Gene expression changes in damaged osteoarthritic cartilage identify a signature of non-chondrogenic and mechanical responses

Gene expression profiling and the isocitrate dehydrogenase mutational landscape of temozolomide‑resistant glioblastoma

Glioblastoma multiforme (GBM) is an aggressive brain cancer that occurs more frequently than other brain tumors. The present study aimed to reveal a novel mechanism of temozolomide resistance in GBM using bioinformatics and wet lab analyses, including meta-Z analysis, Kaplan-Meier survival analysis, protein-protein interaction (PPI) network establishment, cluster analysis of co-expressed gene networks, and hierarchical clustering of upregulated and downregulated genes. Next-generation sequencing and quantitative PCR analyses revealed downregulated [tyrosine kinase with immunoglobulin and epidermal growth factor homology domains 1 (TIE1), calcium voltage-gated channel auxiliary subunit α2Δ1 (CACNA2D1), calpain 6 (CAPN6) and a disintegrin and metalloproteinase with thrombospondin motifs 6 (ADAMTS6)] and upregulated [serum amyloid (SA)A1, SAA2, growth differentiation factor 15 (GDF15) and ubiquitin specific peptidase 26 (USP26)] genes. Different statistical models were developed for these genes using the Z-score for P-value conversion, and Kaplan-Meier plots were constructed using several patient cohorts with brain tumors. The highest number of nodes was observed in the PPI network was for ADAMTS6 and TIE1. The PPI network model for all genes contained 35 nodes and 241 edges. Immunohistochemical staining was performed using isocitrate dehydrogenase (IDH)-wild-type or IDH-mutant GBM samples from patients and a significant upregulation of TIE1 (P<0.001) and CAPN6 (P<0.05) protein expression was demonstrated in IDH-mutant GBM in comparison with IDH-wild-type GBM. Structural analysis revealed an IDH-mutant model demonstrating the mutant residues (R132, R140 and R172). The findings of the present study will help the future development of novel biomarkers and therapeutics for brain tumors.

Unveiling inflammatory and prehypertrophic cell populations as key contributors to knee cartilage degeneration in osteoarthritis using multi-omics data integration

OBJECTIVES

Single-cell and spatial transcriptomics analysis of human knee articular cartilage tissue to present a comprehensive transcriptome landscape and osteoarthritis (OA)-critical cell populations.

METHODS

Single-cell RNA sequencing and spatially resolved transcriptomic technology have been applied to characterise the cellular heterogeneity of human knee articular cartilage which were collected from 8 OA donors, and 3 non-OA control donors, and a total of 19 samples. The novel chondrocyte population and marker genes of interest were validated by immunohistochemistry staining, quantitative real-time PCR, etc. The OA-critical cell populations were validated through integrative analyses of publicly available bulk RNA sequencing data and large-scale genome-wide association studies.

RESULTS

We identified 33 cell population-specific marker genes that define 11 chondrocyte populations, including 9 known populations and 2 new populations, that is, pre-inflammatory chondrocyte population (preInfC) and inflammatory chondrocyte population (InfC). The novel findings that make this an important addition to the literature include: (1) the novel InfC activates the mediator MIF-CD74; (2) the prehypertrophic chondrocyte (preHTC) and hypertrophic chondrocyte (HTC) are potentially OA-critical cell populations; (3) most OA-associated differentially expressed genes reside in the articular surface and superficial zone; (4) the prefibrocartilage chondrocyte (preFC) population is a major contributor to the stratification of patients with OA, resulting in both an inflammatory-related subtype and a non-inflammatory-related subtype.

CONCLUSIONS

Our results highlight InfC, preHTC, preFC and HTC as potential cell populations to target for therapy. Also, we conclude that profiling of those cell populations in patients might be used to stratify patient populations for defining cohorts for clinical trials and precision medicine.

CHMP5 attenuates osteoarthritis via inhibiting chondrocyte apoptosis and extracellular matrix degradation: involvement of NF-κB pathway

BACKGROUND

Osteoarthritis (OA), the most common joint disease, is linked with chondrocyte apoptosis and extracellular matrix (ECM) degradation. Charged multivesicular body protein 5 (CHMP5), a member of the multivesicular body, has been reported to serve as an anti-apoptotic protein to participate in leukemia development. However, the effects of CHMP5 on apoptosis and ECM degradation in OA remain unclear.

METHODS

In this study, quantitative proteomics was performed to analyze differential proteins between normal and OA patient articular cartilages. The OA mouse model was constructed by the destabilization of the medial meniscus (DMM). In vitro, interleukin-1 beta (IL-1β) was used to induce OA in human chondrocytes. CHMP5 overexpression and silencing vectors were created using an adenovirus system. The effects of CHMP5 on IL-1β-induced chondrocyte apoptosis were investigated by CCK-8, flow cytometry, and western blot. The effects on ECM degradation were examined by western blot and immunofluorescence. The potential mechanism was explored by western blot and Co-IP assays.

RESULTS

Downregulated CHMP5 was identified by proteomics in OA patient cartilages, which was verified in human and mouse articular cartilages. CHMP5 overexpression repressed cell apoptosis and ECM degradation in OA chondrocytes. However, silencing CHMP5 exacerbated OA chondrocyte apoptosis and ECM degradation. Furthermore, we found that the protective effect of CHMP5 against OA was involved in nuclear factor kappa B (NF-κB) signaling pathway.

CONCLUSIONS

This study demonstrated that CHMP5 repressed IL-1β-induced chondrocyte apoptosis and ECM degradation and blocked NF-κB activation. It was shown that CHMP5 might be a novel potential therapeutic target for OA in the future.

Potential therapeutic strategies for osteoarthritis via CRISPR/Cas9 mediated gene editing

Osteoarthritis (OA) is an incapacitating and one of the most common physically degenerative conditions with an assorted etiology and a highly complicated molecular mechanism that to date lacks an efficient treatment. The capacity to design biological networks and accurately modify existing genomic sites holds an apt potential for applications across medical and biotechnological sciences. One of these highly specific genomes editing technologies is the CRISPR/Cas9 mechanism, referred to as the clustered regularly interspaced short palindromic repeats, which is a defense mechanism constituted by CRISPR associated protein 9 (Cas9) directed by small non-coding RNAs (sncRNA) that bind to target DNA through Watson-Crick base pairing rules where subsequent repair of the target DNA is initiated. Up-to-date research has established the effectiveness of the CRISPR/Cas9 mechanism in targeting the genetic and epigenetic alterations in OA by suppressing or deleting gene expressions and eventually distributing distinctive anti-arthritic properties in both in vitro and in vivo osteoarthritic models. This review aims to epitomize the role of this high-throughput and multiplexed gene editing method as an analogous therapeutic strategy that could greatly facilitate the clinical development of OA-related treatments since it's reportedly an easy, minimally invasive technique, and a comparatively less painful method for osteoarthritic patients.

ETS2 overexpression ameliorates cartilage injury in osteoarthritis by the ETS2/miR-155/STAT1/DNMT1 feedback loop pathway

Osteoarthritis (OA) is the most common irreversible chronic joint dysfunction disease, which is pathologically characterized by disturbance of articular cartilage homeostasis leading to subsequent inflammatory response and cartilage extracellular matrix (ECM) degradation. Increasing evidence has demonstrated the dysregulation of transcription factors play crucial roles in the occurrence and development of osteoarthritis (OA), but the potential functions and mechanism of most transcription factors in OA has not been completely illuminated. In this study, we identified that transcription factor V-ets erythroblastosis virus E26 oncogene homolog 2 (ETS2) was significantly down-regulated in OA cartilage and IL-1β-induced OA chondrocytes. Functional experiments in vitro demonstrated that the overexpressed ETS2 strikingly enhanced proliferation, outstandingly suppressed apoptosis, and dramatically reduced inflammation and ECM degradation in IL-1β-induced OA chondrocytes, whereas the knockdown of ETS2 led to the opposite effects. Further in vivo studies have shown that up-regulated ETS2 dramatically ameliorates cartilage injury in DMM-induced OA mice. Mechanical studies have disclosed that DNMT1-mediated downregulation of ETS2 dramatically promotes STAT1 by inhibiting miR-155 transcription, and increased STAT1 initiates a feedback loop that may enhance DNMT1-mediated hypermethylation of ETS2 to inhibit ETS2 expression, thus forming a DNMT1/ETS2/miR-155/STAT1 feedback loop that inhibits MAPK signaling pathways and aggravates OA cartilage injury. In all, our results revealed that overexpression of ETS2 markedly ameliorated OA cartilage injury through the ETS2/miR-155/STAT1/DNMT1 feedback loop, providing a new perspective on the pathogenesis and therapeutic strategies for OA.

The recombinant Link module of human TSG-6 suppresses cartilage damage in models of osteoarthritis: A potential disease-modifying OA drug

OBJECTIVE

To investigate the role of endogenous TSG-6 in human osteoarthritis (OA) and assess the disease-modifying potential of a TSG-6-based biological treatment in cell, explant and animal models of OA.

DESIGN

Knee articular cartilages from OA patients were analyzed for TSG-6 protein and mRNA expression using immunohistochemistry and RNAscope, respectively. The inhibitory activities of TSG-6 and its isolated Link module (Link_TSG6) on cytokine-induced degradation of OA cartilage explants were compared. Human mesenchymal stem/stromal cell-derived chondrocyte pellet cultures were used to determine the effects of Link_TSG6 and full-length TSG-6 on IL-1α-, IL-1β-, or TNF-stimulated ADAMTS4, ADAMTS5, and MMP13 mRNA expression. Link_TSG6 was administered i.a. to the rat ACLTpMMx model; cartilage damage and tactile allodynia were assessed.

