Chronic Pressure Overload Results in Deficiency of Mitochondrial Membrane Transporter ABCB7 Which Contributes to Iron Overload, Mitochondrial Dysfunction, Metabolic Shift and Worsens Cardiac Function

Ultraviolet irradiation benefits left ventricular hypertrophy and mitochondrial morphology of cardiomyocytes in hypertensive rats

Insufficient exposure to sunlight increases the risk of cardiovascular diseases. Hypertensive left ventricular (LV) hypertrophy exacerbates the risks of myocardial ischemia, ventricular arrhythmias, sudden cardiac death, and heart failure. This study aimed to determine the effects of ultraviolet (UV) irradiation on LV hypertrophy and mitochondrial morphology. Eighteen 7-week-old Dahl salt-sensitive (Dahl S) rats were categorized into three groups (n = 6 each) and fed sodium chloride (NaCl) diets, as follows: UV-irradiated [UVB+A (+), 8% NaCl], non-UV-irradiated [UV (-), 8% NaCl], and control [UV (-), 0.3% NaCl]. UV irradiation was administered at a low intensity of 100 mJ/cm2 for 6 days per week. Echocardiography and mitochondrial analyses were performed to evaluate LV hypertrophy and cardiomyocytes, and skin tissues were stained with hematoxylin and eosin to assess the pathological abnormalities at 12 weeks of age. LV mass was significantly reduced in the UVB+A (+) and control groups compared to that in the UV (-) group. Mitochondrial structural abnormalities in cardiomyocytes were observed only in the UV (-) group, but not in the UVB+A (+) or control group. Pathological skin abnormalities were not observed in any of the three groups. These findings suggest the potential benefits of UV irradiation in hypertensive models.

Total Glucosides of Paeony Ameliorate Myocardial Injury in Chronic Heart Failure Rats by Suppressing PARP-1

Total glucosides of paeony (TGP) have a potential protective effect on chronic heart failure (CHF) rats, but the mechanism remains unclear. PARP inhibition prevents the decrease in myocardial contractility. Therefore, we aim to investigate the effects and mechanisms of TGP on CHF and the role of PARP-1 in CHF. Left anterior descending ligation rats and adriamycin-treated H9C9 cells were used as CHF models, and captopril as a positive control for in vivo experiments. We found that TGP alleviated myocardial remodeling and improved cardiac morphology and function. TGP also reduced myocardial apoptosis and autophagy, decreased inflammatory factor release, and inhibited the PARP-1 and NF-κB proteins. Through cell transfection, we found that PAPR-1 knockdown inhibited NF-κB nuclear translocation. Additionally, TGP inhibited apoptosis, autophagy, and inflammation in CHF cells, while PARP-1 overexpression partially antagonized them. In conclusion, TGP has the potential to improve CHF and PARP-1 may be a potential target.

Ferroptosis in cardiovascular diseases: role and mechanism

In multicellular organisms, regulatory cell death is a crucial aspect of growth and development. Ferroptosis, which was postulated roughly ten years ago, is a mode of cell death that differs from apoptosis, autophagy, and pyrodeath. This distinct pattern of cell death is triggered by an imbalance between oxidants and antioxidants and strongly associated with the metabolism of iron, lipids, amino acids, and glutathione. A growing body of research has implicated ferroptosis in the incidence and progression of many organ traumas and degenerative diseases. Recently, ferroptosis has gained attention as a crucial regulatory mechanism underlying the initiation and development of a variety of cardiovascular diseases, including myocardial ischemia/reperfusion injury, cardiomyopathy, arrhythmia, chemotherapy, and Corona Virus-2-induced cardiac injury. Pharmacological therapies that inhibit ferroptosis have great potential for the management of cardiovascular disorders. This review discusses the prevalence and regulatory mechanisms of ferroptosis, effect of ferroptosis on the immune system, significance of ferroptosis in cardiovascular diseases, and potential therapeutic value of regulating ferroptosis in a variety of heart diseases.

