Exogenous Pancreatic Kallikrein Improves Diabetic Cardiomyopathy in Streptozotocin-Induced Diabetes

ACMSD mediated de novo NAD+ biosynthetic impairment in cardiac endothelial cells as a potential therapeutic target for diabetic cardiomyopathy

OBJECT

The highly conserved α-amino-β-carboxymuconate-ε-semialdehyde decarboxylase (ACMSD) is the key enzyme that regulates the de novo NAD+ synthesis from tryptophan. NAD+ metabolism in diabetic cardiomyopathy (DCM) was not elucidated yet.

METHODS

Mice were assigned to non-diabetic (NDM) group, streptozocin (STZ)-induced diabetic (DM) group, and nicotinamide (NAM) treated (DM + NAM) group. ACMSD mediated NAD+ metabolism were studied both in mice and patients with diabetes.

RESULTS

NAD+ level was significantly lower in the heart of DM mice than that of the NDM group. Supplementation with NAM could partially increased myocardial capillary density and ameliorated myocardial fibrosis by increasing NAD+ level through salvage pathway. Compared with NDM mice, the expression of ACMSD in myocardial endothelial cells of DM mice was significantly increased. It was further confirmed that in endothelial cells, high glucose promoted the expression of ACMSD. Inhibition of ACMSD could increase de novo NAD+ synthesis and improve endothelial cell function by increasing Sirt1 activity. Targeted mass spectrometry analysis indicated increased ACMSD enzyme activity in diabetic patients, higher ACMSD activity increased risk of heart diastolic dysfunction.

CONCLUSION

In summary, increased expression of ACMSD lead to impaired de novo NAD+ synthesis in diabetic heart. Inhibition of ACMSD could potentially improve DCM.

STAT4 regulates cardiomyocyte apoptosis in rat models of diabetic cardiomyopathy

OBJECTIVE

This study aimed to investigate the protective role of the signal transducer and activator of transcription 4 (STAT4) in diabetic cardiomyopathy.

MATERIALS AND METHODS

Male Sprague-Dawley (SD) rats (6-8 weeks old) were purchased from the Experimental Animal Center of Zhengzhou University. The rats were randomly divided into the control and diabetic cardiomyopathy groups. Rat models of diabetic cardiomyopathy were established by a high-sugar and high-fat diet combined with a peritoneal injection of streptozocin. Pathological changes in the heart were visualized using Hematoxylin-eosin (HE) staining and Masson's staining. Moreover, cell apoptosis was detected using terminal deoxyribonucleotidyl transferase (TdT)-mediated biotin-16-dUTP nick-end labeling (TUNEL) staining and Annexin V apoptosis detection kit. Furthermore, H9C2 cells were transfected with lentivirus overexpressing STAT4 and treated with high glucose. The CCK-8 assay was performed to determine cell viability. Finally, Western blotting was used to determine the expression of STAT4, Bax, and Bcl-2.

RESULTS

The myocardial tissue of the diabetic cardiomyopathy models showed hypertrophy, myocardial fibrosis and collagen deposition. Furthermore, TUNEL staining showed increased apoptosis and decreased expression of STAT4 in the myocardial cells. Moreover, the myocardial tissues of the DCM models showed increased expression of Bax/Bcl-2 and a high percentage of Annexin V positive cells. The H9C2 cells showed decreased expression of STAT4 following high glucose treatment. However, the H9C2 cells overexpressing STAT4 showed decreased expression of Bax/Bcl-2 and reduced percentage of Annexin V positive cells.

CONCLUSION

The DCM group had decreased myocardial expression of STAT4. Furthermore, overexpression of STAT4 was shown to reduce high glucose-induced apoptosis.

SGLT2 inhibitor dapagliflozin prevents atherosclerotic and cardiac complications in experimental type 1 diabetes

Introduction

Cardiovascular disease (CVD) is two to five times more prevalent in diabetic patients and is the leading cause of death. Therefore, identification of novel therapeutic strategies that reduce the risk of CVD is a research priority. Clinical trials showed that reduction in the relative risk of heart failure by sodium-glucose cotransporter 2 inhibitors (SGLT2i) are partly beyond their glucose lowering effects, however, the molecular mechanisms are still elusive. Here we investigated the role of SGLT2i dapagliflozin (DAPA) in the prevention of diabetes-induced cardiovascular complications.

Methods

Type 1 diabetes was induced with streptozotocin (65 mg/bwkg, ip.) in adult, male Wistar rats. Following the onset of diabetes rats were treated for six weeks with DAPA (1 mg/bwkg/day, po.).

Results

DAPA decreased blood glucose levels (D: 37±2.7 vs. D+DAPA: 18±5.6 mmol/L; p<0.05) and prevented metabolic decline. Aortic intima-media thickening was mitigated by DAPA. DAPA abolished cardiac hypertrophy, and myocardial damage. Cardiac inflammation and fibrosis were also moderated after DAPA treatment.

Conclusions

These data support the preventive and protective role of SGLT2i in diabetes-associated cardiovascular disease. SGLT2i may provide novel therapeutic strategy to hinder the development of cardiovascular diseases in type 1 diabetes, thereby improve the outcomes.

