Diabetic Mouse Hearts Research Articles

Ncor2/PPARα-Dependent Upregulation of MCUb in the Type 2 Diabetic Heart Impacts Cardiac Metabolic Flexibility and Function.

The contribution of altered mitochondrial Ca2+ handling to metabolic and functional defects in type 2 diabetic (T2D) mouse hearts is not well understood. In this study, we show that the T2D heart is metabolically inflexible and almost exclusively dependent on mitochondrial fatty acid oxidation as a consequence of mitochondrial calcium uniporter complex (MCUC) inhibitory subunit MCUb overexpression. Using a recombinant endonuclease-deficient Cas9-based gene promoter pulldown approach coupled with mass spectrometry, we found that MCUb is upregulated in the T2D heart due to loss of glucose homeostasis regulator nuclear receptor corepressor 2 repression, and chromatin immunoprecipitation assays identified peroxisome proliferator-activated receptor α as a mediator of MCUb gene expression in T2D cardiomyocytes. Upregulation of MCUb limits mitochondrial matrix Ca2+ uptake and impairs mitochondrial energy production via glucose oxidation by depressing pyruvate dehydrogenase complex activity. Gene therapy displacement of endogenous MCUb with a dominant-negative MCUb transgene (MCUbW246R/V251E) in vivo rescued T2D cardiomyocytes from metabolic inflexibility and stimulated cardiac contractile function and adrenergic responsiveness by enhancing phospholamban phosphorylation via protein kinase A. We conclude that MCUb represents one newly discovered molecular effector at the interface of metabolism and cardiac function, and its repression improves the outcome of the chronically stressed diabetic heart.

Empagliflozin Decreases Lactate Generation in an NHE-1 Dependent Fashion and Increases α-Ketoglutarate Synthesis From Palmitate in Type II Diabetic Mouse Hearts.

Aims/hypothesis: Changes in cardiac metabolism and ion homeostasis precede and drive cardiac remodeling and heart failure development. We previously demonstrated that sodium/glucose cotransporter 2 inhibitors (SGLT2i's) have direct cardiac effects on ion homeostasis, possibly through inhibition of the cardiac sodium/hydrogen exchanger (NHE-1). Here, we hypothesize that Empagliflozin (EMPA) also possesses direct and acute cardiac effects on glucose and fatty acid metabolism of isolated type II diabetes mellitus (db/db) mouse hearts. In addition, we explore whether direct effects on glucose metabolism are nullified in the presence of an NHE-1 inhibitor.Methods: Langendorff-perfused type II diabetic db/db mouse hearts were examined in three different series: 1: 13C glucose perfusions (n = 32); 2: 13C palmitate perfusions (n = 13); and 3: 13C glucose + 10 μM Cariporide (specific NHE-1 inhibitor) perfusions (n = 17). Within each series, EMPA treated hearts (1 μM EMPA) were compared with vehicle-perfused hearts (0.02% DMSO). Afterwards, hearts were snap frozen and lysed for stable isotope analysis and metabolomics using LC-MS techniques. Hearts from series 1 were also analyzed for phosphorylation status of AKT, STAT3, AMPK, ERK, and eNOS (n = 8 per group).Results: Cardiac mechanical performance, oxygen consumption and protein phosphorylation were not altered by 35 min EMPA treatment. EMPA was without an overall acute and direct effect on glucose or fatty acid metabolism. However, EMPA did specifically decrease cardiac lactate labeling in the 13C glucose perfusions (13C labeling of lactate: 58 ± 2% vs. 50 ± 3%, for vehicle and EMPA, respectively; P = 0.02), without changes in other glucose metabolic pathways. In contrast, EMPA increased cardiac labeling in α-ketoglutarate derived from 13C palmitate perfusions (13C labeling of α-KG: 79 ± 1% vs. 86 ± 1% for vehicle and EMPA, respectively; P = 0.01). Inhibition of the NHE by Cariporide abolished EMPA effects on lactate labeling from 13C glucose.Conclusions: The present study shows for the first time that the SGLT2 inhibitor Empagliflozin has acute specific metabolic effects in isolated diabetic hearts, i.e., decreased lactate generation from labeled glucose and increased α-ketoglutarate synthesis from labeled palmitate. The decreased lactate generation by EMPA seems to be mediated through NHE-1 inhibition.

Endothelial FGFR1 (Fibroblast Growth Factor Receptor 1) Deficiency Contributes Differential Fibrogenic Effects in Kidney and Heart of Diabetic Mice.

