PKCδ is required for Jagged-1 induction of human mesenchymal stem cell osteogenic differentiation

Osteoporosis GWAS-implicated DNM3 locus contextually regulates osteoblastic and chondrogenic fate of mesenchymal stem/progenitor cells through oscillating miR-199a-5p levels

Genome wide association study (GWAS)-implicated bone mineral density (BMD) signals have been shown to localize in cis-regulatory regions of distal effector genes using 3D genomic methods. Detailed characterization of such genes can reveal novel causal genes for BMD determination. Here, we elected to characterize the "DNM3" locus on chr1q24, where the long non-coding RNA DNM3OS and the embedded microRNA MIR199A2 (miR-199a-5p) are implicated as effector genes contacted by the region harboring variation in linkage disequilibrium with BMD-associated sentinel single nucleotide polymorphism, rs12041600. During osteoblast differentiation of human mesenchymal stem/progenitor cells (hMSC), miR-199a-5p expression was temporally decreased and correlated with the induction of osteoblastic transcription factors RUNX2 and Osterix. Functional relevance of miR-199a-5p downregulation in osteoblastogenesis was investigated by introducing miR-199a-5p mimic into hMSC. Cells overexpressing miR-199a-5p depicted a cobblestone-like morphological change and failed to produce BMP2-dependent extracellular matrix mineralization. Mechanistically, a miR-199a-5p mimic modified hMSC propagated normal SMAD1/5/9 signaling and expressed osteoblastic transcription factors RUNX2 and Osterix but depicted pronounced upregulation of SOX9 and enhanced expression of essential chondrogenic genes ACAN, COMP, and COL10A1. Mineralization defects, morphological changes, and enhanced chondrogenic gene expression associated with miR-199a-5p mimic over-expression were restored with miR-199a-5p inhibitor suggesting specificity of miR-199a-5p in chondrogenic fate specification. The expression of both the DNM3OS and miR-199a-5p temporally increased and correlated with hMSC chondrogenic differentiation. Although miR-199a-5p overexpression failed to further enhance chondrogenesis, blocking miR-199a-5p activity significantly reduced chondrogenic pellet size, extracellular matrix deposition, and chondrogenic gene expression. Taken together, our results indicate that oscillating miR-199a-5p levels dictate hMSC osteoblast or chondrocyte terminal fate. Our study highlights a functional role of miR-199a-5p as a BMD effector gene at the DNM3 BMD GWAS locus, where patients with cis-regulatory genetic variation which increases miR-199a-5p expression could lead to reduced osteoblast activity.

Protein kinase C signaling "in" and "to" the nucleus: Master kinases in transcriptional regulation

PKC is a multifunctional family of Ser-Thr kinases widely implicated in the regulation of fundamental cellular functions, including proliferation, polarity, motility, and differentiation. Notwithstanding their primary cytoplasmic localization and stringent activation by cell surface receptors, PKC isozymes impel prominent nuclear signaling ultimately impacting gene expression. While transcriptional regulation may be wielded by nuclear PKCs, it most often relies on cytoplasmic phosphorylation events that result in nuclear shuttling of PKC downstream effectors, including transcription factors. As expected from the unique coupling of PKC isozymes to signaling effector pathways, glaring disparities in gene activation/repression are observed upon targeting individual PKC family members. Notably, specific PKCs control the expression and activation of transcription factors implicated in cell cycle/mitogenesis, epithelial-to-mesenchymal transition and immune function. Additionally, PKCs isozymes tightly regulate transcription factors involved in stepwise differentiation of pluripotent stem cells toward specific epithelial, mesenchymal, and hematopoietic cell lineages. Aberrant PKC expression and/or activation in pathological conditions, such as in cancer, leads to profound alterations in gene expression, leading to an extensive rewiring of transcriptional networks associated with mitogenesis, invasiveness, stemness, and tumor microenvironment dysregulation. In this review, we outline the current understanding of PKC signaling "in" and "to" the nucleus, with significant focus on established paradigms of PKC-mediated transcriptional control. Dissecting these complexities would allow the identification of relevant molecular targets implicated in a wide spectrum of diseases.

Bone Organoids: Recent Advances and Future Challenges

Bone defects stemming from tumorous growths, traumatic events, and diverse conditions present a profound conundrum in clinical practice and research. While bone has the inherent ability to regenerate, substantial bone anomalies require bone regeneration techniques. Bone organoids represent a new concept in this field, involving the 3D self-assembly of bone-associated stem cells guided in vitro with or without extracellular matrix material, resulting in a tissue that mimics the structural, functional, and genetic properties of native bone tissue. Within the scientific panorama, bone organoids ascend to an esteemed status, securing significant experimental endorsement. Through a synthesis of current literature and pioneering studies, this review offers a comprehensive survey of the bone organoid paradigm, delves into the quintessential architecture and ontogeny of bone, and highlights the latest progress in bone organoid fabrication. Further, existing challenges and prospective directions for future research are identified, advocating for interdisciplinary collaboration to fully harness the potential of this burgeoning domain. Conclusively, as bone organoid technology continues to mature, its implications for both clinical and research landscapes are poised to be profound.

Cross Talk Between Cells and the Current Bioceramics in Bone Regeneration: A Comprehensive Review

The conventional approach for addressing bone defects and stubborn non-unions typically involves the use of autogenous bone grafts. Nevertheless, obtaining these grafts can be challenging, and the procedure can lead to significant morbidity. Three primary treatment strategies for managing bone defects and non-unions prove resistant to conventional treatments: synthetic bone graft substitutes (BGS), a combination of BGS with bioactive molecules, and the use of BGS in conjunction with stem cells. In the realm of synthetic BGS, a multitude of biomaterials have emerged for creating scaffolds in bone tissue engineering (TE). These materials encompass biometals like titanium, iron, magnesium, and zinc, as well as bioceramics such as hydroxyapatite (HA) and tricalcium phosphate (TCP). Bone TE scaffolds serve as temporary implants, fostering tissue ingrowth and the regeneration of new bone. They are meticulously designed to enhance bone healing by optimizing geometric, mechanical, and biological properties. These scaffolds undergo continual remodeling facilitated by bone cells like osteoblasts and osteoclasts. Through various signaling pathways, stem cells and bone cells work together to regulate bone regeneration when a portion of bone is damaged or deformed. By targeting signaling pathways, bone TE can improve bone defects through effective therapies. This review provided insights into the interplay between cells and the current state of bioceramics in the context of bone regeneration.

Biomedical engineering approaches for the delivery of JAGGED1 as a potential tissue regenerative therapy

JAG1 is a ligand that activates the NOTCH signaling pathway which plays a crucial role in determining cell fate behavior through cell-to-cell signaling. JAG1-NOTCH signaling is required for mesenchymal stem cell (MSC) differentiation into cardiomyocytes and cranial neural crest (CNC) cells differentiation into osteoblasts, making it a regenerative candidate for clinical therapy to treat craniofacial bone loss and myocardial infarction. However, delivery of soluble JAG1 has been found to inhibit NOTCH signaling due to the requirement of JAG1 presentation in a bound form. For JAG1-NOTCH signaling to occur, JAG1 must be immobilized within a scaffold and the correct orientation between the NOTCH receptor and JAG1 must be achieved. The lack of clinically translatable JAG1 delivery methods has driven the exploration of alternative immobilization approaches. This review discusses the role of JAG1 in disease, the clinical role of JAG1 as a treatment, and summarizes current approaches for JAG1 delivery. An in-depth review was conducted on literature that used both in vivo and in vitro delivery models and observed the canonical versus non-canonical NOTCH pathway activated by JAG1. Studies were then compared and evaluated based on delivery success, functional outcomes, and translatability. Delivering JAG1 to harness its ability to control cell fate has the potential to serve as a therapeutic for many diseases.

