United States

The transcription factor OTX2 is implicated in pituitary, ocular and craniofacial development. Mutations have been described in patients with variable congenital hypopituitarism (CH) ranging from isolated growth hormone deficiency (IGHD) to combined pituitary hormone deficiency (CPHD) with/without an ectopic posterior pituitary (EPP).We aimed (i) to establish the contribution of OTX2 mutations in the etiology of CH in a sub-cohort of patients and to study their functional consequences and (ii) establish a detailed human OTX2 expression profile in a hypothalamo-pituitary (HP) context. We screened 127 patients from national (n=103) and international centers (n=24) on the septo-optic dysplasia (SOD) spectrum with variable eye abnormalities. Eye abnormalities included micro/anophthalmia, retinal dystrophy and/or coloboma in 29 of these patients, with the rest having optic nerve hypoplasia (ONH). An EPP was reported on MRI in 35 patients. The cohort previously tested negative for mutations in HESX1, SOX2, SOX3, PROKR2 and GH1. Transactivation assays involved a dual-luciferase reporter in murine hypothalamic GT1-7 neurons transiently transfected with OTX2 constructs. In situ hybridization was performed to analyze human brain OTX2 expression during embryogenesis. Seven heterozygous OTX2 changes were identified: two chromosomal deletions spanning OTX2 in patients with micro/anophthalmia, GHD and an EPP, with one patient having cerebellar hypoplasia. Three missense substitutions resulting in truncated proteins: (i) the previously reported p.S138* and (ii) p.C170*, in two patients with retinal dystrophy, EPP and IGHD respectively, and (iii) the novel p.E79* in a patient with micro/anophthalmia, EPP and CPHD. A novel insertion-deletion resulting in a truncated protein p.S167* in a patient with microphthalmia, GHD, ONH, EPP and an enlarged abnormal pituitary, and a novel deletion resulting in a frameshift p.Val139Aspfs*39 in a patient with microcephaly, microphthalmia, ONH and an EPP were also identified. The human OTX2 variants caused a significant reduction in transactivation compared to wild type. Our gene expression data identified human OTX2 transcripts in the posterior pituitary, retina, ear, thalamus, choroid plexus, and in the hypothalamus during embryogenesis, but not in RP. To conclude, we identified OTX2 variants in 7 unrelated CH patients with eye abnormalities including 3 with retinal dystrophy and one with a cerebellar abnormality. As OTX2 is involved at multiple levels during HP development, these patients should be monitored for evolving endocrinopathies. Human OTX2 is expressed in the posterior pituitary, the retina and the ear at CS19 and 20 (between 6-7 weeks gestation), and in areas of the hindbrain at CS23, but not in RP at any stage analyzed in this study. The endocrine phenotypes in patients with OTX2 mutations are most likely of hypothalamic origin.

ENDO 2020

OTX2 Mutations in Congenital Hypopituitarism Patients

ENDO 2021

ENDO is the leading meeting for endocrinology research and clinical care worldwide. 

technical paper

Welcome to **ENDO** - the place where leading experts, researchers, and the most respected clinicians in the field come together to share the latest findings in hormone science and discuss breakthroughs in clinical care.

**Endocrine Society** is a global community of physicians and scientists dedicated to accelerating scientific breakthroughs and improving patient health and well being.
<br><br>
For 100 years, the Endocrine Society has been at the forefront of hormone science and public health. **[Read about our history](https://www.endocrine.org/our-community/advancing-endocrinology-and-public-health/history)** and how we continue to serve the endocrine community.

ENDO is the place where leading experts, researchers, and the most respected clinicians in the field come together to share the latest findings in hormone science and discuss breakthroughs in clinical care.

