SLC30A8 encodes the zinc transporter ZnT8. SLC30A8 haploinsufficiency protects against type 2 diabetes (T2D), suggesting that ZnT8 inhibitors may prevent T2D. We show here that, while adult chow fed Slc30a8 haploinsufficient and knockout (KO) mice have normal glucose tolerance, they are protected against diet-induced obesity (DIO), resulting in improved glucose tolerance. We hypothesize that this protection against DIO may represent one mechanism whereby SLC30A8 haploinsufficiency protects against T2D in humans and that, while SLC30A8 is predominantly expressed in pancreatic islet beta cells, this may involve a role for ZnT8 in extra-pancreatic tissues. Consistent with this latter concept we show in humans, using electronic health record-derived phenotype analyses, that the ‘C’ allele of the non-synonymous rs13266634 SNP, which confers a gain of ZnT8 function, is associated not only with increased T2D risk and blood glucose, but also with increased risk for hemolytic anemia and decreased mean corpuscular hemoglobin (MCH). In Slc30a8 KO mice, MCH was unchanged but reticulocytes, platelets and lymphocytes were elevated. Both young and adult Slc30a8 KO mice exhibit a delayed rise in insulin after glucose injection, but only the former exhibit increased basal insulin clearance and impaired glucose tolerance. Young Slc30a8 KO mice also exhibit elevated pancreatic G6pc2 gene expression, potentially mediated by decreased islet zinc levels. These data indicate that the absence of ZnT8 results in a transient impairment in some aspects of metabolism during development. These observations in humans and mice suggest the potential for negative effects associated with T2D prevention using ZnT8 inhibitors.
Kristen E Syring, Karin J Bosma, Slavina B Goleva, Kritika Singh, James K Oeser, Christopher A Lopez, Eric P Skaar, Owen P McGuinness, Lea K Davis, David R Powell, and Richard M O’Brien
Hans-Peter Holthoff, Kerstin Uhland, Gabor Laszlo Kovacs, Andreas Reimann, Kristin Adler, Clara Wenhart, and Martin Ungerer
Graves’ disease is an autoimmune disorder, which is characterized by stimulatory antibodies targeting the human thyrotropin receptor (TSHR), resulting in hyperthyroidism and multiple organ damage. We systematically investigated monomeric and dimeric fusion proteins of the A subunit of TSHR for efficacy to bind to the monoclonal patient antibody M22, to interact with Graves’ patient serum samples, and to impact on anti-TSHR antibody titers, hyperthyroidism, tachycardia and other in vivo read-outs in a long-term mouse model of Graves’ disease induced by immunization with a recombinant adenovirus encoding TSHR A. Binding assays and functional measurements of TSHR-dependent cAMP formation showed binding of monomeric TSHR-His and dimeric TSHR-Fc to the anti-TSHR antibody M22 at low-effective concentrations (EC50 of 5.7 nmol/L and 8.6 nmol/L) and inhibition of the effects of this antibody at high efficiencies (IC50 values of 16–20 nmol/L). Both proteins also block the effects of polyclonal anti-TSHR antibodies occurring in Graves’ patient sera with somewhat lower average efficiencies (mean IC50 values of 29 nmol/L and 68 nmol/L). However, in vivo characterization of epicutaneous patch administrations of TSHR-Fc at doses of 0.3 and 0.6 mg/kg body weight in a murine Graves’ disease model did not result in any improvement of disease parameters. In conclusion, high affinity binding of TSHR-Fc to pathological anti-TSHR antibodies was not matched by efficacy to improve Graves’ disease parameter in a long-term mouse model.
