Evidence for Spexin As a Novel Luteinizing Hormone (LH)-Releasing Factor in Goldfish Via Direct Action at Pituitary Level: - Receptor Specificity, Signal Transduction and Interactions with LH Regulators in Fish Model
Presentation Number: SUN 487
Date of Presentation: April 2nd, 2017
Ani Ma*, Matthew K. H. Wong, Mu-Lan He, Wendy K.W. Ko and Anderson O L Wong
University of Hong Kong, Hong Kong, China
Spexin (SPX), a neuropeptide first identified by bioinformatics, has been recently reported as a regulator for luteinizing hormone (LH) in fish model. However, the receptor specificity and signal transduction for SPX action as well as its functional interactions with other LH regulators are still unknown. In our study, SPX immunoreactivity was detected by immunohistochemical staining in nerve fibers and various pituitary cells in goldfish pituitary. Intraperitoneal but not intracerebroventricular injection of SPX was shown to elevate plasma LH level in goldfish. In pituitary cells prepared from male, female and mixed sexes of goldfish, SPX treatment was effective in triggering LH secretion, and both basal as well as SPX-induced LH release could be enhanced with increasing level of gonadosomatic index of the fish used in pituitary cell preparation. In pituitary cells prepared from mixed sexes of goldfish, similar to SPX, GnRH and PACAP were both effective in elevating LH release and SPX co-treatment was found to potentiate the LH-releasing effect of PACAP but with no enhancement for GnRH induction. Dopaminergic activation by the dopamine analog apomorphine or D2 receptor agonist LY171555, in contrast, inhibited basal and blocked SPX-induced LH release at pituitary cell level. In parallel studies, SPX-induced LH release was also reduced by pretreatment of the cell culture with testosterone and estrogen, respectively. In the same model, the LH-releasing effect of SPX could be mimicked by galanin and GalR2 agonist M617 but negated by the galanin antagonist galantide and GalR2 antagonist M871 but not GalR3 antagonist SNAP37889. Furthermore, SPX induction was also effective in increasing intracellular Ca2+ level and triggering phosphorylation of MEK1/2, ERK1/2, P38 MAPK and Akt. Using a pharmacological approach, SPX-induced LH release was shown to be reduced/totally abolished by the inhibitors for the PLC/IP3/PKC, Ca2+/CaM/CaMK-II, PI3K/Akt, MEK1/2/ERK1/2 and JNK cascades but similar treatment with blockers for P38 MAPK or cAMP/PKA pathway was not effective in this regard. Our results, as a whole, suggest that (i) SPX originated from the hypothalamus or produced locally in goldfish pituitary could induce LH release via direct action acting at pituitary cell level, (ii) SPX-induced LH secretion was mediated via pituitary galanin type-2 receptor functionally coupled to PLC/IP3/PKC, Ca2+/CaM/CaMK-II, PI3K/Akt and MAPK cascades, and (iii) SPX could interact with both stimulatory (PACAP) and inhibitory signals (dopamine) from the hypothalamus as well as the steroid feedback from the gonad (testosterone & estrogen) to modulate LH release from goldfish pituitary cells. Our findings for the first time provide evidence that SPX can serve as a novel LH-releasing factor in fish model via direct action acting at the pituitary level.
Nothing to Disclose: AM, MKHW, MLH, WKWK, AOLW