Parkin-mediated mitophagy directs perinatal cardiac metabolic maturation in mice

DUT (p.Y116C)-Mutation-Induced Thrombocytopenia in Rabbits

Thrombocytopenia is a hematologic disorder characterized by an abnormally low platelet count in peripheral blood. Recent studies have identified mutations in DUT as the primary cause of bone marrow failure and diabetes mellitus syndrome (BMFDMS), a condition commonly associated with thrombocytopenia. In this study, a novel rabbit model of thrombocytopenia carrying the DUT c.3020A>G (p.Y116C) mutation was established using SpRY-ABEmax-mediated base editing. This model accurately recapitulates the clinical manifestations of human thrombocytopenia. Phenotypic analysis has revealed that mutant rabbits exhibited significant reductions in megakaryocyte numbers, platelet counts, and survival rates when compared to wild-type controls. Mechanistic investigations showed that the DUT mutation leads to mitochondrial structural abnormalities and functional impairments. Notably, platelets from DUT (p.Y116C)-mutant rabbits exhibited markedly reduced DUT protein expression and enhanced mitophagy, potentially mediated through the Park2 pathway. This study presents the first genetic model of thrombocytopenia that closely mimics the human DUT (p.Y116C) mutation, offering new insights into the relationship between DUT mutations and platelet function, and highlighting potential therapeutic targets for human thrombocytopenia.

Identification of mitophagy-related genes in patients with acute myocardial infarction

Mitophagy is involved in acute myocardial infarction (AMI) process. However, the role of mitophagy-related genes (MRGs) in the AMI process is not well illustrated. We identified MRGs involved in AMI by bioinformatics analysis. The external datasets were employed for the validation of the MRGs, alongside the execution of cellular and animal experiments. Forty-five MRGs were detected, and machine learning identified the top four hub genes, namely ALDH2, ACSL1, IL1B, and GABARAPL1. Additionally, an external validation set was used to screen for three diagnostic markers (ACSL1, IL1B, and GABARAPL1) among these hub genes. Immune infiltration analysis revealed changes in the immune microenvironment among patients with AMI. Finally, the significant upregulation of ACSL1, IL1B, and GABARAPL1 in both cellular and animal models was confirmed. The occurrence of mitophagy was observed in the cell model through transmission electron microscopy (TEM). Our study demonstrated that ACSL1, IL1B, and GABARAPL1 possess potential biomarkers for AMI.

Autophagy in adult stem cell homeostasis, aging, and disease therapy

Autophagy is a crucial cellular process that facilitates the degradation of damaged organelles and protein aggregates, and the recycling of cellular components for the energy production and macromolecule synthesis. It plays an indispensable role in maintaining cellular homeostasis. Over recent decades, research has increasingly focused on the role of autophagy in regulating adult stem cells (SCs). Studies suggest that autophagy modulates various cellular processes and states of adult SCs, including quiescence, proliferation, self-renewal, and differentiation. The primary role of autophagy in these contexts is to sustain homeostasis, withstand stressors, and supply energy. Notably, the dysfunction of adult SCs during aging is correlated with a decline in autophagic activity, suggesting that autophagy is also involved in SC- and aging-associated disorders. Given the diverse cellular processes mediated by autophagy and the intricate mechanisms governing adult SCs, further research is essential to elucidate both universal and cell type-specific regulatory pathways of autophagy. This review discusses the role of autophagy in regulating adult SCs during quiescence, proliferation, self-renewal, and differentiation. Additionally, it summarizes the relationship between SC aging and autophagy, providing therapeutical insights into treating and ameliorating aging-associated diseases and cancers, and ultimately promoting longevity.

Programmed mitophagy at the oocyte-to-zygote transition promotes species immortality

The quality of mitochondria inherited from the oocyte determines embryonic viability, metabolic health throughout progeny lifetime, and future generation endurance. High levels of endogenous reactive oxygen species and exogenous toxicants are threats to mitochondrial DNA (mtDNA) in fully developed oocytes. Deleterious mtDNA is commonly detected in developed oocytes, but is absent in embryos, suggesting the existence of a cryptic purifying selection mechanism. Here we discover that in C. elegans, the onset of oocyte-to-zygote transition (OZT) developmentally triggers a rapid mitophagy event. We show that mitophagy at OZT (MOZT) requires mitochondrial fragmentation, the macroautophagy pathway, and the mitophagy receptor FUNDC1, but not the prevalent mitophagy factors PINK1 and BNIP3. Impaired MOZT leads to increased deleterious mtDNA inheritance and decreases embryonic survival. Inherited mtDNA damage accumulates across generations, leading to the extinction of descendent populations. Thus, MOZT represents a strategy that preserves mitochondrial health during the mother-to-offspring transmission and promotes species continuity.

Developmental mitochondrial complex I activity determines lifespan

Aberrant mitochondrial function has been associated with an increasingly large number of human disease states. Observations from in vivo models where mitochondrial function is altered suggest that maladaptations to mitochondrial dysfunction may underpin disease pathology. We hypothesized that the severity of this maladaptation could be shaped by the plasticity of the system when mitochondrial dysfunction manifests. To investigate this, we have used inducible fly models of mitochondrial complex I (CI) dysfunction to reduce mitochondrial function at two stages of the fly lifecycle, from early development and adult eclosion. Here, we show that in early life (developmental) mitochondrial dysfunction results in severe reductions in survival and stress resistance in adulthood, while flies where mitochondrial function is perturbed from adulthood, are long-lived and stress resistant despite having up to a 75% reduction in CI activity. After excluding developmental defects as a cause, we went on to molecularly characterize these two populations of mitochondrially compromised flies, short- and long-lived. We find that our short-lived flies have unique transcriptomic, proteomic and metabolomic responses, which overlap significantly in discrete models of CI dysfunction. Our data demonstrate that early mitochondrial dysfunction via CI depletion elicits a maladaptive response, which severely reduces survival, while CI depletion from adulthood is insufficient to reduce survival and stress resistance.

Thermogenesis and Energy Metabolism in Brown Adipose Tissue in Animals Experiencing Cold Stress

Cold exposure is a regulatory biological functions in animals. The interaction of thermogenesis and energy metabolism in brown adipose tissue (BAT) is important for metabolic regulation in cold stress. Brown adipocytes (BAs) produce uncoupling protein 1 (UCP1) in mitochondria, activating non-shivering thermogenesis (NST) by uncoupling fuel combustion from ATP production in response to cold stimuli. To elucidate the mechanisms underlying thermogenesis and energy metabolism in BAT under cold stress, we explored how cold exposure triggers the activation of BAT thermogenesis and regulates overall energy metabolism. First, we briefly outline the precursor composition and function of BA. Second, we explore the roles of the cAMP- protein kinase A (PKA) and adenosine monophosphate-activated protein kinase (AMPK) signaling pathways in thermogenesis and energy metabolism in BA during cold stress. Then, we analyze the mechanism by which BA regulates mitochondria homeostasis and energy balance during cold stress. This research reveals potential therapeutic targets, such as PKA, AMPK, UCP1 and PGC-1α, which can be used to develop innovative strategies for treating metabolic diseases. Furthermore, it provides theoretical support for optimizing cold stress response strategies, including the pharmacological activation of BAT and the genetic modulation of thermogenic pathways, to improve energy homeostasis in livestock.

