Hydrostatic pressure stimulates synthesis of elastin in cultured optic nerve head astrocytes

Elastin is a major component of the extracellular matrix (ECM) of the lamin a cribrosa in the optic nerve head in humans and nonhuman primates. The lam ina cribrosa appears to be the site of damage to the retinal ganglion cell axons in glaucomatous optic neuropathy, characterized in many patients by e levated intraocular pressure (IOP). Type 1B astrocytes are the major cell t ype in the lamina, synthesize elastic fibers during development, express in creased elastin mRNA, and synthesize abnormal elastin in glaucoma. In this study, we determined the effect of elevated hydrostatic pressure on the syn thesis of elastin by type 1B astrocytes in culture. Type 1B astrocytes were exposed to gradients of hydrostatic pressure and tested for proliferation, morphology, synthesis, and deposition of elastin. Trichloroacetic acid (TC A) and immunoprecipitation of radiolabeled protein determined total new pro tein and elastin synthesis. Proteins from the conditioned media were analyz ed by Western blot. Levels of elastin mRNA were determined by in situ hybri dization. Cell proliferation increased similar to2-fold after exposure to p ressure for one day, similar to5-fold after 3 and 5 days of exposure to pre ssure. Confocal and electron microscopic cytochemistry showed a marked incr ease in intracellular elastin in astrocytes exposed to pressure, as compare d with controls. Intracellular elastin was associated with the RER-Golgi re gion and with the cytoskeleton. Total protein and elastin synthesis increas ed significantly (P < 0.05) at 3- and 5-day exposure to pressure, as well a s the level of elastin mRNA. Elastin protein in the media increased with th e level of pressure. These results indicate that hydrostatic pressure stimu lates type 1B astrocytes to synthesize and secrete soluble elastin into the media. In glaucoma, type 1B astrocytes may respond to IOP-related stress w ith increased expression of elastin and formation of elastotic fibers leadi ng to loss of elasticity and tissue remodeling. (C) 2000 Wiley-Liss, Inc.