Hypoxia-inducible factor 1α promotes interleukin 1β and tumour necrosis factor α expression in lipopolysaccharide-stimulated human dental pulp cells

Abstract

Aim: To elucidate the role of HIF1α in pro-inflammatory cytokine mRNA expression from lipopolysaccharide (LPS)-stimulated human dental pulp cells (hDPCs).

Methodology: mRNA expression of interleukin (IL) 1β and tumour necrosis factor (TNF) α in LPS-stimulated hDPCs was determined by quantitative RT-PCR. Expression of nuclear factor kappa B (NFκB) p65 and phospho-NFκB p65 was analysed by Western blotting. Activation of NFκB signalling was measured by luciferase assay using a reporter vector containing an NFκB response element. Enforced expression of HIF1α was induced by transfection of expression vectors with native or constitutively active forms of HIF1α. Expression of HIF1α protein in hDPCs was evaluated by immunocytochemistry and Western blotting. One-way analysis of variance and the Tukey-Kramer test were performed to determine a significant difference (P < 0.05).

Results: mRNA expression of IL1β and TNFα, protein expression of phospho-NFκB p65 and LPS-induced NFκB signalling activity were promoted in low oxygen conditions (1% O₂ ; P < 0.05). These findings were replicated following enforced expression and stabilization of HIF1α in hDPCs. Dimethyloxalylglycine, an inhibitor of prolyl hydroxylase (a HIF1α degrading enzyme), promoted IL1β and TNFα mRNA expression and NFκB signalling in LPS-stimulated hDPCs (P < 0.05). HIF1α expression was detected in hDPCs cultured in low oxygen conditions (1% O₂ ). LPS stimulation further enhanced HIF1α expression in hDPCs, especially within their nuclei.

Conclusion: HIF1α promoted mRNA expression of IL1β and TNFα via NFκB signalling in LPS-stimulated hDPCs, suggesting that HIF1α is involved in the progress of inflammation in dental pulp.

Keywords: HIF1α; NFκB signalling; human dental pulp cells; lipopolysaccharide; pro-inflammatory cytokine.