Subcutaneously Transplanted Fresh Cartilage in Allogeneic and Xenogeneic Immunocompetent Mouse.

Cartilage is considered to be immune privileged in general. Clinically, live cells are removed from subcutaneously transplanted allogeneic cartilage mainly for preservation and for infection control. However, because maintaining cartilage feature requires live chondrocyte, it would be beneficial to subcutaneously transplant cartilage with live chondrocyte even if it was allogeneic. We harvested femoral head from 3-week-old male C57BL/6 mice, subcutaneously transplanted to 6-week-old male mice, BALB/c, BALB/c nu/nu, or C57BL/6-Tg (enhanced green fluorescent protein [EGFP] under the control of the CMV-IE enhancer, chicken beta-actin promoter, rabbit beta-globin genomic DNA [CAG promoter]), as allogeneic, allogeneic immunodeficient control, or syngeneic transplantation. We also transplanted cartilaginous particles from human induced pluripotent stem cells derived from human leukocyte antigen homozygous donor to 6-week-old male mice either BALB/c and BALB/c nu/nu as xenogeneic or xenogeneic immunodeficient control. The transplantation periods were 1, 2, 3, 4, 8, 12, and 24 weeks. As the result, we did not observe exposure of the transplant or apparent macroscopic inflammatory in all samples. Histological analysis suggested that the femoral head showed focal ossification and thinning in syngeneic transplantation. In allogeneic transplantation, slight invasion of CD3 (+) T cell and the denaturation of the cartilage were observed, suggesting immune reaction against allogeneic cartilage. In xenogeneic transplantation, slight invasion of CD3 (+) cell and CD4 (+) cell and the structure of the perichondrium-like tissue got unclear, suggesting slight immune reaction against xenogeneic cartilage. Our findings suggest that we should carefully investigate for appropriate procedure to control immune reaction against allogeneic cartilage with live chondrocyte and to maintain its cartilage feature for long time.

Cathepsin K degrades osteoprotegerin to promote osteoclastogenesis in vitro.

Osteoblasts produce the receptor activator of nuclear factor-kappa B ligand (RANKL) and osteoprotegerin, the inducer and the suppressor of osteoclast differentiation and activation. We previously proposed that the degradation of osteoprotegerin by lysine-specific gingipain of Porphyromonas gingivalis and neutrophil elastase is one of the mechanisms of bone resorption associated with infection and inflammation. In the present study, we found that cathepsin K (CTSK) also degraded osteoprotegerin in an acidic milieu and the buffer with a pH of 7.4. The 37 k fragment of osteoprotegerin produced by the reaction with CTSK was further degraded into low molecular weight fragments, including a 13 k fragment, depending on the reaction time. The N-terminal amino acid sequence of the 37 k fragment matched that of the intact osteoprotegerin, indicating that CTSK preferentially hydrolyzes the death domain-like region of osteoprotegerin, not its RANKL-binding region. The 13 k fragment of osteoprotegerin was the C-terminal 13 k portion within the RANKL-binding region of the 37 k fragment. Finally, CTSK restored RANKL-dependent osteoclast differentiation that was suppressed by the addition of osteoprotegerin. Collectively, CTSK is a possible positive regulator of osteoclastogenesis.

Runx2 and Runx3 differentially regulate articular chondrocytes during surgically induced osteoarthritis development.

The Runt-related transcription factor (Runx) family plays various roles in the homeostasis of cartilage. Here, we examined the role of Runx2 and Runx3 for osteoarthritis development in vivo and in vitro. Runx3-knockout mice exhibited accelerated osteoarthritis following surgical induction, accompanied by decreased expression of lubricin and aggrecan. Meanwhile, Runx2 conditional knockout mice showed biphasic phenotypes: heterozygous knockout inhibited osteoarthritis and decreased matrix metallopeptidase 13 (Mmp13) expression, while homozygous knockout of Runx2 accelerated osteoarthritis and reduced type II collagen (Col2a1) expression. Comprehensive transcriptional analyses revealed lubricin and aggrecan as transcriptional target genes of Runx3, and indicated that Runx2 sustained Col2a1 expression through an intron 6 enhancer when Sox9 was decreased. Intra-articular administration of Runx3 adenovirus ameliorated development of surgically induced osteoarthritis. Runx3 protects adult articular cartilage through extracellular matrix protein production under normal conditions, while Runx2 exerts both catabolic and anabolic effects under the inflammatory condition.

