neuron; complex I enzymatic activity microplate assay kit measured the mitochondrial complex I activity; ATP determination kit measured ATP levels in mitochondria isolated from cells or striatal tissues; western blot measured the levels of Drp1 and mitophagic proteins. RESULTS: We observed that MGF could mitigate motor deficiency and improve the expression of tyrosine hydroxylase in the substantia nigra of MPTP-induced PD mice. Furthermore, MGF not only ameliorated mitochondrial ultrastructure, but also improved mitochondrial ATP content. Within mitochondria, MGF could reduce Drp1 expression and reverse the expressions of mitophagic proteins, including PINK1, Parkin, NIX, BNIP3, FUNDC1, and p62. CONCLUSION: Present study indicates that MGF benefits mitochondrial networks by recovering mitochondrial ultrastructure and ATP contents, reducing mitochondrial Drp1, and modulating mitophagic proteins in the MPTP-induced PD mice model, which revealed a novel acting mechanism of MGF in PD's treatment.

Recent Advances in Molecular Pathways and Therapeutic Implications Targeting Mitochondrial Dysfunction for Alzheimer's Disease.

Alzheimer's disease (AD) is a neurodegenerative disorder which leads to mental deterioration due to aberrant accretion of misfolded proteins in the brain. According to mitochondrial cascade hypothesis, mitochondrial dysfunction is majorly involved in the pathogenesis of AD. Many drugs targeting mitochondria to treat and prevent AD are in different phases of clinical trials for the evaluation of safety and efficacy as mitochondria are involved in various cellular and neuronal functions. Mitochondrial dynamics is regulated by fission and fusion processes mediated by dynamin-related protein (Drp1). Inner membrane fusion takes place by OPA1 and outer membrane fusion is facilitated by mitofusin1 and mitofusin2 (Mfn1/2). Excessive calcium release also impairs mitochondrial functions; to overcome this, calcium channel blockers like nilvadipine are used. Another process acting as a regulator of mitochondrial function is mitophagy which is involved in the removal of damaged and non-functional mitochondria however this process is also altered in AD due to mutations in Presenilin1 (PS1) and Amyloid Precursor Protein (APP) gene. Mitochondrial dynamics is altered in AD which led to the discovery of various fission protein (like Drp1) inhibitors and drugs that promote fusion. Modulations in AMPK, SIRT1 and Akt pathways can also come out to be better therapeutic strategies as these pathways regulate functions of mitochondria. Oxidative phosphorylation is major generator of Reactive Oxygen Species (ROS) leading to mitochondrial damage; therefore reduction in production of ROS by using antioxidants like MitoQ, Curcumin and Vitamin Eis quiteeffective.

TMEM16F and dynamins control expansive plasma membrane reservoirs.

Cells can expand their plasma membrane laterally by unfolding membrane undulations and by exocytosis. Here, we describe a third mechanism involving invaginations held shut by the membrane adapter, dynamin. Compartments open when Ca activates the lipid scramblase, TMEM16F, anionic phospholipids escape from the cytoplasmic monolayer in exchange for neutral lipids, and dynamins relax. Deletion of TMEM16F or dynamins blocks expansion, with loss of dynamin expression generating a maximally expanded basal plasma membrane state. Re-expression of dynamin2 or its GTPase-inactivated mutant, but not a lipid binding mutant, regenerates reserve compartments and rescues expansion. Dynamin2-GFP fusion proteins form punctae that rapidly dissipate from these compartments during TMEM16F activation. Newly exposed compartments extend deeply into the cytoplasm, lack numerous organellar markers, and remain closure-competent for many seconds. Without Ca, compartments open slowly when dynamins are sequestered by cytoplasmic dynamin antibodies or when scrambling is mimicked by neutralizing anionic phospholipids and supplementing neutral lipids. Activation of Ca-permeable mechanosensitive channels via cell swelling or channel agonists opens the compartments in parallel with phospholipid scrambling. Thus, dynamins and TMEM16F control large plasma membrane reserves that open in response to lateral membrane stress and Ca influx.

NIK promotes metabolic adaptation of glioblastoma cells to bioenergetic stress.

