Notch and HES5 are regulated during human cartilage differentiation

Identification of HES4 as a novel prognostic marker and therapeutic target in hepatocellular carcinoma

Hairy and enhancer of Split 4 (HES4) is thought to have a substantial impact on the pathogenesis and progression of malignancies. However, the prognostic significance and mechanism of HES4 have not been reported in Hepatocellular carcinoma (HCC). A comprehensive bioinformatics analysis of HES4 expression, clinicopathological characteristics, tumor microenvironment status, and drug sensitivity were performed based on TCGA, GTEx, and GEO. Paired HCC samples and cell lines were used to validate the dysfunction of HES4 in vitro. The expression of HES4 at both mRNA and protein levels was significantly upregulated in HCC tissues. High level of HES4 was associated with unfavorable outcomes. Enrichment analysis demonstrated strong associations of HES4 with HCC progression pathways. In addition, elevated HES4 expression was positively correlated with increased sensitivity to various chemotherapy drugs and associated with resistance to immunotherapy. As a transcription factor, the target genes regulated by HES4 were mostly risky genes, and a novel prediction model based on HES4 target genes was generated for HCC risk stratification. The AUCs of 1-, 3-, and 5-year year overall survival (OS) were 0.829, 0.732, and 0.700, respectively. HES4 overexpression is associated with poor clinical outcomes and tumor progression. HES4 may serve as a novel prognostic marker and therapeutic target in HCC.

Insights into the Notch signaling pathway in degenerative musculoskeletal disorders: Mechanisms and perspectives

Degenerative musculoskeletal disorders are a group of age-related diseases of the locomotive system that severely affects the patient's ability to work and cause adverse sequalae such as fractures and even death. The incidence and prevalence of degenerative musculoskeletal disorders is rising owing to the aging of the world's population. The Notch signaling pathway, which is expressed in almost all organ systems, extensively regulates cell proliferation and differentiation as well as cellular fate. Notch signaling shows increased activity in degenerative musculoskeletal disorders and retards the progression of degeneration to some extent. The review focuses on four major degenerative musculoskeletal disorders (osteoarthritis, intervertebral disc degeneration, osteoporosis, and sarcopenia) and summarizes the pathophysiological functions of Notch signaling in these disorders, especially its role in stem/progenitor cells in each disorder. Finally, a conclusion will be presented to explore the research and application of the perspectives on Notch signaling in degenerative musculoskeletal disorders.

Sustained notch signaling inhibition with a gamma-secretase inhibitor prevents traumatic heterotopic ossification

Background

Traumatic heterotopic ossification (THO) is a devastating sequela following traumatic injuries and orthopedic surgeries. To date, the exact molecular mechanism of THO formation is still unclear, which hinders the development of effective treatments. The process of THO formation is believed to recapitulate a series of spatiotemporal cellular and signaling events that occur during skeletal development. The Notch signaling pathway is a critical genetic regulator in embryological bone development and fracture healing. However, few data are available concerning whether Notch signaling regulates THO development and maturation.

Methods

We firstly detected the expressions of Notch target genes in both mouse and human THO samples with quantitative RT-PCR and immunohistochemistry (IHC). Then, tissue-resident mesenchymal progenitor cells (TMPCs) were isolated, and the abilities of the proliferation and osteogenic and chondrogenic differentiation of TMPCs were examined under the intervention of the gamma-secretase inhibitor-DAPT at different time points. Finally, DAPT was also administrated in THO mice by burn and Achilles tenotomy injury, and ectopic cartilage and bone formation were monitored by histology and micro-CT.

Results

Several Notch target genes were upregulated in both mouse and human THO tissues. Sustained Notch signaling inhibition by DAPT reduced proliferation, osteogenic and chondrogenic differentiation of TMPCs in a time-dependent manner. Moreover, DAPT administration within 3 weeks could inhibit ectopic cartilage and bone formation in a mouse THO model without affecting the total body bone mass.

Conclusions

The Notch signaling serves as an important therapeutic target during THO formation. And sustained gamma-secretase inhibition by DAPT has great potential in repressing chondrogenic and osteogenic differentiation of TMPCs, as well as inhibited ectopic cartilage and bone formation in vivo.

The translational potential of this article

Sustained Notch inhibition via systemic DAPT (or other similar gamma-secretase inhibitors) administration has promising clinical utility for inhibiting THO formation, providing new insight into THO prophylaxis and treatment.

Complex deformation of cartilage micropellets following mechanical stimulation promotes chondrocyte gene expression

BACKGROUND

Articular cartilage (AC)'s main function is to resist to a stressful mechanical environment, and chondrocytes are responding to mechanical stress for the development and homeostasis of this tissue. However, current knowledge on processes involved in response to mechanical stimulation is still limited. These mechanisms are commonly investigated in engineered cartilage models where the chondrocytes are included in an exogeneous biomaterial different from their natural extracellular matrix. The aim of the present study is to better understand the impact of mechanical stimulation on mesenchymal stromal cells (MSCs)-derived chondrocytes generated in their own extracellular matrix.

METHODS

A fluidic custom-made device was used for the mechanical stimulation of cartilage micropellets obtained from human MSCs by culture in a chondrogenic medium for 21 days. Six micropellets were positioned into the conical wells of the device chamber and stimulated with different signals of positive pressure (amplitude, frequency and duration). A camera was used to record the sinking of each micropellet into their cone, and micropellet deformation was analyzed using a finite element model. Micropellets were harvested at different time points after stimulation for RT-qPCR and histology analysis.

RESULTS

Moderate micropellet deformation was observed during stimulation with square pressure signals as mean von Mises strains between 6.39 and 14.35% were estimated for amplitudes of 1.75-14 kPa superimposed on a base pressure of 50% of the amplitude. The compression, tension and shear observed during deformation did not alter micropellet microstructure as shown by histological staining. A rapid and transient increase in the expression of chondrocyte markers (SOX9, AGG and COL2B) was measured after a single 30-min stimulation with a square pressure signal of 3.5 kPa amplitude superimposed on a minimum pressure of 1.75 kPa, at 1 Hz. A small change of 1% of cyclical deformations when using a square pressure signal instead of a constant pressure signal induced a fold change of 2 to 3 of chondrogenic gene expression. Moreover, the expression of fibrocartilage (COL I) or hypertrophic cartilage (COL X, MMP13 and ADAMTS5) was not significantly regulated, except for COL X.

CONCLUSIONS

Our data demonstrate that the dynamic deformation of cartilage micropellets by fluidic-based compression modulates the expression of chondrocyte genes responsible for the production of a cartilage-like extracellular matrix. This lays the foundations for further investigating the chondrocyte mechanobiology and the cartilage growth under mechanical stimulation.

Transcription factors in the pathogenesis of pulmonary arterial hypertension-Current knowledge and therapeutic potential

Pulmonary arterial hypertension (PAH) is a disease characterized by elevated pulmonary vascular resistance and pulmonary artery pressure. Mortality remains high in severe cases despite significant advances in management and pharmacotherapy. Since currently approved PAH therapies are unable to significantly reverse pathological vessel remodeling, novel disease-modifying, targeted therapeutics are needed. Pathogenetically, PAH is characterized by vessel wall cell dysfunction with consecutive remodeling of the pulmonary vasculature and the right heart. Transcription factors (TFs) regulate the process of transcribing DNA into RNA and, in the pulmonary circulation, control the response of pulmonary vascular cells to macro- and microenvironmental stimuli. Often, TFs form complex protein interaction networks with other TFs or co-factors to allow for fine-tuning of gene expression. Therefore, identification of the underlying molecular mechanisms of TF (dys-)function is essential to develop tailored modulation strategies in PAH. This current review provides a compendium-style overview of TFs and TF complexes associated with PAH pathogenesis and highlights their potential as targets for vasculoregenerative or reverse remodeling therapies.