RSPO2 defines a distinct undifferentiated progenitor in the tendon/ligament and suppresses ectopic ossification.

Ectopic endochondral ossification in the tendon/ligament is caused by repetitive mechanical overload or inflammation. Tendon stem/progenitor cells (TSPCs) contribute to tissue repair, and some express lubricin [proteoglycan 4 (PRG4)]. However, the mechanisms of ectopic ossification and association of TSPCs are not yet known. Here, we investigated the characteristics of Prg4-positive (+) cells and identified that R-spondin 2 (RSPO2), a WNT activator, is specifically expressed in a distinct Prg4+ TSPC cluster. The Rspo2+ cluster was characterized as mostly undifferentiated, and RSPO2 overexpression suppressed ectopic ossification in a mouse Achilles tendon puncture model via chondrogenic differentiation suppression. RSPO2 expression levels in patients with ossification of the posterior longitudinal ligament were lower than those in spondylosis patients, and RSPO2 protein suppressed chondrogenic differentiation of human ligament cells. RSPO2 was induced by inflammatory stimulation and mechanical loading via nuclear factor κB. Rspo2+ cells may contribute to tendon/ligament homeostasis under pathogenic conditions.

Effects of conditioned medium obtained from human adipose-derived stem cells on skin inflammation.

Introduction: Cell therapy using adipose-derived mesenchymal stem cells (ASCs) is a promising avenue of regenerative medicine for the treatment of various diseases. It has been considered that ASCs exert their therapeutic effects through the secretion of multiple factors that are critical for tissue remodeling or the suppression of inflammation. Recently, conditioned medium (CM) from ASCs that contains a complex of secreted factors has received attention as a cost-effective alternative to cell therapy. Methods: We investigated the effects of CM obtained from ASCs (ASCs-CM) using human dermal fibroblasts (hDFs) and human epidermal keratinocytes with or without interleukin (IL)-1ß and examined mRNA levels of marker genes. We also examined alterations in cell proliferation and morphology of hDFs following treatment with ASCs-CM. We further investigated the effects of ASCs-CM treatment on prevention of skin inflammation using a mouse model. Results: In hDFs and human epidermal keratinocytes, the ASCs-CM treatment suppressed pro-inflammatory factors and enhanced regenerative and remodeling factors with or without interleukin (IL)-1ß exposure. The ASCs-CM treatment also enhanced cell proliferation of hDFs and prevented morphological changes in response to IL-1ß exposure. Furthermore, in a mouse model of skin inflammation, treatment with ASCs-CM reduced the inflammatory reactions, including redness and thickness. Conclusions: CM from ASCs may represent a potential alternative to ASC therapy for the treatment of inflammatory skin conditions.

Extracellular acidification augments sclerostin and osteoprotegerin production by Ocy454 mouse osteocytes.

Osteocytes sense the microenvironmental stimuli, including mechanical stress, and regulate bone resorption by osteoclasts and bone formation by osteoblasts. Diabetes and cancer metastasis to bone raise l-lactic acid in the bone tissue, causing acidification. Here, we investigated the effects of l-lactic acid and extracellular acidification on the function of mouse Ocy454 osteocytes. L- and d-lactic acid with low chiral selectivity and acidification of the medium raised the production of sclerostin and osteoprotegerin by Ocy454 cells. The mRNA expression of their genes increased after either treatment of L- and d-lactic acid or acidification of the medium. Furthermore, the conditioned medium of Ocy454 cells cultured in an acidic environment suppressed the induction of alkaline phosphatase activity in MC3T3-E1 cells, which was recovered by the anti-sclerostin antibody. While it is reported that HDAC5 inhibits the transcription of the sclerostin gene, extracellular acidification reduced the nuclear localization of HDAC5 in Ocy454 cells. While calmodulin kinase II (CaMKII) is known to phosphorylate and induce extranuclear translocation of HDAC5, KN-62, an inhibitor of CaMKII lowered the expression of the sclerostin gene in Ocy454 cells. Collectively, extracellular acidification is a microenvironmental factor that modulates osteocyte functions.

Regulation of osteoarthritis development by ADAM17/Tace in articular cartilage.

