Inhibition of a novel Dickkopf-1-LDL receptor-related proteins 5 and 6 axis prevents diabetic cardiomyopathy in mice.

BACKGROUND AND AIMS: Anti-hypertensive agents are one of the most frequently used drugs worldwide. However, no blood pressure-lowering strategy is superior to placebo with respect to survival in diabetic hypertensive patients. Previous findings show that Wnt co-receptors LDL receptor-related proteins 5 and 6 (LRP5/6) can directly bind to several G protein-coupled receptors (GPCRs). Because angiotensin II type 1 receptor (AT1R) is the most important GPCR in regulating hypertension, this study examines the possible mechanistic association between LRP5/6 and their binding protein Dickkopf-1 (DKK1) and activation of the AT1R and further hypothesizes that the LRP5/6-GPCR interaction may affect hypertension and potentiate cardiac impairment in the setting of diabetes. METHODS: The roles of serum DKK1 and DKK1-LRP5/6 signalling in diabetic injuries were investigated in human and diabetic mice. RESULTS: Blood pressure up-regulation positively correlated with serum DKK1 elevations in humans. Notably, LRP5/6 physically and functionally interacted with AT1R. The loss of membrane LRP5/6 caused by injection of a recombinant DKK1 protein or conditional LRP5/6 deletions resulted in AT1R activation and hypertension, as well as ß-arrestin1 activation and cardiac impairment, possibly because of multiple GPCR alterations. Importantly, unlike commonly used anti-hypertensive agents, administration of the anti-DKK1 neutralizing antibody effectively prevented diabetic cardiac impairment in mice. CONCLUSIONS: These findings establish a novel DKK1-LRP5/6-GPCR pathway in inducing diabetic injuries and may resolve the long-standing conundrum as to why elevated blood DKK1 has deleterious effects. Thus, monitoring and therapeutic elimination of blood DKK1 may be a promising strategy to attenuate diabetic injuries.

Cardioprotective effects of asiaticoside against diabetic cardiomyopathy: Activation of the AMPK/Nrf2 pathway.

Diabetic cardiomyopathy (DCM) is a chronic microvascular complication of diabetes that is generally defined as ventricular dysfunction occurring in patients with diabetes and unrelated to known causes. Several mechanisms have been proposed to contribute to the occurrence and persistence of DCM, in which oxidative stress and autophagy play a non-negligible role. Diabetic cardiomyopathy is involved in a variety of physiological and pathological processes. The 5' adenosine monophosphate-activated protein kinase/nuclear factor-erythroid 2-related factor 2 (AMPK/Nrf2) are expressed in the heart, and studies have shown that asiaticoside (ASI) and activated AMPK/Nrf2 have a protective effect on the myocardium. However, the roles of ASI and AMPK/Nrf2 in DCM are unknown. The intraperitoneal injection of streptozotocin (STZ) and high-fat feed were used to establish the DCM models in 100 C57/BL mice. Asiaticoside and inhibitors of AMPK/Nrf2 were used for intervention. Cardiac function, oxidative stress, and autophagy were measured in mice. DCM mice displayed increased levels of oxidative stress while autophagy levels declined. In addition, AMPK/Nrf2 was activated in DCM mice with ASI intervention. Further, we discovered that AMPK/Nrf2 inhibition blocked the protective effect of ASI by compound C and treatment with ML-385. The present study demonstrates that ASI exerts a protective effect against DCM via the potential activation of the AMPK/Nrf2 pathway. Asiaticoside is a potential therapeutic target for DCM.

Nrf2 prevents diabetic cardiomyopathy via antioxidant effect and normalization of glucose and lipid metabolism in the heart.

Metabolic disorders and oxidative stress are the main causes of diabetic cardiomyopathy. Activation of nuclear factor erythroid 2-related factor 2 (Nrf2) exerts a powerful antioxidant effect and prevents the progression of diabetic cardiomyopathy. However, the mechanism of its cardiac protection and direct action on cardiomyocytes are not well understood. Here, we investigated in a cardiomyocyte-restricted Nrf2 transgenic mice (Nrf2-TG) the direct effect of Nrf2 on cardiomyocytes in DCM and its mechanism. In this study, cardiomyocyte-restricted Nrf2 transgenic mice (Nrf2-TG) were used to directly observe whether cardiomyocyte-specific overexpression of Nrf2 can prevent diabetic cardiomyopathy and correct glucose and lipid metabolism disorders in the heart. Compared to wild-type mice, Nrf2-TG mice showed resistance to diabetic cardiomyopathy in a streptozotocin-induced type 1 diabetes mouse model. This was primarily manifested as improved echocardiography results as well as reduced myocardial fibrosis, cardiac inflammation, and oxidative stress. These results showed that Nrf2 can directly act on cardiomyocytes to exert a cardioprotective role. Mechanistically, the cardioprotective effects of Nrf2 depend on its antioxidation activity, partially through improving glucose and lipid metabolism by directly targeting lipid metabolic pathway of AMPK/Sirt1/PGC-1α activation via upstream genes of sestrin2 and LKB1, and indirectly enabling AKT/GSK-3ß/HK-Ⅱ activity via AMPK mediated p70S6K inhibition.

