Inhibition of Notch1 promotes hedgehog signalling in a HES1-dependent manner in chondrocytes and exacerbates experimental osteoarthritis

The involvement of signaling pathways in the pathogenesis of osteoarthritis: An update

Osteoarthritis (OA) is one of the most common disabling pathologies, characterized by joint pain and reduced function, significantly worsening the quality of life. Even if important progresses have been made in OA research, little is yet known about the precise cellular and molecular mechanisms underlying OA. Understanding dysregulated signaling networks and their crosstalk in OA may offer a strong opportunity for the development of combined targeted therapies. Hence, this review highlights the recent findings on the main pathways involved in OA development, including Wnt, Notch, Hedgehog, MAPK, AMPK, and JAK/STAT, providing insights on current targeted therapies in OA patients' management.

The translational potential of this article

The identification of key signaling pathways involved in OA development and the investigation of their signaling crosstalk could pave the way for more effective treatments and improved management of OA patients in the future.

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.

MYL3 protects chondrocytes from senescence by inhibiting clathrin-mediated endocytosis and activating of Notch signaling

As the unique cell type in articular cartilage, chondrocyte senescence is a crucial cellular event contributing to osteoarthritis development. Here we show that clathrin-mediated endocytosis and activation of Notch signaling promotes chondrocyte senescence and osteoarthritis development, which is negatively regulated by myosin light chain 3. Myosin light chain 3 (MYL3) protein levels decline sharply in senescent chondrocytes of cartilages from model mice and osteoarthritis (OA) patients. Conditional deletion of Myl3 in chondrocytes significantly promoted, whereas intra-articular injection of adeno-associated virus overexpressing MYL3 delayed, OA progression in male mice. MYL3 deficiency led to enhanced clathrin-mediated endocytosis by promoting the interaction between myosin VI and clathrin, further inducing the internalization of Notch and resulting in activation of Notch signaling in chondrocytes. Pharmacologic blockade of clathrin-mediated endocytosis-Notch signaling prevented MYL3 loss-induced chondrocyte senescence and alleviated OA progression in male mice. Our results establish a previously unknown mechanism essential for cellular senescence and provide a potential therapeutic direction for OA.

YY1/miR-140-5p/Jagged1/Notch axis mediates cartilage progenitor/stem cells fate reprogramming in knee osteoarthritis

Osteoarthritis is a multifactorial disease characterized by cartilage degeneration, while cartilage progenitor/stem cells (CPCs) are responsible for endogenous cartilage repair. However, the relevant regulatory mechanisms of CPCs fate reprogramming in OA are rarely reported. Recently, we observed fate disorders in OA CPCs and found that microRNA-140-5p (miR-140-5p) protects CPCs from fate changes in OA. This study further mechanistically investigated the upstream regulator and downstream effectors of miR-140-5p in OA CPCs fate reprogramming. As a result, luciferase reporter assay and validation assays revealed that miR-140-5p targets Jagged1 and inhibits Notch signaling in human CPCs, and the loss-/gain-of-function experiments and rescue assays discovered that miR-140-5p improves OA CPCs fate, but this effect can be counteracted by Jagged1. Moreover, increased transcription factor Ying Yang 1 (YY1) was associated with OA progression, and YY1 could disturb CPCs fate via transcriptionally repressing miR-140-5p and enhancing the Jagged1/Notch signaling. Finally, the relevant changes and mechanisms of YY1, miR-140-5p, and Jagged1/Notch signaling in OA CPCs fate reprogramming were validated in rats. Conclusively, this study identified a novel YY1/miR-140-5p/Jagged1/Notch signaling axis that mediates OA CPCs fate reprogramming, wherein YY1 and Jagged1/Notch signaling exhibits an OA-stimulative role, and miR-140-5p plays an OA-protective effect, providing attractive targets for OA therapeutics.