Metaboloepigenetics: Role in the Regulation of Flow-Mediated Endothelial (Dys)Function and Atherosclerosis

Endothelial dysfunction is the main initiating factor in atherosclerosis. Through mechanotransduction, shear stress regulates endothelial cell function in both homeostatic and diseased states. Accumulating evidence reveals that epigenetic changes play critical roles in the etiology of cardiovascular diseases, including atherosclerosis. The metabolic regulation of epigenetics has emerged as an important factor in the control of gene expression in diseased states, but to the best of our knowledge, this connection remains largely unexplored in endothelial dysfunction and atherosclerosis. In this review, we (1) summarize how shear stress (or flow) regulates endothelial (dys)function; (2) explore the epigenetic alterations that occur in the endothelium in response to disturbed flow; (3) review endothelial cell metabolism under different shear stress conditions; and (4) suggest mechanisms which may link this altered metabolism to the regulation of the endothelial epigenome by modulations in metabolite availability. We believe that metabolic regulation plays an important role in endothelial epigenetic reprogramming and could pave the way for novel metabolism-based therapeutic strategies.

Mitochondrial quality control: Biochemical mechanism of cardiovascular disease

Mitochondria play a key role in the regulation of energy homeostasis and ATP production in cardiac cells. Mitochondrial dysfunction can trigger several pathological events that contribute to the development and progression of cardiovascular diseases. These mechanisms include the induction of oxidative stress, dysregulation of intracellular calcium cycling, activation of the apoptotic pathway, and alteration of lipid metabolism. This review focuses on the role of mitochondria in intracellular signaling associated with cardiovascular diseases, emphasizing the contributions of reactive oxygen species production and mitochondrial dynamics. Indeed, mitochondrial dysfunction has been implicated in every aspect of cardiovascular disease and is currently being evaluated as a potential target for therapeutic interventions. To treat cardiovascular diseases and improve overall heart health, it is important to better understand these biochemical systems. These findings allow the achievement of targeted therapies and preventive measures. Therefore, this review investigates different studies that demonstrate how changes in mitochondrial dynamics like fusion, fission, and mitophagy contribute to the development or worsening of disorders related to heart diseases by summarizing current research on their role.

Parkin inhibits iron overload-induced cardiomyocyte ferroptosis by ubiquitinating ACSL4 and modulating PUFA-phospholipids metabolism

Iron overload is strongly associated with heart disease. Ferroptosis is a new form of regulated cell death indicated in cardiac ischemia-reperfusion (I/R) injury. However, the specific molecular mechanism of myocardial injury caused by iron overload in the heart is still unclear, and the involvement of ferroptosis in iron overload-induced myocardial injury is not fully understood. In this study, we observed that ferroptosis participated in developing of iron overload and I/R-induced cardiomyopathy. Mechanistically, we discovered that Parkin inhibited iron overload-induced ferroptosis in cardiomyocytes by promoting the ubiquitination of long-chain acyl-CoA synthetase 4 (ACSL4), a crucial protein involved in ferroptosis-related lipid metabolism pathways. Additionally, we identified p53 as a transcription factor that transcriptionally suppressed Parkin expression in iron-overloaded cardiomyocytes, thereby regulating iron overload-induced ferroptosis. In animal studies, cardiac-specific Parkin knockout mice (Myh6-CreER T2 /Parkin fl/fl ) fed a high-iron diet presented more severe myocardial damage, and the high iron levels exacerbated myocardial I/R injury. However, the ferroptosis inhibitor Fer-1 significantly suppressed iron overload-induced ferroptosis and myocardial I/R injury. Moreover, Parkin effectively protected against impaired mitochondrial function and prevented iron overload-induced mitochondrial lipid peroxidation. These findings unveil a novel regulatory pathway involving p53-Parkin-ACSL4 in heart disease by inhibiting of ferroptosis.

Functional transformation of macrophage mitochondria in cardiovascular diseases

Mitochondria are pivotal in the modulation of macrophage activation, differentiation, and survival. Furthermore, macrophages are instrumental in the onset and progression of cardiovascular diseases. Hence, it is imperative to investigate the role of mitochondria within macrophages in the context of cardiovascular disease. In this review, we provide an updated description of the origin and classification of cardiac macrophages and also focused on the relationship between macrophages and mitochondria in cardiovascular diseases with respect to (1) proinflammatory or anti-inflammatory macrophages, (2) macrophage apoptosis, (3) macrophage pyroptosis, and (4) macrophage efferocytosis. Clarifying the relationship between mitochondria and macrophages can aid the exploration of novel therapeutic strategies for cardiovascular disease.

Age-associated metabolic and epigenetic barriers during direct reprogramming of mouse fibroblasts into induced cardiomyocytes

Heart disease is the leading cause of mortality in developed countries, and novel regenerative procedures are warranted. Direct cardiac conversion (DCC) of adult fibroblasts can create induced cardiomyocytes (iCMs) for gene and cell-based heart therapy, and in addition to holding great promise, still lacks effectiveness as metabolic and age-associated barriers remain elusive. Here, by employing MGT (Mef2c, Gata4, Tbx5) transduction of mouse embryonic fibroblasts (MEFs) and adult (dermal and cardiac) fibroblasts from animals of different ages, we provide evidence that the direct reprogramming of fibroblasts into iCMs decreases with age. Analyses of histone posttranslational modifications and ChIP-qPCR revealed age-dependent alterations in the epigenetic landscape of DCC. Moreover, DCC is accompanied by profound mitochondrial metabolic adaptations, including a lower abundance of anabolic metabolites, network remodeling, and reliance on mitochondrial respiration. In vitro metabolic modulation and dietary manipulation in vivo improve DCC efficiency and are accompanied by significant alterations in histone marks and mitochondrial homeostasis. Importantly, adult-derived iCMs exhibit increased accumulation of oxidative stress in the mitochondria and activation of mitophagy or dietary lipids; they improve DCC and revert mitochondrial oxidative damage. Our study provides evidence that metaboloepigenetics plays a direct role in cell fate transitions driving DCC, highlighting the potential use of metabolic modulation to improve cardiac regenerative strategies.

Mitochondrial quality control: a pathophysiological mechanism and potential therapeutic target for chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a prevalent chronic respiratory disease worldwide. Mitochondrial quality control mechanisms encompass processes such as mitochondrial biogenesis, fusion, fission, and autophagy, which collectively maintain the quantity, morphology, and function of mitochondria, ensuring cellular energy supply and the progression of normal physiological activities. However, in COPD, due to the persistent stimulation of harmful factors such as smoking and air pollution, mitochondrial quality control mechanisms often become deregulated, leading to mitochondrial dysfunction. Mitochondrial dysfunction plays a pivotal role in the pathogenesis of COPD, contributing toinflammatory response, oxidative stress, cellular senescence. However, therapeutic strategies targeting mitochondria remain underexplored. This review highlights recent advances in mitochondrial dysfunction in COPD, focusing on the role of mitochondrial quality control mechanisms and their dysregulation in disease progression. We emphasize the significance of mitochondria in the pathophysiological processes of COPD and explore potential strategies to regulate mitochondrial quality and improve mitochondrial function through mitochondrial interventions, aiming to treat COPD effectively. Additionally, we analyze the limitations and challenges of existing therapeutic strategies, aiming to provide new insights and methods for COPD treatment.

FOXO3 Activates MFN2 Expression to Maintain the Autophagy Response in Cancer Cells Under Amino Acid Deprivation

The lack of amino acids triggers the autophagic response. Some studies have shown such starvation conditions also induce mitochondrial fusion, revealing a close correlation between the two processes. Although Mitofusin-2 (MFN2) has been demonstrated to play a role in fusion regulation, its role in the autophagic response and the variables that activate MFN2 under stress remain unknown. In this investigation, we screened and confirmed that forkhead box protein O3 (FOXO3) participates in MFN2's expression during short periods of starvation. Luciferase reporter test proved that FOXO3 facilitates MFN2's transcription by binding to its promoter region, and FOXO3 downregulation directly depresses MFN2's expression. Consequently, inhibiting the FOXO3-MFN2 axis results in the loss of mitochondrial fusion, disrupting the normal morphology of mitochondria, impairing the degradation of substrates, and reducing autophagosome accumulation, ultimately leading to the blockage of the autophagy. In conclusion, our work demonstrates that the FOXO3-MFN2 pathway is essential for adaptive changes in mitochondrial morphology and cellular autophagy response under nutritional constraints.

