Dynamic Ovarian Lymphatic Remodeling Is Associated with Macrophage Accumulation During Follicular Development and Ovulation in Mice

The ovarian lymphatic vasculature has emerged as a potential regulator of ovarian function, yet its role in follicular development remains poorly defined. Here, we aimed to elucidate the dynamic changes in ovarian lymphatic vessels during follicular development and to determine whether lymphatic vessels contribute to ovarian function by regulating the immune microenvironment. Ovarian lymphatic remodeling was characterized during different follicular stages, throughout the estrous cycle, and following superovulation using immunofluorescence imaging. Lymphangiogenesis was inhibited with the vascular endothelial growth factor receptor 3 (VEGFR3) inhibitor SAR131675 to evaluate the effects on follicular development and macrophage accumulation in mice. Transcriptomic, tissue localization, and migration assays with C-C motif chemokine ligand 21 (CCL21)- or C-C chemokine receptor type 7 (CCR7)- blocking antibodies were used to investigate CCL21-CCR7 signaling in lymphatic endothelial cell (LEC)-mediated macrophage migration. Ovarian lymphatic vessels underwent dynamic remodeling, with lymphatic density peaking during the luteal phase. Macrophages preferentially localized near lymphatic vessels, and their abundance paralleled lymphatic remodeling across reproductive stages. Inhibition of lymphangiogenesis reduced follicular development, ovulation, corpus luteum formation, and macrophage accumulation. Mechanistically, ovarian lymphatic endothelial cells highly expressed CCL21, which promoted macrophage migration through CCR7 signaling. Collectively, these findings identify ovarian lymphatic vessels as previously unrecognized regulators of the ovarian immune microenvironment, with CCL21-CCR7 signaling mediating lymphatic endothelial cell–macrophage communication to support ovarian function.