Melatonin attenuates diabetic cardiomyopathy by increasing autophagy of cardiomyocytes via regulation of VEGF-B/GRP78/PERK signaling pathway.

AIMS: Diabetic cardiomyopathy (DCM) is a major cause of mortality in patients with diabetes, and the potential strategies for treating DCM are insufficient. Melatonin (Mel) has been shown to attenuate DCM, however, the underlying mechanism remains unclear. The role of vascular endothelial growth factor-B (VEGF-B) in DCM is little known. In present study, we aimed to investigate whether Mel alleviated DCM via regulation of VEGF-B and explored its underlying mechanisms. METHODS AND RESULTS: We found that Mel significantly alleviated cardiac dysfunction and improved autophagy of cardiomyocytes in type 1 diabetes mellitus (T1DM) induced cardiomyopathy mice. VEGF-B was highly expressed in DCM mice in comparison with normal mice, and its expression was markedly reduced after Mel treatment. Mel treatment diminished the interaction of VEGF-B and Glucose-regulated protein 78 (GRP78) and reduced the interaction of GRP78 and protein kinase RNA -like ER kinase (PERK). Furthermore, Mel increased phosphorylation of PERK and eIF2α, then up-regulated the expression of ATF4. VEGF-B-/- mice imitated the effect of Mel on wild type diabetic mice. Interestingly, injection with Recombinant adeno-associated virus serotype 9 (AAV9)-VEGF-B or administration of GSK2656157 (GSK), an inhibitor of phosphorylated PERK abolished the protective effect of Mel on DCM. Furthermore, rapamycin, an autophagy agonist displayed similar effect with Mel treatment; while 3-Methyladenine (3-MA), an autophagy inhibitor neutralized the effect of Mel on high glucose-treated neonatal rat ventricular myocytes. CONCLUSIONS: These results demonstrated that Mel attenuated DCM via increasing autophagy of cardiomyocytes, and this cardio-protective effect of Mel was dependent on VEGF-B/GRP78/PERK signaling pathway.

Irisin attenuates type 1 diabetic cardiomyopathy by anti-ferroptosis via SIRT1-mediated deacetylation of p53.

BACKGROUND: Diabetic cardiomyopathy (DCM) is a serious complication in patients with type 1 diabetes mellitus (T1DM), which still lacks adequate therapy. Irisin, a cleavage peptide off fibronectin type III domain-containing 5, has been shown to preserve cardiac function in cardiac ischemia-reperfusion injury. Whether or not irisin plays a cardioprotective role in DCM is not known. METHODS AND RESULTS: T1DM was induced by multiple low-dose intraperitoneal injections of streptozotocin (STZ). Our current study showed that irisin expression/level was lower in the heart and serum of mice with STZ-induced TIDM. Irisin supplementation by intraperitoneal injection improved the impaired cardiac function in mice with DCM, which was ascribed to the inhibition of ferroptosis, because the increased ferroptosis, associated with increased cardiac malondialdehyde (MDA), decreased reduced glutathione (GSH) and protein expressions of solute carrier family 7 member 11 (SLC7A11) and glutathione peroxidase 4 (GPX4), was ameliorated by irisin. In the presence of erastin, a ferroptosis inducer, the irisin-mediated protective effects were blocked. Mechanistically, irisin treatment increased Sirtuin 1 (SIRT1) and decreased p53 K382 acetylation, which decreased p53 protein expression by increasing its degradation, consequently upregulated SLC7A11 and GPX4 expressions. Thus, irisin-mediated reduction in p53 decreases ferroptosis and protects cardiomyocytes against injury due to high glucose. CONCLUSION: This study demonstrated that irisin could improve cardiac function by suppressing ferroptosis in T1DM via the SIRT1-p53-SLC7A11/GPX4 pathway. Irisin may be a therapeutic approach in the management of T1DM-induced cardiomyopathy.

Growth differentiation factor 11 regulates high glucose-induced cardiomyocyte pyroptosis and diabetic cardiomyopathy by inhibiting inflammasome activation.

