Unbreak my heart: targeting mitochondrial autophagy in diabetic cardiomyopathy

Targeting autophagy in diabetic cardiomyopathy: From molecular mechanisms to pharmacotherapy

Diabetic cardiomyopathy (DCM) is a cardiac microvascular complication caused by metabolic disorders. It is characterized by myocardial remodeling and dysfunction. The pathogenesis of DCM is associated with abnormal cellular metabolism and organelle accumulation. Autophagy is thought to play a key role in the diabetic heart, and a growing body of research suggests that modulating autophagy may be a potential therapeutic strategy for DCM. Here, we have summarized the major signaling pathways involved in the regulation of autophagy in DCM, including Adenosine 5'-monophosphate-activated protein kinase (AMPK), mechanistic target of rapamycin (mTOR), Forkhead box subfamily O proteins (FOXOs), Sirtuins (SIRTs), and PTEN-inducible kinase 1 (PINK1)/Parkin. Given the significant role of autophagy in DCM, we further identified natural products and chemical drugs as regulators of autophagy in the treatment of DCM. This review may help to better understand the autophagy mechanism of drugs for DCM and promote their clinical application.

Noncoding RNAs as therapeutic targets in autophagy-related diabetic cardiomyopathy

Diabetic cardiomyopathy, a multifaceted complication of diabetes mellitus, remains a major challenge in clinical management due to its intricate pathophysiology. Emerging evidence underscores the pivotal role of autophagy dysregulation in the progression of diabetic cardiomyopathy, providing a novel avenue for therapeutic intervention. Noncoding RNAs (ncRNAs), a diverse class of regulatory molecules, have recently emerged as promising candidates for targeted therapeutic strategies. The exploration of various classes of ncRNAs, including microRNAs (miRNAs), long noncoding RNAs (lncRNAs), and circular RNAs (circRNAs) reveal their intricate regulatory networks in modulating autophagy and influencing the pathophysiological processes associated with diabetic cardiomyopathy. The nuanced understanding of the molecular mechanisms underlying ncRNA-mediated autophagic regulation offers a rationale for the development of precise and effective therapeutic interventions. Harnessing the regulatory potential of ncRNAs presents a promising frontier for the development of targeted and personalized therapeutic strategies, aiming to ameliorate the burden of diabetic cardiomyopathy in affected individuals. As research in this field advances, the identification and validation of specific ncRNA targets hold immense potential for the translation of these findings into clinically viable interventions, ultimately improving outcomes for patients with diabetic cardiomyopathy. This review encapsulates the current understanding of the intricate interplay between autophagy and diabetic cardiomyopathy, with a focus on the potential of ncRNAs as therapeutic targets.

The double burden: type 1 diabetes and heart failure-a comprehensive review

Heart failure (HF) is increasing at an alarming rate, primary due to the rising in aging, obesity and diabetes. Notably, individuals with type 1 diabetes (T1D) face a significantly elevated risk of HF, leading to more hospitalizations and increased case fatality rates. Several risk factors contribute to HF in T1D, including poor glycemic control, female gender, smoking, hypertension, elevated BMI, and albuminuria. However, early and intensive glycemic control can mitigate the long-term risk of HF in individuals with T1D. The pathophysiology of diabetes-associated HF is complex and multifactorial, and the underlying mechanisms in T1D remain incompletely elucidated. In terms of treatment, much of the evidence comes from type 2 diabetes (T2D) populations, so applying it to T1D requires caution. Sodium-glucose cotransporter 2 inhibitors have shown benefits in HF outcomes, even in non-diabetic populations. However, most of the information about HF and the evidence from cardiovascular safety trials related to glucose lowering medications refer to T2D. Glycemic control is key, but the link between hypoglycemia and HF hospitalization risk requires further study. Glycemic variability, common in T1D, is an independent HF risk factor. Technological advances offer the potential to improve glycemic control, including glycemic variability, and may play a role in preventing HF. In summary, HF in T1D is a complex challenge with unique dimensions. This review focuses on HF in individuals with T1D, exploring its epidemiology, risk factors, pathophysiology, diagnosis and treatment, which is crucial for developing tailored prevention and management strategies for this population.

Secreted frizzled-related protein 2 ameliorates diabetic cardiomyopathy by activating mitophagy

OBJECTIVES

Secreted frizzled-related protein 2 (SFRP2), a novel adipokine that used to be considered an inhibitor of the canonical Wnt pathway, may play a protective role in metabolic disorders. However, its effect on diabetic cardiomyopathy was still unclear. Accumulating evidence indicates that mitophagy can protect cardiac function in the diabetic heart. The present study aimed to explore the roles of SFRP2 on diabetic cardiomyopathy, focusing on the effects and mechanisms for regulating mitophagy.

METHODS

Wild-type H9c2 cells, Sfrp2 overexpression and knockdown H9c2 cells were exposed to a glucolipotoxic milieu. Reactive oxygen species (ROS) production, cell viability, apoptosis, mitophagy and lysosomal activity were detected. The interaction of SFRP2 with frizzled 5 (FZD5), and its effect on expression and intracellular localization of transcription factor EB (TFEB) and β-catenin were also explored. Diabetic rats and Sfrp2 overexpression diabetic rats were constructed to further document the findings from the in vitro study.

RESULTS

The expression of SFRP2 was low and mitophagy was inhibited in H9c2 cells in a glucolipotoxic milieu. Sfrp2 overexpression activated mitophagy and reduced H9c2 cells injury, whereas Sfrp2 deficiency inhibited mitophagy and worsened this injury. Consistent with the in vitro findings, Sfrp2 overexpression ameliorated the impairment in cardiac function of diabetic rats by activating mitophagy. Sfrp2 overexpression upregulated the expression of calcineurin and TFEB, but did not affect β-catenin in vitro and in vivo. The calcineurin inhibitor tacrolimus can inhibit mitophagy and worsen cell injury in Sfrp2 overexpression H9c2 cells. Furthermore, we found that FZD5 is required for the SFRP2-induced activation of the calcineurin/TFEB pathway and interacts with SFRP2 in H9c2 cells. Transfection with small interfering RNA targeting FZD5 opposed the effects of Sfrp2 overexpression on mitophagy and cell survival in a glucolipotoxic environment.

CONCLUSIONS

SFRP2 can protect the diabetic heart by interacting with FZD5 and activating the calcineurin/TFEB pathway to upregulate mitophagy in H9c2 cells.

Empagliflozin ameliorates diabetic cardiomyopathy probably via activating AMPK/PGC-1α and inhibiting the RhoA/ROCK pathway

BACKGROUND

Diabetic cardiomyopathy (DCM) increases the risk of hospitalization for heart failure (HF) and mortality in patients with diabetes mellitus. However, no specific therapy to delay the progression of DCM has been identified. Mitochondrial dysfunction, oxidative stress, inflammation, and calcium handling imbalance play a crucial role in the pathological processes of DCM, ultimately leading to cardiomyocyte apoptosis and cardiac dysfunctions. Empagliflozin, a novel glucose-lowering agent, has been confirmed to reduce the risk of hospitalization for HF in diabetic patients. Nevertheless, the molecular mechanisms by which this agent provides cardioprotection remain unclear.

AIM

To investigate the effects of empagliflozin on high glucose (HG)-induced oxidative stress and cardiomyocyte apoptosis and the underlying molecular mechanism.

METHODS

Twelve-week-old db/db mice and primary cardiomyocytes from neonatal rats stimulated with HG (30 mmol/L) were separately employed as in vivo and in vitro models. Echocardiography was used to evaluate cardiac function. Flow cytometry and TdT-mediated dUTP-biotin nick end labeling staining were used to assess apoptosis in myocardial cells. Mitochondrial function was assessed by cellular ATP levels and changes in mitochondrial membrane potential. Furthermore, intracellular reactive oxygen species production and superoxide dismutase activity were analyzed. Real-time quantitative PCR was used to analyze Bax and Bcl-2 mRNA expression. Western blot analysis was used to measure the phosphorylation of AMP-activated protein kinase (AMPK) and myosin phosphatase target subunit 1 (MYPT1), as well as the peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) and active caspase-3 protein levels.

RESULTS

In the in vivo experiment, db/db mice developed DCM. However, the treatment of db/db mice with empagliflozin (10 mg/kg/d) for 8 wk substantially enhanced cardiac function and significantly reduced myocardial apoptosis, accompanied by an increase in the phosphorylation of AMPK and PGC-1α protein levels, as well as a decrease in the phosphorylation of MYPT1 in the heart. In the in vitro experiment, the findings indicate that treatment of cardiomyocytes with empagliflozin (10 μM) or fasudil (FA) (a ROCK inhibitor, 100 μM) or overexpression of PGC-1α significantly attenuated HG-induced mitochondrial injury, oxidative stress, and cardiomyocyte apoptosis. However, the above effects were partly reversed by the addition of compound C (CC). In cells exposed to HG, empagliflozin treatment increased the protein levels of p-AMPK and PGC-1α protein while decreasing phosphorylated MYPT1 levels, and these changes were mitigated by the addition of CC. Adding FA and overexpressing PGC-1α in cells exposed to HG substantially increased PGC-1α protein levels. In addition, no sodium-glucose cotransporter (SGLT)2 protein expression was detected in cardiomyocytes.

CONCLUSION

Empagliflozin partially achieves anti-oxidative stress and anti-apoptotic effects on cardiomyocytes under HG conditions by activating AMPK/PGC-1α and suppressing of the RhoA/ROCK pathway independent of SGLT2.

