SOX9 protein is stabilized by TGF-β and regulates PAPSS2 mRNA expression in chondrocytes

The Role of Exerkines in the Treatment of Knee Osteoarthritis: From Mechanisms to Exercise Strategies

With the increasing prevalence of knee osteoarthritis (KOA), the limitations of traditional treatments, such as their limited efficacy in halting disease progression and their potential side effects, are becoming more evident. This situation has prompted scientists to seek more effective strategies. In recent years, exercise therapy has gained prominence in KOA treatment due to its safety, efficacy, and cost-effectiveness, which are underpinned by the molecular actions of exerkines. Unlike conventional therapies, exerkines offer specific advantages by targeting inflammatory responses, enhancing chondrocyte proliferation, and slowing cartilage degradation at the molecular level. This review explores the potential mechanisms involved in and application prospects of exerkines in KOA treatment and provides a comprehensive analysis of their role. Studies show that appropriate exercise not only promotes overall health, but also positively impacts KOA by stimulating exerkine production. The effectiveness of exerkines, however, is influenced by exercise modality, intensity, and duration of exercise, making the development of personalized exercise plans crucial for KOA patients. Based on these insights, this paper proposes targeted exercise strategies designed to maximize exerkine benefits, aiming to provide novel perspectives for KOA prevention and treatment.

Prg4 and Osteoarthritis: Functions, Regulatory Factors, and Treatment Strategies

Proteoglycan 4 (PRG4), also known as lubricin, plays a critical role in maintaining joint homeostasis by reducing friction between articular cartilage surfaces and preventing cartilage degradation. Its deficiency leads to early-onset osteoarthritis (OA), while overexpression can protect against cartilage degeneration. Beyond its lubricating properties, PRG4 exerts anti-inflammatory effects by interacting with Toll-like receptors, modulating inflammatory responses within the joint. The expression of Prg4 is regulated by various factors, including mechanical stimuli, inflammatory cytokines, transcription factors such as Creb5 and FoxO, and signaling pathways like TGF-β, EGFR, and Wnt/β-catenin. Therapeutic strategies targeting PRG4 in OA have shown promising results, including recombinant PRG4 protein injections, gene therapies, and small molecules that enhance endogenous Prg4 expression or mimic its function. Further research into the molecular mechanisms regulating Prg4 expression will be essential in developing more effective OA treatments. Understanding the interplay between Prg4 and other signaling pathways could reveal novel therapeutic targets. Additionally, advancements in gene therapy and biomaterials designed to deliver PRG4 in a controlled manner may hold potential for the long-term management of OA, improving patient outcomes and delaying disease progression.

Duhuo Jisheng Decoction in reduction of inflammatory response via Transforming growth factor-β/Smad signaling pathway for repairing rabbit articular cartilage Injury: A Randomized Controlled Trial

OBJECTIVE

This study aims to investigate the mechanism underlying the effect of Duhuo Jisheng Decoction on the repair of rabbit articular cartilage injury through a reduction in the inflammatory response mediated by the Transforming growth factor (TGF)-β/Smad signaling pathway.

METHODS

A rabbit articular cartilage injury model was constructed using a ring bone extraction drill. Twenty-four Japanese white rabbits were randomly divided into six groups, namely Sham operation, model, low-dose Duhuo Jisheng Decoction, medium-dose Duhuo Jisheng Decoction, high-dose Duhuo Jisheng Decoction, and positive control groups. The treatment lasted 12 weeks. Gross observation, International Cartilage Repair Society score, Wakitani score, and Micro-computed tomography analysis were used to evaluate the structural repair of cartilage injury. Histology and immunohistochemistry were used to observe the proteoglycan, P-TβRII, P-Smad2, and type II collagen expression levels. Enzyme-linked immunosorbent assay was used to analyze the concentrations of Matrix Metalloproteinase-13 and Syndecan-4 in the joint fluid; and RT-PCR and Western Blot were used to observe the mRNA and protein expressions of ALK5, Sox-9, P-Smad3, and TGF-β1 at the injury repair site.

RESULTS

The repair effect of cartilage injury, as seen through gross observation and quantitative scoring, was better in all the Duhuo Jisheng Decoction treatment groups than in the model group. The medium dose group of Duhuo Jisheng Decoction had the best repair effect. We observed remarkable structural restoration of cartilage injury in the medium-dose Duhuo Jisheng Decoction group, with the subchondral bone presenting a distinct hierarchy, and parameters such as bone volume fraction and trabecular separation/spacing being significantly augmented. We found high expression levels of proteoglycans, P-TβRII, P-Smad2, and type II collagen. The concentrations of Matrix Metalloproteinase-13 and Syndecan-4 in the joint fluid were significantly lower following treatment. The low gene expression levels of ALK5, Sox-9, P-Smad3, and TGF-β1 in the injury site of the model group could be reversed in the medium-dose Duhuo Jisheng Decoction group.

CONCLUSION

Duhuo Jisheng Decoction can repair rabbit cartilage injury and reverse the levels of inflammatory factors in the joint fluid. The mechanism underlying its therapeutic effect is related to the activation of the TGF-β/Smad signaling pathway. This study provides a reliable basis for using Duhuo Jisheng Decoction to treat cartilage injury following knee osteoarthritis.

Sericin promotes chondrogenic proliferation and differentiation via glycolysis and Smad2/3 TGF-β signaling inductions and alleviates inflammation in three-dimensional models

Knee osteoarthritis is a chronic joint disease mainly characterized by cartilage degeneration. The treatment is challenging due to the lack of blood vessels and nerve supplies in cartilaginous tissue, causing a prominent limitation of regenerative capacity. Hence, we investigated the cellular promotional and anti-inflammatory effects of sericin, Bombyx mori-derived protein, on three-dimensional chondrogenic ATDC5 cell models. The results revealed that a high concentration of sericin promoted chondrogenic proliferation and differentiation and enhanced matrix production through the increment of glycosaminoglycans, COL2A1, COL X, and ALP expressions. SOX-9 and COL2A1 gene expressions were notably elevated in sericin treatment. The proteomic analysis demonstrated the upregulation of phosphoglycerate mutase 1 and triosephosphate isomerase, a glycolytic enzyme member, reflecting the proliferative enhancement of sericin. The differentiation capacity of sericin was indicated by the increased expressions of procollagen12a1, collagen10a1, rab1A, periostin, galectin-1, and collagen6a3 proteins. Sericin influenced the differentiation capacity via the TGF-β signaling pathway by upregulating Smad2 and Smad3 while downregulating Smad1, BMP2, and BMP4. Importantly, sericin exhibited an anti-inflammatory effect by reducing IL-1β, TNF-α, and MMP-1 expressions and accelerating COL2A1 production in the early inflammatory stage. In conclusion, sericin demonstrates potential in promoting chondrogenic proliferation and differentiation, enhancing cartilaginous matrix synthesis through glycolysis and TGF-β signaling pathways, and exhibiting anti-inflammatory properties.

Downregulation of extracellular matrix protein 1 effectively ameliorates osteoarthritis progression in vivo

Osteoarthritis (OA) is the most common joint disease whose important pathological feature is degeneration of articular cartilage. Although extracellular matrix protein 1 (ECM1) serves as a central regulator of chondrocyte proliferation and hypertrophy, its role in OA remains largely unknown. This study aims to decipher the roles of ECM1 in OA development and therapy in animal models. In the present study, ECM1 expression was examined in clinical OA samples, experimental OA mice and OA cell models. Mice subjected to destabilised medial meniscus (DMM) surgery were intra-articularly injected with adeno-associated virus (AAV) expressing ECM1 (AAV-ECM1) or AAV containing shECM1 (AAV-shECM1). Histological analysis was performed to determine cartilage damage. mRNA sequencing was performed to explore the molecular mechanism. In addition, the downstream signaling was further confirmed by using specific inhibitors. Our data showed that ECM1 was upregulated in the cartilage of patients with OA, OA mice as well as OA cell models. Moreover, ECM1 over-expressing in knee joints by AAV-ECM1 accelerated OA progression, while knockdown of ECM1 by AAV-shECM1 alleviated OA development. Mechanistically, cartilage destruction increased ECM1 expression, which consequently exacerbated OA progression partly by decreasing PRG4 expression in the TGF-β/PKA/CREB-dependent manner. In conclusion, our study revealed the important role of ECM1 in OA progression. Targeted ECM1 inhibition is a potential strategy for OA therapy.

