Regulation of glucose transporter GLUT 4 in type 2 diabetes mellitus: role of resistance to insulin

• Grant number: 98/03514-3
• Support Opportunities: Research Projects - Thematic Grants
• Start date: September 01, 1998
• End date: October 31, 2002
• Field of knowledge: Health Sciences - Medicine - Medical Clinics
• Principal Investigator: Ubiratan Fabres Machado
• Grantee: Ubiratan Fabres Machado
• Host Institution: Instituto de Ciências Biomédicas (ICB). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Pesquisadores principais: Maria Tereza Nunes

Abstract

In some regions in the world approximately 40% of the population can come down with Diabetes Mellitus type 2 (DM2). Along with degenerative complications, DM accounts for the major cause of morbidity and mortality; consequently, it is top priority in developed countries as far as public health is concerned. Considering both DM2 and its morbid complications, it is known that insulin resistance is such a key ethiopathogenic factor, and the manipulation of insulin resistance can represent the manipulation of the very DM2. Insulin resistance mainly alters carbohydrate homeostase and is characterized primarily by a reduced capacity of the target tissues to uptake glucose under insulin stimulation. A compensatory hyperinsulinaemia is activate, which refeeds the resistance and can lead to pancreatic failure, Glucose transport in mammal cells can be performed by different isoforms of protein transporter (GLUTs). In insulin-sensitive tissues, two isoforms can be found: GLUT I and GLUT 4, the latter is the isoform translocated to the plasma membrane under insulin stimulation, acutely increasing the tissue capacity to uptake glucose. The events involved in the intracellular signalling of insulin has been widely studied in insulin resistance. As to protein GLUT 4, though a reduction in the content of tissue from obese DM2 animals has been demonstrated, the results found in the literature are still controversial. In addition, nothing is known about the modulation promoted by insulin resistance in the regulating mechanisms sof GLUT 4 gene expression. Based on that, the purpose of this project is to investigate the regulation os GLUT 4 (and GLUT I when necessary) gene expression in insulin-sensitive tissues: white and brown adipose tissues, skeletal and cardiac muscle, in situations where either a reduction or na increase in insulin sensitivity is evinced. The effect will be investigated in the long-term (obese and3 hyperinsulinemic 12-month-old Wistar rats) and in the short-term (1-month-o ld Wistar rats submitted to 48-hour fasting). Parallel studies about the increase in insulin sensitivity will be carried out with the purpose to make sure that the regulation is being performed by the hormonal sensitivity status. In this case, the long-term increase in insulin sensitivity (Wistar rats submitted to meal feeding: a feeding protocol known for its capacity to increase hormonal sensitivity), and the short-term increase in insulin sensitivity (refeeding of animals submitted to 48-hour fasting) will be investigated, in the latter the effect of the diet composition (carbohydrate X lipids) will be tested. By carrying out these protocols, the following will be investigated 1. Insulin sensitivity level (glycaemia and insulinaemia analysis); 2. Abundance of GLUT 4 tissue (Western blotting analysis)- 3. Abundance of GLUT 4 MRNA (Northern blotting analysis); 4. Transcriptional regulation of GLUT gene (analysis of MRNA abundance and acute blockade of transcription with actinomycin D); 5. Post-transcriptional regulation of GLUT 4 MRNA (MRNA migration analysis and evaluation of Poly -A terminal chain responsible for MRNA stabilization); 6. Post-translational regulation of GLUT 4 (comparison between abundance of MRNA and protein GLUT 4, and counterproof using blockade of protein synthesis with cycloheximide and blockade of glycosylation with tunicamycin). Moreover, when necessary to understand the regulation of GLUT 4 gene expression, events of intracellular signalling of insulin shall be investigated. Upon the studies mentioned above, it is believed that some light will be shed on the regulation of gene expression of glucose transporters proteins, specially GLUT 4, under conditions of altered insulin sensitivity. Knowledge from the investigations proposed can, in the future, help the establishment of preventive and/or healing measures for insulin resistance, that is, for Diabetes Mellitus type 2 itself. (AU)

Scientific publications

(References retrieved automatically from Web of Science and SciELO through information on FAPESP grants and their corresponding numbers as mentioned in the publications by the authors)

D.T. FURUYA; R. BINSACK; U.F. MACHADO. Low ethanol consumption increases insulin sensitivity in Wistar rats. Brazilian Journal of Medical and Biological Research, v. 36, n. 1, p. 125-130, 2003-01-00. (98/03514-3)

P.M. SERAPHIM; M.T. NUNES; U.F. MACHADO. GLUT4 protein expression in obese and lean 12-month-old rats: insights from different types of data analysis. Brazilian Journal of Medical and Biological Research, v. 34, n. 10, p. 1353-1362, 2001-10-00. (98/03514-3)

DE CARVALHO PAPA‚ P.; VARGAS‚ A.M.; TAVARES DA SILVA‚ J.L.; NUNES‚ M.T.; MACHADO‚ U.F.. GLUT4 protein is differently modulated during development of obesity in monosodium glutamate-treated mice. Life Sciences, v. 71, n. 16, p. 1917-1928, 2002. (98/03514-3)