Activation of cAMP/PKA and ERK signaling pathways and potential role of Phoenixin in the reproductive axis of spotted scat ( Scatophagus argus )

Phoenixin (Pnx) exerts its physiological function primarily through its putative receptor GPR173 in mammals. However, the signaling pathways and the function of Pnx in the regulation of reproduction in teleosts remain poorly understood. Accordingly, this study presents an investigation of the signaling pathways and their functions in the regulation of reproduction in the spotted scat (Scatophagus argus). After transfection of Gpr173a into HEK-293 T cells, the results of the dual luciferase reporter assay indicated that Pnx-14 did not alter CRE-luc or SRE-luc activity. In addition, Pnx-20 could significantly increase SRE-luc activity. After transfection with Gpr173b, Pnx-14 could significantly increase CRE-luc activity while simultaneously inhibiting SRE-luc activity. Pnx-20 could significantly enhance SRE-luc activity. In vitro hypothalamic experiments, the expression of genes regulated by Pnx-14 and Pnx-20 can be suppressed in the presence of the cAMP/PKA inhibitor H89. Pnx-20 can also significantly increase the phosphorylation level of ERK1/2. Intracerebroventricular (ICV) injection of Pnx-20 significantly elevated estradiol levels in females. Conversely, ICV administration of Pnx-14 and Pnx-20 significantly reduced 11-ketotestosterone levels in males. Furthermore, ICV injection of Pnx-14 and Pnx-20 was shown to regulate the expression of reproduction-related genes in the hypothalamus, pituitary, and gonads of both females and males. These findings suggest that Pnx-14 may activate the cAMP/PKA or ERK pathway by Gpr173b. Similarly, Pnx-20 may activate the ERK pathway by Gpr173a and Gpr173b, thereby influencing the reproductive axis in the spotted scat.