Three-dimensional hydrogel with human Wharton jelly-derived mesenchymal stem cells towards nucleus pulposus niche

Introduction: A regenerative strategy employing extracellular matrix (ECM)-based biomaterials and stem cells provide a better approach to mimicking the three-dimensional (3D) microenvironment of intervertebral disc for endogenous tissue regeneration. However, there is currently limited understanding regarding the human Wharton Jelly derived-mesenchymal stem cells (hWJ-MSCs) towards nucleus pulposus (NP)-like cells. Our study focused on the development of 3D bioengineered hydrogel based on the predominant ECM of native NP, including type II collagen (COLII) and hyaluronic acid (HA), which aims to tailor the needs of the microenvironment in NP. Methods: We have fabricated a 3D hydrogel using from COLII enriched with HA by varying the biomacromolecule concentration and characterised it for degradation, stability and swelling properties. The WJ-MSC was then encapsulated in the hydrogel system to guide the cell differentiation into NP-like cells. Results: We successfully fabricated COLII hydrogel (2 mg/ml) and HA 10 mg/ml at a weight ratio of HA and COLII at 1:9 and 4.5:9, and both hydrogels physically maintained their 3D sphere-shaped structure after complete gelation. The higher composition of HA in the hydrogel system indicated a higher water intake capacity in the hydrogel with a higher amount of HA. All hydrogels showed over 60% hydrolytic stability over a month. The hydrogel showed an increase in degradation on day 14. The hWJ-MSCs encapsulated in hydrogel showed a round morphology shape that was homogenously distributed within the hydrogel of both groups. The viability study indicated a higher cell growth of hWJ-MSCs encapsulated in all hydrogel groups until day 14. Discussion: Overall, our findings demonstrate that HA/COLII hydrogel provides an optimal swelling capacity, stability, degradability, and non-cytotoxic, thus mimics the NP microenvironment in guiding hWJ-MSCs towards NP phenotype, which is potentially used as an advanced cell delivery system for intervertebral disc regeneration.

The Role of SOX9 in IGF-II-Mediated Pulmonary Fibrosis

Pulmonary fibrosis (PF) associated with systemic sclerosis (SSc) results in significant morbidity and mortality. We previously reported that insulin-like growth factor-II (IGF-II) is overexpressed in lung tissues and fibroblasts from SSc patients, and IGF-II fosters fibrosis by upregulating collagen type I, fibronectin, and TGFβ. We now show that IGF-II augments mRNA levels of profibrotic signaling molecules TGFβ2 (p ≤ 0.01) and TGFβ3 (p ≤ 0.05), collagen type III (p ≤ 0.01), and the collagen posttranslational modification enzymes P4HA2 (p ≤ 0.05), P3H2 (p ≤ 0.05), LOX (p = 0.065), LOXL2 (p ≤ 0.05), LOXL4 (p ≤ 0.05) in primary human lung fibroblasts. IGF-II increases protein levels of TGFβ2 (p ≤ 0.01), as well as COL3A1, P4HA2, P4Hβ, and LOXL4 (p ≤ 0.05). In contrast, IGF-II decreases mRNA levels of the collagen degradation enzymes cathepsin (CTS) K, CTSB, and CTSL and protein levels of CTSK (p ≤ 0.05). The SRY-box transcription factor 9 (SOX9) is overexpressed in SSc lung tissues at the mRNA (p ≤ 0.05) and protein (p ≤ 0.01) levels compared to healthy controls. IGF-II induces SOX9 in lung fibroblasts (p ≤ 0.05) via the IGF1R/IR hybrid receptor, and SOX9 regulates TGFβ2 (p ≤ 0.05), TGFβ3 (p ≤ 0.05), COL3A1 (p ≤ 0.01), and P4HA2 (p ≤ 0.001) downstream of IGF-II. Our results identify a novel IGF-II signaling axis and downstream targets that are regulated in a SOX9-dependent and -independent manner. Our findings provide novel insights on the role of IGF-II in promoting pulmonary fibrosis.

Synergistic prevention and reparative effects of sesquiterpene farnesol in a rabbit model of surgical resection-induced osteoarthritis

Articular cartilage may regenerate poorly after injury or during aging. In vitro, farnesol can modulate extracellular matrix synthesis and restore chondrocyte phenotypes by increasing type II collagen (COL II) and glycosaminoglycan (GAG) production. Here, we evaluated farnesol's preventive and reparative effects against osteoarthritis (OA) in vivo. We induced OA in rabbits through resection of the lateral collateral ligament and meniscus. After 2 weeks, the affected limb was treated with 0.5 ml of 0.4 mM farnesol, hyaluronan (HA) nanoparticle-encapsulated 0.8 mM farnesol (Farn/HA), or HA nanoparticles intra-articularly. After 2 and 6 treatment weeks, synovial inflammatory cytokine levels were analyzed. We also removed the entire joint cartilage from lateral femoral condyles for histological investigation. The half-maximum inhibitory concentration of farnesol was 0.5 mM. Farn/HA had relatively low cytotoxicity showing cells remained viable after being treated with 1 mM a concentration Farn/HA. Untreated lateral condyle exhibited extensive wear. By contrast, 0.4 mM farnesol or 0.8 mM Farn/HA led to a relatively transparent and bright appearance. After 2 and 6 treatment weeks, farnesol, particularly 0.8 mM Farn/HA, reduced matrix metalloproteinase 1 and 13 levels considerably. Therefore, 0.8 mM Farn/HA, which enabled slow drug release, demonstrated the highest anti-inflammatory and OA preventive effects. After 6 treatment weeks, farnesol also promoted COL II and GAG synthesis and, thus, aided healing.

Protein Tyrosine Kinase 7 (PTK7) Promotes Metastasis in Hepatocellular Carcinoma via SOX9 Regulation and TGF-β Signaling

BACKGROUND & AIMS

Metastasis is found in most advanced hepatocellular carcinoma (HCC) patients, and it drives tumor recurrence and systemic failure. There is no effective treatment owing to its complex biological features. Many of the molecular drivers of metastasis are crucial players in normal physiology but behave unconventionally during cancer progression. Targeting these molecular drivers for therapy and differentiating them from a physiological background require a detailed examination of the novel mechanisms involved in their activation during metastasis.

METHODS

Publicly available transcriptomic data such as that of TCGA-LIHC and Gene Expression Omnibus were utilized to identify novel targets upregulated in advanced and metastatic HCC. Validation of candidates was assisted by immunohistochemistry performed on tissue microarrays derived from more than 100 HCC patients. Expression of protein tyrosine kinase 7 (PTK7) was studied under the treatment of transforming growth factor-β1 and knockdown of SRY-Box Transcription Factor 9 (SOX9) to delineate upstream regulation, while CRISPR-mediated knockout and lentiviral overexpression of PTK7 in HCC cells were performed to study their functional and signaling consequences. Manipulated HCC cells were injected into mice models either by orthotopic or tail-vein injection to observe for any in vivo pro-metastatic effects.