The homeodomain transcription factor SIX3 is necessary for normal reproductive processes in mice. The loss of a single allele results in haploinsufficient phenotypes that are reflective of individuals with Kallmann Syndrome, such as hypogonadism, reduced GnRH neurons, and anosmia. Six3 heterozygous mice have reproductive impairments including an increased time to first litter, increased estrous cycle lengths in females, and fewer litters in males compared to wildtype controls. Prior studies found that deleting SIX3 specifically from GnRH neurons did not recapitulate the same phenotypes produced from a global knockout of the Six3 allele and imposed no reproductive abnormalities. This suggests that the role of SIX3 in reproduction is due to SIX3 populations outside of GnRH neurons. Using qPCR and RNA-seq, we have verified that Six3 is expressed in arcuate nucleus (ARC) and anteroventral periventricular nucleus (AVPV) populations of kisspeptin neurons and can regulate the kisspeptin promoter in vitro. This led us to hypothesize that SIX3 in kisspeptin neurons is required for Kiss1 regulation and maximal fertility. We selectively deleted Six3 from kisspeptin neurons by crossing a Six3-floxed mouse with a Kiss1-Cre mouse to produce Six3 flox/flox; Kiss1-Cre positive mice (cKO) and Six3 flox/flox, Kiss-Cre negative littermates (controls). In female mice, we found that the loss of SIX3 from kisspeptin neurons disrupted the estrous cycle and reduced fertility. Compared to controls, cKO mice had fewer cycles in a 16-day period (0.38 vs 1.44; p=0.004; n=8-9), and spent a greater percentage of time in diestrus (80.5 vs 61.8; p=0.002; n=8-9) and a smaller percentage of time in estrus (15.6 vs 29.2; p=0.030; n=8-9). The loss of kisspeptin-specific SIX3 also resulted in reduced fecundity, with the cKO female mice having fewer pups within 90 days (15.0 vs 34.4; p=0.048; n=5-6) compared to controls. In addition to its importance in female mice, kisspeptin-specific SIX3 also plays a role in male fertility. We found that male cKO mice had reduced motile sperm (52.2% vs 72.5%; p=0.012; n=7-9) compared to controls. We also assayed levels of Kiss1 mRNA in the male arcuate nucleus and observed decreased Kiss1 levels compared to controls (0.34 vs 1.01; p=0.042; n=3-4). These results support our hypothesis that SIX3 in kisspeptin neurons is necessary for critical reproductive processes in both females and males, including progression through the estrous cycle, fecundity, and sperm motility, potentially through Kiss1 regulation.

The Expression of the Homeodomain Transcription Factor SIX3 within Kisspeptin Neurons Is Necessary for Reproduction in Mice

Circadian Regulation of Chromatin State Mediates Pancreatic Incretin ResponseThe circadian clock is programmed by an autoregulatory transcription feedback loop present in brain and peripheral tissues that coordinates metabolism with nutritional state and the sleep-wake cycle. Epidemiologic and genetic studies indicate circadian disruption as a risk factor in the development of diabetes. We have demonstrated that conditional ablation of the β cell clock in adult life leads to hypoinsulinemic diabetes, and through mRNA-sequencing in mouse and human islets we revealed clock control of gene networks involved in insulin secretion, nutrient sensing, and exocytosis. A remaining question is: How does the core molecular clock modulate time-of-day dependent chromatin state to regulate pancreatic islet response to glucose and insulin secretagogues? Here we report that loss of the pancreatic β cell molecular clock results in closed chromatin at cAMP-responsive gene regulatory elements and dysregulated cAMP-dependent coregulator recruitment following cAMP agonism, consistent with a role for the molecular clock in mediating cell response to environmental stimuli. Further, tandem analyses of ATAC- and ChIP-sequencing in synchronized islets revealed dynamic chromatin accessibility across the 24-hour cycle at genes regulating insulin secretion and at genomic regions enriched for signal-inducible and circadian transcription factor motifs. Our genome-wide sequencing reveals a new role for the clock in global chromatin remodeling underlying the incretin response in pancreatic β cells.

Circadian Regulation of Chromatin State Mediates Pancreatic Islet Incretin Response

