MicroRNA‐22 suppresses NLRP3/CASP1 inflammasome pathway‐mediated proinflammatory cytokine production by targeting the HIF‐1α and NLRP3 in human dental pulp fibroblasts

AIM: To investigate the synergetic regulatory effect of miR‐22 on HIF‐1α and NLRP3, subsequently regulating the production of the NLRP3/CASP1 inflammasome pathway‐mediated proinflammatory cytokines IL‐1β and IL‐18 in human dental pulp fibroblasts (HDPFs) during the progression of pulpitis. METHODOLOGY: Fluorescence in situ hybridization (FISH) and immunofluorescence (IF) were performed to determine the localization of miR‐22‐3p, NLRP3 and HIF‐1α in human dental pulp tissues (HDPTs). The miR‐22 mimics and inhibitor or plasmid of NLRP3 or HIF‐1α were used to upregulate or downregulate miR‐22 or NLRP3 or HIF‐1α in HDPFs, respectively. Computational prediction via TargetScan 5.1 and a luciferase reporter assay were conducted to confirm target association. The mRNA and protein expression of HIF‐1α, NLRP3, caspase‐1, IL‐1β and IL‐18 were determined by qRT‐PCR and western blotting, respectively. The release of IL‐1β and IL‐18 was analysed by ELISA. The significance of the differences between the experimental and control groups was determined by one‐way analysis of variance, p < .05 indicated statistical significance. RESULTS: A decrease in miR‐22 and an increase in HIF‐1α and NLRP3 in HDPTs occurred during the transformation of reversible pulpitis into irreversible pulpitis compared with that in the healthy pulp tissues (p < .05). In the normal HDPTs, miR‐22‐3p was extensively expressed in dental pulp cells. HIF‐1α and NLRP3 were mainly expressed in the odontoblasts and vascular endothelial cells. Whereas in the inflamed HDPTs, the odontoblast layers were disrupted. HDPFs were positive for miR‐22‐3p, HIF‐1α and NLRP3. Computational prediction via TargetScan 5.1 and luciferase reporter assays confirmed that both NLRP3 and HIF‐1α were direct targets of miR‐22 in HDPFs. The miR‐22 inhibitor further promoted the activation of NLRP3/CASP1 inflammasome pathway induced by ATP plus LPS and hypoxia (p < .05). In contrast, the miR‐22 mimic significantly inhibited the NLRP3/CASP1 inflammasome pathway activation induced by ATP plus LPS and hypoxia (p < .05). CONCLUSION: MiR‐22, as a synergetic negative regulator, is involved in controlling the secretion of proinflammatory cytokines mediated by the NLRP3/CASP1 inflammasome pathway by targeting NLRP3 and HIF‐1α. These results provide a novel function and mechanism of miR‐22‐HIF‐1α‐NLRP3 signalling in the control of proinflammatory cytokine secretion, thus indicating a potential therapeutic strategy for future endodontic treatment.