Abstract
Odontoblasts are derived from dental papilla mesenchymal cells and have an important role in defense against bacterial infection, whereas autophagy can recycle long-lived proteins and damaged organelles to sustain cellular homeostasis. Thus, this study explores the role of autophagy in odontoblast differentiation with lipopolysaccharide (LPS) stimulation in vitro and the colocalization of p-NF-κB and LC3 in caries teeth. The odontoblasts differentiation was enhanced through LPS stimulation, and this outcome was reflected in the increased number of mineralized nodules and alkaline phosphatase (ALP) activity. The expression levels of the autophagy markers LC3, Atg5, Beclin1 and TFE3 increased time dependently, as well along with the amount of autophagosomes and autophagy fluxes. This result suggests that autophagy was enhanced in odontoblasts cultured with mineralized-induced media containing LPS. To confirm the role of autophagy in differentiated odontoblasts with LPS stimulation, chloroquine (CQ) or rapamycin were used to either block or enhance autophagy. The number of mineralized nodules decreased when autophagy was inhibited, but this number increased with rapamycin treatment. Phosphorylated nuclear factor-κB (NF-κB) expression was negatively related to autophagy and could inhibit odontoblast differentiation. Furthermore, p-NF-κB and LC3 colocalization could be detected in cells stimulated with LPS. The nucleus translocation of p-NF-κB in odontoblasts was enhanced when autophagy was inhibited by Atg5 small interfering RNA. In addition, the colocalization of p-NF-κB and LC3 in odontoblasts and sub-odontoblastic layers was observed in caries teeth with reactionary dentin. Therefore, our findings provide a novel insight into the role of autophagy in regulating odontoblast differentiation by suppressing NF-κB activation in inflammatory environments.
Highlights
Dentin is the main hard tissue of the tooth that is formed by odontoblasts, which stem from neural crest-derived odontogenic mesenchymal cells.[1,2] The dental papilla gives rise to odontoblasts,[2,3] and dentinogenic markers dentin sialoprotein (DSP), dentin matrix protein-1 (DMP1) and osterix (OSX) are increased during odontoblast differentiation.[3,4] Odontoblasts are responsible for the production of physiological primary and secondary dentin.[5,6] these cells, along with dental pulp tissues, are frequently infected with bacteria from dental caries.[7]
Inflammation induced the upregulation of autophagy, which promoted odontoblast differentiation capacity by suppressing nuclear factor-κB (NF-κB) nuclear translocation and activation
A previous study reported that tumor necrosis factor-α (TNF-α) can stimulate the differentiation of dental pulp cells to odontoblastic phenotypes through p38.33 Goldberg et al.[32] pointed out that osteoblast/odontoblast-like differentiation can be promoted by activating dendritic cells via a mild inflammatory process
Summary
Dentin is the main hard tissue of the tooth that is formed by odontoblasts, which stem from neural crest-derived odontogenic mesenchymal cells.[1,2] The dental papilla gives rise to odontoblasts,[2,3] and dentinogenic markers dentin sialoprotein (DSP), dentin matrix protein-1 (DMP1) and osterix (OSX) are increased during odontoblast differentiation.[3,4] Odontoblasts are responsible for the production of physiological primary and secondary dentin.[5,6] these cells, along with dental pulp tissues, are frequently infected with bacteria from dental caries.[7]. Autophagy is a cellular process that recycles damaged organelles and long-lived proteins to maintain cell energy homeostasis.[10] This process is initiated by the formation of double membrane vesicles. NF-κB has an important role in the regulation of inflammatory responses.[7] A current study suggested that the reduced expression of NFκB in dental pulp stem cells in the presence of inflammatory cytokines enhances odontoblastic differentiation and collagen matrix formation.[27] A previous study showed that NF-κB inhibits the bone formation of osteoblast stems from initial inflammatory environment.[28] the relationship between autophagy and NF-κB remains vague, as well as their involvement in odontoblast differentiation with LPS stimulation
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