MANF facilitates breast cancer cell survival under glucose-starvation conditions via PRKN-mediated mitophagy regulation

During tumor expansion, breast cancer (BC) cells often experience reactive oxygen species accumulation and mitochondrial damage because of glucose shortage. However, the mechanism by which BC cells deal with the glucose-shortage-induced oxidative stress remains unclear. Here, we showed that MANF (mesencephalic astrocyte derived neurotrophic factor)-mediated mitophagy facilitates BC cell survival under glucose-starvation conditions. MANF-mediated mitophagy also promotes fatty acid oxidation in glucose-starved BC cells. Moreover, during glucose starvation, SENP1-mediated de-SUMOylation of MANF increases cytoplasmic MANF expression through the inhibition of MANF's nuclear translocation and hence renders mitochondrial distribution of MANF. MANF mediates mitophagy by binding to PRKN (parkin RBR E3 ubiquitin protein ligase), a key mitophagy regulator, in the mitochondria. Under conditions of glucose starvation, protein oxidation inhibits PRKN activity; nevertheless, the CXXC motif of MANF alleviates protein oxidation in RING II-domain of PRKN and restores its E3 ligase activity. Furthermore, MANF-PRKN interactions are essential for BC tumor growth and metastasis. High MANF expression predicts poor outcomes in patients with BC. Our results highlight the prosurvival role of MANF-mediated mitophagy in BC cells during glucose starvation, suggesting MANF as a potential therapeutic target.Abbreviation: 2DG, 2-deoxy-D-glucose; 5TG, 5-thio-D-glucose; ACSL4/FACL4, acyl-CoA synthetase long chain family member 4; Baf A1, bafilomycin A1; BRCA, breast cancer; CHX, cycloheximide; DMF, distant metastasis-free; DMFS, distant metastasis-free survival; ECM, extracellular matrix; ER, endoplasmic reticulum; ERS, endoplasmic reticulum stress; F-1,6-BP, fructose-1,6-bisphosphate; FAO, fatty acid oxidation; GSH, reduced glutathione; GSVA, gene set variation analysis; HCC, hepatocellular carcinoma; ICC, intrahepatic cholangiocarcinoma; IF, immunofluorescence; MANF, mesencephalic astrocyte derived neurotrophic factor; Mdivi-1, mitochondrial division inhibitor 1; MFI, mean fluorescence intensity; NAC, N-acetyl-L-cysteine; OCR, oxygen-consumption rate; OS, overall survival; PMI, SQSTM1/p62-mediated mitophagy inducer; PPP, pentose phosphate pathway; PRKN, parkin RBR E3 ubiquitin protein ligase; RBR, RING in between RING; RFS, relapse-free survival; ROS, reactive oxygen species; SAPLIPs, saposin-like proteins; TCGA, The Cancer Genome Atlas; TNBC, triple-negative breast cancer; WT, wild type.

Targeting mitochondrial transfer: a new horizon in cardiovascular disease treatment

Cardiovascular diseases (CVDs) are the leading cause of mortality among individuals with noncommunicable diseases worldwide. Obesity is associated with an increased risk of developing cardiovascular disease (CVD). Mitochondria are integral to the cardiovascular system, and it has been reported that mitochondrial transfer is associated with the pathogenesis of multiple CVDs and obesity. This review offers a comprehensive examination of the relevance of mitochondrial transfer to cardiovascular health and disease, emphasizing the critical functions of mitochondria in energy metabolism and signal transduction within the cardiovascular system. This highlights how disruptions in mitochondrial transfer contribute to various CVDs, such as myocardial infarction, cardiomyopathies, and hypertension. Additionally, we provide an overview of the molecular mechanisms governing mitochondrial transfer and its potential implications for CVD treatment. This finding underscores the therapeutic potential of mitochondrial transfer and addresses the various mechanisms and challenges in its implementation. By delving into mitochondrial transfer and its targeted modulation, this review aims to advance our understanding of cardiovascular disease treatment, presenting new insights and potential therapeutic strategies in this evolving field.

The molecular mechanisms of cardiac development and related diseases

Cardiac development is a complex and intricate process involving numerous molecular signals and pathways. Researchers have explored cardiac development through a long journey, starting with early studies observing morphological changes and progressing to the exploration of molecular mechanisms using various molecular biology methods. Currently, advancements in stem cell technology and sequencing technology, such as the generation of human pluripotent stem cells and cardiac organoids, multi-omics sequencing, and artificial intelligence (AI) technology, have enabled researchers to understand the molecular mechanisms of cardiac development better. Many molecular signals regulate cardiac development, including various growth and transcription factors and signaling pathways, such as WNT signaling, retinoic acid signaling, and Notch signaling pathways. In addition, cilia, the extracellular matrix, epigenetic modifications, and hypoxia conditions also play important roles in cardiac development. These factors play crucial roles at one or even multiple stages of cardiac development. Recent studies have also identified roles for autophagy, metabolic transition, and macrophages in cardiac development. Deficiencies or abnormal expression of these factors can lead to various types of cardiac development abnormalities. Nowadays, congenital heart disease (CHD) management requires lifelong care, primarily involving surgical and pharmacological treatments. Advances in surgical techniques and the development of clinical genetic testing have enabled earlier diagnosis and treatment of CHD. However, these technologies still have significant limitations. The development of new technologies, such as sequencing and AI technologies, will help us better understand the molecular mechanisms of cardiac development and promote earlier prevention and treatment of CHD in the future.

Aloe Emodin Alleviates Radiation-Induced Heart Disease via Blocking P4HB Lactylation and Mitigating Kynurenine Metabolic Disruption

Aloe emodin is an anthraquinone of traditional Chinese medicine monomer, which plays a protective action in cardiovascular diseases. However, the regulatory mechanisms of aloe emodin in the protection of radiation-induced heart damage (RIHD) are unclear. As a novel post-translational modification, lactylation is considered as a critical mediator in inflammatory cascade and cardiac injury. Here, using a cross of differential omics and 4D label-free lactylation omics, protein disulfide-isomerase (P4HB) is identified as a novel target for lactylation, and aloe emodin inhibits the binding of lactate to the K311 site of P4HB. Aloe emodin stabilizes kynurenine metabolism through inhibition of aspartate aminotransferase (GOT2) accumulation on damaged mitochondria. Mechanistically, aloe emodin inhibits phosphorylated glycogen synthase kinase 3B (p-GSK3B) transcription in the nucleus to repress the interaction of prostaglandin G/H synthase 2 (PTGS2) with SH3 domain of SH3 domain-containing GRB2-like protein B1 (SH3GLB1), thereby disrupting the functions of mitochondrial complexes and reducing SH3GLB1-mediated mitoROS accumulation, eventually suppressing calcium-binding and coiled-coil domain-containing protein 2 (NDP52)-induced mitophagy. This study unveils the regulatory role of aloe emodin in RIHD alleviation through PTGS2/SH3GLB1/NDP52 axis, indicates aloe emodin stabilizes GOT2-mediated kynurenine metabolism through P4HB lactylation. Collectively, this study provides novel insights into the regulatory mechanisms underlying the protective role of aloe emodin in cardiac injury, and opens new avenues for therapeutic strategies of aloe emodin in preventing RIHD by regulating lactylation.

