Calcitriol Suppressed Isoproterenol-induced Proliferation of Cardiac Fibroblasts via Integrin β3/FAK/Akt Pathway

Cardiac fibroblasts (CFs) proliferation and extracellular matrix deposition are important features of cardiac fibrosis. Various studies have indicated that vitamin D displays an anti-fibrotic property in chronic heart diseases. This study explored the role of vitamin D in the growth of CFs via an integrin signaling pathway.

MTT and 5-ethynyl-2'-deoxyuridine assays were performed to determine cell viability. Western blotting was performed to detect the expression of proliferating cell nuclear antigen (PCNA) and integrin signaling pathway. The fibronectin was observed by ELISA. Immunohistochemical staining was employed to evaluate the expression of integrin β3.

The PCNA expression in the CFs was enhanced after isoproterenol (ISO) stimulation accompanied by an elevated expression of integrin beta-3 (β3). The blockade of the integrin β3 with a specific integrin β3 antibody reduced the PCNA expression induced by the ISO. Decreasing the integrin β3 by siRNA reduced the ISO-triggered phosphorylation of FAK and Akt. Both the FAK inhibitor and Akt inhibitor suppressed the PCNA expression induced by the ISO in the CFs. Calcitriol (CAL), an active form of vitamin D, attenuated the ISO-induced CFs proliferation by downregulating the integrin β3 expression, and phosphorylation of FAK and Akt. Moreover, CAL reduced the increased levels of fibronectin and hydroxyproline in the CFs culture medium triggered by the ISO. The administration of calcitriol decreased the integrin β3 expression in the ISO-induced myocardial injury model.

These findings revealed a novel role for CAL in suppressing the CFs growth by the downregulation of the integrin β3/FAK/Akt pathway.