RESULTS

PTK7 was discovered to be the kinase most significantly upregulated in advanced and metastatic HCC, at both transcriptomic and proteomic level. Bioinformatic analyses and functional assays performed in HCC cell lines revealed transforming growth factor-β signaling and SOX9 to be important activators of PTK7 expression. Functionally, enrichment of PTK7 expression could positively regulate metastatic potential of HCC cells in vitro and in lung metastasis models performed in immunodeficient mice. The up-regulation of PTK7 recruited the epithelial-mesenchymal transition components, zinc finger protein SNAI2 (SLUG) and zinc finger E-box-binding homeobox 1 (ZEB1).

CONCLUSIONS

Our study proposes PTK7 as a novel molecular driver in metastatic HCC, particularly in a transforming growth factor-β-activated microenvironment. The preferential expression of PTK7 resulted in a previously unobserved regulatory effect on the recruitment of epithelial-mesenchymal transition components, which established PTK7 as a potential determinant of specific epithelial-mesenchymal transition status. Therefore, our data support the continual development of PTK7-targeted agents as antimetastatic therapies.

Mast4 determines the cell fate of MSCs for bone and cartilage development

Mesenchymal stromal cells (MSCs) differentiation into different lineages is precisely controlled by signaling pathways. Given that protein kinases play a crucial role in signal transduction, here we show that Microtubule Associated Serine/Threonine Kinase Family Member 4 (Mast4) serves as an important mediator of TGF-β and Wnt signal transduction in regulating chondro-osteogenic differentiation of MSCs. Suppression of Mast4 by TGF-β1 led to increased Sox9 stability by blocking Mast4-induced Sox9 serine 494 phosphorylation and subsequent proteasomal degradation, ultimately enhancing chondrogenesis of MSCs. On the other hand, Mast4 protein, which stability was enhanced by Wnt-mediated inhibition of GSK-3β and subsequent Smurf1 recruitment, promoted β-catenin nuclear localization and Runx2 activity, increasing osteogenesis of MSCs. Consistently, Mast4-/- mice demonstrated excessive cartilage synthesis, while exhibiting osteoporotic phenotype. Interestingly, Mast4 depletion in MSCs facilitated cartilage formation and regeneration in vivo. Altogether, our findings uncover essential roles of Mast4 in determining the fate of MSC development into cartilage or bone.

Transcriptomic Profiling of Gene Expression Associated with Granulosa Cell Tumor Development in a Mouse Model

Ovarian granulosa cell tumors (GCTs) are rare sex cord-stromal tumors, accounting for ~5% ovarian tumors. The etiology of GCTs remains poorly defined. Genetically engineered mouse models are potentially valuable for understanding the pathogenesis of GCTs. Mice harboring constitutively active TGFβ signaling (TGFBR1-CA) develop ovarian GCTs that phenocopy several hormonal and molecular characteristics of human GCTs. To determine molecular alterations in the ovary upon TGFβ signaling activation, we performed transcriptomic profiling of gene expression associated with GCT development using ovaries from 1-month-old TGFBR1-CA mice and age-matched controls. RNA-sequencing and bioinformatics analysis coupled with the validation of select target genes revealed dysregulations of multiple cellular events and signaling molecules/pathways. The differentially expressed genes are enriched not only for known GCT-related pathways and tumorigenic events but also for signaling events potentially mediated by neuroactive ligand-receptor interaction, relaxin signaling, insulin signaling, and complements in TGFBR1-CA ovaries. Additionally, a comparative analysis of our data in mice with genes dysregulated in human GCTs or granulosa cells overexpressing a mutant FOXL2, the genetic hallmark of adult GCTs, identified some common genes altered in both conditions. In summary, this study has revealed the molecular signature of ovarian GCTs in a mouse model that harbors the constitutive activation of TGFBR1. The findings may be further exploited to understand the pathogenesis of a class of poorly defined ovarian tumors.

Regulatory Mechanisms of Prg4 and Gdf5 Expression in Articular Cartilage and Functions in Osteoarthritis

Owing to the rapid aging of society, the numbers of patients with joint disease continue to increase. Accordingly, a large number of patients require appropriate treatment for osteoarthritis (OA), the most frequent bone and joint disease. Thought to be caused by the degeneration and destruction of articular cartilage following persistent and excessive mechanical stimulation of the joints, OA can significantly impair patient quality of life with symptoms such as knee pain, lower limb muscle weakness, or difficulty walking. Because articular cartilage has a low self-repair ability and an extremely low proliferative capacity, healing of damaged articular cartilage has not been achieved to date. The current pharmaceutical treatment of OA is limited to the slight alleviation of symptoms (e.g., local injection of hyaluronic acid or non-steroidal anti-inflammatory drugs); hence, the development of effective drugs and regenerative therapies for OA is highly desirable. This review article summarizes findings indicating that proteoglycan 4 (Prg4)/lubricin, which is specifically expressed in the superficial zone of articular cartilage and synovium, functions in a protective manner against OA, and covers the transcriptional regulation of Prg4 in articular chondrocytes. We also focused on growth differentiation factor 5 (Gdf5), which is specifically expressed on the surface layer of articular cartilage, particularly in the developmental stage, describing its regulatory mechanisms and functions in joint formation and OA pathogenesis. Because several genetic studies in humans and mice indicate the involvement of these genes in the maintenance of articular cartilage homeostasis and the presentation of OA, molecular targeting of Prg4 and Gdf5 is expected to provide new insights into the aetiology, pathogenesis, and potential treatment of OA.

Dysregulated overexpression of Sox9 induces fibroblast activation in pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a fatal fibrotic lung disease associated with unremitting fibroblast activation including fibroblast-to-myofibroblast transformation (FMT), migration, resistance to apoptotic clearance, and excessive deposition of extracellular matrix (ECM) proteins in the distal lung parenchyma. Aberrant activation of lung-developmental pathways is associated with severe fibrotic lung disease; however, the mechanisms through which these pathways activate fibroblasts in IPF remain unclear. Sry-box transcription factor 9 (Sox9) is a member of the high-mobility group box family of DNA-binding transcription factors that are selectively expressed by epithelial cell progenitors to modulate branching morphogenesis during lung development. We demonstrate that Sox9 is upregulated via MAPK/PI3K-dependent signaling and by the transcription factor Wilms' tumor 1 in distal lung-resident fibroblasts in IPF. Mechanistically, using fibroblast activation assays, we demonstrate that Sox9 functions as a positive regulator of FMT, migration, survival, and ECM production. Importantly, our in vivo studies demonstrate that fibroblast-specific deletion of Sox9 is sufficient to attenuate collagen deposition and improve lung function during TGF-α-induced pulmonary fibrosis. Using a mouse model of bleomycin-induced pulmonary fibrosis, we show that myofibroblast-specific Sox9 overexpression augments fibroblast activation and pulmonary fibrosis. Thus, Sox9 functions as a profibrotic transcription factor in activating fibroblasts, illustrating the potential utility of targeting Sox9 in IPF treatment.

Baicalin promotes chondrocyte viability and the synthesis of extracellular matrix through TGF-β/Smad3 pathway in chondrocytes

BACKGROUND

Osteoarthritis (OA) is common in the elderly. Baicalin (BA) is a flavonoid monomer extracted from Scutellaria baicalensis Georgi, which has been reported to have anti-inflammatory, anti-deformation and anti-bacterial effects.

METHODS

Cultures of micromass and 3D alginate beads, Alcian blue and Safranin O (SO)/fast green staining were used to investigate chondrocyte viability and extracellular matrix (ECM) synthesis in chondrocytes of all groups. The expression of SOX9, Smad3, Aggrecan (ACAN), type II collagen (Col2α), matrix metallopetidase 9 (MMP9), MMP13 and ADAMTS5 in chondrocytes of all groups were detected by western blot or qRT-PCR.