Fibulin2: a negative regulator of BMSC osteogenic differentiation in infected bone fracture healing

Bone fracture remains a common occurrence, with a population-weighted incidence of approximately 3.21 per 1000. In addition, approximately 2% to 50% of patients with skeletal fractures will develop an infection, one of the causes of disordered bone healing. Dysfunction of bone marrow mesenchymal stem cells (BMSCs) plays a key role in disordered bone repair. However, the specific mechanisms underlying BMSC dysfunction caused by bone infection are largely unknown. In this study, we discovered that Fibulin2 expression was upregulated in infected bone tissues and that BMSCs were the source of infection-induced Fibulin2. Importantly, Fibulin2 knockout accelerated mineralized bone formation during skeletal development and inhibited inflammatory bone resorption. We demonstrated that Fibulin2 suppressed BMSC osteogenic differentiation by binding to Notch2 and inactivating the Notch2 signaling pathway. Moreover, Fibulin2 knockdown restored Notch2 pathway activation and promoted BMSC osteogenesis; these outcomes were abolished by DAPT, a Notch inhibitor. Furthermore, transplanted Fibulin2 knockdown BMSCs displayed better bone repair potential in vivo. Altogether, Fibulin2 is a negative regulator of BMSC osteogenic differentiation that inhibits osteogenesis by inactivating the Notch2 signaling pathway in infected bone.

Probing Notch1-Dll4 signaling in regulating osteogenic differentiation of human mesenchymal stem cells using single cell nanobiosensor

Human mesenchymal stem cells (hMSCs) have great potential in cell-based therapies for tissue engineering and regenerative medicine due to their self-renewal and multipotent properties. Recent studies indicate that Notch1-Dll4 signaling is an important pathway in regulating osteogenic differentiation of hMSCs. However, the fundamental mechanisms that govern osteogenic differentiation are poorly understood due to a lack of effective tools to detect gene expression at single cell level. Here, we established a double-stranded locked nucleic acid (LNA)/DNA (LNA/DNA) nanobiosensor for gene expression analysis in single hMSC in both 2D and 3D microenvironments. We first characterized this LNA/DNA nanobiosensor and demonstrated the Dll4 mRNA expression dynamics in hMSCs during osteogenic differentiation. By incorporating this nanobiosensor with live hMSCs imaging during osteogenic induction, we performed dynamic tracking of hMSCs differentiation and Dll4 mRNA gene expression profiles of individual hMSC during osteogenic induction. Our results showed the dynamic expression profile of Dll4 during osteogenesis, indicating the heterogeneity of hMSCs during this dynamic process. We further investigated the role of Notch1-Dll4 signaling in regulating hMSCs during osteogenic differentiation. Pharmacological perturbation is applied to disrupt Notch1-Dll4 signaling to investigate the molecular mechanisms that govern osteogenic differentiation. In addition, the effects of Notch1-Dll4 signaling on hMSCs spheroids differentiation were also investigated. Our results provide convincing evidence supporting that Notch1-Dll4 signaling is involved in regulating hMSCs osteogenic differentiation. Specifically, Notch1-Dll4 signaling is active during osteogenic differentiation. Our results also showed that Dll4 is a molecular signature of differentiated hMSCs during osteogenic induction. Notch inhibition mediated osteogenic differentiation with reduced Alkaline Phosphatase (ALP) activity. Lastly, we elucidated the role of Notch1-Dll4 signaling during osteogenic differentiation in a 3D spheroid model. Our results showed that Notch1-Dll4 signaling is required and activated during osteogenic differentiation in hMSCs spheroids. Inhibition of Notch1-Dll4 signaling mediated osteogenic differentiation and enhanced hMSCs proliferation, with increased spheroid sizes. Taken together, the capability of LNA/DNA nanobiosensor to probe gene expression dynamics during osteogenesis, combined with the engineered 2D/3D microenvironment, enables us to study in detail the role of Notch1-Dll4 signaling in regulating osteogenesis in 2D and 3D microenvironment. These findings will provide new insights to improve cell-based therapies and organ repair techniques.

Non-canonical Wnt signaling participates in Jagged1-induced osteo/odontogenic differentiation in human dental pulp stem cells

Osteoblast differentiation requires the interaction of various cell signaling pathways to modulate cell responses. Notch and Wnt signaling are among the crucial pathways that control numerous biological processes, including osteo/odontogenic differentiation. The aim of the present study was to examine the involvement of Wnt signaling in the Jagged1-induced osteo/odontogenic differentiation in human dental pulp stem cells (hDPSCs). The Wnt-related gene expression was analyzed from publicly available data of Jagged1-treated human dental pulp cells. The mRNA expression of Wnt ligands (WNT2B, WNT5A, WNT5B, and WNT16) and Wnt inhibitors (DKK1, DKK2, and SOST) were confirmed using real-time polymerase chain reaction. Among the Wnt ligands, WNT2B and WNT5A mRNA levels were upregulated after Jagged1 treatment. In contrast, the Wnt inhibitors DKK1, DKK2, and SOST mRNA levels were downregulated. Recombinant WNT5A, but not WNT2B, significantly promoted in vitro mineral deposition by hDPSCs. Wnt signaling inhibition using IWP-2, but not DKK1, inhibited Jagged1-induced alkaline phosphatase (ALP) activity, mineralization, and osteo/odontogenic marker gene expression in hDPSCs. In conclusion, Jagged1 promoted hDPSC osteo/odontogenic differentiation by modulating the non-canonical Wnt pathway.

The miR-98-3p/JAG1/Notch1 axis mediates the multigenerational inheritance of osteopenia caused by maternal dexamethasone exposure in female rat offspring

As a synthetic glucocorticoid, dexamethasone is widely used to treat potential premature delivery and related diseases. Our previous studies have shown that prenatal dexamethasone exposure (PDE) can cause bone dysplasia and susceptibility to osteoporosis in female rat offspring. However, whether the effect of PDE on bone development can be extended to the third generation (F3 generation) and its multigenerational mechanism of inheritance have not been reported. In this study, we found that PDE delayed fetal bone development and reduced adult bone mass in female rat offspring of the F1 generation, and this effect of low bone mass caused by PDE even continued to the F2 and F3 generations. Furthermore, we found that PDE increases the expression of miR-98-3p but decreases JAG1/Notch1 signaling in the bone tissue of female fetal rats. Moreover, the expression changes of miR-98-3p/JAG1/Notch1 caused by PDE continued from the F1 to F3 adult offspring. Furthermore, the expression levels of miR-98-3p in oocytes of the F1 and F2 generations were increased. We also confirmed that dexamethasone upregulates the expression of miR-98-3p in vitro and shows targeted inhibition of JAG1/Notch1 signaling, leading to poor osteogenic differentiation of bone marrow mesenchymal stem cells. In conclusion, maternal dexamethasone exposure caused low bone mass in female rat offspring with a multigenerational inheritance effect, the mechanism of which is related to the inhibition of JAG1/Notch1 signaling caused by the continuous upregulation of miR-98-3p expression in bone tissues transmitted by F2 and F3 oocytes.

