Mitochondria on Guard: Role of Mitochondrial Fusion and Fission in the Regulation of Apoptosis

PRDX4 mitigates diabetic retinopathy by inhibiting reactive gliosis, apoptosis, ER stress, oxidative stress, and mitochondrial dysfunction in Müller cells

Diabetic retinopathy (DR) is a neurovascular complication of diabetes. As a crucial player in the retinal physiology, Müller cells are affected in DR, impairments of Müller cell function lead to retinal malfunctions. Therefore, searching for approaches to mitigate diabetes-induced injury in Müller cells is imperative for delaying DR. Peroxiredoxin 4 (PRDX4), an important endoplasmic reticulum (ER)-resident antioxidant, was explored in this study for its potential protective role against DR. Streptozotocin-induced mouse model of diabetes and high glucose (HG)-induced Müller cells were utilized to assess the impact of PRDX4. Compared with WT mice, PRDX4 knockout exacerbated retinal neurodegeneration, reactive gliosis, cell apoptosis, ER stress, oxidative stress, and mitochondrial dysfunction in diabetic retinas. Knockdown of PRDX4 aggravated HG-induced reactive gliosis, apoptosis, ER stress, oxidative stress, and mitochondrial dysfunction in Müller cells. Conversely, PRDX4 overexpression in Müller cells protected against HG-induced cell damage. Mechanistically, PRDX4 promoted the degradation of dipeptidyl peptidase-4, which is associated with DR in type 1 diabetics, thereby alleviating HG-stimulated Müller cell abnormalities. Our study indicated that PRDX4 is a crucial protective regulator in DR progression via destabilization of dipeptidyl peptidase-4 protein and suggested that enhancement of PRDX4 level may represent a promising approach for treating DR.

Mitochondrial elongation confers protection against doxorubicin-induced cardiotoxicity

Doxorubicin (DOX)-induced cardiac damage remains a leading cause of death amongst cancer survivors. DOX-induced cardiotoxicity (DIC) is mediated by disturbed mitochondrial dynamics, but it remains debated that the mechanisms by which DOX disrupted equilibrium between mitochondrial fission and fusion. In the present study, we observed that DOX induced mitochondrial elongation in multiple cardiovascular cell lines. Mechanically, DOX not only downregulated the mitochondrial fusion proteins including Mitofusin 1/2 (MFN1/2) and Optic atrophy 1 (OPA1), but also induced lower motility of dynamin-related protein 1(Drp1) and its phosphorylation on 637 serine, which could inhibit mitochondrial fission. Interestingly, DOX failed to induce mitochondrial elongation in cardiomyocytes co-treated with protein kinase A (PKA) inhibitor H89 or expressing phosphodeficient Drp1-S637A variants. Besides, carbonyl cyanide 3-chlorophenylhydrazone (CCCP) was able to blocked the mitochondrial elongation induced by DOX treatment, which could be phenocopied by OPA1 knockdown. Therefore, we speculated that DOX inhibited mitochondrial fission and fusion simultaneously, yet enabled mitochondrial fusion dominate the mitochondrial dynamics, resulting in mitochondrial elongation as the main manifestation. Notably, blocking mitochondrial elongation by inhibiting Drp1-S637 phosphorylation or OPA1 knockdown aggravated DOX-induced cardiomyocytes death. Based on these results, we propose a novel mechanistic model that DOX-induced mitochondrial elongation is attributed to the equilibrium disturbance of mitochondrial dynamics, which serves as an adaptive response and confers protection against DIC.

Suppressing mitochondrial inner membrane protein (IMMT) inhibits the proliferation of breast cancer cells through mitochondrial remodeling and metabolic regulation

Metabolic reprogramming is widely recognized as a hallmark of malignant tumors, and the targeting of metabolism has emerged as an appealing approach for cancer treatment. Mitochondria, as pivotal organelles, play a crucial role in the metabolic regulation of tumor cells, and their morphological and functional alterations are intricately linked to the biological characteristics of tumors. As a key regulatory subunit of mitochondria, mitochondrial inner membrane protein (IMMT), plays a vital role in degenerative diseases, but its role in tumor is almost unknown. The objective of this research was to investigate the roles that IMMT play in the development and progression of breast cancer (BC), as well as to elucidate the underlying biological mechanisms that drive these effects. In this study, it was confirmed that the expression of IMMT in BC tissues was significantly higher than that in normal tissues. The analysis of The Cancer Genome Atlas (TCGA) database revealed that IMMT can serve as an independent prognostic factor for BC patients. Additionally, verification in clinical specimens of BC demonstrated a positive association between high IMMT expression and larger tumor size (> 2 cm), Ki-67 expression (> 15%), and HER-2 status. Furthermore, in vitro experiments have substantiated that the suppression of IMMT expression resulted in a reduction in cell proliferation and alterations in mitochondrial cristae, concomitant with the liberation of cytochrome c, but it did not elicit mitochondrial apoptosis. Through Gene Set Enrichment Analysis (GSEA) analysis, we have predicted the associated metabolic genes and discovered that IMMT potentially modulates the advancement of BC through its interaction with 16 metabolic-related genes, and the changes in glycolysis related pathways have been validated in BC cell lines after IMMT inhibition. Consequently, this investigation furnishes compelling evidence supporting the classification of IMMT as prognostic marker in BC, and underscoring its prospective utility as a novel target for metabolic therapy.

The meaning of adaptation in aging: insights from cellular senescence, epigenetic clocks and stem cell alterations

With recent rapid progress in research on aging, there is increasing evidence that many features commonly considered to be mechanisms or drivers of aging in fact represent adaptations. Here, we examine several such features, including cellular senescence, epigenetic aging and stem cell alterations. We draw a distinction between the causes and consequences of aging and define short-term consequences as 'responses' and long-term ones as 'adaptations'. We also discuss 'damaging adaptations', which despite having beneficial effects in the short term, lead to exacerbation of the initial insult and acceleration of aging. Features commonly recognized as 'basic mechanisms of the aging process' are critically examined for the possibility of their adaptation-driven emergence from processes such as cell competition and the wound-like features of the aging body. Finally, we speculate on the meaning of these interactions for the aging process and their relevance for the development of antiaging interventions.

Regulation of Normal and Neoplastic Proliferation and Metabolism by the Extended Myc Network

The Myc Network, comprising a small assemblage of bHLH-ZIP transcription factors, regulates many hundreds to thousands of genes involved in proliferation, energy metabolism, translation and other activities. A structurally and functionally related set of factors known as the Mlx Network also supervises some of these same functions via the regulation of a more limited but overlapping transcriptional repertoire. Target gene co-regulation by these two Networks is the result of their sharing of three members that suppress target gene expression as well as by the ability of both Network's members to cross-bind one another's consensus DNA sites. The two Networks also differ in that the Mlx Network's control over transcription is positively regulated by several glycolytic pathway intermediates and other metabolites. These distinctive properties, functions and tissue expression patterns potentially allow for sensitive control of gene regulation in ways that are differentially responsive to environmental and metabolic cues while allowing for them to be both rapid and of limited duration. This review explores how such control might occur. It further discusses how the actual functional dependencies of the Myc and Mlx Networks rely upon cellular context and how they may differ between normal and neoplastic cells. Finally, consideration is given to how future studies may permit a more refined understanding of the functional interrelationships between the two Networks.

Mitochondrial Dynamics: Pathogenesis and Therapeutic Targets of Vascular Diseases

Vascular diseases, particularly atherosclerosis, are associated with high morbidity and mortality. Endothelial cell (EC) or vascular smooth muscle cell (VSMC) dysfunction leads to blood vessel abnormalities, which cause a series of vascular diseases. The mitochondria are the core sites of cell energy metabolism and function in blood vessel development and vascular disease pathogenesis. Mitochondrial dynamics, including fusion and fission, affect a variety of physiological or pathological processes. Multiple studies have confirmed the influence of mitochondrial dynamics on vascular diseases. This review discusses the regulatory mechanisms of mitochondrial dynamics, the key proteins that mediate mitochondrial fusion and fission, and their potential effects on ECs and VSMCs. We demonstrated the possibility of mitochondrial dynamics as a potential target for the treatment of vascular diseases.