Deletion of RBP-Jkappa gene in mesenchymal cells causes rickets like symptoms in the mouse

Crosstalk between different signalling pathways provide deep insights for how molecules play synergistic roles in developmental and pathological conditions. RBP-Jkappa is the key effector of the canonical Notch pathway. Previously we have identified that Wnt5a, a conventional non-canonical Wnt pathway member, was under the direct transcriptional control of RBP-Jkappa in dermal papilla cells. In this study we further extended this regulation axis to the other two kind of skeletal cells: chondrocytes and osteoblasts. Mice with conditional mesenchymal deletion of RBP-Jkappa developed Rickets like symptoms. Molecular analysis suggested local defects of Wnt5a expression in chondrocytes and osteoblasts at both mRNA and protein levels, which impeded chondrocyte and osteoblast differentiation. The defects existing in the RBP-Jkappa deficient mutants could be rescued by recombinant Wnt5a treatment at both cellular level and tissue/organ level. Our results therefore provide a model of studying the connection of Notch and Wnt5a pathways with Rickets.

Pleiotropic Roles of NOTCH1 Signaling in the Loss of Maturational Arrest of Human Osteoarthritic Chondrocytes

Notch signaling has been identified as a critical regulator of cartilage development and homeostasis. Its pivotal role was established by both several joint specific Notch signaling loss of function mouse models and transient or sustained overexpression. NOTCH1 is the most abundantly expressed NOTCH receptors in normal cartilage and its expression increases in osteoarthritis (OA), when chondrocytes exit from their healthy “maturation arrested state” and resume their natural route of proliferation, hypertrophy, and terminal differentiation. The latter are hallmarks of OA that are easily evaluated in vitro in 2-D or 3-D culture models. The aim of our study was to investigate the effect of NOTCH1 knockdown on proliferation (cell count and Picogreen mediated DNA quantification), cell cycle (flow cytometry), hypertrophy (gene and protein expression of key markers such as RUNX2 and MMP-13), and terminal differentiation (viability measured in 3-D cultures by luminescence assay) of human OA chondrocytes. NOTCH1 silencing of OA chondrocytes yielded a healthier phenotype in both 2-D (reduced proliferation) and 3-D with evidence of decreased hypertrophy (reduced expression of RUNX2 and MMP-13) and terminal differentiation (increased viability). This demonstrates that NOTCH1 is a convenient therapeutic target to attenuate OA progression.

Effect of Salinomycin on Expression Pattern of Genes Associated with Apoptosis in Endometrial Cancer Cell Line

Background

Salinomycin is part of a group of ionophore antibiotics characterized by an activity towards tumor cells. To this day, the mechanism through which salinomycin induces their apoptosis is not fully known yet. The goal of this study was to assess the expression pattern of genes and the proteins coded by them connected with the process of programmed cell death in an endometrial cancer cell Ishikawa culture exposed to salinomycin and compared to the control.

Materials and Methods

Analysis of the effect of salinomycin on Ishikawa endometrial cancer cells (ECACC 99040201) included a cytotoxicity MTT test (with a concentration range of 0.1-100 µM), assessment of the induction of apoptosis and necrosis by salinomycin at a concentration of 1 µM as well the assessment of the expression of the genes chosen in the microarray experiment (microarray HG-U 133A_2) and the proteins coded by them connected with apoptosis (RTqPCR, ELISA assay). The statistical significance level for all analyses carried out as part of this study was p<0.05.

Results

It was observed that salinomycin causes the death of about 50% of cells treated by it (50.74±0.80% of all cells) at a concentration of 1µM. The decrease in the number of living cells was determined directly after treatment of the cells with the drug (time 0). The average percent of late apoptotic cells was 1.65±0.24% and 0.57±0.01% for necrotic cells throughout the entire observation period.

Discussion

Microarray analysis indicated the following number of mRNA differentiating the culture depending on the time of incubation with the drug: H_12 vs C = 114 mRNA, H_8 vs C = 84 mRNA, H_48 vs. C = 27 mRNA, whereas 5 mRNAs were expressed differently at all times. During the whole incubation period of the cells with the drug, the following dependence of the expression profile of the analyzed transcripts was observed: Bax>p53>FASL>BIRC5>BCL2L.

Conclusion

The analysis carried out indicated that salinomycin, at a concentration of 1 µM, stopped the proliferation of 50% of endometrial cancer cells, mainly by inducing the apoptotic process of the cells. The molecular exponent of the induction of programmed cell death was an observed increase in the transcriptional activity of pro-apoptotic genes: Bax;p53;FASL and a decrease in the expression of anti-apoptotic genes: BCL2L2; BIRC5.

Notch Signaling in Skeletal Development, Homeostasis and Pathogenesis

Skeletal development is a complex process which requires the tight regulation of gene activation and suppression in response to local signaling pathways. Among these pathways, Notch signaling is implicated in governing cell fate determination, proliferation, differentiation and apoptosis of skeletal cells-osteoblasts, osteoclasts, osteocytes and chondrocytes. Moreover, human genetic mutations in Notch components emphasize the critical roles of Notch signaling in skeletal development and homeostasis. In this review, we focus on the physiological roles of Notch signaling in skeletogenesis, postnatal bone and cartilage homeostasis and fracture repair. We also discuss the pathological gain- and loss-of-function of Notch signaling in bone and cartilage, resulting in osteosarcoma and age-related degenerative diseases, such as osteoporosis and osteoarthritis. Understanding the physiological and pathological function of Notch signaling in skeletal tissues using animal models and human genetics will provide new insights into disease pathogenesis and offer novel approaches for the treatment of bone/cartilage diseases.

Anti-osteoarthritis effect of a combination treatment with human adipose tissue-derived mesenchymal stem cells and thrombospondin 2 in rabbits

BACKGROUND

Osteoarthritis (OA), a chronic age-related disease characterized by the slowly progressive destruction of articular cartilage, is one of the leading causes of disability. As a new strategy for treatment of OA, mesenchymal stem cells (MSCs) have the potential for articular cartilage regeneration. Meanwhile, thrombospondin 2 (TSP2) promotes the chondrogenic differentiation of MSCs.

AIM

To investigate whether TSP2 induces chondrogenic differentiation of human adipose-derived MSCs (hADMSCs) and potentiates the therapeutic effects of hADMSCs in OA rabbits.

METHODS

We investigated the chondrogenic potential of TSP2 in hADMSCs by analyzing the expression of chondrogenic markers as well as NOTCH signaling genes in normal and TSP2 small interfering RNA (siRNA)-treated stem cells. Anterior cruciate ligament transection surgery was performed in male New Zealand white rabbits, and 8 wk later, hADMSCs (1.7 × 106 or 1.7 × 107 cells) were injected into the injured knees alone or in combination with intra-articular injection of TSP2 (100 ng/knee) at 2-d intervals. OA progression was monitored by gross, radiological, and histological examinations.