Oxidative stress induces mitochondrial iron overload and ferroptotic cell death

Oxidative stress has been shown to induce cell death in a wide range of human diseases including cardiac ischemia/reperfusion injury, drug induced cardiotoxicity, and heart failure. However, the mechanism of cell death induced by oxidative stress remains incompletely understood. Here we provide new evidence that oxidative stress primarily induces ferroptosis, but not apoptosis, necroptosis, or mitochondria-mediated necrosis, in cardiomyocytes. Intriguingly, oxidative stress induced by organic oxidants such as tert-butyl hydroperoxide (tBHP) and cumene hydroperoxide (CHP), but not hydrogen peroxide (H2O2), promoted glutathione depletion and glutathione peroxidase 4 (GPX4) degradation in cardiomyocytes, leading to increased lipid peroxidation. Moreover, elevated oxidative stress is also linked to labile iron overload through downregulation of the transcription suppressor BTB and CNC homology 1 (Bach1), upregulation of heme oxygenase 1 (HO-1) expression, and enhanced iron release via heme degradation. Strikingly, oxidative stress also promoted HO-1 translocation to mitochondria, leading to mitochondrial iron overload and lipid reactive oxygen species (ROS) accumulation. Targeted inhibition of mitochondrial iron overload or ROS accumulation, by overexpressing mitochondrial ferritin (FTMT) or mitochondrial catalase (mCAT), respectively, markedly inhibited oxidative stress-induced ferroptosis. The levels of mitochondrial iron and lipid peroxides were also markedly increased in cardiomyocytes subjected to simulated ischemia and reperfusion (sI/R) or the chemotherapeutic agent doxorubicin (DOX). Overexpressing FTMT or mCAT effectively prevented cardiomyocyte death induced by sI/R or DOX. Taken together, oxidative stress induced by organic oxidants but not H2O2 primarily triggers ferroptotic cell death in cardiomyocyte through GPX4 and Bach1/HO-1 dependent mechanisms. Our results also reveal mitochondrial iron overload via HO-1 mitochondrial translocation as a key mechanism as well as a potential molecular target for oxidative stress-induced ferroptosis in cardiomyocytes.

Mitigation of Fibrosis after Myocardial Infarction in Rats by Using a Porcine Cholecyst Extracellular Matrix

Fibrosis that occurs after nonfatal myocardial infarction (MI) is an irreversible reparative cardiac tissue remodeling process characterized by progressive deposition of highly cross-linked type I collagen. No currently available therapeutic strategy prevents or reverses MI-associated fibrotic scarring of myocardium. In this study, we used an epicardial graft prepared of porcine cholecystic extracellular matrix to treat experimental nonfatal MI in rats. Graft-assisted healing was characterized by reduced fibrosis, with scanty deposition of type I collagen. Histologically, the tissue response was associated with a favorable regenerative reaction predominated by CD4-positive helper T lymphocytes, enhanced angiogenesis, and infiltration of proliferating cells. These observations indicate that porcine cholecystic extracellular matrix delayed the fibrotic reaction and support its use as a potential biomaterial for mitigating fibrosis after MI. Delaying the progression of cardiac tissue remodeling may widen the therapeutic window for management of scarring after MI.

Improving mitochondrial function in preclinical models of heart failure: therapeutic targets for future clinical therapies?

INTRODUCTION

Heart failure is a complex clinical syndrome resulting from the unsuccessful compensation of symptoms of myocardial damage. Mitochondrial dysfunction is a process that occurs because of an attempt to adapt to the disruption of metabolic and energetic pathways occurring in the myocardium. This, in turn, leads to further dysfunction in cardiomyocyte processes. Currently, many therapeutic strategies have been implemented to improve mitochondrial function, but their effectiveness varies widely.

AREAS COVERED

This review focuses on new models of therapeutic strategies targeting mitochondrial function in the treatment of heart failure.

EXPERT OPINION

Therapeutic strategies targeting mitochondria appear to be a valuable option for treating heart failure. Currently, the greatest challenge is to develop new research models that could restore the disrupted metabolic processes in mitochondria as comprehensively as possible. Only the development of therapies that focus on improving as many dysregulated mitochondrial processes as possible in patients with heart failure will be able to bring the expected clinical improvement, along with inhibition of disease progression. Combined strategies involving the reduction of the effects of oxidative stress and mitochondrial dysfunction, appear to be a promising possibility for developing new therapies for a complex and multifactorial disease such as heart failure.

