The permeability transition pore controls cardiac mitochondrial maturation and myocyte differentiation

Au@Pt Nanoparticles Enhance Maturation and Contraction of Mouse Embryonic Stem Cells-Derived and Neonatal Mouse Cardiomyocytes

BACKGROUND

Cardiomyocytes derived from pluripotent stem cells (PSCs) hold great promise in heart damage repair in vivo and drug screening in vitro. However, PSC-derived cardiomyocytes exhibit immature structural and functional properties, which hinder their widespread application. To address this challenge, we designed bimetallic gold-platinum nanoparticles (Au@Pt NPs) endowed with intrinsic oxidase-like, peroxidase-like, and catalase-like activities and high electrical conductivity for promoting cardiomyocyte maturation.

METHODS

Mouse embryonic stem cell (ESC)-derived and neonatal mouse cardiomyocytes were used to evaluate the effects of Au@Pt NPs on cardiomyocyte maturation. The expression and alignment of cardiomyocyte myofibril proteins were analyzed by qRT-PCR, western blot, and immunofluorescence staining. Cellular functionality was analyzed by the multi-electrode array.

RESULTS

By adding Au@Pt NPs at different stages of cardiac differentiation of mouse ESCs, we found that treatment with Au@Pt NPs at the late stage could promote the maturation of differentiated cardiomyocytes, evidenced by increased expression of mature myofibril protein isoforms, more aligned myofibrils, and enhanced sarcomere length. Additionally, Au@Pt NPs can enhance the expression of mature sarcomere components, increase sarcomere length, and significantly boost beating amplitude and conduction velocity in neonatal mouse cardiomyocytes. Furthermore, Au@Pt NPs promoted cell cycle arrest, increased intracellular reactive oxygen species levels, and promoted contractility by inducing the ERK1/2 signaling pathway.

CONCLUSION

Our results indicate that the bimetallic Au@Pt NPs with intrinsic oxidase-like, peroxidase-like, and catalase-like activities and high electrical conductivity could promote the maturation of ESCs-derived and neonatal mouse cardiomyocytes, providing a promising approach for cardiomyocyte maturation and cell therapy for cardiovascular disease.

Effect of introducing somatic mitochondria into an early embryo on zygotic gene activation†

Unlike differentiated somatic cells, which possess elongated mitochondria, undifferentiated cells, such as those of preimplantation embryos, possess round, immature mitochondria. Mitochondrial morphology changes dynamically during cell differentiation in a process called mitochondrial maturation. The significance of the alignment between cell differentiation and mitochondrial maturity in preimplantation development remains unclear. In this study, we analyzed mouse embryos into which liver-derived somatic mitochondria were introduced (SM-embryos). Most SM-embryos were arrested at the two-cell stage. Some of the introduced somatic mitochondria became round, while others remained elongated and large. RNA-sequencing revealed a disruption of both minor and major zygotic gene activation (ZGA) in SM-embryos. Minor ZGA did not terminate before major ZGA, and the onset of major ZGA was inhibited, as shown by histone modification analyses of histone H3 lysine 4 trimethylation and histone H3 lysine 27 acetylation. Further analysis of metabolites involved in histone modification regulation in SM-embryos showed a significantly lower NAD+/NADH ratio in SM-embryos than in control embryos. Additionally, the mitochondrial membrane potential, an indicator of mitochondrial function, was lower in SM-embryos than in control embryos. Our results demonstrated that introducing somatic mitochondria into an embryo induces mitochondrial dysfunction, thereby disrupting metabolite production, leading to a disruption in ZGA and inducing developmental arrest. Our findings reveal that the alignment between cell differentiation and mitochondrial maturity is essential for early embryonic development.

Mitochondrial damage-associated molecular patterns: New perspectives for mitochondria and inflammatory bowel diseases

Mitochondria are key regulators of inflammatory responses and mitochondrial dysfunction is closely linked to various inflammatory diseases. Increasing genetic and experimental evidence suggests that mitochondria play a critical role in inflammatory bowel disease (IBD). In the complex environment of the intestinal tract, intestinal epithelial cells (IECs) and their mitochondria possess unique phenotypic features, shaping each other and regulating intestinal homeostasis and inflammation through diverse mechanisms. Here, we focus on intestinal inflammation in IBD induced by mitochondrial damage-associated molecular patterns (mtDAMPs), which comprise mitochondrial components and metabolic products. The pathogenic mechanisms of mtDAMP signaling pathways mediated by two major mtDAMPs, mitochondrial DNA (mtDNA) and mitochondrial reactive oxygen species (mtROS), are discussed.

Cryo-EM structure of the brine shrimp mitochondrial ATP synthase suggests an inactivation mechanism for the ATP synthase leak channel

Mammalian mitochondria undergo Ca2+-induced and cyclosporinA (CsA)-regulated permeability transition (mPT) by activating the mitochondrial permeability transition pore (mPTP) situated in mitochondrial inner membranes. Ca2+-induced prolonged openings of mPTP under certain pathological conditions result in mitochondrial swelling and rupture of the outer membrane, leading to mitochondrial dysfunction and cell death. While the exact molecular composition and structure of mPTP remain unknown, mammalian ATP synthase was reported to form voltage and Ca2+-activated leak channels involved in mPT. Unlike in mammals, mitochondria of the crustacean Artemia franciscana have the ability to accumulate large amounts of Ca2+ without undergoing the mPT. Here, we performed structural and functional analysis of A. franciscana ATP synthase to study the molecular mechanism of mPTP inhibition in this organism. We found that the channel formed by the A. franciscana ATP synthase dwells predominantly in its inactive state and is insensitive to Ca2+, in contrast to porcine heart ATP synthase. Single-particle cryo-electron microscopy (cryo-EM) analysis revealed distinct structural features in A. franciscana ATP synthase compared with mammals. The stronger density of the e-subunit C-terminal region and its enhanced interaction with the c-ring were found in A. franciscana ATP synthase. These data suggest an inactivation mechanism of the ATP synthase leak channel and its possible contribution to the lack of mPT in this organism.

Vertebrates show coordinated elevated expression of mitochondrial and nuclear genes after birth

Interactions between mitochondrial and nuclear factors are essential to life. Nevertheless, the importance of coordinated regulation of mitochondrial-nuclear gene expression (CMNGE) to changing physiological conditions is poorly understood and is limited to certain tissues and organisms. We hypothesized that CMNGE is important for development across vertebrates and, hence, should be conserved. As a first step, we analyzed more than 1400 RNA-seq experiments performed during prenatal development, in neonates, and in adults across vertebrate evolution. We find conserved sharp elevation of CMNGE after birth, including oxidative phosphorylation (OXPHOS) and mitochondrial ribosome genes, in the heart, hindbrain, forebrain, and kidney across mammals, as well as in Gallus gallus and in the lizard Anolis carolinensis This is accompanied by elevated expression of TCA cycle enzymes and reduction in hypoxia response genes, suggesting a conserved cross-tissue metabolic switch after birth/hatching. Analysis of about 70 known regulators of mitochondrial gene expression reveals consistently elevated expression of PPARGC1A (also known as Pgc-1alpha) and CEBPB after birth/hatching across organisms and tissues, thus highlighting them as candidate regulators of CMNGE upon transition to the neonate. Analyses of Danio rerio, Xenopus tropicalis, Caenorhabditis elegans, and Drosophila melanogaster reveal elevated CMNGE prior to hatching in X. tropicalis and in D. melanogaster, which is associated with the emergence of muscle activity. Lack of such an ancient pattern in mammals and in chickens suggests that it was lost during radiation of terrestrial vertebrates. Taken together, our results suggest that regulated CMNGE after birth reflects an essential metabolic switch that is under strong selective constraints.