BACKGROUND: Diabetic cardiomyopathy (DCM) is a crucial complication of long-term chronic diabetes that can lead to myocardial hypertrophy, myocardial fibrosis, and heart failure. There is increasing evidence that DCM is associated with pyroptosis, a form of inflammation-related programmed cell death. Growth differentiation factor 11 (GDF11) is a member of the transforming growth factor ß superfamily, which regulates oxidative stress, inflammation, and cell survival to mitigate myocardial hypertrophy, myocardial infarction, and vascular injury. However, the role of GDF11 in regulating pyroptosis in DCM remains to be elucidated. This research aims to investigate the role of GDF11 in regulating pyroptosis in DCM and the related mechanism. METHODS AND RESULTS: Mice were injected with streptozotocin (STZ) to induce a diabetes model. H9c2 cardiomyocytes were cultured in high glucose (50 mM) to establish an in vitro model of diabetes. C57BL/6J mice were preinjected with adeno-associated virus 9 (AAV9) intravenously via the tail vein to specifically overexpress myocardial GDF11. GDF11 attenuated pyroptosis in H9c2 cardiomyocytes after high-glucose treatment. In diabetic mice, GDF11 alleviated cardiomyocyte pyroptosis, reduced myocardial fibrosis, and improved cardiac function. Mechanistically, GDF11 inhibited pyroptosis by preventing inflammasome activation. GDF11 achieved this by specifically binding to apoptosis-associated speck-like protein containing a CARD (ASC) and preventing the assembly and activation of the inflammasome. Additionally, the expression of GDF11 during pyroptosis was regulated by peroxisome proliferator-activated receptor α (PPARα). CONCLUSION: These findings demonstrate that GDF11 can treat diabetic cardiomyopathy by alleviating pyroptosis and reveal the role of the PPARα-GDF11-ASC pathway in DCM, providing ideas for new strategies for cardioprotection.

Role of arachidonic acid in ischemic heart disease under different comorbidities: risk or protection?

In a translational study involving animal models and human subjects, Lv et al. demonstrate that arachidonic acid (AA) exhibits cardioprotective effects in diabetic myocardial ischemia, suggesting a departure from its known role in promoting ferroptosis-a form of cell death characterized by iron-dependent lipid peroxidation. However, the study does not address how underlying diabetic conditions might influence the metabolic pathways of AA, which are critical for fully understanding its impact on heart disease. Diabetes can significantly alter lipid metabolism, which in turn might affect the enzymatic processes involved in AA's metabolism, leading to different outcomes in the disease process. Further examination of the role of diabetes in modulating AA's effects could enhance the understanding of its protective mechanism in ischemic conditions. This could also lead to more targeted and effective therapeutic strategies for managing myocardial ischemia in diabetic patients, such as optimizing AA levels to prevent heart damage while avoiding exacerbating factors like ferroptosis.

Dapagliflozin reduces systemic inflammation in patients with type 2 diabetes without known heart failure.

OBJECTIVE: Sodium glucose cotransporter 2 (SGLT2) inhibitors significantly improve cardiovascular outcomes in diabetic patients; however, the mechanism is unclear. We hypothesized that dapagliflozin improves cardiac outcomes via beneficial effects on systemic and cardiac inflammation and cardiac fibrosis. RESEARCH AND DESIGN METHODS: This randomized placebo-controlled clinical trial enrolled 62 adult patients (mean age 62, 17% female) with type 2 diabetes (T2D) without known heart failure. Subjects were randomized to 12 months of daily 10 mg dapagliflozin or placebo. For all patients, blood/plasma samples and cardiac magnetic resonance imaging (CMRI) were obtained at time of randomization and at the end of 12 months. Systemic inflammation was assessed by plasma IL-1B, TNFα, IL-6 and ketone levels and PBMC mitochondrial respiration, an emerging marker of sterile inflammation. Global myocardial strain was assessed by feature tracking; cardiac fibrosis was assessed by T1 mapping to calculate extracellular volume fraction (ECV); and cardiac tissue inflammation was assessed by T2 mapping. RESULTS: Between the baseline and 12-month time point, plasma IL-1B was reduced (- 1.8 pg/mL, P = 0.003) while ketones were increased (0.26 mM, P = 0.0001) in patients randomized to dapagliflozin. PBMC maximal oxygen consumption rate (OCR) decreased over the 12-month period in the placebo group but did not change in patients receiving dapagliflozin (- 158.9 pmole/min/106 cells, P = 0.0497 vs. - 5.2 pmole/min/106 cells, P = 0.41), a finding consistent with an anti-inflammatory effect of SGLT2i. Global myocardial strain, ECV and T2 relaxation time did not change in both study groups. GOV REGISTRATION: NCT03782259.