Autophagy and apoptosis: regulatory factors of chondrocyte phenotype transition in osteoarthritis

Osteoarthritis (OA) is the main pathogenic factor in diseases that cause joint deformities. As the main manifestation of the progress of OA, cartilage degradation has been closely associated with the degeneration of chondrocytes, which is induced by inflammatory factors and other trauma factors. Autophagy and apoptosis are the main mechanisms for cells to maintain homeostasis and play crucial roles in OA. Under the influence of external environmental factors (such as aging and injury), the metabolism of cells can be altered, which may affect the extent of autophagy and apoptosis. With the progression of OA, these changes can alter the cell phenotypes, and the cells of different phenotypes display distinct differences in morphology and function. In this review, we have summarized the alteration in cell metabolism, autophagy, and the extent of apoptosis during OA progression and its effects on the cell phenotypes to provide new ideas for further research on the mechanisms of phenotypic transition and therapeutic strategies so as to reverse the cell phenotypes.

Silencing of NOTCH3 Signaling in Meniscus Smooth Muscle Cells Inhibits Fibrosis and Exacerbates Degeneration in a HEYL-Dependent Manner

The mechanisms of meniscus fibrosis and novel ways to enhance fibrosis is unclear. This work reveals human meniscus fibrosis initiated at E24 weeks. Smooth muscle cell cluster is identified in embryonic meniscus, and the combined analysis with previous data suggests smooth muscle cell in embryonic meniscus as precursors of progenitor cells in the mature meniscus. NOTCH3 is constantly expressed in smooth muscle cells throughout embryogenesis to adulthood. Inhibition of NOTCH3 signaling in vivo inhibits meniscus fibrosis and exacerbates degeneration. Continuous histological sections show that HEYL, NOTCH3 downstream target gene, is expressed consistently with NOTCH3. HEYL knockdown in meniscus cells attenuated the COL1A1 upregulation by CTGF and TGF-β stimulation. Thus, this study discovers the existence of smooth muscle cells and fibers in the meniscus. Inhibition of NOTCH3 signaling in meniscus smooth muscle cells in a HEYL-dependent manner prevented meniscus fibrosis and exacerbated degeneration. Therefore, NOTCH3/HEYL signaling might be a potential therapeutic target for meniscus fibrosis.

The Role of Selenium-Mediated Notch/Hes1 Signaling Pathway in Kashin-Beck Disease Patients and Cartilage Injury Models

Kashin-Beck disease (KBD) is a nutrition-related osteoarthropathy, and selenium (Se) deficiency is an environmental risk factor for KBD. Notch/Hes1 signaling pathway plays a vital role in regulating cartilage, but its exact mechanisms in KBD remain unknown. The Se contents were determined using the hydride atomic fluorescence spectrometry assay technique, and the mRNA levels were detected via quantitative real-time PCR. The chondrocyte injury models were established by Se deficiency and tert-butyl hydroperoxide (tBHP), respectively; apoptosis and necrosis rates were detected using Hoechst 33,342/PI and Annexin V-FITC/PI. The results showed that the Se levels in the flour of KBD areas were lower than that of the non-KBD areas, and the Se levels in the plasma of KBD patients were lower than that of the controls. The expressions of Notch1, Jagged1, and Hes1 were higher in the whole blood of KBD patients than those of the controls, and Notch1 was negatively correlated with the expression of BCL2, while was positively correlated with BAX. In injury, chondrocytes induced by low Se and tBHP, the expression of Notch1, Jagged1, and Hes1 increased, apoptosis and necrosis rates increased in Se deficiency and tBHP groups, while Se supplementation reversed it. Decreased plasma Se in KBD patients may be related to low dietary Se. Se deficiency might be involved in the pathological process of KBD by activating the Notch/Hes1 signaling pathway to induce excessive apoptosis of chondrocytes, the activation of Notch/Hes1 promotes oxidative injury, and Se supplementation could reverse it. The importance of Notch/Hes1 signaling pathway in KBD development will provide a new potential target for KBD.

miR-140-5p protects cartilage progenitor/stem cells from fate changes in knee osteoarthritis

