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.

Nuclear Receptor Corepressors NCOR1 and SMRT Regulate Metabolism via Intestinal Regulation of Carbohydrate Transport.

Nuclear receptor action is mediated in part by the nuclear receptor corepressor 1 (NCOR1) and the silencing mediator of retinoic acid and thyroid hormone receptor (SMRT). NCOR1 and SMRT regulate metabolic pathways that govern body mass, insulin sensitivity, and energy expenditure, representing an understudied area in the realm of metabolic health and disease. Previously, we found that NCOR1 and SMRT are essential for maintaining metabolic homeostasis and their knockout (KO) leads to rapid weight loss and hypoglycemia, which is not survivable. Because of a potential defect in glucose absorption, we sought to determine the role of NCOR1 and SMRT specifically in intestinal epithelial cells (IECs). We used a postnatal strategy to disrupt NCOR1 and SMRT throughout IECs in adult mice. These mice were characterized metabolically and underwent metabolic phenotyping, body composition analysis, and glucose tolerance testing. Jejunal IECs were isolated and profiled by bulk RNA sequencing. We found that the postnatal KO of NCOR1 and SMRT from IECs leads to rapid weight loss and hypoglycemia with a significant reduction in survival. This was accompanied by alterations in glucose metabolism and activation of fatty acid oxidation in IECs. Metabolic phenotyping confirmed a reduction in body mass driven by a loss of body fat without altered food intake. This appeared to be mediated by a reduction of key intestinal carbohydrate transporters, including SGLT1, GLUT2, and GLUT5. Intestinal NCOR1 and SMRT act in tandem to regulate glucose levels and body weight. This in part may be mediated by regulation of intestinal carbohydrate transporters.

A kidney-hypothalamus axis promotes compensatory glucose production in response to glycosuria.

The kidneys facilitate energy conservation through reabsorption of nutrients including glucose. Almost all the filtered blood glucose is reabsorbed by the kidneys. Loss of glucose in urine (glycosuria) is offset by an increase in endogenous glucose production to maintain normal energy supply in the body. How the body senses this glucose loss and consequently enhances glucose production is unclear. Using renal Slc2a2 (also known as Glut2) knockout mice, we demonstrate that elevated glycosuria activates the hypothalamic-pituitary-adrenal axis, which in turn drives endogenous glucose production. This phenotype was attenuated by selective afferent renal denervation, indicating the involvement of the afferent nerves in promoting the compensatory increase in glucose production. In addition, through plasma proteomics analyses we observed that acute phase proteins - which are usually involved in the body's defense mechanisms against a threat - were the top candidates which were either upregulated or downregulated in renal Slc2a2 KO mice. Overall, afferent renal nerves contribute to promoting endogenous glucose production in response to elevated glycosuria and loss of glucose in urine is sensed as a biological threat in mice. These findings may be useful in improving the efficiency of drugs like SGLT2 inhibitors that are intended to treat hyperglycemia by enhancing glycosuria but are met with a compensatory increase in endogenous glucose production.

Synaptotagmin-1 antagonizes paraquat intracellular accumulation and nephrocyte toxicity by up-regulating SERBP1/GLUT2 expression.

Acute kidney injury (AKI) is common and an independent risk factor for mortality in patients with paraquat (PQ) poisoning. Currently, no specific antidote is available. Synaptotagmin-1 (SYT1) has been identified as a key protein that facilitates PQ efflux in PQ-resistant A549 cells, thereby preventing PQ-induced lung injury. However, the protective effect of STY1 on PQ-induced AKI remains to be elucidated. This study exposed human kidney 2 (HK-2) cells overexpressing SYT1 to PQ. These cells exhibited significantly lower levels of growth inhibition, reactive oxygen species production, early apoptosis, and PQ accumulation compared to the parent HK-2 cells. Transcriptomic screening and Western blot analysis revealed that SYT1 overexpression significantly promoted the expression of glucose transporter 2 (GLUT2). Inhibition of GLUT2 completely abolished the protective effects of SYT1 overexpression in HK-2 cells and restored intracellular PQ concentrations. Further immunoprecipitation-shotgun and RNA interference experiments revealed that SYT1 binds to and stabilizes the protein SERPINE1 mRNA-binding protein 1 (SERBP1), enhancing the stability of GLUT2 mRNA and its protein levels. In summary, SYT1 antagonizes PQ intracellular accumulation and prevents nephrocyte toxicity by up-regulating SERBP1/GLUT2 expression. This study identifies a potential target for the treatment of PQ-induced AKI.

