Although vascular development is normal in Eng(+/-) mice, angiogenic abnormalities were observed in the adult mice and their isolated endothelial cells. These results suggest that a normal level of endoglin is required for full angiogenic activity.

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Transforming growth factor-L L (TGF-L L) plays a pivotal role in the extracellular matrix accumulation observed in chronic progressive tissue fibrosis, but the intracellular signaling mechanism by which TGF-L L stimulates this process remains poorly understood. We examined whether mitogenactivated protein kinase (MAPK) routes were involved in TGF-L L1-induced collagen expression in L 6 E 9 myoblasts. TGF-L L1 induced p38 and extracellular signal-regulated kinase (ERK) 1/2 phosphorylation whereas no effect on Jun N-terminal kinase phosphorylation was observed. Biochemical blockade of p38 but not of the ERK MAPK pathway abolished TGF-L L1-induced K K 2 (I) collagen mRNA expression and accumulation. These data indicate that TGF-L L1-induced p38 activation is involved in TGF-L L1-stimulated collagen synthesis. ß

Background/aims: TGF-β1 plays a major role in extracellular matrix (ECM) accumulation in tissue fibrosis. Connective tissue growth factor appears to play a critical role in this effect. Endoglin is a component of the transforming growth factor b (TGF-β) receptor complex. Endoglin is upregulated by TGF-β1, but its functional role in ECM regulation is unknown. Using rat myoblasts as a model system, we have assessed the role of endoglin on regulating CTGF expression and ECM synthesis and accumulation in the presence or absence of TGF-β1. Methods: L6E9 myoblast cell line was transfected with human endoglin, and collagen, fibronectin and CTGF production was assessed by Western blot and by proline incorporation to collagen proteins. Results: Northern blot analysis revealed that parental rat myoblasts L₆E₉ do not express endogenous endoglin. Upon endoglin transfection, endoglin-expressing cells displayed a decreased CTGF expression and decreased collagen and fibronectin accumulation respect to mock transfectants. Northern blot analysis also revealed a decreased α ₂ (I) procollagen mRNA expression in endoglin transfectants. TGF-β1 treatment induced an increase in CTGF expression and collagen synthesis and accumulation in L6E9 myoblasts. This effect was significantly lower in endoglin-transfected than in mock-transfected cells. Conclusion: These results demonstrate that endoglin expression negatively regulates basal and TGF-β1-induced CTGF and collagen expression and synthesis.

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 [³H]-Proline incorporation into collagen proteins. Total and activated MAPK and their role on collagen synthesis were assessed by Western blot. Results: TGF-β1 induced an increase on α₂ (I) collagen mRNA expression and collagen accumulation in mock-transfected myoblasts, whereas the response was much lower in endoglintransfected cells. TGF-β1 activated the ERK1/2 and p38 MAPK pathways but not the JNK pathway in L6E9 myoblasts. TGF-β1-induced α₂ (I) collagen mRNA expression and collagen accumulation were completely inhibited by SB203580, in either mock or endoglintransfected 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 MAPK activation in L6E9 myoblasts. Furthermore, endoglin expression reduces basal and TGF-β1 induced collagen synthesis when ERK1/2 pathway is operating.