Postnatal expression of phoenixin-14 and GPR173 gene and protein in the mice testis and its effect on steroidogenesis...

Phoenixin-14 is a neuropeptide that has been shown to bind to GPR173 for biological functions. Its expression has been shown in various tissues, including the ovaries of porcine, human, and rat. However, no information is available on its expression in postnatal mouse testes. Phoenixin-14 is derived from the gene Smim20. Here we report that Smim20 and Gpr173 mRNA expression shows a decline from PND7 to PND65, with the highest expression at PND7 and the lowest at PND65. Due to the limited availability of commercial phoenixin-14 antibody, we raised an antibody in a rat and validated it by ELISA, immunohistochemistry and dot blot assay for immunohistochemical localization. Immunolocalization of phoenixin-14 and GPR173 showed their presence in the seminiferous tubules and Leydig cells. The Leydig cells of PND65 mice showed strong immunostaining of GPR173 and moderate staining of phoenixin-14. Our co-localization study showed that phoenixin-14 and GPR173 are co-expressed in the testis. These results provide evidence that phoenixin-14 and GPR173 expression are regulated in the testis during postnatal developmental stages. The presence of phoenixin-14 and GPR173 in the germ cells suggests their possible role in and in Leydig cells in steroidogenesis. The gene expression of Cyp11a1 and Cyp17a1 was also elevated in PND28-PND65, which coincides with elevated testosterone levels reported elsewhere. Thus, postnatal changes in phoenixin-14 and GPR173 could also be involved in the regulation of testosterone secretion. Our in vitro study further supports that phoenixin-14 stimulates testosterone secretion at two different doses (10 and 100 nM); however, the lower dose showed higher secretion along with elevated gene expression of steroidogenic markers (Cyp11a1, Cyp17a1, Star and Hsd17b1). In conclusion, testicular phoenixin/GPR173 could be regulating testosterone secretion at different postnatal stages.