Cancers, including glioblastoma multiforme (GBM), undergo coordinated reprogramming of metabolic pathways that control glycolysis and oxidative phosphorylation (OXPHOS) to promote tumor growth in diverse tumor microenvironments. Adaptation to limited nutrient availability in the microenvironment is associated with remodeling of mitochondrial morphology and bioenergetic capacity. We recently demonstrated that NF-κB-inducing kinase (NIK) regulates mitochondrial morphology to promote GBM cell invasion. Here, we show that NIK is recruited to the outer membrane of dividing mitochondria with the master fission regulator, Dynamin-related protein1 (DRP1). Moreover, glucose deprivation-mediated metabolic shift to OXPHOS increases fission and mitochondrial localization of both NIK and DRP1. NIK deficiency results in decreased mitochondrial respiration, ATP production, and spare respiratory capacity (SRC), a critical measure of mitochondrial fitness. Although IκB kinase α and ß (IKKα/ß) and NIK are required for OXPHOS in high glucose media, only NIK is required to increase SRC under glucose deprivation. Consistent with an IKK-independent role for NIK in regulating metabolism, we show that NIK phosphorylates DRP1-S616 in vitro and in vivo. Notably, a constitutively active DRP1-S616E mutant rescues oxidative metabolism, invasiveness, and tumorigenic potential in NIK-/- cells without inducing IKK. Thus, we establish that NIK is critical for bioenergetic stress responses to promote GBM cell pathogenesis independently of IKK. Our data suggest that targeting NIK may be used to exploit metabolic vulnerabilities and improve therapeutic strategies for GBM.

Anti-inflammatory and neuroprotective effects of natural cordycepin in rotenone-induced PD models through inhibiting Drp1-mediated mitochondrial fission.

Accumulating evidences suggest that inflammation-mediated neurons dysfunction participates in the initial and development of Parkinson's disease (PD), whereas mitochondria have been recently recognized as crucial regulators in NLRP3 inflammasome activation. Cordycepin, a major component of cordyceps militaris, has been shown to possess neuroprotective and anti-inflammatory activity. However, the effects of cordycepin in rotenone-induced PD models and the possible mechanisms are still not fully understood. Here, we observed that motor dysfunction and dopaminergic neurons loss induced by rotenone exposure were ameliorated by cordycepin. Cordycepin also reversed Drp1-mediated aberrant mitochondrial fragmentation through increasing AMPK phosphorylation and maintained normal mitochondrial morphology. Additionally, cordycepin effectively increased adenosine 5'-triphosphate (ATP) content, mitochondrial membrane potential (MMP), and reduced mitochondrial ROS levels, as well as inhibited complex 1 activity. More importantly, cordycepin administration inhibited the expression of NLRP3 inflammasome components and the release of pro-inflammatory cytokine in rotenone-induced rats and cultured neuronal PC12 cells. Moreover, we demonstrated that the activation of NLRP3 inflammasome within neurons could be suppressed by the mitochondrial division inhibitor (Mdivi-1). Collectively, the present study provides evidence that cordycepin exerts neuroprotective effects partially through preventing neural NLRP3 inflammasome activation induced by Drp1-dependent mitochondrial fragmentation in rotenone-injected PD models.

Polyphyllin VII induces mitochondrial apoptosis by regulating the PP2A/AKT/DRP1 signaling axis in human ovarian cancer.

