Jagged1 is essential for osteoblast development during maxillary ossification

Additional Insights Into the Role of Osteocalcin in Osteoblast Differentiation and in the Early Steps of Developing Alveolar Process of Rat Molars

This study investigated whether osteocalcin (OCN) is present in osteoblast precursors and its relationship with initial phases of alveolar process formation. Samples of maxillae of 16-, 18-, and 20-day-old rat embryos (E16, E18, and E20, respectively), and 05-, 10-, and 15-day-old postnatal rats (P05, P10, and P15, respectively) were fixed and embedded in paraffin or araldite. Immunohistochemistry for osterix (Osx), alkaline phosphatase (ALP), and OCN detection was performed and the number of immunolabelled cells was computed. Non-decalcified sections were subjected to the von Kossa method combined with immunohistochemistry for Osx or OCN detection. For OCN immunolocalization, samples were fixed in 0.5% glutaraldehyde/2% formaldehyde and embedded in LR White resin. The highest number of ALP- and OCN-immunolabelled cells was observed in dental follicle of E16 specimens, mainly in basal portions of dental alveolus. In corresponding regions, osteoblasts in differentiation adjacent to von Kossa-positive bone matrix exhibited Osx and OCN immunoreactivity. Ultrastructural analysis revealed OCN immunoreactive particles inside osteoblast in differentiation, and in bone matrix associated with collagen fibrils and within matrix vesicles, at early stages of alveolar process formation. Our results indicate that OCN plays a role in osteoblast differentiation and may regulate calcium/phosphate precipitation during early mineralization of the alveolar process.

Notch1 is a marker for in situ resting osteocytes in a 3-dimensional gel culture model

PURPOSE

Osteocytes in vivo exhibit different functional states, but no specific marker to distinguish these is currently available.

MATERIALS AND METHODS

To simulate the differentiation process of pre-osteoblasts to osteocytes in vitro, MC3T3-E1 cells were cultured on type I collagen gel and a three-dimensional (3D) culture system was established. The Notch expression of osteocyte-like cells in 3D culture system was compared with that of in situ osteocytes in bone tissues.

RESULTS

Immunohistochemistry demonstrated that Notch1 was not detected in "resting" in situ osteocytes, but was detected in normal cultured osteocyte-like cell line MLO-Y4. Osteocytes obtained from conventional osteogenic-induced osteoblasts and long-term cultured MLO-Y4 cells could not replicate the Notch1 expression pattern from in situ osteocytes. From day 14-35 of osteogenic induction, osteoblasts in 3D culture system gradually migrated into the gel to form canaliculus-like structures similar to bone canaliculus. On day 35, stellate-shaped osteocyte-like cells were observed, and expression of DMP1 and SOST, but not Runx2, was detected. Notch1 was not detected by immunohistochemistry, and Notch1 mRNA level was not significantly different from that of in situ osteocytes. In MC3T3-E1 cells, down-regulation of Notch2 increased Notch1, Notch downstream genes (β-catenin and Nfatc1), and Dmp1. In MLO-Y4 cells, Notch2 decreased after Notch1 siRNA transfection. Downregulation of Notch1 or Notch2 decreased Nfatc1, β-catenin, and Dmp1, and increased Sost.

CONCLUSIONS

We established "resting state" osteocytes using an in vitro 3D model. Notch1 can be a useful marker to help differentiate the functional states of osteocytes (activated vs. resting state).

Mouse embryo phenotyping using X-ray microCT

Microscopic X-ray computed tomography (microCT) is a structural ex vivo imaging technique providing genuine isotropic 3D images from biological samples at micron resolution. MicroCT imaging is non-destructive and combines well with other modalities such as light and electron microscopy in correlative imaging workflows. Protocols for staining embryos with X-ray dense contrast agents enable the acquisition of high-contrast and high-resolution datasets of whole embryos and specific organ systems. High sample throughput is achieved with dedicated setups. Consequently, microCT has gained enormous importance for both qualitative and quantitative phenotyping of mouse development. We here summarize state-of-the-art protocols of sample preparation and imaging procedures, showcase contemporary applications, and discuss possible pitfalls and sources for artefacts. In addition, we give an outlook on phenotyping workflows using microscopic dual energy CT (microDECT) and tissue-specific contrast agents.

Effects of decellularized extracellular matrix derived from Jagged1-treated human dental pulp stem cells on biological responses of stem cells isolated from apical papilla

Objective: Indirect Jagged1 immobilization efficiently activates canonical Notch signaling in human dental pulp stem cells (hDPSCs). This study aimed to investigate the characteristics of the Jagged1-treated hDPSC-derived decellularized extracellular matrix (dECM) and its biological activity on odonto/osteogenic differentiation of stem cells isolated from apical papilla (SCAPs).

Methods: Bioinformatic database of Jagged1-treated hDPSCs was analyzed using NetworkAnalyst. hDPSCs seeded on the Jagged1 immobilized surface were maintained with normal or osteogenic induction medium (OM) followed by decellularization procedure, dECM-N, or dECM-OM, respectively. SCAPs were reseeded on each dECM with either the normal medium or the OM. Cell viability was determined by MTT assay. Characteristics of dECMs and SCAPs were evaluated by SEM, EDX, immunofluorescent staining, and alcian blue staining. Mineralization was assessed by alizarin red S, Von Kossa, and alkaline phosphatase staining. Statistical significance was considered at p < 0.05.

Results: RNA-seq database revealed upregulation of several genes involved in ECM organization, ECM–receptor interaction, and focal adhesion in Jagged1-treated hDPSCs. Immobilized Jagged1 increased the osteogenesis of the hDPSC culture with OM. dECMs showed fibrillar-like network structure and maintained major ECM proteins, fibronectin, type I-collagen, and glycosaminoglycans. A decrease in calcium and phosphate components was observed in dECMs after the decellularized process. Cell viability on dECMs did not alter by 7 days. Cell attachment and f-actin cytoskeletal organization of SCAPs proliferated on Jagged1-treated dECMs were comparable to those of the control dECMs. SCAPs exhibited significantly higher mineralization on dECM-N in OM and markedly enhanced on dECM-OM with normal medium or OM conditions.