RESULTS

The present study demonstrates that BA neutralized the IL-1β-induced downregulation of chondrocyte viability and ECM secretion, including ACAN and Col2α. The downregulation of SOX9, and the upregulation of MMP9, MMP13 and ADAMTS5 induced by IL-1β were reversed by BA treatment. Moreover, BA increased the nuclear translocation of Smad3 and SOX9 in chondrocytes cultured by micromass and 3D alginate beads. Interestingly, Smad3 inhibitor SIS3 reversed the promoting effect of BA on chondrocyte viability, ECM secretion, SOX9 and Smad3 nuclear translocation, and the inhibiting effect of BA on MMP9 and ADAMTS5 expressions. BA treatment also attenuated the decrease of Smad3 phosphorylation, SOX9 expression and the damage of cartilage integrity in mice which were induced by destabilization of the medial meniscus (DMM).

CONCLUSION

BA promotes chondrocyte viability and the cell matrix synthesis through TGF-β/Smad3 pathway in IL-1β-treated chondrocytes and DMM treated mice. BA is a potential therapeutic target for OA.

Molecular Mechanisms of Chondrocyte Proliferation and Differentiation

Cartilage is a kind of connective tissue that buffers pressure and is essential to protect joint movement. It is difficult to self-recover once cartilage is damaged due to the lack of blood vessels, lymph, and nerve tissues. Repair of cartilage injury is mainly achieved by stimulating chondrocyte proliferation and extracellular matrix (ECM) synthesis. Cartilage homeostasis involves the regulation of multiple growth factors and the transduction of cellular signals. It is a very complicated process that has not been elucidated in detail. In this review, we summarized a variety of signaling molecules related to chondrocytes function. Especially, we described the correlation between chondrocyte-specific regulatory factors and cell signaling molecules. It has potential significance for guiding the treatment of cartilage injury.

Proteoglycan 4 Modulates Osteogenic Smooth Muscle Cell Differentiation during Vascular Remodeling and Intimal Calcification

Calcification is a prominent feature of late-stage atherosclerosis, but the mechanisms driving this process are unclear. Using a biobank of carotid endarterectomies, we recently showed that Proteoglycan 4 (PRG4) is a key molecular signature of calcified plaques, expressed in smooth muscle cell (SMC) rich regions. Here, we aimed to unravel the PRG4 role in vascular remodeling and intimal calcification. PRG4 expression in human carotid endarterectomies correlated with calcification assessed by preoperative computed tomographies. PRG4 localized to SMCs in early intimal thickening, while in advanced lesions it was found in the extracellular matrix, surrounding macro-calcifications. In experimental models, Prg4 was upregulated in SMCs from partially ligated ApoE-/- mice and rat carotid intimal hyperplasia, correlating with osteogenic markers and TGFb1. Furthermore, PRG4 was enriched in cells positive for chondrogenic marker SOX9 and around plaque calcifications in ApoE-/- mice on warfarin. In vitro, PRG4 was induced in SMCs by IFNg, TGFb1 and calcifying medium, while SMC markers were repressed under calcifying conditions. Silencing experiments showed that PRG4 expression was driven by transcription factors SMAD3 and SOX9. Functionally, the addition of recombinant human PRG4 increased ectopic SMC calcification, while arresting cell migration and proliferation. Mechanistically, it suppressed endogenous PRG4, SMAD3 and SOX9, and restored SMC markers' expression. PRG4 modulates SMC function and osteogenic phenotype during intimal remodeling and macro-calcification in response to TGFb1 signaling, SMAD3 and SOX9 activation. The effects of PRG4 on SMC phenotype and calcification suggest its role in atherosclerotic plaque stability, warranting further investigations.

TGF-β Signaling Promotes Glioma Progression Through Stabilizing Sox9

Gliomas are brain and spinal cord malignancies characterized by high malignancy, high recurrence and poor prognosis, the underlying mechanisms of which remain largely elusive. Here, we found that the Sry-related high mobility group box (Sox) family transcription factor, Sox9, was upregulated and correlated with poor prognosis of clinical gliomas. Sox9 promotes migration and invasion of glioma cells and in vivo development of xenograft tumors from inoculated glioma cells. Sox9 functions downstream of the transforming growth factor-β (TGF-β) pathway, in which TGF-β signaling prevent proteasomal degradation of the Sox9 protein in glioma cells. These findings provide novel insight into the wide interplay between TGF-β signaling and oncogenic transcription factors, and have implications for targeted therapy and prognostic assessment of gliomas.

Molecular mechanisms of mechanical load-induced osteoarthritis

INTRODUCTION

Mechanical loading enhances the progression of osteoarthritis. However, its molecular mechanisms have not been established.

OBJECTIVE

The aim of this review was to summarize the probable mechanisms of mechanical load-induced osteoarthritis.

METHODS

A comprehensive search strategy was used to search PubMed and EMBASE databases (from the 15th of January 2015 to the 20th of October 2020). Search terms included "osteoarthritis", "mechanical load", and "mechanism".

RESULTS

Abnormal mechanical loading activates the interleukin-1β, tumour necrosis factor-α, nuclear factor kappa-B, Wnt, transforming growth factor-β, microRNAs pathways, and the oxidative stress pathway. These pathways induce the pathological progression of osteoarthritis. Mechanical stress signal receptors such as integrin, ion channel receptors, hydrogen peroxide-inducible clone-5, Gremlin-1, and transient receptor potential channel 4 are present in the articular cartilages.

CONCLUSION

This review highlights the molecular mechanisms of mechanical loading in inducing chondrocyte apoptosis and extracellular matrix degradation. These mechanisms provide potential targets for osteoarthritis prevention and treatment.

Canonical and noncanonical TGF-β signaling regulate fibrous tissue differentiation in the axial skeleton

Previously, we showed that embryonic deletion of TGF-β type 2 receptor in mouse sclerotome resulted in defects in fibrous connective tissues in the spine. Here we investigated how TGF-β regulates expression of fibrous markers: Scleraxis, Fibromodulin and Adamtsl2. We showed that TGF-β stimulated expression of Scleraxis mRNA by 2 h and Fibromodulin and Adamtsl2 mRNAs by 8 h of treatment. Regulation of Scleraxis by TGF-β did not require new protein synthesis; however, protein synthesis was required for expression of Fibromodulin and Adamtsl2 indicating the necessity of an intermediate. We subsequently showed Scleraxis was a potential intermediate for TGF-β-regulated expression of Fibromodulin and Adamtsl2. The canonical effector Smad3 was not necessary for TGF-β-mediated regulation of Scleraxis. Smad3 was necessary for regulation of Fibromodulin and Adamtsl2, but not sufficient to super-induce expression with TGF-β treatment. Next, the role of several noncanonical TGF-β pathways were tested. We found that ERK1/2 was activated by TGF-β and required to regulate expression of Scleraxis, Fibromodulin, and Adamtsl2. Based on these results, we propose a model in which TGF-β regulates Scleraxis via ERK1/2 and then Scleraxis and Smad3 cooperate to regulate Fibromodulin and Adamtsl2. These results define a novel signaling mechanism for TGFβ-mediated fibrous differentiation in sclerotome.