Cartilage progenitor/stem cells (CPCs) are promising seed cells for cartilage regeneration, but their fate changes and regulatory mechanisms in osteoarthritis (OA) pathogenesis remain unclear. This study aimed to investigate the role and potential mechanism of the microRNA-140-5p (miR-140-5p), whose protective role in knee OA has been confirmed by our previous studies, in OA CPCs fate reprogramming. Firstly, the normal and OA CPCs were isolated, and the fate indicators, miR-140-5p, Jagged1, and Notch signals were detected and analyzed. Then, the effect of miR-140-5p and the Notch pathway on CPCs fate reprogramming and miR-140-5p on Jagged1/Notch signaling was investigated in IL-1β-induced chondrocytes in vitro. Finally, the effect of miR-140-5p on OA CPCs fate reprogramming and the potential mechanisms were validated in OA rats. As a result, CPCs percentage was increased in the mild OA cartilage-derived total chondrocytes while decreased in the advanced OA group. Significant fate changes (including reduced cell viability, migration, chondrogenesis, and increased apoptosis), increased Jagged1 and Notch signals, and reduced miR-140-5p were observed in OA CPCs and associated with OA progression. IL-1β induced OA-like changes in CPCs fate, which could be exacerbated by miR-140-5p inhibitor while alleviated by DAPT (a specific Notch inhibitor) and miR-140-5p mimic. Finally, the in vitro phenomenal and mechanistic findings were validated in OA rats. Overall, miR-140-5p protects CPCs from fate changes via inhibiting Jagged1/Notch signaling in knee OA, providing attractive targets for OA therapeutics.

Chondrocyte Hypertrophy in Osteoarthritis: Mechanistic Studies and Models for the Identification of New Therapeutic Strategies

Articular cartilage shows limited self-healing ability owing to its low cellularity and avascularity. Untreated cartilage defects display an increased propensity to degenerate, leading to osteoarthritis (OA). During OA progression, articular chondrocytes are subjected to significant alterations in gene expression and phenotype, including a shift towards a hypertrophic-like state (with the expression of collagen type X, matrix metalloproteinases-13, and alkaline phosphatase) analogous to what eventuates during endochondral ossification. Present OA management strategies focus, however, exclusively on cartilage inflammation and degradation. A better understanding of the hypertrophic chondrocyte phenotype in OA might give new insights into its pathogenesis, suggesting potential disease-modifying therapeutic approaches. Recent developments in the field of cellular/molecular biology and tissue engineering proceeded in the direction of contrasting the onset of this hypertrophic phenotype, but knowledge gaps in the cause-effect of these processes are still present. In this review we will highlight the possible advantages and drawbacks of using this approach as a therapeutic strategy while focusing on the experimental models necessary for a better understanding of the phenomenon. Specifically, we will discuss in brief the cellular signaling pathways associated with the onset of a hypertrophic phenotype in chondrocytes during the progression of OA and will analyze in depth the advantages and disadvantages of various models that have been used to mimic it. Afterwards, we will present the strategies developed and proposed to impede chondrocyte hypertrophy and cartilage matrix mineralization/calcification. Finally, we will examine the future perspectives of OA therapeutic strategies.

Role of the hedgehog signaling pathway in rheumatic diseases: An overview

Hedgehog (Hh) signaling pathway is an evolutionarily conserved signal transduction pathway that plays an important regulatory role during embryonic development, cell proliferation, and differentiation of vertebrates, and it is often inhibited in adult tissues. Recent evidence has shown that Hh signaling also plays a key role in rheumatic diseases, as alterations in their number or function have been identified in rheumatoid arthritis, osteoarthritis, ankylosing spondylitis, systemic sclerosis, and Sjogren’s Syndrome. As a result, emerging studies have focused on the blockade of this pathogenic axis as a promising therapeutic target in several autoimmune disorders; nevertheless, a greater understanding of its contribution still requires further investigation. This review aims to elucidate the most recent studies and literature data on the pathogenetic role of Hh signaling in rheumatic diseases.

Dynamic changes in O-GlcNAcylation regulate osteoclast differentiation and bone loss via nucleoporin 153

