Mitochondrial Dynamics in Mitochondrial Diseases

Energy Metabolism: From Physiological Changes to Targets in Sepsis-induced Cardiomyopathy

Sepsis is a systemic inflammatory response syndrome caused by a variety of dysregulated responses to host infection with life-threatening multi-organ dysfunction. Among the injuries or dysfunctions involved in the course of sepsis, cardiac injury and dysfunction often occur and are associated with the pathogenesis of hemodynamic disturbances, also defined as sepsis-induced cardiomyopathy (SIC). The process of myocardial metabolism is tightly regulated and adapts to various cardiac output demands. The heart is a metabolically flexible organ capable of utilizing all classes of energy substrates, including carbohydrates, lipids, amino acids, and ketone bodies to produce ATP. The demand of cardiac cells for energy metabolism changes substantially in septic cardiomyopathy with distinct etiological causes and different times. This review describes changes in cardiomyocyte energy metabolism under normal physiological conditions and some features of myocardial energy metabolism in septic cardiomyopathy, and briefly outlines the role of the mitochondria as a center of energy metabolism in the septic myocardium, revealing that changes in energy metabolism can serve as a potential future therapy for infectious cardiomyopathy.

Nicotinamide Mononucleotide and Nicotinamide Riboside Reverse Ovarian Aging in Rats Via Rebalancing Mitochondrial Fission and Fusion Mechanisms

PURPOSE

This study examined the effects of nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR) on folliculogenesis and mitochondrial dynamics (fission and fusion mechanisms) in ovaries of middle-aged female rats.

METHODS

Experimental groups were young, middle-aged (control), middle-aged + NMN and middle-aged + NR. NMN was administered at a concentration of 500 mg/kg intraperitoneally but NR at a concentration of 200 mg/kg by gavage. Follicle stimulating hormone (FSH) and luteinizing hormone (LH) levels were analyzed by ELISA. Hematoxylin-eosin staining sections were used for histopathological examination and follicles-counting. Expression levels of mitochondrial fission (Drp1, Mff and Fis1) and fusion (Mfn1, Mfn2, Opa1, Fam73a and Fam73b) genes as well as Sirt1 gene were analyzed by RT-PCR. Expression levels of fission-related proteins (DRP1, MFF, FIS1 and SIRT1) were analyzed by Western Blot.

RESULTS

Higher ovarian index, more corpus luteum and antral follicles were detected in NMN and NR groups compared to the control. NMN or NR could rebalance LH/FSH ratio. The control group was determined to possess higher expression levels of fission genes and lower expression levels of fusion genes when compared the young group. In comparison with the control group, both NMN and NR group were found to exhibit less mitochondrial fission but more mitochondrial fussion. Higher gene and protein levels for Sirt1 were measured in NMN and NR groups compared to the control group.

CONCLUSION

This study reveals that NMN alone or NR alone can rebalance mitochondrial dynamics by decreasing excessive fission in middle-aged rat ovaries, thus alleviating mitochondrial stress and correcting aging-induced folliculogenesis abnormalities.

Mitochondrial Dysfunction by FADDosome Promotes Gastric Mucosal Injury in Portal Hypertensive Gastropathy

Mucosal epithelial death is an essential pathological characteristic of portal hypertensive gastropathy (PHG). FADDosome can regulate mucosal homeostasis by controlling mitochondrial status and cell death. However, it remains ill-defined whether and how the FADDosome is involved in the epithelial death of PHG. The FADDosome formation, mitochondrial dysfunction, glycolysis process and NLRP3 inflammasome activation in PHG from both human sections and mouse models were investigated. NLRP3 wild-type (NLRP3-WT) and NLRP3 knockout (NLRP3-KO) littermate models, critical element inhibitors and cell experiments were utilized. The mechanism underlying FADDosome-regulated mitochondrial dysfunction and epithelial death in PHG was explored. Here, we found that FADD recruited caspase-8 and receptor-interacting serine/threonine-protein kinase 1 (RIPK1) to form the FADDosome to promote Drp1-dependent mitochondrial fission and dysfunction in PHG. Also, FADDosome modulated NOX2 signaling to strengthen Drp1-dependent mitochondrial fission and alter glycolysis as well as enhance mitochondrial reactive oxygen species (mtROS) production. Moreover, due to the dysfunction of electron transport chain (ETC) and alteration of antioxidant enzymes activity, this altered glycolysis also contributed to mtROS production. Subsequently, the enhanced mtROS production induced NLRP3 inflammasome activation to result in the epithelial pyroptosis and mucosal injury in PHG. Thus, the FADDosome-regulated pathways may provide a potential therapeutic target for PHG.

The effect of adipose-derived mesenchymal stem cell transplantation on ovarian mitochondrial dysfunction in letrozole-induced polycystic ovary syndrome in rats: the role of PI3K-AKT signaling pathway

OBJECTIVE

The present study aimed to elucidate how mesenchymal stem cells (MSCs) application could efficiently attenuate pathological changes of letrozole-induced poly cystic ovary syndrome (PCOS) by modulating mitochondrial dynamic via PI3K-AKT pathway.

METHODS

Thirty-two female rats were randomly divided into four experimental groups: Sham, PCOS, PCOS + MSCs, and PCOS + MSCs + LY294002. The Sham group received 0.5% w/v carboxymethyl cellulose (CMC); the PCOS group received letrozole (1 mg/kg, daily) in 0.5% CMC for 21 days. Animals in the PCOS + MSCs group received 1 × 106 MSCs/rat (i.p,) on the 22th day of the study. In the PCOS + MSCs + LY294002 group, rats received LY294002 (PI3K-AKT inhibitor) 40 min before MSC transplantation. Mitochondrial dynamic gene expression, mitochondrial membrane potential (MMP), citrate synthase (CS) activity, oxidative stress, inflammation, ovarian histological parameters, serum hormone levels, homeostatic model assessment for insulin resistance (HOMA-IR), insulin and glucose concentrations, p-PI3K and p-AKT protein levels were evaluated at the end of the experiment.

RESULTS

PCOS rats showed a significant disruption of mitochondrial dynamics and histological changes, lower MMP, CS, ovary super oxide dismutase (SOD) and estrogen level. They also had a notable rise in insulin and glucose concentrations, HOMA-IR, testosterone level, tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) levels, ovarian malondialdehyde (MDA) content as well as a notable decrease in p-PI3K and p-AKT protein levels compared to the Sham group. In the PCOS + MSCs group, the transplantation of MSCs could improve the above parameters. Administration of LY294002 (PI3K-AKT pathway inhibitor) deteriorated mitochondrial dynamic markers, oxidative stress status, inflammation markers, hormonal levels, glucose, and insulin levels and follicular development compared to the PCOS + MSCs group.

CONCLUSIONS

This study demonstrated that the protective effects of MSC transplantation in regulating mitochondrial dynamics, promoting mitochondrial biogenesis, competing with redox status and inflammation response were mainly mediated through the PI3K-AKT pathway in the PCOS model.

Mitochondrial Outer Membrane Translocase MoTom20 Modulates Mitochondrial Morphology and Is Important for Infectious Growth of the Rice Blast Fungus Magnaporthe oryzae

Mitochondria are highly dynamic organelles that constantly change their morphology to adapt to the cellular environment through fission and fusion, which is critical for a cell to maintain normal cellular functions. Despite the significance of this process in the development and pathogenicity of the rice blast fungus Magnaporthe oryzae, the underlying mechanism remains largely elusive. Here, we identified and characterized a mitochondrial outer membrane translocase, MoTom20, in M. oryzae. Targeted gene deletion revealed that MoTom20 plays an important role in vegetative growth, conidiogenesis, penetration, and infectious growth of M. oryzae. The growth rate, conidial production, appressorium turgor, and pathogenicity are decreased in the ΔMotom20 mutant compared with the wild-type and complemented strains. Further analysis revealed that MoTom20 localizes in mitochondrion and plays a key role in regulating mitochondrial fission and fusion balance, which is critical for infectious growth. Finally, we found that MoTom20 is involved in fatty-acid utilization, and its yeast homolog ScTom20 is able to rescue the defects of ΔMotom20 in mitochondrial morphology and pathogenicity. Overall, our data demonstrate that MoTom20 is a key regulator for mitochondrial morphology maintenance, which is important for infectious growth of the rice blast fungus M. oryzae. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Exploring the Gut-Mitochondrial Axis: p66Shc Adapter Protein and Its Implications for Metabolic Disorders

This review investigates the multifaceted role of the p66Shc adaptor protein and the gut microbiota in regulating mitochondrial function and oxidative stress, and their collective impact on the pathogenesis of chronic diseases. The study delves into the molecular mechanisms by which p66Shc influences cellular stress responses through Rac1 activation, Forkhead-type transcription factors inactivation, and mitochondria-mediated apoptosis, alongside modulatory effects of gut microbiota-derived metabolites and endotoxins. Employing an integrative approach, the review synthesizes findings from a broad array of studies, including molecular biology techniques and analyses of microbial metabolites' impacts on host cellular pathways. The results underscore a complex interplay between microbial metabolites, p66Shc activation, and mitochondrial dysfunction, highlighting the significance of the gut microbiome in influencing disease outcomes through oxidative stress pathways. Conclusively, the review posits that targeting the gut microbiota-p66Shc-mitochondrial axis could offer novel therapeutic strategies for mitigating the development and progression of metabolic diseases. This underscores the potential of dietary interventions and microbiota modulation in managing oxidative stress and inflammation, pivotal factors in chronic disease etiology.

