Pulmonary arterial hypertension (PAH), a progressive fatal disease, manifests by vascular remodeling of pul- monary arteries (PA), elevated right ventricular afterload, right heart failure, and death. A key component of pulmonary vascular remodeling is the progressive wall thickening of small PA due to increased proliferation and impaired apoptosis of pulmonary arterial vascular smooth muscle cells (PAVSMC). PAVSMC in advanced PAH undergo complex signaling reprograming resulting in persistent activation of pro-proliferative pro-survival pathways and formation of a unique PAH-specific phenotype with intrinsic proliferative/survival potential. This proposal focuses on the potential role of the Hipp growth suppressor pathway as a critical signaling hub, sup- porting a proliferative, apoptosis-resistant PAH PAVSMC phenotype and VSM remodeling. We have found that Hippo is inactivated in PAVSMC from subjects with idiopathic PAH that leads to activation of its reciprocal ef- fectors Yap/Taz, consequent up-regulation of pro-proliferative pro-survival HIF1?, Notch3, ?-catenin, mTORC2-Akt, and mTORC1, and increased PAVSMC proliferation and survival. Our preliminary data show that Hippo inactivation in PAH PAVSMC depends on integrin linked kinase 1 (ILK1) and suggest existence of a Yap-Fibronectin-ILK1 feedback loop that locks Hippo in an inactive state. We also found that restoration of Hippo function by ILK inhibitor reverses PAH-specific signaling abnormalities, selectively inhibits growth, pro- motes apoptosis in human PAH, and reduces established pulmonary vascular remodeling and PH in sugen/hypoxia mouse model. We will critically investigate the role of Hippo signaling in increased proliferation and survival of human PAH PAVSMC and will evaluate it as a candidate target pathway to selectively inhibit growth and induce apoptosis in phenotypically altered PAH PAVSMC and reverse or attenuate established pulmonary vascular remodeling. Specifically, we will:
(Aim1) critically compare Hippo key components MST1/2 and LATS1 and its effectors Yap/Taz in human specimens and PAVSMC from PAH and donor lung and de- termine it roles in PAVSMC proliferation and survival, pulmonary vascular remodeling and PH using PAVSMC from idiopathic PAH and donor lung and mice with VSM-specific Mst1/2, Lats1, and Yap knockout;
(Aim 2) de- termine whether Hippo inactivation in PAH PAVSMC is self-supported by Yap and/or Taz-dependent activation of ILK1 through increased fibronectin production and define whether Hippo inactivation up-regulates pro- proliferative pro-survival HIF1?, Notch3, Wnt/?-catenin, mTORC2-Akt and mTORC1 pathways (selected by combination of bioinformatic analysis and gain- and loss-of function approach);
and (Aim 3) evaluate whether targeting Hippo selectively suppresses proliferation and induces apoptosis in vitro in human PAH PAVSMC, and reverses or attenuates established pulmonary vascular remodeling and PH in vivo in rat sugen/hypoxia model. This study will identify new critical mechanism(s) supporting proliferative/apoptosis resistant PAVSM phenotype in PAH and will dissect new remodeling-focused molecular targets for therapeutic intervention.
These studies will define the role of Hippo signaling in regulating increased proliferation and survival of PAVSMC in pulmonary arterial hypertension (PAH); will provide insights into the molecular mechanisms that are important in pathogenesis of PAH; and will explore whether Hippo signaling could serve as a target pathway for pulmonary vascular remodeling-focused therapeutic interventions.