FGF21-Sirtuin 3 Axis Confers the Protective Effects of Exercise Against Diabetic Cardiomyopathy by Governing Mitochondrial Integrity.

BACKGROUND: Exercise is an effective nonpharmacological strategy to alleviate diabetic cardiomyopathy (DCM) through poorly defined mechanisms. FGF21 (fibroblast growth factor 21), a peptide hormone with pleiotropic benefits on cardiometabolic homeostasis, has been identified as an exercise responsive factor. This study aims to investigate whether FGF21 signaling mediates the benefits of exercise on DCM, and if so, to elucidate the underlying mechanisms. METHODS: The global or hepatocyte-specific FGF21 knockout mice, cardiomyocyte-selective ß-klotho (the obligatory co-receptor for FGF21) knockout mice, and their wild-type littermates were subjected to high-fat diet feeding and injection of streptozotocin to induce DCM, followed by a 6-week exercise intervention and assessment of cardiac functions. Cardiac mitochondrial structure and function were assessed by electron microscopy, enzymatic assays, and measurements of fatty acid oxidation and ATP production. Human induced pluripotent stem cell-derived cardiomyocytes were used to investigate the receptor and postreceptor signaling pathways conferring the protective effects of FGF21 against toxic lipids-induced mitochondrial dysfunction. RESULTS: Treadmill exercise markedly induced cardiac expression of ß-klotho and significantly attenuated diabetes-induced cardiac dysfunction in wild-type mice, accompanied by reduced mitochondrial damage and increased activities of mitochondrial enzymes in hearts. However, such cardioprotective benefits of exercise were largely abrogated in mice with global or hepatocyte-selective ablation of FGF21, or cardiomyocyte-specific deletion of ß-klotho. Mechanistically, exercise enhanced the cardiac actions of FGF21 to induce the expression of the mitochondrial deacetylase SIRT3 by AMPK-evoked phosphorylation of FOXO3, thereby reversing diabetes-induced hyperacetylation and functional impairments of a cluster of mitochondrial enzymes. FGF21 prevented toxic lipids-induced mitochondrial dysfunction and oxidative stress by induction of the AMPK/FOXO3/SIRT3 signaling axis in human induced pluripotent stem cell-derived cardiomyocytes. Adeno-associated virus-mediated restoration of cardiac SIRT3 expression was sufficient to restore the responsiveness of diabetic FGF21 knockout mice to exercise in amelioration of mitochondrial dysfunction and DCM. CONCLUSIONS: The FGF21-SIRT3 axis mediates the protective effects of exercise against DCM by preserving mitochondrial integrity and represents a potential therapeutic target for DCM. REGISTRATION: URL: https://www. CLINICALTRIALS: gov; Unique identifier: NCT03240978.

Endothelial MICU1 alleviates diabetic cardiomyopathy by attenuating nitrative stress-mediated cardiac microvascular injury.

BACKGROUND: Myocardial microvascular injury is the key event in early diabetic heart disease. The injury of myocardial microvascular endothelial cells (CMECs) is the main cause and trigger of myocardial microvascular disease. Mitochondrial calcium homeostasis plays an important role in maintaining the normal function, survival and death of endothelial cells. Considering that mitochondrial calcium uptake 1 (MICU1) is a key molecule in mitochondrial calcium regulation, this study aimed to investigate the role of MICU1 in CMECs and explore its underlying mechanisms. METHODS: To examine the role of endothelial MICU1 in diabetic cardiomyopathy (DCM), we used endothelial-specific MICU1ecKO mice to establish a diabetic mouse model and evaluate the cardiac function. In addition, MICU1 overexpression was conducted by injecting adeno-associated virus 9 carrying MICU1 (AAV9-MICU1). Transcriptome sequencing technology was used to explore underlying molecular mechanisms. RESULTS: Here, we found that MICU1 expression is decreased in CMECs of diabetic mice. Moreover, we demonstrated that endothelial cell MICU1 knockout exacerbated the levels of cardiac hypertrophy and interstitial myocardial fibrosis and led to a further reduction in left ventricular function in diabetic mice. Notably, we found that AAV9-MICU1 specifically upregulated the expression of MICU1 in CMECs of diabetic mice, which inhibited nitrification stress, inflammatory reaction, and apoptosis of the CMECs, ameliorated myocardial hypertrophy and fibrosis, and promoted cardiac function. Further mechanistic analysis suggested that MICU1 deficiency result in excessive mitochondrial calcium uptake and homeostasis imbalance which caused nitrification stress-induced endothelial damage and inflammation that disrupted myocardial microvascular endothelial barrier function and ultimately promoted DCM progression. CONCLUSIONS: Our findings demonstrate that MICU1 expression was downregulated in the CMECs of diabetic mice. Overexpression of endothelial MICU1 reduced nitrification stress induced apoptosis and inflammation by inhibiting mitochondrial calcium uptake, which improved myocardial microvascular function and inhibited DCM progression. Our findings suggest that endothelial MICU1 is a molecular intervention target for the potential treatment of DCM.

