The role of LTBP2 in glaucoma

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Summary: A unique animal model of glaucoma with spontaneously arising mutation in LTBP2 has been established. This gene is implicated in heterogeneous glaucoma phenotypes, including human primary congenital glaucoma (PCG) as well as some forms of adult-onset open angle glaucoma. As the only known large animal homolog of inherited glaucoma in humans, this model has considerable potential for translational research. Posterior segment pathology has been extensively characterized and closely recapitulates features of human glaucomatous optic neuropathy. However, the role played by LTBP2 in the eye remains unknown and the precise cellular and molecular mechanisms responsible for the underlying elevated intraocular pressure (IOP) in this form of glaucoma remain unresolved. The objective of this proposal is to identify and localize, as potential targets for therapeutic intervention, key pathobiological mechanisms that contribute to both early onset and progressive IOP elevation in this model. In addition to perturbing LTBP2’s acknowledged role in microfibril assembly, enhanced TGF beta signaling, contributing to extracellular matrix (ECM) accumulation within the trabecular meshwork (TM) has been proposed as a mechanism for IOP elevation in this “microfibrillopathy”. However, preliminary studies in our animal model have not established whether significant increase in aqueous humor TGF beta concentrations represent a cause or effect of IOP elevation. Our central hypothesis is that LTBP2 is both an important regulator of outflow pathway development and remodeling in the perinatal period and a regulator of TM cell and ECM biology and pro-fibrotic pathways throughout life, extending beyond development. We will pursue two specific Aims: Aim 1: To determine the effects of absent or reduced LTBP2 expression on development of proximal and distal aqueous outflow pathways, we will test the hypothesis that LTBP2 plays an important role in outflow pathway development and remodeling using a combination of in vivo and in situ approaches to examine distal outflow morphology and ultrastructure of the proximal outflow pathway (TM and juxtacanalicular tissue) and ECM components of these pathways in wildtype and LTBP2+/- and LTBP2-/- eyes. Aim 2: To determine the pathological effects of absent or reduced LTBP2 expression on TM cell (TMC) biology, we will use TMC cultures derived from wildtype, LTBP2+/- and LTBP2-/- eyes. In Aim 2, we will test the hypotheses that reduced LTBP2 expression will a) negatively impact TMC attachment and proliferation in vitro and b) enhance the pathologic effects of TGFβ on actin cytoskeleton and promotion of ECM fibrosis. Successful completion of these Aims will generate new knowledge on the complex role of LTBP2 in physiology and pathology of the aqueous outflow pathways, providing a critical foundation to advance our overall goal of designing and testing innovative therapeutic approaches to glaucoma in our unique translational model.