The spatiotemporal expression and mineralization regulation of p75 neurotrophin receptor in the early tooth development

p75NTR promotes tooth rhythmic mineralization via upregulation of BMAL1/CLOCK

The circadian clock plays a critical role in dentomaxillofacial development. Tooth biomineralization is characterized by the circadian clock; however, the mechanisms underlying the coordination of circadian rhythms with tooth development and biomineralization remain unclear. The p75 neurotrophin receptor (p75NTR) is a clock factor that regulates the oscillatory components of the circadian rhythm. This study aims to investigate the impact of p75NTR on the rhythmic mineralization of teeth and elucidate its underlying molecular mechanisms. We generated p75NTR knockout mice to examine the effects of p75NTR deficiency on tooth mineralization. Ectomesenchymal stem cells (EMSCs), derived from mouse tooth germs, were used for in vitro experiments. Results showed a reduction in tooth mineral density and daily mineralization rate in p75NTR knockout mice. Deletion of p75NTR decreased the expression of DMP1, DSPP, RUNX2, and ALP in tooth germ. Odontogenic differentiation and mineralization of EMSCs were activated by p75NTR. Histological results demonstrated predominant detection of p75NTR protein in odontoblasts and stratum intermedium cells during rapid formation phases of dental hard tissue. The mRNA expression of p75NTR exhibited circadian variations in tooth germs and EMSCs, consistent with the expression patterns of the core clock genes Bmal1 and Clock. The upregulation of BMAL1/CLOCK expression by p75NTR positively regulated the mineralization ability of EMSCs, whereas BMAL1 and CLOCK exerted a negative feedback regulation on p75NTR by inhibiting its promoter activity. Our findings suggest that p75NTR is necessary to maintain normal tooth biomineralization. Odontogenic differentiation and mineralization of EMSCs is regulated by the p75NTR-BMAL1/CLOCK signaling axis. These findings offer valuable insights into the associations between circadian rhythms, tooth development, and biomineralization.

Dynamic expression of Mage-D1 in rat dental germs and potential role in mineralization of ectomesenchymal stem cells

Mage-D1 (MAGE family member D1) is involved in a variety of cell biological effects. Recent studies have shown that Mage-D1 is closely related to tooth development, but its specific regulatory mechanism is unclear. The purpose of this study was to investigate the expression pattern of Mage-D1 in rat dental germ development and its differential mineralization ability to ectomesenchymal stem cells (EMSCs), and to explore its potential mechanism. Results showed that the expression of Mage-D1 during rat dental germ development was temporally and spatially specific. Mage-D1 promotes the proliferation ability of EMSCs but inhibits their migration ability. Under induction by mineralized culture medium, Mage-D1 promotes osteogenesis and tooth-forming ability. Furthermore, the expression pattern of Mage-D1 at E19.5 d rat dental germ is similar to p75 neurotrophin receptor (p75NTR), distal-less homeobox 1 (Dlx1) and msh homeobox 1 (Msx1). In addition, Mage-D1 is binding to p75NTR, Dlx1, and Msx1 in vitro. These findings indicate that Mage-D1 is play an important regulatory role in normal mineralization of teeth. p75NTR, Dlx1, and Msx1 seem to be closely related to the underlying mechanism of Mage-D1 action.

Neural Regulations in Tooth Development and Tooth-Periodontium Complex Homeostasis: A Literature Review

The tooth-periodontium complex and its nerves have active reciprocal regulation during development and homeostasis. These effects are predominantly mediated by a range of molecules secreted from either the nervous system or the tooth-periodontium complex. Different strategies mimicking tooth development or physiological reparation have been applied to tooth regeneration studies, where the application of these nerve- or tooth-derived molecules has been proven effective. However, to date, basic studies in this field leave many vacancies to be filled. This literature review summarizes the recent advances in the basic studies on neural responses and regulation during tooth-periodontium development and homeostasis and points out some research gaps to instruct future studies. Deepening our understanding of the underlying mechanisms of tooth development and diseases will provide more clues for tooth regeneration.