Articular damages in multi-generational female offspring due to prenatal caffeine exposure correlates with H3K9 deacetylation of TGFβ signaling pathway

Adverse environment during pregnancy could lead to maternal glucocorticoid overexposure in utero, and then induce the intrauterine growth retardation (IUGR) and the programmed change in cartilage development. The transforming growth factor β (TGFβ) signaling pathway plays a crucial role in the process of chondrogenesis, cartilage growth, development, maturation, and phenotype maintenance. Our previous results had shown that prenatal caffeine exposure (PCE) could result in the damaged articular cartilage in offspring rats. However, whether this change could transmit to multiple generations was still unknown. In this study, pregnant Wistar rats received either saline or caffeine (120 mg/kg, i.g.) once daily from gestational day 9-20 (GD9-20). The female offspring mated with normal male rats to generate the following generations. We obtained the articular cartilages in subsequent F1 to F3 female offspring. The H3K9 acetylation and expression of the TGFβ signaling pathway were detected; the content of the cartilage matrix was detected. The results showed that PCE reduced the H3K9 acetylation and the expression of the TGFβ signaling pathway, then reduced the extracellular matrix in F1, F2, and F3 generations. in vitro, corticosterone could induce the H3K9 deacetylation of the TGFβ signaling pathway, thus inhibiting the expression of the TGFβ signaling pathway and extracellular matrix. The overall results revealed that PCE induced a multi-generational damaged articular cartilage in female offspring rats, which was partially related to the maternal high glucocorticoid-induced H3K9 hypoacetylation of TGFβ signaling pathway.

Extracellular matrix mechanics regulate transfection and SOX9-directed differentiation of mesenchymal stem cells

Gene delivery within hydrogel matrices can potentially direct mesenchymal stem cells (MSCs) towards a chondrogenic fate to promote regeneration of cartilage. Here, we investigated whether the mechanical properties of the hydrogel containing the gene delivery systems could enhance transfection and chondrogenic programming of primary human bone marrow-derived MSCs. We developed collagen-I-alginate interpenetrating polymer network hydrogels with tunable stiffness and adhesion properties. The hydrogels were activated with nanocomplexed SOX9 polynucleotides to direct chondrogenic differentiation of MSCs. MSCs transfected within the hydrogels showed higher expression of chondrogenic markers compared to MSCs transfected in 2D prior to encapsulation. The nanocomplex uptake and resulting expression of transfected SOX9 were jointly enhanced by increased stiffness and cell-adhesion ligand density in the hydrogels. Further, transfection of SOX9 effectively induced MSCs chondrogenesis and reduced markers of hypertrophy compared to control matrices. These findings highlight the importance of matrix stiffness and adhesion as design parameters in gene-activated matrices for regenerative medicine. STATEMENT OF SIGNIFICANCE: Gene-activated matrices (GAMs) are biodegradable polymer networks integrating gene therapies, and they are promising technologies for supporting tissue regeneration. Despite this interest, there is still limited information on how to rationally design these systems. Here, we provide a systematic study of the effect of matrix stiffness and cell adhesion ligands on gene transfer efficiency. We show that high stiffness and the presence of cell-binding sites promote transfection efficiency and that this result is related to more efficient internalization and trafficking of the gene therapies. GAMs with optimized mechanical properties can induce cartilage formation and result in tissues with better characteristics for articular cartilage tissue engineering as compared to previously described standard methods.

Hypoallergenic infant formula lacks transforming growth factor beta activity and has a lower anti-inflammatory activity than regular infant formula

Hypoallergenic formulas are recommended for infants who are not breastfed and cannot tolerate cow milk formulas due to allergy. These formulas are hydrolyzed to break down larger protein chains into shorter, easy-to-digest, and potentially less allergenic proteins. Hydrolysis, however, possibly occurs at the expense of the transforming growth factor beta (TGF-β) and anti-inflammatory activity that is inherent in regular formula. Our objective was to determine the TGF-β and the anti-inflammatory activity of commercially available hypoallergenic and regular formulas. Human gingival fibroblasts were incubated with reconstituted formulas followed by detection of TGF-β target genes and activation of Smad2/3 signaling. Gingival fibroblasts and the oral squamous cell carcinoma cell line HSC-2 were also exposed to formulas before adding interleukin (IL)1β and tumor necrosis factor (TNF)α to provoke expression of pro-inflammatory cytokines. For murine bone marrow-derived macrophages, pro-inflammatory cytokine expression was stimulated with saliva. Changes in p65 nuclear translocation and phosphorylation of smad3 and p38 were analyzed by immunostaining. Our study demonstrated that regular formula, but not hypoallergenic formula, enhanced the expression of TGF-β target genes IL11, PRG4, and NOX4 in gingival fibroblasts. Hypoallergenic formulas also failed to initiate nuclear translocation of Smad2/3 and phosphorylation of Smad3. Moreover, regular formulas were more potent than hypoallergenic formulas in reducing the expression of pro-inflammatory cytokines in gingival fibroblasts, HSC-2 epithelial cells, and murine bone marrow macrophages. Hypoallergenic and regular formulas had a similar capacity to reduce p65 nuclear translocation and phosphorylation of p38 in fibroblasts. These findings suggest that hypoallergenic formulas lack in vitro TGF-β activity and have a lower anti-inflammatory activity compared with regular formulas.

Positive Effects of a Young Systemic Environment and High Growth Differentiation Factor 11 Levels on Chondrocyte Proliferation and Cartilage Matrix Synthesis in Old Mice

OBJECTIVE

To investigate the effects of a young systemic environment and growth differentiation factor 11 (GDF-11) on aging cartilage.

METHODS

A heterochronic parabiosis model (2-month-old mouse and 12-month-old mouse [Y/O]), an isochronic parabiosis model (12-month-old mouse and 12-month-old mouse [O/O]), and 12-month-old mice alone (O) were evaluated. Knee joints and chondrocytes from old mice were examined by radiography, histology, cell proliferation assays, immunohistochemistry, Western blotting, and quantitative reverse transcriptase-polymerase chain reaction 16 weeks after parabiosis surgery. GDF-11 was injected into 12-month-old mouse joints daily for 16 weeks. Cartilage degeneration, cell proliferation, and osteoarthritis-related gene expression were evaluated.

RESULTS

Osteoarthritis Research Society International scores in old mice were significantly lower in the Y/O group than in the O/O and O groups (both P < 0.05). The percentage of 5-ethynyl-2'-deoxyuridine-positive chondrocytes in old mice was significantly higher in the Y/O group than in the other groups (P < 0.05). Type II collagen (CII) and SOX9 messenger RNA levels differed in cartilage from old mice in the Y/O group compared to the O/O and O groups (both P < 0.05). RUNX-2, CX, and matrix metalloproteinase 13 levels were significantly lower in cartilage from old mice in the Y/O group compared to the O/O and O groups (both P < 0.05). Similar results were obtained for protein expression levels and after GDF-11 treatment in vitro and in vivo. Phosphorylated Smad2/3 (pSmad2/3) levels were higher in the recombinant GDF-11-treated group than in the control group.

CONCLUSION

A young systemic environment promotes chondrocyte proliferation and cartilage matrix synthesis in old mice. GDF-11, a "young factor," contributes to these effects through the up-regulation of pSmad2/3.

KISS1 in breast cancer progression and autophagy

Tumor suppressors are cellular proteins typically expressed in normal (non-cancer) cells that not only regulate such cellular functions as proliferation, migration and adhesion, but can also be secreted into extracellular space and serve as biomarkers for pathological conditions or tumor progression. KISS1, a precursor for several shorter peptides, known as metastin (Kisspeptin-54), Kisspeptin-14, Kisspeptin-13 and Kisspeptin-10, is one of those metastasis suppressor proteins, whose expression is commonly downregulated in the metastatic tumors of various origins. The commonly accepted role of KISS1 in metastatic tumor progression mechanism is the ability of this protein to suppress colonization of disseminated cancer cells in distant organs critical for the formation of the secondary tumor foci. Besides, recent evidence suggests involvement of KISS1 in the mechanisms of tumor angiogenesis, autophagy and apoptosis regulation, suggesting a possible role in both restricting and promoting cancer cell invasion. Here, we discuss the role of KISS1 in regulating metastases, the link between KISS1 expression and the autophagy-related biology of cancer cells and the perspectives of using KISS1 as a potential diagnostic marker for cancer progression as well as a new anti-cancer therapeutics.

