Progesterone prevents premature LH surge/ovulation by remodeling GnRH neuron activity

Progestin-primed ovarian stimulation (PPOS), a clinically effective strategy originating in China and widely adopted internationally to prevent premature luteinizing hormone (LH) surge and ovulation, lacks a clear understanding of its central neuroendocrine mechanisms. We investigated hypothalamic mechanisms underlying PPOS-mediated suppression of LH surge, focusing on neuronal activity patterns, transcriptional regulation, and gonadotropin-releasing hormone (GnRH) neuron electrophysiological dynamics. Using Fos TetTag mice, we labeled activity-dependent hypothalamic neurons during PPOS; transcriptomic analysis identified key regulatory pathways in these neurons; SIRT1 inhibition with EX527 was used to test its functional role; and in vivo electrophysiology assessed GnRH neuron firing dynamics, which directly regulate LH secretion. PPOS induced region-specific hypothalamic alterations, characterized by reduced activity in the preoptic area and increased activity in the arcuate nucleus (ARC). Transcriptomic analysis and immunofluorescence staining revealed upregulation of sirtuin 1 (SIRT1) in activated ARC neurons, accompanied by suppression of KISS1 expression. Pharmacological inhibition of SIRT1 reduced its expression but failed to fully restore KISS1 levels or LH surge, suggesting that targeting SIRT1 alone is insufficient to reverse the multi-gene regulatory disruption underlying LH suppression. Electrophysiological recordings demonstrated that PPOS increased baseline firing of GnRH neurons but impaired their transition to surge-associated high-frequency bursting required for LH surge generation. PPOS suppresses the preovulatory LH surge through coordinated hypothalamic circuit remodeling involving SIRT1-related transcriptional regulation and disruption of GnRH neuronal firing dynamics. These findings provide mechanistic insight into how PPOS modulates hypothalamic circuits and GnRH neuron output, supporting the optimization of ovarian stimulation strategies in assisted reproduction.