Control of mitochondrial morphology by a human mitofusin

Beyond fission and fusion-Diving into the mysteries of mitochondrial shape

Mitochondrial shape and network formation have been primarily associated with the well-established processes of fission and fusion. However, recent research has unveiled an intricate and multifaceted landscape of mitochondrial morphology that extends far beyond the conventional fission-fusion paradigm. These less-explored dimensions harbor numerous unresolved mysteries. This review navigates through diverse processes influencing mitochondrial shape and network formation, highlighting the intriguing complexities and gaps in our understanding of mitochondrial architecture. The exploration encompasses various scales, from biophysical principles governing membrane dynamics to molecular machineries shaping mitochondria, presenting a roadmap for future research in this evolving field.

Mitochondrial motility modulators coordinate quality control dynamics to promote neuronal health

Dysfunction in mitochondrial maintenance and trafficking is commonly correlated with the development of neurodegenerative disorders such as Parkinson's disease and Alzheimer's disease. Thus, biomedical research has been dedicated to understanding how architecturally complex neurons maintain and transport their mitochondria. However, the systems that coordinate mitochondrial QC (quality control) dynamics and trafficking in response to neuronal activity and stress are less understood. Additionally, the degree of integration between the processes of mitochondrial trafficking and QC is unclear. Recent work indicates that mitochondrial motility modulators (i.e., anchors and tethers) help coordinate mitochondrial health by mediating distinct, stress-level-appropriate QC pathways following mitochondrial damage. This review summarizes current evidence supporting the role of two mitochondrial motility modulators, Syntaphilin and Mitofusin 2, in coordinating mitochondrial QC to promote neuronal health. Exploring motility modulators' intricate regulatory molecular landscape may reveal new therapeutic targets for delaying disease progression and enhancing neuronal survival post-insult.

Fenofibrate reduces cardiac remodeling by mitochondrial dynamics preservation in a renovascular model of cardiac hypertrophy

Fenofibrate, a PPAR-α agonist clinically used to lower serum lipid levels, reduces cardiac remodeling and improves cardiac function. However, its mechanism of action is not completely elucidated. In this study we examined the effect of fenofibrate on mitochondria in a rat model of renovascular hypertension, focusing on mediators controlling mitochondrial dynamics and autophagy. Rats with two-kidney one-clip (2K1C) hypertension were treated with fenofibrate 150 mg/kg/day (2K1C-FFB) or vehicle (2K1C-VEH) for 8 weeks. Systolic blood pressure and cardiac functional were in-vivo assessed, while cardiomyocyte size and protein expression of mediators of cardiac hypertrophy and mitochondrial dynamics were ex-vivo examined by histological and Western blot analyses. Fenofibrate treatment counteracted the development of hypertension and the increase of left ventricular mass, relative wall thickness and cross-sectional area of cardiomyocytes. Furthermore, fenofibrate re-balanced the expression Mfn2, Drp1 and Parkin, regulators of fusion, fission, mitophagy respectively. Regarding autophagy, the LC3-II/LC3-I ratio was increased in 2K1C-VEH and 2K1C-FFB, whereas the autophagy was increased only in 2K1C-FFB. In cultured H9C2 cardiomyoblasts, fenofibrate reversed the Ang II-induced mRNA up-regulation of hypertrophy markers Nppa and Myh7, accumulation of reactive oxygen species and depolarization of the mitochondrial membrane exerting protection mediated by up-regulation of the Uncoupling protein 2. Our results indicate that fenofibrate acts directly on cardiomyocytes and counteracts the pressure overload-induced cardiac maladaptive remodeling. This study reveals a so far hidden mechanism involving mitochondrial dynamics in the beneficial effects of fenofibrate, support its repurposing for the treatment of cardiac hypertrophy and provide new potential targets for its pharmacological function.

Is mitochondrial morphology important for cellular physiology?

Mitochondria are double membrane-bound organelles the network morphology of which in cells is shaped by opposing events of fusion and fission executed by dynamin-like GTPases. Mutations in these genes can perturb the form and functions of mitochondria in cell and animal models of mitochondrial diseases. An expanding array of chemical, mechanical, and genetic stressors can converge on mitochondrial-shaping proteins and disrupt mitochondrial morphology. In recent years, studies aimed at disentangling the multiple roles of mitochondrial-shaping proteins beyond fission or fusion have provided insights into the homeostatic relevance of mitochondrial morphology. Here, I review the pleiotropy of mitochondrial fusion and fission proteins with the aim of understanding whether mitochondrial morphology is important for cell and tissue physiology.

Atg44/Mdi1/mitofissin facilitates Dnm1-mediated mitochondrial fission

Mitochondria undergo fission and fusion, and their coordinated balance is crucial for maintaining mitochondrial homeostasis. In yeast, the dynamin-related protein Dnm1 is a mitochondrial fission factor acting from outside the mitochondria. We recently reported the mitochondrial intermembrane space protein Atg44/mitofissin/Mdi1/Mco8 as a novel fission factor, but the relationship between Atg44 and Dnm1 remains elusive. Here, we show that Atg44 is required to complete Dnm1-mediated mitochondrial fission under homeostatic conditions. Atg44-deficient cells often exhibit enlarged mitochondria with accumulated Dnm1 and rosary-like mitochondria with Dnm1 foci at constriction sites. These mitochondrial constriction sites retain the continuity of both the outer and inner membranes within an extremely confined space, indicating that Dnm1 is unable to complete mitochondrial fission without Atg44. Moreover, accumulated Atg44 proteins are observed at mitochondrial constriction sites. These findings suggest that Atg44 and Dnm1 cooperatively execute mitochondrial fission from inside and outside the mitochondria, respectively.Abbreviation: ATG: autophagy related; CLEM: correlative light and electron microscopy; EM: electron microscopy; ER: endoplasmic reticulum; ERMES: endoplasmic reticulum-mitochondria encounter structure; GA: glutaraldehyde; GFP: green fluorescent protein; GTP: guanosine triphosphate: IMM: inner mitochondrial membrane; IMS: intermembrane space; OMM: outer mitochondrial membrane; PB: phosphate buffer; PBS: phosphate-buffered saline; PFA: paraformaldehyde; RFP: red fluorescent protein; WT: wild type.

UCP2 and pancreatic cancer: conscious uncoupling for therapeutic effect

Pancreatic cancer has an exaggerated dependence on mitochondrial metabolism, but methods to specifically target the mitochondria without off target effects in normal tissues that rely on these organelles is a significant challenge. The mitochondrial uncoupling protein 2 (UCP2) has potential as a cancer-specific drug target, and thus, we will review the known biology of UCP2 and discuss its potential role in the pathobiology and future therapy of pancreatic cancer.

Epigenetic Regulation of Cardiomyocyte Maturation by Arginine Methyltransferase CARM1

BACKGROUND

During the neonatal stage, the cardiomyocyte undergoes a constellation of molecular, cytoarchitectural, and functional changes known collectively as cardiomyocyte maturation to increase myocardial contractility and cardiac output. Despite the importance of cardiomyocyte maturation, the molecular mechanisms governing this critical process remain largely unexplored.

METHODS

We leveraged an in vivo mosaic knockout system to characterize the role of Carm1, the founding member of protein arginine methyltransferase, in cardiomyocyte maturation. Using a battery of assays, including immunohistochemistry, immuno-electron microscopy imaging, and action potential recording, we assessed the effect of loss of Carm1 function on cardiomyocyte cell growth, myofibril expansion, T-tubule formation, and electrophysiological maturation. Genome-wide transcriptome profiling, H3R17me2a chromatin immunoprecipitation followed by sequencing, and assay for transposase-accessible chromatin with high-throughput sequencing were used to investigate the mechanisms by which CARM1 (coactivator-associated arginine methyltransferase 1) regulates cardiomyocyte maturation. Finally, we interrogated the human syntenic region to the H3R17me2a chromatin immunoprecipitation followed by sequencing peaks for single-nucleotide polymorphisms associated with human heart diseases.

RESULTS

We report that mosaic ablation of Carm1 disrupts multiple aspects of cardiomyocyte maturation cell autonomously, leading to reduced cardiomyocyte size and sarcomere thickness, severe loss and disorganization of T tubules, and compromised electrophysiological maturation. Genomics study demonstrates that CARM1 directly activates genes that underlie cardiomyocyte cytoarchitectural and electrophysiological maturation. Moreover, our study reveals significant enrichment of human heart disease-associated single-nucleotide polymorphisms in the human genomic region syntenic to the H3R17me2a chromatin immunoprecipitation followed by sequencing peaks.

CONCLUSIONS

This study establishes a critical and multifaceted role for CARM1 in regulating cardiomyocyte maturation and demonstrates that deregulation of CARM1-dependent cardiomyocyte maturation gene expression may contribute to human heart diseases.

