Objectives: 

Transforming growth factor beta (TGF-beta) is one of the most important factors involved in fibrotic disorders, which are characterized by an excess of extracellular matrix (ECM) accumulation. It is well known that TGF-beta1 upregulates collagens, fibronectin and PAI-1 synthesis in SMCs, ECs and fibroblasts, and inhibits collagenase production. Endoglin (CD105) is part of TGF-beta receptors complex, and modulates the TGF-beta-Smad signalling pathways. Endoglin upregulation has been demonstrated in ECM accumulation. There are two different alternatively spliced isoforms of endoglin, L-endoglin (L, long) and S-endoglin (S, short). Little is known about the effect of S-endoglin expression in the cell. Preliminary studies from our laboratory have revealed that S-endoglin expression increased collagen I and reduced cell proliferation, but Smads pathways inhibition showed that other routes are involved. To further investigate the effect of S-endoglin expression, we have analyzed the MAPK signalling pathways role on ECM production.

Materials: 

We worked with stable transfectants of the rat myoblast cell line L6E9, expressing human L-endoglin or S-endoglin, and their controls. We used basic cell culture technics and cell treatments with TGF-b1 and selective inhibitors of MAPK pathways. After obtaining cell lysates, we analyzed protein levels by Western blot.

Results: 

We found that TGF-beta1 activates p38 and ERK1/2 in L6E9 myoblasts. S-endoglin expression increased p38 and ERK1/2 phosphorylation, while L-endoglin reduced it, compared to control. Collagen I and connective tissue growth factor (CTGF) expression was higher in S-endoglin myoblasts than in control cells. Selective inhibition p38 or ERK1/2 pathways has effects on TGF-beta induced collagen I and CTGF production, which is also modulated by the endoglin isoforms.

Conclusions: 

TGF-beta1 induced p38 and ERK1/2 activation is involved in TGF-beta1-induced ECM production. Endoglin isoforms differentially modulate this effect: while L-endoglin reduces MAPK and ECM levels, S-endoglin increases them.