Abstract P235: The Absence Of Inhibitory G Protein Regulation By Rgs2 Increases Basal Phosphodiesterase Activity To Decrease Forskolin-stimulated Camp Generation And Enhances Myogenic Response In Uterine Arteries Of Non-pregnant Mice

Abstract

G protein regulation by regulators of G protein signaling (RGS) proteins is crucial to maintaining normal vascular tone for promoting uterine vascular bed perfusion. However, the specific regulatory mechanisms involved are incompletely understood. Previously, we showed that loss of regulation of Gi/o and Gq/11 by RGS2 contributes to enhanced myogenic tone and decreased uterine blood flow in non-pregnant mice. Similarly, RGS5, closely related to RGS2, was found to fine-tune G protein signaling and modulate GPCR-evoked vascular reactivity. RGS2 and RGS5 are co-expressed in the uterine vascular bed. However, it is unclear whether their regulatory activities are coordinated in fine-tuning G protein signaling to modulate vascular tone. Here, we tested whether the combined activity of RGS2 and 5 reduces myogenic tone by negatively regulating Gi/o signaling to promote cAMP-dependent uterine artery relaxation. We used commercially available kits to measure forskolin-stimulated cAMP generation and basal phosphodiesterase (PDE) activity in freshly isolated uterine arteries from non-pregnant wild type, Rgs5 KO and Rgs2 KO mice. Basal tone and myogenic response to increasing intraluminal pressure were assessed using ex vivo pressure myography. We found that the absence of RGS2 but not RGS5 decreased forskolin-stimulated cAMP generation. Conversely, basal PDE activity was augmented in both Rgs2 KO and Rgs5 KO arteries, though the increase was less robust in Rgs5 KO arteries. Basal tone and myogenic response were reduced in Rgs5 KO arteries compared to WT or Rgs2 KO arteries in the absence or presence of nitric oxide synthase blockade with L-NAME. Activating Gi/o with dopamine increased myogenic constriction in all genotypes but less robustly in Rgs5 KO arteries, while pre-incubation of the vessels with exogenous cAMP or PDE inhibition with IBMX normalized maximal myogenic response to similar levels in all groups. Collectively, these findings indicate that altered Gi/o regulation due to RGS2 absence enhances myogenic tone by promoting PDE-mediated inhibition of cAMP-dependent vasodilation. While both RGS2 and RGS5 negatively regulate this novel Gi/o-PDE-cAMP signaling pathway, RGS5 dampens the inhibitory efficacy of RGS2 towards Gi/o in uterine arteries.