CD44 Is Involved in Mineralization of Dental Pulp Cells

Molecular insights into the proteomic composition of porcine treated dentin matrix

Background

Human-treated dentin matrix (hTDM) has recently been studied as a natural extracellular matrix-based biomaterial for dentin pulp regeneration. However, porcine-treated dentin matrix (pTDM) is a potential alternative scaffold due to limited availability. However, there is a dearth of information regarding the protein composition and underlying molecular mechanisms of pTDM.Methods: hTDM and pTDM were fabricated using human and porcine teeth, respectively, and their morphological characteristics were examined using scanning electron microscopy. Stem cells derived from human exfoliated deciduous teeth (SHEDs) were isolated and characterized using flow cytometry and multilineage differentiation assays. SHEDs were cultured in three-dimensional environments with hTDM, pTDM, or biphasic hydroxyapatite/tricalcium phosphate. The expression of odontogenesis markers in SHEDs were assessed using real-time polymerase chain reaction and immunochemical staining. Subsequently, SHEDs/TDM and SHEDs/HA/TCP complexes were transplanted subcutaneously into nude mice. The protein composition of pTDM was analyzed using proteomics and compared to previously published data on hTDM.Results: pTDM and hTDM elicited comparable upregulation of odontogenesis-related genes and proteins in SHEDs. Furthermore, both demonstrated the capacity to stimulate root-related tissue regeneration in vivo. Proteomic analysis revealed the presence of 278 protein groups in pTDM, with collagens being the most abundant. Additionally, pTDM and hTDM shared 58 identical proteins, which may contribute to their similar abilities to induce odontogenesis.

Conclusions

Both hTDM and pTDM exhibit comparable capabilities in inducing odontogenesis, potentially owing to their distinctive bioactive molecular networks.

Chemokine‑like receptor 1‑positive cells are present in the odontoblast layer in tooth tissue in rats and humans

Cluster of differentiation (CD)44 is a marker of dental pulp stem cells and is involved in odontoblast differentiation and calcification. Chemokine-like receptor 1 (CMKLR1), also known as chemerin receptor 23 (ChemR23) is also expressed in odontoblasts and dental pulp stem cells and is involved in inflammation suppression and tooth regeneration. Resolvin E1, a bioactive lipid, is a CMKLR1 ligand that mediates the chemerin-CMKLR1 interaction and suppresses pulpal inflammation. The present study clarified the intracellular and tissue localization of CD44 and CMKLR1 by immunohistochemical staining of normal pulp and pulp with pulpitis from 12-week-old male Wistar rat teeth or human teeth. In addition, the localization of CD44 and CMKLR1 in human dental pulp stem cells was observed by immunofluorescence staining. The present study also examined the involvement of resolvin E1 in inhibiting inflammation and calcification by western blotting. CD44- and CMKLR1-positive cells were confirmed in the odontoblast layer in normal dental pulp of rats and humans. CD44 was mainly localized in the cell membrane and CMKLR1 was mainly found in the cytoplasm of human dental pulp stem cells. CMKLR1 was also confirmed in the odontoblast layer in rats and humans with pulpitis but CD44 was not present. Following treatment of dental pulp stem cells with lipoteichoic acid, which imitates Gram-positive bacterial infection, resolvin E1 did not suppress the expression of cyclooxygenase-2 or of the odontoblast differentiation marker, dentin sialophosphoprotein. Furthermore, resolvin E1 induced the differentiation of dental pulp stem cells into odontoblasts even in the presence of the inflammatory stimulus.