Jessica L Huang, Sharon Lee, Pelle Hoek, Talitha van der Meulen, Richard Van, and Mark O Huising
There is great interest in generating functionally mature beta cells from stem cells, as loss of functional beta cell mass contributes to the pathophysiology of diabetes. Identifying markers of beta cell maturity is therefore very helpful for distinguishing stem cells that have been successfully differentiated into fully mature beta cells from stem cells that did not. Urocortin 3 (UCN3) is a peptide hormone whose expression is associated with the acquisition of functional maturity in beta cells. The onset of its expression occurs after other beta cell maturity markers are already expressed and its loss marks the beginning of beta cell dedifferentiation. Its expression pattern is therefore tightly correlated with beta cell maturity. While this makes UCN3 an excellent marker of beta cell maturity, it is not established whether UCN3 is required for beta cell maturation. Here, we compared gene expression and function of beta cells from Ucn3-null mice relative to WT mice to determine whether beta cells are functionally mature in the absence of UCN3. Our results show that genetic deletion of Ucn3 does not cause a loss of beta cell maturity or an increase in beta cell dedifferentiation. Furthermore, virgin beta cells, first identified as insulin-expressing, UCN3-negative beta cells, can still be detected at the islet periphery in Ucn3-null mice. Beta cells from Ucn3-null mice also exhibit normal calcium response when exposed to high glucose. Collectively, these observations indicate that UCN3 is an excellent mature beta cell marker that is nevertheless not necessary for beta cell maturation.
Julian C Lui
The resting zone houses a group of slowly proliferating ‘reserve’ chondrocytes and has long been speculated to serve as the stem cell niche of the postnatal growth plate. But are these resting chondrocytes bona fide stem cells? Recent technological advances in lineage tracing and next-generation sequencing have finally allowed researchers to answer this question. Several recent studies have also shed light into the signaling pathways and molecular mechanisms involved in the maintenance of resting chondrocytes, thus providing us with important new insights into the role of the resting zone in the paracrine and endocrine regulation of childhood bone growth.
Bethany R L Aykroyd, Simon J Tunster, and Amanda N Sferruzzi-Perri
The placenta regulates materno-fetal nutrient transfer and secretes hormones that enable maternal physiological support of the pregnancy. In mice, these functions are performed by the labyrinth (Lz) and junctional (Jz) zones, respectively. Insulin-like growth factor 2 (Igf2) is an imprinted gene expressed by the conceptus that is important for promoting fetal growth and placenta formation. However, the specific role of Igf2 in the Jz in regulating placental endocrine function and fetal development is unknown. This study used a novel model to investigate the effect of conditional loss of Igf2 in the Jz (Jz-Igf2UE) on placental endocrine cell formation and the expression of hormones and IGF signaling components in placentas from female and male fetuses. Jz-Igf2UE altered gross placental structure and expression of key endocrine and signaling genes in a sexually dimorphic manner. The volumes of spongiotrophoblast and glycogen trophoblast in the Jz were decreased in placentas from female but not male fetuses. Expression of insulin receptor was increased and expression of the MAPK pathway genes (Mek1, P38α) decreased in the placental Jz of female but not male fetuses. In contrast, expression of the type-1 and -2 IGF receptors and the MAPK pathway genes (H-ras, N-ras, K-ras) was decreased in the placental Jz from male but not female fetuses. Expression of the steroidogenic gene, Cyp17a1, was increased and placental lactogen-2 was decreased in the placenta of both sexes. In summary, we report that Jz-Igf2UE alters the cellular composition, IGF signaling components and hormone expression of the placental Jz in a manner largely dependent on fetal sex.
