Insulin action in cultured human skeletal muscle cells during differentiation: assessment of cell surface GLUT4 and GLUT1 content

Abstract

In mature human skeletal muscle, insulin-stimulated glucose transport is mediated primarily via the GLUT4 glucose transporter. However, in contrast to mature skeletal muscle, cultured muscle expresses significant levels of the GLUT1 glucose transporter. To assess the relative contribution of these two glucose transporters, we used a novel photolabelling techniques to assess the cell surface abundance of GLUT1 and GLUT4 specifically in primary cultures of human skeletal muscle. We demonstrate that insulin-stimulated glucose transport in cultured human skeletal muscle is mediated by GLUT4, as no effect on GLUT1 appearance at the plasma membrane was noted. Furthermore, GLUT4 mRNA and protein increased twofold (p < 0.05), after differentiation, whereas GLUT1 mRNA and protein decreased 55% (p < 0.005). Incubation of differentiated human skeletal muscle cells with a non-peptide insulin mimetic significantly (p < 0.05) increased glucose uptake and glycogen synthesis. Thus, cultured myotubes are a useful tool to facilitate biological and molecular validation of novel pharmacological agents aimed to improve glucose metabolism in skeletal muscle.

Are cultured human myotubes far from home?

“…This insulin concentration is markedly above the physiological concentration in the picomolar range. Insulin stimulation increases glycogen synthesis about 2-fold in human myotubes, which is similar to in vivo observations , Al-Khalili, et al, 2003, Al-Khalili, et al, 2005. In intact muscle, glycogen content is linked to glucose uptake, and reduced glycogen content increases glucose uptake (Jensen, et al, 1997).…”

“…In response to insulin stimulation, GLUT4, but not GLUT1, is translocated to the cell surface of the skeletal muscle cells, resulting in an increase in glucose uptake (Ploug and Ralston, 1998). However, the ratio of GLUT1:GLUT4 is higher in human myotubes compared to adult skeletal muscle (Sarabia, et al, 1992), resulting in a lower insulin responsiveness of glucose transport (Al-Khalili, et al, 2003, Sarabia, et al, 1992. Insulin typically increases glucose uptake by 40-50 % in myotubes (Aas, et al, 2002, Al-Khalili, et al, 2003, McIntyre, et al, 2004, Montell, et al, 2001.…”

“…However, the ratio of GLUT1:GLUT4 is higher in human myotubes compared to adult skeletal muscle (Sarabia, et al, 1992), resulting in a lower insulin responsiveness of glucose transport (Al-Khalili, et al, 2003, Sarabia, et al, 1992. Insulin typically increases glucose uptake by 40-50 % in myotubes (Aas, et al, 2002, Al-Khalili, et al, 2003, McIntyre, et al, 2004, Montell, et al, 2001. Even though the effect of insulin is lower in myotubes than in intact skeletal muscle, the responsible molecular mechanisms of glucose transport remain the same (Al-Khalili, et al, 2003).…”

“…Insulin typically increases glucose uptake by 40-50 % in myotubes (Aas, et al, 2002, Al-Khalili, et al, 2003, McIntyre, et al, 2004, Montell, et al, 2001. Even though the effect of insulin is lower in myotubes than in intact skeletal muscle, the responsible molecular mechanisms of glucose transport remain the same (Al-Khalili, et al, 2003). Due to a decreased insulin responsiveness of human myotubes, insulin concentrations in the range of 0.1 -1 µM are often applied in studies of human myotubes , Aguer, et al, 2011, Al-Khalili, et al, 2003, Bell, et al, 2010, Gaster, et al, 2004, Jackson, et al, 2000, Rune, et al, 2009a.…”

“…Even though the effect of insulin is lower in myotubes than in intact skeletal muscle, the responsible molecular mechanisms of glucose transport remain the same (Al-Khalili, et al, 2003). Due to a decreased insulin responsiveness of human myotubes, insulin concentrations in the range of 0.1 -1 µM are often applied in studies of human myotubes , Aguer, et al, 2011, Al-Khalili, et al, 2003, Bell, et al, 2010, Gaster, et al, 2004, Jackson, et al, 2000, Rune, et al, 2009a. This insulin concentration is markedly above the physiological concentration in the picomolar range.…”