Teeth were first disinfected with 75% ethanol and then washed with phosphate-buffered saline. Briefly, PDLSCs were separated from periodontal ligament in the middle one-third of the root. Subsequently, MSCs were digested in a solution of 3 mg\/mL collagenase type I (Worthington Biochemical Corp., Lakewood, NJ, USA) and 4 mg\/mL dispase (Roche Diagnostics Corp., Indianapolis, IN, USA) for 1 h at 37\u00b0C. Single-cell suspensions were obtained by cell passage through a 70-\u03bcm strainer (Falcon, BD Labware, Franklin Lakes, NJ, USA). MSCs were grown in a humidified, 5% CO2 incubator at 37\u00b0C in DMEM alpha modified Eagle\u2019s medium (Invitrogen, Carlsbad, CA, USA), supplemented with 15% fetal bovine serum (FBS; Invitrogen, Carlsbad, CA, USA), 2 mmol\/L glutamine, 100 U\/mL penicillin and 100 \u00b5g\/mL streptomycin (Invitrogen, Carlsbad, CA, USA). The culture medium was changed every 3 days. MSCs at passages 3-5 were used in subsequent experiments. Human embryonic kidney 293T cells were maintained in complete DMEM with 10% FBS, 100 U\/mL penicillin and 100 \u00b5g\/mL streptomycin.