Privileged proteins with a second residence: dual targeting and conditional re-routing of mitochondrial proteins

Almost all mitochondrial proteins are encoded by nuclear genes and synthesized in the cytosol as precursor proteins. Signals in the amino acid sequence of these precursors ensure their targeting and translocation into mitochondria. However, in many cases, only a certain fraction of a specific protein is transported into mitochondria, while the rest either remains in the cytosol or undergoes reverse translocation to the cytosol, and can populate other cellular compartments. This phenomenon is called dual localization which can be instigated by different mechanisms. These include alternative start or stop codons, differential transcripts, and ambiguous or competing targeting sequences. In many cases, dual localization might serve as an economic strategy to reduce the number of required genes; for example, when the same groups of enzymes are required both in mitochondria and chloroplasts or both in mitochondria and the nucleus/cytoplasm. Such cases frequently employ ambiguous targeting sequences to distribute proteins between both organelles. However, alternative localizations can also be used for signaling, for example when non-imported precursors serve as mitophagy signals or when they represent transcription factors in the nucleus to induce the mitochondrial unfolded stress response. This review provides an overview regarding the mechanisms and the physiological consequences of dual targeting.

Mitophagy and its regulatory mechanisms in the biological effects of nanomaterials

Mitophagy is a selective cellular process critical for the removal of damaged mitochondria. It is essential in regulating mitochondrial number, ensuring mitochondrial functionality, and maintaining cellular equilibrium, ultimately influencing cell destiny. Numerous pathologies, such as neurodegenerative diseases, cardiovascular disorders, cancers, and various other conditions, are associated with mitochondrial dysfunctions. Thus, a detailed exploration of the regulatory mechanisms of mitophagy is pivotal for enhancing our understanding and for the discovery of novel preventive and therapeutic options for these diseases. Nanomaterials have become integral in biomedicine and various other sectors, offering advanced solutions for medical uses including biological imaging, drug delivery, and disease diagnostics and therapy. Mitophagy is vital in managing the cellular effects elicited by nanomaterials. This review provides a comprehensive analysis of the molecular mechanisms underpinning mitophagy, underscoring its significant influence on the biological responses of cells to nanomaterials. Nanoparticles can initiate mitophagy via various pathways, among which the PINK1-Parkin pathway is critical for cellular defense against nanomaterial-induced damage by promoting mitophagy. The role of mitophagy in biological effects was induced by nanomaterials, which are associated with alterations in Ca2+ levels, the production of reactive oxygen species, endoplasmic reticulum stress, and lysosomal damage.

Mitophagy Facilitates Cytosolic Proteostasis to Preserve Cardiac Function

Background

Protein quality control (PQC) is critical for maintaining sarcomere structure and function in cardiac myocytes, and mutations in PQC pathway proteins, such as CRYAB (arginine to glycine at position 120, R120G) and BAG3 (proline to lysine at position 209, P209L) induce protein aggregate pathology with cardiomyopathy in humans. Novel observations in yeast and mammalian cells demonstrate mitochondrial uptake of cytosolic protein aggregates. We hypothesized that mitochondrial uptake of cytosolic protein aggregates and their removal by mitophagy, a lysosomal degradative pathway essential for myocardial homeostasis, facilitates cytosolic protein quality control in cardiac myocytes.

Methods

Mice with inducible cardiac myocyte specific ablation of TRAF2 (TRAF2icKO), which impairs mitophagy, were assessed for protein aggregates with biochemical fractionation and super-resolution imaging in comparison to floxed controls. Induced pluripotent stem cell (iPSC)-derived cardiac myocytes with R120G knock-in to the CRYAB locus were assessed for localization of the CRYAB protein. Transgenic mice expressing R120G CRYAB protein (R120G-TG) were subjected to both TRAF2 gain-of-function (with AAV9-cardiac Troponin T promoter-driven TRAF2 transduction) and TRAF2 loss-of-function (with tamoxifen-inducible ablation of one Traf2 allele) in cardiac myocytes to determine the effect of mitophagy modulation on cardiac structure, function, and protein aggregate pathology.

Results

Cardiomyocyte-specific ablation of TRAF2 results accumulation of mitochondrial and cytosolic protein aggregates and DESMIN mis-localization to protein aggregates. Isolated mitochondria take up cardiomyopathy-associated aggregate-prone cytosolic chaperone proteins, namely arginine to glycine (R120G) CRYAB mutant and proline to lysine (P209L) BAG3 mutant. R120G-CRYAB mutant protein increasingly localizes to mitochondria in human and mouse cardiomyocytes. R120G-TG mice demonstrate upregulation of TRAF2 in the mitochondrial fraction with increased mitophagy as compared with wild type. Adult-onset inducible haplo-insufficiency of TRAF2 resulted in accelerated mortality, impaired left ventricular systolic function and increased protein aggregates in R120G-TG mice as compared with controls. Conversely, AAV9-mediated TRAF2 transduction in R120G-TG mice reduced mortality and attenuated left ventricular systolic dysfunction, with reduced protein aggregates and restoration of normal localization of DESMIN, a cytosolic scaffolding protein chaperoned by CRYAB, as compared with control AAV9-GFP group.

Conclusions

TRAF2-mediated mitophagy in cardiac myocytes facilitates removal of cytosolic protein aggregates and can be stimulated to ameliorate proteotoxic cardiomyopathy.

A dynamical systems model for the total fission rate in Drp1-dependent mitochondrial fission

Mitochondrial hyperfission in response to cellular insult is associated with reduced energy production and programmed cell death. Thus, there is a critical need to understand the molecular mechanisms coordinating and regulating the complex process of mitochondrial fission. We develop a nonlinear dynamical systems model of dynamin related protein one (Drp1)-dependent mitochondrial fission and use it to identify parameters which can regulate the total fission rate (TFR) as a function of time. The TFR defined from a nondimensionalization of the model undergoes a Hopf bifurcation with bifurcation parameter [Formula: see text] where [Formula: see text] is the total concentration of mitochondrial fission factor (Mff) and k+ and k- are the association and dissociation rate constants between oligomers on the outer mitochondrial membrane. The variable μ can be thought of as the maximum build rate over the disassembling rate of oligomers. Though the nondimensionalization of the system results in four dimensionless parameters, we found the TFR and the cumulative total fission (TF) depend strongly on only one, μ. Interestingly, the cumulative TF does not monotonically increase as μ increases. Instead it increases with μ to a certain point and then begins to decrease as μ continues to increase. This non-monotone dependence on μ suggests interventions targeting k+, k-, or [Formula: see text] may have a non-intuitive impact on the fission mechanism. Thus understanding the impact of regulatory parameters, such as μ, may assist future therapeutic target selection.

Mitochondrial dynamics in pulmonary disease: Implications for the potential therapeutics

Mitochondria are dynamic organelles that continuously undergo fusion/fission to maintain normal cell physiological activities and energy metabolism. When mitochondrial dynamics is unbalanced, mitochondrial homeostasis is broken, thus damaging mitochondrial function. Accumulating evidence demonstrates that impairment in mitochondrial dynamics leads to lung tissue injury and pulmonary disease progression in a variety of disease models, including inflammatory responses, apoptosis, and barrier breakdown, and that the role of mitochondrial dynamics varies among pulmonary diseases. These findings suggest that modulation of mitochondrial dynamics may be considered as a valid therapeutic strategy in pulmonary diseases. In this review, we discuss the current evidence on the role of mitochondrial dynamics in pulmonary diseases, with a particular focus on its underlying mechanisms in the development of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), chronic obstructive pulmonary disease (COPD), asthma, pulmonary fibrosis (PF), pulmonary arterial hypertension (PAH), lung cancer and bronchopulmonary dysplasia (BPD), and outline effective drugs targeting mitochondrial dynamics-related proteins, highlighting the great potential of targeting mitochondrial dynamics in the treatment of pulmonary disease.

