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

Aim To elucidate the role of HIF1 alpha in pro-inflammatory cytokine mRNA expression from lipopolysaccharide (LPS)-stimulated human dental pulp cells (hDPCs). Methodology mRNA expression of interleukin (IL) 1 beta and tumour necrosis factor (TNF) alpha in LPS-stimulated hDPCs was determined by quantitative RT-PCR. Expression of nuclear factor kappa B (NF kappa B) p65 and phospho-NF kappa B p65 was analysed by Western blotting. Activation of NF kappa B signalling was measured by luciferase assay using a reporter vector containing an NF kappa B response element. Enforced expression of HIF1 alpha was induced by transfection of expression vectors with native or constitutively active forms of HIF1 alpha. Expression of HIF1 alpha 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 IL1 beta and TNF alpha, protein expression of phospho-NF kappa B p65 and LPS-induced NF kappa B signalling activity were promoted in low oxygen conditions (1% O-2; P < 0.05). These findings were replicated following enforced expression and stabilization of HIF1 alpha in hDPCs. Dimethyloxalylglycine, an inhibitor of prolyl hydroxylase (a HIF1 alpha degrading enzyme), promoted IL1 beta and TNF alpha mRNA expression and NF kappa B signalling in LPS-stimulated hDPCs (P < 0.05). HIF1 alpha expression was detected in hDPCs cultured in low oxygen conditions (1% O-2). LPS stimulation further enhanced HIF1 alpha expression in hDPCs, especially within their nuclei. Conclusion HIF1 alpha promoted mRNA expression of IL1 beta and TNF alpha via NF kappa B signalling in LPS-stimulated hDPCs, suggesting that HIF1 alpha is involved in the progress of inflammation in dental pulp.