RAMP1-dependent hormonal regulation of CGRP and its receptor in the trigeminal ganglion

Menstrual migraine (MM) is a debilitating neurological disorder triggered by fluctuations in ovarian hormones, particularly estrogen. While the calcitonin gene-related peptide (CGRP) system is central to migraine pathophysiology, the molecular mechanisms linking hormonal changes to CGRP signaling remain unclear. This study investigates how sex hormones regulate CGRP-related gene expression in the trigeminal ganglion (TG), with a focus on the receptor activity-modifying protein 1 (RAMP1), using both wild-type (WT) and Ramp1 knockout (KO) mice. We analyzed gene expression in the TG across the estrous cycle and following systemic estrogen or progesterone administration. Expression of Ramp1, Calca (encoding CGRPα), Calcrl (encoding CRLR), estrogen receptors, and related genes was assessed by RT-qPCR. WT and Ramp1 KO mice of both sexes were used to explore hormone-dependent gene regulation and RAMP1’s functional role. Ramp1 expression varied across the estrous cycle, peaking in proestrus and declining in diestrus, inversely correlated with Calca. Calcrl levels remained unchanged. Ramp1 expression correlated significantly with Esr2 (encoding ERβ), suggesting estrogen receptor–mediated regulation. Estrogen treatment upregulated Ramp1 in both sexes; Calca was downregulated in females but upregulated in males. Progesterone had more modest effects, primarily altering Ramp3 expression. In Ramp1 KO mice, the cyclical variation of Calca, Ramp2, and Ramp3 seen in WT mice was absent, and basal Calca expression was elevated in males, indicating that RAMP1 is essential for hormonal regulation of the CGRP system. Additionally, our findings support a role for estrogen-driven epigenetic mechanisms, such as DNA methylation, in the long-term regulation of Ramp1. This study highlights RAMP1 as a key mediator linking hormonal fluctuations to CGRP signaling in the TG. Hormone-dependent gene expression changes were sex-specific and disrupted in Ramp1 KO mice, supporting its role in migraine susceptibility. These findings provide mechanistic insight into hormonal migraine and suggest that both acute hormone signaling and long-term epigenetic regulation shape individual sensitivity to CGRP-based therapies.