Estrogen Deficiency Promotes Cerebral Aneurysm Rupture by Upregulation of Th17 Cells and Interleukin‐17A Which Downregulates E‐Cadherin

BACKGROUND: Estrogen deficiency is associated with the development of cerebral aneurysms; however, the mechanism remains unknown. We explored the pathway of cerebral aneurysm development by investigating the potential link between estrogen deficiency and inflammatory factors. METHODS AND RESULTS: First, we established the role of interleukin‐17 (IL‐17)A. We performed a cytokine screen demonstrating that IL‐17A is significantly expressed in mouse and human aneurysms (P=0.03). Likewise, IL‐17A inhibition was shown to prevent aneurysm formation by 42% (P=0.02) and rupture by 34% (P<0.05). Second, we found that estrogen deficiency upregulates T helper 17 cells and IL‐17A and promotes aneurysm rupture. Estrogen‐deficient mice had more ruptures than control mice (47% versus 7%; P=0.04). Estradiol supplementation or IL‐17A inhibition decreased the number of ruptures in estrogen‐deficient mice (estradiol 6% versus 37%; P=0.04; IL‐17A inhibition 18% versus 47%; P=0.018). Third, we found that IL‐17A‐blockade protects against aneurysm formation and rupture by increased E‐cadherin expression. IL‐17‐inhibited mice had increased E‐cadherin expression (P=0.003). E‐cadherin inhibition reversed the protective effect of IL‐17A inhibition and increased the rate of aneurysm formation (65% versus 28%; P=0.04) and rupture (12% versus 0%; P=0.22). However, E‐cadherin inhibition alone does not significantly increase aneurysm formation in normal mice or in estrogen‐deficient mice. In cell migration assays, E‐cadherin inhibition promoted macrophage infiltration across endothelial cells (P<0.05), which may be the mechanism for the estrogen deficiency/IL‐17/E‐cadherin aneurysm pathway. CONCLUSIONS: Our data suggest that estrogen deficiency promotes cerebral aneurysm rupture by upregulating IL‐17A, which downregulates E‐cadherin, encouraging macrophage infiltration in the aneurysm vessel wall.