Increased estrogen receptor alpha in experimental aortic aneurysms in females compared with males

Abstract

INTRODUCTION Estrogen receptor alpha (ERα) has been identified in the vessel wall, offering vasoprotective effects when upregulated. Estrogens are known to mediate the inflammatory mileu, and inflammation has long been associated with abdominal aortic aneurysm (AAA) formation. Therefore it is theorized that increased estrogen receptor in females contributes to their relative resistance to AAAs. The study’s objective was determining gender differences in ERα levels during experimental AAA formation. METHODS Infrarenal aortas of male and female C57 mice (n=18 and n=16, respectively) were infused with 0.4% elastase. Diameters were measured at day 0 and day 14. Aortic mRNA expression of ERα was determined on day 3 by RTPCR, while ERα protein levels were measured via Western blot. Immunohistochemistry using rabbit antibody for ERα was performed on day 14 samples and quantified. Zymography was done for MMP2 and 9 activity levels. Samples of human AAAs were collected and Western blot performed. Data were compared for significance using a student t-test. RESULTS Infrarenal aortic diameter increased in elastase-perfused males (ME) by 80% at 14 days post perfusion, while females (FE) increased by only 35% (p=0.0012). FE had 10x greater ERα mRNA expression compared with ME at day three (p=0.003). Similarly, ERα protein levels were 100% higher in FE compared to ME on day 14 (p=0.035). ERα protein levels were 80% higher in female human patients with AAA than in their male counterparts (p=0.029). ERα visualized via immunohistochemistry was 1.5 fold higher in FE than ME (p=0.029). MMP2 and 9 activity levels were decreased in female as compared with male aortas. CONCLUSION(S) This study demonstrates an increase in aortic wall ERα in females compared with males that correlates inversely with MMP activity and AAA formation. These findings, coupled with observations that exogenous estrogen inhibits AAA formation in males, further suggest that estrogen supplementation may be important to prevent AAA formation and growth.

Sex Differences in Abdominal Aortic Aneurysm: The Role of Sex Hormones

“…68 Increased levels of Serpine1 decrease MMPs by reducing plasmin in the blood and can modulate plasminogen-mediated apoptosis of vascular SMCs. 68 Laser et al 37 showed an increase of aortic wall Esr1 in female compared with male mice aortas, which was inversely correlated with MMP activity, suggesting a protective role of Esr1 during AAA formation likely because of a decreased inflammation. Another study concluded that genetic susceptibility is important in AAA development, as significantly more macrophages were found in C57BL/6 male than female mice, but there was no difference between sexes in B6129 mice.…”

“…36 Interestingly, women with AAAs >5.5 cm had lower levels of MMP9 compared with women with AAA <5.5 cm, which could be explained either by MMP9 degradation in the aneurysmal wall or a reduction in the MMP9 production as the aneurysm grows. 36 Laser et al 37 found that ESR1 protein levels were 80% higher in the aortic wall of women than in men with AAA. Furthermore, aromatase, an essential enzyme of estrogen synthesis, was expressed in aortic cells expressing smooth muscle markers (SMaA) and macrophage markers (CD68 and Mac-2) in human AAA tissues.…”

Sexual Dimorphism of Abdominal Aortic Aneurysms

“…Results demonstrate that aortas from elastase-perfused female rats and mice have lower MMP activity than males [33,47]. Likewise, ovariectomy of female Wistar rats increased aortic MMP-2 and -9 activity [39].…”

“…Deletion of aromatase abolished the protective efects of female gender on elastase-induced AAAs [53]. Aortas from female mice had higher expression levels of ER α compared to male mice by day 3 of elastase perfusion [47]. Increased ERα expression was also detected in female human AAA patients compared to males [47].…”

“…Aortas from female mice had higher expression levels of ER α compared to male mice by day 3 of elastase perfusion [47]. Increased ERα expression was also detected in female human AAA patients compared to males [47]. Tamoxifen, a selective estrogen receptor modulator, decreased AAA development in male rats associated with decreased aortic neutrophil content, MMP-9 activity, and oxidative stress [54].…”