Abstract
Objectives: Formation of reparative dentin is a complex process in which dead odontoblasts are replaced by odontoblast-like cells following recruitment and differentiation of dental pulp stem cells (DPSCs). The process involves an inflammatory response, but the nature and effect of this response is debatable. Danger associated molecular patterns (DAMPs) released from dying cells induce inflammation via activation of inflammasomes. The aim is to investigate the ability of dead odontoblasts to induce inflammasome-dependent inflammation and whether this inflammatory response is reparative.
Methods: NLRP3 inflammasome expression in healthy and carious teeth was determined by immunohistochemistry. Odontoblast-like cells were subjected to freezing-thawing cycles to produce odontoblast necrotic cell lysate (ONCL). Following treatment of THP-1 macrophages with ONCL, ELISA and multiplex arrays were used to measure levels of cytokines release. Western blotting was used to determine if p38 MAPK and NF-κB were involved in the downstream signalling. The chemoattractant properties of ONCL on DPCs was assessed by trans-well migration assays. Alizarin Red, alkaline phosphatase (ALP) activity assays and RT-qPCR were used to determine the odontogenic differentiation of DPCs.
Results: NLRP3 was expressed in the dental pulp, with higher expression in carious compared to non-carious teeth. Release of the inflammatory cytokines IL-1β, IL-6, IL-8, TNFα and angiogenic growth factors, angiogenin and angiopoietin by THP-1 macrophages treated with ONCL was comparable to that induced by bacterial LTA. IL-1β release from THP-1 treated with ONCL was reduced upon treatment with caspase-1 inhibitor. p38 MAPK and NF-κB were activated downstream of ONCL treatment. ONCL induced migration of DPCs as shown by trans-well migration assays. An increase in ALP activity, odont/osteogenic genes and mineralisation occurred following IL-1β treatment.
Conclusions: NLRP3 is highly expressed in the dental pulp of carious teeth. Dead odontoblasts activated an inflammasome-dependent inflammatory response and induced DPCs migration and subsequent odontogenic differentiation.
Methods: NLRP3 inflammasome expression in healthy and carious teeth was determined by immunohistochemistry. Odontoblast-like cells were subjected to freezing-thawing cycles to produce odontoblast necrotic cell lysate (ONCL). Following treatment of THP-1 macrophages with ONCL, ELISA and multiplex arrays were used to measure levels of cytokines release. Western blotting was used to determine if p38 MAPK and NF-κB were involved in the downstream signalling. The chemoattractant properties of ONCL on DPCs was assessed by trans-well migration assays. Alizarin Red, alkaline phosphatase (ALP) activity assays and RT-qPCR were used to determine the odontogenic differentiation of DPCs.
Results: NLRP3 was expressed in the dental pulp, with higher expression in carious compared to non-carious teeth. Release of the inflammatory cytokines IL-1β, IL-6, IL-8, TNFα and angiogenic growth factors, angiogenin and angiopoietin by THP-1 macrophages treated with ONCL was comparable to that induced by bacterial LTA. IL-1β release from THP-1 treated with ONCL was reduced upon treatment with caspase-1 inhibitor. p38 MAPK and NF-κB were activated downstream of ONCL treatment. ONCL induced migration of DPCs as shown by trans-well migration assays. An increase in ALP activity, odont/osteogenic genes and mineralisation occurred following IL-1β treatment.
Conclusions: NLRP3 is highly expressed in the dental pulp of carious teeth. Dead odontoblasts activated an inflammasome-dependent inflammatory response and induced DPCs migration and subsequent odontogenic differentiation.
| Original language | English |
|---|---|
| Journal | Journal of Dental Research |
| Volume | 99 |
| Issue number | Spec Iss A |
| Publication status | Published - Jul 2020 |