CCN2/CTGF expression via cellular uptake of BMP-1 is associated with reparative dentinogenesis

Bone morphogenetic protein-4 induced matrix turnover and osteogenic differentiation-related molecules of stem cells from apical papilla and its associated ALK/Smad signaling

Background/purpose

Revascularization procedures are used over apexification to treat teeth with necrotic pulp tissues and incomplete root formation. Clinically, inducing proliferation, migration, matrix deposition, and differentiation of stem cells from apical papilla (SCAPs) are critical for pulp regeneration. The study aimed to elucidate the impact of bone morphogenetic protein-4 (BMP-4) on plasminogen activation molecules and the osteogenic/odontogenic differentiation of SCAPs, as well as understand the related signaling mechanisms.

Materials and methods

SCAPs were exposed to BMP-4 with or without signal transduction inhibitors. Cell viability was assessed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. mRNA levels were quantified using real-time PCR. Protein expression in SCAPs was analyzed through immunofluorescent staining or western blotting. Cellular protein production was measured with enzyme-linked immunosorbent assay.

Results

BMP-4 induced suppressor of mother against decapentaplegic (Smad)1/5/8 and Smad2/3 phosphorylation and activation. It also promoted higher expression of osteogenic and odontogenic markers, including Osterix, N-cadherin, and secreted protein acidic and rich in cysteine (SPARC), in SCAPs. Additionally, BMP-4 stimulated connective tissue growth factor (CTGF), plasminogen activator inhibitor-1 (PAI-1), and urokinase plasminogen activator receptor (uPAR) expression, but inhibited uPA expression and production in SCAPs, indicating its role in matrix remodeling and cell migration. Inhibition of Smad2/3 with SB431542 and Smad1/5/8 with LDN193189 attenuated the BMP-4-induced expression Osx, N-cadherin, CTGF, SPARC, uPAR and PAI-1.

Conclusion

These results indicate that BMP-4 stimulates the osteogenic and odontogenic differentiation of SCAPs by regulating matrix turnover and mineralization-related proteins. Furthermore, these processes are associated with the induction of Smad2/3 and Smad1/5/8 of SCAPs by BMP-4.

The Genes Involved in Dentinogenesis

The development and repair of dentin are strictly regulated by hundreds of genes. Abnormal dentin development is directly caused by gene mutations and dysregulation. Understanding and mastering this signal network is of great significance to the study of tooth development, tissue regeneration, aging, and repair and the treatment of dental diseases. It is necessary to understand the formation and repair mechanism of dentin in order to better treat the dentin lesions caused by various abnormal properties, whether it is to explore the reasons for the formation of dentin defects or to develop clinical drugs to strengthen the method of repairing dentin. Molecular biology of genes related to dentin development and repair are the most important basis for future research.

Functions of Matricellular Proteins in Dental Tissues and Their Emerging Roles in Orofacial Tissue Development, Maintenance, and Disease

Matricellular proteins (MCPs) are defined as extracellular matrix (ECM) associated proteins that are important regulators and integrators of microenvironmental signals, contributing to the dynamic nature of ECM signalling. There is a growing understanding of the role of matricellular proteins in cellular processes governing tissue development as well as in disease pathogenesis. In this review, the expression and functions of different MP family members (periostin, CCNs, TSPs, SIBLINGs and others) are presented, specifically in relation to craniofacial development and the maintenance of orofacial tissues, including bone, gingiva, oral mucosa, palate and the dental pulp. As will be discussed, each MP family member has been shown to have non-redundant roles in development, tissue homeostasis, wound healing, pathology and tumorigenesis of orofacial and dental tissues.