Proteomic and Global DNA Methylation Modulation in Lipid Metabolism Disorders with a Marine-Derived Bioproduct

Dyslipidemia is a significant risk factor for cardiovascular disease and stroke. Our recent findings showed that RCI-1502, a bioproduct derived from the muscle of the European S. pilchardus, has lipid-lowering effects in the liver and heart in high-fat diet (HFD) fed mice. In the present follow-up study, we investigated the therapeutic potential of RCI-1502 on gene expression and DNA methylation in HFD-fed mice and in patients with dyslipidemia. Using LC-MS/MS, we identified 75 proteins in RCI-1502 that are primarily involved in binding and catalytic activity and which regulate pathways implicated in cardiovascular diseases. In HFD-fed mice, RCI-1502 treatment significantly reduced the expression of cardiovascular disease-related genes, including vascular cell adhesion molecule and angiotensin. RCI-1502 also decreased DNA methylation levels, which were elevated in HFD-fed mice, to levels similar to those in control animals. Furthermore, peripheral blood leukocyte DNA from dyslipidemic patients exhibited higher DNA methylation levels than healthy individuals, suggesting a potential association with cardiovascular risk. Serum analysis also revealed that RCI-1502 treatment regulated cholesterol and triglyceride levels in patients with dyslipidemia. Our findings appear to suggest that RCI-1502 is an epigenetic modulator for the treatment of cardiovascular diseases, specifically in individuals with dyslipidemia.

Proteomics as a Tool for the Study of Mitochondrial Proteome, Its Dysfunctionality and Pathological Consequences in Cardiovascular Diseases

The focus of this review is on the proteomic approaches applied to the study of the qualitative/quantitative changes in mitochondrial proteins that are related to impaired mitochondrial function and consequently different types of pathologies. Proteomic techniques developed in recent years have created a powerful tool for the characterization of both static and dynamic proteomes. They can detect protein-protein interactions and a broad repertoire of post-translation modifications that play pivotal roles in mitochondrial regulation, maintenance and proper function. Based on accumulated proteomic data, conclusions can be derived on how to proceed in disease prevention and treatment. In addition, this article will present an overview of the recently published proteomic papers that deal with the regulatory roles of post-translational modifications of mitochondrial proteins and specifically with cardiovascular diseases connected to mitochondrial dysfunction.

Iron Metabolism in Cardiovascular Disease: Physiology, Mechanisms, and Therapeutic Targets

The cardiovascular system requires iron to maintain its high energy demands and metabolic activity. Iron plays a critical role in oxygen transport and storage, mitochondrial function, and enzyme activity. However, excess iron is also cardiotoxic due to its ability to catalyze the formation of reactive oxygen species and promote oxidative damage. While mammalian cells have several redundant iron import mechanisms, they are equipped with a single iron-exporting protein, which makes the cardiovascular system particularly sensitive to iron overload. As a result, iron levels are tightly regulated at many levels to maintain homeostasis. Iron dysregulation ranges from iron deficiency to iron overload and is seen in many types of cardiovascular disease, including heart failure, myocardial infarction, anthracycline-induced cardiotoxicity, and Friedreich's ataxia. Recently, the use of intravenous iron therapy has been advocated in patients with heart failure and certain criteria for iron deficiency. Here, we provide an overview of systemic and cellular iron homeostasis in the context of cardiovascular physiology, iron deficiency, and iron overload in cardiovascular disease, current therapeutic strategies, and future perspectives.

Sirt6 deficiency contributes to mitochondrial fission and oxidative damage in podocytes via ROCK1-Drp1 signalling pathway

OBJECTIVES

Increasing evidence suggests that mitochondrial dysfunction is the key driver of angiotensin II (Ang II)-induced kidney injury. This study was designed to investigate whether Sirtuin 6 (Sirt6) could affect Ang II-induced mitochondrial damage and the potential mechanisms.