Fundamentals of Membrane Lipid Replacement: A Natural Medicine Approach to Repairing Cellular Membranes and Reducing Fatigue, Pain, and Other Symptoms While Restoring Function in Chronic Illnesses and Aging

Membrane Lipid Replacement (MLR) uses natural membrane lipid supplements to safely replace damaged, oxidized lipids in membranes in order to restore membrane function, decrease symptoms and improve health. Oral MLR supplements contain mixtures of cell membrane glycerolphospholipids, fatty acids, and other lipids, and can be used to replace and remove damaged cellular and intracellular membrane lipids. Membrane injury, caused mainly by oxidative damage, occurs in essentially all chronic and acute medical conditions, including cancer and degenerative diseases, and in normal processes, such as aging and development. After ingestion, the protected MLR glycerolphospholipids and other lipids are dispersed, absorbed, and internalized in the small intestines, where they can be partitioned into circulating lipoproteins, globules, liposomes, micelles, membranes, and other carriers and transported in the lymphatics and blood circulation to tissues and cellular sites where they are taken in by cells and partitioned into various cellular membranes. Once inside cells, the glycerolphospholipids and other lipids are transferred to various intracellular membranes by lipid carriers, globules, liposomes, chylomicrons, or by direct membrane-membrane interactions. The entire process appears to be driven by 'bulk flow' or mass action principles, where surplus concentrations of replacement lipids can stimulate the natural exchange and removal of damaged membrane lipids while the replacement lipids undergo further enzymatic alterations. Clinical studies have demonstrated the advantages of MLR in restoring membrane and organelle function and reducing fatigue, pain, and other symptoms in chronic illness and aging patients.

Axotomy Induces Drp1-Dependent Fragmentation of Axonal Mitochondria

It is well established that CNS axons fail to regenerate, undergo retrograde dieback, and form dystrophic growth cones due to both intrinsic and extrinsic factors. We sought to investigate the role of axonal mitochondria in the axonal response to injury. A viral vector (AAV) containing a mitochondrially targeted fluorescent protein (mitoDsRed) as well as fluorescently tagged LC3 (GFP-LC3), an autophagosomal marker, was injected into the primary motor cortex, to label the corticospinal tract (CST), of adult rats. The axons of the CST were then injured by dorsal column lesion at C4-C5. We found that mitochondria in injured CST axons near the injury site are fragmented and fragmentation of mitochondria persists for 2 weeks before returning to pre-injury lengths. Fragmented mitochondria have consistently been shown to be dysfunctional and detrimental to cellular health. Inhibition of Drp1, the GTPase responsible for mitochondrial fission, using a specific pharmacological inhibitor (mDivi-1) blocked fragmentation. Additionally, it was determined that there is increased mitophagy in CST axons following Spinal cord injury (SCI) based on increased colocalization of mitochondria and LC3. In vitro models revealed that mitochondrial divalent ion uptake is necessary for injury-induced mitochondrial fission, as inhibiting the mitochondrial calcium uniporter (MCU) using RU360 prevented injury-induced fission. This phenomenon was also observed in vivo. These studies indicate that following the injury, both in vivo and in vitro, axonal mitochondria undergo increased fission, which may contribute to the lack of regeneration seen in CNS neurons.

Astragalus protects PC12 cells from 6-hydroxydopamine-induced neuronal damage: A serum pharmacological study

Accumulating evidence has already indicated that traditional Chinese medicine (TCM) possesses tremendous potential for treating neurodegenerative diseases. Astragalus, also named Huangqi, is a famous traditional medical herb that can be applied to treat cerebral ischemia and prevent neuronal degeneration. Nevertheless, the underlying mechanisms remain largely unexplored. In the present study, Astragalus-containing serum (ASMES) was prepared and added into the culture medium of PC12 cells to explore its neuroprotective effect on 6-hydroxydopamine (6-OHDA)-caused neuronal toxicity. Our data showed that ASMES significantly ameliorated the cellular viability of cultured PC12 cells against the neurotoxicity induced by 6-OHDA (P < 0.05). Moreover, ASMES significantly decreased the cell apoptosis triggered by 6-OHDA (P < 0.01). Furthermore, 2',7'-dichlorofluorescin diacetate assay was performed to detect the changes in oxidative stress, and we showed that 6-OHDA elevated the production of reactive oxygen species (ROS), whereas ASMES significantly reversed these changes (P < 0.01). Besides, mitochondrial membrane potential (MMP) assay showed that ASMES could restore 6-OHDA-damaged MMP in cultured PC12 cells (P < 0.05). In conclusion, Astragalus could protect PC12 cells from 6-OHDA-caused neuronal toxicity, and possibly, the ROS-mediated apoptotic pathway participated in this process. Collectively, our findings provided valuable insights into the potential in treatment of neurodegenerative diseases.

Gastrodin protects H9c2 cardiomyocytes against oxidative injury by ameliorating imbalanced mitochondrial dynamics and mitochondrial dysfunction

Gastrodin (GAS) is the main bioactive component of Tianma, a traditional Chinese medicine widely used to treat neurological disorders as well as cardio- and cerebrovascular diseases. In the present study, the protective effects of GAS on H9c2 cells against ischemia-reperfusion (IR)-like injury were found to be related to decreasing of oxidative stress. Furthermore, GAS could protect H9c2 cells against oxidative injury induced by H2O2. Pretreatment of GAS at 20, 50, and 100 μM for 4 h significantly ameliorated the decrease in cell viability and increase in apoptosis of H9c2 cells treated with 400 μM H2O2 for 3 h. Furthermore, we showed that H2O2 treatment induced fragmentation of mitochondria and significant reduction in networks, footprint, and tubular length of mitochondria; H2O2 treatment strongly inhibited mitochondrial respiration; H2O2 treatment induced a decrease in the expression of mitochondrial fusion factors Mfn2 and Opa1, and increase in the expression of mitochondrial fission factor Fis1. All these alterations in H2O2-treated H9c2 cells could be ameliorated by GAS pretreatment. Moreover, we revealed that GAS pretreatment enhanced the nuclear translocation of Nrf2 under H2O2 treatment. Knockdown of Nrf2 expression abolished the protective effects of GAS on H2O2-treated H9c2 cells. Our results suggest that GAS may protect H9c2 cardiomycytes against oxidative injury via increasing the nuclear translocation of Nrf2, regulating mitochondrial dynamics, and maintaining the structure and functions of mitochondria.

Role of Mitofusins and Mitophagy in Life or Death Decisions

Mitochondria entail an incredible dynamism in their morphology, impacting death signaling and selective elimination of the damaged organelles. In turn, by recycling the superfluous or malfunctioning mitochondria, mostly prevalent during aging, mitophagy contributes to maintain a healthy mitochondrial network. Mitofusins locate at the outer mitochondrial membrane and control the plastic behavior of mitochondria, by mediating fusion events. Besides deciding on mitochondrial interconnectivity, mitofusin 2 regulates physical contacts between mitochondria and the endoplasmic reticulum, but also serves as a decisive docking platform for mitophagy and apoptosis effectors. Thus, mitofusins integrate multiple bidirectional inputs from and into mitochondria and ensure proper energetic and metabolic cellular performance. Here, we review the role of mitofusins and mitophagy at the cross-road between life and apoptotic death decisions. Furthermore, we highlight the impact of this interplay on disease, focusing on how mitofusin 2 and mitophagy affect non-alcoholic fatty liver disease.

Activation of TNFR1 and TLR4 following oxygen glucose deprivation promotes mitochondrial fission in C6 astroglial cells

Astrocytes have emerged as active players in the innate immune response triggered by various types of insults. Recent literature suggests that mitochondria are key participants in innate immunity. The present study investigates the role of ischemia-induced innate immune response on p65/PGC-1α mediated mitochondrial dynamics in C6 astroglial cells. OGD conditions induced astroglial differentiation in C6 cells and increased the expression of hypoxia markers; HIF-1α, HO-1 and Cox4i2. OGD conditions resulted in induction of innate immune response in terms of expression of TNFR1 and TLR4 along with increase in IL-6 and TNF-α levels. OGD conditions resulted in decreased expression of I-κB with a concomitant increase in phos-p65 levels. The expression of PGC-1α, a key regulator of mitochondrial biogenesis, was also increased. Immunochemical staining suggested that phos-p65 and PGC-1α was co-localized. Studies on mitochondrial fusion (Mfn-1) and fission (DRP1) markers revealed shift toward fission. In addition, mitochondrial membrane potential decreased with increased DNA degradation and apoptosis confirming mitochondrial fission under OGD conditions. However, inhibition of phos-p65 by MG132 reduced the co-localization of phos-p65/ PGC-1α and significantly increased the Mfn-1 expression. The findings demonstrate the involvement of TNFR1 and TLR4 mediated immune response followed by interaction between phos-p65 and PGC-1α in promoting fission in C6 cells under hypoxic condition.

