Conditioning causes an increase in glucose transporter-4 levels in mononuclear cells in sled dogs

Abstract

This study was designed to investigate the effects of physical conditioning on the expression of the insulin sensitive glucose transporter 4 protein (GLUT4) on mononuclear cells and HOMA-IR levels in dogs and compared to results reported in human skeletal muscle and the skeletal muscle of rodent models. Blood was sampled from conditioned dogs (n=8) and sedentary dogs (n=8). The conditioned dogs were exercised four months prior the experiment and were following a uniform training protocol, whereas the sedentary dogs were not. GLUT4 expression in mononuclear cells and plasma insulin levels were measured using commercially available enzyme-linked immunosorbent assay (ELISA). Blood glucose levels were determined using blood plasma. HOMA-IR was calculated using plasma insulin and blood glucose levels using the linear approximation formula. Our results indicate that the state of conditioning had a significant effect on the GLUT4 expression at the surface of mononuclear cells. HOMA-IR was also affected by conditioning in dogs. GLUT4 levels in mononuclear cells of sled dogs were inversely correlated with the homeostasis model assessment of insulin sensitivity. This study demonstrates that conditioning increases GLUT4 levels in mononuclear cells of sled dogs as it has been previously reported in skeletal muscle. Our results support the potential of white blood cells as a proxy tissue for studying insulin signaling and may lead to development of a minimally invasive and direct marker of insulin resistance. This may be the first report of GLUT4 in mononuclear cells in response to exercise and measured with ELISA.

The effect of acute exercise on GLUT4 levels in peripheral blood mononuclear cells of sled dogs

“…It still remains unclear whether exercise and muscle contraction, which stimulates GLUT4 translocation locally, would also have an effect on the expression or translocation of GLUT4 in circulating mononuclear. In a previous study we have shown that four months of long term conditioning significantly increased GLUT4 content in mononuclear cells of sled dogs [25] . The present study was undertaken to address the question of whether the observed increase in skeletal muscle GLUT4 protein after one acute bout of exercise, measured by highly invasive biopsies, can also be measured in peripheral mononuclear cells, assessed via minimally-invasive blood sampling, to further examine the potential use of this technique as reliable and feasible technique in a clinical setting.…”

“…The protocol for the assessment of GLUT4 protein concentrations translocated to the surface of mononuclear cells has been described elsewhere [25] . We controlled for the measurement of GLUT4 translocated to the cell membrane, and not total GLUT4, in comparing sonicated to unsonicated samples.…”

Weight Gain, Conditioning and Metabolic Syndrome: A Sled Dog Model

“…Because GHbA1c is associated with long-term elevated glucose levels and since these dogs were not at risk for diabetes, we evaluated TNF in the next part of the study and investigated the effect of weight gain. Our previous finding that conditioning increased the insulin sensitive glucose transporter, GLUT4, in mononuclear cells of sled dogs prompted our initial inquiry on the effects of exercise on other biomarkers associated with insulin resistance (Schnurr et al, 2014;. TNF and adiponectin were measured in the sedentary sled dogs after weight gain.…”

“…Sled dogs are at low risk for developing T2D; their increased energy expenditure when compared to other elite athletes, make them an ideal model for studying the effects of exercise and metabolism (Hinchcliff et al, 2000). Recent work in our lab has shown that both acute and chronic exercise increases GLUT4, the insulinsensitive glucose transporter, in mononuclear cells of sled dogs (Schnurr et al, 2014;. Therefore, the aim of this present study was to investigate the effects of exercise or weight gain separately on biomarkers associated with insulin resistance in sled dogs.…”

A Potential Role for GLUT4 in Predicting Sepsis in Critically ill Children

“…The quanti cation of GLUT4 expression on the surface of peripheral blood lymphocytes might be a potentially useful method for the early detection of individuals at a high risk of diabetes (35,36). GLUT4 levels in peripheral blood mononuclear cells have been investigated using indirect immuno uorescence in sled dogs (37), and in ammatory monocyte populations in humans (38)(39)(40), which could be used as a method to estimate the in uence of insulin on GLUT protein translocation and the dynamics of glucose uptake. GLUT4 was also detected in granulocytes and could be used to assess the immune response in diabetes (41) or the response of the plasma membrane to insulin during infection (33,42).…”