Endothelial-to-mesenchymal transition (EndMT) has been shown to contribute to organ fibrogenesis. We have reported that N-acetyl-seryl-aspartyl- lysyl-proline (AcSDKP) restored levels of diabetes mellitus-suppressed FGFR1 (fibroblast growth factor receptor 1), the endothelial receptor essential for combating EndMT. However, the molecular regulation and biological/pathological significance of the AcSDKP-FGFR1 relationship has not been elucidated yet. Here, we demonstrated that endothelial FGFR1 deficiency led to AcSDKP-resistant EndMT and severe fibrosis associated with EndMT-stimulated fibrogenic programming in neighboring cells. Diabetes mellitus induced severe kidney fibrosis in endothelial FGFR1-deficient mice (FGFR1fl/fl; VE-cadherin-Cre: FGFR1EKO) but not in control mice (FGFR1fl/fl); AcSDKP completely or partially suppressed kidney fibrosis in control or FGFR1EKO mice. Severe fibrosis was also induced in hearts of diabetic FGFR1EKO mice; however, AcSDKP had no effect on heart fibrosis in FGFR1EKO mice. AcSDKP also had no effect on EndMT in either kidney or heart but partially suppressed epithelial-to-mesenchymal transition in kidneys of diabetic FGFR1EKO mice. The medium from FGFR1-deficient endothelial cells stimulated TGFβ (transforming growth factor β)/Smad-dependent epithelial-to-mesenchymal transition in cultured human proximal tubule epithelial cell line, AcSDKP inhibited such epithelial-to-mesenchymal transition. These data demonstrated that endothelial FGFR1 is essential as an antifibrotic core molecule as the target of AcSDKP.

Si-Miao-Yong-An decoction preserves cardiac function and regulates GLC/AMPK/NF-κB and GLC/PPARα/PGC-1α pathways in diabetic mice

BackgroundDiabetic cardiomyopathy (DCM) is a main cause of heart failure and death in diabetic patients. However, countermeasures to limit the development of this disease remain insufficient. Si-Miao-Yong-An decoction (SMYA), a Chinese herbal prescription, exhibits both lipid-lowering and cardiovascular preserving effects, and may have an effect on DCM management. PurposeThe current study is aimed to investigate the effects of SMYA on the cardiac function in diabetic mice and the underlying mechanisms involved. MethodsStreptozotocin-induced diabetic mice were fed intragastrically with SMYA every day for 15 weeks. Cardiac function was assessed by echocardiograph. Histopathological alterations in the heart were determined by hematoxylin/eosin, wheat germ agglutinin, Masson’s trichrome, Terminal dUTP nick end-labeling, Oil red O staining, and transmission electron microscopy. The potential involvements of GLC/AMPK/NF-κB and GLC/PPARα/PGC-1α signaling pathways were investigated by western blot and/or immunohistochemical staining. ResultsTreatment of diabetic mice with SMYA improved insulin sensitivity, and attenuated the increases of water consumption, food intake, blood glucose, and serum GLC. Furthermore, SMYA ameliorated cardiac systolic and diastolic functions, suppressed the myocardial hypertrophy, fibrosis, apoptosis, inflammation, and lipid accumulation as well as preserved the myofilaments arrangement and mitochondrial integrity. Finally, SMYA downregulated the expressions of GCGR, PGC-1α, PPARα and the phosphorylation of NF-κB, as well as upregulated the phosphorylation of AMPK in the hearts of diabetic mice. ConclusionsSMYA may ameliorate glucolipid metabolism and cardiac function through the regulation of GLC/AMPK/NF-κB and GLC/PPARα/PGC-1α signaling pathways in diabetic mice, suggesting that this prescription could provide a new source of drug candidates to protect against DCM.

Diet reversal rescues mouse diabetic cardiomyopathy by counteracting the decreased reticulum-mitochondria interactions and the ensuing mitochondrial Ca2+ uptake impairment

Type 2 diabetic cardiomyopathy has been linked to Ca2+ signaling alterations, notably a decreased mitochondrial Ca2+ uptake. Recent discovery of Ca2+ microdomains between cardiac mitochondria and reticulum launched a new investigation avenue for cardiometabolic diseases. Hereby, we aimed to investigate if the mitochondrial Ca2+ mishandling is due to a dysregulation of the reticulum-mitochondria interactions or of the mitochondrial Ca2+ uniporter in the diabetic mouse heart. Mice fed for 16 weeks with a high fat high sucrose diet (HFHSD) displayed a cardiac insulin resistance combined to cardiac fibrosis, hypertrophy and contractile dysfunction (decreased strain rate) versus standard diet-fed mice (SD). Fractionation of HFHSD mice hearts revealed a decreased protein content of their mitochondria associated-reticulum membranes, together with a lower expression of tethering proteins quantified by mass spectrometry. On functional terms, reduced IP3R-VDAC proximity and co-immunoprecipitation were associated with a reduced IP3-stimulated Ca2+ transfer to mitochondria in isolated HFHSD cardiomyocytes, yet no changes in mitochondrial calcium uniporter protein expression and function were detected. Moreover, HFHSD cardiomyocytes displayed no significant changes in the reticular Ca2+ release level and the amplitude of cytosolic Ca2+ transients. Eight weeks of diet reversal restored the cardiac insulin signaling, MAM content, Ca2+ transfer and cardiac function in HFHSD mice. Therefore, our data indicate that disruption of the cardiac reticulum-mitochondria interactions is an early and reversible event impairing mitochondrial Ca2+ handling and contributing to the cardiac contractile dysfunction in the diabetic mouse heart, which could be counteracted by diet reversal.

