Nording, H.; Baron, L.; Sauter, M.; Hagemann, L.; von Esebeck, J.; Schommer, N.; Duerschmied, D.; Marquardt, J.; Lerchenmueller, C.; Zuern, C.; Bibli, I.; Augustin, H.; Mueller, O. J.; Langer, H. F.

Sex-specific differences in cardiovascular disease outcomes remain incompletely understood at the molecular level. Here, we identified the platelet complement receptor C5aR1 as a critical mediator of sex-specific revascularization following hindlimb ischemia through an estradiol-regulated mechanism. Ischemic tissue exhibited robust complement activation with C3b and C5a accumulation that correlated strongly with deposition of the anti-angiogenic factor CXCL4 (PF4). Mechanistically, C5a stimulation of platelets triggered CXCL4 secretion, and platelet-specific deletion of C5aR1 (using PF4-Cre-C5aR1fl/fl mice) significantly improved revascularization in male mice associated with decreased CXCL4 deposition, while sex-specific differences were not observed in cre-negative animals. Male mice exhibited substantially higher platelet C5aR1 expression and enhanced C5a-induced CXCL4 secretion compared to females, resulting in greater CXCL4 accumulation in the ischemic tissue. Importantly, estradiol stimulation of megakaryocytes suppressed C5aR1 expression during pro-platelet formation, uncovering a hormone-dependent regulatory mechanism. This estradiol-C5aR1-CXCL4 axis provides a molecular explanation for sex-specific differences in ischemic revascularization known from patient studies, as sex-specific deposition of the anti-angiogenic platelet-derived factor CXCL4 was C5aR1-dependent. These findings establish a novel and unexpected mechanistic link between sex hormones, a complement-platelet crosstalk and the angiogenic response to ischemia with potential clinical implications for sex-tailored therapeutic strategies.