Phosphodiesterases Mediate the Augmentation of Myogenic Constriction by Inhibitory G Protein Signaling and is Negatively Modulated by the Dual Action of RGS2 and 5

Abstract

G protein regulation by regulators of G protein signaling (RGS) proteins of the R4/B family plays a key role in vascular tone maintenance; However, the regulatory mechanisms are poorly understood. Previous studies showed that the loss of Gi/o and Gq/11 regulation by RGS2 and RGS5 is involved in augmented vascular tone and decreased uterine blood flow in mice. RGS2 and 5 are structurally and functionally closely related and are co-expressed in the resistance vasculature, including the uterine vascular bed. However, whether and how RGS2 and 5 coordinate their regulatory activities to finetune G protein signaling and regulate vascular tone are unclear. Here, we tested the hypothesis that the integrated activity of RGS2 and 5 modulates vascular tone by negatively regulating Gi/o signaling to promote cAMP-dependent attenuation of uterine artery (UA) myogenic tone (MT). Using pressure myography, we examined MT of UA segments isolated from non-pregnant wild type (WT), Rgs2−/−, Rgs5−/−, and Rgs2/5 dbKO mice in the absence and presence of exogenous cAMP or chemical inhibition of Gi/o signaling, while nitric oxide tone was continuously suppressed with the eNOS inhibitor, L-NAME. We found that MT was reduced in Rgs5−/− relative to WT or Rgs2−/− UA in the absence or presence of L-NAME. Activating Gi/o with dopamine increased, whereas exogenous cAMP decreased MT in Rgs5−/− UA to similar levels in WT UA. Dual deletion of Rgs2 and 5 abolished the reduction of MT due to the absence of only Rgs5 and enhanced dopamine-induced Gi/o effects in Rgs2/5 dbKO UA. Conversely, and as in WT UA, Gi/o inhibition with pertussis toxin or the application of exogenous cAMP decreased MT in Rgs2/5 dbKO to similar levels in Rgs5−/− UA. Application of the pan-phosphodiesterase (PDE) inhibitor, IBMX, concentration dependently decreased and normalized MT in all genotypes, and blocked dopamine-mediated MT augmentation in Rgs2−/−, Rgs5−/−, and Rgs2/5 dbKO UA. These results indicate that activated Gi/o augments MT by promoting PDE-mediated inhibition of cAMP-dependent vasodilatation; and while both RGS2 and 5 negatively regulate this novel Gi/o-PDE-cAMP signaling pathway, RGS5 dampens the inhibitory efficacy of RGS2 towards Gi/o in uterine arteries.