Aquaporin 1 and pulmonary hypertension

PROJECT SUMMARY Pulmonary arterial hypertension (PAH) is a severely debilitating disease with no cure. Morphometric studies revealed that the development of pulmonary hypertension is associated with robust structural remodeling of the small pulmonary arteries, characterized by thickening of the endothelial and smooth muscle cell layers and formation of occlusive lesions. In addition to increased proliferation and migration of vascular cells, failure of appropriate apoptosis (i.e., apoptotic resistance) contributes to remodeling via lack of cell turnover. Our laboratory identified a new candidate as a regulator of pulmonary arterial smooth muscle cell (PASMC) function: aquaporins (AQPs). AQPs are a family of proteins that form transmembrane channels which facilitate the transport of water into and out of cells. We have evidence that aquaporin 1 (AQP1), the first family member identified, is expressed in PASMCs and pulmonary microvascular endothelial cells (PMVECs), upregulated in a rat model of PAH and modulates susceptibility to apoptosis. Our preliminary data also indicate that increased AQP1 protein is associated with elevated β-catenin expression, a protein that regulates migratory, proliferative and survival responses. The mechanism by which AQP1 regulates β-catenin levels is currently unknown; we have generated exciting data indicating a critical role for a specific region of the AQP1 C-terminal tail. This region contains a previously unrecognized putative binding site for GSK3β, an endogenous regulator of β-catenin abundance. Based on these data, we hypothesize that in PAH PASMCs and PMVECs, increased AQP1 levels contribute to cell growth and survival by sequestering GSK3β and reducing its activity/nuclear localization; as a consequence, β-catenin accumulates, promoting migration and proliferation and preventing apoptosis. The Aims of this study are to: 1) determine whether AQP1 regulates β-catenin via binding to GSK3β; 2) identify the mechanism by which AQP1 facilitates cell growth and survival; and 3) evaluate whether cell-specific disruption of AQP1 prevents or reverses PAH.