[Roles of adenosine monophosphate activated protein kinase in skeletal muscle atrophy in rats with severe scald]

Objective: To investigate the expression and phosphorylation level change of adenosine monophosphate activated protein kinase (AMPK) in skeletal muscle of severely scald rats and its roles in skeletal muscle atrophy in severely scalded rats. Methods: The experimental research method was applied. Totally 100 6-week-old male Wistar rats were divided into sham injury group and scald group according to the random number table, with 50 rats in each group. After weighing the body weight, rats in scald group were inflicted with full-thickness scald of 30% total body surface area on the back, and rats in sham injury group were simulated with scald. At 6 h and on 1, 3, 5, and 7 d post injury, 10 rats in each group were taken to measure their body weights and weights of extensor digitorum longus and soleus muscle. At 6 h and on 1, 3, 5, and 7 d post injury, the tibialis anterior muscles were collected, the mRNA expressions of muscle atrophy F-box protein (MAFbx) and muscle-specific RING finger protein 1 (MuRF1) were detected by real-time fluorescent quantitative reverse transcription polymerase chain reaction; the content of adenosine monophosphate (AMP), adenosine diphosphate, and adenosine triphosphate (ATP) were detected by high performance liquid chromatography, and AMP/ATP ratio and energy charge were calculated; the protein expressions of AMPK-α and phosphorylated AMPK-α (p-AMPK-α) were detected by Western blotting, and the p-AMPK-α/AMPK-α ratio was calculated, with sample number of 4 in each time point of each group. Data were statistically analyzed with analysis of variance for factorial design and least significant difference test. Results: The body weights of rats in 2 groups before injury and at each time point post injury were close (P>0.05). At 6 h post injury, the weight of extensor digitorum longus of rats in scald group was (0.107±0.007) g, which was significantly heavier than (0.086±0.0607) g of sham injury group (P<0.01). On 3 d post injury, the weight of extensor digitorum longus of rats in scald group was (0.083±0.016) g, which was significantly lighter than (0.102±0.005) g of sham injury group (P<0.01). The weight of soleus of rats in 2 groups were close at each time point post injury (P>0.05). Compared with those of sham injury group, the mRNA expression of MAFbx in tibialis anterior muscle of rats in scald group was significantly up-regulated at 6 h post injury (P<0.01), and the mRNA expressions of MuRF1 in tibial anterior muscle of rats in scald group were significantly up-regulated at 6 h and on 1 d post injury (P<0.01). At 6 h and on 7 d post injury, compared with those of false injury group, the AMP/ATP ratios of the tibial anterior muscle of rats in scald group were significantly increased (P<0.05 or P<0.01), and energy charges of the tibial anterior muscle of rats in scald group were significantly decreased (P<0.01). At each time point post injury, the protein expressions of AMPK-α of the tibial anterior muscle of rats in 2 groups were close (P>0.05). The p-AMPK-α/AMPK-α ratios of the tibial anterior muscle of rats in scald group at 6 h and on 7 d post injury were significantly higher than those in sham injury group (P<0.05 or P<0.01). Conclusions: The decrease in energy charge and increase in AMP/ATP ratio of skeletal muscle of rats after severe scald activate AMPK. The activation of AMPK in the early stage of injury is consistent with the up-regulation of MAFbx and MuRF1 expressions and down-regulation of skeletal muscle weight. The above-mentioned changes may be one of the molecular mechanisms of skeletal muscle atrophy in rats with severe scald.