G Protein-Coupled Receptor Signaling in Growth and Inflammation of Vascular Smooth Muscle
Bullock, Michael T
Cardiovascular disease (CVD) remains the primary cause of morbidity and mortality in the United States and worldwide. The exaggerated release of serine proteases and reduced blood flow and ensuing development of extracellular acidosis in affected tissues have previously been theorized to contribute to CVD pathophysiology. A broad family of transmembrane receptors known as G protein-coupled receptors (GPCRs) has been implicated in various roles of cardiovascular pathophysiology, yet the roles of several specific GPCR subfamilies in CVD pathology remain unclear. In this study, two understudied GPCR subfamily members of interest are the serine protease-activated receptor PAR2 and the proton sensing receptor GPR68, both identified in vascular smooth muscle cells (VSMCs) and believed to signal through multiple intracellular G proteins. In the stimulatory Gs pathway, activation of cyclic AMP contributes to stimulation of multiple downstream effectors; however, the discrete influence of PAR2 and GPR68 and their precise G signaling pathways in CVD remain unclear. In this study, we hypothesized that PAR stimulation, via serine proteases, and GPR68, through acidosis, promote proliferation and inflammation in VSM and that these operate via stimulatory Gs signaling. Using an arterial distension injury model, whole vessel PAR2 expression and activity were both increased 30 minutes after injury compared to sham-operated controls. In cultured VSMCs, cumulative data suggest that PAR2 induction is regulated after stimulation through b-arrestin signaling. Interestingly, in the presence of vascular distension injury, we saw decreased arterial wall GPR68 expression compared to controls after 30 minutes. Using a carotid artery ligation injury, which more adequately mimics vascular ischemia/acidosis, in GPR68-deficient (gene knockout (KO)) mice, we saw reduced vascular remodeling and neointimal formation compared to wild type (WT) controls. In vitro, GPR68 KO cells exhibited increased proliferation in both growth stimulated (10-20% serum) and hypoxic (1% oxygen (O2)) conditions after 48 and 72 hours. Cell cycle data displayed increased proliferation rate of KO cells (~12 hours) compared to WT cells. In WT cells, evidence points towards reduced Gs signaling via the cAMP targets Rap1A/1B and ERK1/2 under acidotic and hypoxic conditions, whereas no changes were observed in GPR68 KO cells in acidic versus normal conditions. Following treatment under ischemia/hypoxia conditions, b-arrestin appears to be upregulated compared to normoxic WT cells, suggesting its involvement in the regulation of GPR68. Further, WT cells treated with acidotic media displayed increased levels of the inflammatory cytokine interleukin-6 (IL-6) compared to WT and KO cells in normal pH media. These cumulative findings suggest that both PAR2 and GPR68 have capacity to regulate VSMC growth and inflammation as foundations of CVD. With this information, insight into these crucial yet understudied GPCR pathways, PAR2 and GPR68, may provide targets of interest in CVD treatment and/or management.
Bullock, Michael T. (June 2021). G Protein-Coupled Receptor Signaling in Growth and Inflammation of Vascular Smooth Muscle (Master's Thesis, East Carolina University). Retrieved from the Scholarship. (http://hdl.handle.net/10342/9386.)
Bullock, Michael T. G Protein-Coupled Receptor Signaling in Growth and Inflammation of Vascular Smooth Muscle. Master's Thesis. East Carolina University, June 2021. The Scholarship. http://hdl.handle.net/10342/9386. September 21, 2023.
Bullock, Michael T, “G Protein-Coupled Receptor Signaling in Growth and Inflammation of Vascular Smooth Muscle” (Master's Thesis., East Carolina University, June 2021).
Bullock, Michael T. G Protein-Coupled Receptor Signaling in Growth and Inflammation of Vascular Smooth Muscle [Master's Thesis]. Greenville, NC: East Carolina University; June 2021.
East Carolina University