INTRODUCTION: A disintegrin and metalloproteinase 17 (Adam17), also known as TNFα-converting enzyme (Tace), is a membrane-anchored protein involved in shedding of TNF, IL-6 receptor, ligands of epidermal growth factor receptor (EGFR), and Notch receptor. This study aimed to examine the role of Adam17 in adult articular cartilage and osteoarthritis (OA) pathophysiology. MATERIALS AND METHODS: Adam17 expression was examined in mouse knee joints during OA development. We analyzed OA development in tamoxifen-inducible chondrocyte-specific Adam17 knockout mice of a resection of the medial meniscus and medial collateral ligament (medial) model, destabilization of the medial meniscus (DMM) model, and aging model. We analyzed downstream pathways by in vitro experiments, and further performed intra-articular administration of an Adam17 inhibitor TAPI-0 for surgically induced mouse OA. RESULTS: Adam17 expression in mouse articular cartilage was increased by OA progression. In all models, Adam17 knockout mice showed ameliorated progression of articular cartilage degradation. Adam17 knockout decreased matrix metallopeptidase 13 (Mmp13) expression in both in vivo and in vitro experiments, whereas Adam17 activation by phorbol-12-myristate-13-acetate (PMA) increased Mmp13 and decreased aggrecan in mouse primary chondrocytes. Adam17 activation enhanced release of soluble TNF and transforming growth factor alpha, a representative EGF ligand, from mouse primary chondrocytes, while it did not change release of soluble IL-6 receptor or nuclear translocation of Notch1 intercellular domain. Intra-articular administration of the Adam17 inhibitor ameliorated OA progression. CONCLUSIONS: This study demonstrates regulation of OA development by Adam17, involvement of EGFR and TNF pathways, and the possibility of Adam17 as a therapeutic target for OA.

Involvement of Transient Receptor Potential Vanilloid Channel 2 in the Induction of Lubricin and Suppression of Ectopic Endochondral Ossification in Mouse Articular Cartilage.

OBJECTIVE: Transient receptor potential vanilloid channel 2 (TRPV2) is a Ca2+ -permeable channel and plays a role in mediating intracellular Ca2+ current via mechanical stimuli. This study was undertaken to examine the expression and role of TRPV2 in adult articular cartilage and the development of osteoarthritis (OA). METHODS: We examined TRPV2 expression in mouse and human articular cartilage. We analyzed the development of OA in Col2a1-CreERt2 ;Trpv2fl/fl mice and Trpv2fl/fl littermates in the resection of the medial meniscus and medial collateral ligament model (n = 5 each), the destabilization of the medial meniscus model (n = 5 each), and the aging mouse model (n = 8-9 each). We examined marker protein expression in these joints, Ca2+ influx by mechanical stimuli, and downstream pathways in vitro. RESULTS: TRPV2 was expressed in mouse and human articular cartilage and ectopic ossification lesions. In all mouse models of OA examined, Col2a1-CreERt2 ;Trpv2fl/fl mice were observed to have enhanced degradation of articular cartilage accompanied by decreased expression of lubricin/Prg4, and marked formation of periarticular ectopic ossification. Mechanical stress-induced Ca2+ influx was decreased by Trpv2 knockout (KO). Prg4 induction by fluid-flow shear stress was diminished in Trpv2-KO mouse chondrocytes, and this was mediated by the Ca2+ /calmodulin-dependent protein kinase kinase-cyclic AMP response element binding protein axis. Hypertrophic differentiation was enhanced in Trpv2-KO mouse chondrocytes. Increased activity of calcineurin and nuclear translocation of nuclear factor in activated T cells 1 induced by fluid-flow shear stress or TRP agonist treatment was reversed by Trpv2 knockout. CONCLUSION: Our findings demonstrate regulation of articular cartilage by TRPV2 through Prg4 induction and suppression of ectopic ossification.

Lubricin Contributes to Homeostasis of Articular Cartilage by Modulating Differentiation of Superficial Zone Cells.