RESULTS

In hADMSC culture, treatment with TSP2 increased the expression of chondrogenic markers (SOX9 and collagen II) as well as NOTCH signaling genes (JAGGED1 and NOTCH3), which were inhibited by TSP2 siRNA treatment. In vivo, OA rabbits treated with hADMSCs or TSP2 alone exhibited lower degree of cartilage degeneration, osteophyte formation, and extracellular matrix loss 8 wk after cell transplantation. Notably, such cartilage damage was further alleviated by the combination of hADMSCs and TSP2. In addition, synovial inflammatory cytokines, especially tumor-necrosis factor-α, markedly decreased following the combination treatment.

CONCLUSION

The results indicate that TSP2 enhances chondrogenic differentiation of hADMSCs via JAGGED1/NOTCH3 signaling, and that combination therapy with hADMSCs and TSP2 exerts synergistic effects in the cartilage regeneration of OA joints.

Notch Signaling Regulates MMP-13 Expression via Runx2 in Chondrocytes

Notch signaling is involved in the early onset of osteoarthritis. The aim of this study was to investigate the role of Notch signaling changes during proliferation and differentiation of chondrocyte, and to testify the mechanism of MMP-13 regulation by Notch and Runx2 expression changes during osteoarthritis. In this study, Chondrocytes were isolated from rat knee cartilages. Notch signaling was activated/inhibited by Jagged-1/DAPT. Proliferative capacity of Chondrocytes was analyzed by CCK-8 staining and EdU labeling. ColX, Runx2 and MMP-13 expressions were analyzed as cell differentiation makers. Then, Runx2 gene expression was interfered using lentivirus transfection (RNAi) and was over-expressed by plasmids transfected siRNA in chondrocytes, and MMP-13 expression was analyzed after Jagged-1/DAPT treatment. In vivo, an intra-articular injection of shRunx2 lentivirus followed with Jagged1/DAPT treatments was performed in rats. MMP-13 expression in articular cartilage was detected by immunohistochemistry. Finally, MMP-13 expression changes were analyzed in chondrocytes under IL-1β stimulation. Our findings showed that, CCK-8 staining and EdU labeling revealed suppression of cell proliferation by Notch signaling activation after Jagged-1 treatment in chondrocytes. Promoted differentiation was also observed, characterized by increased expressions of Col X, MMP-13 and Runx2. Meanwhile, Sox9, aggrecan and Col II expressions were down-regulated. The opposite results were observed in Notch signaling inhibited cells by DAPT treatment. In addition, Runx2 RNAi significantly attenuated the ‘regulatory sensitivity’ of Notch signaling on MMP-13 expression both in vitro and in vivo. However, we found there wasn’t significant changes of this ‘regulatory sensitivity’ of Notch signaling after Runx2 over-expression. Under IL-1β circumstance, MMP-13 expression could be reduced by both DAPT treatment and Runx2 RNAi, while Runx2 interference also attenuated the ‘regulatory sensitivity’ of Notch in MMP-13 under IL-1β stimulation. In conclusion, Notch signaling is an important regulator on rat chondrocyte proliferation and differentiation, and this regulatory effect was partially mediated by proper Runx2 expression under both normal and IL-1β circumstances. In the meanwhile, DAPT treatment could effectively suppress expression of MMP-13 stimulated by IL-1 β.

Cyclic tensile strain promotes the ECM synthesis of cranial base synchondrosis chondrocytes by upregulating miR-140-5p

OBJECTIVE

This study aimed to explore the role of miR-140-5p in cranial base synchondrosis chondrocytes (CBSCs) under cyclic tensile strain (CTS).

SETTING AND SAMPLE POPULATION

A total of 25 1-week-old Sprague Dawley rats from Shanghai Laboratory Animal Center, Chinese Academy of Sciences, were used.

MATERIAL AND METHODS

The second passage of CBSCs was applied with CTS at 10% elongation (1 Hz) for 24 hours. MiR-140-5p levels in CBSCs were detected by qRT-PCR. The role of miR-140-5p in CBSCs was evaluated by transfection of mimics and inhibitor. RNA sequencing and online search of miRNA databases (TargetScan, miRDB and miRanda) were used in prediction of miR-140-5p targets. A luciferase reporter assay was applied to identify the target gene of miR-140-5p.

RESULTS

Compared with the control, the expression of Col2a1 and Sox9 was significantly higher after CTS (P < .05). Also, CBSCs demonstrated higher expression of miR-140-5p after CTS loading for 24 hours (P < .05). Overexpression of miR-140-5p promoted ECM synthesis under CTS loading environment, while suppression of miR-140-5p inhibited the effect. Bloc1s2 was a putative target gene of miR-140-5p.

CONCLUSIONS

The expression of ECM in CBSCs could be promoted by CTS and miR-140-5p might play a role in this process through targeting Bloc1s2.

Inhibition of notch signaling pathway temporally postpones the cartilage degradation progress of temporomandibular joint arthritis in mice

PURPOSE

The aim of this study is to explore the role of Notch signaling pathway in the initiation and progression of temporomandibular joint osteoarthritis (TMJOA).

METHODS

48 mice were divided into DAPT-TMJOA, Control-TMJOA and Control-Sham groups. Animals received discectomy/Sham surgery in their right TMJ, following the DAPT/saline intra-articular injections every week. Mice were sacrificed at 1/4/8 weeks post-surgery. Safranin-O and H&E staining were performed on the TMJ sections for the modified Mankin's score. qPCR and immunohistochemistry were used to evaluate Notch1, Jagged1 and Hes5 expressions.

RESULTS

The mRNA expressions of Notch1, Jagged1 and Hes5 were significantly increased in Control-TMJOA group compared with Control-Sham group. Immunostaining revealed a dramatic elevation of Notch1, Jagged1 and Hes5 signals distributed in the cartilage at 1 and 4 weeks after discectomy. However, the increased number of those immuno-positive cells turned down at 8 weeks after surgery. DAPT treatment partially rescued the elevated mRNA expression and immuno-positive cell numbers of Notch1, Jagged1 and Hes5. More importantly, the cartilage destruction during TMJOA was delayed by DAPT treatment, analyzed by modified Mankin's score.

CONCLUSION

Notch signaling participates in the onset and development of TMJOA. Inhibiting Notch signaling activation by DAPT can partially delay the progress of TMJOA.

Time-dependent changes in gene expression induced in vitro by interleukin-1β in equine articular cartilage

Osteoarthritis is an inflammatory and degenerative joint disease commonly affecting horses. To identify genes of relevance for cartilage pathology in osteoarthritis we studied the time-course effects of interleukin (IL)-1β on equine articular cartilage. Articular cartilage explants from the distal third metacarpal bone were collected postmortem from three horses without evidence of joint disease. The explants were stimulated with IL-1β for 27 days and global gene expression was measured by microarray. Gene expression was compared to that of unstimulated explants at days 3, 9, 15, 21 and 27. Release of inflammatory proteins was measured using Proximity Extension Assay. Stimulation with IL-1β led to time-dependent changes in gene expression related to inflammation, the extracellular matrix (ECM), and phenotypic alterations. Gene expression and protein release of cytokines, chemokines, and matrix-degrading enzymes increased in the stimulated explants. Collagen type II was downregulated from day 15, whereas other ECM molecules were downregulated earlier. In contrast molecules involved in ECM signaling (perlecan, chondroitin sulfate proteoglycan 4, and syndecan 4) were upregulated. At the late time points, genes related to a chondrogenic phenotype were downregulated, and genes related to a hypertrophic phenotype were upregulated, suggesting a transition towards hypertrophy later in the culturing period. The data suggest that this in vitro model mimics time course events of in vivo inflammation in OA and it may be valuable as an in vitro tool to test treatments and to study disease mechanisms.

