Sex-dimorphic effects of glucose transporter-2 gene knockdown on hypothalamic primary astrocyte phosphoinositide-3-kinase (PI3K)/protein kinase B (PKB/Akt)/mammalian target of rapamycin (mTOR) cascade protein expression and phosphorylation.

Glucose transporter-2 (GLUT2), a unique high capacity/low affinity, highly efficient membrane transporter and sensor, regulates hypothalamic astrocyte glucose phosphorylation and glycogen metabolism. The phosphoinositide-3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling pathway participates in glucose homeostasis, but its sensitivity to glucose-sensory cues is unknown. Current research used a hypothalamic astrocyte primary culture model to investigate whether glucoprivation causes PI3K/Akt/mTOR pathway activation in one or both sexes by GLUT2-dependent mechanisms. Glucoprivation did not alter astrocyte PI3K levels, yet up-regulated both phosphorylated derivatives in female and down-regulated male p60 phosphoprotein expression. GLUT2 siRNA pretreatment diminished glucoprivic patterns of PI3K and phospho-PI3K expression in each sex. Astrocyte Akt and phospho-Akt/Thr308 proteins exhibited divergent, sex-contingent responses to GLUT2 gene knockdown or glucoprivation. GLUT2 siRNA pretreatment exacerbated glucoprivic-associated Akt diminution in the female, and either amplified (male) or reversed (female) glucoprivic regulation of phospho-Akt/Thr308 expression. GLUT2 gene silencing down- (male) or up-(female) regulated mTOR protein, and phospho-mTOR protein in male. Male astrocyte mTOR and phospho-mTOR profile were refractory to glucoprivation, but glucose-deprived females showed GLUT2-independent mTOR inhibition and GLUT2-dependent phospho-mTOR up-augmentation. Results identify a larger number of glucoprivic-sensitive PI3K/Akt/mTOR pathway proteins in female versus male astrocytes, and document divergent responses of common glucose-sensitive targets. GLUT2 stimulates phosphoPI3K protein expression in each sex, but imposes differential control of PI3K, Akt, phospho-Akt/Thr308, mTOR, and phospho-mTOR profiles in male versus female. Data implicate GLUT2 as a driver of distinctive pathway protein responses to glucoprivation in female, but not male.

Increase in the Expression of Glucose Transporter 2 (GLUT2) on the Peripheral Blood Insulin-Producing Cells (PB-IPC) in Type 1 Diabetic Patients after Receiving Stem Cell Educator Therapy.

Multicenter international clinical trials demonstrated the clinical safety and efficacy by using stem cell educator therapy to treat type 1 diabetes (T1D) and other autoimmune diseases. Previous studies characterized the peripheral blood insulin-producing cells (PB-IPC) from healthy donors with high potential to give rise to insulin-producing cells. PB-IPC displayed the molecular marker glucose transporter 2 (GLUT2), contributing to the glucose transport and sensing. To improve the clinical efficacy of stem cell educator therapy in the restoration of islet ß-cell function, we explored the GLUT2 expression on PB-IPC in recent onset and longstanding T1D patients. In the Food and Drug Administration (FDA)-approved phase 2 clinical studies, patients received one treatment with the stem cell educator therapy. Peripheral blood mononuclear cells (PBMC) were isolated for flow cytometry analysis of PB-IPC and other immune markers before and after the treatment with stem cell educator therapy. Flow cytometry revealed that both recent onset and longstanding T1D patients displayed very low levels of GLUT2 on PB-IPC. After the treatment with stem cell educator therapy, the percentages of GLUT2+CD45RO+ PB-IPC were markedly increased in these T1D subjects. Notably, we found that T1D patients shared common clinical features with patients with other autoimmune and inflammation-associated diseases, such as displaying low or no expression of GLUT2 on PB-IPC at baseline and exhibiting a high profile of the inflammatory cytokine interleukin (IL)-1ß. Flow cytometry demonstrated that their GLUT2 expressions on PB-IPC were also markedly upregulated, and the levels of IL-1ß-positive cells were significantly downregulated after the treatment with stem cell educator therapy. Stem cell educator therapy could upregulate the GLUT2 expression on PB-IPC and restore their function in T1D patients, leading to the improvement of clinical outcomes. The clinical data advances current understanding about the molecular mechanisms underlying the stem cell educator therapy, which can be expanded to treat patients with other autoimmune and inflammation-associated diseases.