MATERIALS AND METHODS

Podocyte-specific Sirt6 knockout mice were infused with Ang II and cultured podocytes were stimulated with Ang II to evaluate the effects of Sirt6 on mitochondrial structure and function in podocytes. Immunofluorescence staining was used to detect protein expression and mitochondrial morphology in vitro. Electron microscopy was used to assess mitochondrial morphology in mice. Western blotting was used to quantify protein expression.

RESULTS

Mitochondrial fission and decreased Sirt6 expression were observed in podocytes from Ang II-infused mice. In Sirt6-deficient mice, Ang II infusion induced increased apoptosis and mitochondrial fragmentation in podocytes than that in Ang II-infused wild-type mice. In cultured human podocytes, Sirt6 knockdown exacerbated Ang II-induced mitochondrial fission, whereas Sirt6 overexpression ameliorated the Ang II-induced changes in the balance between mitochondrial fusion and fission. Functional studies revealed that Sirt6 deficiency exacerbated mitochondrial fission by promoting dynamin-related protein 1 (Drp1) phosphorylation. Furthermore, Sirt6 mediated Drp1 phosphorylation by promoting Rho-associated coiled coil-containing protein kinase 1 (ROCK1) expression.

CONCLUSION

Our study has identified Sirt6 as a vital factor that protects against Ang II-induced mitochondrial fission and apoptosis in podocytes via the ROCK1-Drp1 signalling pathway.

New Progress in the Molecular Regulations and Therapeutic Applications in Cardiac Oxidative Damage Caused by Pressure Overload

Chronic pressure overload is a key risk factor for mortality due to its subsequent development of heart failure, in which the underlying molecular mechanisms remain vastly undetermined. In this review, we updated the latest advancements for investigating the role and relevant mechanisms of oxidative stress involved in the pathogenesis of pressure-overload-induced cardiomyopathy and cardiac dysfunction, focusing on significant biological sources of reactive oxygen species (free radical) production, antioxidant defenses, and their association with the cardiac metabolic remodeling in the stressed heart. We also summarize the newly developed preclinical therapeutic approaches in animal models for pressure-overload-induced myocardial damage. This review aims to enhance the current understanding of the mechanisms of chronic hypertensive heart failure and potentially improve the development of better therapeutic strategies for the associated diseases.

Triad role of hepcidin, ferroportin, and Nrf2 in cardiac iron metabolism: From health to disease

Iron is an essential trace element required for several vital physiological and developmental processes, including erythropoiesis, bone, and neuronal development. Iron metabolism and oxygen homeostasis are interlinked to perform a vital role in the functionality of the heart. The metabolic machinery of the heart utilizes almost 90 % of oxygen through the electron transport chain. To handle this tremendous level of oxygen, the iron metabolism in the heart is utmost crucial. Iron availability to the heart is therefore tightly regulated by (i) the hepcidin/ferroportin axis, which controls dietary iron absorption, storage, and recycling, and (ii) iron regulatory proteins 1 and 2 (IRP1/2) via hypoxia inducible factor 1 (HIF1) pathway. Despite iron being vital to the heart, recent investigations have demonstrated that iron imbalance is a common manifestation in conditions of heart failure (HF), since free iron readily transforms between Fe²⁺ and Fe³⁺via the Fenton reaction, leading to reactive oxygen species (ROS) production and oxidative damage. Therefore, to combat iron-mediated oxidative stress, targeting Nrf2/ARE antioxidant signaling is rational. The involvement of Nrf2 in regulating several genes engaged in heme synthesis, iron storage, and iron export is beginning to be uncovered. Consequently, it is possible that Nrf2/hepcidin/ferroportin might act as an epicenter connecting iron metabolism to redox alterations. However, the mechanism bridging the two remains obscure. In this review, we tried to summarize the contemporary insight of how cardiomyocytes regulate intracellular iron levels and discussed the mechanisms linking cardiac dysfunction with iron imbalance. Further, we emphasized the impact of Nrf2 on the interplay between systemic/cardiac iron control in the context of heart disease, particularly in myocardial ischemia and HF.

