To examine the physiological role of the GLUT4/muscle-fat specific facultative glucose transporter in regulating glucose homeostasis, we have generated transgenic mice expressing high levels of this protein in an appropriate tissue-specific manner. Examination of two independent founder lines demonstrated that high-level expression of GLUT4 protein resulted in a marked reduction of fasting glucose levels (≈70 mg/dl) compared to wild-type mice (≈130 mg/dl). Surprisingly, 30 min following an oral glucose challenge the GLUT4 transgenic mice had only a slight elevation in plasma glucose levels (≈90 mg/dl), whereas wild-type mice displayed a typical 2- to 3-fold increase (≈250-300 mg/dl). In parallel to the changes in plasma glucose, insulin levels were ≈2 -fold lower in the transgenic mice compared to the wild-type mice. Furthermore, isolated adipocytes from the GLUT4 transgenic mice had increased basal glucose uptake and subcellular fractionation indicated elevated levels of cell surface-associated GLUT4 protein. Consistent with these results, in situ immunocytochemical localization of GLUT4 protein in adipocytes and cardiac myocytes indicated a marked increase in plasma membrane-associated GLUT4 protein in the basal state. Taken together these data demonstrate that increased expression of the human GLUT4 gene in vivo results in a constitutively high level of cell surface GLUT4 protein expression and more efficient metabolic control over fluctuations in plasma glucose concentrations.
|Original language||English (US)|
|Number of pages||5|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|Publication status||Published - Dec 1 1993|
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