OR13-08 Secretoneurin Modulates Gonadotrope Function Cyclically to Regulate LH Secretion

Abstract Disclosure: A. Herdman: None. A. Lagasse: None. A. Haney: None. S. Byrum: None. U. Boehm: None. M.C. MacNicol: None. A.M. MacNicol: None. G.V. Childs: None. A.K. Odle: None. Secretogranin II (SGII) has long been associated with regulation of luteinizing hormone (LH) storage and secretion. Following cleavage by prohormone convertases, various bioactive peptides are produced from SGII, including secretoneurin (SN). Exogenous SN stimulation has previously been shown to trigger LH secretion in the mouse LβT2 gonadotrope cell line and in goldfish pituitaries; however, the mechanisms and functions of SN in the mammalian pituitary have yet to be elucidated. We hypothesize that (1) mammalian SGII and SN expression vary based on puberty, sex, and estrous cycle stage, and (2) SN alters gonadotrope function cyclically to regulate LH secretion. To understand how SN may be regulated across the estrous cycle, SgII and prohormone convertase mRNAs associated with generation of SN (Pcsk1 and Pcsk2) were quantified via qPCR in whole, adult female murine pituitaries collected at 0900 on the morning of each stage of the estrous cycle (proestrus (P), estrus (E), metestrus (M), diestrus (D)), and P 2000 and E 0400 (n=6/cycle timepoint). SgII mRNA expression was highest at P 0900, falling significantly during the secondary FSH surge (E 0400, p<0.05). Similarly, Pcsk1/Pcsk2 expression significantly decreased from D 0900 and P 0900 to the preovulatory LH surge at P 2000 (p<0.05). These dramatic shifts indicate that production of SGII, and perhaps SN, may be cyclically regulated. Western Blot analysis of whole pituitaries revealed that SGII products, but not full-length SGII, generally decrease with age (from mid-postnatal period into adulthood) in both males and females, and males generally have more SGII-derived proteins than females. To determine how SN may affect gonadotrope functions independently vs in combination with GnRH, adult female pituitaries from mice expressing GnRHR-driven Cre and a floxed fluorescent reporter were collected at D 0900 and P 0900 (n=72). Pituitaries were dispersed and treated for 3h with: Vehicle, SN (1 uM), GnRH (1 nM), or SN + GnRH (n=9 per stage/treatment). Gonadotropes were purified and pooled (n=3 purified populations/pool, n=3 pools/treatment). Mass spectrometry-based proteomics and differential abundance analyses were used to profile the gonadotrope proteome of each group. SN treatment led to changes in >200 proteins total (both stages), of which 98% were stage-specific, indicating that SN regulates gonadotropes in a cycle-dependent manner. In both P and D groups, treatment with SN and SN+GnRH increased LH secretion over baseline levels (p<0.01, p<0.05). These results confirm that exogenous SN is capable of stimulating LH secretion not only from the LβT2 cell line, but also from primary murine pituitary cultures. Our data indicate that pituitary SGII/SN expression may vary based on physiological demands such as pubertal development, sex, and estrous cycle, and that SN regulates gonadotropes in a cycle-dependent manner distinct from GnRH. Presentation: Sunday, July 13, 2025