Bone mass is maintained by the balance between osteoclast-induced bone resorption and osteoblast-triggered bone formation. In inflammatory arthritis such as rheumatoid arthritis (RA), however, increased osteoclast differentiation and activity skew this balance resulting in progressive bone loss. O-GlcNAcylation is a posttranslational modification with attachment of a single O-linked β-D-N-acetylglucosamine (O-GlcNAc) residue to serine or threonine residues of target proteins. Although O-GlcNAcylation is one of the most common protein modifications, its role in bone homeostasis has not been systematically investigated. We demonstrate that dynamic changes in O-GlcNAcylation are required for osteoclastogenesis. Increased O-GlcNAcylation promotes osteoclast differentiation during the early stages, whereas its downregulation is required for osteoclast maturation. At the molecular level, O-GlcNAcylation affects several pathways including oxidative phosphorylation and cell-cell fusion. TNFα fosters the dynamic regulation of O-GlcNAcylation to promote osteoclastogenesis in inflammatory arthritis. Targeted pharmaceutical or genetic inhibition of O-GlcNAc transferase (OGT) or O-GlcNAcase (OGA) arrests osteoclast differentiation during early stages of differentiation and during later maturation, respectively, and ameliorates bone loss in experimental arthritis. Knockdown of NUP153, an O-GlcNAcylation target, has similar effects as OGT inhibition and inhibits osteoclastogenesis. These findings highlight an important role of O-GlcNAcylation in osteoclastogenesis and may offer the potential to therapeutically interfere with pathologic bone resorption.

Wharton's jelly mesenchymal stem cell-derived small extracellular vesicles as natural nanoparticles to attenuate cartilage injury via microRNA regulation

The main strategy of tissue repair and regeneration focuses on the application of mesenchymal stem cells and cell-based nanoparticles, but there are still multiple challenges that may have negative impacts on human safety and therapeutic efficacy. Cell-free nanotechnology can effectively overcome these obstacles and limitations. Mesenchymal stem cell (MSC)-derived natural small extracellular vesicles (sEVs) represent ideal nanotherapeutics due to their low immunogenicity and lack of tumorigenicity. Here, sEVs harvested from Wharton's jelly mesenchymal stem cells (WJMSCs) were identified. In vitro results showed that WJMSC-sEVs efficiently entered chondrocytes in the osteoarthritis (OA) model, further promoted chondrocyte migration and proliferation and modulated immune reactivity. In vivo, WJMSC-sEVs notably promoted chondrogenesis, which was consistent with the effect of WJMSCs. RNA sequencing results revealed that sEV-microRNA-regulated biocircuits can significantly contribute to the treatment of OA, such as by promoting the activation of the calcium signaling pathway, ECM-receptor interaction pathway and NOTCH signaling pathway. In particular, let-7e-5p, which is found in WJMSC-sEVs, was shown to be a potential core molecule for promoting cartilage regeneration by regulating the levels of STAT3 and IGF1R. Our findings suggest that WJMSC-sEV-induced chondrogenesis is a promising innovative and feasible cell-free nanotherapy for OA treatment.

Effects of salinity acclimation on histological characteristics and miRNA expression profiles of scales in juvenile rainbow trout (Oncorhynchus mykiss)

Background

The scales serve as an ideal model for studying the regulatory mechanism of bone homeostasis in fish. To explore the effect of salinity acclimation on bone metabolism of juvenile rainbow trout (Oncorhynchus mykiss), three sampling time points during salinity acclimation (7D, 14D and 21D) were selected to detect variations in histological characteristics. In the histological analysis, osteoblast marker enzymes alkaline phosphatase (ALP), osteoclast marker tartrate-resistant acid phosphatase (TRAcP) and calcium salt deposit areas (Von Kossa′s) were detected. Changes in calcium (Ca), phosphorus (P) and the molar mass ratio of calcium to phosphorus (Ca/P) in the scales were also detected by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). In addition, the global MicroRNA (miRNA) expression profiles during salinity acclimation were examined using Illumina sequencing platform because of their important regulatory roles in teleost biological processes.

Results

Twelve independent miRNA libraries were constructed, a total of 664 known and 92 putative novel miRNAs were identified. A total of 290 differentially expressed (DE) miRNAs were found in clusters with significant trends in the cluster analysis, and five types of clustering patterns were obtained; 22,374 DE predicted target genes of the aforementioned 290 DE miRNAs were obtained, 5957 of which clustered in six types of clustering patterns with a significant trend. To better understand the functions of the DE miRNAs, GO and KEGG analysis was performed on the 5957 target genes, as a result, they were significantly enriched in bone metabolism related signaling pathways such as MAPK signaling pathway, Calcium signaling pathway, Wnt signaling pathway, Mineral absorption and NF-kappa B signaling pathway. Six DE miRNAs were randomly selected and their expression were verified by quantitative real-time PCR (qRT-PCR), the expression trends were consistent with the results of transcriptome sequencing.