The multifaceted role of mitochondria in cardiac function: insights and approaches

Cardiovascular disease (CVD) remains a global economic burden even in the 21st century with 85% of deaths resulting from heart attacks. Despite efforts in reducing the risk factors, and enhancing pharmacotherapeutic strategies, challenges persist in early identification of disease progression and functional recovery of damaged hearts. Targeting mitochondrial dysfunction, a key player in the pathogenesis of CVD has been less successful due to its role in other coexisting diseases. Additionally, it is the only organelle with an agathokakological function that is a remedy and a poison for the cell. In this review, we describe the origins of cardiac mitochondria and the role of heteroplasmy and mitochondrial subpopulations namely the interfibrillar, subsarcolemmal, perinuclear, and intranuclear mitochondria in maintaining cardiac function and in disease-associated remodeling. The cumulative evidence of mitochondrial retrograde communication with the nucleus is addressed, highlighting the need to study the genotype-phenotype relationships of specific organelle functions with CVD by using approaches like genome-wide association study (GWAS). Finally, we discuss the practicality of computational methods combined with single-cell sequencing technologies to address the challenges of genetic screening in the identification of heteroplasmy and contributory genes towards CVD.

Bioenergetic-active exosomes for cartilage regeneration and homeostasis maintenance

Cartilage regeneration relies on adequate and continuous bioenergy supply to facilitate cellular differentiation and extracellular matrix synthesis. Chondrocytes frequently undergo energy stress under pathological conditions, characterized by disrupted cellular metabolism and reduced adenosine triphosphate (ATP) levels. However, there has limited progress in modulating energy metabolism for cartilage regeneration thus far. Here, we developed bioenergetic-active exosomes (Suc-EXO) to promote cartilage regeneration and homeostasis maintenance. Suc-EXO exhibited a 5.42-fold increase in ATP content, enabling the manipulation of cellular energy metabolism by fueling the TCA cycle. With continuous energy supply, Suc-EXO promoted BMSC chondrogenic differentiation via the P2X7-mediated PI3K-AKT pathway. Moreover, Suc-EXO improved chondrocyte anabolism and mitochondrial homeostasis via the P2X7-mediated SIRT3 pathway. In a rabbit cartilage defect model, the Suc-EXO-encapsulated hydrogel notably promoted cartilage regeneration and maintained neocartilage homeostasis, leading to 2.26 and 1.53 times increase in Col2 and ACAN abundance, respectively. These findings make a remarkable breakthrough in modulating energy metabolism for cartilage regeneration, offering immense potential for clinical translation.

Mitochondrial non-energetic function and embryonic cardiac development

The initial contraction of the heart during the embryonic stage necessitates a substantial energy supply, predominantly derived from mitochondrial function. However, during embryonic heart development, mitochondria influence beyond energy supplementation. Increasing evidence suggests that mitochondrial permeability transition pore opening and closing, mitochondrial fusion and fission, mitophagy, reactive oxygen species production, apoptosis regulation, Ca2+ homeostasis, and cellular redox state also play critical roles in early cardiac development. Therefore, this review aims to describe the essential roles of mitochondrial non-energetic function embryonic cardiac development.

SIRT1 Ameliorates Lamin A/C Deficiency-Induced Cardiac Dysfunction by Promoting Mitochondrial Bioenergetics

Dilated cardiomyopathy (DCM) is associated with high mortality despite advanced therapies. The LMNA gene encodes lamin A/C and is the second most frequently mutated gene associated with DCM, for which therapeutic options are limited. Here we generated Lmna -/- mice and found they exhibited cardiac dysfunction at the age of 1 month but not at 2 weeks. Proteomics showed down-regulation of mitochondrial function-related pathways in Lmna -/- hearts. Moreover, early injured mitochondria with decreased cristae density and sirtuin 1 (SIRT1) down-regulation were observed in 2-week-old Lmna -/- hearts. Adenoviral overexpression of SIRT1 in lamin A/C knockdown neonatal rat ventricular myocytes improved mitochondrial oxidative respiration capacity. Adeno-associated virus-mediated SIRT1 overexpression alleviated mitochondrial injury, cardiac systolic dysfunction, ventricular dilation, and fibrosis, and prolonged lifespan in Lmna -/- mice. Mechanistically, LMNA maintains mitochondrial bioenergetics through the SIRT1-PARKIN axis. Our results suggest that targeting the SIRT1 signaling pathway is expected to be a novel therapeutic strategy for LMNA mutation-associated DCM.

Iron chelators as mitophagy agents: Potential and limitations

Mitochondrial autophagy (mitophagy) is very important process for the maintenance of cellular homeostasis, functionality and survival. Its dysregulation is associated with high risk and progression numerous serious diseases (e.g., oncological, neurodegenerative and cardiovascular ones). Therefore, targeting mitophagy mechanisms is very hot topic in the biological and medicinal research. The interrelationships between the regulation of mitophagy and iron homeostasis are now becoming apparent. In short, mitochondria are central point for the regulation of iron homeostasis, but change in intracellular cheatable iron level can induce/repress mitophagy. In this review, relationships between iron homeostasis and mitophagy are thoroughly discussed and described. Also, therapeutic applicability of mitophagy chelators in the context of individual diseases is comprehensively and critically evaluated.

ER Stress and Mitochondrial Perturbations Regulate Cell Death in Retinal Detachment: Exploring the Role of HIF1α

Purpose

Retinal detachment (RD) leads to photoreceptor (PR) hypoxia due to separation from the retinal pigment epithelium (RPE). Hypoxia stabilizes retinal hypoxia-inducible factor 1-alpha (HIF1α), crucial for PR survival during RD. This study explores the regulatory role of HIF1α in PR cell survival pathways during RD.

Methods

Experimental RD was created in C57BL/6J and HIF1αΔrod mice by injecting 1% hyaluronic acid into the subretinal space. The 661W photoreceptor cells were exposed to hypoxic conditions. Markers of endoplasmic reticulum stress (ERS), mitophagy, and accumulation of polyubiquinated proteins were evaluated using RT-PCR and western blot analyses. Cell death of PR cells was quantified using trypan blue exclusion assay and TUNEL staining. Retinal cell death was assessed using a DNA fragmentation assay.

Results

In C57BL/6J mice and 661W cells, there were increases in HIF1α protein levels: 2.2-fold after RD (P = 0.04) and threefold after hypoxia (P = 0.057). Both the in vivo and in vitro RD models showed increased protein expression of ERS markers (including BIP, CHOP, and IRE1α), mitophagy markers (Parkin, PINK, and FUNDC1), and polyubiquitinated proteins. In 661W cells, hypoxia resulted in a loss of mitochondrial membrane potential, an increase in mitochondrial reactive oxygen species, and a decrease in intracellular adenosine triphosphate levels. Lack of HIF1α in rods blocked the upregulation of mitophagy markers after RD.

Conclusions

RD results in the activation of ERS, mitophagy, mitochondrial dysfunction, and accumulation of polyubiquitinated proteins. Results suggest a role for HIF1α in activation of the mitophagy pathway after RD, which may serve to protect the PR cells.

The interplay between mitochondrial dynamics and autophagy: From a key homeostatic mechanism to a driver of pathology

The complex relationship between mitochondrial dynamics and autophagy illustrates how two cellular housekeeping processes are intimately linked, illuminating fundamental principles of cellular homeostasis and shedding light on disparate pathological conditions including several neurodegenerative disorders. Here we review the basic tenets of mitochondrial dynamics i.e., the concerted balance between fusion and fission of the organelle, and its interplay with macroautophagy and selective mitochondrial autophagy, also dubbed mitophagy, in the maintenance of mitochondrial quality control and ultimately in cell viability. We illustrate how conditions of altered mitochondrial dynamics reverberate on autophagy and vice versa. Finally, we illustrate how altered interplay between these two key cellular processes participates in the pathogenesis of human disorders affecting multiple organs and systems.