The regulation of the apoptotic pore-An immunological tightrope walk

Apoptotic pore formation in mitochondria is the pivotal point for cell death during mitochondrial apoptosis. It is regulated by BCL-2 family proteins in response to various cellular stress triggers and mediates mitochondrial outer membrane permeabilization (MOMP). This allows the release of mitochondrial contents into the cytosol, which triggers rapid cell death and clearance through the activation of caspases. However, under conditions of low caspase activity, the mitochondrial contents released into the cytosol through apoptotic pores serve as inflammatory signals and activate various inflammatory responses. In this chapter, we discuss how the formation of the apoptotic pore is regulated by BCL-2 proteins as well as other cellular or mitochondrial proteins and membrane lipids. Moreover, we highlight the importance of sublethal MOMP in the regulation of mitochondrial-activated inflammation and discuss its physiological consequences in the context of pathogen infection and disease and how it can potentially be exploited therapeutically, for example to improve cancer treatment.

OMA1-Mediated Mitochondrial Dynamics Balance Organellar Homeostasis Upstream of Cellular Stress Responses

In response to cellular metabolic and signaling cues, the mitochondrial network employs distinct sets of membrane-shaping factors to dynamically modulate organellar structures through a balance of fission and fusion. While these organellar dynamics mediate mitochondrial structure/function homeostasis, they also directly impact critical cell-wide signaling pathways such as apoptosis, autophagy, and the integrated stress response (ISR). Mitochondrial fission is driven by the recruitment of the cytosolic dynamin-related protein-1 (DRP1), while fusion is carried out by mitofusins 1 and 2 (in the outer membrane) and optic atrophy-1 (OPA1) in the inner membrane. This dynamic balance is highly sensitive to cellular stress; when the transmembrane potential across the inner membrane (Δψm) is lost, fusion-active OPA1 is cleaved by the overlapping activity with m-AAA protease-1 (OMA1 metalloprotease, disrupting mitochondrial fusion and leaving dynamin-related protein-1 (DRP1)-mediated fission unopposed, thus causing the collapse of the mitochondrial network to a fragmented state. OMA1 is a unique regulator of stress-sensitive homeostatic mitochondrial balance, acting as a key upstream sensor capable of priming the cell for apoptosis, autophagy, or ISR signaling cascades. Recent evidence indicates that higher-order macromolecular associations within the mitochondrial inner membrane allow these specialized domains to mediate crucial organellar functionalities.

A detailed review of pharmacology of MFN1 (mitofusion-1)-mediated mitochondrial dynamics: Implications for cellular health and diseases

The mitochondria are responsible for the production of cellular ATP, the regulation of cytosolic calcium levels, and the organization of numerous apoptotic proteins through the release of cofactors necessary for the activation of caspases. This level of functional adaptability can only be attained by sophisticated structural alignment. The morphology of the mitochondria does not remain unchanged throughout time; rather, it undergoes change as a result of processes known as fusion and fission. Fzo in flies, Fzo1 in yeast, and mitofusins in mammals are responsible for managing the outer mitochondrial membrane fusion process, whereas Mgm1 in yeast and optic atrophy 1 in mammals are responsible for managing the inner mitochondrial membrane fusion process. The fusion process is composed of two phases. MFN1, a GTPase that is located on the outer membrane of the mitochondria, is involved in the process of linking nearby mitochondria, maintaining the potential of the mitochondrial membrane, and apoptosis. This article offers specific information regarding the functions of MFN1 in a variety of cells and organs found in living creatures. According to the findings of the literature review, MFN1 plays an important part in a number of diseases and organ systems; nevertheless, the protein's function in other disease models and cell types has to be investigated in the near future so that it can be chosen as a promising marker for the therapeutic and diagnostic potentials it possesses. Overall, the major findings of this review highlight the pivotal role of mitofusin (MFN1) in regulating mitochondrial dynamics and its implications across various diseases, including neurodegenerative disorders, cardiovascular diseases, and metabolic syndromes. Our review identifies novel therapeutic targets within the MFN1 signaling pathways and underscores the potential of MFN1 modulation as a promising strategy for treating mitochondrial-related diseases. Additionally, the review calls for further research into MFN1's molecular mechanisms to unlock new avenues for clinical interventions, emphasizing the need for targeted therapies that address MFN1 dysfunction.

CCCP inhibits DPV infection in DEF cells by attenuating DPV manipulated ROS, apoptosis, and mitochondrial stability

Duck plague virus (DPV) is extremely infectious and lethal, so antiviral drugs are urgently needed. Our previous study shows that DPV infection with duck embryo fibroblast (DEF) induces reactive oxygen species (ROS) changes and promotes apoptosis. In this study, we tested the antiviral effect of the carbonyl cyanide m-chlorophenyl hydrazone (CCCP), a common mitochondrial autophagy inducer. Our results demonstrated a dose-dependent anti-DPV effect of CCCP, CCCP-treatment blocked the intercellular transmission of DPV after infection, and we also proved that CCCP could have an antiviral effect up to 48 hpi. The addition of CCCP reversed the DPV-induced ROS changes, CCCP can inhibit virus-induced apoptosis; meanwhile, CCCP can affect mitochondrial fusion and activate mitophagy to inhibit DPV. In conclusion, CCCP can be an effective antiviral candidate against DPV.

Proteomic analysis of mitochondria associated membranes in renal ischemic reperfusion injury

BACKGROUND

The mitochondria and endoplasmic reticulum (ER) communicate via contact sites known as mitochondria associated membranes (MAMs). Many important cellular functions such as bioenergetics, mitophagy, apoptosis, and calcium signaling are regulated by MAMs, which are thought to be closely related to ischemic reperfusion injury (IRI). However, there exists a gap in systematic proteomic research addressing the relationship between these cellular processes.

METHODS

A 4D label free mass spectrometry-based proteomic analysis of mitochondria associated membranes (MAMs) from the human renal proximal tubular epithelial cell line (HK-2 cells) was conducted under both normal (N) and hypoxia/reperfusion (HR) conditions. Subsequent differential proteins analysis aimed to characterize disease-relevant signaling molecules. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis was applied to total proteins and differentially expressed proteins, encompassing Biological Process (BP), Cell Component (CC), Molecular Function (MF), and KEGG pathways. Further, Protein-Protein Interaction Network (PPI) exploration was carried out, leading to the identification of hub genes from differentially expressed proteins. Notably, Mitofusion 2 (MFN2) and BCL2/Adenovirus E1B 19-kDa interacting protein 3(BNIP3) were identified and subsequently validated both in vitro and in vivo. Finally, the impact of MFN2 on MAMs during hypoxia/reoxygenation was explored through regulation of gene expression. Subsequently, a comparative proteomics analysis was conducted between OE-MFN2 and normal HK-2 cells, providing further insights into the underlying mechanisms.

RESULTS

A total of 4489 proteins were identified, with 3531 successfully quantified. GO/KEGG analysis revealed that MAM proteins were primarily associated with mitochondrial function and energy metabolism. Differential analysis between the two groups showed that 688 proteins in HR HK-2 cells exhibited significant changes in expression level with P-value < 0.05 and HR/N > 1.5 or HR/N < 0.66 set as the threshold criteria. Enrichment analysis of differentially expressed proteins unveiled biological processes such as mRNA splicing, apoptosis regulation, and cell division, while molecular functions were predominantly associated with energy metabolic activity. These proteins play key roles in the cellular responses during HR, offering insights into the IRI mechanisms and potential therapeutic targets. The validation of hub genes MFN2 and BNIP3 both in vitro and vivo was consistent with the proteomic findings. MFN2 demonstrated a protective role in maintaining the integrity of mitochondria associated membranes (MAMs) and mitigating mitochondrial damage following hypoxia/reoxygenation injury, this protective effect may be associated with the activation of the PI3K/AKT pathway.

CONCLUSIONS

The proteins located in mitochondria associated membranes (MAMs) are implicated in crucial roles during renal ischemic reperfusion injury (IRI), with MFN2 playing a pivotal regulatory role in this context.

Inhibitors of Rho/MRTF/SRF Transcription Pathway Regulate Mitochondrial Function

RhoA-regulated gene transcription by serum response factor (SRF) and its transcriptional cofactor myocardin-related transcription factors (MRTFs) signaling pathway has emerged as a promising therapeutic target for pharmacological intervention in multiple diseases. Altered mitochondrial metabolism is one of the major hallmarks of cancer, therefore, this upregulation is a vulnerability that can be targeted with Rho/MRTF/SRF inhibitors. Recent advances identified a novel series of oxadiazole-thioether compounds that disrupt the SRF transcription, however, the direct molecular target of these compounds is unclear. Herein, we demonstrate the Rho/MRTF/SRF inhibition mechanism of CCG-203971 and CCG-232601 in normal cell lines of human lung fibroblasts and mouse myoblasts. Further studies investigated the role of these molecules in targeting mitochondrial function. We have shown that these molecules hyperacetylate histone H4K12 and H4K16 and regulate the genes involved in mitochondrial function and dynamics. These small molecule inhibitors regulate mitochondrial function as a compensatory mechanism by repressing oxidative phosphorylation and increasing glycolysis. Our data suggest that these CCG molecules are effective in inhibiting all the complexes of mitochondrial electron transport chains and further inducing oxidative stress. Therefore, our present findings highlight the therapeutic potential of CCG-203971 and CCG-232601, which may prove to be a promising approach to target aberrant bioenergetics.

