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Background Downregulation of claudin-5 in the heart is associated with the end-stage heart failure. However, the underlying mechanism ofclaudin-5 is unclear. Here we investigated the molecular actions of claudin-5 in perspective of mitochondria in cardiomyocytes to better understand the role of claudin-5 in cardioprotection during ischemia. Methods Myocardial ischemia/reperfusion (I/R; 30 min/24 h) and hypoxia/reoxygenation (H/R; 24 h/4 h) were used in this study. Confocal microscopy and transmission electron microscope (TEM) were used to observe mitochondrial morphology. Results Claudin-5 was detected in murine heart tissue and neonatal rat cardiomyocytes (NRCM). Its protein level was severely decreased after myocardial I/R or H/R. Confocal microscopy showedclaudin-5 presented in the mitochondria of NRCM. H/R-induced claudin-5 downregulation was accompanied by mitochondrial fragmentation. The mitofusin 2 (Mfn2) expressionwas dramatically decreased while the dynamin-related protein (Drp) 1 expression was significantly increased after H/R. The TEM indicatedH/R-induced mitochondrial swelling and fission. Adenoviral claudin-5 overexpression reversed these structural disintegration of mitochondria. The mitochondria-centered intrinsic pathway of apoptosis triggered by H/R and indicated by the cytochrome c and cleaved caspase 3 in the cytoplasm of NRCMs was also reduced by overexpressing claudin-5. Claudin-5 overexpression in mouse heart also significantly decreased cleaved caspase 3 and the infarct size in ischemic heart with improved systolic function. Conclusion We demonstrated for the first time the presence of claudin-5 in the mitochondria in cardiomyocytes and provided the firm evidence for the cardioprotective role of claudin-5 in the preservation of mitochondrial dynamics and cell fate against hypoxia- or ischemia-induced stress.

Doxorubicin (DOX)-induced cardiotoxicity has been one of the major limitations for its clinical use. Although extensive studies have been conducted to decipher the molecular mechanisms underlying DOX cardiotoxicity, no effective preventive or therapeutic measures have yet been identified. Microarray analysis showed that multiple long non-coding RNAs (lncRNAs) are differentially expressed between control- and DOX-treated cardiomyocytes. Functional enrichment analysis indicated that the differentially expressed genes are annotated to cardiac hypertrophic pathways. Among differentially expressed lncRNAs, cardiomyocyte mitochondrial dynamic-related lncRNA 1 (CMDL-1) is the most significantly downregulated lncRNA in cardiomyocytes after DOX exposure. The protein-RNA interaction analysis showed that CMDL-1 may target dynamin-related protein 1 (Drp1). Mechanistic analysis shows that lentiviral overexpression of CMDL-1 prevents DOX-induced mitochondrial fission and apoptosis in cardiomyocytes. However, overexpression of CMDL-1 cannot effectively reduce mitochondrial fission when Drp1 is minimally expressed by small interfering RNA Drp1 (siDrp1). Overexpression of CMDL-1 promotes the association between CMDL-1 and Drp1, as well as with phosphorylated (p-)Drp1, as evidenced by RNA immunoprecipitation analysis. These data indicate the role of CMDL-1 in posttranslational modification of a target protein via regulating its phosphorylation. Collectively, our data indicate that CMDL-1 may play an anti-apoptotic role in DOX cardiotoxicity by regulating Drp1 S637 phosphorylation. Thus, CMDL-1 may serve as a potential therapeutic target in DOX cardiotoxicity., Graphical abstract, Under physiological conditions, CMDL-1 may bind to Drp1 and enhance its phosphorylation at S637, and prevent mitochondrial fission. During DOX exposure, a reduced CMDL-1 expression decreases its binding to Drp1 and prevents Drp1 phosphorylation, thereby activating mitochondrial fission and apoptosis, suggesting that CMDL-1 may serve as a novel therapeutic target.

Aconitine, a highly toxic alkaloid derived from Aconitum L., affects the central nervous system and peripheral nervous system. However, the underlying mechanism of aconitine-induced neurotoxicity remains unclear. This study investigates the effects and mechanism of aconitine on mitochondrial energy metabolism in SH-SY5Y cells. Results demonstrated that aconitine exposure suppressed cell proliferation and led to an increase in reactive oxygen species (ROS) and excessive lactate dehydrogenase (LDH) release. Aconitine (400 μmol/L) induced abnormal mitochondrial energy metabolism that quantified by the significant decrease in ATP production, basal respiration, proton leak, maximal respiration, and succinate dehydrogenase (SDH) activity. Phosphorylation of AMPK was significantly reduced in aconitine-treated SH-SY5Y cells. The AMPK activator AIACR pretreatment effectively promoted ATP production to ameliorate mitochondrial energy metabolism disorder caused by aconitine. Mitochondrial biosynthesis was inhibited after treatment with 400 μmol/L aconitine, which was characterized by mitochondria number, TFAM expression, and mtDNA copy number. Moreover, aconitine prompted the down-regulation of mitochondrial fusion proteins OPA1, Mfn1 and Mfn2, and the up-regulation of mitochondrial fission proteins p-Drp1 and p-Mff. These results suggest that aconitine induces mitochondrial energy metabolism dysfunction in SH-SY5Y cells, which may involve the inhibition of AMPK signaling and abnormal mitochondrial dynamics.

Pathological cardiac hypertrophy begins as an adaptive response to increased workload; however, sustained hemodynamic stress will lead it to maladaptation and eventually cardiac failure. Mitochondria, being the powerhouse of the cells, can regulate cardiac hypertrophy in both adaptive and maladaptive phases; they are dynamic organelles that can adjust their number, size, and shape through a process called mitochondrial dynamics. Recently, several studies indicate that promoting mitochondrial fusion along with preventing mitochondrial fission could improve cardiac function during cardiac hypertrophy and avert its progression toward heart failure. However, some studies also indicate that either hyperfusion or hypo-fission could induce apoptosis and cardiac dysfunction. In this review, we summarize the recent knowledge regarding the effects of mitochondrial dynamics on the development and progression of cardiac hypertrophy with particular emphasis on the regulatory role of mitochondrial dynamics proteins through the genetic, epigenetic, and post-translational mechanisms, followed by discussing the novel therapeutic strategies targeting mitochondrial dynamic pathways., Graphical abstract, This review summarizes the current knowledge regarding the role of mitochondrial dynamics (MD) in cardiac hypertrophy with particular emphasis on the regulatory role of mitochondrial dynamic proteins through the genetic, epigenetic, and post-translational mechanisms, followed by discussing the novel therapeutic strategies targeting MD pathways.

Excessive generation of reactive oxygen species (ROS) have great impacts on the development of periodontitis. Dynamin-related protein 1 (Drp1) mediated mitochondrial fission is the main reason and the result of excessive ROS generation. However, whether Drp1 and crosstalk between ROS and Drp1 contribute to the process of periodontitis remains elusive. We herein investigated the role and functional significance of crosstalk between ROS and Drp1 in periodontitis. Firstly, human periodontal ligament cells (hPDLCs) were treated with hydrogen peroxide (H2O2) and ROS inhibitor N-acetyl-cysteine (NAC) or Drp1 inhibitor mitochondrial division inhibitor 1 (Mdivi-1). Cell viability, apoptosis, osteogenic differentiation, expression of Drp1, and mitochondrial function were investigated. Secondly, mice with periodontitis were treated with NAC or Mdivi-1. Finally, gingival tissues were collected from periodontitis patients and healthy individuals to evaluate ROS and Drp1 levels. H2O2 induced cellular injury and inflammation, excessive ROS production, mitochondrial abnormalities, and increased expression of p-Drp1 and Drp1 in hPDLCs, which could be reversed by NAC and Mdivi-1. Moreover, both NAC and Mdivi-1 ameliorated tissue damage and inflammation, and decreased expression of p-Drp1 and Drp1 in mice with periodontitis. More importantly, patients with periodontitis presented significantly higher levels of ROS-induced oxidative damage and p-Drp1 than that in healthy individuals and correlated with clinical parameters. In summary, ROS-Drp1 crosstalk greatly promotes the development of periodontitis. Pharmacological blockade of this crosstalk might be a novel therapeutic strategy for periodontitis.

