NLRP6 suppresses the inflammatory response of human periodontal ligament cells by inhibiting NF-κB and ERK signal pathways.

AIM: To explore the function and mechanisms of NLRP6 (NOD-, LRR- and pyrin domain-containing 6) in the inflammatory response of human periodontal ligament cells (HPDLCs).

METHODOLOGY: Tissues associated with apical periodontitis were obtained from three patients who underwent endodontic microsurgery. The expression of NLRP6 in 3 human apical periodontitis tissues and HPDLCs was examined by immunohistochemistry and immunofluorescence, respectively. The expressions of NLRP6, Phospho(p)- p65, p65, IκB-α, p- IκB-α, ERK, p- ERK, NLRP3, Pro interleukin (IL)-1β, Pro caspase-1 and apoptosis-associated speck-like protein containing a CARD (ASC) were examined by western blot. The gene expression and secretion of proinflammatory cytokines were detected using quantitative real-time polymerase chain reaction and enzyme-linked immunosorbent assay. Data were analysed statistically with independent sample t-tests.

RESULTS: NLRP6 was expressed in inflammatory periapical tissues and HPDLCs. Lipopolysaccharide (LPS) from Escherichia coli induced NLRP6 in HPDLCs (P < 0.05). After silencing NLRP6, E. coli LPS-induced activation of NF-κB and ERK signalling was enhanced, which was also accompanied by elevated levels of IL-6 and tumour necrosis factor-α (TNF-α) (P < 0.05). Moreover, knockdown of NLRP6 led to up-regulation of NLRP3, Pro IL-1β and Pro caspase-1 (P < 0.05), whereas down-regulation of ASC (P < 0.05), which may contribute to unchanged levels of IL-1β in HPDLCs inflammation.

CONCLUSION: NLRP6 was functionally expressed in inflamed periapical tissues and HPDLCs. NLRP6 negatively regulated the production of IL-6 and TNF-α in HPDLCs inflammation by inhibiting NF-κB and ERK signal pathways.