RESULTS

TSG-6 is predominantly associated with chondrocytes in regions of cartilage damage where high TSG-6 expression aligns with low MMP13, the major collagenase implicated in OA progression. Link_TSG6 is more potent than full-length TSG-6 at inhibiting cytokine-mediated matrix breakdown in human OA cartilage explants;>50% of donor cartilages, from 59 tested, were responsive to Link_TSG6 treatment. Link_TSG6 also displayed more potent effects in 3D pellet cultures, suppressing ADAMTS4, ADAMTS5, and MMP13 gene expression, which was consistent with reduced aggrecanase and collagenase activities in explant cultures. Link_TSG6 treatment reduced touch-evoked pain behavior and dose-dependently inhibited cartilage damage in a rodent model of surgically-induced OA.

CONCLUSIONS

Link_TSG6 has enhanced chondroprotective activity compared to the full-length TSG-6 protein and shows potential as a disease modifying OA drug via its inhibition of aggrecanase and collagenase activity.

Hyaluronan and Proteoglycan Link Protein 1 Activates the BMP4/Smad1/5/8 Signaling Pathway to Promote Osteogenic Differentiation: an Implication in Fracture Healing

Osteoblast regeneration, characterized by osteoblast differentiation, is the basis of fracture healing and accelerates fracture repair. It has been reported that hyaluronan and proteoglycan link protein 1 (HAPLN1) is overexpressed during osteoblast differentiation and regulates cartilage regeneration, but its function in fracture healing remains unclear. To elucidate this issue, we collected clinical blood samples of fracture healing, established a femoral fracture rat model, and induced an osteoblast differentiation cell model. We found that HAPLN1 was overexpressed in the serum of patients with fracture healing and the bone tissues of rats with fracture healing. Furthermore, the expression of HAPLN1 was increased time dependently during the osteogenic differentiation of MC3T3-E1 cells. HAPLN1 silencing prevented osteoblast differentiation and mineralization in MC3T3-E1 cells as evidenced by decreased osteoblast differentiation-related factors, suppressed alkaline phosphatase activities, and reduced alizarin red positive staining. Mechanically, the bone morphogenic protein 4 (BMP4)/Smad1/5/8 pathway, a facilitator of osteoblastic differentiation, was found to be inhibited by HAPLN1 knockdown, and inhibition of BMP4/Smad1/5/8 signaling enhanced the effects caused by HAPLN1 silencing. These findings demonstrated that HAPLN1 might promote fracture healing by facilitating osteogenic differentiation through the BMP4/Smad1/5/8 pathway, indicating that targeting HAPLN1 may be a feasible therapeutic candidate for fracture repair.

ASPN Synergizes with HAPLN1 to Inhibit the Osteogenic Differentiation of Bone Marrow Mesenchymal Stromal Cells and Extracellular Matrix Mineralization of Osteoblasts

OBJECTIVE

Bone marrow mesenchymal stromal cells (BMSCs) are major sources of osteogenic precursor cells in bone remodeling, which directly participate in osteoporosis (OP) progression. However, the involved specific mechanisms of BMSCs in OP warrant mass investigations. Initially, our bioinformatics analysis uncovered the prominent up-regulation of Asporin (ASPN) and proteoglycan link protein 1 (HAPLN1) in osteoblasts (OBs) of OP patients and their possible protein interaction. Hence, this study aimed to explore the effects of ASPN and HAPLN1 on osteogenic differentiation of BMSCs, extracellular matrix (ECM) mineralization of OBs, and osteoclastogenesis, hoping to offer research basis for OP treatment.

METHODS

GSE156508 dataset was used for analysis and screening to acquire the differentially expressed genes in OBs of OP patients, followed by the predicative analysis via STRING. OP mouse models were induced by ovariectomy (OVX), and ASPN and HAPLN1 expression was determined. BMSCs and bone marrow macrophages (BMMs) were isolated from OVX mice and induced for osteogenic differentiation and osteoclastogenesis, respectively. After knockdown experiments, we assessed adipogenic differentiation and osteogenic differentiation in BMSCs. Osteogenic (OPN, OCN, and COL1A1) and osteoclast (Nfatc1 and c-Fos) marker protein expression was determined. The binding of ASPN to HAPLN1 was analyzed.

RESULTS

High expression of ASPN and HAPLN1 and their protein interaction were observed in OBs of OP patients via bioinformatics and in bone tissues of OVX mice. ASPN interacted with HAPLN1 in BMSCs of OVX mice. ASPN/HAPLN1 knockdown increased ALP, OPN, OCN, and COL1A1 protein expression and ECM mineralization in BMSCs while decreasing Nfatc1 and c-Fos expression in BMMs. These effects were aggravated by the simultaneous knockdown of ASPN and HAPLN1.

CONCLUSION

Our results indicate that ASPN synergises with HAPLN1 to suppress the osteogenic differentiation of BMSCs and ECM mineralization of OBs and promote the osteoclastogenesis in OP.

NEAT1-mediated miR-150-5p downregulation regulates b-catenin expression in OA chondrocytes

We investigated the role of miR-150-5p in osteoarthritic (OA) chondrocytes, as well as the possible regulatory role of long non-coding RNAs (lncRNAs) in miR-150-5p expression. TargetScan, StarBase, DIANA-LncBase, and Open Targets databases were used to predict miR-150-5p target genes, lncRNAs/miR-150-5p interactions, and OA-related genes. Protein-protein interaction (PPI) network was constructed using the Search Tool for the Retrieval of Interacting Genes/Proteins (STRING). Gene ontology (GO) and pathway analysis were performed using Enrichr database. A publicly available RNA-seq dataset was retrieved to identify differentially expressed lncRNAs in damaged vs intact cartilage. We re-analyzed the retrieved RNA-seq data and revealed 177 differentially expressed lncRNAs in damage vs intact cartilage, including Nuclear Paraspeckle Assembly Transcript 1(NEAT1). MiR-150-5p, NEAT1, b-catenin, matrix metallopeptidase 13 (MMP-13), and ADAM metallopeptidase with thrombospondin type 1 motif 5 (ADAMTS-5) expressions were assessed by reverse transcription-quantitative PCR (RT-qPCR) and western blot assay. Knockout and transfection experiments were conducted to investigate the role of NEAT1/miR-150-5p/b-catenin in cartilage degradation. Bioinformatics analysis revealed that b-catenin was an OA-related miR-150-5p target. MiR-150-5p overexpression in OA chondrocytes resulted in decreased expression of b-catenin, as well as MMP-13 and ADAMTS-5, both being Wnt/b-catenin downstream target genes. NEAT1/miR-150-5p interaction was predicted by bioinformatics analysis, while NEAT1 knockout led to increased expression of miR-150-5p in OA chondrocytes. Moreover, inhibition of miR-150-5p reversed the repressive effects of NEAT1 silencing in b-catenin expression in OA chondrocytes. Our results support a possible catabolic role of NEAT1/miR-150-5p interaction in OA progression by regulating b-catenin expression.

Calcitriol-Loaded Multifunctional Nanospheres with Superlubricity for Advanced Osteoarthritis Treatment

Osteoarthritis (OA) is characterized by the lubrication dysfunction of a cartilage sliding interface caused by chronic joint inflammation, and effective nonsurgical therapy for advanced OA remains lacking. Addressing chronic joint inflammation, lubrication dysfunction, and cartilage-tissue degradation simultaneously may hopefully tackle this challenge. Herein, we developed superlubricative zein@alginate/strontium@calcitriol (ZASC) nanospheres to treat advanced OA. ZASC was confirmed to significantly improve joint lubrication through traditional tribological tests and our proposed tribological experiment to mimic the intra-articular condition based on the human medial tibiofemoral joint tissues. This finding was attributed to the hydration lubrication formed around the alginate-strontium spheres that enabled ball-bearing lubrication and the filling of cartilage defects. Moreover, ZASCs that released calcitriol in a sustained manner showed proliferative, anti-inflammatory, and anti-apoptosis effects in vitro. Further experiments demonstrated that ZASC exerted chondroprotective effects by inhibiting the breakdown of the extracellular matrix in patient-derived OA cartilage explants. In vivo results demonstrated that ZASC can effectively maintain a normal gait to improve joint function, inhibit abnormal bone remodeling and cartilage degradation in early OA and can effectively reverse the advanced OA progression. Therefore, ZASC is a potentially nonsurgical therapeutic strategy for advanced OA treatments.

FOXM1: Functional Roles of FOXM1 in Non-Malignant Diseases

Forkhead box (FOX) proteins are a wing-like helix family of transcription factors in the DNA-binding region. By mediating the activation and inhibition of transcription and interactions with all kinds of transcriptional co-regulators (MuvB complexes, STAT3, β-catenin, etc.), they play significant roles in carbohydrate and fat metabolism, biological aging and immune regulation, development, and diseases in mammals. Recent studies have focused on translating these essential findings into clinical applications in order to improve quality of life, investigating areas such as diabetes, inflammation, and pulmonary fibrosis, and increase human lifespan. Early studies have shown that forkhead box M1 (FOXM1) functions as a key gene in pathological processes in multiple diseases by regulating genes related to proliferation, the cell cycle, migration, and apoptosis and genes related to diagnosis, therapy, and injury repair. Although FOXM1 has long been studied in relation to human diseases, its role needs to be elaborated on. FOXM1 expression is involved in the development or repair of multiple diseases, including pulmonary fibrosis, pneumonia, diabetes, liver injury repair, adrenal lesions, vascular diseases, brain diseases, arthritis, myasthenia gravis, and psoriasis. The complex mechanisms involve multiple signaling pathways, such as WNT/β-catenin, STAT3/FOXM1/GLUT1, c-Myc/FOXM1, FOXM1/SIRT4/NF-κB, and FOXM1/SEMA3C/NRP2/Hedgehog. This paper reviews the key roles and functions of FOXM1 in kidney, vascular, lung, brain, bone, heart, skin, and blood vessel diseases to elucidate the role of FOXM1 in the development and progression of human non-malignant diseases and makes suggestions for further research.