Cancer immunotherapy has emerged as a promising option for various malignant tumors therapy. Unfortunately, the existence of an immunosuppressive tumor microenvironment (ITM) and the absence of an effective delivery strategy limit its further application. To reverse the ITM and exploit a favorable delivery system for cancer immunotherapy, twin-like charge-switchable nanoparticles (shMFN1-NPs + DOX-NPs, termed as MIX-NPs) were developed to selectively target tumor-associated macrophages (TAMs) and cancer cells, respectively. The shMFN1-NPs (150 nm) and DOX-NPs (160 nm) both had uniform spherical-shaped structures and showed favorable tumor tissue accumulation. Based on the pH-responsive core-shell separation, the nanoparticles obtained an excellent balance between the circulation time and cellular uptake. Mitochondrial dynamics are involved in macrophage polarization by regulating a novel signaling network, involving the modulation from fusion (M2-TAMs) to mitochondrial fission (M1-TAMs). M2-TAMs targeting nanoparticles shMFN1-NPs were fabricated to deliver shMFN1 for repolarization of TAMs from the M2 to M1 phenotype by inhibiting mitochondrial fusion. Moreover, DOX-NPs effectively triggered the immunogenic cell death (ICD) of cancer cells, and the succeeding maturation of dendritic cells (DCs) promoted the infiltration and activation of CD8+ T cells. MIX-NPs displayed the strongest antitumor efficacy (TIR = 83%) in the subcutaneous 4T1 tumor model. MIX-NPs suppressed the myeloid-derived suppressor cells (MDSCs) and regulatory T lymphocytes (Tregs) to further remodel the ITM. Taken together, our developed drug delivery strategy reversed the ITM and activated the antitumor immune response, providing a profound prospective treatment strategy in cancer immunotherapy.

Introduction Foot process effacement and mitochondrial fission associate with kidney disease pathogenesis. Electron microscopy is the gold-standard method for their visualization, but the observable area of electron microscopy is smaller than light microscopy. It is important to develop alternative ways to quantitatively evaluate these microstructural changes because the lesion site of renal diseases can be focal. Methods We analyzed elastica-Masson trichrome (EMT) and periodic acid-Schiff (PAS) stained kidney sections using structured illumination microscopy (SIM). Results EMT staining revealed three-dimensional (3D) structures of foot process, whereas ponceau xylidine acid fuchsin azophloxine solution induced fluorescence. Conversion of foot process images into their constituent frequencies by Fourier transform showed that the concentric square of (1/4)2-(1/16)2 in the power spectra (PS) included information for normal periodic structures of foot processes. Foot process integrity, assessed by PS, negatively correlated with proteinuria. EMT-stained sections revealed fragmented mitochondria in mice with mitochondrial injuries and patients with tubulointerstitial nephritis; Fourier transform quantified associated mitochondrial injury. Quantified mitochondrial damage in patients with immunoglobulin A (IgA) nephropathy predicted a decline in estimated glomerular filtration rate (eGFR) after kidney biopsy but did not correlate with eGFR at biopsy. PAS-stained sections, excited by a 640 nm laser, combined with the coefficient of variation values, quantified subtle changes in the basement membranes of patients with membranous nephropathy stage I. Conclusions Kidney microstructures are quantified from sections prepared in clinical practice using SIM.

In a new article in the Journal of Investigative Dermatology, Wang et al. (2021) report that mitochondrial quality control modulates responses to endoplasmic reticulum (ER) stress in melanoma. They implicate a linear pathway of XBP1, MARCH5, and MFN2 that act together to regulate mitochondrial fission and mitophagy and ultimately mediate melanoma cell sensitivity to ER stress. This work informs therapeutic combinations and biomarker strategies for targeting melanoma organellar homeostasis as well as for life‒death decisions.

Adult hippocampal neurogenesis supports the structural and functional plasticity of the brain, while its decline is associated with neurodegeneration common in Alzheimer’s disease (AD). Although the dysregulation of certain microRNAs (miRNAs) in AD have been observed, the effects of miRNAs on hippocampal neurogenesis are largely unknown. In this study, we demonstrated miR-351-5p as a causative factor in hippocampal neural progenitor cell death through modulation of the mitochondrial guanosine triphosphatase (GTPase), Miro2. Downregulation of Miro2 by siMiro2 induced cell death, similar to miR-351-5p, whereas ectopic Miro2 expression using an adenovirus abolished these effects. Excessively fragmented mitochondria and dysfunctional mitochondria were indexed by decreased mitochondrial potential, and increased reactive oxygen species were identified in miR-351-5p-induced cell death. Moreover, subsequent induction of mitophagy via Pink1 and Parkin was observed in the presence of miR-351-5p and siMiro2. The suppression of mitochondrial fission by Mdivi-1 completely inhibited cell death by miR-351-5p. miR-351-5p expression increased whereas the level of Miro2 decreased in the hippocampus of AD model mice, emulating expression in AD patients. Collectively, the data indicate the mitochondrial fission and accompanying mitophagy by miR-351-5p/Miro2 axis as critical in hippocampal neural progenitor cell death, and a potential therapeutic target in AD., Graphical Abstract, Woo et al. revealed that miR-351-5p is the causative factor for hippocampal neural progenitor cell death through modulation of Miro2. They suggest that mitochondrial fission by the miR-351-5p/Miro2 axis, and accompanying mitophagy, is a critical event in hippocampal neural progenitor cell death, which could be a potential therapeutic target in AD.

Lipopolysaccharide (LPS) has been known to cause alveolar epithelial cell (AEC) apoptosis and barrier breakdown that characterize acute lung injury (ALI) and acute respiratory distress syndrome. We aimed to investigate whether mitoquinone (MitoQ), a mitochondria-targeted antioxidant, could alleviate LPS-induced AEC damage in ALI and its underlying mechanisms. In vitro studies in AEC A549 cell line, we noted that LPS could induce dynamin-related protein 1 (Drp1)-mediated mitochondrial fission, AEC apoptosis and barrier breakdown, which could be reversed with MitoQ and mitochondrial division inhibitor 1 treatment. Moreover, the protective role of MitoQ was attenuated with Drp1 overexpression. Nuclear factor E2-related factor 2 (Nrf2) downregulation could block the effect of MitoQ by decreasing the expression of Nrf2 target genes in LPS-treated AEC, such as heme oxygenase-1 (HO-1) and NAD(P)H:quinone oxidoreductase 1 (NQO1). Nrf2 gene knockdown in LPS-treated A549 cells prevented the protective effect of MitoQ from decreasing Drp1-mediated mitochondrial fission, AEC apoptosis and barrier breakdown. The lung protective effect of MitoQ by regulating the Drp1-mediated mitochondrial fission, AEC apoptosis and barrier breakdown was further confirmed in vivo with LPS-induced ALI mouse model. Additionally, the protective effect of MitoQ was inhibited by Nrf2 inhibitor ML385. We therefore conclude that MitoQ exerts ALI-protective effects by preventing Nrf2/Drp1-mediated mitochondrial fission, AEC apoptosis as well as barrier breakdown.

Excessive alcohol users have increased risk of developing respiratory infections in part due to oxidative stress-induced alveolar macrophage (AM) phagocytic dysfunction. Chronic ethanol exposure increases cellular oxidative stress in AMs via upregulation of NADPH oxidase (Nox) 4, and treatment with the peroxisome proliferator-activated receptor gamma (PPARγ) ligand, rosiglitazone, decreases ethanol-induced Nox4. However, the mechanism by which ethanol induces Nox4 expression and the PPARγ ligand reverses this defect has not been elucidated. Since microRNA (miR)-92a has been predicted to target Nox4 for destabilization, we hypothesized that ethanol exposure decreases miR-92a expression and leads to Nox4 upregulation. Previous studies have implicated mitochondrial-derived oxidative stress in AM dysfunction. We further hypothesized that ethanol increases mitochondrial-derived AM oxidative stress and dysfunction via miR-92a, and that treatment with the PPARγ ligand, pioglitazone, could reverse these derangements. To test these hypotheses, a mouse AM cell line, MH-S cells, was exposed to ethanol in vitro, and primary AMs were isolated from a mouse model of chronic ethanol consumption to measure Nox4, mitochondrial target mRNA (qRT-PCR) and protein levels (confocal microscopy), mitochondria-derived reactive oxygen species (confocal immunofluorescence), mitochondrial fission (electron microscopy), and mitochondrial bioenergetics (extracellular flux analyzer). Ethanol exposure increased Nox4, enhanced mitochondria-derived oxidative stress, augmented mitochondrial fission, and impaired mitochondrial bioenergetics. Transfection with a miR-92a mimic in vitro or pioglitazone treatment in vivo diminished Nox4 levels, resulting in improvements in these ethanol-mediated derangements. These findings demonstrate that pioglitazone may provide a novel therapeutic approach to mitigate ethanol-induced AM mitochondrial derangements.