Ovarian cancer is a gynecological malignancy with high mortality. Adjuvant therapy such as chemoradiotherapy inevitably leads to side effects and drug resistance. In recent years, traditional Chinese medicine has been widely studied for its safety, effectiveness, and unique pharmacological effects. Polyphyllin VII is an important component of Rhizoma paridis saponins, and has cytotoxic effects on many types of cancer cells. The aim of the present study was to evaluate the anti­tumor activity of polyphyllin VII in human ovarian cancer cells. Recent studies found that polyphyllin VII induces mitochondrial pathway apoptosis by increasing mitochondrial division, but the specific mechanism was unclear. The results of this study revealed that polyphyllin VII could effectively induce mitochondrial dysfunction, including increased mitochondrial division and reactive oxygen species (ROS) production. Notably, the mitochondrial location of dynamin­related protein 1 (DRP1) plays an important role in its function. In addition, polyphyllin VII enhanced the mitochondrial localization of DRP1 which is mediated by increased protein phosphatase 2A (PP2A) activity, and decreased AKT activity. A specific PP2A inhibitor, LB100, attenuated mitochondrial division and apoptosis in cells caused by polyphyllin VII, confirming the function of the PP2A/AKT pathway in polyphyllin VII treatment. Additionally, xenotransplantation experiments have also confirmed the anti­tumor effect of polyphyllin VII in vivo. Therefore, interference of the mitochondrial translocation of DRP1 through PP2A/AKT pathway may be an attractive and effective therapeutic approach by polyphyllin VII in ovarian cancer. This may provide new strategies for polyphyllin VII in the clinical treatment of ovarian cancer.

Inhibition of Drp1 SUMOylation by ALR protects the liver from ischemia-reperfusion injury.

Hepatic ischemic reperfusion injury (IRI) is a common complication of liver surgery. Although an imbalance between mitochondrial fission and fusion has been identified as the cause of IRI, the detailed mechanism remains unclear. Augmenter of liver regeneration (ALR) was reported to prevent mitochondrial fission by inhibiting dynamin-related protein 1 (Drp1) phosphorylation, contributing partially to its liver protection. Apart from phosphorylation, Drp1 activity is also regulated by small ubiquitin-like modification (SUMOylation), which accelerates mitochondrial fission. This study aimed to investigate whether ALR-mediated protection from hepatic IRI might be associated with an effect on Drp1 SUMOylation. Liver tissues were harvested from both humans and from heterozygous ALR knockout mice, which underwent IRI. The SUMOylation and phosphorylation of Drp1 and their modulation by ALR were investigated. Hepatic Drp1 SUMOylation was significantly increased in human transplanted livers and IRI-livers of mice. ALR-transfection significantly decreased Drp1 SUMOylation, attenuated the IRI-induced mitochondrial fission and preserved mitochondrial stability and function. This study showed that the binding of transcription factor Yin Yang-1 (YY1) to its downstream target gene UBA2, a subunit of SUMO-E1 enzyme heterodimer, was critical to control Drp1 SUMOylation. By interacting with YY1, ALR inhibits its nuclear import and dramatically decreases the transcriptional level of UBA2. Consequently, mitochondrial fission was significantly reduced, and mitochondrial function was maintained. This study showed that the regulation of Drp1 SUMOylation by ALR protects mitochondria from fission, rescuing hepatocytes from IRI-induced apoptosis. These new findings provide a potential target for clinical intervention to reduce the effects of IRI during hepatic surgery.

Pistacia integerrima alleviated Bisphenol A induced toxicity through Ubc13/p53 signalling.

Exposure to environmental toxicants such as Bisphenol A (BPA) has raised serious health issues globally particularly in developing countries. It is ubiquitously used in the manufacturing of canned food and feeding bottles. BPA generated reactive oxygen species can lead to several diseases including cardiotoxicity. However, the endpoints stimulated in BPA cardiotoxicity yet need to be investigated. The current study was aimed to investigate the underlying molecular pathways which may contribute in revealing the protective effects of Pistacia integerrima against BPA induced oxidative stress. The dose of 100 µg/kg BW of BPA, 200 mg/kg BW P. integerrima, and 4 mg/kg BW melatonin was administered to Sprague Dawley rats. Present results of western blotting and qRT-PCR showed the increased expression of p53, PUMA and Drp1, while downregulation of Ubc13 in heart tissues of BPA treated group whereas the levels were reversed upon treatment with P. integerrima. The role of BPA in heart tissue apoptosis was further confirmed by the increased level of P-p53, cytochrome C and disrupted cellular architecture whereas the P. integerrima has shown its ameliorative potential by mitigating the adverse effects of BPA. Moreover, the oxidant, antioxidant, lipid, and liver markers profile has also revealed the therapeutic potential of P. integerrima by maintaining the levels in the normal range. However, melatonin has also manifested the normalized expression of apoptotic markers, biochemical markers, and tissue architecture. Conclusively, the data suggest that P. integerrima may be a potential candidate for the treatment of BPA induced toxicity by neutralizing the oxidative stress through Ubc13/p53 pathway.