Lubricin encoded by the proteoglycan 4 (Prg4) gene is produced from superficial zone (SFZ) cells of articular cartilage and synoviocytes, which is indispensable for lubrication of joint surfaces. Loss-of-function of human and mouse Prg4 results in early-onset arthropathy accompanied by lost SFZ cells and hyperplastic synovium. Here, we focused on increases in the thickness of articular cartilage in Prg4-knockout joints and analyzed the underlying mechanisms. In the late stage of articular cartilage development, the articular cartilage was thickened at 2 to 4 weeks and the SFZ disappeared at 8 weeks in Prg4-knockout mice. Similar changes were observed in cultured Prg4-knockout femoral heads. Cell tracking showed that Prg4-knockout SFZ cells at 1 week of age expanded to deep layers after 1 week. In in vitro experiments, overexpression of Prg4 lacking a mucin-like domain suppressed differentiation of ATDC5 cells markedly, whereas pellets of Prg4-knockout SFZ cells showed enhanced differentiation. RNA sequencing identified matrix metalloproteinase 9 (Mmp9) as the top upregulated gene by Prg4 knockout. Mmp9 expressed in the SFZ was further induced in Prg4-knockout mice. The increased expression of Mmp9 by Prg4 knockout was canceled by IκB kinase (IKK) inhibitor treatment. Phosphorylation of Smad2 was also enhanced in Prg4-knockout cell pellets, which was canceled by the IKK inhibitor. Expression of Mmp9 and phosphorylated Smad2 during articular cartilage development was enhanced in Prg4-knockout joints. Lubricin contributes to homeostasis of articular cartilage by suppressing differentiation of SFZ cells, and the nuclear factor-kappa B-Mmp9-TGF-ß pathway is probably responsible for the downstream action of lubricin. © 2020 American Society for Bone and Mineral Research (ASBMR).

Ear Cartilage Reconstruction Combining Induced Pluripotent Stem Cell-Derived Cartilage and Three-Dimensional Shape-Memory Scaffold.

Microtia is a congenital malformation of the auricle. The conventional therapy for microtia is reconstruction of the auricle by using the patient's own costal cartilage. Because it is invasive to harvest costal cartilages, less invasive ways for auricular reconstruction need to be established. Recent reports have indicated a new method for the production of cartilaginous particles from human induced pluripotent stem cells. To adopt this method to create an auricular-shaped regenerative cartilage, a novel scaffold with the property of a three-dimensional shape memory was created. A scaffold with a three-dimensional shape of auricular frames composed of a helix and an antihelix, which was designed to mimic an auricular framework carved from autologous costal cartilage and transplanted in auricular reconstruction, was prepared, filled with cartilaginous particles, and subcutaneously transplanted in nude rats. The auricular-shaped regenerative cartilage maintained the given shape and cartilage features in vivo for 1 year. Our findings suggest a novel approach for auricular reconstruction.

Evidence that TD-198946 enhances the chondrogenic potential of human synovium-derived stem cells through the NOTCH3 signaling pathway.

Human synovium-derived stem cells (hSSCs) are an attractive source of cells for cartilage repair. At present, the quality of tissue and techniques used for cartilage regeneration have scope for improvement. A small compound, TD-198946, was reported to enhance chondrogenic induction from hSSCs; however, other applications of TD-198946, such as priming the cell potential of hSSCs, remain unknown. Our study aimed to examine the effect of TD-198946 pretreatment on hSSCs. HSSCs were cultured with or without TD-198946 for 7 days during expansion culture and then converted into a three-dimensional pellet culture supplemented with bone morphogenetic protein-2 (BMP2) and/or transforming growth factor beta-3 (TGFß3). Chondrogenesis in cultures was assessed based on the GAG content, histology, and expression levels of chondrogenic marker genes. Cell pellets derived from TD-198946-pretreated hSSCs showed enhanced chondrogenic potential when chondrogenesis was induced by both BMP2 and TGFß3. Moreover, cartilaginous tissue was efficiently generated from TD-198946-pretreated hSSCs using a combination of BMP2 and TGFß3. Microarray analysis revealed that NOTCH pathway-related genes and their target genes were significantly upregulated in TD-198946-treated hSSCs, although TD-198946 alone did not upregulate chondrogenesis related markers. The administration of the NOTCH signal inhibitor diminished the effect of TD-198946. Thus, TD-198946 enhances the chondrogenic potential of hSSCs via the NOTCH3 signaling pathway. This study is the first to demonstrate the gradual activation of NOTCH3 signaling during chondrogenesis in hSSCs. The priming of NOTCH3 using TD-198946 provides a novel insight regarding the regulation of the differentiation of hSSCs into chondrocytes.

The small compound, TD-198946, protects against intervertebral degeneration by enhancing glycosaminoglycan synthesis in nucleus pulposus cells.