Pericyte coverage of cardiac capillaries is decreased in diabetic obese mice

Heart failure with preserved ejection fraction (HFpEF) which results from diastolic dysfunction is a growing epidemiologic problem. The pathophysiology of this disease is poorly understood nevertheless a theory suggests a central role of microvessel disease. Our goal is to investigate the role of pericyte in the pathophysiology of cardiac microvessel disease and diastolic dysfunction. Pericytes are mural cells known to be essential for microvascular integrity especially in the brain, and in the retina. We have used Leptin receptor deficient (Leprdb/db) female mice as a model of HFpEF and assessed pericyte coverage of cardiac capillaries. Besides, to identify factors that may cause pericyte loss in the heart, we performed, cell viability assays using cultured human pericytes from placenta. In Leprdb/db mice, end-diastolic pressure (EDP) signing diastolic dysfunction is significantly increased from 3 month of age [12.0 ± 1.4 vs 4.4 ± 0.4 mmHg ( P < 0.001)]. It is correlated with signs of microvessel disease especially vascular leakage and endothelial cell activation. Interestingly, we found that pericyte coverage of cardiac capillaries is significantly reduced in Leprdb/db female mice from 6 weeks of age [93.88 ± 2.30 vs 54.67 ± 5.32 ( P < 0.001)]. Notably, this anomaly precedes the onset of endothelial dysfunction and diastolic dysfunction. Cell culture assay showed that oxidized LDLs but not high glucose or TNFα significantly decrease pericyte survival [100.00 ± 6.48 vs 76.22 ± 4.49 with 30 μg/mL ( P < 0.01)]. Our results show that pericyte coverage of capillaries is significantly decreased in the heart of diabetic obese mice probably because of increased oxidized LDL and support that degeneration of cardiac pericytes may contribute to the development of cardiac microvessel disease and diastolic dysfunction in diabetic obese mice and may be due to oxidized LDL.

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.

Application of untargeted lipidomics based on UHPLC-high resolution tandem MS analysis to profile the lipid metabolic disturbances in the heart of diabetic cardiomyopathy mice

Diabetic cardiomyopathy (DCM) is a distinct form of heart disease caused by diabetes. Lipid accumulation has been reported to present in the hearts of DCM animals, however characterization of disordered lipids, and their roles in the etiology and progress of DCM remain largely undefined. In present study, an untargeted lipidomics based on ultra-high performance liquid chromatography coupled with hybrid quadrupole-orbitrap mass spectrometers was established for global detection of lipids in the hearts of DCM mice. DCM mice showed significant cardiac dysfunction with decreased left ventricular fractional shortening (FS) and ratio of peak early filling velocity to atrial filling velocity (MV E/A). Histological lesion, fibrosis, hypertrophy, and lipid accumulation were also observed in the heart of DCM mice. By lipidomics analysis, a total of 244 lipids were identified, of which 89 lipids were significantly changed. The disordered metabolic profile of lipids in DCM mice heart were characterized by the accumulation of triacylglycerol, glycerophospholipid, cholesterol-sulfate, ceramide and sphingomyelin, as well as by the loss of glycerophospholipid. The lipid alterations in the heart were correlated with the development of cardiac dysfunction, lipotoxicity, inflammation and insulin resistance. Correlations between lipid metabolism disorders and DCM progress should be further explored.

Novel Dual-Fluorescent Mitophagy Reporter Reveals a Reduced Mitophagy Flux in Type 1 Diabetic Mouse Heart.

Patients with diabetes are susceptible to heart failure. Defective mitochondria can cause cardiac damage. Mitochondrial autophagy or mitophagy is a quality control mechanism that eliminates dysfunctional mitochondria through lysosome degradation. Mitophagy is essential for maintaining a pool of healthy mitochondria for normal cardiac function. However, the effect of diabetes on the functional status of cardiac mitophagy remains unclear. To determine and compare cardiac mitophagy flux between diabetic and nondiabetic mice. Using a novel dual fluorescent mitophagy reporter termed mt-Rosella, we labeled and traced mitochondrial fragments that are sequestered by the autophagosome and delivered to and degraded in the lysosome. Mitophagic activity was reduced in high-glucose-treated cardiomyocytes and in the heart tissue of type 1 diabetic mice. Mitophagy was impaired in the heart of diabetic mice, suggesting that restoring or accelerating mitophagy flux may be a useful strategy to reduce cardiac injury caused by diabetes.