Cardioprotection by isosteviol derivate JC105: A unique drug property to activate ERK1/2 only when cells are exposed to hypoxia-reoxygenation.

In the present study, we have investigated potential cardioprotective properties of Isosteviol analogue we recently synthesized and named JC105. Treatment of heart embryonic H9c2 cells with JC105 (10 µM) significantly increased survival of cells exposed to hypoxia-reoxygenation. JC105 (10 µM) activated ERK1/2, DRP1 and increased levels of cardioprotective SUR2A in hypoxia-reoxygenation, but did not have any effects on ERK1/2, DRP1 and/or SUR2A in normoxia. U0126 (10 µM) inhibited JC105-mediated phosphorylation of ERK1/2 and DRP1 without affecting AKT or AMPK, which were also not regulated by JC105. Seahorse bioenergetic analysis demonstrated that JC105 (10 µM) did not affect mitochondria at rest, but it counteracted all mitochondrial effects of hypoxia-reoxygenation. Cytoprotection afforded by JC105 was inhibited by U0126 (10 µM). Taken all together, these demonstrate that (a) JC105 protects H9c2 cells against hypoxia-reoxygenation and that (b) this effect is mediated via ERK1/2. The unique property of JC105 is that selectively activates ERK1/2 in cells exposed to stress, but not in cells under non-stress conditions.

Seneciphylline, a main pyrrolizidine alkaloid in Gynura japonica, induces hepatotoxicity in mice and primary hepatocytes via activating mitochondria-mediated apoptosis.

Herbal drug-induced liver injury has been reported worldwide and gained global attention. Thousands of hepatic sinusoidal obstruction syndrome (HSOS) cases have been reported after consumption of herbal medicines and preparations containing pyrrolizidine alkaloids (PAs), which are natural phytotoxins globally distributed. And herbal medicines, such as Gynura japonica, are the current leading cause of PA-induced HSOS. The present study aimed to reveal the mechanism underlying the hepatotoxicity of seneciphylline (Seph), a main PA in G. japonica. Results showed that Seph induced severe liver injury through apoptosis in mice (70 mg/kg Seph, orally) and primary mouse and human hepatocytes (5-50 µM Seph). Further research uncovered that Seph induced apoptosis by disrupting mitochondrial homeostasis, inducing mitochondrial depolarization, mitochondrial membrane potential (MMP) loss, and cytochrome c (Cyt c) release and activating c-Jun N-terminal kinase (JNK). The Seph-induced apoptosis in hepatocytes could be alleviated by Mdivi-1 (50 µM, a dynamin-related protein 1 inhibitor), as well as SP600125 (25 µM, a specific JNK inhibitor) and ZVAD-fmk (50 µM, a general caspase inhibitor). Moreover, the Seph-induced MMP loss in hepatocytes was also rescued by Mdivi-1. In conclusion, Seph induced liver toxicity via activating mitochondrial-mediated apoptosis in mice and primary hepatocytes. Our results provide further information on Seph detoxification and herbal medicines containing Seph such as G. japonica.

Perillyl Alcohol Mitigates Behavioural Changes and Limits Cell Death and Mitochondrial Changes in Unilateral 6-OHDA Lesion Model of Parkinson's Disease Through Alleviation of Oxidative Stress.

