Abstract: Objective：To explore the role of miR-21 in inflammatory response and osteogenic differentiation ofperiodontal ligament stem cell (PDLSCs). Methods：Gingiva samples from periodontitis patients and healthy people were collected and real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was performed to detect the expression of miR-21. 10 ng/mLtumor necrosis factor (TNF-α) was used to stimulate PDLSCs, mimicking inflammatory environment in vitro. QRT-PCR was performed to detect the expression of miR-21. MiR-21 mimics and inhibitors were utilized respectively to overexpress and knockdown miR-21 in PDLSCs. QRT-PCR and alkaline phosphatase (ALP) staining were performed to confirm the role of miR-21 on the osteogenic differentiation of PDLSCs. Results：The expression of miR-21 was upregulated in the gingiva tissues from periodontitis patients(P＜0.05). The miR-21 expression in PDLSCs was also upregulated under TNF-α stimulation (P＜0.01). Overexpression of miR-21 down-regulated the expression of cytokines IL-6, IL-1βinduced by TNF-α in PDLSCs(P＜0.05). Conversely, knocking down miR-21 promoted the expression of those genes(P＜0.05). During the osteogenesis induction of PDLSCs, the expression of miR-21 was significantly increased (P＜0.01). Overexpression of miR-21 enhanced and knocking down miR-21 alleviated the expression of osteogenic related genes RUNX2, OCNand the ALP staining (P＜0.05). In the inflammatory microenvironment, miR-21 overexpression could alleviate the inhibition effect of TNF-α stimulation on osteogenesis of PDLSCs (P＜0.05).Conclusions：MiR-21 alleviates the expression of cytokines induced by TNF-α in PDLSCs and promotes osteogenic differentiation of PDLSCs in the inflammatory microenvironment.

Key words: miR-21, periodontal ligament stem cells, miR-21, periodontal ligament stem cells, inflammation response, inflammation response, osteogenic differentiation, osteogenic differentiation