Role of membrane estrogen receptor alpha on the negative feedback of estrogens on <scp>luteinizing hormone</scp> secretion

Estrogen receptor alpha (ERα) is critical for reproduction, but the relative contributions of its nuclear and membrane signaling are unclear.The present study investigated the role of membrane ERα (mERα) using two complementary approaches: a mouse model lacking mERα signaling (C451A-ERα mice) and estetrol (E₄), a natural estrogen described to prevent membrane ERα activation in different cell types. While ovariectomy (OVX) induced a comparable luteinizing hormone (LH) increase in both wild-type and C451A-ERα females, C451A-ERα females failed to respond to chronic estradiol (E₂) (1 μg) exposure, indicating dysregulated negative feedback. This lack of LH regulation in C451A-ERα females was mirrored by an absence of change in the number of neurons immunoreactive (ir) for kisspeptin (Kp) in both the rostral periventricular area of the third ventricle (RP3V) and the arcuate nucleus (ARC), for progesterone receptor (PR)-ir nuclei in the preoptic area and hypothalamus, and for neurokinin 3 receptor (NK₃R) in the ARC. Interestingly, increasing the dose of E₂ to 5 μg restored normal negative feedback and normal numbers of Kp-ir neurons and PR-ir nuclei, but not the surface covered by Kp-ir fibers and the number of NK₃R-ir neurons in the ARC. By contrast, E₄ mimicked the negative feedback of E₂ on circulating LH in OVX WT females following both acute and chronic treatment and potentiated rather than blocked the effects of E₂ when administered along with it. E₄ also mimicked the stimulatory effects of E₂ on the number of PR-ir nuclei in several preoptic and hypothalamic regions and the percentage of area covered by Kp-ir material in the ARC, as well as its inhibitory action on the number of Kp-ir neurons in the ARC. Therefore, the C451A-ERα mutation interferes with the control of the negative feedback through distinct mechanisms differing by their dose-dependency to E₂. By contrast, E₄ mimicked all effects of E₂ on the negative feedback and the associated neural circuits, indicating that E₄ acts as a weak ERα agonist in this context. Together, these results suggest that C451A-ERα modifies the sensitivity to E₂, impacting the negative feedback of E₂ on LH regulation.