LC/MS analysis of secretion of dental pulp cell. Methanol/chloroform precipitation was performed for protein purification. Resulting pellets were resolved by MS buffer (8 M urea and 50 mM Tris–HCl pH 8.0), followed by reduction in 5 mM DTT (FUJIFILM WAKO) and alkylation in 27.5 mM iodoacetamide (FUJIFILM WAKO) for 30 min in the dark at room temperature. After being diluted eight times in 50 mM Tris–HCl pH 8.0, proteins were digested overnight with 50 ng Lys-C (FUJIFILM WAKO) and trypsin (Promega, Madison, WI) at 37°C. Peptides were purified using GL-Tips SDB (GL Science, Tokyo, Japan) based on the manufacturer's protocol. The concentration of peptides was measured using a Pierce™ quantitative colorimetric peptide assay kit (Thermo Fisher Scientific). Subsequently, peptides (268 ng each) were injected into an EASY-nLC™ connected to a Q-Exactive PLUSTM (Thermo Fisher Scientific) mass spectrometry system. Protein identification and label-free quantification were performed using Proteome Discoverer 2.2™ (Thermo Fisher Scientific).