Responses and signaling pathways in human optic nerve head astrocytes exposed to hydrostatic pressure in vitro

In this study, we examined the effects of mechanical stress induced by elevated hydrostatic pressure (HP) on the migration of human optic nerve head (ONH) astrocytes, using an in vitro model that follows repopulation of a cell-free area (CFA) created on a monolayer of cultured astrocytes. alpha-Tubulin staining detected phenotypic changes in astrocytes exposed to HP. The influence of proliferation in closure of the CFA was determined by incorporation of BrdU under 1.5-cm H2O, control pressure (CP), and 10-cm H2O HP with or without 5-fluorouracil. Under control and experimental conditions, closure of the CFA occurred mostly by migration and less by proliferation. Exposure to 10-cm H2O HP induced faster closure of the CFA at 1, 3, and 5 days. The signaling pathways involved in responses to HP were determined using genistein, tyrphostin A25, AG1478, and AG1295, inhibitors of receptor tyrosine kinases; wortmannin and LY294002, inhibitors of phosphatidyl inositol 3-kinase (PI-3K); and SC58236, an inhibitor of inducible cyclooxygenase-2 (COX2). Genistein and tyrphostin A25 blocked HP-induced migration at 1, 3, and 5 days, but did not affect closure of the CFA under CP. AG1478 and AG1295 blocked HP-induced migration and partially inhibit closure of the CFA under CP. LY294002 blocked HP-induced migration. SC58236 markedly inhibited closure of the CFA under CP by inhibiting COX2 activity. Exposure to HP, a physical stress, induced faster closure of the CFA via activation of members of the epidermal growth factor receptor (EGFR) family and PI-3K pathways. Under CP, closure of the CFA in response to denudation, a form of injury, is due to activation of COX2 in ONH astrocytes.