Abstract 3606: The Atheroprotective Effects of HSP27 are Mediated by the Differential Expression of Multiple Inflammatory Genes
We identified Heat Shock Protein 27 (HSP27) as a biomarker of atherosclerosis (ATVB, 2005) and demonstrated that over-expression of human HSP27 is atheroprotective in female apoE−/−mice (Circ Res, in press). To identify key HSP27-regulated genes involved in atheroprotection. We compared the expression profile of a universally atherosclerosis-prone site, the lesser curvature (LC) of aortic arch, in female HSP27 over-expressing (ApoE−/−HSP27o/e) mice (n=7) and female ApoE−/− littermate controls (with greater atherosclerotic burden due to their lack of atheroprotection; n=7). All mice were 10 weeks old and fed a high fat diet for 4 weeks. The relatively atherosclerosis-free greater curvature (GC) of aortic arch was also collected from both groups of mice and Affymetrix Mouse Exon 1.0 ST Arrays were used to determine transcriptional profiles of atherosclerotic lesions (LC) vs normal aorta (GC) from both groups of mice. Comparing the LC vs GC in the ApoE−/− mice we noted several inflammatory mediators previously documented in array studies (e.g., MMP12, CD5L, IL6) - thereby validating our model. As well, we identified some genes previously thought to be unrelated to atherosclerosis. The comparison of the LC of the apoE−/−HSP27o/e vs LC of the apoE−/− mice resulted in the identification of 13 up-regulated genes and 16 down-regulated genes (using a threshold for change of 3-fold). Employing Ingenuity Pathway Analysis we noted that the cardiovascular / inflammatory networks had the highest gene scores and TNFα was a key regulator. Two genes in the inflammatory pathway, a regulator of G-protein signaling and a small peptide hormone, were especially interesting as their expression patterns were markedly altered (in opposite directions) with HSP27 atheroprotection. The expression of the up-regulated regulator of G-protein signaling was confirmed in murine aortae by immunohistochemistry and found to be exclusively present in macrophages. Using Western blotting we noted that HSP27 over-expression upregulated the levels of this protein in mouse macrophages. HSP27 atheroprotection involves a program of differential gene expression, some of which involves proteins found in blood-borne macrophages.