Conclusions

The DE miRNAs and DE target genes identified in this study might play an important role in regulation of bone metabolism during salinity acclimation, relative genes or pathways could serve as key candidates for further studies to elucidate molecular mechanism of teleost bone metabolism, and help performing salinity acclimation and developing marine culture of salmonid species.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08531-7.

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.

Comprehensive Analysis of Key Genes, Signaling Pathways and miRNAs in Human Knee Osteoarthritis: Based on Bioinformatics

Background: Osteoarthritis (OA) is one of the main causes of disability in the elderly population, accompanied by a series of underlying pathologic changes, such as cartilage degradation, synovitis, subchondral bone sclerosis, and meniscus injury. The present study aimed to identify key genes, signaling pathways, and miRNAs in knee OA associated with the entire joint components, and to explain the potential mechanisms using computational analysis.

Methods: The differentially expressed genes (DEGs) in cartilage, synovium, subchondral bone, and meniscus were identified using the Gene Expression Omnibus 2R (GEO2R) analysis based on dataset from GSE43923, GSE12021, GSE98918, and GSE51588, respectively and visualized in Volcano Plot. Venn diagram analyses were performed to identify the overlapping DEGs (overlapping DEGs) that expressed in at least two types of tissues mentioned above. Gene Ontology (GO) enrichment analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, protein-protein interaction (PPI) analysis, and module analysis were conducted. Furthermore, qRT-PCR was performed to validate above results using our clinical specimens.

Results: As a result, a total of 236 overlapping DEGs were identified, of which 160 were upregulated and 76 were downregulated. Through enrichment analysis and constructing the PPI network and miRNA-mRNA network, knee OA-related key genes, such as HEY1, AHR, VEGFA, MYC, and CXCL12 were identified. Clinical validation by qRT-PCR experiments further supported above computational results. In addition, knee OA-related key miRNAs such as miR-101, miR-181a, miR-29, miR-9, and miR-221, and pathways such as Wnt signaling, HIF-1 signaling, PI3K-Akt signaling, and axon guidance pathways were also identified. Among above identified knee OA-related key genes, pathways and miRNAs, genes such as AHR, HEY1, MYC, GAP43, and PTN, pathways like axon guidance, and miRNAs such as miR-17, miR-21, miR-155, miR-185, and miR-1 are lack of research and worthy for future investigation.

Conclusion: The present informatic study for the first time provides insight to the potential therapeutic targets of knee OA by comprehensively analyzing the overlapping genes differentially expressed in multiple joint components and their relevant signaling pathways and interactive miRNAs.

The effect induced by alternated mechanical loading on Notch-1 in mandibular condylar cartilage of growing rabbits

Aims

The aim of our study is to investigate the effect induced by alternated mechanical loading on Notch-1 in mandibular condylar cartilage (MCC) of growing rabbits.

Methods

A total of 64 ten-day-old rabbits were randomly divided into two groups according to dietary hardness: normal diet group (pellet) and soft diet group (powder). In each group, the rabbits were further divided into four subgroups by feeding time: two weeks, four weeks, six weeks, and eight weeks. Animals would be injected 5-bromo-2′-deoxyuridine (BrdU) every day for one week before sacrificing. Histomorphometric analysis of MCC thickness was performed through haematoxylin and eosin (HE) staining. Immunochemical analysis was done to test BrdU and Notch-1. The quantitative real-time polymerase chain reaction (qRT-PCR) and western blot were used to measure expression of Notch-1, Jagged-1, and Delta-like 1 (Dll-1).

Results

The thickness of MCC in the soft diet group was thinner than the one in normal diet group. Notch-1 was restricted in fibrous layer, proliferative layer, and hypertrophic layer. The expression of Notch-1 increased from two weeks to six weeks and then fell down. Notch-1 in normal diet group was higher than that in soft diet group in anterior part of MCC. The statistical differences of Notch-1 were shown at two, four, and six weeks (p < 0.05). The result of western blot and quantitative real-time PCR (qRT-PCR) showed the expression of Dll-1 and Jagged-1 rose from two to four weeks and started to decrease at four weeks. BrdU distributed in all layers of cartilage and subchondral bone. The number of BrdU-positive cells, which were less in soft diet group, was decreasing along with the experiment period. The significant difference was found at four, six, and eight weeks in anterior and posterior parts (p < 0.05).

