Synaptotagmins family affect glucose transport in retinal pigment epithelial cells through their ubiquitination-mediated degradation and glucose transporter-1 regulation

BACKGROUND Synaptotagmins(SYTs)are a family of 17 membrane transporters that function as calcium ion sensors during the release of Ca2+-dependent neurotransmitters and hormones.However,few studies have reported whether members of the SYT family play a role in glucose uptake in diabetic retinopathy(DR)through Ca2+/glucose transporter-1(GLUT1)and the possible regulatory mechanism of SYTs.AIM To elucidate the role of the SYT family in the regulation of glucose transport in retinal pigment epithelial cells and explore its potential as a therapeutic target for the clinical management of DR.METHODS DR was induced by streptozotocin in C57BL/6J mice and by high glucose medium in human retinal pigment epithelial cells(ARPE-19).Bioinformatics analysis,reverse transcriptase-polymerase chain reaction,Western blot,flow cytometry,ELISA,HE staining,and TUNEL staining were used for analysis.RESULTS Six differentially expressed proteins(SYT2,SYT3,SYT4,SYT7,SYT11,and SYT13)were found between the DR and control groups,and SYT4 was highly expressed.Hyperglycemia induces SYT4 overexpression,manipulates Ca2+influx to induce GLUT1 fusion with the plasma membrane,promotes abnormal expression of the glucose transporter GLUT1 and excessive glucose uptake,induces ARPE-19 cell apoptosis,and promotes DR progression.Parkin deficiency inhibits the proteasomal degradation of SYT4 in DR,resulting in SYT4 accumulation and enhanced GLUT1 fusion with the plasma membrane,and these effects were blocked by oe-Parkin treatment.Moreover,dysregulation of the myelin transcription factor 1(Myt1)-induced transcription of SYT4 in DR further activated the SYT4-mediated stimulus-secretion coupling process,and this process was inhibited in the oe-MYT1-treated group.CONCLUSION Our study reveals the key role of SYT4 in regulating glucose transport in retinal pigment epithelial cells during the pathogenesis of DR and the underlying mechanism and suggests potential therapeutic targets for clinical DR.

Chlorogenic Acid Maintains Glucose Homeostasis through Modulating the Expression of SGLT-1,GLUT-2,and PLG in Different Intestinal Segments of Sprague-Dawley Rats Fed a High-Fat Diet

Objective To reveal the effects and related mechanisms of chlorogenic acid(CGA)on intestinal glucose homeostasis.Methods Forty male Sprague-Dawley rats were randomly and equally divided into four groups:normal chow(NC),high-fat diet(HFD),HFD with low-dose CGA(20 mg/kg,HFD-LC),and HFD with high-dose CGA(90 mg/kg,HFD-HC).The oral glucose tolerance test was performed,and fast serum insulin(FSI)was detected using an enzyme-linked immunosorbent assay.The m RNA expression levels of glucose transporters(Sglt-1 and Glut-2)and proglucagon(Plg)in different intestinal segments(the duodenum,jejunum,ileum,and colon)were analyzed using quantitative real-time polymerase chain reaction.SGLT-1 protein and the morphology of epithelial cells in the duodenum and jejunum was localized by using immunofluorescence.Results At both doses,CGA ameliorated the HFD-induced body weight gain,maintained FSI,and increased postprandial 30-min glucagon-like peptide 1 secretion.High-dose CGA inhibited the HFD-induced elevation in Sglt-1 expression.Both CGA doses normalized the HFD-induced downregulation of Glut-2 and elevated the expression of Plg in all four intestinal segments.Conclusion An HFD can cause a glucose metabolism disorder in the rat intestine and affect body glucose homeostasis.CGA can modify intestinal glucose metabolism by regulating the expression of intestinal glucose transporters and Plg,thereby controlling the levels of blood glucose and insulin to maintain glucose homeostasis.

Effects of suppressing glucose transporter-1 by an antisense oligodeoxynucleotide on the growth of human hepatocellular carcinoma cells