Renalase Attenuates Mouse Fatty Liver Ischemia/Reperfusion Injury through Mitigating Oxidative Stress and Mitochondrial Damage via Activating SIRT1

Liver ischemia/reperfusion (IR) injury is a severe complication of liver surgery. Moreover, nonalcoholic fatty liver disease (NAFLD) patients are particularly vulnerable to IR injury, with higher rates of postoperative morbidity and mortality after liver surgeries. Our previous study found that renalase (RNLS) was highly sensitive and responsive to oxidative stress, which may be a promising biomarker for the evaluation of the severity of liver IR injury. However, the role of RNLS in liver IR injury remains unclear. In the present study, we intensively explored the role and mechanism of RNLS in fatty liver IR injury in vivo and in vitro. C57BL/6 mice were divided into 2 groups feeding with high-fat diet (HFD) and control diet (CD), respectively. After 20 weeks' feeding, they were suffered from portal triad blockage and reflow to induce liver IR injury. Additionally, oleic acid (OA) and tert-butyl hydroperoxide (t-BHP) were used in vitro to induce steatotic hepatocytes and to simulate ROS burst and mimic cellular oxidative stress following portal triad blockage and reflow, respectively. Our data showed that RNLS was downregulated in fatty livers, and RNLS administration effectively attenuated IR injury by reducing ROS production and improving mitochondrial function through activating SIRT1. Additionally, the downregulation of RNLS in the fatty liver was mediated by a decrease of signal transduction and activator of transcription 3 (STAT3) expression under HFD conditions. These findings make RNLS a promising therapeutic strategy for the attenuation of liver IR injury.

Mitochondria as playmakers of apoptosis, autophagy and senescence

Mitochondria are the key energy-producing organelles and cellular source of reactive species. They are responsible for managing cell life and death by a balanced homeostasis passing through a network of structures, regulated principally via fission and fusion. Herein we discuss about the most advanced findings considering mitochondria as dynamic biophysical systems playing compelling roles in the regulation of energy metabolism in both physiologic and pathologic processes controlling cell death and survival. Precisely, we focus on the mitochondrial commitment to the onset, maintenance and counteraction of apoptosis, autophagy and senescence in the bioenergetic reprogramming of cancer cells. In this context, looking for a pharmacological manipulation of cell death processes as a successful route for future targeted therapies, there is major biotechnological challenge in underlining the location, function and molecular mechanism of mitochondrial proteins. Based on the critical role of mitochondrial functions for cellular health, a better knowledge of the main molecular players in mitochondria disfunction could be decisive for the therapeutical control of degenerative diseases, including cancer.

Mitochondrial network structure homeostasis and cell death

Mitochondria are the major cellular energy‐producing organelles and intracellular source of reactive oxygen species. These organelles are responsible for driving cell life and death through mitochondrial network structure homeostasis, which is determined by a balance of fission and fusion. Recent advances revealed that a number of components of the fission and fusion machinery, including dynamin‐related protein 1 (Drp1), mitofusin1/2 (Mfn1/2) and Optic atrophy 1 (OPA1), that have been implicated in mitochondrial shape changes are indispensible for autophagy, apoptosis and necroptosis. Drp1 is the main regulator of mitochondrial fission and has become a key point of contention. The controversy focuses on whether Drp1 is directly involved in the regulation of cell death and, if involved, whether is it a stimulator or a negative regulator of cell death. Here, we examine the relevance of the homeostasis of the mitochondrial network structure in 3 different types of cell death, including autophagy, apoptosis and necroptosis. Furthermore, a variety of cancers often exhibit a fragmented mitochondrial phenotype. Thus, the fragmented ratio can reflect tumor progression that predicts prognosis and therapeutic response. In addition, we investigate whether the targeting of the mitochondrial fission protein Drp1 could be a novel therapeutic approach.

Mitochondrial fission and mitophagy depend on cofilin-mediated actin depolymerization activity at the mitochondrial fission site

Mitochondria fission and mitophagy are fundamentally crucial to cellular physiology and play important roles in cancer progression. Developing a comprehensive understanding of the molecular mechanism underlying mitochondrial fission and mitophagy will provide novel strategies for cancer prevention and treatment. Actin has been shown to participate in mitochondrial fission and mitophagy regulation. Cofilin is best known as an actin-depolymerizing factor. However, the molecular mechanism by which cofilin regulates mitochondrial fission and mitophagy remains largely unknown. Here we report that knockdown of cofilin attenuates and overexpression of cofilin potentiates mitochondrial fission as well as PINK1/PARK2-dependent mitophagy induced by staurosporine (STS), etoposide (ETO), and carbonyl cyanide 3-chlorophenylhydrazone (CCCP). Cofilin-mediated-PINK1 (PTEN-induced putative kinase 1) accumulation mainly depends on its regulation of mitochondrial proteases, including peptidase mitochondrial processing beta (MPPβ), presenilin-associated rhomboid-like protease (PARL), and ATPase family gene 3-like 2 (AFG3L2), via mitochondrial membrane potential activity. We also found that the interaction and colocalization of G-actin/F-actin with cofilin at mitochondrial fission sites undergo constriction after CCCP treatment. Pretreatment with the actin polymerization inhibitor latrunculin B (LatB) increased and actin-depolymerization inhibitor jasplakinolide (Jas) decreased mitochondrial translocation of actin induced by STS, ETO, and CCCP. Both LatB and Jas abrogated CCCP-mediated mitochondrial fission and mitophagy. Our data suggest that G-actin is the actin form that is translocated to mitochondria, and the actin-depolymerization activity regulated by cofilin at the mitochondrial fission site is crucial for inducing mitochondrial fission and mitophagy.

The Role for Myc in Coordinating Glycolysis, Oxidative Phosphorylation, Glutaminolysis, and Fatty Acid Metabolism in Normal and Neoplastic Tissues

That cancer cells show patterns of metabolism different from normal cells has been known for over 50 years. Yet, it is only in the past decade or so that an appreciation of the benefits of these changes has begun to emerge. Altered cancer cell metabolism was initially attributed to defective mitochondria. However, we now realize that most cancers do not have mitochondrial mutations and that normal cells can transiently adopt cancer-like metabolism during periods of rapid proliferation. Indeed, an encompassing, albeit somewhat simplified, conceptual framework to explain both normal and cancer cell metabolism rests on several simple premises. First, the metabolic pathways used by cancer cells and their normal counterparts are the same. Second, normal quiescent cells use their metabolic pathways and the energy they generate largely to maintain cellular health and organelle turnover and, in some cases, to provide secreted products necessary for the survival of the intact organism. By contrast, undifferentiated cancer cells minimize the latter functions and devote their energy to producing the anabolic substrates necessary to maintain high rates of unremitting cellular proliferation. Third, as a result of the uncontrolled proliferation of cancer cells, a larger fraction of the metabolic intermediates normally used by quiescent cells purely as a source of energy are instead channeled into competing proliferation-focused and energy-consuming anabolic pathways. Fourth, cancer cell clones with the most plastic and rapidly adaptable metabolism will eventually outcompete their less well-adapted brethren during tumor progression and evolution. This attribute becomes increasingly important as tumors grow and as their individual cells compete in a constantly changing and inimical environment marked by nutrient, oxygen, and growth factor deficits. Here, we review some of the metabolic pathways whose importance has gained center stage for tumor growth, particularly those under the control of the c-Myc (Myc) oncoprotein. We discuss how these pathways differ functionally between quiescent and proliferating normal cells, how they are kidnapped and corrupted during the course of transformation, and consider potential therapeutic strategies that take advantage of common features of neoplastic and metabolic disorders.