Nano titanium implants induce osteogenesis, but how osteoblasts respond to this physical stimulation remains unclear. In this study, we tried to reveal the role of the mitochondrial fission-fusion of osteoblasts in response to a nano titanium surface during the process of osteogenesis, which is important for the design of the surface structure of titanium implants. A TiO2 nanotube array (nano titanium, NT) was fabricated by anodization, and a smooth surface (smooth titanium, ST) was used as a control. We investigated changes in the mitochondrial fission-fusion (MFF) dynamics in MC3T3-E1 cells on the NT surface with those on the ST surface by performing transmission electron microscopy (TEM), confocal laser scanning microscope (CLSM) and real-time PCR. At the same time, we also detected changes in the MFF and osteogenic differentiation of MC3T3-E1 cells after DRP1 downregulation with RNA interference. Cells on the NT surface exhibited more mitochondrial fusion than those on the ST surface, and DRP1 was the key regulatory molecule. Interestingly, DRP1 increased for only a short time at the early stage on the NT surface, and when DRP1 was inhibited by siRNA at the early stage, the osteogenic differentiation of MC3T3-E1 cells significantly decreased. In conclusion, DRP1-regulated mitochondrial dynamics played a key role in the nanotopography-accelerated osteogenic differentiation of MC3T3-E1 cells.

Glutamine and glucose are both oxidized in the mitochondria to supply the majority of usable energy for processes of cellular function. Low levels of plasma and skeletal muscle glutamine are associated with severe illness. We hypothesized that glutamine deficiency would disrupt mitochondrial integrity and impair cell function. C2C12 mouse myoblasts were cultured in control media supplemented with 5.6 mmol/L glucose and 2 mmol/L glutamine, glutamine depletion (Gln-) or glucose depletion (Glc-) media. We compared mitochondrial morphology and function, as well as cell proliferation, myogenic differentiation, and heat-shock response in these cells. Glc- cells exhibited slightly elongated mitochondrial networks and increased mitochondrial mass, with normal membrane potential (ΔΨm). Mitochondria in Gln- cells became hyperfused and swollen, which were accompanied by severe disruption of cristae and decreases in ΔΨm, mitochondrial mass, the inner mitochondrial membrane remodeling protein OPA1, electron transport chain complex IV protein expression, and markers of mitochondrial biogenesis and bioenergetics. In addition, Gln- increased the autophagy marker LC3B-II on the mitochondrial membrane. Notably, basal mitochondrial respiration was increased in Glc- cells as compared to control cells, whereas maximal respiration remained unchanged. In contrast, basal respiration, maximal respiration and reserve capacity were all decreased in Gln- cells. Consistent with the aforementioned mitochondrial deficits, Gln- cells had lower growth rates and myogenic differentiation, as well as a higher rate of cell death under heat stress conditions than Glc- and control cells. We conclude that glutamine is essential for mitochondrial integrity and function; glutamine depletion impairs myoblast proliferation, differentiation, and the heat-shock response.

Mitochondrial damage is a critical contributor to cardiac ischemia/reperfusion (I/R) injury. Mitochondrial quality control (MQC) mechanisms, a series of adaptive responses that preserve mitochondrial structure and function, ensure cardiomyocyte survival and cardiac function after I/R injury. MQC includes mitochondrial fission, mitochondrial fusion, mitophagy and mitochondria-dependent cell death. The interplay among these responses is linked to pathological changes such as redox imbalance, calcium overload, energy metabolism disorder, signal transduction arrest, the mitochondrial unfolded protein response and endoplasmic reticulum stress. Excessive mitochondrial fission is an early marker of mitochondrial damage and cardiomyocyte death. Reduced mitochondrial fusion has been observed in stressed cardiomyocytes and correlates with mitochondrial dysfunction and cardiac depression. Mitophagy allows autophagosomes to selectively degrade poorly structured mitochondria, thus maintaining mitochondrial network fitness. Nevertheless, abnormal mitophagy is maladaptive and has been linked to cell death. Although mitochondria serve as the fuel source of the heart by continuously producing adenosine triphosphate, they also stimulate cardiomyocyte death by inducing apoptosis or necroptosis in the reperfused myocardium. Therefore, defects in MQC may determine the fate of cardiomyocytes. In this review, we summarize the regulatory mechanisms and pathological effects of MQC in myocardial I/R injury, highlighting potential targets for the clinical management of reperfusion.

Myeloid cell leukemia-1 (Mcl-1) is a structurally and functionally unique anti-apoptotic Bcl-2 protein. While elevated levels of Mcl-1 contribute to tumor cell survival and drug resistance, loss of Mcl-1 in cardiac myocytes leads to rapid mitochondrial dysfunction and heart failure development. Although Mcl-1 is an anti-apoptotic protein, previous studies indicate that its functions extend beyond regulating apoptosis. Mcl-1 is localized to both the mitochondrial outer membrane and matrix. Here, we have identified that Mcl-1 in the outer mitochondrial membrane mediates mitochondrial fission, which is independent of its anti-apoptotic function. We demonstrate that Mcl-1 interacts with Drp1 to promote mitochondrial fission in response to various challenges known to perturb mitochondria morphology. Induction of fission by Mcl-1 reduces nutrient deprivation-induced cell death and the protection is independent of its BH3 domain. Finally, cardiac-specific overexpression of Mcl-1(OM), but not Mcl-1(Matrix), contributes to a shift in the balance towards fission and leads to reduced exercise capacity, suggesting that a pre-existing fragmented mitochondrial network leads to decreased ability to adapt to an acute increase in workload and energy demand. Overall, these findings highlight the importance of Mcl-1 in maintaining mitochondrial health in cells.

The dynamic processes of mitochondrial fission and fusion are tightly regulated, determine mitochondrial shape, and influence mitochondrial functions. For example, fission and fusion mediate energy output, production of reactive oxygen species (ROS), and mitochondrial quality control. As our understanding of the molecular machinery and mechanisms regulating dynamic changes in the mitochondrial network continues to grow, we are beginning to unravel important signaling pathways that integrate physiological cues to modulate mitochondrial morphology and function. Here, we highlight reciprocal regulation of mitochondrial fusion and fission as an emerging trend in the regulation of mitochondrial function.

Background Mitochondrial homeostasis is a highly dynamic process involving continuous fission and fusion cycles and mitophagy to maintain mitochondrial functionality. Imiquimod (IMQ), a Toll-like receptor (TLR) 7 ligand, is used to treat various skin malignancies. IMQ also induces apoptotic and autophagic cell death in various cancers through a TLR7-independent pathway. Objective To investigate whether IMQ-induced ROS production is involved in mitochondrial dysfunction, mitochondrial fragmentation and mitophagy in skin cancer cells. Methods BCC/KMC-1, B16F10 and A375 skin cancer cells, AGS gastric cancer cells and primary human keratinocytes were treated with 50 μg/mL IMQ. After 4 h, ROS were detected by CM-H2DCFDA, DHE, and MitoSOX Red staining. After 24 h, cell viability and the mitochondrial membrane potential were evaluated by a CCK-8 assay and JC-1 staining, respectively. Oxygen consumption was assessed with an Oroboros instrument. Mitochondrial morphology and mitophagy were evaluated by MitoTracker and LysoTracker staining. Mitochondrial dynamics markers, including MFN-1, DRP-1 and OPA1, and mitophagy markers, including LC3, S65-phosphorylated ubiquitin, PINK1 and TOM20, were detected by immunoblotting. Results IMQ not only induced severe ROS production but also resulted in increased mitochondrial membrane potential loss, mitochondrial fission and mitophagy and decreased oxygen consumption in skin cancer cells compared with normal keratinocytes. Pretreatment with the antioxidant NAC reduced IMQ-induced ROS production and attenuated IMQ-induced mitochondrial fission and mitophagy in skin cancer cells. Conclusions IMQ-induced ROS might be associated with mitochondrial dysfunction, mitochondrial fission and mitophagy in cancer cells. Alleviating IMQ-induced ROS production would reduce mitochondrial fission-to-fusion skewing and further reduce IMQ-induced mitophagy.

Cardiac hypertrophy is an adaptive response to manage an excessive cardiac workload and maintain normal cardiac function. However, sustained hypertrophy leads to cardiomyopathy, cardiac failure, and death. Adrenergic receptors play a key role in regulating cardiac function under normal and pathological conditions. Mitochondria are responsible for 90% of ATP production in cardiomyocytes. Mitochondrial function is dynamically regulated by fusion and fission processes. Changes in mitochondrial dynamics and metabolism are central issues in cardiac hypertrophy. Stimulating cardiomyocytes with adrenergic agonists generates hypertrophy and increases mitochondrial fission, which in turn is associated with decreased ATP synthesis. Miro1 is a mitochondrial outer membrane protein involved in mitochondrial dynamics and transport in neurons. The objective of this work was to evaluate whether Miro1 regulates cardiomyocyte hypertrophy through changes in mitochondrial dynamics. In neonatal rat ventricular myocytes, we showed that phenylephrine induced cardiomyocyte hypertrophy and increased Miro1 mRNA and protein levels. Moreover, alpha-adrenergic stimulation provoked a mitochondrial fission pattern in the cardiomyocytes. Miro1 knockdown prevented both the cardiomyocyte hypertrophy and mitochondrial fission pattern. Our results suggest that Miro1 participates in phenylephrine-induced cardiomyocyte hypertrophy through mitochondrial fission.