Decellularized extracellular matrix mediates tissue construction and regeneration

Contributing to organ formation and tissue regeneration, extracellular matrix (ECM) constituents provide tissue with three-dimensional (3D) structural integrity and cellular-function regulation. Containing the crucial traits of the cellular microenvironment, ECM substitutes mediate cell–matrix interactions to prompt stem-cell proliferation and differentiation for 3D organoid construction in vitro or tissue regeneration in vivo. However, these ECMs are often applied generically and have yet to be extensively developed for specific cell types in 3D cultures. Cultured cells also produce rich ECM, particularly stromal cells. Cellular ECM improves 3D culture development in vitro and tissue remodeling during wound healing after implantation into the host as well. Gaining better insight into ECM derived from either tissue or cells that regulate 3D tissue reconstruction or organ regeneration helps us to select, produce, and implant the most suitable ECM and thus promote 3D organoid culture and tissue remodeling for in vivo regeneration. Overall, the decellularization methodologies and tissue/cell-derived ECM as scaffolds or cellular-growth supplements used in cell propagation and differentiation for 3D tissue culture in vitro are discussed. Moreover, current preclinical applications by which ECM components modulate the wound-healing process are reviewed.

Mesenchymal Stem Cells, Bioactive Factors, and Scaffolds in Bone Repair: From Research Perspectives to Clinical Practice

Mesenchymal stem cell-based therapies are promising tools for bone tissue regeneration. However, tracking cells and maintaining them in the site of injury is difficult. A potential solution is to seed the cells onto a biocompatible scaffold. Construct development in bone tissue engineering is a complex step-by-step process with many variables to be optimized, such as stem cell source, osteogenic molecular factors, scaffold design, and an appropriate in vivo animal model. In this review, an MSC-based tissue engineering approach for bone repair is reported. Firstly, MSC role in bone formation and regeneration is detailed. Secondly, MSC-based bone tissue biomaterial design is analyzed from a research perspective. Finally, examples of animal preclinical and human clinical trials involving MSCs and scaffolds in bone repair are presented.

Bioactivity and Delivery Strategies of Phytochemical Compounds in Bone Tissue Regeneration

Plant-derived secondary metabolites represent a reservoir of phytochemicals for regenerative medicine application because of their varied assortment of biological properties including anti-oxidant, anti-inflammatory, antibacterial, and tissue remodeling properties. In addition, bioactive phytochemicals can be easily available, are often more cost-effective in large-scale industrialization, and can be better tolerated compared to conventional treatments mitigating the long-lasting side effects of synthetic compounds. Unfortunately, their poor bioavailability and lack of long-term stability limit their clinical impact. Nanotechnology-based delivery systems can overcome these limitations increasing bioactive molecules’ local effectiveness with reduction of the possible side effects on healthy bone. This review explores new and promising strategies in the area of delivery systems with particular emphasis on solutions that enhance bioavailability and/or health effects of plant-derived phytochemicals such as resveratrol, quercetin, epigallocatechin-3-gallate, and curcumin in bone tissue regeneration.

Interleukin 15 participates in Jagged1-induced mineralization in human dental pulp cells

OBJECTIVES

Crosstalk between Notch and other cell signaling molecules has been implicated to regulate the osteogenic differentiation. Understanding the interaction between Notch and IL15 is essential to reveal molecular mechanism. Thus, the objective of the present study was to investigate whether IL15 participates in the Notch signaling-induced mineral deposition in human dental pulp cells (hDPs).

METHODS

hDPs were explanted from dental pulp tissues. To activate Notch signaling, the cells were seeded on Jagged1-immobilized surfaces. The mRNA expression was evaluated using real-time polymerase chain reaction. hDPs were treated with 5-50 ng/mL IL15. Cell viability and proliferation were determined using an MTT assay. Mineral deposition was examined using alizarin red s and Von Kossa staining. In some experiments, the cells were pretreated with a JAK inhibitor prior to stimulation.

RESULTS

Jagged1 induced IL15 and IL15RA expression in hDPs. IL15 treatment significantly increased mineral deposition at 14 d and upregulated ALP, OCN, OSX, ANKH, and ENPP1 mRNA expression. IL15-induced mineralization was attenuated by JAK inhibitor pretreatment. Further, JAK inhibitor pretreatment inhibited the effect of Jagged1 on hDP mineral deposition.

CONCLUSION

IL15 promoted the osteogenic differentiation in hDPs. Moreover, IL15 participated in the Jagged1-induced mineralization in hDPs.

The interaction of Notch and Wnt signaling pathways in vertebrate regeneration

Regeneration is an evolutionarily conserved process in animal kingdoms, however, the regenerative capacities differ from species and organ/tissues. Mammals possess very limited regenerative potential to replace damaged organs, whereas non-mammalian species usually have impressive abilities to regenerate organs. The regeneration process requires proper spatiotemporal regulation from key signaling pathways. The canonical Notch and Wnt signaling pathways, two fundamental signals guiding animal development, have been demonstrated to play significant roles in the regeneration of vertebrates. In recent years, increasing evidence has implicated the cross-talking between Notch and Wnt signals during organ regeneration. In this review, we summarize the roles of Notch signaling and Wnt signaling during several representative organ regenerative events, emphasizing the functions and molecular bases of their interplay in these processes, shedding light on utilizing these two signaling pathways to enhance regeneration in mammals and design legitimate therapeutic strategies.

Relevance of Notch Signaling for Bone Metabolism and Regeneration

Notch1-4 receptors and their signaling pathways are expressed in almost all organ systems and play a pivotal role in cell fate decision by coordinating cell proliferation, differentiation and apoptosis. Differential expression and activation of Notch signaling pathways has been observed in a variety of organs and tissues under physiological and pathological conditions. Bone tissue represents a dynamic system, which is constantly remodeled throughout life. In bone, Notch receptors have been shown to control remodeling and regeneration. Numerous functions have been assigned to Notch receptors and ligands, including osteoblast differentiation and matrix mineralization, osteoclast recruitment and cell fusion and osteoblast/osteoclast progenitor cell proliferation. The expression and function of Notch1-4 in the skeleton are distinct and closely depend on the temporal expression at different differentiation stages. This review addresses the current knowledge on Notch signaling in adult bone with emphasis on metabolism, bone regeneration and degenerative skeletal disorders, as well as congenital disorders associated with mutant Notch genes. Moreover, the crosstalk between Notch signaling and other important pathways involved in bone turnover, including Wnt/β-catenin, BMP and RANKL/OPG, are outlined.

Insights into the mechanism of vascular endothelial cells on bone biology

In the skeletal system, blood vessels not only function as a conduit system for transporting gases, nutrients, metabolic waste, or cells but also provide multifunctional signal molecules regulating bone development, regeneration, and remodeling. Endothelial cells (ECs) in bone tissues, unlike in other organ tissues, are in direct contact with the pericytes of blood vessels, resulting in a closer connection with peripheral connective tissues. Close-contact ECs contribute to osteogenesis and osteoclastogenesis by secreting various cytokines in the paracrine or juxtacrine pathways. An increasing number of studies have revealed that extracellular vesicles (EVs) derived from ECs can directly regulate maturation process of osteoblasts and osteoclasts. The different pathways focus on targets at different distances, forming the basis of the intimate spatial and temporal link between bone tissue and blood vessels. Here, we provide a systematic review to elaborate on the function of ECs in bone biology and its underlying mechanisms based on three aspects: paracrine, EVs, and juxtacrine. This review proposes the possibility of a therapeutic strategy targeting blood vessels, as an adjuvant treatment for bone disorders.

