Low temperature protects mammalian cells from apoptosis initiated by various stimuli in vitro

Mild hypothermia shows protective effects on patients with brain damage and cardiac arrest. To elucidate the molecular mechanisms underlying these effects, we examined the effects of low temperature (32°C) on cells exposed to a variety of stress in vitro. We found that 32°C suppressed induction of apoptosis by cytotoxic stimuli such as adriamycin, etoposide, thapsigargin, NaCl, H2O2, and anti-Fas antibody. In adriamycin-treated BALB/3T3 cells, the down-shift in temperature from 37°C to 32°C increased the Bcl-xL protein level and decreased the mRNA level of Puma and mitochondrial translocation of Bax, suppressing caspase-9-mediated apoptosis. Furthermore, the protein level and stability of p53 were decreased, and its nuclear export was increased concomitant with Mdm2 mRNA upregulation. The low temperature effect was not observed in p53−/−/Mdm2−/− mouse embryonic fibroblasts, suggesting that the effect is mediated by suppression of the p53 pathway. In contrast, while thapsigargin-induced apoptosis was suppressed by the low temperature, no effect on the p53 protein level was observed. Furthermore, the survival rate of p53−/−/Mdm2−/− cells exposed to thapsigargin was increased when cultured at 32°C compared with 37°C. In conclusion, mild hypothermia protects cells from a variety of stress by p53-dependent and p53-independent mechanisms.