Abstract 5192: G Protein-coupled Receptor Kinase-5 Attenuates Atherosclerosis by Reducing PDGF-induced Smooth Muscle Cell Proliferation and Migration
G protein-coupled receptor kinase-5 (GRK5) is a Ser/Thr kinase that up-regulates in atherosclerotic arteries; it phosphorylates and desensitizes many receptors important to atherogenesis, including heptahelical receptors and the platelet-derived growth factor receptor- β (PDGFRβ). We therefore tested the hypothesis that GRK5 reduces atherogenesis, by comparing atherosclerosis in male C57BL/6-congenic apoe−/−/grk5−/− and apoe−/− mice, fed a Western diet for 12 wk from age 5 wk, with equivalent serum cholesterols and blood pressures. Aortic atherosclerosis (en face) was 50% greater in grk5−/− (n=20) than in grk5+/+ (n=18) mice: Sudanophilic lesions covered 10.6±0.8% versus 7.0±0.5% of aortic area, respectively (p<0.001). To test whether this difference could result from GRK5-mediated regulation of arterial smooth muscle cells (SMCs) in vivo, we denuded the common carotid endothelium with a 0.36-mm wire in 25-wk-old male B6-congenic WT and grk5 KO mice, using a procedure we previously showed (by bone marrow transplant) produces neointimal hyperplasia comprising SMCs derived only from arterial media. Before injury, GRK5 KO and WT carotids had identical luminal and medial areas. However, 4 wk after injury, neointimal area was 350% greater in GRK5 KO (0.06±0.01 mm2) than in WT mice (0.017±0.007 mm2) (n=5/group, p<0.02), but medial areas were equivalent. Two wk after injury, medial SMCs showed 80±20% greater PDGFRβ activation per cell in GRK5 KO than in WT arteries (n=3/group, p<0.02), judged by quantitative immunofluorescence microscopy for PDGFRβ -phospho-Tyr1021; total PDGFRβ levels were equivalent in KO and WT arteries. In vitro, SMC proliferation evoked by PDGF or 2.5% FBS was greater in GRK5 KO than in WT SMCs (3 lines/genotype, p<0.05), by 80±30% and 33±8%, respectively (assessed by SMC counting). Migration (in modified Boyden chambers) was also greater in GRK5 KO than WT SMCs, by 70±20%, 160±20% and 200±30%, respectively, in response to PDGF, 10% FBS, and activated macrophages (p<0.05), despite equivalent GRK5 KO and WT CD4+ lymphocyte migration. We conclude that GRK5 attenuates atherosclerosis, at least in part, by reducing SMC migration and proliferation evoked through the PDGFRβ, and perhaps other SMC receptors activated by macrophages.