LNGFR targets the Wnt/β-catenin pathway and promotes the osteogenic differentiation in rat ectomesenchymal stem cells

S100A6 Regulates nucleus pulposus cell apoptosis via Wnt/β-catenin signaling pathway: an in vitro and in vivo study

BACKGROUND

Intervertebral disc degeneration (IDD) is a common musculoskeletal degenerative disease, which often leads to low back pain and even disability, resulting in loss of labor ability and decreased quality of life. Although many progresses have been made in the current research, the underlying mechanism of IDD remains unclear. The apoptosis of nucleus pulposus (NP) cells (NPCs) is an important pathological mechanism in intervertebral disc degeneration (IDD). This study evaluated the relationship between S100A6 and NPCs and its underlying mechanism.

METHODS

Mass spectrometry, bioinformatics, and quantitative real-time polymerase chain reaction (qRT-PCR) analyses were used to screen and verify hub genes for IDD in human IVD specimens with different degeneration degrees. Western blotting, immunohistochemistry (IHC), and/or immunofluorescence (IF) were used to detect the expression level of S100A6 in human NP tissues and NPCs. The apoptotic phenotype of NPCs and Wnt/β-catenin signaling pathway were evaluated using flow cytometry, western blotting, and IF. S100A6 was overexpressed or knocked down in NPCs to determine its impact on apoptosis and Wnt/β-catenin signaling pathway activity. Moreover, we used the XAV-939 to inhibit and SKL2001 to activate the Wnt/β-catenin signaling pathway. The therapeutic effect of S100A6 inhibition on IDD was also evaluated.

RESULTS

S100A6 expression increased in IDD. In vitro, increased S100A6 expression promoted apoptosis in interleukin (IL)-1β-induced NPCs. In contrast, the inhibition of S100A6 expression partially alleviated the progression of annulus fibrosus (AF) puncture-induced IDD in rats. Mechanistic studies revealed that S100A6 regulates NPC apoptosis via Wnt/β-catenin signaling pathway.

CONCLUSIONS

This study showed that S100A6 expression increased during IDD and promoted NPCs apoptosis by regulating the Wnt/β-catenin signaling pathway, suggesting that S100A6 is a promising new therapeutic target for IDD.

Transplantation of Wnt5a-modified Bone Marrow Mesenchymal Stem Cells Promotes Recovery After Spinal Cord Injury via the PI3K/AKT Pathway

Spinal cord injury (SCI) is a severe neurological condition that can lead to paralysis or even death. This study explored the potential benefits of bone marrow mesenchymal stem cell (BMSC) transplantation for repairing SCI. BMSCs also differentiate into astrocytes within damaged spinal cord tissues hindering the cell transplantation efficacy, therefore it is crucial to enhance their neuronal differentiation rate to facilitate spinal cord repair. Wnt5a, an upstream protein in the non-classical Wnt signaling pathway, has been implicated in stem cell migration, differentiation, and neurite formation but its role in the neuronal differentiation of BMSCs remains unclear. Thus, this study investigated the role and underlying mechanisms of Wnt5a in promoting neuronal differentiation of BMSCs both in vivo and in vitro. Wnt5a enhanced neuronal differentiation of BMSCs in vitro while reducing astrocyte differentiation. Additionally, high-throughput RNA sequencing revealed a correlation between Wnt5a and phosphoinositide 3-kinase (PI3K)/protein kinase B(AKT) signaling, which was confirmed by the use of the PI3K inhibitor LY294002 to reverse the effects of Wnt5a on BMSC neuronal differentiation. Furthermore, transplantation of Wnt5a-modified BMSCs into SCI rats effectively improved the histomorphology (Hematoxylin and eosin [H&E], Nissl and Luxol Fast Blue [LFB] staining), motor function scores (Footprint test and Basso-Beattie-Bresnahan [BBB]scores)and promoted neuron production, axonal formation, and remodeling of myelin sheaths (microtubule associated protein-2 [MAP-2], growth-associated protein 43 [GAP43], myelin basic protein [MBP]), while reducing astrocyte production (glial fibrillary acidic protein [GFAP]). Therefore, targeting the Wnt5a/PI3K/AKT pathway could enhance BMSC transplantation for SCI treatment.

