Abstract:
The importance of kisspeptin in regulating vertebrate reproduction
has been well established, but the exact mechanism
continues to unfold. Unlike mammals, many lower vertebrates
possess a dual kisspeptin system, Kiss1 and Kiss2. To decipher
the roles of the kisspeptins in fish, we identified two potential
kisspeptin antagonists, pep 234 and pep 359, by screening
analogs for their ability to inactivate striped bass Kiss1 and Kiss2
receptors expressed in COS7 cells. Pep 234 (a mammalian KISS1
antagonist) antagonizes Kiss1r signaling activated by Kiss1 and
Kiss2, and pep 359 (a novel analog) antagonizes Kiss2 activation
of both receptors. In vitro studies using brain slices demonstrated
that only Kiss2 can upregulate the expression of the
hypophysiotropic gnrh1, which was subsequently diminished
by pep 234 and pep 359. In primary pituitary cell cultures, the
two antagonists revealed a complex network of putative
endogenous and exogenous regulation by kisspeptin. While both
kisspeptins stimulate Fsh expression and secretion, Kiss2
predominately induces Lh secretion. Pep 234 and 359 treatment
of spawning males hindered sperm production. This effect was
accompanied with decreased brain gnrh1 and gnrh2 mRNA
levels and peptide content in the pituitary, and increased levels
of pituitary Lh, probably due to attenuation of Lh release.
Strikingly, the mRNA levels of arginine-vasotocin, the neurons of
which in the preoptic area coexpress kiss2r, were dramatically
reduced by the antagonists. Our results demonstrate differential
actions of Kiss1 and Kiss2 systems along the hypothalamicpituitary
axis and interactions with other neuropeptides, and
further reinforce the importance of kisspeptin in the execution
of spawning.