Genomic Divergence in Swedish Warmblood Horses Selected for Equestrian Disciplines

The equestrian sport horse Swedish Warmblood (SWB) originates from versatile cavalry horses. Most modern SWB breeders have specialized their breeding either towards show jumping or dressage disciplines. The aim of this study was to explore the genomic structure of SWB horses to evaluate the presence of genomic subpopulations, and to search for signatures of selection in subgroups of SWB with high or low breeding values (EBVs) for show jumping. We analyzed high density genotype information from 380 SWB horses born in the period 2010-2011, and used Principal Coordinates Analysis and Discriminant Analysis of Principal Components to detect population stratification. Fixation index and Cross Population Extended Haplotype Homozygosity scores were used to scan the genome for potential signatures of selection. In accordance with current breeding practice, this study highlights the development of two separate breed subpopulations with putative signatures of selection in eleven chromosomes. These regions involve genes with known function in, e.g., mentality, endogenous reward system, development of connective tissues and muscles, motor control, body growth and development. This study shows genetic divergence, due to specialization towards different disciplines in SWB horses. This latter evidence can be of interest for SWB and other horse studbooks encountering specialized breeding.

Protein-Degrading Enzymes in Osteoarthritis

OBJECTIVE

TGFβ1 plays an important role in the metabolism of articular cartilage and bone; however, the pathological mechanism and targets of TGFβ1 in cartilage degradation and uncoupling of subchondral bone remodeling remain unclear. Therefore, in this study, we investigated the relationship between TGFβ1 and major protein-degrading enzymes, and evaluated the role of high levels of active TGFβ1 in the thickening of subchondral bone and calcification of articular cartilage.

MATERIALS AND METHODS

The expression of TGFβ1 and protein-degrading enzymes in clinical samples of articular cartilage and subchondral bone obtained from the knee joint of patients with osteoarthritis was detected by immunohistochemistry. The expression levels of TGFβ1, MMP-3, MMP-13 and IL-1β in cartilage and subchondral bone tissues were detected by absolute real-time quantitative RT-PCR. The expression of TGFβ1, nestin and osterix in subchondral bone was detected by Western blot analysis and immunohistochemistry. The degree of subchondral bone thickening was determined by micro-computed tomography (CT) imaging.

RESULTS

Expression of TGFβ1 and cartilage-degrading enzymes was higher in the cartilage-disrupted group than that in the intact group. Furthermore, expression of TGFβ1, nestin and osterix was significantly higher in the OA group than that in the control group. Micro-CT imaging showed that in the OA group, the subchondral bone plate is thickened and the density is increased. The trabecular bone structure is thick plate-like structure, the thickness of the trabecular bone is increased and the gap is small.

CONCLUSIONS

The data suggest that highly active TGFβ1 activates the expression of cartilage-degrading enzymes. Abnormally activated TGFβ1 may induce formation of the subchondral bone and expansion of the calcified cartilage area, eventually leading to degradation of the cartilage tissue.

FOXO1 transcription factor regulates chondrogenic differentiation through transforming growth factor β1 signaling

The forkhead box O (FOXO) proteins are transcription factors involved in the differentiation of many cell types. Type II collagen (Col2) Cre-Foxo1-knockout and Col2-Cre-Foxo1,3,4 triple-knockout mice exhibit growth plate malformation. Moreover, recent studies have reported that in some cells, the expressions and activities of FOXOs are promoted by transforming growth factor β1 (TGFβ1), a growth factor playing a key role in chondrogenic differentiation. Here, using a murine chondrogenic cell line (ATDC5), mouse embryos, and human mesenchymal stem cells, we report the mechanisms by which FOXOs affect chondrogenic differentiation. FOXO1 expression increased along with chondrogenic differentiation, and FOXO1 inhibition suppressed chondrogenic differentiation. TGFβ1/SMAD signaling promoted expression and activity of FOXO1. In ATDC5, FOXO1 knockdown suppressed expression of sex-determining region Y box 9 (Sox9), a master regulator of chondrogenic differentiation, resulting in decreased collagen type II α1 (Col2a1) and aggrecan (Acan) expression after TGFβ1 treatment. On the other hand, chemical FOXO1 inhibition suppressed Col2a1 and Acan expression without suppressing Sox9 To investigate the effects of FOXO1 on chondrogenic differentiation independently of SOX9, we examined FOXO1's effects on the cell cycle. FOXO1 inhibition suppressed expression of p21 and cell-cycle arrest in G₀/G₁ phase. Conversely, FOXO1 overexpression promoted expression of p21 and cell-cycle arrest. FOXO1 inhibition suppressed expression of nascent p21 RNA by TGFβ1, and FOXO1 bound the p21 promoter. p21 inhibition suppressed expression of Col2a1 and Acan during chondrogenic differentiation. These results suggest that FOXO1 is necessary for not only SOX9 expression, but also cell-cycle arrest during chondrogenic differentiation via TGFβ1 signaling.

MicroRNA-455-3p promotes TGF-β signaling and inhibits osteoarthritis development by directly targeting PAK2

MicroRNAs (miRNAs, miR) play a key role in the pathogenesis of osteoarthritis (OA). Few studies have examined the regulatory role of P21-activated kinases (PAKs), a family of serine/threonine kinases, in OA. The aim of this study was to determine whether miR-455-3p can regulate cartilage degeneration in OA by targeting PAK2. MiR-455-3p knockout mice showed significant degeneration of the knee cartilage. MiR-455-3p expression increased and PAK2 expression decreased in the late stage of human adipose-derived stem cell (hADSC) chondrogenesis and in chondrocytes affected by OA. Furthermore, in both miR-455-3p-overexpressing chondrocytes and PAK2-suppressing chondrocytes, cartilage-specific genes were upregulated, and hypertrophy-related genes were downregulated. A luciferase reporter assay confirmed that miR-455-3p regulates PAK2 expression by directly targeting the 3′-untranslated regions (3′UTRs) of PAK2 mRNA. IPA-3, a PAK inhibitor, inhibited cartilage degeneration due to OA. Moreover, suppressing PAK2 promoted R-Smad activation in the TGF/Smad signaling pathway in chondrocytes. Altogether, our results suggest that miR-455-3p promotes TGF-β/Smad signaling in chondrocytes and inhibits cartilage degeneration by directly suppressing PAK2. These results thus indicate that miR-455-3p and PAK2 are novel potential therapeutic agents and targets, respectively, for the treatment of OA.

Functional insights into a short RNA strand that prevents cartilage degeneration could lead to new therapeutic strategies for treating osteoarthritis. The microRNA miR-455-3p regulates genes in tissues throughout the body, but Weiming Liao and Zhiqi Zhang of the First Affiliated Hospital of Sun Yat-sen University in Guangzhou, China have observed that it appears to play a particularly prominent role in cartilage-producing chondrocyte cells. Liao, Zhang and colleagues have now explored this mechanism in detail, and determined that miR-455-3p selectively blocks the effects of a protein called PAK2 in chondrocytes. PAK2 normally inhibits an important signaling pathway underlying cartilage generation, and such inhibition has previously been observed in MDCK epithelial cells. The authors conclude that this microRNA or other drugs that replicate its PAK2-inhibiting effects could prevent or slow the joint damage associated with this degenerative disorder.

