B21 Decreased expression and reduced translocation to the sarcolemma of the insulin-sensitive glucose transporter GLUT4 in skeletal muscle of R6/2 MICE

Abstract

<h3>Background and aims</h3> Several observations indicate a catabolic metabolism in HD patients despite sufficient caloric intake. Furthermore, an impaired glucose tolerance with high insulin levels has been shown in clinical studies. Glucose transporter 4 (GLUT4) is the main insulin-sensitive glucose transporter in skeletal muscle. So far it is unclear whether changes in expression and translocation of GLUT4 in muscle cells in HD contribute to impaired glucose tolerance. The expression and translocation to insulin stimulation were studied in skeletal muscle of R6/2 mice. <h3>Methods</h3> Skeletal muscle of 12-weeks-old R6/2 and wild type mice were dissected and enzymatically dissociated with collagenase. Half of the dissociated myotubes of each group were incubated with insulin and applied for subcellular fractionation by differential centrifugation. The GLUT4 content in the different fractions was detected by western blot. In addition cryosections of quadriceps muscles were labelled with antibodies against GLUT4 by immunofluorescence. <h3>Results</h3> Expression of GLUT4 were significantly lower in R6/2 skeletal muscle compared to WT. Less GLUT4 is translocated into the surface membrane in R6/2 skeletal muscle after insulin stimulation. Immunohistochemical stainings of GLUT4 shows a more diffuse distribution throughout the myotubes, whereas GLUT4 is more confined to the sarcolemma in WT skeletal muscles. <h3>Conclusions</h3> Skeletal muscle of R6/2 mice display a reduced basal expression of GLUT4 and less GLUT4 is translocated to the sarcolemma after insulin stimulation. These changes might contribute to alterations of glucose metabolism in skeletal muscle of the HD mouse model R6/2. Further experiments are performed to study the impact of Rab11 in the context of the alteration of GLUT4 vesicle trafficking in HD. Rab11 is a GTPase involved in the recycling of early endosomes and was shown before to change endosome recycling in HD.