Parkin plays a crucial role in acute viral myocarditis by regulating mitophagy activity

Rationale: Parkin (an E3 ubiquitin protein ligase) is an important regulator of mitophagy. However, the role of Parkin in viral myocarditis (VMC) remains unclear. Methods: Coxsackievirus B3 (CVB3) infection was induced in mice to create VMC. Cardiac function and inflammatory response were evaluated by echocardiography, histological assessment, and molecular analyses. AAV9 (adeno-associated virus 9), transmission electron microscopy (TEM) and western blotting were used to investigate the mechanisms by which Parkin regulates mitophagy and cardiac inflammation. Results: Our data indicated that Parkin- and BNIP3 (BCL2 interacting protein 3 like)-mediated mitophagy was activated in VMC mice and neonatal rat cardiac myocytes (NRCMs) infected with CVB3, which blocked autophagic flux by inhibiting autophagosome-lysosome fusion. Parkin silencing aggravated mortality and accelerated the development of cardiac dysfunction in CVB3-treated mice. While silencing of Parkin did not significantly increase inflammatory response through activating NF-κB pathway and production of inflammatory cytokines post-VMC, the mitophagy activity were reduced, which stimulated the accumulation of damaged mitochondria. Moreover, Parkin silencing exacerbated VMC-induced apoptosis. We consistently found that Parkin knockdown disrupted mitophagy activity and inflammatory response in NRCMs. Conclusion: This study elucidated the important role of Parkin in maintaining cardiac function and inflammatory response by regulating mitophagy activity and the NF-κB pathway during acute VMC. Although the functional impact of mitophagy remains unclear, our findings suggest that Parkin silencing may accelerate VMC development.

Mitochondria in Retinal Ganglion Cells: Unraveling the Metabolic Nexus and Oxidative Stress

This review explored the role of mitochondria in retinal ganglion cells (RGCs), which are essential for visual processing. Mitochondrial dysfunction is a key factor in the pathogenesis of various vision-related disorders, including glaucoma, hereditary optic neuropathy, and age-related macular degeneration. This review highlighted the critical role of mitochondria in RGCs, which provide metabolic support, regulate cellular health, and respond to cellular stress while also producing reactive oxygen species (ROS) that can damage cellular components. Maintaining mitochondrial function is essential for meeting RGCs' high metabolic demands and ensuring redox homeostasis, which is crucial for their proper function and visual health. Oxidative stress, exacerbated by factors like elevated intraocular pressure and environmental factors, contributes to diseases such as glaucoma and age-related vision loss by triggering cellular damage pathways. Strategies targeting mitochondrial function or bolstering antioxidant defenses include mitochondrial-based therapies, gene therapies, and mitochondrial transplantation. These advances can offer potential strategies for addressing mitochondrial dysfunction in the retina, with implications that extend beyond ocular diseases.

Opa1 processing is dispensable in mouse development but is protective in mitochondrial cardiomyopathy

Mitochondrial fusion and fission accompany adaptive responses to stress and altered metabolic demands. Inner membrane fusion and cristae morphogenesis depends on optic atrophy 1 (Opa1), which is expressed in different isoforms and is cleaved from a membrane-bound, long to a soluble, short form. Here, we have analyzed the physiological role of Opa1 isoforms and Opa1 processing by generating mouse lines expressing only one cleavable Opa1 isoform or a non-cleavable variant thereof. Our results show that expression of a single cleavable or non-cleavable Opa1 isoform preserves embryonic development and the health of adult mice. Opa1 processing is dispensable under metabolic and thermal stress but prolongs life span and protects against mitochondrial cardiomyopathy in OXPHOS-deficient Cox10-/- mice. Mechanistically, loss of Opa1 processing disturbs the balance between mitochondrial biogenesis and mitophagy, suppressing cardiac hypertrophic growth in Cox10-/- hearts. Our results highlight the critical regulatory role of Opa1 processing, mitochondrial dynamics, and metabolism for cardiac hypertrophy.

Mitophagy modulation for the treatment of cardiovascular diseases

BACKGROUND

Defects of mitophagy, the selective form of autophagy for mitochondria, are commonly observed in several cardiovascular diseases and represent the main cause of mitochondrial dysfunction. For this reason, mitophagy has emerged as a novel and potential therapeutic target.

METHODS

In this review, we discuss current evidence about the biological significance of mitophagy in relevant preclinical models of cardiac and vascular diseases, such as heart failure, ischemia/reperfusion injury, metabolic cardiomyopathy and atherosclerosis.

RESULTS

Multiple studies have shown that cardiac and vascular mitophagy is an adaptive mechanism in response to stress, contributing to cardiovascular homeostasis. Mitophagy defects lead to cell death, ultimately impairing cardiac and vascular function, whereas restoration of mitophagy by specific compounds delays disease progression.

CONCLUSIONS

Despite previous efforts, the molecular mechanisms underlying mitophagy activation in response to stress are not fully characterized. A comprehensive understanding of different forms of mitophagy active in the cardiovascular system is extremely important for the development of new drugs targeting this process. Human studies evaluating mitophagy abnormalities in patients at high cardiovascular risk also represent a future challenge.

INF2-mediated actin polymerization at ER-organelle contacts regulates organelle size and movement

Proper regulation of organelle dynamics is critical for cellular function, but the mechanisms coordinating multiple organelles remain poorly understood. Here we show that actin polymerization mediated by the endoplasmic reticulum (ER)-anchored formin INF2 acts as a master regulator of organelle morphology and movement. Using high-resolution imaging, we demonstrate that INF2-polymerized actin filaments assemble at ER contact sites on mitochondria, endosomes, and lysosomes just prior to their fission. Genetic manipulation of INF2 activity alters the size, shape and motility of all three organelles. Our findings reveal a conserved mechanism by which the ER uses actin polymerization to control diverse organelles, with implications for understanding organelle dysfunction in neurodegenerative and other diseases. This work establishes INF2-mediated actin assembly as a central coordinator of organelle dynamics and inter-organelle communication.

TBK1 is ubiquitinated by TRIM5α to assemble mitophagy machinery

Ubiquitination of mitochondrial proteins provides a basis for the downstream recruitment of mitophagy machinery, yet whether ubiquitination of the machinery itself contributes to mitophagy is unknown. Here, we show that K63-linked polyubiquitination of the key mitophagy regulator TBK1 is essential for its mitophagy functions. This modification is catalyzed by the ubiquitin ligase TRIM5α and is required for TBK1 to interact with and activate a set of ubiquitin-binding autophagy adaptors including NDP52, p62/SQSTM1, and NBR1. Autophagy adaptors, along with TRIM27, enable TRIM5α to engage with TBK1 following mitochondrial damage. TRIM5α's ubiquitin ligase activity is required for the accumulation of active TBK1 on damaged mitochondria in Parkin-dependent and Parkin-independent mitophagy pathways. Our data support a model in which TRIM5α provides a mitochondria-localized, ubiquitin-based, self-amplifying assembly platform for TBK1 and mitophagy adaptors that is ultimately necessary for the recruitment of the core autophagy machinery.

The role of mitochondrial dynamics in oocyte and early embryo development

Mitochondrial dysfunction is widely implicated in various human diseases, through mechanisms that go beyond mitochondria's well-established role in energy generation. These dynamic organelles exert vital control over numerous cellular processes, including calcium regulation, phospholipid synthesis, innate immunity, and apoptosis. While mitochondria's importance is acknowledged in all cell types, research has revealed the exceptionally dynamic nature of the mitochondrial network in oocytes and embryos, finely tuned to meet unique needs during gamete and pre-implantation embryo development. Within oocytes, both the quantity and morphology of mitochondria can significantly change during maturation and post-fertilization. These changes are orchestrated by fusion and fission processes (collectively known as mitochondrial dynamics), crucial for energy production, content exchange, and quality control as mitochondria adjust to the shifting energy demands of oocytes and embryos. The roles of proteins that regulate mitochondrial dynamics in reproductive processes have been primarily elucidated through targeted deletion studies in animal models. Notably, impaired mitochondrial dynamics have been linked to female reproductive health, affecting oocyte quality, fertilization, and embryo development. Dysfunctional mitochondria can lead to fertility problems and can have an impact on the success of pregnancy, particularly in older reproductive age women.