Mitochondrial Amount Determines Doxorubicin-Induced Cardiotoxicity in Cardiomyocytes

Doxorubicin, an anthracycline commonly used for treating cancer patients, is known for its cardiotoxic side-effects. Although dose-dependent, but susceptibility remains variable among patients, and childhood-exposure-adult-onset remains challenging. Besides topoisomerase toxicity, Doxorubicin is also toxic to the mitochondria yet the underlying late onset mechanism remains elusive. Here, it is observed that the mitochondrial copy number in PBMCs of patients treated with anthracycline chemotherapy is negatively correlated with the change in plasma BNP levels after treatment. Isogenic hiPSC-CMs are generated with high, norm, and low mitochondrial copy numbers using mitochondrial transplantation and the YFP-Parkin system. Remarkably, lower mitochondria copy number translates to lower IC50, suggesting increased susceptibility. Mitochondria supplementation by intramyocardial injection prevents doxorubicin induced heart failure. Mechanistically, doxorubicin treatment leads to mPTP opening and mitochondrial DNA (mtDNA) leakage. This mtDNA leakage event activates the cGAS-STING pathway and drives inflammation and myocardial senescence. Cardiomyocyte-specific knockout of Sting (Myh6-Cre/Stingflox/flox; StingCKO) and over expression of mitochondrial tagged DNase1 in mice partially rescue doxorubicin-induced cardiac dysfunction. In conclusion, the work establishes a negative correlation between cardiomyocyte mitochondrial copy number and doxorubicin toxicity. Molecularly, it is demonstrated that mtDNA leakage activates cGAS-STING pathway and accelerates myocardial dysfunction. These insights offer new co-administration strategies for cancer patients.

Promotion of maturation in CDM3-induced embryonic stem cell-derived cardiomyocytes by palmitic acid

BACKGROUND

Myocardial infarction leads to myocardial necrosis, and cardiomyocytes are non-renewable. Fatty acid-containing cardiomyocyte maturation medium promotes maturation of stem cell-derived cardiomyocytes.

OBJECTIVE

To study the effect palmitic acid on maturation of cardiomyocytes derived from human embryonic stem cells (hESCs) to optimize differentiation for potential treatment of myocardial infarction by hESCs.

METHODS

hESCs were differentiated into cardiomyocytes using standard chemically defined medium 3 (CDM3). Up to day 20 of differentiation, 200 Mm palmitic acid were added, and then the culture was continued for another 8 days to mimic the environment in which human cardiomyocytes mainly use fatty acids as the main energy source. Light microscopy, transmission electron microscopy, immunofluorescence, reverse transcription-polymerase chain reaction, and cellular ATP assays, were carried out to analyze the expression of relevant cardiomyocyte-related genes, cell morphology, metabolism levels, and other indicators cardiomyocyte maturity.

RESULTS

Cardiomyocytes derived from hESCs under exogenous palmitic acid had an elongated pike shape and a more regular arrangement. Sarcomere stripes were clear, and the cells color was clearly visible. The cell perimeter and elongation rate were also increased. Myogenic fibers were abundant, myofibrillar z-lines were regularly, the numbers of mitochondria and mitochondrial cristae were higher, more myofilaments were observed, and the structure of round-like discs was occasionally seen. Expression of mature cardiomyocyte-associated genes TNNT2, MYL2 and MYH6, and cardiomyocyte-associated genes KCNJ4, RYR2,and PPARα, was upregulated (p < 0.05). Expression of MYH7, MYL7, KCND2, KCND3, GJA1 and TNNI1 genes was unaffected (p > 0.05). Expression of mature cardiomyocyte-associated sarcomere protein MYL2 was significantly increased (p < 0.05), MYH7 protein expression was unaffected (p > 0.05). hESC-derived cardiomyocytes exposed to exogenous palmitic acid produced more ATP per unit time (p < 0.05).

CONCLUSION

Exogenous palmitic acid induced more mature hESC-CMs in terms of the cellular architecture, expression of cardiomyocyte maturation genes adnprotein, and metabolism.

Mitochondrial dysfunction in pancreatic acinar cells: mechanisms and therapeutic strategies in acute pancreatitis

Acute pancreatitis (AP) is an inflammatory disease of the pancreas and a complex process involving multiple factors, with mitochondrial damage playing a crucial role. Mitochondrial dysfunction is now considered a key driver in the development of AP. This dysfunction often presents as increased oxidative stress, altered membrane potential and permeability, and mitochondrial DNA damage and mutations. Under stress conditions, mitochondrial dynamics and mitochondrial ROS production increase, leading to decreased mitochondrial membrane potential, imbalanced calcium homeostasis, and activation of the mitochondrial permeability transition pore. The release of mitochondrial DNA (mtDNA), recognized as damage-associated molecular patterns, can activate the cGAS-STING1 and NF-κB pathway and induce pro-inflammatory factor expression. Additionally, mtDNA can activate inflammasomes, leading to interleukin release and subsequent tissue damage and inflammation. This review summarizes the relationship between mitochondria and AP and explores mitochondrial protective strategies in the diagnosis and treatment of this disease. Future research on the treatment of acute pancreatitis can benefit from exploring promising avenues such as antioxidants, mitochondrial inhibitors, and new therapies that target mitochondrial dysfunction.

CTRP6-mediated cardiac protection in heart failure via the AMPK/SIRT1/PGC-1α signalling pathway

Heart failure (HF) remains a significant global health concern with limited effective treatments available. C1q/TNF-related protein 6 (CTRP6) is a member of the CTRP family analogous to adiponectin and its role in HF pathogenesis remains unclear. Here, we investigated the impact of CTRP6 on HF progression. To mimic heart failure with reduced ejection fraction (HFrEF), we used isoproterenol injection in mice and administered adenovirus vectors expressing CTRP6 (Ad-CTRP6) via tail vein injection. We assessed cardiac function through echocardiography and histology. CTRP6's effects on hypertrophy, fibrosis, apoptosis, oxidative stress and mitochondrial function were analysed. Downstream pathways (phosphorylated AMP-activated protein kinase (p-AMPK), sirtuin 1 (SIRT1) and peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α) were studied in heart tissues. In vitro, isoproterenol-stimulated H9c2 cardiomyocytes were treated with CTRP6 to examine viability, apoptosis, F-actin and signalling proteins. Compound C was used to assess AMPK involvement. CTRP6 expression was lower in the plasma of HF patients. In an isoproterenol-induced HFrEF mouse model, adenovirus-mediated overexpression of CTRP6 ameliorated cardiac dysfunction and reduced cardiomyocyte apoptosis, oxidative stress, inflammation and myocardial injury markers. Mechanistically, CTRP6 activation of the AMPK/SIRT1/PGC-1α signalling pathway restored mitochondrial homeostasis, evidenced by reduced mitochondrial reactive oxygen species levels, increased ATP content, and enhanced mitochondrial complex I/III activities in cardiac tissues. In vitro studies using isoproterenol-stimulated H9c2 cardiomyocytes corroborated these findings, demonstrating that CTRP6 upregulation attenuated hypertrophy, apoptosis, oxidative stress and mitochondrial dysfunction. Furthermore, these effects were partially reversed by the AMPK inhibitor Compound C, implicating the involvement of the AMPK pathway in CTRP6-mediated cardioprotection. CTRP6 alleviates HF progression through the AMPK/SIRT1/PGC-1α signalling pathway.

Cyclophilin D plays a critical role in the survival of senescent cells

Senescent cells play a causative role in many diseases, and their elimination is a promising therapeutic strategy. Here, through a genome-wide CRISPR/Cas9 screen, we identify the gene PPIF, encoding the mitochondrial protein cyclophilin D (CypD), as a novel senolytic target. Cyclophilin D promotes the transient opening of the mitochondrial permeability transition pore (mPTP), which serves as a failsafe mechanism for calcium efflux. We show that senescent cells exhibit a high frequency of transient CypD/mPTP opening events, known as 'flickering'. Inhibition of CypD using genetic or pharmacologic tools, including cyclosporin A, leads to the toxic accumulation of mitochondrial Ca2+ and the death of senescent cells. Genetic or pharmacological inhibition of NCLX, another mitochondrial calcium efflux channel, also leads to senolysis, while inhibition of the main Ca2+ influx channel, MCU, prevents senolysis induced by CypD inhibition. We conclude that senescent cells are highly vulnerable to elevated mitochondrial Ca2+ ions, and that transient CypD/mPTP opening is a critical adaptation mechanism for the survival of senescent cells.

A Mitochondrial Basis for Heart Failure Progression

In health, the human heart is able to match ATP supply and demand perfectly. It requires 6 kg of ATP per day to satisfy demands of external work (mechanical force generation) and internal work (ion movements and basal metabolism). The heart is able to link supply with demand via direct responses to ADP and AMP concentrations but calcium concentrations within myocytes play a key role, signalling both inotropy, chronotropy and matched increases in ATP production. Calcium/calmodulin-dependent protein kinase (CaMKII) is a key adapter to increased workload, facilitating a greater and more rapid calcium concentration change. In the failing heart, this is dysfunctional and ATP supply is impaired. This review aims to examine the mechanisms and pathologies that link increased energy demand to this disrupted situation. We examine the roles of calcium loading, oxidative stress, mitochondrial structural abnormalities and damage-associated molecular patterns.

