MK2 and pulmonary hypertension

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PROJECT SUMMARY Pulmonary arterial hypertension (PAH) is a deadly, debilitating disease with no cure. The development of PAH is associated with robust structural remodeling of the small pulmonary arteries, including intimal thickening and formation of vaso-occlusive lesions. In addition to abnormally increased proliferation of vascular cells, failure of appropriate apoptosis (i.e., apoptotic resistance) contributes to remodeling via lack of cell turnover. Our laboratory recently discovered that the expression of the protein-serine kinase, MAPKAP2 (MK2), is markedly downregulated in pulmonary microvascular endothelial cells (PMVECs) from the SU5416+hypoxia (SuHx) rat model of PAH. Little is known regarding the control of MK2 expression; however, our preliminary data indicate that MK2 is regulated by hypoxia-inducible factors (HIFs), a family of transcription factors suggested to be involved in the development of PAH. Loss of MK2 is associated with cytosolic sequestration of caspase-3, preventing apoptosis. Moreover, we linked reduced MK2 levels with upregulation of the water channel, aquaporin 1 (AQP1), which we previously have shown promotes pro-proliferative effects in pulmonary vascular cells. However, the mechanism by which MK2 might influence AQP1 expression is unknown. Based on these data, we hypothesize that in PAH PMVECs, HIF-dependent downregulation of MK2 results in cytosolic sequestering of caspase-3 and upregulation of AQP1, leading to apoptotic resistance and hyperproliferation, respectively. Thus, the Aims of this study are to: 1) determine whether loss of MK2 during PAH mediates cytosolic sequestering of caspase-3; 2) determine the mechanism by which MK2 controls AQP1 expression; and 3) evaluate whether increasing the expression of MK2 reverses changes in cell phenotype and vascular remodeling in PAH. We will use a comprehensive, multidisciplinary approach combining in vitro and in vivo models of PAH to explore the effect of modulating factors in this pathway on PMVEC cell function and development and reversal of PAH. The successful completion of the proposed studies will impact the field by: 1) describing signaling pathways mediated by MK2 that are involved in the development and progression of PAH; 2) providing new information regarding regulation of MK2 expression; 3) identifying specific interactions between caspase-3, MK2 and AQP1 that are responsible for controlling caspase-3 subcellular localization and AQP1-induced PMVEC growth; and 4) directing subsequent studies aimed at development of new therapeutics.