Degeneration of the nucleus pulposus (NP) might serve as a trigger for intervertebral disc degeneration (IDD). A recent drug screening study revealed that the thienoindazole derivative, TD-198946, is a novel drug for the treatment of osteoarthritis. Because of the environmental and functional similarities between articular cartilage and intervertebral disc, TD-198946 is expected to prevent IDD. Herein, we sought to evaluate the effects of TD-198946 on IDD. TD-198946 enhanced glycosaminoglycan (GAG) production and the related genes in mouse NP cells and human NP cells (hNPCs). Further, Kyoto Encyclopedia of Genes and Genomes pathway analysis using the mRNA sequence of hNPCs suggested that the mechanism of action of TD-198946 primarily occurred via the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway. The Akt inhibitor suppressed the enhancement of GAG production induced by TD-198946. The effects of TD-198946 on IDD at two different time points (immediate treatment model, immediately after the puncture; latent treatment model, 2 weeks after the puncture) were investigated using a mouse tail-disc puncture model. At both time points, TD-198946 prevented a loss in disc height. Histological analysis also demonstrated the preservation of the NP structures. TD-198946 exhibited therapeutic effects on IDD by enhancing GAG production via PI3K/Akt signaling.

Associations of clinical outcomes and MRI findings in intra-articular administration of autologous adipose-derived stem cells for knee osteoarthritis.

INTRODUCTION: Clinical studies of intra-articular injection of mesenchymal stem cells for osteoarthritis (OA) indicate its efficacy. Here, we retrospectively investigated the associations of pretherapeutic magnetic resonance imaging (MRI) findings with the clinical outcomes up to 6 months, after intra-articular administration of adipose-derived stem cells (ASCs) to knee OA patients. METHODS: We first analyzed alterations of the visual analog scale (VAS) and knee injury and osteoarthritis outcome score (KOOS) in 57 knees of 34 patients from whom clinical scores were obtained before ASC therapy, and at 1, 3, and 6 months. Among the patients, we further examined MRI findings of 34 knees of 19 patients whose pretherapeutic MRI data were available. RESULTS: The mean improvement of VAS and KOOS-total during 6 months was 2.6 ± 4.0 (from 6.1 ± 2.5 to 3.5 ± 2.9, P < 0.001) and 10.2 ± 12.4 (from 54.4 ± 12.7 to 64.6 ± 13.8, P < 0.01), respectively. Scales related to pain and symptoms improved earlier than those related to activities of daily living (ADL) and sports/recreation. Improvement of VAS and KOOS-sports/recreation was significantly higher in patients with more severe cartilage lesions. Similarly, osteophyte lesions were associated significantly with improvement of VAS and KOOS-ADL, and BML was associated with KOOS-ADL and KOOS-sports/recreation. CONCLUSIONS: In intra-articular administration of autologous ASCs for knee OA, improvement of VAS and KOOS-sports/recreation was significantly higher in patients with more severe cartilage lesions. Similarly, osteophyte lesions were associated significantly with improvement of VAS and KOOS-ADL, and BML was associated with KOOS-ADL and KOOS-sports/recreation. Clinical studies with larger numbers of patients and various kinds of data are necessary to predict therapeutic effects.

Hypoxia-inducible factor-1 alpha maintains mouse articular cartilage through suppression of NF-κB signaling.

HIF-1α, an essential transcription factor under hypoxic condition, is indispensable for chondrocytes during skeletal development but its expression and roles in articular chondrocytes are yet to be revealed. We examined HIF-1α protein expression and the hypoxic condition during mouse osteoarthritis (OA) development using state of the art hypoxic probes and found that its expression decreased as OA progressed, coinciding with the change in hypoxic conditions in articular cartilage. Gain- and loss-of-function of HIF-1α in cell culture experiments showed that HIF-1α suppressed catabolic genes such as Mmp13 and Hif2a. We confirmed these anticatabolic effects by measuring glycosaminoglycan release from wild type and conditional knock-out mice femoral heads cultured ex vivo. We went on to surgically induce OA in mice with chondrocyte-specific deletion of Hif1a and found that the development of OA was exacerbated. Increased expression of catabolic factors and activation of NF-κB signalling was clearly evident in the knock-out mice. By microarray analysis, C1qtnf3 was identified as a downstream molecule of HIF-1α, and experiments showed it exerted anti-catabolic effects through suppression of NF-κB. We conclude that HIF-1α has an anti-catabolic function in the maintenance of articular cartilage through suppression of NF-κB signalling.

