Endoglin modulation of TGF-β1-induced collagen synthesis is dependent on ERK1/2 MAPK activation

Background/Aims: Transforming growth factor-β1 (TGF-β1) plays a pivotal role in the extracellular matrix accumulation observed in fibrotic diseases. Endoglin is an important component of the TGF-β receptor complex highly expressed in tissues undergoing fibrotic processes. Endoglin expression regulates the effect of TGF-β on extracellular matrix synthesis. The purpose of our study has been to understand the molecular mechanism by which endoglin exerts its effects on fibrosis and the possible role of MAP kinases in these effects. Methods: We have assessed in mock and in endoglin-transfected L6E9 myoblasts the effect of TGF-β1 on collagen mRNA by Northern blot and effect of TGF-β1 on collagen content in the cultured medium by [ ³ H]-Proline incorporation into collagen proteins. Total and activated MARK and their role on collagen synthesis were assessed by Western blot. Results: TGF-β1 induced an increase on α ₂ (I) collagen mRNA expression and collagen accumulation in mock-transfected myoblasts, whereas the response was much lower in endoglin-transfected cells. TGF-β1 activated the ERK1/2 and p38 MARK pathways but not the JNK pathway in L6E9 myoblasts. TGF-β1-induced α ₂ (I) collagen mRNA expression and collagen accumulation were completely inhibited by SB203580, in either mock or endoglin-transfected myoblasts. PD98059 increased TGF-β1 induced-collagen synthesis and accumulation in endoglin-transfected myoblasts but not in mock cells. Conclusion: Our studies demonstrate that TGF-β1-induced collagen synthesis is mediated by p38 MARK activation in L6E9 myoblasts. Furthermore, endoglin expression reduces basal and TGF-β1 induced collagen synthesis when ERK1/2 pathway is operating.