Transcriptomic changes in porcine articular cartilage one year following disruption of the anterior cruciate ligament

To determine the transcriptomic changes seen in early- to mid-stage posttraumatic osteoarthritis (PTOA) development, 72 Yucatan minipigs underwent transection of the anterior cruciate ligament. Subjects were randomized to no further intervention, ligament reconstruction, or ligament repair, followed by articular cartilage harvesting and RNA-sequencing at three different postoperative timepoints (1, 4, and 52 weeks). Six additional subjects received no ligament transection and provided cartilage tissue to serve as controls. Differential gene expression analysis between post-transection cartilage and healthy cartilage revealed an initial increase in transcriptomic differences at 1 and 4 weeks followed by a stark reduction in transcriptomic differences at 52 weeks. This analysis also showed how different treatments genetically modulate the course of PTOA following ligament disruption. Specific genes (e.g., MMP1, POSTN, IGF1, PTGFR, HK1) were identified as being upregulated in the cartilage of injured subjects across all timepoints regardless of treatment. At the 52-week timepoint, 4 genes (e.g., A4GALT, EFS, NPTXR, ABCA3) that-as far as we know-have yet to be associated with PTOA were identified as being concordantly differentially expressed across all treatment groups when compared to controls. Functional pathway analysis of injured subject cartilage compared to control cartilage revealed overarching patterns of cellular proliferation at 1 week, angiogenesis, ECM interaction, focal adhesion, and cellular migration at 4 weeks, and calcium signaling, immune system activation, GABA signaling, and HIF-1 signaling at 52 weeks.

Spatial Lipidomic Profiling of Mouse Joint Tissue Demonstrates the Essential Role of PHOSPHO1 in Growth Plate Homeostasis

Lipids play a crucial role in signaling and metabolism, regulating the development and maintenance of the skeleton. Membrane lipids have been hypothesized to act as intermediates upstream of orphan phosphatase 1 (PHOSPHO1), a major contributor to phosphate generation required for bone mineralization. Here, we spatially resolve the lipid atlas of the healthy mouse knee and demonstrate the effects of PHOSPHO1 ablation on the growth plate lipidome. Lipids spanning 17 subclasses were mapped across the knee joints of healthy juvenile and adult mice using matrix-assisted laser desorption ionization imaging mass spectrometry (MALDI-IMS), with annotation supported by shotgun lipidomics. Multivariate analysis identified 96 and 80 lipid ions with differential abundances across joint tissues in juvenile and adult mice, respectively. In both ages, marrow was enriched in phospholipid platelet activating factors (PAFs) and related metabolites, cortical bone had a low lipid content, whereas lysophospholipids were strikingly enriched in the growth plate, an active site of mineralization and PHOSPHO1 activity. Spatially-resolved profiling of PHOSPHO1-knockout (KO) mice across the resting, proliferating, and hypertrophic growth plate zones revealed 272, 306, and 296 significantly upregulated, and 155, 220, and 190 significantly downregulated features, respectively, relative to wild-type (WT) controls. Of note, phosphatidylcholine, lysophosphatidylcholine, sphingomyelin, lysophosphatidylethanolamine, and phosphatidylethanolamine derived lipid ions were upregulated in PHOSPHO1-KO versus WT. Our imaging pipeline has established a spatially-resolved lipid signature of joint tissues and has demonstrated that PHOSPHO1 ablation significantly alters the growth plate lipidome, highlighting an essential role of the PHOSPHO1-mediated membrane phospholipid metabolism in lipid and bone homeostasis. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Activated intestinal microbiome-associated tryptophan metabolism upregulates aryl hydrocarbon receptor to promote osteoarthritis in a rat model

OBJECTIVE

To evaluate the role of aryl hydrocarbon receptor in the pathogenesis of osteoarthritis (OA) and its association with intestinal microbiome-related tryptophan metabolism.

METHODS

Cartilage was isolated from OA patients undergoing total knee arthroplasty and analyzed for expression of aryl hydrocarbon receptor (AhR) and cytochrome P450 of family 1, subfamily A, and polypeptide 1 (CyP1A1). To gain mechanistic insights, OA model was induced in Sprague Dawley rats after antibiotic pretreatment combined with a tryptophan-rich diet (or not). The severity of OA was assessed eight weeks after surgery according to the Osteoarthritis Research Society International grading system. Expression of AhR, CyP1A1 as well as markers of bone and cartilage metabolism, inflammation, and intestinal microbiome-related tryptophan metabolism was assessed.

RESULTS

Severity of OA in cartilage from patients positively correlated with expression of AhR and CyP1A1 in chondrocytes. In the rat model of OA, antibiotic pretreatment led to lower expression of AhR and CyP1A1 and lower serum levels of lipopolysaccharide (LPS). Conversely, antibiotics upregulated Col2A1 and SOX9 in cartilage, which mitigated the cartilage damage and synovitis, reduced the relative abundance of Lactobacillus. Additional tryptophan supplementation activated intestinal microbiome-related tryptophan metabolism, antagonizing the effects of antibiotics, exacerbating OA synovitis.

CONCLUSION

Our study established an underlying intestinal microbiome associated tryptophan metabolism-OA connection which sets a new target for exploring OA pathogenesis. The alteration of tryptophan metabolism might prompt the activation and synthesis of AhR, accelerating the development of OA.

Good Manufacturing Practice-compliant change of raw material in the manufacturing process of a clinically used advanced therapy medicinal product-a comparability study

The development of medicinal products often continues throughout the different phases of a clinical study and may require challenging changes in raw and starting materials at later stages. Comparability between the product properties pre- and post-change thus needs to be ensured. Here, we describe and validate the regulatory compliant change of a raw material using the example of a nasal chondrocyte tissue-engineered cartilage (N-TEC) product, initially developed for treatment of confined knee cartilage lesions. Scaling up the size of N-TEC as required for the treatment of larger osteoarthritis defects required the substitution of autologous serum with a clinical-grade human platelet lysate (hPL) to achieve greater cell numbers necessary for the manufacturing of larger size grafts. A risk-based approach was performed to fulfill regulatory requirements and demonstrate comparability of the products manufactured with the standard process (autologous serum) already applied in clinical indications and the modified process (hPL). Critical attributes with regard to quality, purity, efficacy, safety and stability of the product as well as associated test methods and acceptance criteria were defined. Results showed that hPL added during the expansion phase of nasal chondrocytes enhances proliferation rate, population doublings and cell numbers at passage 2 without promoting the overgrowth of potentially contaminant perichondrial cells. N-TEC generated with the modified versus standard process contained similar content of DNA and cartilaginous matrix proteins with even greater expression levels of chondrogenic genes. The increased risk for tumorigenicity potentially associated with the use of hPL was assessed through karyotyping of chondrocytes at passage 4, revealing no chromosomal changes. Moreover, the shelf-life of N-TEC established for the standard process could be confirmed with the modified process. In conclusion, we demonstrated the introduction of hPL in the manufacturing process of a tissue engineered product, already used in a late-stage clinical trial. Based on this study, the national competent authorities in Switzerland and Germany accepted the modified process which is now applied for ongoing clinical tests of N-TEC. The described activities can thus be taken as a paradigm for successful and regulatory compliant demonstration of comparability in advanced therapy medicinal products manufacturing.

Mechanotransduction pathways in articular chondrocytes and the emerging role of estrogen receptor-α

In the synovial joint, mechanical force creates an important signal that influences chondrocyte behavior. The conversion of mechanical signals into biochemical cues relies on different elements in mechanotransduction pathways and culminates in changes in chondrocyte phenotype and extracellular matrix composition/structure. Recently, several mechanosensors, the first responders to mechanical force, have been discovered. However, we still have limited knowledge about the downstream molecules that enact alterations in the gene expression profile during mechanotransduction signaling. Recently, estrogen receptor α (ERα) has been shown to modulate the chondrocyte response to mechanical loading through a ligand-independent mechanism, in line with previous research showing that ERα exerts important mechanotransduction effects on other cell types, such as osteoblasts. In consideration of these recent discoveries, the goal of this review is to position ERα into the mechanotransduction pathways known to date. Specifically, we first summarize our most recent understanding of the mechanotransduction pathways in chondrocytes on the basis of three categories of actors, namely mechanosensors, mechanotransducers, and mechanoimpactors. Then, the specific roles played by ERα in mediating the chondrocyte response to mechanical loading are discussed, and the potential interactions of ERα with other molecules in mechanotransduction pathways are explored. Finally, we propose several future research directions that may advance our understanding of the roles played by ERα in mediating biomechanical cues under physiological and pathological conditions.

Osteoarthritis: pathogenic signaling pathways and therapeutic targets

Osteoarthritis (OA) is a chronic degenerative joint disorder that leads to disability and affects more than 500 million population worldwide. OA was believed to be caused by the wearing and tearing of articular cartilage, but it is now more commonly referred to as a chronic whole-joint disorder that is initiated with biochemical and cellular alterations in the synovial joint tissues, which leads to the histological and structural changes of the joint and ends up with the whole tissue dysfunction. Currently, there is no cure for OA, partly due to a lack of comprehensive understanding of the pathological mechanism of the initiation and progression of the disease. Therefore, a better understanding of pathological signaling pathways and key molecules involved in OA pathogenesis is crucial for therapeutic target design and drug development. In this review, we first summarize the epidemiology of OA, including its prevalence, incidence and burdens, and OA risk factors. We then focus on the roles and regulation of the pathological signaling pathways, such as Wnt/β-catenin, NF-κB, focal adhesion, HIFs, TGFβ/ΒΜP and FGF signaling pathways, and key regulators AMPK, mTOR, and RUNX2 in the onset and development of OA. In addition, the roles of factors associated with OA, including MMPs, ADAMTS/ADAMs, and PRG4, are discussed in detail. Finally, we provide updates on the current clinical therapies and clinical trials of biological treatments and drugs for OA. Research advances in basic knowledge of articular cartilage biology and OA pathogenesis will have a significant impact and translational value in developing OA therapeutic strategies.

Combining single-cell transcriptomics and CellTagging to identify differentiation trajectories of human adipose-derived mesenchymal stem cells

BACKGROUND

Mesenchymal stromal cells (MSCs) have attracted great attention in the application of cell-based therapy because of their pluripotent differentiation and immunomodulatory ability. Due to the limited number of MSCs isolated from donor tissues, a large number of MSCs need to be expanded in a traditional two-dimensional cell culture device to obtain a sufficient therapeutic amount. However, long-term cultivation of MSCs in vitro has been proven to reduce their differentiation potential and change their immunomodulatory characteristics. We aimed to explore the cellular heterogeneity and differentiation potential of different MSCs expanded in vitro and reconstruct the complex cloning track of cells in the process of differentiation.

