Cavin-2 promotes fibroblast-to-myofibroblast trans-differentiation and aggravates cardiac fibrosis

Aims Transforming growth factor beta (TGF-beta) signalling is one of the critical pathways in fibroblast activation, and several drugs targeting the TGF-beta/Smad signalling pathway in heart failure with cardiac fibrosis are being tested in clinical trials. Some caveolins and cavins, which are components of caveolae on the plasma membrane, are known for their association with the regulation of TGF-beta signalling. Cavin-2 is particularly abundant in fibroblasts; however, the detailed association between Cavin-2 and cardiac fibrosis is still unclear. We tried to clarify the involvement and role of Cavin-2 in fibroblasts and cardiac fibrosis.Methods and results To clarify the role of Cavin-2 in cardiac fibrosis, we performed transverse aortic constriction (TAC) operations on four types of mice: wild-type (WT), Cavin-2 null (Cavin-2 KO), Cavin-2(flox/flox) , and activated fibroblast-specific Cavin-2 conditional knockout (Postn-Cre/Cavin-2(flox/flox) , Cavin-2 cKO) mice. We collected mouse embryonic fibroblasts (MEFs) from WT and Cavin-2 KO mice and investigated the effect of Cavin-2 in fibroblast trans-differentiation into myofibroblasts and associated TGF-beta signalling. Four weeks after TAC, cardiac fibrotic areas in both the Cavin-2 KO and the Cavin-2 cKO mice were significantly decreased compared with each control group (WT 8.04 +/- 1.58% vs. Cavin-2 KO 0.40 +/- 0.03%, P < 0.01; Cavin-2(flox/flox) , 7.19 +/- 0.50% vs. Cavin-2 cKO 0.88 +/- 0.44%, P < 0.01). Fibrosis-associated mRNA expression (Col1a1, Ctgf, and Col3) was significantly attenuated in the Cavin-2 KO mice after TAC. alpha 1 type I collagen deposition and non-vascular alpha SMA-positive cells (WT 43.5 +/- 2.4% vs. Cavin-2 KO 25.4 +/- 3.2%, P < 0.01) were reduced in the heart of the Cavin-2 cKO mice after TAC operation. The levels of alpha SMA protein (0.36-fold, P < 0.05) and fibrosis-associated mRNA expression (Col1a1, 0.69-fold, P < 0.01; Ctgf, 0.27-fold, P < 0.01; Col3, 0.60-fold, P < 0.01) were decreased in the Cavin-2 KO MEFs compared with the WT MEFs. On the other hand, alpha SMA protein levels were higher in the Cavin-2 overexpressed MEFs compared with the control MEFs (2.40-fold, P < 0.01). TGF-beta 1-induced Smad2 phosphorylation was attenuated in the Cavin-2 KO MEFs compared with WT MEFs (0.60-fold, P < 0.01). Heat shock protein 90 protein levels were significantly reduced in the Cavin-2 KO MEFs compared with the WT MEFs (0.69-fold, P < 0.01).Conclusions Cavin-2 loss suppressed fibroblast trans-differentiation into myofibroblasts through the TGF-beta/Smad signalling. The loss of Cavin-2 in cardiac fibroblasts suppresses cardiac fibrosis and may maintain cardiac function.