Skeletal Muscle Cell Line XM13A1
Introduction
The XM13A1 cell line is a novel human muscle line derived from muscle tissue taken from a 30-40 year old non-diabetic female. It offers many advantages over rodent cell lines such as C2C12 and L6 cells. This cell line is available today for licensing for research and drug discovery.
Background
The XM13A1 cell line contains a mixed cell population derived from normal human skeletal muscle. The immortality of these cells is conferred by the actions of the temperature sensitive form of the SV40 Large T antigen gene. The temperature sensitive T antigen is active at 33°C and inactive at 37°C and above. This means that cells are immortalized at 33°C, but that immortalization can be reversed by culturing cells at 37°C (Figure 1). This is important for functional studies as cells revert to normal phenotype after immortalization is reversed. This allows the cells to differentiate from myoblasts into multinucleate myotubes.
Figure 1 Temperature sensitive cell division in XM13A1 cells: Early passage cells proliferate at a faster rate at 37°C and show reduced temperature dependence. This may be because the natural proliferative processes are still intact. At later passages, cells would normally senesce, thus cells transfected with temperature sensitive Large T antigen show proliferation at 33°C but not at 37°C.
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Figure 2 Creatine kinase activity in differentiating XM13A1 cells: XM13A1 cells, at passage 5, 10 or 16, were seeded to 6-well plates and allowed to grow to a confluent monolayer, at 33°C. Plates were transferred to 37°C and medium replaced with differentiation medium. Medium was changed every 3 days and extracts prepared every 2 days for creatine kinase activity measurement. Activities are reported as % over basal and are the average of two independent samples.
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Figure 3 Insulin-responsiveness in XM13A1 myoblasts: XM13A1 cells, at (a) passage 5, (b) passage 10, (c) passage 16 and (d) passage 21, were seeded to 96-well plates for glycogen synthesis determinations. Myoblasts were seeded in serum free medium at 15,000 cells per well 18 h prior to insulin treatment. Subsequently, cells were treated with the indicated concentrations of insulin, in medium containing radioactively labelled glucose. Glycogen synthesis is indicated as % over basal rate and is the average, with SEM, of 6 independent treatments.
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Other markers of differentiation found in conditionally immortalized human skeletal muscle cells include myogenin, GLUT4, UCP 3 and Glycogen Synthase.
Functional activities include:
- Glycogen synthesis stimulated by LiCl and IGF
- AICAR stimulated 2 de-oxy-glucose uptake
- Insulin-resistance induced by glucosamine and saturated fatty acids