ß-Cell keratin 8 maintains islet mechanical integrity, mitochondrial ultrastructure, and ß-cell glucose transporter 2 plasma membrane targeting.

Islet ß-cell dysfunction is an underlying factor for type I diabetes (T1D) development. Insulin sensing and secretion are tightly regulated in ß-cells at multiple subcellular levels. The epithelial intermediate filament (IF) protein keratin (K) 8 is the main ß-cell keratin, constituting the filament network with K18. To identify the cell-autonomous functions of K8 in ß-cells, mice with targeted deletion of ß-cell K8 (K8flox/flox; Ins-Cre) were analyzed for islet morphology, ultrastructure, and integrity, as well as blood glucose regulation and streptozotocin (STZ)-induced diabetes development. Glucose transporter 2 (GLUT2) localization was studied in ß-cells in vivo and in MIN6 cells with intact or disrupted K8/K18 filaments. Loss of ß-cell K8 leads to a major reduction in K18. Islets without ß-cell K8 are more fragile, and these ß-cells display disjointed plasma membrane organization with less membranous E-cadherin and smaller mitochondria with diffuse cristae. Lack of ß-cell K8 also leads to a reduced glucose-stimulated insulin secretion (GSIS) response in vivo, despite undisturbed systemic blood glucose regulation. K8flox/flox, Ins-Cre mice have a decreased sensitivity to STZ compared with K8 wild-type mice, which is in line with decreased membranous GLUT2 expression observed in vivo, as GLUT2 is required for STZ uptake in ß-cells. In vitro, MIN6 cell plasma membrane GLUT2 is rescued in cells overexpressing K8/K18 filaments but mistargeted in cells with disrupted K8/K18 filaments. ß-Cell K8 is required for islet and ß-cell structural integrity, normal mitochondrial morphology, and GLUT2 plasma membrane targeting, and has implications on STZ sensitivity as well as systemic insulin responses.NEW & NOTEWORTHY Keratin 8 is the main cytoskeletal protein in the cytoplasmic intermediate filament network in ß-cells. Here for the first time, we assessed the ß-cell autonomous mechanical and nonmechanical roles of keratin 8 in ß-cell function. We demonstrated the importance of keratin 8 in islet and ß-cell structural integrity, maintaining mitochondrial morphology and GLUT2 plasma membrane targeting.

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.

Glucose transporter-2 regulation of VMN GABA neuron metabolic sensor and transmitter gene expression.