Expression of Notch signaling pathway during osteoarthritis in the temporomandibular joint

PURPOSE

Our study aim was to characterize the expression of Notch molecules during temporomandibular joint osteoarthritis (TMJOA), thus exploring the mechanism and roles that Notch signaling possibly plays in the initiation and progression of TMJOA.

MATERIALS AND METHODS

A total of 126 mice were divided randomly into experimental groups, a sham-surgery group and a normal control group. In the experimental group, total discectomy was performed in the right temporomandibular joint (TMJ) to induce TMJOA; the sham-operation group underwent the same procedure without disc removal, and the normal control group was left undisturbed. Fourteen mice in each group were sacrificed in batches respectively at 1, 2, and 4 weeks postoperatively. Histology was performed to examine TMJOA in eight condyles each group, and a modified Mankin scoring system was used for evaluation. Immunohistochemistry was carried out to characterize the expression of the Notch markers Notch1, Jagged1, Hes1, and Hes5. Real-time polymerase chain reaction (RT-PCR) was performed for further detection and analysis of Notch markers in six condyles in each group.

RESULTS

Notch1, Jagged1, and Hes5 were activated in the experimental group, with expression levels that increased dramatically over time, whereas the control group showed no fluctuation. Hes1 expression was suppressed at the beginning but was up-regulated afterward.

CONCLUSIONS

Our data suggest that Notch signaling is activated in TMJOA with a much more abundant expression in osteoarthritis cartilage.

Effects of microgravity simulation on zebrafish transcriptomes and bone physiology-exposure starting at 5 days post fertilization

Physiological modifications in near weightlessness, as experienced by astronauts during space flight, have been the subject of numerous studies. Various animal models have been used on space missions or in microgravity simulation on ground to understand the effects of gravity on living animals. Here, we used the zebrafish larvae as a model to study the effect of microgravity simulation on bone formation and whole genome gene expression. To simulate microgravity (sim-μg), we used two-dimensional (2D) clinorotation starting at 5 days post fertilization to assess skeletal formation after 5 days of treatment. To assess early, regulatory effects on gene expression, a single day clinorotation was performed. Clinorotation for 5 days caused a significant decrease of bone formation, as shown by staining for cartilage and bone structures. This effect was not due to stress, as assessed by measuring cortisol levels in treated larvae. Gene expression results indicate that 1-day simulated microgravity affected musculoskeletal, cardiovascular, and nuclear receptor systems. With free-swimming model organisms such as zebrafish larvae, the 2D clinorotation setup appears to be a very appropriate approach to sim-μg. We provide evidence for alterations in bone formation and other important biological functions; in addition several affected genes and pathways involved in bone, muscle or cardiovascular development are identified.

Characterization of Notch Signaling During Osteogenic Differentiation in Human Osteosarcoma Cell Line MG63

Osteogenic differentiation is a multi-step process controlled by a complex molecular framework. Notch is an evolutionarily conserved intercellular signaling pathway playing a prominent role in cell fate and differentiation, although the mechanisms by which this pathway regulates osteogenesis remain controversial. This study aimed to investigate, in vitro, the involvement of Notch pathway during all the developmental stages of osteogenic differentiation in human osteosarcoma cell line MG63. Cells were cultured in basal condition (control) and in osteoinductive medium (OM). Notch inhibitors were also added in OM to block Notch pathway. During osteogenic differentiation, early (alkaline phosphatase activity and collagen type I) and late osteogenic markers (osteocalcin levels and matrix mineralization), as well as the gene expression of the main osteogenic transcription factors (Runx2, Osterix, and Dlx5) increased. Time dependent changes in the expression of specific Notch receptors were identified in OM versus control with a significant reduction in the expression of Notch1 and Notch3 receptors in the early phase of differentiation, and an increase of Notch2 and Notch4 receptors in the late phase. Among Notch nuclear target genes, Hey1 expression was significantly higher in OM than control, while Hes5 expression decreased. Osteogenic markers were reduced and Hey1 was significantly inhibited by Notch inhibitors, suggesting a role for Notch through the canonical pathway. In conclusion, Notch pathway might be involved with a dual role in osteogenesis of MG63, through the activation of Notch2, Notch4, and Hey1, inducing osteoblast differentiation and the depression of Notch1, Notch3, and Hes5, maintaining an undifferentiated status. J. Cell. Physiol. 231: 2652-2663, 2016. © 2016 Wiley Periodicals, Inc.

Multifaceted signaling regulators of chondrogenesis: Implications in cartilage regeneration and tissue engineering

Defects of articular cartilage present a unique clinical challenge due to its poor self-healing capacity and avascular nature. Current surgical treatment options do not ensure consistent regeneration of hyaline cartilage in favor of fibrous tissue. Here, we review the current understanding of the most important biological regulators of chondrogenesis and their interactions, to provide insight into potential applications for cartilage tissue engineering. These include various signaling pathways, including: fibroblast growth factors (FGFs), transforming growth factor β (TGF-β)/bone morphogenic proteins (BMPs), Wnt/β-catenin, Hedgehog, Notch, hypoxia, and angiogenic signaling pathways. Transcriptional and epigenetic regulation of chondrogenesis will also be discussed. Advances in our understanding of these signaling pathways have led to promising advances in cartilage regeneration and tissue engineering.

HES5 promotes cell proliferation and invasion through activation of STAT3 and predicts poor survival in hepatocellular carcinoma

OBJECTIVES

HES5 is a member of the basic helix-loop-helix (bHLH) family of transcription factors, and involved in cell differentiation and proliferation in a variety of tissues other than HCC. Therefore, we have characterized HES5 and investigated its role during hepatocarcinogenesis.

METHODS

We first examined the expression of HES5 in eight paired frozen HCC and adjacent noncancerous liver tissues by Western blot. Immunohistochemistry was performed to confirm our results in 58 HCC samples and evaluated the relativity between the expression of HES5 and clinicopathological variables and estimated the prognostic significance. Moreover, Western blot examined the expression of downstream proteins by siRNA HES5. Flow cytometer assay was performed to investigate the role of HES5 in the process of HCC.

RESULTS

We found that HES5 was upregulated in HCC specimens. The data showed that high expression of HES5 was tightly associated with histological grade (P<0.01) and metastasis (P<0.01), and positively correlated with proliferation marker Ki-67 (P<0.01). Moreover, the results show that abnormal expression of HES5 influences cell growth and cell cycle of HCC cell lines. Furthermore, HES5 knockdown resulted in the reduction of p-STAT3.

CONCLUSION

These results suggested that suppression of the HES5 leading to inhibition of proliferation may be one of the mechanisms against HCC.

