David Cool (Committee Member), James Olson (Committee Member), Mark Rich (Committee Member), Jeffrey Travers (Committee Member), Lucile Wrenshall (Advisor)
Doctor of Philosophy (PhD)
Atherosclerosis is an inflammatory disorder of the vasculature leading to the development of plaques within vessel walls. A critical component of atherosclerosis involves migration and proliferation of vascular smooth muscle cells (VSMCs) into the developing plaque, however, its mechanism is not yet understood. Previous studies have reported that IL-2 is deposited within the vasculature and IL-2 accumulates within atherosclerotic plaques due to secretion by infiltrating Th-1 cells. A limited number of studies suggest that VSMCs express a partial IL-2 receptor, comprising the ß and ¿ subunit. This suggests that IL-2 may elicit a physiological response in VSMCs. Considering IL-2’s proliferative function among cells of the immune system, we hypothesized that VSMCs respond to IL-2 by proliferation and migration in vitro. Since the IL-2 receptor has the highest affinity as a heterotrimeric protein comprised of a, ß, and ¿ subunits, it is likely that VSMCs also express the IL-2 receptor a subunit. We observed a pronounced increase of DNA synthesis in IL-2 treated VSMCs by using the CLICK-IT assay. Using the Boyden Chamber assay, we showed that IL-2 caused significant VSMC migration. IL-2R a mRNA was detected in VSMCs by RT-PCR using intron-spanning primers and confirmed by sequencing. IL-2 receptor a protein of the expected molecular weight was observed in VSMC lysates by western blot analysis using a protein specific antibody. Additional studies using immunofluorescence and cell-fractionation revealed that IL2R a subunit localizes to the nuclear envelope of VSMCs. Finally, we have found IL-2 activates the MAPK and PI3K/AKT signaling pathways within VSMCs. Expression of the tripartite IL-2 receptor (a, ß, ¿) within VSMCs is a novel observation. Working through this receptor IL-2 may induce proliferation and migration of VSMC’s into sites of developing plaques thereby contributing to the pathogenesis of atherosclerosis.
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