Designing Biomaterials to Modulate Notch Signaling in Tissue Engineering and Regenerative Medicine

The design of cell-instructive biomaterials for tissue engineering and regenerative medicine is at a crossroads. Although the conventional tissue engineering approach is top-down (cells seeded to macroporous scaffolds and mature to form tissues), bottom-up tissue engineering strategies are becoming appealing. With such developments, we can study cell signaling events, thus enabling functional tissue assembly in physiologic and diseased models. Among many important signaling pathways, the Notch signaling pathway is the most diverse in its influence during tissue morphogenesis and repair following injury. Although Notch signaling is extensively studied in developmental biology and cancer biology, our knowledge of designing biomaterial-based Notch signaling platforms and incorporating Notch signaling components into engineered tissue systems is limited. By incorporating Notch signaling to tissue engineering scaffolds, we can direct cell-specific responses and improve engineered tissue maturation. This review will discuss recent progress in the development of Notch signaling biomaterials as a promising target to control cellular fate decisions, including the influences of ligand identity, biophysical material cues, ligand presentation strategies, and mechanotransduction. Notch signaling is consequently of interest to direct, control, and reprogram cellular behavior on a biomaterial surface. We anticipate that discussions in this article will allow for enhanced knowledge and insight into designing Notch targeted biomaterials for various tissue engineering and cell fate determinations. Impact statement Notch signaling is recognized as an important pathway in tissue engineering and regenerative medicine; however, there is no systematic review on this topic. The comprehensive review and perspectives presented here provide an in-depth discussion on ligand presentation strategies both in 2D and in 3D cell culture environments involving biomaterials/scaffolds. In addition, this review article provides insight into the challenges in designing cell surrogate biomaterials capable of providing Notch signals. To the best of the authors' knowledge, this is the first review relevant to the fields of tissue engineering.

NOTCH2 participates in Jagged1-induced osteogenic differentiation in human periodontal ligament cells

Jagged1 activates Notch signaling and subsequently promotes osteogenic differentiation in human periodontal ligament cells (hPDLs). The present study investigated the participation of the Notch receptor, NOTCH2, in the Jagged1-induced osteogenic differentiation in hPDLs. NOTCH2 and NOTCH4 mRNA expression levels increased during hPDL osteogenic differentiation. However, the endogenous NOTCH2 expression levels were markedly higher compared with NOTCH4. NOTCH2 expression knockdown using shRNA in hPDLs did not dramatically alter their proliferation or osteogenic differentiation compared with the shRNA control. After seeding on Jagged1-immobilized surfaces and maintaining the hPDLs in osteogenic medium, HES1 and HEY1 mRNA levels were markedly reduced in the shNOTCH2-transduced cells compared with the shControl group. Further, shNOTCH2-transduced cells exhibited less alkaline phosphatase enzymatic activity and in vitro mineralization than the shControl cells when exposed to Jagged1. MSX2 and COL1A1 mRNA expression after Jagged1 activation were reduced in shNOTCH2-transduced cells. Endogenous Notch signaling inhibition using a γ-secretase inhibitor (DAPT) attenuated mineralization in hPDLs. DAPT treatment significantly promoted TWIST1, but decreased ALP, mRNA expression, compared with the control. In conclusion, Notch signaling is involved in hPDL osteogenic differentiation. Moreover, NOTCH2 participates in the mechanism by which Jagged1 induced osteogenic differentiation in hPDLs.

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.

Targeting Nuclear NOTCH2 by Gliotoxin Recovers a Tumor-Suppressor NOTCH3 Activity in CLL

NOTCH signaling represents a promising therapeutic target in chronic lymphocytic leukemia (CLL). We compared the anti-neoplastic effects of the nuclear NOTCH2 inhibitor gliotoxin and the pan-NOTCH γ-secretase inhibitor RO4929097 in primary CLL cells with special emphasis on the individual roles of the different NOTCH receptors. Gliotoxin rapidly induced apoptosis in all CLL cases tested, whereas RO4929097 exerted a variable and delayed effect on CLL cell viability. Gliotoxin-induced apoptosis was associated with inhibition of the NOTCH2/FCER2 (CD23) axis together with concomitant upregulation of the NOTCH3/NR4A1 axis. In contrast, RO4929097 downregulated the NOTCH3/NR4A1 axis and counteracted the spontaneous and gliotoxin-induced apoptosis. On the cell surface, NOTCH3 and CD23 expression were mutually exclusive, suggesting that downregulation of NOTCH2 signaling is a prerequisite for NOTCH3 expression in CLL cells. ATAC-seq confirmed that gliotoxin targeted the canonical NOTCH signaling, as indicated by the loss of chromatin accessibility at the potential NOTCH/CSL site containing the gene regulatory elements. This was accompanied by a gain in accessibility at the NR4A1, NFκB, and ATF3 motifs close to the genes involved in B-cell activation, differentiation, and apoptosis. In summary, these data show that gliotoxin recovers a non-canonical tumor-suppressing NOTCH3 activity, indicating that nuclear NOTCH2 inhibitors might be beneficial compared to pan-NOTCH inhibitors in the treatment of CLL.

Phospholipase D: A new mediator during high phosphate-induced vascular calcification associated with chronic kidney disease

Vascular calcification (VC) is the pathological accumulation of calcium phosphate crystals in one of the layers of blood vessels, leading to loss of elasticity and causing severe calcification in vessels. Medial calcification is mostly seen in patients with chronic kidney disease (CKD) and diabetes. Identification of key enzymes and their actions during calcification will contribute to understand the onset of pathological calcification. Phospholipase D (PLD1, PLD2) is active at the earlier steps of mineralization in osteoblasts and chondrocytes. In this study, we aimed to determine their effects during high-phosphate treatment in mouse vascular smooth muscle cell line MOVAS, in the ex vivo model of the rat aorta, and in the in vivo model of adenine-induced CKD. We observed an early increase in PLD1 gene and protein expression along with the increase in the PLD activity in vascular muscle cell line, during calcification induced by ascorbic acid and β-glycerophosphate. Inhibition of PLD1 by the selective inhibitor VU0155069, or the pan-PLD inhibitor, halopemide, prevented calcification. The mechanism of PLD activation is likely to be protein kinase C (PKC)-independent since bisindolylmaleimide X hydrochloride, a pan-PKC inhibitor, did not affect the PLD activity. In agreement, we found an increase in Pld1 gene expression and PLD activity in aortic explant cultures treated with high phosphate, whereas PLD inhibition by halopemide decreased calcification. Finally, an increase in both Pld1 and Pld2 expression occurred simultaneously with the appearance of VC in a rat model of CKD. Thus, PLD, especially PLD1, promotes VC in the context of CKD and could be an important target for preventing onset or progression of VC.

