Proliferating oral epithelial cells in culture are capable of both extracellular and intracellular degradation of interstitial collagen.

The potential of epithelial cells to degrade interstitial collagen was studied by culturing human masticatory mucosa on decalcified dentin matrix. Morphological changes were observed in the underlying collagen substratum and in the connective tissue of the explant. Degradation of the substratum was initiated two days after the first contact with epithelial cells exhibiting basal cell markers. Electron microscopic studies confirmed extensive collagen degradation in the vicinity of these cells. No collagen degradation was observed underneath the connective tissue portion of the explant. Experiments in which the explant was partially separated from the underlying substratum by a filter further showed that connective tissue was apparently not involved in the collagen degradation by the epithelial cells. Lysis of connective tissue of the explant was observed in association with epithelial cells that showed a disrupted basal lamina and release of vesicular material from the exposed cell membrane. Collagen fibers were visible inside some epithelial cells suggesting intracellular collagenolysis. Primary cultures of human gingival epithelial cells and porcine periodontal ligament epithelial cells (epithelial cell rests of Malassez) that expressed similar basal cell cytokeratins as the active cells of the mucosal explants secreted collagenase, gelatinase and TIMP to the culture medium. They also contained acid collagenolytic proteinases. When cultured on a porous polycarbonate membrane the epithelial cells secreted collagenolytic enzymes from the pores at cell membrane sites lacking basal lamina. These results provide evidence that proliferating basal epithelial cells have a strong capacity for collagen degradation. It seems that the absence of basement membrane is the signal for these cells to secrete matrix degrading enzymes.