The effect of hyaluronic acid conditioned media on hDPSCs differentiation through CD44 and transforming growth factor-β1 expressions

Hyaluronic acid (HA) has the capability to influence dentin niche which is important in regenerative process. The CD44 as a specific receptor of HA was found to be related to dentin mineralization process. Meanwhile, transforming growth factor β1 (TGF-β1) has a vital role in the transition from proliferation into the differentiation of human dental pulp stem cell human dental pulp stem cells (hDPSCs) to become odontoblast cells and dentin mineralization. This study aims to analyzed HA's effect on dentin mineralization through CD44 and TGF-β1 expressions. Stem cells were cultured in four different supplemented conditioned media (control, +10 μg/mL, +20 μg/mL, and + 30 μg/mL of HA). Evaluation of CD44 expression was analyzed using flow cytometry and TGF-β1 was analyzed using enzyme-linked immunosorbent assay reader. Qualitative result using Alizarin red test after 21 days was done to confirm the formation of mineralization nodules. It was shown that HA expression of CD44 and TGF-β1 on hDPSCs were higher in AH groups compared to the control group and 30 μg/mL HA induced the highest TGF-β1 expression on hDPSCs. Alizarin red test also showed the highest mineralization nodules in the same group. Therefore, from this study, we found that supplemented 30 μg/mL of HA was proved in initiating hDPSCs differentiation process and promote dentin mineralization.

Metabolic shift and the effect of mitochondrial respiration on the osteogenic differentiation of dental pulp stem cells

Background

Metabolism shifts from glycolysis to mitochondrial oxidative phosphorylation are vital during the differentiation of stem cells. Mitochondria have a direct function in differentiation. However, the metabolic shift and the effect of mitochondria in regulating the osteogenic differentiation of human dental pulp stem cells (hDPSCs) remain unclear.

Methods

Human dental pulp stem cells were collected from five healthy donors. Osteogenic differentiation was induced by osteogenic induction medium. The activities of alkaline phosphatase, hexokinase, pyruvate kinase, and lactate dehydrogenase were analyzed by enzymatic activity kits. The extracellular acidification rate and the mitochondrial oxygen consumption rate were measured. The mRNA levels of COL-1, ALP, TFAM, and NRF1 were analyzed. The protein levels of p-AMPK and AMPK were detected by western blotting.

Results

Glycolysis decreased after a slight increase, while mitochondrial oxidative phosphorylation continued to increase when cells grew in osteogenic induction medium. Therefore, the metabolism of differentiating cells switched to mitochondrial respiration. Next, inhibiting mitochondrial respiration with carbonyl cyanide-chlorophenylhydrazone, a mitochondrial uncoupler inhibited hDPSCs differentiation with less ALP activity and decreased ALP and COL-1 mRNA expression. Furthermore, mitochondrial uncoupling led to AMPK activation. 5-Aminoimidazole-4-carboxamide ribonucleotide, an AMPK activator, simulated the effect of mitochondrial uncoupling by inhibiting osteogenic differentiation, mitochondrial biogenesis, and mitochondrial morphology. Mitochondrial uncoupling and activation of AMPK depressed mitochondrial oxidative phosphorylation and inhibited differentiation, suggesting that they may serve as regulators to halt osteogenic differentiation from impaired mitochondrial oxidative phosphorylation.

Shikonin induces odontoblastic differentiation of dental pulp stem cells via AKT-mTOR signaling in the presence of CD44

Purpose: In our previous study, we demonstrated that hyaluronan induces odontoblastic differentiation of dental pulp stem cells via interactions with CD44. However, it remains unclear whether CD44 expression by dental pulp stem cells is required for odontoblastic differentiation.Methods: We searched for a compound other than hyaluronan that induces odontoblastic differentiation of dental pulp stem cells and used western blotting to determine whether CD44 is involved in the induction of odontoblastic differentiation by the compound. We further validated the cell signaling details of the compound-induced expression of dentin sialophosphoprotein (DSPP), which is known as a marker of odontoblastic differentiation.Results: We investigated shikonin, which is one of the derivatives of naphthoquinone, the skeleton of vitamin K. Shikonin-induced expression of DSPP was inhibited by PI3K, AKT, and mTOR inhibitors. Additionally, shikonin-induced expression of DSPP was inhibited in dental pulp stem cells transfected with siRNA against CD44.Conclusions: Shikonin can stimulate dental pulp stem cells to undergo odontoblastic differentiation through a mechanism involving the AKT-mTOR signaling pathway and CD44. Although expression of CD44 is important for inducing odontoblastic differentiation of dental pulp stem cells, the relationship between the AKT-mTOR signaling pathway and CD44 expression, in the context of shikonin stimulation, has not yet been elucidated. This study suggests that shikonin may be useful for inducing odontoblastic differentiation of dental pulp stem cells, and that it may have clinical applications, including protection of the dental pulp.

