2.9. Terminal deoxynucleotidyl transferase‐mediated dUTP nick end labelling (TUNEL) staining

Tissue sections were deparaffinized and hydrated in xylene and gradient concentrations of ethanol, then incubated in proteinase K at room temperature for 30 minutes and stained with TUNEL kit (Sigma‐Aldrich). Label solution was used instead of TUNEL reagent in the negative control group. All the images were captured by a fluorescence microscope (DFC700T, Leica). Cells that were positive for TUNEL staining and aligned with DAPI staining were considered apoptotic cells and counted.