Comparative evaluation of the antihyperglycemic effects of three extracts of sea mustard (Undaria pinnatifida): In vitro and in vivo studies.

Undaria pinnatifida (UP) contains multiple bioactive substances, such as polyphenols, polysaccharides, and amino acids, which are associated with various biological properties. This study aimed to evaluate the antihyperglycemic effects of three extracts obtained from UP. UP was extracted under three different conditions: a low-temperature water extract at 50 °C (UPLW), a high-temperature water extract at 90 °C (UPHW), and a 70 % ethanol extract (UPE). Nontargeted chemical profiling using high-performance liquid chromatography-triple/time-of-flight mass spectrometry (HPLC-Triple TOF-MS/MS) was conducted on the three UP extracts. Subsequently, α-glucosidase inhibitory (AGI) activity, glucose uptake, and the mRNA expression of sodium/glucose cotransporter 1 (SGLT1) and glucose transporter 2 (GLUT2) were evaluated in Caco-2 cell monolayers. Furthermore, an oral carbohydrate tolerance test was performed on C57BL/6 mice. The mice were orally administered UP at 300 mg/kg body weight (B.W.), and the blood glucose level and area under the curve (AUC) were measured. Compared with glucose, UPLW, UPHW and UPE significantly inhibited both glucose uptake and the mRNA expression of SGLT1 and GLUT2 in Caco-2 cell monolayers. After glucose, maltose, and sucrose loading, the blood glucose levels and AUC of the UPLW group were significantly lower than those of the control group. These findings suggest that UPLW has antihyperglycemic effects by regulating glucose uptake through glucose transporters and can be expected to alleviate postprandial hyperglycemia. Therefore, UPLW may have potential as a functional food ingredient for alleviating postprandial hyperglycemia.

Bisphenol a accelerates the glucolipotoxicity-induced dysfunction of rat insulinoma cell lines: An implication for a potential risk of environmental bisphenol a exposure for individuals susceptible to type 2 diabetes.

Epidemiological studies have suggested a correlation between bisphenol A (BPA) and type 2 diabetes (T2DM). The effects of BPA on ß-cell dysfunction may reveal the risks from an in vitro perspective. We used the rat insulinoma (INS-1) cell lines (a type of ß-cells) to set up normal or damaged models (DM), which were exposed to various concentrations of BPA (0.001, 0.01, 0.1, 1, 10 and 100 µM). An increase in reactive oxygen species (ROS) and apoptosis, and a decrease in cell viability were observed in INS-1 cells exposed to high doses of BPA for 48 h. Interestingly, exposure to lower doses of BPA for 24 h resulted in increased ROS levels and apoptosis rates in INS-1 in the DM group, along with decreased cell viability, suggesting that BPA exerts toxicity to INS-1 cells, particularly to the DM group. Insulin levels and Glut2 expression, glucose consumption, intracellular Ca2+ and insulin secretion were increased in INS-1 cells after 48 h exposure to high dose of BPA. Stronger effects were observed in the DM group, even those exposed to low doses of BPA for 24 h. Moreover, BPA inhibited high glucose-stimulated insulin secretion in these cells. Our research suggests that low doses of BPA exacerbate the dysfunction caused by glucolipotoxicity, implying environmental BPA exposure poses a risk for individuals with prediabetes or T2DM.

Mixed-Lineage Leukaemia Gene Regulates Glucose-Sensitive Gene Expression and Insulin Secretion in Pancreatic Beta Cells.

The escalating prevalence of diabetes mellitus underscores the need for a comprehensive understanding of pancreatic beta cell function. Interest in glucose effectiveness has prompted the exploration of novel regulatory factors. The myeloid/lymphoid or mixed-lineage leukaemia gene (MLL) is widely recognised for its role in leukemogenesis and nuclear regulatory mechanisms through its histone methyltransferase activity in active chromatin. However, its function within pancreatic endocrine tissues remains elusive. Herein, we unveil a novel role of MLL in glucose metabolism and insulin secretion. MLL knockdown in ßHC-9 pancreatic beta cells diminished insulin secretion in response to glucose loading, paralleled by the downregulation of the glucose-sensitive genes SLC2a1 and SLC2a2. Similar observations were made in MLL heterozygous knockout mice (MLL+/-), which exhibited impaired glucose tolerance and reduced insulin secretion without morphological anomalies in pancreatic endocrine cells. The reduction in insulin secretion was independent of changes in beta cell mass or insulin granule morphology, suggesting the regulatory role of MLL in glucose-sensitive gene expression. The current results suggest that MLL interacts with circadian-related complexes to modulate the expression of glucose transporter genes, thereby regulating glucose sensing and insulin secretion. Our findings shed light on insulin secretion control, providing potential avenues for therapeutics against diabetes.