YiQiFuMai Powder Injection Protects against Ischemic Stroke via Inhibiting Neuronal Apoptosis and PKCδ/Drp1-Mediated Excessive Mitochondrial Fission

YiQiFuMai (YQFM) powder injection has been reported to be used in cardiovascular and nervous system diseases with marked efficacy. However, as a treatment against diseases characterized by hypoxia, lassitude, and asthenia, the effects and underlying mechanisms of YQFM in neuronal mitochondrial function and dynamics have not been fully elucidated. Here, we demonstrated that YQFM inhibited mitochondrial apoptosis and activation of dynamin-related protein 1 (Drp1) in cerebral ischemia-injured rats, producing a significant improvement in cerebral infarction and neurological score. YQFM also attenuated oxidative stress-induced mitochondrial dysfunction and apoptosis through increasing ATP level and mitochondria membrane potential (Δψm), inhibiting ROS production, and regulating Bcl-2 family protein levels in primary cultured neurons. Moreover, YQFM inhibited excessive mitochondrial fission, Drp1 phosphorylation, and translocation from cytoplasm to mitochondria induced by oxidative stress. We provided the first evidence that YQFM inhibited the activation, association, and translocation of PKCδ and Drp1 upon oxidative stress. Taken together, we demonstrate that YQFM ameliorates ischemic stroke-induced neuronal apoptosis through inhibiting mitochondrial dysfunction and PKCδ/Drp1-mediated excessive mitochondrial fission. These findings not only put new insights into the unique neuroprotective properties of YQFM associated with the regulation of mitochondrial function but also expand our understanding of the underlying mechanisms of ischemic stroke.

Hydrogen sulfide inhibits mitochondrial fission in neuroblastoma N2a cells through the Drp1/ERK1/2 signaling pathway

Hydrogen sulfide (H2S) has been demonstrated to have various effects on mitochondrial function. The aim of the present study was to investigate the effects of H2S on mitochondrial fission and the potential underlying mechanisms of these effects. Transmission electron microscopy analysis demonstrated that sodium hydrosulfide (NaHS, a donor of H2S) inhibited mitochondrial fission in a dose‑ and time‑dependent manner. Treating neuro‑2a (N2a) mouse neuroblastoma cells with 400 µM NaHS for 16 h significantly increased the % of elongated mitochondria and reduced the number of mitochondria per cell compared with untreated cells. In addition, the viability and ATP generation of N2a cells that were treated with various concentrations of NaHS was examined. The results demonstrated that treatment with 400 and 600 µM NaHS increased cell viability and ATP generation compared with untreated cells. To further understand the effects of H2S on mitochondrial morphology, the protein and mRNA expression levels of dynamin 1 like (Dnm1l, also known as Drp1) were examined, and the results demonstrated that NaHS dose‑dependently reduced Drp1 mRNA and protein levels, consistent with the mitochondrial morphology changes. To determine whether H2S affects mitochondrial morphology through Drp1 expression, Drp1 was overexpressed in N2a cells using a lentivirus encoding the Drp1 cDNA. It was observed that Drp1 overexpression reversed the effects of NaHS. Furthermore, NaHS promoted the phosphorylation of extracellular signal‑regulated kinase (ERK) 1/2, and the effects of NaHS on Drp1 expression were abolished by an ERK1/2 inhibitor (PD98059). The results of the present study indicate that the H2S‑induced decrease in Drp1 mRNA and protein levels and mitochondrial fission may involve the ERK1/2 signaling pathway. The present study suggests that H2S may be used in the future as a potential therapeutic for diseases that may be mediated by abnormal mitochondria fragmentation, such as Alzheimer's disease.

Membrane Lipid Replacement for chronic illnesses, aging and cancer using oral glycerolphospholipid formulations with fructooligosaccharides to restore phospholipid function in cellular membranes, organelles, cells and tissues

Membrane Lipid Replacement is the use of functional, oral supplements containing mixtures of cell membrane glycerolphospholipids, plus fructooligosaccharides (for protection against oxidative, bile acid and enzymatic damage) and antioxidants, in order to safely replace damaged, oxidized, membrane phospholipids and restore membrane, organelle, cellular and organ function. Defects in cellular and intracellular membranes are characteristic of all chronic medical conditions, including cancer, and normal processes, such as aging. Once the replacement glycerolphospholipids have been ingested, dispersed, complexed and transported, while being protected by fructooligosaccharides and several natural mechanisms, they can be inserted into cell membranes, lipoproteins, lipid globules, lipid droplets, liposomes and other carriers. They are conveyed by the lymphatics and blood circulation to cellular sites where they are endocytosed or incorporated into or transported by cell membranes. Inside cells the glycerolphospholipids can be transferred to various intracellular membranes by lipid globules, liposomes, membrane-membrane contact or by lipid carrier transfer. Eventually they arrive at their membrane destinations due to 'bulk flow' principles, and there they can stimulate the natural removal and replacement of damaged membrane lipids while undergoing further enzymatic alterations. Clinical trials have shown the benefits of Membrane Lipid Replacement in restoring mitochondrial function and reducing fatigue in aged subjects and chronically ill patients. Recently Membrane Lipid Replacement has been used to reduce pain and other symptoms as well as removing hydrophobic chemical contaminants, suggesting that there are additional new uses for this safe, natural medicine supplement. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.

Inhibition of dynamin-related protein 1 protects against myocardial ischemia-reperfusion injury in diabetic mice

Background

Many cardioprotective pharmacological agents failed to exert their protective effects in diabetic hearts subjected to myocardial ischemia/reperfusion (MI/R). Identify the molecular basis linking diabetes with MI/R injury is scientifically important and may provide effective therapeutic approaches. Dynamin-related protein 1 (Drp1)-mediated mitochondrial fission plays an important role in MI/R injury under non-diabetic conditions. Importantly, recent studies indicated that Drp1-mediated mitochondrial fission is enhanced in the myocardium of diabetic mice. The above evidences suggested that Drp1 may be one critical molecule linking diabetes with MI/R injury. We hypothesized that inhibition of Drp1 may be effective to reduce MI/R injury in diabetic hearts.

Methods

High-fat diet and streptozotocin-induced diabetic mice were subjected to MI/R or sham operation. Mdivi-1 (1.2 mg/kg), a small molecule inhibitor of Drp1 or vehicle was administrated 15 min before the onset of reperfusion. Outcome measures included mitochondrial morphology, mitochondrial function, myocardial injury, cardiac function and oxidative stress.

Results

Mitochondrial fission was significantly increased following MI/R as evidenced by enhanced translocation of Drp1 to mitochondria and decreased mitochondrial size. Delivery of Mdivi-1 into diabetic mice markedly inhibited Drp1 translocation to the mitochondria and reduced mitochondrial fission following MI/R. Inhibition of Drp1 in diabetic hearts improved mitochondrial function and cardiac function following MI/R. Moreover, inhibition of Drp1 reduced myocardial infarct size and serum cardiac troponin I and lactate dehydrogenase activities. These cardioprotective effects were associated with decreased cardiomyocyte apoptosis and malondialdehyde production and increased activities of antioxidant enzyme manganese superoxide dismutase.

Conclusions

Pharmacological inhibition of Drp1 prevents mitochondrial fission and reduces MI/R injury in diabetic mice. The findings suggest Drp1 may be a potential novel therapeutic target for diabetic cardiac complications.

Altered Mitochondrial Anatomy of Trigeminal Ganglia Neurons in Diabetes

Neurons from sensory ganglia are exposed to oxidative attack in diabetes. Altered mitochondrial morphologies are due to impaired dynamics (fusion, fission) and to cristae remodeling. This study aimed to evaluate using transmission electron microscopy mitochondrial changes in diabetic trigeminal ganglia suggestive for ignition of apoptosis, in absence of "classical" morphological signs of apoptosis. We used samples of trigeminal ganglia (from six type 2 diabetes human donors and five streptozotocin (STZ)-induced diabetic rats). In human diabetic samples we found three main distributions of mitochondria: (a) small "dark" normal mitochondria, seemingly resulted from fission processes; (b) small "dark" damaged mitochondria, with side-vesiculations (single- and double-coated), large matrix vesicles and cytosolic leakage of reactive species, mixed with larger "light" mitochondria, swollen, and with crystolysis; (c) prevailing "light" mitochondria. In STZ-treated rats a type (c) distribution prevailed, except for nociceptive neurons where we found a different distribution: large and giant mitochondria, suggestive for impaired mitochondrial fission, mitochondrial fenestrations, matrix vesicles interconnected by lamellar cristae, and mitochondrial leakage into the cytosol. Thus, the ultrastructural pattern of mitochondria damage in diabetic samples of sensory neurons may provide clues on the initiation of intrinsic apoptosis, even if the classical morphological signs of apoptosis are not present. Further studies, combining use of biochemical and ultrastructural techniques, may allow a better quantification of the degree in which mitochondrial damage, with membrane alterations and cytosolic leaks, may be used as morphological signs suggesting the point-of-no return for apoptosis. Anat Rec, 299:1561-1570, 2016. © 2016 Wiley Periodicals, Inc.

