Fibroblast-specific activation of Rnd3 protects against cardiac remodeling in diabetic cardiomyopathy via suppression of Notch and TGF-ß signaling.

Rationale: Extracellular matrix (ECM) remodeling, a key pathological feature in diabetic cardiomyopathy (DCM), is triggered by oxidative stress, inflammation, and various metabolic disorders in the heart. Cardiac fibroblasts (CFs) are the primary source of ECM proteins and the ultimate effector cells in ECM remodeling. CFs are turned on and differentiated into myofibroblasts in response to profibrotic signaling. Rnd3 is a small Rho-GTPase involved in the regulation of cell-cycle distribution, cell migration, and cell morphogenesis. Emerging evidence suggests a link between Rnd3 expression and onset of cardiovascular diseases. However, the role of Rnd3 in DCM remains unknown. Methods: Flow cytometry was employed to separate different types of cardiac cells. Type 2 diabetes mellitus was established in Rnd3 fibroblast-specific knockout and transgenic mice. RNA sequencing and chromatin immunoprecipitation assay were used to discern signaling pathways involved. Results: Rnd3 expression was reduced in cardiac tissues of diabetic mice, with CFs being the primary cell type. Fibroblast-specific upregulation of Rnd3 in vivo was protective against DCM, whereas Rnd3 downregulation in fibroblasts accentuated cardiac oxidative stress, fibrosis, ventricular remodeling, and dysfunction. Moreover, in vitro Rnd3 overexpression significantly attenuated reactive oxygen species production, CF migration and proliferation under high levels of glucose (35 mmol/L) and palmitic acid (500 µmol/L) challenge. Furthermore, RNA sequencing indicated that Notch and TGF-ß signaling were significantly suppressed upon Rnd3 overexpression. Mechanistically, Rnd3 regulated Notch and TGF-ß signaling by interacting with NICD and ROCK1, respectively. Specifically, glucotoxicity and lipotoxicity control Rnd3 expression by regulating the binding of Nr1H2 and Rnd3 promoter. Conclusions: Our findings provide compelling evidence in that fibroblast-specific activation of Rnd3 protects against cardiac remodeling in DCM, indicating promises of targeting Rnd3 in the treatment of DCM.

Sirt6-Mediated Endothelial-to-Mesenchymal Transition Contributes Toward Diabetic Cardiomyopathy via the Notch1 Signaling Pathway.

BACKGROUND: Endothelial-to-mesenchymal transition (EndMT) is an important source of myofibroblasts that directly affects cardiac function in diabetic cardiomyopathy (DCM) via an unknown underlying mechanism. Sirt6 is a member of the Sirtuin family of NAD(+)-dependent enzymes that plays an important role in glucose and fatty acid metabolism. In this study, we investigated whether Sirt6 participates in EndMT during the development of T2DM and the possible underlying regulatory mechanisms. METHODS: Endothelium-specific Sirt6 knockout (Sirt6-KOEC) mice (C57BL/6 genetic background) were generated using the classic Cre/loxp gene recombination system. T2DM was induced in eight-week-old male mice by feeding with a high-fat diet for three weeks followed by i.p. injection with 30 mg/kg of streptozotocin. The weight, lipids profiles, insulin, food intake and water intake of experimental animals were measured on a weekly basis. Cardiac microvascular endothelial cells (CMECs) were obtained from adult male mice; the isolated cells were cultured with high glucose (HG; 33 mmol/L) and palmitic acid (PA; 500 µmol/L) in DMEM for 24 h, or with normal glucose (NG; 5 mmol/L) as the control. RESULTS: Sirt6 expression is significantly downregulated in CMECs treated with HG+PA. Additionally, Sirt6-KOEC was found to worsen DCM, as indicated by aggravated perivascular fibrosis, cardiomyocyte hypertrophy, and decreased cardiac function. In vitro, Sirt6 knockdown exacerbated the proliferation, and migration of CMECs exposed to HG+PA. Mechanistically, Sirt6 knockdown significantly enhanced Notch1 activation in CMECs treated with HG+PA, whereas Notch1 adenoviral interference significantly blunted the effects of Sirt6 knockdown on CMECs. CONCLUSION: This study is the first to demonstrate that Sirt6 participates in EndMT via the Notch1 signaling pathway in CMECs stimulated with HG+PA. Therefore, the findings of this study suggest that Sirt6 could provide a potential treatment strategy for DCM.