Statistical analysis
Graph Pad Prism 7.0 and SPSS 16.0 software were used for statistical evaluation. Group differences in cell and animal experiments were compared using independent-samples Student t tests. Prior to analysis, all data underwent the Kolmogorov-Smirnov normality test and Levene’s test; results showed that all data from different group of data satisfied the normality and homogeneity of variance. Data are expressed as mean ± SEM. P < 0.05 was considered statistically significant.