Performance of a Biodegradable Composite with Hydroxyapatite as a Scaffold in Pulp Tissue Repair

Vital pulp therapy is an important endodontic treatment. Strategies using growth factors and biological molecules are effective in developing pulp capping materials based on wound healing by the dentin-pulp complex. Our group developed biodegradable viscoelastic polymer materials for tissue-engineered medical devices. The polymer contents help overcome the poor fracture toughness of hydroxyapatite (HAp)-facilitated osteogenic differentiation of pulp cells. However, the composition of this novel polymer remained unclear. This study evaluated a novel polymer composite, P(CL-co-DLLA) and HAp, as a direct pulp capping carrier for biological molecules. The biocompatibility of the novel polymer composite was evaluated by determining the cytotoxicity and proliferation of human dental stem cells in vitro. The novel polymer composite with BMP-2, which reportedly induced tertiary dentin, was tested as a direct pulp capping material in a rat model. Cytotoxicity and proliferation assays revealed that the biocompatibility of the novel polymer composite was similar to that of the control. The novel polymer composite with BMP-2-induced tertiary dentin, similar to hydraulic calcium-silicate cement, in the direct pulp capping model. The BMP-2 composite upregulated wound healing-related gene expression compared to the novel polymer composite alone. Therefore, we suggest that novel polymer composites could be effective carriers for pulp capping.

Immunolocalization of transforming growth factor-beta1, connective tissue growth factor, phosphorylated-SMAD2/3, and phosphorylated-ERK1/2 during mouse incisor development

BACKGROUND/AIMS

Connective tissue growth factor (CTGF) is a downstream mediator of transforming growth factor-beta 1 (TGF-β₁) and TGF-β₁-induced CTGF expression is regulated through SMAD and mitogen-activated protein kinase (MAPK) signaling pathways. However, little is known about the localization of CTGF and TGF-β₁ signaling cascades during incisor development. Therefore, we aimed to investigate the distribution pattern of TGF-β₁, CTGF, phosphorylated-SMAD2/3 (p-SMAD2/3), and phosphorylated-ERK1/2 (p-ERK1/2) in the developing mouse incisors.

MATERIALS AND METHODS

ICR mice heads of embryonic (E) day 16.5, postnatal (PN) day 0.5 and PN3.5 were processed for immunohistochemistry.

RESULTS

From E16.5 to PN3.5, moderate to strong staining for TGF-β₁ and CTGF was localized in stellate reticulum (SR), transit amplifying (TA) cells, outer enamel epithelium (OEE), preameloblasts (PA), preodontoblasts (PO), and dental papilla (DP). p-SMAD2/3 was weakly positive in SR and OEE at E16.5 and PN0.5 but was strongly positive in SR and OEE at PN3.5. Particularly, in the stem cell niche, p-SMAD2/3 was only localized in SR cells adjacent to OEE. There was no staining for p-SMAD2/3 in TA cells, PA and PO, although weak to moderate staining for p-SMAD2/3 was seen in DP. From E16.5 to PN3.5, p-ERK1/2 was negative in TA cells, OEE, PA and PO, whereas weak to moderate staining for p-ERK1/2 was observed in SR. DP was moderately stained for p-ERK1/2.

CONCLUSIONS

TGF-β₁ and CTGF show a similar expression, while p-SMAD2/3 and p-ERK1/2 exhibit differential distribution pattern, which indicates that CTGF and TGF-β₁ signaling cascades might play a regulatory role in incisor development.

The in vitro effects of CCN2 on odontoblast-like cells

OBJECTIVE

To investigate the in vitro effects of CCN2 on odontoblast-like cells proliferation and differentiation.

DESIGN

MDPC-23 cells were cultured in DMEM supplemented with 5% FBS. CCN2 was either added to culture media or coated onto culture polystyrene, addition or coating of dH2O was served as control. In the addition group, CCN2 (100 ng/mL) was added into culture media. In the coating group, CCN2 at the concentration of 1000 ng/mL was employed. Cell proliferation was performed using CCK-8 assay. Cell differentiation and mineralization were analyzed by ALPase activity assay, real time RT-PCR and alizarin red staining. One-way ANOVA with post-hoc tukey HSD test was used for statistical analysis.