METHODS

Single cell transcriptome sequencing was combined with 'CellTagging', which is a composite barcode indexing method that can capture the cloning history and cell identity in parallel to track the differentiation process of the same cell over time.

RESULTS

Through the single-cell transcriptome and CellTagging, we found that the heterogeneity of human adipose tissue derived stem cells (hADSCs) in the early stage of culture was very limited. With the passage, the cells spontaneously differentiated during the process of division and proliferation, and the heterogeneity of the cells increased. By tracing the differentiation track of cells, we found most cells have the potential for multidirectional differentiation, while a few cells have the potential for unidirectional differentiation. One subpopulation of hADSCs with the specific osteoblast differentiation potential was traced from the early stage to the late stage, which indicates that the differentiation trajectories of the cells are determined in the early stages of lineage transformation. Further, considering that all genes related to osteogenic differentiation have not yet been determined, we identified that there are some genes that are highly expressed specifically in the hADSC subsets that can successfully differentiate into osteoblasts, such as Serpin Family E Member 2 (SERPINE2), Secreted Frizzled Related Protein 1 (SFRP1), Keratin 7 (KRT7), Peptidase Inhibitor 16 (PI16), and Carboxypeptidase E (CPE), which may be key regulatory genes for osteogenic induction, and finally proved that the SERPINE2 gene can promote the osteogenic process.

CONCLUSION

The results of this study contribute toward the exploration of the heterogeneity of hADSCs and improving our understanding of the influence of heterogeneity on the differentiation potential of cells. Through this study, we found that the SERPINE2 gene plays a decisive role in the osteogenic differentiation of hADSCs, which lays a foundation for establishing a more novel and complete induction system.

Acute loading has minor influence on human articular cartilage gene expression and glycosaminoglycan composition in late-stage knee osteoarthritis: a randomised controlled trial

OBJECTIVE

Osteoarthritis (OA) remains clinically challenging. Regular physical exercise improves symptoms though it is unclear whether exercise influences cartilage at the molecular level. Thus, we aimed to determine the effect of acute loading on gene expression and glycosaminoglycan (GAG) content in human OA cartilage.

DESIGN

Patients with primary knee OA participated in this single-blind randomised controlled trial initiated 3.5 h prior to scheduled joint replacement surgery with or without loading by performing one bout of resistance exercise (one-legged leg press). Cartilage from the medial tibia condyle was sampled centrally, under the meniscus, and from peripheral osteophytes. Samples were analysed for gene expression by real-time reverse transcriptase polymerase chain reaction, and hyaluronidase-extracted matrix was analysed for GAG composition by immuno- and dimethyl-methylene blue assays.

RESULTS

Of 32 patients randomised, 31 completed the intervention: mean age 69 ± 7.5 years (SD), 58% female, BMI 29.4 ± 4.4 kg/m². Exercise increased chondroitin sulphate extractability [95% CI: 1.01 to 2.46; P = 0.0486] but cartilage relevant gene expression was unchanged. Regionally, the submeniscal area showed higher MMP-3, MMP-13, IGF-1Ea, and CTGF, together with lower lubricin and COMP expression compared to the central condylar region. Further, osteophyte expression of MMP-1, MMP-13, IGF-1Ea, and TGF-β3 was higher than articular cartilage and lower for aggrecan, COMP, and FGF-2. Hyaluronidase-extracted matrix from central condylar cartilage contained more GAGs but less chondroitin sulphate compared to submeniscal cartilage.

CONCLUSION

Acute exercise had minor influence on cartilage GAG dynamics, indicating that osteoarthritic cartilage is not significantly affected by acute exercise. However, the regional differences suggest a chronic mechanical influence on human cartilage.

CLINICALTRIALS

GOV REGISTRATION NUMBER

NCT03410745.

Modulation of the long non-coding RNA Mir155hg by high, but not moderate, hydrostatic pressure in cartilage precursor cells

Osteoarthritis (OA) is the most common joint disease in older adults and is characterized by a gradual degradation of articular cartilage due to decreased cartilage matrix gene expression and increased expression of genes involved in protein degradation, apoptosis and inflammation. Due to the high water content of cartilage, one of the main physical stimuli sensed by chondrocytes is hydrostatic pressure. We previously showed that high pressure above 20 MPa induced gene expression changes in chondrocyte precursor cells similar to what is observed in OA. Micro-RNAs are small non-coding RNAs essential to many physiological and pathological process including OA. As the micro-RNA miR-155 has been found increased in OA chondrocytes, we investigated the effects of high pressure on the expression of the miR-155 host gene Mir155hg. The chondrocyte progenitor cell line ATDC5 was pressurized under hydrostatic pressure up to 25 MPa and the expression of Mir155hg or the resulting micro-RNAs were measured; pharmacological inhibitors were used to identify the signaling pathways involved in the regulation of Mir155hg. We found that Mir155hg is strongly and rapidly up-regulated by high, but not moderate, pressure in chondrocyte progenitor cells. This up-regulation likely involves the membrane channel pannexin-1 and several intracellular signaling molecules including PKC and Src. MiR-155-5p and -3p were also up-regulated by pressure though somewhat later than Mir155hg, and a set of known miR-155-5p target genes, including Ikbke, Smarca4 and Ywhae, was affected by pressure, suggesting that Mir155hg may have important roles in cartilage physiology.

Angiopoietin-like 3-derivative LNA043 for cartilage regeneration in osteoarthritis: a randomized phase 1 trial

Osteoarthritis (OA) is a common, debilitating, chronic disease with no disease-modifying drug approved to date. We discovered LNA043-a derivative of angiopoietin-like 3 (ANGPTL3)-as a potent chondrogenesis inducer using a phenotypic screen with human mesenchymal stem cells. We show that LNA043 promotes chondrogenesis and cartilage matrix synthesis in vitro and regenerates hyaline articular cartilage in preclinical OA and cartilage injury models in vivo. LNA043 exerts at least part of these effects through binding to the fibronectin receptor, integrin α5β1 on mesenchymal stem cells and chondrocytes. In a first-in-human (phase 1), randomized, double-blinded, placebo-controlled, single ascending dose, single-center trial ( NCT02491281 ; sponsored by Novartis Pharmaceuticals), 28 patients with knee OA were injected intra-articularly with LNA043 or placebo (3:1 ratio) either 2 h, 7 d or 21 d before total knee replacement. LNA043 met its primary safety endpoint and showed short serum pharmacokinetics, cartilage penetration and a lack of immunogenicity (secondary endpoints). Post-hoc transcriptomics profiling of cartilage revealed that a single LNA043 injection reverses the OA transcriptome signature over at least 21 d, inducing the expression of hyaline cartilage matrix components and anabolic signaling pathways, while suppressing mediators of OA progression. LNA043 is a novel disease-modifying OA drug candidate that is currently in a phase 2b trial ( NCT04864392 ) in patients with knee OA.

Histone H3K27 demethylase UTX compromises articular chondrocyte anabolism and aggravates osteoarthritic degeneration

Epigenome alteration in chondrocytes correlates with osteoarthritis (OA) development. H3K27me3 demethylase UTX regulates tissue homeostasis and deterioration, while its role was not yet studied in articulating joint tissue in situ. We now uncovered that increased UTX and H3K27me3 expression in articular chondrocytes positively correlated with human knee OA. Forced UTX expression upregulated the H3K27me3 enrichment at transcription factor Sox9 promoter, inhibiting key extracellular matrix molecules collagen II, aggrecan, and glycosaminoglycan in articular chondrocytes. Utx overexpression in knee joints aggravated the signs of OA, including articular cartilage damage, synovitis, osteophyte formation, and subchondral bone loss in mice. Chondrocyte-specific Utx knockout mice developed thicker articular cartilage than wild-type mice and showed few gonarthrotic symptoms during destabilized medial meniscus- and collagenase-induced joint injury. In vitro, Utx loss changed H3K27me3-binding epigenomic landscapes, which contributed to mitochondrial activity, cellular senescence, and cartilage development. Insulin-like growth factor 2 (Igf2) and polycomb repressive complex 2 (PRC2) core components Eed and Suz12 were, among others, functional target genes of Utx. Specifically, Utx deletion promoted Tfam transcription, mitochondrial respiration, ATP production and Igf2 transcription but inhibited Eed and Suz12 expression. Igf2 blockade or forced Eed or Suz12 expression increased H3K27 trimethylation and H3K27me3 enrichment at Sox9 promoter, compromising Utx loss-induced extracellular matrix overproduction. Taken together, UTX repressed articular chondrocytic activity, accelerating cartilage loss during OA. Utx loss promoted cartilage integrity through epigenetic stimulation of mitochondrial biogenesis and Igf2 transcription. This study highlighted a novel noncanonical role of Utx, in concert with PRC2 core components, in controlling H3K27 trimethylation and articular chondrocyte anabolism and OA development.

The regional turnover of cartilage collagen matrix in late-stage human knee osteoarthritis

OBJECTIVE

Cartilage collagen has very limited repair potential, though some turnover and incorporation has not been fully excluded. We aim to determine the regional turnover of human osteoarthritis cartilage.

DESIGN

Patients scheduled for knee joint replacement surgery due to osteoarthritis were recruited in this prospective study of four weeks duration. Deuterium oxide (D₂O) was administered orally by weekly boluses at 70% D₂O, initially 150 ml followed by three boluses of 50 ml. Cartilage from the medial tibia plateau was sampled centrally, under the meniscus, and from osteophytes and treated enzymatically with hyaluronidase and trypsin. Samples were analysed for deuterium incorporation in alanine using mass spectrometry and for gene expression by real-time reverse transcriptase polymerase chain reaction.