Review on the protective mechanism of astragaloside IV against cardiovascular diseases

Cardiovascular disease is a global health problem. Astragaloside IV (AS-IV) is a saponin compound extracted from the roots of the Chinese herb Astragalus. Over the past few decades, AS-IV has been shown to possess various pharmacological properties. It can protect the myocardium through antioxidative stress, anti-inflammatory effects, regulation of calcium homeostasis, improvement of myocardial energy metabolism, anti-apoptosis, anti-cardiomyocyte hypertrophy, anti-myocardial fibrosis, regulation of myocardial autophagy, and improvement of myocardial microcirculation. AS-IV exerts protective effects on blood vessels. For example, it can protect vascular endothelial cells through antioxidative stress and anti-inflammatory pathways, relax blood vessels, stabilize atherosclerotic plaques, and inhibit the proliferation and migration of vascular smooth muscle cells. Thus, the bioavailability of AS-IV is low. Toxicology indicates that AS-IV is safe, but should be used cautiously in pregnant women. In this paper, we review the mechanisms of AS-IV prevention and treatment of cardiovascular diseases in recent years to provide a reference for future research and drug development.

Epigallocatechin-3-gallate attenuates myocardial fibrosis in diabetic rats by activating autophagy

Epigallocatechin-3-gallate (EGCG) possesses anti-fibrotic potential in diverse tissues; however, the molecular mechanisms underlying the impacts of EGCG on diabetes-induced myocardial fibrosis remain unclear. This present study aimed to unravel the anti-fibrotic effects of EGCG on the heart in type 2 diabetic rats and investigate its molecular mechanisms. Rats were randomly assigned to the following four groups: Normal (NOR), diabetic cardiomyopathy (DCM), DCM + 40 mg/kg EGCG, and DCM + 80 mg/kg EGCG groups. After 8 weeks of EGCG treatment, fasting blood glucose, left ventricular hemodynamic indices, heart index, and myocardial injury-related parameters were measured. Hematoxylin and eosin staining and Sirius Red staining were used to evaluate myocardial pathological alterations and collagen accumulation. The contents of myocardial hydroxyproline, collagen-I, collagen-III, transforming growth factor (TGF)-β1, matrix metalloprotease (MMP)-2, and MMP-9 were measured. The gene expression levels of myocardial TGF-β1, MMP-2, and MMP-9 were detected. Autophagic regulators, including adenosine 5'-monophosphate-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR), and autophagic markers, including microtubule-associated protein-1 light chain 3 and Beclin1 were estimated. The results indicated that diabetes significantly decreased cardiac contractile function and aggravated myocardial hypertrophy and injury. Furthermore, diabetes repressed the activation of autophagy in myocardial tissue and promoted cardiac fibrosis. Following ingestion with different doses of EGCG, myocardial contractile dysfunction, hypertrophy and injury were ameliorated; myocardial autophagy was activated, and myocardial fibrosis was alleviated in the EGCG treatment groups. In conclusion, these findings suggested that EGCG could attenuate cardiac fibrosis in type 2 diabetic rats, and its underlying mechanisms associated with activation of autophagy via modulation of the AMPK/mTOR pathway and then repression of the TGF-β/MMPs pathway.

Research progress on the relationship between autophagy and chronic complications of diabetes

Diabetes is a common metabolic disease whose hyperglycemic state can induce diverse complications and even threaten human health and life security. Currently, the treatment of diabetes is restricted to drugs that regulate blood glucose and have certain accompanying side effects. Autophagy, a research hotspot, has been proven to be involved in the occurrence and progression of the chronic complications of diabetes. Autophagy, as an essential organismal defense mechanism, refers to the wrapping of cytoplasmic proteins, broken organelles or pathogens by vesicles, which are then degraded by lysosomes to maintain the stability of the intracellular environment. Here, we review the relevant aspects of autophagy and the molecular mechanisms of autophagy in diabetic chronic complications, and further analyze the impact of improving autophagy on diabetic chronic complications, which will contribute to a new direction for further prevention and treatment of diabetic chronic complications.

Cardiomyocyte-specific knockout of ADAM17 ameliorates left ventricular remodeling and function in diabetic cardiomyopathy of mice

Angiotensin-converting enzyme 2 (ACE2) has proven beneficial in attenuating diabetic cardiomyopathy (DCM) but has been found to be a substrate of a disintegrin and metalloprotease protein-17 (ADAM17). However, whether ADAM17 plays a role in the pathogenesis and intervention of DCM is obscure. In this study, we created cardiomyocyte-specific knockout of ADAM17 (A17^α-MHCKO) mice, and left ventricular dimension, function, pathology and molecular biology were assessed in ADAM17^fl/fl control, A17^α-MHCKO control, ADAM17^fl/fl diabetic and A17^α-MHCKO diabetic mice. Both differentiated H9c2 cells and neonatal rat cardiomyocytes (NRCMs) were used to explore the molecular mechanisms underlying the effect of ADAM17 on DCM. The results showed that protein expression and activity of ADAM17 were upregulated whereas the protein expression of ACE2 was downregulated in the myocardium of diabetic mice. Cardiomyocyte-specific knockout of ADAM17 mitigated cardiac fibrosis and cardiomyocyte apoptosis and ameliorated cardiac dysfunction in mice with DCM. Bioinformatic analyses detected a number of genes enriched in metabolic pathways, in particular the AMPK signaling pathway, expressed differentially between the hearts of A17^α-MHCKO and ADAM17^fl/fl diabetic mice. The mechanism may involve activated AMPK pathway, increased autophagosome formation and improved autophagic flux, which reduced the apoptotic response in cardiomyocytes. In addition, hypoxia-inducible factor-1α (HIF-1α) might act as an upstream mediator of upregulated ADAM17 and ADAM17 might affect AMPK signaling via α1 A-adrenergic receptor (ADRA1A). These results indicated that ADAM17 activity and ACE2 shedding were enhanced in DCM, which was reversed by cardiomyocyte-specific ADAM17 knockout. Thus, inhibition of ADAM17 may provide a promising approach to the treatment of DCM.

Proposed mechanisms underlying the salutary effects of ADAM17 deficiency on diabetic cardiomyopathy. ADAM17 deficiency increases autophagosome formation and improves autophagic flux via reducing ACE2 shedding, activating AMPK pathway, and promoting TFEB nuclear translocation, which reduces the apoptotic response in cardiomyocytes and attenuates left ventricular remodeling and dysfunction in DCM of mice.

The Role of Mitochondria in Metabolic Syndrome–Associated Cardiomyopathy

With the rapid development of society, the incidence of metabolic syndrome (MS) is increasing rapidly. Evidence indicated that patients diagnosed with MS usually suffered from cardiomyopathy, called metabolic syndrome–associated cardiomyopathy (MSC). The clinical characteristics of MSC included cardiac hypertrophy and diastolic dysfunction, followed by heart failure. Despite many studies on this topic, the detailed mechanisms are not clear yet. As the center of cellular metabolism, mitochondria are crucial for maintaining heart function, while mitochondria dysfunction plays a vital role through mechanisms such as mitochondrial energy deprivation, calcium disorder, and ROS (reactive oxygen species) imbalance during the development of MSC. Accordingly, in this review, we will summarize the characteristics of MSC and especially focus on the mechanisms related to mitochondria. In addition, we will update new therapeutic strategies in this field.

Transcriptomics Coupled to Proteomics Reveals Novel Targets for the Protective Role of Spermine in Diabetic Cardiomyopathy

Background

Diabetic cardiomyopathy (DbCM) is the main complication and the cause of high mortality of diabetes. Exploring the transcriptomics and proteomics of DbCM is of great significance for understanding the biology of the disease and for guiding new therapeutic targets for the potential therapeutic effect of spermine (SPM).

Methods and Results

By using a mouse DbCM model, we analyzed the overall transcriptome and proteome of the myocardium, before/after treatment with SPM. The general state and cardiac structure and function changes of each group were also compared. Diabetes induced an increased blood glucose and serum triglyceride content, a decreased body weight, serum insulin level, and cardiac function-related indexes, accompanied by disrupted myocardial tissue morphology and ultrastructure damage. Using RNA sequencing (RNA-seq), we identified thousands of differentially expressed genes (DEGs) in DbCM with or without SPM treatment. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis demonstrated that the DEGs were significantly enriched in lipid metabolism and amino acid metabolism pathways. Specifically, quantitative real-time PCR (qRT-PCR) confirmed that SPM protected DbCM by reversing the expressions of lipid metabolism and amino acid metabolism-related genes, including Alox15, Gm13033, pla2g12a, Ptges, Pnpla2, and Acot1. To further reveal the pathogenesis of DbCM, we used proteome-based data-independent acquisition (DIA) and identified 139 differentially expressed proteins (DEPs) with 67 being upregulated and 72 being downregulated in DbCM. Venn intersection analysis showed 37 coexpressed genes and proteins in DbCM, including 29 upregulation and 8 downregulation in DbCM. In the protein-protein interaction (PPI) network constructed by the STRING database, the metabolism-related coexpressed genes and proteins, such as Acot2, Ephx2, Cyp1a1, Comt, Acox1, Hadhb, Hmgcs2, Acot1, Inmt, and Cat, can interact with the identified DEGs and DEPs.

Conclusion

The biomarkers and canonical pathways identified in this study may hold the key to understand the mechanisms of DbCM pathobiology and provide new targets for the therapeutic effect of SPM against DbCM by targeting lipid and amino acid metabolism pathways.

Inhibition of Sestrin2 overexpression in diabetic cardiomyopathy ameliorates cardiac injury via restoration of mitochondrial function

Mitochondrial dysfunction-induced apoptosis plays a crucial role in the progression of diabetic cardiomyopathy (DCM). Sestrin2 is an important oxidative stress response protein and is involved in the maintenance of mitochondrial function, especially under stress. The aim of the present study was to investigate the role of Sestrin2 in DCM and to explore the underlying mechanisms. H9c2 cardiomyocytes were induced with high glucose (HG) medium (33 mmol/l glucose) for an in vitro DCM model. C57BL/6 mice were induced for the in vivo DCM model by intraperitoneal streptozotocin injection. H9c2 cardiomyocytes were exposed to HG and infected with lentiviruses to express Sestrin2 short hairpin RNA (shRNA). The study found that cell viability and mitochondrial function were impaired while cell apoptosis and oxidative stress were increased in DCM. Sestrin2 was significantly upregulated in myocardial tissues of DCM mice and H9c2 cardiomyocytes in HG conditions. Downregulation of Sestrin2 increased cell viability, decreased cell apoptosis, and attenuated oxidative stress in H9c2 cells exposed to HG. Moreover, HG-induced mitochondrial injury was alleviated by Sestrin2 silencing. In conclusion, our finding indicated that the inhibition of enhanced Sestrin2 expression ameliorates cardiac injury in DCM, which might be largely attributed to the restoration of mitochondrial function.

