Endocrine Abstracts

Kisspeptins, peptide products of the KiSS-1 gene, are pleiotropic hormones best recognized as novel regulators of puberty onset and the reproductive system. Thus, the hypothalamus expresses both KiSS-1 and its receptor, GPR54. Hypothalamic KiSS-1 is attenuated by food restriction (72 h fast),and this provides a plausible link between negative energy balance and the disruption of reproductive function. Hypothalamic KiSS-1 mRNA levels are also reduced following sex steroid treatment.

In previous studies we demonstrated that adipokines such as leptin and resistin are expressed, not only in adipose tissue, but in the brain and pituitary as well. In view of the evidence for a hypothalamic leptin-kisspeptin signalling pathway in the control of LH and FSH secretion (Tena-Sempere 2006), we tested the hypothesis that adipose tissue would also express KiSS-1. Using DNAse-treated RNA isolated from rat visceral fat, KiSS-1 mRNA was readily detected using specific primers and probes for RealTime RT-PCR. In subsequent experiments we investigated whether adipose KiSS-1 mRNA could also be regulated by food restriction or by sex steroid treatment. In marked contrast to the reported inhibition of KiSS-1 gene expression in hypothalamus, we observed a significant increase in KiSS-1 mRNA (2–3 fold; P<0.01) following 24 h of food restriction in male and female rats. A significant decrease in hypothalamic KiSS-1 gene expression was not detected. The effect of sex steroids on adipose KiSS-1 mRNA was also the opposite of that seen by others in hypothalamus. Rats were gonadectomized and 10 days later treated with a single injection of oestradiol (females; 20 μg in oil; s.c.) or testosterone propionate (males; I mg in oil; s.c.) and killed 48 h later. KiSS-1 mRNA was strikingly increased in adipose tissue by both oestradiol (8-fold; P<0.01) and testosterone (5-fold; P<0.01). Also, and in agreement with a previous report (Navarro et al. 2004), we observed that hypothalamic kiSS-1 expression was significantly reduced by sex hormone treatment.

We conclude that KiSS-1 gene expression is readily detectable in adipose tissue and is differentially regulated compared to hypothalamus. Further studies are needed to (a) quantify the protein products of the KiSS-1 gene (kisspeptins); (b) determine whether they are secreted from adipose tissue and (c) confirm whether they should be regarded as adipokines.