2225-PUB: Direct Actions of the Dual SGLT1/2 Inhibitor Sotagliflozin on Functional Recovery following Global Ischemia in Diabetic and Healthy Mouse Hearts

Sotagliflozin is a dual sodium-dependent glucose transporter (SGLT) inhibitor with the potential to be cardio-protective in people with and without diabetes. Here, we used an ex vivo Langendorff reperfusion model to investigate if direct infusion with sotagliflozin in hearts from diabetic and healthy mice improves functional recovery from global ischemia. Male C57Bl/6 mice were fed either a control chow (CON) or high fat diet (HFD; 60% of calories from fat) for 46-48 weeks. Fasting blood glucose measurements were performed and body composition measured using nuclear magnetic resonance. Constant pressure Langendorff perfusion experiments were performed on hearts from each diet group. Following equilibration, hearts were infused with either sotagliflozin (90 nM) or dimethyl sulfoxide (VEH) for 10 min prior to a 25 min period of global ischemia. The infusions were recommenced for the first 15 min of 45 min reperfusion. Post ischemic recovery was assessed as % baseline recovery. HFD mice were heavier (54 vs. 34 g) with increased fat mass (42 vs. 19 %) and increased fasting blood glucose (9.6 vs. 8.0 mmol/L). Paradoxically, their functional recovery from global ischemia was, in general, better when compared with hearts from CON mice and there was no effect of sotagliflozin infusion. In CON mice, early post-ischemic coronary flow was greater with sotagliflozin infusion when compared with VEH. Functional recovery in dP/dtmax and dP/dtmin was also greater with sotagliflozin infusion when compared with VEH. In conclusion, HFD exerted a protective effect on heart function, despite inducing obesity and hyperglycemia. Ongoing studies are examining the effects of sotagliflozin in an alternative model of T2DM. In lean mice, sotagliflozin increased functional recovery from global ischemia, highlighting the potential benefits of an antidiabetic agent in acute coronary care. Disclosure E.S. Dorey: None. B. Cotter: None. T.P. Mullins: None. M.E. Reichelt: None. L.A. Gallo: None. Funding Diabetes Australia

Multi-Omics Analysis of Diabetic Heart Disease in the db/db Model Reveals Potential Targets for Treatment by a Longevity-Associated Gene.

Characterisation of animal models of diabetic cardiomyopathy may help unravel new molecular targets for therapy. Long-living individuals are protected from the adverse influence of diabetes on the heart, and the transfer of a longevity-associated variant (LAV) of the human BPIFB4 gene protects cardiac function in the db/db mouse model. This study aimed to determine the effect of LAV-BPIFB4 therapy on the metabolic phenotype (ultra-high-performance liquid chromatography-mass spectrometry, UHPLC-MS) and cardiac transcriptome (next-generation RNAseq) in db/db mice. UHPLC-MS showed that 493 cardiac metabolites were differentially modulated in diabetic compared with non-diabetic mice, mainly related to lipid metabolism. Moreover, only 3 out of 63 metabolites influenced by LAV-BPIFB4 therapy in diabetic hearts showed a reversion from the diabetic towards the non-diabetic phenotype. RNAseq showed 60 genes were differentially expressed in hearts of diabetic and non-diabetic mice. The contrast between LAV-BPIFB4- and vehicle-treated diabetic hearts revealed eight genes differentially expressed, mainly associated with mitochondrial and metabolic function. Bioinformatic analysis indicated that LAV-BPIFB4 re-programmed the heart transcriptome and metabolome rather than reverting it to a non-diabetic phenotype. Beside illustrating global metabolic and expressional changes in diabetic heart, our findings pinpoint subtle changes in mitochondrial-related proteins and lipid metabolism that could contribute to LAV-BPIFB4-induced cardio-protection in a murine model of type-2 diabetes.

Systemic Delivery of siRNA Specific for Silencing TLR4 Gene Expression Reduces Diabetic Cardiomyopathy in a Mouse Model of Streptozotocin-Induced Type1 Diabetes.