Acid sphingomyelinase promotes diabetic cardiomyopathy via NADPH oxidase 4 mediated apoptosis.

BACKGROUND: Increased acid sphingomyelinase (ASMase) activity is associated with insulin resistance and cardiac dysfunction. However, the effects of ASMase on diabetic cardiomyopathy (DCM) and the molecular mechanism(s) underlying remain to be elucidated. We here investigated whether ASMase caused DCM through NADPH oxidase 4-mediated apoptosis. METHODS AND RESULTS: We used pharmacological and genetic approaches coupled with study of murine and cell line samples to reveal the mechanisms initiated by ASMase in diabetic hearts. The protein expression and activity of ASMase were upregulated, meanwhile ceramide accumulation was increased in the myocardium of HFD mice. Inhibition of ASMase with imipramine (20 mg Kg-1 d-1) or siRNA reduced cardiomyocyte apoptosis, fibrosis, and mitigated cardiac hypertrophy and cardiac dysfunction in HFD mice. The similar effects were observed in cardiomyocytes treated with high glucose (HG, 30 mmol L-1) + palmitic acid (PA, 100 µmol L-1) or C16 ceramide (CER, 20 µmol L-1). Interestingly, the cardioprotective effect of ASMase inhibition was not accompanied by reduced ceramide accumulation, indicating a ceramide-independent manner. The mechanism may involve activated NADPH oxidase 4 (NOX4), increased ROS generation and triggered apoptosis. Suppression of NOX4 with apocynin prevented HG + PA and CER incubation induced Nppb and Myh7 pro-hypertrophic gene expression, ROS production and apoptosis in H9c2 cells. Furthermore, cardiomyocyte-specific ASMase knockout (ASMaseMyh6KO) restored HFD-induced cardiac dysfunction, remodeling, and apoptosis, whereas NOX4 protein expression was downregulated. CONCLUSIONS: These results demonstrated that HFD-mediated activation of cardiomyocyte ASMase could increase NOX4 expression, which may stimulate oxidative stress, apoptosis, and then cause metabolic cardiomyopathy.

Treatment with recombinant Sirt1 rewires the cardiac lipidome and rescues diabetes-related metabolic cardiomyopathy.

BACKGROUND: Metabolic cardiomyopathy (MCM), characterized by intramyocardial lipid accumulation, drives the progression to heart failure with preserved ejection fraction (HFpEF). Although evidence suggests that the mammalian silent information regulator 1 (Sirt1) orchestrates myocardial lipid metabolism, it is unknown whether its exogenous administration could avoid MCM onset. We investigated whether chronic treatment with recombinant Sirt1 (rSirt1) could halt MCM progression. METHODS: db/db mice, an established model of MCM, were supplemented with intraperitoneal rSirt1 or vehicle for 4 weeks and compared with their db/ + heterozygous littermates. At the end of treatment, cardiac function was assessed by cardiac ultrasound and left ventricular samples were collected and processed for molecular analysis. Transcriptional changes were evaluated using a custom PCR array. Lipidomic analysis was performed by mass spectrometry. H9c2 cardiomyocytes exposed to hyperglycaemia and treated with rSirt1 were used as in vitro model of MCM to investigate the ability of rSirt1 to directly target cardiomyocytes and modulate malondialdehyde levels and caspase 3 activity. Myocardial samples from diabetic and nondiabetic patients were analysed to explore Sirt1 expression levels and signaling pathways. RESULTS: rSirt1 treatment restored cardiac Sirt1 levels and preserved cardiac performance by improving left ventricular ejection fraction, fractional shortening and diastolic function (E/A ratio). In left ventricular samples from rSirt1-treated db/db mice, rSirt1 modulated the cardiac lipidome: medium and long-chain triacylglycerols, long-chain triacylglycerols, and triacylglycerols containing only saturated fatty acids were reduced, while those containing docosahexaenoic acid were increased. Mechanistically, several genes involved in lipid trafficking, metabolism and inflammation, such as Cd36, Acox3, Pparg, Ncoa3, and Ppara were downregulated by rSirt1 both in vitro and in vivo. In humans, reduced cardiac expression levels of Sirt1 were associated with higher intramyocardial triacylglycerols and PPARG-related genes. CONCLUSIONS: In the db/db mouse model of MCM, chronic exogenous rSirt1 supplementation rescued cardiac function. This was associated with a modulation of the myocardial lipidome and a downregulation of genes involved in lipid metabolism, trafficking, inflammation, and PPARG signaling. These findings were confirmed in the human diabetic myocardium. Treatments that increase Sirt1 levels may represent a promising strategy to prevent myocardial lipid abnormalities and MCM development.