P75 neurotrophin receptor positively regulates the odontogenic/osteogenic differentiation of ectomesenchymal stem cells via nuclear factor kappa-B signaling pathway

p75NTR, a neural crest stem cell marker, is continuously expressed in mesenchymal cells during tooth development. Importantly, high expression of p75NTR in the late bell stage implicates its involvement in odontogenesis and mineralization. However, the regulatory mechanisms underlying p75NTR involvement in odonto/osteogenic differentiation remain unclear. Here, we investigate the effect and potential mechanisms underlying p75NTR involvement in odonto/osteogenic differentiation. We dissected EMSCs from the first branchial arches of mice embryo and compared the proliferation and migration of p75NTR+/+ and p75NTR-/-EMSCs by transwell, scratch and cell counting kit 8(CCK8)assays. The differentiation ability and the involvement of nuclear factor kappa-B (NF-κB) pathway were investigated through alkaline phosphatase and immunofluorescence assay, real-time PCR, and western blot. During induction of dental epithelium conditioned medium, p75NTR+/+ EMSCs exhibited deeper Alkaline phosphatase (ALP) staining and higher expression of odonto/osteogenic genes/proteins (e.g., dentin sialoprotein (DSPP) than p75NTR+/+ EMSCs. Moreover, p75NTR+/+ EMSCs exhibited higher nuclear P65 expression than p75NTR-/-EMSCs. Inhibition of NF-κB pathway with Bay11-7082 in p75NTR+/+EMSCs substantially decreased DSPP expression level. However, activation of NF-κB pathway with Bay11-7082 in p75NTR-/-EMSCs enhanced DSPP expression level. Thus, p75NTR possibly plays a paramount role in the proliferation and differentiation of EMSCs via NF-κB pathway.

[Mage-D1 binding to activated p75NTR positively regulates mineralization of rat ectomesenchymal stem cells in vitro]

OBJECTIVE

To detect the binding of Mage-D1 with activated p75NTR and explore their role in regulating mineralization of ectomesenchymal stem cells (EMSCs).

METHODS

EMSCs were isolated from the tooth germs of embryonic SD rats (19.5 days of gestation) by tissue explant culture and were identified for surface markers using flow cytometry. The cultured cells were divided into blank control group, 100 ng/mL nerve growth factor (NGF) stimulation group, and lentivirus-mediated Mage-D1 interference (SH-Mage-D1) group. Proximity ligation assay was used to detect the binding of Mage-D1 with activated p75NTR in the EMSCs, and the binding strength was compared among the 3 groups. Alizarin red staining and ALP staining were used to observe mineralization of the induced cells. The expressions of ALP, Runx2, OCN, BSP, OPN, Msx1 and Dlx1 at both the mRNA and protein levels were detected using RT-PCR and Western blotting.

RESULTS

The isolated EMSCs expressed high levels of cell surface markers CD44, CD90, CD29, CD146, and CD105 with a low expression of CD45. The results of proximity ligation assay showed that the binding of Mage-D1 with activated p75NTR in the cells increased over time, and the binding strength was significantly greater in NFG-treated cells than in the cells in the other two groups (P < 0.05). Alizarin red staining and ALP staining of the induced cells showed that the changes in the mineralization nodules were consistent with those of ALP activity. The cells treated with 100 ng/mL NGF exhibited significantly increased expressions of ALP, Runx2, OCN, BSP, OPN, Col1, Msx1 and Dlx1 as compared with the cells in the other two groups (P < 0.05).

CONCLUSION

Mage-D1 directly binds to activated p75NTR in embryonic rat EMSCs to positively regulate the mineralization of the EMSCs.

Temporo-spatial distribution of stem cell markers CD146 and p75NTR during odontogenesis in mice

Mesenchymal and epithelial stem cells were identified in dental tissues; however, knowledge about the odontogenic stem cells is limited, and there are some questions regarding their temporo-spatial dynamics in tooth development.

OBJECTIVE

Our study aimed to analyze the expression of the stem cell markers CD146 and p75NTR during the different stages of odontogenesis.

METHODOLOGY

The groups consisted of 13.5, 15.5, 17.5 days old embryos, and 14 days postnatal BALB/c mice. The expression of CD146 and p75NTR was evaluated by immunohistochemistry.

RESULTS

Our results showed that positive cells for both markers were present in all stages of tooth development, and the number of positive cells increased with the progression of this process. Cells of epithelial and ectomesenchymal origin were positive for CD146, and the expression of p75NTR was mainly detected in the dental papilla and dental follicle. In the postnatal group, dental pulp cells were positive for CD146, and the reduced enamel epithelium and the oral mucosa epithelium showed immunostaining for p75NTR.