IntroductionDiabetic cardiomyopathy is a cardiac dysfunction in patients with diabetes which may lead to overt heart failure and death. Toll-like receptor (TLR) signaling triggers diabetic cardiomyopathy through various mechanisms, one of which is the upregulation of TLR4 expression. The aim of this study was to delineate the role of TLR4 in diabetic cardiomyopathy.MethodsC57BL/6 mice were injected with streptozotocin to induce diabetes. The experimental and control groups were treated with 5 μg of TLR4 small interfering RNA (siRNA) or scrambled siRNA. Cardiac histopathology was evaluated by hematoxylin and eosin, Sirius red, and immunofluorescence staining after treatment with TLR4 siRNA. The myocardial fibrosis and inflammatory factors were detected by quantitative real-time polymerase chain reaction after treatment with TLR4 siRNA. The myocardial function was evaluated by echocardiography after treatment with TLR4 siRNA.ResultsCompared with non-diabetic mouse hearts, hypertrophy, fibrosis, inflammation of cardiomyocytes, and myocardial dysfunction were significantly increased in diabetic mice (p < 0.05). Knockdown of TLR4 decreased hypertrophy, fibrosis, inflammation of cardiomyocytes, and myocardial dysfunction (p < 0.05). Cardiomyocytic cross-sectional areas in hearts of TLR4 siRNA-treated diabetic mice were similar to those of the sham-treated mice (p > 0.05). The induction of expression of cardiac fetal genes, beta-myosin heavy chain (β-MHC) and atrial natriuretic peptide (ANP), which are two markers of cardiac hypertrophy, was significantly reduced in TLR4 siRNA-treated hearts compared with controls (p < 0.05). Moreover, siRNA-mediated silencing of TLR4 reduced diabetes-induced collagen deposition (p < 0.05). Paralleled with changes in collagen deposition and the expression of collagen I and collagen III, knockdown of TLR4 also reduced the expression of transforming growth factor-β1 (TGFβ1) mRNA (p < 0.05). The increased expression of intercellular cell adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1) was significantly attenuated by TLR4 siRNA treatment in the hearts of diabetic mice (p < 0.05). Furthermore, both fractional shortening (FS) and ejection fraction (EF) values were preserved in TLR4 siRNA-treated diabetic mice compared with control siRNA-treated mice (31.80% ± 2.82% vs. 28.50% ± 5.83% for FS, p < 0.05) (57.95% ± 6.48% vs. 45.34% ± 4.25% for EF, p < 0.05).ConclusionOur study used siRNA to specifically silence TLR4 gene expression in the diabetic mouse heart in vivo and to investigate the role that TLR4 plays in diabetic cardiomyopathy. It is likely that silencing of the TLR4 gene through siRNA could prevent the development of diabetic cardiomyopathy.

Suppression of Organismal Death Pathway in the Heart Tissues of Diabetic Mice by NP‐ 6A4, A Peptide Agonist of the Angiotensin II Receptor AT2R

BackgroundDiabetes accelerates cardiac dysfunction and aging. Angiotensin II type 2 receptor AT2R is a member of the anti‐inflammatory arm of the renin‐angiotensin‐aldosterone (RAAS) system. NP‐6A4 is an AT2R peptide agonist with the FDA orphan drug designation for pediatric cardiomyopathy. To test the hypothesis that NP‐6A4‐AT2R signaling is cardioprotective in chronic diabetes, we investigated the changes in cardiac proteome of 63‐week old diabetic mice after a 55‐week treatment with NP‐6A4.Methods and ResultsAll studies were conducted in accordance with the FASEB Statement of Principles for the use of Animals in Research and Education. Diabetes was induced in 8‐week old male c57Bl6 mice via intraperitoneal delivery of streptozotocin (STZ: 50mg/kg/day: 5 days; n=11). Fasting insulin levels were decreased in the STZ‐treated mice (~0.2±0.03 ng/mL versus ~0.94±0.08ng/mL in control mice; p&lt;0.05), but fasting glucose was increased (313±29mg/dL p&lt;0.05). STZ‐treated mice also showed a reduction in body weight by ~10–14% compared to control mice (p&lt;0.05). NP‐6A4 treatment (5mg/kg/day; n=5) of STZ‐treated mice did not change these metabolic parameters. Whole proteome analysis of the cardiac tissues of these 63‐week old mice identified a total of 2760 protein groups in 15 samples with the following criteria: &gt;=2 unique peptides per protein, peptide spectrum FDR &lt;1%. For quantification, a threshold minimum of 4 spectral counts (average of each group of replicates) was used. This resulted in a quantified proteome of 1,569 proteins. NP‐6A4 treated mice hearts exhibited 109 significant differences (p&lt;0.01) compared to vehicle treated diabetic mice hearts with 100 proteins showing increased and 9 proteins showing decreased abundance. Analysis of these data using Ingenuity Pathway Analysis (IPA) showed that 32 of deferentially expressed proteins in diabetic mouse heart induced a pathway designated ‘suppression of organismal death’ (Z score −4.706). Comparing NP‐6A4‐treated mice hearts to healthy mice hearts resulted in 311 significant differences (p&lt;0.01), with 253 proteins increased and 58 proteins decreased. Moreover, 82 of these differentially expressed proteins in the NP‐6A4‐treated mice hearts, compared to healthy control mice hearts, also induced the pathway ‘suppression of organismal death’ (Z score‐3.415).ConclusionA 55‐week treatment with NP‐6A4 induced a cardioprotective pathway in diabetic mouse heart that has the potential to suppress organismal death when compared to age‐matched healthy mice or vehicle treated diabetic mice. This observation suggests that continuous treatment with NP‐6A4 in chronic diseases such as diabetes has the potential to confer cardiac protection and prevent organ failure.Support or Funding InformationThis work was supported by NIH NHLBI 1R01HL118376‐01 (LP), and NIH NHLBI 1R01HL138988‐01A1 (LP) and a small grant from Novopyxis Inc. (LP).