RESULTS

MDPC-23 cells exhibited robust proliferative activity upon exposure to either soluble or immobilized CCN2. ALP activity of cells cultured on CCN2-modified surface was continuously strengthened from day six (0.831 ± 0.024 units/μg protein versus 0.563 ± 0.006 units/μg protein of control) till day eight (1.035 ± 0.139 units/μg protein versus 0.704 ± 0.061 units/μg protein of control). Gene expression of BSP, OCN and OPN were promoted by soluble CCN2 after 48 h exposure. Moreover, gene expression of BSP, OCN, OPN, ALP, COL1 A1, Runx-2, DSPP and DMP-1 was significantly enhanced by immobilized CCN2. Finally, mineralization of MDPC-23 cells was accelerated by both soluble and immobilized CCN2 to different extent.

CONCLUSIONS

The findings indicate that CCN2 promoted proliferation, odontogenic gene expression and mineralization of MDPC-23 cells. It is proposed that CCN2 may be a promising adjunctive formula for dentin regeneration.

Cell Biological Assays for Measuring Odontogenic Activities of CCN Proteins

In postnatal dentin formation, odontoblast differentiation occurs in the pulp tissue regenerative process under pathological condition. Odontoblasts and newly differentiated odontoblast-like cells beneath the caries lesion form tertiary dentin and are highly odontogenic. To observe the activity of dentinogenesis occur within the hard tissue, a combination of immunohistological analysis and immunodetection of dentinogenesis specific molecules, such as dentin sialophosphoprotein (DSPP) and/or its cleaved products dentin sialoprotein (DSP) and dentin phosphoprotein (DPP), is a reliable approach. Besides, recent studies have revealed that the expression of CCN family member 2 (CCN2), a member of the CCN family protein, is confirmed in accordance with tooth development and reparative dentin formation. Therefore, CCN2 could serve as a marker for dentinogenesis. Here, we describe a method for visualizing the CCN2 signal as an odontogenic activity in formalin-fixed paraffin-embedded (FFPE) sections of demineralized human teeth and human dental pulp cells.

Immunolocalization of connective tissue growth factor, transforming growth factor-beta1 and phosphorylated-SMAD2/3 during the postnatal tooth development and formation of junctional epithelium

Connective tissue growth factor (CTGF) is a downstream mediator of transforming growth factor-beta 1 (TGF-β₁) and TGF-β₁-induced CTGF expression is regulated through SMAD pathway. However, there is no literature showing the expression of TGF-β₁-SMAD2/3-CTGF signaling pathway during postnatal tooth development and the formation of junctional epithelium (JE). Hence, we aimed to analyze the localization of TGF-β₁, CTGF and phosphorylated SMAD2/3 (p-SMAD2/3) in the developing postnatal rat molars. Wistar rats were killed at postnatal (PN) 0.5, 3.5, 7, 14 and 21days and the upper jaws were processed for immunohistochemistry. At PN0.5 and PN3.5, weak staining for TGF-β₁ and CTGF was evident in preameloblasts (PA), while moderate to strong staining was seen in odontoblasts (OD), dental papilla (DPL), secretary ameloblasts (SA), preodontoblasts (PO) and polarized odontoblasts (PoO). There was no staining for p-SMAD2/3 in PA, SA, PO and PoO, although strong staining was localized in DPL. OD was initially moderately positive and then negative for p-SMAD2/3. At PN7, intense staining for TGF-β₁ and CTGF was observed in SA, OD, dental pulp (DP) and predentin respectively. p-SMAD2/3 was strongly expressed in DP and moderately expressed in SA and OD. At PN14 and PN21, both reduced enamel epithelium (REE) and JE showed a strong reaction for TGF-β₁ and CTGF. p-SMAD2/3 was intensely and weakly expressed in REE and JE respectively. These data demonstrate that the expression of CTGF, TGF-β₁ and p-SNAD2/3 is tissue-specific and stage-specific, and indicate a regulatory role for a TGF-β₁-SMAD2/3-CTGF signaling pathway in amelogenesis, dentinogenesis and formation of JE.