BACKGROUND:The glucose transporter-1(Glut-1),a key ratelimiting factor in the transport and metabolism of glucose in cancer cells,is over-expressed in many human cancer cells and this overexpression is correlated with poor biological behavior. The increased levels of Glut-1 expression in hepatocellular carcinoma(HCC)cells functionally affect tumorigenicity.This study was undertaken to investigate effects of suppressing Glut-1 by an antisense oligodeoxynucleotide(AS-ODN)on the growth of human hepatocellular carcinoma(HepG-2)cells. METHODS:We used AS-ODN targeting against the Glut-1 gene in a HepG-2 cell line.There were four experimental groups: empty pcDNA3.1 vector(mock transfection),pcDNA3.1-anti-Glut(+),pcDNA3.1-Glut(+),and non-transfected HepG-2 cells. The Glut-1 mRNA expression was detected by RT-PCR and the Glut-1 protein expression by Western blotting after cell culture, and the glucose uptake was detected after glucose stimulation in each group. RESULTS:Compared with non-transfected HepG-2 or Glut-1 pcDNA3.1,a down-regulation of Glut-1 mRNA in HepG-2 cells transfected with anti-Glut-1 pcDNA3.1 was noted(P<0.05).Glut-1 protein in HepG-2 cells transfected with Glut-1 AS-ODN was decreased compared with non-transfected HepG-2,Glut-1 pcDNA3.1,or empty vectors. Glucose uptake by the HepG-2 cells transfected with AS-ODN was decreased at 1 hour after glucose stimulation.CONCLUSIONS:The application of Glut-1 AS-ODN can down-regulate the expression of Glut-1 at mRNA and protein,and inhibit glucose uptake partially in HepG-2 cells.The Glut-1 gene maybe a potential therapeutic target for HCC.

IDENTIFICATION OF GLUCOSE TRANSPORTER- 1 AND ITS FUNCTIONAL ASSAY IN MOUSE GLOMERULAR MESANGIAL CELLS CULTURED IN VITRO

To evaluate the role of glucose transporter- l (GLUT1) in the glucose uptake of glomerular mesangial cells. Methods. Cultured C57/SJL mouse mesangial cells were used in the study. The expression of GLUT1 mRNA was detected by RT- PCR. The expression of GLUT1 protein was detected by immunofluorescence and flow cytometry. The uptake of glucose and its kinetics were determined by 2- deoxy- [3H]- D- glucose uptake. Results. Both GLUT1 mRNA and protein were found in mouse glomerular mesangial cells. 2- deoxy- D- glucose uptake and kinetics assay showed that this glucose transporter had high affinity for glucose and the glucose uptake specificity was further confirmed by phloretin. Conclusion. Functional GLUT1 did present in mouse mesangial cells cultured in vitro and it might be the predominant transporter mediated the uptake of glucose into mesangial cells.

Constructing recombinant replication-defective adenoviral vectors that express glucose transporter-1 through in vitro ligation

BACKGROUND： We constructed a homologous recombination bacterial method based on the pAdEasy system, a widely used system, for generating recombinant adenoviral vectors that express glucose transporter- 1 （GLUT 1） in rats, OBJECTIVE： This study was designed to investigate the feasibility of generating recombinant replication-defective adenoviral vectors that express GLUT1 in rats by in vitro ligation based on the Adeno-X^TM system. DESIGN： An in vitro cell-based experiment. SETTING： This study was performed at the Linbaixin Medical Research Center of the Second Hospital Affiliated to Sun Yat-sen University and Central Laboratory for Prevention and Treatment of Tumor, Sun Yat-sen University between January and August 2004. MATERIALS： Male, adult, Sprague Dawley rats were used to extract total RNA from brain tissue. E. coli DH5 a and human embryonic kidney 293 cells （HEK293 cells） used in the present study were cryo-preserved by the Second Hospital Affiliated to Sun Yat-sen University. Rabbit anti-rat GLUT1 polyclonal antibody （Chemicon, U.S.A.） and primers （Shanghai Boya Bioengineering Co., Ltd） were also used. METHODS： E1/E3-deleted replication-defective adenoviral vectors were used. Using in vitro ligation, the target gene was first sub-cloned into a shuttle vector plasmid to obtain the fragment containing target gene expression cassettes by enzyme digestion. Subsequently, the fragment was co-transformed with linearized adenoviral backbone vector into the E. coli strain. The recombinant adenoviral plasmid was transfected into HEK293 cells to assembly recombinant adenoviral vectors with replication capabilities. The procedure was repeated several times for recombinant adenoviral vectors amplification. MAIN OUTCOME MEASURES： Efficiency of recombinant adenoviral vectors to express the target gene was measured by gene and protein expression through polymerase chain reaction and Western Blot assays, respectively. RESULTS： Results demonstrated that recombinant adenoviral vectors successfully expressed GLUT1 protein, with a relative molecular mass of 55000 in HEK293 cells. These results suggest that recombinant adenoviral vectors obtained by homologous bacterial recombination feature high efficiency, rapidness, and simplicity. CONCLUSION： We successfully amplified the rat GLUT1 gene and constructed replication-defective adenoviral vectors expressing GLUT1. The replication-defective adenoviral vectors proved to successfully express the target gene in HEK293 cells.