Autocrine Action of Thrombospondin-2 Determines the Chondrogenic Differentiation Potential and Suppresses Hypertrophic Maturation of Human Umbilical Cord Blood-Derived Mesenchymal Stem Cells

Previous studies have shown that mesenchymal stem cell (MSC)-based therapies have varying efficacies for the treatment of various diseases, including cartilage defects. In this study, we demonstrated that the chondrogenic differentiation potential of human umbilical cord blood-derived MSCs (hUCB-MSCs) obtained from different individual donors varies, and we investigated the molecular basis for this variation. Microarray gene expression analysis identified thrombospondin-2 (TSP2) as a candidate gene underlying the interindividual variation in the chondrogenic differentiation potential of hUCB-MSCs. To assess the association between TSP-2 and the differentiation potential, we evaluated chondrogenic differentiation of hUCB-MSCs treated with TSP2 siRNA. In addition, we studied the effect of supplementing exogenous recombinant TSP-2 on TSP2 siRNA-treated hUCB-MSCs. We found that TSP-2 autocrinally promoted chondrogenic differentiation of hUCB-MSCs via the Notch signaling pathway, which was confirmed in MSCs from other sources such as bone marrow and adipose tissue. Interestingly, we observed that TSP-2 attenuated hypertrophy, which inevitably occurs during chondrogenic differentiation of hUCB-MSCs. Our findings indicated that the variable chondrogenic differentiation potential of MSCs obtained from different donors is influenced by the TSP-2 level in the differentiating cells. Thus, the TSP-2 level can be used as a marker to select MSCs with superior chondrogenic differentiation potential for use in cartilage regeneration therapy.

Zebrafish Bone and General Physiology Are Differently Affected by Hormones or Changes in Gravity

Teleost fish such as zebrafish (Danio rerio) are increasingly used for physiological, genetic and developmental studies. Our understanding of the physiological consequences of altered gravity in an entire organism is still incomplete. We used altered gravity and drug treatment experiments to evaluate their effects specifically on bone formation and more generally on whole genome gene expression. By combining morphometric tools with an objective scoring system for the state of development for each element in the head skeleton and specific gene expression analysis, we confirmed and characterized in detail the decrease or increase of bone formation caused by a 5 day treatment (from 5dpf to 10 dpf) of, respectively parathyroid hormone (PTH) or vitamin D3 (VitD3). Microarray transcriptome analysis after 24 hours treatment reveals a general effect on physiology upon VitD3 treatment, while PTH causes more specifically developmental effects. Hypergravity (3g from 5dpf to 9 dpf) exposure results in a significantly larger head and a significant increase in bone formation for a subset of the cranial bones. Gene expression analysis after 24 hrs at 3g revealed differential expression of genes involved in the development and function of the skeletal, muscular, nervous, endocrine and cardiovascular systems. Finally, we propose a novel type of experimental approach, the "Reduced Gravity Paradigm", by keeping the developing larvae at 3g hypergravity for the first 5 days before returning them to 1g for one additional day. 5 days exposure to 3g during these early stages also caused increased bone formation, while gene expression analysis revealed a central network of regulatory genes (hes5, sox10, lgals3bp, egr1, edn1, fos, fosb, klf2, gadd45ba and socs3a) whose expression was consistently affected by the transition from hyper- to normal gravity.

Cell and matrix modulation in prenatal and postnatal equine growth cartilage, zones of Ranvier and articular cartilage

Formation of synovial joints includes phenotypic changes of the chondrocytes and the organisation of their extracellular matrix is regulated by different factors and signalling pathways. Increased knowledge of the normal processes involved in joint development may be used to identify similar regulatory mechanisms during pathological conditions in the joint. Samples of the distal radius were collected from prenatal and postnatal equine growth plates, zones of Ranvier and articular cartilage with the aim of identifying Notch signalling components and cells with stem cell-like characteristics and to follow changes in matrix protein localisation during joint development. The localisation of the Notch signalling components Notch1, Delta4, Hes1, Notch dysregulating protein epidermal growth factor-like domain 7 (EGFL7), the stem cell-indicating factor Stro-1 and the matrix molecules cartilage oligomeric matrix protein (COMP), fibromodulin, matrilin-1 and chondroadherin were studied using immunohistochemistry. Spatial changes in protein localisations during cartilage maturation were observed for Notch signalling components and matrix molecules, with increased pericellular localisation indicating new synthesis and involvement of these proteins in the formation of the joint. However, it was not possible to characterise the phenotype of the chondrocytes based on their surrounding matrix during normal chondrogenesis. The zone of Ranvier was identified in all horses and characterised as an area expressing Stro-1, EGFL7 and chondroadherin with an absence of COMP and Notch signalling. Stro-1 was also present in cells close to the perichondrium, in the articular cartilage and in the fetal resting zone, indicating stem cell-like characteristics of these cells. The presence of stem cells in the articular cartilage will be of importance for the repair of damaged cartilage. Perivascular chondrocytes and hypertrophic cells of the cartilage bone interface displayed positive staining for EGFL7, which is a novel finding and suggests a role of EGFL7 in the vascular infiltration of growth cartilage.

Transplantation of adipose-derived stem cells combined with decellularized cartilage ECM: a novel approach to nasal septum perforation repair

Nasal septal perforation, a defect of the nasal mucoperichondrium and cartilage, may induce epistaxis, persistent rhinorrhea and nasal obstruction. Cell-based tissue engineering is a promising therapeutic method for the treatment of nasal septal perforation. However, lack of an adequate source of cells and unsuitable biomaterials greatly hinder the development of cell-based therapy. In this paper, we proposed the application of adipose-derived stem cells combined with decellularized cartilage ECM as a potential graft for the damaged nasal septum, which could help to repair the mucosal and cartilage tissues in the treatment of nasal septal perforation. This new technology could play a novel role in the repair of nasal septal perforation, and in regeneration of damaged nasal cartilage.

Notch signaling is involved in human articular chondrocytes de-differentiation during osteoarthritis

CONTEXT

During osteoarthritis (OA), chondrocytes undergo de-differentiation, resulting in the acquisition of a fibroblast-like morphology, decreased expression of collagen type II (colII) and aggrecan, and increased expression of collagen type I (colI), metalloproteinase 13 (MMP13) and nitric oxide synthase (eNOS). Notch signaling plays a crucial role during embryogenesis. Several studies showed that Notch is expressed in adulthood.

OBJECTIVE

The aim of our study was to confirm the involvement of Notch signaling in human OA at in vitro and ex vivo levels.

MATERIALS AND METHODS

Normal human articular chondrocytes were cultured during four passages either treated or not with a Notch inhibitor: DAPT. Human OA cartilage was cultured with DAPT for five days. Chondrocytes secreted markers and some Notch pathway components were analyzed using Western blotting and qPCR.

RESULTS

Passaging chondrocytes induced a decrease in the cartilage markers: colII and aggrecan. DAPT-treated chondrocytes and OA cartilage showed a significant increase in healthy cartilage markers. De-differentiation markers, colI, MMP13 and eNOS, were significantly reduced in DAPT-treated chondrocytes and OA cartilage. Notch1 expression was proportional to colI, MMP13 and eNOS expression and inversely proportional to colII and aggrecan expression in nontreated cultured chondrocytes. Notch ligand: Jagged1 increased in chondrocytes culture. DAPT treatment resulted in reduced Jagged1 expression. Notch target gene HES1 increased during chondrocyte culture and was reduced when treated with DAPT.

CONCLUSION

Targeting Notch signaling during OA might lead to the restitution of the typical chondrocyte phenotype and even to chondrocyte redifferentiation during the pathology.