The mechanisms and roles of mitochondrial dynamics in C. elegans

If mitochondria are the powerhouses of the cell, then mitochondrial dynamics are the power grid that regulates how that energy output is directed and maintained in response to unique physiological demands. Fission and fusion dynamics are highly regulated processes that fine-tune the mitochondrial networks of cells to enable appropriate responses to intrinsic and extrinsic stimuli, thereby maintaining cellular and organismal homeostasis. These dynamics shape many aspects of an organism's healthspan including development, longevity, stress resistance, immunity, and response to disease. In this review, we discuss the latest findings regarding the mechanisms and roles of mitochondrial dynamics by focussing on the nematode Caenorhabditis elegans. Whole live-animal studies in C. elegans have enabled a true organismal-level understanding of the impact that mitochondrial dynamics play in homeostasis over a lifetime.

Quantifying nanoscopic alterations associated with mitochondrial dysfunction using three-dimensional single-molecule localization microscopy

Mitochondrial morphology provides unique insights into their integrity and function. Among fluorescence microscopy techniques, 3D super-resolution microscopy uniquely enables the analysis of mitochondrial morphological features individually. However, there is a lack of tools to extract morphological parameters from super-resolution images of mitochondria. We report a quantitative method to extract mitochondrial morphological metrics, including volume, aspect ratio, and local protein density, from 3D single-molecule localization microscopy images, with single-mitochondrion sensitivity. We validated our approach using simulated ground-truth SMLM images of mitochondria. We further tested our morphological analysis on mitochondria that have been altered functionally and morphologically in controlled manners. This work sets the stage to quantitatively analyze mitochondrial morphological alterations associated with disease progression on an individual basis.

Cell metabolism pathways involved in the pathophysiological changes of diabetic peripheral neuropathy

Diabetic peripheral neuropathy is a common complication of diabetes mellitus. Elucidating the pathophysiological metabolic mechanism impels the generation of ideal therapies. However, existing limited treatments for diabetic peripheral neuropathy expose the urgent need for cell metabolism research. Given the lack of comprehensive understanding of energy metabolism changes and related signaling pathways in diabetic peripheral neuropathy, it is essential to explore energy changes and metabolic changes in diabetic peripheral neuropathy to develop suitable treatment methods. This review summarizes the pathophysiological mechanism of diabetic peripheral neuropathy from the perspective of cellular metabolism and the specific interventions for different metabolic pathways to develop effective treatment methods. Various metabolic mechanisms (e.g., polyol, hexosamine, protein kinase C pathway) are associated with diabetic peripheral neuropathy, and researchers are looking for more effective treatments through these pathways.

Mitochondrial quality control alterations and placenta-related disorders

Mitochondria are ubiquitous in eukaryotic cells. Normal maintenance of function is the premise and basis for various physiological activities. Mitochondrial dysfunction is commonly observed in a wide range of pathological conditions, such as neurodegenerative, metabolic, cardiovascular, and various diseases related to foetal growth and development. The placenta is a highly energy-dependent organ that acts as an intermediary between the mother and foetus and functions to maintain foetal growth and development. Recent studies have demonstrated that mitochondrial dysfunction is associated with placental disorders. Defects in mitochondrial quality control mechanisms may lead to preeclampsia and foetal growth restriction. In this review, we address the quality control mechanisms of mitochondria and the relevant pathologies of mitochondrial dysfunction in placenta-related diseases, such as preeclampsia and foetal growth restriction. This review also investigates the relation between mitochondrial dysfunction and placental disorders.

Phosphatidate phosphatase Lipin1 involves in diabetic encephalopathy pathogenesis via regulating synaptic mitochondrial dynamics

Diabetic encephalopathy (DE) is a common central nervous system complication of diabetes mellitus without effective therapy currently. Recent studies have highlighted synaptic mitochondrial damages as a possible pathological basis for DE, but the underlying mechanisms remain unclear. Our previous work has revealed that phosphatidate phosphatase Lipin1, a critical enzyme involved with phospholipid synthesis, is closely related to the pathogenesis of DE. Here, we demonstrate that Lipin1 is significantly down-regulated in rat hippocampus of DE. Knock-down of Lipin1 within hippocampus of normal rats induces dysregulation of homeostasis in synaptic mitochondrial dynamics with an increase of mitochondrial fission and a decrease of fusion, then causes synaptic mitochondrial dysfunction, synaptic plasticity deficits as well as cognitive impairments, similar to that observed in response to chronic hyperglycemia exposure. In contrast, an up-regulation of Lipin1 within hippocampus in the DE model ameliorates this cascade of dysfunction. We also find that the effect of Lipin1 that regulating mitochondrial dynamics results from maintaining appropriate phospholipid components in the mitochondrial membrane. In conclusion, alterations in hippocampal Lipin1 contribute to hippocampal synaptic mitochondrial dysfunction and cognitive deficits observed in DE. Targeting Lipin1 might be a potential therapeutic strategy for the clinical treatment of DE.

Selective inhibitors targeting Fis1/Mid51 protein-protein interactions protect against hypoxia-induced damage in cardiomyocytes

Cardiovascular diseases (CVDs) are the most common non-communicable diseases globally. An estimated 17.9 million people died from CVDs in 2019, representing 32% of all global deaths. Mitochondria play critical roles in cellular metabolic homeostasis, cell survival, and cell death, as well as producing most of the cell's energy. Protein-protein interactions (PPIs) have a significant role in physiological and pathological processes, and aberrant PPIs are associated with various diseases, therefore they are potential drug targets for a broad range of therapeutic areas. Due to their ability to mimic natural interaction motifs and cover relatively larger interaction region, peptides are very promising as PPI inhibitors. To expedite drug discovery, computational approaches are widely used for screening potential lead compounds. Here, we developed peptides that inhibit mitochondrial fission 1 (Fis1)/mitochondrial dynamics 51 kDa (Mid51) PPI to reduce the cellular damage that can lead to various human pathologies, such as CVDs. Based on a rational design approach we developed peptide inhibitors of the Fis1/Mid51 PPI. In silico and in vitro studies were done to evaluate the biological activity and molecular interactions of the peptides. Two peptides, CVP-241 and CVP-242 were identified based on low binding energy and molecular dynamics simulations. These peptides inhibit Fis1/Mid51 PPI (-1324.9 kcal mol-1) in docking calculations (CVP-241, -741.3 kcal mol-1, and CVP-242, -747.4 kcal mol-1), as well as in vitro experimental studies Fis1/Mid51 PPI (KD 0.054 µM) Fis1/Mid51 PPI + CVP-241 (KD 3.43 µM), and Fis1/Mid51 PPI + CVP-242 (KD 44.58 µM). Finally, these peptides have no toxicity to H9c2 cells, and they increase cell viability in cardiomyocytes (H9c2 cells). Consequently, the identified inhibitor peptides could serve as potent molecules in basic research and as leads for therapeutic development.