JAG1, MEF2C and BDNF polymorphisms associated with bone mineral density in women from Northern México

Introduction: Osteoporosis is characterized by a low bone mineral density. Genetic composition is one of the most influential factors in determining bone mineral density (BMD). There are few studies on genes associated with BMD in the Mexican population. Objective: To investigate the association of eight single nucleotide polymorphisms (SNP) of JAG1, MEF2C and BDNF genes with BMD in women of Northern México. Materials and methods: This study involved 124 unrelated Mexican women between 40 and 80 years old. BMD was determined by dual X-ray absorptiometry. Genotyping was performed using allelic discrimination by real time PCR. We analyzed the SNP of JAG1 (rs6514116, rs2273061, rs2235811 and rs6040061), MEF2C (rs1366594, rs12521522 and rs11951031), and BDNF (rs6265) and the data using linear regression. Results: The JAG1 SNP rs2235811 was associated with the BMD of the total body under the dominant inheritance model (p=0,024). Although the other SNPs were not associated with BMD in any of the inheritance models studied, a trend was observed. Conclusion: Our results suggest that the SNP rs2235811 in the JAG1 gene might contribute to the variation in BMD in women from northern México.

Intraoperative delivery of the Notch ligand Jagged-1 regenerates appendicular and craniofacial bone defects

Each year, 33% of US citizens suffer from a musculoskeletal condition that requires medical intervention, with direct medical costs approaching $1 trillion USD per year. Despite the ubiquity of skeletal dysfunction, there are currently limited safe and efficacious bone growth factors in clinical use. Notch is a cell-cell communication pathway that regulates self-renewal and differentiation within the mesenchymal/osteoblast lineage. The principal Notch ligand in bone, Jagged-1, is a potent osteoinductive protein that positively regulates post-traumatic bone healing in animals. This report describes the temporal regulation of Notch during intramembranous bone formation using marrow ablation as a model system and demonstrates decreased bone formation following disruption of Jagged-1 in mesenchymal progenitor cells. Notch gain-of-function using recombinant Jagged-1 protein on collagen scaffolds promotes healing of craniofacial (calvarial) and appendicular (femoral) surgical defects in both mice and rats. Localized delivery of Jagged-1 promotes bone apposition and defect healing, while avoiding the diffuse bone hypertrophy characteristic of the clinically problematic bone morphogenetic proteins. It is concluded that Jagged-1 is a bone-anabolic agent with therapeutic potential for regenerating traumatic or congenital bone defects.

Indirect immobilized Jagged1 suppresses cell cycle progression and induces odonto/osteogenic differentiation in human dental pulp cells

Notch signaling regulates diverse biological processes in dental pulp tissue. The present study investigated the response of human dental pulp cells (hDPs) to the indirect immobilized Notch ligand Jagged1 in vitro. The indirect immobilized Jagged1 effectively activated Notch signaling in hDPs as confirmed by the upregulation of HES1 and HEY1 expression. Differential gene expression profiling using an RNA sequencing technique revealed that the indirect immobilized Jagged1 upregulated genes were mainly involved in extracellular matrix organization, disease, and signal transduction. Downregulated genes predominantly participated in the cell cycle, DNA replication, and DNA repair. Indirect immobilized Jagged1 significantly reduced cell proliferation, colony forming unit ability, and the number of cells in S phase. Jagged1 treated hDPs exhibited significantly higher ALP enzymatic activity, osteogenic marker gene expression, and mineralization compared with control. Pretreatment with a γ-secretase inhibitor attenuated the Jagged1-induced ALP activity and mineral deposition. NOTCH2 shRNA reduced the Jagged1-induced osteogenic marker gene expression, ALP enzymatic activity, and mineral deposition. In conclusion, indirect immobilized Jagged1 suppresses cell cycle progression and induces the odonto/osteogenic differentiation of hDPs via the canonical Notch signaling pathway.

Notch pathway is active during osteogenic differentiation of human bone marrow mesenchymal stem cells induced by pulsed electromagnetic fields

Pulsed electromagnetic fields (PEMFs) have been used to treat bone diseases, particularly nonunion healing. Although it is known that PEMFs promote the osteogenic differentiation of human mesenchymal stem cells (hMSCs), to date PEMF molecular mechanisms remain not clearly elucidated. The Notch signalling is a highly conserved pathway that regulates cell fate decisions and skeletal development. The aim of this study was to investigate if the known PEMF-induced osteogenic effects may involve the modulation of the Notch pathway. To this purpose, during in vitro osteogenic differentiation of bone marrow hMSCs in the absence and in the presence of PEMFs, osteogenic markers (alkaline phosphatase activity, osteocalcin and matrix mineralization), the messenger ribonucleic acid expression of osteogenic transcription factors (Runx2, Dlx5, Osterix) as well as of Notch receptors (Notch1-4), their ligands (Jagged1, Dll1 and Dll4) and nuclear target genes (Hes1, Hes5, Hey1, Hey2) were investigated. PEMFs stimulated all osteogenic markers and increased the expression of Notch4, Dll4, Hey1, Hes1 and Hes5 in osteogenic medium compared to control. In the presence of DAPT and SAHM1, used as Notch pathway inhibitors, the expression of the osteogenic markers, including Runx2, Dlx5, Osterix, as well as Hes1 and Hes5 were significantly inhibited, both in unexposed and PEMF-exposed hMSCs. These results suggest that activation of Notch pathway is required for PEMFs-stimulated osteogenic differentiation. These new findings may be useful to improve autologous cell-based regeneration of bone defects in orthopaedics.

Efficient Generation of Chemically Induced Mesenchymal Stem Cells from Human Dermal Fibroblasts

Human mesenchymal stromal/stem cells (MSCs) are multipotent and currently undergoing hundreds of clinical trials for disease treatments. To date, no studies have generated induced MSCs from skin fibroblasts with chemicals or growth factors. Here, we established the first chemical method to convert primary human dermal fibroblasts into multipotent, induced MSC-like cells (iMSCs). The conversion method uses a defined cocktail of small molecules and growth factors, and it can achieve efficient conversion with an average rate of 38% in 6 days. The iMSCs have much higher clonogenicity than fibroblasts, and they can be maintained and expanded in regular MSC medium for at least 8 passages and further differentiated into osteoblasts, adipocytes, and chondrocytes. Moreover, the iMSCs can suppress LPS-mediated acute lung injury as effectively as bone marrow-derived mesenchymal stem cells. This finding may greatly benefit stem cell biology, cell therapy, and regenerative medicine.

Notch Signaling Participates in TGF-β-Induced SOST Expression Under Intermittent Compressive Stress

Notch signaling is regulated by mechanical stimuli in various cell types. It has previously been reported that intermittent compressive stimuli enhanced sclerostin (SOST) expression in human periodontal ligament cells (hPDLs) by regulating transforming growth factor-β (TGF-β) expression. The aim of the present study was to determine the involvement of Notch signaling in the TGF-β-induced SOST expression in hPDLs. Cells were treated with intermittent compressive stress in a computer-controlled apparatus for 24 h. The mRNA and protein expression of the cells were determined by real-time polymerase chain reaction and Western blot analysis, respectively. In some experiments, the target signaling pathway was impeded by the addition of a TGF-β receptor kinase inhibitor (SB431542) or a γ-secretase inhibitor (DAPT). The results demonstrated that hPDLs under intermittent compressive stress exhibited significantly higher NOTCH2, NOTCH3, HES1, and HEY1 mRNA expression compared with control, indicating that mechanical stress induced Notch signaling. DAPT pretreatment markedly reduced the intermittent stress-induced SOST expression. The expression of NOTCH2, NOTCH3, HES1, and HEY1 mRNA under compressive stress was significantly reduced after pretreatment with SB431542, coinciding with a reduction in SOST expression. Recombinant human TGF-β1 enhanced SOST, Notch receptor, and target gene expression in hPDLs. Further, DAPT treatment attenuated rhTGF-β1-induced SOST expression. In summary, intermittent compressive stress regulates Notch receptor and target gene expression via the TGF-β signaling pathway. In addition, Notch signaling participates in TGF-β-induced SOST expression in hPDLs. J. Cell. Physiol. 232: 2221-2230, 2017. © 2016 Wiley Periodicals, Inc.

