Pressure Regulation of Human Trabecular Meshwork Genes

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ABSTRACT Glaucoma is an optic neuropathy which causes irreversible blindness. Our approach to study glaucoma consists of selecting a well-established clinical condition associated with the disease and investigating the clinical parameter at the molecular level. Elevated intraocular pressure (IOP) is the major risk factor for the development of glaucoma. In humans, 90% of the aqueous humor exits the eye through the trabecular meshwork (TM). Thus, a dysfunctional TM results in increased resistance and elevated IOP. Because the physiology of a tissue is governed by the expression of its genes, during the previous grant cycle we examined TM differential expression under conditions of elevated IOP. After analyzing many chip arrays comparing normal and high IOP perfused post-mortem human eyes, we unraveled a number of genes involved in calcification processes. We further uncovered that such processes were not only present in the TM, but also that they seemed to be more active in TMs from glaucomatous patients. Based on these findings, we hypothesize that TM calcification is linked to regulation of IOP and outflow facility. That genes and mechanisms that govern physiological and pathological calcification in the bone and vascular tissues are active in the TM, and that these processes, as well as efforts to inhibit them, are part of the regulatory systems that control aqueous humor outflow. We further hypothesize that failure to maintain TM mineralization in check will affect deposited collagen and elastin cross-linking with deleterious consequences to ECM hardening. To test these hypotheses we propose to further characterize the identified mechanism through three new avenues. The first will investigate the phenomenon in vivo, through the use of transgenic mice. The second will investigate the process in human organ cultures. The third will use primary human TM cells to determine the involvement of two pathways (WNT and LOX-related elastin/collagen cross-linking) in TM mineralization. These two pathways have been independently associated with vascular calcification and osteoblastic differentiation and, with conditions affecting TM function. Results to be obtained with the development of these hypotheses will provide new understanding on the mechanisms regulating outflow resistance and would potentially lead to new treatments for glaucoma.