Irisin stimulates gonadotropins gene expression in tilapia (Oreochromis niloticus) pituitary cells

The link between energy metabolism and reproduction is well known in vertebrates. Irisin, the product of fibronectin type III domain-containing protein 5 (FNDC5) gene, plays an important role in energy homeostasis. However, biological actions of irisin on reproduction remain elusive. To address this gap, we examined the direct effects of irisin on luteinizing hormone β (LHβ) and follicle-stimulating hormone β (FSHβ) gene expression in tilapia pituitary cells. As a first step, the transcripts of FNDC5 were detected in the proximal pars distalis (PPD), but not in the rostral pars distalis (RPD) and neurointermediate lobe (NIL) of the tilapia pituitary by RT-PCR. In the tilapia pituitary, irisin immunoreactive signals were also detected in PPD region. In primary cultures of tilapia pituitary cells, irisin was effective in stimulating both LHβ and FSHβ mRNA levels in vivo and in vitro. In cultured pituitary cells of tilapia, removal of endogenous irisin by immunoneutralization using irisin antiserum inhibited LHβ and FSHβ gene expression. Salmon gonadotrophin releasing hormone (sGnRH) increased LHβ and FSHβ mRNA levels in tilapia pituitary but these stimulatory actions were not either enhanced by treatment with irisin or blocked by irisin antiserum. Furthermore, the stimulation on LHβ and FSHβ mRNA expression was coincident with the enhancement of LHβ and FSHβ mRNA stability after irisin treatment. These results provide evidence that irisin may serve as a novel intrapituitary factor maintaining gonadotropins gene expression in tilapia pituitary.