In arsenic-endemic regions of the world, arsenic exposure correlates with diabetes mellitus. Multiple animal models of inorganic arsenic (iAs, as As3+) exposure have revealed that iAs-induced glucose intolerance manifests as a result of pancreatic β-cell dysfunction. To define the mechanisms responsible for this β-cell defect, the MIN6-K8 mouse β-cell line was exposed to environmentally relevant doses of iAs. Exposure to 0.1–1 µM iAs for 3 days significantly decreased glucose-induced insulin secretion (GIIS). Serotonin and its precursor, 5-hydroxytryptophan (5-HTP), were both decreased. Supplementation with 5-HTP, which loads the system with bioavailable 5-HTP and serotonin, rescued GIIS, suggesting that recovery of this pathway was sufficient to restore function. Exposure to iAs was accompanied by an increase in mRNA expression of UDP-glucuronosyltransferase 1 family, polypeptide a6a ( Ugt1a6a), a phase-II detoxification enzyme that facilitates the disposal of cyclic amines, including serotonin, via glucuronidation. Elevated Ugt1a6a and UGT1A6 expression levels were observed in mouse and human islets, respectively, following 3 days of iAs exposure. Consistent with this finding, the enzymatic rate of serotonin glucuronidation was increased in iAs-exposed cells. Knockdown by siRNA of Ugt1a6a during iAs exposure restored GIIS in MIN6-K8 cells. This effect was prevented by blockade of serotonin biosynthesis, suggesting that the observed iAs-induced increase in Ugt1a6a affects GIIS by targeting serotonin or serotonin-related metabolites. Although it is not yet clear exactly which element(s) of the serotonin pathway is/are most responsible for iAs-induced GIIS dysfunction, this study provides evidence that UGT1A6A, acting on the serotonin pathway, regulates GIIS under both normal and pathological conditions.

Objective: Arsenic is an endocrine-disrupting chemical associated with diabetes risk. Increased adiposity is a significant risk factor for diabetes and its comorbidities. Here, the impact of chronic arsenic exposure on adiposity and metabolic health was assessed in mice. Methods: Male C57BL/6J mice were provided ad libitum access to a normal or high-fat diet and water +/− 50 mg/L of sodium arsenite. Changes in body weight, body composition, insulin sensitivity, energy expenditure, and locomotor activity were measured. Measures of adiposity were compared with accumulated arsenic in the liver. Results: Despite uniform arsenic exposure, internal arsenic levels varied significantly among arsenic-exposed mice. Hepatic arsenic levels in exposed mice negatively correlated with overall weight gain, individual adipose depot masses, and hepatic triglyceride accumulation. No effects were observed in mice on a normal diet. For mice on a high-fat diet, arsenic exposure reduced fasting insulin levels, homeostatic model assessment of insulin resistance and β-cell function, and systemic insulin resistance. Arsenic exposure did not alter energy expenditure or activity. Conclusions: Collectively, these data indicate that arsenic is antiobesogenic and that concentration at the source poorly predicts arsenic accumulation and phenotypic outcomes. In future studies, investigators should consider internal accumulation of arsenic rather than source concentration when assessing the outcomes of arsenic exposure.Obesity (2020) 28, 932-941.

Local modulation of glucocorticoid action in adipocytes regulates adiposity and systemic insulin sensitivity. However, the specific cofactors that mediate glucocorticoid receptor (GR) action in adipocytes remain unclear. Here we show that the silencing mediator of retinoid and thyroid hormone receptors (SMRT) is recruited to GR in adipocytes and regulates ligand-dependent GR function. Decreased SMRT expression in adipocytes in vivo increases expression of glucocorticoid-responsive genes. Moreover, adipocytes with decreased SMRT expression exhibit altered glucocorticoid regulation of lipolysis. We conclude that SMRT regulates the metabolic functions of GR in adipocytes in vivo. Modulation of GR-SMRT interactions in adipocytes represents a novel approach to control the local degree of glucocorticoid action and thus influence adipocyte metabolic function.

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Selenoproteins are a group of selenocysteine-containing proteins with major roles in cellular antioxidant defense and thyroid hormone metabolism. Selenoprotein expression is determined by hierarchical mechanisms that result in tissue-specific levels. Current data inadequately explain the abundance of various selenoproteins under normal and pathological conditions, including in pancreatic β-cells. Selenocysteine insertion sequence binding protein 2 (SBP2) is a critical protein in selenoprotein translation that also plays an essential role in stabilizing selenoprotein transcripts by antagonizing nonsense-mediated decay (NMD). Importantly, dysfunctional SBP2 is associated with endocrine disorders in humans. Here we describe the impact of induced Sbp2 deficiency in pancreatic β-cells on selenoprotein transcript profiles in the pancreatic islets of C57BL/6J mice. Sex differences were noted in control mice, in which female islets showed 5 selenoproteins decreased and one increased versus male islets. Induced Sbp2 deficiency in pancreatic β-cells altered expression of only 3 selenoprotein transcripts in male islets, whereas 14 transcripts were reduced in female islets. In all cases, decreased transcription was observed in genes known to be regulated by NMD. The differential impact of Sbp2 deletion on selenoprotein transcription between sexes suggests sex-specific hierarchical mechanisms of selenoprotein expression that may influence islet biology and consequentially metabolic disease risk.

Selenium is an essential trace element of interest for its potential role in glucose homeostasis. The present study investigated the impact of selenium supplementation as selenomethionine (SeMet) on insulin secretion in MIN6‐K8 cells, a pancreatic β‐cell model. We found that SeMet enhanced percent glucose‐induced insulin secretion, while also increasing tolbutamide‐ and KCl‐induced percent insulin secretion. RNA‐sequencing showed that SeMet supplementation altered expression of several selenoproteins, including glutathione peroxidase 3 (Gpx3) and selenoprotein P (SelP). Targeted knockdown of Gpx3 increased both percent and total insulin release, while SelP knockdown increased insulin content and insulin release. Collectively, these studies support a putative role for selenium and selenoproteins in the regulation of insulin secretion, glucose homeostasis, and diabetes risk.

Chronic arsenic exposure via drinking water is associated with diabetes in human pop-ulations throughout the world. Arsenic is believed to exert its diabetogenic effects via multiple mechanisms, including alterations to insulin secretion and insulin sensitivity. In the past, acute arsenicosis has been thought to be partially treatable with selenium supplementation, though a potential interaction between selenium and arsenic had not been evaluated under longer-term exposure models. The purpose of the present study was to explore whether selenium status may augment arsenic’s effects during chronic arsenic exposure. To test this possibility, mice were exposed to arsenic in their drinking water and provided ad libitum access to either a diet replete with selenium (Control) or deficient in selenium (SelD). Arsenic significantly improved glucose tolerance and decreased insulin secretion and β-cell function in vivo. Dietary selenium deficiency resulted in similar effects on glucose tolerance and insulin secretion, with significant interactions between arsenic and dietary conditions in select insulin-related parameters. The findings of this study highlight the complexity of arsenic’s metabolic effects and suggest that selenium deficiency may interact with arsenic exposure on β-cell-related physiological parameters.

In the original publication of the article, Figure 1 has been published with an error. Instead of the Greek symbol mu, the fraction 1/4 has been inserted into the y axis.The correct Fig. 1 is given in this correction.The original article has been updated.