Hypothermia-induced ischemic tolerance is associated with Drp1 inhibition in cerebral ischemia-reperfusion injury of mice

Excessive mitochondrial fission activation has been implicated in cerebral ischemia-reperfusion (IR) injury. Hypothermia is effective in preventing cerebral ischemic damage. However, effects of hypothermia on ischemia-induced mitochondrial fission activation is not well known. Therefore, the aim of this study was to investigate whether hypothermia protect the brain by inhibiting mitochondrial fission-related proteins activation following cerebral IR injury. Adult male C57BL/6 mice were subjected to transient forebrain ischemia induced by 15min of bilateral common carotid artery occlusion (BCCAO). Mice were divided into three groups (n=48 each): Hypothermia (HT) group, with mild hypothermia (32-34°C) for 4h; Normothermia (NT) group, similarly as HT group except for cooling; Sham group, with vessels exposed but without occlusion or cooling. Hematoxylin and eosin (HE), Nissl staining, Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining and behavioral testing (n=6 each) demonstrated that hypothermia significantly decreased ischemia-induced neuronal injury. The expressions of Dynamin related protein 1 (Drp1) and Cytochrome C (Cyto C) (n=6 each) in mice hippocampus were measured at 3, 6, 24, and 72h of reperfusion. IR injury significantly increased expressions of total Drp1, phosphorylated Drp1 (P-Drp1 S616) and Cyto C under normothermia. However, mild hypothermia inhibited Drp1 activation and Cyto C cytosolic release, preserved neural cells integrity and reduced neuronal necrosis and apoptosis. These findings indicated that mild hypothermia-induced neuroprotective effects against ischemia-reperfusion injury is associated with suppressing mitochondrial fission-related proteins activation and apoptosis execution.

Age decreases mitochondrial motility and increases mitochondrial size in vascular smooth muscle

KEY POINTS

Age is proposed to be associated with altered structure and function of mitochondria; however, in fully-differentiated cells, determining the structure of more than a few mitochondria at a time is challenging. In the present study, the structures of the entire mitochondrial complements of cells were resolved from a pixel-by-pixel covariance analysis of fluctuations in potentiometric fluorophore intensity during 'flickers' of mitochondrial membrane potential. Mitochondria are larger in vascular myocytes from aged rats compared to those in younger adult rats. A subpopulation of mitochondria in myocytes from aged, but not younger, animals is highly-elongated. Some mitochondria in myocytes from younger, but not aged, animals are highly-motile. Mitochondria that are motile are located more peripherally in the cell than non-motile mitochondria.

ABSTRACT

Mitochondrial function, motility and architecture are each central to cell function. Age-associated mitochondrial dysfunction may contribute to vascular disease. However, mitochondrial changes in ageing remain ill-defined because of the challenges of imaging in native cells. We determined the structure of mitochondria in live native cells, demarcating boundaries of individual organelles by inducing stochastic 'flickers' of membrane potential, recorded as fluctuations in potentiometric fluorophore intensity (flicker-assisted localization microscopy; FaLM). In freshly-isolated myocytes from rat cerebral resistance arteries, FaLM showed a range of mitochondrial X-Y areas in both young adult (3 months; 0.05-6.58 μm(2) ) and aged rats (18 months; 0.05-13.4 μm(2) ). In cells from young animals, most mitochondria were small (mode area 0.051 μm(2) ) compared to aged animals (0.710 μm(2) ). Cells from older animals contained a subpopulation of highly-elongated mitochondria (5.3% were >2 μm long, 4.2% had a length:width ratio >3) that was rare in younger animals (0.15% of mitochondria >2 μm long, 0.4% had length:width ratio >3). The extent of mitochondrial motility also varied. 1/811 mitochondria observed moved slightly (∼0.5 μm) in myocytes from older animals, whereas, in the younger animals, directed and Brownian-like motility occurred regularly (215 of 1135 mitochondria moved within 10 min, up to distance of 12 μm). Mitochondria positioned closer to the cell periphery showed a greater tendency to move. In conclusion, cerebral vascular myocytes from young rats contained small, motile mitochondria. In aged rats, mitochondria were larger, immobile and could be highly-elongated. These age-associated alterations in mitochondrial behaviour may contribute to alterations in cell signalling, energy supply or the onset of proliferation.

Mitochondrial E3 ubiquitin ligase MARCH5 controls mitochondrial fission and cell sensitivity to stress-induced apoptosis through regulation of MiD49 protein

The data presented support a critical role for MARCH5 in the regulation of mitochondrial fission and cell viability. Through ubiquitin- and proteasome-dependent degradation of MiD49, MARCH5 acts as a negative regulator of mitochondrial fission and thereby initiates a mechanism that affords the cell protection from stress-induced apoptosis.

Ubiquitin- and proteasome-dependent outer mitochondrial membrane (OMM)-associated degradation (OMMAD) is critical for mitochondrial and cellular homeostasis. However, the scope and molecular mechanisms of the OMMAD pathways are still not well understood. We report that the OMM-associated E3 ubiquitin ligase MARCH5 controls dynamin-related protein 1 (Drp1)-dependent mitochondrial fission and cell sensitivity to stress-induced apoptosis. MARCH5 knockout selectively inhibited ubiquitination and proteasomal degradation of MiD49, a mitochondrial receptor of Drp1, and consequently led to mitochondrial fragmentation. Mitochondrial fragmentation in MARCH5^−/− cells was not associated with inhibition of mitochondrial fusion or bioenergetic defects, supporting the possibility that MARCH5 is a negative regulator of mitochondrial fission. Both MARCH5 re-expression and MiD49 knockout in MARCH5^−/− cells reversed mitochondrial fragmentation and reduced sensitivity to stress-induced apoptosis. These findings and data showing MARCH5-dependent degradation of MiD49 upon stress support the possibility that MARCH5 regulation of MiD49 is a novel mechanism controlling mitochondrial fission and, consequently, the cellular response to stress.

Autophagy of mitochondria: a promising therapeutic target for neurodegenerative disease

The autophagic process is the only known mechanism for mitochondrial turnover and it has been speculated that dysfunction of autophagy may result in mitochondrial error and cellular stress. Emerging investigations have provided new understanding of how autophagy of mitochondria (also known as mitophagy) is associated with cellular oxidative stress and its impact on neurodegeneration. This impaired autophagic function may be considered as a possible mechanism in the pathogenesis of several neurodegenerative disorders including Parkinson's disease, Alzheimer's disease, multiple sclerosis, amyotrophic lateral sclerosis, and Huntington disease. It can be suggested that autophagy dysfunction along with oxidative stress is considered main events in neurodegenerative disorders. New therapeutic approaches have now begun to target mitochondria as a potential drug target. This review discusses evidence supporting the notion that oxidative stress and autophagy are intimately associated with neurodegenerative disease pathogenesis. This review also explores new approaches that can prevent mitochondrial dysfunction, improve neurodegenerative etiology, and also offer possible cures to the aforementioned neurodegenerative diseases.

Echinacoside Protects against 6-Hydroxydopamine-Induced Mitochondrial Dysfunction and Inflammatory Responses in PC12 Cells via Reducing ROS Production

Parkinson's disease (PD) is a neurodegenerative disorder characterized by progressive loss of dopaminergic (DA) neurons at the substantia nigra. Mitochondrial dysfunction and inflammatory responses are involved in the mechanism of cell damage in PD. 6-Hydroxydopamine (6-OHDA), a dopamine analog, specifically damages dopaminergic neurons. Echinacoside (ECH) is a phenylethanoid glycoside isolated from the stems of Cistanche salsa, showing a variety of neuroprotective effects in previous studies. The present study was to investigate its effect against 6-OHDA-induced neurotoxicity and possible mechanisms in PC12 cells. The results showed that 6-OHDA reduced cell viability, decreased oxidation-reduction activity, decreased mitochondrial membrane potential, and induced mitochondria-mediated apoptosis compared with untreated PC12 cells. However, echinacoside treatment significantly attenuated these changes induced by 6-OHDA. In addition, echinacoside also could significantly alleviate the inflammatory responses induced by 6-OHDA. Further research showed that echinacoside could reduce 6-OHDA-induced ROS production in PC12 cells. These results suggest that the underlying mechanism of echinacoside against 6-OHDA-induced neurotoxicity may be involve in attenuating mitochondrial dysfunction and inflammatory responses by reducing ROS production.

