Abstract 461: Inhibition of Four- and- a- Half LIM Domain Protein-2 Decreases Atherosclerosis in Apoe -/- Mice model: Role of Immune T- Cells

Abstract

OBJECTIVE Four-and-a-half LIM domain protein-2 (FHL2), a member of the FHL family of proteins, is expressed in endothelial and vascular smooth muscle cells. FHL2 negatively regulates endothelial cell survival and migration, but its role in atherogenesis is unknown. METHODS AND RESULTS To investigate the role of FHL2 in atherosclerosis, we crossed FHL2 knockout (FHL2-/-) with apolipoprotein (Apo) E-deficient (ApoE -/-) mice, and fed them a high fat diet for 7 weeks. Despite a total plasma cholesterol levels comparable to the ApoE-/- mice, FHL2-/-ApoE-/- mice showed a strong increase in plasma HDL-cholesterol as compared to ApoE -/- mice (P<0.01; n=6) and had significantly smaller atherosclerotic plaques in the aortic sinus (0.14±0.02 vs. 0.29±0.04 mm 2 ) and aorta (6.9±0.9 vs 10.3±1%) (P<0.05; n=6), assessed by oil red O staining, compared with ApoE-/- mice. The relative monocyte/ macrophage content within atherosclerotic plaques, determined by MOMA-2 immunostaining, was equivalent in both animal groups. However, we observed an enhanced relative content of collagen (16±2 vs 8.6±3 %) and smooth muscle cells (4.5±0.8 vs 1.8±0.5%) within the plaques in the aortic sinus of FHL2-/-ApoE-/- mice compared with ApoE-/- mice, determined by Sirius red and alpha-actin staining respectively. These results suggest that absence of FHL2 promotes smaller and more stable plaques. The reduced plaque size in FHL2-/-ApoE-/- mice could be explained, at least in part, by the 40% reduction in ICAM-1 mRNA expression observed in aortas (p<0.05 vs ApoE-/-). Moreover, although the relative monocyte/ macrophage content in spleens was equivalent in both animal groups, FACS analysis of T cells in spleens showed a significant increase in CD4+CD25+Foxp3+ regulatory T cell numbers, in FHL2-/-ApoE-/- compared with ApoE-/- mice (19.5±1.6 vs. 16.2±2% of CD3+CD4+ cells, respectively) (P<0.005). CONCLUSIONS These results suggest that FHL2 may play an important role in atherosclerosis by promoting plaque formation, through upregulation of adhesion molecule expression and suppression of regulatory T cells.