Enhancement of chondrogenic differentiation supplemented by a novel small compound for chondrocyte-based tissue engineering.

PURPOSE: Chondrocyte -based tissue engineering has been a promising option for the treatment of cartilage lesions. In previous literature, TD198946 has been shown to promote chondrogenic differentiation which could prove useful in cartilage regeneration therapies. Our study aimed to investigate the effects of TD198946 in generating engineered cartilage using dedifferentiated chondrocyte-seeded collagen scaffolds treated with TD198946. METHODS: Articular chondrocytes were isolated from mini pig knees and expanded in 2-dimensional cell culture and subsequently used in the experiments. 3-D pellets were then cultured for two weeks. Cells were also cultured in a type I collagen scaffolds for four weeks. Specimens were cultured with TD198946, BMP-2, or both in combination. Outcomes were determined by gene expression levels of RUNX1, SOX9, ACAN, COL1A1, COL2A1 and COL10A1, the glycosaminoglycan content, and characteristics of histology and immunohistochemistry. Furthermore, the maturity of the engineered cartilage cultured for two weeks was evaluated through subcutaneous implantation in nude mice for four weeks. RESULTS: Addition of TD198946 demonstrated the upregulation of gene expression level except for ACAN, type II collagen and glycosaminoglycan synthesis in both pellet and 3D scaffold cultures. TD198946 and BMP-2 combination cultures showed higher chondrogenic differentiation than TD198946 or BMP-2 alone. The engineered cartilage maintained its extracellular matrices for four weeks post implantation. In contrast, engineered cartilage treated with either TD198946 or BMP-2 alone was mostly absorbed. CONCLUSIONS: Our results indicate that TD198946 could improve quality of engineered cartilage by redifferentiation of dedifferentiated chondrocytes pre-implantation and promoting collagen and glycosaminoglycan synthesis.

Primary culture of mouse adipose and fibrous synovial fibroblasts under normoxic and hypoxic conditions.

Synovial fibroblasts have attracted considerable attention in studies of joint diseases. Although mice are useful and powerful in in vitro and in vivo experiments, primary cultures of mouse synovial fibroblasts are notoriously difficult because the mouse synovial tissues are much smaller and cell cycle arrests can be induced more easily in murine cells than in human cells. Here, we report a precise protocol for the isolation and culture of fibroblasts from mouse adipose and fibrous knee joint synovia. In both adipose and fibrous synovial fibroblasts, proliferation was decreased in addition to a higher rate of cellular senescence under normoxic conditions (20% O2); however, it was maintained over 20 days with low cellular senescence under hypoxic conditions (3% O2). The marker gene expression in adipose and fibrous synovial fibroblasts was not markedly altered after a 3-week culture. Both cells displayed similar potencies for chondrogenic, osteogenic, and adipogenic differentiation, and responses to a proinflammatory cytokine. The present method provides a sufficient amount of mouse synovial fibroblasts for in vitro and in vivo experiments in joint biology and the pathophysiology of osteoarthritis and rheumatoid arthritis.

Wnt/ß-catenin signaling contributes to articular cartilage homeostasis through lubricin induction in the superficial zone.

