RA-FLSs cell apoptosis in different experimental groups was measured by Annexin V-fluorescein isothiocyanate (FITC)/propidium iodide (PI) apoptosis detection kit (BD Biosciences, San Jose, CA) according to the manufacturer’s instructions [28 (link)]. FLSs cells in the logarithmic growth phase were collected and inoculated into a six-well plate. Then, 5 μL Annexin V-FITC and PI were added to the sample for 15 min in the dark and thus detected by flow cytometer (BD, San Jose, CA, USA).