Mitochondrial respiratory pathways in immature rat heart tissue using different cardioplegic solutions

INTRODUCTION

Minor defects in the mitochondrial ATP-generating system and post-cardioplegia oxidative phosphorylation can negatively impact cardiac function in immature hearts. This study aimed to examine the mitochondrial respiratory pathway using three different cardioplegic solutions (Custodiol HTK, St. Thomas, and Del Nido) during moderate (1 h) and long (3 h) ischemic periods.

METHODS

A total of 41 male Wistar albino rats were utilized in this study. Five experiments were conducted without the use of any cardioplegic solution (CP0 group). To assess both moderate and prolonged ischemic periods, six experiments were carried out in each of the following groups: CP1 group (St. Thomas solution), CP2 group (Custodiol HTK solution), and CP3 group (Del Nido solution).

RESULTS

After 1 h, the highest mitochondrial respiration rate was observed in the CP3 group and the lowest in the CP1 group (p = 0.006). After adding ADP substrate, the highest mitochondrial ATP-production-coupled respiration was recorded in the CP3 group, which was similar to the control group CP0. After 3 h, while evaluating the ratio between mitochondrial respiration ATP-production coupled and basal respiration, significant differences were found between CP1 group and CP3 group (p = 0.035), as well as between the CP1 and CP0 groups (p = 0.045). Additionally, by assessing the condition of the outer mitochondrial membrane using the Cyt C effect (Cyt/Phos [ADP]), significant differences were observed between the CP1 and CP3 group (p = 0.004), as well as between CP1 and CP0 groups (p = 0.003).

CONCLUSION

Del Nido cardioplegic solution provided optimal mitochondrial protection under moderate and long myocardial ischemia conditions.

The Role of Mitochondrial Permeability Transition in Bone Metabolism, Bone Healing, and Bone Diseases

Bone is a dynamic organ with an active metabolism and high sensitivity to mitochondrial dysfunction. The mitochondrial permeability transition pore (mPTP) is a low-selectivity channel situated in the inner mitochondrial membrane (IMM), permitting the exchange of molecules of up to 1.5 kDa in and out of the IMM. Recent studies have highlighted the critical role of the mPTP in bone tissue, but there is currently a lack of reviews concerning this topic. This review discusses the structure and function of the mPTP and its impact on bone-related cells and bone-related pathological states. The mPTP activity is reduced during the osteogenic differentiation of mesenchymal stem cells (MSCs), while its desensitisation may underlie the mechanism of enhanced resistance to apoptosis in neoplastic osteoblastic cells. mPTP over-opening triggers mitochondrial swelling, regulated cell death, and inflammatory response. In particular, mPTP over-opening is involved in dexamethasone-induced osteoblast dysfunction and bisphosphonate-induced osteoclast apoptosis. In vivo, the mPTP plays a significant role in maintaining bone homeostasis, with many bone disorders linked to its excessive opening. Genetic deletion or pharmacological inhibition of the over-opening of mPTP has shown potential in enhancing bone injury recovery and alleviating bone diseases. Here, we review the findings on the relationship of the mPTP and bone at both the cellular and disease levels, highlighting novel avenues for pharmacological approaches targeting mitochondrial function to promote bone healing and manage bone-related disorders.

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.

Oxidative stress modulating nanomaterials and their biochemical roles in nanomedicine

Many pathological conditions are predominantly associated with oxidative stress, arising from reactive oxygen species (ROS); therefore, the modulation of redox activities has been a key strategy to restore normal tissue functions. Current approaches involve establishing a favorable cellular redox environment through the administration of therapeutic drugs and redox-active nanomaterials (RANs). In particular, RANs not only provide a stable and reliable means of therapeutic delivery but also possess the capacity to finely tune various interconnected components, including radicals, enzymes, proteins, transcription factors, and metabolites. Here, we discuss the roles that engineered RANs play in a spectrum of pathological conditions, such as cancer, neurodegenerative diseases, infections, and inflammation. We visualize the dual functions of RANs as both generator and scavenger of ROS, emphasizing their profound impact on diverse cellular functions. The focus of this review is solely on inorganic redox-active nanomaterials (inorganic RANs). Additionally, we deliberate on the challenges associated with current RANs-based approaches and propose potential research directions for their future clinical translation.

Exploring the multifaceted role of adenosine nucleotide translocase 2 in cellular and disease processes: A comprehensive review

Adenosine nucleotide translocases (ANTs) are a family of proteins abundant in the inner mitochondrial membrane, primarily responsible for shuttling ADP and ATP across the mitochondrial membrane. Additionally, ANTs are key players in balancing mitochondrial energy metabolism and regulating cell death. ANT2 isoform, highly expressed in undifferentiated and proliferating cells, is implicated in the development and drug resistance of various tumors. We conduct a detailed analysis of the potential mechanisms by which ANT2 may influence tumorigenesis and drug resistance. Notably, the significance of ANT2 extends beyond oncology, with roles in non-tumor cell processes including blood cell development, gastrointestinal motility, airway hydration, nonalcoholic fatty liver disease, obesity, chronic kidney disease, and myocardial development, making it a promising therapeutic target for multiple pathologies. To better understand the molecular mechanisms of ANT2, this review summarizes the structural properties, expression patterns, and basic functions of the ANT2 protein. In particular, we review and analyze the controversy surrounding ANT2, focusing on its role in transporting ADP/ATP across the inner mitochondrial membrane, its involvement in the composition of the mitochondrial permeability transition pore, and its participation in apoptosis.

Mitochondrial permeability transition dictates mitochondrial maturation upon switch in cellular identity of hematopoietic precursors

The mitochondrial permeability transition pore (mPTP) is a supramolecular channel that regulates exchange of solutes across cristae membranes, with executive roles in mitochondrial function and cell death. The contribution of the mPTP to normal physiology remains debated, although evidence implicates the mPTP in mitochondrial inner membrane remodeling in differentiating progenitor cells. Here, we demonstrate that strict control over mPTP conductance shapes metabolic machinery as cells transit toward hematopoietic identity. Cells undergoing the endothelial-to-hematopoietic transition (EHT) tightly control chief regulatory elements of the mPTP. During EHT, maturing arterial endothelium restricts mPTP activity just prior to hematopoietic commitment. After transition in cellular identity, mPTP conductance is restored. In utero treatment with NIM811, a molecule that blocks sensitization of the mPTP to opening by Cyclophilin D (CypD), amplifies oxidative phosphorylation (OXPHOS) in hematopoietic precursors and increases hematopoiesis in the embryo. Additionally, differentiating pluripotent stem cells (PSCs) acquire greater organization of mitochondrial cristae and hematopoietic activity following knockdown of the CypD gene, Ppif. Conversely, knockdown of Opa1, a GTPase critical for proper cristae architecture, induces cristae irregularity and impairs hematopoiesis. These data elucidate a mechanism that regulates mitochondrial maturation in hematopoietic precursors and underscore a role for the mPTP in the acquisition of hematopoietic fate.

Alcohol exposure during pregnancy induces cardiac mitochondrial damage in offspring mice

BACKGROUND

Prenatal alcohol exposure (PAE) has been linked to congenital heart disease and fetal alcohol syndrome. The heart primarily relies on mitochondria to generate energy, so impaired mitochondrial function due to alcohol exposure can significantly affect cardiac development and function. Our study aimed to investigate the impact of PAE on myocardial and mitochondrial functions in offspring mice.

METHODS

We administered 30% alcohol (3 g/kg) to pregnant C57BL/6 mice during the second trimester. We assessed cardiac function by transthoracic echocardiography, observed myocardial structure and fibrosis through staining tests and electron transmission microscopy, and detected cardiomyocyte apoptosis with dUTP nick end labeling assay and real-time quantitative PCR. Additionally, we measured the reactive oxygen species content, ATP level, and mitochondrial DNA copy number in myocardial mitochondria. Mitochondrial damage was evaluated by assessing the level of mitochondrial membrane potential and the opening degree of mitochondrial permeability transition pores.

RESULTS

Our findings revealed that PAE caused cardiac systolic dysfunction, ventricular enlargement, thinned ventricular wall, cardiac fibrosis in the myocardium, scattered loss of cardiomyocytes, and disordered arrangement of myocardial myotomes in the offspring. Furthermore, we observed a significant increase in mitochondrial reactive oxygen species content, a decrease in mitochondrial membrane potential, ATP level, and mitochondrial DNA copy number, and sustained opening of mitochondrial permeability transition pores in the heart tissues of the offspring.

