Enhanced cell accumulation and collagen processing by keratocytes cultured under agarose and in media containing IGF-I, TGF-β or PDGF

We previously showed an agarose overlay on keratocytes cultured in media containing pharmacological levels of insulin enhanced collagen processing and collagen fibril formation. In this study, we compared collagen processing by keratocytes cultured in media containing physiological levels of IGF-I, TGF-β, FGF-2, and PDGF in standard and in agarose overlay cultures. Pepsin digestion/SDS PAGE was used to determine the levels of procollagen secreted into the media and the collagen content of the ECM associated with the cell layer. Distribution of collagen type I and fibronectin in the ECM of the agarose cultures was determined by immunoflorescence. Collagen fibril and keratocyte morphology was evaluated by electron microscopy. The agarose overlay significantly enhanced the cell number in the IGF-I, TGF-β and PDGF treated cultures by 2-3 fold. The overlay also significantly enhanced the processing of procollagen to collagen fibrils from 29% in standard cultures to 63-68% in agarose cultures for the IGF-I and PDGF cultures, and from 66% in standard culture to 85% in agarose culture for the TGF-β cultures. Cell accumulation and collagen processing was not enhanced by agarose overlay of the FGF-2 treated cultures. Collagen type I and fibronectin were more uniformly distributed and the collagen fibrils smaller in the ECM of the TGF-β treated cultures. Keratocytes in the FGF-2 treated cultures were in close cell contact with few collagen fibrils while IGF-I, TGF-β, and PDGF cultures had an extensive ECM with abundant collagen fibrils. The results of this study indicate that the agarose overlay enhances collagen fibril assembly and cell accumulation by keratocytes when both collagen synthesis and cell proliferation are stimulated.