Deletion of EP4 on Bone Marrow–Derived Cells Enhances Inflammation and Angiotensin II–Induced Abdominal Aortic Aneurysm Formation

Objective— To examine whether a lack of prostaglandin E receptor 4 (EP4) on bone marrow–derived cells would increase local inflammation and enhance the formation of abdominal aortic aneurysm (AAA) in vivo. Methods and Results— Prostaglandin E 2 (PGE 2 ) through activation of EP4, can mute inflammation. Hypercholesterolemic low-density lipoprotein receptor knockout (LDLR −/− ) mice transplanted with either EP4 +/+ (EP4 +/+ /LDLR −/− ) or EP4 −/− (EP4 −/− /LDLR −/− ) bone marrow received infusions of angiotensin II to induce AAA. Deficiency of EP4 on bone marrow–derived cells increased the incidence (50% of male EP4 +/+ /LDLR −/− mice versus 88.9% of male EP4 −/− /LDLR −/− mice developed AAA; and 22% of female EP4 +/+ /LDLR −/− mice versus 83.3% of female EP4 −/− /LDLR −/− mice developed AAA) and severity of AAA, increased monocyte chemoattractant protein-1 (2.72-fold in males and 1.64-fold in females), and enhanced infiltration of macrophages (3.8-fold in males and 2.44-fold in females) and T cells (1.88-fold in males and 1.66-fold in females) into AAA lesions. Lack of EP4 on bone marrow–derived cells augmented elastin fragmentation, increased apoptotic markers, and decreased smooth muscle cell accumulation within AAA lesions. Conclusion— Deficiency of EP4 on bone marrow–derived cells boosted inflammation and AAA formation induced by angiotensin II in hyperlipidemic mice. This study affirms the pathophysiologic importance of PGE 2 signaling through EP4 as an endogenous anti-inflammatory pathway involved in experimental aneurysm formation.