Secretoneurin stimulates the production and release of luteinizing hormone in mouse LβT2 gonadotropin cells

Abstract

-Secretoneurin (SN) is a functional secretogranin II (SgII)-derived peptide that stimulates luteinizing hormone (LH) production and its release in the goldfish. However, the effects of SN on the pituitary of mammalian species and the underlying mechanisms remain poorly understood. To study SN in mammals, we adopted the mouse L␤T2 gonadotropin cell line that has characteristics consistent with normal pituitary gonadotrophs. Using radioimmunoassay and real-time RT-PCR, we demonstrated that static treatment with SN induced a significant increment of LH release and production in L␤T2 cells in vitro. We found that GnRH increased cellular SgII mRNA level and total SN-immunoreactive protein release into the culture medium. We also report that SN activated the extracellular signal-regulated kinases (ERK) in either 10-min acute stimulation or 3-h chronic treatment. The SN-induced ERK activation was significantly blocked by pharmacological inhibition of MAPK kinase (MEK) with PD-98059 and protein kinase C (PKC) with bisindolylmaleimide. SN also increased the total cyclic adenosine monophosphate (cAMP) levels similarly to GnRH. However, SN did not activate the GnRH receptor. These data indicate that SN activates the protein kinase A (PKA) and cAMP-induced ERK signaling pathways in the LH-secreting mouse L␤T2 pituitary cell line. secretogranin II; gonadotropin-releasing hormone AS ONE OF THE MAJOR GRANIN PROTEINS, secretogranin II (SgII) was initially characterized in bovine anterior pituitary (31). It is an ϳ600-amino acid, very acidic, tyrosine-sulfated protein located in secretory granules of vertebrate neuroendocrine cells (4,8,22,26). Numerous small potentially bioactive peptides are derived from SgII precursor processing, but only the 33-to 34-amino acid segment, termed secretoneurin (SN), is conserved from fish to mammals (13,48). In human pituitary, SgII immunoreactivity (IR) is localized to gonadotrophs, thyrotrophs, and corticotrophs (39). SgII IR was detected in the secretory granules and colocalized with LH in bovine gonadotroph, indicating the copackaging of granins and gonadotropins to form secretory granules (3). Two types of secretory granules were visualized in rat gonadotrophs: a large-sized moderately electron-dense granule and a small-sized electron-dense granule. The latter granule contained exclusively the immunoreactive signals of SgII and LH (41). In addition to the pituitaries of cow, rat and mouse, SgII was found in the LH-positive granules from female sheep gonadotrophs (6). The above immunocytochemical studies and other work on in vivo LH release (7) reveal an important association of SgII-related products and LH in mammalian gonadotrophs.Nicol et al. (28) utilized radioimmunoassay (RIA) to investigate protein release from the mouse L␤T2 gonadotroph cell line. They observed that pulsatile GnRH treatments resulted in the marked increments of both LH and SgII release together at each time point, suggesting a close correlation between the secretions of these two proteins. Nicol et al. (29) also demo...

The secretogranin-II derived peptide secretoneurin modulates electric behavior in the weakly pulse type electric fish, Brachyhypopomus gauderio

“…The most conspicuous SN-ir was found in the magnocellular and parvocellular cells of the preoptic nucleus that project heavily to the neural lobe of the goldfish pituitary (Canosa et al, 2011). It has been reported in goldfish and mouse that native SN peptides stimulate luteinizing hormone release in vitro, thus revealing a role in the control of vertebrate reproduction (Zhao et al, 2006(Zhao et al, , 2010(Zhao et al, , 2011. SN also stimulates feeding behavior in goldfish (Trudeau et al, 2012).…”

Spexin and a Novel Cichlid-Specific Spexin Paralog Both Inhibit FSH and LH Through a Specific Galanin Receptor (Galr2b) in Tilapia

“…Recently, a plethora of neuropeptides involved in the control of reproduction were investigated. Most of them are stimulatory neuropeptides, such as neurokinin B (19), neuropeptide Y (20), secretoneurin (21), galanin (22), agouti-related peptide (23), kisspeptin (24), and melanocortin (25). However, the study of neuropeptides that relay their signal through inhibitory pathways is more challenging, and hence are less studied.…”

Characterization of the EM66 Biomarker in the Pituitary and Plasma of Healthy Subjects With Different Gonadotroph Status and Patients With Gonadotroph Tumor

“…More precisely, SgII resides within secretory granules in gonadotrophs and is released along with LH after GnRH stimulation (26, 28). In addition, treatment of the mouse pituitary gonadotroph cell line LβT2 with GnRH increased SgII mRNA levels as well as secretoneurin (SN, an EM66 flanking-peptide that also derives from cleavage of SgII) levels in the culture media after static incubation (29). However, it was observed that pulsatile GnRH stimulation also increased the secretion of SN but did not alter SgII mRNA levels in LβT2 cells (30).…”