Notch signaling in chondrocytes modulates endochondral ossification and osteoarthritis development

Here we examined the involvement of Notch signaling in the endochondral ossification process, which is crucial for osteoarthritis (OA) development. Intracellular domains of Notch1 and -2 were translocated into the nucleus of chondrocytes with their differentiation in mouse limb cartilage and in mouse and human OA articular cartilage. A tissue-specific inactivation of the Notch transcriptional effector recombination signal binding protein for Ig kappa J (RBPjκ) in chondroprogenitor cells of SRY-box containing gene 9 (Sox9)-Cre;Rbpj(fl/fl) mouse embryos caused an impaired terminal stage of endochondral ossification in the limb cartilage. The RBPjκ inactivation in adult articular cartilage after normal skeletal growth using type II collagen (Col2a1)-Cre(ERT);Rbpj(fl/fl) mice by tamoxifen injection caused resistance to OA development in the knee joint. Notch intracellular domain with the effector RBPjκ stimulated endochondral ossification through induction of the target gene Hes1 in chondrocytes. Among the Notch ligands, Jagged1 was strongly induced during OA development. Finally, intraarticular injection of N-[N-(3,5-diflurophenylacetate)-L-alanyl]-(S)-phenylglycine t-butyl ester (DAPT), a small compound Notch inhibitor, to the mouse knee joint prevented OA development. The RBPjκ-dependent Notch signaling in chondrocytes modulates the terminal stage of endochondral ossification and OA development, representing an extracellular therapeutic target of OA.

Notch-1 mediates hypoxia-induced angiogenesis in rheumatoid arthritis

OBJECTIVE

To examine the effect of hypoxia on Notch-1 signaling pathway components and angiogenesis in inflammatory arthritis.

METHODS

The expression and regulation of Notch-1, its ligand delta-like protein 4 (DLL-4) and downstream signaling components (hairy-related transcription factor 1 [HRT-1], HRT-2), and hypoxia-inducible factor 1α (HIF-1α) under normoxic and hypoxic conditions (1-3%) were assessed in synovial tissue specimens from patients with inflammatory arthritis and controls and in human dermal microvascular endothelial cells (HDMECs) by immunohistology, dual immunofluorescence staining (Notch-1/factor VIII), Western blotting, and real-time polymerase chain reaction. In vivo synovial tissue oxygen levels (tissue PO2) were measured under direct visualization at arthroscopy. HDMEC activation under hypoxic conditions in the presence of Notch-1 small interfering RNA (siRNA), the γ-secretase inhibitor DAPT, or dimethyloxalylglycine (DMOG) was assessed by Matrigel tube formation assay, migration assay, invasion assay, and matrix metalloproteinase 2 (MMP-2)/MMP-9 zymography.

RESULTS

Expression of Notch-1, its ligand DLL-4, and HRT-1 was demonstrated in synovial tissue, with the strongest expression localized to perivascular/vascular regions. Localization of Notch-1 to synovial endothelium was confirmed by dual immunofluorescence staining. Notch-1 intracellular domain (NICD) expression was significantly higher in synovial tissue from patients with tissue PO2 of <20 mm Hg (<3% O2) than in those with tissue PO2 of >20 mm Hg (>3% O2). Exposure of HDMECs to 3% hypoxia induced HIF-1α and NICD protein expression and DLL-4, HRT-1, and HRT-2 messenger RNA expression. DMOG directly induced NICD expression, while Notch-1 siRNA inhibited hypoxia-induced HIF-1α expression, suggesting that Notch-1/HIF-1α signaling is bidirectional. Finally, 3% hypoxia-induced angiogenesis, endothelial cell migration, endothelial cell invasion, and proMMP-2 and proMMP-9 activities were inhibited by Notch-1 siRNA and/or the γ-secretase inhibitor DAPT.

CONCLUSION

Our findings indicate that Notch-1 is expressed in synovial tissue and that increased NICD expression is associated with low in vivo tissue PO2. Furthermore, Notch-1/HIF-1α interactions mediate hypoxia-induced angiogenesis and invasion in inflammatory arthritis.

Expression patterns of Notch receptors and their ligands in human osteoarthritic and healthy articular cartilage

Notch pathway plays a pivotal role in cell fate determination. There is much interest surrounding its therapeutic potential, in osteoarthritis, but the expression profile of Notch-related molecules, as well as their relation with cartilage pathological parameters, remains unclear. The purpose of our study is to analyze the expression pattern of Notch family members, type II and type I collagen, in normal (healthy) and osteoarthritic human knee cartilage. Osteoarthritic cartilages were obtained from 3 patients undergoing a total knee replacement. Macroscopically normal cartilage was dissected from 3 human knees at the time of autopsy or surgery. Immunohistochemical staining was performed using Notch1,2,3 and 4, Delta, Jagged, type II collagen and type I collagen antibodies. In healthy cartilage, type II collagen was abundantly expressed while type I was absent. This latter increased proportionally to the osteoarthritic grade. Type II collagen expression remained intense in osteoarthritic cartilage. In healthy cartilage as well as in cartilage with minor lesions, Notch family member's proteins were not or just weakly expressed at the surface and in the cells. However, Notch molecules were over-expressed in osteoarthritic cartilage compared to healthy one. This expression pattern was different according to the cartilage zone and the severity of OA. Our data suggest that Notch signaling is activated in osteoarthritic cartilage, compared to healthy cartilage, with a much more abundant expression in the most damaged areas.

Notch1 signaling regulates chondrogenic lineage determination through Sox9 activation

Notch signaling is involved in several cell lineage determination processes during embryonic development. Recently, we have shown that Sox9 is most likely a primary target gene of Notch1 signaling in embryonic stem cells (ESCs). By using our in vitro differentiation protocol for chondrogenesis from ESCs through embryoid bodies (EBs) together with our tamoxifen-inducible system to activate Notch1, we analyzed the function of Notch signaling and its induction of Sox9 during EB differentiation towards the chondrogenic lineage. Temporary activation of Notch1 during early stages of EB, when lineage determination occurs, was accompanied by rapid and transient Sox9 upregulation and resulted in induction of chondrogenic differentiation during later stages of EB cultivation. Using siRNA targeting Sox9, we knocked down and adjusted this early Notch1-induced Sox9 expression peak to non-induced levels, which led to reversion of Notch1-induced chondrogenic differentiation. In contrast, continuous Notch1 activation during EB cultivation resulted in complete inhibition of chondrogenic differentiation. Furthermore, a reduction and delay of cardiac differentiation observed in EBs after early Notch1 activation was not reversed by siRNA-mediated Sox9 knockdown. Our data indicate that Notch1 signaling has an important role during early stages of chondrogenic lineage determination by regulation of Sox9 expression.

Hypoxia activates the notch signaling pathway in cells of the intervertebral disc: implications in degenerative disc disease

OBJECTIVE

To investigate whether hypoxia regulates Notch signaling, and whether Notch plays a role in intervertebral disc cell proliferation.

METHODS

Reverse transcription-polymerase chain reaction and Western blotting were used to measure expression of Notch signaling components in intervertebral disc tissue from mature rats and from human discs. Transfections were performed to determine the effects of hypoxia and Notch on target gene activity.

