Abstract: BACKGROUND: Studies have shown that long non-coding RNA small nucleolar RNA host gene 4 (lncRNA SNHG4) is involved in the progress of many inflammatory diseases, but the effect of lncRNA SNHG4 on the osteogenic differentiation of human periodontal ligament stem cells during the treatment of periodontitis is still unclear.  
OBJECTIVE: To investigate the effect of lncRNA SNHG4 on the osteogenic differentiation of human periodontal ligament stem cells by regulating miR-152-3p.
METHODS: Human periodontal ligament stem cells were isolated from periodontal membranes of premolars extracted for orthodontic purposes. After human periodontal ligament stem cells were induced to differentiate into osteoblasts for 0, 7, and 14 days, the expression levels of RUNX family transcription factor 2, osteocalcin mRNA, lncRNA SNHG4 and miR-152-3p in human periodontal ligament stem cells were detected by qRT-PCR. The third-generation human periodontal ligament stem cells were divided into the NC group, pcDNA group, pcDNA-SNHG4 group, inhibitor NC group, miR-152-3p inhibitor group, pcDNA-SNHG4+mimic NC group, and pcDNA-SNHG4+miR-152-3p mimic group. The expression of lncRNA SNHG4 and miR-152-3p in human periodontal ligament stem cells was detected by qRT-PCR. The proliferation of human periodontal ligament stem cells was detected by CCK-8 assay. Alkaline phosphatase activity was detected by colorimetry. The formation of mineralized nodules was detected by alizarin red staining. Western blot assay was used to detect the expression of RUNX family transcription factor 2, osteocalcin and alkaline phosphatase proteins. A double luciferase reporter gene experiment was applied to verify the relationship between lncRNA SNHG4 and miR-152-3p.  
RESULTS AND CONCLUSION:  (1) The expression of RUNX family transcription factor 2, osteocalcin mRNA and lncRNA SNHG4 in human periodontal ligament stem cells after 7 and 14 days of osteogenic induction was higher than that after 0 days of osteogenic induction, while the expression of miR-152-3p was lower (P < 0.05). (2) Overexpression of lncRNA SNHG4 or inhibition of miR-152-3p was able to enhance the proliferation of human periodontal ligament stem cells, the alkaline phosphatase activity, mineralized nodule formation, the expression of RUNX family transcription factor 2, osteocalcin, and alkaline phosphatase proteins (P < 0.05). miR-152-3p mimic attenuated the promoting effect of overexpression of lncRNA SNHG4 on osteogenic differentiation of human periodontal ligament stem cells. LncRNA SNHG4 had a targeting relationship with miR-152-3p. (3) These findings indicate that overexpression of lncRNA SNHG4 may promote the osteogenic differentiation of human periodontal ligament stem cells by inhibiting miR-152-3p.

Key words: long non-coding RNA, small nucleolar RNA host gene 4, periodontal ligament stem cell, osteogenic differentiation