Aldose reductase inhibition alleviates diabetic cardiomyopathy and is associated with a decrease in myocardial fatty acid oxidation.

BACKGROUND: Cardiovascular diseases, including diabetic cardiomyopathy, are major causes of death in people with type 2 diabetes. Aldose reductase activity is enhanced in hyperglycemic conditions, leading to altered cardiac energy metabolism and deterioration of cardiac function with adverse remodeling. Because disturbances in cardiac energy metabolism can promote cardiac inefficiency, we hypothesized that aldose reductase inhibition may mitigate diabetic cardiomyopathy via normalization of cardiac energy metabolism. METHODS: Male C57BL/6J mice (8-week-old) were subjected to experimental type 2 diabetes/diabetic cardiomyopathy (high-fat diet [60% kcal from lard] for 10 weeks with a single intraperitoneal injection of streptozotocin (75 mg/kg) at 4 weeks), following which animals were randomized to treatment with either vehicle or AT-001, a next-generation aldose reductase inhibitor (40 mg/kg/day) for 3 weeks. At study completion, hearts were perfused in the isolated working mode to assess energy metabolism. RESULTS: Aldose reductase inhibition by AT-001 treatment improved diastolic function and cardiac efficiency in mice subjected to experimental type 2 diabetes. This attenuation of diabetic cardiomyopathy was associated with decreased myocardial fatty acid oxidation rates (1.15 ± 0.19 vs 0.5 ± 0.1 µmol min-1 g dry wt-1 in the presence of insulin) but no change in glucose oxidation rates compared to the control group. In addition, cardiac fibrosis and hypertrophy were also mitigated via AT-001 treatment in mice with diabetic cardiomyopathy. CONCLUSIONS: Inhibiting aldose reductase activity ameliorates diastolic dysfunction in mice with experimental type 2 diabetes, which may be due to the decline in myocardial fatty acid oxidation, indicating that treatment with AT-001 may be a novel approach to alleviate diabetic cardiomyopathy in patients with diabetes.

Diabetic cardiomyopathy - Zinc preventive and therapeutic potentials by its anti-oxidative stress and sensitizing insulin signaling pathways.

Oxidative stress and insulin resistance are two key mechanisms for the development of diabetic cardiomyopathy (DCM, cardiac remodeling and dysfunction). In this review, we discussed how zinc and metallothionein (MT) protect the heart from type 1 or type 2 diabetes (T1D or T2D) through its anti-oxidative function and insulin-mediated PI3K/Akt signaling activation. Both T1D and T2D-induced DCM, shown by cardiac structural remodeling and dysfunction, in wild-type mice, but not in cardiomyocyte-specific overexpressing MT mice. In contrast, mice with global MT gene deletion were more susceptible to the development of DCM. When we used zinc to treat mice with either T1D or T2D, cardiac remodeling and dysfunction were significantly prevented along with increased cardiac MT expression. To support the role of zinc homeostasis in insulin signaling pathways, treatment of diabetic mice with zinc showed the preservation of phosphorylation levels of insulin-mediated glucose metabolism-related Akt2 and GSK-3ß and even rescued cardiac pathogenesis induced by global deletion of Akt2 gene in a MT-dependent manner. These results suggest the protection by zinc from DCM is through both the induction of MT and sensitization of insulin signaling. Combined our own and other works, this review comprehensively summarized the roles of zinc homeostasis in the development and progression of DCM and its therapeutic implications. At the end, we provided pre-clinical and clinical evidence for the preventive and therapeutic potential of zinc supplementation through its anti-oxidative stress and sensitizing insulin signaling actions. Understanding the intricate connections between zinc and DCM provides insights for the future interventional approaches.

ONX0914 inhibition of immunoproteasome subunit LMP7 ameliorates diabetic cardiomyopathy via restraining endothelial-mesenchymal transition.