Myeloid cell leukemia-1 (Mcl-1) is involved in the regulation of mitochondrial fission and fusion. This report aims to explore whether Mcl-1 can interact with mitochondrial fission factor (Mff) and regulate Mff-mediated mitochondrial fragmentation and apoptosis. Fluorescence images of living cells coexpressing YFP-Mff and CFP-Mcl-1 showed that Mcl-1 markedly inhibited Mff-mediated mitochondrial fragmentation and apoptosis, suggesting that Mcl-1 played a key role in inhibiting mitochondrial fission. The cells coexpressing YFP-Mff and CFP-Mcl-1 exhibited consistent fluorescence resonance energy transfer (FRET) efficiency with that of the cells coexpressing CFP-Mcl-1 and YFP, demonstrating that Mcl-1 did not directly bind to Mff on mitochondria. Collectively, Mcl-1 inhibits Mff-mediated mitochondrial fission and apoptosis not via directly binding to Mff on mitochondria.

Background: Electroacupuncture (EA) mitigates endotoxin-induced acute lung injury (ALI) during bacterial sepsis, but the mechanisms are unclear. This study aimed to investigate the potential mechanisms of EA improving endotoxin-induced ALI. Methods: Endotoxin-induced ALI was established by lipopolysaccharide (LPS) administration. Electroacupuncture was started 5 days before LPS administration and non-acupoint EA (punctured at non-acupoints with shallow insertion and no electrical stimulation) was used as the control treatment. In addition, hemin was applied to active HO-1 and ZnPP to suppress HO-1. Briefly, 70 rabbits were divided into seven treatment groups: untreated control (C), LPS, LPS + EA, LPS + non-acupoint EA, LPS + EA + hemin, LPS + EA + ZnPP, and LPS + EA + ZnPP + hemin. Lung samples were collected at 6 h after LPS administration for analysis of tissue injury (edema, inflammation, hemorrhage, necrosis), oxidative stress, mitochondrial membrane potential (MMP), respiratory control ratio (RCR), ATP production, and changes in expression of mitochondrial fusion and fission markers. Results: Electroacupuncture alleviated LPS-induced lung injury and mitochondria dysfunction as indicated by decreasing wet/dry tissue weight ratio, lung injury score, ROS production, and suppressing expression of mitochondrial fission proteins. Furthermore, EA also increased ATP content, mitochondrial membrane potential, respiratory control ratio, and expressions of mitochondrial fusion proteins (LPS + EA group vs. LPS group). These effects of EA were further enhanced by pretreatment with hemin (LPS + EA + hemin group) but suppressed by Znpp-IX (LPS + EA + ZnPP and LPS + EA + ZnPP + hemin groups). Conclusions: Electroacupuncture protects against endotoxin-induced ALI by upregulating heme oxygenase-1 expression, thereby preserving the balance between mitochondrial fusion and fission. Keywords: Heme oxygenase-1, Electroacupuncture, Lung injury, Mitochondrial dynamics

Mitochondrial dynamics are crucial for cellular survival in response to various stresses. Previously, we reported that Drp1 promoted mitochondrial fission after x-irradiation and its inhibition resulted in reduced cellular radiosensitivity and mitotic catastrophe. However, the mechanisms of radiation-induced mitotic catastrophe related to mitochondrial fission remain unclear. In this study, we investigated the involvement of cellular ATP production, ROS generation, and Ca2+ levels in mitotic catastrophe in EMT6 cells. Knockdown of Drp1 and Fis1, which are mitochondrial fission regulators, resulted in elongated mitochondria and significantly attenuated cellular radiosensitivity. Reduced mitochondrial fission mainly decreased mitotic catastrophe rather than necrosis and apoptosis after irradiation. Cellular ATP contents in Drp1 and Fis1 knockdown cells were similar to those in control cells. N-acetylcysteine and 2-glucopyranoside ascorbic acid have no effect on mitotic catastrophe after irradiation. The cellular [Ca2+]i level increased after irradiation, which was completely suppressed by Drp1 and Fis1 inhibition. Furthermore, BAPTA-AM significantly reduced radiation-induced mitotic catastrophe, indicating that cellular Ca2+ is a key mediator of mitotic catastrophe induction after irradiation. These results suggest that mitochondrial fission is associated with radiation-induced mitotic catastrophe via cytosolic Ca2+ regulation. (C) 2019 Elsevier Inc. All rights reserved.

Mitochondrial plasticity is a key regulator of cell fate decisions. Mitochondrial division involves Dynamin-related protein-1 (Drp1) oligomerization, which constricts membranes at endoplasmic reticulum (ER) contact sites. The mechanisms driving the final steps of mitochondrial division are still unclear. Here, we found that microdomains of phosphatidylinositol 4-phosphate [PI(4)P] on trans-Golgi network (TGN) vesicles were recruited to mitochondria-ER contact sites and could drive mitochondrial division downstream of Drp1. The loss of the small guanosine triphosphatase ADP-ribosylation factor 1 (Arf1) or its effector, phosphatidylinositol 4-kinase IIIβ [PI(4)KIIIβ], in different mammalian cell lines prevented PI(4)P generation and led to a hyperfused and branched mitochondrial network marked with extended mitochondrial constriction sites. Thus, recruitment of TGN-PI(4)P-containing vesicles at mitochondria-ER contact sites may trigger final events leading to mitochondrial scission.

Hematopoietic stem cells (HSCs) remain quiescent to preserve long-term integrity. In this issue of Cell Stem Cell, Hinge et al. (2020) and Liang et al. (2020) demonstrate that HSCs achieve this by regulating mitochondrial fission and lysosomal activity, suppressing glucose uptake, and maintaining healthy punctate mitochondria with low metabolic activity.

Brain-derived neurotrophic factor (BDNF)/tropomyosin-related kinase B (TrkB) pathway is associated with ischemic heart diseases (IHD). 7,8-dihydroxyflavone (7,8-DHF), BDNF mimetic, is a potent agonist of TrkB. We aimed to investigate the effects and the underlying mechanisms of 7,8-DHF on cardiac ischemia. Myocardial ischemic mouse model was induced by ligation of left anterior descending coronary artery. 7,8-DHF (5 mg/kg) was administered intraperitoneally two days after ischemia for four weeks. Echocardiography, HE staining and transmission electron microscope were used to examine the function, histology and ultrastructure of the heart. H9c2 cells were treated with hydrogen peroxide (H2O2), 7,8-DHF or TrkB inhibitor ANA-12. The effects of 7,8-DHF on cell viability, mitochondrial membrane potential (MMP) and mitochondrial superoxide generation were examined. Furthermore, mitochondrial fission and protein expression of mitochondrial dynamics (Mfn2 [mitofusin 2], OPA1 [optic atrophy 1], Drp1 [dynamin-related protein 1] and Fis-1 [fission 1]) was detected by mitotracker green staining and western blot, respectively. 7,8-DHF attenuated cardiac dysfunction and cardiomyocyte abnormality of myocardial ischemic mice. Moreover, 7,8-DHF increased cell viability and reduced cell death accompanied by improving MMP, inhibiting mitochondrial superoxide and preventing excessive mitochondrial fission of H2O2-treated H9c2 cells. The cytoprotective effects of 7,8-DHF were antagonized by ANA-12. Mechanistically, 7,8-DHF repressed OMA1-dependent conversion of L-OPA1 into S-OPA1, which was abolished by Akt inhibitor. In conclusion, 7,8-DHF protects against cardiac ischemic injury by inhibiting the proteolytic cleavage of OPA1. These findings provide a novel pharmacological effect of 7,8-DHF on mitochondrial dynamics and a new potential target for IHD.

Chronic abuse of psychoactive drugs including cocaine causes addiction, dependence, and brain disorders through the alteration of neuronal plasticity. Mitochondrial fission and fusion, collectively called as mitochondrial dynamics, participates in not only the maintenance of neuronal homeostasis but also reorganization of neuronal circuits. The purpose of this study is to examine effects of direct and repeated exposure of cocaine on mitochondrial dynamics in neuronal cells in vitro. Repeated exposure to 600 μM cocaine (2∼3 times per week) of Neuro2a mouse neuroblastoma cells for 3 weeks resulted in decrease of mitochondrial transmembrane potential, activation of autophagy, and upregulation of Parkin, a protein involved in mitochondrial autophagy. Increased expression of mitochondrial fission genes and significant increase in the ser-616 phosphorylated-DRP1, the key regulator of mitochondrial fission, were observed in the cells exposed repeatedly to 600 μM cocaine. Electron microscopy showed significant increase in the number of mitochondria in cocaine-treated cells compared with control cells. Thus, our results show that repeated cocaine exposure not only causes mitochondrial dysfunction but also alters mitochondrial dynamics in Neuro2a cells. Changes in the mitochondrial dynamics might be involved in neural adaptation during repeated cocaine exposure.

