Induction of autophagy protects human dental pulp cells from lipopolysaccharide-induced pyroptotic cell death

The NOD-like receptor protein 3/caspase-1 inflammasome can be activated in human dental pulp tissue and fibroblasts; however, the underlying mechanisms are poorly understood. In the present study, lipopolysaccharide (LPS) was used to treat dental pulp cells to establish an inflammation model. Cell viability was examined by sulforhodamine B assay. Interleukin (IL)-1 beta, caspase-1, microtubule-associated protein-1 light chain 3-II/I and p62 were determined by western blotting and ELISA. The phosphorylation (p-) levels of NF-kappa B and NF-kappa B inhibitor (I kappa B)alpha protein were observed by western blotting. The results demonstrated that LPS induced pyroptotic cell death in cultured dental pulp cells, which was supported by the increased levels of IL-1 beta, IL-18 and caspase-1. Rapamycin and 3-methyladenine (3-MA) were used to activate and inhibit autophagy, and it was observed that LPS increased autophagy and rapamycin reduced LPS-induced dental pulp cell pyroptosis. However, 3-MA aggravated LPS-induced dental pulp cell pyroptosis. In addition, LPS inhibited the expression of I kappa B alpha, but increased the expression of p-NF-kappa B. Compared with the LPS group, 3-MA further inhibited the expression of I kappa B alpha but promoted the expression of p-NF-kappa B. However, rapamycin produced the opposite results to LPS. Under LPS treatment, the NF-kappa B pathway inhibitor BAY11-7082 further enhanced the inhibitory effects of rapamycin, but inhibited the promoting effects of 3-MA on the protein expression levels of IL-1 beta and caspase-1. The results of the present study demonstrated that there is an important crosstalk between autophagy, pyroptosis and the NF-kappa B pathway, and that the modulation of pyroptosis in dental pulp cells may be a promising strategy to pulpitis therapy.