Conclusion: Jagged1-treated hDPSC-derived dECMs are biocompatible and increase odonto/osteogenic differentiation of SCAPs. The results suggested the potential of Jagged1 dECMs, which could be further developed into ECM scaffolds for application in regenerative medicine.

Notch signaling enhances bone regeneration in the zebrafish mandible

Loss or damage to the mandible caused by trauma, treatment of oral malignancies, and other diseases is treated using bone-grafting techniques that suffer from numerous shortcomings and contraindications. Zebrafish naturally heal large injuries to mandibular bone, offering an opportunity to understand how to boost intrinsic healing potential. Using a novel her6:mCherry Notch reporter, we show that canonical Notch signaling is induced during the initial stages of cartilage callus formation in both mesenchymal cells and chondrocytes following surgical mandibulectomy. We also show that modulation of Notch signaling during the initial post-operative period results in lasting changes to regenerate bone quantity one month later. Pharmacological inhibition of Notch signaling reduces the size of the cartilage callus and delays its conversion into bone, resulting in non-union. Conversely, conditional transgenic activation of Notch signaling accelerates conversion of the cartilage callus into bone, improving bone healing. Given the conserved functions of this pathway in bone repair across vertebrates, we propose that targeted activation of Notch signaling during the early phases of bone healing in mammals may both augment the size of the initial callus and boost its ossification into reparative bone.

Induction of osteogenesis by bone-targeted Notch activation

Declining bone mass is associated with aging and osteoporosis, a disease characterized by progressive weakening of the skeleton and increased fracture incidence. Growth and lifelong homeostasis of bone rely on interactions between different cell types including vascular cells and mesenchymal stromal cells (MSCs). As these interactions involve Notch signaling, we have explored whether treatment with secreted Notch ligand proteins can enhance osteogenesis in adult mice. We show that a bone-targeting, high affinity version of the ligand Delta-like 4, termed Dll4_(E12), induces bone formation in male mice without causing adverse effects in other organs, which are known to rely on intact Notch signaling. Due to lower bone surface and thereby reduced retention of Dll4_(E12), the same approach failed to promote osteogenesis in female and ovariectomized mice but strongly enhanced trabecular bone formation in combination with parathyroid hormone. Single cell analysis of stromal cells indicates that Dll4_(E12) primarily acts on MSCs and has comparably minor effects on osteoblasts, endothelial cells, or chondrocytes. We propose that activation of Notch signaling by bone-targeted fusion proteins might be therapeutically useful and can avoid detrimental effects in Notch-dependent processes in other organs.

Regulation of TNF-Induced Osteoclast Differentiation

Increased osteoclast (OC) differentiation and activity is the critical event that results in bone loss and joint destruction in common pathological bone conditions, such as osteoporosis and rheumatoid arthritis (RA). RANKL and its decoy receptor, osteoprotegerin (OPG), control OC differentiation and activity. However, there is a specific concern of a rebound effect of denosumab discontinuation in treating osteoporosis. TNFα can induce OC differentiation that is independent of the RANKL/RANK system. In this review, we discuss the factors that negatively and positively regulate TNFα induction of OC formation, and the mechanisms involved to inform the design of new anti-resorptive agents for the treatment of bone conditions with enhanced OC formation. Similar to, and being independent of, RANKL, TNFα recruits TNF receptor-associated factors (TRAFs) to sequentially activate transcriptional factors NF-κB p50 and p52, followed by c-Fos, and then NFATc1 to induce OC differentiation. However, induction of OC formation by TNFα alone is very limited, since it also induces many inhibitory proteins, such as TRAF3, p100, IRF8, and RBP-j. TNFα induction of OC differentiation is, however, versatile, and Interleukin-1 or TGFβ1 can enhance TNFα-induced OC formation through a mechanism which is independent of RANKL, TRAF6, and/or NF-κB. However, TNFα polarized macrophages also produce anabolic factors, including insulin such as 6 peptide and Jagged1, to slow down bone loss in the pathological conditions. Thus, the development of novel approaches targeting TNFα signaling should focus on its downstream molecules that do not affect its anabolic effect.

TNF-Polarized Macrophages Produce Insulin-like 6 Peptide to Stimulate Bone Formation in Rheumatoid Arthritis in Mice

The risk of osteoporosis is increased in rheumatoid arthritis (RA). Anti-tumor necrosis factor (TNF) therapy has markedly improved the outcomes of RA patients but does not improve osteoporosis in some reports. This could be a combined result of disease severity and other therapeutic agents, such as glucocorticoids that accelerate osteoporosis progression. We evaluated the effects of anti-TNF therapy on osteoporosis in an animal model of RA and explored the possible mechanisms involved. Six-week-old TNF transgenic (TNF-Tg) mice with early stage erosive arthritis were treated with TNF antibody (Ab) or control immunoglobulin (IgG) weekly for 4 weeks. We found that TNF Ab completely blocked the development of erosive arthritis in TNF-Tg mice, but only slightly increased vertebral bone mass, associated with reduction in parameters of both bone resorption and formation. Similarly, TNF Ab slightly increased trabecular bone mass in tibias of 8-month-old TNF-Tg mice with advanced erosive arthritis. Interestingly, TNFα increased osteoblast differentiation from mouse bone marrow stromal cells (BMSCs) containing large number of macrophages but not from pure mesenchymal progenitor cells (MPCs). TNFα-polarized macrophages (TPMs) did not express iNos and Arginase 1, typical markers of inflammatory and resident macrophages. Interestingly, TPMs stimulated osteoblast differentiation, unlike resident and inflammatory macrophages polarized by IL-4 and interferon-λ, respectively. RNA-seq analysis indicated that TPMs produced several anabolic factors, including Jagged1 and insulin like 6 (INSL6). Importantly, inhibition of either Jagged1 or INSL6 blocked TNFα-induced osteoblast differentiation. Furthermore, INSL6 Ab significantly decreased the expansion of TNF-induced MPCs in BMSCs, and anti-TNF Ab reduced INSL6 expression by macrophages in vitro and in TNF-Tg mice in vivo. We conclude that TPMs produce INSL6 to stimulate bone formation and anti-TNF Ab blocks not only enhanced bone resorption but also the anabolic effect of TPMs on bone, limiting its effect to increase bone mass in this model of RA. © 2021 American Society for Bone and Mineral Research (ASBMR).

