Abstract 15760: Inhibition of PI3kα Overcomes Apoptosis Resistance of Smooth Muscle Cells in Pulmonary Hypertension and Thereby Reverses Established Vascular Remodeling
Pulmonary hypertension (PH) is hallmarked by vascular remodeling in pulmonary arterioles. Therapeutic reversal of established vascular remodeling is impeded by apoptosis resistance of pulmonary arterial smooth muscle cells (PASMCs). PI 3-kinase (PI3K) dependent activation of AKT protects against SMC apoptosis. Here, we tested the hypothesis that inhibition of the PI3Kα isoform overcomes apoptosis resistance of PASMCs and reverses established remodeling in PH. Western blot analysis revealed increased AKT activation in lungs from PH patients compared to healthy donors demonstrating enhanced PI3K signalling in PH. To test whether PI3Kα signaling contributes to apoptosis resistance in diseased PASMCs, we challenged cells from both, SU5416/hypoxia treated rats and healthy control animals with H2O2 in the absence or presence of the PI3Kα inhibitor PIK75, respectively. H2O2 (200 μM) induced apoptosis was significantly decreased in diseased PASMCs in comparison to control cells (1.11±0.05 fold vs. 2.10±0.07 fold) as analysed by nucleosome ELISA. Intriguingly, PI3Kα inhibition overcomes apoptosis resistance of diseased PASMCs as addition of PIK75 (300nM) led to the same increase of apoptosis as in control cells (10.71±2.70 vs. 12.96±3.72). To analyze the effects of PI3Kα inhibition in animals with established PH, rats were exposed to SU5416/hypoxia (21 days) followed by PIK75 treatment (14 days normoxia). TUNEL and caspase-3 stainings of pulmonary vessels revealed a significant increased ratio of apoptotic cells in pulmonary vessels from PIK75 treated animals compared to controls (33.45±3.02%, n=5 vs. 13.90±1.63%, n=5). Consequently, muscularization, medial wall thickness and RVSP (41.2mmHg, n=6 vs. 81.0mmHg, n=5) were significantly reduced in PIK75 treated animals. Furthermore, SU5416/hypoxia-induced right ventricular hypertrophy demonstrated as (RV / LV + septum) ratio was reversed (0.37±0.15 vs. 0.53±0.04, p<0.05). These results demonstrate that PI3Kα inhibition overcomes apoptosis resistance of diseased PASMCs in vitro and in vivo and thereby reversed established PH. Since PI3K signalling is enhanced in PH patients, apoptosis induction via PI3Kα inhibition is a promising strategy to reverse established vascular remodeling in PH.
Author Disclosures: M. Vantler: None. E.M. Berghausen: None. A. Behringer: None. R. Savai: None. S. Savai Pullamsetti: None. S. Baldus: None. S. Rosenkranz: None.
- © 2016 by American Heart Association, Inc.