Glucose transporter-2 (GLUT2) monitors cellular glucose uptake. Astrocyte GLUT2 controls glucose counterregulatory hormone secretion. In vivo gene silencing and laser-catapult-microdissection tools were used here to investigate whether ventromedial hypothalamic nucleus (VMN) GLUT2 may regulate dorsomedial (VMNdm) and/or ventrolateral (VMNvl) γ-aminobutyric acid (GABA) neurotransmission to control this endocrine outflow in female rats. VMN GLUT2 gene knockdown suppressed or stimulated hypoglycemia-associated glutamate decarboxylase (GAD)1 and GAD2 mRNA expression in VMNdm versus VMNvl GABAergic neurons, respectively. GLUT2 siRNA pretreatment also modified co-expressed transmitter marker gene profiles in each cell population. VMNdm GABA neurons exhibited GLUT2 knockdown-sensitive up-regulated 5'-AMP-activated protein kinase-alpha1 (AMPKα1) and -alpha2 (AMPKα2) transcripts during hypoglycemia. Hypoglycemic augmentation of VMNvl GABA neuron AMPKα2 was refractory to GLUT2 siRNA. GLUT2 siRNA blunted (VMNdm) or exacerbated (VMNvl) hypoglycemic stimulation of GABAergic neuron steroidogenic factor-1 (SF-1) mRNA. Results infer that VMNdm and VMNvl GABA neurons may exhibit divergent, GLUT2-dependent GABA neurotransmission patterns in the hypoglycemic female rat. Data also document differential GLUT2 regulation of VMNdm versus VMNvl GABA nerve cell SF-1 gene expression. Evidence for intensification of hypoglycemic hypercorticosteronemia and -glucagonemia by GLUT2 siRNA infers that VMN GLUT2 function imposes an inhibitory tone on these hormone profiles in this sex.

Effects of Three Kinds of Carbohydrate Pharmaceutical Excipients-Fructose, Lactose and Arabic Gum on Intestinal Absorption of Gastrodin through Glucose Transport Pathway in Rats.

BACKGROUND: Some glucoside drugs can be transported via intestinal glucose transporters (IGTs), and the presence of carbohydrate excipients in pharmaceutical formulations may influence the absorption of them. This study, using gastrodin as probe drug, aimed to explore the effects of fructose, lactose, and arabic gum on intestinal drug absorption mediated by the glucose transport pathway. METHODS: The influence of fructose, lactose, and arabic gum on gastrodin absorption was assessed via pharmacokinetic experiments and single-pass intestinal perfusion. The expression of sodium-dependent glucose transporter 1 (SGLT1) and sodium-independent glucose transporter 2 (GLUT2) was quantified via RT‒qPCR and western blotting. Alterations in rat intestinal permeability were evaluated through H&E staining, RT‒qPCR, and immunohistochemistry. RESULTS: Fructose reduced the area under the curve (AUC) and peak concentration (Cmax) of gastrodin by 42.7% and 63.71%, respectively (P < 0.05), and decreased the effective permeability coefficient (Peff) in the duodenum and jejunum by 58.1% and 49.2%, respectively (P < 0.05). SGLT1 and GLUT2 expression and intestinal permeability remained unchanged. Lactose enhanced the AUC and Cmax of gastrodin by 31.5% and 65.8%, respectively (P < 0.05), and increased the Peff in the duodenum and jejunum by 33.7% and 26.1%, respectively (P < 0.05). SGLT1 and GLUT2 levels did not significantly differ, intestinal permeability increased. Arabic gum had no notable effect on pharmacokinetic parameters, SGLT1 or GLUT2 expression, or intestinal permeability. CONCLUSION: Fructose, lactose, and arabic gum differentially affect intestinal drug absorption through the glucose transport pathway. Fructose competitively inhibited drug absorption, while lactose may enhance absorption by increasing intestinal permeability. Arabic gum had no significant influence.

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.

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.

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.

The role of GLUT2 in glucose metabolism in multiple organs and tissues.

The glucose transporter family has an important role in the initial stage of glucose metabolism; Glucose transporters 2 (GLUTs, encoded by the solute carrier family 2, SLC2A genes) is the major glucose transporter in ß-cells of pancreatic islets and hepatocytes but is also expressed in the small intestine, kidneys, and central nervous system; GLUT2 has a relatively low affinity to glucose. Under physiological conditions, GLUT2 transports glucose into cells and allows the glucose concentration to reach balance on the bilateral sides of the cellular membrane; Variation of GLUT2 is associated with various endocrine and metabolic disorders; In this study, we discussed the role of GLUT2 in participating in glucose metabolism and regulation in multiple organs and tissues and its effects on maintaining glucose homeostasis.

Association Between the SLC2A2 Gene rs1499821 Polymorphism and Caries Susceptibility.