Neurogenic Hypertension Mediated Mitochondrial Abnormality Leads to Cardiomyopathy: Contribution of UPRmt and Norepinephrine-miR- 18a-5p-HIF-1α Axis

Aims: Hypertension increases the risk of heart disease. Hallmark features of hypertensive heart disease is sympathoexcitation and cardiac mitochondrial abnormality. However, the molecular mechanisms for specifically neurally mediated mitochondrial abnormality and subsequent cardiac dysfunction are unclear. We hypothesized that enhanced sympatho-excitation to the heart elicits cardiac miR-18a-5p/HIF-1α and mitochondrial unfolded protein response (UPRmt) signaling that lead to mitochondrial abnormalities and consequent pathological cardiac remodeling. Methods and Results: Using a model of neurogenic hypertension (NG-HTN), induced by intracerebroventricular (ICV) infusion of Ang II (NG-HTN; 20 ng/min, 14 days, 0.5 μl/h, or Saline; Control, 0.9%) through osmotic mini-pumps in Sprague-Dawley rats (250-300 g), we attempted to identify a link between sympathoexcitation (norepinephrine; NE), miRNA and HIF-1α signaling and UPRmt to produce mitochondrial abnormalities resulting in cardiomyopathy. Cardiac remodeling, mitochondrial abnormality, and miRNA/HIF-1α signaling were assessed using histology, immunocytochemistry, electron microscopy, Western blotting or RT-qPCR. NG-HTN demonstrated increased sympatho-excitation with concomitant reduction in UPRmt, miRNA-18a-5p and increased level of HIF-1α in the heart. Our in silico analysis indicated that miR-18a-5p targets HIF-1α. Direct effects of NE on miRNA/HIF-1α signaling and mitochondrial abnormality examined using H9c2 rat cardiomyocytes showed NE reduces miR-18a-5p but increases HIF-1α. Electron microscopy revealed cardiac mitochondrial abnormality in NG-HTN, linked with hypertrophic cardiomyopathy and fibrosis. Mitochondrial unfolded protein response was decreased in NG-HTN indicating mitochondrial proteinopathy and proteotoxic stress, associated with increased mito-ROS and decreased mitochondrial membrane potential (ΔΨm), and oxidative phosphorylation. Further, there was reduced cardiac mitochondrial biogenesis and fusion, but increased mitochondrial fission, coupled with mitochondrial impaired TIM-TOM transport and UPRmt. Direct effects of NE on H9c2 rat cardiomyocytes also showed cardiomyocyte hypertrophy, increased mitochondrial ROS generation, and UPRmt corroborating the in vivo data. Conclusion: In conclusion, enhanced sympatho-excitation suppress miR-18a-5p/HIF-1α signaling and increased mitochondrial stress proteotoxicity, decreased UPRmt leading to decreased mitochondrial dynamics/OXPHOS/ΔΨm and ROS generation. Taken together, these results suggest that ROS induced mitochondrial transition pore opening activates pro-hypertrophy/fibrosis/inflammatory factors that induce pathological cardiac hypertrophy and fibrosis commonly observed in NG-HTN.

Quercetin Attenuates Cardiac Hypertrophy by Inhibiting Mitochondrial Dysfunction Through SIRT3/PARP-1 Pathway

Cardiac hypertrophy is an important characteristic in the development of hypertensive heart disease. Mitochondrial dysfunction plays an important role in the pathology of cardiac hypertrophy. Recent studies have shown that sirtuin 3 (SIRT3)/poly (ADP-ribose) polymerase-1 (PARP-1) pathway modulation inhibits cardiac hypertrophy. Quercetin, a natural flavonol agent, has been reported to attenuate cardiac hypertrophy. However, the molecular mechanism is not completely elucidated. In this study, we aimed to explore the mechanism underlying the protective effect of quercetin on cardiac hypertrophy. Spontaneously hypertensive rats (SHRs) were treated with quercetin (20 mg/kg/d) for 8 weeks to evaluate the effects of quercetin on blood pressure and cardiac hypertrophy. Additionally, the mitochondrial protective effect of quercetin was assessed in H9c2 cells treated with Ang II. SHRs displayed aggravated cardiac hypertrophy and fibrosis, which were attenuated by quercetin treatment. Quercetin also improved cardiac function, reduced mitochondrial superoxide and protected mitochondrial structure in vivo. In vitro, Ang II increased the mRNA level of hypertrophic markers including atrial natriuretic factor (ANF) and β-myosin heavy chain (β-MHC), whereas quercetin ameliorated this hypertrophic response. Moreover, quercetin prevented mitochondrial function against Ang II induction. Importantly, mitochondrial protection and PARP-1 inhibition by quercetin were partly abolished after SIRT3 knockdown. Our results suggested that quercetin protected mitochondrial function by modulating SIRT3/PARP-1 pathway, contributing to the inhibition of cardiac hypertrophy.