JAGGED1 stimulates cranial neural crest cell osteoblast commitment pathways and bone regeneration independent of canonical NOTCH signaling

Craniofacial bone loss is a complex clinical problem with limited regenerative solutions. Currently, BMP2 is used as a bone-regenerative therapy in adults, but in pediatric cases of bone loss, it is not FDA-approved due to concerns of life-threatening inflammation and cancer. Development of a bone-regenerative therapy for children will transform our ability to reduce the morbidity associated with current autologous bone grafting techniques. We discovered that JAGGED1 (JAG1) induces cranial neural crest (CNC) cell osteoblast commitment during craniofacial intramembranous ossification, suggesting that exogenous JAG1 delivery is a potential craniofacial bone-regenerative approach. In this study, we found that JAG1 delivery using synthetic hydrogels containing O9-1 cells, a CNC cell line, into critical-sized calvarial defects in C57BL/6 mice provided robust bone-regeneration. Since JAG1 signals through canonical (Hes1/Hey1) and non-canonical (JAK2) NOTCH pathways in CNC cells, we used RNAseq to analyze transcriptional pathways activated in CNC cells treated with JAG1 ± DAPT, a NOTCH-canonical pathway inhibitor. JAG1 upregulated expression of multiple NOTCH canonical pathway genes (Hes1), which were downregulated in the presence of DAPT. JAG1 also induced bone chemokines (Cxcl1), regulators of cytoskeletal organization and cell migration (Rhou), signaling targets (STAT5), promoters of early osteoblast cell proliferation (Prl2c2, Smurf1 and Esrra), and, inhibitors of osteoclasts (Id1). In the presence of DAPT, expression levels of Hes1 and Cxcl1 were decreased, whereas, Prl2c2, Smurf1, Esrra, Rhou and Id1 remain elevated, suggesting that JAG1 induces osteoblast proliferation through these non-canonical genes. Pathway analysis of JAG1 + DAPT-treated CNC cells revealed significant upregulation of multiple non-canonical pathways, including the cell cycle, tubulin pathway, regulators of Runx2 initiation and phosphorylation of STAT5 pathway. In total, our data show that JAG1 upregulates multiple pathways involved in osteogenesis, independent of the NOTCH canonical pathway. Moreover, our findings suggest that JAG1 delivery using a synthetic hydrogel, is a bone-regenerative approach with powerful translational potential.

Obesity regulates miR-467/HoxA10 axis on osteogenic differentiation and fracture healing by BMSC-derived exosome LncRNA H19

This study explored the therapeutic effect of bone marrow mesenchymal stem cell‐derived exosomes on the treatment of obesity‐induced fracture healing. Quantitative real‐time PCR was used to detect the expression of lncRNA H19, miR‐467 and Hoxa10 and combined with WB detection to detect osteogenic markers (RUNX2, OPN, OCN). Determine whether exosomes have entered BMSCs by immunofluorescence staining. Alkaline phosphatase (ALP) and alizarin red staining (ARS) staining were used to detect ALP activity and calcium deposition. We found that high‐fat treatment can inhibit the secretion of BMSCs‐derived exosomes and affect the expression of H19 carried by them. In vivo and in vitro experiments show that high‐fat or obesity factors can inhibit the expression of osteogenic markers and reduce the staining activity of ALP and ARS. The treatment of exosomes from normal sources can reverse the phenomenon of osteogenic differentiation and abnormal fracture healing. Further bioinformatics analysis found that miR‐467 as a regulatory molecule of lncRNA H19 and Hoxa10, and we verified the targeting relationship of the three through dual luciferase report experiments. Further, we found similar phenomena in ALP and ARS staining. Bone marrow mesenchymal stem cell‐derived exosomes improve fracture healing caused by obesity.

Functional Diversification of SRSF Protein Kinase to Control Ubiquitin-Dependent Neurodevelopmental Signaling

Conserved protein kinases with core cellular functions have been frequently redeployed during metazoan evolution to regulate specialized developmental processes. The Ser/Arg (SR)-rich splicing factor (SRSF) protein kinase (SRPK), which is implicated in splicing regulation, is one such conserved eukaryotic kinase. Surprisingly, we show that SRPK has acquired the capacity to control a neurodevelopmental ubiquitin signaling pathway. In mammalian embryonic stem cells and cultured neurons, SRPK phosphorylates Ser-Arg motifs in RNF12/RLIM, a key developmental E3 ubiquitin ligase that is mutated in an intellectual disability syndrome. Processive phosphorylation by SRPK stimulates RNF12-dependent ubiquitylation of nuclear transcription factor substrates, thereby acting to restrain a neural gene expression program that is aberrantly expressed in intellectual disability. SRPK family genes are also mutated in intellectual disability disorders, and patient-derived SRPK point mutations impair RNF12 phosphorylation. Our data reveal unappreciated functional diversification of SRPK to regulate ubiquitin signaling that ensures correct regulation of neurodevelopmental gene expression.

Integrative analysis of long non-coding RNA and mRNA in broilers with valgus-varus deformity

BACKGROUND

Bone abnormality and leg disease in commercial broiler flocks are increasingly prominent, causing serious economic losses to the broiler breeding industry. Valgus-varus deformity (VVD) is a common deformity of the long bone in broilers that manifests as an outward or inward deviation of the tibiotarsus or tarsometatarsus. There is a paucity of studies on the molecular mechanisms of VVD.