CONCLUSIONS

These results indicated that PAE had adverse effects on the cardiac structure and function of the newborn mice and could trigger oxidative stress in their myocardia and contribute to mitochondrial dysfunction.

Mitochondria-tau association promotes cognitive decline and hippocampal bioenergetic deficits during the aging

Current studies indicate that pathological modifications of tau are associated with mitochondrial dysfunction, synaptic failure, and cognitive decline in neurological disorders and aging. We previously showed that caspase-3 cleaved tau, a relevant tau form in Alzheimer's disease (AD), affects mitochondrial bioenergetics, dynamics and synaptic plasticity by the opening of mitochondrial permeability transition pore (mPTP). Also, genetic ablation of tau promotes mitochondrial function boost and increased cognitive capacities in aging mice. However, the mechanisms and relevance of these alterations for the cognitive and mitochondrial abnormalities during aging, which is the primary risk factor for AD, has not been explored. Therefore, in this study we used aging C57BL/6 mice (2-15 and 28-month-old) to evaluate hippocampus-dependent cognitive performance and mitochondrial function. Behavioral tests revealed that aged mice (15 and 28-month-old) showed a reduced cognitive performance compared to young mice (2 month). Concomitantly, isolated hippocampal mitochondria of aged mice showed a significant decrease in bioenergetic-related functions including increases in reactive oxygen species (ROS), mitochondrial depolarization, ATP decreases, and calcium handling defects. Importantly, full-length and caspase-3 cleaved tau were preferentially present in mitochondrial fractions of 15 and 28-month-old mice. Also, aged mice (15 and 28-month-old) showed an increase in cyclophilin D (CypD), the principal regulator of mPTP opening, and a decrease in Opa-1 mitochondrial localization, indicating a possible defect in mitochondrial dynamics. Importantly, we corroborated these findings in immortalized cortical neurons expressing mitochondrial targeted full-length (GFP-T4-OMP25) and caspase-3 cleaved tau (GFP-T4C3-OMP25) which resulted in increased ROS levels and mitochondrial fragmentation, along with a decrease in Opa-1 protein expression. These results suggest that tau associates with mitochondria and this binding increases during aging. This connection may contribute to defects in mitochondrial bioenergetics and dynamics which later may conduce to cognitive decline present during aging.

Role of the mitochondrial protein cyclophilin D in skin wound healing and collagen secretion

Central for wound healing is the formation of granulation tissue, which largely consists of collagen and whose importance stretches past wound healing, including being implicated in both fibrosis and skin aging. Cyclophilin D (CyD) is a mitochondrial protein that regulates the permeability transition pore, known for its role in apoptosis and ischemia-reperfusion. To date, the role of CyD in human wound healing and collagen generation has been largely unexplored. Here, we show that CyD was upregulated in normal wounds and venous ulcers, likely adaptive as CyD inhibition impaired reepithelialization, granulation tissue formation, and wound closure in both human and pig models. Overexpression of CyD increased keratinocyte migration and fibroblast proliferation, while its inhibition reduced migration. Independent of wound healing, CyD inhibition in fibroblasts reduced collagen secretion and caused endoplasmic reticulum collagen accumulation, while its overexpression increased collagen secretion. This was confirmed in a Ppif-KO mouse model, which showed a reduction in skin collagen. Overall, this study revealed previously unreported roles of CyD in skin, with implications for wound healing and beyond.

Cardiac lipidomic profiles in mice undergo changes from fetus to adult

AIMS

Lipids are essential cellular components with many important biological functions. Disturbed lipid biosynthesis and metabolism has been shown to cause cardiac developmental abnormality and cardiovascular diseases. In this study, we aimed to investigate the composition and the molecular profiles of lipids in mammalian hearts between embryonic and adult stages and uncover the underlying links between lipid and cardiac development and maturation.

MATERIALS AND METHODS

We collected mouse hearts at the embryonic day 11.5 (E11.5), E15.5, and the age of 2 months, 4 months and 10 months, and performed lipidomic analysis to determine the changes of the composition, molecular species, and relative abundance of cardiac lipids between embryonic and adult stages. Additionally, we also performed the electronic microscopy and RNA sequencing in both embryonic and adult mouse hearts.

KEY FINDINGS

The relative abundances of certain phospholipids and sphingolipids including cardiolipin, phosphatidylglycerol, phosphatidylethanolamine, and ceramide, are different between embryonic and adult hearts. Such lipidomic changes are accompanied with increased densities of mitochondrial membranes and elevated expression of genes related to mitochondrial formation in adult mouse hearts. We also analyzed individual molecular species of phospholipids and sphingolipids, and revealed that the composition and distribution of lipid molecular species in hearts also change with development.

SIGNIFICANCE

Our study provides not only a lipidomic view of mammalian hearts when developing from the embryonic to the adult stage, but also a potential pool of lipid indicators for cardiac cell development and maturation.

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.

Myoglobin modulates the Hippo pathway to promote cardiomyocyte differentiation

The endogenous mechanisms that propagate cardiomyocyte differentiation and prevent de-differentiation remain unclear. While the expression of the heme protein myoglobin increases by over 50% during cardiomyocyte differentiation, a role for myoglobin in regulating cardiomyocyte differentiation has not been tested. Here, we show that deletion of myoglobin in cardiomyocyte models decreases the gene expression of differentiation markers and stimulates cellular proliferation, consistent with cardiomyocyte de-differentiation. Mechanistically, the heme prosthetic group of myoglobin catalyzes the oxidation of the Hippo pathway kinase LATS1, resulting in phosphorylation and inactivation of yes-associated protein (YAP). In vivo, myoglobin-deficient zebrafish hearts show YAP dephosphorylation and accelerated cardiac regeneration after apical injury. Similarly, myoglobin knockdown in neonatal murine hearts shows increased YAP dephosphorylation and cardiomyocyte cycling. These data demonstrate a novel role for myoglobin as an endogenous driver of cardiomyocyte differentiation and highlight myoglobin as a potential target to enhance cardiac development and improve cardiac repair and regeneration.

Human cardiosphere-derived cells with activated mitochondria for better myocardial regenerative therapy

Cell transplantation is a promising therapeutic strategy for myocardial regeneration therapy. To improve therapeutic effects, we developed a culture medium additive that enhances the mitochondrial function of cardiomyocytes for transplantation. A mitochondrial targeting drug delivery system (MITO-Porter system) was used to deliver mitochondrial activation molecules to mouse-derived cardiac progenitor cells. In this study, we investigated whether the mitochondrial function of human-derived myocardial precursor cells could be enhanced using MITO-Porter. Human cardiosphere-derived cells (CDCs) were isolated from myocardium which was excised during surgery for congenital heart disease. MITO-Porter was added to the cell culture medium to generate mitochondrial activated CDCs (human MITO cells). The human MITO cells were transplanted into myocardial ischemia-reperfusion model rat, and the effect was investigated. The transplanted human MITO cells improved the cardiac function and suppressed myocardial fibrosis compared to conventional cell transplantation methods. These effects were observed not only with myocardial administration but also by intravenous administration of human MITO cells. This study is the first study that assessed whether the mitochondrial delivery of functional compounds improved the outcome of human-derived myocardial cell transplantation therapy.

Cardiomyocyte maturation alters molecular stress response capacities and determines cell survival upon mitochondrial dysfunction

Cardiomyocyte maturation during pre- and postnatal development requires multiple intertwined processes, including a switch in energy generation from glucose utilization in the embryonic heart towards fatty acid oxidation after birth. This is accompanied by a boost in mitochondrial mass to increase capacities for oxidative phosphorylation and ATP generation required for efficient contraction. Whether cardiomyocyte differentiation is paralleled by augmented capacities to deal with reactive oxygen species (ROS), physiological byproducts of the mitochondrial electron transport chain (ETC), is less clear. Here we show that expression of genes and proteins involved in redox homeostasis and protein quality control within mitochondria increases after birth in the mouse and human heart. Using primary embryonic, neonatal and adult mouse cardiomyocytes in vitro we investigated how excessive ROS production induced by mitochondrial dysfunction affects cell survival and stress response at different stages of maturation. Embryonic and neonatal cardiomyocytes largely tolerate inhibition of ETC complex III by antimycin A (AMA) as well as ATP synthase (complex V) by oligomycin but are susceptible to complex I inhibition by rotenone. All three inhibitors alter the intracellular distribution and ultrastructure of mitochondria in neonatal cardiomyocytes. In contrast, adult cardiomyocytes treated with AMA undergo rapid morphological changes and cellular disintegration. At the molecular level embryonic cardiomyocytes activate antioxidative defense mechanisms, the integrated stress response (ISR) and ER stress but not the mitochondrial unfolded protein response upon complex III inhibition. In contrast, adult cardiomyocytes fail to activate the ISR and antioxidative proteins following AMA treatment. In conclusion, our results identified fundamental differences in cell survival and stress response in differentiated compared to immature cardiomyocytes subjected to mitochondrial dysfunction. The high stress tolerance of immature cardiomyocytes might allow outlasting unfavorable intrauterine conditions thereby preventing fetal or perinatal heart disease and may contribute to the regenerative capacity of the embryonic and neonatal mammalian heart.

