Regulation of UPRmt activation in the development of pulmonary vascular remodeling in PAH

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Project Summary/Abstract Pulmonary Arterial Hypertension (PAH) is a severe and progressive disease with a high mortality rate of nearly 40% over 5 years. Pulmonary artery endothelial and smooth muscle cells (PAECs and PASMCs) undergo intracellular signaling changes that promote a proliferative, apoptosis resistant phenotype that causes occlusion of the pulmonary vasculature leading to increased resistance. There is a critical need to uncover the mechanisms that promote vascular cell remodeling. Our long-term goal is to identify pathways or molecules to target for therapeutic intervention in order to alleviate the vascular abnormalities that are central to PAH development and progression. Sphk1 and sphingosine-1 phosphate are increased in the lungs and pulmonary artery smooth muscle cells of PAH patients and in the lungs of rodent models of hypoxia mediated pulmonary hypertension (HPH). Mitochondrial (mt) dysfunction also contributes to PAH via altered regulation of multiple mt processes, which leads to impaired vasorelaxation and increased vascular cell proliferation. However, the effect of the Sphk1/S1P signaling axis on mt function in the initiation or progression of PAH is not well understood. Our preliminary studies demonstrate that S1P promotes activation of the UPRmt and regulates mt dynamics in human PAECs and PASMCs. The specific objective of the proposed study is to determine the role of UPRmt signaling mediators on vascular cell function. Our central hypothesis is that activation of the Sphk1/S1P/S1PR signaling axis modulates the UPRmt pathway to promote vascular remodeling which leads to PAH development. This hypothesis will be tested by investigating the following specific aims: AIM 1: To investigate the role of the UPRmt in S1PRs/S1P/Sphk1 promotion of pulmonary vascular cell proliferation and hypoxia induced PH (HPH) development. Our working hypothesis is that the Sphk1/S1P/ S1PR signaling axis modulates mitochondrial function, which is a central cause underlying the pathological proliferation of PASMCs and PAECs to mediate PAH development. AIM 2: To determine the effects of UPRmt inhibition on vascular remodeling and HPH development. Our working hypothesis is that hypoxia induces activation of UPRmt in vivo resulting in vascular remodeling and PAH. AIM 3: Determine if coordinated signaling occurs between pulmonary vascular cells and mitochondrial processes to regulate vascular remodeling and HPH. Our working hypothesis is that coordinated signaling among the UPRmt, mitochondrial fission and mitochondrial respiration promote vascular remodeling.