Insulin-like growth factor-1 stimulation of hypothalamic KiSS-1 gene expression is mediated by Akt: effect of alcohol.
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Kisspeptin, as well as insulin-like growth factor-1 (IGF-1), act centrally to stimulate luteinizing hormone-releasing hormone (LHRH) secretion at puberty. IGF-1 can induce KiSS-1 gene expression as an early pubertal event; however, the signaling pathway mediating this effect is not known. Since alcohol (ALC) blocks IGF-1 induced LHRH release acutely, we assessed whether this drug could affect IGF-1 stimulated prepubertal KiSS-1 gene expression following a binge type of exposure. Immature female rats were administered either ALC (3 g/kg) or water via gastric gavage at 07.30 h. At 09.00 h the ALC and control groups were subdivided where half received either saline or IGF-1 (200 ng) into the third ventricle. A second dose of ALC (1.5, 2 and 3 g/kg) or water was administered at 11.30 h. These regimens produced moderate blood alcohol concentrations of 77, 89 and 117 mg/dl, respectively, over the time course of the experiment. Rats were sacrificed 6 h after the IGF-1 injection and tissues containing the anteroventral periventricular (AVPV) and arcuate (ARC) nuclei were collected. IGF-1 stimulated (P<0.01) KiSS-1 gene expression in the AVPV nucleus at 6 h, but did not affect expression of the kisspeptin receptor, GPR54. While ALC did not alter basal expression of either gene, its dose dependently blocked IGF-1-induced KiSS-1 gene expression in the AVPV nucleus. No changes were observed in the ARC nucleus. Assessment of IGF-1 signaling indicated that the acute administration of IGF-1, ALC, or both did not alter the basal expression of IGF-1 receptor protein. However, IGF-1 stimulated (P<0.05) phosphorylated Akt protein over basal levels, an action blocked by ALC. Our results indicate that the IGF-1 induction of KiSS-1 gene expression is mediated by Akt activation, and that ALC alters this important prepubertal action of IGF-1.
