BMPR2 mutations, Neointimal Transformation and Pulmonary Arterial Hypertension

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Patients served by the Veterans Health Administration who have chronic cardiopulmonary conditions are at high risk for death because of pulmonary hypertension (PH). A particularly dangerous form of PH, referred to as pulmonary arterial hypertension (PAH), is a vascular disease with high prevalence and poor survival among US veterans. PAH is characterized by gene variants, chronic inflammation and an occlusive remodeling of the vascular intima (neointima). Heterozygous germline mutations in BMPR2 (bone morphogenetic protein receptor 2) is the principle genetic risk factor for hereditary PAH. There is an unmet need to understand how environmental cues induce PAH in otherwise healthy BMPR2 mutation carriers. We recently showed in a new ‘2-hit’ rat model that Bmpr2 mutations, when coupled with pulmonary inflammation, elicit severe PAH in otherwise phenotypically-silent Bmpr2+/- mutant rats. PAH in this model features a proliferative and inflammatory neointima with characteristics shared by human disease. TGF-b blockade ameliorates advanced PAH and neointimal transformation in Bmpr2+/- animals and is a promising clinical therapy. Pilot single cell RNA-seq analyses of the disease rat lungs revealed that Bmpr2 mutations and an inflamed lung microenvironment cause a ‘transcriptional convergence’ of endothelial cells (ECs, originating from pulmonary arteries, arterioles and capillaries) to form the transformed neointima. Based on these results, we postulate that PAH occurs in Bmpr2 mutants because discrete endothelial transcriptional programs are modulated and result in an inflamed neointima. This proposal explores how genetic and environmental triggers may lead to neointimal formation and PAH at the cellular and molecular levels; proposed studies also search for druggable targets driving EC transformation following TGF-b treatment. Specific Aim 1 evaluates how Bmpr2 deficiency causes transcriptional convergence of ECs to form the PAH neointima and has three subaims which are to establish a molecular atlas of rat lungs in health and PAH using cutting-edge single molecular techniques (Aim 1a), then to elucidate the cellular origins of neointima by tracking specific endothelial lineage cells in evolving disease (Aim 1b), and finally to identify molecular programs responsible for the formation and maintenance of vascular lesions (Aim 1c). Specific Aim 2 explores how BMPR2 deficiency in human pulmonary arterial ECs provokes proliferative endothelial inflammation and focuses on the influence of BMPR2 deficiency on inflammatory 5- lipoxygenase (5-LO), NF-kB and IL-6 signaling. Here, the mechanisms by which BMPR2 insufficiency induces 5-LO epigenetic and post-translational modification, NF-kB transcriptional activities and classical- or trans-IL-6 signaling will be assessed. Specific Aim 3 tests whether TGF-b blockade reverses PAH by eliminating transcriptionally-convergent ECs (i.e., neointimal cells) in the lungs of Bmpr2 mutant rats. This aim investigates whether and how TGF-b inhibition reverses PAH by promoting the transcriptional ‘deconvergence’ of ECs and explores the reversibility and potential druggability of molecular targets. The overarching goal of this proposal is to create a better understanding about the formation of the neointimal layer in PAH, a pathological process responsible for vascular occlusion, high pulmonary artery pressures and right heart failure. These studies may also offer clear directions for future therapeutic avenues of direct benefit to our veteran patients.