Stimulation of Notch Signaling in Mouse Osteoclast Precursors

Notch signaling is a key component of multiple physiological and pathological processes. The nature of Notch signaling, however, makes in vitro investigation of its varying and sometimes contradictory roles a challenge. As a component of direct cell-cell communication with both receptors and ligands bound to the plasma membrane, Notch signaling cannot be activated in vitro by simple addition of ligands to culture media, as is possible with many other signaling pathways. Instead, Notch ligands must be presented to cells in an immobilized state. Variations in methods of Notch signaling activation can lead to different outcomes in cultured cells. In osteoclast precursors, in particular, differences in methods of Notch stimulation and osteoclast precursor culture and differentiation have led to disagreement over whether Notch signaling is a positive or negative regulator of osteoclast differentiation. While closer comparisons of osteoclast differentiation under different Notch stimulation conditions in vitro and genetic models have largely resolved the controversy regarding Notch signaling and osteoclasts, standardized methods of continuous and temporary stimulation of Notch signaling in cultured cells could prevent such discrepancies in the future. This protocol describes two methods for stimulating Notch signaling specifically in cultured mouse osteoclast precursors, though these methods should be applicable to any adherent cell type with minor adjustments. The first method produces continuous stimulation of Notch signaling and involves immobilizing Notch ligand to a tissue culture surface prior to the seeding of cells. The second, which uses Notch ligand bound to agarose beads allows for temporary stimulation of Notch signaling in cells that are already adhered to a culture surface. This protocol also includes methods for detecting Notch activation in osteoclast precursors as well as representative transcriptional markers of Notch signaling activation.

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.

TLR3 or TLR4 Activation Enhances Mesenchymal Stromal Cell-Mediated Treg Induction via Notch Signaling

Mesenchymal stromal cells (MSCs) are the subject of numerous clinical trials, largely due to their immunomodulatory and tissue regenerative properties. Toll-like receptors (TLRs), especially TLR3 and TLR4, are highly expressed on MSCs and their activation can significantly modulate the immunosuppressive and anti-inflammatory functions of MSCs. While MSCs can recruit and promote the generation of regulatory T cells (Tregs), the effect of TLR activation on MSC-mediated Treg induction is unknown. In this study, we investigated the effect of ligand-mediated activation of TLR3 and TLR4 on Treg induction by human MSCs. We found that generation of Tregs in human CD4(+) lymphocyte and MSC cocultures was enhanced by either TLR3 or TLR4 activation of MSCs and that the increase was abolished by TLR3 and TLR4 gene-silencing. Augmented Treg induction by TLR-activated MSCs was cell contact-dependent and associated with increased gene expression of the Notch ligand, Delta-like 1. Moreover, inhibition of Notch signaling abrogated the augmented Treg levels in the MSC cocultures. Our data show that TLR3 or TLR4 activation of MSCs increases Treg induction via the Notch pathway and suggest new means to enhance the potency of MSCs for treating disorders with an underlying immune dysfunction, including steroid resistant acute graft-versus-host disease. Stem Cells 2017;35:265-275.

THBS2 Is a Candidate Modifier of Liver Disease Severity in Alagille Syndrome

BACKGROUND & AIMS

Alagille syndrome is an autosomal-dominant, multisystem disorder caused primarily by mutations in JAG1, resulting in bile duct paucity, cholestasis, cardiac disease, and other features. Liver disease severity in Alagille syndrome is highly variable, however, factors influencing the hepatic phenotype are unknown. We hypothesized that genetic modifiers may contribute to the variable expressivity of this disorder.

METHODS

We performed a genome-wide association study in a cohort of Caucasian subjects with known pathogenic JAG1 mutations, comparing patients with mild vs severe liver disease, followed by functional characterization of a candidate locus.

RESULTS

We identified a locus that reached suggestive genome-level significance upstream of the thrombospondin 2 (THBS2) gene. THBS2 codes for a secreted matricellular protein that regulates cell proliferation, apoptosis, and angiogenesis, and has been shown to affect Notch signaling. By using a reporter mouse line, we detected thrombospondin 2 expression in bile ducts and periportal regions of the mouse liver. Examination of Thbs2-null mouse livers showed increased microvessels in the portal regions of adult mice. We also showed that thrombospondin 2 interacts with NOTCH1 and NOTCH2 and can inhibit JAG1-NOTCH2 interactions.

CONCLUSIONS

Based on the genome-wide association study results, thrombospondin 2 localization within bile ducts, and demonstration of interactions of thrombospondin 2 with JAG1 and NOTCH2, we propose that changes in thrombospondin 2 expression may further perturb JAG1-NOTCH2 signaling in patients harboring a JAG1 mutation and lead to a more severe liver phenotype. These results implicate THBS2 as a plausible candidate genetic modifier of liver disease severity in Alagille syndrome.

Notch signaling promotes osteoclast maturation and resorptive activity

The role of Notch signaling in osteoclast differentiation is controversial with conflicting experimental evidence indicating both stimulatory and inhibitory roles. Differences in experimental protocols and in vivo versus in vitro models may explain the discrepancies between studies. In this study, we investigated cell autonomous roles of Notch signaling in osteoclast differentiation and function by altering Notch signaling during osteoclast differentiation using stimulation with immobilized ligands Jagged1 or Delta-like1 or by suppression with γ-secretase inhibitor DAPT or transcriptional inhibitor SAHM1. Stimulation of Notch signaling in committed osteoclast precursors resulted in larger osteoclasts with a greater number of nuclei and resorptive activity whereas suppression resulted in smaller osteoclasts with fewer nuclei and suppressed resorptive activity. Conversely, stimulation of Notch signaling in osteoclast precursors prior to induction of osteoclastogenesis resulted in fewer osteoclasts. Our data support a mechanism of context-specific Notch signaling effects wherein Notch stimulation inhibits commitment to osteoclast differentiation, but enhances the maturation and function of committed precursors.

