TUNEL staining
The apoptosis cells in the skin lesions of mice were detected using the One Step TUNEL Apoptosis Assay Kit (C1086, Beyotime). After deparaffinization and rehydration, skin slices were treated with proteinase K (20 µg/ml) for 20 min at 37℃ and then rinsed in PBS three times. According to the manufacturer’s instructions, sections were stained with TUNEL staining reagents at 37°C for 60 min. Following several washes with PBS, nuclei were stained with DAPI Staining Solution (C1005, Beyotime) for 3 min at room temperature. Images were obtained using an inverted fluorescence microscope (Leica, DMI3000B), in which TUNEL-positive cells produced green fluorescence, and DAPI yielded blue fluorescence.