SET overexpression in HEK293 cells regulates mitochondrial uncoupling proteins levels within a mitochondrial fission/reduced autophagic flux scenario

We hypothesized that SET, a protein accumulated in some cancer types and Alzheimer disease, is involved in cell death through mitochondrial mechanisms. We addressed the mRNA and protein levels of the mitochondrial uncoupling proteins UCP1, UCP2 and UCP3 (S and L isoforms) by quantitative real-time PCR and immunofluorescence as well as other mitochondrial involvements, in HEK293 cells overexpressing the SET protein (HEK293/SET), either in the presence or absence of oxidative stress induced by the pro-oxidant t-butyl hydroperoxide (t-BHP). SET overexpression in HEK293 cells decreased UCP1 and increased UCP2 and UCP3 (S/L) mRNA and protein levels, whilst also preventing lipid peroxidation and decreasing the content of cellular ATP. SET overexpression also (i) decreased the area of mitochondria and increased the number of organelles and lysosomes, (ii) increased mitochondrial fission, as demonstrated by increased FIS1 mRNA and FIS-1 protein levels, an apparent accumulation of DRP-1 protein, and an increase in the VDAC protein level, and (iii) reduced autophagic flux, as demonstrated by a decrease in LC3B lipidation (LC3B-II) in the presence of chloroquine. Therefore, SET overexpression in HEK293 cells promotes mitochondrial fission and reduces autophagic flux in apparent association with up-regulation of UCP2 and UCP3; this implies a potential involvement in cellular processes that are deregulated such as in Alzheimer's disease and cancer.

Non-invasive detection of early retinal neuronal degeneration by ultrahigh resolution optical coherence tomography

Optical coherence tomography (OCT) has revolutionises the diagnosis of retinal disease based on the detection of microscopic rather than subcellular changes in retinal anatomy. However, currently the technique is limited to the detection of microscopic rather than subcellular changes in retinal anatomy. However, coherence based imaging is extremely sensitive to both changes in optical contrast and cellular events at the micrometer scale, and can generate subtle changes in the spectral content of the OCT image. Here we test the hypothesis that OCT image speckle (image texture) contains information regarding otherwise unresolvable features such as organelle changes arising in the early stages of neuronal degeneration. Using ultrahigh resolution (UHR) OCT imaging at 800 nm (spectral width 140 nm) we developed a robust method of OCT image analyses, based on spatial wavelet and texture-based parameterisation of the image speckle pattern. For the first time we show that this approach allows the non-invasive detection and quantification of early apoptotic changes in neurons within 30 min of neuronal trauma sufficient to result in apoptosis. We show a positive correlation between immunofluorescent labelling of mitochondria (a potential source of changes in cellular optical contrast) with changes in the texture of the OCT images of cultured neurons. Moreover, similar changes in optical contrast were also seen in the retinal ganglion cell- inner plexiform layer in retinal explants following optic nerve transection. The optical clarity of the explants was maintained throughout in the absence of histologically detectable change. Our data suggest that UHR OCT can be used for the non-invasive quantitative assessment of neuronal health, with a particular application to the assessment of early retinal disease.

Mitochondrial dynamics: biology and therapy in lung cancer

INTRODUCTION

Lung cancer mortality rates remain at unacceptably high levels. Although mitochondrial dysfunction is a characteristic of most tumor types, mitochondrial dynamics are often overlooked. Altered rates of mitochondrial fission and fusion are observed in lung cancer and can influence metabolic function, proliferation and cell survival.

AREAS COVERED

In this review, the authors outline the mechanisms of mitochondrial fission and fusion. They also identify key regulatory proteins and highlight the roles of fission and fusion in metabolism and other cellular functions (e.g., proliferation, apoptosis) with an emphasis on lung cancer and the interaction with known cancer biomarkers. They also examine the current therapeutic strategies reported as altering mitochondrial dynamics and review emerging mitochondria-targeted therapies.

EXPERT OPINION

Mitochondrial dynamics are an attractive target for therapeutic intervention in lung cancer. Mitochondrial dysfunction, despite its molecular heterogeneity, is a common abnormality of lung cancer. Targeting mitochondrial dynamics can alter mitochondrial metabolism, and many current therapies already non-specifically affect mitochondrial dynamics. A better understanding of mitochondrial dynamics and their interaction with currently identified cancer 'drivers' such as Kirsten-Rat Sarcoma Viral Oncogene homolog will lead to the development of novel therapeutics.

Purpurin triggers caspase-independent apoptosis in Candida dubliniensis biofilms

Candida dubliniensis is an important human fungal pathogen that causes oral infections in patients with AIDS and diabetes mellitus. However, C. Dubliniensis has been frequently reported in bloodstream infections in clinical settings. Like its phylogenetically related virulent species C. albicans, C. Dubliniensis is able to grow and switch between yeast form and filamentous form (hyphae) and develops biofilms on both abiotic and biotic surfaces. Biofilms are recalcitrant to antifungal therapies and C. Dubliniensis readily turns drug resistant upon repeated exposure. More than 80% of infections are associated with biofilms. Suppression of fungal biofilms may therefore represent a viable antifungal strategy with clinical relevance. Here, we report that C. dubliniensis biofilms were inhibited by purpurin, a natural anthraquinone pigment isolated from madder root. Purpurin inhibited C. dubliniensis biofilm formation in a concentration-dependent manner; while mature biofilms were less susceptible to purpurin. Scanning electron microscopy (SEM) analysis revealed scanty structure consisting of yeast cells in purpurin-treated C. dubliniensis biofilms. We sought to delineate the mechanisms of the anti-biofilm activity of purpurin on C. Dubliniensis. Intracellular ROS levels were significantly elevated in fungal biofilms and depolarization of MMP was evident upon purpurin treatment in a concentration-dependent manner. DNA degradation was evident. However, no activated metacaspase could be detected. Together, purpurin triggered metacaspase-independent apoptosis in C. dubliniensis biofilms.

Viruses as modulators of mitochondrial functions

Mitochondria are multifunctional organelles with diverse roles including energy production and distribution, apoptosis, eliciting host immune response, and causing diseases and aging. Mitochondria-mediated immune responses might be an evolutionary adaptation by which mitochondria might have prevented the entry of invading microorganisms thus establishing them as an integral part of the cell. This makes them a target for all the invading pathogens including viruses. Viruses either induce or inhibit various mitochondrial processes in a highly specific manner so that they can replicate and produce progeny. Some viruses encode the Bcl2 homologues to counter the proapoptotic functions of the cellular and mitochondrial proteins. Others modulate the permeability transition pore and either prevent or induce the release of the apoptotic proteins from the mitochondria. Viruses like Herpes simplex virus 1 deplete the host mitochondrial DNA and some, like human immunodeficiency virus, hijack the host mitochondrial proteins to function fully inside the host cell. All these processes involve the participation of cellular proteins, mitochondrial proteins, and virus specific proteins. This review will summarize the strategies employed by viruses to utilize cellular mitochondria for successful multiplication and production of progeny virus.

Inhibition of mitochondrial fission attenuates Aβ-induced microglia apoptosis

Mitochondrial division inhibitor 1 (mdivi-1), a selective inhibitor of mitochondrial fission protein dynamin-related protein 1 (Drp1), has been reported to display neuroprotective properties in different animal models. In the present study, we investigated the protective effect of mdivi-1 on β-amyloid protein (Aβ)-induced cytotoxicity and its potential mechanisms in BV-2 and primary microglial cells. We found that mitochondrial fission was increased in Aβ treatment and inhibition of mitochondrial fission by mdivi-1 significantly reduced Aβ-induced expression of CD11b (a marker of microglial activation), viability loss and apoptotic rate increase in BV-2 and primary microglial cells. Moreover, we also found that mdivi-1 treatment markedly reversed mitochondrial membrane potential loss, cytochrome c (CytC) release and caspase-3 activation. Altogether, our data suggested that mdivi-1 exerts neuroprotective effects against Aβ-induced microglial apoptosis, and the underlying mechanism may be through inhibiting mitochondrial membrane potential loss, CytC release and suppression of the mitochondrial apoptosis pathway.

