Our overarching hypothesis is that FXR1 activity may be a compensatory, anti-inflammatory activity in VSMC. Vascular smooth muscle cells (VSMC) play a critical role in the etiology and progression of many vascular diseases including atherosclerosis and restenosis. Reduction of inflammatory gene expression in VSMC is a rational approach to limit the severity of these diseases. Our laboratory has found that one anti-inflammatory interleukin, IL-19, can decrease vascular inflammation by reduction in mRNA stability of inflammatory transcripts by reduction of activity of HuR, an mRNA stability protein. HuR translocates from the nucleus to the cytoplasm where it recognizes elements present almost exclusively in the 3'UTR of pro-inflammatory genes. Proteins and pathways which limit HuR translocation may reduce inflammatory mRNA stability, but are currently understudied. Using LC-MS/MS to identify HuR-interacting proteins under different inflammatory conditions, we identified one protein termed Fragile X-related protein (FXR1), which interacts with HuR in inflammatory, but not basal conditions, a novel finding. Importantly, FXR1 mRNA expression is enhanced in muscle cells, and it's promoter contains multiple cholesterol-response elements. Nothing has been reported on expression of FXR1 in VSMC or function for FXR1 in vascular disease. We present preliminary data showing that FXR1 expression is increased in injured arteries and TNF? and oxLDL stimulated human VSMC, and this expression is increased by IL-19. We show that siRNA knock down of FXR1 in VSMC increases inflammatory mRNA stability, abundance of inflammatory proteins, and cholesterol uptake, while over-expression of FXR1 decreases mRNA stability and inflammatory protein abundance. Our hypothesis is that FXR1 expression is a compensatory, negative-regulatory mechanism and functions by decreasing HuR activity and vascular inflammation by decreasing the stability of pro-inflammatory transcripts by numerous mechanisms. The overall goal of this application is twofold: 1- to identify the molecular mechanisms of FXR1 function in regulation of HuR activity and mRNA stability of pro-inflammatory transcripts in VSMC, and; 2- determine if modulation of FXR1 activity can reduce severity of atherosclerosis and vascular restenosis.
The majority of cells in atherosclerotic lesions are vascular smooth muscle cell (VSMC)-derived, and inflammatory gene expression in these cells regulates vascular disease. Our overarching hypothesis is that Fragile X related protein-1 (FXR1) activity may be a compensatory, anti-inflammatory gene regulatory factor in VSMC. This grant will determine the molecular mechanisms of how FXR1 modulates inflammatory gene abundance in VSMC, and regulate atherosclerosis and restenosis in vivo.
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