Upregulation of G protein-linked receptor kinases with advancing age in rat aorta

The age-related decline in beta-adrenergic receptor (beta-AR)-mediated vasorelaxation is associated with desensitization of beta-ARs without significant downregulation. The primary mode of this homologous beta-AR desensitization, in general, is via G protein receptor kinases (GRK). Therefore, we hypothesize that age-related changes in GRKs are causative to this etiology in rat aorta. Herein, we investigate the activity and cellular distribution (cytoplasmic vs. membrane) of several GRK isoforms and beta-arrestin proteins. GRK activity was assessed in extracts from aortic tissue of 6-wk, 6-mo, 12-mo, and 24-mo-old male Fischer-344 rats using a rhodopsin phosphorylation assay. We also performed immunoblots on lysates from aorta with specific antibodies to GRK-2, -3, -5, and beta-arrestin-1. Results show an age-related increase in GRK activity. Furthermore, expression of GRK-2 (cytoplasmic and membrane), GRK-3 (cytoplasmic and membrane), and beta-arrestin (soluble) increased with advancing age, whereas GRK-5 (membrane) expression remained unchanged. These results suggest that age is associated with increased activity and expression of specific GRKs. This increase likely results in enhanced phosphorylation and desensitization of beta-ARs. These biochemical changes are consistent with observed aging physiology.