G2A Deficiency in Mice Promotes Macrophage Activation and Atherosclerosis

G2A is a stress-inducible G protein-coupled receptor that is expressed on several cell types within atherosclerotic lesions. We demonstrated previously that G2A deficiency in mice increased aortic monocyte recruitment and increased monocyte: endothelial interactions. To investigate the impact of G2A deficiency in macrophages, we isolated peritoneal macrophages from G2A(+/+) ApoE (-/-) and G2A (-/-) ApoE (-/-) mice. G2A (-/-) ApoE (-/-) macrophages had significantly lower apoptosis than control macrophages. The prosurvival genes BCL-2, BCL-xL, and cFLIP were increased in G2A (-/-) ApoE (-/-) macrophages. Macrophages from G2A (-/-) ApoE (-/-) mice also had increased proinflammatory status that was indicative of a M1 macrophage phenotype. This was indicated by significantly increased nuclear translocation of nuclear factor kappa B, as well as production of interleukin-12p40, tumor necrosis factor alpha, and interleukin-6, and reduced expression of arginase-I. Moreover, G2A (-/-) ApoE (-/-) macrophages had reduced ability to engulf apoptotic cells in vitro. We examined atherosclerosis in mice fed a Western diet for 10 weeks and found that G2A deficiency increased lesion size in the aortic root by 50%. Plasma lipid levels were not changed in G2A (-/-) ApoE (-/-) mice. However, we found that absence of G2A increased the number of aortic macrophages and attenuated apoptosis in this cell type. Moreover, bone marrow transplantation studies indicated that deficiency of G2A in marrow-derived cells significantly contributed to atherosclerosis development. In the absence of G2A, increased macrophage activation and decreased apoptosis is associated with accumulation of macrophages in the aorta and increased atherosclerosis. ( Circ Res. 2009; 104: 318-327.)