BACKGROUNDInflammation plays a pivotal role in cardiac remodeling, especially in myocardial fibrosis. Abnormal growth of cardiac fibroblasts is critically involved in the pathophysiology of cardiac hypertrophy/remodeling. Previous study has demonstrated that many inflammation stimulating factors trigger transforming growth factor-β (TGF-β) induction and reactive myocardial fibrosis. Activin A (ACT A) is a member of TGF-β superfamily, and follistatin (FS) is an activin-binding protein, i.e. an antagonist of ACT A. Our previous studies have shown that ACT A-FS imbalance occurs in rats with heart failure (HF), and overexpression of ACT A can lead to ventricular remodeling, and resultant HF. Low expression of FS after myocardial infarction further exacerbated HF. The pathogenic change resulting from overexpression of ACT A is consistent with that of overexpression of angiotensin II (AngII). Ventricular remodeling includes cardiocyte remodeling and myocardial interstitial collagen deposition and fibrosis. Therefore, the present study was designed to investigate the effects of inflammatory factors on the ACT A-FS and the secretions of cardiac fibroblasts in order to explore in depth the mechanism of myocardial fibrosis.

METHODSA rat model with HF was established, and the results showed that there was a greater degree of cardiac fibrosis in HF rats. In addition, we found that there was an imbalance of the ACT A/FS system in HF rats, which was characterized by increased levels of ACT A. Further, primary rat cardiac fibroblasts were cultured and the MTT assay was performed to determine the effect of the inflammatory factor-bacterial endotoxin lipopolysaccharide (LPS) on cardiac fibroblast proliferation.

RESULTSThe results showed that LPS can stimulate the cardiac fibroblasts to proliferate in a dose-dependent manner. Cellular immunohistochemical staining showed that the rat cardiac fibroblasts themselves could express ACT A and FS proteins, and stimulation by LPS could apparently promote the cultured primary rat cardiac fibroblasts to secrete ACT A, but inhibit the secretion of FS. The results also showed that ACT A promoted, in a dose-dependent manner, the proliferation of the cultured primary rat cardiac fibroblasts, and the expression of collagen types I and III. Moreover, ACT A promoted, in a dose dependent manner, the cardiac fibroblasts to secrete nitric oxide (NO), and unregulated the expression of inducible nitric oxide synthase (iNOS) mRNA.

CONCLUSIONSThese results suggest that the inflammatory mediator LPS can promote ACT A-FS imbalance in cardiac fibroblasts, mainly overexpression of ACT A. Overexpression of ACT A promotes the proliferation and the secretion of collagens in cardiac fibroblasts through autocrine/paracrine stimulation of NO, and is involved in the pathological process of myocardial fibrosis.