Regulation of the expression and function of glucose transporter-1 by TGF- β1 and high glucose in mesangial cells

Objective To study the effects of high glucose and transforming growth factor β1 (TGF β1) on the expression and function of glucose transporter 1 (GLUT1) in mouse mesangial cells Methods Cultured mouse mesangial cells were used The expression of GLUT1 mRNA was detected by Northern Blot; glucose uptake and its kinetics were determined with a 2 Deoxy [ 3H] D glucose uptake assay Results Mesangial cells exposed to enriched glucose medium (20?mmol/L) for 72 hours demonstrated a decrease in both GLUT1 mRNA and V max for uptake of the glucose analog, 2 deoxy D glucose (2DOG), as compared to mesangial cells cultured in physiologic glucose concentrations(5 5?mmol/L) In contrast, hypertonic mannitol had no effect on GLUT1 mRNA levels TGF β1 treatment for 10 hours stimulated 2DOG uptake, both in 5 5?mmol/L and 20?mmol/L glucose medium, by approximately 4 28 fold in a dose dependent manner (2?ng/ml maximum) Kinetic analysis of 2DOG uptake revealed an increase in V max and a decrease in K m in the presence of TGF β1 TGF β1 also up regulated the expression of GLUT1 mRNA in mesangial cells The addition of anti TGF β neutralizing antibody (30?μg/ml) in mesangial cells cultured in enriched glucose medium (20?mmol/L) led to a 40% decrease in 2DOG uptake Conclusions The expression of GLUT1 can be suppressed by exposure of mesangial cells to high glucose medium, which may serve as a protective mechanism against possible adverse effects of excessive glucose flux into cells TGF β1 stimulates glucose uptake by enhancing the expression and function of GLUT1 in mesangial cells This effect is independent of the glucose milieu in the cultured medium

乳腺浸润性导管癌血氧水平依赖功能磁共振成像与葡萄糖转运蛋白1表达的关系

目的 探讨血氧水平依赖功能磁共振成像（BOLD-fMRI）的R2＊值与乳腺浸润性导管癌组织葡萄糖转运蛋白1 （GLUT-1）表达的相关性.方法 回顾性分析2011年12月至2013年6月本院接受乳腺癌手术治疗且术后病理证实为乳腺浸润性导管癌患者77例的临床资料,所有患者均于术前行乳腺BOLD-fMRI检查并测定肿瘤组织的R2＊值.免疫组化染色检测肿瘤组织GLUT-1的表达.Spearman相关分析肿瘤组织BOLD-fMRI R2＊值与GLUT-1表达的关系.结果 病理学检查显示77例患者均为乳腺浸润性导管癌,肿瘤分级为Ⅰ级3例、Ⅱ级48例、Ⅲ级26例,其中伴腋窝淋巴结转移40例.免疫组化显示肿瘤组织GLUT-1表达阴性6例、弱阳性11例、中度阳性25例、强阳性35例,GLUT-1表达阳性率为92.2％（71/77）.腋窝淋巴结转移组GLUT-1表达显著高于无腋窝淋巴结转移组（x2=5.718,P=0.016）.BOLD-fMRI检查显示乳腺浸润性导管癌呈混杂信号,R2＊值为26.4～90.5 Hz,平均（54.9±16.9）Hz.Spearman相关分析表明,乳腺浸润性导管癌肿瘤组织R2＊值与GLUT-1的表达呈正相关（r=0.587,P=0.000）.结论 BOLD-fMRI可用于无创性评价乳腺浸润性导管癌组织慢性乏氧及葡萄糖代谢水平.

Characterization of monocarboxylate transporter activity in hepatocellular carcinoma

AIM: To assess the immunoexpression of hypoxia-related markers in samples from cirrhosis and primary and metastatic hepatocellular carcinoma (HCC).

Hepatitis C virus infection and insulin resistance

Approximately 170 million people worldwide are chronically infected with hepatitis C virus(HCV).Chronic HCV infection is the leading cause for the development of liver fibrosis,cirrhosis,hepatocellular carcinoma(HCC)and is the primary cause for liver transplantation in the western world.Insulin resistance is one of the pathological features in patients with HCV infection and often leads to development of typeⅡdiabetes.Insulin resistance plays an important role in the development of various complications associated with HCV infection.Recent evidence indicates that HCV associated insulin resistance may result in hepatic fibrosis,steatosis,HCC and resistance to anti-viral treatment.Thus,HCV associated insulin resistance is a therapeutic target at any stage of HCV infection.HCV modulates normal cellular gene expression and interferes with the insulin signaling pathway.Various mechanisms have been proposed in regard to HCV mediated insulin resistance,involving up regulation of inflammatory cytokines,like tumor necrosis factor-α,phosphorylation of insulin-receptor substrate-1,Akt,up-regulation of gluconeogenic genes like glucose 6 phosphatase,phosphoenolpyruvate carboxykinase 2,and accumulation of lipid droplets.In this review,we summarize the available information on how HCV infection interferes with insulin signaling pathways resulting in insulin resistance.