Glucose Transporters Are Key Components of the Human Glucostat.

Mouse models are extensively used in metabolic studies. However, inherent differences between the species, notably their blood glucose levels, hampered data translation into clinical settings. In this study, we confirmed GLUT1 to be the predominantly expressed glucose transporter in both adult and fetal human ß-cells. In comparison, GLUT2 is detected in a small yet significant subpopulation of adult ß-cells and is expressed to a greater extent in fetal ß-cells. Notably, GLUT1/2 expression in INS+ cells from human stem cell-derived islet-like clusters (SC-islets) exhibited a closer resemblance to that observed in fetal islets. Transplantation of primary human islets or SC-islets, but not murine islets, lowered murine blood glucose to the human glycemic range, emphasizing the critical role of ß-cells in establishing species-specific glycemia. We further demonstrate the functional requirements of GLUT1 and GLUT2 in glucose uptake and insulin secretion through chemically inhibiting GLUT1 in primary islets and SC-islets and genetically disrupting GLUT2 in SC-islets. Finally, we developed a mathematical model to predict changes in glucose uptake and insulin secretion as a function of GLUT1/2 expression. Collectively, our findings illustrate the crucial roles of GLUTs in human ß-cells, and identify them as key components in establishing species-specific glycemic set points.

The inflammatory injury of porcine small intestinal epithelial cells induced by deoxynivalenol is related to the decrease in glucose transport.

The present study aimed to investigate the effects of deoxynivalenol (DON) stimulation on inflammatory injury and the expression of the glucose transporters sodium-dependent glucose transporter 1 (SGLT1) and glucose transporter protein 2 (GLU2) in porcine small intestinal epithelial cells (IPEC-J2). Additionally, the study aimed to provide initial insights into the connection between the expression of glucose transporters and the inflammatory injury of IPEC-J2 cells. DON concentration and DON treatment time were determined using the CCK­8 assay. Accordingly, 1.0 µg/mL DON and treatment for 24 h were chosen for subsequent experiments. Then IPEC-J2 cells were treated without DON (CON, N = 6) or with 1 µg/mL DON (DON, N = 6). Lactate dehydrogenase (LDH) content, apoptosis rate, and proinflammatory cytokines including interleukin (IL)-1ß, Il-6, and tumor necrosis factor α (TNF-α) were measured. Additionally, the expression of AMP-activated protein kinase α1 (AMPK-α1), the content of glucose, intestinal alkaline phosphatase (AKP), and sodium/potassium-transporting adenosine triphosphatase (Na+/K+-ATPase) activity, and the expression of SGLT1 and GLU2 of IPEC-J2 cells were also analyzed. The results showed that DON exposure significantly increased LDH release and apoptosis rate of IPEC-J2 cells. Stimulation with DON resulted in significant cellular inflammatory damage, as evidenced by a significant increase in proinflammatory cytokines (IL-1ß, IL-6, and TNF-α). Additionally, DON caused damage to the glucose absorption capacity of IPEC-J2 cells, indicated by decreased levels of glucose content, AKP activity, Na+/K+-ATPase activity, AMPK-α1 protein expression, and SGLT1 expression. Correlation analysis revealed that glucose absorption capacity was negatively correlated with cell inflammatory cytokines. Based on the findings of this study, it can be preliminarily concluded that the cell inflammatory damage caused by DON may be associated with decreased glucose absorption.

Glucose is one of the most basic nutrients necessary to sustain animal life and plays a crucial role in animal body composition and energy metabolism. Previous studies suggested a link between glucose absorption and inflammatory injury. In the present study, deoxynivalenol (DON) stimulation caused severe inflammatory injury and reduced the glucose absorption capacity of IPEC-J2 cells. Pearson's correlation analysis revealed a negative correlation between glucose absorption capacity and cell inflammatory cytokines. Ultimately, it can be speculated that the cellular inflammatory response triggered by DON may be related to the altered expression of glucose transporters.

GLUT2 expression by glial fibrillary acidic protein-positive tanycytes is required for promoting feeding-response to fasting.