Conclusion

The structure and proliferation of MCC in rabbits were sensitive to dietary loading changes. The proper mechanical loading was essential for transduction of Notch signalling pathway and development of mandibular condylar cartilage.

Cite this article: Bone Joint Res 2021;10(7):437–444.

Localization of DLL1- and NICD-positive osteoblasts in cortical bone during postnatal growth in rats

The long bone midshaft expands by forming primary osteons at the periosteal surface of cortical bone in humans and rodents. Osteoblastic bone formation in the vascular cavity in the center of primary osteons is delayed during cortical bone development. The mechanisms of the formation of primary osteons is not fully understood, however. Focusing on NOTCH1 signaling, an inhibitory signaling on osteoblastic bone formation, our immunohistochemical analysis revealed Delta like1 (DLL1), a ligand of NOTCH1, and the NOTCH1 intracellular domain (NICD, an activated form of NOTCH1) immunoreactivity, in the cuboidal osteoblasts lining the bone surface in the vascular cavity of primary osteons during postnatal growth in rats. Interestingly, five days after treatment of primary osteoblasts with ascorbic acid and β glycerophosphate, protein levels of both DLL1 and NICD increased transiently, indicating that DLL1 activates NOTCH1 in primary cultured osteoblasts. Thus, the results imply that DLL1-NOTCH1 signaling in osteoblasts is associated with primary osteonal bone formation.

Contextual Regulation of Skeletal Physiology by Notch Signaling

PURPOSE OF REVIEW

This article reviews the past 2 years of research on Notch signaling as it relates to bone physiology, with the goal of reconciling seemingly discrepant findings and identifying fruitful areas of potential future research.

RECENT FINDINGS

Conditional animal models and high-throughput omics have contributed to a greater understanding of the context-dependent role of Notch signaling in bone. However, significant gaps remain in our understanding of how spatiotemporal context and epigenetic state dictate downstream Notch phenotypes. Biphasic activation of Notch signaling orchestrates progression of mesenchymal progenitor cells through the osteoblast lineage, but there is a limited understanding of ligand- and receptor-specific functions. Paracrine Notch signaling through non-osteoblastic cell types contributes additional layers of complexity, and we anticipate impactful future work related to the integration of these cell types and signaling mechanisms.

Mice harboring a Hajdu Cheney Syndrome mutation are sensitized to osteoarthritis

Osteoarthritis is a joint disease characterized by cartilage degradation, altered gene expression and inflammation. NOTCH1 and NOTCH2 receptors and the JAGGED1 ligand regulate chondrocyte biology; however, the contribution of Notch signaling to osteoarthritis is controversial. Hajdu Cheney Syndrome (HCS) is a rare genetic disorder affecting the skeleton and associated with NOTCH2 mutations that lead to NOTCH2 gain-of-function. A murine model of the disease (Notch2^tm1.1Ecan) was used to test whether the HCS mutation increases the susceptibility to osteoarthritis. The knee of three-month-old Notch2^tm1.1Ecan male mice and control sex-matched littermates was destabilized by resection of the medial meniscotibial ligament, and changes in the joint analyzed two months thereafter. Expression of Notch target genes was increased in the femoral heads of Notch2^tm1.1Ecan mice, documenting Notch signal activation. Periarticular bone and cartilage structures were unaffected in Notch2^tm1.1Ecan mutants subjected to sham surgery, indicating that NOTCH2 gain-of-function had no discernible impact on joint structure under basal conditions. However, destabilization of the medial meniscus increased osteophyte volume and thickened subchondral bone in Notch2^tm1.1Ecan mice compared to wild type littermates. Moreover, destabilized Notch2^tm1.1Ecan mutants exhibited histological signs of moderate to severe cartilage degeneration, demonstrating joint sensitization to the development of osteoarthritis. Chondrocyte cultures from Notch2^tm1.1Ecan mutants expressed increased Il6 mRNA levels following exposure to JAGGED1, possibly explaining the susceptibility of Notch2^tm1.1Ecan mice to osteoarthritis. In conclusion, Notch2^tm1.1Ecan mutants are sensitized to the development of osteoarthritis in destabilized joints and NOTCH2 activation may play a role in the pathogenesis of the disease.