Kehinde Samuel Olaniyi and Lawrence Aderemi Olatunji
Adipose dysfunction and inflammation with or without hepatic defects underlie metabolic obesity. Glutamine (GLU) improves glucoregulation and metabolic indices but its effects on adipose function and hepatic lipid deposition in estrogen-progestin oral contraceptive (EPOC) users are unknown. Therefore, we hypothesized that GLUT supplementation would protect against adipose dysfunction and excess hepatic lipid influx and deposition in EPOC-treated animals by suppressing adenosine deaminase/xanthine oxidase (ADA/XO) activity and improving glucose-6-phosphate dehydrogenase (G6PD)-dependent antioxidant defense. Female Wistar rats weighing 150–180 g were allotted into control, GLUT, EPOC and EPOC + GLUT groups (six rats/group). The groups received vehicle (distilled water, p.o.), GLUT (1 g/kg), EPOC containing 1.0 µg ethinylestradiol plus 5.0 µg levonorgestrel and EPOC plus GLUT, respectively, daily for 8 weeks. Results showed that the administration of EPOC caused glucose dysregulation and increased triglyceride-glucose index and visceral adiposity, but the body weight and liver weight were not affected. However, EPOC significantly decreased adipose lipid, G6PD and glutathione and increased glycogen synthesis, ADA, XO, uric acid, lipid peroxidation, lactate production and gamma-glutamyl transferase activity (GGT). On the other hand, EPOC increased hepatic lipid, ADA, XO, uric acid, lipid peroxidation and lactate production and decreased glycogen synthesis, G6PD and glutathione. Nevertheless, supplementation with glutamine attenuated these alterations. Collectively, the present results indicate that EPOC causes metabolically induced obesity which is associated with adipose dysfunction and hepatic metabolic disturbance. The findings also suggest that glutamine confers metabo-protection with corresponding improvement in adipose and hepatic metabolic function by suppression of ADA/XO activity and enhancement of G6PD-dependent antioxidant defense.
Yue Yu, Rui Guo, Yunjin Zhang, Hongbo Shi, Haoran Sun, Xia Chu, Xiaoyan Wu, Huimin Lu, and Changhao Sun
Chronic exposure of pancreatic β-cells to saturated fatty acid (palmitic or stearic acid) is a leading cause of impaired insulin secretion. However, the molecular mechanisms underlying stearic-acid-induced β-cell dysfunction remain poorly understood. Emerging evidence indicates that miRNAs are involved in various biological functions. The aim of this study was to explore the differential expression of miRNAs and mRNAs, specifically in stearic-acid-treated- relative to palmitic-acid-treated β-cells, and to establish their co-expression networks. β-TC-6 cells were treated with stearic acid, palmitic acid or normal medium for 24 h. Differentially expressed miRNAs and mRNAs were identified by high-throughput sequencing and bioinformatic analysis. Co-expression network, gene ontology (GO) and pathway analyses were then conducted. Changes in the expression of selected miRNAs and mRNAs were verified in β-TC-6 cells and mouse islets. Sequencing analysis detected 656 known and 1729 novel miRNAs. miRNA-mRNA network and Venn-diagram analysis yielded two differentially expressed miRNAs and 63 mRNAs exclusively in the stearic-acid group. miR-374c-5p was up-regulated by a 1.801 log2(fold-change) and miR-297b-5p was down-regulated by a −4.669 log2(fold-change). We found that miR-297b-5p and miR-374c-5p were involved in stearic-acid-induced lipotoxicity to β-TC-6 cells. Moreover, the effects of miR-297b-5p and miR-374c-5p on the alterations of candidate mRNAs expressions were verified. This study indicates that expression changes of specific miRNAs and mRNAs may contribute to stearic-acid-induced β-cell dysfunction, which provides a preliminary basis for further functional and molecular mechanism studies of stearic-acid-induced β-cell dysfunction in the development of type 2 diabetes.
Lei Yu, Haoran Wang, Xiaoxue Han, Honghui Liu, Dalong Zhu, Wenhuan Feng, Jinhui Wu, and Yan Bi
Non-alcoholic fatty liver disease (NAFLD) is difficult to manage due to the lack of effective treatments. Increased oxygen consumption caused by overnutrition, along with reduced oxygen delivery to liver cells induces hepatic steatosis. Here, we investigated the efficacy of oxygen therapy (OT) to alleviate hepatic steatosis. The effect of OT on hepatic steatosis was evaluated in high-fat-diet (HFD)-fed mice and palmitic acid (PA)-treated primary hepatocytes. Liver biopsy tissue samples were used to determine the relationship between the expression of hypoxia-inducible factor-2α (HIF-2α) and the progression of NAFLD. The role of HIF-2α in the OT group was determined based on the overexpression of HIF-2α in vitro. OT safely alleviated hepatic hypoxia and improved hepatic steatosis by inhibiting hepatic de novo lipogenesis in HFD-fed mice and PA-treated primary hepatocytes, and this was accompanied by reduced expression of HIF-2α and hepatic de novo lipogenesis. The analysis of liver tissues from individuals with or without NAFLD revealed a positive correlation between hepatic HIF-2α expression and NAFLD progression. Overexpression of HIF-2α in vitro inhibited the beneficial effect of OT against hepatic lipogenesis and steatosis. OT might be a viable treatment option for NAFLD and functions by alleviating hypoxia and inhibiting the liver HIF-2α signaling pathway.