Pparg is a nuclear receptor that regulates glucose and lipid metabolism. Thiazolidinediones (TZD) are PPARG agonists that may reduce hepatic steatosis through their effects in adipose tissue. However, some studies suggest that expression and activation of hepatocyte Pparg promotes steatosis. In this study, we have assessed the relevance of hepatocyte Pparg, and its TZD-mediated activation in the development and/or reduction of steatosis, with adult-onset hepatocyte-specific Pparg knockout (PpargΔHep) mice. We reported that a single iv injection of AAV8-TBG-Cre in Pparg-floxed mice, knocked out hepatocyte Pparg expression (PpargΔHep mice), and that prevented diet-induced steatosis. In this study, a group of 5 wk-old Pparg-floxed mice were fed a low fat (LF) or a high fat (HF) diet for 7 weeks before generating control and PpargΔHep mice. Then, half of the HF-fed mice in each group were switched to a HF diet supplemented with the TZD Rosiglitazone maleate, for 5 weeks. HF diet induced mild obesity (36.8 +/- 1.4 g of body weight [BW]), while TZD slightly increased BW (41.3 +/- 1.3 g) and insulin sensitivity. Liver weight was not altered in HF-fed mice with or without TZD, and we did not observe any effect induced by PpargΔHep. Due to the mild phenotype observed in this cohort, we generated a 2nd cohort adjusting for age and length of diet. Briefly, 10 wk-old Pparg-floxed mice were fed a LF or HF diet for 16 weeks before generating control and PpargΔHep mice. Then, half of the HF-fed mice in each group were switched to a HF diet supplemented with Rosiglitazone maleate for 7 weeks. In this group of mice, HF diet induced obesity (50.1 +/- 1.05 g BW), and increased liver weight independent of hepatic Pparg expression. TZD treatment exacerbated obesity (62.4 +/- 1.2g BW) and adiposity, but increased insulin sensitivity as compared to mice fed a HF diet without TZD. Interestingly, PpargΔHep mice fed a HF diet with TZD showed enlarged subcutaneous white and brown adipose tissue weight, and a dramatic reduction in liver weight and steatosis as compared to obese control mice treated with TZD. The expression of hepatic Cd36, Cidea, Cidec, and Fabp4 was increased by TZD in a Pparg-dependent manner in HF-fed mice. Altogether, this data suggest that hepatocyte Pparg expression may offset the antisteatogenic actions of TZD in mice with severe obesity. In obese and insulin resistant individuals, TZD-mediated activation of hepatocyte Pparg may exacerbate steatosis.

Hepatocyte Peroxisome Proliferator-Activated Receptor Gamma (PPARG) Offsets the Anti-Steatogenic Effects of Thiazolidinediones in Obese Male Mice

Glucocorticoids are required for metabolic adaptations during times of stress. However, chronic glucocorticoid exposure is associated with metabolic disorders such as insulin resistance. Glucocorticoids mainly convey their signals through an intracellular glucocorticoid receptor (GR). GR is a transcription factor that requires interactions with transcriptional coregulators to modulate the transcription of GR primary target genes, which in turn regulate specific aspects of physiology. Euchromatic Histone Methyltransferase 2 (Ehmt2) is a transcriptional coregulator for GR that can act as a corepressor or a coactivator. We found that glucocorticoid-induced insulin resistance was exacerbated when Ehmt2 levels were reduced in the liver. Intriguingly, this phenotype resulted from the transactivation function of Ehmt2. This is because a mutation at the lysine 182 automethylation site, which is required for the coactivation but not the corepression function of Ehmt2, results in similar exacerbated GC-induced insulin resistance. These results suggest that Ehmt2 coactivation dependent GR primary target genes restrict the extent of glucocorticoid-induced insulin resistance. Gene expression analysis identified Dusp4 (a.k.a. Mkp-2) as an Ehmt2 coactivation dependent GR-activated gene, which when overexpressed in liver, attenuated glucocorticoid-induced insulin resistance. Thus, we have identified a novel GR-Ehmt2-Dusp4 axis that plays a key role in controlling the extent of the development of insulin resistance. Notably, the classical view of how GC induce hepatic insulin resistance is that GR activates genes that inhibit insulin signaling and enhance hepatic gluconeogenesis. Our study, however, provides a revolutionary concept in which the extent of GC-induced insulin resistance is controlled by the balance of GR-activated genes that promote insulin sensitivity or insulin resistance.

