2.6. TUNEL Assay

TUNEL assay was performed according to the manufacturer's protocol. In brief, after dewaxed and hydrated, the tissue sections were incubated with proteinase K for 20 min at room temperature. After incubated with equilibration buffer, sections were covered with TUNEL reaction mixture for 1 h at 37°C. Finally, the sections were washed in PBS three times and counterstained with DAPI. The sections were examined and photographed under fluorescence microscopy (DFC310 FX, Leica, Germany). Apoptosis index (AI) = apoptotic cell number/total cell number × 100% [17].