Mir-195-5p targets Smad7 regulation of the Wnt/β-catenin pathway to promote osteogenic differentiation of vascular smooth muscle cells

In this study, we sought to investigate the mechanisms of action of miR-195-5p in the osteogenic differentiation of vascular smooth muscle cells (VSMCs), and thereby provide novel insights and a reference for the targeted therapy of arterial media calcification. VSMC differentiation was induced using sodium β-glycerophosphate, and we investigated the effects of transfecting cells with miR-195-5p mimics, vectors overexpressing Smad7, and the Wnt/β-catenin pathway inhibitor (KYA1797K) on VSMC differentiation by determining cell viability and apoptosis, and the mRNA and protein expression of factors associated with osteogenic differentiation and the Wnt/β-catenin pathway. The results revealed that miR-195-5p mimics enhanced the osteogenic differentiation of VSMCs induced by β-glycerophosphate, whereas the overexpression of Smad7 reversed this phenomenon. In addition, KYA1797K was found to promote the effects of Smad7 overexpression. In conclusion, by targeting, Smad7, miR-195-5p promotes the Wnt/β-catenin pathway. and thus the osteogenic differentiation of VSMCs. These findings will provide a reference for elucidating the mechanisms whereby miR-195-5p regulates osteogenic differentiation.

Human dental pulp stem cells derived extracellular matrix promotes mineralization via Hippo and Wnt pathways

Extracellular matrix (ECM) is an intricate structure providing the microenvironment niche that influences stem cell differentiation. This study aimed to investigate the efficacy of decellularized ECM derived from human dental pulp stem cells (dECM_DPSCs) and gingival-derived mesenchymal stem cells (dECM_GSCs) as an inductive scaffold for osteogenic differentiation of GSCs. The proteomic analysis demonstrated that common and signature matrisome proteins from dECM_DPSCs and dECM_GSCs were related to osteogenesis/osteogenic differentiation. RNA sequencing data from GSCs reseeded on dECM_DPSCs revealed that dECM_DPSCs upregulated genes related to the Hippo and Wnt signaling pathways in GSCs. In the inhibitor experiments, results revealed that dECM_DPSCs superiorly promoted GSCs osteogenic differentiation, mainly mediated through Hippo and Wnt signaling. The present study emphasizes the promising translational application of dECM_DPSCs as a bio-scaffold rich in favorable regenerative microenvironment for tissue engineering.

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.

Single cell RNA sequencing reveals mesenchymal heterogeneity and critical functions of Cd271 in tooth development

BACKGROUND

Accumulating evidence suggests that the maxillary process, to which cranial crest cells migrate, is essential to tooth development. Emerging studies indicate that Cd271 plays an essential role in odontogenesis. However, the underlying mechanisms have yet to be elucidated.

AIM

To establish the functionally heterogeneous population in the maxillary process, elucidate the effects of Cd271 deficiency on gene expression differences.

METHODS

p75NTR knockout (Cd271^-/-) mice (from American Jackson laboratory) were used to collect the maxillofacial process tissue of p75NTR knockout mice, and the wild-type maxillofacial process of the same pregnant mouse wild was used as control. After single cell suspension, the cDNA was prepared by loading the single cell suspension into the 10x Genomics Chromium system to be sequenced by NovaSeq6000 sequencing system. Finally, the sequencing data in Fastq format were obtained. The FastQC software is used to evaluate the quality of data and CellRanger analyzed the data. The gene expression matrix is read by R software, and Seurat is used to control and standardize the data, reduce the dimension and cluster. We search for marker genes for subgroup annotation by consulting literature and database; explore the effect of p75NTR knockout on mesenchymal stem cells (MSCs) gene expression and cell proportion by cell subgrouping, differential gene analysis, enrichment analysis and protein-protein interaction network analysis; understand the interaction between MSCs cells and the differentiation trajectory and gene change characteristics of p75NTR knockout MSCs by cell communication analysis and pseudo-time analysis. Last we verified the findings single cell sequencing in vitro.

RESULTS

We identified 21 cell clusters, and we re-clustered these into three subclusters. Importantly, we revealed the cell–cell communication networks between clusters. We clarified that Cd271 was significantly associated with the regulation of mineralization.

