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Background Cardiac extracellular matrix is critically involved in cardiac homeostasis, and accumulation of chondroitin sulfate glycosaminoglycans (CS-GAGs) was previously shown to exacerbate heart failure by augmenting inflammation and fibrosis at the chronic phase. However, the mechanism by which CS-GAGs affect cardiac functions remains unclear, especially at the acute phase. Methods and Results We explored a role of CS-GAG in heart failure using mice with target deletion of ChGn-2 (chondroitin sulfate N-acetylgalactosaminyltransferase-2) that elongates CS chains of glycosaminoglycans. Heart failure was induced by transverse aortic constriction in mice. The role of CS-GAG derived from cardiac fibroblasts in cardiomyocyte death was analyzed. Cardiac fibroblasts were subjected to cyclic mechanical stretch that mimics increased workload in the heart. Significant CS-GAGs accumulation was detected in the heart of wild-type mice after transverse aortic constriction, which was substantially reduced in ChGn-2 -/- mice. Loss of ChGn-2 deteriorated the cardiac dysfunction caused by pressure overload, accompanied by augmented cardiac hypertrophy and increased cardiomyocyte apoptosis. Cyclic mechanical stretch increased ChGn-2 expression and enhanced glycosaminoglycan production in cardiac fibroblasts. Conditioned medium derived from the stretched cardiac fibroblasts showed cardioprotective effects, which was abolished by CS-GAGs degradation. We found that CS-GAGs elicits cardioprotective effects via dual pathway; direct pathway through interaction with CD44, and indirect pathway through binding to and activating insulin-like growth factor-1. Conclusions Our data revealed the cardioprotective effects of CS-GAGs; therefore, CS-GAGs may play biphasic role in the development of heart failure; cardioprotective role at acute phase despite its possible unfavorable role in the advanced phase.

Aims: Transforming growth factor β (TGF‐β) signalling is one of the critical pathways in fibroblast activation, and several drugs targeting the TGF‐β/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‐β 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‐2flox/flox, and activated fibroblast‐specific Cavin‐2 conditional knockout (Postn‐Cre/Cavin‐2flox/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‐β 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‐2flox/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. α1 type I collagen deposition and non‐vascular αSMA‐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 αSMA 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, αSMA protein levels were higher in the Cavin‐2 overexpressed MEFs compared with the control MEFs (2.40‐fold, P < 0.01). TGF‐β1‐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‐β/Smad signalling. The loss of Cavin‐2 in cardiac fibroblasts suppresses cardiac fibrosis and may maintain cardiac function. [ABSTRACT FROM AUTHOR]

Introduction: Heart failure (HF) is a debilitating disease associated with high morbidity and mortality. The high mortality rate reflects the inadequacy of modern therapy and calls for new mechanistic treatments. A significant cause of HF is the adverse tissue remodeling with fibrosis. Excessive extracellular matrix (ECM) turnover is involved in the unfortunate outcome. Trans-differentiation of fibroblasts into myofibroblasts is a defining feature of fibrosis. Myofibroblasts express α-smooth muscle actin (αSMA) and secrete ECM proteins. The signals that control the trans-differentiation include the transforming growth factor (TGF)-β1-Smad pathway and Rho GTPase-dependent actin polymerization. Cavins and caveolins are the major protein components of caveolae. The previous report showed that some of cavin family proteins affect cardiac fibrosis and function. However, the structural role of SDPR/Cavin-2 has been well elucidated, the role of SDPR/Cavin-2 in cardiac fibrosis remains unknown. Objective: We investigated the functional role of SDPR/Cavin-2 in cardiac fibrosis and cardiac function induced by pressure overload. Methods and Results: To examine the role of SDPR/Cavin-2 in cardiac function, we performed transverse aortic constriction (TAC) operations on WT mice and Cavin-2-/- mice. Four weeks after TAC procedure, left ventricular fractional shortening was significantly preserved in Cavin-2-/- mice compared with WT mice. Also, the fibrosis area was significantly decreased in Cavin-2-/- mice. (fibrosis area; 0.4± 0.02 % in Cavin-2 KO vs. 8.0 ± 1.44 % in WT, p<0.01). Moreover, mRNA expression of fibrosis-related genes was attenuated in the hearts of Cavin-2-/- mice four weeks after TAC. Immunohistostaining of mice hearts showed that αSMA positive cells were decreased in Cavin-2-/- mice after TAC. In vitro study, we isolated mouse embryonic fibroblasts (MEFs) from Cavin-2-/- mice and WT mice. Western blotting and immunostaining of MEFs showed that αSMA protein level was decreased in TGF-β1 stimulated MEFs derived from Cavin-2-/- mice. However, phosphorylation of Smad2/3 was not different in both WT MEFs, and SDPR-KO MEFs, SDPR deficiency significantly attenuated MRTF and SRF gene expressions in MEFs. Conclusions: Our observations suggest that SDPR/Cavin-2 contributes to the development of cardiac fibrosis and systolic dysfunction with the differentiation of fibroblasts into myofibroblasts via the actin-MRTF-SRF gene transcription pathway. [ABSTRACT FROM AUTHOR]