NAD+ acts on mitochondrial SirT3 to prevent axonal caspase activation and axonal degeneration

In chronic degenerative syndromes, neuronal death occurs over long periods, during which cells progressively lose their axons and, ultimately, their cell bodies. Although apoptosis is recognized as a key event in neuronal death, the molecular mechanisms involved in CNS axons degeneration are poorly understood. Due to the highly polarized phenotypes of CNS neurons, the different neuronal subcompartments are likely to be targeted by light repetitive and localized aggression. Such locally initiated deleterious signal transduction pathways could theoretically spread through the cytoplasm. However, where axon-degenerative signals initiate, what these early signals are, and how they lead to axon degeneration are unanswered questions that limit our understanding of neurodegenerative diseases and our ability to identify novel therapeutic targets. Using a microfluidic culture device adapted to CNS primary neurons, allowing specific access to the axonal and somatodendritic compartments, we analyzed the molecular pathways involved in axonal degeneration of differentiated neurons. We show here that local application of proapoptotic stimuli on the somatodentritic compartment triggers a dying-back pattern involving caspase-dependent axonal degeneration. Using complementary pharmacological and genetic approaches, we further demonstrate that NAD(+) and grape wine polyphenols prevent axonal apoptosis and act via mitochondrial SirT3 activation in axons.

From structure to function: mitochondrial morphology, motion and shaping in vascular smooth muscle

The diversity of mitochondrial arrangements, which arise from the organelle being static or moving, or fusing and dividing in a dynamically reshaping network, is only beginning to be appreciated. While significant progress has been made in understanding the proteins that reorganise mitochondria, the physiological significance of the various arrangements is poorly understood. The lack of understanding may occur partly because mitochondrial morphology is studied most often in cultured cells. The simple anatomy of cultured cells presents an attractive model for visualizing mitochondrial behaviour but contrasts with the complexity of native cells in which elaborate mitochondrial movements and morphologies may not occur. Mitochondrial changes may take place in native cells (in response to stress and proliferation), but over a slow time-course and the cellular function contributed is unclear. To determine the role mitochondrial arrangements play in cell function, a crucial first step is characterisation of the interactions among mitochondrial components. Three aspects of mitochondrial behaviour are described in this review: (1) morphology, (2) motion and (3) rapid shape changes. The proposed physiological roles to which various mitochondrial arrangements contribute and difficulties in interpreting some of the physiological conclusions are also outlined.

Alterations in c-Myc phenotypes resulting from dynamin-related protein 1 (Drp1)-mediated mitochondrial fission

The c-Myc (Myc) oncoprotein regulates numerous phenotypes pertaining to cell mass, survival and metabolism. Glycolysis, oxidative phosphorylation (OXPHOS) and mitochondrial biogenesis are positively controlled by Myc, with myc−/− rat fibroblasts displaying atrophic mitochondria, structural and functional defects in electron transport chain (ETC) components, compromised OXPHOS and ATP depletion. However, while Myc influences mitochondrial structure and function, it is not clear to what extent the reverse is true. To test this, we induced a state of mitochondrial hyper-fission in rat fibroblasts by de-regulating Drp1, a dynamin-like GTPase that participates in the terminal fission process. The mitochondria from these cells showed reduced mass and interconnectivity, a paucity of cristae, a marked reduction in OXPHOS and structural and functional defects in ETC Complexes I and V. High rates of abortive mitochondrial fusion were observed, likely reflecting ongoing, but ultimately futile, attempts to normalize mitochondrial mass. Cellular consequences included reduction of cell volume, ATP depletion and activation of AMP-dependent protein kinase. In response to Myc deregulation, apoptosis was significantly impaired both in the absence and presence of serum, although this could be reversed by increasing ATP levels by pharmacologic means. The current work demonstrates that enforced mitochondrial fission closely recapitulates a state of Myc deficiency and that mitochondrial integrity and function can affect Myc-regulated cellular behaviors. The low intracellular ATP levels that are frequently seen in some tumors as a result of inadequate vascular perfusion could favor tumor survival by countering the pro-apoptotic tendencies of Myc overexpression.

Mitochondrial dysfunction and cancer metastasis

Mitochondria have an essential role in powering cells by generating ATP following the metabolism of pyruvate derived from glycolysis. They are also the major source of generating reactive oxygen species (ROS), which have regulatory roles in cell death and proliferation. Mutations in mitochondrial DNA (mtDNA) and dysregulation of mitochondrial metabolism have been frequently described in human tumors. Although the role of oxidative stress as the consequence of mtDNA mutations and/or altered mitochondrial functions has been demonstrated in carciongenesis, a causative role of mitochondria in tumor progression has only been demonstrated recently. Specifically, the subject of this mini-review focuses on the role of mitochondria in promoting cancer metastasis. Cancer relapse and the subsequent spreading of cancer cells to distal sites are leading causes of morbidity and mortality in cancer patients. Despite its clinical importance, the underlying mechanisms of metastasis remain to be elucidated. Recently, it was demonstrated that mitochondrial oxidative stress could actively promote tumor progression and increase the metastatic potential of cancer cells. The purpose of this mini-review is to summarize current investigations of the roles of mitochondria in cancer metastasis. Future development of diagnostic and therapeutic strategies for patients with advanced cancer will benefit from the new knowledge of mitochondrial metabolism in epithelial cancer cells and the tumor stroma.

Mitochondrial dynamics associated with oxygen-glucose deprivation in rat primary neuronal cultures

Our objective was to investigate the mitochondrial dynamics following oxygen-glucose deprivation (OGD) in cultured rat cortical neurons. We documented changes in morphology, protein expression, and DNA levels in mitochondria following OGD and examined the roles of mitochondrial fission [dynamin-related protein 1 (Drp1), fission protein-1 (Fis1)] and fusion [mitofusin-1 (Mfn1), mitofusin-2 (Mfn2), and optic atrophy-1 protein (OPA1)] proteins on mitochondrial biogenesis and morphogenesis. We tested the effects of two Drp1 blockers [15-deoxy-Δ12,14-Prostaglandin J2 (PGJ2) and Mitochondrial Division Inhibitor (Mdivi-1)] on mitochondrial dynamics and cell survival. One hour of OGD had minimal effects on neuronal viability but mitochondria appeared condensed. Three hours of OGD caused a 60% decrease in neuronal viability accompanied by a transition from primarily normal/tubular and lesser number of rounded mitochondria during normoxia to either poorly labeled or small and large rounded mitochondria. The percentage of rounded mitochondria remained the same. The mitochondrial voltage-dependent anion channel, Complex V, and mitoDNA levels increased after OGD associated with a dramatic reduction in Drp1 expression, less reduction in Mfn2 expression, an increase in Mfn1 expression, with no changes in either OPA1 or Fis1. Although PGJ2 increased polymerization of Drp1, it did not reduce cell death or alter mitochondrial morphology following OGD and Mdivi-1 did not protect neurons against OGD. In summary, mitochondrial biogenesis and maintained fusion occurred in neurons along with mitochondrial fission following OGD; thus Mfn1 but not Drp1 may be a major regulator of these processes.

The member of high temperature requirement family HtrA2 participates in neuronal apoptosis after intracerebral hemorrhage in adult rats

The members of high-temperature requirement (HtrA) family are evolutionarily conserved serine proteases that combine a trypsin-like protease domain with at least one PDZ interaction domain. HtrA2, a special one, is mainly located in mitochondria and required for maintaining homeostasis. Once released into cytoplasm, HtrA2 contributes to apoptosis via caspase-dependent and -independent pathways. Accumulating evidence has showed its pro-apoptotic effect in cancers and central nervous system (CNS) diseases. However, the distribution and function of HtrA2 in CNS diseases remains to be further explored. To investigate HtrA2's roles in the pathophysiology of intracerebral hemorrhage (ICH), an ICH rat model was established and assessed by behavioral tests. Western blot and immunohistochemistry revealed a remarkable up-regulation of HtrA2 surrounding the hematoma after ICH; and immunofluorescence showed HtrA2 was strikingly increased in neurons, but not in astrocytes and oligodendrocytes. Terminal deoxynucleotidyl transferase-mediated biotinylated-dUTP nick-end labeling staining suggested the involvement of HtrA2 in neuronal apoptosis after ICH. Additionally, HtrA2 co-localized with active-caspase-3 around the hematoma and the expression of active-caspase-3 was parallel with that of HtrA2 in a time-dependent manner. Furthermore, hemin was used to stimulus a neuronal cell line PC12 to mimic ICH model in vitro. We analyzed the relationship of HtrA2 with X-linked inhibitor of apoptosis protein (XIAP) in PC12 cells by Western blot, immunofluorescence and co-immunoprecipitation. The connection of HtrA2 with XIAP was strengthened in apoptotic cells after hemin treatment. Thus, we speculated that HtrA2 might exert an important function in regulating caspase-dependent neuronal apoptosis through interacting with XIAP following ICH.