CONCLUSION

This study provides comprehensive mechanistic insights into the maxillary- process-derived MSCs and demonstrates that Cd271 is significantly associated with the odontogenesis in mesenchymal populations.

Tideglusib enhances odontogenic differentiation in human dental pulp stem cells in vitro

AIM

Tideglusib is a small molecule agonist of the canonical Wnt pathway. The present study investigated the influence of Tideglusib on human dental pulp stem cell (hDPSC) proliferation, apoptosis, migration and odonto/osteogenic differentiation.

METHODOLOGY

hDPSCs were treated with 50, 100 nM or 200 nM Tideglusib. β-catenin accumulation was detected by immunofluorescence staining. Colony-forming unit ability was assessed by staining with Coomassie blue. Cell cycle progression and cell apoptosis were investigated using flow cytometry. Cell migration was examined using an in vitro wound-healing assay. Osteogenic differentiation was examined using alkaline phosphatase (ALP) staining, alizarin red S staining and osteogenic-related gene expression. The gene expression profile was examined using a high-throughput RNA sequencing technique. All experiments were repeated using cells derived from at least four different donors (n = 4). The Mann-Whitney U-test was used to identify significant differences between two independent group comparisons. For three or more group comparisons, statistical differences were assessed using the Kruskal-Wallis test followed by pairwise comparison. The significance level was set at 5% (p < .05).

RESULTS

Tideglusib activated the Wnt signalling pathway in hDPSCs as demonstrated by an increase in cytoplasmic β-catenin accumulation and nuclear translocation. Tideglusib did not affect hDPSC proliferation, cell cycle progression, cell apoptosis or cell migration. In contrast, 50 and 100 nM Tideglusib significantly enhanced mineralization and osteogenic marker gene expression (RUNX2, ALP, BMP2 and DSPP; p < .05).

CONCLUSIONS

Tideglusib enhanced the odonto/osteogenic differentiation of hDPSCs. Therefore, incorporating this bioactive molecule in a pulp-capping material could be a promising strategy to promote dentine repair.

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.

GPI-anchored glutathione S-transferase as marker allows affinity sorting of transfection-positive cells

Cell transfection efficiency is still a limiting factor in gene function research. A method that allows isolation and enrichment of the transfection-positive cells is an effective solution. Here, we report a transfection-positive cell sorting system that utilizes GPI-anchored GST (Glutathione S-transferase) as a plasmid marker. The Glutathione S-transferase fusion protein will be expressed and displayed on the cell surface through GPI anchor, and hence permits the positive cells to be isolated using Glutathione (GSH) Magnetic Beads. We prove that the system works efficiently in both the adherent Lenti-X 293T cells and the suspension K-562 cells. The affinity cell sorting procedure efficiently enriched positive cells from 20% to 98% in K-562 cells. The applications in gene knockdown and overexpression experiments in K-562 cells dramatically enhanced the extent of gene alteration, with the gene knockdown efficiency increasing from 7% to 60% and the gene overexpression level rising from 47 to 253 times. This Glutathione S-transferase affinity transfection-positive cell sorting method is simple and fast to operate, large-instrument free, low cost, and hence possesses great potential in gene function study in vitro.

A potential role of p75NTR in the regulation of circadian rhythm and incremental growth lines during tooth development

Objective: Tooth morphogenesis and the formation of hard tissues have been reported to be closely related to circadian rhythms. This study investigates the spatiotemporal expression and relationship of p75NTR with core clock genes, mineralization-related or odontogenesis-related genes, and aims to derive the potential role of p75NTR in regulating circadian rhythm and incrementality growth line formation during tooth development.

Materials and methods: The dynamic morphology of the rat dental germ was observed at seven stages (E14.5 d, E16.5 d, E18.5 d, P.N. 4 d, P.N. 7 d, P.N. 10 d, and P.N. 15 d). Next, the expressions of p75NTR and other target factors were traced. The ectomesenchymal stem cells (EMSCs) were isolated from the E18.5d rat dental germs and synchronized using 50% of fetal bovine serum. Then, they were cultured in light/light (L.L.), dark/dark (D.D.), and light/dark (L.D.) conditions for 48 h. The total RNA was collected every 4 h, and the circadian rhythm dynamics of target factors were observed. To reveal the mechanism further, p75NTR was down-regulated in p75NTR^ExIII−/− mice and up-regulated in immortalized mouse dental apical papilla progenitor cells. The change tendencies of other target factors were also detected.