Lisa L Koorneef, Jan Kroon, Eva M G Viho, Lucas F Wahl, Kim M L Heckmans, Marloes M A R van Dorst, Menno Hoekstra, René Houtman, Hazel Hunt, and Onno C Meijer
Glucocorticoids mediate numerous essential processes in the human body via binding to the glucocorticoid receptor (GR). Excessive GR signaling can cause disease, and GR antagonists can be used to treat many symptoms of glucocorticoid-induced pathology. The purpose of this study was to characterize the tissue-specific properties of the selective GR antagonist CORT125281. We evaluated the antagonistic effects of CORT125281 upon acute and subchronic corticosterone exposure in mice. In the acute corticosterone setting, hypothalamus-pituitary-adrenal-axis activity was investigated by measurement of basal- and stress-induced corticosterone levels, adrenocorticotropic hormone levels and pituitary proopiomelanocortin expression. GR signaling was evaluated by RT-PCR analysis of GR-responsive transcripts in liver, muscle, brown adipose tissue (BAT), white adipose tissue (WAT) and hippocampus. Pretreatment with a high dose of CORT125281 antagonized GR activity in a tissue-dependent manner. We observed complete inhibition of GR-induced target gene expression in the liver, partial blockade in muscle and BAT and no antagonism in WAT and hippocampus. Tissue distribution only partially explained the lack of effective antagonism. CORT125281 treatment did not disinhibit the hypothalamus-pituitary-adrenal neuroendocrine axis. In the subchronic corticosterone setting, CORT125281 partially prevented corticosterone-induced hyperinsulinemia, but not hyperlipidemia and immune suppression. In conclusion, CORT125281 antagonizes GR transcriptional activity in a tissue-dependent manner and improves corticosterone-induced hyperinsulinemia. Tailored dosing of CORT125281 may allow tissue-specific inhibition of GR transcriptional activity.
Alejandra Abeledo-Machado, Pablo Anibal Pérez, María Andrea Camilletti, Erika Yanil Faraoni, Florencia Picech, Juan Pablo Petiti, Silvina Gutiérrez, and Graciela Diaz-Torga
Serum prolactin levels gradually increase from birth to puberty in both male and female rats, with higher levels observed in female since the first days of life. The increase in lactotroph secretion was attributed to the maturation of prolactin-inhibiting and prolactin-releasing factors; however, those mechanisms could not fully explain the gender differences observed. Prolactin secretion from isolated lactotrophs, in the absence of hypothalamic control, also increases during the first weeks of life, suggesting the involvement of intra-pituitary factors. We postulate that pituitary transforming growth factor beta 1 (TGFβ1) is involved in the regulation of prolactin secretion as well as in the gender differences observed at early postnatal age. Several components of the local TGFβ1 system were evaluated during postnatal development (11, 23, and 45 days) in female and male Sprague–Dawley rats. In vivo assays were performed to study local TGFβ1 activation and its impact on prolactin secretion. At day 11, female pituitaries present high levels of active TGFβ1, concomitant with the highest expression of TGFβ1 target genes and the phospho-Smad3 immunostaining in lactotrophs. The steady increase in prolactin secretion inversely correlates with active TGFβ1 levels only in females. Dopamine and estradiol induce TGFβ1 activation at day 11, in both genders, but its activation induces the inhibition of prolactin secretion only in females. Our findings demonstrate that: (1) TGFβ1 activation is regulated by dopamine and estradiol; (2) the inhibitory regulation of local TGFβ1 on prolactin secretion is gender specific; and (3) this mechanism is responsible, at least partially, for the gender differences observed being relevant during postnatal development.