Matrine Protects Cardiomyocytes Against Hyperglycemic Stress by Promoting Mitofusin 2-Induced Mitochondrial Fusion

Matrine, an active component of Sophora flavescens Ait root extracts, has been used in China for years to treat cancer and viral hepatitis. In the present study, we explored the effects of matrine on hyperglycemia-treated cardiomyocytes. Cardiomyocyte function, oxidative stress, cellular viability, and mitochondrial fusion were assessed through immunofluorescence, quantitative real-time PCR (qRT-PCR), enzyme-linked immunosorbent assays, and RNA interference. Matrine treatment suppressed hyperglycemia-induced oxidative stress in cardiomyocytes by upregulating transcription of nuclear factor erythroid 2-like 2 and heme oxygenase-1. Matrine also improved cardiomyocyte contractile and relaxation function during hyperglycemia, and it reduced hyperglycemia-induced cardiomyocyte death by inhibiting mitochondrial apoptosis. Matrine treatment increased the transcription of mitochondrial fusion-related genes and thus attenuated the proportion of fragmented mitochondria in cardiomyocytes. Inhibiting mitochondrial fusion by knocking down mitofusin 2 (Mfn2) abolished the cardioprotective effects of matrine during hyperglycemia. These results demonstrate that matrine could be an effective drug to alleviate hyperglycemia-induced cardiomyocyte damage by activating Mfn2-induced mitochondrial fusion.

Exogenous pancreatic kininogenase protects against renal fibrosis in rat model of unilateral ureteral obstruction

Tissue kallikrein has protective function against various types of injury. In this study, we investigated whether exogenous pancreatic kininogenase (PK) conferred renoprotection in a rat model of unilateral ureteral obstruction (UUO) and H₂O₂-treated HK-2 cells in vitro. SD rats were subjected to UUO surgery, then PK (7.2 U/g per day, ip) was administered for 7 or 14 days. After the treatment, rats were euthanized; the obstructed kidneys were harvested for further examination. We found that PK administration significantly attenuated interstitial inflammation and fibrosis, and downregulated the expression of proinflammatory (MCP-1, TLR-2, and OPN) and profibrotic (TGF-β1 and CTGF) cytokines in obstructed kidney. UUO-induced oxidative stress, closely associated with excessive apoptotic cell death and autophagy via PI3K/AKT/FoxO1a signaling, which were abolished by PK administration. We further showed that PK administration increased the expression of bradykinin receptors 1 and 2 (B1R and B2R) mRNA and the production of NO and cAMP in kidney tissues. Coadministration with either B1R antagonist (des-Arg9-[Leu8]-bradykinin) or B2R antagonist (icatibant) abrogated the renoprotective effects of PK, and reduced the levels of NO and cAMP in obstructed kidney. In H₂O₂-treated HK-2 cells, addition of PK (6 pg/mL) significantly decreased ROS production, regulated the expression of oxidant and antioxidant enzymes, suppressed the expression of TGF-β1 and MCP-1, and inhibited cell apoptosis. Our data demonstrate that PK treatment protects against the progression of renal fibrosis in obstructed kidneys.

Overexpression of Sirt6 promotes M2 macrophage transformation, alleviating renal injury in diabetic nephropathy

In this study, we aimed to investigate the associations between Sirt6, macrophages and diabetic nephropathy (DN). Immunohistochemical, western blot and RT-qPCR analyses were performed to detect the expression levels of Sirt6, the markers of podocytes and monocytes and related inflammatory factors in the tissues of rats with streptozocin-induced DN. A series of cell experiments in isolated culture or the co-culture of macrophages and podocytes were conducted to examine the effects of the overexpression of Sirt6 on macrophage transformation, podocyte apoptosis and associated genes, and analyses were performed using RT-qPCR, flow cytometry and western blot analysis, where appropriate. In the rat model of DN, injured podocytes were represented by the decreased protein expression levels of Nephrin and Sirt6, and by an increased Desmin expression. Additionally, the M1 phenotype transformation of macrophages was evidenced by the increased expression levels of CD86, tumor necrosis factor (TNF)-α and inducible nitric oxide synthase (iNOS), and by the decreased expression levels of CD206, Sirt6, interleukin (IL)-4 and IL-10. In vitro assays of macrophages and podocytes demonstrated that glucose promoted macrophage M1 transformation and podocyte apoptosis in a dose-dependent manner and attenuated Sirt6 expression. Macrophages transformed into the M2 phenotype following the overexpression of Sirt6 by the successful transfection of macrophages with a Sirt6 overexpression plasmid. Sirt6 was also overexpressed in podocytes. In a Transwell co-culture system, the overexpression of Sirt6 in macrophages (but not the overexpression of Sirt6 in podocytes) protected the podocytes from high-glucose-induced injury. However, the apoptosis of the podocytes overexpressing Sirt6 (induced by transfection with a Sirt6 overexpression plasmid) still increased when these podocytes were co-cultured with macrophages in high-glucose medium. These protective effects were evidenced by the inhibition of apoptosis, the upregulation of the expression levels of Bcl-2 and CD206, as well as by the decreased expression levels of Bax and CD86. On the whole, the findings of this study suggest that Sirt6 protects podocytes against injury in a mimicked diabetic kidney microenvironment by activating M2 macrophages, indicating that Sirt6 can act as an immune response regulatory factor in DN-associated renal inflammatory injury.