Results: The clock genes Bmal1, Clock, Per1, and Per2 were all expressed in tooth germs before the formation of dental hard tissues and demonstrated a regular oscillating expression pattern in EMSCs from dental germs. Their expression was affected by the L.D. stimulus, and most of them were promoted by D.D. conditions. p75NTR presented a similar expression pattern and a positive or negative relationship with most clock genes, mineralization-related and odontogenesis-related factors, such as brain and muscle ARNT-like protein-1 (Bmal1), runt-related transcription factor 2 (Runx2), alkaline phosphatase (ALP), MSH-like 1 (MSX1), dentin matrix acidic phosphoprotein 1 (Dmp1), and dentin sialophosphoprotein (Dspp). Moreover, the arrangement, morphology, and even boundary in pre-odontoblast/pre-ameloblast layers were disordered in the p75NTR^ExIII−/− mice.

Conclusion: Circadian rhythm was found to affect tooth development. p75NTR might play a crucial role in regulating clock genes in the mineralization and formation of the dental hard tissues. p75NTR is actively involved in the odontoblast-ameloblast junction and cell polarity establishment during tooth morphogenesis.

6-Bromoindirubin-3′-Oxime Regulates Colony Formation, Apoptosis, and Odonto/Osteogenic Differentiation in Human Dental Pulp Stem Cells

6-bromoindirubin-3′-oxime (BIO) is a candidate small molecule that effectively modulates Wnt signalling owing to its stable property. The present study investigated the influence of BIO on the odonto/osteogenic differentiation of human dental pulp stem cells (hDPSCs). hDPSCs were treated with 200, 400, or 800 nM BIO, and the effects on hDPSC responses and osteogenic differentiation were assessed. BIO-mediated Wnt activation was confirmed by β-catenin nuclear translocation detected by immunofluorescence staining. BIO attenuated colony formation and cell migration determined by in vitro wound-healing assay. BIO increased early apoptotic cell population evaluated using flow cytometry. For osteogenic induction, BIO promoted alkaline phosphatase (ALP) activity and mineralisation in a dose-dependent manner. ALP, RUNX2, OCN, OSX, ANKH, DMP1, and DSPP mRNA expression were significantly upregulated. The OPG/RANKL expression ratio was also increased. Further, BIO attenuated adipogenic differentiation as demonstrated by decreased lipid accumulation and adipogenic-related gene expression. Bioinformatic analysis of RNA sequencing data from the BIO-treated hDPSCs revealed that BIO modulated pathways related to autophagy and actin cytoskeleton regulation. These findings demonstrated that BIO treatment promoted hDPSC osteogenic differentiation. Therefore, this small molecule is a strong candidate as a bioactive molecule to enhance dentin repair.

A Gene Transfer-Positive Cell Sorting System Utilizing Membrane-Anchoring Affinity Tag

Gene delivery efficiency is an essential limit factor in gene study and gene therapy, especially for cells that are hard for gene transfer. Here we develop an affinity cell sorting system that allows efficient enrichment of gene transfer-positive cells. The system expresses an enhanced green fluorescent protein (EGFP) fused with an N-terminal high-affinity Twin-Strep-Tag (TST) that will be anchored to the cell membrane at the out-surface through a glycosylphosphatidylinositol (GPI) membrane-anchoring structure. The EGFP permits microscopy and flow cytometry analysis of the gene transfer-positive cells, and the TST tag at the N terminal of EGFP allows efficient affinity sorting of the positive cells using Strep-Tactin magnetic beads. The cell sorting system enables efficient isolation of gene transfer-positive cells in a simple, convenient, and fast manner. Cell sorting on transfected K-562 cells resulted in a final positive cell percentage of up to 95.0% with a positive cell enrichment fold of 5.8 times. The applications in gene overexpression experiments could dramatically increase the gene overexpression fold from 10 times to 58 times, and in shRNA gene knockdown experiments, cell sorting increased the gene knockdown efficiency from 12% to 53%. In addition, cell sorting in CRISPR/Cas9 genome editing experiments allowed more significant gene modification, with an editing percentage increasing from 20% to 79%. The gene transfer-positive cell sorting system holds great potential for all gene transfer studies, especially on those hard-to-transfect cells.