Cellular Senescence, Mitochondrial Dysfunction, and Their Link to Cardiovascular Disease

Cardiovascular diseases (CVDs), a group of disorders affecting the heart or blood vessels, are the primary cause of death worldwide, with an immense impact on patient quality of life and disability. According to the World Health Organization, CVD takes an estimated 17.9 million lives each year, where more than four out of five CVD deaths are due to heart attacks and strokes. In the decades to come, an increased prevalence of age-related CVD, such as atherosclerosis, coronary artery stenosis, myocardial infarction (MI), valvular heart disease, and heart failure (HF) will contribute to an even greater health and economic burden as the global average life expectancy increases and consequently the world's population continues to age. Considering this, it is important to focus our research efforts on understanding the fundamental mechanisms underlying CVD. In this review, we focus on cellular senescence and mitochondrial dysfunction, which have long been established to contribute to CVD. We also assess the recent advances in targeting mitochondrial dysfunction including energy starvation and oxidative stress, mitochondria dynamics imbalance, cell apoptosis, mitophagy, and senescence with a focus on therapies that influence both and therefore perhaps represent strategies with the most clinical potential, range, and utility.

So close, yet so far away: the relationship between MAM and cardiac disease

Mitochondria-associated membrane (MAM) serve as crucial contact sites between mitochondria and the endoplasmic reticulum (ER). Recent research has highlighted the significance of MAM, which serve as a platform for various protein molecules, in processes such as calcium signaling, ATP production, mitochondrial structure and function, and autophagy. Cardiac diseases caused by any reason can lead to changes in myocardial structure and function, significantly impacting human health. Notably, MAM exhibits various regulatory effects to maintain cellular balance in several cardiac diseases conditions, such as obesity, diabetes mellitus, and cardiotoxicity. MAM proteins independently or interact with their counterparts, forming essential tethers between the ER and mitochondria in cardiomyocytes. This review provides an overview of key MAM regulators, detailing their structure and functions. Additionally, it explores the connection between MAM and various cardiac injuries, suggesting that precise genetic, pharmacological, and physical regulation of MAM may be a promising strategy for preventing and treating heart failure.

Death-associated protein 3 in cancer-discrepant roles of DAP3 in tumours and molecular mechanisms

Cancer, ranks as the secondary cause of death, is a group of diseases that are characterized by uncontrolled tumor growth and distant metastasis, leading to increased mortality year-on-year. To date, targeted therapy to intercept the aberrant proliferation and invasion is crucial for clinical anticancer treatment, however, mutant expression of target genes often leads to drug resistance. Therefore, it is essential to identify more molecules that can be targeted to facilitate combined therapy. Previous studies showed that death associated protein 3 (DAP3) exerts a pivotal role in regulating apoptosis signaling of tumors, meanwhile, aberrant DAP3 expression is associated with the tumorigenesis and disease progression of various cancers. This review provides an overview of the molecule structure of DAP3 and the discrepant roles played by DAP3 in various types of tumors. Considering the molecular mechanism of DAP3-regulated cancer development, new potential treatment strategies might be developed in the future.

Mitochondria: A Promising Convergent Target for the Treatment of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease characterized by the progressive loss of motor neurons, for which current treatment options are limited. Recent studies have shed light on the role of mitochondria in ALS pathogenesis, making them an attractive therapeutic intervention target. This review contains a very comprehensive critical description of the involvement of mitochondria and mitochondria-mediated mechanisms in ALS. The review covers several key areas related to mitochondria in ALS, including impaired mitochondrial function, mitochondrial bioenergetics, reactive oxygen species, metabolic processes and energy metabolism, mitochondrial dynamics, turnover, autophagy and mitophagy, impaired mitochondrial transport, and apoptosis. This review also highlights preclinical and clinical studies that have investigated various mitochondria-targeted therapies for ALS treatment. These include strategies to improve mitochondrial function, such as the use of dichloroacetate, ketogenic and high-fat diets, acetyl-carnitine, and mitochondria-targeted antioxidants. Additionally, antiapoptotic agents, like the mPTP-targeting agents minocycline and rasagiline, are discussed. The paper aims to contribute to the identification of effective mitochondria-targeted therapies for ALS treatment by synthesizing the current understanding of the role of mitochondria in ALS pathogenesis and reviewing potential convergent therapeutic interventions. The complex interplay between mitochondria and the pathogenic mechanisms of ALS holds promise for the development of novel treatment strategies to combat this devastating disease.

Mitochondrial Mechanisms in Immunity and Inflammatory Conditions: Beyond Energy Management

Significance: The growing importance of mitochondria in the immune response and inflammation is multifaceted. Unraveling the different mechanisms by which mitochondria have a relevant role in the inflammatory response beyond the energy management of the process is necessary for improving our understanding of the host immune defense and the pathogenesis of various inflammatory diseases and syndromes. Critical Issues: Mitochondria are relevant in the immune response at different levels, including releasing activation molecules, changing its structure and function to accompany the immune response, and serving as a structural base for activating intermediates as NLRP3 inflammasome. In this scientific journey of dissecting mitochondrial mechanisms, new questions and interesting aspects arise, such as the involvement of mitochondrial-derived vesicles in the immune response with the putative role of preventing uncontrolled situations. Recent Advances: Researchers are continuously rethinking the role of mitochondria in acute and chronic inflammation and related disorders. As such, mitochondria have important roles as centrally positioned signaling hubs in regulating inflammatory and immune responses. In this review, we present the current understanding of mitochondrial mechanisms involved, beyond the largely known mitochondrial dysfunction, in the onset and development of inflammatory situations. Future Directions: Mitochondria emerge as an interesting and multifaceted platform for studying and developing pharmaceutical and therapeutic approaches. There are many ongoing studies aimed to describe the effects of specific mitochondrial targeted molecules and treatments to ameliorate the consequences of exacerbated inflammatory components of pathologies and syndromes, resulting in an open area of increasing research interest.

Role of bio-flavonols and their derivatives in improving mitochondrial dysfunctions associated with pancreatic tumorigenesis

Mitochondria, a cellular metabolic center, efficiently fulfill cellular energy needs and regulate crucial metabolic processes, including cellular proliferation, differentiation, apoptosis, and generation of reactive oxygen species. Alteration in the mitochondrial functions leads to metabolic imbalances and altered extracellular matrix dynamics in the host, utilized by solid tumors like pancreatic cancer (PC) to get energy benefits for fast-growing cancer cells. PC is highly heterogeneous and remains unidentified for a longer time because of its complex pathophysiology, retroperitoneal position, and lack of efficient diagnostic approaches, which is the foremost reason for accounting for the seventh leading cause of cancer-related deaths worldwide. PC cells often respond poorly to current therapeutics because of dense stromal barriers in the pancreatic tumor microenvironment, which limit the drug delivery and distribution of antitumor immune cell populations. As an alternative approach, various natural compounds like flavonoids are reported to possess potent antioxidant and anticancerous properties and are less toxic than current chemotherapeutic drugs. Therefore, we aim to summarize the current state of knowledge regarding the pharmacological properties of flavonols in PC in this review from the perspective of mitigating mitochondrial dysfunctions associated with cancer cells. Our literature survey indicates that flavonols efficiently regulate cellular metabolism by scavenging reactive oxygen species, mitigating inflammation, and arresting the cell cycle to promote apoptosis in tumor cells via intrinsic mitochondrial pathways. In particular, flavonols proficiently inhibit the cancer-associated proliferation and inflammatory pathways such as EGFR/MAPK, PI3K/Akt, and nuclear factor κB in PC. Overall, this review provides in-depth evidence about the therapeutic potential of flavonols for future anticancer strategies against PC; still, more multidisciplinary human interventional studies are required to dissect their pharmacological effect accurately.

Mitochondrial hyperfusion induces metabolic remodeling in lung endothelial cells by modifying the activities of electron transport chain complexes I and III

OBJECTIVE

Pulmonary hypertension (PH) is a progressive disease with vascular remodeling as a critical structural alteration. We have previously shown that metabolic reprogramming is an early initiating mechanism in animal models of PH. This metabolic dysregulation has been linked to remodeling the mitochondrial network to favor fission. However, whether the mitochondrial fission/fusion balance underlies the metabolic reprogramming found early in PH development is unknown.

METHODS

Utilizing a rat early model of PH, in conjunction with cultured pulmonary endothelial cells (PECs), we utilized metabolic flux assays, Seahorse Bioassays, measurements of electron transport chain (ETC) complex activity, fluorescent microscopy, and molecular approaches to investigate the link between the disruption of mitochondrial dynamics and the early metabolic changes that occur in PH.