Diabetic cardiomyopathy (DCM) is a chronic metabolic disease with few effective therapeutic options. Immunoproteasome is an inducible proteasome that plays an important role in the regulation of many cardiovascular diseases, while its role in DCM remains under discussion. The present study aims to demonstrate whether inhibiting immunoproteasome subunit low molecular weight polypeptide 7 (LMP7) could alleviate DCM. Here, we established a type I diabetes mellitus mouse model by streptozotocin (STZ) in 8-week-old male wild-type C57BL/6J mice. We found that immunoproteasome subunit LMP7 was overexpressed in the heart of diabetic mice, while inhibiting LMP7 with pharmacological inhibitor ONX0914 significantly alleviated myocardial fibrosis and improved cardiac function. Besides, compared with diabetic mice, ONX0914 treatment reduced protein levels of mesenchymal markers (Vimentin, α-smooth muscle actin, and SM22α) and increased endothelial markers (VE-cadherin and CD31). In TGFß1 stimulated HUVECs, we also observed that ONX0914 could inhibit endothelial-mesenchymal transition (EndMT). Mechanistically, we prove that ONX0914 could regulate autophagy activity both in vivo and vitro. Meanwhile, the protective effect of ONX0914 on TGFß1 stimulated HUVECs could be abolished by 3-methyladenine (3MA) or hydroxychloroquine (CQ). All in all, our data highlight that inhibition of LMP7 with ONX0914 could ameliorate EndMT in diabetic mouse hearts at least in part via autophagy activation. Thus, LMP7 may be a potential therapeutic target for the DCM.

2-Arachidonoylglycerol Attenuates Myocardial Fibrosis in Diabetic Mice Via the TGF-ß1/Smad Pathway.

PURPOSE: Diabetic cardiomyopathy (DM) is the cause of late cardiac dysfunction in diabetic patients. Myocardial fibrosis is the main pathological mechanism, and it is associated with transforming growth factor-ß1(TGF-ß1) expression up-regulation. 2-Arachidonoylglycerol (2-AG) is an endogenous cannabinoid that can effectively improve myocardial cell energy metabolism and cardiac function. Here, we evaluated the protective effect of 2-AG on diabetic cardiomyopathy. METHODS: Male C57BL/6 mice were injected with 2-AG intraperitoneally for 4 weeks (10 micro g/kg/day) after 12 weeks of diabetic modeling. After 4 weeks, heart function was evaluated by echocardiography. Heart structure was assessed by hematoxylin and eosin staining. Cardiac fibrosis was analyzed using immunohistochemistry, Sirius red stain, and western blot. RESULTS: After modeling in diabetic mice, cardiac ultrasonography showed decreased cardiac function and pathological findings showed myocardial fibrosis. 2-AG could effectively inhibit the up-regulation of TGF-ß1 and Smad2/3, reduce myocardial fibrosis, and ultimately improve cardiac function in diabetic mice. CONCLUSION: 2-AG reduces cardiac fibrosis via the TGF-ß1/Smad2/3 pathway and is a potential pathway for the treatment of cardiac dysfunction in diabetic mice.

Ginsenoside Rg3 Protects against Diabetic Cardiomyopathy and Promotes Adiponectin Signaling via Activation of PPAR-γ.

Ginsenoside Rg3 extracted from Panax notoginseng has therapeutic effects on diabetes and heart diseases. However, the underlying mechanism of ginsenoside Rg3 on diabetic cardiomyopathy (DCM) remains unclear. 24-week-old diabetic db/db mice were treated with ginsenoside Rg3 for 12 weeks, then body weight, serum lipids, adiponectin levels, as well as cardiac function and pathological morphology, were measured. The targets of ginsenoside Rg3 and its regulation of the adiponectin pathway were also evaluated on 3T3-L1 or H9c2 cells. Ginsenoside Rg3 directly bound to PPAR-γ, improving adiponectin secretion and promoting adiponectin signaling. Significantly attenuated overweight, hyperglycemia, and hyperlipidemia, as well as alleviated lipid accumulation and dysfunction in adipose, liver, and heart tissues, were observed in the ginsenoside Rg3-treated group. Ginsenoside Rg3 could be a promising drug targeting PPAR-γ to treat diabetic cardiomyopathy.

Esculeoside A Decreases Diabetic Cardiomyopathy in Streptozotocin-Treated Rats by Attenuating Oxidative Stress, Inflammation, Fibrosis, and Apoptosis: Impressive Role of Nrf2.

