Abstract 15092: The Yin-yang of Bmpr2 and Ces1 in the Pulmonary Endothelium Aad Its Role in Pulmonary Arterial Hypertension

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Background/Hypothesis: Pulmonary Arterial Hypertension (PAH) is a life-threatening disease characterized by loss of pulmonary microvessels and vascular remodeling. Loss of function BMPR2 mutations contribute to pulmonary endothelial cell (EC) apoptosis and oxidative stress, but their reduced penetrance suggests need for additional modifiers. Carboxylesterase1 (CES1) is endoplasmic reticulum (ER) enzyme responsible for detoxification, proteostasis, and redox balance. Similar to BMPR2 mutations, we found that loss of CES1 is associated with oxidative stress and apoptosis. In this study, we explore a plausible link between BMPR2 pathway and CES1 regulation in promoting EC survival and angiogenesis. Methods: PECs & lung tissue from healthy donors and PAH patients were obtained from PHBI. To induce oxidative stress, we used H 2 O 2 (100 μM) & methamphetamine HCl (METH, 0.5-2mM). Both siRNA and pharmacological approaches were used to inhibit BMPR2, Nrf2, and CES1 expression. Caspase and Matrigel assays were used to assess PEC survival and tube formation, respectively. Results: RNAseq of BMPR2-mutant PECs showed significantly less CES1 expression, which correlated with reduced protein expression in PEC lysates and within lung vascular lesions. In healthy PECs, BMP9 stimulation led to increase in CES1 expression that was absent post BMPR2 knockdown. CES1 gene transcription was by BMPR2-dependent activation of Nrf2, a transcription factor responsible for antioxidant gene expression and mitochondrial biogenesis. Inhibition of Nrf2 activation by ML385 (5μM) abrogates BMP9 induced CES1 mRNA levels similar to BMPR2 knockdown. The connection between BMPR2 and CES1 was further strengthened by CES1 knockdown studies in PECs that demonstrated reduction in BMPR2 protein synthesis associated with ER stress and reduced autophagy. Finally, lung examination in CRISPR generated CES1 +/- mice demonstrated increased microvascular muscularization at normoxia compared to wild type mice. Conclusion: BMPR2 and CES1 are part of common signaling pathway that protects PECs against oxidative stress and mitochondrial damage through a positive feedback loop. Interventions that restore CES1 activity could rescue BMPR2 signaling and serve as novel PAH therapeutics.