RESULTS

We observed increased fusion mediators, including Mfn1, Mfn2, and Opa1, and unchanged fission mediators, including Drp1 and Fis1, in a two-week monocrotaline-induced PH animal model (early-stage PH). We were able to establish a connection between increases in fusion mediator Mfn1 and metabolic reprogramming. Using an adenoviral expression system to enhance Mfn1 levels in pulmonary endothelial cells and utilizing 13C-glucose labeled substrate, we found increased production of 13C lactate and decreased TCA cycle metabolites, revealing a Warburg phenotype. The use of a 13C5-glutamine substrate showed evidence that hyperfusion also induces oxidative carboxylation. The increase in glycolysis was linked to increased hypoxia-inducible factor 1α (HIF-1α) protein levels secondary to the disruption of cellular bioenergetics and higher levels of mitochondrial reactive oxygen species (mt-ROS). The elevation in mt-ROS correlated with attenuated ETC complexes I and III activities. Utilizing a mitochondrial-targeted antioxidant to suppress mt-ROS, limited HIF-1α protein levels, which reduced cellular glycolysis and reestablished mitochondrial membrane potential.

CONCLUSIONS

Our data connects mitochondrial fusion-mediated mt-ROS to the Warburg phenotype in early-stage PH development.

MTCH2 cooperates with MFN2 and lysophosphatidic acid synthesis to sustain mitochondrial fusion

Fusion of the outer mitochondrial membrane (OMM) is regulated by mitofusin 1 (MFN1) and 2 (MFN2), yet the differential contribution of each of these proteins is less understood. Mitochondrial carrier homolog 2 (MTCH2) also plays a role in mitochondrial fusion, but its exact function remains unresolved. MTCH2 overexpression enforces MFN2-independent mitochondrial fusion, proposedly by modulating the phospholipid lysophosphatidic acid (LPA), which is synthesized by glycerol-phosphate acyl transferases (GPATs) in the endoplasmic reticulum (ER) and the OMM. Here we report that MTCH2 requires MFN1 to enforce mitochondrial fusion and that fragmentation caused by loss of MTCH2 can be specifically counterbalanced by overexpression of MFN2 but not MFN1, partially independent of its GTPase activity and mitochondrial localization. Pharmacological inhibition of GPATs (GPATi) or silencing ER-resident GPATs suppresses MFN2's ability to compensate for the loss of MTCH2. Loss of either MTCH2, MFN2, or GPATi does not impair stress-induced mitochondrial fusion, whereas the combined loss of MTCH2 and GPATi or the combined loss of MTCH2 and MFN2 does. Taken together, we unmask two cooperative mechanisms that sustain mitochondrial fusion.

Iron Dyshomeostasis and Mitochondrial Function in the Failing Heart: A Review of the Literature

Cardiac contraction and relaxation require a substantial amount of energy provided by the mitochondria. The failing heart is adenosine triphosphate (ATP)- and creatine-depleted. Studies have found iron is involved in almost every aspect of mitochondrial function, and previous studies have shown myocardial iron deficiency in heart failure (HF). Many clinicians advocated intravenous iron repletion for HF patients meeting the conventional criteria for systemic iron deficiency. While clinical trials showed improved quality of life, iron repletion failed to significantly impact survival or significant cardiovascular adverse events. There is evidence that in HF, labile iron is trapped inside the mitochondria causing oxidative stress and lipid peroxidation. There is also compelling preclinical evidence demonstrating the detrimental effects of both iron overload and depletion on cardiomyocyte function. We reviewed the mechanisms governing myocardial and mitochondrial iron content. Mitochondrial dynamics (i.e., fusion, fission, mitophagy) and the role of iron were also investigated. Ferroptosis, as an important regulated cell death mechanism involved in cardiomyocyte loss, was reviewed along with agents used to manipulate it. The membrane stability and iron content of mitochondria can be altered by many agents. Some studies are showing promising improvement in the cardiomyocyte function after iron chelation by deferiprone; however, whether the in vitro and in vivo findings will be reflected on on clinical grounds is still unclear. Finally, we briefly reviewed the clinical trials on intravenous iron repletion. There is a need for more well-simulated animal studies to shed light on the safety and efficacy of chelation agents and pave the road for clinical studies.

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.

Mitochondrial GTP metabolism controls reproductive aging in C. elegans

Healthy mitochondria are critical for reproduction. During aging, both reproductive fitness and mitochondrial homeostasis decline. Mitochondrial metabolism and dynamics are key factors in supporting mitochondrial homeostasis. However, how they are coupled to control reproductive health remains unclear. We report that mitochondrial GTP (mtGTP) metabolism acts through mitochondrial dynamics factors to regulate reproductive aging. We discovered that germline-only inactivation of GTP- but not ATP-specific succinyl-CoA synthetase (SCS) promotes reproductive longevity in Caenorhabditis elegans. We further identified an age-associated increase in mitochondrial clustering surrounding oocyte nuclei, which is attenuated by GTP-specific SCS inactivation. Germline-only induction of mitochondrial fission factors sufficiently promotes mitochondrial dispersion and reproductive longevity. Moreover, we discovered that bacterial inputs affect mtGTP levels and dynamics factors to modulate reproductive aging. These results demonstrate the significance of mtGTP metabolism in regulating oocyte mitochondrial homeostasis and reproductive longevity and identify mitochondrial fission induction as an effective strategy to improve reproductive health.

Pediatric Neuromuscular Diseases

The diagnostic and referral workflow for children with neuromuscular disorders is evolving, particularly as newborn screening programs are expanding in tandem with novel therapeutic developments. However, for the children who present with symptoms and signs of potential neuromuscular disorders, anatomic localization, guided initially by careful history and physical examination, continues to be the cardinal initial step in the diagnostic evaluation. It is important to consider whether the localization is more likely to be in the lower motor neuron, peripheral nerve, neuromuscular junction, or muscle. After that, disease etiologies can be divided broadly into inherited versus acquired categories. Considerations of localization and etiologies will help generate a differential diagnosis, which in turn will guide diagnostic testing. Once a diagnosis is made, it is important to be aware of current treatment options, as a number of new therapies for some of these disorders have been approved in recent years. Families are also increasingly interested in clinical research, which may include natural history studies and interventional clinical trials. Such research has proliferated for rare neuromuscular diseases, leading to exciting advances in diagnostic and therapeutic technologies, promising dramatic changes in the landscape of these disorders in the years to come.

Mitochondrial Proteomes in Neural Cells: A Systematic Review

Mitochondria are ancient endosymbiotic double membrane organelles that support a wide range of eukaryotic cell functions through energy, metabolism, and cellular control. There are over 1000 known proteins that either reside within the mitochondria or are transiently associated with it. These mitochondrial proteins represent a functional subcellular protein network (mtProteome) that is encoded by mitochondrial and nuclear genomes and significantly varies between cell types and conditions. In neurons, the high metabolic demand and differential energy requirements at the synapses are met by specific modifications to the mtProteome, resulting in alterations in the expression and functional properties of the proteins involved in energy production and quality control, including fission and fusion. The composition of mtProteomes also impacts the localization of mitochondria in axons and dendrites with a growing number of neurodegenerative diseases associated with changes in mitochondrial proteins. This review summarizes the findings on the composition and properties of mtProteomes important for mitochondrial energy production, calcium and lipid signaling, and quality control in neural cells. We highlight strategies in mass spectrometry (MS) proteomic analysis of mtProteomes from cultured cells and tissue. The research into mtProteome composition and function provides opportunities in biomarker discovery and drug development for the treatment of metabolic and neurodegenerative disease.

The nonstructural protein 1 of respiratory syncytial virus hijacks host mitophagy as a novel mitophagy receptor to evade the type I IFN response in HEp-2 cells

Mitochondria are good targets for viruses to manipulate their hosts. However, it remains obscure whether respiratory syncytial virus (RSV) target mitochondria to suppress the type I interferon (IFN) responses. Here, we show that nonstructural protein 1 (NS1) protein of RSV interacts with Tu translation elongation factor mitochondrial (TUFM), which can lead to its localization in mitochondria and finally induce TUFM-dependent mitophagy and inhibition of IFNβ. Mechanically, NS1-mediated TUFM-dependent mitophagy does not depend on the PINK1-PARKIN pathway and classic mitophagy receptors. Importantly, NS1 may act as a new receptor protein to bridge mitochondria and autophagosomes by interacting with TUFM and LC3B. The LIR motif of NS1 protein is essential for its interaction with LC3B and is of great importance for its mitophagy induction and IFNβ suppression. Finally, NS1-induced TUFM-dependent mitophagy was essential for its attenuated IFNβ response using autophagy-deficient cells and mice. Our study provides a novel mitophagy receptor molecular and a new antiviral option by suppressing antiviral innate immune via targeting TUFM-dependent mitophagy. IMPORTANCE It is a worthy concern for us to understand virus-host interactions which affect progression and prognosis of disease. We demonstrated that the non-structural protein 1 of respiratory syncytial virus (RSV NS1) may act as a novel mitophagy receptor to induce mitophagy by binding LC3B and mitochondrial protein TUFM, and finally dampen interferon (IFN) responses induced by RIG1 and RSV infection. TUFM is beneficial for RSV replication in vivo and vitro. It is new and interesting that RSV NS1 may function as a mitophagy receptor to interact with LC3B. The LIR motif of NS1 protein is essential for its interaction with LC3B. We further confirm that RSV NS1 inhibited IFNβ response and promoted RSV replication in autophagy-dependent mechanisms in vivo and vitro. Our study contributes to understanding virus-host interaction, enriching our insights into RSV pathogenic mechanism and exploiting new antiviral treatments targeting TUFM.