Onset and Progression of Human Osteoarthritis-Can Growth Factors, Inflammatory Cytokines, or Differential miRNA Expression Concomitantly Induce Proliferation, ECM Degradation, and Inflammation in Articular Cartilage?

Osteoarthritis (OA) is a degenerative whole joint disease, for which no preventative or therapeutic biological interventions are available. This is likely due to the fact that OA pathogenesis includes several signaling pathways, whose interactions remain unclear, especially at disease onset. Early OA is characterized by three key events: a rarely considered early phase of proliferation of cartilage-resident cells, in contrast to well-established increased synthesis, and degradation of extracellular matrix components and inflammation, associated with OA progression. We focused on the question, which of these key events are regulated by growth factors, inflammatory cytokines, and/or miRNA abundance. Collectively, we elucidated a specific sequence of the OA key events that are described best as a very early phase of proliferation of human articular cartilage (AC) cells and concomitant anabolic/catabolic effects that are accompanied by incipient pro-inflammatory effects. Many of the reviewed factors appeared able to induce one or two key events. Only one factor, fibroblast growth factor 2 (FGF2), is capable of concomitantly inducing all key events. Moreover, AC cell proliferation cannot be induced and, in fact, is suppressed by inflammatory signaling, suggesting that inflammatory signaling cannot be the sole inductor of all early OA key events, especially at disease onset.

Single-cell RNA-seq analysis reveals the progression of human osteoarthritis

Objectives

Understanding the molecular mechanisms underlying human cartilage degeneration and regeneration is helpful for improving therapeutic strategies for treating osteoarthritis (OA). Here, we report the molecular programmes and lineage progression patterns controlling human OA pathogenesis using single-cell RNA sequencing (scRNA-seq).

Methods

We performed unbiased transcriptome-wide scRNA-seq analysis, computational analysis and histological assays on 1464 chondrocytes from 10 patients with OA undergoing knee arthroplasty surgery. We investigated the relationship between transcriptional programmes of the OA landscape and clinical outcome using severity index and correspondence analysis.

Results

We identified seven molecularly defined populations of chondrocytes in the human OA cartilage, including three novel phenotypes with distinct functions. We presented gene expression profiles at different OA stages at single-cell resolution. We found a potential transition among proliferative chondrocytes, prehypertrophic chondrocytes and hypertrophic chondrocytes (HTCs) and defined a new subdivision within HTCs. We revealed novel markers for cartilage progenitor cells (CPCs) and demonstrated a relationship between CPCs and fibrocartilage chondrocytes using computational analysis. Notably, we derived predictive targets with respect to clinical outcomes and clarified the role of different cell types for the early diagnosis and treatment of OA.

Conclusions

Our results provide new insights into chondrocyte taxonomy and present potential clues for effective and functional manipulation of human OA cartilage regeneration that could lead to improved health.

Molecular characterization of mesenchymal stem cells in human osteoarthritis cartilage reveals contribution to the OA phenotype

Adult human articular cartilage harbors a population of CD166+ mesenchymal stem cell-like progenitors that become more numerous during osteoarthritis (OA). While their role is not well understood, here we report that they are indeed part of cellular clusters formed in OA cartilage, which is a pathological hallmark of this disease. We hypothesize that these cells, termed OA mesenchymal stem cells (OA-MSCs), contribute to OA pathogenesis. To test this hypothesis, we generated and characterized multiple clonally derived stable/immortalized human OA-MSC cell lines, which exhibited the following properties. Firstly, two mesenchymal stem cell populations exist in human OA cartilage. While both populations are multi-potent, one preferentially undergoes chondrogenesis while the other exhibits higher osteogenesis potential. Secondly, both OA-MSCs exhibit significantly higher expression of hypertrophic OA cartilage markers COL10A1 and RUNX2, compared to OA chondrocytes. Induction of chondrogenesis in OA-MSCs further stimulated COL10A1 expression and MMP-13 release, suggesting that they contribute to OA phenotypes. Finally, knocking down RUNX2 is insufficient to inhibit COL10A1 in OA-MSCs and also requires simultaneous knockdown of NOTCH1 thereby suggesting altered gene regulation in OA stem cells in comparison to chondrocytes. Overall, our findings suggest that OA-MSCs may drive pathogenesis of cartilage degeneration and should therefore be a novel cell target for OA therapy.

