Calcineurin regulation of GLUT4 transcription / by Ellis B. Jensen.
| Author/creator | Jensen, Ellis B. author. |
| Other author | Dohm, G. Lynis, degree supervisor. |
| Other author | East Carolina University. Department of Biology. |
| Format | Theses and dissertations |
| Production | 2002. |
| Description | v, 54 leaves : illustrations ; 28 cm |
| Supplemental Content | Access via ScholarShip |
| Subjects |
| Summary | Transcription of the glucose transporter 4 (GLUT4) gene is increased by exercise. Since calcium is released during exercise, it may be a potential regulator of GLUT4 gene expression. Calcium, acting through calcineurin, nuclear factor of activated T cells (NFAT), and myocyte enhancer factor 2 (MEF2), regulates fiber-type-specific expression of a number of genes. Calcium released during muscle contraction could activate GLUT4 gene expression through activation of calcineurin, which could then activate NFAT and/or MEF2 to cause GLUT4 gene expression to increase. To determine the affects of calcineurin on GLUT4 gene expression, GLUT4 mRNA levels were compared in wild-type mice, mice overexpressing active calcineurin, and in mice treated with cyclosporin A (CsA) - a calcineurin inhibitor. In addition, the effects of denervation and exercise were investigated in wild-type mice, mice overexpressing calcineurin, and in mice treated with CsA. Two lines of calcineurin-transgenic mice were used in this study. Each line expresses constitutively-active calcineurin, but the calcineurin line 1 (CAN LI) mice express much more active calcineurin than does the calcineurin line 2 (CAN L2) strain. While not significant, the mean levels of GLUT4 message ribonucleic acid (mRNA) were somewhat higher at rest in the two strains of calcineurin-overexpressing transgenic mice than in their wild type counterparts. The mean resting GLUT4 mRNA level was lower in the mice treated with CsA than in vehicle-treated controls. The CAN LI mice showed a greater change in the amount of GLUT4 mRNA in response to 72 hours of denervation than did the wild-type controls. The CAN L2 mice and the CsA-treated mice gave similar responses in GLUT4 mRNA to denervation as their respective controls. The CAN L2 and CsA-treated mice both showed no difference in GLUT4 mRNA after exercise. To determine ifthe fiber-type expression pattern GLUT4 follows is due to calcineurin signaling through NFAT, GLUT4 and chloramphenicol acetyl transferase (CAT) gene expression levels were measured in red and white muscle tissues of transgenic mice that have varying lengths of the human GLUT4 promoter driving the expression of a GLUT4 gene with an attached CAT gene. The 1.6 kilobase (kb) promoter contains more NFAT binding sites than the 895 base pair (bp). Both the 1.6 kb and 895 bp constructs demonstrated similar ability to express GLUT4 in a fiber-type-specific manner. Increasing and decreasing the activity of calcineurin did not significantly alter basal muscle GLUT4 mRNA. Overexpression of active calcineurin increased the denervation response of GLUT4 mRNA, but did not alter the exercise response. GLUT4 mRNA was also measured in mice carrying a transgene driven by different lengths of the human GLUT4 promoter. As the difference between transgene expression was the same in the mice with long or short segments of the GLUT4 promoter, activation of NFAT does not appear to be responsible for the fiber-type-dependent expression of GLUT4. These results do not support a role for calcineurin in regulation ofGLUT4. |
| General note | Presented to the faculty of the Department of Biology. |
| General note | Advisor: G. Lynis Dohm |
| Dissertation note | M.S. East Carolina University 2002 |
| Bibliography note | Includes bibliographical references (leaves 50-54). |
| Genre/form | Academic theses. |
| Genre/form | Rules. |
| Genre/form | Academic theses. |
| Genre/form | Thèses et écrits académiques. |