Potential of RNA-binding protein human antigen R as a driver of osteogenic differentiation in osteoporosis

Background

Emerging evidence has correlated the human antigen R (HuR) with the low-density lipoprotein receptor-related protein 6 (LRP6) gene, an important therapeutic target for osteoporosis. Herein, we sought to probe the regulatory role of HuR in the LRP6 gene and their interaction in the progression of osteoporosis.

Methods

HuR and downstream potential target genes were predicted by bioinformatics analysis to identify their potential functions in bone metabolism following osteoporosis. The effect of HuR on the osteoblastic differentiation and viability and apoptosis of mouse embryo osteoblast precursor cells (MC3T3-E1) was evaluated after artificial modulation of HuR expression.

Results

Bone phenotypes were observed in ovariectomized mice in response to adenovirus-mediated HuR overexpression. Poor expression of HuR was identified in the bone tissues of ovariectomized mice. Silencing of HuR inhibited the osteoblastic differentiation of MC3T3-E1 cells, as evidenced by decreased expression of Runx2 and Osterix along with reduced ALP activity. Mechanistically, HuR stabilized LRP6 mRNA and promoted its translation by binding to the 3'UTR of LRP6 mRNA, leading to activation of the downstream Wnt pathway. By this mechanism, osteoblastic differentiation of MC3T3-E1 cells was induced. In ovariectomized mice, overexpression of HuR alleviated osteoporosis-related phenotypes.

Conclusion

Overall, these data together support the promoting role of HuR in the osteoblastic differentiation, highlighting a potential novel strategy for osteoporosis treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13018-022-03073-w.

Overexpression of sonic hedgehog enhances the osteogenesis in rat ectomesenchymal stem cells

Ectoderm-derived mesenchymal stem cells (EMSCs) were used as potential seed cells for bone tissue engineering to treat bone defects due to their capability of rapid proliferation and osteogenic differentiation. Sonic hedgehog (Shh) signaling was reported to play an important role in the development of bone tissue, but its role is not understood. The present study investigated the role of Shh molecule in osteogenic differentiation of rat EMSCs in vitro. Rat EMSCs were isolated form nasal respiratory mucosa and identified with immunofluorescence and analyzed with other methods, including reverse transcriptase polymerase chain reaction (qPCR) and western blotting. EMSCs expressed CD90, CD105, nestin, and vimentin. On the seventh day of osteogenic induction, expression levels of Shh and Gli1 was higher according to the result of qPCR and Western blotting. After induction for 14 days, higher alkaline phosphatase (ALP) activity and more mineralized nodules were seen in comparison to the cells that did not undergo induction. Shh signaling appears to enhance osteogenic differentiation of rat EMSCs, suggesting that Shh signaling directs the lineage differentiation of ectodermal stem cells and represents a promising strategy for skeletal tissue regeneration.

High hydrostatic pressure (30 atm) enhances the apoptosis and inhibits the proteoglycan synthesis and extracellular matrix level of human nucleus pulposus cells via promoting the Wnt/β-catenin pathway

Hydrostatic pressure is known to regulate bovine nucleus pulposus cell metabolism, but its mechanism in human nucleus pulposus cells (HNPCs) remains obscure, which attracts our attention and becomes the focus in this study. Specifically, HNPCs were treated with SKL2001 (an agonist in the Wnt/β-catenin pathway) or XAV-939 (an inhibitor of the Wnt/β-catenin pathway), and pressurized under the hydrostatic pressure of 1, 3 and 30 atm. The viability, apoptosis and proteoglycan synthesis of treated HNPC were assessed by CCK-8, flow cytometry and radioisotope incorporation assays. The levels of extracellular matrix, Collagen-II, matrix metalloproteinase 3 (MMP3), Wnt-3a and β-catenin were measured by toluidine blue staining, immunocytochemistry and Western blot. Appropriate hydrostatic stimulation (3 atm) enhanced the viability and proteoglycan synthesis yet inhibited the apoptosis of HNPCs, which also up-regulated extracellular matrix and Collagen-II levels, and down-regulated MMP3, Wnt-3a and β-catenin levels in treated HNPCs. Furthermore, high hydrostatic pressure (30 atm) inhibited the viability and proteoglycan synthesis, and promoted the morphological change and apoptosis of HNPCs, which also down-regulated extracellular matrix and Collagen-II levels and up-regulated MMP3, Wnt-3a and β-catenin levels. Besides, SKL2001 reversed the effects of hydrostatic pressure (3 atm) on inhibiting Wnt-3a, β-catenin, and MMP3 levels and promoting Collagen-II level in HNPC; whereas, XAV-939 reversed the effects of high hydrostatic pressure (30 atm) on promoting MMP3, Wnt-3a, and β-catenin levels and inhibiting Collagen-II level and proteoglycan synthesis of HNPCs. Collectively, high hydrostatic pressure promoted the apoptosis and inhibited the viability of HNPCs via activating the Wnt/β-catenin 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.