Mitophagy in Diabetic Cardiomyopathy: Roles and Mechanisms

Cardiovascular disease is the leading complication of diabetes mellitus (DM), and diabetic cardiomyopathy (DCM) is a major cause of mortality in diabetic patients. Multiple pathophysiologic mechanisms, including myocardial insulin resistance, oxidative stress and inflammation, are involved in the development of DCM. Recent studies have shown that mitochondrial dysfunction makes a substantial contribution to the development of DCM. Mitophagy is a type of autophagy that takes place in dysfunctional mitochondria, and it plays a key role in mitochondrial quality control. Although the precise molecular mechanisms of mitophagy in DCM have yet to be fully clarified, recent findings imply that mitophagy improves cardiac function in the diabetic heart. However, excessive mitophagy may exacerbate myocardial damage in patients with DCM. In this review, we aim to provide a comprehensive overview of mitochondrial quality control and the dual roles of mitophagy in DCM. We also propose that a balance between mitochondrial biogenesis and mitophagy is essential for the maintenance of cellular metabolism in the diabetic heart.

Advances in Cardiotoxicity Induced by Altered Mitochondrial Dynamics and Mitophagy

Mitochondria are the most abundant organelles in cardiac cells, and are essential to maintain the normal cardiac function, which requires mitochondrial dynamics and mitophagy to ensure the stability of mitochondrial quantity and quality. When mitochondria are affected by continuous injury factors, the balance between mitochondrial dynamics and mitophagy is broken. Aging and damaged mitochondria cannot be completely removed in cardiac cells, resulting in energy supply disorder and accumulation of toxic substances in cardiac cells, resulting in cardiac damage and cardiotoxicity. This paper summarizes the specific underlying mechanisms by which various adverse factors interfere with mitochondrial dynamics and mitophagy to produce cardiotoxicity and emphasizes the crucial role of oxidative stress in mitophagy. This review aims to provide fresh ideas for the prevention and treatment of cardiotoxicity induced by altered mitochondrial dynamics and mitophagy.

S-Propargyl-Cysteine Attenuates Diabetic Cardiomyopathy in db/db Mice Through Activation of Cardiac Insulin Receptor Signaling

Background: Endogenous hydrogen sulfide (H₂S) is emerging as a key signal molecule in the development of diabetic cardiomyopathy. The aim of this study was to explore the effect and underlying mechanism of S-propargyl-cysteine (SPRC), a novel modulator of endogenous H₂S, on diabetic cardiomyopathy in db/db diabetic mice.

Methods and Results: Vehicle or SPRC were orally administered to 8-month-old male db/db mice and their wild type littermate for 12 weeks. SPRC treatment ameliorated myocardial hypertrophy, fibrosis, and cardiac systolic dysfunction assessed by histopathological examinations and echocardiography. The functional improvement by SPRC was accompanied by a reduction in myocardial lipid accumulation and ameliorated plasma lipid profiles. SPRC treatment improved glucose tolerance in db/db mice, with fasting blood glucose and peripheral insulin resistance remaining unchanged. Furthermore, insulin receptor signaling involving the phosphorylation of protein kinase B (Akt/PKB) and glycogen synthase kinase 3β (GSK3β) were elevated and activated by SPRC treatment. Primary neonatal mice cardiomyocytes were cultured to explore the mechanisms of SPRC on diabetic cardiomyopathy in vitro. Consistent with the results in vivo, SPRC not only up-regulated insulin receptor signaling pathway in cardiomyocytes in dose-dependent manner in the basal state, but also relieved the suppression of insulin receptor signaling induced by high concentrations of glucose and insulin. Furthermore, SPRC also enhanced the expression of glucose transporter 4 (GLUT4) and ³H glucose uptake in cardiomyocytes.

Conclusions: In this study, we found a novel beneficial effect of SPRC on diabetic cardiomyopathy, which was associated with activation of insulin receptor signaling. SPRC may be a promising medication for diabetic cardiomyopathy in type 2 diabetes mellitus patients.

Extracorporeal Shock Wave Enhanced Exogenous Mitochondria into Adipose-Derived Mesenchymal Stem Cells and Further Preserved Heart Function in Rat Dilated Cardiomyopathy

This study tested whether extracorporeal shock wave (ECSW) supported-exogenous mitochondria (Mito) into adipose-derived mesenchymal stem cells (ADMSCs) would preserve left-ventricular-ejection-fraction (LVEF) in doxorubicin/12 mg/kg-induced dilated cardiomyopathy (DCM) rat. Adult-male-SD rats were equally categorized into group 1 (sham-control), group 2 (DCM), group 3 (DCM + ECSW/1.5 mJ/mm² for 140 shots/week × 3 times/since day 14 after DCM induction), group 4 (DCM + ECSW/1.5 mJ/mm²/100 shots-assisted mito delivery (500 μg) into ADMSCs/1.2 × 10⁶ cells, then implanted into LV myocardium day 14 after DCM induction) and group 5 (DCM + ECSW-assisted mito delivery into ADMSCs/1.2 × 10⁶ cells, then implanted into LV, followed by ECSW/1.5 mJ/mm² for 140 shots/week × 3 times/since day 14 after DCM induction) and euthanized by day 49. Microscopic findings showed mitochondria were abundantly enhanced by ECSW into H9C2 cells. The q-PCR showed a significant increase in relative number of mitDNA in mitochondrial-transferred H9C2 cells than in control group (p < 0.01). The angiogenesis/angiogenesis factors (VEGF/SDF-1α/IG-F1) in HUVECs were significantly progressively increased by a stepwise-increased amount of ECSW energy (0.1/0.25/0.35 mJ/mm²) (all p < 0.001). The 49-day LVEF was highest in group 1 and significantly progressively increased from groups 2 to 5 (all p < 0.0001). Cardiomyocyte size/fibrosis exhibited an opposite pattern of LVEF, whereas cellular/protein levels of angiogenesis factors (VEGF/SDF-1α) in myocardium were significantly progressively increased from groups 1 to 5 (all p < 0.0001). The protein expressions of apoptotic/mitochondrial (cleaved-caspase-3/cleaved-PARP/mitochondrial-Bax/cytosolic-cytochrome-C), fibrotic (p-Smad3/TGF-ß), oxidative-stress (NOX-1/NOX-2) and pressure-overload/heart failure (BNP/ß-MHC) biomarkers exhibited an opposite pattern of LVEF among the five groups (all p < 0.0001). ECSW-assisted mitochondrial-delivery into ADMSCs plus ECSW offered an additional benefit for preserving LVEF in DCM rat.

Energy, Entropy and Quantum Tunneling of Protons and Electrons in Brain Mitochondria: Relation to Mitochondrial Impairment in Aging-Related Human Brain Diseases and Therapeutic Measures

Adult human brains consume a disproportionate amount of energy substrates (2-3% of body weight; 20-25% of total glucose and oxygen). Adenosine triphosphate (ATP) is a universal energy currency in brains and is produced by oxidative phosphorylation (OXPHOS) using ATP synthase, a nano-rotor powered by the proton gradient generated from proton-coupled electron transfer (PCET) in the multi-complex electron transport chain (ETC). ETC catalysis rates are reduced in brains from humans with neurodegenerative diseases (NDDs). Declines of ETC function in NDDs may result from combinations of nitrative stress (NS)-oxidative stress (OS) damage; mitochondrial and/or nuclear genomic mutations of ETC/OXPHOS genes; epigenetic modifications of ETC/OXPHOS genes; or defects in importation or assembly of ETC/OXPHOS proteins or complexes, respectively; or alterations in mitochondrial dynamics (fusion, fission, mitophagy). Substantial free energy is gained by direct O2-mediated oxidation of NADH. Traditional ETC mechanisms require separation between O2 and electrons flowing from NADH/FADH2 through the ETC. Quantum tunneling of electrons and much larger protons may facilitate this separation. Neuronal death may be viewed as a local increase in entropy requiring constant energy input to avoid. The ATP requirement of the brain may partially be used for avoidance of local entropy increase. Mitochondrial therapeutics seeks to correct deficiencies in ETC and OXPHOS.

BRD4 inhibition by JQ1 prevents high-fat diet-induced diabetic cardiomyopathy by activating PINK1/Parkin-mediated mitophagy in vivo

BRD4 is a member of the BET family of epigenetic regulators. Inhibition of BRD4 by the selective bromodomain inhibitor JQ1, alleviates thoracic aortic constriction-induced cardiac hypertrophy and heart failure. However, whether BRD4 inhibition by JQ1 has therapeutic effect on diabetic cardiomyopathy, a major cause of heart failure in patients with Type 2 diabetes, remains unknown. Here, we discover a novel link between BRD4 and PINK1/Parkin-mediated mitophagy during diabetic cardiomyopathy. Upregulation of BRD4 in diabetic mouse hearts inhibits PINK1/Parkin-mediated mitophagy, resulting in accumulation of damaged mitochondria and subsequent impairment of cardiac structure and function. BRD4 inhibition by JQ1 improves mitochondrial function, and repairs the cardiac structure and function of the diabetic heart. These effects depended on rewiring of the BRD4-driven transcription and repression of PINK1. Deletion of Pink1 suppresses mitophagy, exacerbates cardiomyopathy, and abrogates the therapeutic effect of JQ1 on diabetic cardiomyopathy. Our results illustrate a valid therapeutic strategy for treating diabetic cardiomyopathy by inhibition of BRD4.

