Angiotensin II AT(1)-receptor induces biglycan in neonatal cardiac fibroblasts via autocrine release of TGFbeta in vitro

After myocardial infarction, angiotensin II (AngII) promotes ventricular remodeling and deposition of extracellular matrix (ECM), e.g., collagen type 1 and 3. Whether AngII regulates the expression of small leucine-rich proteoglycans (SLRP) which are important modulators of collagen fibrillogenesis and are induced after experimental myocardial infarction in rats is not known. The aim of the present study was therefore to analyse in cultured cardiac fibroblasts the expression and secretion of the SLRP biglycan in response to AngII. Cardiac fibroblasts were isolated from neonatal Wistar Kyoto rats and used in the first passage. Expression of AT(1)- and AT(2)-receptors was verified by RT-PCR. Expression of protoeglycans was analyzed after metabolic labeling with [35S]-sulfate, by SDS-PAGE and Western analysis. In addition, mRNA expression was examined by means of RT-PCR and Northern analysis. The activity of the biglycan promoter was analyzed using three biglycan promoter-luciferase fusion constructs. Biglycan was found to be the predominant proteoglycan produced by neonatal cardiac fibroblasts in vitro. In response to AngII (10(-7) M), secretion of total [35S]-labeled proteoglycans and mRNA of biglycan were increased to 116+/-1.8% and 121+/-11% (n=5, mean+/-S.E.M.) of unstimulated controls, respectively. Biglycan induction in response to AngII was sensitive to Losartan (10(-5) M) and unaffected by PD123177 (10(-6) M), suggesting that the AT(1)-receptor mediates the induction of biglycan. Direct activation of the biglycan promoter downstream of the AT(1)-receptor was excluded by promoter activity assays. Instead, increased release of transforming growth factor beta 1 (TGFbeta1) was detected by ELISA in response to AT(1)-receptor stimulation. Furthermore, neutralising antibodies to TGFbeta1 inhibited biglycan induction in response to AngII. The results indicate that in cardiac fibroblasts AngII via the AT(1)-receptor causes autocrine release of TGFbeta1, which in turn induces biglycan expression and secretion.