Novel Relationship between Mitofusin 2-Mediated Mitochondrial Hyperfusion, Metabolic Remodeling, and Glycolysis in Pulmonary Arterial Endothelial Cells

The disruption of mitochondrial dynamics has been identified in cardiovascular diseases, including pulmonary hypertension (PH), ischemia-reperfusion injury, heart failure, and cardiomyopathy. Mitofusin 2 (Mfn2) is abundantly expressed in heart and pulmonary vasculature cells at the outer mitochondrial membrane to modulate fusion. Previously, we have reported reduced levels of Mfn2 and fragmented mitochondria in pulmonary arterial endothelial cells (PAECs) isolated from a sheep model of PH induced by pulmonary over-circulation and restoring Mfn2 normalized mitochondrial function. In this study, we assessed the effect of increased expression of Mfn2 on mitochondrial metabolism, bioenergetics, reactive oxygen species production, and mitochondrial membrane potential in control PAECs. Using an adenoviral expression system to overexpress Mfn2 in PAECs and utilizing 13C labeled substrates, we assessed the levels of TCA cycle metabolites. We identified increased pyruvate and lactate production in cells, revealing a glycolytic phenotype (Warburg phenotype). Mfn2 overexpression decreased the mitochondrial ATP production rate, increased the rate of glycolytic ATP production, and disrupted mitochondrial bioenergetics. The increase in glycolysis was linked to increased hypoxia-inducible factor 1α (HIF-1α) protein levels, elevated mitochondrial reactive oxygen species (mt-ROS), and decreased mitochondrial membrane potential. Our data suggest that disrupting the mitochondrial fusion/fission balance to favor hyperfusion leads to a metabolic shift that promotes aerobic glycolysis. Thus, therapies designed to increase mitochondrial fusion should be approached with caution.

A big picture of the mitochondria-mediated signals: From mitochondria to organism

Mitochondria, well-known for years as the powerhouse and biosynthetic center of the cell, are dynamic signaling organelles beyond their energy production and biosynthesis functions. The metabolic functions of mitochondria, playing an important role in various biological events both in physiological and stress conditions, transform them into important cellular stress sensors. Mitochondria constantly communicate with the rest of the cell and even from other cells to the organism, transmitting stress signals including oxidative and reductive stress or adaptive signals such as mitohormesis. Mitochondrial signal transduction has a vital function in regulating integrity of human genome, organelles, cells, and ultimately organism.

Mitochondrial Fragmentation Promotes Inflammation Resolution Responses in Macrophages via Histone Lactylation

During the inflammatory response, macrophage phenotypes can be broadly classified as pro-inflammatory/classically activated "M1", or pro-resolving/alternatively "M2" macrophages. Although the classification of macrophages is general and assumes there are distinct phenotypes, in reality macrophages exist across a spectrum and must transform from a pro-inflammatory state to a proresolving state following an inflammatory insult. To adapt to changing metabolic needs of the cell, mitochondria undergo fusion and fission, which have important implications for cell fate and function. We hypothesized that mitochondrial fission and fusion directly contribute to macrophage function during the pro-inflammatory and proresolving phases. In the present study, we find that mitochondrial length directly contributes to macrophage phenotype, primarily during the transition from a pro-inflammatory to a proresolving state. Phenocopying the elongated mitochondrial network (by disabling the fission machinery using siRNA) leads to a baseline reduction in the inflammatory marker IL-1β, but a normal inflammatory response to LPS, similar to control macrophages. In contrast, in macrophages with a phenocopied fragmented phenotype (by disabling the fusion machinery using siRNA) there is a heightened inflammatory response to LPS and increased signaling through the ATF4/c-Jun transcriptional axis compared to control macrophages. Importantly, macrophages with a fragmented mitochondrial phenotype show increased expression of proresolving mediator arginase 1 and increased phagocytic capacity. Promoting mitochondrial fragmentation caused an increase in cellular lactate, and an increase in histone lactylation which caused an increase in arginase 1 expression. These studies demonstrate that a fragmented mitochondrial phenotype is critical for the proresolving response in macrophages and specifically drive epigenetic changes via lactylation of histones following an inflammatory insult.

Role of UPRmt and mitochondrial dynamics in host immunity: it takes two to tango

The immune system of a host contains a group of heterogeneous cells with the prime aim of restraining pathogenic infection and maintaining homeostasis. Recent reports have proved that the various subtypes of immune cells exploit distinct metabolic programs for their functioning. Mitochondria are central signaling organelles regulating a range of cellular activities including metabolic reprogramming and immune homeostasis which eventually decree the immunological fate of the host under pathogenic stress. Emerging evidence suggests that following bacterial infection, innate immune cells undergo profound metabolic switching to restrain and countervail the bacterial pathogens, promote inflammation and restore tissue homeostasis. On the other hand, bacterial pathogens affect mitochondrial structure and functions to evade host immunity and influence their intracellular survival. Mitochondria employ several mechanisms to overcome bacterial stress of which mitochondrial UPR (UPR^mt) and mitochondrial dynamics are critical. This review discusses the latest advances in our understanding of the immune functions of mitochondria against bacterial infection, particularly the mechanisms of mitochondrial UPR^mt and mitochondrial dynamics and their involvement in host immunity.

Mitochondrial dysfunction-targeting therapeutics of natural products in Parkinson's disease

Parkinson's disease (PD), the second most common neurodegenerative disease worldwide, often occurs in middle-aged and elderly individuals. The pathogenesis of PD is complex and includes mitochondrial dysfunction, and oxidative stress. Recently, natural products with multiple structures and their bioactive components have become one of the most important resources for small molecule PD drug research targeting mitochondrial dysfunction. Multiple lines of studies have proven that natural products display ameliorative benefits in PD treatment by regulating mitochondrial dysfunction. Therefore, a comprehensive search of recent published articles between 2012 and 2022 in PubMed, Web of Science, Elesvier, Wliey and Springer was carried out, focusing on original publications related to natural products against PD by restoring mitochondrial dysfunction. This paper presented the mechanisms of various kinds of natural products on PD-related mitochondrial dysfunction regulation and provided evidence that natural products are promising to be developed as drugs for PD therapeutics.

Mitochondrial transfer from bone mesenchymal stem cells protects against tendinopathy both in vitro and in vivo

BACKGROUND

Although mesenchymal stem cells (MSCs) have been effective in tendinopathy, the mechanisms by which MSCs promote tendon healing have not been fully elucidated. In this study, we tested the hypothesis that MSCs transfer mitochondria to injured tenocytes in vitro and in vivo to protect against Achilles tendinopathy (AT).

METHODS

Bone marrow MSCs and H₂O₂-injured tenocytes were co-cultured, and mitochondrial transfer was visualized by MitoTracker dye staining. Mitochondrial function, including mitochondrial membrane potential, oxygen consumption rate, and adenosine triphosphate content, was quantified in sorted tenocytes. Tenocyte proliferation, apoptosis, oxidative stress, and inflammation were analyzed. Furthermore, a collagenase type I-induced rat AT model was used to detect mitochondrial transfer in tissues and evaluate Achilles tendon healing.

RESULTS

MSCs successfully donated healthy mitochondria to in vitro and in vivo damaged tenocytes. Interestingly, mitochondrial transfer was almost completely blocked by co-treatment with cytochalasin B. Transfer of MSC-derived mitochondria decreased apoptosis, promoted proliferation, and restored mitochondrial function in H₂O₂-induced tenocytes. A decrease in reactive oxygen species and pro-inflammatory cytokine levels (interleukin-6 and -1β) was observed. In vivo, mitochondrial transfer from MSCs improved the expression of tendon-specific markers (scleraxis, tenascin C, and tenomodulin) and decreased the infiltration of inflammatory cells into the tendon. In addition, the fibers of the tendon tissue were neatly arranged and the structure of the tendon was remodeled. Inhibition of mitochondrial transfer by cytochalasin B abrogated the therapeutic efficacy of MSCs in tenocytes and tendon tissues.

CONCLUSIONS

MSCs rescued distressed tenocytes from apoptosis by transferring mitochondria. This provides evidence that mitochondrial transfer is one mechanism by which MSCs exert their therapeutic effects on damaged tenocytes.