Background and Objectives: This experiment evaluated the preventative influence of the tomato-derived Esculeoside A (ESA) on diabetic cardiomyopathy in type 1 diabetes mellitus (T1DM) in rats induced by streptozotocin (STZ). It also examined whether the activation of Nrf2 signaling affords this protection. Materials and Methods: Adult male Wistar control nondiabetic rats and rats with T1DM (STZ-T1DM) were given either carboxymethylcellulose as a vehicle or ESA (100 mg/kg) (eight rats/group) orally daily for 12 weeks. A group of STZ-T1DM rats was also treated with 100 mg/kg ESA and co-treated i.p. with 2 mg/kg (twice/week), brusatol, and Nrf2 inhibitors for 12 weeks. Results and Conclusions: Treatment with ESA prevented the gain in heart weight and cardiomyocyte hypertrophy and improved the left ventricular (LV) systolic and diastolic function (LV) in the STZ-T1DM rat group. Likewise, it reduced their serum levels of triglycerides, cholesterol, and low-density lipoproteins (LDL-c), as well as their LV mRNA, cytoplasmic total, and nuclear total levels of NF-κB. ESA also reduced the total levels of malondialdehyde, tumor necrosis factor-α, interleukine-6 (IL-6), Bax, cytochrome-c, and caspase-3 in the LV of the STZ-T1DM rats. In parallel, ESA enhanced the nuclear and cytoplasmic levels of Nrf2 and the levels of superoxide dismutase, glutathione, and heme oxygenase-1, but decreased the mRNA and cytoplasmic levels of keap-1 in the LVs of the STZ-T1DM rats. Interestingly, ESA did not affect the fasting insulin and glucose levels of the diabetic rats. All of these beneficially protective effects of ESA were not seen in the ESA-treated rats that received brusatol. In conclusion, ESA represses diabetic cardiomyopathy in STZ-diabetic hearts by activating the Nrf2/antioxidant/NF-κB axis.

Neuregulin-4 attenuates diabetic cardiomyopathy by regulating autophagy via the AMPK/mTOR signalling pathway.

BACKGROUND: Diabetic cardiomyopathy is characterized by left ventricle dysfunction, cardiomyocyte apoptosis, and interstitial fibrosis and is a serious complication of diabetes mellitus (DM). Autophagy is a mechanism that is essential for maintaining normal heart morphology and function, and its dysregulation can produce pathological effects on diabetic hearts. Neuregulin-4 (Nrg4) is an adipokine that exerts protective effects against metabolic disorders and insulin resistance. The aim of this study was to explore whether Nrg4 could ameliorate DM-induced myocardial injury by regulating autophagy. METHODS: Four weeks after the establishment of a model of type 1 diabetes in mice, the mice received Nrg4 treatment (with or without an autophagy inhibitor) for another 4 weeks. The cardiac functions, histological structures and cardiomyocyte apoptosis were investigated. Autophagy-related protein levels along with related signalling pathways that regulate autophagy were evaluated. In addition, the effects of Nrg4 on autophagy were also determined in cultured primary cardiomyocytes. RESULTS: Nrg4 alleviated myocardial injury both in vivo and in vitro. The autophagy level was decreased in type 1 diabetic mice, and Nrg4 intervention reactivated autophagy. Furthermore, Nrg4 intervention was found to activate autophagy via the AMPK/mTOR signalling pathway. Moreover, when autophagy was suppressed or the AMPK/mTOR pathway was inhibited, the beneficial effects of Nrg4 were diminished. CONCLUSION: Nrg4 intervention attenuated diabetic cardiomyopathy by promoting autophagy in type 1 diabetic mice. Additionally, Nrg4 induced autophagy via the AMPK/mTOR signalling pathway.

Hydrogen sulfide postconditioning rendered cardioprotection against myocardial ischemia-reperfusion injury is compromised in rats with diabetic cardiomyopathy.

The present study aimed to investigate the efficacy of hydrogen sulfide (H2S) post-conditioning (HPOC) against ischemia-reperfusion (I/R) challenged diabetic rat hearts with or without cardiomyopathy using the Langendorff perfusion system. Male Wistar rats were randomly divided into different groups such as normal, diabetes mellitus (DM), and diabetic cardiomyopathy (DCM). Hearts from these groups were subjected to normal perfusion, I/R, and HPOC and were analyzed for cardiac physiology, cardiomyocyte injury, mitochondrial function, oxidative stress, and H2S metabolism. The results showed that HPOC protocol reduced the cardiac injury and improved the haemodynamics in normal and DM effectively, but not in DCM (RPP in mmHg*beats/min*103: HPOC- 32 ± 2, DM-HPOC-19 ± 1, DCM-HPOC-6 ± 2, LVDP in mmHg: HPOC- 96 ± 3, DM-HPOC-73 ± 2, DCM-HPOC-50 ± 3). DCM rats at the basal level exhibited perturbed myocardial architecture, mitochondrial dysfunction, and impaired glycolytic flux that failed to improve by HPOC treatment after I/R. HPOC exhibited a nominal improvement in the gene expression and activities of the H2S metabolizing enzymes such as cystathionine beta-synthase, rhodanese, and cystathionine-gamma-lyase in DCM hearts. Collectively, our results suggest that altered myocardial architecture along with exacerbated oxidative stress and mitochondrial dysfunction contribute towards the failure of HPOC cardioprotection against I/R-induced myocardial tissue injury in DCM.