The Transcriptional Coactivation Function of EHMT2 Restricts Chronic Glucocorticoid Exposure Induced Insulin Resistance

Humans and mice with Melanocortin 4 receptor (MC4R) deficiency remain protected from hyperglycemia despite chronic obesity and insulin resistance. We have observed that elevated glycosuria in MC4R deficient mice protects them from hyperglycemia. Moreover, our results indicate that circulating epinephrine may couple MC4R signaling with kidney glucose reabsorption. However, the direct role of epinephrine in regulating kidney glucose reabsorption remains unclear. We hypothesize that epinephrine is essential for maintaining glucose homeostasis via kidney glucose reabsorption. To test this hypothesis, we performed oral glucose tolerance tests (OGTTs) and intraperitoneal insulin tolerance tests (ITTs) in phenylethanolamine-N-methyltransferase (Pnmt) knockout (KO) mice that specifically lack epinephrine but have normal norepinephrine levels. Pnmt KO mice exhibited reduced insulin sensitivity compared to their Wild-Type (WT) littermates (Area under the curve for ITT: 9,700±256 vs. 8,482±417 mg/dL.min, p<0.05). Paradoxically, we observed improved rather than impaired glucose tolerance in Pnmt KO mice compared to their WT controls (Area under the curve for OGTT: 32,546±1,592 vs. 40,058±1,918 mg/dL.min, p<0.05). To ascertain if Pnmt KO mice, like MC4R deficient mice, show elevated glycosuria, we quantified their 24 urine glucose levels after oral glucose (250 mg) challenge. Indeed, Pnmt KO mice demonstrated elevated glycosuria compared to their WT littermates (Urine glucose: Baseline, 24.63±2.2 vs. 11.14±0.82 mg/dl; post glucose challenge: 67.83±5 vs. 16.09±1.13 mg/dl, p<0.001), again validating the phenotype similar to that of MC4R deficient mice. To determine the glucose transporters involved in mediating elevated glycosuria in the Pnmt KO mice, we measured the levels of different renal glucose transporters using western blot. We found that GLUT2 was decreased by ~26% in Pnmt KO mice compared to their WT littermates. Levels of other glucose transporters were not changed, indicating that suppression of renal GLUT2 mediates elevated glycosuria in the epinephrine deficient mice. We validated the direct effect of epinephrine on GLUT2 levels in vitro using mouse primary renal proximal tubule epithelial cells. Indeed, epinephrine selectively increased GLUT2, but did not affect other glucose transporters in the mouse kidney primary cells. Our findings establish the essential role of epinephrine in glucose reabsorption via the renal glucose transporter GLUT2. Therefore, modulating the renal adrenergic system, or, kidney-specific GLUT2 may afford alternative strategies to regulate glycosuria and ultimately mitigate diabetes.

Epinephrine Is Essential for Normal Renal Glucose Reabsorption via the Glucose Transporter GLUT2

If we knew then what we know now would we have approached the development of Endocrine therapies differently?

During development of the central nervous system, neural cells respond to several external cues that influence cell proliferation, differentiation, axonal growth and synaptogenesis. Thyroid hormone plays a critical role in each of these processes. Previously, we showed that Krüppel-like factor 9 (KLF9), a zinc finger transcription factor, is strongly and directly induced by liganded thyroid hormone receptors, and it mediates the actions of thyroid hormone on neuronal differentiation during late fetal development. Here we analyzed the molecular mechanisms by which KLF9 maintains neuronal structure, and inhibits regeneration in juvenile and adult neuronal cells. We also investigated the actions of the closely related transcription factor KLF13, which is paralogous to KLF9. We engineered the adult mouse hippocampus-derived cell line HT22 to control Klf9 or Klf13 expression by addition of doxycycline. We also used CRISPR/Cas9 genome editing to generate Klf9 or Klf13 knock out (KO), and Klf9+Klf13 double KO HT22 cell lines. To induce neurite outgrowth, we treated cells with forskolin (FK)+IBMX, which increases intracellular cAMP; elevated cAMP is a hallmark of regenerative responses of neurons to injury. Our results show that FK+IBMX increased neurite length in the parent HT22 cell line, and this action was enhanced in Klf9 and Klf13 single KO cells, and was even greater in double KO cells. By contrast, the stimulatory effect of FK+IBMX on neurite outgrowth was blocked by simultaneous forced expression of Klf9 or Klf13 in parent HT22 cells. This effect on neurite outgrowth was confirmed in primary mouse hippocampal neurons, where electroporation of expression plasmids for Klf9 or Klf13 suppressed FK+IBMX-induced neurite extension compared with empty vector-transfected cells. Analysis of RNA-seq data obtained from HT22 cells following 8 hr of induced Klf9 or Klf13 expression showed that both proteins impact the cAMP signaling pathway. Using transfection-reporter assays and chromatin immunoprecipitation, we confirmed that several genes in this pathway are direct targets of both KLFs. Our findings suggest that KLF9 and KLF13 may cooperate to maintain the differentiated state of mammalian neurons and thereby block regeneration, in part, by repressing the cAMP signaling pathway.