Early intramyocardial implantation of exogenous mitochondria effectively preserved left ventricular function in doxorubicin-induced dilated cardiomyopathy rat

This study tested the hypothesis that early implantation of mitochondria (Mito) into left myocardium could effectively protect heart against doxorubicin/12 mg/kg-induced dilated cardiomyopathy (DCM) in rat. Adult-male SD rats (n = 18) were equally categorized into group 1 (sham control), group 2 (DCM) and group 3 [DCM + Mito (500 μg/rat intramyocardial injection by day-21 after DCM induction)] and euthanized by day 60. In vitro studies showed that exogenously-transferred Mito was abundantly identified in H9C2 cells. The q-PCR showed significant increase in relative number of mitDNA in Mito-transferred H9C2 cells than in control group (P<0.001). The mRNA-gene and protein expressions of NRF1/NRF2/Tfam/PGC-1α/ERRα/Mfn2 were significantly increased in low-dose Mito-transferred and more significantly increased in high-dose Mito-transferred H29C2 cells than in control group (all P<0.01). Day-60 left-ventricular-ejection-fraction (LVEF) was significantly lower in group 2 than in groups 1 and 3, and significantly lower in group 3 than in group 1 (P<0.0001). The ratios of lung and heart weights to tibial length and myocardial histopathological findings of fibrotic area/myocardial injured score/γ-H2AX+ cells exhibited an opposite pattern to LVEF among the three groups (all P<0.0001). The myocardial protein expressions of oxidative-stress (NOX-1/NOX-2/oxidized protein/p22phox), autophagic (beclin-1/Atg-5/ratio of CL3B-II/CL3B-I), and apoptotic/mitochondrial-damaged (cleaved-caspase-3/mitochondrial Bax/cleaved-PARP/cytosolic-cytochrome-C/DRP1/cyclophilin D1) biomarkers exhibited an opposite pattern, whereas the protein expressions of mitochondrial integrity (mitochondrial-cytochrome-C/mitochondrial-complex I/II/III/IV and Mfn2/PGC-1) exhibited an identical pattern to LVEF among the groups (all P<0.001). In conclusion, early Mito therapy effectively preserved LVEF and myocardial integrity in DCM rat.

Silencing of peroxisome proliferator-activated receptor-alpha alleviates myocardial injury in diabetic cardiomyopathy by downregulating 3-hydroxy-3-methylglutaryl-coenzyme A synthase 2 expression

Diabetic cardiomyopathy (DCM) is a cardiac disorder, which affects around 12% diabetic patients, resulting in overt heart death. Our initial bioinformatic analysis identified the differentially expressed gene 3-hydroxy-3-methylglutaryl-coenzyme A synthase 2 (HMGCS2) in DCM, which may be activated by peroxisome proliferator-activated receptor-alpha (PPARα) based on previous evidence. Therefore, the present study aims to explore the effect of PPARα on the development of DCM through regulating HMGCS2. The expression of PPARα and HMGCS2 was detected by reverse transcription quantitative polymerase chain reaction in cardiomyocytes and high-glucose-cultured cardiomyocytes. The proliferation and apoptosis of cardiomyocytes were examined by 5-ethynyl-2'-deoxyuridine assay and flow cytometry, separately. Mitoehondrial membrane potential (MMP) and intracellular reactive oxygen species (ROS) levels were determined. Then, the protein levels of B-cell lymphoma 2, Bcl-2-associated X protein, and cleaved Caspase-3 were detected by Western blot analysis. The myocardial apoptosis index, heart weight, and serum lipids of rats were examined. At last, the expressions of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), transforming growth factor β1 (TGFβ1), peroxisome proliferator activator receptor gamma coactivator-1 alpha (PGC1α), nuclear respiratory factor (NRF)-1, NRF-2, NAD(P)H oxidase 1, and superoxide dismutase-1 were examined. HMGCS2 was the most differentially expressed gene in DCM. The levels of HMGCS2 and PPARα were upregulated in patients with DCM. HMGCS2 silencing was shown to inhibit HMGCS2 expression to suppress the apoptosis of high-glucose-induced cardiomyocytes and the loss of MMP, reduce the accumulation of ROS, and promote cardiomyocyte proliferation. Silencing of HMGCS2 and PPARα alleviated myocardial injury, decreased blood glucose, and lipid in DCM rats, downregulated the expression of ANP, BNP, and TGFβ1 to reduce myocardial injury, and elevated PGC1α, NRF-1, and NRF-2 levels to enhance oxidative stress levels. Our results demonstrated that silencing of PPARα could alleviate cardiomyocyte injury and oxidative stress via a mechanism related to the downregulation of HMGCS2, which could provide a novel target for DCM treatment.

Increasing Fatty Acid Oxidation Prevents High-Fat Diet-Induced Cardiomyopathy Through Regulating Parkin-Mediated Mitophagy

BACKGROUND

Increased fatty acid oxidation (FAO) has long been considered a culprit in the development of obesity/diabetes mellitus-induced cardiomyopathy. However, enhancing cardiac FAO by removing the inhibitory mechanism of long-chain fatty acid transport into mitochondria via deletion of acetyl coenzyme A carboxylase 2 (ACC2) does not cause cardiomyopathy in nonobese mice, suggesting that high FAO is distinct from cardiac lipotoxicity. We hypothesize that cardiac pathology-associated obesity is attributable to the imbalance of fatty acid supply and oxidation. Thus, we here seek to determine whether further increasing FAO by inducing ACC2 deletion prevents obesity-induced cardiomyopathy, and if so, to elucidate the underlying mechanisms.

METHODS

We induced high FAO in adult mouse hearts by cardiac-specific deletion of ACC2 using a tamoxifen-inducible model (ACC2 iKO). Control and ACC2 iKO mice were subjected to high-fat diet (HFD) feeding for 24 weeks to induce obesity. Cardiac function, mitochondria function, and mitophagy activity were examined.

RESULTS

Despite both control and ACC2 iKO mice exhibiting a similar obese phenotype, increasing FAO oxidation by deletion of ACC2 prevented HFD-induced cardiac dysfunction, pathological remodeling, and mitochondria dysfunction, as well. Similarly, increasing FAO by knockdown of ACC2 prevented palmitate-induced mitochondria dysfunction and cardiomyocyte death in vitro. Furthermore, HFD suppressed mitophagy activity and caused damaged mitochondria to accumulate in the heart, which was attenuated, in part, in the ACC2 iKO heart. Mechanistically, ACC2 iKO prevented HFD-induced downregulation of parkin. During stimulation for mitophagy, mitochondria-localized parkin was severely reduced in control HFD-fed mouse heart, which was restored, in part, in ACC2 iKO HFD-fed mice.

CONCLUSIONS

These data show that increasing cardiac FAO alone does not cause cardiac dysfunction, but protects against cardiomyopathy in chronically obese mice. The beneficial effect of enhancing cardiac FAO in HFD-induced obesity is mediated, in part, by the maintenance of mitochondria function through regulating parkin-mediated mitophagy. Our findings also suggest that targeting the parkin-dependent mitophagy pathway could be an effective strategy against the development of obesity-induced cardiomyopathy.

Mechanisms underlying diabetic cardiomyopathy: From pathophysiology to novel therapeutic targets

Diabetic cardiomyopathy (DC) is defined as a clinical condition of cardiac dysfunction that occurs in the absence of coronary atherosclerosis, valvular disease, and hypertension in patients with diabetes mellitus (DM). Despite the increasing worldwide prevalence of DC, due to the global epidemic of DM, the underlying pathophysiology of DC has not been fully elucidated. In addition, the clinical criteria for diagnosing DC have not been established, and specific therapeutic options are not currently available. The current paradigm suggests the impaired cardiomyocyte function arises due to a number of DM-related metabolic disturbances including hyperglycemia, hyperinsulinemia, and hyperlipidemia, which lead to diastolic dysfunction and signs and symptoms of heart failure. Other factors, which have been implicated in the progression of DC, include mitochondrial dysfunction, increased oxidative stress, impaired calcium handling, inflammation, and cardiomyocyte apoptosis. Herein, we review the current theories surrounding the occurrence and progression of DC, and discuss the recent advances in diagnostic methodologies and therapeutic strategies. Moreover, apart from conventional animal DC models, we highlight alternative disease models for studying DC such as the use of patient-derived human induced pluripotent stem cells (hiPSCs) for studying the mechanisms underlying DC. The ability to obtain hiPSC-derived cardiomyocytes from DM patients with a DC phenotype could help identify novel therapeutic targets for preventing and delaying the progression of DC, and for improving clinical outcomes in DM patients.

Astragaloside-IV protects H9C2(2-1) cardiomyocytes from high glucose-induced injury via miR-34a-mediated autophagy pathway

Diabetic cardiomyopathy (DCM) is an important cardiac disorder in patients with diabetes. High glucose (HG) levels lead to inflammation of cardiomyocytes, oxidative stress, and long-term activation of autophagy, resulting in myocardial fibrosis and remodelling. Astragaloside-IV (AS-IV) has a wide range of pharmacological effects. This study aimed to investigate the effects of AS-IV on injury induced by HG in rat cardiomyocytes (H9C2(2-1)) and the involvement of the miR-34a-mediated autophagy pathway. An AS-IV concentration of 100 μM was selected based on H9C2(2-1) cell viability using the cell counting kit-8 (CCK-8). We found that 33 mM HG induced a morphologic change in cells and caused excessive oxidative stress, whereas AS-IV inhibited lipid peroxidation and increased superoxide dismutase activity. In terms of mRNA expression, HG increased miR-34a and inhibited Bcl2 and Sirt1, whereas AS-IV and miR-34a-inhibitor reversed the above effects. Further, LC3-GFP adenovirus infection and western blotting showed that HG increased autophagy, which was reversed synergistically by AS-IV and miR-34a-inhibitor. Bcl2 and pAKT/AKT protein expressions in the HG group was significantly lower than that in controls, but AS-IV and miR-34a-inhibitor antagonized the process. Thus, AS-IV inhibits HG-induced oxidative stress and autophagy and protects cardiomyocytes from injury via the miR-34a/Bcl2/(LC3II/LC3I) and pAKT/Bcl2/(LC3II/LC3I) pathways.

