Protein kinase Cβ mediates downregulated expression of glucagon-like peptide-1 receptor in hypertensive rat renal arteries.

Abstract

Glucagon-like peptide-1 (GLP-1) exerts its actions via activating GLP-1 receptor (GLP-1R). Our previous study showed a reduced GLP-1R expression in spontaneously hypertensive rat (SHR) renal arteries. The present study investigated the mechanisms underlying GLP-1R downregulation in hypertension. Intrarenal arteries of normotensive Wistar-Kyoto rat (WKY) and SHR were suspended in the myograph for force measurement. GLP-1R expression was evaluated by both immunofluorescence and western blotting. Protein kinase Cα (PKCα), PKCβ, PKCδ, and total PKC levels were assayed by western blotting. Immunofluorescence revealed reduced GLP-1R level in SHR renal arteries compared with WKY renal arteries. GLP-1R agonist exendin-4 induced concentration-dependent relaxations in WKY arteries, which mainly depended on the presence of endothelium. GLP-1R antagonist exendin 9-39 inhibited this relaxation in WKY arteries, whereas the relaxations were significantly less in SHR arteries. Ex-vivo treatment with PKC inhibitor GFX, PKCα and PKCβ inhibitor Gö6976, and PKCβ inhibitor hispidin but not PKCδ inhibitor rottlerin improved the impaired relaxations and restored the diminished GLP-1R expression in SHR arteries. Furthermore, PKCβ level was greater in SHR than WKY arteries, with no difference in PKCα, PKCδ, or total PKC expressions between two rat strains. Treatment with PKC-activating agent phorbol-12-myristate-13-acetate attenuated exendin-4-induced relaxations and reduced GLP-1R expression in WKY arteries, which were reversed by GFX, Gö6976, or hispidin. More relevantly, immunofluorescence of human renal arteries also showed a reduced GLP-1R level in hypertensive patients. The present results provide novel evidence that the reduced GLP-1R expression in SHR renal arteries is most likely mediated through PKCβ upregulation; the latter probably contributes to the impaired GLP-1R-mediated vasorelaxations in hypertension.