Neuropeptide Y Induces Cardiomyocyte Hypertrophy via Attenuating miR-29a-3p in Neonatal Rat Cardiomyocytes

BACKGROUND

Neuropeptide Y (NPY) has been well known to induce Cardiomyocyte Hypertrophy (CH), which is possibly caused by disruption of cardiac cell energy balance. As mitochondria is losely related to energy metabolism, in this study, we investigated the changes in mitochondrial Dynamics-related protein (Drp1) expression under the action of NPY. miRNA-29a, a endogenous noncoding small molecule RNA which is involved in many cardiac diseases, by using a bioinformatics tool, we found a potential binding site of miRNA-29a on the Drp1 mRNA, and suggesting that miRNA-29a might play a regulatory role.

OBJECTIVE

To investigate the role of miR-29a-3p in the process of NPY-induced CH, and further explore it's predicted relationship with Drp1.

METHODS

The expression levels of miR-29a-3p and Atrial Natriuretic Peptide (ANP) were performed by the method of fluorescence quantitative PCR, in addition, expression of Drp1 in treated and control groups were performed by western blot analysis.] Results: We found NPY leads to the CH and up-regulation of ANP expression levels. We also found significant up-regulation of Drp1 expression and down-regulation of miR-29a-3p expression in NPY-treated cells. The decrease in miR-29a-3p expression may lead the increase expression level of Drp1. We found that the expression of ANP increased after NPY treatment. When Drp1 protein was silenced, the high expression of ANP was inhibited.

CONCLUSION

In this study, we found up-regulation of Drp1 in cells treated with NPY. Drp1 mRNA is a predicted target for miR-29a-3p, and the expression of Drp1 was attenuated by miR-29a-3p. Therefore, NPY leads to down-regulation of miR-29a-3p expression, up-regulation of Drp1 expression, and NPY leads to CH. Correspondingly, miR-29a-3p can counteract the effects of NPY. This may be a new way, which could be used in diagnosis and treatment plan for CH.

The mitochondrial iron transporter ABCB7 is required for B cell development, proliferation, and class switch recombination in mice

Iron-sulfur (Fe-S) clusters are cofactors essential for the activity of numerous enzymes including DNA polymerases, helicases, and glycosylases. They are synthesized in the mitochondria as Fe-S intermediates and are exported to the cytoplasm for maturation by the mitochondrial transporter ABCB7. Here, we demonstrate that ABCB7 is required for bone marrow B cell development, proliferation, and class switch recombination, but is dispensable for peripheral B cell homeostasis in mice. Conditional deletion of ABCB7 using Mb1-cre resulted in a severe block in bone marrow B cell development at the pro-B cell stage. The loss of ABCB7 did not alter expression of transcription factors required for B cell specification or commitment. While increased intracellular iron was observed in ABCB7-deficient pro-B cells, this did not lead to increased cellular or mitochondrial reactive oxygen species, ferroptosis, or apoptosis. Interestingly, loss of ABCB7 led to replication-induced DNA damage in pro-B cells, independent of VDJ recombination, and these cells had evidence of slowed DNA replication. Stimulated ABCB7-deficient splenic B cells from CD23-cre mice also had a striking loss of proliferation and a defect in class switching. Thus, ABCB7 is essential for early B cell development, proliferation, and class switch recombination.

