G protein-coupled receptor expression and function in Pulmonary Artery Smooth Muscle Cells : : Novel Targets in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is characterized by increased pulmonary vascular resistance, in part due to increased proliferation of pulmonary artery smooth muscle cells (PASMC). Since the second messenger 3'5'-cyclic adenosine monophosphate (cAMP) decreases proliferation of PASMC, G protein-coupled receptors (GPCRs) that couple to G[alpha]s are attractive targets for PAH. We used a TaqMan ® GPCR array to identify the GPCRs expressed by PASMC isolated from normal subjects and from patients with PAH. The data revealed that human PASMC express >135 GPCRs, at least 50 of which regulate cAMP formation. We found that GPCR expression correlates with function e.g., of G[alpha]s-coupled GPCRs with formation of cAMP and inhibition of cell proliferation (a functional response to receptor activation), thus documenting that we had identified physiologically relevant GPCRs. Our studies of PAH-PASMC with GPCR arrays revealed that PAH is associated with an increase (>2-fold) in the expression of 41 GPCRs. The greatest increase in GPCR expression was of two orphan receptors, namely GPR113 and GPR75, whose expression was absent in normal PASMC. We also found the mRNA and protein expression of GPR113 and GPR75 were increased in animal models of PAH. Importantly, treatment of PAH-PASMC with a GPR75 antibody blunted the increased proliferation of PASMC and increased cellular cAMP levels. Taken together, the data in this thesis provide evidence that the GPCR microarray can identify GPCRs that contribute to the physiology of PASMC and can uncover new drug targets, such as GPR75 for PAH--a disease that requires therapies beyond those currently in us