Update publication information. The protein samples stored at -80 °C were thawed and treated with lysis buffer (8M urea, 1% protease inhibitor, 50mM NH4HCO3) for 5 minutes in room temperature. After ultrasonic cracking on ice and centrifugation at 14000g for 10 min at 20 °C, the amount of total protein of each MSC sample was detected by bicinchoninic acid assay (Beijing Solarbio Science & Technology Co., Ltd., Beijing, China) using NanoDrop ND-1000 spectrophotometer (Thermo Fisher Scientific, Inc., Sunnyvale, CA, USA). Protein digestion was carried out by a filter-aided sample preparation technique. Briefly, 50 μg of a sample was loaded onto a Microcon filter unit YM-30 (Millipore) and washed with 8 M urea, followed by protein alkylation with 50 mM iodoacetamide in 8 M urea in darkness for 20 min. After alkylation, the filters were washed twice with 8 M urea and twice with 40 mM ammonium bicarbonate. Trypsin (Promega, Madison, WI, USA) was added to the samples at 100:1 protein-to-enzyme ratio and incubated overnight at 37 °C. Later the same