Statistical analysis
Data are presented as mean ± standard error of the mean (SEM). All statistical analyses were performed using SPSS Statistics, version 19.0 (IBM Corp, Armonk, NY, USA). Analysis of variance and Student’s t-test were used to assess differences between groups. Differences with p<0.05 were regarded as statistically significant. All experiments were performed independently at least twice with similar results. Representative results are shown.