Induction of Autophagy and Changes in Cellular Metabolism in Glucose Starved C2C12 Myotubes

Abstract

Mouse myoblast C2C12 cells are commonly used as a model system for investigating the metabolic regulation of skeletal muscle. As it is therefore important to understand the metabolic features of C2C12 cells, we examined the effect of glucose starvation on autophagy in C2C12 myotubes. After culture of C2C12 myotubes with high (HG, 25.0 mm) or low (LG, 5.6 mm) glucose concentrations, the concentration of glucose in the LG group had decreased to 0 mm after 24 h of culture and was around 17 mm after 48 h of culture in the HG group. The concentration of lactate increased from 0 to approximately 9 mm at 24 h and then dropped slightly in the LG group, while it increased linearly to 21 mm in the HG group at 48 h. The phosphorylation of p70 S6 kinase, marker for the protein translation initiation was significantly lower and the ratio of LC3-II/LC3-I, marker for the induction of autophagy was significantly higher in the LG group. GLUT1 and hexokinase II expression were significantly higher in the LG group. Together, these changes in glucose and lactate concentrations in the culture media suggest that C2C12 myotubes depend on anaerobic glycolysis. Our findings also suggest that glucose depletion stimulates the expression of key molecules involved in glycolysis and that cellular autophagy is also activated in C2C12 myotubes.

Autophagy under glucose starvation enhances protein translation initiation in response to re‐addition of glucose in C2C12 myotubes

“…Glucose starvation for 24 h decreases the phosphorylation levels of p70S6K. This is in line with previous studies suggesting that glucose is essential to maintain the phosphorylation levels of p70S6K [10,11]. In addition, we found that re-addition of glucose augmented the phosphorylation levels of p70S6K in 24-h glucosestarved cells but not in the nonstarved myotubes.…”

“…Glucose deprivation is a known factor for stimulating protein breakdown. The autophagy-lysosome system [9][10][11] and ubiquitin-proteasome system [28,29] are also reported to be accelerated by glucose starvation. Thus, we examined the role of the autophagy-lysosome system and the ubiquitin-proteasome system in our glucose re-addition-induced activation of p70S6K by using pharmacologic inhibitors.…”

“…In mammalian cells, the main regulators of autophagy are hormonal and nutrient factors [7,8]. Glucose [9][10][11] and amino acid [8,12,13] deprivation/ starvation is known to induce autophagy. However, the effects of glucose starvation on autophagy are comparatively less studied than those of amino acids starvation.…”

Proliferation of Lung Epithelial Cells Is Regulated by the Mechanisms of Autophagy Upon Exposure of Soots

“…It is well established that glucose starvation of cells induces autophagy in cells ( Nakai et al, 2020 ). Therefore, we tested whether soot treatment can inhibit starvation-induced autophagy.…”

“…Fullerene Soot Inhibits Starvation-Induced Autophagy and Induces Proliferation of A549 Cells, Which Is Reversed by Akt-Inhibitor X It is well established that glucose starvation of cells induces autophagy in cells (Nakai et al, 2020). Therefore, we tested whether soot treatment can inhibit starvation-induced autophagy.…”