In this study, we aim to assess the phytomedicinal potential of perillyl alcohol (PA), a dietary monoterpenoid, in a unilateral 6-hydroxydopamine (6-OHDA) lesion rat model of Parkinson's disease (PD). We observed that PA supplementation alleviated behavioural abnormalities such as loss of coordination, reduced rearing and motor asymmetry in lesioned animals. We also observed that PA-treated animals exhibited reduced oxidative stress, DNA fragmentation and caspase 3 activity indicating alleviation of apoptotic cell death. We found reduced mRNA levels of pro-apoptotic regulator BAX and pro-inflammatory mediators IL18 and TNFα in PA-treated animals. Further, PA treatment successfully increased mRNA and protein levels of Bcl2, mitochondrial biogenesis regulator PGC1α and tyrosine hydroxylase (TH) in lesioned animals. We observed that PA treatment blocked BAX and Drp1 translocation to mitochondria, an event often associated with the inception of apoptosis. Further, 6-OHDA exposure reduced expression of electron transport chain complexes I and IV, thereby disturbing energy metabolism. Conversely, expression levels of both complexes were upregulated with PA treatment in lesioned rats. Finally, we found that protein levels of Nrf2, the transcription factor responsible for antioxidant gene expression, were markedly reduced in cytosolic and nuclear fraction on 6-OHDA exposure, and PA increased expression of Nrf2 in both fractions. We believe that our data hints towards PA having the ability to provide cytoprotection in a hemiparkinsonian rat model through alleviation of motor deficits, oxidative stress, mitochondrial dysfunction and apoptosis.

Prognostic impact of Dynamin related protein 1 (Drp1) in epithelial ovarian cancer.

BACKGROUND: The mitochondrial fission protein, Dynamin related protein 1 (Drp1), and its upstream protein calcium/calmodulin-dependent protein kinase I (CaMKI) play a critical role in chemoresistance in ovarian cancer (OVCA). Thus, we examined the expression of Drp1, CaMKI and their phosphorylated forms and their prognostic impact in epithelial OVCA patients. METHODS: Expression analysis was performed by immunohistochemistry (IHC) of paraffin-embedded tumor samples from 49 patients with epithelial OVCA. Staining intensity and the percentage of positively stained tumor cells were used to calculate an immunoreactive score (IRS) of 0-12. The expression scores calculated were correlated with clinicopathological parameters and patient survival. RESULTS: High immunoreactivity of phospho-Drp1Ser637 was significantly correlated with high-grade serous carcinoma (HGSC) (p = 0.034), residual postoperative tumor of > 1 cm (p = 0.006), and non-responders to adjuvant chemotherapy (p = 0.007), whereas high expression of CaMKI was significantly correlated with stage III/IV [International Federation of Gynecologists and Obstetricians (FIGO)] (p = 0.011) and platinum-resistant recurrence (p = 0.030). ROC curve analysis showed that Drp1, phospho-Drp1Ser637 and CaMKI could significantly detect tumor progression with 0.710, 0.779, and 0.686 of area under the curve (AUC), respectively. The Kaplan-Meier survival curve showed that patients with high Drp1, phospho-Drp1Ser637 and CaMKI levels had significantly poorer progression free survival (PFS) (p = 0.003, p < 0.001 and p = 0.017, respectively). Using multivariate analyses, phospho-Drp1Ser637 was significantly associated with PFS [p = 0.043, hazard ratio (HR) 3.151, 95% confidence interval (CI) 1.039-9.561]. CONCLUSIONS: Drp1 and CaMKI are novel potential candidates for the detection and prognosis of epithelial OVCA and as such further studies should be performed to exploit their therapeutic significance.

Low doses of BPA induced abnormal mitochondrial fission and hypertrophy in human embryonic stem cell-derived cardiomyocytes via the calcineurin-DRP1 signaling pathway: A comparison between XX and XY cardiomyocytes.