RESULTS

In this study, 6 cDNA libraries were constructed from spleen samples from VVD birds and normal birds. A total of 1951 annotated lncRNAs, 7943 novel lncRNAs and 30252 mRNAs were identified by RNA-sequencing. In addition, 420 differentially expressed (DE) mRNAs and 124 differentially expressed lncRNAs (adjusted P-value < 0.05) were obtained. A total of 16 dysregulated genes were confirmed by qPCR to be consistent with the results of the RNA-Seq. The functional lncRNA-mRNA co-expression network was constructed using differentially expressed mRNAs and target genes of the differentially expressed lncRNAs. 11 DE genes were obtained from the analysis. In order to gain insight into the interactions of genes, lncRNAs and pathways associated with VVD, we focused on the following pathways, which are involved in immunity and bone development: the Jak-stat signaling pathway, Toll-like receptor signaling pathway, Wnt-signaling pathway, mTOR signaling pathway, VEGF signaling pathway, Notch signaling pathway, TGF-beta signaling pathway and Fanconi anemia pathway. All together, 30 candidate DE genes were obtained from these pathways. We then analyzed the interaction between the DE genes and their corresponding lncRNAs. From these interaction network analyses we found that GARS, NFIC, PIK3R1, BMP6, NOTCH1, ACTB and CREBBP were the key core nodes of these networks.

CONCLUSION

This study showed that differentially expressed genes and signaling pathways were related to immunity or bone development. These results increase the understanding of the molecular mechanisms of VVD and provide some reference for the etiology and pathogenesis of VVD.

How faithfully does intramembranous bone regeneration recapitulate embryonic skeletal development?

Postnatal intramembranous bone regeneration plays an important role during a wide variety of musculoskeletal regeneration processes such as fracture healing, joint replacement and dental implant surgery, distraction osteogenesis, stress fracture healing, and repair of skeletal defects caused by trauma or resection of tumors. The molecular basis of intramembranous bone regeneration has been interrogated using rodent models of most of these conditions. These studies reveal that signaling pathways such as Wnt, TGFβ/BMP, FGF, VEGF, and Notch are invoked, reminiscent of embryonic development of membranous bone. Discoveries of several skeletal stem cell/progenitor populations using mouse genetic models also reveal the potential sources of postnatal intramembranous bone regeneration. The purpose of this review is to compare the underlying molecular signals and progenitor cells that characterize embryonic development of membranous bone and postnatal intramembranous bone regeneration.

Canonical Notch signaling is required for bone morphogenetic protein-mediated human osteoblast differentiation

Osteoblast differentiation of bone marrow-derived human mesenchymal stem cells (hMSC) can be induced by stimulation with canonical Notch ligand, Jagged1, or bone morphogenetic proteins (BMPs). However, it remains elusive how these two pathways lead to the same phenotypic outcome. Since Runx2 is regarded as a master regulator of osteoblastic differentiation, we targeted Runx2 with siRNA in hMSC. This abrogated both Jagged1 and BMP2 mediated osteoblastic differentiation, confirming the fundamental role for Runx2. However, while BMP stimulation increased Runx2 and downstream Osterix protein expression, Jagged1 treatment failed to upregulate either, suggesting that canonical Notch signals require basal Runx2 expression. To fully understand the transcriptomic profile of differentiating osteoblasts, RNA sequencing was performed in cells stimulated with BMP2 or Jagged1. There was common upregulation of ALPL and extracellular matrix genes, such as ACAN, HAS3, MCAM, and OLFML2B. Intriguingly, genes encoding components of Notch signaling (JAG1, HEY2, and HES4) were among the top 10 genes upregulated by both stimuli. Indeed, ALPL expression occurred concurrently with Notch activation and inhibiting Notch activity for up to 24 hours after BMP administration with DAPT (a gamma secretase inhibitor) completely abrogated hMSC osteoblastogenesis. Concordantly, RBPJ (recombination signal binding protein for immunoglobulin kappa J region, a critical downstream modulator of Notch signals) binding could be demonstrated within the ALPL and SP7 promoters. As such, siRNA-mediated ablation of RBPJ decreased BMP-mediated osteoblastogenesis. Finally, systemic Notch inhibition using diabenzazepine (DBZ) reduced BMP2-induced calvarial bone healing in mice supporting the critical regulatory role of Notch signaling in BMP-induced osteoblastogenesis.

Notch Signaling and Embryonic Development: An Ancient Friend, Revisited

The evolutionary highly conserved Notch pathway, which first developed during evolution in metazoans and was first discovered in fruit flies (Drosophila melanogaster), governs many core processes including cell fate decisions during embryonic development. A huge mountain of scientific evidence convincingly demonstrates that Notch signaling represents one of the most important pathways that regulate embryogenesis from sponges, roundworms, Drosophila melanogaster, and mice to humans. In this review, we give a brief introduction on how Notch orchestrates the embryonic development of several selected tissues, summarizing some of the most relevant findings in the central nervous system, skin, kidneys, liver, pancreas, inner ear, eye, skeleton, heart, and vascular system.

Extracellular Matrix Composition and Remodeling: Current Perspectives on Secondary Palate Formation, Cleft Lip/Palate, and Palatal Reconstruction

Craniofacial development comprises a complex process in humans in which failures or disturbances frequently lead to congenital anomalies. Cleft lip with/without palate (CL/P) is a common congenital anomaly that occurs due to variations in craniofacial development genes, and may occur as part of a syndrome, or more commonly in isolated forms (non-syndromic). The etiology of CL/P is multifactorial with genes, environmental factors, and their potential interactions contributing to the condition. Rehabilitation of CL/P patients requires a multidisciplinary team to perform the multiple surgical, dental, and psychological interventions required throughout the patient's life. Despite progress, lip/palatal reconstruction is still a major treatment challenge. Genetic mutations and polymorphisms in several genes, including extracellular matrix (ECM) genes, soluble factors, and enzymes responsible for ECM remodeling (e.g., metalloproteinases), have been suggested to play a role in the etiology of CL/P; hence, these may be considered likely targets for the development of new preventive and/or therapeutic strategies. In this context, investigations are being conducted on new therapeutic approaches based on tissue bioengineering, associating stem cells with biomaterials, signaling molecules, and innovative technologies. In this review, we discuss the role of genes involved in ECM composition and remodeling during secondary palate formation and pathogenesis and genetic etiology of CL/P. We also discuss potential therapeutic approaches using bioactive molecules and principles of tissue bioengineering for state-of-the-art CL/P repair and palatal reconstruction.

