Genes expressed in the human trabecular meshwork during pressure-induced homeostatic response

Physiological pressure inside the eye is maintained by a resistance mechanism provided by the trabecular meshwork tissue. In most cases, prolonged, elevated pressure leads to an eye pathology characterized by retinal ganglion cell (RGC) degeneration, optic nerve damage, and non-remedial blindness. We are investigating the regulation of trabecular meshwork genes in response to elevated pressure. Using perfused organ cultures from postmortem human donors, we have previously demonstrated the presence of a homeostatic mechanism at 2-4 days of pressure insult (Borrás et al. 2002, Invest Ophthalmol Vis Sci 43:33-40). Here, we sought to identify trabecular meshwork genes whose expression was altered during this homeostatic period. By macroarray hybridization, we compared the expression profiles of high-pressure (HP) and normal-pressure (NP) treated eyes from the same individual (n = 3 pairs). Our results identified 40 upregulated and 14 downregulated genes. The highest proportion of upregulated genes encoded proteins involved in signal transduction (32%). Among the potentially relevant genes, PIP 5K1C, VIP, tropomodulin, and MMP2 encoded mediators known to influence outflow resistance. Others encoded functions which are new for the trabecular meshwork, but which are intrinsic to unrelated tissues. These new mechanisms appear as they could be of benefit for trabecular meshwork function. Matrix Gla protein (MGP), perlecan, osteomodulin, and osteoblast-specific factor are essential in cartilage and bone physiology whereas spectrin and ICAM4 are specific for blood cells and crucial in maintaining their shape and adhesion. In addition, MGP transcripts were stimulated by extracellular calcium and downregulated by TGF-beta1. We propose that MGP might be an important player in the adaptive homeostatic mechanism by contributing to maintain a softer trabecular meshwork tissue and facilitate aqueous humor outflow.