RESULTS

Twenty participants completed the study: mean (SD) age 64 ± 9.1 years, 45% female, BMI 29.5 ± 4.8 kg/m². Enzymatically treated cartilage from central and submeniscal regions showed similar enrichments at 0.063% APE, while osteophytes showed significantly greater enrichment at 0.072% APE (95% confidence interval of difference) [0.004-0.015]). Fractional synthesis rates were similar for central 0.027%/day and submeniscal cartilage 0.022%/day but 10-fold higher in osteophytes 0.22%/day [0.098-0.363]. When compared to central cartilage, submeniscal cartilage had increased gene expression of MMP-3 and decreased lubricin expression. Untreated cartilage had higher turnover (enrichments at 0.073% APE) than enzymatically treated cartilage (0.063% APE).

CONCLUSIONS

In OA, despite regional differences in gene expression, the turnover of the articular cartilage matrix across the entire joint surface is very limited, but higher turnover was observed in osteophyte cartilage.

Transcriptional regulation of cyclophilin D by BMP/Smad signaling and its role in osteogenic differentiation

Cyclophilin D (CypD) promotes opening of the mitochondrial permeability transition pore (MPTP) which plays a key role in both cell physiology and pathology. It is, therefore, beneficial for cells to tightly regulate CypD and MPTP but little is known about such regulation. We have reported before that CypD is downregulated and MPTP deactivated during differentiation in various tissues. Herein, we identify BMP/Smad signaling, a major driver of differentiation, as a transcriptional regulator of the CypD gene, Ppif. Using osteogenic induction of mesenchymal lineage cells as a BMP/Smad activation-dependent differentiation model, we show that CypD is in fact transcriptionally repressed during this process. The importance of such CypD downregulation is evidenced by the negative effect of CypD 'rescue' via gain-of-function on osteogenesis both in vitro and in a mouse model. In sum, we characterized BMP/Smad signaling as a regulator of CypD expression and elucidated the role of CypD downregulation during cell differentiation.

The Added Value of the “Co” in Co-Culture Systems in Research on Osteoarthritis Pathology and Treatment Development

Osteoarthritis (OA) is a highly prevalent disease and a major health burden. Its development and progression are influenced by factors such as age, obesity or joint overuse. As a whole organ disease OA affects not only cartilage, bone and synovium but also ligaments, fatty or nervous tissue surrounding the joint. These joint tissues interact with each other and understanding this interaction is important in developing novel treatments. To incorporate and study these interactions in OA research, several co-culture models have evolved. They combine two or more cell types or tissues and investigate the influence of amongst others inflammatory or degenerative stimuli seen in OA. This review focuses on co-cultures and the differential processes occurring in a given tissue or cell as a consequence of being combined with another joint cell type or tissue, and/or the extent to which a co-culture mimics the in vivo processes. Most co-culture models depart from synovial lining and cartilage culture, but also fat pad and bone have been included. Not all of the models appear to reflect the postulated in vivo OA pathophysiology, although some of the discrepancies may indicate current assumptions on this process are not entirely valid. Systematic analysis of the mutual influence the separate compartments in a given model exert on each other and validation against in vivo or ex vivo observation is still largely lacking and would increase their added value as in vitro OA models.

Selenophosphate synthetase 1 deficiency exacerbates osteoarthritis by dysregulating redox homeostasis

Aging and mechanical overload are prominent risk factors for osteoarthritis (OA), which lead to an imbalance in redox homeostasis. The resulting state of oxidative stress drives the pathological transition of chondrocytes during OA development. However, the specific molecular pathways involved in disrupting chondrocyte redox homeostasis remain unclear. Here, we show that selenophosphate synthetase 1 (SEPHS1) expression is downregulated in human and mouse OA cartilage. SEPHS1 downregulation impairs the cellular capacity to synthesize a class of selenoproteins with oxidoreductase functions in chondrocytes, thereby elevating the level of reactive oxygen species (ROS) and facilitating chondrocyte senescence. Cartilage-specific Sephs1 knockout in adult mice causes aging-associated OA, and augments post-traumatic OA, which is rescued by supplementation of N-acetylcysteine (NAC). Selenium-deficient feeding and Sephs1 knockout have synergistic effects in exacerbating OA pathogenesis in mice. Therefore, we propose that SEPHS1 is an essential regulator of selenium metabolism and redox homeostasis, and its dysregulation governs the progression of OA.

Osteoarthritis is caused by the gradual accumulation of oxidative stress in cartilage. Here, the authors show that dysregulation of the selenium metabolic pathway underlies a shift in redox homeostasis in chondrocytes, leading to chronic osteoarthritic changes in joints.

Engineering osteoarthritic cartilage model through differentiating senescent human mesenchymal stem cells for testing disease-modifying drugs

Significant cellular senescence has been observed in cartilage harvested from patients with osteoarthritis (OA). In this study, we aim to develop a senescence-relevant OA-like cartilage model for developing disease-modifying OA drugs (DMOADs). Specifically, human bone marrow-derived mesenchymal stromal cells (MSCs) were expanded in vitro up to passage 10 (P10-MSCs). Following their senescent phenotype formation, P10-MSCs were subjected to pellet culture in chondrogenic medium. Results from qRT-PCR, histology, and immunostaining indicated that cartilage generated from P10-MSCs displayed both senescent and OA-like phenotypes without using other OA-inducing agents, when compared to that from normal passage 4 (P4)-MSCs. Interestingly, the same gene expression differences observed between P4-MSCs and P10-MSC-derived cartilage tissues were also observed between the preserved and damaged OA cartilage regions taken from human samples, as demonstrated by RNA Sequencing data and other analysis methods. Lastly, the utility of this senescence-initiated OA-like cartilage model in drug development was assessed by testing several potential DMOADs and senolytics. The results suggest that pre-existing cellular senescence can induce the generation of OA-like changes in cartilage. The P4- and P10-MSCs derived cartilage models also represent a novel platform for predicting the efficacy and toxicity of potential DMOADs on both preserved and damaged cartilage in humans.

Novel role of estrogen receptor-α on regulating chondrocyte phenotype and response to mechanical loading

OBJECTIVE

In knee cartilage from patients with osteoarthritis (OA), both preserved cartilage and damaged cartilage are observed. In this study, we aim to compare preserved with damaged cartilage to identify the molecule(s) that may be responsible for the mechanical loading-induced differences within cartilage degradation.

METHODS

Preserved and damaged cartilage were harvested from the same OA knee joint. RNA Sequencing was performed to examine the transcriptomic differences between preserved and damaged cartilage cells. Estrogen receptor-α (ERα) was identified, and its function of was tested through gene knockin and knockout. The role of ERα in mediating chondrocyte response to mechanical loading was examined via compression of chondrocyte-laded hydrogel in a strain-controlled manner. Findings from the studies on human samples were verified in animal models.

RESULTS

Level of estrogen receptor α (ERα) was significantly reduced in damaged cartilage compared to preserved cartilage, which were observed in both human and mice samples. Knockdown of ESR1, the gene encoding ERα, resulted in an upregulation of senescence- and OA-relevant markers in chondrocytes. Conversely, knockin of ESR1 partially reversed the osteoarthritic and senescent phenotype of OA chondrocytes. Using a three-dimensional (3D) culture model, we demonstrated that mechanical overload significantly suppressed ERα level in chondrocytes with concomitant upregulation of osteoarthritic phenotype. When ESR1 expression was suppressed, mechanical loading enhanced hypertrophic and osteogenic transition.

CONCLUSION

Our study demonstrates a new estrogen-independent role of ERα in mediating chondrocyte phenotype and its response to mechanical loading, and suggests that enhancing ERα level may represent a new method to treat osteoarthritis.

A molecular map of long non-coding RNA expression, isoform switching and alternative splicing in osteoarthritis

Osteoarthritis is a prevalent joint disease and a major cause of disability worldwide with no curative therapy. Development of disease-modifying therapies requires a better understanding of the molecular mechanisms underpinning disease. A hallmark of osteoarthritis is cartilage degradation. To define molecular events characterizing osteoarthritis at the whole transcriptome level, we performed deep RNA sequencing in paired samples of low- and high-osteoarthritis grade knee cartilage derived from 124 patients undergoing total joint replacement. We detected differential expression between low- and high-osteoarthritis grade articular cartilage for 365 genes and identified a 38-gene signature in osteoarthritis cartilage by replicating our findings in an independent dataset. We also found differential expression for 25 novel long non-coding RNA genes (lncRNAs) and identified potential lncRNA interactions with RNA-binding proteins in osteoarthritis. We assessed alterations in the relative usage of individual gene transcripts and identified differential transcript usage for 82 genes, including ABI3BP, coding for an extracellular matrix protein, AKT1S1, a negative regulator of the mTOR pathway and TPRM4, coding for a transient receptor potential channel. We further assessed genome-wide differential splicing, for the first time in osteoarthritis, and detected differential splicing for 209 genes, which were enriched for extracellular matrix, proteoglycans and integrin surface interactions terms. In the largest study of its kind in osteoarthritis, we find that isoform and splicing changes, in addition to extensive differences in both coding and non-coding sequence expression, are associated with disease and demonstrate a novel layer of genomic complexity to osteoarthritis pathogenesis.