Mouse Models for Diseases in the Cholangiocyte Lineage

Cholangiopathies are an important group of liver diseases affecting the biliary system, and the purpose of this review is to describe how diseases in the biliary system can be studied in mouse models. A particular focus is placed on mouse models for Alagille syndrome, a cholangiopathy with a strong genetic link to dysfunctional Notch signaling. Recently, a number of different genetic mouse models based on various manipulations of the Notch signaling pathway have been generated to study Alagille syndrome, and we discuss the resulting phenotypes, and possible causes for the phenotypic heterogeneity among the various models. In the final section, we provide a more general discussion on how well mouse models can be expected to mimic human liver disease, as well as an outlook toward the need for new technologies that can help us to gain new insights from mouse models for liver disease.

Gene expression profiling of Jagged1-treated human periodontal ligament cells

OBJECTIVE

Jagged1 regulates several biological functions in human periodontal ligament cells (hPDLs). The present study aimed to evaluate mRNA expression profiling of Jagged1-treated hPDLs using microarray technique.

METHODS

Notch ligands, Jagged1, were indirectly immobilized on tissue culture surface. Subsequently, hPDLs were seeded on Jagged1 immobilized surface and maintained in growth medium for 48 hr. Total RNA was collected and processed. Gene expression profiling was examined using microarray technique. Real-time polymerase chain reaction and immunofluorescence staining were employed to determine mRNA and protein expression levels, respectively. Cell proliferation and colony-forming unit assay were performed. Cell cycle was evaluated using propidium iodide staining and flow cytometry analysis.

RESULTS

The isolated cells demonstrated fibroblast-like morphology and exhibited the co-expression of CD44, CD90, and CD105 surface markers. After stimulated with Jagged1, the total of 411 genes was differentially expressed, consisting both coding and non-coding genes. For coding genes, 165 and 160 coding genes were upregulated and downregulated, respectively. Pathway analysis revealed that the upregulated genes were mainly involved in cellular interactions, signal transduction, and collagen formation and degradation while the downregulated genes were in the events and phases in cell cycle. Jagged1 significantly decreased cell proliferation, reduced colony-forming unit ability, and induced G0/G1 cell cycle arrest in hPDLs.

CONCLUSION

Jagged1 regulates various biological pathways in hPDLs. This gene expression profiling could help to understand the mechanisms potentially involved in the Notch signaling regulation in periodontal homeostasis.

BMP9-induced osteoblastic differentiation requires functional Notch signaling in mesenchymal stem cells

Mesenchymal stem cells (MSCs) are multipotent progenitors that can differentiate into multiple lineages including osteoblastic lineage. Osteogenic differentiation of MSCs is a cascade that recapitulates most, if not all, of the molecular events occurring during embryonic skeletal development, which is regulated by numerous signaling pathways including bone morphogenetic proteins (BMPs). Through a comprehensive analysis of the osteogenic activity, we previously demonstrated that BMP9 is the most potent BMP for inducing bone formation from MSCs both in vitro and in vivo. However, as one of the least studied BMPs, the essential mediators of BMP9-induced osteogenic signaling remain elusive. Here we show that BMP9-induced osteogenic signaling in MSCs requires intact Notch signaling. While the expression of Notch receptors and ligands are readily detectable in MSCs, Notch inhibitor and dominant-negative Notch1 effectively inhibit BMP9-induced osteogenic differentiation in vitro and ectopic bone formation in vivo. Genetic disruption of Notch pathway severely impairs BMP9-induced osteogenic differentiation and ectopic bone formation from MSCs. Furthermore, while BMP9-induced expression of early-responsive genes is not affected by defective Notch signaling, BMP9 upregulates the expression of Notch receptors and ligands at the intermediate stage of osteogenic differentiation. Taken together, these results demonstrate that Notch signaling may play an essential role in coordinating BMP9-induced osteogenic differentiation of MSCs.

A non-canonical JAGGED1 signal to JAK2 mediates osteoblast commitment in cranial neural crest cells

During craniofacial development, cranial neural crest (CNC) cells migrate into the developing face and form bone through intramembranous ossification. Loss of JAGGED1 (JAG1) signaling in the CNC cells is associated with maxillary hypoplasia or maxillary bone deficiency (MBD) in mice and recapitulates the MBD seen in humans with Alagille syndrome. JAGGED1, a membrane-bound NOTCH ligand, is required for normal craniofacial development, and Jagged1 mutations in humans are known to cause Alagille Syndrome, which is associated with cardiac, biliary, and bone phenotypes and these children experience increased bony fractures. Previously, we demonstrated deficient maxillary osteogenesis in Wnt1-cre;Jagged1^f/f (Jag1CKO) mice by conditional deletion of Jagged1 in maxillary CNC cells. In this study, we investigated the JAG1 signaling pathways in a CNC cell line. Treatment with JAG1 induced osteoblast differentiation and maturation markers, Runx2 and Ocn, respectively, Alkaline Phosphatase (ALP) production, as well as classic NOTCH1 targets, Hes1 and Hey1. While JAG1-induced Hes1 and Hey1 expression levels were predictably decreased after DAPT (NOTCH inhibitor) treatment, JAG1-induced Runx2 and Ocn levels were surprisingly constant in the presence of DAPT, indicating that JAG1 effects in the CNC cells are independent of the canonical NOTCH pathway. JAG1 treatment of CNC cells increased Janus Kinase 2 (JAK2) phosphorylation, which was refractory to DAPT treatment, highlighting the importance of the non-canonical NOTCH pathway during CNC cells osteoblast commitment. Pharmacologic inhibition of JAK2 phosphorylation, with and without DAPT treatment, upon JAG1 induction reduced ALP production and, Runx2 and Ocn gene expression. Collectively, these data suggest that JAK2 is an essential component downstream of a non-canonical JAG1-NOTCH1 pathway through which JAG1 stimulates expression of osteoblast-specific gene targets in CNC cells that contribute to osteoblast differentiation and bone mineralization.

Temporary inhibition of the plasminogen activator inhibits periosteal chondrogenesis and promotes periosteal osteogenesis during appendicular bone fracture healing

INTRODUCTION

Aminocaproic acid is approved as an anti-fibrinolytic for use in joint replacement and spinal fusion surgeries to limit perioperative blood loss. Previous animal studies have demonstrated a pro-osteogenic effect of aminocaproic acid in spine fusion models. Here, we tested if aminocaproic acid enhances appendicular bone healing and we sought to uncover the effect of aminocaproic acid on osteoprogenitor cells (OPCs) during bone regeneration.