The Complex Interplay between Imbalanced Mitochondrial Dynamics and Metabolic Disorders in Type 2 Diabetes

Type 2 diabetes mellitus (T2DM) is a global burden, with an increasing number of people affected and increasing treatment costs. The advances in research and guidelines improve the management of blood glucose and related diseases, but T2DM and its complications are still a big challenge in clinical practice. T2DM is a metabolic disorder in which insulin signaling is impaired from reaching its effectors. Mitochondria are the "powerhouses" that not only generate the energy as adenosine triphosphate (ATP) using pyruvate supplied from glucose, free fatty acid (FFA), and amino acids (AA) but also regulate multiple cellular processes such as calcium homeostasis, redox balance, and apoptosis. Mitochondrial dysfunction leads to various diseases, including cardiovascular diseases, metabolic disorders, and cancer. The mitochondria are highly dynamic in adjusting their functions according to cellular conditions. The shape, morphology, distribution, and number of mitochondria reflect their function through various processes, collectively known as mitochondrial dynamics, including mitochondrial fusion, fission, biogenesis, transport, and mitophagy. These processes determine the overall mitochondrial health and vitality. More evidence supports the idea that dysregulated mitochondrial dynamics play essential roles in the pathophysiology of insulin resistance, obesity, and T2DM, as well as imbalanced mitochondrial dynamics found in T2DM. This review updates and discusses mitochondrial dynamics and the complex interactions between it and metabolic disorders.

The Potential Use of Mitochondrial Extracellular Vesicles as Biomarkers or Therapeutical Tools

The mitochondria play a crucial role in cellular metabolism, reactive oxygen species (ROS) production, and apoptosis. Aberrant mitochondria can cause severe damage to the cells, which have established a tight quality control for the mitochondria. This process avoids the accumulation of damaged mitochondria and can lead to the release of mitochondrial constituents to the extracellular milieu through mitochondrial extracellular vesicles (MitoEVs). These MitoEVs carry mtDNA, rRNA, tRNA, and protein complexes of the respiratory chain, and the largest MitoEVs can even transport whole mitochondria. Macrophages ultimately engulf these MitoEVs to undergo outsourced mitophagy. Recently, it has been reported that MitoEVs can also contain healthy mitochondria, whose function seems to be the rescue of stressed cells by restoring the loss of mitochondrial function. This mitochondrial transfer has opened the field of their use as potential disease biomarkers and therapeutic tools. This review describes this new EVs-mediated transfer of the mitochondria and the current application of MitoEVs in the clinical environment.

Mitochondrial pores at the crossroad between cell death and inflammatory signaling

Mitochondria are cellular organelles with a major role in many cellular processes, including not only energy production, metabolism, and calcium homeostasis but also regulated cell death and innate immunity. Their proteobacterial origin makes them a rich source of potent immune agonists, normally hidden within the mitochondrial membrane barriers. Alteration of mitochondrial permeability through mitochondrial pores thus provides efficient mechanisms not only to communicate mitochondrial stress to the cell but also as a key event in the integration of cellular responses. In this regard, eukaryotic cells have developed diverse signaling networks that sense and respond to the release of mitochondrial components into the cytosol and play a key role in controlling cell death and inflammatory pathways. Modulating pore formation at mitochondria through direct or indirect mechanisms may thus open new opportunities for therapy. In this review, we discuss the current understanding of the structure and molecular mechanisms of mitochondrial pores and how they function at the interface between cell death and inflammatory signaling to regulate cellular outcomes.

Activity-based anorexia in adolescent female rats causes changes in brain mitochondrial dynamics

Anorexia Nervosa (AN) is associated with a high rate of morbidity and mortality as well as a high rate of relapse. The molecular mechanisms underlying the progression of the disorder or the relapses are largely unknown. Patients with AN have been shown to have increased oxidative stress, but its involvement in the development in the disease is unknown. We have previously shown that adolescent female rats undergoing the activity-based anorexia (ABA) paradigm also show signs of oxidative stress. Due to their role in the release of reactive oxygen species (ROS), mitochondria are of high interest in diseases exhibiting oxidative stress. In this study, the impact of ABA on brain mitochondrial dynamics was examined. We found transient changes in the medial prefrontal cortex, hypothalamus, and hippocampus following 25% weight loss and changes in the amygdala at a 10-day weight recovery timepoint. These changes point towards damage in the mitochondria contributing to the oxidative stress.

Neurodegeneration, Mitochondria, and Antibiotics

Neurodegenerative diseases are characterized by the progressive loss of neurons, synapses, dendrites, and myelin in the central and/or peripheral nervous system. Actual therapeutic options for patients are scarce and merely palliative. Although they affect millions of patients worldwide, the molecular mechanisms underlying these conditions remain unclear. Mitochondrial dysfunction is generally found in neurodegenerative diseases and is believed to be involved in the pathomechanisms of these disorders. Therefore, therapies aiming to improve mitochondrial function are promising approaches for neurodegeneration. Although mitochondrial-targeted treatments are limited, new research findings have unraveled the therapeutic potential of several groups of antibiotics. These drugs possess pleiotropic effects beyond their anti-microbial activity, such as anti-inflammatory or mitochondrial enhancer function. In this review, we will discuss the controversial use of antibiotics as potential therapies in neurodegenerative diseases.

Loss of pex5 sensitizes zebrafish to fasting due to deregulated mitochondria, mTOR, and autophagy

Animal models have been utilized to understand the pathogenesis of Zellweger spectrum disorders (ZSDs); however, the link between clinical manifestations and molecular pathways has not yet been clearly established. We generated peroxin 5 homozygous mutant zebrafish (pex5^-/-) to gain insight into the molecular pathogenesis of peroxisome dysfunction. pex5^-/- display hallmarks of ZSD in humans and die within one month after birth. Fasting rapidly depletes lipids and glycogen in pex5^-/- livers and expedites their mortality. Mechanistically, deregulated mitochondria and mechanistic target of rapamycin (mTOR) signaling act together to induce metabolic alterations that deplete hepatic nutrients and accumulate damaged mitochondria. Accordingly, chemical interventions blocking either the mitochondrial function or mTOR complex 1 (mTORC1) or a combination of both improve the metabolic imbalance shown in the fasted pex5^-/- livers and extend the survival of animals. In addition, the suppression of oxidative stress by N-acetyl L-cysteine (NAC) treatment rescued the apoptotic cell death and early mortality observed in pex5^-/-. Furthermore, an autophagy activator effectively ameliorated the early mortality of fasted pex5^-/-. These results suggest that fasting may be detrimental to patients with peroxisome dysfunction, and that modulating the mitochondria, mTORC1, autophagy activities, or oxidative stress may provide a therapeutic option to alleviate the symptoms of peroxisomal diseases associated with metabolic dysfunction.

Mitochondria: Emerging Consequential in Sickle Cell Disease

Advanced mitochondrial multi-omics indicate a multi-facet involvement of mitochondria in the physiology of the cell, changing the perception of mitochondria from being just the energy-generating organelles to organelles that highly influence cell structure, function, signaling, and cell fate. This sets mitochondrial dysfunction in the centerstage of numerous acquired and genetic diseases. Sickle cell disease is also being increasingly associated with mitochondrial anomalies and the pathophysiology of sickle cell disease finds mitochondria at crucial intersections in the pathological cascade. Altered mitophagy, increased ROS, and mitochondrial DNA all contribute to the condition and its severity. Such mitochondrial aberrations lead to consequent mitochondrial retention in red blood cells in sickle cell diseases, increased oxidation in the cellular environment, inflammation, worsened vaso-occlusive crisis, etc. There are increasing studies indicating mitochondrial significance in sickle cell disease, consequently providing an opportunity to target it for improving the outcomes of treatment. Identification of the impaired mitochondrial attributes in sickle cell disease and their modulation by therapeutic interventions can impart a better management of the disease. This review aims to describe the mitochondria in the perspective of sicke cell disease so as to provide the reader an overview of the emerging mitochondrial stance in sickle cell disease.

Mitochondrial Control in Inflammatory Gastrointestinal Diseases

Mitochondria play a central role in the pathophysiology of inflammatory bowel disease (IBD) and colorectal cancer (CRC). The maintenance of mitochondrial function is necessary for a stable immune system. Mitochondrial dysfunction in the gastrointestinal system leads to the excessive activation of multiple inflammatory signaling pathways, leading to IBD and increased severity of CRC. In this review, we focus on the mitochondria and inflammatory signaling pathways and its related gastrointestinal diseases.

