Abstract: BACKGROUND: Studies have found that long non-coding RNAs (lncRNAs) play a key regulatory role in the pathogenesis of periodontitis. The signaling axis composed of hypoxia-inducible factor 1α (HIF1α) and peroxisome proliferator-activated receptor γ (PPARγ) is of great significance in the regulation of inflammation, and its association with lncRNA-TNFRSF13C has become a key entry point for research in this field.  
OBJECTIVE: To investigate the mechanism of lncRNA-TNFRSF13C targeting the HIF1α-PPARγ signaling axis in periodontitis. 
METHODS: (1) Periodontal ligament cells were divided into periodontal ligament cell group, lipopolysaccharide+periodontal ligament cell group, lipopolysaccharide+periodontal ligament cell+lncRNA-TNFRSF13C-NC group, lipopolysaccharide+periodontal ligament cell+lncRNA-TNFRSF13C sno group, and lipopolysaccharide+periodontal ligament cell+lncRNA-TNFRSF13C siRNA group. RT-PCR was used to detect the expression of lncRNA-TNFRSF13C, HIF1α, and PPARγ. MTT assay was used to detect cell proliferation, DAPI staining was used to detect cell apoptosis, and western blot was used to detect HIF1α and PPARγ protein expression. Dual-luciferase reporter assay was performed by designing and cloning the full-length sequence of lncRNA-TNFRSF13C and its mutant to confirm the interaction between lncRNA-TNFRSF13C and the HIF1α-PPARγ signaling axis. (2) Thirty SPF-grade male Sprague-Dawley rats were randomly divided into normal group, model group, and lncRNA-TNFRSF13C siRNA group, with 10 rats in each group. Periodontitis models were established in the latter two groups by periodontal injection of Porphyromonas gingivalis. After successful modeling, the lncRNA-TNFRSF13C siRNA group was injected with 40 mg/kg lncRNA-TNFRSF13C siRNA via the tail vein. Hematoxylin-eosin staining was used to detect the pathological morphology of periodontal tissue in each group.   
RESULTS AND CONCLUSION: (1) Compared with the periodontal ligament cell group, the expression of lncRNA-TNFRSF13C and HIF1α mRNA was increased in the lipopolysaccharide+periodontal ligament cell group (P < 0.05), while PPARγ mRNA expression was decreased (P < 0.05). Compared with the lipopolysaccharide+periodontal ligament cell group, there was no significant difference in the expression of lncRNA-TNFRSF13C, HIF1α, and PPARγ mRNA in the lncRNA-TNFRSF13C-NC group (P > 0.05); and the expression of lncRNA-TNFRSF13C and HIF1α mRNA was increased in the lncRNA-TNFRSF13C sno group (P < 0.05), while PPARγ mRNA expression was decreased (P < 0.05). Compared with the lncRNA-TNFRSF13C sno group, the expression of lncRNA-TNFRSF13C and HIF1α mRNA was decreased in the lncRNA-TNFRSF13C siRNA group (P < 0.05), while PPARγ mRNA expression was increased (P < 0.05). (2) Compared with the periodontal ligament cell group, cell proliferation was decreased and apoptosis was increased in the lipopolysaccharide+periodontal ligament cell group (P < 0.05). Compared with the lipopolysaccharide+periodontal ligament cell group, there was no significant difference in cell proliferation in the lncRNA-TNFRSF13C-NC group (P > 0.05); and cell proliferation was decreased and apoptosis was increased in the lncRNA-TNFRSF13C sno group (P < 0.05). Compared with the lncRNA-TNFRSF13C sno group, cell proliferation was increased and apoptosis was decreased in the lncRNA-TNFRSF13C siRNA group (P < 0.05). (3) Compared with the periodontal ligament cell group, HIF1α protein expression was increased and PPARγ protein expression was decreased in the lipopolysaccharide+periodontal ligament cell group (P < 0.05). Compared with the lipopolysaccharide+periodontal ligament cell group, there was no significant difference in HIF1α and PPARγ protein expression in the lncRNA-TNFRSF13C-NC group (P > 0.05); and HIF1α protein expression was increased and PPARγ protein expression was decreased in the lncRNA-TNFRSF13C sno group (P < 0.05). Compared with the lncRNA-TNFRSF13C sno group, HIF1α protein expression was decreased and PPARγ protein expression was increased in the lncRNA-TNFRSF13C siRNA group (P < 0.05). (4) Dual-luciferase reporter assay results showed that transfection with lncRNA-TNFRSF13C significantly increased the luciferase activity of HIF1α-3′-UTR-WT (P < 0.05) and decreased the luciferase activity of PPARγ-3′-UTR-WT (P < 0.05), but had no significant effect on the mutant genes (P > 0.05). (5) In the model group, the periodontal tissue of rats showed congestion, edema, and infiltration by a large number of inflammatory cells, with disorganized and ruptured periodontal ligament fibers, and epithelial hyperplasia or ulcers were observed. Compared with the model group, the pathological structure of rats was significantly improved in the lncRNA-TNFRSF13C siRNA group. To conclude, inhibition of lncRNA-TNFRSF13C can effectively regulate the activity of lipopolysaccharide-induced periodontal ligament cells and improve the pathological morphology of periodontal tissue in rats with periodontitis. Its mechanism of action may be related to the targeted regulation of the HIF1α-PPARγ signaling axis.  

Key words: long non-coding RNA, tumor necrosis factor receptor superfamily, HIF1α-PPARγ signaling axis, periodontitis, hypoxia-inducible factor 1, lncRNA-TNFRSF13C