Feeding behavior is a complex process that depends on the ability of the brain to integrate hormonal and nutritional signals, such as glucose. One glucosensing mechanism relies on the glucose transporter 2 (GLUT2) in the hypothalamus, especially in radial glia-like cells called tanycytes. Here, we analyzed whether a GLUT2-dependent glucosensing mechanism is required for the normal regulation of feeding behavior in GFAP-positive tanycytes. Genetic inactivation of Glut2 in GFAP-expressing tanycytes was performed using Cre/Lox technology. The efficiency of GFAP-tanycyte targeting was analyzed in the anteroposterior and dorsoventral axes by evaluating GFP fluorescence. Feeding behavior, hormonal levels, neuronal activity using c-Fos, and neuropeptide expression were also analyzed in the fasting-to-refeeding transition. In basal conditions, Glut2-inactivated mice had normal food intake and meal patterns. Implementation of a preceeding fasting period led to decreased total food intake and a delay in meal initiation during refeeding. Additionally, Glut2 inactivation increased the number of c-Fos-positive cells in the ventromedial nucleus in response to fasting and a deregulation of Pomc expression in the fasting-to-refeeding transition. Thus, a GLUT2-dependent glucose-sensing mechanism in GFAP-tanycytes is required to control food consumption and promote meal initiation after a fasting period.

GLUT3 inhibitor discovery through in silico ligand screening and in vivo validation in eukaryotic expression systems.

The passive transport of glucose and related hexoses in human cells is facilitated by members of the glucose transporter family (GLUT, SLC2 gene family). GLUT3 is a high-affinity glucose transporter primarily responsible for glucose entry in neurons. Changes in its expression have been implicated in neurodegenerative diseases and cancer. GLUT3 inhibitors can provide new ways to probe the pathophysiological role of GLUT3 and tackle GLUT3-dependent cancers. Through in silico screening of an ~ 8 million compounds library against the inward- and outward-facing models of GLUT3, we selected ~ 200 ligand candidates. These were tested for in vivo inhibition of GLUT3 expressed in hexose transporter-deficient yeast cells, resulting in six new GLUT3 inhibitors. Examining their specificity for GLUT1-5 revealed that the most potent GLUT3 inhibitor (G3iA, IC50 ~ 7 µM) was most selective for GLUT3, inhibiting less strongly only GLUT2 (IC50 ~ 29 µM). None of the GLUT3 inhibitors affected GLUT5, three inhibited GLUT1 with equal or twofold lower potency, and four showed comparable or two- to fivefold better inhibition of GLUT4. G3iD was a pan-Class 1 GLUT inhibitor with the highest preference for GLUT4 (IC50 ~ 3.9 µM). Given the prevalence of GLUT1 and GLUT3 overexpression in many cancers and multiple myeloma's reliance on GLUT4, these GLUT3 inhibitors may discriminately hinder glucose entry into various cancer cells, promising novel therapeutic avenues in oncology.

Evidence for a Genotype-Phenotype Correlation in Patients with Pathogenic GLUT2 (SLC2A2) Variants.

Fanconi-Bickel syndrome (FBS) is a very rare but distinct clinical entity with the combined features of hepatic glycogen storage disease, generalized proximal renal tubular dysfunction with disproportionately severe glucosuria, and impaired galactose tolerance. Here, we report five cases (out of 93 diagnosed in our lab) with pathogenic variants on both GLUT2 (SLC2A2) alleles. They come from 3 families and presented with an exceptionally mild clinical course. This course was correlated to data from old and most recent expression and transport studies in Xenopus oocytes. GLUT2 genotype in patients 1 and 2 was p.[153_4delLI];[P417R] with the first variant exhibiting normal membrane expression and partially retained transport activity (5.8%) for 2-deoxyglucose. In patient 3, the very first GLUT2 variant ever detected (p.V197I) was found, but for the first time it was present in a patient in the homozygous state. This variant had also shown unaffected membrane expression and remarkable residual activity (8%). The genotype in patient 4, p.[153_4delLI];[(E440A)], again included the 2-amino-acid deletion with residual transporter function, and patient 5 is the first found to be homozygous for this variant. Our results provide further evidence for a genotype-phenotype correlation in patients with GLUT2 variants; non-functional variants result in the full picture of FBS while dysfunctional variants may result in milder presentations, even glucosuria only, without other typical signs of FBS.

The Roles of Liver Inflammation and the Insulin Signaling Pathway in PM2.5 Instillation-Induced Insulin Resistance in Wistar Rats.