Acupotomy alleviates knee osteoarthritis in rabbit by regulating chondrocyte mitophagy Pink1-Parkin pathway

OBJECTIVE

To investigate the effect of acupotomy, on mitophagy and the Pink1-Parkin pathway in chondrocytes from rabbits with knee osteoarthritis (KOA).

METHODS

A KOA model was established via the modified Videman method. Rabbits were randomly divided into a control group (CON), KOA group and KOA + acupotomy group (Acu). Rabbits in the acupotomy group were subjected to acupotomy for 4 weeks after model establishment. The behavior of the rabbits before and after intervention was recorded. Cartilage degeneration was evaluated by optical microscopy and fluorescence microscopy. The level of mitophagy was evaluated by transmission electron microscopy, immunofluorescence and enzyme-linked immunosorbent assay (ELISA). The expression of phosphatase and tensin homolog (PTEN)-induced kinase 1 (Pink1)-Parkin mitophagy pathway components was evaluated by immunofluorescence, Western blotting and real-time polymerase chain reaction.

RESULTS

In rabbits with KOA, joint pain, mobility disorders and cartilage degeneration were observed, the Mankin score was increased, collagen type Ⅱ (Col-Ⅱ) expression was significantly decreased, mitophagy was inhibited, mitochondrial function was impaired, and factors associated with the Pink1-Parkin pathway were inhibited. Acupotomy regulated the expression of Pink1-Parkin pathway-related proteins, the mitophagy-related protein microtubule-associated protein-1 light chain-3, the translocase of the outer membrane, and the inner mitochondrial membrane 23; increased the colocalization of mitochondria and autophagosomes; promoted the removal of damaged mitochondria; restored mitochondrial adenosine-triphosphate (ATP) production; and alleviated cartilage degeneration in rabbits with KOA.

CONCLUSIONS

Acupotomy played a role in alleviating KOA in rabbits by activating mitophagy in chondrocytes via the regulation of proteins that are related to the Pink1-Parkin pathway.

Alterations of PINK1-PRKN signaling in mice during normal aging

The ubiquitin kinase-ligase pair PINK1-PRKN identifies and selectively marks damaged mitochondria for elimination via the autophagy-lysosome system (mitophagy). While this cytoprotective pathway has been extensively studied in vitro upon acute and complete depolarization of mitochondria, the significance of PINK1-PRKN mitophagy in vivo is less well established. Here we used a novel approach to study PINK1-PRKN signaling in different energetically demanding tissues of mice during normal aging. We demonstrate a generally increased expression of both genes and enhanced enzymatic activity with aging across tissue types. Collectively our data suggest a distinct regulation of PINK1-PRKN signaling under basal conditions with the most pronounced activation and flux of the pathway in mouse heart compared to brain or skeletal muscle. Our biochemical analyses complement existing mitophagy reporter readouts and provide an important baseline assessment in vivo, setting the stage for further investigations of the PINK1-PRKN pathway during stress and in relevant disease conditions.

Mechanistic insights into fasting-induced autophagy in the aging heart

Autophagy is a prosurvival mechanism for the clearance of accumulated abnormal proteins, damaged organelles, and excessive lipids within mammalian cells. A growing body of data indicates that autophagy is reduced in aging cells. This reduction leads to various diseases, such as myocardial hypertrophy, infarction, and atherosclerosis. Recent studies in animal models of an aging heart showed that fasting-induced autophagy improved cardiac function and longevity. This improvement is related to autophagic clearance of damaged cellular components via either bulk or selective autophagy (such as mitophagy). In this editorial, we summarize the mechanisms of autophagy in normal and aging hearts. In addition, the protective effect of fasting-induced autophagy in cardiac aging has been highlighted.

Coordinated metabolic responses to cyclophilin D deletion in the developing heart

In the embryonic heart, the activation of the mitochondrial electron transport chain (ETC) coincides with the closure of the cyclophilin D (CypD) regulated mitochondrial permeability transition pore (mPTP). However, it remains to be established whether the absence of CypD has a regulatory effect on mitochondria during cardiac development. Using a variety of assays to analyze cardiac tissue from wildtype and CypD knockout mice from embryonic day (E)9.5 to adult, we found that mitochondrial structure, function, and metabolism show distinct transitions. Deletion of CypD altered the timing of these transitions as the mPTP was closed at all ages, leading to coupled ETC activity in the early embryo, decreased citrate synthase activity, and an altered metabolome particularly after birth. Our results suggest that manipulating CypD activity may control myocyte proliferation and differentiation and could be a tool to increase ATP production and cardiac function in immature hearts.

Mitochondrial dynamics and mitochondrial autophagy: Molecular structure, orchestrating mechanism and related disorders

Mitochondrial dynamics and autophagy play essential roles in normal cellular physiological activities, while abnormal mitochondrial dynamics and mitochondrial autophagy can cause cancer and related disorders. Abnormal mitochondrial dynamics usually occur in parallel with mitochondrial autophagy. Both have been reported to have a synergistic effect and can therefore complement or inhibit each other. Progress has been made in understanding the classical mitochondrial PINK1/Parkin pathway and mitochondrial dynamical abnormalities. Still, the mechanisms and regulatory pathways underlying the interaction between mitophagy and mitochondrial dynamics remain unexplored. Like other existing reviews, we review the molecular structure of proteins involved in mitochondrial dynamics and mitochondrial autophagy, and how their abnormalities can lead to the development of related diseases. We will also review the individual or synergistic effects of abnormal mitochondrial dynamics and mitophagy leading to cellular proliferation, differentiation and invasion. In addition, we explore the mechanisms underlying mitochondrial dynamics and mitochondrial autophagy to contribute to targeted and precise regulation of mitochondrial function. Through the study of abnormal mitochondrial dynamics and mitochondrial autophagy regulation mechanisms, as well as the role of early disease development, effective targets for mitochondrial function regulation can be proposed to enable accurate diagnosis and treatment of the associated disorders.

The role of metabolism in cardiac development

Metabolism is the fundamental process that sustains life. The heart, in particular, is an organ of high energy demand, and its energy substrates have been studied for more than a century. In recent years, there has been a growing interest in understanding the role of metabolism in the early differentiation of pluripotent stem cells and in cancer research. Studies have revealed that metabolic intermediates from glycolysis and the tricarboxylic acid cycle act as co-factors for intracellular signal transduction, playing crucial roles in regulating cell behaviors. Mitochondria, as the central hub of metabolism, are also under intensive investigation regarding the regulation of their dynamics. The metabolic environment of the fetus is intricately linked to the maternal metabolic status, and the impact of the mother's nutrition and metabolic health on fetal development is significant. For instance, it is well known that maternal diabetes increases the risk of cardiac and nervous system malformations in the fetus. Another notable example is the decrease in the risk of neural tube defects when pregnant women are supplemented with folic acid. These examples highlight the profound influence of the maternal metabolic environment on the fetal organ development program. Therefore, gaining insights into the metabolic environment within developing fetal organs is critical for deepening our understanding of normal organ development. This review aims to summarize recent findings that build upon the historical recognition of the environmental and metabolic factors involved in the developing embryo.

