Four groups of cells, including the control LO2 group, the senescent LO2 group, and the 100 nM SME-treated control or senescent LO2 for 24 h group, were lysed by RIPA lysis buffer (Cat# P0013K, Beyotime, China) added with Protease inhibitors cocktail, and the supernatant was added to acetone in a 1:5 vol at -30℃ for precipitation and dissolved with 8 M urea.