Objectives: This study was designed to analyze the association between the SLC2A2 rs1499821 polymorphism and caries susceptibility in the Chinese Han, Zhuang, and Baikuyao populations. Materials and Methods: The present case-control study included 1067 12-year-old children: 481 with caries (142 Han, 166 Zhuang and 173 Baikuyao) and 586 who were caries-free (135 Han, 178 Zhuang and 273 Baikuyao). Questionnaires about diet and oral habits were obtained from all subjects. All of the children received dental examinations and DNA collection. The SLC2A2 rs1499821 SNP was genotyped using the SNPscan technique. Results: The rs1499821 T polymorphism was significantly associated with caries susceptibility in both the Han population and the combined populations of the three ethnic subgroups. SLC2A2 rs1499821 was associated with caries susceptibility in the dominant model in the Han (p = 0.045) population and the combined (p = 0.038) group. The CT+TT genotypes at rs1499821 were associated with a higher risk of caries in the Han (OR = 1.69, adjusted 95% CI: 1.01-2.81) and combined (OR = 1.33, adjusted 95% CI: 1.02-1.74) populations. In both Han (p = 0.009) and the combined populations (p = 0.004), there were statistically significant associations between the frequency of sweet food intake and dental caries. However, the rs1499821 polymorphisms did not associate with the frequency of sweet food intake in these ethnic subgroups. Conclusion: In the Han population, the SLC2A2 rs1499821 T allele and the frequency of sweet food intake may be regarded as risk factors for caries susceptibility. The SLC2A2 rs1499821 T allele had no association with the frequency of sweet food intake in any of the three ethnic groups.

Clinical Study on the Relationship between the SNP rs8192675 (C/C) Site of SLC2A2 Gene and the Hypoglycemic Effect of Metformin in Type 2 Diabetes.

This study investigates the correlation between the gene polymorphism of rs8192675 (C/C) locus of SLC2A2 in patients with type 2 diabetes (T2DM) and the efficacy of metformin. For this purpose, we have selected 110 T2DM patients (T2DM group) and 110 healthy people (control group) who were treated in our hospital from January 2019 to January 2020 as the research subjects. PCR-restriction fragment length polymorphism (PCR-RFLP) method detects the distribution frequency of gene polymorphism. The patients in the T2DM group were treated with metformin and followed up for 90 days to analyze the relationship between the efficacy of metformin and the SLC2A2 gene polymorphism. The genotypes of SLC2A2 rs8192675 in the control group and in the T2DM group conformed to the Hardy-Weinberg equilibrium law. Compared with the control group, the CT type and the CC type at rs8192675 in the T2DM group were significantly higher (P < 0.05). For rs8192675, there was no significant difference in TT, CT, CC FPG, 2hPBG, and HbA1c levels before treatment (P > 0.05); after metformin treatment, the reduction in FPG, 2hPBG, and HbA1c in CC patients was lower than that of TT and CT patients (P < 0.05). SLC2A2 gene polymorphism site rs8192675 CC type T2DM patients are sensitive to metformin and have a better hypoglycemic effect.

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.

Cyanidin-3-rutinoside stimulated insulin secretion through activation of L-type voltage-dependent Ca2+ channels and the PLC-IP3 pathway in pancreatic ß-cells.

