Urotensin-II (U-II) and its receptor UT are upregulated in the pathological setting of various cardiovascular diseases including atherosclerosis. However, their exact role in atherosclerosis remains to be determined. In the present study, we hypothesized that selective overexpression of UT in an SMC-specific fashion would increase atherosclerotic lesion formation in a hypercholesterolemic mouse model. The objectives were to demonstrate the role of UT in this mouse model of atherosclerosis, and to elucidate some of the mechanism involved in the process. We used four strains of mice; wildtype (WT), UT+ (a transgenic strain expressing human UT driven by the alpha-SM22 promoter), ApoE knockout (ko), and UT+/ApoE ko. All animals were fed a high-fat diet for 12 weeks. Western blot analysis revealed a significant increase in UT expression in UT+ and ApoE ko mice (P<0.05). Serum cholesterol and triglyceride levels were significantly increased in ApoE ko and in UT+/ApoE ko but not in UT + mice when compared to wild type mice (P<0.0001). Analysis of aortas showed a significant increase in atherosclerotic lesion in the UT +, ApoE ko and UT+/ApoE ko compared to WT mice (P<0.05). Oral administration of the UT receptor antagonist SB-657510A for 10 weeks in a group of ApoE ko mice fed a high fat diet resulted in a significant reduction of lesion (P<0.001). Immunohistochemistry revealed the presence of strong expression of UT and U-II proteins in the atheroma of UT+, ApoE ko and UT+/ApoE ko mice, particularly in foam cells. SB-657510A also significantly reduced ACAT-1 protein expression in the atherosclerotic lesion of ApoE ko mice (P<0.05). The present findings suggest that the use of UT receptor antagonists may reduce lesion formation through reduced foam cell formation and lipid uptake, demonstrating an important role for UT in the pathogenesis of atherosclerosis.

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