To elucidate the mechanism of how the liver participates in PM2.5-caused insulin resistance. A novel Wistar rat model was developed in this study by instilling a suspension of lyophilized PM2.5 sample (2.5 mg/kg, 5 mg/kg, or 10 mg/kg) collected from the atmosphere. Systemic insulin resistance indicators, including serum fasting blood glucose (FBG), fasting insulin (FINS), Homeostatic Model Assessment for Insulin Resistance (HOMA-IR), and hemoglobin A1 (HbA1), were upregulated by the PM2.5 instillation. The area under the curve (AUCglu) calculated by intraperitoneal glucose tolerance testing (IPGTT) was also significantly greater in the PM2.5 instillation groups. Additionally, PM2.5 instillation was found to cause liver damage and inflammation. The serum levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), total bilirubin (TBIL), tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6) were significantly elevated by PM2.5 instillation. PM2.5 also triggered IL-6 and TNF-α transcription but inhibited mRNA synthesis and suppressed signaling activation of the insulin-phosphoinositide 3-kinase- (PI3K-) Akt-glucose transporter 2 (GLUT2) pathway in the rat liver by reducing the ratio of phosphorylated Akt to phosphorylated insulin receptor substrate 1 (IRS-1). Thus, PM2.5-induced inflammation activation and insulin signaling inhibition in the rat liver contribute to the development of systemic insulin resistance.

Co-expression and prognosis analyses of GLUT1-4 and RB1 in breast cancer.

BACKGROUND: Current treatment methods for patients with triple-negative breast cancer (TNBC) are very limited, and the prognosis of TNBC is relatively poor. It has been reported that glucose transporter 1 (GLUT1) is overexpressed in breast cancer cells; however, its association with the prognosis is mostly unclear. Moreover, retinoblastoma gene 1 (RB1) might be used as a biomarker for the sensitivity of breast cancer cells to GLUT1 inhibitors, which brought us to the hypothesis that there might be a close correlation between the expression of GLUT1-4 and the expression of RB1. METHODS: In this study, we systematically analyzed the co-expression of GLUT1-4 and the influence of GLUT1-4 gene expression on the prognosis of breast cancer using data mining methods. We also explored possible relationships between GLUT1-4 and RB1 expression in breast cancer tissues. We used public databases such as ONCOMINE, GEPIA, LinkedOmics, and COEXPEDIA. RESULTS: According to the results, the mRNA expression of SLC2A1 was significantly higher in breast cancer, while the expression levels of SLC2A2-4 were downregulated. The results also indicate that GLUT1 expression does not have significant influence on the overall survival of patients with breast cancer. The mRNA expression of SLC2A1 and RB1 is significantly correlated, which means that tissues with high RB1 mRNA expression might have relatively higher mRNA expression of SLC2A1; however, further study analyzing their roles in the expression regulation pathways with human samples is needed to verify the hypothesis. CONCLUSIONS: The mRNA expression of SLC2A1 was significantly higher in breast cancer. The overall survival of breast cancer patients wasn't significantly correlated with GLUT1-4 expression. The mRNA expression of SLC2A1 and RB1 is significantly correlated according to the analysis conducted in LinkedOmics. It provides reference for future possible individualized treatment of TNBC using GLUT1 inhibitors, especially in patients with higher mRNA expression of RB1. Further study analyzing the roles of these two genes in the regulation pathways is needed.

Storage and Utilization of Glycogen by Mouse Liver during Adaptation to Nutritional Changes Are GLP-1 and PASK Dependent.

Glucagon-like peptide 1 (GLP-1) and PAS kinase (PASK) control glucose and energy homeostasis according to nutritional status. Thus, both glucose availability and GLP-1 lead to hepatic glycogen synthesis or degradation. We used a murine model to discover whether PASK mediates the effect of exendin-4 (GLP-1 analogue) in the adaptation of hepatic glycogen metabolism to nutritional status. The results indicate that both exendin-4 and fasting block the Pask expression, and PASK deficiency disrupts the physiological levels of blood GLP1 and the expression of hepatic GLP1 receptors after fasting. Under a non-fasted state, exendin-4 treatment blocks AKT activation, whereby Glucokinase and Sterol Regulatory Element-Binding Protein-1c (Srebp1c) expressions were inhibited. Furthermore, the expression of certain lipogenic genes was impaired, while increasing Glucose Transporter 2 (GLUT2) and Glycogen Synthase (GYS). Moreover, exendin-4 treatment under fasted conditions avoided Glucose 6-Phosphatase (G6pase) expression, while maintaining high GYS and its activation state. These results lead to an abnormal glycogen accumulation in the liver under fasting, both in PASK-deficient mice and in exendin-4 treated wild-type mice. In short, exendin-4 and PASK both regulate glucose transport and glycogen storage, and some of the exendin-4 effects could therefore be due to the blocking of the Pask expression.