Dihydromyricetin Prevents Diabetic Cardiomyopathy via miR-34a Suppression by Activating Autophagy.

The pro-aging miRNA, miR-34a, is hyperactivated in the cardiac myocardial tissues of patients and mice with diabetes, leading to diabetic cardiomyopathy (DCM). Increasing evidence suggests that dihydromyricetin (DHM) can be used to effectively treat cardiomyopathy. In this study, we investigated whether DHM affects the expression of miR-34a in DCM. The expression of miR-34a in high-glucose-induced cardiomyocytes and in the heart tissue of diabetic mice was determined by microRNA isolation and quantitative reverse transcription-polymerase chain reaction. Lipofectamine 3000 was used to transfect cardiomyocytes with miR-34a inhibitor, miR-34a mimics, and miR-control. These agents were intravenously injected into the tail vein of streptozotocin-induced diabetic mice. Autophagy and apoptosis were assessed in high-glucose-induced cardiomyocytes and cardiac tissue in diabetic mice by western blotting, immunofluorescence, Masson staining, hematoxylin and eosin staining (H&E), and electron microscopy. DHM clearly ameliorated the cardiac dysfunction in the diabetic mice. The expression of miR-34a was up-regulated in high-glucose-induced cardiomyocytes and in the hearts of diabetic mice, thus impairing autophagy. Treatment with DHM decreased the expression of miR-34a and rescued the impairment of autophagy in high-glucose-induced cardiomyocytes and in the heart tissue of diabetic mice, while the miR-34a mimic offset the effect of DHM with respect to the development of DCM by inhibiting autophagy. By decreasing the expression of miR-34a, DHM restores impaired autophagy, and thus ameliorates DCM. Therefore, DHM may potentially be used in the treatment of DCM.

High-mobility group AT-hook 1 promotes cardiac dysfunction in diabetic cardiomyopathy via autophagy inhibition

High-mobility group AT-hook1 (HMGA1, formerly HMG-I/Y), an architectural transcription factor, participates in a number of biological processes. However, its effect on cardiac remodeling (refer to cardiac inflammation, apoptosis and dysfunction) in diabetic cardiomyopathy remains largely indistinct. In this study, we found that HMGA1 was upregulated in diabetic mouse hearts and high-glucose-stimulated cardiomyocytes. Overexpression of HMGA1 accelerated high-glucose-induced cardiomyocyte inflammation and apoptosis, while HMGA1 knockdown relieved inflammation and apoptosis in cardiomyocytes in response to high glucose. Overexpression of HMGA1 in mice heart by adeno-associated virus 9 (AAV9) delivery system deteriorated the inflammatory response, increased apoptosis and accelerated cardiac dysfunction in streptozotocin-induced diabetic mouse model. Knockdown of HMGA1 by AAV9-shHMGA1 in vivo ameliorated cardiac remodeling in diabetic mice. Mechanistically, we found that HMGA1 inhibited the formation rather than the degradation of autophagy by regulating P27/CDK2/mTOR signaling. CDK2 knockdown or P27 overexpression blurred HMGA1 overexpression-induced deteriorating effects in vitro. P27 overexpression in mice heart counteracted HMGA1 overexpression-induced increased cardiac remodeling in diabetic mice. The luciferase reporter experiment confirmed that the regulatory effect of HMGA1 on P27 was mediated by miR-222. In addition, a miR-222 antagomir counteracted HMGA1 overexpression-induced deteriorating effects in vitro. Taken together, our data indicate that HMGA1 aggravates diabetic cardiomyopathy by directly regulating miR-222 promoter activity, which inhibits P27/mTOR-induced autophagy.

Akap1 deficiency exacerbates diabetic cardiomyopathy in mice by NDUFS1-mediated mitochondrial dysfunction and apoptosis.