A human mitofusin 2 mutation can cause mitophagic cardiomyopathy

Cardiac muscle has the highest mitochondrial density of any human tissue, but mitochondrial dysfunction is not a recognized cause of isolated cardiomyopathy. Here, we determined that the rare mitofusin (MFN) 2 R400Q mutation is 15-20× over-represented in clinical cardiomyopathy, whereas this specific mutation is not reported as a cause of MFN2 mutant-induced peripheral neuropathy, Charcot-Marie-Tooth disease type 2A (CMT2A). Accordingly, we interrogated the enzymatic, biophysical, and functional characteristics of MFN2 Q400 versus wild-type and CMT2A-causing MFN2 mutants. All MFN2 mutants had impaired mitochondrial fusion, the canonical MFN2 function. Compared to MFN2 T105M that lacked catalytic GTPase activity and exhibited normal activation-induced changes in conformation, MFN2 R400Q and M376A had normal GTPase activity with impaired conformational shifting. MFN2 R400Q did not suppress mitochondrial motility, provoke mitochondrial depolarization, or dominantly suppress mitochondrial respiration like MFN2 T105M. By contrast to MFN2 T105M and M376A, MFN2 R400Q was uniquely defective in recruiting Parkin to mitochondria. CRISPR editing of the R400Q mutation into the mouse Mfn2 gene induced perinatal cardiomyopathy with no other organ involvement; knock-in of Mfn2 T105M or M376V did not affect the heart. RNA sequencing and metabolomics of cardiomyopathic Mfn2 Q/Q400 hearts revealed signature abnormalities recapitulating experimental mitophagic cardiomyopathy. Indeed, cultured cardiomyoblasts and in vivo cardiomyocytes expressing MFN2 Q400 had mitophagy defects with increased sensitivity to doxorubicin. MFN2 R400Q is the first known natural mitophagy-defective MFN2 mutant. Its unique profile of dysfunction evokes mitophagic cardiomyopathy, suggesting a mechanism for enrichment in clinical cardiomyopathy.

RICH2 decreases the mitochondrial number and affects mitochondrial localization in diffuse low-grade glioma-related epilepsy

Epilepsy, a common complication of diffuse low-grade gliomas (DLGGs; diffuse oligodendroglioma and astrocytoma collectively), severely compromises the quality of life of patients. DLGG epileptogenicity may primarily be generated by interactions between the tumor and the neocortex. Neuronal uptake of dysfunctional mitochondria from the extracellular environment can lead to abnormal neuronal discharge. Mitochondrial dysfunction is frequently observed in gliomas that can transmigrate across the plasma membranes. Here, we examined the role of the Rho GTPase-activating protein 44 (RICH2) in mitochondrial dynamics and DLGG-related epilepsy. We investigated the association between mitochondrial and RICH2 expression in human DLGG tissues using immunohistochemistry. We examined the association between RICH2 and epilepsy in nude mouse glioma models by electrophysiology. The effect of RICH2 on mitochondrial morphology and calcium motility were assessed by single cell fluorescence microscopy. Quantitative RT-PCR (qRT-PCR) and Western blot analysis were performed to characterize RICH2 induced expression changes in the genes related to mitochondrial dynamics, mitogenesis and mitochondrial function. We found that RICH2 expression was higher in oligodendroglioma than in astrocytoma and was correlated with better prognosis and higher epilepsy rate in patients. The expression of mitochondria may be associated with clinical DLGG-related epilepsy and reduced by RICH2 overexpression. And RICH2 could promote DLGG-related epilepsy in tumorigenic nude mice. RICH2 overexpression decreased calcium flow and the mitochondria released from glioma cells (SW1088 and U251) into the extracellular environment, potentially via downregulation of MFN-1/MFN-2 levels which suggests reduced mitochondrial fusion. In addition, we observed decreased mitochondrial trafficking into neurons (released from glioma cells and trafficked into neurons), which could explain the higher incidence of DLGG-related epilepsy due to reduced neuroprotection. Furthermore, RICH2 downregulated MAPK/ERK/HIF-1 pathway. In conclusion, these results suggest that RICH2 could promote epilepsy by (i) inhibiting mitochondrial fusion via MFN downregulation and Drp-1 upregulation; (ii) altering the MAPK/ERK/Hif-1 signaling axis. RICH2 may be a potential target in the treatment of DLGG-related epilepsy.

An integrative analysis of genotype-phenotype correlation in Charcot Marie Tooth type 2A disease with MFN2 variants: A case and systematic review

Dominant genetic variants in the mitofusin 2 (MFN2) gene lead to Charcot-Marie-Tooth type 2A (CMT2A), a neurodegenerative disease caused by genetic defects that directly damage axons. In this study, we reported a proband with a pathogenic variant in the GTPase domain of MFN2, c.494A > G (p.His165Arg). To date, at least 184 distinct MFN2 variants identified in 944 independent probands have been reported in 131 references. However, the field of medical genetics has long been challenged by how genetic variation in the MFN2 gene is associated with disease phenotypes. Here, by collating the MFN2 variant data and patient clinical information from Leiden Open Variant Database 3.0, NCBI clinvar database, and available related references in PubMed, we determined the mutation frequency, age of onset, sex ratio, and geographical distribution. Furthermore, the results of an analysis examining the relationship between variants and phenotypes from multiple genetic perspectives indicated that insertion and deletions (indels), copy number variants (CNVs), duplication variants, and nonsense mutations in single nucleotide variants (SNVs) tend to be pathogenic, and the results emphasized the importance of the GTPase domain to the structure and function of MFN2. Overall, three reliable classification methods of MFN2 genotype-phenotype associations provide insights into the prediction of CMT2A disease severity. Of course, there are still many MFN2 variants that have not been given clear clinical significance, which requires clinicians to make more accurate clinical diagnoses.

The regulatory role of adipocyte mitochondrial homeostasis in metabolism-related diseases

Adipose tissue is the most important energy storage organ in the body, maintaining its normal energy metabolism function and playing a vital role in keeping the energy balance of the body to avoid the harm caused by obesity and a series of related diseases resulting from abnormal energy metabolism. The dysfunction of adipose tissue is closely related to the occurrence of diseases related to obesity metabolism. Among various organelles, mitochondria are the main site of energy metabolism, and mitochondria maintain their quality through autophagy, biogenesis, transfer, and dynamics, which play an important role in maintaining metabolic homeostasis of adipocytes. On the other hand, mitochondria have mitochondrial genomes which are vulnerable to damage due to the lack of protective structures and their proximity to sites of reactive oxygen species generation, thus affecting mitochondrial function. Notably, mitochondria are closely related to other organelles in adipocytes, such as lipid droplets and the endoplasmic reticulum, which enhances the function of mitochondria and other organelles and regulates energy metabolism processes, thus reducing the occurrence of obesity-related diseases. This article introduces the structure and quality control of mitochondria in adipocytes and their interactions with other organelles in adipocytes, aiming to provide a new perspective on the regulation of mitochondrial homeostasis in adipocytes on the occurrence of obesity-related diseases, and to provide theoretical reference for further revealing the molecular mechanism of mitochondrial homeostasis in adipocytes on the occurrence of obesity-related diseases.

Atypical peripheral actin band formation via overactivation of RhoA and nonmuscle myosin II in mitofusin 2-deficient cells

Cell spreading and migration play central roles in many physiological and pathophysiological processes. We have previously shown that MFN2 regulates the migration of human neutrophil-like cells via suppressing Rac activation. Here, we show that in mouse embryonic fibroblasts, MFN2 suppresses RhoA activation and supports cell polarization. After initial spreading, the wild-type cells polarize and migrate, whereas the Mfn2-/- cells maintain a circular shape. Increased cytosolic Ca2+ resulting from the loss of Mfn2 is directly responsible for this phenotype, which can be rescued by expressing an artificial tether to bring mitochondria and endoplasmic reticulum to close vicinity. Elevated cytosolic Ca2+ activates Ca2+/calmodulin-dependent protein kinase II, RhoA, and myosin light-chain kinase, causing an overactivation of nonmuscle myosin II, leading to a formation of a prominent F-actin ring at the cell periphery and increased cell contractility. The peripheral actin band alters cell physics and is dependent on substrate rigidity. Our results provide a novel molecular basis to understand how MFN2 regulates distinct signaling pathways in different cells and tissue environments, which is instrumental in understanding and treating MFN2-related diseases.