Piperlongumine attenuates oxidative stress, inflammatory, and apoptosis through modulating the GLUT-2/4 and AKT signaling pathway in streptozotocin-induced diabetic rats.

The current study was done to measure the role of piperlongumine (PL) on hyperglycemia interrelated oxidative stress-mediated inflammation and apoptosis, inflammatory stress, and the diabetic insulin receptor substrate 2 (IRS2), protein kinase B (AKT), and glucose transporter 2 (GLUT-2)/4 signaling pathway in streptozotocin (STZ)-persuaded diabetic animals. Diabetes was initiated in experimental animals via a single dose intraperitoneal inoculation of STZ. Diabetic rats revealed an augmented blood-glucose level with drastically diminished plasma-insulin status. The functions of antioxidants were diminished with enhanced lipid peroxidation, conjugated dienes, and protein carbonyls noticed in diabetic rats'  plasma and pancreatic tissues. An elevation of nuclear factor-κB (NF-κB), tumor necrosis factor-α, and interleukin-6 proteins was noticed in pancreatic tissues as well as IRS2, AKT, GLUT-2, and GLUT-4 marker expressions were quantified in the hepatic tissue of control and diabetic rats. Oral administration of PL for 30 days drastically lowered glucose and higher insulin status in STZ-induced diabetic rats. Impressively, PL oral supplementation considerably restored the antioxidant levels and reduced inflammation and diabetic marker expressions in STZ-diabetic rats. These results were supported through a histological study. Moreover, PL also augmented the level of B-cell lymphoma 2 and diminished the level of Bcl-2-associated X protein in STZ-treated rat's hepatic tissues. Thus, we concluded that PL excellently rescued pancreatic ß cells through mitigating hyperglycemia via dynamic insulin secretion, activating antioxidants, and inhibiting inflammation and apoptosis in the pancreatic and hepatic tissue of diabetic rats.

Specific Lactobacillus probiotic strains decrease transepithelial glucose transport through GLUT2 downregulation in intestinal epithelial cell models.

Although human clinical studies have suggested probiotic effects on blood glucose levels, knowledge about molecular mechanisms is still scarce. To test the hypothesis that selected Lactobacillus probiotic bacteria could regulate the activity of enterocyte glucose transporters, we aimed to measure in vitro effects of selected Lactobacillus probiotic bacteria on transcription and translation of intestinal glucose transporters sodium-dependent glucose cotransporter 1 (SGLT1) and glucose transporter 2 (GLUT2) as well as transepithelial glucose transport. Lactobacillus plantarum strains (PCS20 and PCS26), Lactobacillus rhamnosus GG (LGG) (ATCC 53103) and Lactobacillus acidophilus (L acidophilus) (ATCC 4356) were co-cultivated with noncarcinogenic porcine enterocytes (CLAB) and human epithelial colorectal adenocarcinoma cells (Caco-2) (ATCC HTB-37). Changes in transcription and expression of SGLT1 and GLUT2 were strain and cell line-specific. In CLAB, LGG was the most potent SGLT1 up-regulator, and PCS26 the most potent down-regulator of GLUT2 transcription, which was also reflected on the protein level. In Caco-2, all tested strains tended to downregulate GLUT2 gene expression, while L acidophilus most effectively reduced GLUT2 protein levels. Statistically significant effect of PCS26 and L acidophilus on GLUT2 molecular and protein levels in CLAB and Caco-2 cell lines, respectively, was also followed by a decreased rate of transepithelial glucose transport. Careful selection of specific Lactobacillus probiotic strains could be used to downregulate glucose absorption in intestinal epithelial cells and thereby could be beneficial as a support treatment of pathologies related to glucose homeostasis.

Insulinoma induces a hyperinsulinemia-mediated decrease of GLUT2 and GLP1 receptor in normal pancreatic ß-cells.

