Abstract 891: SM22-GRK5 Induced Hypertension (HBP) is Mediated by the β1-Adrenergic Receptor (β1AR) Coupling to Gi
Abnormal βAR signaling is associated with HBP and contributes to the increased contractile state of vascular smooth muscle (VSM). G protein receptor kinases (GRK) have been shown to phosphorylate and regulate βARs. Expression level of GRK5 has been shown to be upregulated in aorta of angiotensin II infused rats and our lab has shown that transgenic overexpression (OVX) of VSM-specific GRK5 using the SM22 promoter causes HBP. Blood pressure (BP) in SM22-GRK5 mice can be restored to control values either using pertussis toxin or chronic β1AR inhibition (via CGP20712A), but not β2AR inhibition (via ICI 118,551). Therefore, the hypothesis of this study is that OVX of SM22-GRK5 causes β1ARs to change preference for G proteins and couple to Gi, rather than Gs, thus impairing β1AR induced relaxation.
METHODS: SM22-GRK5 mice were bred with both β1AR knockout (KO) and β2AR KO mice. Conscious BP was measured in freely moving mice with an implanted radiotelemetric catheter (DSI) 4 days post insertion. We also measured isoproterenol (ISO) induced relaxation in endothelium-denuded thoracic aortic rings from β2KO/SM22-GRK5 mice.
RESULTS: β2KO/SM22-GRK5 mice had a significantly higher mean conscious BP than β1KO/SM22-GRK5 mice (129.5±4.1 mmHg vs. 104.3±3.6 mmHg, n=4.5, P<.05). β2KO/SM22-GRK5 also exhibited a significantly higher heart rate than β1KO/SM22-GRK5 mice (640±35 vs. 444±15 beats per minute, n=5,6, P<.05). Thoracic aortic rings from β2KO/SM22-GRK5 mice with or without pertussis toxin (Ptx) to inhibit Gi signaling (pretreatment with 200 ng/ml Ptx for 1.5h) were preconstricted with 3x10–7 M phenylephrine and an ISO dose response relaxation curve was performed (1x10 –9 M to 1x10 – 6 M). Rings from β2KO/SM22-GRK5 mice treated with Ptx relaxed significantly more than those without Ptx at 3x10 –7 M ISO (64.5±6.1 vs. 95.6±4.0%, n=3, P<.05) and 3x10 – 6 M ISO (50.2±9.8 vs. 77.1±8.7, n=3, P<.05).
CONCLUSIONS: Deletion of β1AR restores HBP in our SM22-GRK5 mice to normal values. Inhibition of Gi signaling by Ptx in β2KO/SM22-GRK5 mice enhances relaxation in response to ISO. These data suggest that the HBP present in our SM22-GRK5 mice is mediated by β1AR. Furthermore, this data suggests that SM22-GRK5 OVX causes β1ARs to couple to Gi, thus impairing β1AR mediated relaxation.