Nerve growth factor promotes osteogenic differentiation of MC3T3-E1 cells via BMP-2/Smads pathway

BACKGROUND

Exogenous nerve growth factor (NGF) can induce osteogenic precursor cell differentiation and promote fracture healing. However, the molecular mechanism by which NGF induces osteogenesis is not well understood. BMP-2 has good osteogenic efficacy and is one of the most osteogenic-inducing growth factors known. Therefore, this study aimed to determine whether NGF induces osteogenic differentiation of mouse embryonic osteogenic precursor cell line MC3T3-E1 by BMP-2 and search further mechanisms of NGF on BMP-2.

METHODS

MC3T3-E1 cells were treated with NGF at a concentration gradient for indicated times, after which the cell viability was measured by CCK-8 kit. Osteogenic differentiation was detected with quantification of alkaline phosphatase (ALP) activity also visualized with ALP staining. The transcription and expression of relevant genes were detected by qPCR and western blotting, respectively. NGF's effect on BMP2 was studied with qPCR and luciferase reporter assay. The phosphorylation of Smads was probed with specific antibodies by western blotting, and the location of Smads was observed through immunofluorescence.

RESULTS

We found that NGF promoted proliferation and osteogenic differentiation of MC3T3-E1, increased the expression level of BMP-2, as well as the phosphorylation and nuclear translocation of Smad1/5/8. However, neutralization of BMP-2 with si-BMP-2 or BMP-2 signal inhibitors reversed NGF induced phosphorylation and nuclear translocation of Smad1/5/8, as well as the expression of Runx2, type I collagen, osteocalcin and osteopontin. In addition, si-BMP-2 abrogated NGF-induced ALP activity.

CONCLUSION

NGF induced osteogenic differentiation of MC3T3-E1 cells through BMP-2/Smads pathway and induction of Runx2. Our study would provide a theoretical basis for clinical treatment of fractures using NGF.

Spatio-temporal immunolocalization of VEGF-A, Runx2, and osterix during the early steps of intramembranous ossification of the alveolar process in rat embryos

Vascular endothelial growth factor A (VEGF-A) is expressed by several cell types and is a crucial factor for angiogenic-osteogenic coupling. However, the immunolocalization of VEGF-A during the early stages of the alveolar process formation remains underexplored. Thus, we analyzed the spatio-temporal immunolocalization of VEGF-A and its relationship with Runt-related transcription factor 2 (Runx2) and osterix (Osx) during the early steps of intramembranous ossification of the alveolar process in rat embryos. Embryo heads (E) of 16, 18 and 20-day-old rats were processed for paraffin embedding. Histomorphometry and immunohistochemistry to detect VEGF-A, Runx2, and Osx (osteoblast differentiation markers) were performed. The volume density of bone tissue including bone cells and blood vessels increased significantly in E18 and E20. Cells showing high VEGF-A immunoreactivity were initially observed within a perivascular niche in the ectomesenchyme; afterwards, these cells were diffusely located near bone formation sites. Runx2-and Osx-immunopositive cells were observed in corresponded regions of cells showing strong VEGF-A immunoreactivity. Although these immunostained cells were observed in all specimens, this immunolocalization pattern was more evident in E16 specimens and gradually decreased in E18 and E20 specimens. Double immunofluorescence labelling showed intracellular co-localization of Osx and VEGF-A in cells surrounding the developing alveolar process, indicating a crucial role of VEGF-A in osteoblast differentiation. Our results showed VEGF-A immunoexpression in osteoblasts and its precursors during the maxillary alveolar process formation of rat embryos. Moreover, the VEGF-A-positive cells located within a perivascular niche at the early stages of the alveolar process development suggest a crosstalk between endothelium and ectomesenchymal cells, reinforcing the angiogenic-osteogenic coupling in this process.