CONCLUSIONS

These results suggest that the staining pattern of CD146 and p75NTR underwent temporal and spatial changes during odontogenesis and both markers were expressed by epithelial and mesenchymal cell types, which is relevant due to the significance of the epithelial-ectomesenchymal interactions in tooth development.

Gene expression patterns of neurotrophin receptors during neuronal differentiation of human exfoliated deciduous teeth

OBJECTIVE

In the current study, we aimed to investigate the expression profile of TrkA, TrkB, TrkC, and p75NTR neurotrophin receptors because of their roles in the functional differentiation of human exfoliated deciduous teeth (SHED) cells into neural-like cells before and after differentiation of SHED cells into neural-like cells.

DESIGN

Total RNAs isolated from dental pulp tissue, SHED cells, and neural-like cells were reverse transcribed into complementary DNA. Neurotrophin receptor expression at mRNA and protein levels were compared in these three cell types by means of real-time PCR and western blot methods.

RESULTS

TrkA mRNA increased (713.6 ± 251.5) significantly (p < 0.01) in neural-like cells difference from SHED and TrkB mRNA enhanced to 3618 times in these cells. The expression pattern of TrkC was very similar to the pattern of TrkA, and B. p75NTR mRNA increased 41.99 ± 21.61 fold in neural-like cells and 9.805 ± 4.06 fold in SHED cells. Almost the same pattern was observed for the expression of these receptors at the protein levels. Alterations with different grades and trends in neurotrophin receptors mRNA and protein expression levels were observed in these cells.

CONCLUSION

Neurotrophin receptors are important in the existence and differentiation of SHED cells into neuron cells. Therefore, because of the neurogenic potential and accessibility of SHED cells, derived cells from SHED cells can be distinguished as an ideal source for tissue engineering.

p75NTR optimizes the osteogenic potential of human periodontal ligament stem cells by up-regulating α1 integrin expression

Human periodontal ligament stem cells (hPDLSCs) are a promising source in regenerative medicine. Due to the complexity and heterogeneity of hPDLSCs, it is critical to isolate homogeneous hPDLSCs with high regenerative potential. In this study, p75 neurotrophin receptor (p75NTR) was used to isolate p75NTR⁺ and p75NTR⁻ hPDLSCs by fluorescence‐activated cell sorting. Differences in osteogenic differentiation among p75NTR⁺, p75NTR⁻ and unsorted hPDLSCs were observed. Differential gene expression profiles between p75NTR⁺ and p75NTR⁻ hPDLSCs were analysed by RNA sequencing. α1 Integrin (ITGA1) small interfering RNA and ITGA1‐overexpressing adenovirus were used to transfect p75NTR⁺ and p75NTR⁻ hPDLSCs. The results showed that p75NTR⁺ hPDLSCs demonstrated superior osteogenic capacity than p75NTR⁻ and unsorted hPDLSCs. Differentially expressed genes between p75NTR⁺ and p75NTR⁻ hPDLSCs were highly involved in the extracellular matrix‐receptor interaction signalling pathway, and p75NTR⁺ hPDLSCs expressed higher ITGA1 levels than p75NTR⁻ hPDLSCs. ITGA1 silencing inhibited the osteogenic differentiation of p75NTR⁺ hPDLSCs, while ITGA1 overexpression enhanced the osteogenic differentiation of p75NTR⁻ hPDLSCs. These findings indicate that p75NTR optimizes the osteogenic potential of hPDLSCs by up‐regulating ITGA1 expression, suggesting that p75NTR can be used as a novel cell surface marker to identify and purify hPDLSCs to promote their applications in regenerative medicine.

p75NTR-/- mice exhibit an alveolar bone loss phenotype and inhibited PI3K/Akt/β-catenin pathway

OBJECTIVES

The aim of this study was to investigate the role of p75 neurotrophin receptor (p75NTR) in regulating the mouse alveolar bone development and the mineralization potential of murine ectomesenchymal stem cells (EMSCs). Moreover, we tried to explore the underlying mechanisms associated with the PI3K/Akt/β-catenin pathway.

MATERIALS AND METHODS

p75NTR knockout (p75NTR-/- ) mice and wild-type (WT) littermates were used. E12.5d p75NTR-/- and WT EMSCs were isolated in the same pregnant p75NTR-/+ mice from embryonic maxillofacial processes separately. Mouse alveolar bone mass was evaluated using micro-CT. Differential osteogenic differentiation pathways between p75NTR-/- and WT EMSCs were analysed by RNA-sequencing. The PI3K inhibitor LY294002 and PI3K agonist 740Y-P were used to regulate the PI3K/Akt pathway in EMSCs. p75NTR overexpression lentiviruses, p75NTR knock-down lentiviruses and recombined mouse NGF were used to transfect cells.

