Changes In Glucose Transport Research Articles

Establishment of An Alloxan-induced Diabetes Model in Daphnia Pulex.

Objective To establish a Daphnia model of alloxan-induced diabetes. Methods Daphnia were exposed to three different concentrations of alloxan (3, 5, and 10 mmol/L) for 30 minutes. Blood glucose and survival rate were recorded for 72 hours after alloxan insult. Sequence analysis and phylogenetic inference for glucose transporters (GLUT) were clustered with the maximum-likelihood method. Using reverse transcription and quantitative polymerase chain reaction techniques, we investigated the transcriptional changes of GLUT at 12 hours after alloxan (5 mmol/L) exposure. Results Compared with control, 3 mmol/L, and 5 mmol/L as well as 10 mmol/L alloxan initially induced transient blood glucose decline by 15% for 2 hours and 12 hours respectively. In Daphnia with 5 and 10 mmol/L alloxan, their blood glucose was persistently raised by about 150% since after 24-hour insult. Survival rate of Daphnia exposure to alloxan with concentrations of 3, 5, and 10 mmol/L were 90%, 75%, and 25% respectively. We predicted seven GLUT genes in the Daphnia genome and successfully amplified them using real-time polymerase chain reaction. Two of seven GLUT transcripts were down-regulated in Daphnia with 5 mmol/L alloxan-induced diabetes. Conclusion Alloxan-induced diabetes model was successfully established in the Daphnia pulex, suggesting diabetes-relevant experiments can be conducted using Daphnia.

Abstract PR429

Background & Objectives: To establish a Daphnia model of alloxan-induced diabetes contributing to conduct diabetes-relevant experiments in daphnid. Materials & Methods: Daphnid were exposure to 30-min 3 concentrations of alloxan (3 mM, 5 mM and 10 mM). Blood glucose and survival rate were recorded for 72 hrs after alloxan insult. Sequence analysis and phylogenetic inference for glucose transporters (GLUTs) were clustered with the maximum-likelihood method. Using reverse transcription and quantitative PCR techniques, we investigated the transcriptional changes of GLUTs at 12 hrs after alloxan (5 mM) exposure. Results: Compared with control, 3 mM, and 5 mM as well as 10 mM alloxan initially induced transient blood glucose decline by 15% for 2 hrs and 12 hrs respectively. In daphnid with 5 and 10 mM alloxan, their blood glucose was persistently raised about 250% since after 24-hr insult. Survival rate of daphnid with 3 mM, 5mM and 10 mM were 90%, 75% and 25%. We predicted seven GLUTs genes in the Daphnia genome and successfully amplified them using RT-PCR. Two of 7 GLUTs transcripts were downregulated in Daphnia with 5 mM alloxan-induced diabetes. Conclusion: This study provides the first evidence that alloxan can induce diabetes in Daphnia pulex possibly by downregulation of glucose transporters (GLUT1 and GLUT2), a new invertebrate model for diabetes.

Testicular glucose and its transporter GLUT 8 as a marker of age-dependent variation and its role in steroidogenesis in mice.

The present study evaluates the hypothesis, that glucose is essential for steroidogenesis and inadequate supply of glucose to the testis may be responsible for decline in steroidogenesis in mice during aging. Mice of different age groups (birth, weaning, puberty, reproductively active, and senescence) were utilized for this study. The changes in glucose, glucose transporter (GLUT), and insulin receptor (IR) level in the testis were evaluated and compared with the testicular steroidogenic parameters such as steroidogenic acute regulatory protein (StAR), 3β-hydroxy steroid dehydrogenase (3β-HSD) and circulating testosterone levels. The result showed significant correlation between changes in GLUT 8 and glucose levels with changes in StAR level in the testis and circulating testosterone level in the mice from birth to senescence. Immunohistochemical analysis showed intense immunostaining of GLUT 8 and IR in the interstitial cells, most likely Leydig cells, in testis of pubertal and reproductively active mice suggesting their relevance in steroidogenesis. The in vitro study showed a significant positive correlation between luteinizing hormone (LH)-induced increase in GLUT 8 and StAR (r = 0.82; P < 0.05) proteins level in the testes with increase in testosterone (r = 0.97; P < 0.05) synthesis of reproductively active mice. This study also showed increased release of lactate with increased uptake of glucose by the testis. Further, intra-testicular treatment of 2-deoxy glucose, to reproductively active mice caused a significant decrease in 3β-HSD enzyme activity in the testis. Based on these findings, it may be concluded that the changes in glucose level either directly or indirectly lead to changes in testicular steroidogenesis during aging.

Chronic stress modulates regional cerebral glucose transporter expression in an age-specific and sexually-dimorphic manner

Facilitative glucose transporters (GLUT) mediate glucose uptake across the blood–brain-barrier into neurons and glia. Deficits in specific cerebral GLUT isoforms are linked to developmental and neurological dysfunction, but less is known about the range of variation in cerebral GLUT expression in normal conditions and the effects of environmental influences on cerebral GLUT expression. Knowing that puberty is a time of increased cerebral plasticity, metabolic demand, and shifts in hormonal balance for males and females, we first assessed gene expression of five GLUT subtypes in four brain regions in male and female adolescent and adult Wistar rats. The data indicated that sex differences in GLUT expression were most profound in the hypothalamus, and the transition from adolescence to adulthood had the most profound effect on GLUT expression in the hippocampus. Next, given the substantial energetic demands during adolescence and prior demonstrations of the adverse effects of adolescent stress, we determined the extent to which chronic stress altered GLUT expression in males and females in both adolescence and adulthood. Chronic stress significantly altered cerebral GLUT expression in males and females throughout both developmental stages but in a sexually dimorphic and brain region-specific manner. Collectively, our data demonstrate that cerebral GLUTs are expressed differentially based on brain region, sex, age, and stress exposure. These results suggest that developmental and environmental factors influence GLUT expression in multiple brain regions. Given the importance of appropriate metabolic balance within the brain, further assessment of the functional implications of life stage and environmentally-induced changes in GLUTs are warranted.