Modelling autosomal dominant optic atrophy associated with OPA1 variants in iPSC-derived retinal ganglion cells

Autosomal dominant optic atrophy (DOA) is the most common inherited optic neuropathy, characterized by the preferential loss of retinal ganglion cells (RGCs), resulting in optic nerve degeneration and progressive bilateral central vision loss. More than 60% of genetically confirmed patients with DOA carry variants in the nuclear OPA1 gene, which encodes for a ubiquitously expressed, mitochondrial GTPase protein. OPA1 has diverse functions within the mitochondrial network, facilitating inner membrane fusion and cristae modelling, regulating mitochondrial DNA maintenance and coordinating mitochondrial bioenergetics. There are currently no licensed disease-modifying therapies for DOA and the disease mechanisms driving RGC degeneration are poorly understood. Here, we describe the generation of isogenic, heterozygous OPA1 null induced pluripotent stem cell (iPSC) (OPA1+/-) through clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 gene editing of a control cell line, in conjunction with the generation of DOA patient-derived iPSC carrying OPA1 variants, namely, the c.2708_2711delTTAG variant (DOA iPSC), and previously reported missense variant iPSC line (c.1334G>A, DOA plus [DOA]+ iPSC) and CRISPR/Cas9 corrected controls. A two-dimensional (2D) differentiation protocol was used to study the effect of OPA1 variants on iPSC-RGC differentiation and mitochondrial function. OPA1+/-, DOA and DOA+ iPSC showed no differentiation deficit compared to control iPSC lines, exhibiting comparable expression of all relevant markers at each stage of differentiation. OPA1+/- and OPA1 variant iPSC-RGCs exhibited impaired mitochondrial homeostasis, with reduced bioenergetic output and compromised mitochondrial DNA maintenance. These data highlight mitochondrial deficits associated with OPA1 dysfunction in human iPSC-RGCs, and establish a platform to study disease mechanisms that contribute to RGC loss in DOA, as well as potential therapeutic interventions.

Prenatal exposure to environmental pro-oxidants induces mitochondria-mediated epigenetic changes: a cross-sectional pilot study

Mitochondria play a central role in maintaining cellular and metabolic homeostasis during vital development cycles of foetal growth. Optimal mitochondrial functions are important not only to sustain adequate energy production but also for regulated epigenetic programming. However, these organelles are subtle targets of environmental exposures, and any perturbance in the defined mitochondrial machinery during the developmental stage can lead to the re-programming of the foetal epigenetic landscape. As these modifications can be transferred to subsequent generations, we herein performed a cross-sectional study to have an in-depth understanding of this intricate phenomenon. The study was conducted with two arms: whereas the first group consisted of in utero pro-oxidant exposed individuals and the second group included controls. Our results showed higher levels of oxidative mtDNA damage and associated integrated stress response among the exposed individuals. These disturbances were found to be closely related to the observed discrepancies in mitochondrial biogenesis. The exposed group showed mtDNA hypermethylation and changes in allied mitochondrial functioning. Altered expression of mitomiRs and their respective target genes in the exposed group indicated the possibilities of a disturbed mitochondrial-nuclear cross talk. This was further confirmed by the modified activity of the mitochondrial stress regulators and pro-inflammatory mediators among the exposed group. Importantly, the disturbed DNMT functioning, hypermethylation of nuclear DNA, and higher degree of post-translational histone modifications established the existence of aberrant epigenetic modifications in the exposed individuals. Overall, our results demonstrate the first molecular insights of in utero pro-oxidant exposure associated changes in the mitochondrial-epigenetic axis. Although, our study might not cement an exposure-response relationship for any particular environmental pro-oxidant, but suffice to establish a dogma of mito-epigenetic reprogramming at intrauterine milieu with chronic illness, a hitherto unreported interaction.

The E3 Ubiquitin Ligase SYVN1 Plays an Antiapoptotic Role in Polycystic Ovary Syndrome by Regulating Mitochondrial Fission

Polycystic ovary syndrome (PCOS) is one of the most common hormonal disorders among premenopausal women. PCOS is accompanied by many other reproductive, endocrinal, and metabolic disorders thus amassing the difficulties encountered by the women affected. However, there is limited information on its molecular etiology. Synoviolin (SYVN1) is an E3 ubiquitin ligase that is thought to participate in the pathology of PCOS. However, the expression and function of SYVN1 in PCOS are unknown. In this study, we found that downregulation of SYVN1 expression was followed by increased apoptosis in the granulosa cells (GCs) of patients with PCOS. Subsequent in vitro experiments indicated that the overexpression of SYVN1 inhibited apoptosis and mitochondrial fission. Furthermore, using immunoprecipitation and western blotting, we identified that SYVN1 promoted the degradation of Drp1 via the proteasome-dependent pathway. Additionally, we generated a PCOS model in female Sprague Dawley rats and treated them with an SYVN1 inhibitor, LS-102. We observed that the inhibition of SYVN1 increased Drp1 levels and exacerbated the degeneration of GCs in the PCOS rat model. Finally, in vitro and in vivo experiments showed that SYVN1 inhibits apoptosis and mitochondrial fission by promoting Drp1 degradation in GCs. These results highlight the function of SYVN1 in PCOS and provide a potential target for the clinical treatment of PCOS.

Resveratrol: A potential therapeutic natural polyphenol for neurodegenerative diseases associated with mitochondrial dysfunction

Most polyphenols can cross blood-brain barrier, therefore, they are widely utilized in the treatment of various neurodegenerative diseases (ND). Resveratrol, a natural polyphenol contained in blueberry, grapes, mulberry, etc., is well documented to exhibit potent neuroprotective activity against different ND by mitochondria modulation approach. Mitochondrial function impairment is the most common etiology and pathological process in various neurodegenerative disorders, viz. Alzheimer’s disease, Parkinson’s disease, Huntington’s disease and amyotrophic lateral sclerosis. Nowadays these ND associated with mitochondrial dysfunction have become a major threat to public health as well as health care systems in terms of financial burden. Currently available therapies for ND are limited to symptomatic cures and have inevitable toxic effects. Therefore, there is a strict requirement for a safe and highly effective drug treatment developed from natural compounds. The current review provides updated information about the potential of resveratrol to target mitochondria in the treatment of ND.

Mitochondrial DNA maintenance defects: potential therapeutic strategies

Mitochondrial DNA (mtDNA) replication depends on the mitochondrial import of hundreds of nuclear encoded proteins that control the mitochondrial genome maintenance and integrity. Defects in these processes result in an expanding group of disorders called mtDNA maintenance defects that are characterized by mtDNA depletion and/or multiple mtDNA deletions with variable phenotypic manifestations. As it applies for mitochondrial disorders in general, current treatment options for mtDNA maintenance defects are limited. Lately, with the development of model organisms, improved understanding of the pathophysiology of these disorders, and a better knowledge of their natural history, the number of preclinical studies and existing and planned clinical trials has been increasing. In this review, we discuss recent preclinical studies and current and future clinical trials concerning potential therapeutic options for the different mtDNA maintenance defects.

STAT6 in mitochondrial outer membrane impairs mitochondrial fusion by inhibiting MFN2 dimerization

Although it is reported that mitochondria-localized nuclear transcription factors (TFs) regulate mitochondrial processes such as apoptosis and mitochondrial transcription/respiration, the functions and mechanisms of mitochondrial dynamics regulated by mitochondria-localized nuclear TFs are yet to be fully characterized. Here, we identify STAT6 as a mitochondrial protein that is localized in the outer membrane of mitochondria (OMM). STAT6 in OMM inhibits mitochondrial fusion by blocking MFN2 dimerization. This implies that STAT6 has a critical role in mitochondrial dynamics. Moreover, mitochondrial accumulation of STAT6 in response to hypoxic conditions reveals that STAT6 is a regulator of mitochondrial processes including fusion/fission mechanisms.

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STAT6 has mitochondrial-targeting sequences and anchoring transmembrane segments

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STAT6 in OMM attenuates mitochondrial fusion by blocking MFN2 dimerization

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Hypoxia-induced STAT6 mitochondrial accumulation inhibits tumorigenesis

Integrated metabolism and epigenetic modifications in the macrophages of mice in responses to cold stress

The negative effects of low temperature can readily induce a variety of diseases. We sought to understand the reasons why cold stress induces disease by studying the mechanisms of fine-tuning in macrophages following cold exposure. We found that cold stress triggers increased macrophage activation accompanied by metabolic reprogramming of aerobic glycolysis. The discovery, by genome-wide RNA sequencing, of defective mitochondria in mice macrophages following cold exposure indicated that mitochondrial defects may contribute to this process. In addition, changes in metabolism drive the differentiation of macrophages by affecting histone modifications. Finally, we showed that histone acetylation and lactylation are modulators of macrophage differentiation following cold exposure. Collectively, metabolism-related epigenetic modifications are essential for the differentiation of macrophages in cold-stressed mice, and the regulation of metabolism may be crucial for alleviating the harm induced by cold stress.

