TRANSIENT LOSS OF ALPHA-B-CRYSTALLIN - AN EARLY CELLULAR-RESPONSE TO MECHANICAL STRETCH

Human trabecular meshwork (HTM) is distended and stretched with increa ses in intraocular pressure. During this stretching, there is a rearra ngement of actin filaments. The HTM cells express alpha B-crystallin, a small heat shock protein that may have a role in the stabilization a nd regulation of the cytoskeleton in mammalian cells. The levels of al pha B-crystallin were examined in trabecular meshwork cells after mech anical stretch. Human TM primary cell cultures, plated onto silicone s heets, were subjected to a single 10% linear stretch and samples were prepared at various times after stretch for immunoblotting or Northern blotting Immunoblots of total protein extracts with antibody specific for alpha B-crystallin detected a 26% decrease of cellular alpha B-cr ystallin levels within 2 minutes. After 1 hour alpha B-crystallin leve ls had decreased 90% compared to control cells. The levels of alpha B- crystallin began to recover in cells stretched for 2 hours and returne d to initial levels by 24 hours. Northern blots probed with alpha B-cr ystallin exon III cDNA detected a transcript of 0.65 kb in human TM ce lls and the levels of the alpha B mRNA remained constant during alpha B-crystallin protein decrease. Later, levels of the 0.65 kb transcript of alpha B-crystallin increased during the cellular recovery. These r esults suggest that decreased levels of alpha B-crystallin after mecha nical stretch were probably not due to transcriptional changes but rat her to increased degradation of alpha B-crystallin protein. An increas e in mRNA levels may play a role in the recovery of alpha B-crystallin during reorganization of the cytoskeleton and attachment to the subst ratum. These data raise the possibility of a specific proteolysis of a lpha B-crystallin protein in cells after a physiological challenge. (C ) 1997 Academic Press.