There have been several clinical reports of transient postoperative hyperglycemia in patients with insulinoma, but the effect of insulinoma on normal ß-cells has not been investigated. We examined the glucose transporter 2 (GLUT2) and glucagon-like peptide 1 receptor (GLP1R) expression in normal pancreatic ß-cells of five patients with insulinoma and five patients with normal glucose tolerance (NGT) as controls. The positive rate of GLUT2-or GLP1R-positive islets in the nontumor area was calculated by the ratio with the analyzed islets. For functional in vitro analyses, q-PCR and Western blotting were performed after insulin loading on MIN6 cells. The expression rates of both GLUT2 and GLP1R were significantly lower in nontumor area islets of insulinoma patients than in patients with NGT (GLUT2: 31.6 ± 15.3% vs 95.9 ± 6.7%, p < 0.01, GLP1R: 66.8 ± 15.0% vs 96.7 ± 5.0%, p < 0.01). Exposure of MIN6 cells to high concentrations of insulin resulted in a significant decrease in GLUT2 protein for 12 h and GLP1R protein for 24 h (GLUT2; 1.00 ± 0.079 vs 0.81 ± 0.04. p = 0.02, GLP1R; 1.00 ± 0.10 vs 0.50 ± 0.24, p = 0.03) but not in those mRNAs. Our findings show that insulinoma is associated with the downregulation of GLUT2 and GLP1R expression in nontumor area islets. These phenomena may be caused by high levels of insulin.

Berberine Decreases Intestinal GLUT2 Translocation and Reduces Intestinal Glucose Absorption in Mice.

Postprandial hyperglycemia is an important causative factor of type 2 diabetes mellitus, and permanent localization of intestinal GLUT2 in the brush border membrane is an important reason of postprandial hyperglycemia. Berberine, a small molecule derived from Coptidis rhizome, has been found to be potent at lowering blood glucose, but how berberine lowers postprandial blood glucose is still elusive. Here, we investigated the effect of berberine on intestinal glucose transporter 2 (GLUT2) translocation and intestinal glucose absorption in type 2 diabetes mouse model. Type 2 diabetes was induced by feeding of a high-fat diet and injection of streptozotocin and diabetic mice were treated with berberine for 6 weeks. The effects of berberine on intestinal glucose transport and GLUT2 translocation were accessed in isolated intestines and intestinal epithelial cells (IEC-6), respectively. We found that berberine treatment improved glucose tolerance and systemic insulin sensitivity in diabetic mice. Furthermore, berberine decreased intestinal glucose transport and inhibited GLUT2 translocation from cytoplasm to brush border membrane in intestinal epithelial cells. Mechanistically, berberine inhibited intestinal insulin-like growth factor 1 (IGF-1R) phosphorylation and thus reduced localization of PLC-ß2 in the membrane, leading to decreased GLUT2 translocation. These results suggest that berberine reduces intestinal glucose absorption through inhibiting IGF-1R-PLC-ß2-GLUT2 signal pathway.

Autoimmune activation of the GnRH receptor induces insulin resistance independent of obesity in a female rat model.

Polycystic ovary syndrome (PCOS), a metabolic and reproductive disease, is frequently associated with type 2 diabetes. We have demonstrated activating autoantibodies (AAb) directed toward the second extracellular loop (ECL2) of the gonadotropin-releasing hormone receptor (GnRHR) are present in a significant subgroup of PCOS patients. It is unclear whether GnRHR-AAb can induce peripheral tissue insulin resistance (IR) in animal models. Sixteen rats were divided equally into a GnRHR ECL2 peptide-immunized group (IMM group) and a control group (CON group). Sera GnRHR-AAb titer, luteinizing hormone (LH), and testosterone (T) were higher in IMM rats compared with CON rats. No significant difference in fasting blood glucose was observed between the two groups. However, the plasma glucose level at other time points of the IMM group was higher than that of the CON group during an intraperitoneal glucose tolerance test (IPGTT) and an insulin tolerance test (ITT) (p < 0.01). These data support the likelihood of the GnRHR-AAb induction of glucose intolerance and IR. Compared with the CON group, the IMM group showed a significant increase in insulin-stimulated phosphorylation of IRS-1 (p-IRS-1 S636/639) and a decrease in insulin-stimulated phosphorylation of Akt (p-AKT S473). Expression of the glucose transport genes including GLUT-2 in liver and GLUT-4 in white adipose tissue and skeletal muscle was significantly decreased in IMM rats compared with the CON rats. Serum levels of proinflammatory cytokines (TNF-α, IL-1α, and IL-18) were increased, while anti-inflammatory cytokines (IL-4 and IL-10) were decreased in the IMM group. Taken together, elevated GnRHR-AAb enhanced LH, hyperandrogenism, and inflammation. These changes are likely related to the observed peripheral tissue IR through the downregulation of the insulin-stimulated IRS/PI3K/Akt/Glut signaling pathway.

