TLR5 activation induces expression of the pro‐inflammatory mediator Urokinase Plasminogen Activator via NF‐κB and MAPK signalling pathways in human dental pulp cells

Abstract

Aim To explore the involvement of TLR5 in pulp inflammation and to examine the effects of TLR5 activation with its ligand, FlaB protein, on pro‐inflammatory gene expression. Methodology TLR5 expression in dental pulp tissues and human dental pulp cells (hDPCs) were determined by immunohistochemistry, immunocytochemistry, Western blots and RT‐PCR analyses. To examine the role of TLR5, hDPCs were treated with recombinant FlaB protein (500 ng mL−1) to activate the receptor or with a small interfering RNA against TLR5 (si‐TLR5) to downregulate the receptor. After exposure to FlaB, the expression of inflammation‐related proteins was screened using a protein array kit. Western blots or qRT‐PCR analyses were performed to identify changes in the expression of uPA (urokinase plasminogen activator), TIMPs (tissue inhibitor of metalloproteinases), and IL‐6 and to determine their signalling pathways. Statistical analysis was performed using one‐way analysis of variance (anova) with Tukey post hoc test; P < 0.05 was considered statistically significant. Result TLR5 expression was identified in pulp tissues and hDPCs. In the protein array analysis, treatment with FlaB significantly increased uPA expression (P < 0.01) and significantly decreased TIMP1/4 (P < 0.05). FlaB treatment also significantly increased expression of the inflammatory marker IL‐6 (P < 0.01). FlaB treatment increased phosphorylation of the NF‐κB p65 subunit, JNK, p38 and ERK. Chemical inhibitors of NF‐κB (Bay11‐7082), p38 (SB202190) or ERK (U0126) decreased the FlaB induction of uPA expression. Downregulation of TLR5 expression by siRNA decreased the FlaB induction of uPA protein and p65 phosphorylation. Conclusion TLR5 activation with FlaB treatment induced the expression of uPA via the NF‐κB and MAPK signalling pathways. Flagellin‐bearing oral bacteria may cause pulp inflammation through TLR5. The findings provide new clues to control pulpal diseases by targeting TLR5 signalling pathways.

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Melatonin exerts anti-fibrinolytic effects by regulating IL-1β-induced changes in uPA, uPAR, and PAI-1 expression/production in human dental pulp cells

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