Cardiac maturation

The heart undergoes a dynamic maturation process following birth, in response to a wide range of stimuli, including both physiological and pathological cues. This process entails substantial re-programming of mitochondrial energy metabolism coincident with the emergence of specialized structural and contractile machinery to meet the demands of the adult heart. Many components of this program revert to a more "fetal" format during development of pathological cardiac hypertrophy and heart failure. In this review, emphasis is placed on recent progress in our understanding of the transcriptional control of cardiac maturation, encompassing the results of studies spanning from in vivo models to cardiomyocytes derived from human stem cells. The potential applications of this current state of knowledge to new translational avenues aimed at the treatment of heart failure is also addressed.

Control of NAD+ homeostasis by autophagic flux modulates mitochondrial and cardiac function

Impaired autophagy is known to cause mitochondrial dysfunction and heart failure, in part due to altered mitophagy and protein quality control. However, whether additional mechanisms are involved in the development of mitochondrial dysfunction and heart failure in the setting of deficient autophagic flux remains poorly explored. Here, we show that impaired autophagic flux reduces nicotinamide adenine dinucleotide (NAD+) availability in cardiomyocytes. NAD+ deficiency upon autophagic impairment is attributable to the induction of nicotinamide N-methyltransferase (NNMT), which methylates the NAD+ precursor nicotinamide (NAM) to generate N-methyl-nicotinamide (MeNAM). The administration of nicotinamide mononucleotide (NMN) or inhibition of NNMT activity in autophagy-deficient hearts and cardiomyocytes restores NAD+ levels and ameliorates cardiac and mitochondrial dysfunction. Mechanistically, autophagic inhibition causes the accumulation of SQSTM1, which activates NF-κB signaling and promotes NNMT transcription. In summary, we describe a novel mechanism illustrating how autophagic flux maintains mitochondrial and cardiac function by mediating SQSTM1-NF-κB-NNMT signaling and controlling the cellular levels of NAD+.

NDP52 SUMOylation contributes to low-dose X-rays-induced cardiac hypertrophy through PINK1/Parkin-mediated mitophagy via MUL1/SUMO2 signalling

Radiation-induced heart damage caused by low-dose X-rays has a significant impact on tumour patients' prognosis, with cardiac hypertrophy being the most severe noncarcinogenic adverse effect. Our previous study demonstrated that mitophagy activation promoted cardiac hypertrophy, but the underlying mechanisms remained unclear. In the present study, PARL-IN-1 enhanced excessive hypertrophy of cardiomyocytes and exacerbated mitochondrial damage. Isobaric tags for relative and absolute quantification-based quantitative proteomics identified NDP52 as a crucial target mediating cardiac hypertrophy induced by low-dose X-rays. SUMOylation proteomics revealed that the SUMO E3 ligase MUL1 facilitated NDP52 SUMOylation through SUMO2. Co-IP coupled with LC-MS/MS identified a critical lysine residue at position 262 of NDP52 as the key site for SUMO2-mediated SUMOylation of NDP52. The point mutation plasmid NDP52K262R inhibited mitophagy under MUL1 overexpression, as evidenced by inhibition of LC3 interaction with NDP52, PINK1 and LAMP2A. A mitochondrial dissociation study revealed that NDP52K262R inhibited PINK1 targeting to endosomes early endosomal marker (EEA1), late/lysosome endosomal marker (LAMP2A) and recycling endosomal marker (RAB11), and laser confocal microscopy confirmed that NDP52K262R impaired the recruitment of mitochondria to the autophagic pathway through EEA1/RAB11 and ATG3, ATG5, ATG16L1 and STX17, but did not affect mitochondrial delivery to lysosomes via LAMP2A for degradation. In conclusion, our findings suggest that MUL1-mediated SUMOylation of NDP52 plays a crucial role in regulating mitophagy in the context of low-dose X-ray-induced cardiac hypertrophy. Two hundred sixty-second lysine of NDP52 is identified as a key SUMOylation site for low-dose X-ray promoting mitophagy activation and cardiac hypertrophy. Collectively, this study provides novel implications for the development of therapeutic strategies aimed at preventing the progression of cardiac hypertrophy induced by low-dose X-rays.

Evaluation of Oxygen Consumption Rates In Situ

An analysis of the mitochondrial respiration function represented by the oxygen consumption rate is necessary to assess mitochondrial bioenergetics and redox function. This protocol describes two alternative techniques to evaluate mitochondrial respiration function in situ: (1) measure oxygen consumption rates via an electrode; (2) measure oxygen consumption rates via a seahorse instrument. These in situ approaches provide more physiological access to mitochondria to evaluate mitochondrial respiration function in a relatively integrated cellular system.

Mitochondrial Dynamics in Pulmonary Hypertension

Mitochondria are essential organelles for energy production, calcium homeostasis, redox signaling, and other cellular responses involved in pulmonary vascular biology and disease processes. Mitochondrial homeostasis depends on a balance in mitochondrial fusion and fission (dynamics). Mitochondrial dynamics are regulated by a viable circadian clock. Hypoxia and nicotine exposure can cause dysfunctions in mitochondrial dynamics, increases in mitochondrial reactive oxygen species generation and calcium concentration, and decreases in ATP production. These mitochondrial changes contribute significantly to pulmonary vascular oxidative stress, inflammatory responses, contractile dysfunction, pathologic remodeling, and eventually pulmonary hypertension. In this review article, therefore, we primarily summarize recent advances in basic, translational, and clinical studies of circadian roles in mitochondrial metabolism in the pulmonary vasculature. This knowledge may not only be crucial to fully understanding the development of pulmonary hypertension, but also greatly help to create new therapeutic strategies for treating this devastating disease and other related pulmonary disorders.

GRAF1 integrates PINK1-Parkin signaling and actin dynamics to mediate cardiac mitochondrial homeostasis

The serine/threonine kinase, PINK1, and the E3 ubiquitin ligase, Parkin, are known to facilitate LC3-dependent autophagosomal encasement and lysosomal clearance of dysfunctional mitochondria, and defects in this process contribute to a variety of cardiometabolic and neurological diseases. Although recent evidence indicates that dynamic actin remodeling plays an important role in PINK1/Parkin-mediated mitochondrial autophagy (mitophagy), the underlying signaling mechanisms remain unknown. Here, we identify the RhoGAP GRAF1 (Arhgap26) as a PINK1 substrate that regulates mitophagy. GRAF1 promotes the release of damaged mitochondria from F-actin anchors, regulates mitochondrial-associated Arp2/3-mediated actin remodeling and facilitates Parkin-LC3 interactions to enhance mitochondria capture by autophagosomes. Graf1 phosphorylation on PINK1-dependent sites is dysregulated in human heart failure, and cardiomyocyte-restricted Graf1 depletion in mice blunts mitochondrial clearance and attenuates compensatory metabolic adaptations to stress. Overall, we identify GRAF1 as an enzyme that coordinates cytoskeletal and metabolic remodeling to promote cardioprotection.

The role of mitochondrial dynamics in disease

Mitochondria are multifaceted and dynamic organelles regulating various important cellular processes from signal transduction to determining cell fate. As dynamic properties of mitochondria, fusion and fission accompanied with mitophagy, undergo constant changes in number and morphology to sustain mitochondrial homeostasis in response to cell context changes. Thus, the dysregulation of mitochondrial dynamics and mitophagy is unsurprisingly related with various diseases, but the unclear underlying mechanism hinders their clinical application. In this review, we summarize the recent developments in the molecular mechanism of mitochondrial dynamics and mitophagy, particularly the different roles of key components in mitochondrial dynamics in different context. We also summarize the roles of mitochondrial dynamics and target treatment in diseases related to the cardiovascular system, nervous system, respiratory system, and tumor cell metabolism demanding high-energy. In these diseases, it is common that excessive mitochondrial fission is dominant and accompanied by impaired fusion and mitophagy. But there have been many conflicting findings about them recently, which are specifically highlighted in this view. We look forward that these findings will help broaden our understanding of the roles of the mitochondrial dynamics in diseases and will be beneficial to the discovery of novel selective therapeutic targets.