title: Decline in caveolin-1 expression and scaffolding of G protein receptor kinase-2 with age in Fischer 344 aortic vascular smooth muscle.
abstract: Beta-adrenergic receptor (beta-AR)-mediated vasorelaxation declines with age in humans and animal models. This is not caused by changes in expression of beta-AR, G alpha s, adenylyl cyclase, or protein kinase A but is associated with decreased cAMP production. Expression and activity of G protein receptor kinase-2 (GRK-2), which phosphorylates and desensitizes the beta-AR, increases with age in rat aortic tissue. Caveolin scaffolds the beta-AR, GRK, and other proteins within "signaling pockets" and inhibits GRK activity when bound. We questioned the effect of age on caveolin-1 expression and interaction between caveolin-1 and GRK-2 in vascular smooth muscle (VSM) isolated from 2-, 6-, 12-, and 24-mo-old male Fischer 344 rat aorta. Western blot analysis found expression of caveolin-1 declined with age (6-, 12- and 24-mo-old rat aortas express 92, 50, and 42% of 2-mo-old rat aortas, respectively). Results from density-buoyancy analysis showed a lower percentage of GRK in caveolin-1-specific fractions with age (6-, 12- and 24-mo-old rat aortas express 95, 56, and 12% of 2-mo-old rat aortas, respectively). Coimmunoprecipitation confirmed this finding; density of GRK in caveolin-1 immunoprecipitates was 97, 30, and 21% of 2-mo-old aortas compared with 6-, 12- and 24-mo-old animals, respectively. Immunohistocytochemistry and confocal microscopy confirmed that GRK-2 and caveolin-1 colocalize in VSM. These results suggest that in nonoverexpressed, intact tissue, the decline in beta-AR-mediated vasorelaxation may be caused by both a reduction in caveolin-1 expression and a reduction in binding of GRK-2 by caveolin-1. This could lead to an increase in the fraction of free GRK-2, which could phosphorylate and desensitize the beta-AR.
authors.affiliation: Portland Veterans Affairs Medical Center, Research Service, Portland, Oregon 97201, USA.
authors.forename: William E
authors.initials: WE
authors.lastname: Schutzer
authors.forename: John F
authors.initials: JF
authors.lastname: Reed
authors.forename: Scott L
authors.initials: SL
authors.lastname: Mader
mesh_terms: D000375:Aging / Q000378:metabolism*; D000818:Animals; D001011:Aorta / Q000378:metabolism; D051242:Caveolin 1; D022461:Caveolins / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D054769:G-Protein-Coupled Receptor Kinase 2; D006973:Hypertension / Q000378:metabolism*; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344; D011943:Receptors, Adrenergic, beta / Q000378:metabolism; D014664:Vasodilation / Q000502:physiology; D051552:beta-Adrenergic Receptor Kinases
chemical_list: C495537:Cav1 protein, rat; D051242:Caveolin 1; D022461:Caveolins; D011943:Receptors, Adrenergic, beta; D017868:Cyclic AMP-Dependent Protein Kinases; C496569:Grk2 protein, rat; D051552:beta-Adrenergic Receptor Kinases; D054769:G-Protein-Coupled Receptor Kinase 2