RESULTS

Cells of the nucleus pulposus and annulus fibrosus of rat disc tissue expressed components of the Notch signaling pathway. Expression of Notch-2 was higher than that of the other Notch receptors in both the nucleus pulposus and annulus fibrosus. In both tissues, hypoxia increased Notch1 and Notch4 messenger RNA (mRNA) expression. In the annulus fibrosus, mRNA expression of the Notch ligand Jagged1 was induced by hypoxia, while Jagged2 mRNA expression was highly sensitive to hypoxia in both tissues. A Notch signaling inhibitor, L685458, blocked hypoxic induction of the activity of the Notch-responsive luciferase reporters 12xCSL and CBF1. Expression of the Notch target gene Hes1 was induced by hypoxia, while coexpression with the Notch-intracellular domain increased Hes1 promoter activity. Moreover, inhibition of Notch signaling blocked disc cell proliferation. Analysis of human disc tissue showed that there was increased expression of Notch signaling proteins in degenerated discs.

CONCLUSION

In intervertebral disc cells, hypoxia promotes expression of Notch signaling proteins. Notch signaling is an important process in the maintenance of disc cell proliferation, and thus offers a therapeutic target for the restoration of cell numbers during degenerative disc disease.

Cell fate mediators Notch and Twist in mouse mandibular condylar cartilage

OBJECTIVE

The objectives of this study were to examine if Twist and Notch 1 are present in the mandibular condylar cartilage (MCC) and whether their gene expression can be altered by exogenous FGF-2 and TGF-β2.

DESIGN

Half-heads from CD-1 mice pups harvested at embryonic day 17 (E17) were fixed, decalcified, and sectioned in the sagittal plane for immunohistochemical detection of Notch and Twist using confocal microscopy. Other mandibular condyles and adjacent ramus from E17 mice were cultured in serum-free DMEM containing 0, 3, or 30 ng/mL of FGF-2 (10-12 condyles per treatment group). This experimental design was repeated with medium containing 0, 3, or 30 ng/mL of TGF-β2. After 3 days of culture, the pooled RNA from each group was extracted for examination of Notch and Twist gene expression using quantitative real-time RT-PCR.

RESULTS

Immunohistochemical examination revealed that Notch and Twist were localized to the prechondroblastic and upper chondroblastic layers of the cartilage. Exogenous FGF-2 up-regulated Notch 1, Twist 1 and Twist 2 gene expression in MCC explants from E17 mice, whilst TGF-β2 had the opposite effect.

CONCLUSIONS

The gene expression data demonstrate that MCC explants are sensitive to growth factors known to affect Notch and Twist in other tissues. The subset of cells in which Twist and Notch immunoreactivity was found is suggestive of a role for FGF-2 and TGF-β2 as regulators of cell differentiation of the bipotent MCC cell population, consistent with the role of Notch and Twist as downstream mediators of these growth factors in other tissues.

The role of the Notch pathway in healthy and osteoarthritic articular cartilage: from experimental models to ex vivo studies

Osteoarthritis is the most prevalent form of arthritis in the world. With the progressive ageing of the population, it is becoming a major public health problem. The involvement of certain signaling pathways, such as the Notch pathway, during cartilage pathology has been reported. In this review, we report on studies that investigated the expression pattern of the Notch family members in articular cartilage and the eventual involvement of this pathway in the modulation of the physiology and pathology of chondrocytes. Temporal and/or spatial modulation of this signaling pathway may help these cells to synthesize a new functional extracellular matrix and restore the functional properties of the articular cartilage.

Hes1, a new target for interleukin 1beta in chondrocytes

OBJECTIVES

To investigate the effects of interleukin 1beta (IL1beta) treatment on the Notch1/Hes1 pathway in chondrocytes in vitro.

METHODS

Mouse articular chondrocytes in primary culture were challenged with IL1beta, alone or combined with Notch1 and IL1beta pathway inhibitors. Notch1 and Hes1 expressions were investigated by immunocytochemistry, western blot and real-time quantitative (q)PCR. IL1beta-responsive genes were assessed by real-time qPCR and a specific siRNA against Hes1 was used to identify Hes1 target genes.

RESULTS

Notch1 labelling remained nuclear and stable in intensity irrespective of treatment, suggesting a steady state activation of this pathway in our model. IL1beta transiently increased Hes1 mRNA (2.5-fold) and protein expression in treated versus naive chondrocytes. Hes1 mRNA level then decreased below control and its cyclic pattern of expression was lost. This was associated with nuclear translocation of the cytoplasmic Hes1 protein. IL1beta induced increase in Hes1 mRNA was transcriptional, occurred through nuclear factor (NF)kappaB activation and appeared to be associated with downregulation by its own protein. Hes1 induction was insensitive to the gamma-secretase inhibitor N-(N-(3,5-difluorophenacetyl)-l-alanyl)-S-phenylglycine t-butyl ester (DAPT), which suggested its independence from novel Notch1 activation. Hes1 expression was efficiently silenced by a specific siRNA. This experiment revealed that Hes1 did not mediate IL1beta-induced downregulation of Sox9, type II collagen and aggrecan transcription but mediated IL1beta induction of matrix metalloproteinase (MMP)13 and ADAM metallopeptidase with thrombospondin type 1 motif, 5 (ADAMTS5). The Hes1-related repressor Hey1 was expressed at a very low level and was not inducible by IL1beta.

CONCLUSION

Hes1 is a novel IL1beta target gene in chondrocytes which influences a discrete subset of genes linked to cartilage matrix remodelling and/or degradation.

Expression of Notch family members in cultured murine articular chondrocytes

The Notch family is involved in cell differentiation during embryogenesis. Osteoarthritic chondrocytes undergo morphological and biochemical changes leading to the de-differentiation process. In the study reported here, we were interested in the involvement of the Notch pathway in murine articular chondrocyte de-differentiation. Articular chondrocytes were subjected to several cell culture passages and treated with or without a Notch inhibitor, N-[N-(3, 5-difluorophenacetyl-L-alanyl)]-S-phenylglycine t-Butyl Ester (DAPT). Chondrocyte morphology was studied using optical microscopy. Immunocytochemistry and immunoblot were performed to study the expression of collagens and Notch family members. Without DAPT treatment, chondrocyte de-differentiation resulted in fibroblast-like morphology. This was confirmed by immunocytochemical staining and immunoblot analysis, which showed an increase in collagen type I (col I) and a decrease in collagen type II (col II) expression. With DAPT treatment, de-differentiation was delayed. Immunocytochemistry and immunoblot analysis showed during the first passages inhibition of col II expression, which then was re-instituted during the last passage, suggesting chondrocyte re-differentiation. In the study reported here, we showed that inhibition of the Notch receptor not only delayed the de-differentiation process, but also chondrocyte re-differentiation, which confirms the involvement of the Notch pathway in chondrocyte de-differentiation.