RESULTS

The alveolar bone mass was found reduced in the p75NTR knockout mouse comparing to the WT mouse. During mineralization induction, p75NTR-/- EMSCs displayed decreased osteogenic capacity and downregulated PI3K/Akt/β-catenin signalling. The PI3K/Akt/β-catenin pathway positively regulates the potential of differential mineralization in EMSCs. The promotive effect of p75NTR overexpression can be attenuated by LY294002, while the inhibitory effect of p75NTR knock-down on Runx2 and Col1 expression can be reversed by 740Y-P.

CONCLUSION

Deletion of p75NTR reduced alveolar bone mass in mice. P75NTR positively regulated the osteogenic differentiation of EMSCs via enhancing the PI3K/Akt/β-catenin pathway.

The role and potential mechanism of p75NTR in mineralization via in vivo p75NTR knockout mice and in vitro ectomesenchymal stem cells

OBJECTIVE

The aim of this study is to investigate the role and potential mechanism of p75NTR in mineralization in vivo using p75NTR-knockout mice and in vitro using ectomesenchymal stem cells (EMSCs).

MATERIALS AND METHODS

Femur bone mass and daily incisor mineralization speed were assessed in an in vivo p75NTR-knockout mouse model. The molecular signatures alkaline phosphatase (ALP), collagen type 1 (Col1), melanoma-associated antigen (Mage)-D1, bone sialoprotein (BSP), osteocalcin (OCN), osteopontin (OPN), distal-less homeobox 1 (Dlx1) and Msh homeobox 1 (Msx1) were examined in vitro in EMSCs isolated from p75NTR+/+ and p75NTRExIII-/- mice.

RESULTS

p75NTR-knockout mice were smaller in body size than heterozygous and wild-type mice. Micro-computed tomography and structural quantification showed that the osteogenic ability of p75NTRExIII -knockout mice was significantly decreased compared with that of wild-type mice (P < .05). Weaker ALP and alizarin red staining and reduced expression of ALP, Col1, Runx2, BSP, OCN and OPN were also observed in p75NTRExIII-/- EMSCs. Moreover, the distance between calcein fluorescence bands in p75NTRExIII -knockout mice was significantly smaller than that in wild type and heterozygous mice (P < .05), indicating the lower daily mineralization speed of incisors in p75NTRExIII -knockout mice. Further investigation revealed a positive correlation between p75NTR and Mage-D1, Dlx1, and Msx1.

CONCLUSION

p75NTR not only promotes osteogenic differentiation and tissue mineralization, but also shows a possible relationship with the circadian rhythm of dental hard tissue formation.

The spatiotemporal expression and mineralization regulation of p75 neurotrophin receptor in the early tooth development

OBJECTIVE

The aim of this study was to investigate the spatiotemporal expression and potential role of p75NTR in tooth morphogenesis and tissue mineralization.

MATERIALS AND METHODS

The dynamic morphology of the four stages (from the beginning of E12.5 d, then E13.5 d and E15.5 d, to the end of E18.5 d) was observed, and the expressions of p75NTR and Runx2 were traced. The ectomesenchymal stem cells (EMSCs) were harvested in vitro, and the biological characteristics were observed. Moreover, the mineralization capability of EMSCs was evaluated. The relations between p75NTR and ALP, Col-1 and Runx2 were investigated.

RESULTS

The morphologic results showed that the dental lamina appeared at E12.5 d, the bud stage at E13.5 d, the cap stage at E15.5 d and the bell stage at E18.5 d. p75NTR and Runx2 showed the similar expression pattern. EMSCs from the four stages showed no significant difference in proliferation. But the positive rate of p75NTR in the E12.5 d cells was significantly lower than that in the other three stages (P < 0.05). Moreover, the higher positive rate of p75NTR the cells were, the stronger mineralization capability they showed. p75NTR was well positively correlated with the mineralization-related markers ALP, Col-1 and Runx2, which increased gradually with the mature of dental germs.

CONCLUSION

p75NTR might play an important role in the regulation of tooth morphogenesis, especially dental hard tissue formation.