Statistical analysis

If not stated otherwise, the results are presented as mean + standard error of the mean (SEM). Kolmogorov–Smirnov test (n = 5–7) and D'Agostino-Pearson omnibus test (n ≥ 8) were applied to analyze data sets for Gaussian distribution. Grubb's test was used on normal distributed data sets (n ≥ 5) to identify statistical outliers (http://www.graphpad.com/quickcalcs/grubbs1/). Unpaired and paired two-tailed Student's t-test or two-way analysis of variance (ANOVA) combined with Holm-Sidak's multiple comparison test were applied to determine statistical significance. Prism 6 (GraphPad Software, San Diego, CA, USA) was used for data plotting and statistical analyses.