Kisspeptin Directly Regulates Neuropeptide Y Synthesis and Secretion via the ERK1/2 and p38 Mitogen-Activated Protein Kinase Signaling Pathways in NPY-Secreting Hypothalamic Neurons

Abstract

Kisspeptin is a key component of reproduction that directly stimulates GnRH neurons. However, recent studies indicate that kisspeptin can indirectly stimulate GnRH neurons through unidentified afferent networks. Neuropeptide Y (NPY) is another key reproductive hormone that is an afferent stimulator of GnRH neurons. Herein, we report kisspeptin receptor Kiss1r mRNA expression in native NPY neurons FAC-sorted from NPY-GFP transgenic mice. Thus, we hypothesized that kisspeptin indirectly stimulates GnRH neurons through direct regulation of NPY neurons. Using hypothalamic NPY-secreting cell lines, we determined that kisspeptin stimulates NPY mRNA expression and secretion in the mHypoE-38 cells, but not the mHypoE-42 cells, using quantitative RT-PCR and enzyme immunoassays. Furthermore, agouti-related peptide, ghrelin, neurotensin, or Kiss1r mRNA expression was not changed upon exposure to kisspeptin in either cell line. These results concur with our previous work identifying the mHypoE-38 cell line as a putative reproductive NPY neuron and the mHypoE-42 cell line as a potential feeding-related NPY neuron. In the mHypoE-38 cells, kisspeptin activated the ERK1/2 and p38 MAPK kinases as shown by Western blot analysis. Moreover, inhibiting the ERK1/2 and p38 pathways with U0126 and SB239063, respectively, prevented kisspeptin induction of NPY mRNA expression and secretion. Altogether, we find that kisspeptin directly regulates NPY synthesis and secretion via the ERK1/2 and p38 MAPK pathways in a NPY-secreting cell line, and we propose NPY neurons as an afferent network by which kisspeptin indirectly stimulates GnRH secretion.