Date of Award

3-30-2022

Document Type

Doctoral Dissertation - Open Access

Degree Name

Doctor of Philosophy

Department

Pharmacology

First Advisor

Sachin Gupte, MD. Ph.D.

Second Advisor

Michal Schwartzman, Ph.D.

Abstract

Pulmonary Hypertension (PH) is a cardiopulmonary disease estimated to affect between 20 million to 70 million individuals globally, with poor prognosis and inadequate treatment. Recent studies show the orphan G Protein Coupled Receptor 75 (GPR75) is upregulated in the pulmonary vessels of PH patients, especially in females. Therefore, we hypothesized that Gpr75 knock down (Gpr75-/-) mice will be protected from developing PH. To test our hypothesis, we challenged isolated intra-lobar pulmonary artery (IPA) from wild-type (WT; N=40) and Gpr75-/- (N=19) mice with hypoxia to examine their hypoxic vasoconstrictive (HPV) response, which is a physiological response of pulmonary circulation to balance ventilation-to-perfusion ratio that becomes maladaptive in chronic hypoxia leading to the development of PH. IPA of Gpr75-/- mice developed very little or no HPV response as compared to the WT mice. Next, Gpr75-/- (N=8) as compared with WT (N=18) kept in hypoxic (10% O2) conditions for 5-weeks developed less PH as indicated by significantly less increase in right ventricular systolic pressure (RVSP) and diastolic pressure (RVDP). Gpr75-/- mice also expressed less inflammatory gene (Ccl2, Ccl5, Cxcl12, and Prom1) and gene encoding rho associated coiled-coil containing protein kinase 2 (Rock2), which are often overexpressed in lungs and pulmonary arteries of PH mice and patients, but expressed more genes that encode bone morphogenetic protein receptor 1a (Bmpr1a) and myosin heavy chain 11 (Myh11), a smooth muscle specific protein gene that is often reduced in lungs and pulmonary arteries of PH mice and patients. Vascular reactivity of WT and Gpr75-/- mice was also examined by challenging isolated intra-lobar pulmonary arteries with vasoconstricting agents such as potassium chloride (KCl), thromboxane mimetic (U46619), cyclic nucleotide channel inhibitor (ZD7288), and endothelin-1 (ET-1). The Gpr75-/- as compared with wild-type pulmonary arteries contracted less to all the contractile agents. Since GPR75 is a G-protein coupled receptor, to determine second messengers that potentially contribute to regulating contractile function of pulmonary arteries we measured cAMP and IP3 in lungs of wild-type and Gpr75-/- mice. While we found no difference in the IP3 levels between the WT and Gpr75-/- groups, cAMP levels were significantly higher in Gpr75-/- compared to levels in WT mice. These results suggest GPR75 plays a major role in the development of PH by potentially attenuating cAMP-dependent signaling and concomitantly augmenting pulmonary constriction in response to hypoxia.

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