Effects of retinoids and thiazolidinediones on proliferation, insulin release, insulin mRNA, GLUT 2 transporter protein and mRNA of INS-1 cells.

Both 9-cis-retinoic acid (9cRA) and all-trans-retinoic acid (ATRA) are active metabolites of vitamin A (retinol). There exists an interaction between retinoid receptors and peroxisome proliferator-activated receptors (PPARgamma). To define their functions in an insulin secreting system the effects of ATRA, 9cRA and the PPARgamma agonist rosiglitazone on cell proliferation, insulin release and glucose transporter (GLUT) 2 of INS-1 cells were tested. Retinoic acid receptor (RAR-alpha and -gamma) and retinoid X receptor (RXR-alpha and -beta) proteins are present (immunoblots). Both 9cRA and ATRA inhibit INS-1 cell proliferation ([3H]-thymidine assay) in a concentration dependent manner. Both 9cRA and ATRA increased insulin release, but only ATRA ralsed the GLUT 2 mRNA in a bell-shaped concentration response curve after 48 h. The insulinotropic effect of one compound is not significantly superimposed by the other indicating that the same binding sites are used by 9cRA and ATRA. The acute and chronic effects of the PPARgamma agonist rosiglitazone on insulin release were additionally determined since glitazones act as transcription factors together with RXR agonists. At high concentrations (100 microM) rosiglitazone inhibited glucose (8.3 mM) stimulated insulin secretion (acute experiment over 60 min). Insulin secretion, however, was increased during a 24 h treatment at a concentration of 10 microM and again inhibited at 100 microM. Changes in preproinsulin mRNA expression were not observed. Rosiglitazone (100 microM) increased GLUT 2 mRNA paralleled by an increase of GLUT 2 protein, but only after 24 h of treatment. This data indicate that RAR and RXR mediate insulin release. The changes in GLUT 2 have no direct impact on insulin release; the inhibition seen at high concentrations of either compound is possibly the result of the observed inhibition of cell proliferation. Effects of rosiglitazone on preproinsulin mRNA and GLUT 2 (mRNA and protein) do not play a role in modulating insulin secretion. With the presence of an RXR receptor agonist the effect of rosiglitazone on insulin release becomes stimulatory. Thus the effects of RAR-, RXR agonists and rosiglitazone depend on their concentrations, the duration of their presence and are due to specific interactions.

CHANGES IN GLUCOSE-TRANSPORT ASSOCIATED WITH MALIGNANT TRANSFORMATION (REVIEW)

It has been known for many years that changes in glucose metabolism are associated with neoplasia and research on this phenomenon has focused on the enhancement of glucose transport by malignant transformation. Viral transformation of fibroblastic cells provided the first system in which this enhancement could be studied using non-metabolizable glucose analogs. Kinetic and immunological analyses demonstrated that this was due to an increase in the number of glucose carriers at the plasma membrane. In the last 10 years glucose transporter (GLUT) proteins have been characterized by molecular cloning allowing direct examination of the molecular mechanisms of induction of transporter expression. GLUT proteins are a family of at least six separate isoforms which are encoded by distinct genes and differ in tissue distribution and regulation. Two of these isoforms, GLUT1 and GLUT3, are responsible for the changes associated with malignant transformation. The processes involved in the disregulation of these isoforms in the transformation of cultured fibroblastic and hematopoietic cells are described. Analysis of clinical samples indicates that GLUT1 and GLUT3 are often overexpressed in malignant tissue where they may aid tumor growth.

Transcripts for the high and low affinity hexose transporters in rat myoblasts.

The present investigation examined the glucose transporter (GLUT) transcript levels in glucose-grown rat L6 myoblasts, which possessed a high (HAHT) and a low (LAHT) affinity hexose transport system. The most prominent GLUT transcript detected in these cells was a GLUT 3-recognizable 4.1-kilobase transcript. Mutants defective in HAHT contained only residual levels of the GLUT 3 transcript and transporter. Corresponding changes in GLUT 3 transcript levels and HAHT activity were observed in myotubes, confluent cultures, and myogenesis-impaired cells. The other prominent GLUT transcripts detected were the GLUT 4-recognizable 2.8- and 1.4-kilobase transcripts. The close correlation between the GLUT 4 isoform and LAHT activity was indicated by the absence of this isoform in LAHT- mutants, and their corresponding changes in myoblasts grown under different conditions. These findings suggested the HAHT and LAHT transporters might be coded or regulated by the genes responsible for the GLUT 3 and 4 transcripts, respectively. Although relatively high levels of the GLUT 1 transcript and transporter were detected in glucose-grown HAHT-LAHT- mutants, these cells did not exhibit any GLUT 1 transport activity. Since the GLUT 1 transporter was not functional, it was not likely responsible for the HAHT and LAHT activities observed in glucose-grown L6 myoblasts.