BACKGROUND: Both loss- and gain-of-function of Wnt/ß-catenin signaling in chondrocytes result in exacerbation of osteoarthritis (OA). Here, we examined the activity and roles of Wnt/ß-catenin signaling in the superficial zone (SFZ) of articular cartilage. METHODS: Wnt/ß-catenin signaling activity was analyzed using TOPGAL mice. We generated Prg4-CreERT2;Ctnnb1fl/fl and Prg4-CreERT2;Ctnnb1-ex3fl/wt mice for loss- and gain-of-function, respectively, of Wnt/ß-catenin signaling in the SFZ. Regulation of Prg4 expression by Wnt/ß-catenin signaling was examined in vitro, as were upstream and downstream factors of Wnt/ß-catenin signaling in SFZ cells. RESULTS: Wnt/ß-catenin signaling activity, as determined by the TOPGAL reporter, was high specifically in the SFZ of mouse adult articular cartilage, where Prg4 is abundantly expressed. In SFZ-specific ß-catenin-knockout mice, OA development was significantly accelerated, which was accompanied by decreased Prg4 expression and SFZ destruction. In contrast, Prg4 expression was enhanced and cartilage degeneration was suppressed in SFZ-specific ß-catenin-stabilized mice. In primary SFZ cells, Prg4 expression was downregulated by ß-catenin knockout, while it was upregulated by ß-catenin stabilization by exon 3 deletion or treatment with CHIR99021. Among Wnt ligands, Wnt5a, Wnt5b, and Wnt9a were highly expressed in SFZ cells, and recombinant human WNT5A and WNT5B stimulated Prg4 expression. Mechanical loading upregulated expression of these ligands and further promoted Prg4 transcription. Moreover, mechanical loading and Wnt/ß-catenin signaling activation increased mRNA levels of Creb1, a potent transcription factor for Prg4. CONCLUSIONS: We demonstrated that Wnt/ß-catenin signaling regulates Prg4 expression in the SFZ of mouse adult articular cartilage, which plays essential roles in the homeostasis of articular cartilage.

Correction to: Adamts17 is involved in skeletogenesis through modulation of BMP­Smad1/5/8 pathway.

In the published article, the Fig. 4a was published incorrectly.

Simple and Robust Differentiation of Human Pluripotent Stem Cells toward Chondrocytes by Two Small-Molecule Compounds.

A simple induction protocol to differentiate chondrocytes from pluripotent stem cells (PSCs) using small-molecule compounds is beneficial for cartilage regenerative medicine and mechanistic studies of chondrogenesis. Here, we demonstrate that chondrocytes are robustly induced from human PSCs by simple combination of two compounds, CHIR99021, a glycogen synthase kinase 3 inhibitor, and TTNPB, a retinoic acid receptor (RAR) agonist, under serum- and feeder-free conditions within 5-9 days. An excellent differentiation efficiency and potential to form hyaline cartilaginous tissues in vivo were demonstrated. Comprehensive gene expression and open chromatin analyses at each protocol stage revealed step-by-step differentiation toward chondrocytes. Genome-wide analysis of RAR and ß-catenin association with DNA showed that retinoic acid and Wnt/ß-catenin signaling collaboratively regulated the key marker genes at each differentiation stage. This method provides a promising cell source for regenerative medicine and, as an in vitro model, may facilitate elucidation of the molecular mechanisms underlying chondrocyte differentiation.

Adamts17 is involved in skeletogenesis through modulation of BMP-Smad1/5/8 pathway.

Fibrillin microfibrils are ubiquitous elements of extracellular matrix assemblies that play crucial roles in regulating the bioavailability of growth factors of the transforming growth factor beta superfamily. Recently, several "a disintegrin and metalloproteinase with thrombospondin motifs" (ADAMTS) proteins were shown to regulate fibrillin microfibril function. Among them, ADAMTS17 is the causative gene of Weill-Marchesani syndrome (WMS) and Weill-Marchesani-like syndrome, of which common symptoms are ectopia lentis and short stature. ADAMTS17 has also been linked to height variation in humans; however, the molecular mechanisms whereby ADAMTS17 regulates skeletal growth remain unknown. Here, we generated Adamts17-/- mice to examine the role of Adamts17 in skeletogenesis. Adamts17-/- mice recapitulated WMS, showing shorter long bones, brachydactyly, and thick skin. The hypertrophic zone of the growth plate in Adamts17-/- mice was shortened, with enhanced fibrillin-2 deposition, suggesting increased incorporation of fibrillin-2 into microfibrils. Comprehensive gene expression analysis of growth plates using laser microdissection and RNA sequencing indicated alteration of the bone morphogenetic protein (BMP) signaling pathway after Adamts17 knockout. Consistent with this, phospho-Smad1 levels were downregulated in the hypertrophic zone of the growth plate and in Adamts17-/- primary chondrocytes. Delayed terminal differentiation of Adamts17-/- chondrocytes, observed both in primary chondrocyte and primordial metatarsal cultures, and was prevented by BMP treatment. Our data indicated that Adamts17 is involved in skeletal formation by modulating BMP-Smad1/5/8 pathway, possibly through inhibiting the incorporation of fibrillin-2 into microfibrils. Our findings will contribute to further understanding of disease mechanisms and will facilitate the development of therapeutic interventions for WMS.