METHODS

We employed a well-established murine femur fracture model in adult C57BL/6J mice after receiving two peri-operative injections of aminocaproic acid. Routine histological assays, biomechanical testing and micro-CT analyses were utilized to assess callus volume, and strength, progenitor cell proliferation, differentiation, and remodeling in vivo. Two disparate ectopic transplantation models were used to study the effect of the growth factor milieu within the early fracture hematoma on osteoprogenitor cell fate decisions.

RESULTS

Aminocaproic acid treated femur fractures healed with a significantly smaller cartilaginous callus, and this effect was also observed in the ectopic transplantation assays. We hypothesized that aminocaproic acid treatment resulted in a stabilization of the early fracture hematoma, leading to a change in the growth factor milieu created by the early hematoma. Gene and protein expression analysis confirmed that aminocaproic acid treatment resulted in an increase in Wnt and BMP signaling and a decrease in TGF-β-signaling, resulting in a shift from chondrogenic to osteogenic differentiation in this model of endochondral bone formation.

CONCLUSION

These experiments demonstrate for the first time that inhibition of the plasminogen activator during fracture healing using aminocaproic acid leads to a change in cell fate decision of periosteal osteoprogenitor cells, with a predominance of osteogenic differentiation, resulting in a larger and stronger bony callus. These findings may offer a promising new use of aminocaproic acid, which is already FDA-approved and offers a very safe risk profile.

Role of Notch Signaling in the Physiological Patterning of Posterofrontal and Sagittal Cranial Sutures

BACKGROUND

The mutations in a Notch signaling ligand, jagged 1, are associated with unilateral coronal craniosynostosis in humans. However, the underlying mechanisms of Notch signaling in cranial suture biology still remain unclear.

METHODS

The temporal and spatial patterns of Notch signaling expression were examined in the posterofrontal and sagittal sutures of Sprague-Dawley rats by real-time quantitative reverse-transcription polymerase chain reaction at postnatal ages of 2, 15, and 25 days. The role of Notch signaling in the proliferation and differentiation of osteoblasts isolated from calvarial was examined in vitro by EdU incorporation assays and real-time quantitative reverse-transcription polymerase chain reaction after activating and inhibiting Notch signaling.

RESULTS

The mRNA levels of Notch family members (including Jagged 1, Delta 1, 3, 4, Notch 1-4, Hes 1, and Hes 5) decreased during the posterofrontal cranial suture fusion in rat. However, in the patent sagittal sutures, the mRNA levels of Notch family members (Jagged 2, Delta 1, Notch 1, Notch 3, Hes 5, and Hey 1) increased during suture development. The EdU incorporation assays revealed that the induction of Notch signaling in calvaria osteobalsts using Jagged 1 promoted the proliferation rates in those cells in vitro. Further studies showed that activation of Notch signaling calvaria osteobalsts using Jagged 1 led to the suppression of late osteogenetic markers such as type I collagen and osteocalcin.

CONCLUSIONS

The regulation of Notch signaling is of crucial importance during the physiological patterning of posterofrontal and sagittal cranial sutures. Thus, targeting this pathway may prove significant for the development of future therapeutic applications in craniosynostosis.

Effect of low-level laser therapy on the healing of sites grafted with coagulum, deproteinized bovine bone, and biphasic ceramic made of hydroxyapatite and β-tricalcium phosphate. In vivo study in rats

OBJECTIVE

The aim of this study was to evaluate the effect of low-level laser therapy (LLLT) on the healing of biomaterial graft areas (i.e., coagulum, deproteinized bovine bone, and biphasic ceramics comprising hydroxyapatite and β-tricalcium phosphate).

MATERIAL AND METHODS

Ninety rats were divided into two groups according to laser irradiation use (λ 808 nm, 100 mW, φ ∼600 μm, seven sessions with 28 J of irradiation dose in total): a laser group and a control group. Each of these groups was divided into three subgroups of 15 animals each according to the type of biomaterial used: Coagulum (COA), deproteinized bovine bone (DBB), and hydroxyapatite/β-tricalcium phosphate (HA/βTCP). Biomaterials were inserted into Teflon domes, and these domes were grafted to the lateral aspect of the mandibular branch of the rats. The animals were sacrificed after 30, 60, and 90 days. Scarring patterns were evaluated by microtomography and histometry. The expression levels of BMP2, osteocalcin (OCN), and alkaline phosphatase (ALP) were evaluated by immunohistochemistry. The mRNA expression levels of ALP, BMP2, Jagged1, Osterix, Runx2, and TGFβ1 were determined by RT-qPCR.

RESULTS

The animals treated with LLLT exhibited increased mineralized tissues and bone, particularly after 90 days. These increases were associated with increased BMP2, OCN, and ALP protein expression and ALP, BMP2, and Jagged1 mRNA expression.

CONCLUSION

LLLT improved the osteoconductive potential of DBB and HA/βTCP grafts and bone formation in ungrafted areas. Lasers Surg. Med. © 2018 Wiley Periodicals, Inc.

Controlled JAGGED1 delivery induces human embryonic palate mesenchymal cells to form osteoblasts

Osteoblast commitment and differentiation are controlled by multiple growth factors including members of the Notch signaling pathway. JAGGED1 is a cell surface ligand of the Notch pathway that is necessary for murine bone formation. The delivery of JAGGED1 to induce bone formation is complicated by its need to be presented in a bound form to allow for proper Notch receptor signaling. In this study, we investigate whether the sustained release of JAGGED1 stimulates human mesenchymal cells to commit to osteoblast cell fate using polyethylene glycol malemeide (PEG-MAL) hydrogel delivery system. Our data demonstrated that PEG-MAL hydrogel constructs are stable in culture for at least three weeks and maintain human mesenchymal cell viability with little cytotoxicity in vitro. JAGGED1 loaded on PEG-MAL hydrogel (JAGGED1-PEG-MAL) showed continuous release from the gel for up to three weeks, with induction of Notch signaling using a CHO cell line with a Notch1 reporter construct, and qPCR gene expression analysis in vitro. Importantly, JAGGED1-PEG-MAL hydrogel induced mesenchymal cells towards osteogenic differentiation based on increased Alkaline phosphatase activity and osteoblast genes expression including RUNX2, ALP, COL1, and BSP. These results thus indicated that JAGGED1 delivery in vitro using PEG-MAL hydrogel induced osteoblast commitment, suggesting that this may be a viable in vivo approach to bone regeneration. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 552-560, 2018.

