Positive effect of collagen V and VI on triglyceride accumulation during differentiation in cultures of bovine intramuscular adipocytes.

Ethyl-3,4-dihydroxybenzoate (EDHB), a specific inhibitor of collagen synthesis, was used to study the role of collagen in the differentiation of bovine intramuscular preadipocytes (BIP). Triglyceride (TG) accumulation levels of BIP cells were dose-dependently inhibited by EDHB and were reduced to 50 % at a 0.1 mM concentration. EDHB addition prevented the accretion of collagens (types I-VI) on the cell surface, which generally increases during adipose conversion. Western blotting and immunofluorescence studies showed in detail that triple-helical conformation of procollagen molecules was drastically interrupted by EDHB, and as a result, their matrix assembly was not performed in the extracellular space of adipocytes. Particularly, the development of collagen types IV, V and VI during differentiation was severely damaged. When exogenous collagens were supplied to make up for the lack of endogenous products, cultured EDHB-treated cells on type V and VI collagen-coated dishes were the only ones among six collagens to accumulate more TG, although their TG content did not reach that of normal adipocytes. This result implies the importance and the active role of collagens V and VI for adipogenesis. However, these findings also indicate that collagen newly synthesized and organized by the adipocyte itself during differentiation is still necessary for the growth of adipose tissue.