Sulfide quinone oxidoreductase contributes to voltage sensing of the mitochondrial permeability transition pore

Pathological opening of the mitochondrial permeability transition pore (mPTP) is implicated in the pathogenesis of many disease processes such as myocardial ischemia, traumatic brain injury, Alzheimer's disease, and diabetes. While we have gained insight into mPTP biology over the last several decades, the lack of translation of this knowledge into successful clinical therapies underscores the need for continued investigation and use of different approaches to identify novel regulators of the mPTP with the hope of elucidating new therapeutic targets. Although the mPTP is known to be a voltage-gated channel, the identity of its voltage sensor remains unknown. Here we found decreased gating potential of the mPTP and increased expression and activity of sulfide quinone oxidoreductase (SQOR) in newborn Fragile X syndrome (FXS) mouse heart mitochondria, a model system of coenzyme Q excess and relatively decreased mPTP open probability. We further found that pharmacological inhibition and genetic silencing of SQOR increased mPTP open probability in vitro in adult murine cardiac mitochondria and in the isolated-perfused heart, likely by interfering with voltage sensing. Thus, SQOR is proposed to contribute to voltage sensing by the mPTP and may be a component of the voltage sensing apparatus that modulates the gating potential of the mPTP.

Striated preferentially expressed gene deficiency leads to mitochondrial dysfunction in developing cardiomyocytes

A deficiency of striated preferentially expressed gene (Speg), a member of the myosin light chain kinase family, results in abnormal myofibril structure and function of immature cardiomyocytes (CMs), corresponding with a dilated cardiomyopathy, heart failure and perinatal death. Mitochondrial development plays a role in cardiomyocyte maturation. Therefore, this study investigated whether Speg deficiency ( - / - ) in CMs would result in mitochondrial abnormalities. Speg wild-type and Speg-/- C57BL/6 littermate mice were utilized for assessment of mitochondrial structure by transmission electron and confocal microscopies. Speg was expressed in the first and second heart fields at embryonic (E) day 7.5, prior to the expression of mitochondrial Na+/Ca2+/Li+ exchanger (NCLX) at E8.5. Decreases in NCLX expression (E11.5) and the mitochondrial-to-nuclear DNA ratio (E13.5) were observed in Speg-/- hearts. Imaging of E18.5 Speg-/- hearts revealed abnormal mitochondrial cristae, corresponding with decreased ATP production in cells fed glucose or palmitate, increased levels of mitochondrial superoxide and depolarization of mitochondrial membrane potential. Interestingly, phosphorylated (p) PGC-1α, a key mediator of mitochondrial development, was significantly reduced in Speg-/- hearts during screening for targeted genes. Besides Z-line expression, Speg partially co-localized with PGC-1α in the sarcomeric region and was found in the same complex by co-immunoprecipitation. Overexpression of a Speg internal serine/threonine kinase domain in Speg-/- CMs promoted translocation of pPGC-1α into the nucleus, and restored ATP production that was abolished by siRNA-mediated silencing of PGC-1α. Our results demonstrate a critical role of Speg in mitochondrial development and energy metabolism in CMs, mediated in part by phosphorylation of PGC-1α.

Increased dosage of DYRK1A leads to congenital heart defects in a mouse model of Down syndrome

Down syndrome (DS) is caused by trisomy of human chromosome 21 (Hsa21). DS is a gene dosage disorder that results in multiple phenotypes including congenital heart defects. This clinically important cardiac pathology is the result of a third copy of one or more of the approximately 230 genes on Hsa21, but the identity of the causative dosage-sensitive genes and hence mechanisms underlying this cardiac pathology remain unclear. Here, we show that hearts from human fetuses with DS and embryonic hearts from the Dp1Tyb mouse model of DS show reduced expression of mitochondrial respiration genes and cell proliferation genes. Using systematic genetic mapping, we determined that three copies of the dual-specificity tyrosine phosphorylation-regulated kinase 1A (Dyrk1a) gene, encoding a serine/threonine protein kinase, are associated with congenital heart disease pathology. In embryos from Dp1Tyb mice, reducing Dyrk1a gene copy number from three to two reversed defects in cellular proliferation and mitochondrial respiration in cardiomyocytes and rescued heart septation defects. Increased dosage of DYRK1A protein resulted in impairment of mitochondrial function and congenital heart disease pathology in mice with DS, suggesting that DYRK1A may be a useful therapeutic target for treating this common human condition.

Single-cell RNA sequencing reveals the role of mitochondrial dysfunction in the cardiogenic toxicity of perfluorooctane sulfonate in human embryonic stem cells

Perfluorooctane sulfonate (PFOS), an endocrine-disrupting chemical pollutant, affects embryonic heart development; however, the mechanisms underlying its toxicity have not been fully elucidated. Here, Single-cell RNA sequencing (scRNA-seq) was used to investigate the overall effects of PFOS on myocardial differentiation from human embryonic stem cells (hESCs). Additionally, apoptosis, mitochondrial membrane potential, and ATP assays were performed. Downregulated cardiogenesis-related genes and inhibited cardiac differentiation were observed after PFOS exposure in vitro. The percentages of cardiomyocyte and cardiac progenitor cell clusters decreased significantly following exposure to PFOS, while the proportion of primitive endoderm cell was increased in PFOS group. Moreover, PFOS inhibited myocardial differentiation and blocked cellular development at the early- and middle-stage. A Gene Ontology analysis and pseudo-time trajectory illustrated that PFOS disturbed multiple processes related to cardiogenesis and oxidative phosphorylation in the mitochondria. Furthermore, PFOS decreased mitochondrial membrane potential and induced apoptosis. These results offer meaningful insights into the cardiogenic toxicity of PFOS exposure during heart formation as well as the adverse effects of PFOS on mitochondria.

Environmental Signals

Environmental factors have long been known to play a role in the pathogenesis of congenital heart disease (CHD), but this has not been a major focus of research in the modern era. Studies of human exposures and animal models demonstrate that demographics (age, race, socioeconomic status), diseases (e.g., diabetes, hypertension, obesity, stress, infection, high altitude), recreational and therapeutic drug use, and chemical exposures are associated with an increased risk for CHD. Unfortunately, although studies suggest that exposures to these factors may cause CHD, in most cases, the data are not strong, are inconclusive, or are contradictory. Although most studies concentrate on the effects of maternal exposure, paternal exposure to some agents can also modify this risk. From a mechanistic standpoint, recent delineation of signaling and genetic controls of cardiac development has revealed molecular pathways that may explain the effects of environmental signals on cardiac morphogenesis and may provide further tools to study the effects of environmental stimuli on cardiac development. For example, environmental factors likely regulate cellular signaling pathways, transcriptional and epigenetic regulation, proliferation, and physiologic processes that can control the development of the heart and other organs. However, understanding of the epidemiology and risk of these exposures and the mechanistic basis for any effects on cardiac development remains incomplete. Further studies defining the relationship between environmental exposures and human CHD and the mechanisms involved should reveal strategies to prevent, diagnose, and treat CHD induced by environmental signals.