Mechanical Cues: Bidirectional Reciprocity in the Extracellular Matrix Drives Mechano-Signalling in Articular Cartilage

The composition and organisation of the extracellular matrix (ECM), particularly the pericellular matrix (PCM), in articular cartilage is critical to its biomechanical functionality; the presence of proteoglycans such as aggrecan, entrapped within a type II collagen fibrillar network, confers mechanical resilience underweight-bearing. Furthermore, components of the PCM including type VI collagen, perlecan, small leucine-rich proteoglycans—decorin and biglycan—and fibronectin facilitate the transduction of both biomechanical and biochemical signals to the residing chondrocytes, thereby regulating the process of mechanotransduction in cartilage. In this review, we summarise the literature reporting on the bidirectional reciprocity of the ECM in chondrocyte mechano-signalling and articular cartilage homeostasis. Specifically, we discuss studies that have characterised the response of articular cartilage to mechanical perturbations in the local tissue environment and how the magnitude or type of loading applied elicits cellular behaviours to effect change. In vivo, including transgenic approaches, and in vitro studies have illustrated how physiological loading maintains a homeostatic balance of anabolic and catabolic activities, involving the direct engagement of many PCM molecules in orchestrating this slow but consistent turnover of the cartilage matrix. Furthermore, we document studies characterising how abnormal, non-physiological loading including excessive loading or joint trauma negatively impacts matrix molecule biosynthesis and/or organisation, affecting PCM mechanical properties and reducing the tissue’s ability to withstand load. We present compelling evidence showing that reciprocal engagement of the cells with this altered ECM environment can thus impact tissue homeostasis and, if sustained, can result in cartilage degradation and onset of osteoarthritis pathology. Enhanced dysregulation of PCM/ECM turnover is partially driven by mechanically mediated proteolytic degradation of cartilage ECM components. This generates bioactive breakdown fragments such as fibronectin, biglycan and lumican fragments, which can subsequently activate or inhibit additional signalling pathways including those involved in inflammation. Finally, we discuss how bidirectionality within the ECM is critically important in enabling the chondrocytes to synthesise and release PCM/ECM molecules, growth factors, pro-inflammatory cytokines and proteolytic enzymes, under a specified load, to influence PCM/ECM composition and mechanical properties in cartilage health and disease.

Low-Input RNA-Sequencing in Patients with Cartilage Lesions, Osteoarthritis, and Healthy Cartilage

OBJECTIVE

To analyze and compare cartilage samples from 3 groups of patients utilizing low-input RNA-sequencing.

DESIGN

Cartilage biopsies were collected from patients in 3 groups (n = 48): Cartilage lesion (CL) patients had at least ICRS grade 2, osteoarthritis (OA) samples were taken from patients undergoing knee replacement, and healthy cartilage (HC) was taken from ACL-reconstruction patients without CLs. RNA was isolated using an optimized protocol. RNA samples were assessed for quality and sequenced with a low-input SmartSeq2 protocol.

RESULTS

RNA isolation yielded 48 samples with sufficient quality for sequencing. After quality control, 13 samples in the OA group, 9 in the HC group, and 9 in the CL group were included in the analysis. There was a high degree of co-clustering between the HC and CL groups with only 6 genes significantly up- or downregulated. OA and the combined HC/CL group clustered significantly separate from each other, yielding 659 significantly upregulated and 1,369 downregulated genes. GO-term analysis revealed that genes matched to cartilage and connective tissue development terms.

CONCLUSION

The gene expression profiles from the 3 groups suggest that there are no major differences in gene expression between cartilage from knees with a cartilage injury and knees without an apparent cartilage injury. OA cartilage, as expected, showed markedly different gene expression from the other 2 groups. The gene expression profiles resulting from this low-input RNA-sequencing study offer opportunities to discover new pathways not previously recognized that may be explored in future studies.

Long non-coding RNA expression profiling of subchondral bone reveals AC005165.1 modifying FRZB expression during osteoarthritis

Objective

To gain insight in the expression profile of long non-coding RNAs (lncRNAs) in OA subchondral bone.

Methods

RNA sequencing data of macroscopically preserved and lesioned OA subchondral bone of patients that underwent joint replacement surgery due to OA (N = 22 pairs; 5 hips, 17 knees, Research osteoArthrits Articular Tissue (RAAK study) was run through an in-house pipeline to detect expression of lncRNAs. Differential expression analysis between preserved and lesioned bone was performed. Spearman correlations were calculated between differentially expressed lncRNAs and differentially expressed mRNAs identified previously in the same samples. Primary osteogenic cells were transfected with locked nucleic acid (LNA) GapmeRs targeting AC005165.1 lncRNA, to functionally investigate its potential mRNA targets.

Results

In total, 2816 lncRNAs were well-expressed in subchondral bone and we identified 233 lncRNAs exclusively expressed in knee and 307 lncRNAs exclusively in hip. Differential expression analysis, using all samples (N = 22 pairs; 5 hips, 17 knees), resulted in 21 differentially expressed lncRNAs [false discovery rate (FDR) < 0.05, fold change (FC) range 1.19–7.39], including long intergenic non-protein coding RNA (LINC) 1411 (LINC01411, FC = 7.39, FDR = 2.20 × 10⁻⁸), AC005165.1 (FC = 0.44, FDR = 2.37 × 10⁻⁶) and empty spiracles homeobox 2 opposite strand RNA (EMX2OS, FC = 0.41, FDR = 7.64 × 10⁻³). Among the differentially expressed lncRNAs, five were also differentially expressed in articular cartilage, including AC005165.1, showing similar direction of effect. Downregulation of AC005165.1 in primary osteogenic cells resulted in consistent downregulation of highly correlated frizzled related protein (FRZB).

Conclusion

The current study identified a novel lncRNA, AC005165.1, being dysregulated in OA articular cartilage and subchondral bone. Downregulation of AC005165.1 caused a decreased expression of OA risk gene FRZB, an important member of the wnt pathway, suggesting that AC005165.1 could be an attractive potential therapeutic target with effects in articular cartilage and subchondral bone.

Transcriptomic and epigenomic analyses uncovered Lrrc15 as a contributing factor to cartilage damage in osteoarthritis

In osteoarthritis (OA), articular chondrocytes display phenotypic and functional changes associated with epigenomic alterations. These changes contribute to the disease progression, which is characterized by dysregulated reparative processes and abnormal extracellular matrix remodeling leading to cartilage degradation. Recent studies using a murine model of posttraumatic OA highlighted the contribution of changes in DNA hydroxymethylation (5hmC) to OA progression. Here, we integrated transcriptomic and epigenomic analyses in cartilage after induction of OA to show that the structural progression of OA is accompanied by early transcriptomic and pronounced DNA methylation (5mC) changes in chondrocytes. These changes accumulate over time and are associated with recapitulation of developmental processes, including cartilage development, chondrocyte hypertrophy, and ossification. Our integrative analyses also uncovered that Lrrc15 is differentially methylated and expressed in OA cartilage, and that it may contribute to the functional and phenotypic alterations of chondrocytes, likely coordinating stress responses and dysregulated extracellular matrix remodeling.

Chondrocytes from Osteoarthritis Patients Adopt Distinct Phenotypes in Response to Central TH1/TH2/TH17 Cytokines

Chronic low-grade inflammation plays a central role in the pathogenesis of osteoarthritis (OA), and several pro- and anti-inflammatory cytokines have been implicated to mediate and regulate this process. Out of these cytokines, particularly IFNγ, IL-1β, IL-4 and IL-17 are associated with different phenotypes of T helper (T_H) cells and macrophages, both examples of cells known for great phenotypic and functional heterogeneity. Chondrocytes also display various phenotypic changes during the course of arthritis. We set out to study the hypothesis of whether chondrocytes might adopt polarized phenotypes analogous to T_H cells and macrophages. We studied the effects of IFNγ, IL-1β, IL-4 and IL-17 on gene expression in OA chondrocytes with RNA-Seq. Chondrocytes were harvested from the cartilage of OA patients undergoing knee replacement surgery and then cultured with or without the cytokines for 24 h. Total RNA was isolated and sequenced, and GO (Gene Ontology) functional analysis was performed. We also separately investigated genes linked to OA in recent genome wide expression analysis (GWEA) studies. The expression of more than 2800 genes was significantly altered in chondrocytes treated with IL-1β [in the C(IL-1β) phenotype] with a fold change (FC) > 2.5 in either direction. These included a large number of genes associated with inflammation, cartilage degradation and attenuation of metabolic signaling. The profile of genes differentially affected by IFNγ (the C(IFNγ) phenotype) was relatively distinct from that of the C(IL-1β) phenotype and included several genes associated with antigen processing and presentation. The IL-17-induced C(IL-17) phenotype was characterized by the induction of a more limited set of proinflammatory factors compared to C(IL-1β) cells. The C(IL-4) phenotype induced by IL-4 displayed a differential expression of a rather small set of genes compared with control, primarily those associated with TGFβ signaling and the regulation of inflammation. In conclusion, our results show that OA chondrocytes can adopt diverse phenotypes partly analogously to T_H cells and macrophages. This phenotypic plasticity may play a role in the pathogenesis of arthritis and open new therapeutic avenues for the development of disease-modifying treatments for (osteo)arthritis.

Elucidating mechano-pathology of osteoarthritis: transcriptome-wide differences in mechanically stressed aged human cartilage explants

Background

Failing of intrinsic chondrocyte repair after mechanical stress is known as one of the most important initiators of osteoarthritis. Nonetheless, insight into these early mechano-pathophysiological processes in age-related human articular cartilage is still lacking. Such insights are needed to advance clinical development. To highlight important molecular processes of osteoarthritis mechano-pathology, the transcriptome-wide changes following injurious mechanical stress on human aged osteochondral explants were characterized.

Methods

Following mechanical stress at a strain of 65% (65%MS) on human osteochondral explants (n_65%MS = 14 versus n_control = 14), RNA sequencing was performed. Differential expression analysis between control and 65%MS was performed to determine mechanical stress-specific changes. Enrichment for pathways and protein-protein interactions was analyzed with Enrichr and STRING.

Results

We identified 156 genes significantly differentially expressed between control and 65%MS human osteochondral explants. Of note, IGFBP5 (FC = 6.01; FDR = 7.81 × 10⁻³) and MMP13 (FC = 5.19; FDR = 4.84 × 10⁻²) were the highest upregulated genes, while IGFBP6 (FC = 0.19; FDR = 3.07 × 10⁻⁴) was the most downregulated gene. Protein-protein interactions were significantly higher than expected by chance (P = 1.44 × 10⁻¹⁵ with connections between 116 out of 156 genes). Pathway analysis showed, among others, enrichment for cellular senescence, insulin-like growth factor (IGF) I and II binding, and focal adhesion.

