Inhibition of atherogenesis in BLT1-deficient mice reveals a role for LTB4 and BLT1 in smooth muscle cell recruitment

Background - It is known that 5-lipoxygenase and its product, leukotriene B4 (LTB4), are highly expressed in several human pathologies, including atherosclerotic plaque. LTB4 signals primarily through its high-affinity G protein - coupled receptor BLT1, which is expressed on specific leukocyte subsets. BLT1 receptor expression and function on other atheroma-associated cell types is unknown. Methods and Results - To directly assess the role of the LTB4-BLT1 pathway in atherogenesis, we bred BLT1(-/-) mice into the atherosclerosis-susceptible apoE(-/-) strain. Compound-deficient apoE(-/-)/Blt1(-/-) mice fed a Western-type diet had a marked reduction in plaque formation compared with apoE(-/-) controls. Immunohistochemical analysis of atherosclerotic lesions in compound-deficient mice revealed a striking decrease in smooth muscle cells (SMCs) and significant decreases in macrophages and T cells. We report here novel evidence of the expression and function of BLT1 on vascular SMCs. LTB4 triggered SMC chemotaxis, which was pertussis toxin sensitive in Blt1(-/-) SMCs and absent in Blt1(-/-) cells, suggesting that BLT1 was the dominant receptor mediating effector functions through a G protein - coupled signaling pathway. Furthermore, BLT1 colocalized with SMCs in human atherosclerotic lesions. Conclusions - These new findings extend the role of inducible BLT1 to nonleukocyte populations and suggest an important target for intervention to modulate the response to vascular injury.