SummaryThe integrated signaling of insulin and gonadotropin-releasing hormone in the pituitary gonadotropes may have a profound bearing on reproductive function, although the cross-receptor signaling mechanisms are unclear. We demonstrate that the insulin receptor is constitutively localized to noncaveolar lipid raft microdomains in the pituitary gonadotrope cell line LβT2. The localization to rafts is consistent with similar localization of the GnRH receptor. Insulin receptor phosphorylation occurs in raft domains and activates the downstream signaling targets Insulin Receptor Substrate1 and Akt/ Protein Kinase B. Although insulin alone does not strongly activate the extracellular signal-regulated kinase second messenger cascade, co-stimulation potentiates the phosphorylation of the extracellular signal-regulated kinase by gonadotropin-releasing hormone. The co-stimulatory effect of insulin and gonadotropin-releasing hormone is also evident in increased activation of cap-dependent translation. In contrast, co-stimulation attenuates Akt/Protein Kinase B activation. Our results show that both gonadotropin-releasing hormone and insulin are capable of mutually altering their respective regulatory signaling cascades. We suggest that this provides a mechanism to integrate neuropeptide and energy homeostatic signals to modulate reproductive function.

Context We hypothesize, based on the degree of residual hypothalamic-pituitary function, that some, but not all, children with growth hormone deficiency (GHD) may have beneficial growth responses to the orally administered GH secretagogue LUM-201. Objective To determine if pretreatment testing can identify predictive enrichment markers (PEM) for subjects with adequate residual function that are responsive to LUM-201. Methods Analysis of a completed, randomized, placebo-controlled trial of LUM-201 a recombinant human growth hormone (rhGH) in which all randomized subjects had pretreatment testing Setting International multicenter study conducted in pediatric endocrinology clinics. Participants 68 naïve-to-treatment, prepubertal children with established diagnoses of GHD. Outcome Measures Sensitivity, specificity and predictive accuracy of potential markers to predict 6-month growth responses to oral LUM-201 and daily rhGH. Results Two PEM were identified: baseline insulin like growth factor- -I (IGF-I) concentration > 30 ng/mL and peak GH to single dose LUM-201 2: 5 ng/mL are defined as PEM-positive.PEM -positive status enriches a population for better growth responses to LUM-201.PEM -negative status enriches a population for better growth responses to rhGH. Conclusion The combination of peak GH to single-dose LUM-201 and baseline IGF-I concentration are effective PEMs for 6-month growth responses to LUM-201 and rhGH in prepubertal children with GHD.

Creatine Transporter Deficiency (CTD) is an inborn error of metabolism presenting with intellectual disability, behavioral disturbances and epilepsy. There is currently no cure for this disorder. Here, we employed novel biomarkers for monitoring brain function, together with well-established behavioral readouts for CTD mice, to longitudinally study the therapeutic efficacy of cyclocreatine (cCr) at the preclinical level. Our results show that cCr treatment is able to partially correct hemodynamic responses and EEG abnormalities, improve cognitive deficits, revert autistic-like behaviors and protect against seizures. This study provides encouraging data to support the potential therapeutic benefit of cyclocreatine or other chemically modified lipophilic analogs of Cr.

The study of gene expression in gonadotropes has largely focused on the variety of mechanisms regulating transcription of the gonadotropin genes and ancillary factors that contribute to the overall phenotype and function of these cells in reproduction. However, there are aspects of the response to GNRH signaling that are not readily explained by changes at the level of transcription. As our understanding of regulation at the level of mRNA translation has increased, it has become evident that GNRH receptor signaling engages multiple aspects of translational regulation. This includes activation of cap-dependent translation initiation, translational pausing caused by the unfolded protein response and RNA binding protein interaction. Gonadotropin mRNAs and the mRNAs of other factors that control the transcriptional and signaling responses to GNRH have been identified as targets of regulation at the level of translation. In this review we examine the impact of translational control of the expression of gonadotropin genes and other genes relevant to GNRH-mediated control of gonadotrope function.

