The expression of α2β1 integrin and α smooth muscle actin in fibroblasts grown on collagen

The maturation of connective tissue involves the organization of collagen fibres by resident fibroblasts. Fibroblast attachment to collagen has been demonstrated to involve cell surface receptors, integrins of the beta 1 family. Integrins are associated with cytoplasmic actin of microfilaments either directly or through focal adhesions. The major actin isoform of fibroblast microfilaments is beta actin and to a lesser extent alpha smooth muscle (alpha SM) actin. Cultured human dermal fibroblasts derived from adult dermis, newborn foreskin or keloid scar were grown on either uncoated or collagen-coated surfaces. The expression and synthesis of both alpha 2 beta 1 integrin and alpha SM actin were followed by immunohistology and immunoprecipitation. Fibroblasts on uncoated surfaces expressed little alpha 2 beta 1 integrin on their surface, while 20 per cent of them demonstrated alpha SM actin within microfilaments. Fibroblasts grown on a collagen-coated surface minimally expressed alpha SM actin in microfilament structures and a majority of the cells were positive for alpha 2 beta 1 integrin on their membranes. Using [35S]-methionine incorporation and immunoprecipitation, it was shown that fibroblasts grown in uncoated dishes synthesized more alpha SM actin than fibroblasts grown on collagen-coated dishes. In contrast, fibroblasts grown on collagen coated dishes synthesized more alpha 2 beta 1 integrin compared to the same cells grown on uncoated dishes. Fibroblasts maintained on a type I collagen upregulate the expression and synthesis of alpha 2 beta 1 integrin, and downregulate the expression and synthesis of alpha SM actin.