Role of FOXO3a in LPS-induced inflammatory conditions in human dental pulp cells

Objectives: We investigated the involvement of FOXO3a in lipopolysaccharide (LPS)-induced inflammation in primary human dental pulp cells (HDPCs).

Methods: HDPCs that were isolated from donors undergoing tooth extraction for orthodontic purposes were cultured with or without 1 μg/mL LPS at various intervals. The FOXO3a localization in the HDPCs was verified using immunofluorescence. Proinflammatory cytokines, such as interleukin (IL) 1β, IL6, and IL8, as well as their underlying mechanisms were assessed by observing gene and protein expressions through quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot analyses.

Results: LPS treatment enhanced the expressions of IL1β, IL6, and IL8 in HDPCs, concurrently activating nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB). Furthermore, FOXO3a expression was higher in the LPS-stimulated HDPCs, as confirmed by immunofluorescence localization. The results of loss-/gain-of-function approaches confirmed the regulatory role of FOXO3a in inflammatory HDPCs. FOXO3a knockdown attenuated proinflammatory cytokine expression; FOXO3a overexpression augmented their expression levels. FOXO3a inhibited retinoic acid receptor-related orphan receptor alpha (RORα) expression, thereby inactivating NFκB.

Conclusion: Our findings suggest that FOXO3a contributes to homeostasis in HDPCs through modulating the expression of proinflammatory cytokines under inflammatory conditions.