Abstract 94: Ca 2 +/calmodulin-dependent Protein Kinase II ? Gene Deletion Enhances Vascular Remodeling in Response to Injury

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Differentiated vascular smooth muscle (VSM) cells undergo phenotypic switching following injury or primary cell culture. This process includes changes in expression of ion channels, proteins involved in intracellular Ca 2+ homeostasis, as well as changes in Ca 2+ signal effectors. Our previous studies showed that the delta2 isoform of the multifunctional serine/threonine protein kinase Ca 2+ /calmodulin-dependent protein kinase II (CaMKIIδ 2 or CaMKIIδc), was up-regulated in rat carotid artery VSM following balloon injury and contributed positively to cell proliferation, migration and neointima formation. Conversely, CaMKII γ gene isoforms are down-regulated following vascular injury in rats, with as yet unknown functional consequences. We hypothesized that CaMKIIγ expression opposes the vasculoproliferative response promoted by CaMKIIδ. To test this, we generated CaMKIIγ conditional knockout mice by crossing CaMKIIγ loxp/loxp mice with a SM22α (transgelin)-Cre line. Efficient deletion of CaMKIIγ was confirmed in VSM and heart with no compensatory increases in CaMKIIδ expression or observable effects on mouse development, expression of VSMC differentiation marker genes or vascular morphology. Carotid artery ligation-induced neointima formation was markedly enhanced in CaMKIIγ conditional knockout mutant mice compared to littermate controls (Neointima/media area ratios: 0.52 ± 0.20, n=8 vs. 0.03±0.03, n=7) 3 weeks post-ligation with a nearly 2-fold increase in vascular wall proliferation index (0.09±0.006, n=6 vs. 0.05±0.009, n=6) and no change in apoptosis index. CaMKIIγ protein expression is down-regulated following primary culture of aortic VSM. Ectopic re-expression of CaMKIIγ in cultured VSMC from control or global CaMKIIδ-/- knockout mice resulted in a significant reduction in proliferation rates as measured by cell counting and BrdU incorporation and cell migration as assessed by scratch wounding. We conclude from these studies that CaMKIIγ and δ-isoforms have non-equivalent functions in VSM, and specifically, that CaMKIIγ isoforms inhibit the vasculoproliferative response.