Differential expression of transforming growth factor-beta1, connective tissue growth factor, phosphorylated-SMAD2/3 and phosphorylated-ERK1/2 during mouse tooth development

Connective tissue growth factor (CTGF) is a downstream mediator of transforming growth factor-beta 1 (TGF-β₁) and TGF-β₁-induced CTGF expression is regulated through SMAD and mitogen-activated protein kinase (MAPK) signaling pathways. The fine modulation of TGF-β₁ signaling is very important to the process of tooth development. However, little is known about the localization of CTGF, MAPK and SMAD in the context of TGF-β₁ signaling during odontogenesis. Hence, we aimed to investigate the expression of TGF-β₁, CTGF, phosphorylated-SMAD2/3 (p-SMAD2/3) and phosphorylated-ERK1/2 (p-ERK1/2). ICR mice heads of embryonic (E) day 13.5, E14.5, E16.5, postnatal (PN) day 0.5 and PN3.5 were processed for immunohistochemistry. Results revealed that at E13.5, TGF-β₁ and CTGF were strongly expressed in dental epithelium (DE) and dental mesenchyme (DM), while p-SMAD2/3 was intensely expressed in the internal side of DE. p-ERK1/2 was not present in DE or DM. At E14.5 and E16.5, strong staining for TGF-β₁ and CTGF was detected in enamel knot (EK) and dental papilla (DPL). DPL was intensely stained for p-ERK1/2 but negatively stained for p-SMAD2/3. There was no staining for p-SMAD2/3 and p-ERK1/2 in EK. At PN0.5 and PN3.5, moderate to intense staining for TGF-β₁ and CTGF was evident in preameloblasts (PA), secretary ameloblasts (SA) and dental pulp (DP). p-SMAD2/3 was strongly expressed in SA and DP but sparsely localized in PA. p-ERK1/2 was intensely expressed in DP, although negative staining was observed in PA and SA. These data demonstrate that TGF-β₁ and CTGF show an identical expression pattern, while p-SMAD2/3 and p-ERK1/2 exhibit differential expression, and indicate that p-SMAD2/3 and p-ERK1/2 might play a regulatory role in TGF-β₁ induced CTGF expression during tooth development.

Inactivation of bone morphogenetic protein 1 (Bmp1) and tolloid-like 1 (Tll1) in cells expressing type I collagen leads to dental and periodontal defects in mice

Bone morphogenetic protein 1 (BMP1) and tolloid-like 1 (TLL1) belong to the BMP1/tolloid-like proteinase family, which cleaves secretory proteins. The constitutive deletion of the Bmp1 or Tll1 genes causes perinatal or embryonic lethality in mice. In this study, we first studied the β-galactosidase activity in mice in which an IRES-lacZ-Neo cassette was inserted in the intron of either the Bmp1 or the Tll1 gene; the β-galactosidase activities were used to reflect the expression of endogenous Bmp1 and Tll1, respectively. Our X-gal staining results showed that the odontoblasts in the tooth and cells in the periodontal ligament express both Bmp1 and Tll1. We then created Bmp1 ^flox/flox and Tll1 ^flox/flox mice by removing the IRES-lacZ-Neo cassette. By breeding 2.3 kb Col1a1-Cre mice with the Bmp1 ^flox/flox and Tll1 ^flox/flox mice, we further generated Col1a1-Cre;Bmp1 ^flox/flox ;Tll1 ^flox/flox mice in which both Bmp1 and Tll1 were inactivated in the Type I collagen-expressing cells. We employed X-ray radiography, histology and immunohistochemistry approaches to characterize the Col1a1-Cre;Bmp1 ^flox/flox ;Tll1 ^flox/flox mice. Our results showed that the molars of the Col1a1-Cre;Bmp1 ^flox/flox ;Tll1 ^flox/flox mice had wider predentin, thinner dentin and larger pulp chambers than those of the normal controls. The dentinal tubules of the molars in the Col1a1-Cre;Bmp1 ^flox/flox ;Tll1 ^flox/flox mice appeared disorganized. The level of dentin sialophosphoprotein in the molars of the 6-week-old Col1a1-Cre;Bmp1 ^flox/flox ;Tll1 ^flox/flox mice was lower than in the normal controls. The periodontal ligaments of the Col1a1-Cre;Bmp1 ^flox/flox ;Tll1 ^flox/flox mice were disorganized and had less fibrillin-1. Our findings indicate that the proteinases encoded by Bmp1 and Tll1 genes play essential roles in the development and maintenance of mouse dentin and periodontal ligaments.