Kruppel-Like Factors 9 and 13 Cooperate to Maintain Mammalian Neuronal Differentiation

Background Genetic mutations and histological appearances suggest that APCCs are precursors to some aldosterone producing adenomas (APA). They are hypothesised to contribute to post-operative non-cure and recurrence of primary aldosteronism (PA) but are currently undetectable pre-operatively. SLC35F1 is a possible nucleotide sugar transporter. On microarray it is highly expressed in APCCs, but not in the rest of the adrenal cortex (1). Our aim was to investigate the role of SLC35F1 in APCCs, determine its subcellular localisation and establish whether expression is consistent with pathological APCC subtypes (as suggested by recent evidence from in situ metabolomic studies (2)). Methods Comparative bioinformatic analysis of the SLC35F1 amino acid sequence was carried out. Ex vivo 4uM adrenal sections, from 6 PA patients in the MATCH study, were stained on serial sections with anti-CYP11B2 (Gomez-Sanchez) or anti-SLC35F1 (Novus NBP1-86755). In vitro, H295R cells were transfected with SLC35F1 cDNA. Subcellular localisation of SLC35F1-GFP was studied by comparison to organelle markers (golgin 97, RAB11, wheat germ agglutinin, calnexin and Tom20) using confocal microscopy. Overexpression and siRNA knock-down in H295R cells was correlated to aldosterone production. Results SLC35F1 is a decamembrane-spanning transporter molecule predicted to have a negatively charged pocket in the substrate binding site, implying a transport substrate with a positive charge. Strong staining of CYP11B2 in clusters of cells in adrenal cortex, consistent with APCCs, were present in all six adrenal glands (25 APCCs). Serial sections showed specific SLC35F1 staining of APCCs, in cytoplasm and plasma membrane. SLC35F1 staining was absent from normal cortex. 12 APCCs (48%) were SLC35F1-negative. Visualisation of transiently expressed SLC35F1 demonstrated localisation to the endoplasmic reticulum in H295R cells (Pearson’s coefficient r=0.758) with no plasma membrane localisation (r=-0.07). Preliminary transfection data suggest direct involvement in aldosterone production. Conclusions Expression of SLC35F1 in the plasma membrane and cytosol of APCC cells supports a role in pathological aldosterone production by APCCs. The inferred transport substrate of SLC35F1 is the NAD(P)(H) precursor, nicotinamide riboside, a positively-charged nucleotide sugar. If confirmed, the essential requirement for NAD(P)H in steroidogenesis, and heterogeneity of SLC35F1-staining in APCCs, is consistent with a metabolically active, possibly pathological, subtype of APCCs. Detection of SLC35F1 in vivo may therefore facilitate sub-classification of PA patients.1). Nishimoto et. al. PNAS. 2015 Aug 18;112(33):E4591-9. 2). Murakami et. al. 2019 Hypertension. In press.

Expression of SLC35F1 in the Plasma Membrane of Cells of Aldosterone Producing Cell Clusters (APCCs) and Its Possible Role in Aldosterone Synthesis

