Leptin receptor null mice with reexpression of LepR in GnRHR expressing cells display elevated FSH levels but remain in a prepubertal state.

Leptin signals energy sufficiency to the reproductive hypothalamic-pituitary-gonadal (HPG) axis. Studies using genetic models have demonstrated that hypothalamic neurons are major players mediating these effects. Leptin receptor (LepR) is also expressed in the pituitary gland and in the gonads, but the physiological effects of leptin in these sites are still unclear. Female mice with selective deletion of LepR in a subset of gonadotropes show normal pubertal development but impaired fertility. Conditional deletion approaches, however, often result in redundancy or developmental adaptations, which may compromise the assessment of leptin's action in gonadotropes for pubertal maturation. To circumvent these issues, we adopted a complementary genetic approach and assessed if selective reexpression of LepR only in gonadotropes is sufficient to enable puberty and improve fertility of LepR null female mice. We initially assessed the colocalization of gonadotropin-releasing hormone receptor (GnRHR) and LepR in the HPG axis using GnRHR-IRES-Cre (GRIC) and LepR-Cre reporter (tdTomato or enhanced green fluorescent protein) mice. We found that GRIC and leptin-induced phosphorylation of STAT3 are expressed in distinct hypothalamic neurons. Whereas LepR-Cre was observed in theca cells, GRIC expression was rarely found in the ovarian parenchyma. In contrast, a subpopulation of gonadotropes expressed the LepR-Cre reporter gene (tdTomato). We then crossed the GRIC mice with the LepR null reactivable (LepR(loxTB)) mice. These mice showed an increase in FSH levels, but they remained in a prepubertal state. Together with previous findings, our data indicate that leptin-selective action in gonadotropes serves a role in adult reproductive physiology but is not sufficient to allow pubertal maturation in mice.