Cyanidin-3-rutinoside (C3R) is an anthocyanin with anti-diabetic properties found in red-purple fruits. However, the molecular mechanisms of C3R on Ca2+-dependent insulin secretion remains unknown. This study aimed to identify C3R's mechanisms of action in pancreatic ß-cells. Rat INS-1 cells were used to elucidate the effects of C3R on insulin secretion, intracellular Ca2+ signaling, and gene expression. The results showed that C3R at 60, 100, and 300 µM concentrations significantly increased insulin secretion via intracellular Ca2+ signaling. The exposure of cells with C3R concentrations up to 100 µM did not affect cell viability. Pretreatment of cells with nimodipine (voltage-dependent Ca2+ channel (VDCC) blocker), U73122 (PLC inhibitor), and 2-APB (IP3 receptor blocker) inhibited the intracellular Ca2+ signals by C3R. Interestingly, C3R increased intracellular Ca2+ signals and insulin secretion after depletion of endoplasmic reticulum Ca2+ stores by thapsigargin. However, insulin secretion was abolished under extracellular Ca2+-free conditions. Moreover, C3R upregulated mRNA expression for Glut2 and Kir6.2 genes. These findings indicate that C3R stimulated insulin secretion by promoting Ca2+ influx via VDCCs and activating the PLC-IP3 pathway. C3R also upregulates the expression of genes necessary for glucose-induced insulin secretion. This is the first study describing the molecular mechanisms by which C3R stimulates Ca2+-dependent insulin secretion from pancreatic ß-cells. These findings contribute to our understanding on how anthocyanins improve hyperglycemia in diabetic patients.

Murine remote ischemic preconditioning upregulates preferentially hepatic glucose transporter-4 via its plasma membrane translocation, leading to accumulating glycogen in the liver.

AIMS: We previously showed that hindlimb ischemia-reperfusion (IR) enhanced glucose uptake in the liver through the activation of the parasympathetic nervous system. Although we suggested that the key glucose transporter (GLUT) in this hepatic glucose uptake was GLUT4 by western blotting, the molecular weight of GLUT4 was nearly the same as that of GLUT2, which is predominantly expressed in the liver. We primarily conducted a histological evaluation to determine whether IR specifically accelerates the overexpression of GLUT4, rather than GLUT2, in the hepatocytes in vitro and in vivo. MAIN METHODS: A total of 54 male C57BL/6J mice were used and subjected to 3 min hindlimb ischemia repeated three times with 3 min interval. Focusing on the area connecting portal and central veins, the GLUT4 and GLUT2 expression in the hepatocytes were examined by real-time PCR and immunohistochemically. Moreover, the alteration of GLUT4 and GLUT2 expression by acetylcholine in the primary hepatocytes were examined by immunofluorescence. KEY FINDINGS: IR significantly upregulated the GLUT4, rather than GLUT2, expression in both mRNA and protein in the liver. Histological examination revealed marked glycogen storage in zone1, the periportal area, coincident with the enhanced GLUT4 immunoreactivity, in the IR-treated liver. Incubation of primary hepatocytes with acetylcholine induced the appearance of GLUT4 on the membrane peripheries. SIGNIFICANCE: The overexpression of GLUT4 on the membrane peripheries contributed to increasing glucose uptake found in IR-treated livers. This acceleration of glucose uptake via GLUT4 may induce marked glycogen storage in zone1 through energy production linked with increased glucose preference.

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.

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.

Differentiation of Human-Induced Pluripotent Stem Cell-Derived Endocrine Progenitors to Islet-like Cells Using a Dialysis Suspension Culture System.

The production of functional islet-like cells from human-induced pluripotent stem cells (hiPSCs) is a promising strategy for the therapeutic use and disease modeling for type 1 diabetes. However, the production cost of islet-like cells is extremely high due to the use of expensive growth factors for differentiation. In a conventional culture method, growth factors and beneficial autocrine factors remaining in the culture medium are removed along with toxic metabolites during the medium change, and it limits the efficient utilization of those factors. In this study, we demonstrated that the dialysis suspension culture system is possible to reduce the usage of growth factors to one-third in the differentiation of hiPSC-derived endocrine progenitor cells to islet-like cells by reducing the medium change frequency with the refinement of the culture medium. Furthermore, the expression levels of hormone-secretion-related genes and the efficiency of differentiation were improved with the dialysis suspension culture system, possibly due to the retaining of autocrine factors. In addition, we confirmed several improvements required for the further study of the dialysis culture system. These findings showed the promising possibility of the dialysis suspension culture system for the low-cost production of islet-like cells.