Mechanical stimulation orchestrates the osteogenic differentiation of human bone marrow stromal cells by regulating HDAC1

Mechanical stimulation and histone deacetylases (HDACs) have essential roles in regulating the osteogenic differentiation of bone marrow stromal cells (BMSCs) and bone formation. However, little is known regarding what regulates HDAC expression and therefore the osteogenic differentiation of BMSCs during osteogenesis. In this study, we investigated whether mechanical loading regulates HDAC expression directly and examined the role of HDACs in mechanical loading-triggered osteogenic differentiation and bone formation. We first studied the microarrays of samples from patients with osteoporosis and found that the NOTCH pathway and skeletal development gene sets were downregulated in the BMSCs of patients with osteoporosis. Then we demonstrated that mechanical stimuli can regulate osteogenesis and bone formation both in vivo and in vitro. NOTCH signaling was upregulated during cyclic mechanical stretch (CMS)-induced osteogenic differentiation, whereas HDAC1 protein expression was downregulated. The perturbation of HDAC1 expression also had a significant effect on matrix mineralization and JAG1-mediated Notch signaling, suggesting that HDAC1 acts as an endogenous attenuator of Notch signaling in the mechanotransduction of BMSCs. Chromatin immunoprecipitation (ChIP) assay results suggest that HDAC1 modulates the CMS-induced histone H3 acetylation level at the JAG1 promoter. More importantly, we found an inhibitory role of Hdac1 in regulating bone formation in response to hindlimb unloading in mice, and pretreatment with an HDAC1 inhibitor partly rescued the osteoporosis caused by mechanical unloading. Our results demonstrate, for the first time, that mechanical stimulation orchestrates genes expression involved in the osteogenic differentiation of BMSCs via the direct regulation of HDAC1, and the therapeutic inhibition of HDAC1 may be an efficient strategy for enhancing bone formation under mechanical stimulation.

Glucocorticoids impair bone formation of bone marrow stromal stem cells by reciprocally regulating microRNA-34a-5p

The inhibitory effects of glucocorticoids (GCs) on bone marrow stromal stem cell (BMSC) proliferation and osteoblastic differentiation are an important pathway through which GCs decrease bone formation. We found that microRNA-34a-5p was a critical player in dexamethasone (Dex)-inhibited BMSC proliferation and osteogenic differentiation. MicroRNA-34a-5p might be used as a therapeutic target for GC-impaired bone formation.

INTRODUCTION

The inhibitory effects of glucocorticoids (GCs) on bone marrow stromal stem cell (BMSC) proliferation and osteoblastic differentiation are an important pathway through which GCs decrease bone formation. The mechanisms of this process are still not completely understood. Recent studies implicated an important role of microRNAs in GC-mediated responses in various cellular processes, including cell proliferation and differentiation. Therefore, we hypothesized that these regulatory molecules might be implicated in the process of GC-decreased BMSC proliferation and osteoblastic differentiation.

METHODS

Western blot, quantitative real-time PCR, and cell proliferation and osteoblastic differentiation assays were employed to investigate the role of microRNAs in GC-inhibited BMSC proliferation and osteoblastic differentiation.

RESULTS

We found that microRNA-34a-5p was reciprocally regulated by Dex during the process of BMSC proliferation and osteoblastic differentiation. Furthermore, we confirmed that microRNA-34a-5p was a critical player in Dex-inhibited BMSC proliferation and osteogenic differentiation. Mechanistic studies showed that Dex inhibited BMSC proliferation by microRNA-34a-5p targeting cell cycle factors, including CDK4, CDK6, and Cyclin D1. Furthermore, downregulation of microRNA-34a-5p by Dex leads to Notch signaling activation, resulting in inhibition of BMSC osteogenic differentiation.

CONCLUSIONS

These results showed that microRNA-34a-5p, a crucial regulator for BMSC proliferation and osteogenic differentiation, might be used as a therapeutic target for GC-impaired bone formation.

Effect of Jagged-1 and Dll-1 on osteogenic differentiation by stem cells from human exfoliated deciduous teeth

OBJECTIVE

The aim of the present study was to determine the influence of Notch ligands, Jagged-1 and Dll-1, on osteogenic differentiation by stem cells from human exfoliated deciduous teeth.

DESIGN

Notch ligands were immobilized on tissue culture surface using an indirect affinity immobilization technique. Cells from the remaining of dental pulp tissues from human deciduous teeth were isolated and characterized using flow cytometry and differentiation assay. Alkaline phosphatase (ALP) enzymatic activity, osteogenic marker gene expression, and mineralization were determined using ALP assay, real-time polymerase chain reaction, and alizarin red staining, respectively.

RESULTS

The isolated cells exhibited CD44, CD90, and CD105 expression but lack of CD45 expression. Further, these cells were able to differentiate toward osteogenic lineage. The upregulation of HES-1 and HEY-1 was observed in those cells on Dll-1 and Jagged-1 coated surface. The significant increase of ALP activity and mineralization was noted in those cells seeded on Jagged-1 surface and these results were attenuated when cells were pretreated with gamma secretase inhibitor. The significant upregulation of ALP and collagen type I gene expression was also observed in those cells seeded on Jagged-1 surface. The inconsistent Dll-1 induced osteogenic differentiation was found and high Dll-1 immobilized dose (50 nM) slightly enhanced alkaline phosphatase enzymatic activity. However, the statistical significant difference was not obtained as compared to the hFc control.

CONCLUSION

The surface immobilization of Notch ligands, Jagged-1 and Dll-1, likely to enhance osteogenic differentiation of SHEDs. However, Jagged-1 had more ability in enhancing osteogenic differentiation than Dll-1 in our model.

Extracellular signaling molecules to promote fracture healing and bone regeneration

To date, the delivery of signaling molecules for bone regeneration has focused primarily on factors that directly affect the bone formation pathways (osteoinduction) or that serve to increase the number of bone forming progenitor cells. The first commercialized growth factors approved for bone regeneration, Bone Morphogenetic Protein 2 and 7 (BMP2 and BMP7), are direct inducers of osteoblast differentiation. As well, newer generations of potential therapeutics that target the Wnt signaling pathway are also direct osteoinducers. On the other hand, some signaling molecules may play a role as mitogens and serve to increase the number of bone producing cells or may increase vascularization. This is true for factors such as Platelet Derived Growth Factor (PDGF) or Fibroblast Growth Factor (FGF). Vascular Endothelial Growth Factor (VEGF) likely has a special role. Not only does it induce new blood vessel formation, it also has direct effects on osteoblasts through endothelial cell-based BMP production. In addition to these pathways that classically have targeted bone production, there are also opportunities to target other aspects of the bone healing process such as inflammation, vascularization, and cell ingress to the fracture site. Bone regeneration is highly complex with defined, yet overlapping stages of healing. We will review established and novel extracellular signaling factors associated with various stages of fracture healing that could be targeted to promote enhanced bone regeneration. Importantly, multiple potential cell and tissues could be targeted to enhance healing in addition to focusing solely on osteoinductive therapeutics.

Notch inhibits chondrogenic differentiation of mesenchymal progenitor cells by targeting Twist1

While Notch signaling plays a critical role in the regulation of cartilage formation, its downstream targets are unknown. To address this we performed gain and losses of function experiments and demonstrate that Notch inhibition of chondrogenesis acts via up-regulation of the transcription factor Twist1. Upon Notch activation, murine limb bud mesenchymal progenitor cells in micromass culture displayed an inhibition of chondrogenesis. Twist1 was found to be exclusively expressed in mesenchymal progenitor cells at the onset stage of chondrogenesis during Notch activation. Inhibition of Notch signaling in these cells significantly reduced protein expression of Twist1. Furthermore, the inhibition effect of NICD1 on MPC chondrogenesis was markedly reduced by knocking down of Twist1. Constitutively active Notch signaling significantly enhanced Twist1 promoter activity; whereas mutation studies indicated that a putative NICD/RBPjK binding element in the promoter region is required for the Notch-responsiveness of the Twist1 promoter. Finally, chromatin immunoprecipitation assays further confirmed that the Notch intracellular domain influences Twist1 by directly binding to the Twist1 promoter. These data provide a novel insight into understanding the molecular mechanisms behind Notch inhibition of the onset of chondrogenesis.