Disturbance of Mitochondrial Dynamics, Endoplasmic Reticulum-Mitochondria Crosstalk, Redox Homeostasis, and Inflammatory Response in the Brain of Glutaryl-CoA Dehydrogenase-Deficient Mice: Neuroprotective Effects of Bezafibrate

Patients with glutaric aciduria type 1 (GA1), a neurometabolic disorder caused by deficiency of glutaryl-CoA dehydrogenase (GCDH) activity, commonly manifest acute encephalopathy associated with severe striatum degeneration and progressive cortical and striatal injury whose pathogenesis is still poorly known. We evaluated redox homeostasis, inflammatory response, mitochondrial biogenesis and dynamics, endoplasmic reticulum (ER)-mitochondria crosstalk, and ER stress in the brain of GCDH-deficient (Gcdh^-/-) and wild-type (Gcdh^+/+) mice fed a high Lys chow, which better mimics the human neuropathology mainly characterized by striatal lesions. Increased lipid peroxidation and altered antioxidant defenses, including decreased concentrations of reduced glutathione and increased activities of superoxide dismutase, catalase, and glutathione transferase, were observed in the striatum and cerebral cortex of Gcdh^-/- mice. Augmented Iba-1 staining was also found in the dorsal striatum and neocortex, whereas the nuclear content of NF-κB was increased, and the cytosolic content of IκBα decreased in the striatum of the mutant animals, indicating a pro-inflammatory response. Noteworthy, in vivo treatment with the pan-PPAR agonist bezafibrate normalized these alterations. It was also observed that the ER-mitochondria crosstalk proteins VDAC1 and IP3R were reduced, whereas the ER stress protein DDIT3 was augmented in Gcdh^-/- striatum, signaling disturbances of these processes. Finally, DRP1 content was elevated in the striatum of Gcdh^-/- mice, indicating activated mitochondrial fission. We presume that some of these novel pathomechanisms may be involved in GA1 neuropathology and that bezafibrate should be tested as a potential adjuvant therapy for GA1.

The mitochondrial profile in women with polycystic ovary syndrome: impact of exercise

Polycystic ovary syndrome (PCOS) is a common endocrine disorder affecting pre-menopausal women and involves metabolic dysregulation. Despite the high prevalence of insulin resistance, the existence of mitochondrial dysregulation and its role in the pathogenesis of PCOS is not clear. Exercise is recommended as the first-line therapy for women with PCOS. In particular, high-intensity interval training (HIIT) is known to improve metabolic health and enhance mitochondrial characteristics. In this narrative review, the existing knowledge of mitochondrial characteristics in skeletal muscle and adipose tissue of women with PCOS and the effect of exercise interventions in ameliorating metabolic and mitochondrial health in these women are discussed. Even though the evidence on mitochondrial dysfunction in PCOS is limited, some studies point to aberrant mitochondrial functions mostly in skeletal muscle, while there is very little research in adipose tissue. Although most exercise intervention studies in PCOS report improvements in metabolic health, they show diverse and inconclusive findings in relation to mitochondrial characteristics. A limitation of the current study is the lack of comprehensive mitochondrial analyses and the diversity in exercise modalities, with only one study investigating the impact of HIIT alone. Therefore, further comprehensive large-scale exercise intervention studies are required to understand the association between metabolic dysfunction and aberrant mitochondrial profile, and the molecular mechanisms underlying the exercise-induced metabolic adaptations in women with PCOS.

The role of DRP1- PINK1-Parkin-mediated mitophagy in early cadmium-induced liver damage

Cadmium (Cd) is an important environmental pollutant that causes varying degrees of damage to multiple systems of the body. However, the specific mechanism of Cd-induced liver mitophagy remains unclear. In the present study, 5-week-old BALB/c mice and a mouse liver parenchyma cell line (AML12) were studied using a combination of in vivo and in vitro studies. We found that Cd damaged liver cells, destroy the structure and function of mitochondria, and increased the production of superoxide anions. This study further examined the effect of Cd on mitochondrial dynamics and mitophagy and showed that Cd increased mitochondrial division and induced mitophagy. The PINK1-Parkin pathway is a classical mitophagy pathway. Cd-induced mitophagy was inhibited after significantly knocking down Pink1. Mdivi-1 can effectively inhibit mitochondrial division. In this study, Mdivi-1 inhibited the expression of DRP1 and significantly inhibited the occurrence of mitophagy induced by Cd. We further examined the effect of Cd on mitophagy flux. Cd did not increase lysosomal colocalization with mitochondria. In summary, Cd increase the level of oxidative stress, destroy the structure and function of mitochondria, destroy the homeostasis of mitochondrial division and fusion, induce mitophagy through the PINK1-Parkin pathway. Mitophagy plays a protective role in early cadmium-induced liver damage.

Potential Combination Drug Therapy to Prevent Redox Stress and Mitophagy Dysregulation in Retinal Müller Cells under High Glucose Conditions: Implications for Diabetic Retinopathy

Chronic hyperglycemia-induced thioredoxin-interacting protein (TXNIP) expression, associated oxidative/nitrosative stress (ROS/RNS), and mitochondrial dysfunction play critical roles in the etiology of diabetic retinopathy (DR). However, there is no effective drug treatment to prevent or slow down the progression of DR. The purpose of this study is to examine if a combination drug treatment targeting TXNIP and the mitochondria-lysosome pathway prevents high glucose-induced mitochondrial stress and mitophagic flux in retinal Müller glial cells in culture, relevant to DR. We show that diabetes induces TXNIP expression, redox stress, and Müller glia activation (gliosis) in rat retinas when compared to non-diabetic rat retinas. Furthermore, high glucose (HG, 25 mM versus low glucose, LG 5.5 mM) also induces TXNIP expression and mitochondrial stress in a rat retinal Müller cell line, rMC1, in in vitro cultures. Additionally, we develop a mitochondria-targeted mCherry and EGFP probe tagged with two tandem COX8a mitochondrial target sequences (adenovirus-CMV-2×mt8a-CG) to examine mitophagic flux in rMC1. A triple drug combination treatment was applied using TXNIP-IN1 (which inhibits TXNIP interaction with thioredoxin), Mito-Tempo (mitochondrial anti-oxidant), and ML-SA1 (lysosome targeted activator of transient calcium channel MCOLN1/TRPML1 and of transcription factor TFEB) to study the mitochondrial-lysosomal axis dysregulation. We found that HG induces TXNIP expression, redox stress, and mitophagic flux in rMC1 versus LG. Treatment with the triple drug combination prevents mitophagic flux and restores transcription factor TFEB and PGC1α nuclear localization under HG, which is critical for lysosome biosynthesis and mitogenesis, respectively. Our results demonstrate that 2×mt8a-CG is a suitable probe for monitoring mitophagic flux, both in live and fixed cells in in vitro experiments, which may also be applicable to in vivo animal studies, and that the triple drug combination treatment has the potential for preventing retinal injury and disease progression in diabetes.

CRISPR-Cas9 correction of OPA1 c.1334G>A: p.R445H restores mitochondrial homeostasis in dominant optic atrophy patient-derived iPSCs

Autosomal dominant optic atrophy (DOA) is the most common inherited optic neuropathy in the United Kingdom. DOA has an insidious onset in early childhood, typically presenting with bilateral, central visual loss caused by the preferential loss of retinal ganglion cells. 60%-70% of genetically confirmed DOA cases are associated with variants in OPA1, a ubiquitously expressed GTPase that regulates mitochondrial homeostasis through coordination of inner membrane fusion, maintenance of cristae structure, and regulation of bioenergetic output. Whether genetic correction of OPA1 pathogenic variants can alleviate disease-associated phenotypes remains unknown. Here, we demonstrate generation of patient-derived OPA1 c.1334G>A: p.R445H mutant induced pluripotent stem cells (iPSCs), followed by correction of OPA1 through CRISPR-Cas9-guided homology-directed repair (HDR) and evaluate the effect of OPA1 correction on mitochondrial homeostasis. CRISPR-Cas9 gene editing demonstrated an efficient method of OPA1 correction, with successful gene correction in 57% of isolated iPSCs. Correction of OPA1 restored mitochondrial homeostasis, re-establishing the mitochondrial network and basal respiration and ATP production levels. In addition, correction of OPA1 re-established the levels of wild-type (WT) mitochondrial DNA (mtDNA) and reduced susceptibility to apoptotic stimuli. These data demonstrate that nuclear gene correction can restore mitochondrial homeostasis and improve mtDNA integrity in DOA patient-derived cells carrying an OPA1 variant.

