Effect of mild hypothermia on expression of autophagy-related proteins in hippocampus after traumatic brain injury in rats

Objective To investigate the effect of mild hypothermia on expression of autophagy-related proteins LC3 and Beclin-1 in the hippocampus of rats with traumatic brain injury (TBI). Methods Sixty healthy male adult SD rats were divided into sham group, TBI group, hypothermia-treated group (31-33℃) according to the random number, with 20 rats per group. Rat models of TBI were established using the Marmarou's method. After 4 h of normothermia or hypothermia, the rats were killed 6, 12, 24, and 48 h later. Co-localization of LC3 with neuron specific protein (NeuN) or mammalian target of rapamycinm (mTOR) was determined by double immunofluorescence. Levels of LC3, Beclin-1 and p-mTOR proteins were detected by Western blot analysis. Results LC3 co-localization with NeuN (or mTOR) was observed under confocal laser scanning microscope. In TBI group LC3 and Beclin-1 levels were seen to rise at 6 h, peaked at 24 h and fell slightly at 48 h, but the levels were still higher than these in sham group (P<0.05). In TBI group p-mTOR level began to decrease at 6 h, reached the lowest point at 12 h, and then ascended at 24 and 48 h, but the level was still lower than that in sham group (P<0.05). Mild hypothermia contributed to remarkable decreases in LC3 and Beclin-1 expressions, while up-regulating p-mTOR after injury(P<0.05). Conclusion Mild hypothermia appears to be neuroprotective as it inhibits autophagy in hippocampal neurons after TBI in rats through activation of mTOR signaling pathway. Key words: Traumatic brain injury; Mild hypothermia; Autophagy; Hippocampus