The notch signaling regulates CD105 expression, osteogenic differentiation and immunomodulation of human umbilical cord mesenchymal stem cells

Mesenchymal stem cells (MSCs) are a group of multipotent cells with key properties of multi-lineage differentiation, expressing a set of relatively specific surface markers and unique immunomodulatory functions. IDO1, a catabolic enzyme of tryptophan, represents a critical molecule mediating immunomodulatory functions of MSCs. However, the signaling pathways involved in regulating these key properties still remain elusive. To investigate the involvement of Notch signaling as well as other potential signaling pathway(s) in regulating these critical properties of MSCs, we treated human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) with γ-secreatase inhibitor I (GSI-I), which inhibits both Notch signaling and ubiquitin-proteasome activities. It was shown that the GSI-I treatment resulted in apoptosis, reduced expression of surface markers CD73, CD90 and CD105, reduced osteogenic differentiation, and reduction of the hUC-MSCs-mediated suppression of Th1 lymphocyte proliferation and the IFN-γ-induced IDO1 expression. Through distinguishing the effects of GSI-I between Notch inhibition and proteasome inhibition, it was further observed that, whereas both Notch inhibition and proteasome inhibition were attributable to the reduced CD105 expression and osteogenic differentiation, but not to the induced apoptosis. However, Notch inhibition, but not proteasome inhibition, only contributed to the significant effect of GSI-I on Th1 proliferation probably through reducing IDO1 promoter activity. In conclusion, the Notch signaling may represent a very important cell signaling capable of regulating multiple critical properties, especially the immunomodulatory functions of MSCs.

NOTCH-Mediated Maintenance and Expansion of Human Bone Marrow Stromal/Stem Cells: A Technology Designed for Orthopedic Regenerative Medicine

Human bone marrow-derived stromal/stem cells (BMSCs) have great therapeutic potential for treating skeletal disease and facilitating skeletal repair, although maintaining their multipotency and expanding these cells ex vivo have proven difficult. Because most stem cell-based applications to skeletal regeneration and repair in the clinic would require large numbers of functional BMSCs, recent research has focused on methods for the appropriate selection, expansion, and maintenance of BMSC populations during long-term culture. We describe here a novel biological method that entails selection of human BMSCs based on NOTCH2 expression and activation of the NOTCH signaling pathway in cultured BMSCs via a tissue culture plate coated with recombinant human JAGGED1 (JAG1) ligand. We demonstrate that transient JAG1-mediated NOTCH signaling promotes human BMSC maintenance and expansion while increasing their skeletogenic differentiation capacity, both ex vivo and in vivo. This study is the first of its kind to describe a NOTCH-mediated methodology for the maintenance and expansion of human BMSCs and will serve as a platform for future clinical or translational studies aimed at skeletal regeneration and repair.

Notch signaling in mesenchymal stem cells harvested from geriatric mice

OBJECTIVES

Morbidity associated with geriatric fractures may be attributed, in part, to compromised mesenchymal stem cell (MSC) function within the fracture callus. The Notch signaling pathway is important for the healing of nonskeletal tissues in an age-dependent manner, but the effect of Notch on age-dependent fracture healing and MSC dysfunction has not been substantiated. The objective of this study was to examine Notch signaling in MSCs obtained from young and geriatric mice.

METHODS

Marrow-derived MSCs were harvested from the femora of 5- and 25-month-old C57BL/6 mice. We assessed in vivo MSC number using CFU-F, proliferation using an Alamar Blue assay, osteoblast differentiation by Alizarin Red S staining, and adipogenic differentiation using Oil Red O staining. Notch receptor and ligand expression was assessed using quantitative PCR, and Notch signaling was assessed by evaluating Notch target gene expression (Hey and HES) under basal conditions and when cells were plated to Jagged-1 ligand.

RESULTS

MSC from geriatric mice exhibit reduced MSC number (CFU-F), proliferation, adipogenesis, and inconsistent osteogenesis. The highest expressed Notch receptor is Notch 2, and the highest expressed ligand is Jagged-1, but there were no differences in ligand and receptor gene expression between young and old MSCs. Interestingly, geriatric MSCs show decreased basal Notch signaling activity but are fully responsive to Jagged-1 stimulation.

CONCLUSIONS

These data suggest that therapeutic targeting of Notch signaling should be explored in clinical therapies to improve geriatric fracture healing.

Elevation of protein kinase Cα stimulates osteogenic differentiation of mesenchymal stem cells through the TAT-mediated protein transduction system

Mesenchymal stem cells (MSCs) can differentiate toward various lineages, including the osteogenic lineage, and thus hold great potential for clinic purposes. By using pharmacological inhibitors, protein kinase C (PKC) signaling has been shown to either negatively or positively regulate differentiation of bone, however, due to the low transfection efficiency in MSCs, the role of individual PKC isoforms is still not fully understood. In this study, we established a TAT peptide-mediated transduction system that efficiently delivered PKCα proteins into MSCs in a non-invasive fashion. The increased PKCα protein levels significantly promoted osteogenic differentiation in the murine mesenchymal C3H10T1/2 cells and in primary MSCs from both human and mouse, as demonstrated by the enhanced activity of the osteoblast marker, alkaline phosphatase, and the enhanced expression of the key transcription factor runx2. Mineralization is an important functional indication for bone differentiation. Our results further showed that PKCα promoted expression of the important osteocalcin gene and the accumulation of calcium minerals. Taken together, this study provides direct evidence showing that PKCα positively regulates osteogenic differentiation and demonstrates that the TAT peptide-mediated method enables functional study of specific PKC isoforms in MSCs without using viral infection. This may promote the application of PKCs in therapeutic treatment.

Induction of STEAP4 correlates with 1,25-dihydroxyvitamin D3 stimulation of adipogenesis in mesenchymal progenitor cells derived from human adipose tissue

The vitamin D receptor (VDR) is expressed in human adipocytes and is transiently induced during early adipogenesis in mesenchymal progenitor cell models. VDR null mice exhibit enhanced energy expenditure and reduced adiposity even when fed high fat diets. Adipocyte-specific transgenic-expression of human VDR in mice enhances adipose tissue mass, indicating that VDR activation in adipocytes enhances lipid storage in vivo. In these studies, we conducted genomic profiling and differentiation assays in primary cultures of human adipose-derived mesenchymal progenitor cells to define the role of the VDR and its ligand 1,25-dihydroxyvitamin D3 (1,25D) in adipogenesis. In the presence of adipogenic media, 1,25D promoted lipid accumulation and enhanced the expression of FABP4, FASN, and PPARγ. Mesenchymal cells derived from 6-month old VDR null mice exhibited impaired adipogenesis ex vivo but differentiation was restored by stable expression of human VDR. STEAP4, a gene that encodes a metalloreductase linked to obesity, insulin sensitivity, metabolic homeostasis and inflammation, was highly induced in human adipose cells differentiated in the presence of 1,25D but was minimally affected by 1,25D in undifferentiated precursors. These studies provide a molecular basis for recent epidemiological associations between vitamin D status, body weight and insulin resistance which may have relevance for prevention or treatment of metabolic syndrome and obesity.