Male C57BL/6 wild-type mice (aged 6–8 weeks, 20–25 g) were obtained from the Experimental Animal Center of Nanjing Medical University. Male C57BL/6-KitW−sh/KitW−sh (kitW−sh) mice were generated in our laboratory, and colonies of these mice were maintained for studies. All the mice were housed in a temperature-controlled room with a 12 h light/12 h dark cycle and sufficient food and water.