Mitochondrial dynamics and mitophagy are important aspects of mitochondrial quality control, and are linked to neurodegenerative diseases and muscular diseases. Fis1, a protein on the mitochondrial outer membrane, is thought to mediate mitochondrial fission. However, Fis1 null worms and mammalian cells only display mild fission defects but show aberrant mitophagy. To assess Fis1 function in vivo, we generated conditional knock-out Fis1 mice to allow for specific Fis1 deletion in adult skeletal muscle. In the absence of Fis1 in Type I muscle, mitochondrial hyperfusion, respiratory chain deficiency, and increased mitophagy were found. Moreover, abnormal mitophagy was aggravated by endurance exhaustive exercise stress (EEE), suggesting that Fis1 is involved in maintaining normal mitophagy in mitochondria-rich Type I muscle during exercise. Additionally, Fis1 loss induced delayed onset muscle ultrastructure change (DOMUC) in Type I muscle and strong inflammation in response to acute exhaustive exercise (EE). Thus, we identify a role for Fis1 in maintaining normal mitochondrial structure and function at rest and under exercise stress.

Mitochondrial morphology is a crucial determinant of mitochondrial and cellular function. Opposing fusion and fission events shape the tubular mitochondrial reticulum and ensure mitochondrial transport within cells. Cellular stress and pathophysiological conditions can lead to fragmentation of the mitochondrial network, which facilitates mitophagy and is associated with cell death. However, mitochondrial shape changes are also intertwined with the cellular metabolism, and metabolic switches can induce but also result from alterations in mitochondrial morphology. Here, we discuss recent advances in the field of mitochondrial dynamics, demonstrating cell- and tissue-specific effects of mitochondrial fragmentation on cellular metabolism, cell survival, and mitochondrial quality control.

Biological functions of extracellular vesicles (EVs) are being discovered to be critical in neurodegenerative disorders, including Parkinson's disease (PD). A previous study using cellular models of PD has suggested that EVs derived from microglia exposed to aggregated α-synuclein (α-Syn) leads to enhanced neurotoxicity. However, the function of EVs derived from microglia not treated with aggregated a-Syn or treated with monomeric α-Syn are unclear. Here, employing a widely used cellular model of PD, i.e. SH-SY5Y cells treated with MPP+, a well-established parkinsonian toxicant, we revealed that microglial EVs, when not stimulated by aggregated α-Syn, appeared to be protective, and the mechanisms, though remain to be defined further, appeared to involve mitochondrial dynamics, especially mitochondrial fission.

The purpose of our study is to understand the protective role of miR-455-3p against abnormal amyloid precursor protein (APP) processing, amyloid beta (Aβ) formation, defective mitochondrial biogenesis/dynamics and synaptic damage in AD progression. In-silico analysis of miR-455-3p has identified the APP gene as a putative target. Using mutant APP cells, miR-455-3p construct, biochemical and molecular assays, immunofluorescence and transmission electron microscopy (TEM) analyses, we studied the protective effects of miR-455-3p on – 1) APP regulation, amyloid beta (Aβ)(1-40) & (1-42) levels, mitochondrial biogenesis & dynamics; 3) synaptic activities and 4) cell viability & apoptosis. Our luciferase reporter assay confirmed the binding of miR-455-3p at the 3’UTR of APP gene. Immunoblot, sandwich ELISA and immunostaining analyses revealed that the reduced levels of the mutant APP, Aβ(1-40) & Aβ(1-42), and C99 by miR-455-3p. We also found the reduced levels of mRNA and proteins of mitochondrial biogenesis (PGC1α, NRF1, NRF2, and TFAM) and synaptic genes (synaptophysin and PSD95) in mutant APP cells; on the other hand, mutant APP cells that express miR-455-3p showed increased mRNA and protein levels of biogenesis and synaptic genes. Additionally, expression of mitochondrial fission proteins (DRP1 and FIS1) were decreased while the fusion proteins (OPA1, Mfin1 and Mfn2) were increased by miR-455-3p. Our TEM analysis showed a decrease in mitochondria number and an increase in the size of mitochondrial length in mutant APP cells transfected with miR-455-3p. Based on these observations, we cautiously conclude that miR-455-3p regulate APP processing and protective against mutant APP-induced mitochondrial and synaptic abnormalities in AD.

E5 protein, the major oncoprotein of the bovine Deltapapillomavirus genus, has been detected in 17 of the 19 urothelial cancers by molecular and morphological procedures. In 10 urothelial cancers, the oxygen sensitive subunit HIF-1α, which is upregulated by hypoxia, was overexpressed. Mitophagy, the selective autophagic removal of dysfunctional mitochondria, was upregulated in hypoxic neoplastic cells infected by BPVs which was mediated by FUNDC1, a mitochondrial outer-membrane protein. The FUNDC1 receptor was amplified by PCR, and amplicon sequencing showed a 100% homology with bovine FUNDC1 sequences deposited in GenBank (accession number: NM_001104982). Both transcripts and protein levels of FUNDC1 were significantly decreased in hypoxic neoplastic cells relative to healthy, non-neoplastic cells. FUNDC1 interacted with the LC3 protein, a marker of autophagosome (mitophagosome) membrane, the Hsc70/Hsp70 chaperone, and Bag3 co-chaperone. Bag3 may play a role in mitophagosome formation together with the Synpo2 protein, and may be involved in the degradation of Hsc70/Hsp70-bound CHIP-ubiquitinated cargoes, in association with its chaperone. Ultrastructural findings revealed the presence of mitochondria exhibiting severe fragmentation and loss of cristae, as well as numerous mitochondria-containing autophagosomes. Total and phosphorylated GTPase dynamin-related protein 1 (DRP1), which plays a crucial role in mitochondrial fission, a pre-requisite for mitophagy, was overexpressed at the mitochondrial level. Total and phosphorylated mitochondrial fission factor (Mff), mitochondrial fission protein 1 (Fis1), mitochondrial dynamics 51 (MiD51), and MiD49, which are DRP1 receptors responsible and/or co-responsible for its mitochondrial recruitment were overexpressed.

Mitochondrial dysfunction is a key contributor to septic cardiomyopathy. Although recent literature implicates dynamin related protein 1 (Drp1) and its mitochondrial adaptor fission 1 (Fis1) in the development of pathologic fission and mitochondrial failure in neurodegenerative disease, little is known about the role of Drp1/Fis1 interaction in the context of sepsis-induced cardiomyopathy. Our study tests the hypothesis that Drp1/Fis1 interaction is a major driver of sepsis-mediated pathologic fission, leading to mitochondrial dysfunction in the heart. Methods H9C2 cardiomyocytes were treated with lipopolysaccharide (LPS) to evaluate changes in mitochondrial membrane potential, oxidative stress, cellular respiration, and mitochondrial morphology. Balb/c mice were treated with LPS, cardiac function was measured by echocardiogaphy, and mitochondrial morphology determined by electron microscopy (EM). Drp1/Fis1 interaction was inhibited by P110 to determine whether limiting mitochondrial fission can reduce LPS-induced oxidative stress and cardiac dysfunction. Results LPS-treated H9C2 cardiomyocytes demonstrated a decrease in mitochondrial respiration followed by an increase in mitochondrial oxidative stress and a reduction in membrane potential. Inhibition of Drp1/Fis1 interaction with P110 attenuated LPS-mediated cellular oxidative stress and preserved membrane potential. In vivo, cardiac dysfunction in LPS-treated mice was associated with increased mitochondrial fragmentation. Treatment with P110 reduced cardiac mitochondrial fragmentation, prevented decline in cardiac function, and reduced mortality. Conclusions Sepsis decreases cardiac mitochondrial respiration and membrane potential while increasing oxidative stress and inducing pathologic fission. Treatment with P110 was protective in both in vitro and in vivo models of septic cardiomyopathy, suggesting a key role of Drp1/Fis1 interaction, and a potential target to reduce its morbidity and mortality.