Specific concentration of hyaluronan amide derivative induces osteogenic mineralization of human mesenchymal stromal cells: Evidence of RUNX2 and COL1A1 genes modulation

Hyaluronic acid (HA) is an ideal material for tissue regeneration. The aim of this study was to investigate whether a hyaluronan amide derivative (HAD) can enhance the mineralization of human mesenchymal stem cells (hMSCs). Osteogenically induced hMSCs cultured with or without HAD at different concentrations (0.5 mg/ml or 1 mg/ml) were analyzed for mineral matrix deposition, metabolic activity, cellular proliferation, and the expression of 14 osteogenic genes. Unmodified HA (HYAL) was used as control. We demonstrated that only cells treated daily until day 28 with 0.5 mg/ml HAD, but not with 1 mg/ml of HAD and HYAL, showed a significant induction of mineralization at day 14 compared to the osteogenic control group. HAD at both concentrations tested, significantly decreased the expression of the proliferating marker MKI67 at day 2. By contrast, increased metabolic activity was induced only by HYAL from day 14. HAD at both concentrations significantly down modulated SNAI2, DLX5, RUNX2, COL1A1, and IBSP genes, while significantly up regulated COL15A1. The induction of mineralization of 0.5 mg/ml of HAD at day 14 was significantly dependent on a specific modulation of RUNX2 and COL1A1. Our data demonstrate that only 0.5 mg/ml of HAD, but not HYAL, modulated hMSCs osteogenic differentiation, suggesting that the physicochemical features and concentration of HA products could differently affect osteogenic maturation.

The effect of strontium chloride on human periodontal ligament stem cells

The complete repair of periodontal structures remains an exciting challenge that prompts researchers to develop new treatments to restore the periodontium. Recent research has suggested strontium ion to be an attractive candidate to improve osteogenic activity. In this study, we have isolated a clonal finite cell line derived from human periodontal ligament (PDL) in order to assess whether and in which way different doses of SrCl₂ (from 0.5 to 500 μg/ml) can influence both the proliferation and the mineralization process, for future application in oral diseases. PDL cells were cloned by dilution plating technique and characterized by FACS. Cell proliferation analysis and mineralization were performed by [³H]-thymidine incorporation and spectrofluorometric assay. Results have evidenced that the higher SrCl₂ concentrations tested, from 25 to 500 μg/ml, have increased the proliferation activity after only 24 h of treatment. Interestingly, the same higher concentrations have decreased the mineralization, which was conversely increased by the lower ones, from 0.5 to 10 μg/ml. Our findings suggest the possible use of SrCl₂ in appropriate delivery systems that release, at different time points, the specific dose, depending on the biological response that we want to induce on periodontal ligament stem cells, providing a more efficient periodontal regeneration.

Hyaluronan induces odontoblastic differentiation of dental pulp stem cells via CD44

Background

Dental pulp tissue contains many undifferentiated mesenchymal cells, which retain the ability to differentiate into mature cells. Induced pluripotent stem cells have been developed from various cell sources, including dental pulp-derived stem cells, and evaluated for potential application to regenerative therapy. Dental pulp tissues overexpress CD44, a cell-adhesion factor involved in the induction of mineralization. In this study, we investigated the effects of hyaluronan—a known CD44 ligand—on dental pulp stem cells (DPSCs).

Methods

DPSC CD44 expression was analyzed using immunofluorescence staining, flow cytometry, and western blotting. Cell proliferation was evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Effects of hyaluronan on the cell cycle were analyzed by flow cytometry. Alkaline phosphatase activity was employed as marker of mineralization and measured by fluorometric quantification and western blotting. Bone morphogenetic protein (BMP)-2, BMP-4, dentin sialophosphoprotein (DSPP), and dentin matrix acidic phosphoprotein 1 (DMP-1) levels were measured using real-time polymerase chain reaction. Odontoblastic differentiation and the close cell signaling examination of DPSC differentiation were determined using western blotting.