Scaffoldless tissue-engineered cartilage for studying transforming growth factor beta-mediated cartilage formation

Reduced transforming growth factor beta (TGF-β) signaling is associated with osteoarthritis (OA). TGF-β is thought to act as a chondroprotective agent and provide anabolic cues to cartilage, thus acting as an OA suppressor in young, healthy cartilage. A potential approach for treating OA is to identify the factors that act downstream of TGF-β's anabolic pathway and target those factors to promote cartilage regeneration or repair. The aims of the present study were to (a) develop a scaffoldless tissue-engineered cartilage model with reduced TGF-β signaling and disrupted cartilage formation and (b) validate the system for identifying the downstream effectors of TGF-β that promote cartilage formation. Sox9 was used to validate the model because Sox9 is known to promote cartilage formation and TGF-β regulates Sox9 activity. Primary bovine articular chondrocytes were grown in Transwell supports to form cartilage tissues. An Alk5/TGF-β type I receptor inhibitor, SB431542, was used to attenuate TGF-β signaling, and an adenovirus encoding FLAG-Sox9 was used to drive the expression of Sox9 in the in vitro-generated cartilage. SB431542-treated tissues exhibited reduced cartilage formation including reduced thicknesses and reduced proteoglycan staining compared with control tissue. Expression of FLAG-Sox9 in SB431542-treated cartilage allowed the formation of cartilage despite antagonism of the TGF-β receptor. In summary, we developed a three-dimensional in vitro cartilage model with attenuated TGF-β signaling. Sox9 was used to validate the model for identification of anabolic agents that counteract loss of TGF-β signaling. This model has the potential to identify additional anabolic factors that could be used to repair or regenerate damaged cartilage.

Dissection of the molecular targets and signaling pathways of Guzhi Zengsheng Zhitongwan based on the analysis of serum proteomics

Background

Guzhi Zengsheng Zhitongwan (GZZSZTW) is an effective formula of traditional Chinese herbal medicine and has been widely applied in the treatment of joint diseases for many years. The aim of this study was to dissect the molecular targets and signaling pathways of Guzhi Zengsheng Zhitongwan based on the analysis of serum proteomics.

Methods

The Chinese herbs of GZZSZTW were immersed in 5 l distilled water and boiled with reflux extraction method. The extract was filtered, concentrated and freeze-dried. The chemical profile of GZZSZTW extract was determined by high-performance lipid chromatography (HPLC). The 7-week old Sprague-Dawley (SD) rats in GZZSZTW groups were received oral administration at doses of 0.8, 1.05, and 1.3 g/kg per day and the rats in blank group were fed with drinking water. Serum samples were collected from the jugular veins. Primary chondrocyte viability was evaluated by CCK-8 assay. A full spectrum of the molecular targets and signaling pathways of GZZSZTW were investigated by isobaric tags for relative and absolute quantitation (iTRAQ) analysis and a systematic bioinformatics analysis accompanied with parallel reaction monitoring (PRM) and siRNA validation.

Results

GZZSZTW regulated a series of functional proteins and signaling pathways responsible for cartilage development, growth and repair. Functional classification analysis indicated that these proteins were mainly involved in the process of cell surface dynamics. Pathway analysis mapped these proteins into several signalling pathways involved in chondrogenesis, chondrocyte proliferation and differentiation, and cartilage repair, including hippo signaling pathway, cGMP-PKG signaling pathway, cell cycle and calcium signaling pathway. Protein–protein interaction analysis and siRNA knockdown assay identified an interaction network consisting of TGFB1, RHO GTPases, ILK, FLNA, LYN, DHX15, PKM, RAB15, RAB1B and GIPC1.

Conclusions

Our results suggest that the effects of GZZSZTW on treating joint diseases might be achieved through the TGFB1/RHO interaction network coupled with other proteins and signaling pathways responsible for cartilage development, growth and repair. Therefore, the present study has greatly expanded our knowledge and provided scientific support for the underlying therapeutic mechanisms of GZZSZTW on treating joint diseases. It also provided possible alternative strategies for the prevention and treatment for joint diseases by using traditional Chinese herbal formulas.

Mechanical stimulation promotes the proliferation and the cartilage phenotype of mesenchymal stem cells and chondrocytes co-cultured in vitro

Mesenchymal stem cells and chondrocytes are an important source of the cells for cartilage tissue engineering. Therefore, the culture and expansion methods of these cells need to be improved to overcome the aging of chondrocytes and induced chondrogenic differentiation of mesenchymal stem cells. The aim of this study was to expand the cells for cartilage tissue engineering by combining the advantages of growing cells in co-culture and under a mechanically-stimulated environment. Rabbit chondrocytes and co-cultured cells (bone mesenchymal stem cells and chondrocytes) were subjected to cyclic sinusoidal dynamic tensile mechanical stimulationusing the FX-4000 tension system. Chondrocyte proliferation was assayed by flow cytometry and CFSE labeling. The cell cartilage phenotype was determined by detecting GAG, collagen II and TGF-β1 protein expression by ELISA and the Col2α1, TGF-β1 and Sox9 gene expression by RT-PCR. The results show that the co-culture improved both the proliferation ability of chondrocytes and the cartilage phenotype of co-cultured cells. A proper cyclic sinusoidal dynamic tensile mechanical stimulation improved the proliferation ability and cartilage phenotype of chondrocytes and co-cultured cells. These results suggest that the co-culture of mesenchymal stem cells with chondrocytes and proper mechanical stimulation may be an appropriate way to rapidly expand the cells that have an improved cartilage phenotype for cartilage tissue engineering.

Hypoxia and TGF-β3 Synergistically Mediate Inner Meniscus-Like Matrix Formation by Fibrochondrocytes

The interactions of hypoxia and TGF-β3 in aggregates of human meniscus fibrochondrocytes are synergistic in nature, suggesting combinatorial strategies using these factors are promising for tissue engineering the inner meniscus regions. Hypoxia alone in the absence of TGF-β supplementation may be insufficient to initiate an inner meniscus-like extracellular matrix-forming response in this model.

Prg4 prevents osteoarthritis induced by dominant-negative interference of TGF-ß signaling in mice

Objective

Prg4, also known as Lubricin, acts as a joint/boundary lubricant. Prg4 has been used to prevent surgically induced osteoarthritis (OA) in mice. Surgically induced OA serves as a good model for post-traumatic OA but is not ideal for recapitulating age-related OA. Reduced expression of the TGF-β type II receptor (TGFβR2) is associated with age-related OA in clinical samples, so we previously characterized a mouse model that exhibits OA due to expression of a mutated dominant-negative form of TGFβR2 (DNIIR). Prg4 expression was significantly reduced in DNIIR mice. Furthermore, we showed that Prg4 was a transcriptional target of TGF-ß via activation of Smad3, the main signal transducing protein for TGF-ß. The objective of the present study was to determine whether maintenance of Prg4, a down-stream transcriptional target of TGF-ß, prevents OA associated with attenuated TGF-ß signaling in mice.

Design

Wild-type, DNIIR, and bitransgenic mice that express both DNIIR and Prg4, were compared. Mice were assessed with a foot misplacement behavioral test, μCT, histology, and Western blot.

Results

Compared to DNIIR mice, bitransgenic DNIIR+Prg4 mice missed 1.3 (0.4, 2.1) fewer steps while walking (mean difference (95% confidence interval)), exhibited a cartilage fibrillation score that was 1.8 (0.4, 3.1) points lower, exhibited cartilage that was 28.2 (0.5, 55.9) μm thicker, and exhibited an OARSI score that was 6.8 (-0.9, 14.5) points lower. However, maintenance of Prg4 expression did not restore levels of phosphorylated Smad3 in DNIIR mice, indicating Prg4 does not simply stimulate TGF-ß signaling.

Conclusions

Our results indicate that maintenance of Prg4 expression prevents OA progression associated with reduced TGF-β signaling in mice. Since there was no evidence that Prg4 acts by stimulating the TGF-ß signaling cascade, we propose that Prg4, a transcriptional target of TGF-ß, attenuates OA progression through its joint lubrication function.