The neuropeptide GNRH 1 stimulates the secretion of the reproductive hormone LH in pituitary gonadotropes. Other secretory cell types depend on the unfolded protein response (UPR) pathway to regulate protein synthesis and protect against endoplasmic reticulum (ER) stress in response to differentiation or secretory stimuli. This study investigated the role of the UPR in GNRH action within the LbetaT2 gonadotrope model. Cells were treated with GNRH, and the activation of UPR signaling components and general translational status was examined. The ER-resident stress sensors, Atf6, Eif2ak3, and Ern1, are all present, and GNRH stimulation results in the phosphorylation of eukaryotic translation initiation factor 2A kinase 3 and its downstream effector, eukaryotic translation initiation factor 2A. Additionally, activation of the UPR was confirmed both in LbetaT2 as well as mouse primary pituitary cells through identifying GNRH-induced splicing of Xbp1 mRNA, a transcription factor activated by splicing by the ER stress sensor, ER to nucleus signaling 1. Ribosome profiling revealed that GNRH stimulation caused a transient attenuation in translation, a hallmark of the UPR, remodeling ribosomes from actively translating polysomes to translationally inefficient ribonucleoprotein complexes and monosomes. The transient attenuation of specific mRNAs was also observed. Overall, the results show that GNRH activates components of the UPR pathway, and this pathway may play an important physiological role in adapting the ER of gonadotropes to the burden of their secretory demand.

The neuropeptide gonadotropin-releasing hormone stimulates synthesis and secretion of the glycoprotein gonadotropic hormones and activates the unfolded protein response, which causes a transient reduction of endoplasmic reticulum-associated mRNA translation. Hormone-treated cell extracts were fractionated to resolve mRNA in active polyribosomes from mRNA in inactive complexes. Quantitative real-time PCR and expression array analysis were used to determine hormone-induced redistribution of mRNAs between fractions and individual mRNAs were found to be redistributed differentially. Among the affected mRNAs relevant to gonadotropin synthesis, the luteinizing hormone subunit genes Lhb and Cga were enriched in the ribonucleoprotein pool. The MAP kinase phosphatase Dusp1 was enriched in the polyribosome pool. Enrichment of Dusp1 mRNA in the polyribosome pool was independent of the unfolded protein response, sensitive to ERK inhibition, and dependent on the 3′ untranslated region. The results show that GnRH exerts translational control to modulate physiologically relevant gene expression through two distinct signaling pathways.

Creatine transporter deficiency (CTD) is a metabolic disorder resulting in cognitive, motor, and behavioral deficits. Cyclocreatine (cCr), a creatine analog, has been explored as a therapeutic strategy for the treatment of CTD. We developed a rapid, selective, and accurate HILIC ultra‐performance liquid chromatography‐tandem mass spectrometry (UPLC‐MS/MS) method to simultaneously quantify the intracellular concentrations of cCr, creatine (Cr), creatine‐d3 (Cr‐d3), phosphocyclocreatine (pcCr), and phosphocreatine (pCr). Using HILIC‐UPLC‐MS/MS, we measured cCr and Cr‐d3 uptake and their conversion to the phosphorylated forms in primary human control and CTD fibroblasts. Altogether, the data demonstrate that cCr enters cells and its dominant intracellular form is pcCr in both control and CTD patient cells. Therefore, cCr may replace creatine as a therapeutic strategy for the treatment of CTD.

Context Recombinant human growth hormone (rhGH) is approved for treatment of pediatric GH deficiency (PGHD), with greatest growth responses observed in those with severe GHD. Orally administered GH secretagogues (GHS) may be useful treatment in patients with moderate GHD. Distinguishing children with severe vs. moderate GHD could identify children who would be better treated with rhGH or GHS. Objectives Evaluate baseline insulin-like growth factor-I (IGF-I) and stimulated peak GH response as predictors of 12-month height velocity (HV) in children with GHD. Design Data on children with GHD were analyzed in a legacy data base (GeNeSIS data). Participants 514 naïve to rhGH-treatment, prepubertal children with idiopathic isolated GHD (IGHD) for whom stimulated GH, baseline serum IGF-I and first year HV during rhGH treatment data are available. Outcome Measures Children with severe or moderate GHD were categorized based on GH and IGF-I data and evaluated based on baseline auxologic and hormone profiles and first year growth response to rhGH. Results Cohorts of severe and moderate GHD were 81/514 (15.8%) and 433/514 (84.2%). Cohorts differed significantly with regard to indicators of GHD (e.g., baseline height standard deviation score [SDS], height SDS minus target height SDS, HV, HV SDS, and change in height SDS during rhGH treatment). Multiple regression analysis showed IGF-I and stimulated GH were significant predictors of HV independent of other known variables. Expected first year HV in moderate GHD was 8.3 cm/year. Conclusions The combination of peak GH to GH stimulation testing and baseline IGF-I concentration are predictive enrichment markers for annualized HV responses to rhGH therapy.