Endocrine-Adapted Pituitary Macrophages Regulate Gonadotropin Secretion through CXCL5-CXCR2-MAPK Signaling

Chronic inflammation disrupts hormonal balance in the Hypothalamic-Pituitary-Gonadal (HPG) axis, contributing to reproductive disorders. While immune cells in the hypothalamus and ovaries have been extensively studied, their impact on the pituitary remains largely unexplored. Our research identifies pituitary macrophages (PitMacs) as the dominant pituitary immune cell population with a role in regulating reproductive gonadotropin secretion both in vitro and in vivo. Using a targeted AAV-based depletion strategy, we demonstrate that a reduction of PitMacs decreases serum gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), in female mice. PitMacs are transcriptomically distinct from other tissue-resident macrophages and harbor a unique translational program that reflects the pituitarys endocrine identity, including active translation of growth hormone (Gh) and prolactin (Prl). Cytokine profiling identified CXCL5 and IFN-{gamma} as key PitMac-derived mediators of gonadotropin regulation. Mechanistically, CXCL5 signals through CXCR2 to activate the MAPK pathway, converging with Gonadotropin-Releasing Hormone (GnRH) signaling in a time-dependent manner to regulate LH secretion and GnRH receptor surface expression. These findings establish PitMacs as essential endocrine-immune integrators, opening new avenues for understanding inflammation-driven reproductive disorders. One Sentence SummaryPituitary macrophages are unique hormone-producing immune cells that regulate hormone secretion via cytokine signaling.