INTRODUCTION
The brain governs sexual maturation, pubertal development, and fertility through a hormonal communication network connecting the hypothalamus, the pituitary gland, and the gonads. Disruption of the hypothalamic-pituitary-gonadal axis results in delayed or absent puberty and infertility. Gonadotropin-releasing hormone (GnRH) is the master regulator of reproduction in mammals. It is secreted in a pulsatile manner by hypothalamic GnRH neurons that release this neuropeptide at the median eminence to regulate pituitary hormone secretion and gonadal function. Although kisspeptin neurons are the main regulators of GnRH neuronal activity, the contribution of microglia, the resident immune cells of the brain, remains largely unexplored.
RATIONALE
Receptor activator of nuclear factor κB (RANK) signaling is well established in bone, immune system, and mammary gland biology. This pathway is tightly regulated by sex hormones, and RANK genetic variants have been associated with timing of menarche and menopause. In the brain, RANK is predominantly expressed in microglia and can modulate microglia functionality during neuroinflammation. Given the emerging role of microglia in shaping neuronal circuits, we assessed whether RANK signaling in microglia contributes to the regulation of GnRH neurons and fertility.
RESULTS
Using multiple complementary genetically modified mouse models, we found that embryonic or pubertal depletion of Rank systemically or selectively in microglia leads to severe reproductive defects. These mice displayed reduced circulating levels of sex hormones, delayed sexual maturation, and infertility, phenocopying key features of hypogonadotropic hypogonadism, a rare human reproductive disorder. Notably, we identified rare variants in the RANK gene in patients with this condition, supporting a conserved role for RANK signaling in human reproductive physiology.
Single-cell transcriptional profiling following Rank loss revealed defective activation of hypothalamic microglia, accompanied by morphological alterations in the median eminence. Rank loss reduced microglia phagocytic activity, decreased microglia-GnRH neuron interactions and engulfment of GnRH terminal projections, and impaired responsiveness of GnRH neurons to kisspeptin stimulation.
CONCLUSION
Our study reveals an essential role for hypothalamic microglia in the control of GnRH neuron function and fertility. We identified RANK signaling as a critical pathway enabling proper microglia activation and supporting effective GnRH neuronal activity. These findings uncover a previously unrecognized mechanism through which microglia RANK signaling regulates sexual maturation and fertility.
