ABSENCE OF FOUR-AND-A-HALF LIM DOMAIN PROTEIN 2 DECREASES ATHEROSCLEROSIS IN APOE-/- MICE: ROLE OF MONOCYTIC IMMUNE CELLS

BACKGROUND: Four-and-a-half LIM domain protein-2 (FHL2) is expressed in endothelial and vascular smooth muscle cells. It 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, FHL2-deficient (FHL2-/-) mice were crossed with ApoE-deficient (ApoE -/-) mice, to generate ApoE/FHL2-/mice. After 7 weeks of high fat diet, ApoE/FHL2-/mice had significantly smaller (P<0.05) atherosclerotic plaques than ApoE-/mice in the aortic sinus (0.14 0.02 vs. 0.29 0.04 mm2), the brachiocephalic artery (0.03 0.008 vs. 0.07 0.01mm2) and the aorta (6.9 0.9 vs 10.3 1%), assessed by oil red O staining. This was associated with enhanced collagen (16 2 vs 8.6 3 %) and smooth muscle cell (4.5 0.8 vs 1.8 0.5%) contents within the plaques of ApoE/FHL2-/mice. Moreover, macrophage content within plaques was reduced 2-fold in ApoE/FHL2-/vs ApoE-/mice (P<0.05). This could be explained, in part, by the 40% reduction in aortic ICAM-1 mRNA and 55% reduction in VCAM-1 protein expression in the plaque. Furthermore, aortic gene expression of Cx3cl1 andCcl5 was increased in ApoE/FHL2-/vs ApoE-/mice, suggesting that different monocyte populations might be recruited to the plaques. Peritoneal thioglycollate injection elicited equivalent numbers of monocytes and macrophages in both groups, but a significantly lower number of pro-inflammatory Ly6C high monocytes were recruited in ApoE/FHL2-/vs ApoE-/mice (8 3 vs 18 4%). Furthermore, mRNA levels of Cx3cr1 were 2-fold higher in monocytes from ApoE/FHL2-/mice compared with ApoE-/mice. Finally, we also investigated the potential importance of myeloid cell FHL2 deficiency in atherosclerosis. ApoE-/or ApoE/ FHL2-/-micewere lethally irradiated and transplantedwithApoE-/or ApoE/FHL2-/bonemarrow. After recovery and 7weeks of high fat diet, both chimeric groups developed smaller plaques than ApoE-/mice transplanted with ApoE-/bone marrow. CONCLUSION: These results suggest that FHL2 in both myeloid and vascular cells may play an important role in atherosclerosis by promoting pro-inflammatory chemokine production, adhesion molecule expression, and pro-inflammatory monocyte recruitment.