Conclusions

Our results faithfully represent transcriptomic wide consequences of mechanical stress in human aged articular cartilage with MMP13, IGF binding proteins, and cellular senescence as the most notable results. Acquired knowledge on the as such identified initial, osteoarthritis-related, detrimental responses of chondrocytes may eventually contribute to the development of effective disease-modifying osteoarthritis treatments.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-021-02595-8.

Curcumin-Alleviated Osteoarthritic Progression in Rats Fed a High-Fat Diet by Inhibiting Apoptosis and Activating Autophagy via Modulation of MicroRNA-34a

Purpose

The mechanism underlying curcumin’s protective effect on osteoarthritis (OA) has not been clarified. This study aimed to determine whether curcumin exerts a chondroprotective effect by inhibiting apoptosis via upregulation of E2F1/PITX1 and activation of autophagy via the Akt/mTOR pathway by targeting microRNA-34a (miR-34a).

Methods

Male Sprague–Dawley rats were fed a normal diet (ND) or high-fat diet (HFD) for 28 weeks. Five rats from each diet group were selected randomly for histological analysis of OA characteristics. Rats fed a HFD were given a single intra-stifle joint injection of the miR-34a mimic agomir-34a or negative control agomir (NC), followed by weekly low-dose (200 μg/kg body weight) or high-dose (400 μg/kg body weight) curcumin intra-joint injections from weeks 29 to 32. The rats’ stifle joints were submitted to histological analysis and to an apoptotic assay. Expression of miR-34a was detected using a real-time RT-PCR. E2F1 and PITX1 protein levels were determined by Western blot analysis, and the expressions of Beclin1, LC3B, p62, phosphorylated (p)-Akt, and p-mTOR were measured using immunofluorescence analysis.

Results

We found that rats fed a HFD had OA-like lesions in their articular cartilage and had increased apoptosis of chondrocytes and decreased autophagy compared to rats fed a ND. Curcumin treatment alleviated OA changes, inhibited apoptosis, and upregulated autophagy. Agomir-34a treatment reduced E2F1, PITX1, Beclin1, and LC3B expression and increased p62, p-Akt, and p-mTOR expression in HFD-fed rats given low- or high-dose curcumin. Greater numbers of apoptotic cells, lesser expression of p62, p-Akt, and p-mTOR, and greater expression of E2F1, PITX1, and LC3B were observed in the agomir-34a and high-dose curcumin-treated group than in agomir-34a and low-dose curcumin-treated group.

Conclusion

Curcumin’s chondroprotective effect was mediated by its suppression of miR-34a, apparently by reducing apoptosis, via upregulation of E2F1/PITX1, and by augmenting autophagy, likely via the Akt/mTOR pathway.

Flightless I is a catabolic factor of chondrocytes that promotes hypertrophy and cartilage degeneration in osteoarthritis

Synovial macrophages that are activated by cartilage fragments initiate synovitis, a condition that promotes hypertrophic changes in chondrocytes leading to cartilage degeneration in OA. In this study, we analyzed the molecular response of chondrocytes under condition of this type of stimulation to identify a molecular therapeutic target. Stimulated macrophages promoted hypertrophic changes in chondrocytes resulting in production of matrix-degrading enzymes of cartilage. Among the top-upregulated genes, FliI was found to be released from activated chondrocytes and exerted autocrine/paracrine effects on chondrocytes leading to an increase in expression of catabolic and hypertrophic factors. Silencing FliI in stimulated cells significantly reduced expression of catabolic and hypertrophic factors in cocultured chondrocytes. Our further results demonstrated that the FliI-TLR4-ERK1/2 axis is involved in the hypertrophic signaling of chondrocytes and catabolism of cartilage. Our findings provide a new insight into the pathogenesis of OA and identify a potentially new molecular target for diagnostics and therapeutics.

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Activated macrophages promote the secretion of FliI from chondrocytes

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FliI acts as a DAMP-triggering molecule in cartilage

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FliI promotes chondrocyte hypertrophy and cartilage catabolism

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FliI represents attractive target for therapeutic intervention

The role of TNFRSF11B in development of osteoarthritic cartilage

OBJECTIVES

Osteoarthritis (OA) is a complex genetic disease with different risk factors contributing to its development. One of the genes, TNFRSF11B, previously identified with gain-of-function mutation in a family with early-onset OA with chondrocalcinosis, is among the highest upregulated genes in lesioned OA cartilage (RAAK-study). Here, we determined the role of TNFRSF11B overexpression in development of OA.

METHODS

Human primary articular chondrocytes (9 donors RAAK study) were transduced using lentiviral particles with or without TNFRSF11B. Cells were cultured for 1 week in a 3D in-vitro chondrogenic model . TNFRSF11B overexpression was confirmed by RT-qPCR, immunohistochemistry and ELISA. Effects of TNFRSF11B overexpression on cartilage matrix deposition, matrix mineralization, and genes highly correlated to TNFRSF11B in RNA-sequencing dataset (r>|0.75|) were determined by RT-qPCR. Additionally, glycosaminoglycans and collagen deposition were visualized with Alcian blue staining and immunohistochemistry (COL1 and COL2).

RESULTS

Overexpression of TNFRSF11B resulted in strong upregulation of MMP13, COL2A1 and COL1A1. Likewise, mineralization and osteoblast characteristic markers RUNX2, ASPN and OGN showed a consistent increase. Among 30 genes highly correlated to TNFRSF11B, expression of only 8 changed significantly, with BMP6 showing highest increase (9-fold) while expression of RANK and RANKL remained unchanged indicating previously unknown downstream pathways of TNFRSF11B in cartilage.

CONCLUSION

Results of our 3D in vitro chondrogenesis model indicate that upregulation of TNFRSF11B in lesioned OA cartilage may act as a direct driving factor for chondrocyte to osteoblast transition observed in OA pathophysiology. This transition does not appear to act via the OPG/RANK/RANKL triad common in bone remodeling.

ETHICS APPROVAL AND CONSENT TO PARTICIPATE

The Medical Ethics Committee of the LUMC gave approval for the RAAK study (P08.239). Written informed consent was obtained from all donors.

Characterizing correlations among disease severity measures in osteochondral tissues from osteoarthritic knees

Osteoarthritis (OA) is a complex disease with biologic, biomechanical, and clinical heterogeneity among patients. Relationships among OA tissue metabolism, histopathology, and extracellular matrix (ECM) composition have not been well characterized. It was hypothesized that moderate (r = .4-.69) to strong (r > .7) correlations exist among these different measures of disease severity in osteochondral tissues from OA knees. Joint surfaces were obtained from patients (n = 6) undergoing total knee arthroplasty. Osteochondral explants (n = 136) were created and cultured for 3 days. Culture media were collected for biomarker analyses, and tissue was assessed for viability, histological scoring, and ECM composition. Correlations among media biomarker concentrations, histological scoring, ECM composition, and viability were determined using a Spearman correlation. GRO-α, IL-6, IL-8, and MCP-1 showed strong positive correlations to each other, and moderate positive correlations to NO, PGE2, and MMP-2. Total MMP activity, MMP-9, and MMP-13 had strong positive correlations to each other, and moderate positive correlations to MMP-1. MMP-2 had a moderate to strong positive correlations to histological scores (total and cartilage structure) and collagen content. MMP-2, IL-6, IL-8, and MCP-1 had moderate negative correlations, and MMP-9 had a moderate positive correlation, to viability. GRO-α, IL-6, IL-8, and MCP-1 had moderate positive correlations to collagen content. MMP-9, MMP-13, and total MMP activity had moderate negative correlations to tissue GAG. The data suggest links among proinflammatory and degradative pathways are present in OA osteochondral tissues. Further characterization of these links have the potential to delineate mechanisms of disease and diagnostic and therapeutic targets for knee OA.

Long-term dynamic compression enhancement TGF-β3-induced chondrogenesis in bovine stem cells: a gene expression analysis

Background

Bioengineering has demonstrated the potential of utilising mesenchymal stem cells (MSCs), growth factors, and mechanical stimuli to treat cartilage defects. However, the underlying genes and pathways are largely unclear. This is the first study on screening and identifying the hub genes involved in mechanically enhanced chondrogenesis and their potential molecular mechanisms.

Methods

The datasets were downloaded from the Gene Expression Omnibus (GEO) database and contain six transforming growth factor-beta-3 (TGF-β3) induced bovine bone marrow-derived MSCs specimens and six TGF-β3/dynamic-compression-induced specimens at day 42. Screening differentially expressed genes (DEGs) was performed and then analysed via bioinformatics methods. The Database for Annotation, Visualisation, and Integrated Discovery (DAVID) online analysis was utilised to obtain the Gene Ontology (GO) and Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway enrichment. The protein-protein interaction (PPI) network of the DEGs was constructed based on data from the STRING database and visualised through the Cytoscape software. The functional modules were extracted from the PPI network for further analysis.

Results

The top 10 hub genes ranked by their connection degrees were IL6, UBE2C, TOP2A, MCM4, PLK2, SMC2, BMP2, LMO7, TRIM36, and MAPK8. Multiple signalling pathways (including the PI3K-Akt signalling pathway, the toll-like receptor signalling pathway, the TNF signalling pathway, and the MAPK pathway) may impact the sensation, transduction, and reaction of external mechanical stimuli.

Conclusions

This study provides a theoretical finding showing that gene UBE2C, IL6, and MAPK8, and multiple signalling pathways may play pivotal roles in dynamic compression-enhanced chondrogenesis.