Humans are inevitably exposed to bisphenol A (BPA) via multiple exposure ways. Thus, attention should be raised to the possible adverse effects related to low doses of BPA. Epidemiological studies have outlined BPA exposure and the increased risk of cardiovascular diseases (such as cardiac hypertrophy), which has been confirmed to be sex-specific in rodent animals and present in few in vitro studies, although the molecular mechanism is still unclear. However, whether BPA at low doses equivalent to human internal exposure level could induce cardiac hypertrophy via the calcineurin-DRP1 signaling pathway by disrupting calcium homeostasis is unknown. To address this, human embryonic stem cell (H1, XY karyotype and H9, XX karyotype)-derived cardiomyocytes (CM) were purified and applied to study the low-dose effects of BPA on cardiomyocyte hypertrophy. In our study, when H1- and H9-CM were exposed to noncytotoxic BPA (8 ng/ml), markedly elevated hypertrophic-related mRNA expression levels (such as NPPA and NPPB), enhanced cellular area and reduced ATP supplementation, demonstrated the hypertrophic cardiomyocyte phenotype in vitro. The excessive fission produced by BPA was promoted by CnAß-mediated dephosphorylation of DRP1. At the molecular level, the increase in cytosolic Ca2+ levels by low doses of BPA could discriminate between H1- and H9-CM, which may suggest a potential sex-specific hypertrophic risk in cardiomyocytes in terms of abnormal mitochondrial fission and ATP production by impairing CnAß-DRP1 signaling. In CnAß-knockdown cardiomyocytes, these changes were highly presented in XX-karyotyped cells, rather than in XY-karyotyped cells.

Melatonin Affects Mitochondrial Fission/Fusion Dynamics in the Diabetic Retina.

Mitochondrial fission and fusion are dependent on cellular nutritional states, and maintaining this dynamics is critical for the health of cells. Starvation triggers mitochondrial fusion to maintain bioenergetic efficiency, but during nutrient overloads (as with hyperglycemic conditions), fragmenting mitochondria is a way to store nutrients to avoid waste of energy. In addition to ATP production, mitochondria play an important role in buffering intracellular calcium (Ca2+). We found that in cultured 661W cells, a photoreceptor-derived cell line, hyperglycemic conditions triggered an increase of the expression of dynamin-related protein 1 (DRP1), a protein marker of mitochondrial fission, and a decrease of mitofusin 2 (MFN2), a protein for mitochondrial fusion. Further, these hyperglycemic cells also had decreased mitochondrial Ca2+ but increased cytosolic Ca2+. Treating these hyperglycemic cells with melatonin, a multifaceted antioxidant, averted hyperglycemia-altered mitochondrial fission-and-fusion dynamics and mitochondrial Ca2+ levels. To mimic how people most commonly take melatonin supplements, we gave melatonin to streptozotocin- (STZ-) induced type 1 diabetic mice by daily oral gavage and determined the effects of melatonin on diabetic eyes. We found that melatonin was not able to reverse the STZ-induced systemic hyperglycemic condition, but it prevented STZ-induced damage to the neural retina and retinal microvasculature. The beneficial effects of melatonin in the neural retina in part were through alleviating STZ-caused changes in mitochondrial dynamics and Ca2+ buffering.

Atractylenolide III ameliorates cerebral ischemic injury and neuroinflammation associated with inhibiting JAK2/STAT3/Drp1-dependent mitochondrial fission in microglia.

BACKGROUND: Inflammation is a major contributor to stroke pathology, making it a promising strategy for intervention. Microglia, the resident macrophages in the brain, play essential roles in both the generation and resolution of neuroinflammation. In particular, mitochondrial homeostasis is critical for microglial function and its dysregulation is involved in the pathogenesis of ischemic stroke. Atractylenolide III (A III), a sesquiterpene lactone found in Atractylodes macrocephala Koidz, has been shown to have an inhibitory effect on inflammation. However, its effect specifically on neuroinflammation and microglial mitochondrial homeostasis following stroke remains elusive. HYPOTHESIS: We hypothesized that A III protects against brain ischemia through inhibition of neuroinflammation mediated by JAK2/STAT3/Drp1-dependent mitochondrial fission. METHODS: The neuroprotective and anti-neuroinflammatory effects of A III were investigated in vivo in mice with transient occlusion to the middle cerebral artery (MCAO) and in vitro in oxygen glucose deprivation-reoxygenation (OGDR)-stimulated primary microglia from mice. RESULTS: A III and AG490, an inhibitor of JAK2, treatment reduced brain infarct size, restored cerebral blood flow (CBF), ameliorated brain edema and improved neurological deficits in MCAO mice. Furthermore, A III and AG490 inhibited mRNA and protein expressions of proinflammatory (IL-1ß, TNF-α, and IL-6) and anti-inflammatory cytokines in both MCAO mice and OGDR-stimulated primary microglia. The JAK2/STAT3 pathway was effectively suppressed by A III, similar to the effect of AG490 treatment. In addition, A III and AG490 treatments significantly decreased Drp1 phosphorylation, translocation and mitochondrial fission in primary microglia stimulated with OGDR for 24 h. CONCLUSION: Our study demonstrated that A III was able to reduce complications associated with ischemia through inhibiting neuroinflammation, which was mediated in part by JAK2/STAT3-dependent mitochondrial fission in microglia.