Heart Failure in Type 2 Diabetes Mellitus

Patients with diabetes mellitus have >2× the risk for developing heart failure (HF; HF with reduced ejection fraction and HF with preserved ejection fraction). Cardiovascular outcomes, hospitalization, and prognosis are worse for patients with diabetes mellitus relative to those without. Beyond the structural and functional changes that characterize diabetic cardiomyopathy, a complex underlying, and interrelated pathophysiology exists. Despite the success of many commonly used antihyperglycemic therapies to lower hyperglycemia in type 2 diabetes mellitus the high prevalence of HF persists. This, therefore, raises the possibility that additional factors beyond glycemia might contribute to the increased HF risk in diabetes mellitus. This review summarizes the state of knowledge about the impact of existing antihyperglycemic therapies on HF and discusses potential mechanisms for beneficial or deleterious effects. Second, we review currently approved pharmacological therapies for HF and review evidence that addresses their efficacy in the context of diabetes mellitus. Dysregulation of many cellular mechanisms in multiple models of diabetic cardiomyopathy and in human hearts have been described. These include oxidative stress, inflammation, endoplasmic reticulum stress, aberrant insulin signaling, accumulation of advanced glycated end-products, altered autophagy, changes in myocardial substrate metabolism and mitochondrial bioenergetics, lipotoxicity, and altered signal transduction such as GRK (g-protein receptor kinase) signaling, renin angiotensin aldosterone signaling and β-2 adrenergic receptor signaling. These pathophysiological pathways might be amenable to pharmacological therapy to reduce the risk of HF in the context of type 2 diabetes mellitus. Successful targeting of these pathways could alter the prognosis and risk of HF beyond what is currently achieved using existing antihyperglycemic and HF therapeutics.

Emerging role of mitophagy in cardiovascular physiology and pathology

Healthy mitochondrial function is imperative for most tissues, but especially those with a high energy demand. Robust evidence linking mitochondrial dysfunction with cardiovascular disease has demonstrated that mitochondrial activity is highly relevant to cardiac muscle performance. Mitochondrial homeostasis is maintained through coordination among the processes that comprise the so-called mitochondrial dynamics machinery. The most-studied elements of cardiac mitochondrial dynamics are mitochondrial fission and fusion, biogenesis and degradation. Selective autophagic removal of mitochondria (mitophagy) is essential for clearing away defective mitochondria but can lead to cell damage and death if not tightly controlled. In cardiovascular cells such as cardiomyocytes and cardiac fibroblasts, mitophagy is involved in metabolic activity, cell differentiation, apoptosis and other physiological processes related to major phenotypic changes. Modulation of mitophagy has detrimental and/or beneficial outcomes in various cardiovascular diseases, suggesting that a deeper understanding of the mechanisms underlying mitochondrial degradation in the heart could provide valuable clinical insights. Here, we discuss current evidence supporting the role of mitophagy in cardiac pathophysiology, with an emphasis on different research models and their interpretations; basic concepts related to this selective autophagy; and the most commonly used experimental approaches for studying this mechanism. Finally, we provide a comprehensive literature analysis on the role of mitophagy in heart failure, ischemia/reperfusion, diabetic cardiomyopathy and other cardiovascular diseases, as well as its potential biomedical applications.

Myocardial Energy Stress, Autophagy Induction, and Cardiomyocyte Functional Responses

Significance: Energy stress in the myocardium occurs in a variety of acute and chronic pathophysiological contexts, including ischemia, nutrient deprivation, and diabetic disease settings of substrate disturbance. Although the heart is highly adaptive and flexible in relation to fuel utilization and routes of adenosine-5'-triphosphate (ATP) generation, maladaptations in energy stress situations confer functional deficit. An understanding of the mechanisms that link energy stress to impaired myocardial performance is crucial. Recent Advances: Emerging evidence suggests that, in parallel with regulated enzymatic pathways that control intracellular substrate supply, other processes of "bulk" autophagic macromolecular breakdown may be important in energy stress conditions. Recent findings indicate that cargo-specific autophagic activity may be important in different stress states. In particular, induction of glycophagy, a glycogen-specific autophagy, has been described in acute and chronic energy stress situations. The impact of elevated cardiomyocyte glucose flux relating to glycophagy dysregulation on contractile function is unknown. Critical Issues: Ischemia- and diabetes-related cardiac adverse events comprise the majority of cardiovascular disease morbidity and mortality. Current therapies involve management of systemic comorbidities. Cardiac-specific adjunct treatments targeted to manage myocardial energy stress responses are lacking. Future Directions: New knowledge is required to understand the mechanisms involved in selective recruitment of autophagic responses in the cardiomyocyte energy stress response. In particular, exploration of the links between cell substrate flux, calcium ion (Ca²⁺) flux, and phagosomal cargo flux is required. Strategies to target specific fuel "bulk" management defects in cardiac energy stress states may be of therapeutic value.

SESN2 protects against doxorubicin-induced cardiomyopathy via rescuing mitophagy and improving mitochondrial function

The clinical application of doxorubicin (Dox) in cancer therapy is limited by its serious cardiotoxicity. Our previous studies and others have recognized that mitochondrial dysfunction is the common feature of Dox-induced cardiotoxicity. However, mechanisms underlying mitochondrial disorders remained largely unknown. SESN2, a highly conserved and stress-inducible protein, is involved in mitochondrial function and autophagy in cardiovascular diseases. This study aimed to investigate whether SESN2 affects Dox-induced cardiotoxicity and the underlying mechanisms. Sprague-Dawley rats and neonatal rat cardiomyocytes were treated with Dox. SESN2 expression was assessed. The effects of SESN2 on Dox-induced cardiotoxicity were assessed by functional gain and loss experiments. Echocardiographic parameters, morphological and histological analyses, transmission electron microscope and immunofluorescence assays were used to assess cardiac and mitochondrial function. The protein expression of SESN2 was significantly reduced following Dox stimulation. Both knockout of SESN2 by sgRNA and Dox treatment resulted in the inhibition of Parkin-mediated mitophagy, marked cardiomyocytes apoptosis and mitochondria dysfunction. Ectopic expression of SESN2 effectively protected against Dox-induced cardiomyocyte apoptosis, mitochondrial injury and cardiac dysfunction. Mechanistically, SESN2 interacted with Parkin and p62, promoted accumulation of Parkin to mitochondria and then alleviated Dox-caused inhibition of Parkin mediated mitophagy. Ultimately, the clearance of damaged mitochondria and mitochondrial function were improved following SESN2 overexpression. SESN2 protected against Dox-induced cardiotoxicity through improving mitochondria function and mitophagy. These results established SESN2 as a key player in mitochondrial function and provided a potential therapeutic approach to Dox-induced cardiomyopathy.

LncRNA DCRF regulates cardiomyocyte autophagy by targeting miR-551b-5p in diabetic cardiomyopathy

Background: We generated a rat model of diabetic cardiomyopathy (DCM) and reported significant upregulation of the long non-coding RNA DCRF. This study was designed to determine the molecular mechanisms of DCRF in the development of DCM. Methods: Real-time PCR and RNA fluorescent in situ hybridization were conducted to detect the expression pattern of DCRF in cardiomyocytes. Histological and echocardiographic analyses were used to assess the effect of DCRF knockdown on cardiac structure and function in diabetic rats. mRFP-GFP-LC3 fluorescence microscopy, transmission electron microscopy, and Western blotting were carried out to determine cardiomyocyte autophagy. RNA immunoprecipitation and luciferase reporter assays were performed to elucidate the regulatory role of DCRF/miR-551b-5p/PCDH17 pathway in cardiomyocyte autophagy. Results: Our findings showed that DCRF knockdown reduced cardiomyocyte autophagy, attenuated myocardial fibrosis, and improved cardiac function in diabetic rats. High glucose increased DCRF expression and induced autophagy in cardiomyocytes. RNA immunoprecipitation and luciferase reporter assays indicated that DCRF was targeted by miR-551b-5p in an AGO2-dependent manner and PCDH17 was the direct target of miR-551b-5p. Forced expression of DCRF was found to attenuate the inhibitory effect of miR-551b-5p on PCDH17. Furthermore, DCRF knockdown decreased PCDH17 expression and suppressed autophagy in cardiomyocytes treated with high glucose. Conclusion: Our study suggests that DCRF can act as a competing endogenous RNA to increase PCDH17 expression by sponging miR-551b-5p, thus contributing to increased cardiomyocyte autophagy in DCM.

Regulation of autophagy by tea polyphenols in diabetic cardiomyopathy

OBJECTIVE

To investigate the effect of tea polyphenols on cardiac function in rats with diabetic cardiomyopathy, and the mechanism by which tea polyphenols regulate autophagy in diabetic cardiomyopathy.

METHODS

Sixty Sprague-Dawley (SD) rats were randomly divided into six groups: a normal control group (NC), an obesity group (OB), a diabetic cardiomyopathy group (DCM), a tea polyphenol group (TP), an obesity tea polyphenol treatment group (OB-TP), and a diabetic cardiomyopathy tea polyphenol treatment group (DCM-TP). After successful modeling, serum glucose, cholesterol, and triglyceride levels were determined; cardiac structure and function were inspected by ultrasonic cardiography; myocardial pathology was examined by staining with hematoxylin-eosin; transmission electron microscopy was used to observe the morphology and quantity of autophagosomes; and expression levels of autophagy-related proteins LC3-II, SQSTM1/p62, and Beclin-1 were determined by Western blotting.