Mitochondrial dysfunction and skeletal muscle atrophy: Causes, mechanisms, and treatment strategies

Skeletal muscle, which accounts for approximately 40% of total body weight, is one of the most dynamic and plastic tissues in the human body and plays a vital role in movement, posture and force production. More than just a component of the locomotor system, skeletal muscle functions as an endocrine organ capable of producing and secreting hundreds of bioactive molecules. Therefore, maintaining healthy skeletal muscles is crucial for supporting overall body health. Various pathological conditions, such as prolonged immobilization, cachexia, aging, drug-induced toxicity, and cardiovascular diseases (CVDs), can disrupt the balance between muscle protein synthesis and degradation, leading to skeletal muscle atrophy. Mitochondrial dysfunction is a major contributing mechanism to skeletal muscle atrophy, as it plays crucial roles in various biological processes, including energy production, metabolic flexibility, maintenance of redox homeostasis, and regulation of apoptosis. In this review, we critically examine recent knowledge regarding the causes of muscle atrophy (disuse, cachexia, aging, etc.) and its contribution to CVDs. Additionally, we highlight the mitochondrial signaling pathways involvement to skeletal muscle atrophy, such as the ubiquitin-proteasome system, autophagy and mitophagy, mitochondrial fission-fusion, and mitochondrial biogenesis. Furthermore, we discuss current strategies, including exercise, mitochondria-targeted antioxidants, in vivo transfection of PGC-1α, and the potential use of mitochondrial transplantation as a possible therapeutic approach.

Application of super-resolution microscopy in mitochondria-dynamic diseases

Limited by spatial and temporal resolution, traditional optical microscopy cannot image the delicate ultra-structure organelles and sub-organelles. The emergence of super-resolution microscopy makes it possible. In this review, we focus on mitochondria. We summarize the process of mitochondrial dynamics, the primary proteins that regulate mitochondrial morphology, the diseases related to mitochondrial dynamics. The purpose is to apply super-resolution microscopy developed during recent years to the mitochondrial research. By providing the right research tools, we will help to promote the application of this technique to the in-depth elucidation of the pathogenesis of diseases related to mitochondrial dynamics, assistdiagnosis and develop the therapeutic treatment.

Hypoxia-induced GPCPD1 depalmitoylation triggers mitophagy via regulating PRKN-mediated ubiquitination of VDAC1

Mitophagy, which selectively eliminates the dysfunctional and excess mitochondria by autophagy, is crucial for cellular homeostasis under stresses such as hypoxia. Dysregulation of mitophagy has been increasingly linked to many disorders including neurodegenerative disease and cancer. Triple-negative breast cancer (TNBC), a highly aggressive breast cancer subtype, is reported to be characterized by hypoxia. However, the role of mitophagy in hypoxic TNBC as well as the underlying molecular mechanism is largely unexplored. Here, we identified GPCPD1 (glycerophosphocholine phosphodiesterase 1), a key enzyme in choline metabolism, as an essential mediator in hypoxia-induced mitophagy. Under the hypoxic condition, we found that GPCPD1 was depalmitoylated by LYPLA1, which facilitated the relocating of GPCPD1 to the outer mitochondrial membrane (OMM). Mitochondria-localized GPCPD1 could bind to VDAC1, the substrate for PRKN/PARKIN-dependent ubiquitination, thus interfering with the oligomerization of VDAC1. The increased monomer of VDAC1 provided more anchor sites to recruit PRKN-mediated polyubiquitination, which consequently triggered mitophagy. In addition, we found that GPCPD1-mediated mitophagy exerted a promotive effect on tumor growth and metastasis in TNBC both in vitro and in vivo. We further determined that GPCPD1 could serve as an independent prognostic indicator in TNBC. In conclusion, our study provides important insights into a mechanistic understanding of hypoxia-induced mitophagy and elucidates that GPCPD1 could act as a potential target for the future development of novel therapy for TNBC patients.Abbreviations: ACTB: actin beta; 5-aza: 5-azacytidine; BNIP3: BCL2 interacting protein 3; BNIP3L: BCL2 interacting protein 3 like; CCCP: carbonyl cyanide m-chlorophenyl hydrazone; ChIP: chromatin immunoprecipitation; co-IP: co-immunoprecipitation; CQ: chloroquine; CsA: cyclosporine; DOX: doxorubicin; FIS1: fission, mitochondrial 1; FUNDC1: FUN14 domain containing 1; GPCPD1: glycerophosphocholine phosphodiesterase 1; HAM: hydroxylamine; HIF1A: hypoxia inducible factor 1 subunit alpha; HRE: hypoxia response element; IF: immunofluorescence; LB: lysis buffer; LC3B/MAP1LC3B: microtubule associated protein 1 light chain 3 beta; LC-MS: liquid chromatography-mass spectrometry; LYPLA1: lysophospholipase 1; LYPLA2: lysophospholipase 2; MDA231: MDA-MB-231; MDA468: MDA-MB-468; MFN1: mitofusin 1; MFN2: mitofusin 2; MKI67: marker of proliferation Ki-67; OCR: oxygen consumption rate; OMM: outer mitochondrial membrane; OS: overall survival; PalmB: palmostatin B; PBS: phosphate-buffered saline; PINK1: PTEN induced kinase 1; PRKN: parkin RBR E3 ubiquitin protein ligase; SDS: sodium dodecyl sulfate; TOMM20: translocase of outer mitochondrial membrane 20; TNBC: triple-negative breast cancer; VBIT-4: VDAC inhibitor; VDAC1: voltage dependent anion channel 1; WT: wild type.

Mitofusin 1 overexpression rescues the abnormal mitochondrial dynamics caused by the Mitofusin 2 K357T mutation in vitro

BACKGROUND AND AIMS

Mitofusin 1 (MFN1) and MFN2 are outer mitochondrial membrane fusogenic proteins regulating mitochondrial network morphology. MFN2 mutations cause Charcot-Marie-Tooth type 2A (CMT2A), an axonal neuropathy characterized by mitochondrial fusion defects, which in the case of a GTPase domain mutant, were rescued following wild-type MFN1/2 (MFN1/2WT ) overexpression. In this study, we compared the therapeutic efficiency between MFN1WT and MFN2WT overexpression in correcting mitochondrial defects induced by the novel MFN2K357T mutation located in the highly conserved R3 region.

METHODS

Constructs expressing either MFN2K357T , MFN2WT , or MFN1WT under the ubiquitous chicken β-actin hybrid (CBh) promoter were generated. Flag or myc tag was used for their detection. Differentiated SH-SY5Y cells were single transfected with MFN1WT , MFN2WT , or MFN2K357T , as well as double transfected with MFN2K357T /MFN2WT or MFN2K357T /MFN1WT .

RESULTS

SH-SY5Y cells transfected with MFN2K357T exhibited severe perinuclear mitochondrial clustering with axon-like processes devoid of mitochondria. Single transfection with MFN1WT resulted in a more interconnected mitochondrial network than transfection with MFN2WT , accompanied by mitochondrial clusters. Double transfection of MFN2K357T with either MFN1WT or MFN2WT resolved the mutant-induced mitochondrial clusters and led to detectable mitochondria throughout the axon-like processes. MFN1WT showed higher efficacy than MFN2WT in rescuing these defects.

INTERPRETATION

These results further demonstrate the higher potential of MFN1WT over MFN2WT overexpression to rescue CMT2A-induced mitochondrial network abnormalities due to mutations outside the GTPase domain. This higher phenotypic rescue conferred by MFN1WT , possibly due to its higher mitochondrial fusogenic ability, may be applied to different CMT2A cases regardless of the MFN2 mutation type.

Mechanisms of Modulation of Mitochondrial Architecture

Mitochondrial network architecture plays a critical role in cellular physiology. Indeed, alterations in the shape of mitochondria upon exposure to cellular stress can cause the dysfunction of these organelles. In this scenario, mitochondrial dynamics proteins and the phospholipid composition of the mitochondrial membrane are key for fine-tuning the modulation of mitochondrial architecture. In addition, several factors including post-translational modifications such as the phosphorylation, acetylation, SUMOylation, and o-GlcNAcylation of mitochondrial dynamics proteins contribute to shaping the plasticity of this architecture. In this regard, several studies have evidenced that, upon metabolic stress, mitochondrial dynamics proteins are post-translationally modified, leading to the alteration of mitochondrial architecture. Interestingly, several proteins that sustain the mitochondrial lipid composition also modulate mitochondrial morphology and organelle communication. In this context, pharmacological studies have revealed that the modulation of mitochondrial shape and function emerges as a potential therapeutic strategy for metabolic diseases. Here, we review the factors that modulate mitochondrial architecture.