Zyxin-involved actin regulation is essential in the maintenance of vinculin focal adhesion and chondrocyte differentiation status

Objectives

To investigate the role of zyxin‐involved actin regulation in expression level of vinculin focal adhesion and collagen production of chondrocyte and its possible underlying mechanism.

Materials and methods

Chondrocytes obtained from rabbit articular cartilage were used in this study. The expression of zyxin, actin and vinculin, as well as the extracellular matrix (ECM) protein collagen type I, II and X (COL I, II and X) of chondrocytes were compared between zyxin‐knockdown group and negative control group, and between transforming growth factor‐β1 (TGF‐β1) treatment group and non‐treatment group, respectively.

Results

Knockdown of zyxin increased the ratio of globular actin (G‐actin) to filamentous actin (F‐actin) of chondrocyte, which further inhibited expression of vinculin and chondrogenic marker COL II as well as hypertrophy marker COL X. On the other hand, chondrocytes treated with TGF‐β1 showed an enhanced expression of F‐actin, and a lower expression of zyxin compared to non‐treatment group. In response to TGF‐β1‐induced actin polymerization, expression of vinculin and COL I was increased, while expression of COL II and aggrecan was decreased.

Conclusions

These results demonstrate supporting evidence that in chondrocytes the level of zyxin is closely associated with the state of actin polymerization. In particular, the change of zyxin and F‐actin parallels with the change of COL II and vinculin, respectively, indicating a major role of zyxin‐actin interaction in the synthesis of collagen ECM and the remodelling of cytoskeleton‐ECM adhesion.

TGF-β activity in cow milk and fermented milk products: An in vitro bioassay with oral fibroblasts

OBJECTIVE

Milk is a rich source of transforming growth factor (TGF)-β which supports intestinal mucosal homeostasis of infants. Milk may also have beneficial effects on the integrity of the oral cavity, its being part of the gastrointestinal tract. However, it is unclear if milk and fermented milk products provoke a TGF-β response in oral cells.

MATERIAL AND METHODS

Human gingival fibroblasts were exposed to pasteurized cow milk, yoghurt, sour milk, buttermilk and whey, followed by a reverse transcriptase polymerase chain reaction of the TGF-β target genes interleukin11 (IL11), proteoglycan4 (PRG4), and NADPH oxidase 4 (NOX4). Immunoassays were performed for IL11 and TGF-β in cell culture supernatant and milk products, respectively. Signaling was investigated with the TGF-β receptor type I kinase inhibitor SB431542.

RESULTS

We report here that pasteurized cow milk and the aqueous fractions of yoghurt, sour milk, buttermilk and whey enhanced the expression of IL11, NOX4 and PRG4 in gingival fibroblasts. Moreover, IL11 protein levels in the respective supernatant were significantly increased. Cow milk, yoghurt, sour milk and buttermilk contain approximately 1-2 ng TGF-β1, whereas active TGF-β1 is hardly detectable in whey. SB431542 reduced the response of gingival fibroblasts to pasteurized cow milk and fermented milk products based on IL11 release into the supernatant.

CONCLUSIONS

These results demonstrate that gingival fibroblasts respond to pasteurized cow milk and to fermented milk products with an increased expression of TGF-β target genes.

Human mesenchymal stem cells induced to differentiate as chondrocytes follow a biphasic pattern of extracellular matrix production

Regenerative medicine and tissue engineering studies are actively developing novel means to repair adult articular cartilage defects using biological approaches. One such approach is the harnessing of adult human therapeutic cells such as those referred to as mesenchymal stem cells. Upon exposure to chondrogenic signals, these cells differentiate and initiate the production of a complex and voluminous cartilaginous matrix that is crucial to both the structure and function of cartilage. Furthermore, this complexity requires the time-sensitive activation of a large number of genes to produce the components of this matrix. The current study analyzed the kinetics of matrix production in an aggregate culture model where adult human mesenchymal stem cells were induced to differentiate as chondrocytes. The results indicate the existence of a biphasic mode of differentiation and maturation during which matrix genes and molecules are differentially activated and secreted. These results have important implications for developing novel approaches for the creation of tissue engineered articular cartilage. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1757-1766, 2018.

Impairment of chondrocyte proliferation after exposure of young murine cartilage to an aged systemic environment in a heterochronic parabiosis model

AIM:

The aim of this study was to investigate whether an aged systemic environment could impair young cartilage tissue in mice.

METHODS:

Mice differing in age were randomly divided into three groups. Group 1 was the experimental group (Y/O group) consisting of the heterochronic parabiosis model (2-month-old/12-month-old, young/old). Group 2 was the surgical control group (Y/Y group) with the isochronic parabiosis model (2-month-old/2-month-old, young/young). Group 3 consisted of the ageing control mice (2-month-old alone, Y group). Young knee cartilages collected from all three groups at 4 months after surgery were compared. Fluorescence molecular tomography (FMT) was used to confirm whether the two mice in parabiosis shared a common blood circulation at 2 weeks after surgery. The knee joints of young mice were examined radiologically at 4 months after surgery. Histological scoring was assigned to grade the severity of osteoarthritis (OA). Immunohistochemistry and quantitative reverse transcription polymerase chain reaction were used to evaluate OA-related protein expression and gene expression, and chondrocyte proliferation was determined with EdU staining.

RESULTS:

FMT imaging confirmed cross-circulation in the parabiotic pairs. The percentage of EdU-positive chondrocytes in young mice from the Y/O group was significantly lower compared with those of the Y/Y and Y groups (p <0.05 for both). There was no statistically significant difference in the mRNA expression of collagen type II (Col2), collagen type X (Col10), and matrix metalloproteinase 13 (MMP13) among the three groups (P>0.05), but expression of sex-determining region Y box 9 (Sox9) mRNA in young cartilage from the Y/O group was markedly attenuated compared to those in the Y/Y and Y groups (p <0.05 for both). In the Y/O group, mRNA expression of runt-related transcription factor 2 (Runx2) in young cartilage was significantly increased compared to the Y/Y and Y groups (p <0.05 for both). The changes in Col2, Col10, MMP13, Runx2 and Sox9 at the protein level mimicked the alterations found at the mRNA level. Loss of cartilage proteoglycan in young mice from the Y/O group was significantly greater compared to the Y/Y and Y groups (p <0.05 for both), despite the lack of significant difference among the three groups in OARIS and osteophytosis scores.

CONCLUSION:

Heterochronic parabiosis exerts a negative effect on chondrocyte proliferation in the knee cartilage of young mice.

TGF-β regulates phosphorylation and stabilization of Sox9 protein in chondrocytes through p38 and Smad dependent mechanisms

Members of the TGF-β superfamily are important regulators of chondrocyte function. Sox9, a key transcriptional regulator of chondrogenesis, is required for TGF-β-mediated regulation of specific cartilage genes. TGF-β can signal through a canonical, Smad-mediated pathway or non-conical pathways, including p38. Here we show that both pathways are activated in chondrocytes after treatment with TGF-β and that TGF-β stabilizes Sox9 protein and increases phosphorylation of Sox9. Mutagenesis of potential serine phosphorylation sites on Sox9 was used to demonstrate that serine 211 is required to maintain normal basal levels of Sox9 as well as mediate increased Sox9 levels in response to TGF-β. The serine 211 site is in a motif that is targeted by p38 kinase. We used siRNA and pharmacological agents to show that p38 and Smad3 independently regulate the phosphorylation and stability of Sox9. Previously, we demonstrated that Papss2 is a downstream transcriptional target of Sox9 and TGF-β. Here we show that p38 is required for TGF-β-mediated regulation of Papss2 mRNA. Together the results suggest a new mechanism for TGF-β-mediated gene regulation in chondrocytes via p38 and phosphorylation and stabilization of Sox9. Understanding how TGF-β regulates Sox9 may lead to identification of therapeutic targets for OA.