RESULTS

Compared to the NC group, the OB group had normal blood glucose and a high level of blood lipids; both blood glucose and lipids were increased in the DCM group; ultrasonic cardiograms showed that the fraction shortening was reduced in the DCM group. However, these were improved significantly in the DCM-TP group. Hematoxylin-eosin staining showed disordered cardiomyocytes and hypertrophy in the DCM group; however, no differences were found among the remaining groups. Transmission electron microscopy revealed that the numbers of autophagosomes in the DCM and OB-TP groups were obviously increased compared to the NC and OB groups; the number of autophagosomes in the DCM-TP group was reduced. Western blotting showed that the expression of LC3-II/I and Beclin-1 increased obviously, whereas the expression of SQSTM1/p62 was decreased in the DCM and OB-TP groups (P<0.05).

CONCLUSIONS

Tea polyphenols had an effect on diabetic cardiomyopathy in rat cardiac function and may alter the levels of autophagy to improve glucose and lipid metabolism in diabetes.

Mitophagy in hepatocytes: Types, initiators and role in adaptive ethanol metabolism☆

Mitophagy (mitochondrial autophagy) in hepatocytes is an essential quality control mechanism that removes for lysosomal digestion damaged, effete and superfluous mitochondria. Mitophagy has distinct variants. In type 1 mitophagy, typical of nutrient deprivation, cup-shaped sequestration membranes (phagophores) grow, surround and sequester individual mitochondria into mitophagosomes, often in coordination with mitochondrial fission. After sequestration, the outer compartment of the mitophagosome acidifies and the entrapped mitochondrion depolarizes, followed by fusion with lysosomes. By contrast, mitochondrial depolarization stimulates type 2 mitophagy, which is characterized by coalescence of autophagic microtubule-associated protein 1A/1B-light chain 3 (LC3)-containing structures on mitochondrial surfaces without the formation of a phagophore or mitochondrial fission. Oppositely to type 1 mitophagy, the inhibition of phosphoinositide-3-kinase (PI3K) does not block type 2 mitophagy. In type 3 mitophagy, or micromitophagy, mitochondria-derived vesicles (MDVs) enriched in oxidized proteins bud off from mitochondrial inner and outer membranes and incorporate into multivesicular bodies by vesicle scission into the lumen. In response to ethanol feeding, widespread ethanol-induced hepatocellular mitochondrial depolarization occurs to facilitate hepatic ethanol metabolism. As a consequence, type 2 mitophagy develops in response to the mitochondrial depolarization. After chronic high ethanol feeding, processing of depolarized mitochondria by mitophagy becomes compromised, leading to release of mitochondrial damage-associated molecular patterns (mtDAMPs) that promote inflammatory and profibrogenic responses. We propose that the persistence of mitochondrial responses for acute ethanol metabolism links initial adaptive ethanol metabolism to mitophagy and then to chronic maladaptive changes initiating onset and the progression of alcoholic liver disease (ALD).

Melatonin activates Parkin translocation and rescues the impaired mitophagy activity of diabetic cardiomyopathy through Mst1 inhibition

Mitophagy eliminates dysfunctional mitochondria and thus plays a cardinal role in diabetic cardiomyopathy (DCM). We observed the favourable effects of melatonin on cardiomyocyte mitophagy in mice with DCM and elucidated their underlying mechanisms. Electron microscopy and flow cytometric analysis revealed that melatonin reduced the number of impaired mitochondria in the diabetic heart. Other than decreasing mitochondrial biogenesis, melatonin increased the clearance of dysfunctional mitochondria in mice with DCM. Melatonin increased LC3 II expression as well as the colocalization of mitochondria and lysosomes in HG‐treated cardiomyocytes and the number of typical autophagosomes engulfing mitochondria in the DCM heart. These results indicated that melatonin promoted mitophagy. When probing the mechanism, increased Parkin translocation to the mitochondria may be responsible for the up‐regulated mitophagy exerted by melatonin. Parkin knockout counteracted the beneficial effects of melatonin on the cardiac mitochondrial morphology and bioenergetic disorders, thus abolishing the substantial effects of melatonin on cardiac remodelling with DCM. Furthermore, melatonin inhibited Mammalian sterile 20‐like kinase 1 (Mst1) phosphorylation, thus enhancing Parkin‐mediated mitophagy, which contributed to mitochondrial quality control. In summary, this study confirms that melatonin rescues the impaired mitophagy activity of DCM. The underlying mechanism may be attributed to activation of Parkin translocation via inhibition of Mst1.

Proteostasis in epicardial versus subcutaneous adipose tissue in heart failure subjects with and without diabetes

BACKGROUND

Cardiovascular diseases (CVDs) are leading cause of death and primary cause of morbidity and mortality in diabetic population. Epicardial adipose tissue (EAT) covers the heart's surface and is a source of biomolecules regulating heart and blood vessel physiology. The protective activation of the unfolded protein response (UPR) and autophagy allows the cardiomyocyte reticular network to restore energy and/or nutrient homeostasis and to avoid cell death. However, an excessive or prolonged UPR activation can trigger cell death. UPR activation is an early event of diabetic cardiomyopathies and deregulated autophagy is associated with CVDs.

RESULTS

An upregulation of UPR markers (glucose-regulated protein 78 KDa, glucose-regulated protein 94 KDa, inositol-requiring enzyme 1α, protein kinase RNA-like ER kinase and CCAAT/-enhancer-binding protein homologous protein (CHOP) gene) in EAT compared to subcutaneous adipose tissue (SAT), was observed as well as the UPR-related apoptosis marker caspase-4/procaspase-4 ratio but not in CHOP protein levels. Additionally, levels of ubiquitin and ubiquitinated proteins were decreased in EAT. Moreover, upregulation of autophagy markers (5' adenosine monophosphate-activated protein kinase, mechanistic target of rapamycin, Beclin 1, microtubule-associated protein light chain 3-II, lysosome-associated membrane protein 2, and PTEN-induced putative kinase 1) was observed, as well as an increase in the apoptotic Bim but not the ratio between Bim and the anti-apoptotic Bcl-2 in EAT. Diabetic patients show alterations in UPR activation markers but not in autophagy or apoptosis markers.

CONCLUSION

UPR and autophagy are increased in EAT compared to SAT, opening doors to the identification of early biomarkers for cardiomyopathies and novel therapeutic targets.

Mitochondria and cardiovascular diseases-from pathophysiology to treatment

Mitochondria are the source of cellular energy production and are present in different types of cells. However, their function is especially important for the heart due to the high demands in energy which is achieved through oxidative phosphorylation. Mitochondria form large networks which regulate metabolism and the optimal function is achieved through the balance between mitochondrial fusion and mitochondrial fission. Moreover, mitochondrial function is upon quality control via the process of mitophagy which removes the damaged organelles. Mitochondrial dysfunction is associated with the development of numerous cardiac diseases such as atherosclerosis, ischemia-reperfusion (I/R) injury, hypertension, diabetes, cardiac hypertrophy and heart failure (HF), due to the uncontrolled production of reactive oxygen species (ROS). Therefore, early control of mitochondrial dysfunction is a crucial step in the therapy of cardiac diseases. A number of anti-oxidant molecules and medications have been used but the results are inconsistent among the studies. Eventually, the aim of future research is to design molecules which selectively target mitochondrial dysfunction and restore the capacity of cellular anti-oxidant enzymes.

LncRNA H19 inhibits autophagy by epigenetically silencing of DIRAS3 in diabetic cardiomyopathy

We previously generated a rat model of diabetic cardiomyopathy and found that the expression of long non-coding RNA H19 was downregulated. The present study was aimed to explore the pathogenic role of H19 in the development of diabetic cardiomyopathy. Overexpression of H19 in diabetic rats attenuated cardiomyocyte autophagy and improved left ventricular function. High glucose was found to reduce H19 expression and increase autophagy in cultured neonatal cardiomyocytes. The results of RNA-binding protein immunoprecipitation showed that H19 could directly bind with EZH2 in cardiomyocytes. The chromatin immunoprecipitation assays indicated that H19 knockdown could reduce EZH2 occupancy and H3K27me3 binding in the promoter of DIRAS3. In addition, overexpression of H19 was found to downregulate DIRAS3 expression, promote mTOR phosphorylation and inhibit autophagy activation in cardiomyocytes exposed to high glucose. Furthermore, we also found that high glucose increased DIRAS3 expression in cardiomyocytes and DIRAS3 induced autophagy by inhibiting mTOR signaling. In conclusion, our study suggested that H19 could inhibit autophagy in cardiomyocytes by epigenetically silencing of DIRAS3, which might provide novel insights into understanding the molecular mechanisms of diabetic cardiomyopathy.

Decreased blood glucose at admission has a prognostic impact in patients with severely decompensated acute heart failure complicated with diabetes mellitus

The prognostic impact of a decreased blood glucose level in acute heart failure (AHF) has not been sufficiently clarified. The data from 1234 AHF patients were examined in the present study. The blood glucose (BG) levels were evaluated at admission. The patients were divided into groups based on the following: with or without diabetes mellitus (DM), and BG level ≥ 200 mg/dl (elevated BG) or < 200 mg/dl (decreased BG). The elevated and decreased BG patients were further divided into another three groups: 200 mg/ml ≤ BG < 300 mg/dl (mild-elevated), 300 mg/ml ≤ BG < 400 mg/dl (moderate-elevated) and BG ≥ 400 mg/ml (severe-elevated); and 150 mg/ml ≤ BG < 200 mg/dl (mild-decreased), 100 mg/ml ≤ BG < 150 mg/dl (moderate-decreased) and BG < 100 mg/ml (severe-decreased), respectively. The DM patients had a significantly poorer mortality than the non-DM patients. The prognosis was different between patients with elevated or decreased BG. In DM patients with elevated BG, the severe-elevated patients had a significantly poorer prognosis than moderate- and mild-elevated patients. In the DM patients with decreased BG, the severe-decreased patients had a significantly poorer prognosis than those moderate- and mild-decreased patients. The multivariate Cox regression model showed that a severe-decreased [hazard ratio (HR) 3.245, 95% confidence interval (CI) 1.271-8.282] and severe-elevated (HR 2.300, 95% CI 1.143-4.628) status were independent predictors of 365-day mortality in AHF patients with DM. The mortality was high among AHF patients with DM. Furthermore, both severe hyperglycemia and hypoglycemia were independent predictors of the mortality in patients with AHF complicated with DM.