Cardiac Metabolism

The heart is composed of a heterogeneous mixture of cellular components perfectly intermingled and able to integrate common environmental signals to ensure proper cardiac function and performance. Metabolism defines a cell context-dependent signature that plays a critical role in survival, proliferation, or differentiation, being a recognized master piece of organ biology, modulating homeostasis, disease progression, and adaptation to tissue damage. The heart is a highly demanding organ, and adult cardiomyocytes require large amount of energy to fulfill adequate contractility. However, functioning under oxidative mitochondrial metabolism is accompanied with a concomitant elevation of harmful reactive oxygen species that indeed contributes to the progression of several cardiovascular pathologies and hampers the regenerative capacity of the mammalian heart. Cardiac metabolism is dynamic along embryonic development and substantially changes as cardiomyocytes mature and differentiate within the first days after birth. During early stages of cardiogenesis, anaerobic glycolysis is the main energetic program, while a progressive switch toward oxidative phosphorylation is a hallmark of myocardium differentiation. In response to cardiac injury, different signaling pathways participate in a metabolic rewiring to reactivate embryonic bioenergetic programs or the utilization of alternative substrates, reflecting the flexibility of heart metabolism and its central role in organ adaptation to external factors. Despite the well-established metabolic pattern of fetal, neonatal, and adult cardiomyocytes, our knowledge about the bioenergetics of other cardiac populations like endothelial cells, cardiac fibroblasts, or immune cells is limited. Considering the close intercellular communication and the influence of nonautonomous cues during heart development and after cardiac damage, it will be fundamental to better understand the metabolic programs in different cardiac cells in order to develop novel interventional opportunities based on metabolic rewiring to prevent heart failure and improve the limited regenerative capacity of the mammalian heart.

Caspase-3 cleaved tau impairs mitochondrial function through the opening of the mitochondrial permeability transition pore

Mitochondrial dysfunction is a significant factor in the development of Alzheimer's disease (AD). Previous studies have demonstrated that the expression of tau cleaved at Asp421 by caspase-3 leads to mitochondrial abnormalities and bioenergetic impairment. However, the underlying mechanism behind these alterations and their impact on neuronal function remains unknown. To investigate the mechanism behind mitochondrial dysfunction caused by this tau form, we used transient transfection and pharmacological approaches in immortalized cortical neurons and mouse primary hippocampal neurons. We assessed mitochondrial morphology and bioenergetics function after expression of full-length tau and caspase-3-cleaved tau. We also evaluated the mitochondrial permeability transition pore (mPTP) opening and its conformation as a possible mechanism to explain mitochondrial impairment induced by caspase-3 cleaved tau. Our studies showed that pharmacological inhibition of mPTP by cyclosporine A (CsA) prevented all mitochondrial length and bioenergetics abnormalities in neuronal cells expressing caspase-3 cleaved tau. Neuronal cells expressing caspase-3-cleaved tau showed sustained mPTP opening which is mostly dependent on cyclophilin D (CypD) protein expression. Moreover, the impairment of mitochondrial length and bioenergetics induced by caspase-3-cleaved tau were prevented in hippocampal neurons obtained from CypD knock-out mice. Interestingly, previous studies using these mice showed a prevention of mPTP opening and a reduction of mitochondrial failure and neurodegeneration induced by AD. Therefore, our findings showed that caspase-3-cleaved tau negatively impacts mitochondrial bioenergetics through mPTP activation, highlighting the importance of this channel and its regulatory protein, CypD, in the neuronal damage induced by tau pathology in AD.

Mitochondrial permeability transition regulator, cyclophilin D, is transcriptionally activated by C/EBP during adipogenesis

Age-related bone loss is associated with decreased bone formation, increased bone resorption, and accumulation of bone marrow fat. During aging, differentiation potential of bone marrow stromal (a.k.a. mesenchymal stem) cells (BMSCs) is shifted toward an adipogenic lineage and away from an osteogenic lineage. In aged bone tissue, we previously observed pathological opening of the mitochondrial permeability transition pore (MPTP) which leads to mitochondrial dysfunction, oxidative phosphorylation uncoupling, and cell death. Cyclophilin D (CypD) is a mitochondrial protein that facilitates opening of the MPTP. We found earlier that CypD is downregulated during osteogenesis of BMSCs leading to lower MPTP activity and, thus, protecting mitochondria from dysfunction. However, during adipogenesis, a fate alternative to osteogenesis, the regulation of mitochondrial function and CypD expression is still unclear. In this study, we observed that BMSCs have increased CypD expression and MPTP activity, activated glycolysis, and fragmented mitochondrial network during adipogenesis. Adipogenic C/EBPα acts as a transcriptional activator of expression of the CypD gene, Ppif, during this process. Inflammation-associated transcription factor NF-κB shows a synergistic effect with C/EBPα inducing Ppif expression. Overall, we demonstrated changes in mitochondrial morphology and function during adipogenesis. We also identified C/EBPα as a transcriptional activator of CypD. The synergistic activation of CypD by C/EBPα and the NF-κB p65 subunit during this process suggests a potential link between adipogenic signaling, inflammation, and MPTP gain-of-function, thus altering BMSC fate during aging.

Mitochondrial leak metabolism induces the Spemann-Mangold Organizer via Hif-1α in Xenopus

An instructive role for metabolism in embryonic patterning is emerging, although a role for mitochondria is poorly defined. We demonstrate that mitochondrial oxidative metabolism establishes the embryonic patterning center, the Spemann-Mangold Organizer, via hypoxia-inducible factor 1α (Hif-1α) in Xenopus. Hypoxia or decoupling ATP production from oxygen consumption expands the Organizer by activating Hif-1α. In addition, oxygen consumption is 20% higher in the Organizer than in the ventral mesoderm, indicating an elevation in mitochondrial respiration. To reconcile increased mitochondrial respiration with activation of Hif-1α, we discovered that the "free" c-subunit ring of the F1Fo ATP synthase creates an inner mitochondrial membrane leak, which decouples ATP production from respiration at the Organizer, driving Hif-1α activation there. Overexpression of either the c-subunit or Hif-1α is sufficient to induce Organizer cell fates even when β-catenin is inhibited. We propose that mitochondrial leak metabolism could be a general mechanism for activating Hif-1α and Wnt signaling.

Metabolic Control of Cardiomyocyte Cell Cycle

Current therapies for heart failure aim to prevent the deleterious remodeling that occurs after MI injury, but currently no therapies are available to replace lost cardiomyocytes. Several organisms now being studied are capable of regenerating their myocardium by the proliferation of existing cardiomyocytes. In this review, we summarize the main metabolic pathways of the mammalian heart and how modulation of these metabolic pathways through genetic and pharmacological approaches influences cardiomyocyte proliferation and heart regeneration.

Metabolic Remodeling during Early Cardiac Lineage Specification of Pluripotent Stem Cells

Growing evidence indicates that metabolites and energy metabolism play an active rather than consequential role in regulating cellular fate. Cardiac development requires dramatic metabolic remodeling from relying primarily on glycolysis in pluripotent stem cells (PSCs) to oxidizing a wide array of energy substrates to match the high bioenergetic demands of continuous contraction in the developed heart. However, a detailed analysis of how remodeling of energy metabolism contributes to human cardiac development is lacking. Using dynamic multiple reaction monitoring metabolomics of central carbon metabolism, we evaluated temporal changes in energy metabolism during human PSC 3D cardiac lineage specification. Significant metabolic remodeling occurs during the complete differentiation, yet temporal analysis revealed that most changes occur during transitions from pluripotency to mesoderm (day 1) and mesoderm to early cardiac (day 5), with limited maturation of cardiac metabolism beyond day 5. Real-time metabolic analysis demonstrated that while hPSC cardiomyocytes (hPSC-CM) showed elevated rates of oxidative metabolism compared to PSCs, they still retained high glycolytic rates, confirming an immature metabolic phenotype. These observations support the opportunity to metabolically optimize the differentiation process to support lineage specification and maturation of hPSC-CMs.

Biomimetic Cardiac Tissue Models for In Vitro Arrhythmia Studies

Cardiac arrhythmias are a major cause of cardiovascular mortality worldwide. Many arrhythmias are caused by reentry, a phenomenon where excitation waves circulate in the heart. Optical mapping techniques have revealed the role of reentry in arrhythmia initiation and fibrillation transition, but the underlying biophysical mechanisms are still difficult to investigate in intact hearts. Tissue engineering models of cardiac tissue can mimic the structure and function of native cardiac tissue and enable interactive observation of reentry formation and wave propagation. This review will present various approaches to constructing cardiac tissue models for reentry studies, using the authors' work as examples. The review will highlight the evolution of tissue engineering designs based on different substrates, cell types, and structural parameters. A new approach using polymer materials and cellular reprogramming to create biomimetic cardiac tissues will be introduced. The review will also show how computational modeling of cardiac tissue can complement experimental data and how such models can be applied in the biomimetics of cardiac tissue.

