microRNAs are small noncoding RNA molecules that regulate RNA silencing and posttranscriptional gene expression, and many microRNAs are involved in inflammatory processes. In particular, microRNA 21 (miR-21) is upregulated in inflammatory environment and reported to induce anti-inflammatory responses. However, the involvement of miR-21 in pulpal inflammation and the precise mechanisms of antiinflammatory reactions induced by miR-21 remain unclear. We hypothesized that miR-21-5p expression is induced in lipopolysaccharide (LPS)-stimulated human dental pulp cells (hDPCs) and that miR-21-5p downregulates the proinflammatory cytokine expression in LPS-stimulated hDPCs. We found that miR-21-5p was upregulated in LPS-stimulated hDPCs concomitant with elevated proinflammatory cytokine expression and nuclear factor-kappa B (NF-κB) phosphorylation. miR-21-5p and cytokine expression were downregulated by BAY11-7085 and caffeic acid phenylethyl ester (CAPE), specific and potent NF-κB inhibitors. Enforced expression of miR-21-5p downregulated the Toll-like receptor (TLR)/NF-κB signaling via reducing the expression of TNF receptor-associated factor 6 (TRAF6) and programmed cell death 4 (PDCD4), which further induced the decrease of proinflammatory cytokine expression. hDPCs forcibly overexpressing miR-21-5p downregulated the LPS-induced expression of TNF receptorassociated factor 6 (TRAF6; a component of the Toll-like receptor [TLR]/NF-κB signaling pathway), programmed cell death 4 (PDCD4, a positive regulator of the TLR/NF-κB signaling pathway), and proinflammatory cytokines. In contrast, miR-21-5p inhibitortransfected hDPCs upregulated the expression of TRAF6, PDCD4, and inflammatory cytokines following LPS stimulation. These findings suggest that miR-21-5p expression was induced by the NF-κB signaling pathway, which was in turn negatively regulated by miR-21-5p via downregulation of TRAF6 and PDCD4 expression in LPS-stimulated hDPCs.

This study examined the effects and mechanisms of strontium ranelate (SrRn)—a drug used to treat osteoporosis—on the proliferation and differentiation/mineralization of cloned dental pulp-like cells (mouse dental papillae cells; MDPs). It also determined whether topical application of SrRn to exposed dental pulp tissue promotes the formation of mineralized tissue in vivo. The MDPs were cultured with or without SrRn, and cell proliferation, odonto-/osteoblastic gene expression, mineralized nodule formation, and Akt phosphorylation were evaluated. The formation of mineralized tissue in SrRn-treated pulp tissue in rat upper first molars was evaluated histologically. The SrRn up-regulated cell proliferation and expression of Alp (alkaline phosphatase), Bsp (bone sialoprotein), Dmp (dentin matrix acidic phosphoprotein)-1, Dspp (dentin sialophosphoprotein), and Oc (osteocalcin) in a dose-dependent manner. Mineralized nodule formation was also enhanced by SrRn. NPS-2143, a calcium-sensing receptor (CaSR) antagonist, and siRNA against the CaSR gene blocked SrRn-induced proliferation, odonto-/osteoblastic gene expression, and mineralized nodule formation. SrRn induced Akt phosphorylation, and this was blocked by NPS-2143. Topical application of SrRn to exposed rat molar pulps induced the formation of osteodentin-like mineralized tissue. Our study revealed for the first time that SrRn promotes proliferation and odonto-/osteogenic differentiation/mineralization of MDPs via PI3K/Akt signaling activated by CaSR in vitro; mineralized tissue forms from the dental pulp in vivo.

Accelerated dental pulp mineralization is a common complication in avulsed/luxated teeth, although the mechanisms underlying this remain unclear. We hypothesized that hypoxia due to vascular severance may induce osteo/odontoblast differentiation of dental pulp stem cells (DPSCs). This study examined the role of B-cell CLL/lymphoma 9 (BCL9), which is downstream of hypoxia-inducible factor 1α (HIF1α) and a Wnt/β-catenin transcriptional cofactor, in the osteo/odontoblastic differentiation of human DPSCs (hDPSCs) under hypoxic conditions. hDPSCs were isolated from extracted healthy wisdom teeth. Hypoxic conditions and HIF1α overexpression induced significant upregulation of mRNAs for osteo/odontoblast markers (RUNX2, ALP, OC), BCL9, and Wnt/β-catenin signaling target genes (AXIN2, TCF1) in hDPSCs. Overexpression and suppression of BCL9 in hDPSCs up- and downregulated, respectively, the mRNAs for AXIN2, TCF1, and the osteo/odontoblast markers. Hypoxic-cultured mouse pulp tissue explants showed the promotion of HIF1α, BCL9, and β-catenin expression and BCL9-β-catenin co-localization. In addition, BCL9 formed a complex with β-catenin in hDPSCs in vitro. This study demonstrated that hypoxia/HIF1α-induced osteo/odontoblast differentiation of hDPSCs was partially dependent on Wnt/β-catenin signaling, where BCL9 acted as a key mediator between HIF1α and Wnt/β-catenin signaling. These findings may reveal part of the mechanisms of dental pulp mineralization after traumatic dental injury.