The Roles of Autophagy in Acute Lung Injury Induced by Myocardial Ischemia Reperfusion in Diabetic Rats

Patients with diabetes are vulnerable to myocardial ischemia reperfusion (IR) injury, which may also induce acute lung injury (ALI) due to overaccumulation of reactive oxygen species (ROS) and inflammation cytokine in circulation. Despite autophagy plays a significant role in diabetes and pulmonary IR injury, the role of autophagy in ALI secondary to myocardial IR in diabetes remains largely elusive. We aimed to investigate pulmonary autophagy status and its roles in oxidative stress and inflammation reaction in lung tissues from diabetic rats subjected to myocardial IR. Control or diabetic rats were either treated with or without autophagy inducer rapamycin (Rap) or autophagy inhibitor 3-methyladenine (3-MA) before myocardial IR, which was achieved by occluding the left anterior descending coronary artery for 30 min and followed by reperfusion for 120 min. Diabetic rats subjected to myocardial IR showed more serious ALI with higher lung injury score and WET/DRY ratio and lower PaO₂ as compared with control rats, accompanied with impaired autophagy indicated by reduced LC-3II/LC-3I ratio and Beclin-1 expression, decreased superoxide dismutase (SOD) activity, and increased 15-F2t-Isoprostane formation in lung tissues, as well as increased levels of leukocyte count and proinflammatory cytokines in BAL fluid. Improving autophagy with Rap significantly attenuated all these changes, but the autophagy inhibitor 3-MA exhibited adverse or opposite effects as Rap. In conclusion, diabetic lungs are more vulnerable to myocardial IR, which are involved in impaired autophagy. Improving autophagy could attenuate ALI induced by myocardial IR in diabetic rats, possibly through inhibiting inflammatory reaction and oxidative stress.

Molecular mechanisms of cardiac pathology in diabetes - Experimental insights

Diabetic cardiomyopathy is a distinct pathology independent of co-morbidities such as coronary artery disease and hypertension. Diminished glucose uptake due to impaired insulin signaling and decreased expression of glucose transporters is associated with a shift towards increased reliance on fatty acid oxidation and reduced cardiac efficiency in diabetic hearts. The cardiac metabolic profile in diabetes is influenced by disturbances in circulating glucose, insulin and fatty acids, and alterations in cardiomyocyte signaling. In this review, we focus on recent preclinical advances in understanding the molecular mechanisms of diabetic cardiomyopathy. Genetic manipulation of cardiomyocyte insulin signaling intermediates has demonstrated that partial cardiac functional rescue can be achieved by upregulation of the insulin signaling pathway in diabetic hearts. Inconsistent findings have been reported relating to the role of cardiac AMPK and β-adrenergic signaling in diabetes, and systemic administration of agents targeting these pathways appear to elicit some cardiac benefit, but whether these effects are related to direct cardiac actions is uncertain. Overload of cardiomyocyte fuel storage is evident in the diabetic heart, with accumulation of glycogen and lipid droplets. Cardiac metabolic dysregulation in diabetes has been linked with oxidative stress and autophagy disturbance, which may lead to cell death induction, fibrotic 'backfill' and cardiac dysfunction. This review examines the weight of evidence relating to the molecular mechanisms of diabetic cardiomyopathy, with a particular focus on metabolic and signaling pathways. Areas of uncertainty in the field are highlighted and important knowledge gaps for further investigation are identified. This article is part of a Special issue entitled Cardiac adaptations to obesity, diabetes and insulin resistance, edited by Professors Jan F.C. Glatz, Jason R.B. Dyck and Christine Des Rosiers.

Advanced glycation end products receptor RAGE controls myocardial dysfunction and oxidative stress in high-fat fed mice by sustaining mitochondrial dynamics and autophagy-lysosome pathway

Oxidative stress and mitochondrial dysfunction are recognized as major contributors of cardiovascular damage in diabetes and high fat diet (HFD) fed mice. Blockade of receptor for advanced glycation end products (RAGE) attenuates vascular oxidative stress and development of atherosclerosis. We tested whether HFD-induced myocardial dysfunction would be reversed in RAGE deficiency mice, in association with changes in oxidative stress damage, mitochondrial respiration, mitochondrial fission and autophagy-lysosomal pathway. Cardiac antioxidant capacity was upregulated in RAGE^-/^- mice under normal diet as evidenced by increased superoxide dismutase and sirtuin mRNA expressions. Mitochondrial fragmentation and mitochondrial fission protein Drp1 and Fis1 expressions were increased in RAGE^-/^- mice. Autophagy-related protein expressions and cathepsin-L activity were increased in RAGE^-/^- mice suggesting sustained autophagy-lysosomal flux. HFD induced mitochondrial respiration defects, cardiac contractile dysfunction, disrupted mitochondrial dynamics and autophagy inhibition, which were partially prevented in RAGE^-/^- mice. Our results suggest that cardioprotection against HFD in RAGE^-/^- mice include reactivation of autophagy, as inhibition of autophagic flux by chloroquine fully abrogated beneficial myocardial effects and its stimulation by rapamycin improved myocardial function in HFD wild type mice. As mitochondrial fission is necessary to mitophagy, increased fragmentation of mitochondrial network in HFD RAGE^-/^- mice may have facilitated removal of damaged mitochondria leading to better mitochondrial quality control. In conclusion, modulation of RAGE pathway may improve mitochondrial damage and myocardial dysfunction in HFD mice. Attenuation of cardiac oxidative stress and maintenance of healthy mitochondria population ensuring adequate energy supply may be involved in myocardial protection against HFD.

Restoring diabetes-induced autophagic flux arrest in ischemic/reperfused heart by ADIPOR (adiponectin receptor) activation involves both AMPK-dependent and AMPK-independent signaling

Macroautophagy/autophagy is increasingly recognized as an important regulator of myocardial ischemia-reperfusion (MI-R) injury. However, whether and how diabetes may alter autophagy in response to MI-R remains unknown. Deficiency of ADIPOQ, a cardioprotective molecule, markedly increases MI-R injury. However, the role of diabetic hypoadiponectinemia in cardiac autophagy alteration after MI-R is unclear. Utilizing normal control (NC), high-fat-diet-induced diabetes, and Adipoq knockout (adipoq^-/-) mice, we demonstrated that autophagosome formation was modestly inhibited and autophagosome clearance was markedly impaired in the diabetic heart subjected to MI-R. adipoq^-/- largely reproduced the phenotypic alterations observed in the ischemic-reperfused diabetic heart. Treatment of diabetic and adipoq^-/- mice with AdipoRon, a novel ADIPOR (adiponectin receptor) agonist, stimulated autophagosome formation, markedly increased autophagosome clearance, reduced infarct size, and improved cardiac function (P < 0.01 vs vehicle). Mechanistically, AdipoRon caused significant phosphorylation of AMPK-BECN1 (Ser93/Thr119)-class III PtdIns3K (Ser164) and enhanced lysosome protein LAMP2 expression both in vivo and in isolated adult cardiomyocytes. Pharmacological AMPK inhibition or genetic Prkaa2 mutation abolished AdipoRon-induced BECN1 (Ser93/Thr119)-PtdIns3K (Ser164) phosphorylation and AdipoRon-stimulated autophagosome formation. However, AdipoRon-induced LAMP2 expression, AdipoRon-stimulated autophagosome clearance, and AdipoRon-suppressed superoxide generation were not affected by AMPK inhibition. Treatment with MnTMPyP (a superoxide scavenger) increased LAMP2 expression and stimulated autophagosome clearance in simulated ischemic-reperfused cardiomyocytes. However, no additive effect between AdipoRon and MnTMPyP was observed. Collectively, these results demonstrate that hypoadiponectinemia impairs autophagic flux, contributing to enhanced MI-R injury in the diabetic state. ADIPOR activation restores AMPK-mediated autophagosome formation and antioxidant-mediated autophagosome clearance, representing a novel intervention effective against MI-R injury in diabetic conditions.

Exogenous H2S facilitating ubiquitin aggregates clearance via autophagy attenuates type 2 diabetes-induced cardiomyopathy

Diabetic cardiomyopathy (DCM) is a serious complication of diabetes. Hydrogen sulphide (H₂S), a newly found gaseous signalling molecule, has an important role in many regulatory functions. The purpose of this study is to investigate the effects of exogenous H₂S on autophagy and its possible mechanism in DCM induced by type II diabetes (T2DCM). In this study, we found that sodium hydrosulphide (NaHS) attenuated the augment in left ventricular (LV) mass and increased LV volume, decreased reactive oxygen species (ROS) production and ameliorated H₂S production in the hearts of db/db mice. NaHS facilitated autophagosome content degradation, reduced the expression of P62 (a known substrate of autophagy) and increased the expression of microtubule-associated protein 1 light chain 3 II. It also increased the expression of autophagy-related protein 7 (ATG7) and Beclin1 in db/db mouse hearts. NaHS increased the expression of Kelch-like ECH-associated protein 1 (Keap-1) and reduced the ubiquitylation level in the hearts of db/db mice. 1,4-Dithiothreitol, an inhibitor of disulphide bonds, increased the ubiquitylation level of Keap-1, suppressed the expression of Keap-1 and abolished the effects of NaHS on ubiquitin aggregate clearance and ROS production in H9C2 cells treated with high glucose and palmitate. Overall, we concluded that exogenous H₂S promoted ubiquitin aggregate clearance via autophagy, which might exert its antioxidative effect in db/db mouse myocardia. Moreover, exogenous H₂S increased Keap-1 expression by suppressing its ubiquitylation, which might have an important role in ubiquitin aggregate clearance via autophagy. Our findings provide new insight into the mechanisms responsible for the antioxidative effects of H₂S in the context of T2DCM.