Identity, structure, and function of the mitochondrial permeability transition pore: controversies, consensus, recent advances, and future directions

The mitochondrial permeability transition (mPT) describes a Ca2+-dependent and cyclophilin D (CypD)-facilitated increase of inner mitochondrial membrane permeability that allows diffusion of molecules up to 1.5 kDa in size. It is mediated by a non-selective channel, the mitochondrial permeability transition pore (mPTP). Sustained mPTP opening causes mitochondrial swelling, which ruptures the outer mitochondrial membrane leading to subsequent apoptotic and necrotic cell death, and is implicated in a range of pathologies. However, transient mPTP opening at various sub-conductance states may contribute several physiological roles such as alterations in mitochondrial bioenergetics and rapid Ca2+ efflux. Since its discovery decades ago, intensive efforts have been made to identify the exact pore-forming structure of the mPT. Both the adenine nucleotide translocase (ANT) and, more recently, the mitochondrial F1FO (F)-ATP synthase dimers, monomers or c-subunit ring alone have been implicated. Here we share the insights of several key investigators with different perspectives who have pioneered mPT research. We critically assess proposed models for the molecular identity of the mPTP and the mechanisms underlying its opposing roles in the life and death of cells. We provide in-depth insights into current controversies, seeking to achieve a degree of consensus that will stimulate future innovative research into the nature and role of the mPTP.

A novel mitochondrial complex I ROS inhibitor partially improves muscle regeneration in adult but not old mice

It is unclear whether mitochondrial dysfunction and redox stress contribute to impaired age-related muscle regenerative capacity. Here we characterized a novel compound, BI4500, that inhibits the release of reactive oxygen species (ROS) from the quinone site in mitochondrial complex I (site IQ). We tested the hypothesis that ROS release from site IQ contributes to impaired regenerative capacity in aging muscle. Electron transfer system site-specific ROS production was measured in adult and aged mouse isolated muscle mitochondria and permeabilized gastrocnemius fibers. BI4500 inhibited ROS production from site IQ in a concentration-dependent manner (IC50 = ∼985 nM) by inhibiting ROS release without impairing complex I-linked respiration. In vivo BI4500 treatment decreased ROS production from site IQ. Muscle injury and sham injury were induced using barium chloride or vehicle injection to the tibialis anterior (TA) muscle in adult and aged male mice. On the same day as injury, mice began a daily gavage of 30 mg/kg BI4500 (BI) or placebo (PLA). Muscle regeneration (H&E, Sirius Red, Pax7) was measured at 5 and 35 days after injury. Muscle injury increased centrally nucleated fibers (CNFs) and fibrosis with no treatment or age effect. There was a significant age by treatment interaction for CNFs at 5- and 35-days post injury with significantly more CNFs in BI adults compared to PLA adults. Muscle fiber cross-sectional area (CSA) recovered significantly more in adult BI mice (-89 ± 365 μm2) compared to old PLA (-599 ± 153 μm2) and old BI (-535 ± 222 μm2, mean ± SD). In situ TA force recovery was measured 35 days after injury and was not significantly different by age or treatment. Inhibition of site IQ ROS partially improves muscle regeneration in adult but not old muscle demonstrating a role for CI ROS in the response to muscle injury. Site IQ ROS does not contribute to impaired regenerative capacity in aging.

Mechanistic correlation between mitochondrial permeability transition pores and mitochondrial ATP dependent potassium channels in ischemia reperfusion

Mitochondrial dysfunction is one of the fundamental causes of ischemia reperfusion (I/R) damage. I/R refers to the paradoxical progression of cellular dysfunction and death that occurs when blood flow is restored to previously ischemic tissues. I/R causes a significant rise in mitochondrial permeability resulting in the opening of mitochondrial permeability transition pores (MPTP). The MPTP are broad, nonspecific channels present in the inner mitochondrial membrane (IMM), and are known to mediate the deadly permeability alterations that trigger mitochondrial driven cell death. Protection from reperfusion injury occurs when long-term ischemia is accompanied by short-term ischemic episodes or inhibition of MPTP from opening via mitochondrial ATP dependent potassium (mitoK_ATP) channels. These channels located in the IMM, play an essential role in ischemia preconditioning (PC) and protect against cell death by blocking MPTP opening. This review primarily focuses on the interaction between the MPTP and mitoK_ATP along with their role in the I/R injury. This article also describes the molecular composition of the MPTP and mitoK_ATP in order to promote future knowledge and treatment of diverse I/R injuries in various organs.

The critical role of cardiolipin in metazoan differentiation, development, and maturation

Cardiolipins are phospholipids that are central to proper mitochondrial functioning. Because mitochondria play crucial roles in differentiation, development, and maturation, we would also expect cardiolipin to play major roles in these processes. Indeed, cardiolipin has been implicated in the mechanism of three human diseases that affect young infants, implying developmental abnormalities. In this review, we will: (1) Review the biology of cardiolipin; (2) Outline the evidence for essential roles of cardiolipin during organismal development, including embryogenesis and cell maturation in vertebrate organisms; (3) Place the role(s) of cardiolipin during embryogenesis within the larger context of the roles of mitochondria in development; and (4) Suggest avenues for future research.

Mitochondrial Dysfunction in Cardiac Diseases and Therapeutic Strategies

Mitochondria are the main site of intracellular synthesis of ATP, which provides energy for various physiological activities of the cell. Cardiomyocytes have a high density of mitochondria and mitochondrial damage is present in a variety of cardiovascular diseases. In this paper, we describe mitochondrial damage in mitochondrial cardiomyopathy, congenital heart disease, coronary heart disease, myocardial ischemia-reperfusion injury, heart failure, and drug-induced cardiotoxicity, in the context of the key roles of mitochondria in cardiac development and homeostasis. Finally, we discuss the main current therapeutic strategies aimed at alleviating mitochondrial impairment-related cardiac dysfunction, including pharmacological strategies, gene therapy, mitochondrial replacement therapy, and mitochondrial transplantation. It is hoped that this will provide new ideas for the treatment of cardiovascular diseases.

Deregulation of ER-mitochondria contact formation and mitochondrial calcium homeostasis mediated by VDAC in fragile X syndrome

Loss of fragile X messenger ribonucleoprotein (FMRP) causes fragile X syndrome (FXS), the most prevalent form of inherited intellectual disability. Here, we show that FMRP interacts with the voltage-dependent anion channel (VDAC) to regulate the formation and function of endoplasmic reticulum (ER)-mitochondria contact sites (ERMCSs), structures that are critical for mitochondrial calcium (mito-Ca2+) homeostasis. FMRP-deficient cells feature excessive ERMCS formation and ER-to-mitochondria Ca2+ transfer. Genetic and pharmacological inhibition of VDAC or other ERMCS components restored synaptic structure, function, and plasticity and rescued locomotion and cognitive deficits of the Drosophila dFmr1 mutant. Expressing FMRP C-terminal domain (FMRP-C), which confers FMRP-VDAC interaction, rescued the ERMCS formation and mito-Ca2+ homeostasis defects in FXS patient iPSC-derived neurons and locomotion and cognitive deficits in Fmr1 knockout mice. These results identify altered ERMCS formation and mito-Ca2+ homeostasis as contributors to FXS and offer potential therapeutic targets.

Why Don’t More Mitochondrial Diseases Exhibit Cardiomyopathy?

Background: Although the heart requires abundant energy, only 20–40% of children with mitochondrial diseases have cardiomyopathies. Methods: We looked for differences in genes underlying mitochondrial diseases that do versus do not cause cardiomyopathy using the comprehensive Mitochondrial Disease Genes Compendium. Mining additional online resources, we further investigated possible energy deficits caused by non-oxidative phosphorylation (OXPHOS) genes associated with cardiomyopathy, probed the number of amino acids and protein interactors as surrogates for OXPHOS protein cardiac “importance”, and identified mouse models for mitochondrial genes. Results: A total of 107/241 (44%) mitochondrial genes was associated with cardiomyopathy; the highest proportion were OXPHOS genes (46%). OXPHOS (p = 0.001) and fatty acid oxidation (p = 0.009) defects were significantly associated with cardiomyopathy. Notably, 39/58 (67%) non-OXPHOS genes associated with cardiomyopathy were linked to defects in aerobic respiration. Larger OXPHOS proteins were associated with cardiomyopathy (p < 0.05). Mouse models exhibiting cardiomyopathy were found for 52/241 mitochondrial genes, shedding additional insights into biological mechanisms. Conclusions: While energy generation is strongly associated with cardiomyopathy in mitochondrial diseases, many energy generation defects are not linked to cardiomyopathy. The inconsistent link between mitochondrial disease and cardiomyopathy is likely to be multifactorial and includes tissue-specific expression, incomplete clinical data, and genetic background differences.