The Multifaceted Regulation of Mitochondrial Dynamics During Mitosis

Mitosis ensures genome integrity by mediating precise segregation of the duplicated genetic material. Segregation of subcellular organelles during mitosis also needs to be tightly coordinated in order to warrant their proper inheritance and cellular homeostasis. The inheritance of mitochondria, a powerhouse of the cell, is tightly regulated in order to meet the high energy demand to fuel the mitotic machinery. Mitochondria are highly dynamic organelles, which undergo events of fission, fusion and transport during different cell cycle stages. Importantly, during mitosis several kinases phosphorylate the key mitochondrial factors and drive fragmentation of mitochondria to allow for their efficient distribution and inheritance to two daughter cells. Recent evidence suggests that mitochondrial fission can also actively contribute to the regulation of mitotic progression. This review aims at summarizing established and emerging concepts about the complex regulatory networks which couple crucial mitotic factors and events to mitochondrial dynamics and which could be implicated in human disease.

Drp1-dependent mitochondrial fission mediates corneal injury induced by alkali burn

Corneal alkali burn, one of the most serious ophthalmic emergencies, is difficult to be cured by conservative treatments. It is well known that oxidative stress, inflammation and neovascularization are the main causes of corneal damage after alkali burn, but its underlying mechanism remains to be elucidated. Here, we reported that the expression and phosphorylation (Ser616) of mitochondrial fission protein Drp1 were up-regulated at day 3 after alkali burn, while mitochondrial fusion protein Mfn2 was down-regulated. The phosphorylation of ERK1/2 in corneas was increased at day 1, 3, 7 and peaked at day 3 after alkali burn. In human corneal epithelial cells (HCE-2), NaOH treatment induced mitochondrial fission, intracellular ROS production and mitochondrial membrane potential disruption, which was prevented by Drp1 inhibitor Mdivi-1. In corneas, Mdivi-1 or knockdown of Drp1 by Lenti-Drp1 shRNA attenuated alkali burn-induced ROS production and phosphorylation of IκBα and p65. In immunofluorescence staining, it was detected that Mdivi-1 also prevented NaOH-induced nuclear translocation of p65 in HCE-2 cells. Moreover, the expression of NADPH oxidase NOX2 and NOX4 in corneas peaked at day 7 after alkali burn. Mdivi-1, Lenti-Drp1 shRNA or the mitochondria-targeted antioxidant mito-TEMPO efficiently alleviated activation of NF-κB, expression of NOX2/4 and inflammatory cytokines including IL-6, IL-1β and TNF-α in corneas after alkali burn. In pharmacological experiments, both Mdivi-1 and NADPH oxidases inhibitor Apocynin protected the corneas against alkali burn-induced neovascularization. Intriguingly, the combined administration of Mdivi-1 and Apocynin had a synergistic inhibitory effect on corneal neovascularization after alkali burn. Taken together, these results indicate that Drp1-dependent mitochondrial fission is involved in alkali burn-induced corneal injury through regulating oxidative stress, inflammatory responses and corneal neovascularization. This might provide a novel therapeutic target for corneal injury after alkali burn in the future.

Novel Insights Into the Role of Mitochondria-Derived Peptides in Myocardial Infarction

Mitochondria-derived peptides (MDPs) are a new class of bioactive peptides encoded by small open reading frames (sORFs) within known mitochondrial DNA (mtDNA) genes. MDPs may affect the expression of nuclear genes and play cytoprotective roles against chronic and age-related diseases by maintaining mitochondrial function and cell viability in the face of metabolic stress and cytotoxic insults. In this review, we summarize clinical and experimental findings indicating that MDPs act as local and systemic regulators of glucose homeostasis, immune and inflammatory responses, mitochondrial function, and adaptive stress responses, and focus on evidence supporting the protective effects of MDPs against myocardial infarction. These insights into MDPs actions suggest their potential in the treatment of cardiovascular diseases and should encourage further research in this field.

Blocked O-GlcNAc cycling alters mitochondrial morphology, function, and mass

O-GlcNAcylation is a prevalent form of glycosylation that regulates proteins within the cytosol, nucleus, and mitochondria. The O-GlcNAc modification can affect protein cellular localization, function, and signaling interactions. The specific impact of O-GlcNAcylation on mitochondrial morphology and function has been elusive. In this manuscript, the role of O-GlcNAcylation on mitochondrial fission, oxidative phosphorylation (Oxphos), and the activity of electron transport chain (ETC) complexes were evaluated. In a cellular environment with hyper O-GlcNAcylation due to the deletion of O-GlcNAcase (OGA), mitochondria showed a dramatic reduction in size and a corresponding increase in number and total mitochondrial mass. Because of the increased mitochondrial content, OGA knockout cells exhibited comparable coupled mitochondrial Oxphos and ATP levels when compared to WT cells. However, we observed reduced protein levels for complex I and II when comparing normalized mitochondrial content and reduced linked activity for complexes I and III when examining individual ETC complex activities. In assessing mitochondrial fission, we observed increased amounts of O-GlcNAcylated dynamin-related protein 1 (Drp1) in cells genetically null for OGA and in glioblastoma cells. Individual regions of Drp1 were evaluated for O-GlcNAc modifications, and we found that this post-translational modification (PTM) was not limited to the previously characterized residues in the variable domain (VD). Additional modification sites are predicted in the GTPase domain, which may influence enzyme activity. Collectively, these results highlight the impact of O-GlcNAcylation on mitochondrial dynamics and ETC function and mimic the changes that may occur during glucose toxicity from hyperglycemia.

A preferred sequence for organelle inheritance during polarized cell growth

Some organelles cannot be synthesized anew, so they are segregated into daughter cells during cell division. In Saccharomyces cerevisiae, daughter cells bud from mother cells and are populated by organelles inherited from the mothers. To determine whether this organelle inheritance occurs in a stereotyped manner, we tracked organelles using fluorescence microscopy. We describe a program for organelle inheritance in budding yeast. The cortical endoplasmic reticulum (ER) and peroxisomes are inherited concomitantly with bud emergence. Next, vacuoles are inherited in small buds, followed closely by mitochondria. Finally, the nucleus and perinuclear ER are inherited when buds have nearly reached their maximal size. Because organelle inheritance timing correlates with bud morphology, which is coupled to the cell cycle, we tested whether disrupting the cell cycle alters organelle inheritance order. By arresting cell cycle progression but allowing continued bud growth, we determined that organelle inheritance still occurs when DNA replication is blocked, and that the general inheritance order is maintained. Thus, organelle inheritance follows a preferred order during polarized cell division and does not require completion of S-phase.

Summary: Organelles are interconnected by contact sites, but they must be inherited from mother cells into buds during budding yeast mitosis. We report that this process occurs in a preferred sequence.