The imbalance between mitochondrial fusion and fission has been implicated in cerebral ischemia and several neurodegenerative diseases. However, the role of mitochondrial fission in traumatic brain injury (TBI) remains poorly understood. Mitochondrial fission is mediated by dynamin-related protein 1 (Drp1), which is highly expressed in the nervous system. In the present study, we investigated the changes in Drp1 expression in the ipsilateral hippocampus of rats after TBI and the effects of Mdivi-1 (a selective inhibitor of Drp1) as a post-insult treatment for TBI. Our findings showed that the protein levels of Drp1 were increased at 6 h and peaked at 12 h post-TBI, but we did not observe Drp1 phosphorylation at Ser616, Ser637, Ser40 or Ser44 during this process. We examined the effect of Mdivi-1 on trauma-induced brain damage in both vitro and vivo. In cells, Mdivi-1 significantly attenuated H2O2-induced mitochondrial membrane potential (MMP) dissipation in PC-12 cells. Three days of Mdivi-1 treatment significantly reduced the cortical lesion volume, blood-brain barrier permeability, brain edema and oxidative stress. Mdivi-1 reduced activated caspase-3 release in the cortical border zone and hippocampal dentate gyrus three days after TBI. Furthermore, treatment with Mdivi-1 for 4 weeks rescued neurogenesis in DG and attenuated hippocampal atrophy. Regarding behavioral outcomes, Mdivi-1-treated TBI rats showed a significant improvement in water maze acquisition and retention compared with the saline-treated TBI rats. Moreover, Mdivi-1 treatment reduced anxiety-like behavior in an open-field test. Our results support the notion that Mdivi-1 provides brain protection and improves the behavioral performance in TBI rats.

Hepatic ischemia reperfusion (HIR) has been found to induce brain injury and cognitive dysfunction. Dynamin-related protein 1 (Drp1) mediated mitochondrial fission involves oxidative stress, apoptosis and several neurological diseases. In this study, we investigated whether Drp1 translocation to mitochondria was implicated in HIR induced hippocampus injury in young mice, and further detected the role of calcineurin in the regulation of mitochondrial dynamics. 2-week C57BL/6 mice were chosen to make HIR model. Western blot was used to detect mitochondrial dynamics regulating proteins in whole hippocampal tissues and extracted mitochondria. Transmission electron microscopy was used to observe mitochondrial morphology. TUNEL staining and ELISA (serum S100β/NSE concentrations) were used to evaluate neurons apoptosis and brain injury respectively. Drp1 inhibitor Mdivi-1 and calcineurin inhibitor FK506 were utilized to further confirm the role of Drp1 and calcineurin. Results showed that HIR affected mitochondrial dynamics in a fission-dominant manner with translocation of Drp1 to mitochondria in hippocampus of young mice. HIR induced increased expression of calcineurin and dephosphorylation of Drp1 at Ser637 in hippocampus. Treatment with Mdivi-1 and FK506 upregulated the phosphorylation of Drp1, inhibited Drp1 translocation to mitochondria, and alleviated mitochondrial fragmentation after HIR. What's more, Mdivi-1 and FK506 restrained cytochrome c release and cleaved caspase-3 expression, ameliorated hippocampal neurons apoptosis, and decreased serum S100β/NSE concentrations as well. These data suggest that calcineurin mediated Drp1 dephosphorylation and translocation to mitochondria play a crucial role in HIR induced mitochondrial fragmentation and neurons apoptosis in hippocampus.

Aims Acute kidney injury (AKI) can limit the clinical use of cisplatin in cancer treatment. The drivers of cisplatin-induced AKI include oxidative stress, mitochondrial dysfunction and apoptosis. Previous studies showed renalase protected cultured human renal proximal tubular cell (HK-2) against cisplatin induced necrosis, and renalase-knockout mice subjected to cisplatin showed exacerbated kidney injury. Therefore, it is necessary to determine the exact mechanisms of renalase in cisplatin-induced nephrotoxicity. Main methods To study the protective effect of renalase on cell viability, renal function, apoptosis, reactive oxygen species (ROS) production and mitochondrial dynamics, cultured HK-2 cells and male mice were subjected to cisplatin. Signaling proteins related to apoptosis, survival, and mitochondrial fission were analyzed by Western blot. Key findings In this study, we showed that the protective effect of recombinant renalase in cisplatin-induced AKI was associated with the regulation of ROS production, mitochondrial dynamics and sirtuin-3 (Sirt3) levels in vivo and in vitro. After cisplatin treatment, recombinant renalase restored Sirt3 expression, reduced mitochondrial fission and ROS generation. In HK-2 cells, downregulation of endogenous Sirt3 expression by siRNA transfection abrogated the renalase cytoprotection. Significance Our study suggests that renalase protects against cisplatin-induced AKI by improving mitochondrial function and inhibiting oxidative stress, and in vitro, it functions in a Sirt3-dependent manner.

Exposure to ambient fine particulate matter (PM2.5) is associated with neurodegenerative diseases. Mitochondrion is key to brain degeneration. However, the underlying mechanism of PM2.5-induced brain injury, especially mitochondrial damage, is still unclear. In this study, changes in mitochondrial dynamics, mitochondrial permeability transition pore (mPTP), mitochondrial DNA (mtDNA) and oxidative stress in human SH-SY5Y cells exposed to PM2.5 at different concentrations (0, 25, 100, and 250 μg mL−1) were investigated. The results showed that PM2.5 caused more mitochondrial swell, accompanied by the opening of mPTP and the decrease of ATP levels, mitochondrial membrane potential and mtDNA copy number in SH-SY5Y cells. PM2.5 significantly enhanced the expression of mitochondrial fission/fusion genes (Drp1 and OPA1) and affected the gene expression of CypD, SIRT3, and COX Ⅳ in SH-SY5Y cells. Besides, PM2.5 triggered the increase of cellular ROS, Ca2+ and Aβ-42 levels, inhibition of manganese-superoxide dismutase (SOD2) activities, reduction of GSH levels GSH/GSSG ratio, and elevation of mitochondrial malondialdehyde contents. It suggests that mitochondrial dysfunction and oxidative stress are the potential mechanisms underlying PM2.5-induced brain nerve cell injury, which may be related to neurological diseases. Additionally, our study elucidated that PM2.5 components trigger different cytotoxicity.

Huntington's disease (HD) is a fatal hereditary neurodegenerative disorder, best known for its clinical triad of progressive motor impairment, cognitive deficits and psychiatric disturbances, is caused by CAG-repeat expansion in exon 1 of Huntingtin (HTT). However, in addition to the neurological disease, mutant HTT (mHTT), which is ubiquitously expressed in all tissues, impairs other organ systems. Not surprisingly, cardiovascular dysautonomia as well as the deterioration of circadian rhythms are among the earliest detectable pathophysiological changes in individuals with HD. Mitochondrial dysfunction in the brain and skeletal muscle in HD has been well documented, as the disease progresses. However, not much is known about mitochondrial abnormalities in the heart. In this study, we describe a role for Drp1/Fis1-mediated excessive mitochondrial fission and dysfunction, associated with lysosomal dysfunction in H9C2 expressing long polyglutamine repeat (Q73) and in human iPSC-derived cardiomyocytes transfected with Q77. Expression of long polyglutamine repeat led to reduced ATP production and mitochondrial fragmentation. We observed an increased accumulation of damaged mitochondria in the lysosome that was coupled with lysosomal dysfunction. Importantly, reducing Drp1/Fis1-mediated mitochondrial damage significantly improved mitochondrial function and cell survival. Finally, reducing Fis1-mediated Drp1 recruitment to the mitochondria, using the selective inhibitor of this interaction, P110, improved mitochondrial structure in the cardiac tissue of R6/2 mice. We suggest that drugs focusing on the central nervous system will not address mitochondrial function across all organs, and therefore will not be a sufficient strategy to treat or slow down HD disease progression.

Mitochondria play a central role in various critical cellular processes, including energy synthesis, energy supply and apoptosis. Panax notoginseng, a commonly used traditional Chinese medicine, has various pharmacological effects on the human body. Ginsenosides are representative bioactive components of P. notoginseng. Recently, more attention has focused on ginsenoside Rb1 as an antioxidative and anti-inflammatory agent that can protect the nervous system and the cardiovascular system. Numerous studies have shown that Rb1 exerts these effects by regulating mitochondrial energy metabolism, mitochondrial fission and fusion, apoptosis, oxidative stress and reactive oxygen species release, mitophagy and mitochondrial membrane potential. Thus, the mitochondria are pivotal targets of Rb1. This review summarized the available reports of the effects of ginsenoside Rb1 on the regulation of mitochondria and showed that it has a promising role in treating mitochondrial diseases.

