Kisspeptin Antagonists Reveal Kisspeptin 1 and Kisspeptin 2 Differential Regulation of Reproduction in the Teleost, Morone saxatilis1

Abstract

The importance of kisspeptin in regulating vertebrate reproduction
\nhas been well established, but the exact mechanism
\ncontinues to unfold. Unlike mammals, many lower vertebrates
\npossess a dual kisspeptin system, Kiss1 and Kiss2. To decipher
\nthe roles of the kisspeptins in fish, we identified two potential
\nkisspeptin antagonists, pep 234 and pep 359, by screening
\nanalogs for their ability to inactivate striped bass Kiss1 and Kiss2
\nreceptors expressed in COS7 cells. Pep 234 (a mammalian KISS1
\nantagonist) antagonizes Kiss1r signaling activated by Kiss1 and
\nKiss2, and pep 359 (a novel analog) antagonizes Kiss2 activation
\nof both receptors. In vitro studies using brain slices demonstrated
\nthat only Kiss2 can upregulate the expression of the
\nhypophysiotropic gnrh1, which was subsequently diminished
\nby pep 234 and pep 359. In primary pituitary cell cultures, the
\ntwo antagonists revealed a complex network of putative
\nendogenous and exogenous regulation by kisspeptin. While both
\nkisspeptins stimulate Fsh expression and secretion, Kiss2
\npredominately induces Lh secretion. Pep 234 and 359 treatment
\nof spawning males hindered sperm production. This effect was
\naccompanied with decreased brain gnrh1 and gnrh2 mRNA
\nlevels and peptide content in the pituitary, and increased levels
\nof pituitary Lh, probably due to attenuation of Lh release.
\nStrikingly, the mRNA levels of arginine-vasotocin, the neurons of
\nwhich in the preoptic area coexpress kiss2r, were dramatically
\nreduced by the antagonists. Our results demonstrate differential
\nactions of Kiss1 and Kiss2 systems along the hypothalamicpituitary
\naxis and interactions with other neuropeptides, and
\nfurther reinforce the importance of kisspeptin in the execution
\nof spawning.