Exosomes from adipose-derived mesenchymal stem cells alleviate liver ischaemia reperfusion injury subsequent to hepatectomy in rats by regulating mitochondrial dynamics and biogenesis

Hepatic ischaemia reperfusion injury (HIRI) is a major factor leading to liver dysfunction after liver resection and liver transplantation. Adipose-derived mesenchymal stem cells (ADSCs) have potential therapeutic effects on HIRI. Exosomes derived from ADSCs (ADSCs-exo) have been widely studied as an alternative of ADSCs therapy. Thus, the aim of this study was to evaluate the potential protective effect and related mechanism of ADSCs-exo on HIRI subsequent to hepatectomy. Rats were randomly divided into four groups: Sham, I30R+PH, ADSCs and ADSCs-exo group. After 24 h of reperfusion, liver and serum of the rats were immediately collected. ADSCs-exo improved liver function, inhibited oxidative stress and reduced apoptosis of hepatocytes in HIRI subsequent to hepatectomy in rats. ADSCs-exo significantly promoted the recovery of mitochondrial function, markedly increased the content of ATP in the liver tissue, and improved the ultrastructure of mitochondria in hepatocytes. Moreover, ADSCs-exo significantly increased the expression of OPA-1, MFN-1 and MFN-2 proteins related to mitochondrial fusion, while DRP-1 and Fis-1 mRNA and protein expression associated with mitochondrial fission were significantly decreased after the treatment with ADSCs-exo. In addition, ADSCs-exo significantly increased the expression of PGC-1α, NRF-1 and TFAM genes and proteins related to mitochondrial biogenesis. ADSCs-exo improves liver function induced by HIRI subsequent to hepatectomy in rats and maintains mitochondrial homeostasis by inhibiting mitochondrial fission, promoting mitochondrial fusion and promoting mitochondrial biogenesis. Therefore, ADSCs-exo may be considered as a potential promising alternative to ADSCs in the treatment of HIRI subsequent to hepatectomy.

Dose-Dependent Response to the Environmental Pollutant Dichlorodipheniletylhene (DDE) in HepG2 Cells: Focus on Cell Viability and Mitochondrial Fusion/Fission Proteins

Dichlorodiphenyldichloroethylene (DDE), the primary persistent metabolite of dichlorodiphenyltrichloroethane (DDT), has toxic effects on cells, but its dose-dependent impact on mitochondrial proteins involved in mitochondrial fusion and fission processes associated with cell viability impairment has not yet been analysed. Mitochondrial fusion and fission processes are critical to maintaining the mitochondrial network and allowing the cell to respond to external stressors such as environmental pollutants. Fusion processes are associated with optimizing mitochondrial function, whereas fission processes are associated with removing damaged mitochondria. We assessed the effects of different DDE doses, ranging between 0.5 and 100 µM, on cell viability and mitochondrial fusion/fission proteins in an in vitro hepatic cell model (human hepatocarcinomatous cells, HepG2); the DDE induced a decrease in cell viability in a dose-dependent manner, and its effect was enhanced in conditions of coincubation with dietary fatty acids. Fusion protein markers exhibited an inverted U-shape dose-response curve, showing the highest content in the 2.5–25 μM DDE dose range. The fission protein marker was found to increase significantly, leading to an increased fission/fusion ratio with high DDE doses. The low DDE doses elicited cell adaption by stimulating mitochondrial dynamics machinery, whereas high DDE doses induced cell viability loss associated with mitochondrial dynamics to shift toward fission. Present results are helpful to clarify the mechanisms underlying the cell fate towards survival or death in response to increasing doses of environmental pollutants.

Mechanical forces and metabolic changes cooperate to drive cellular memory and endothelial phenotypes

Endothelial cells line the innermost layer of arterial, venous, and lymphatic vascular tree and accordingly are subject to hemodynamic, stretch, and stiffness mechanical forces. Normally quiescent, endothelial cells have a hemodynamic set point and become "activated" in response to disturbed hemodynamics, which may signal impending nutrient or gas depletion. Endothelial cells in the majority of tissue beds are normally inactivated and maintain vessel barrier functions, are anti-inflammatory, anti-coagulant, and anti-thrombotic. However, under aberrant mechanical forces, endothelial signaling transforms in response, resulting cellular changes that herald pathological diseases. Endothelial cell metabolism is now recognized as the primary intermediate pathway that undergirds cellular transformation. In this review, we discuss the various mechanical forces endothelial cells sense in the large vessels, microvasculature, and lymphatics, and how changes in environmental mechanical forces result in changes in metabolism, which ultimately influence cell physiology, cellular memory, and ultimately disease initiation and progression.

Inheritance of the reduced mitochondria of Giardia intestinalis is coupled to the flagellar maturation cycle

Background

The presence of mitochondria is a distinguishing feature between prokaryotic and eukaryotic cells. It is currently accepted that the evolutionary origin of mitochondria coincided with the formation of eukaryotes and from that point control of mitochondrial inheritance was required. Yet, the way the mitochondrial presence has been maintained throughout the eukaryotic cell cycle remains a matter of study. Eukaryotes control mitochondrial inheritance mainly due to the presence of the genetic component; still only little is known about the segregation of mitochondria to daughter cells during cell division. Additionally, anaerobic eukaryotic microbes evolved a variety of genomeless mitochondria-related organelles (MROs), which could be theoretically assembled de novo, providing a distinct mechanistic basis for maintenance of stable mitochondrial numbers. Here, we approach this problem by studying the structure and inheritance of the protist Giardia intestinalis MROs known as mitosomes.

Results

We combined 2D stimulated emission depletion (STED) microscopy and focused ion beam scanning electron microscopy (FIB/SEM) to show that mitosomes exhibit internal segmentation and conserved asymmetric structure. From a total of about forty mitosomes, a small, privileged population is harnessed to the flagellar apparatus, and their life cycle is coordinated with the maturation cycle of G. intestinalis flagella. The orchestration of mitosomal inheritance with the flagellar maturation cycle is mediated by a microtubular connecting fiber, which physically links the privileged mitosomes to both axonemes of the oldest flagella pair and guarantees faithful segregation of the mitosomes into the daughter cells.

Conclusion

Inheritance of privileged Giardia mitosomes is coupled to the flagellar maturation cycle. We propose that the flagellar system controls segregation of mitochondrial organelles also in other members of this supergroup (Metamonada) of eukaryotes and perhaps reflects the original strategy of early eukaryotic cells to maintain this key organelle before mitochondrial fusion-fission dynamics cycle as observed in Metazoa was established.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01129-7.

LATS2 Deletion Attenuates Myocardial Ischemia-Reperfusion Injury by Promoting Mitochondrial Biogenesis

Reperfusion therapy is the most effective treatment for acute myocardial infarction, but it can damage cardiomyocytes through a mechanism known as myocardial ischemia/reperfusion injury (MIRI). In this study, we investigated whether the large tumor suppressor kinase 2 (LATS2) contributes to the development of myocardial MIRI by disrupting mitochondrial biogenesis. Our in vitro data demonstrate that cardiomyocyte viability was reduced and apoptosis was increased in response to hypoxia/reoxygenation (H/R) injury. However, suppression of LATS2 by shRNA sustained cardiomyocyte viability by maintaining mitochondrial function. Compared to H/R-treated control cardiomyocytes, cardiomyocytes transfected with LATS2 shRNA exhibited increased mitochondrial respiration, improved mitochondrial ATP generation, and more stable mitochondrial membrane potential. LATS2 suppression increased cardiomyocyte viability and mitochondrial biogenesis in a manner dependent on PGC1α, a key regulator of mitochondrial metabolism. These results identify LATS2 as a new inducer of mitochondrial damage and myocardial MIRI and suggest that approaches targeting LATS2 or mitochondrial biogenesis may be beneficial in the clinical management of cardiac MIRI.

Mitostasis, Calcium and Free Radicals in Health, Aging and Neurodegeneration

Mitochondria play key roles in ATP supply, calcium homeostasis, redox balance control and apoptosis, which in neurons are fundamental for neurotransmission and to allow synaptic plasticity. Their functional integrity is maintained by mitostasis, a process that involves mitochondrial transport, anchoring, fusion and fission processes regulated by different signaling pathways but mainly by the peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α). PGC-1α also favors Ca²⁺ homeostasis, reduces oxidative stress, modulates inflammatory processes and mobilizes mitochondria to where they are needed. To achieve their functions, mitochondria are tightly connected to the endoplasmic reticulum (ER) through specialized structures of the ER termed mitochondria-associated membranes (MAMs), which facilitate the communication between these two organelles mainly to aim Ca²⁺ buffering. Alterations in mitochondrial activity enhance reactive oxygen species (ROS) production, disturbing the physiological metabolism and causing cell damage. Furthermore, cytosolic Ca²⁺ overload results in an increase in mitochondrial Ca²⁺, resulting in mitochondrial dysfunction and the induction of mitochondrial permeability transition pore (mPTP) opening, leading to mitochondrial swelling and cell death through apoptosis as demonstrated in several neuropathologies. In summary, mitochondrial homeostasis is critical to maintain neuronal function; in fact, their regulation aims to improve neuronal viability and to protect against aging and neurodegenerative diseases.