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Dopamine (DA) is produced from tyrosine by tyrosine hydroxylase (TH). A recent study has reported that DA promotes the mineralization of murine preosteoblasts. However, the role of DA in odontoblasts has not been examined. Therefore, in this investigation, we researched the expression of TH and DA in odontoblasts and the effects of DA on the differentiation of preodontoblasts (KN‐3 cells). Immunostaining showed that TH and DA were intensely expressed in odontoblasts and preodontoblasts of rat incisors and molars. KN‐3 cells expressed D1‐like and D2‐like receptors for DA. Furthermore, DA promoted odontoblastic differentiation of KN‐3 cells, whereas an antagonist of D1‐like receptors and a PKA signaling blocker, inhibited such differentiation. However, antagonists of D2‐like receptors promoted differentiation. These results suggested that DA in preodontoblasts and odontoblasts might promote odontoblastic differentiation through D1‐like receptors, but not D2‐like receptors, and PKA signaling in an autocrine or paracrine manner and plays roles in dentinogenesis. [ABSTRACT FROM AUTHOR]

Cellular senescence has been suggested to be involved in physiological changes of cytokine production. Previous studies showed that the concentration of tumor necrosis factor‐α (TNF‐α) is higher in the blood of aged people compared with that of young people. So far, the precise effects of TNF‐α on the odontoblastic differentiation of pulp cells have been controversial. Therefore, we aimed to clarify how this cytokine affected pulp cells during aging. Human dental pulp cells (HDPCs) were cultured until reaching the plateau of their growth, and the cells were isolated at actively (young HDPCs; yHDPCs) or inactively (senescent HDPCs; sHDPCs) proliferating stages. sHDPCs expressed senescence‐related molecules while yHDPCs did not. When these HDPCs were cultured in an odontoblast‐inductive medium, both young and senescent cells showed mineralization, but mineralization in sHDPCs was lower compared with yHDPCs. However, the administration of TNF‐α to this culture medium altered these responses: yHDPCs showed downregulated mineralization, while sHDPCs exhibited significantly increased mineralization. Furthermore, the expression of tumor necrosis factor receptor 1 (TNFR1), a receptor of TNF‐α, was significantly upregulated in sHDPCs compared with yHDPCs. Downregulation of TNFR1 expression led to decreased mineralization of TNF‐α‐treated sHDPCs, whereas restored the reduction in TNF‐α‐treated yHDPCs. These results suggested that sHDPCs preserved the odontoblastic differentiation capacity and TNF‐α promoted odontoblastic differentiation of HDPCs with the progress of their population doublings through increased expression of TNFR1. Thus, TNF‐α might exert a different effect on the odontoblastic differentiation of HDPCs depending on their proliferating activity. In addition, the calcification of pulp chamber with age may be related with increased reactivity of pulp cells to TNF‐α. These data could argue the possible involvement of different signaling pathways in tumor necrosis factor‐α‐inducing events depending on the cell aging stage, which might cause different cell responses. [ABSTRACT FROM AUTHOR]

Wnt5a, a non-canonical Wnt protein, is known to play important roles in several cell functions. However, little is known about the effects of Wnt5a on osteoblastic differentiation of periodontal ligament (PDL) cells. Here, we examined the effects of Wnt5a on osteoblastic differentiation and associated intracellular signaling in human PDL stem/progenitor cells (HPDLSCs). We found that Wnt5a suppressed expression of bone-related genes (ALP, BSP, and Osterix) and alizarin red-positive mineralized nodule formation in HPDLSCs under osteogenic conditions. Immunohistochemical analysis revealed that a Wnt5a-related receptor, receptor tyrosine kinase-like orphan receptor 2 (Ror2), was expressed in rat PDL tissue. Interestingly, knockdown of Ror2 by siRNA inhibited the Wnt5a-induced downregulation of bone-related gene expression in HPDLSCs. Moreover, Western blotting analysis showed that phosphorylation of the intracellular signaling molecule, c-Jun N-terminal kinase (JNK) was upregulated in HPDLSCs cultured in osteoblast induction medium with Wnt5a, but knockdown of Ror2 by siRNA downregulated the phosphorylation of JNK. We also examined the effects of JNK inhibition on Wnt5a-induced suppression of osteoblastic differentiation of HPDLSCs. The JNK inhibitor, SP600125 inhibited the Wnt5a-induced downregulation of bone-related gene expression in HPDLSCs. Additionally, SP600125 inhibited the Wnt5a-induced suppression of the alizarin red-positive reaction in HPDLSCs. These results suggest that Wnt5a suppressed osteoblastic differentiation of HPDLSCs through Ror2/JNK signaling. Non-canonical Wnt signaling, including Wnt5a/Ror2/JNK signaling, may function as a negative regulator of mineralization, preventing the development of non-physiological mineralization in PDL tissue. [ABSTRACT FROM AUTHOR]

Appropriate mechanical loading during occlusion and mastication play an important role in maintaining the homeostasis of periodontal ligament (PDL) tissue. Connective tissue growth factor (CTGF/CCN2), a matricellular protein, is known to upregulate extracellular matrix production, including collagen in PDL tissue. However, the underlying mechanisms of CTGF/CCN2 in regulation of PDL tissue integrity remain unclear. In this study, we investigated the effect of CTGF/CCN2 on osteo/cementoblastic and fibroblastic differentiation of human PDL stem cells using the cell line 1-11. CTGF/CCN2 expression in rat PDL tissue and human PDL cells (HPDLCs) was confirmed immunohisto/cytochemically. Mechanical loading was found to increase gene expression and secretion of CTGF/CCN2 in HPDLCs. CTGF/CCN2 upregulated the proliferation and migration of 1-11 cells. Furthermore, increased bone/cementum-related gene expression in this cell line led to mineralization. In addition, combined treatment of 1-11 cells with CTGF/CCN2 and transforming growth factor-β1 (TGF-β1) significantly promoted type I collagen and fibronectin expression compared with that of TGF-β1 treatment alone. Thus, these data suggest the underlying biphasic effects of CTGF/CCN2 in 1-11 cells, inducible osteo/cementoblastic, and fibroblastic differentiation dependent on the environmental condition. CTGF/CCN2 may contribute to preservation of the structural integrity of PDL tissue, implying its potential use as a therapeutic agent for PDL regeneration. J. Cell. Physiol. 229: 150-159, 2014. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]