Ultrastructure of the nebenkern during spermatogenesis in the praying mantid Hierodula membranacea

Spermatogenesis leads to the formation of functional sperm cells. Here we have applied high-pressure freezing in combination with transmission electron microscopy (TEM) to study the ultrastructure of sperm development in subadult males of the praying mantid Hierodula membranacea, a species in which spermatogenesis had not previously been studied. We show the ultrastructure of different stages of sperm development in this species. Thorough examination of TEM data and electron tomographic reconstructions revealed interesting structural features of the nebenkern, an organelle composed of fused mitochondria that has been studied in spermatids of other insect species. We have applied serial-section electron tomography of the nebenkern to demonstrate in three dimensions (3D) that this organelle in H. membranacea is composed of two interwoven mitochondrial derivatives, and that the mitochondrial derivatives are connected by a zipper-like structure at opposing positions. Our approach will enable further ultrastructural analyses of the nebenkern in other organisms.

Mitophagy Promotes Resistance to BH3 Mimetics in Acute Myeloid Leukemia

BH3 mimetics are used as an efficient strategy to induce cell death in several blood malignancies, including acute myeloid leukemia (AML). Venetoclax, a potent BCL-2 antagonist, is used clinically in combination with hypomethylating agents for the treatment of AML. Moreover, MCL1 or dual BCL-2/BCL-xL antagonists are under investigation. Yet, resistance to single or combinatorial BH3-mimetic therapies eventually ensues. Integration of multiple genome-wide CRISPR/Cas9 screens revealed that loss of mitophagy modulators sensitizes AML cells to various BH3 mimetics targeting different BCL-2 family members. One such regulator is MFN2, whose protein levels positively correlate with drug resistance in patients with AML. MFN2 overexpression is sufficient to drive resistance to BH3 mimetics in AML. Insensitivity to BH3 mimetics is accompanied by enhanced mitochondria-endoplasmic reticulum interactions and augmented mitophagy flux, which acts as a prosurvival mechanism to eliminate mitochondrial damage. Genetic or pharmacologic MFN2 targeting synergizes with BH3 mimetics by impairing mitochondrial clearance and enhancing apoptosis in AML.

SIGNIFICANCE

AML remains one of the most difficult-to-treat blood cancers. BH3 mimetics represent a promising therapeutic approach to eliminate AML blasts by activating the apoptotic pathway. Enhanced mitochondrial clearance drives resistance to BH3 mimetics and predicts poor prognosis. Reverting excessive mitophagy can halt BH3-mimetic resistance in AML. This article is highlighted in the In This Issue feature, p. 1501.

Growth hormone remodels the 3D-structure of the mitochondria of inflammatory macrophages and promotes metabolic reprogramming

Introduction

Macrophages are a heterogeneous population of innate immune cells that support tissue homeostasis through their involvement in tissue development and repair, and pathogen defense. Emerging data reveal that metabolism may control macrophage polarization and function and, conversely, phenotypic polarization may drive metabolic reprogramming.

Methods

Here we use biochemical analysis, correlative cryogenic fluorescence microscopy and cryo-focused ion-beam scanning electron microscopy.

Results

We demonstrate that growth hormone (GH) reprograms inflammatory GM-CSF-primed monocyte-derived macrophages (GM-MØ) by functioning as a metabolic modulator. We found that exogenous treatment of GM-MØ with recombinant human GH reduced glycolysis and lactate production to levels similar to those found in anti-inflammatory M-MØ. Moreover, GH treatment of GM-MØ augmented mitochondrial volume and altered mitochondrial dynamics, including the remodeling of the inner membrane to increase the density of cristae.

Conclusions

Our data demonstrate that GH likely serves a modulatory role in the metabolism of inflammatory macrophages and suggest that metabolic reprogramming of macrophages should be considered as a new target to intervene in inflammatory diseases.

A Novel ENU-Induced Mfn2 Mutation Causes Motor Deficits in Mice without Causing Peripheral Neuropathy

Mitochondrial fission and fusion are required for maintaining functional mitochondria. The mitofusins (MFN1 and MFN2) are known for their roles in mediating mitochondrial fusion. Recently, MFN2 has been implicated in other important cellular functions, such as mitophagy, mitochondrial motility, and coordinating endoplasmic reticulum-mitochondria communication. In humans, over 100 MFN2 mutations are associated with a form of inherited peripheral neuropathy, Charcot-Marie-Tooth disease type 2A (CMT2A). Here we describe an ENU-induced mutant mouse line with a recessive neuromuscular phenotype. Behavioral screening showed progressive weight loss and rapid deterioration of motor function beginning at 8 weeks. Mapping and sequencing revealed a missense mutation in exon 18 of Mfn2 (T1928C; Leu643Pro), within the transmembrane domain. Compared to wild-type and heterozygous littermates, Mfn2^L643P/L643P mice exhibited diminished rotarod performance and decreases in activity in the open field test, muscular endurance, mean mitochondrial diameter, sensory tests, mitochondrial DNA content, and MFN2 protein levels. However, tests of peripheral nerve physiology and histology were largely normal. Mutant leg bones had reduced cortical bone thickness and bone area fraction. Together, our data indicate that Mfn2^L643P causes a recessive motor phenotype with mild bone and mitochondrial defects in mice. Lack of apparent nerve pathology notwithstanding, this is the first reported mouse model with a mutation in the transmembrane domain of the protein, which may be valuable for researchers studying MFN2 biology.

Systematic Transmission Electron Microscopy-Based Identification and 3D Reconstruction of Cellular Degradation Machinery

Various intracellular degradation organelles, including autophagosomes, lysosomes, and endosomes, work in tandem to perform autophagy, which is crucial for cellular homeostasis. Altered autophagy contributes to the pathophysiology of various diseases, including cancers and metabolic diseases. This paper aims to describe an approach to reproducibly identify and distinguish subcellular structures involved in macroautophagy. Methods are provided that help avoid common pitfalls. How to distinguish between lysosomes, lipid droplets, autolysosomes, autophagosomes, and inclusion bodies are also discussed. These methods use transmission electron microscopy (TEM), which is able to generate nanometer-scale micrographs of cellular degradation components in a fixed sample. Serial block face-scanning electron microscopy is also used to visualize the 3D morphology of degradation machinery using the Amira software. In addition to TEM and 3D reconstruction, other imaging techniques are discussed, such as immunofluorescence and immunogold labeling, which can be used to classify cellular organelles, reliably and accurately. Results show how these methods may be used to accurately quantify cellular degradation machinery under various conditions, such as treatment with the endoplasmic reticulum stressor thapsigargin or ablation of the dynamin-related protein 1.

The role of circadian clock-controlled mitochondrial dynamics in diabetic cardiomyopathy

Diabetes mellitus is a metabolic disease with a high prevalence worldwide, and cardiovascular complications are the leading cause of mortality in patients with diabetes. Diabetic cardiomyopathy (DCM), which is prone to heart failure with preserved ejection fraction, is defined as a cardiac dysfunction without conventional cardiac risk factors such as coronary heart disease and hypertension. Mitochondria are the centers of energy metabolism that are very important for maintaining the function of the heart. They are highly dynamic in response to environmental changes through mitochondrial dynamics. The disruption of mitochondrial dynamics is closely related to the occurrence and development of DCM. Mitochondrial dynamics are controlled by circadian clock and show oscillation rhythm. This rhythm enables mitochondria to respond to changing energy demands in different environments, but it is disordered in diabetes. In this review, we summarize the significant role of circadian clock-controlled mitochondrial dynamics in the etiology of DCM and hope to play a certain enlightening role in the treatment of DCM.

Mitofusin2 expression is associated with podocyte injury in IgA nephropathy

BACKGROUND

Podocyte injury is associated with IgA nephropathy (IgAN) prognosis. Mitochondrial dysfunction is a major contributor to podocyte injury and death. Mitofusin2 (Mfn2) plays an important role in regulating the morphology and function of mitochondria. This study aimed to investigate the potential of Mfn2 as a biomarker to evaluate the degree of podocyte injury.

METHODS

This single-center, retrospective study enrolled 114 patients with biopsy-proven IgAN. Immunofluorescence and TUNEL staining were applied, and clinical and pathological features were compared between patients with different patterns of Mfn2 expression.

RESULTS

In IgAN, Mfn2 is mainly expressed in podocytes and significantly associated with nephrin, TUNEL, and Parkin staining. Among the 114 IgAN patients, 28 (24.56%) did not exhibit Mfn2 expression in podocytes. The patients in the Mfn2-negative group had lower serum albumin (34.43 ± 4.64 g/L vs. 36.48 ± 3 .52 g/L, P = 0.015) and estimated glomerular filtration rate (eGFR) (76.59 ± 35.38 mL/min vs. 92.13 ± 25.35 mL/min, P = 0.013), higher 24 h proteinuria (2.48 ± 2.72 g/d vs. 1.27 ± 1.31 g/d, P = 0.002), serum creatinine (Scr) (107.39 ± 57.97 μmol/L vs. 84.70 ± 34.95 μmol/L, P = 0.015), blood urea nitrogen (BUN) (7.36 ± 4.45 mmol/L vs. 5.68 ± 2.14 mmol/L, P = 0.008), and higher S/T scores (92.86% vs. 70.93% and 42.85% vs. 15.12%, respectively, P < 0.05). In the Mfn2-negative group, the mitochondria were punctate and round ridges disappeared, and a lower length-to-width ratio and much higher M/A ratio were observed. Correlation analysis showed that the intensity of Mfn2 was negatively correlated with Scr (r = - 0.232, P = 0.013), 24 h proteinuria (r = - 0.541, P = 0.001), and the degree of podocyte effacement (r = - 0.323, P = 0.001), and positively correlated with eGFR (r = 0.213, P = 0.025). Logistic regression analysis showed that the Mfn2-negative group had a higher risk of severe podocyte effacement (≥ 50%) (OR = 3.061, P = 0.019).

