A Sex-Dependent, Tropic Role for Leptin in the Somatotrope as a Regulator of POU1F1 and POU1F1-Dependent Hormones

Abstract

Pituitary somatotropes perform the key function of coordinating organismic growth and body composition with metabolic signals. However, the mechanism by which they sense and respond to metabolic signals via the adipokine leptin is unknown. The complex interplay between the heterogeneous cell types of the pituitary confounds the identification of somatotrope-specific mechanisms. Somatotropes represent 30%-40% of the anterior pituitary population and are derived from a lineage of cells that are activated by the Pit-Oct-Unc domain family domain class 1 transcription factor 1 (POU1F1) to produce GH, prolactin (PRL). and TSH. To determine the mechanism by which leptin controls somatotrope function, we used Cre-LoxP technology and fluorescence-activated cell sorting to purify and study control or leptin receptor-deleted (Lepr null) somatotropes. We report that Lepr-null somatotropes show significant reductions in GH protein (GH) and Gh mRNA. By contrast, enzyme immunoassays detected no changes in ACTH, LH, and FSH levels in mutants, indicating that the control of these hormones is independent of leptin signaling to somatotropes. Reduced TSH and PRL levels were also observed, but interestingly, this reduction occurred only in in Lepr-null somatotropes from mutant females and not from males. Consistent with the sex-specific reduction in Gh mRNA, TSH, and PRL, enzyme immunoassays detected a sex-specific reduction in POU1F1 protein levels in adult female Lepr-null somatotropes. Collectively, this study of purified Lepr-null somatotropes has uncovered an unexpected tropic role for leptin in the control of POU1F1 and all POU1F1-dependent hormones. This supports a broader role for somatotropes as metabolic sensors including sex-specific responses to leptin.

Adipokines (Leptin, Adiponectin, Resistin) Differentially Regulate All Hormonal Cell Types in Primary Anterior Pituitary Cell Cultures from Two Primate Species

“…5C ). In fact, further support for a direct positive association between leptin signaling and GH, PRL and Pit-1 expression levels is a recent report demonstrating that adult female, but not male, mice lacking leptin receptor from somatotropes had reduced GH, PRL and Pit-1 protein levels in somatotropes, suggesting a sex-dependent role for leptin in the control of GH, PRL and Pit-1 levels 70 . Remarkably, this study also showed that Pit-1 protein was increased in response to leptin stimulation, which reinforce the idea that leptin might regulate GH levels through stimulation of Pit-1, but also that Pit-1 might be a target of leptin, at least in female mice.…”

Leptin Regulation of Gonadotrope Gonadotropin-Releasing Hormone Receptors As a Metabolic Checkpoint and Gateway to Reproductive Competence

“…Methods describing our approach to leptin stimulation are detailed in previous studies ( 33 , 52 , 124 , 125 ). Pituitary pieces or cells in 24-h culture are exposed to leptin for 3 h at 37°C, and then extracts of proteins and mRNA are produced, as described ( 126 ). Methods describing our RT-PCR assays are found in the legend to Figure 3 and in Ref.…”

“…Leptin stimulates an increase in pituitary activin subunit mRNA ( InhBa ) level and does not have an effect on inhibin ( InhBb ) or Gnrhr mRNA levels. (C) In a separate set of experiments, we used fluorescence-activated cell sorting (FACS) to purify gonadotropes from control females bearing Lh-cre and floxed alleles of tdTomato-eGFP as described previously ( 126 ). The Cre-recombinase ablates the tdTomato leaving eGFP to be expressed in membranes of gonadotropes.…”

“…In this experiment, a female gonadotrope fraction containing 66,830 cells was split and half of the cells were stimulated for 3 h with 10 nM leptin. Protein extracts of these cells were assayed by EIA for GnRHR ( 127 ). (C) GnRHR proteins were higher in the gonadotropes stimulated with leptin (from 16.67 µg GnRHR/mg protein to 27.6 µg/mg protein).…”

Maternal obesity programs reduced leptin signaling in the pituitary and altered GH/IGF1 axis function leading to increased adiposity in adult sheep offspring

“…The group later reported more extreme cases of GH deficiency and abdominal obesity in male mice that had selective ablation of exon 1 of OB-Rb in somatotropes [ 45 ]. This excision of OB-Rb exon 1 resulted in the loss of all isoforms of the leptin receptor and uncovered a broader role for somatotropes as metabolic sensors including sex-specific responses to leptin [ 45 , 46 ].…”