Mitochondrial health, the epigenome and healthspan

Food nutrients and metabolic supply-demand dynamics constitute environmental factors that interact with our genome influencing health and disease states. These gene-environment interactions converge at the metabolic-epigenome-genome axis to regulate gene expression and phenotypic outcomes. Mounting evidence indicates that nutrients and lifestyle strongly influence genome-metabolic functional interactions determining disease via altered epigenetic regulation. The mitochondrial network is a central player of the metabolic-epigenome-genome axis, regulating the level of key metabolites [NAD(+), AcCoA (acetyl CoA), ATP] acting as substrates/cofactors for acetyl transferases, kinases (e.g. protein kinase A) and deacetylases (e.g. sirtuins, SIRTs). The chromatin, an assembly of DNA and nucleoproteins, regulates the transcriptional process, acting at the epigenomic interface between metabolism and the genome. Within this framework, we review existing evidence showing that preservation of mitochondrial network function is directly involved in decreasing the rate of damage accumulation thus slowing aging and improving healthspan.

Liraglutide relieves myocardial damage by promoting autophagy via AMPK-mTOR signaling pathway in zucker diabetic fatty rat

Liraglutide, a glucose-lowering agent used to treat type 2 diabetic mellitus is reported to exert cardioprotective effects in clinical trials and animal experiments. However, the cardioprotective mechanism of liraglutide on diabetic cardiomyopathy has not been fully illustrated. The present study was performed to investigate whether liraglutide alleviates diabetic myocardium injury by promoting autophagy and its underlying mechanisms. Our results show that liraglutide significantly reduced the levels of creatine kinase (CK) and lactate dehydrogenase (LDH), improved left ventricular functional status and alleviated myocardial fibrosis in the Zucker diabetic fatty (ZDF) rat model. Liraglutide also mitigated high glucose-induced injury in NRCs. However these effects were partly reversed by the autophagic inhibitor chloroquine (CQ). Liraglutide promoted myocardial autophagy in the vivo and in the vitro models. Furthermore, liraglutide-induced enhancement of autophagy was related to increased AMPK phosphorylation and decreased mTOR phosphorylation, which was partially abolished by the AMPK inhibitor compound C (Comp C). Collectively, our data provide evidence that liraglutide mediated diabetic myocardium injury by promoting AMPK-dependent autophagy.

NLRP4 is an essential negative regulator of fructose-induced cardiac injury in vitro and in vivo

High fructose consumption leads to metabolic syndrome and enhances cardiovascular disease risk. However, our knowledge of the molecular mechanism underlying the cardiac disease caused by fructose feeding is still poor. Nod-like receptors (NLRs) are intracellular sensors, responding to a variety of intracellular danger signals to induce injuries. NLRP4 is a negative regulator of nuclear factor-κB (NF-κB) signaling pathway through interactions with kinase IκB kinase (IKK). Here, we illustrated that NLRP4 attenuates pro-inflammatory cytokines releasing, including Transforming growth factor (TGF-β1), Tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-18 (IL-18) and interleukin-6 (IL-6), in fructose-treated cardiac cells by means of RT-qPCR, and western blotting analysis. In addition, NLRP4 could reduce the expression of TANK-binding kinase 1/interferon regulatory factor 3 (TBK1/IRF3), reducing inflammation response and achieving its anti-hypertrophic action. TBK1 plays critical roles in the IRF3 signaling pathway, modulating inflammation response. The inhibition of IKK/NF-κB signaling pathway by NLRP4 is confirmed by NLRP4 over-expression and knockdown. In vivo, high fructose feeding induced cardiac injury, accompanied with reduced expression of NLRP4 in heart tissue samples, indicating the possible role of NLRP4 in ameliorating heart injury. In conclusion, the findings above indicated that NLRP4 is an important mediator of cardiac remodeling in vitro and in vivo through negatively regulating TBK1/IRF3 and IKK/NF-κB signaling pathways, indicating that NLRP4 might be a promising therapeutic target against cardiac inflammation.

Tissue-specific metabolic reprogramming drives nutrient flux in diabetic complications

Diabetes is associated with altered cellular metabolism, but how altered metabolism contributes to the development of diabetic complications is unknown. We used the BKS db/db diabetic mouse model to investigate changes in carbohydrate and lipid metabolism in kidney cortex, peripheral nerve, and retina. A systems approach using transcriptomics, metabolomics, and metabolic flux analysis identified tissue-specific differences, with increased glucose and fatty acid metabolism in the kidney, a moderate increase in the retina, and a decrease in the nerve. In the kidney, increased metabolism was associated with enhanced protein acetylation and mitochondrial dysfunction. To confirm these findings in human disease, we analyzed diabetic kidney transcriptomic data and urinary metabolites from a cohort of Southwestern American Indians. The urinary findings were replicated in 2 independent patient cohorts, the Finnish Diabetic Nephropathy and the Family Investigation of Nephropathy and Diabetes studies. Increased concentrations of TCA cycle metabolites in urine, but not in plasma, predicted progression of diabetic kidney disease, and there was an enrichment of pathways involved in glycolysis and fatty acid and amino acid metabolism. Our findings highlight tissue-specific changes in metabolism in complication-prone tissues in diabetes and suggest that urinary TCA cycle intermediates are potential prognostic biomarkers of diabetic kidney disease progression.

Myocardial redox status, mitophagy and cardioprotection: a potential way to amend diabetic heart?

Diabetic cardiomyopathy (DCM) is one of the major cardiovascular complications in diabetes that increase the mortality of diabetic patients. Mechanisms underlying DCM have not been fully elucidated, hindering targeted design of effective strategies to delay or treat DCM. Mitochondrial dysfunction is recognized as the driving force for the pathogenesis of DCM; therefore, maintaining cardiac mitochondrial quality is crucial for DCM prevention. Mitophagy is the process by which cells degrade abnormal or superfluous mitochondria in order to correct mitochondrial dysfunction, improve mitochondrial quality and maintain cardiac homoeostasis. Although the roles of mitophagy in various cardiomyopathies have been suggested, it remains largely unknown how the process is regulated and whether it is altered in the diabetic heart. In this review, we summarize currently available studies that investigate mitophagy in the heart, including its pathways, features and protective roles in several situations, including DCM. Due to limited data about mitophagy in diabetic hearts, future studies are required to gain a deeper understanding of the regulatory mechanisms of mitophagy in the heart and to develop mitophagy-based strategies for protecting the heart from diabetic injury.

Mitochondrial quality control in the diabetic heart

Diabetes is a well-known risk factor for heart failure. Diabetic heart damage is closely related to mitochondrial dysfunction and increased ROS generation. However, clinical trials have shown no effects of antioxidant therapies on heart failure in diabetic patients, suggesting that simply antagonizing existing ROS by antioxidants is not sufficient to reduce diabetic cardiac injury. A potentially more effective treatment strategy may be to enhance the overall capacity of mitochondrial quality control to maintain a pool of healthy mitochondria that are needed for supporting cardiac contractile function in diabetic patients. Mitochondrial quality is controlled by a number of coordinated mechanisms including mitochondrial fission and fusion, mitophagy and biogenesis. The mitochondrial damage consistently observed in the diabetic hearts indicates a failure of the mitochondrial quality control mechanisms. Recent studies have demonstrated a crucial role for each of these mechanisms in cardiac homeostasis and have begun to interrogate the relative contribution of insufficient mitochondrial quality control to diabetic cardiac injury. In this review, we will present currently available literature that links diabetic heart disease to the dysregulation of major mitochondrial quality control mechanisms. We will discuss the functional roles of these mechanisms in the pathogenesis of diabetic heart disease and their potentials for targeted therapeutical manipulation.

Macrophage Migration Inhibitory Factor (MIF) Deficiency Exacerbates Aging-Induced Cardiac Remodeling and Dysfunction Despite Improved Inflammation: Role of Autophagy Regulation

Aging leads to unfavorable geometric and functional sequelae in the heart. The proinflammatory cytokine macrophage migration inhibitory factor (MIF) plays a role in the maintenance of cardiac homeostasis under stress conditions although its impact in cardiac aging remains elusive. This study was designed to evaluate the role of MIF in aging-induced cardiac anomalies and the underlying mechanism involved. Cardiac geometry, contractile and intracellular Ca²⁺ properties were examined in young (3–4 mo) or old (24 mo) wild type and MIF knockout (MIF^−/−) mice. Our data revealed that MIF knockout exacerbated aging-induced unfavorable structural and functional changes in the heart. The detrimental effect of MIF knockout was associated with accentuated loss in cardiac autophagy with aging. Aging promoted cardiac inflammation, the effect was attenuated by MIF knockout. Intriguingly, aging-induced unfavorable responses were reversed by treatment with the autophagy inducer rapamycin, with improved myocardial ATP availability in aged WT and MIF^−/− mice. Using an in vitro model of senescence, MIF knockdown exacerbated doxorubicin-induced premature senescence in H9C2 myoblasts, the effect was ablated by MIF replenishment. Our data indicated that MIF knockout exacerbates aging-induced cardiac remodeling and functional anomalies despite improved inflammation, probably through attenuating loss of autophagy and ATP availability in the heart.