CONCLUSION

Mfn2 was negatively correlated with proteinuria and renal function. A lack of Mfn2 in podocytes indicates severe podocyte injury and a high degree of podocyte effacement.

Determinants and outcomes of mitochondrial dynamics

Mitochondria are not only central organelles in metabolism and energy conversion but are also platforms for cellular signaling cascades. Classically, the shape and ultrastructure of mitochondria were depicted as static. The discovery of morphological transitions during cell death and of conserved genes controlling mitochondrial fusion and fission contributed to establishing the concept that mitochondrial morphology and ultrastructure are dynamically regulated by mitochondria-shaping proteins. These finely tuned, dynamic changes in mitochondrial shape can in turn control mitochondrial function, and their alterations in human diseases suggest that this space can be explored for drug discovery. Here, we review the basic tenets and molecular mechanisms of mitochondrial morphology and ultrastructure, describing how they can coordinately define mitochondrial function.

FGF19 increases mitochondrial biogenesis and fusion in chondrocytes via the AMPKα-p38/MAPK pathway

Fibroblast growth factor 19 (FGF19) is recognized to play an essential role in cartilage development and physiology, and has emerged as a potential therapeutic target for skeletal metabolic diseases. However, FGF19-mediated cellular behavior in chondrocytes remains a big challenge. In the current study, we aimed to investigate the role of FGF19 on chondrocytes by characterizing mitochondrial biogenesis and fission-fusion dynamic equilibrium and exploring the underlying mechanism. We first found that FGF19 enhanced mitochondrial biogenesis in chondrocytes with the help of β Klotho (KLB), a vital accessory protein for assisting the binding of FGF19 to its receptor, and the enhanced biogenesis accompanied with a fusion of mitochondria, reflecting in the elongation of individual mitochondria and the up-regulation of mitochondrial fusion proteins. We then revealed that FGF19-mediated mitochondrial biogenesis and fusion required the binding of FGF19 to the membrane receptor, FGFR4, and the activation of AMP-activated protein kinase alpha (AMPKα)/peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC-1α)/sirtuin 1 (SIRT1) axis. Finally, we demonstrated that FGF19-mediated mitochondrial biogenesis and fusion was mainly dependent on the activation of p-p38 signaling. Inhibition of p38 signaling largely reduced the high expression of AMPKα/PGC-1α/SIRT1 axis, decreased the up-regulation of mitochondrial fusion proteins and impaired the enhancement of mitochondrial network morphology in chondrocytes induced by FGF19. Taking together, our results indicate that FGF19 could increase mitochondrial biogenesis and fusion via AMPKα-p38/MAPK signaling, which enlarge the understanding of FGF19 on chondrocyte metabolism. Video Abstract.

Disturb mitochondrial associated proteostasis: Neurodegeneration and imperfect ageing

The disturbance in mitochondrial functions and homeostasis are the major features of neuron degenerative conditions, like Parkinson’s disease, Amyotrophic Lateral Sclerosis, and Alzheimer’s disease, along with protein misfolding. The aberrantly folded proteins are known to link with impaired mitochondrial pathways, further contributing to disease pathogenesis. Despite their central significance, the implications of mitochondrial homeostasis disruption on other organelles and cellular processes remain insufficiently explored. Here, we have reviewed the dysfunction in mitochondrial physiology, under neuron degenerating conditions. The disease misfolded proteins impact quality control mechanisms of mitochondria, such as fission, fusion, mitophagy, and proteasomal clearance, to the detriment of neuron. The adversely affected mitochondrial functional roles, like oxidative phosphorylation, calcium homeostasis, and biomolecule synthesis as well as its axes and contacts with endoplasmic reticulum and lysosomes are also discussed. Mitochondria sense and respond to multiple cytotoxic stress to make cell adapt and survive, though chronic dysfunction leads to cell death. Mitochondria and their proteins can be candidates for biomarkers and therapeutic targets. Investigation of internetworking between mitochondria and neurodegeneration proteins can enhance our holistic understanding of such conditions and help in designing more targeted therapies.

Japanese Encephalitis Virus Infection Causes an Imbalance in the Activation of Mitochondrial Fusion/Fission Genes and Triggers the Activation of NOX2-mediated Oxidative Stress and Neuronal Cell Death

Mitochondria dysfunction may be an important contributor to Japanese encephalitis (JE) viral infection disease pathogenesis. In the current study, we define whether changes in mitochondrial DNA copy number (which is the biomarker for mitochondrial function) and alteration in mitochondria dynamics (fusion and fission) contribute to the pathology of the JE virus in vivo mice model. We found decreased mitochondria copy number, reduced activation of mitochondrial fission (FIS1/DRP1), and increased activation of mitochondrial fusion (MFN1/MFN2/OPA1) genes that are associated with increased NOX2-mediated ROS generation and neuronal cell death following JE virus infection. Furthermore, we found that antioxidant glutathione level decreases. In summary, the following study demonstrates that JE viral infection causes an imbalance in mitochondrial fission/fusion gene activation and promotes NOX2-mediated oxidative stress and cell death, suggesting that intervention in mitochondrial dynamics might be a potential therapeutic strategy for combating oxidative stress and inflammatory process in JE viral infection.

Mitofusin-2: Functional switch between mitochondrial function and neurodegeneration

Mitochondria are highly dynamic organelles known to play role in the regulation of several cellular biological processes. However, their dynamics such as number, shape, and biological functions are regulated by mitochondrial fusion and fission process. The balance between the fusion and fission process is most important for the maintenance of mitochondrial structure as well as cellular functions. The alterations within mitochondrial dynamic processes were found to be associated with the progression of neurodegenerative diseases. In recent years, mitofusin-2 (Mfn2), a GTPase has emerged as a multifunctional protein which not only is found to regulate the mitochondrial fusion-fission process but also known to regulate several cellular functions such as mitochondrial metabolism, cellular biogenesis, signalling, and apoptosis via maintaining the ER-mitochondria contact sites. In this review, we summarize the current knowledge of the structural and functional properties of the Mfn2, its transcriptional regulation and their roles in several cellular functions with a focus on current advances in the pathogenesis of neurodegenerative diseases.

Mitochondrial dynamics, elimination and biogenesis during post-ischemic recovery in ischemia-resistant and ischemia-vulnerable gerbil hippocampal regions

Transient ischemic attacks (TIA) result from a temporary blockage in blood circulation in the brain. As TIAs cause disabilities and often precede full-scale strokes, the effects of TIA are investigated to develop neuroprotective therapies. We analyzed changes in mitochondrial network dynamics, mitophagy and biogenesis in sections of gerbil hippocampus characterized by a different neuronal survival rate after 5-minute ischemia-reperfusion (I/R) insult. Our research revealed a significantly greater mtDNA/nDNA ratio in CA2-3, DG hippocampal regions (5.8 ± 1.4 vs 3.6 ± 0.8 in CA1) that corresponded to a neuronal resistance to I/R. During reperfusion, an increase of pro-fission (phospho-Ser616-Drp1/Drp1) and pro-fusion proteins (1.6 ± 0.5 and 1.4 ± 0.3 for Mfn2 and Opa1, respectively) was observed in CA2-3, DG. Selective autophagy markers, PINK1 and SQSTM1/p62, were elevated 24-96 h after I/R and accompanied by significant elevation of transcription factors proteins PGC-1α and Nrf1 (1.2 ± 0.4, 1.78 ± 0.6, respectively) and increased respiratory chain proteins (e.g., 1.5 ± 0.3 for complex IV at I/R 96 h). Contrastingly, decreased enzymatic activity of citrate synthase, reduced Hsp60 protein level and electron transport chain subunits (0.88 ± 0.03, 0.74 ± 0.1 and 0.71 ± 0.1 for complex IV at I/R 96 h, respectively) were observed in I/R-vulnerable CA1. The phospho-Ser616-Drp1/Drp1 was increased while Mfn2 and total Opa1 reduced to 0.88 ± 0.1 and 0.77 ± 0.17, respectively. General autophagy, measured as LC3-II/I ratio, was activated 3 h after reperfusion reaching 2.37 ± 0.9 of control. This study demonstrated that enhanced mitochondrial fusion, followed by late and selective mitophagy and mitochondrial biogenesis might together contribute to reduced susceptibility to TIA.