Release of lysosomal protease from retinal pigment epithelium and fibroblasts during mechanical stresses

Abstract

Mechanical expansion in tissues or in cells may occur under physiological and pathological conditions and is accompanied by increased activity of proteolytic enzymes. In traction detachment, retinal cells are subjected to mechanical strain. The purpose of this study was to ascertain whether retinal pigment epithelium (RPE) cells and fibroblasts in tissue culture release proteases due to mechanical stress and to investigate the importance of the cytoskeleton for mechanotransduction to the lysosomes during cellular stress reactions. Cell layers were grown on silicone-rubber membranes and subjected to mechanical stresses by expansion of the membrane. Concentrations of N-acetyl-beta-glucosaminidase (NAG), acid phosphatase (AP), and lactate dehydrogenase (LDH) were determined in extracellular fluid. Colchicine 0.5 x 10(-5) M was used to disrupt the cytoskeleton prior to expansion. RPE cells and fibroblasts separated during mechanical expansion, which was accompanied by extracellular release of proteolytic activity of NAG (RPE 37.50%; fibroblasts 23.22% above control value), but not of AP. LDH activity did not increase, indicating preserved integrity of the cell membranes during stretching. Colchicine caused immediate detachment of fibroblasts, and RPE did not release significant activity of NAG under subsequent extension. In traction detachment, RPE may release in vivo proteases to cut intercellular adhesions in order to escape mechanical strain. Our results indicate that release of proteases from RPE may be involved in the pathophysiology of traction detachment, facilitating by their degradative action the disconnection between RPE and outer segments. Similarly, fibroblasts may respond to changes in tension of scleral or corneal tissue. Release of proteases following mechanical stress seems to require an intact cytoskeleton.