Amino acid deprivation induces both apoptosis and autophagy in murine C2C12 muscle cells.

Apoptosis and autophagy are closely interconnected types of programmed cell death. In the present study, mouse C2C12 muscle cells were starved in Earle's Balanced Salt Solution or treated with TNF-alpha and cycloheximide to induce autophagy and apoptosis, respectively. The majority of starved C2C12 cells underwent autophagy, as shown by LC3 processing, formation of autophagic vesicles and bulk degradation of long-lived proteins. However, some cells showed features of apoptosis including caspase-3 cleavage, chromatin condensation, DNA fragmentation and annexin V labeling. Caspase-3 cleavage was also induced in culture medium without serum, suggesting that serum withdrawal rather than amino acid deprivation triggered apoptosis. Starvation eliminated multiple pro-apoptotic proteins, but upregulated caspase-8, and rendered starved C2C12 cells much more susceptible to TNF-alpha/cycloheximide-induced apoptosis than non-starved cells. Our data suggest that amino acid deprivation of C2C12 cells induces a complex form of cell death with hallmarks of both apoptosis and autophagy.