Abstract 17231: Contact-Mediated Interaction Between Pulmonary Artery Endothelial and Smooth Muscle Cells Promotes a BMPR2-β-catenin-Notch1 Signal Causing Hyperpolarization of Endothelial Mitochondria and a Stalk Cell-like Phenotype

Abstract

Background: Pulmonary arterial hypertension (PAH) is characterized by endothelial (EC) apoptosis related to loss of distal (D) pulmonary arteries (PA) and abnormal proliferation of smooth muscle-like cells (SMC). These features are mediated by impaired cell metabolism. We observed mitochondrial dysfunction in human PAEC with reduced or mutant BMPR2, the gene associated with familial PAH. Deletion of BMPR2 in murine EC causes failure to regenerate DPA and to recover from hypoxia induced pulmonary hypertension. Loss of BMPR2 in PASMC results in mitochondrial dysfunction associated with enhanced proliferation. Since metabolites and other factors are often transferred by cell contact, we investigated how PASMC-PAEC contact impacts PAEC mitochondrial and cellular function, and could be perturbed by a BMPR2 mutation in PAEC and/or PASMC. Methods and Results: We used a co-culture system in which PAEC and PASMC from lungs of donor control (c-) or PAH patients with a BMPR2 mutation (m-) were either seeded on opposite sides of a 1μm pore insert or separated to assess non-contact mediated responses. When c-PAEC contacted c-PASMC, PAEC mitochondrial membrane potential (Δψ) increased 6-fold compared to mono-cultured or non-contact co-cultured cells (p < 0.001). These PAEC exhibited a significant increase in proliferation (3-fold increase by Ki-67 staining, p<0.01) and survival (73% reduction in caspase activity, p < 0.001); however we observed a decrease in migration and angiogenic capacity in modified Boyden chamber and matrigel assays (52% and 60% reduction, p < 0.001, respectively). We related the increase in Δψ and the above ‘stalk cell-like’ phenotype to an increase in Notch1 intracellular domain (2.5-fold increase, p < 0.001), as they were abrogated by the gamma secretase inhibitor, and enhanced by the co-transcriptional activator β-catenin (4-fold increase, p < 0.001). When m-PAEC and m-PASMC were used in contact cultures, these features were not observed. Conclusions: PASMC in contact with PAEC increase Δψ and produce a Notch and β-catenin mediated stalk cell-like EC phenotype. These features are lost when BMPR2 is deficient in both PAEC and PASMC suggesting that BMPR2-mediated PASMC-EC contact allows PAEC to survive and regenerate in response to damage.