Mechanisms controlling bacterial infection in myeloid cells under hypoxic conditions

Various factors of the tissue microenvironment such as the oxygen concentration influence the host-pathogen interaction. During the past decade, hypoxia-driven signaling via hypoxia-inducible factors (HIF) has emerged as an important factor that affects both the pathogen and the host. In this chapter, we will review the current knowledge of this complex interplay, with a particular emphasis given to the impact of hypoxia and HIF on the inflammatory and antimicrobial activity of myeloid cells, the bacterial responses to hypoxia and the containment of bacterial infections under oxygen-limited conditions. We will also summarize how low oxygen concentrations influence the metabolism of neutrophils, macrophages and dendritic cells. Finally, we will discuss the consequences of hypoxia and HIFα activation for the invading pathogen, with a focus on Pseudomonas aeruginosa, Mycobacterium tuberculosis, Coxiella burnetii, Salmonella enterica and Staphylococcus aureus. This includes a description of the mechanisms and microbial factors, which the pathogens use to sense and react to hypoxic conditions.

Mitochondrial diseases: expanding the diagnosis in the era of genetic testing

Mitochondrial diseases are clinically and genetically heterogeneous. These diseases were initially described a little over three decades ago. Limited diagnostic tools created disease descriptions based on clinical, biochemical analytes, neuroimaging, and muscle biopsy findings. This diagnostic mechanism continued to evolve detection of inherited oxidative phosphorylation disorders and expanded discovery of mitochondrial physiology over the next two decades. Limited genetic testing hampered the definitive diagnostic identification and breadth of diseases. Over the last decade, the development and incorporation of massive parallel sequencing has identified approximately 300 genes involved in mitochondrial disease. Gene testing has enlarged our understanding of how genetic defects lead to cellular dysfunction and disease. These findings have expanded the understanding of how mechanisms of mitochondrial physiology can induce dysfunction and disease, but the complete collection of disease-causing gene variants remains incomplete. This article reviews the developments in disease gene discovery and the incorporation of gene findings with mitochondrial physiology. This understanding is critical to the development of targeted therapies.

Complex Mitochondrial Dysfunction Induced by TPP+-Gentisic Acid and Mitochondrial Translation Inhibition by Doxycycline Evokes Synergistic Lethality in Breast Cancer Cells

The mitochondrion has emerged as a promising therapeutic target for novel cancer treatments because of its essential role in tumorigenesis and resistance to chemotherapy. Previously, we described a natural compound, 10-((2,5-dihydroxybenzoyl)oxy)decyl) triphenylphosphonium bromide (GA-TPP⁺C₁₀), with a hydroquinone scaffold that selectively targets the mitochondria of breast cancer (BC) cells by binding to the triphenylphosphonium group as a chemical chaperone; however, the mechanism of action remains unclear. In this work, we showed that GA-TPP⁺C₁₀ causes time-dependent complex inhibition of the mitochondrial bioenergetics of BC cells, characterized by (1) an initial phase of mitochondrial uptake with an uncoupling effect of oxidative phosphorylation, as previously reported, (2) inhibition of Complex I-dependent respiration, and (3) a late phase of mitochondrial accumulation with inhibition of α-ketoglutarate dehydrogenase complex (αKGDHC) activity. These events led to cell cycle arrest in the G1 phase and cell death at 24 and 48 h of exposure, and the cells were rescued by the addition of the cell-penetrating metabolic intermediates l-aspartic acid β-methyl ester (mAsp) and dimethyl α-ketoglutarate (dm-KG). In addition, this unexpected blocking of mitochondrial function triggered metabolic remodeling toward glycolysis, AMPK activation, increased expression of proliferator-activated receptor gamma coactivator 1-alpha (pgc1α) and electron transport chain (ETC) component-related genes encoded by mitochondrial DNA and downregulation of the uncoupling proteins ucp3 and ucp4, suggesting an AMPK-dependent prosurvival adaptive response in cancer cells. Consistent with this finding, we showed that inhibition of mitochondrial translation with doxycycline, a broad-spectrum antibiotic that inhibits the 28 S subunit of the mitochondrial ribosome, in the presence of GA-TPP⁺C₁₀ significantly reduces the mt-CO1 and VDAC protein levels and the FCCP-stimulated maximal electron flux and promotes selective and synergistic cytotoxic effects on BC cells at 24 h of treatment. Based on our results, we propose that this combined strategy based on blockage of the adaptive response induced by mitochondrial bioenergetic inhibition may have therapeutic relevance in BC.