Hoxa2 Inhibits Bone Morphogenetic Protein Signaling during Osteogenic Differentiation of the Palatal Mesenchyme

Cleft palate is one of the most common congenital birth defects worldwide. The homeobox (Hox) family of genes are key regulators of embryogenesis, with Hoxa2 having a direct role in secondary palate development. Hoxa2^−/− mice exhibit cleft palate; however, the cellular and molecular mechanisms leading to cleft palate in Hoxa2^−/− mice is largely unknown. Addressing this issue, we found that Hoxa2 regulates spatial and temporal programs of osteogenic differentiation in the developing palate by inhibiting bone morphogenetic protein (BMP) signaling dependent osteoblast markers. Expression of osteoblast markers, including Runx2, Sp7, and AlpI were increased in Hoxa2^−/− palatal shelves at embryonic day (E) 13.5 and E15.5. Hoxa2^−/− mouse embryonic palatal mesenchyme (MEPM) cells exhibited increased bone matrix deposition and mineralization in vitro. Moreover, loss of Hoxa2 resulted in increased osteoprogenitor cell proliferation and osteogenic commitment during early stages of palate development at E13.5. Consistent with upregulation of osteoblast markers, Hoxa2^−/− palatal shelves displayed higher expression of canonical BMP signaling in vivo. Blocking BMP signaling in Hoxa2^−/− primary MEPM cells using dorsomorphin restored cell proliferation and osteogenic differentiation to wild-type levels. Collectively, these data demonstrate for the first time that Hoxa2 may regulate palate development by inhibiting osteogenic differentiation of palatal mesenchyme via modulating BMP signaling.

The developmental biology of genetic Notch disorders

Notch signaling regulates a vast array of crucial developmental processes. It is therefore not surprising that mutations in genes encoding Notch receptors or ligands lead to a variety of congenital disorders in humans. For example, loss of function of Notch results in Adams-Oliver syndrome, Alagille syndrome, spondylocostal dysostosis and congenital heart disorders, while Notch gain of function results in Hajdu-Cheney syndrome, serpentine fibula polycystic kidney syndrome, infantile myofibromatosis and lateral meningocele syndrome. Furthermore, structure-abrogating mutations in NOTCH3 result in CADASIL. Here, we discuss these human congenital disorders in the context of known roles for Notch signaling during development. Drawing on recent analyses by the exome aggregation consortium (EXAC) and on recent studies of Notch signaling in model organisms, we further highlight additional Notch receptors or ligands that are likely to be involved in human genetic diseases.

Requirement for Jagged1-Notch2 signaling in patterning the bones of the mouse and human middle ear

Whereas Jagged1-Notch2 signaling is known to pattern the sensorineural components of the inner ear, its role in middle ear development has been less clear. We previously reported a role for Jagged-Notch signaling in shaping skeletal elements derived from the first two pharyngeal arches of zebrafish. Here we show a conserved requirement for Jagged1-Notch2 signaling in patterning the stapes and incus middle ear bones derived from the equivalent pharyngeal arches of mammals. Mice lacking Jagged1 or Notch2 in neural crest-derived cells (NCCs) of the pharyngeal arches display a malformed stapes. Heterozygous Jagged1 knockout mice, a model for Alagille Syndrome (AGS), also display stapes and incus defects. We find that Jagged1-Notch2 signaling functions early to pattern the stapes cartilage template, with stapes malformations correlating with hearing loss across all frequencies. We observe similar stapes defects and hearing loss in one patient with heterozygous JAGGED1 loss, and a diversity of conductive and sensorineural hearing loss in nearly half of AGS patients, many of which carry JAGGED1 mutations. Our findings reveal deep conservation of Jagged1-Notch2 signaling in patterning the pharyngeal arches from fish to mouse to man, despite the very different functions of their skeletal derivatives in jaw support and sound transduction.

The Selective Serotonin Reuptake Inhibitor Fluoxetine Directly Inhibits Osteoblast Differentiation and Mineralization During Fracture Healing in Mice

Chronic use of selective serotonin reuptake inhibitors (SSRIs) for the treatment of depression has been linked to osteoporosis. In this study, we investigated the effect of chronic SSRI use on fracture healing in two murine models of bone regeneration. First, we performed a comprehensive analysis of endochondral bone healing in a femur fracture model. C57/BL6 mice treated with fluoxetine, the most commonly prescribed SSRI, developed a normal cartilaginous soft-callus at 14 days after fracture and demonstrated a significantly smaller and biomechanically weaker bony hard-callus at 28 days. In order to further dissect the mechanism that resulted in a smaller bony regenerate, we used an intramembranous model of bone healing and revealed that fluoxetine treatment resulted in a significantly smaller bony callus at 7 and 14 days postinjury. In order to test whether the smaller bony regenerate following fluoxetine treatment was caused by an inhibition of osteogenic differentiation and/or mineralization, we employed in vitro experiments, which established that fluoxetine treatment decreases osteogenic differentiation and mineralization and that this effect is serotonin-independent. Finally, in a translational approach, we tested whether cessation of the medication would result in restoration of the regenerative potential. However, histologic and μCT analysis revealed non-union formation in these animals with fibrous tissue interposition within the callus. In conclusion, fluoxetine exerts a direct, inhibitory effect on osteoblast differentiation and mineralization, shown in two disparate murine models of bone repair. Discontinuation of the drug did not result in restoration of the healing potential, but rather led to complete arrest of the repair process. Besides the well-established effect of SSRIs on bone homeostasis, our study provides strong evidence that fluoxetine use negatively impacts fracture healing. © 2017 American Society for Bone and Mineral Research.

