ODP343 Phoenixin as a Novel Autocrine/Paracrine Factor Stimulating Prolactin Secretion and Gene Expression at the Pituitary Level in Fish Model

Phoenixin (PNX), a new peptide first identified by bioinformatics, is widely expressed at tissue level and confirmed to be the ligand for the orphan receptor GPR173. Its mature peptide PNX 20 is highly conserved across species and emerged as a novel regulator for reproductive, appetite control, memory retention, plain perception and cardiovascular protection. However, not much is known for the comparative aspects of PNX and the post-receptor signaling mediating PNX action is still unclear. Using grass carp as a model for bony fish/teleost, carp PNX and its receptor GPR173 were cloned and confirmed to be single-copy genes in the carp genome. Using RT-PCR, transcript signals of PNX and GPR173 were found to be widely expressed in different tissues, including the brain-pituitary axis. As revealed by LC/MS/MS and ICC staining, protein signals of PNX and GPR173 could be detected in the pituitary and co-localized in immuno-identified lactotrophs. In primary culture of carp pituitary cells, static incubation with the synthetic peptide of carp PNX 20 was effective in increasing prolactin (PRL) release, PRL cell content and total production of PRL with a parallel rise in PRL mRNA level. The opposite was true for PRL secretion and transcript expression in parallel experiment with removal of endogenous PNX by immunoneutralization using PNX antiserum. Besides the stimulation on PRL signals, similar treatment with PNX 20 could also elevate cAMP and intracellular Ca 2+ levels with rapid phosphorylation of PI3K, Akt, MEK 1/2 and ERK 1/2 in carp pituitary cells. In the same model, except for a lack of effect with PKC blockade, co-treatment with the pharmacological inhibitors for different signalling components of the cAMP/PKA, PLC/IP 3, PI3K/Akt and MAPK cascades was effective in reducing/causing a total blockade of PNX 20 -induced PRL release and gene expression. Our results, as a whole, suggest that (i) PNX produced locally within the carp pituitary, presumably via activation of GPR173, could act as an autocrine/paracrine signal to stimulate PRL secretion and gene expression in carp lactotrophs, and (ii) the stimulatory effects on PRL regulation caused by the local actions of PNX probably are mediated by the cAMP/PKA-, PLC/IP 3 -, PI3K/Akt- and MAPK-dependent signaling mechanisms. Presentation: No date and time listed