PI3K/Akt signaling mediates increased BMP‐1 expression in response to TNF‐α and TGF‐β1 in cardiac fibroblasts

Abstract

Procollagen C-endopeptidase (BMP-1) is a crucial enzyme for conversion of fibrillar procollagens into self-assembling collagen monomers. BMP-1 plays an essential role during cardiac development, growth, and disease by controlling the reorganization of the extracellular matrix (ECM). The pleiotrophic cytokines TGF-β1 and TNF-α have been implicated in cardiac remodeling in response to various pathophysiological stimuli. For regulation of myocardial ECM, the balance of TNF-α and TGF-β signaling in cardiac fibroblasts is critical. In this study, we compared the effects of TNF-α and TGF-β1 on expression of BMP-1 and collagen type I, and the molecular mechanisms involved. Both TNF-α (1–10 ng/ml) and TGF-β1 (1–10 ng/ml) stimulated BMP-1 and collagen type I gene and protein expression in cardiac fibroblasts after 6 and 24 hrs of exposure. However, TNF-α treatment induced a more rapid increase of BMP-1 expression than TGF-β1 (significant at 6 hrs versus 24 hrs for TGF-β1). These TNF-α and TGF-β effects were PI3K/Akt dependent. Blockade of PI3K with wortmannin prevented the up-regulation of BMP-1 and collagen type I, and attenuated the activation of Smad3 and Akt. These findings indicate that the Smad3 pathway is involved in BMP-1 regulation, and may be integrated with PI3K signaling. Further, pretreatment of cardiac fibroblasts with TNF-α impaired TGF-β1 mediated up-regulation of BMP-1 and PI3K signaling. These findings demonstrate that BMP-1 expression is regulated by both TGF-β and TNF-α, and that TNF-α negatively impacts TGF-β1 signaling.