NAFLD (Non Alcoholic Fatty Liver Disease) has become the most common cause of chronic liver disease in many developed countries worldwide and represents a major health concern. The prevalence of NAFLD is sexually dimorphic with men suspected to be more susceptible to the development of hepatic steatosis than women. Women are mostly protected until hormonal imbalance induced by menopause. Nuclear receptor CAR (Constitutive Androstan Receptor) is at the crossroads between endocrine and metabolic regulations and could therefore represent an interesting therapeutic target. It is primarily expressed in the liver and involved in the catabolism of hormones such as thyroid hormones, corticosteroids and estrogens. In addition, several studies reveal a metabolic role of CAR through regulation of major hepatic pathways such as neoglucogenesis, beta-oxidation and de novo lipogenesis. Our research is aimed at better understanding the role of CAR using a mouse model genetically deficient for CAR. To explore the metabolic functions of CAR, knock-out male and female mice were subjected to a high fat diet (HFD) for 16 weeks. Concomitant CAR deletion and high fat diet induces sexually dimorphic metabolic disorders. Knock-out of CAR in males exacerbates HFD-induced fasted hyperglycemia whereas in females, it aggravates body weight gain and adipose tissue accumulation. In accordance with epidemiological studies revealing a protection of women from the development of hepatic steatosis, HFD-fed WT female mice present less important hepatic steatosis than HFD-fed WT male mice. However, following CAR deletion, HFD-fed female mice develop a severe steatosis along with important hepatic injury. Ongoing studies aim to understand the transcriptomic and endocrine dysregulations that may explain these phenotypes. These results reveal a previously unrecognized dimorphic role of CAR in energy homeostasis and highlights its involvement in the protection of female mice towards the development of hepatic steatosis. Overall, this research provides further insights in the pathogenesis of NAFLD and its dimorphic prevalence.

Nuclear Receptor CAR Protects Female Mice from the Development of Diet-Induced Nonalcoholic Fatty Liver Disease

Adrenal corticosteroids, such as glucocorticoids and mineralocorticoids, are indispensable for mediating response to stress, development, limiting inflammation, and maintaining energy and fluid homeostasis. These hormones exert their actions via binding to two closely related nuclear receptors, the glucocorticoid receptor (GR) and mineralocorticoid receptor (MR). The GR has low affinity for corticosteroids, but is expressed in nearly every cell. In contrast, the MR shows a higher affinity for corticosteroids and its expression is largely confined to those tissues where electrolyte exchange and fluid balance are required. GR and MR act as ligand-activated transcription factors which, following interaction with co-regulators and DNA responsive elements, either promote or repress gene transcription. The affinity for the same ligands, structural homology, and binding to the same DNA regions suggest GR and MR can compensate for each other’s actions. Yet, there are specific glucocorticoid and mineralocorticoid-mediated responses indicating GR-MR functional diversity. To investigate this interplay, we developed U-2 OS (human osteosarcoma) cell lines stably expressing GR, MR, and both GR and MR (GRMR). Immunofluorescence analysis showed that treatment of these cell lines with 1 nM of the synthetic glucocorticoid dexamethasone (Dex) induced nuclear traslocation of GR and MR. Conversely, treatment with 1 nM of aldosterone (Aldo) promoted nuclear translocation of the MR only. Moreover, Proximity Ligation Assay revealed that, in the absence of ligand, GR associated with MR in the cytoplasm and, upon 1 nM Dex exposure, GR-MR dimers were detected in the nucleus of GRMR cells. Surprisingly, nuclear GR-MR dimers were also detected in the presence of Aldo, suggesting that it is necessary to activate at least one receptor to induce nuclear traslocation of the heterocomplex. To decipher the functional contribution of GR-MR dimers in the transcriptional response of GR to Dex and MR to Aldo, we performed RNA-seq in GR, MR, and GRMR cells treated with 1 nM of Dex or Aldo. Transcriptome analysis revealed that Dex-activated GR regulated the transcription of 6180 genes. Co-expression of MR resulted in a blunted Dex-mediated gene response which affected only 1608 genes, suggesting a functional antagonism of MR. Aldo-activated MR regulated the transcription of 1660 genes. However, co-expression of GR expanded the Aldo-mediated gene response to 3150 genes. Strikingly, 74% of these genes were also regulated by Dex via GR, suggesting that GR-MR dimers in the presence of aldosterone are able to mimic the glucocorticod transcriptional response. Our data suggest that the role of distinct GR and MR homo- and hetero-dimers is relevant for regulating gene expression. Dissecting the mechanism and investigating the cross-talk between GR and MR may be useful to understanding these two receptors in heath and disease.

OTX2 Mutations in Congenital Hypopituitarism Patients

Downloads

Next from ENDO 2020

The Expression of the Homeodomain Transcription Factor SIX3 within Kisspeptin Neurons Is Necessary for Reproduction in Mice

Similar lecture

Neuroendocrine Regulation of Onset of Puberty

Stay up to date with the latest Underline news!

PRESENTATIONS

CONFERENCES

COMPANY

RESOURCES