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

AIM: To elucidate the role of HIF1alpha in pro-inflammatory cytokine mRNA expression from lipopolysaccharide (LPS)-stimulated human dental pulp cells (hDPCs). METHODOLOGY: mRNA expression of interleukin (IL) 1beta and tumour necrosis factor (TNF) alpha in LPS-stimulated hDPCs was determined by quantitative RT-PCR. Expression of nuclear factor kappa B (NFkappaB) p65 and phospho-NFkappaB p65 was analysed by Western blotting. Activation of NFkappaB signalling was measured by luciferase assay using a reporter vector containing an NFkappaB response element. Enforced expression of HIF1alpha was induced by transfection of expression vectors with native or constitutively active forms of HIF1alpha. Expression of HIF1alpha 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 IL1beta and TNFalpha, protein expression of phospho-NFkappaB p65 and LPS-induced NFkappaB signalling activity were promoted in low oxygen conditions (1% O2 ; P < 0.05). These findings were replicated following enforced expression and stabilization of HIF1alpha in hDPCs. Dimethyloxalylglycine, an inhibitor of prolyl hydroxylase (a HIF1alpha degrading enzyme), promoted IL1beta and TNFalpha mRNA expression and NFkappaB signalling in LPS-stimulated hDPCs (P < 0.05). HIF1alpha expression was detected in hDPCs cultured in low oxygen conditions (1% O2 ). LPS stimulation further enhanced HIF1alpha expression in hDPCs, especially within their nuclei. CONCLUSION: HIF1alpha promoted mRNA expression of IL1beta and TNFalpha via NFkappaB signalling in LPS-stimulated hDPCs, suggesting that HIF1alpha is involved in the progress of inflammation in dental pulp.