Decreased collagen and increased matrix metalloproteinase-13 in experimental abdominal aortic aneurysms in males compared with females.

Background: This study examined differences in sex in collagen regulation during rodent experimental abdominal aortic aneurysm formation.

Methods: Infrarenal aortas of male and female rats were perfused with elastase or saline (control). Aortic diameters were measured at baseline (day 0) and on postoperative days 7 and 14. Transforming growth factor-beta 1, collagen subtypes I and III, and matrix metalloproteinase-13 (MMP-13; collagenase-3) expression and/or protein levels from aortic tissue were determined by real-time reverse transcription polymerase chain reaction and Western blotting. Aortic tissue was stained for total collagen, neutrophils, and macrophages using immunohistochemistry on days 4 and 7.

Results: At 7 and 14 days after perfusion, aortic diameter increased in elastase-perfused males compared with females (P < .001 for each). At 4 and 7 days postperfusion, significantly more neutrophils and macrophages were present in elastase-perfused males compared with females. By 7 days postperfusion, protein levels of transforming growth factor-beta 1 were less in males compared with females (P = .04). Type I collagen levels also decreased on days 7 (P < .001) and 14 (P = .002), and type III collagen levels decreased on days 7 (P < .001) and 14 (P < .001) in males compared with females. With Masson's trichrome stain, less adventitial collagen was observed in the elastase-perfused males compared with females. MMP-13 expression (P < .001) and protein levels (P = .006) in elastase-perfused males were greater than females on day 14.

Conclusion: This study documents a decrease in types I and III collagen with a concurrent increase in MMP-13 after elastase perfusion in males compared with females. These data suggest that alterations in extracellular matrix collagen turnover may be responsible for altered abdominal aortic aneurysm formation between sexes.