Intestinal stem cell-derived enteroids from morbidly obese patients preserve obesity-related phenotypes: Elevated glucose absorption and gluconeogenesis.

OBJECTIVE: The mechanisms behind the efficacy of bariatric surgery (BS) for treating obesity and type 2 diabetes, particularly with respect to the influence of the small bowel, remain poorly understood. In vitro and animal models are suboptimal with respect to their ability to replicate the human intestinal epithelium under conditions induced by obesity. Human enteroids have the potential to accelerate the development of less invasive anti-obesity therapeutics if they can recapitulate the pathophysiology of obesity. Our aim was to determine whether adult stem cell-derived enteroids preserve obesity-characteristic patient-specific abnormalities in carbohydrate absorption and metabolism. METHODS: We established 24 enteroid lines representing 19 lean, overweight, or morbidly obese patients, including post-BS cases. Dietary glucose absorption and gluconeogenesis in enteroids were measured. The expression of carbohydrate transporters and gluconeogenic enzymes was assessed and a pharmacological approach was used to dissect the specific contribution of each transporter or enzyme to carbohydrate absorption and metabolism, respectively. RESULTS: Four phenotypes representing the relationship between patients' BMI and intestinal dietary sugar absorption were found, suggesting that human enteroids retain obese patient phenotype heterogeneity. Intestinal glucose absorption and gluconeogenesis were significantly elevated in enteroids from a cohort of obese patients. Elevated glucose absorption was associated with increased expression of SGLT1 and GLUT2, whereas elevated gluconeogenesis was related to increased expression of GLUT5, PEPCK1, and G6Pase. CONCLUSIONS: Obesity phenotypes preserved in human enteroids provide a mechanistic link to aberrant dietary carbohydrate absorption and metabolism. Enteroids can be used as a preclinical platform to understand the pathophysiology of obesity, study the heterogeneity of obesity mechanisms, and identify novel therapeutics.

O6-methylguanine DNA methyltransferase and glucose transporter 2 in foregut and hindgut gastrointestinal neuroendocrine neoplasms.

BACKGROUND: Streptozocin (STZ) is used for treating both pancreatic (PanNET) and gastrointestinal (GI-NET) neuroendocrine tumors but its therapeutic efficacy is relatively low in GI-NETs. Therefore, it has become pivotal to select GI-NET patients who could benefit from STZ treatment. STZ is transported via the glucose transporter 2 (GLUT2) into the cells and the loss of O6-methylguanine DNA methyltransferase (MGMT) also increases its therapeutic efficacy. Therefore, GLUT2 high and MGMT low status could be the surrogate markers of STZ. METHODS: In this study, we examined the MGMT and GLUT2 status in gastrointestinal neuroendocrine neoplasm (NEN). We studied 84 NEN cases: 33 foregut and 37 hindgut GI-NETs and 14 gastrointestinal neuroendocrine carcinomas (GI-NECs). RESULTS: In GI-NETs, MGMT scores of ≥2 and ≥ 3 were 77% (54/70) and 56% (39/70), respectively, and GLUT2 scores of ≥4 and ≥ 6 were 30% (21/70) and 4.3% (3/70), respectively. Methylation-specific polymerase chain reaction revealed that MGMT promoter methylation was detected only in 2/14 GI-NECs but none of the included GI-NETs. GLUT2 (GLUT2 score) and MGMT immunoreactivity (MGMT and H-scores) were both significantly correlated with Ki-67 labeling index (GLUT2 score: P = 0.0045, ρ = - 0.4570; MGMT score: P = 0.0064, ρ = - 0.4399; H-score: P = 0.0110, ρ = - 0.4135) and MGMT immunoreactivity were significantly correlated with GLUT2 immunoreactivity (MGMT score: P = 0.0198; H-score, P = 0.0004, ρ = 0.5483) in hindgut NETs, but not in foregut NETs. However, discrepancies from the above correlation between GLUT2 and MGMT immunoreactivity were detected in several GI-NET cases which could be potential candidates for STZ therapy. CONCLUSION: The evaluation of MGMT and GLUT2 status could provide an important information in planning STZ therapy in GI-NET patients.