Differential βarrestin1‐Mediated Signaling in Spontaneously Hypertensive versus Normotensive Rat‐Derived Astrocytes

Abstract

ObjectiveTo investigate the role of βarrestin1 in angiotensin II (AngII) type 1 receptor (AT1R)‐mediated signaling in astrocytes isolated from the brainstem of spontaneously hypertensive rats (SHRs) or normotensive rats.BackgroundThe βarrestins (βarrestin1 and‐2) terminate G protein signaling by G protein‐coupled receptors (GPCRs) and, at the same time, they initiate their own “second wave” of signaling from GPCRs, independently of G proteins. The AT1R is one such GPCR that signals via both G proteins and βarrestins in various cell types. It is unknown whether the AT1R signals via βarrestins in the brain. We sought to examine the involvement of βarrestins in the AT1R‐mediated Extracellular signal‐regulated kinase (ERK1/2) mitogen‐activated protein kinase (MAPK) activation and angiotensinogen (AGT) expression in Spontaneously Hypertensive Rat (SHR)‐versus normotensive rat‐derived primary astrocytes.MethodsPrimary cultures of brainstem astrocytes were isolated from the brains of 2–3 days old pups. 100 nM AngII and 10 μM SII (an AngII peptide analog which is a βarrestin‐biased agonist) were used to study AT1R‐mediated ERK1/2 activation and AGT expression. Protein analysis was done using Western blotting and mRNA measurement was done using real‐time PCR. The results in SHR astrocytes were compared to normotensive Wistar rat astrocytes. Protein analysis was done using Western blotting and mRNA measurement using real time PCR.ResultsOur results indicate that βarrestin1 is the major βarrestin isoform in astrocytes from both SHR and normotensive rat brainstem astrocytes. AngII activates ERK1/2 in SHR astrocytes more robustly than in normotensive rat astrocytes. On the other hand, SII strongly activates ERK1/2 in normotensive rat astrocytes and only minimally in SHR astrocytes. In addition, SII, similarly to AngII, upregulates cytoplasmic AGT protein synthesis in both SHR and normotensive rat astrocytes. However, SII has no significant effects on AGT mRNA levels in brainstem astrocytes from either rat model.ConclusionIn this study, we show that AngII‐AT1R‐induced ERK1/2 activation in SHR astrocytes appears to be almost exclusively G protein‐dependent, contrary to normotensive rat astrocytes. Moreover, the AT1R‐mediated βarrestin1‐dependent signaling pathway plays a role in the regulation of AGT protein synthesis in rat astrocytes derived from the brain stem region in both models.Support or Funding Information* This research was funded by Nova Southeastern University President's Faculty Research & Development Grant and Health Profession Division Grant.