Notch signaling during chondrogenesis of human bone marrow stem cells

Notch signaling is an important mechanism involved in early development which helps to determine the differentiation and fate of cells destined to form different tissues in the body. Its role in the differentiation of adult stem cells, such as those found in bone marrow is much less clear. As there is great interest in the potential of human bone marrow stem cells (hMSC) as a source of cells for the repair of articular cartilage and other tissues, it is important to understand if Notch signaling promotes or suppresses differentiation. Using primary human bone marrow stem cells (hMSC) in 3D cell aggregate culture a new study has investigated the expression of the canonical Notch pathway genes during chondrogenesis and showed that the Notch ligand, Jagged1 (JAG1) sharply increased in expression peaking early in differentiation. A Notch target gene, HEY1, was also expressed with a temporal profile, which closely followed the expression of JAG1 and this preceded the rise in type II collagen expression that characterized chondrogenesis. The JAG1 mediated Notch signaling was shown with a Notch inhibitor (DAPT) to be necessary for chondrogenesis, as inhibition days 0-14, or just days 0-5, blocked chondrogenesis, whereas Notch inhibition days 5-14 did not. In further experiments Notch signaling was shown to be critical for full chondrogenesis, as adenoviral hJAG1 transduction of hMSCs, which caused continuous expression of JAG1 and sustained Notch signaling, completely blocked chondrogenesis. In these cultures there was inhibited production of extracellular matrix and failure to differentiate was interpreted as the retention of the hMSC in a pre-chondrogenic state. The results in this study thus showed that JAG1 mediated Notch signaling in hMSC was necessary to initiate chondrogenesis, but must be switched off for chondrogenesis to proceed and it will be important to establish if this is a mechanism common to all chondrocyte differentiation.

Identification of a stem cell niche in the zone of Ranvier within the knee joint

A superficial lesion of the articular cartilage does not spontaneously self-repair and has been suggested to be partly due to lack of progenitor cells within the joint that can reach the site of injury. To study whether progenitor cells are present within the joint, 3-month-old New Zealand white rabbits were exposed to bromodeoxyuridine (BrdU) for 12 consecutive days and were then sacrificed 4, 6, 10, 14, 28 and 56 days after the first BrdU administration. Presence of BrdU and localization of progenitor markers were detected using immunohistochemistry. After 10 days of BrdU exposure, BrdU-positive cells, i.e. proliferating cells, were abundantly detected in the epiphyseal plate, the perichondrial groove of Ranvier, and in all zones of the articular cartilage. After a wash-out period, BrdU-positive cells were still present, i.e. those considered to be progenitor cells, in these regions of the knee except for the proliferative zone of the epiphyseal plate. Cells in the perichondrial groove of Ranvier were further positive for several markers associated with progenitor cells and stem cell niches, including Stro-1, Jagged1, and BMPr1a. Our results demonstrate that a small population of progenitor cells is present in the perichondrial groove of Ranvier as well as within the articular cartilage in the knee. The perichondrial groove of Ranvier also demonstrates the properties of a stem cell niche.

Gene expression profile of multipotent mesenchymal stromal cells: Identification of pathways common to TGFbeta3/BMP2-induced chondrogenesis

Multipotent mesenchymal stromal cells (MSC) display a high potential for the development of novel treatment strategies for cartilage repair. However, the pathways involved in their differentiation to functional non hypertrophic chondrocytes remain largely unknown, despite the work on embryologic development and the identification of key growth factors including TGFbeta, Hh, Wnt and FGF. In this study, we asked if we could identify specific biological networks common to the growth factors used (TGFbeta3 or BMP-2). To address this question, we used DNA microarrays and performed large-scale expression profiling of MSC at different time points during their chondrogenic differentiation. By comparing these data with those obtained during the differentiation of MSC into osteoblasts and adipocytes, we identified 318 genes specific for chondrogenesis and developed a new algorithm to classify the genes according to their kinetic profile. We distributed the selected genes in five classes according to their kinetic of expression. We could reconstruct three phases characterized by functional pathways. The first phase corresponds to cell attachment and apoptosis induction; the second phase is characterized by a proliferation/differentiation step, and the third phase is characterized by a differentiation/hypertrophy pathway. Indeed, these data propose new pathways to understand the complexity of MSC differentiation to chondrocytes.

Involvement of the Notch pathway in the regulation of matrix metalloproteinase 13 and the dedifferentiation of articular chondrocytes in murine cartilage

OBJECTIVE

To demonstrate the activation of the Notch signaling pathway during changes in the phenotype of chondrocytes in vitro, and to assess the influence of Notch on the production of chondrocyte markers.

METHODS

Serial monolayer primary cultures of murine articular chondrocytes (MACs), as a model of chondrocyte dedifferentiation, were prepared. MACs were cultured with or without a Notch inhibitor and transfected with different Notch-expressing vectors. The Notch pathway and chondrocyte marker profiles were assessed by quantitative reverse transcription-polymerase chain reaction, immunoblotting, and immunocytochemistry.

RESULTS

Successive passages of MACs resulted in a loss of type II collagen and aggrecan (chondrocyte differentiation markers), an increase in type I collagen (dedifferentiation marker), an increase in Notch ligands, and augmented target gene activity. The Notch inhibitor decreased the type II collagen protein content but had no effect on Col2a1 messenger RNA, while transfection with the constitutive active forms of the Notch1 receptor led to a decrease in type II collagen in transfected cells. In assays to investigate the mechanism of type II collagen breakdown, matrix metalloproteinase 13 (MMP-13) synthesis was regulated in a Notch-dependent manner, whereas MMP-2 synthesis was unchanged.

CONCLUSION

The Notch signaling pathway is associated with decreased type II collagen production during the dedifferentiation of MACs in vitro. This may be correlated with the increase in MMP-13 production linked to activation of Notch.

Notch signaling in chondrogenesis

The different stages of cartilage development are well described but no transcription factor capable of specifically inducing differentiation to articular cartilage has been identified and little is known about the molecular mechanisms regulating cartilage development. Notch signaling is an evolutionarily conserved pathway taking part in many developmental and cell type specification processes. It has been demonstrated that markers for Notch signaling are differentially expressed during cartilage development and there is evidence for their functional role during this process. Notch signaling has further been implicated in osteoarthritis and Notch1 has been suggested as a marker for chondrogenic progenitor cells. This review summarizes the current knowledge on the role of the Notch signaling pathway in cartilage development and osteoarthritis.

Notch signaling through Jagged-1 is necessary to initiate chondrogenesis in human bone marrow stromal cells but must be switched off to complete chondrogenesis

We investigated Notch signaling during chondrogenesis in human bone marrow stromal cells (hMSC) in three-dimensional cell aggregate culture. Expression analysis of Notch pathway genes in 14-day chondrogenic cultures showed that the Notch ligand Jagged-1 (Jag-1) sharply increased in expression, peaking at day 2, and then declined. A Notch target gene, HEY-1, was also expressed, with a temporal profile that closely followed the expression of Jag-1, and this preceded the rise in type II collagen expression that characterized chondrogenesis. We demonstrated that the shut-down in Notch signaling was critical for full chondrogenesis, as adenoviral human Jag-1 transduction of hMSC, which caused continuous elevated expression of Jag-1 and sustained Notch signaling over 14 days, completely blocked chondrogenesis. In these cultures, there was inhibited production of extracellular matrix, and the gene expression of aggrecan and type II collagen were strongly suppressed; this may reflect the retention of a prechondrogenic state. The JAG-1-mediated Notch signaling was also shown to be necessary for chondrogenesis, as N-[N-(3,5-difluorophenacetyl-L-alanyl)]-(S)-phenylglycine t-butyl ester (DAPT) added to cultures on days 0-14 or just days 0-5 inhibited chondrogenesis, but DAPT added from day 5 did not. The results thus showed that Jag-1-mediated Notch signaling in hMSC was necessary to initiate chondrogenesis, but it must be switched off for chondrogenesis to proceed.