Thrombin induces cell division in rabbit lenses cultured in a completely defined serum-free medium

Experiments were initiated to gain an understanding of the environmental factors that may regulate injury-induced mitosis and wound healing in the mammalian lens. The addition of thrombin or trypsin to a completely defined serum-free medium stimulated cell proliferation and migration in the cultured mammalian lens. A 30 min exposure of the rabbit lens to highly purified thrombin induced DNA synthesis and mitosis throughout the normally amitotic central region of the lens epithelium. Lenses exposed to thrombin for 24 or 52 hr exhibited cell migration and mitosis. The mitotic response brought about by thrombin was totally curtailed by hirudin and antithrombin III. Prothrombin, papain, or pepsin were not mitogenic toward the cultured lens. A 30 min exposure of the lens to trypsin induced cell division and migration, a response that did not occur in the presence of trypsin inhibitors. Lenses cultured in a trypsin-containing medium for 24 hr showed extensive cell death throughout the entire central region of the epithelium. In addition, an endogenous serine protease, plasminogen activator, was detected in cultured rabbit lens epithelial cells. Wound healing in the lens in vivo is accompanied by cellular migration and mitosis. The present experiments demonstrate that a highly purified serine protease, thrombin, which is present at the site of lenticular injury in vivo, is capable of inducing mitosis and migration in lens epithelia. The results suggest that thrombin or other exogenous and endogenous serine proteases might contribute to the process of wound healing in the ocular lens.