ATAD3A oligomerization causes neurodegeneration by coupling mitochondrial fragmentation and bioenergetics defects.

Mitochondrial fragmentation and bioenergetic failure manifest in Huntington's disease (HD), a fatal neurodegenerative disease. The factors that couple mitochondrial fusion/fission with bioenergetics and their impacts on neurodegeneration however remain poorly understood. Our proteomic analysis identifies mitochondrial protein ATAD3A as an interactor of mitochondrial fission GTPase, Drp1, in HD. Here we show that, in HD, ATAD3A dimerization due to deacetylation at K135 residue is required for Drp1-mediated mitochondrial fragmentation. Disturbance of ATAD3A steady state impairs mtDNA maintenance by disrupting TFAM/mtDNA binding. Blocking Drp1/ATAD3A interaction with a peptide, DA1, abolishes ATAD3A oligomerization, suppresses mitochondrial fragmentation and mtDNA lesion, and reduces bioenergetic deficits and cell death in HD mouse- and patient-derived cells. DA1 treatment reduces behavioral and neuropathological phenotypes in HD transgenic mice. Our findings demonstrate that ATAD3A plays a key role in neurodegeneration by linking Drp1-induced mitochondrial fragmentation to defective mtDNA maintenance, suggesting that DA1 might be useful for developing HD therapeutics.

Mitochondrial Dynamin-Related Protein 1 (DRP1) translocation in response to cerebral glucose is impaired in a rat model of early alteration in hypothalamic glucose sensing.

OBJECTIVE: Hypothalamic glucose sensing (HGS) initiates insulin secretion (IS) via a vagal control, participating in energy homeostasis. This requires mitochondrial reactive oxygen species (mROS) signaling, dependent on mitochondrial fission, as shown by invalidation of the hypothalamic DRP1 protein. Here, our objectives were to determine whether a model with a HGS defect induced by a short, high fat-high sucrose (HFHS) diet in rats affected the fission machinery and mROS signaling within the mediobasal hypothalamus (MBH). METHODS: Rats fed a HFHS diet for 3 weeks were compared with animals fed a normal chow. Both in vitro (calcium imaging) and in vivo (vagal nerve activity recordings) experiments to measure the electrical activity of isolated MBH gluco-sensitive neurons in response to increased glucose level were performed. In parallel, insulin secretion to a direct glucose stimulus in isolated islets vs. insulin secretion resulting from brain glucose stimulation was evaluated. Intra-carotid glucose load-induced hypothalamic DRP1 translocation to mitochondria and mROS (H2O2) production were assessed in both groups. Finally, compound C was intracerebroventricularly injected to block the proposed AMPK-inhibited DRP1 translocation in the MBH to reverse the phenotype of HFHS fed animals. RESULTS: Rats fed a HFHS diet displayed a decreased HGS-induced IS. Responses of MBH neurons to glucose exhibited an alteration of their electrical activity, whereas glucose-induced insulin secretion in isolated islets was not affected. These MBH defects correlated with a decreased ROS signaling and glucose-induced translocation of the fission protein DRP1, as the vagal activity was altered. AMPK-induced inhibition of DRP1 translocation increased in this model, but its reversal through the injection of the compound C, an AMPK inhibitor, failed to restore HGS-induced IS. CONCLUSIONS: A hypothalamic alteration of DRP1-induced fission and mROS signaling in response to glucose was observed in HGS-induced IS of rats exposed to a 3 week HFHS diet. Early hypothalamic modifications of the neuronal activity could participate in a primary defect of the control of IS and ultimately, the development of diabetes.