A total of 1× 107 cultured UCA-PSCs and WJ-MSCs at P4 were lysed with 300 μL of SDS lysis buffer containing protease inhibitor and 1 μM PMSF in 1.5-mL tubes. Each sample was ultrasonicated on ice for 3 min. After centrifugation twice at 2000 ×g for 10 min at 4°C, the supernatant was collected for total protein measurement and further LC-MS analysis. Cell supernatants (5 mL/106 cells) of P4 UCA-PSCs and WJ-MSCs cultured in basic DMEM without serum or antibiotics for 48 h were collected. After concentration in 3-KD ultrafiltration centrifuge tubes, the cell supernatants were frozen and resuspended in SDS solution. After centrifugation, the supernatants from UCA-PSC and WJ-MSC cultures were obtained.Secretory proteome of UCA-PSCs and WJ-MSCs was further analyzed.