Glucose-Dependent Insulinotropic Polypeptide Receptor Deficiency Leads to Impaired Bone Marrow Hematopoiesis

The bone marrow (BM) contains controlled specialized microenvironments, or niches, that regulate the quiescence, proliferation, and differentiation of hematopoietic stem and progenitor cells (HSPC). The glucose-dependent insulinotropic polypeptide (GIP) is a gut-derived incretin hormone that mediates postprandial insulin secretion and has anabolic effects on adipose tissue. Previous studies demonstrated altered bone microarchitecture in mice deficient for GIP receptor (Gipr^-/- ), as well as the expression of high-affinity GIP receptor by distinct cells constructing the BM HSPC niche. Nevertheless, the involvement of GIP in the process of BM hematopoiesis remains elusive. In this article, we show significantly reduced representation and proliferation of HSPC and myeloid progenitors in the BM of Gipr^-/- mice. This was further manifested by reduced levels of BM and circulating differentiated immune cells in young and old adult mice. Moreover, GIP signaling was required for the establishment of supportive BM HSPC niches during HSPC repopulation in radioablated BM chimera mice. Finally, molecular profiling of various factors involved in retention, survival, and expansion of HSPC revealed significantly lower expression of the Notch-receptor ligands Jagged 1 and Jagged 2 in osteoblast-enriched bone extracts from Gipr^-/- mice, which are important for HSPC expansion. In addition, there was increased expression of CXCL12, a factor important for HSPC retention and quiescence, in whole-BM extracts from Gipr^-/- mice. Collectively, our data suggest that the metabolic hormone GIP plays an important role in BM hematopoiesis.

Notch: A multi-functional integrating system of microenvironmental signals

The Notch signaling cascade is an evolutionarily ancient system that allows cells to interact with their microenvironmental neighbors through direct cell-cell interactions, thereby directing a variety of developmental processes. Recent research is discovering that Notch signaling is also responsive to a broad variety of stimuli beyond cell-cell interactions, including: ECM composition, crosstalk with other signaling systems, shear stress, hypoxia, and hyperglycemia. Given this emerging understanding of Notch responsiveness to microenvironmental conditions, it appears that the classical view of Notch as a mechanism enabling cell-cell interactions, is only a part of a broader function to integrate microenvironmental cues. In this review, we summarize and discuss published data supporting the idea that the full function of Notch signaling is to serve as an integrator of microenvironmental signals thus allowing cells to sense and respond to a multitude of conditions around them.

Jagged1 expression by osteoblast-lineage cells regulates trabecular bone mass and periosteal expansion in mice

Loss-of-function mutations in the Notch ligand, Jagged1 (Jag1), result in multi-system developmental pathologies associated with Alagille syndrome (ALGS). ALGS patients present with skeletal manifestations including hemi-vertebrae, reduced bone mass, increased fracture incidence and poor bone healing. However, it is not known whether the increased fracture risk is due to altered bone homeostasis (primary) or nutritional malabsorption due to chronic liver disease (secondary). To determine the significance of Jag1 loss in bone, we characterized the skeletal phenotype of two Jag1-floxed conditional knockout mouse models: Prx1-Cre;Jag1(f/f) to target osteoprogenitor cells and their progeny, and Col2.3-Cre;Jag1(f/f) to target mid-stage osteoblasts and their progeny. Knockout phenotypes were compared to wild-type (WT) controls using quantitative micro-computed tomography, gene expression profiling and mechanical testing. Expression of Jag1 and the Notch target genes Hes1 and Hey1 was downregulated in all Jag1 knockout mice. Osteoblast differentiation genes were downregulated in whole bone of both groups, but unchanged in Prx1-Cre;Jag1(f/f) cortical bone. Both knockout lines exhibited changes in femoral trabecular morphology including decreased bone volume fraction and increased trabecular spacing, with males presenting a more severe trabecular osteopenic phenotype. Prx1-Cre;Jag1(f/f) mice showed an increase in marrow mesenchymal progenitor cell number and, counterintuitively, developed increased cortical thickness resulting from periosteal expansion, translating to greater mechanical stiffness and strength. Similar alterations in femoral morphology were observed in mice with canonical Notch signaling disrupted using Prx1-Cre-regulatable dominant-negative mastermind like-protein (dnMAML). Taken together, we report that 1) Jag1 negatively regulates the marrow osteochondral progenitor pool, 2) Jag1 is required for normal trabecular bone formation and 3) Notch signaling through homotypic Jag1 signaling in osteochondral progenitors, but not mature osteoblasts, inhibits periosteal expansion. Therefore, Jag1 signaling within the osteoblast lineage regulates bone metabolism in a compartment-dependent manner. Moreover, loss of Jag1 function in osteoblast lineage cells may contribute to the skeletal phenotype associated with ALGS.

Potential mechanisms underlying the Runx2 induced osteogenesis of bone marrow mesenchymal stem cells

Bone marrow derived mesenchymal stem cells (BM-MSCs) belong a type of pluripotent stem cells and can be induced to differentiate into osteoblasts (OB). Runt-related transcription factor 2 (Runx2) is an osteogenesis specific transcription factor and plays an important role in osteogenesis of BM-MSCs. It can promote the expression of osteogenesis related genes, regulate cell cycle progression, improve bone microenvironment and affect functions of chondrocytes and osteoclasts, which have involvement of a large amount of signal molecules including TGF-β, BMP, Notch, Wnt, Hedgehog, FGF and microRNA. In this paper, we summarize the mechanisms underlying the Runx2 induced osteogenesis of BM-MSCs.

Molecular mechanisms of midfacial developmental defects

The morphogenesis of midfacial processes requires the coordination of a variety of cellular functions of both mesenchymal and epithelial cells to develop complex structures. Any failure or delay in midfacial development as well as any abnormal fusion of the medial and lateral nasal and maxillary prominences will result in developmental defects in the midface with a varying degree of severity, including cleft, hypoplasia, and midline expansion. Despite the advances in human genome sequencing technology, the causes of nearly 70% of all birth defects, which include midfacial development defects, remain unknown. Recent studies in animal models have highlighted the importance of specific signaling cascades and genetic-environmental interactions in the development of the midfacial region. This review will summarize the current understanding of the morphogenetic processes and molecular mechanisms underlying midfacial birth defects based on mouse models with midfacial developmental abnormalities.