This review focuses on the latest developments in tau research for Alzheimer’s disease and other tauopathies, highlighting therapeutic approaches against antiphosphorylated tau using pharmacophore-based molecular and bioinformatics methods. Phosphorylated tau (P-tau) has received much attention in the field of Alzheimer’s disease (AD), as a potential therapeutic target owing to its involvement with synaptic damage and neuronal dysfunction. The continuous failure of amyloid β (Aβ)-targeted therapeutics highlights the urgency to consider alternative therapeutic strategies for AD. The present review describes the latest developments in tau biology and function. It also explains abnormal interactions between P-tau with Aβ and the mitochondrial fission protein Drp1, leading to excessive mitochondrial fragmentation and synaptic damage in AD neurons. This article also addresses 3D pharmacophore-based drug models designed to treat patients with AD and other tauopathies.

Mitochondrial damage is involved in the pathogenesis of post-infarction cardiac injury. However, the upstream regulators of mitochondrial damage have not yet been identified. The aim of our study is to explore the role of Sirt3 in post-infarction cardiac injury with a particular focus on mitochondrial fission and AMPK-Drp1 pathways. Our results indicated that Sirt3 was downregulated in the progression of post-infarction cardiac injury. Overexpression of Sirt3 attenuated cardiac fibrosis, sustained myocardial function, inhibited the inflammatory response, and reduced cardiomyocyte death. Functional studies illustrated that chronic post-infarction cardiac injury was characterized by increased mitochondrial fission, which triggered mitochondrial oxidative stress, metabolic disorders, mitochondrial potential reduction and caspase-9 apoptosis in cardiomyocytes. However, Sirt3 overexpression attenuated mitochondrial fission and thus preserved mitochondrial homeostasis and cardiomyocyte viability. Furthermore, our results confirmed that Sirt3 repressed mitochondrial fission via normalizing AMPK-Drp1 pathways. Inhibition of AMPK activity re-activated Drp1 and thus abrogated the inhibitory effect of Sirt3 on mitochondrial fission. Altogether, our results indicate that Sirt3 enhancement could be an effective approach to retard the development of post-infarction cardiac injury via disrupting mitochondrial fission and normalizing the AMPK-Drp1 axis.

Colorectal cancer (CRC) is one of the leading causes of cancer-related morbidity and mortality worldwide. Accumulating evidence suggests that mitochondrial dynamics are closely implicated in carcinogenesis including CRC. Paris Saponin II (PSII), a major steroidal saponin extracted from Rhizoma Paris polyphylla, has emerged as a potential anticancer agent. However, the effects of PSII on CRC and its underlying mechanisms remain unknown. In the present study, we found PSII induced apoptosis and inhibited colony formation in HT 29 and HCT 116 cells, and cell cycle arrest in G1 phase. PSII inhibited the phosphorylation of ERK1/2 and mitochondrial translocation of dynamin-related protein 1 (Drp1) by dephosphorylating Drp1 at Ser616, leading to the suppression of mitochondrial fission. PSII also suppressed NF-κB activation as a result of the inhibition of IKKβ and p65 translocation. Drp1 knockdown remarkably downregulated the nuclear expression of p65 and its target genes cyclin D1 and c-Myc in HCT 116 cell, confirming the link between mitochondrial fission and NF-κB pathway. Silencing of Drp 1 enhanced the inhibitory effects of PSII on p65 phosphorylation and the expressions of cyclin D1 and c-Myc, revealing that the inhibitory effects of PSII on cyclin D1 and c-Myc were relevant in the suppression of Drp1 and NF-κB activation. An in vivo study demonstrated PSII remarkably decreased the xenograft tumor size and suppressed the phosphorylation of ERK1/2 and Drp1 at Ser616. Taken together, our results suggested that PSII could inhibit colorectal carcinogenesis, at least in part, by regulating mitochondrial fission and NF-κB pathway.

Summary Dynamic processes such as fusion, fission, and trafficking are important in the regulation of cellular organelles, with an abundant literature focused on mitochondria. Mitochondrial dynamics not only help shape its network within cells but also are involved in the modulation of respiration and integrity. Disruptions of mitochondrial dynamics are associated with neurodegenerative disorders. Although proteins that directly bind mitochondria to promote membrane fusion/fission have been studied intensively, machineries that regulate dynamic mitochondrial processes remain to be explored. We have identified an interaction between the mitochondrial fission GTPase Dnm1/DRP1 and the actin-regulatory protein Srv2/CAP at mitochondria. Deletion of Srv2 causes elongated-hyperfused mitochondria and reduces the reserved respiration capacity in yeast cells. Our results further demonstrate that the irregular network morphology in Δsrv2 cells derives from disrupted actin assembly at mitochondria. We suggest that Srv2 functions as a pro-fission factor in shaping mitochondrial dynamics and regulating activity through its actin-regulatory effects., Graphical Abstract, Highlights • Srv2 interacts with fission protein Dnm1 on mitochondria in yeast cells • Srv2 deletion causes an irregular, hyperfused-elongated mitochondrial network • The irregular network derives from loss of Srv2-mediated actin assembly at mitochondria • Srv2 modulates both mitochondrial dynamics and activity, Molecular Biology; Cell Biology; Functional Aspects of Cell Biology

LATS2 is a classical tumor suppressor that affects non-small cell lung cancer proliferation and mobilization. However, its role in lung cancer cell apoptosis is unknown. The aim of our study is to explore whether LATS2 activates mitochondria-related apoptosis in lung cancer cells. In the present study, A549 non-small cell lung cancer cells were transfected with a LATS2 adenovirus to induce LATS2 overexpression. Cell apoptosis was evaluated via the MTT assay, TUNEL staining, western blotting, trypan blue staining and ELISA. Mitochondrial function was measured using an immunofluorescence assay, western blotting and ELISA. The results demonstrated that LATS2 was downregulated in A549 lung cancer cells. Overexpression of LATS2 induced A549 cell apoptosis via activating mitochondrial fission. Subsequently, we confirmed that LATS2 modulated mitochondrial fission via the JNK-Mff signaling pathway. Inhibition of the JNK pathway and/or knockdown of Mff abolished the pro-apoptotic effect of LATS2 on A549 cells. Taken together, our results identified LATS2 as a classical tumor suppressor of lung cancer via triggering mitochondrial fission and activating the JNK-Mff signaling pathway. Our results lay the foundation for detailed study of the molecular mechanisms of LATS2 overexpression and regulation of mitochondrial fission for lung cancer treatment.

Mitochondria change their morphology in response to developmental and environmental cues. During sexual reproduction, bryophytes produce spermatozoids with two mitochondria in the cell body. Although intensive morphological analyses have been conducted thus far, how this fixed number of mitochondria is realized remains unknown. Here, we investigated how mitochondria are reorganized during spermiogenesis in Marchantia polymorpha. We found that the mitochondrial number is reduced to one through fission followed by autophagic degradation during early spermiogenesis, and then the posterior mitochondrion arises by fission of the anterior mitochondrion. Autophagy is also responsible for the removal of other organelles, including peroxisomes, but these other organelles are removed at distinct developmental stages from mitochondrial degradation. We also found that spermiogenesis involves nonautophagic organelle degradation. Our findings highlight the dynamic reorganization of mitochondria, which is regulated distinctly from that of other organelles, and multiple degradation mechanisms operate in organelle remodeling during spermiogenesis in M. polymorpha.

Constitutive explorations have demonstrated that circular RNAs (circRNAs) are closely related to cardiovascular diseases. However, few studies have identified regulatory roles of circRNAs in endothelial repair. In particular, circTMEM165 has first been reported to be highly expressed in hypoxic human umbilical vein endothelial cells (HUVECs), indicating it to be closely linked with endothelial functions and atherosclerosis. Here, we explored the main biological functions of circTMEM165 and its regulatory mechanism in atherosclerosis. We identified that circTMEM165 was downregulated in patients with atherosclerosis and negatively associated with atherosclerosis progression. Functionally, circTMEM165 was found to be abundant in endothelial cells, inhibiting inflammation and adhesion in HUVECs. Particularly, we first observed that lipopolysaccharide (LPS) could induce HUVEC apoptosis and mitochondrial fission, and circTMEM165 was later found to alleviate these effects. Mechanistically, circTMEM165, as a miR-192-3p sponge, upregulated the downstream expression of SCP2, which serves as critical regulator of biological functions of HUVECs. Moreover, the classic rat carotid artery balloon injury model demonstrated that circTMEM165 reduced apoptosis and intimal hyperplasia in vivo. These findings demonstrated the specific role of the circTMEM165/miR-192-3p/SCP2 pathway in regulating endothelial function and indicated that these molecules served as promising targets for the prediction and diagnosis of vascular diseases. Funding Information: This work was supported by The National Natural Science Foundation of China (grant no. 81870331), and The Qingdao municipal science and technology bureau project (grant no. 21-1-4-rkjk-12-nsh). Declaration of Interests: The authors declare no conflict of interest. Ethics Approval Statement: This study was approved by the Ethical Committee of Qingdao University and conducted in accordance with the Declaration of Helsinki. All human subjects provided signed informed consent. And the animal experiments approved by Qingdao University Laboratory Animal Welfare Ethics Committee (No. 201809SD18202012014).

