25-Hydroxycholesterol induces odontoclastic differentiation through RANK-RANKL upregulation and NF-κB activation in odontoblast-like MDPC-23 cells: An in vitro study.

AIM
The physiological effects and cellular mechanism of 25-hydroxycholesterol (25-HC), which is an oxysterol synthesized from cholesterol by cholesterol-25-hydroxylase (CH25H) expressed under inflammatory conditions, are still largely unknown during odontoclastogenesis. This study aimed to evaluate a 25-HC-induced odontoclastogenesis and its cellular mechanisms in odontoblast-like MDPC-23 cells.


METHODOLOGY
To investigate 25-HC-induced odontoclastogenesis of MDPC-23 cells and its cellular mechanism, haemotoxylin and eosin staining, tartrate-resistant acid phosphatase (TRAP) staining, dentine resorption assay, zymography, reactive oxygen species (ROS) detection, immunocytochemistry, and nuclear translocation were performed. The experimental values are presented as mean ± standard deviation and were compared using analysis of variance, followed by post-hoc multiple comparison (Tukey's test) using SPSS software version 22 (IBM Corp.). A P value <0.05 was considered statistically significant.


RESULTS
Lipopolysaccharide or receptor activator of nuclear factor-κB ligand (RANKL) induced the synthesis of 25-HC via the expression of CH25H in MDPC-23 cells (p<0.01). Multinucleated giant cells with morphological characteristics and TRAP activity of the odontoclast were increased by 25-HC in MDPC-23 cells (p<0.01). Moreover, 25-HC increased dentine resorption through the expression and activity of matrix metalloproteinases in MDPC-23 cells. It not only increased the expression of odontoclastogenic biomarkers but also translocated cytosolic nuclear factor-κB (NF-κB) to the nucleus in MDPC-23 cells. Additionally, 25-HC not only increased the production of ROS (p<0.01), expression of inflammatory mediators (p<0.01), pro-inflammatory cytokines, receptor activator of NF-κB (RANK), and RANKL but also suppressed the expression of osteoprotegerin (OPG) in MDPC-23 cells. In contrast, CDDO-Me, a chemical NF-κB inhibitor, decreased TRAP activity (p<0.01) and downregulated the expression of the odontoclastogenic biomarkers, including RANK and RANKL, in MDPC-23 cells.


CONCLUSION
25-HC induced odontoclastogenesis by modulating the RANK-RANKL-OPG axis via NF-κB activation in MDPC-23 cells. Therefore, these findings provide that 25-HC derived from cholesterol metabolism may be involved in the pathophysiological etiological factors of internal tooth resorption.