Role of the Mitochondrial Permeability Transition in Bone Metabolism and Aging

The mitochondrial permeability transition pore (MPTP) and its positive regulator, cyclophilin D (CypD), play important pathophysiological roles in aging. In bone tissue, higher CypD expression and pore activity are found in aging; however, a causal relationship between CypD/MPTP and bone degeneration needs to be established. We previously reported that CypD expression and MPTP activity are downregulated during osteoblast (OB) differentiation and that manipulations in CypD expression affect OB differentiation and function. Using a newly developed OB-specific CypD/MPTP gain-of-function (GOF) mouse model, we here present evidence that overexpression of a constitutively active K166Q mutant of CypD (caCypD) impairs OB energy metabolism and function, and bone morphological and biomechanical parameters. Specifically, in a spatial-dependent and sex-dependent manner, OB-specific CypD GOF led to a decrease in oxidative phosphorylation (OxPhos) levels, higher oxidative stress, and general metabolic adaptations coincident with the decreased bone organic matrix content in long bones. Interestingly, accelerated bone degeneration was present in vertebral bones regardless of sex. Overall, our work confirms CypD/MPTP overactivation as an important pathophysiological mechanism leading to bone degeneration and fragility in aging. © 2023 American Society for Bone and Mineral Research (ASBMR).

1,3,8-Triazaspiro[4.5]decane Derivatives Inhibit Permeability Transition Pores through a FO-ATP Synthase c Subunit Glu119-Independent Mechanism That Prevents Oligomycin A-Related Side Effects

Permeability transition pore (PTP) molecular composition and activity modulation have been a matter of research for several years, especially due to their importance in ischemia reperfusion injury (IRI). Notably, c subunit of ATP synthase (Csub) has been identified as one of the PTP-forming proteins and as a target for cardioprotection. Oligomycin A is a well-known Csub interactor that has been chemically modified in-depth for proposed new pharmacological approaches against cardiac reperfusion injury. Indeed, by taking advantage of its scaffold and through focused chemical improvements, innovative Csub-dependent PTP inhibitors (1,3,8-Triazaspiro[4.5]decane) have been synthetized in the past. Interestingly, four critical amino acids have been found to be involved in Oligomycin A-Csub binding in yeast. However, their position on the human sequence is unknown, as is their function in PTP inhibition. The aims of this study are to (i) identify for the first time the topologically equivalent residues in the human Csub sequence; (ii) provide their in vitro validation in Oligomycin A-mediated PTP inhibition and (iii) understand their relevance in the binding of 1,3,8-Triazaspiro[4.5]decane small molecules, as Oligomycin A derivatives, in order to provide insights into Csub interactions. Notably, in this study we demonstrated that 1,3,8-Triazaspiro[4.5]decane derivatives inhibit permeability transition pores through a FO-ATP synthase c subunit Glu119-independent mechanism that prevents Oligomycin A-related side effects.

Insights into the Role of a Cardiomyopathy-Causing Genetic Variant in ACTN2

Pathogenic variants in ACTN2, coding for alpha-actinin 2, are known to be rare causes of Hypertrophic Cardiomyopathy. However, little is known about the underlying disease mechanisms. Adult heterozygous mice carrying the Actn2 p.Met228Thr variant were phenotyped by echocardiography. For homozygous mice, viable E15.5 embryonic hearts were analysed by High Resolution Episcopic Microscopy and wholemount staining, complemented by unbiased proteomics, qPCR and Western blotting. Heterozygous Actn2 p.Met228Thr mice have no overt phenotype. Only mature males show molecular parameters indicative of cardiomyopathy. By contrast, the variant is embryonically lethal in the homozygous setting and E15.5 hearts show multiple morphological abnormalities. Molecular analyses, including unbiased proteomics, identified quantitative abnormalities in sarcomeric parameters, cell-cycle defects and mitochondrial dysfunction. The mutant alpha-actinin protein is found to be destabilised, associated with increased activity of the ubiquitin-proteasomal system. This missense variant in alpha-actinin renders the protein less stable. In response, the ubiquitin-proteasomal system is activated; a mechanism that has been implicated in cardiomyopathies previously. In parallel, a lack of functional alpha-actinin is thought to cause energetic defects through mitochondrial dysfunction. This seems, together with cell-cycle defects, the likely cause of the death of the embryos. The defects also have wide-ranging morphological consequences.

Mitochondrial remodelling is essential for female germ cell differentiation and survival

Stem cells often possess immature mitochondria with few inner membrane invaginations, which increase as stem cells differentiate. Despite this being a conserved feature across many stem cell types in numerous organisms, how and why mitochondria undergo such remodelling during stem cell differentiation has remained unclear. Here, using Drosophila germline stem cells (GSCs), we show that Complex V drives mitochondrial remodelling during the early stages of GSC differentiation, prior to terminal differentiation. This endows germline mitochondria with the capacity to generate large amounts of ATP required for later egg growth and development. Interestingly, impairing mitochondrial remodelling prior to terminal differentiation results in endoplasmic reticulum (ER) lipid bilayer stress, Protein kinase R-like ER kinase (PERK)-mediated activation of the Integrated Stress Response (ISR) and germ cell death. Taken together, our data suggest that mitochondrial remodelling is an essential and tightly integrated aspect of stem cell differentiation. This work sheds light on the potential impact of mitochondrial dysfunction on stem and germ cell function, highlighting ER lipid bilayer stress as a potential major driver of phenotypes caused by mitochondrial dysfunction.

Monoamine oxidase A-dependent ROS formation modulates human cardiomyocyte differentiation through AKT and WNT activation

During embryonic development, cardiomyocytes undergo differentiation and maturation, processes that are tightly regulated by tissue-specific signaling cascades. Although redox signaling pathways involved in cardiomyogenesis are established, the exact sources responsible for reactive oxygen species (ROS) formation remain elusive. The present study investigates whether ROS produced by the mitochondrial flavoenzyme monoamine oxidase A (MAO-A) play a role in cardiomyocyte differentiation from human induced pluripotent stem cells (hiPSCs). Wild type (WT) and MAO-A knock out (KO) hiPSCs were generated by CRISPR/Cas9 genome editing and subjected to cardiomyocyte differentiation. Mitochondrial ROS levels were lower in MAO-A KO compared to the WT cells throughout the differentiation process. MAO-A KO hiPSC-derived cardiomyocytes (hiPSC-CMs) displayed sarcomere disarray, reduced α- to β-myosin heavy chain ratio, GATA4 upregulation and lower macroautophagy levels. Functionally, genetic ablation of MAO-A negatively affected intracellular Ca2+ homeostasis in hiPSC-CMs. Mechanistically, MAO-A generated ROS contributed to the activation of AKT signaling that was considerably attenuated in KO cells. In addition, MAO-A ablation caused a reduction in WNT pathway gene expression consistent with its reported stimulation by ROS. As a result of WNT downregulation, expression of MESP1 and NKX2.5 was significantly decreased in MAO-A KO cells. Finally, MAO-A re-expression during differentiation rescued expression levels of cardiac transcription factors, contractile structure, and intracellular Ca2+ homeostasis. Taken together, these results suggest that MAO-A mediated ROS generation is necessary for the activation of AKT and WNT signaling pathways during cardiac lineage commitment and for the differentiation of fully functional human cardiomyocytes.

Adaptation of cardiomyogenesis to the generation and maturation of cardiomyocytes from human pluripotent stem cells

The advent of methods for efficient generation and cardiac differentiation of pluripotent stem cells opened new avenues for disease modelling, drug testing, and cell therapies of the heart. However, cardiomyocytes (CM) obtained from such cells demonstrate an immature, foetal-like phenotype that involves spontaneous contractions, irregular morphology, expression of embryonic isoforms of sarcomere components, and low level of ion channels. These and other features may affect cellular response to putative therapeutic compounds and the efficient integration into the host myocardium after in vivo delivery. Therefore, novel strategies to increase the maturity of pluripotent stem cell-derived CM are of utmost importance. Several approaches have already been developed relying on molecular changes that occur during foetal and postnatal maturation of the heart, its electromechanical activity, and the cellular composition. As a better understanding of these determinants may facilitate the generation of efficient protocols for in vitro acquisition of an adult-like phenotype by immature CM, this review summarizes the most important molecular factors that govern CM during embryonic development, postnatal changes that trigger heart maturation, as well as protocols that are currently used to generate mature pluripotent stem cell-derived cardiomyocytes.