Results

Hyaluronan induced expression of the odontoblastic differentiation markers DMP-1 and DSPP. Moreover, the odontoblastic differentiation induced by hyaluronan was mediated by CD44—but not by Akt, Smad1 or MAPK signaling.

Conclusions

Our results indicate that hyaluronan induces odontoblastic differentiation of DPSCs via CD44. This suggests that hyaluronan plays a crucial role in the induction of odontoblastic differentiation from DPSCs. Our findings may aid the development of new, inexpensive, and effective conservative treatments for dental pulp repair.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0399-8) contains supplementary material, which is available to authorized users.

Novel role of zonula occludens-1: A tight junction protein closely associated with the odontoblast differentiation of human dental pulp cells

Zonula occludens-1 (ZO-1), a tight junction protein, contributes to the maintenance of the polarity of odontoblasts and junctional complex formation in odontoblast layer during tooth development. However, expression and possible role of ZO-1 in human dental pulp cells (hDPCs) during repair process remains unknown. Here, we investigated the expression of ZO-1 in hDPCs and the relationship with odontoblast differentiation. We found the processes of two adjacent cells were fused and formed junction-like structure using scanning electron microscopy. Fluorescence immunoassay and Western blot confirmed ZO-1 expression in hDPCs. Especially, ZO-1 was high expressed at the cell-cell junction sites. More interestingly, ZO-1 accumulated at the leading edge of lamellipodia in migrating cells when a scratch assay was performed. Furthermore, ZO-1 gradual increased during odontoblast differentiation and ZO-1 silencing greatly inhibited the differentiation. ZO-1 binds directly to actin filaments and RhoA/ROCK signaling mainly regulates cell cytoskeleton, thus RhoA/ROCK might play a role in regulating ZO-1. Lysophosphatidic acid (LPA) and Y-27632 were used to activate and inhibit RhoA/ROCK signaling, respectively, with or without mineralizing medium. In normal cultured hDPCs, RhoA activation increased ZO-1 expression and especially in intercellular contacts, whereas ROCK inhibition attenuated the effects induced by LPA. However, expression of ZO-1 was upregulated by Y-27632 but not significantly affected by LPA after odontoblast differentiation. Hence, ZO-1 highly expresses in cell-cell junctions and is related to odontoblast differentiation, which may contribute to dental pulp repair or even the formation of an odontoblast layer. RhoA/ROCK signaling is involved in the regulation of ZO-1.

Mineralization Effect of Hyaluronan on Dental Pulp Cells via CD44

INTRODUCTION

CD44 is a cell-surface glycoprotein involved in various cellular functions. Recent studies have suggested that CD44 is involved in early mineralization of odontoblasts. Hyaluronic acid (HA) is the principal ligand for receptor CD44. Whether and how HA regulated the mineralization process of dental pulp cells were investigated.

METHODS

The effects of high-molecular-weight HA on differentiation and mineral deposition of dental pulp cells were tested by using alkaline phosphatase (ALP) activity assay and alizarin red S staining. Osteogenesis real-time polymerase chain reaction array, quantitative polymerase chain reaction, and Western blotting were performed to identify downstream molecules involved in the mineralization induction of HA. CD44 was knocked down and examined to confirm whether the mineralization effect of HA was mediated by receptor CD44. Immunohistochemistry was used to understand the localization patterns of CD44 and the identified downstream proteins in vivo.

RESULTS

Pulse treatment of HA enhanced ALP activity and mineral deposition in dental pulp cells. Tissue-nonspecific ALP, bone morphogenetic protein 7 (BMP7), and type XV collagen (Col15A1) were upregulated via the HA-CD44 pathway in vitro. Immunohistochemistry of tooth sections showed that the staining pattern of BMP7 was very similar to that of CD44.

CONCLUSIONS

Results of this study indicated that high-molecular-weight HA enhanced early mineralization of dental pulp cells mediated via CD44. The process involved important mineralization-associated molecules including tissue-nonspecific ALP, BMP7, and Col15A1. The findings may help develop new strategies in regenerative endodontics.