L-Selectin–Mediated Neutrophil Recruitment in Experimental Rodent Aneurysm Formation

Abstract

Background— This investigation tested the hypothesis that L-selectin is important in experimental abdominal aortic aneurysm (AAA) formation in rodents. Methods and Results— Rat abdominal aortas were perfused with saline (control) or porcine pancreatic elastase and studied on postperfusion days 1, 2, 4, 7, and 14 (n=5 per treatment group per day). Neutrophil (polymorphonucleur leukocyte, PMN) and macrophage counts per high-powered field (HPF) were performed on fixed sections. L-selectin expression and protein levels in aortic tissue were determined by polymerase chain reaction and Western blot, respectively. Elastase-perfused aortic diameters were significantly increased compared with control aortas at all time points except day 1 ( P <0.05). PMN counts significantly increased in elastase-perfused aortas compared with control aortas at days 1, 2, and 4, reaching maximum levels at day 7 (40.8 versus 0.3 PMNs/HPF, P =0.001). L-selectin mRNA expression in elastase-perfused aortas was 18 ( P =0.018), 17 ( P <0.001), and 8 times ( P =0.02) times greater than control aortas at days 1, 2, and 4, respectively. Western blot demonstrated a significant 69% increase in L-selectin protein at day 7 in elastase- as compared with saline-perfused aortas ( P =0.005). Subsequent experiments involved similar studies on postperfusion days 4, 7, and 14 of aortas from C57BL/6 wild-type (WT) mice (n=21) and L-selectin–knockout (LKO) mice (n=19). LKO mice had significantly smaller aortic diameters at day 14 as compared with WT mice (88% versus 123%, P =0.02). PMN counts were significantly greater in elastase-perfused WT mouse aortas as compared with LKO mouse aortas at day 4 after perfusion (12.8 versus 4.8 PMNs/HPF, P =0.02). Macrophage counts were significantly greater at all time points after perfusion in elastase-perfused WT mouse aortas compared with elastase-perfused LKO mouse aortas, with a maximum difference at day 7 after perfusion (13.3 versus 0.5 macrophages/HPF, P <0.001). Conclusion— L-selectin–mediated neutrophil recruitment may be a critical early step in AAA formation.