PTGER4 and abdominal aortic aneurysm: EP4 deficiency in hematopoietic cells partially protected against early atherosclerotic lesions (Babaev et al., 2008), but enhanced the inflammation in advanced atherosclerotic plaques and facilitated the formation of angiotensin II-induced abdominal aortic aneurysms (Tang et al., 2011a, 2011b).