Diabetic cardiomyopathy, characterised by increased oxidative damage and mitochondrial dysfunction, contributes to the increased risk of heart failure in individuals with diabetes. Considering that A-kinase anchoring protein 121 (AKAP1) is localised in the mitochondrial outer membrane and plays key roles in the regulation of mitochondrial function, this study aimed to investigate the role of AKAP1 in diabetic cardiomyopathy and explore its underlying mechanisms. Loss- and gain-of-function approaches were used to investigate the role of AKAP1 in diabetic cardiomyopathy. Streptozotocin (STZ) was injected into Akap1-knockout (Akap1-KO) mice and their wild-type (WT) littermates to induce diabetes. In addition, primary neonatal cardiomyocytes treated with high glucose were used as a cell model of diabetes. Cardiac function was assessed with echocardiography. Akap1 overexpression was conducted by injecting adeno-associated virus 9 carrying Akap1 (AAV9-Akap1). LC-MS/MS analysis and functional experiments were used to explore underlying molecular mechanisms. AKAP1 was downregulated in the hearts of STZ-induced diabetic mouse models. Akap1-KO significantly aggravated cardiac dysfunction in the STZ-treated diabetic mice when compared with WT diabetic littermates, as evidenced by the left ventricular ejection fraction (LVEF; STZ-treated WT mice [WT/STZ] vs STZ-treated Akap1-KO mice [KO/STZ], 51.6% vs 41.6%). Mechanistically, Akap1 deficiency impaired mitochondrial respiratory function characterised by reduced ATP production. Additionally, Akap1 deficiency increased cardiomyocyte apoptosis via enhanced mitochondrial reactive oxygen species (ROS) production. Furthermore, immunoprecipitation and mass spectrometry analysis indicated that AKAP1 interacted with the NADH-ubiquinone oxidoreductase 75kDa subunit (NDUFS1). Specifically, Akap1 deficiency inhibited complex I activity by preventing translocation of NDUFS1 from the cytosol to mitochondria. Akap1 deficiency was also related to decreased ATP production and enhanced mitochondrial ROS-related apoptosis. In contrast, restoration of AKAP1 expression in the hearts of STZ-treated diabetic mice promoted translocation of NDUFS1 to mitochondria and alleviated diabetic cardiomyopathy in the LVEF (WT/STZ injected with adeno-associated virus carrying gfp [AAV9-gfp] vs WT/STZ AAV9-Akap1, 52.4% vs 59.6%; KO/STZ AAV9-gfp vs KO/STZ AAV9-Akap1, 42.2% vs 57.6%). Our study provides the first evidence that Akap1 deficiency exacerbates diabetic cardiomyopathy by impeding mitochondrial translocation of NDUFS1 to induce mitochondrial dysfunction and cardiomyocyte apoptosis. Our findings suggest that Akap1 upregulation has therapeutic potential for myocardial injury in individuals with diabetes.

Salvianolic acid B improves myocardial function in diabetic cardiomyopathy by suppressing IGFBP3

BackgroundSalvianolic acid B (Sal B) is the representative component of phenolic acids derived from the dried root and rhizome of Salvia miltiorrhiza Bge. (Labiatae), which has been widely used for the treatment of cardiovascular and cerebrovascular diseases. However, the effect of Sal B on diabetic cardiomyopathy (DCM) is still unclear. MethodsType 1 diabetes mellitus was induced in C57BL/6 J mice by streptozotocin (STZ) treatment, whereas meanwhile Salvianolic Acid B (Sal B (15 or 30 mg/kg/d) was intraperitoneally injected for 16 weeks. At the end of this period, cardiac function was assessed by echocardiography, and total collagen deposition was evaluated by Masson's trichrome and Picrosirius Red staining. Human umbilical vein endothelial cells exposed to hypoxia were used to investigate the effect of different doses of Sal B on angiogenesis and tube formation in vitro. Transcriptome sequencing was performed to identify potential targets of Sal B. ResultsSal B ameliorated left ventricular dysfunction and remodeling, and decreased collagen deposition in the heart of diabetic mice. Administration of Sal B increased the expression of vascular endothelial growth factor (VEGF) receptor 2 (VEGFR2) and VEGFA in a dose-dependent manner and promoted angiogenesis both in vivo and in vitro. Furthermore, Sal B reduced HG-induced insulin-like growth factor-binding protein 3 (IGFBP3) expression, induced the phosphorylation of extracellular signal-regulated protein kinase and protein kinase B (AKT) activities, enhanced cell proliferation, and activated VEGFR2/VEGFA signaling in endothelial cells. The underlying mechanisms involve SalB that enhances IGFBP3 promoter DNA methylation and induce nuclear translocation of IGFBP3 in HUVECs under hypoxia. ConclusionsSal B promoted angiogenesis and alleviated cardiac fibrosis and cardiac remodeling in DCM by suppressing IGFBP3.

Exercise enhances cardiac function by improving mitochondrial dysfunction and maintaining energy homoeostasis in the development of diabetic cardiomyopathy.