Mitochondrial motility and vascular smooth muscle proliferation

OBJECTIVE

Mitochondria are widely described as being highly dynamic and adaptable organelles, and their movement is thought to be vital for cell function. Yet, in various native cells, including those of heart and smooth muscle, mitochondria are stationary and rigidly structured. The significance of the differences in mitochondrial behavior to the physiological function of cells is unclear and was studied in single myocytes and intact resistance-sized cerebral arteries. We hypothesized that mitochondrial dynamics is controlled by the proliferative status of the cells.

METHODS AND RESULTS

High-speed fluorescence imaging of mitochondria in live vascular smooth muscle cells shows that the organelle undergoes significant reorganization as cells become proliferative. In nonproliferative cells, mitochondria are individual (≈ 2 μm by 0.5 μm), stationary, randomly dispersed, fixed structures. However, on entering the proliferative state, mitochondria take on a more diverse architecture and become small spheres, short rod-shaped structures, long filamentous entities, and networks. When cells proliferate, mitochondria also continuously move and change shape. In the intact pressurized resistance artery, mitochondria are largely immobile structures, except in a small number of cells in which motility occurred. When proliferation of smooth muscle was encouraged in the intact resistance artery, in organ culture, the majority of mitochondria became motile and the majority of smooth muscle cells contained moving mitochondria. Significantly, restriction of mitochondrial motility using the fission blocker mitochondrial division inhibitor prevented vascular smooth muscle proliferation in both single cells and the intact resistance artery.

CONCLUSIONS

These results show that mitochondria are adaptable and exist in intact tissue as both stationary and highly dynamic entities. This mitochondrial plasticity is an essential mechanism for the development of smooth muscle proliferation and therefore presents a novel therapeutic target against vascular disease.

Mitochondrial dysfunction and cellular metabolic deficiency in Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disorder. The pathology of AD includes amyloid-β (Aβ) deposits in neuritic plaques and neurofibrillary tangles composed of hyperphosphorylated tau, as well as neuronal loss in specific brain regions. Increasing epidemiological and functional neuroimaging evidence indicates that global and regional disruptions in brain metabolism are involved in the pathogenesis of this disease. Aβ precursor protein is cleaved to produce both extracellular and intracellular Aβ, accumulation of which might interfere with the homeostasis of cellular metabolism. Mitochondria are highly dynamic organelles that not only supply the main energy to the cell but also regulate apoptosis. Mitochondrial dysfunction might contribute to Aβ neurotoxicity. In this review, we summarize the pathways of Aβ generation and its potential neurotoxic effects on cellular metabolism and mitochondrial dysfunction.

Mitochondrial dynamics: the intersection of form and function

Mitochondria within a cell exist as a population in a dynamic -morphological continuum. The balance of mitochondrial fusion and fission dictates a spectrum of shapes from interconnected networks to fragmented individual units. This plasticity bestows the adaptive flexibility needed to adjust to changing cellular stresses and metabolic demands. The mechanisms that regulate mitochondrial dynamics, their importance in normal cell biology, and the roles they play in disease conditions are only beginning to be understood. Dysfunction of mitochondrial dynamics has been identified as a possible disease mechanism in Parkinson's disease. This chapter will introduce the budding field of mitochondrial dynamics and explore unique characteristics of affected neurons in Parkinson's disease that increase susceptibility to disruptions in mitochondrial dynamics.

Laminarin induces apoptosis of human colon cancer LOVO cells through a mitochondrial pathway

Many scientific studies have shown that laminarin has anti-tumor effects, but the anti-tumor mechanism was unclear. The purpose of this study was to investigate the effect of laminarin on the induction of apoptosis in human colon cancer LOVO cells and the molecular mechanism involved. LOVO cells were treated with different concentrations of laminarin at different times. Morphology observations were performed to determine the effects of laminarin on apoptosis of LOVO cells. Flow cytometry (FCM) was used to detect the level of intracellular reactive oxygen species (ROS) and pH. Laser scanning confocal microscope (LSCM) was used to analyze intracellular calcium ion concentration, mitochondrion permeability transition pore (MPTP) and mitochondrial membrane potential (MMP). Western blotd were performed to analyze the expressions of Cyt-C, Caspase-9 and -3. The results showed the apoptosis morphology, which showed cell protuberance, concentrated cytoplasm and apoptotic bodies, was obvious after 72 h treatment. Laminarin treatment for 24 h increased the intracellular level of ROS and Ca²⁺; decreased pH value; activated intracellular MPTP and decreased MMP in dose-dependent manners. It also induced the release of Cyt-C and the activation of Caspase-9 and -3. In conclusion, laminarin induces LOVO cell apoptosis through a mitochondrial pathway, suggesting that it could be a potent agent for cancer prevention and treatment.

Drosophila larvae lacking the bcl-2 gene, buffy, are sensitive to nutrient stress, maintain increased basal target of rapamycin (Tor) signaling and exhibit characteristics of altered basal energy metabolism

Background

B cell lymphoma 2 (Bcl-2) proteins are the central regulators of apoptosis. The two bcl-2 genes in Drosophila modulate the response to stress-induced cell death, but not developmental cell death. Because null mutants are viable, Drosophila provides an optimum model system to investigate alternate functions of Bcl-2 proteins. In this report, we explore the role of one bcl-2 gene in nutrient stress responses.

Results

We report that starvation of Drosophila larvae lacking the bcl-2 gene, buffy, decreases survival rate by more than twofold relative to wild-type larvae. The buffy null mutant reacted to starvation with the expected responses such as inhibition of target of rapamycin (Tor) signaling, autophagy initiation and mobilization of stored lipids. However, the autophagic response to starvation initiated faster in larvae lacking buffy and was inhibited by ectopic buffy. We demonstrate that unusually high basal Tor signaling, indicated by more phosphorylated S6K, was detected in the buffy mutant and that removal of a genomic copy of S6K, but not inactivation of Tor by rapamycin, reverted the precocious autophagy phenotype. Instead, Tor inactivation also required loss of a positive nutrient signal to trigger autophagy and loss of both was sufficient to activate autophagy in the buffy mutant even in the presence of enforced phosphoinositide 3-kinase (PI3K) signaling. Prior to starvation, the fed buffy mutant stored less lipid and glycogen, had high lactate levels and maintained a reduced pool of cellular ATP. These observations, together with the inability of buffy mutant larvae to adapt to nutrient restriction, indicate altered energy metabolism in the absence of buffy.

Conclusions

All animals in their natural habitats are faced with periods of reduced nutrient availability. This study demonstrates that buffy is required for adaptation to both starvation and nutrient restriction. Thus, Buffy is a Bcl-2 protein that plays an important non-apoptotic role to promote survival of the whole organism in a stressful situation.

The ubiquitin/proteasome system-dependent control of mitochondrial steps in apoptosis

Insights into the role of ubiquitin-dependent signaling in the regulation of apoptosis have provided one of the most significant breakthroughs in recent years for cell death research. It has been revealed that all steps in the apoptotic cascade, including transcriptional regulation of apoptotic gene expression, outer mitochondrial membrane permeabilization and caspase activation, are under the control of the ubiquitin/proteasome system. This makes ubiquitin signaling one on the most critical life and death decision checkpoints in mammalian cells. Here we discuss the ubiquitylation-dependent regulation of the mitochondrial steps in apoptosis, with a focus on the role of regulated protein degradation in this process. The newly identified ubiquitylation-dependent processes in the Bcl-2 family-regulated outer mitochondrial membrane permeabilization, as well as the role of mitochondria-associated ubiquitin ligases and other molecular components of the ubiquitin/proteasome system in the control of mitochondrial steps in apoptosis, are discussed.

Mitochondrial network in the heart

Mitochondria are subcellular organelles that provide energy for the cell. They form a dynamic tubular network and play an important role in maintaining the cell function and integrity. Heart is a powerful organ that supplies the motivation for circulation, thereby requiring large amounts of energy. Thus, the healthiness of cardiomyocytes and mitochondria is necessary for the normal cardiac function. Mitochondria not only lie in the center of the cell apoptotic pathway, but also are the major source of reactive oxygen species (ROS) generation. Mitochondrial morphological change includes fission and fusion that are regulated by a large number of proteins. In this review we discuss the regulators of mitochondrial fission/fusion and their association with cell apoptosis, autophagy and ROS production in the heart.