Recent Insights into the Contribution of the Changing Hypertrophic Chondrocyte Phenotype in the Development and Progression of Osteoarthritis

Osteoarthritis (OA) is an extremely prevalent age-related condition. The economic and societal burden due to the cost of symptomatic treatment, inability to work, joint replacement, and rehabilitation is huge and increasing. Currently, there are no effective medical therapies that delay or reverse the pathological manifestations of OA. Current treatment options are, without exception, focused on slowing down progression of the disease to postpone total joint replacement surgery for as long as possible and keeping the associated pain and joint immobility manageable. Alterations in the articular cartilage chondrocyte phenotype might be fundamental in the pathological mechanisms of OA development. In many ways, the changing chondrocyte phenotype in osteoarthritic cartilage resembles the process of endochondral ossification as seen, for instance, in developing growth plates. However, the relative contribution of endochondral ossification to the changing chondrocyte phenotype in the development and progression of OA remains poorly described. In this review, we will discuss the current knowledge regarding the cartilage endochondral phenotypic changes occurring during OA development and progression, as well as the molecular and environmental effectors driving these changes. Understanding how these molecular mechanisms determine the chondrocyte cell fate in OA will be essential in enabling cartilage regenerative approaches in future treatments of OA.

Targeted Therapies for Pancreatic Cancer

Pancreatic cancer is the third leading cause of cancer related death and by 2030, it will be second only to lung cancer. We have seen tremendous advances in therapies for lung cancer as well as other solid tumors using a molecular targeted approach but our progress in treating pancreatic cancer has been incremental with median overall survival remaining less than one year. There is an urgent need for improved therapies with better efficacy and less toxicity. Small molecule inhibitors, monoclonal antibodies and immune modulatory therapies have been used. Here we review the progress that we have made with these targeted therapies.

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

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

Knockdown of PRMT1 suppresses IL-1β-induced cartilage degradation and inflammatory responses in human chondrocytes through Gli1-mediated Hedgehog signaling pathway

Osteoarthritis (OA) is characterized by articular cartilage degradation and joint inflammation. The purpose of the present study is to elucidate the role of the specific function of PRMT1 in chondrocytes and its association with the pathophysiology of OA. We observed that the expression of PRMT1 was apparently upregulated in OA cartilage, as well as in chondrocytes stimulated with IL-1β. Additionally, knockdown of PRMT1 suppressed interleukin 1 beta (IL-1β)-induced extracellular matrix (ECM) metabolic imbalance by regulating the expression of MMP-13, ADAMTS-5, COL2A1, and ACAN. Furthermore, silencing of PRMT1 dramatically declined the production of prostaglandin E2 (PGE2) and nitric oxide as well as the level of pro-inflammatory cytokine IL-6 and TNF-α. Mechanistic analyses further revealed that IL-1β-induced activation of the Hedgehog/Gli-1 signaling is suppressed upon PRMT1 knockdown. However, the effects of inhibition of PRMT1-mediated IL-1β-induced cartilage matrix degradation and inflammatory response in OA chondrocytes were obviously abolished by Hedgehog agonist Purmorphamine (Pur). Our data collectively suggest that silencing of PRMT1 exerts anti-catabolic and anti-inflammatory effects on IL-1β-induced chondrocytes via suppressing the Gli-1 mediated Hedgehog signaling pathway, indicating that PRMT1 plays a critical role in OA development and serves as a promising therapeutic target for OA.

Role of Notch signaling pathway in pancreatic cancer

Pancreatic cancer (PC) is one of the highly aggressive malignancies in the United States. It has been shown that multiple signaling pathways are involved in the pathogenesis of PC, such as JNK, PI3K/AKT, Rho GTPase, Hedgehog (Hh) and Skp2. In recent years, accumulated evidence has demonstrated that Notch signaling pathway plays critical roles in the development and progression of PC. Therefore, in this review we discuss the recent literature regarding the function and regulation of Notch in the pathogenesis of PC. Moreover, we describe that Notch signaling pathway could be down-regulated by its inhibitors or natural compounds, which could be a novel approach for the treatment of PC patients.