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.

Wnt/β-Catenin Signaling Pathway Regulates Osteogenesis for Breast Cancer Bone Metastasis: Experiments in an In Vitro Nanoclay Scaffold Cancer Testbed

Breast cancer shows a high affinity toward bone, causing bone-related complications, leading to a poor clinical prognosis. The Wnt/β-catenin signaling pathway has been well-documented for the bone regenerative process; however, the regulation of the Wnt/β-catenin pathway in breast cancer bone metastasis is poorly explored. Here, we report that the Wnt/β-catenin signaling pathway has a significant effect on osteogenesis during breast cancer bone metastasis. In this study, we have created a 3D in vitro breast cancer bone metastatic microenvironment using nanoclay-based scaffolds along with osteogenically differentiated human mesenchymal stem cells (MSCs) and human breast cancer cells (MCF-7 and MDA-MB-231). The results showed upregulation in expressions of Wnt-related factors (Wnt-5a, β-catenin, AXIN2, and LRP5) in sequential cultures of MSCs with MCF-7 as compared to sequential cultures of MSCs with MDA-MB-231. Sequential cultures of MSCs with MCF-7 also showed higher β-catenin expression on the protein levels than sequential cultures of MSCs with MDA-MB-231. Stimulation of Wnt/β-catenin signaling in sequential cultures of MSCs with MCF-7 by ET-1 resulted in increased bone formation, whereas inactivation of Wnt/β-catenin signaling by DKK-1 displayed a significant decrease in bone formation, mimicking bone lesions in breast cancer patients. These data collectively demonstrate that Wnt/β-catenin signaling governs osteogenesis within the tumor-harboring bone microenvironment, leading to bone metastasis. The nanoclay scaffold provides a unique testbed approach for analysis of the pathways of cancer metastasis.

HDAC I inhibitor regulates RUNX2 transactivation through canonical and non-canonical Wnt signaling in aortic valvular interstitial cells

OBJECTIVES

The cellular mechanisms of calcific aortic valve (AV) disease and optimal medications for its treatment are poorly elucidated. Glycogen synthase kinase (GSK)-3β and non-canonical wingless-related integration site (Wnt) signaling play crucial roles in regulating the pathogenesis of valvular interstitial cell (VIC) calcification. Histone acetylation was found to regulate VIC calcification. However, whether histone deacetylases (HDACs) modulate the pathophysiology of AV calcification is unclear. Different HDAC isoforms have dissimilar cardiovascular effects. We hypothesized that distinctive HDAC inhibitors modulate runt-related transcription factor 2 (RUNX2) in aortic VICs through the regulation of Wnt signaling.

METHODS

Western blotting, real-time polymerase chain reaction, and proliferation assay were used to analyze osteogenesis marker expression, Wnt signaling, bone morphogenetic protein (BMP) signaling, and proliferation in porcine VICs treated with osteogenic (OST) medium alone or in combination with HDAC inhibitors.

RESULTS

VICs treated with OST medium for 5 days exhibited higher RUNX2 and GSK-3β expression levels than did control cells. A class I HDAC inhibitor (MS-275 at 1 μM) reduced the RUNX2 mRNA and protein expression levels and alkaline phosphatase activity and downregulated non-canonical Wnt/GSK-3β signaling, canonical Wnt/β-catenin signaling, and BMP signaling. By contrast, a combined class IIa (MC1568) and IIb HDAC (tubacin) inhibitor (0.1 μM) increased RUNX2 expression. MS-275, MC1568, and tubacin reduced VIC proliferation; however, the extent of reduction differed. MS-275 reduced RUNX2 and osteocalcin expression in VICs treated with OST medium for an extended period (14 days).

CONCLUSIONS

MS-275 critically regulates RUNX2 transactivation in VICs through both canonical and non-canonical Wnt signaling pathways.

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.