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A2874 - ETV2/PPARg Axis Regulates Endothelial-to-Mesenchymal Transition in Pulmonary Hypertension
Author Block: B. Kang1, D. Lee2, J. Kim2, S. S. Chang1, J. Ma1, R. L. Sutliff1, C. M. Hart1, C. Park2, B. Kang1; 1Medicine, Emory University-Atlanta VAMC, Decatur, GA, United States, 2Medicine, Emory University-Department of Pediatrics, Atlanta, GA, United States.
Rationale: Pulmonary hypertension (PH) is a chronic cardiopulmonary disorder that causes significant morbidity and mortality. Endothelial-to-mesenchymal transition (EndoMT) plays an important role in regulating initiation and progression of PH, suggesting that EndoMT may be a potentially novel and effective therapeutic target in PH. However, the molecular mechanism of EndoMT in the pathogenesis of PH remains largely unknown. Our lab and others have established the importance of peroxisome proliferator-activated receptor gamma (PPARg) in PH. Our studies indicate that PPARg regulates the transcription factor, ETS variant 2 (ETV2), which is indispensable for cardiovascular system development and serves as a master regulator for endothelial cell generation and function. Thus, we hypothesize that the ETV2- PPARg axis plays an important role in EndoMT. Methods: To examine pulmonary vascular derangements in Hypoxia/Sugen PH models, male C57BL/6 mice or Sprague Dawley rats were exposed to hypoxia (10% O2) with Sugen 5416 (HYP/Su) or normoxia (NOR, 21% O2) for 3 weeks. Right ventricular systolic pressure (RVSP) and right ventricular hypertrophy (RVH) were measured. Levels of EndoMT markers in lungs of HYP/Su mice and rats were compared to normoxia (CON) mice and rats using qRT-PCR. In silico analysis of the promoter region of ETV2 reveals four putative binding sites for PPARg. An ETV2 promoter activity assay was used to determine if PPARg transcriptionally regulates ETV expression. Further, to determine if reduction in ETV2/PPARg axis signaling increases the levels of EndoMT markers, PPARg or ETV2 loss or gain of function strategies were employed. Human pulmonary artery endothelial cells (HPAECs) were treated with interleukin 1 beta, tumor necrosis factor alpha, and transforming growth factor beta (TGFB) to generate induced-EndoMT (i-EndoMT) cells. Results: As expected, male mice and rats developed PH and RVH in response to HYP/Su. HYP/Su treatment also increased lung levels of mesenchymal markers, including desmin, TGFB1, SLUG, and alpha-smooth muscle actin. Luciferase-promoter assays showed that PPARg transcriptionally activates the ETV2 promoter. Levels of ETV2 and PPARγ were decreased in i-EndoMT cells whereas markers of EndoMT were increased. Importantly, knockdown in HPAEC PPARg or ETV2 increased levels of EndoMT markers whereas overexpression of ETV2/PPARg axis led to reduced expression of EndoMT markers. Conclusions: Collectively, the ETV2/PPARg axis contributes to regulation of EndoMT and may thereby participate in the pathogenesis of PH. These findings suggest novel molecular pathways involved in EndoMT and PH pathogenesis that merit further exploration.