Effects of Selective Deletion of Tyrosine Hydroxylase from Kisspeptin Cells on Puberty and Reproduction in Male and Female Mice

Abstract

The neuropeptide kisspeptin, encoded by Kiss1, regulates reproduction by stimulating GnRH secretion. Kiss1-syntheizing neurons reside primarily in the hypothalamic anteroventral periventricular (AVPV/PeN) and arcuate nuclei. AVPV/PeN Kiss1 neurons are sexually dimorphic, with females expressing more Kiss1 than males, and participate in estradiol-induced positive feedback control of GnRH secretion. In mice, most AVPV/PeN Kiss1 cells co-express tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine synthesis (in this case, dopamine). Dopamine treatment can inhibit GnRH neurons, but the function of dopamine signaling arising specifically from AVPV/PeN Kiss1 cells is unknown. We generated a novel TH flox mouse and used Cre-Lox technology to selectively ablate TH specifically from Kiss1 cells. We then examined the effects of selective TH knockout on puberty and reproduction in both sexes. In control mice, 90% of AVPV/PeN Kiss1 neurons co-expressed TH, whereas in mice lacking TH exclusively in Kiss1 cells (termed Kiss THKOs), TH was successfully absent from virtually all Kiss1 cells. Despite this absence of TH, both female and male Kiss THKOs displayed normal body weights, puberty onset, and basal gonadotropin levels in adulthood, though testosterone was significantly elevated in adult male Kiss THKOs. The estradiol-induced LH surge was unaffected in Kiss THKO females, and neuronal activation status of kisspeptin and GnRH cells were also normal. Supporting this, fertility and fecundity were normal in Kiss THKOs of both sexes. Thus, despite high colocalization of TH and Kiss1 in the AVPV/PeN, dopamine produced in these cells is not required for puberty or reproduction, and its function remains unknown.

Significance Statement Kisspeptin promotes reproduction, and kisspeptin neurons in the hypothalamic anteroventral periventricular (AVPV/PeN) nucleus mediate estradiol-positive feedback control of GnRH secretion. Dopamine treatment can inhibit GnRH neurons, and most AVPV/PeN kisspeptin cells are also dopaminergic (coexpress tyrosine hydroxylase (TH)), but it is unknown if dopamine specifically in AVPV/PeN kisspeptin cells regulates GnRH neurons. Using Cre-Lox technology, we determined that the selective knockout of TH in kisspeptin cells surprisingly has no effect on puberty, reproductive hormones, or fertility. Thus, despite being highly co-expressed, dopamine in kisspeptin cells is not required for reproduction. Dopamine in these cells likely serves other yet-to-be-identified roles, perhaps unrelated to reproductive neuroendocrinology.