Migration of vascular smooth muscle (VSM) cells occurs during development, wound healing, angiogenesis, and contributes to the progression of vascular disease. Published studies support a role for the ubiquitous multifunctional serine/threonine protein kinase, Ca2+/calmodulin-dependent protein kinase II (CaMKII in regulating VSM cell migration, but the mechanisms of CaMKII activation in this setting, and the relevant substrate targets and mechanisms underlying effects on migration, are unknown. Based on our published and preliminary studies we have hypothesized that localized leading edge activation of CaMKII42 regulates focal adhesion dynamics and acts as a positive feedback to promote VSM cell polarization and directional migration.
In Aim 1 molecular/genetic approaches will be used to manipulate CaMKII42 expression and activity, and the consequences on directional persistence and velocity of individual migrating VSM cells determined. Fluorescence recovery after photobleaching (FRAP) analysis of GFP-tagged focal adhesion components will be used to assess CaMKII4-dependent regulation of focal adhesion dynamics.
In Aim 2 biochemical and advanced fluorescence imaging approaches (confocal FRET and TIRF microscopy) will be used to test a potential mechanism involving a functional CaMKII42 interaction with the Src-family kinase, Fyn, in regulating focal adhesion protein dynamics. VSM cell migration is a property of "synthetic phenotype" cells that have not acquired, or have lost, differentiated contractile protein markers and function. We have determined that up-regulation of a CaMKII4 isoform (42 or 4C) contributes to VSM cell synthetic phenotype functions (proliferation, migration). Recent studies indicate up-regulation of certain Ca2+ conducting cation channels in the TRPC and STIM/Orai families in synthetic phenotype VSM cells is linked functionally to regulation of proliferation and migration. Based on this, in Aim 3 we molecular and fluorescence imaging approaches to test the hypothesis that STIM1/Orai1 mediated Ca2+ entry is functionally linked to leading edge CaMKII activation.
In aim 4 we test the hypothesis that that expression of CaMKII4 isozymes and these Ca2+ channels are co-regulated as a function of VSM phenotype, conferring an integrated pathway for Ca2+-dependent regulation of VSM cell migration in vivo. Results of these novel studies are expected to provide insight into mechanisms by which Ca2+ signals regulate VSM cell migration and to provide a basis for understanding Ca2+-dependent regulation of migration in other cell types and processes such as myofibroblast-mediated wound healing or angiogenesis. Taken with recently published studies in heart and skeletal muscle, these studies in VSM suggest that CaMKII4 isoforms may be generally important in muscle remodeling in response to physiological or pathophysiological stressors.
By elucidating the functional consequences of CaMKII isoforms in response to vascular injury, these studies are expected to provide insights into mechanisms underlying vascular proliferative diseases including atherosclerosis and restenosis follow vascular surgery. Because Ca2+ signals and CaMKII are a ubiquitous regulatory system in all cells and tissues, the information derived from these studies can be reasonably expected to extend to other processes involving vascular cell motility such as myofibroblast-mediated wound healing or angiogenesis.
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