Context: Oxidative phosphorylation (OxPhos) inhibition induces mitochondrial trafficking from BM stromal cells to AML and is accompanied by mitochondrial fission and mitophagy. The mitochondrial coupling and crosstalk with BM stromal cells facilitate the development of resistance to OxPhos inhibition in AML cells. Objective: Acute myeloid leukemia (AML) cells are highly dependent on OxPhos for survival and continually adapt to fluctuations in nutrient and oxygen availability in the environment. We investigated how the BM microenvironment affects the response to OxPhos inhibition in AML by using a novel complex I OxPhos inhibitor, IACS-010759. Design: Primary AML cells from 26 patients, primary normal MSCs, and AML cell lines were utilized and treated with the OxPhos inhibitor IACS-0107598 and/or cytarabine. Cap analysis of gene expression transcriptome analyses for AML PDXs, primary samples, and AML cell lines has been performed. We performed an extracellular flux assay to measure the oxygen consumption rate. To visualize mitochondria, AML cell lines and MSCs were stably transfected with mitochondria-targeted PDHA1-GFP and -dsRed, respectively. Electron microscopy and immunoelectron microscopy analysis have been performed. Results: Cellular adhesion, growth, and apoptosis assays, along with measurements of mtDNA expression and mitochondrial reactive oxygen species generation, indicated that direct interactions with BM stromal cells triggered the compensatory activation of mitochondrial respiration and resistance to OxPhos inhibition in AML cells. Mechanistically, OxPhos inhibition induced (1) transfer of mesenchymal stem cell (MSC)-derived mitochondria to AML cells via tunneling nanotubes under direct-contact co-culture conditions and (2) mitochondrial fission with an increase in functional mitochondria and mitophagy in AML cells. Mitochondrial fission is known to enhance cell migration, and we observed mitochondrial transport to the leading edge of protrusions of migrating AML cells toward MSCs by electron microscopy analysis. We further demonstrated that cytarabine, a commonly used antileukemia agent, increased IACS-010759-triggered mitochondrial transfer from MSCs to AML cells. Conclusions: Our findings indicate an important role of exogenous mitochondrial trafficking from BM stromal cells to AML cells and of endogenous mitochondrial fission and mitophagy in the compensatory adaptation of leukemia cells to energetic stress in the BM microenvironment.

Here, we aimed to understand the relationship between nutrient starvation and mitophagy. We found that amino acid starvation of 4T1 breast cancer cells led to clear mitochondrial fusion, entirely consistent with the established model in which elongating mitochondria evade autophagosomes to sustain cellular bioenergetics. As we further dissected amino acid signals, we surprisingly found that supplementation of regulatory amino acids glutamine, leucine and arginine did not reverse, but led to strong mitochondrial hyperfusion. This hyperfusion response to Gln+Leu+Arg appeared distinct from other known remodelling mechanisms, but was dependent upon mitochondrial fusion proteins Mfn1 and Opa1. However, amino-acid dependent hyperfusion did not involve phosphorylation and inhibition of the mitochondrial fission protein Drp1. The ability of Gln+Leu+Arg supplementation to promote mitochondrial hyperfusion was independent of MTORC1, suggesting that the amino acids were being sensed by the mitochondria directly. Accordingly, metabolite profiling confirmed that Gln+Leu+Arg addback led to metabolic reprogramming and replenishment of cell amino acid and nucleotide pools. We found that loss of function in fumarate hydratase blocked Gln+Leu+Arg-dependent mitochondrial hyperfusion, suggesting that TCA-mediated metabolism of supplemented amino acids was driving remodelling. In addition, inhibition of inosine monophosphate dehydrogenase blocked Gln+Leu+Arg-dependent mitochondrial hyperfusion, suggesting a critical role of purine biosynthesis. Amino acid-dependent hyperfusion, like the previously reported stress-induced mitochondrial hyperfusion response, led to a decreased sensitivity towards apoptosis. Thus, we describe here a novel metabolic mechanism for the direct sensing of cellular amino acid levels that is able to control mitochondrial fusion and cell fate.

During mitochondrial fission, key molecular and cellular factors assemble on the outer mitochondrial membrane, where they coordinate to generate constriction. Constriction sites can eventually divide or reverse upon disassembly of the machinery. However, a role for membrane tension in mitochondrial fission, although speculated, has remained undefined. We capture the dynamics of constricting mitochondria in mammalian cells using live-cell structured illumination microscopy (SIM). By analyzing the diameters of tubules that emerge from mitochondria and implementing a fluorescence lifetime-based mitochondrial membrane tension sensor, we discover that mitochondria are indeed under tension. Under perturbations that reduce mitochondrial tension, constrictions initiate at the same rate, but are less likely to divide. We propose a model based on our estimates of mitochondrial membrane tension and bending energy in living cells which accounts for the observed probability distribution for mitochondrial constrictions to divide., This work was supported in part by the National Centre of Competence in Research Chemical Biology (S. Manley, S. Matile, and A.R.). S. Manley also acknowledges SNSF Project Grant 31003A_182429 (to T.K. and D.M). T.K. received funding from the European Molecular Biology Organization (ALTF-739-2016) and the Munich Cluster for Systems Neurology (SyNergy). A.C. received funding from MCIU, MINECOG19/P66, RYC-18/02, and T1270-19.

Background: Long noncoding RNAs (lncRNA) are important regulators of various cellular functions in development and diseases. Recent studies have shown that the lncRNA Punisher is highly expressed in cardiovascular progenitors and have potential role in cardiovascular diseases. However, its role, especially molecular mechanism, is unclear. Methods: We performed RNA microarray assays to identify targets of PUNISHER. We investigated the effect of PUNISHER on proliferation, invasion, apoptosis and mitochondrial fission by knocking down and overexpressing this lncRNA in VSMCs. The interactions of molecules were studies by the bioinformatic analyses, luciferase report assay, RNA pull down, and RNA immunoprecipitation. Finally, we carried out clinical evaluations in patients with atherosclerosis to evaluate the relevance of PUNISHER in this kind of disease. Findings: In our study, we observed that Punisher suppressed the apoptosis of VSMC which potentially contributed to the progression of atherosclerosis. Intriguingly, Punisher was proved to regulate mitochondria fission and fusion as well as mitochondrial functions in VSMC. Mechanistically, Punisher serves as a ceRNA to regulate downstream target genes. It directly binds to miR-664a-5p and consequently regulates its target OPA1, which regulates the biological function of VSMC. Particularly, these results were in accordance with findings obtained with the clinical evaluation of patients with atherosclerosis. Our data was the first time to investigate the close relationship among OPA1, mitochondrial homeostatis, VSMC apoptosis and atherosclerosis. Interpretation: lncRNA Punisher and miR-664a-5p could serve as the novel and potential targets in the diagnosis and therapeutics of cardiovascular disease. Funding Statement: This work was supported by National Natural Science Foundation of China (No. 81870331, 31701208), Shandong Province: Taishan Scholars Project (tsqn201812044), China Postdoctoral Science Foundation (No. 2017M612189, 2016M590616), Natural Science Foundation of Shandong Province (No. ZR2017MC067), and The People’s livelihood science and technology project of Qingdao (No. 18-2-2-65-jch). Declaration of Interests: The authors have declared that no competing interest exists. Ethics Approval Statement: The research was approved by the Institutional Review Boards of Qingdao University Health Science Center. Informed consent was obtained from all participants prior to study participation. The housing, care and all the experimental procedures were approved by the Animal Care Committee.

Succinate is a metabolite in tricarboxylic acid cycle (TCA) which plays a central role in mitochondrial activity. Excess succinate is known to be transported out of cytosol where it activates succinate receptor (SUCNR1) to enhance inflammation in various contexts. However, the intracellular role of succinate beyond an intermediate metabolite and prior being released extracellularly, is not well characterized. Lipopolysaccharide (LPS) stimulates the elevation of intracellular succinate levels. To reveal the function of intracellular succinate associated with LPS stimulated inflammatory response in microglial cells, we assessed the levels of ROS, cytokines production and mitochondrial fission in primary microglia pretreated with cell-permeable diethyl succinate mimicking increased intracellular succinate. Our results suggest that elevated intracellular succinate exerts a protective role in primary microglia by preventing their conversion into the pro-inflammatory M1 phenotype induced by LPS. This protective effect is SUCNR1 independent and mediated by reducing mitochondrial fission and cellular ROS production.