Role of tyrosine kinases in the pathogenesis of pulmonary arterial hypertension

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Pulmonary arterial hypertension (PAH) is a progressive disease characterized by sustained elevation of pulmonary vascular resistance leading to increased right ventricular (RV) afterload and RV hypertrophy that culminate in RV failure and death. Pulmonary vascular remodeling, the key pathological feature of PAH, is attributable to the increased proliferation and resistance to apoptosis of pulmonary vascular cells. Several growth factors are implicated in the abnormal vascular cell phenotypes. Growth factors bind to their receptor tyrosine kinase (RTK) and initiate downstream signaling pathways that result in cell proliferation and survival. An effective therapeutic strategy should therefore target these abnormal vascular cells thereby interfering and reversing the remodeled pulmonary vasculature. Current vasodilatory therapies mainly provide symptomatic relief and convincing evidence of their direct anti-proliferative/anti-remodeling effects on severely remodeled vessels is largely missing. In the previous funding period, we have shown that inhibition of the platelet derived growth factor receptor (PDGFR) by imatinib reverses vascular remodeling and improved survival in experimental PH. Based on our work, imatinib successfully underwent clinical development in PAH which resulted in a positive phase 3 trial. However, the role of PDGF and growth factor-mediated RTK signaling has still to be elucidated. The project therefore aims to a) analyze the cell- and compartment-specific expression of growth factors and their signaling molecules (Src, PI3K, mTOR, JAK, ERK, P38, JNK, AKT, PLCy and PKC) in experimental and human tissues using techniques such as laser assisted microdissection, real-time PCR, in situ hybridization, immunofluorescence and immunohistochemistry, b) examine the functional role of these molecules on proliferation and apoptosis of primary vascular cells using small molecule inhibitors and siRNA techniques, c) investigate the cell type-specific (endothelial versus smooth-muscle) role of these molecules in PH pathogenesis by employing transgenic animals and d) evaluate the therapeutic efficacy of inhibitors of RTK pathways in clinically relevant animal models of PH. The PH will be assessed using non-invasive imaging techniques (echocardiography, CT-FMT), invasive techniques (Millar pulmonary artery catheter) and histomorphometry. The effects of imatinib therapy will be examined e) by various treatment modes (pulsed vs. continuous), and additionally in the model of pulmonary stenosis. The efficacy of various inhibitors of RTKs administered locally via inhalation will also be explored. Finally, f) the potential indicators/markers of individual responsiveness of PAH patients to TK inhibitors (imatinib) will be analyzed using clinical samples. The overall goal of this project is to further develop the concept that the remodeled vasculature in PH can be reversed/ normalized by targeting RTK signaling pathways.