NOD2 Mediates Odontoblast Differentiation and RANKL Expression

• Published in: Journal of dental research 2014-07, Vol.93 (7), p.678-684
• Main Authors: Lee, S.-I., Kim, G.-T., Kim, H.J., Park, S.-H., Kim, E.-C.
• Format: Article
• Language: English
• Subjects: Acetylmuramyl-Alanyl-Isoglutamine - pharmacology; Adjuvants, Immunologic - pharmacology; Bacteria; Bone marrow; Cell Differentiation - drug effects; Cell Differentiation - physiology; Cell Line; Cytokines; Cytokines - drug effects; Dental pulp; Dental Pulp - cytology; Dentin; Dentistry; Dual Specificity Phosphatase 1 - drug effects; Gene Silencing; Humans; Immune system; Inflammation; Kinases; Ligands; Macrophage Colony-Stimulating Factor - drug effects; Macrophages; MAP kinase; MAP kinase phosphatase; Mitogen-Activated Protein Kinases - drug effects; MKP-1 protein; Muramyl dipeptide; NOD2 protein; Nod2 Signaling Adaptor Protein - agonists; Nod2 Signaling Adaptor Protein - genetics; Nod2 Signaling Adaptor Protein - physiology; Odontoblasts - drug effects; Odontoblasts - physiology; Oligomerization; Osteoblastogenesis; Osteoclastogenesis; Osteoclasts - physiology; Osteoprotegerin - drug effects; Phosphorylation; Proteins; RANK Ligand - analysis; RANK Ligand - drug effects; Research Reports; RNA, Small Interfering - genetics; Root resorption; siRNA; TRANCE protein
• ISSN: 0022-0345; 1544-0591; 1544-0591
• DOI: 10.1177/0022034514535214

The precise regulation of odontoblast differentiation and osteoclastogenic cytokine expression in human dental pulp cells (HDPCs) is crucial for the pathology of bacteria-related pulpitis. Although the up-regulation of nucleotide-binding oligomerization domain-containing protein 2 (NOD2) has been reported in inflamed human dental pulps, the role of NOD2 in the differentiation of HDPCs remains unclear. Here, we show the involvement of NOD2 in odontoblast differentiation together with osteoclastogenic cytokine expression in HDPCs. Treatment with muramyl dipeptide (MDP), a known NOD2-agonist, significantly inhibited odontoblast differentiation of HDPCs, as revealed by reduced ALP activity, osteoblast/odontoblast marker expression, and mineralized nodule formation. Importantly, the forced down-regulation of NOD2 by small interfering RNA (siRNA) recovered MDP-down-regulated odontoblast differentiation. MDP-elicited suppression of odontoblast differentiation resulted from the increased expression of MKP-1 protein and the subsequent decline of MAPKs phosphorylation, which is a prerequisite for odontoblast differentiation. Furthermore, we found that MDP treatment elevated the expression of osteoclastogenic cytokines in HDPCs, which was also reversed by NOD2 silencing. Analysis of these data, taken together, suggests that the regulation of NOD2 expression upon MDP challenge might serve as an intrinsic mechanism that underlies the hindered dentin formation and accelerated dentin resorption in bacterial infection-mediated pulpitis. Abbreviations: HDPCs, human dental pulp cells; NOD2, nucleotide-binding oligomerization domain-containing protein 2; MDP, muramyl dipeptide; siRNA, small interfering RNA; MAPKs, mitogen-activated protein kinases; MKP-1, MAPK phosphatase-1; BMMs, bone-marrow-derived macrophages; and CM, conditioned medium.