Diabetic cardiomyopathy (DCM) is a major cause of morbidity and mortality in diabetic patients. Reactive oxygen species (ROS) produced by oxidative stress play an important role in the development of DCM. DCM involves abnormal energy metabolism, thereby reducing energy production. Exercise has been reported to be effective in protecting the heart against ROS accumulation during the development of DCM. We hypothesize that the AMPK/PGC-1α axis may play a crucial role in exercise-induced bioenergetic metabolism and aerobic respiration on oxidative stress parameters in the development of diabetic cardiomyopathy. Using a streptozotocin/high-fat diet mouse to generate a diabetic model, our aim was to evaluate the effects of exercise on the cardiac function, mitochondrial oxidative capacity, mitochondrial function, and cardiac expression of PGC-1α. Mice fed a high-fat diet were given MO-siPGC-1α or treated with AMPK inhibitor. Mitochondrial structure and effects of switching between the Warburg effect and aerobic respiration were analysed. Exercise improved blood pressure and systolic dysfunction in diabetic mouse hearts. The beneficial effects of exercise were also observed in a mitochondrial function study, as reflected by an enhanced oxidative phosphorylation level, increased membrane potential, and decreased ROS level and oxygen consumption. On the other hand, depletion of PGC-1α attenuated the effects of exercise on the enhancement of mitochondrial function. In addition, PGC-1α may be responsible for reversing the Warburg effect to aerobic respiration, thus enhancing mitochondrial metabolism and energy homoeostasis. In this study, we demonstrate the protective effects of exercise on shifting energy metabolism from fatty acid oxidation to glucose oxidation in an established diabetic stage. These data suggest that exercise is effective at ameliorating diabetic cardiomyopathy by improving mitochondrial function and reducing metabolic disturbances.

PP2Cm overexpression alleviates MI/R injury mediated by a BCAA catabolism defect and oxidative stress in diabetic mice

Diabetic patients are sensitive to myocardial ischemia-reperfusion (MI/R) injury. During diabetes, branched-chain amino acid (BCAA) catabolism is defective and mitochondrial phosphatase 2C (PP2Cm) expression is reduced. This study aims to elucidate the relationship between PP2Cm downregulation and BCAA catabolism defect in diabetic mice against MI/R injury. PP2Cm was significantly downregulated in hearts of diabetic mice. The cardiac function was improved and the myocardial infarct size and apoptosis were decreased in diabetic mice overexpressing PP2Cm after MI/R. In diabetic mice, the cardiac BCAA and its metabolites branched-chain keto-acids (BCKA) levels, and p-BCKDE1α (E1 subunit of BCKA dehydrogenase)/BCKDE1α ratio were increased while the BCKD activity was decreased. Treatment of diabetic mice subjected to MI/R injury with BT2, a BCKD kinase (BDK) inhibitor, alleviated the BCAA catabolism defect, and improved the cardiac function alongside reduced apoptosis. PP2Cm overexpression alleviated the BCAA catabolism defect and MI/R injury. Similarly, MnTBAP ameliorated the oxidative stress and MI/R injury. BCKA treatment of H9C2 cells under simulated ischemia/reperfusion (SI/R) injury significantly decreased cell viability and increased LDH release and apoptosis. These effects were alleviated by BT2 and MnTBAP treatments. These results suggested that PP2Cm directly mediates the BCAA catabolism defect and oxidative stress observed after MI/R in diabetes. Overexpression of PP2Cm alleviates MI/R injury by reducing the catabolism of BCAA and oxidative stress.

Increased arrhythmia susceptibility in type 2 diabetic mice related to dysregulation of ventricular sympathetic innervation.

Patients with type 2 diabetes mellitus (T2DM) have a greater risk of developing life-threatening cardiac arrhythmias. Because the underlying mechanisms and potential influence of diabetic autonomic neuropathy are not well understood, we aimed to assess the relevance of a dysregulation in cardiac autonomic tone. Ventricular arrhythmia susceptibility was increased in Langendorff-perfused hearts isolated from mice with T2DM (db/db). Membrane properties and synaptic transmission were similar at cardiac postganglionic parasympathetic neurons from diabetic and control mice; however, a greater asynchronous neurotransmitter release was present at sympathetic postganglionic neurons from the stellate ganglia of db/db mice. Western blot analysis showed a reduction of tyrosine hydroxylase (TH) from the ventricles of db/db mice, which was confirmed with confocal imaging as a heterogeneous loss of TH-immunoreactivity from the left ventricular wall but not the apex. In vivo stimulation of cardiac parasympathetic (vagus) or cardiac sympathetic (stellate ganglion) nerves induced similar changes in heart rate in control and db/db mice, and the kinetics of pacing-induced Ca2+ transients (recorded from isolated cardiomyocytes) were similar in control and db/db cells. Antagonism of cardiac muscarinic receptors did not affect the frequency or severity of arrhythmias in db/db mice, but sympathetic blockade with propranolol completely inhibited arrhythmogenicity. Collectively, these findings suggest that the increased ventricular arrhythmia susceptibility of type 2 diabetic mouse hearts is due to dysregulation of the sympathetic ventricular control.NEW & NOTEWORTHY Patients with type 2 diabetes mellitus have greater risk of suffering from sudden cardiac death. We found that the increased ventricular arrhythmia susceptibility in type 2 diabetic mouse hearts is due to cardiac sympathetic dysfunction. Sympathetic dysregulation is indicated by an increased asynchronous release at stellate ganglia, a heterogeneous loss of tyrosine hydroxylase from the ventricular wall but not apex, and inhibition of ventricular arrhythmias in db/db mice after β-sympathetic blockade.