SOX9 keeps growth plates and articular cartilage healthy by inhibiting chondrocyte dedifferentiation/osteoblastic redifferentiation

Cartilage is essential throughout vertebrate life. It starts developing in embryos when osteochondroprogenitor cells commit to chondrogenesis, activate a pancartilaginous program to form cartilaginous skeletal primordia, and also embrace a growth-plate program to drive skeletal growth or an articular program to build permanent joint cartilage. Various forms of cartilage malformation and degeneration diseases afflict humans, but underlying mechanisms are still incompletely understood and treatment options suboptimal. The transcription factor SOX9 is required for embryonic chondrogenesis, but its postnatal roles remain unclear, despite evidence that it is down-regulated in osteoarthritis and heterozygously inactivated in campomelic dysplasia, a severe skeletal dysplasia characterized postnatally by small stature and kyphoscoliosis. Using conditional knockout mice and high-throughput sequencing assays, we show here that SOX9 is required postnatally to prevent growth-plate closure and preosteoarthritic deterioration of articular cartilage. Its deficiency prompts growth-plate chondrocytes at all stages to swiftly reach a terminal/dedifferentiated stage marked by expression of chondrocyte-specific (Mgp) and progenitor-specific (Nt5e and Sox4) genes. Up-regulation of osteogenic genes (Runx2, Sp7, and Postn) and overt osteoblastogenesis quickly ensue. SOX9 deficiency does not perturb the articular program, except in load-bearing regions, where it also provokes chondrocyte-to-osteoblast conversion via a progenitor stage. Pathway analyses support roles for SOX9 in controlling TGFβ and BMP signaling activities during this cell lineage transition. Altogether, these findings deepen our current understanding of the cellular and molecular mechanisms that specifically ensure lifelong growth-plate and articular cartilage vigor by identifying osteogenic plasticity of growth-plate and articular chondrocytes and a SOX9-countered chondrocyte dedifferentiation/osteoblast redifferentiation process.

Endoglin Level Is Critical for Cartilage Tissue Formation In Vitro by Passaged Human Chondrocytes

Transforming growth factor beta (TGFβ) signaling is required for in vitro chondrogenesis. In animal models of osteoarthritis (OA), TGFβ receptor alterations are detected in chondrocytes in severe OA cartilage. It is not known whether such changes are dependent on the grade of human OA and if they affect chondrogenesis. Thus, the purpose of this study was to determine if human OA chondrocytes obtained from low-grade or high-grade disease could form cartilage tissue and to assess the role of the co-receptors, endoglin (ENG) and TGFβ receptor 3 (TGFBRIII), in the regulation of this tissue generation in vitro. We hypothesized that the grade of OA disease would not affect the ability of cells to form cartilage tissue and that the TGFβ co-receptor, ENG, would be critical to regulating tissue formation. Chondrocytes isolated from low-grade OA or high-grade OA human articular cartilage (AC) were analyzed directly (P0) or passaged in monolayer to P2. Expression of the primary TGFβ receptor ALK5, and the co-receptors ENG and TGFβRIII, was assessed by image flow cytometry. To assess the ability to form cartilaginous tissue, cells were placed in three-dimensional culture at high density and cultured in chondrogenic media containing TGFβ3. ENG knockdown was used to determine its role in regulating tissue formation. Overall, grade-specific differences in expression of ALK5, ENG, and TGFβRIII in primary or passaged chondrocytes were not detected; however, ENG expression increased significantly after passaging. Despite the presence of ALK5, P0 cells did not form cartilaginous tissue. In contrast, P2 cells derived from low-grade and high-grade OA AC formed hyaline-like cartilaginous tissues of similar quality. Knockdown of ENG in P2 cells inhibited cartilaginous tissue formation compared to controls indicating that the level of ENG protein expression is critical for in vitro chondrogenesis by passaged articular chondrocytes. This study demonstrates that it is not the grade of OA, but the levels of ENG in the presence of ALK5 that influences the ability of human passaged articular chondrocytes to form cartilaginous tissue in vitro in 3D culture. This has implications for cartilage repair therapies. Impact statement These findings are important clinically, given the limited availability of osteoarthritis (OA) cartilage tissue. Being able to use cells from all grades of OA will increase our ability to obtain sufficient cells for cartilage repair. In addition, it is possible that endoglin (ENG) levels, in the presence of ALK5 expression, may be suitable to use as biomarkers to identify cells able to produce cartilage.

Current Models for Development of Disease-Modifying Osteoarthritis Drugs

Osteoarthritis (OA) is a painful and disabling disease that affects millions of people worldwide. Symptom-alleviating treatments exist, although none with long-term efficacy. Furthermore, there are currently no disease-modifying OA drugs (DMOADs) with demonstrated efficacy in OA patients, which is, in part, attributed to a lack of full understanding of the pathogenesis of OA. The inability to translate findings from basic research to clinical applications also highlights the deficiencies in the available OA models at simulating the clinically relevant pathologies and responses to treatments in humans. In this review, the current status in the development of DMOADs will be first presented, with special attention to those in Phase II-IV clinical trials. Next, current in vitro, ex vivo, and in vivo OA models are summarized and the respective advantages and disadvantages of each are highlighted. Of note, the development and application of microphysiological or tissue-on-a-chip systems for modeling OA in humans are presented and the issues that need to be addressed in the future are discussed. Microphysiological systems should be given serious consideration for their inclusion in the DMOAD development pipeline, both for their ability to predict drug safety and efficacy in human clinical trials at present, as well as for their potential to serve as a test platform for personalized medicine. Impact statement At present, no disease-modifying osteoarthritis (OA) drugs (DMOADs) have been approved for widespread clinical use by regulatory bodies. The failure of developing effective DMOADs is likely owing to multiple factors, not the least of which are the intrinsic differences between the intact human knee joint and the preclinical models. This work summarizes the current OA models for the development of DMOADs, discusses the advantages/disadvantages of each, and then proposes future model development to aid in the discovery of effective and personalized DMOADs. The review also highlights the microphysiological systems, which are emerging as a new platform for drug development.

Transient Receptor Potential Ankyrin 1 (TRPA1) Is Involved in Upregulating Interleukin-6 Expression in Osteoarthritic Chondrocyte Models

Transient receptor potential ankyrin 1 (TRPA1) is a membrane-bound ion channel found in neurons, where it mediates nociception and neurogenic inflammation. Recently, we have discovered that TRPA1 is also expressed in human osteoarthritic (OA) chondrocytes and downregulated by the anti-inflammatory drugs aurothiomalate and dexamethasone. We have also shown TRPA1 to mediate inflammation, pain, and cartilage degeneration in experimental osteoarthritis. In this study, we investigated the role of TRPA1 in joint inflammation, focusing on the pro-inflammatory cytokine interleukin-6 (IL-6). We utilized cartilage/chondrocytes from wild-type (WT) and TRPA1 knockout (KO) mice, along with primary chondrocytes from OA patients. The results show that TRPA1 regulates the synthesis of the OA-driving inflammatory cytokine IL-6 in chondrocytes. IL-6 was highly expressed in WT chondrocytes, and its expression, along with the expression of IL-6 family cytokines leukemia inhibitory factor (LIF) and IL-11, were significantly downregulated by TRPA1 deficiency. Furthermore, treatment with the TRPA1 antagonist significantly downregulated the expression of IL-6 in chondrocytes from WT mice and OA patients. The results suggest that TRPA1 is involved in the upregulation of IL-6 production in chondrocytes. These findings together with previous results on the expression and functions of TRPA1 in cellular and animal models point to the role of TRPA1 as a potential mediator and novel drug target in osteoarthritis.

Varying development of femoral and tibial subchondral bone tissue and their interaction with articular cartilage during progressing osteoarthritis

INTRODUCTION

Differences between tibial and femoral joint surfaces and knee compartments concerning coupled bone and cartilage turnover or bone-cartilage cross talk have not been previously examined, although the mechanical and biological interaction of the mineralized subchondral tissues with articular cartilage is of great importance for advancing osteoarthritis.

MATERIALS AND METHODS

Therefore, with the help of immunohistochemistry and real-time polymerase chain reaction (RT-PCR), human knee joint cartilage tissue was investigated for expression of key molecules of the extracellular matrix and cartilage composition (collagen type I and II, aggrecan) plus proteoglycan content (colorimetric analysis). Furthermore, we correlated the results with 3D microcomputed tomography of the underlying subchondral bone (high-resolution micro-CT system). Measurements were performed in dependence of the anatomical site (femoral vs. tibial, medial and lateral each) to identify regional differences during the osteoarthritic process. From an enduring series of 108 patients undergoing implantation of TKA, 34 osteochondral samples with lesions macroscopically classified as ICRS grade 1b (group A) and 34 samples with ICRS grade 3a/3b lesions (group B) were compared with 21 healthy controls.

RESULTS

Concerning 3D analysis, the medial femoral condyle and tibia showed the most significant increase in bone volume fraction and a decrease in the trabecular number in group B frequently accompanied by subchondral bone resorption pits and enchondral ossification. Under physiological conditions, tibia plateaus show lower bone volume fraction than the corresponding femoral site and this difference enlarges with advancing OA. Partially even contradictory behavior was observed such as trabecular separation at the lateral tibial and medial plateau in osteochondral OA samples of the same patients. Collagen type II expression levels show faster and varying changes than type I during the OA process, leading to a lower positive or negative correlation with bone microstructural analysis, especially on the tibia plateau.

CONCLUSIONS

Structural bone and cartilage parameter changes showed varying developments and correlations among each other in the different compartments of the knee. As a clinical conclusion, therapies to postpone or prevent cartilage degeneration by influencing the loss of mineralized bone could be site dependent.

Comparison of Chondrocytes in Knee Osteoarthritis and Regulation by Scaffold Pore Size and Stiffness

In knee osteoarthritis (OA), there is more pronounced cartilage damage in the medial compartment ("lesion zone") than the lateral compartment ("remote zone"). This study fills a gap in the literature by conducting a systematic comparison of cartilage and chondrocyte characteristics from these two zones. It also investigates whether chondrocytes from the different zones respond distinctly to changes in the physical and mechanical microenvironment using three-dimensional porous scaffolds by changing stiffness and pore size. Cartilage was harvested from patients with end-stage varus knee OA. Cartilage from the lesion and remote zones were compared through histological and biomechanical assessments, and through proteomic and gene transcription analyses of chondrocytes. Gelatin scaffolds with varied pore sizes and stiffness were used to investigate in vitro microenvironmental regulation of chondrocytes from the two zones. Cartilage from the lesion and remote zones differed significantly (p < 0.05) in histological and biomechanical characteristics, as well as phenotype, protein, and gene expression of chondrocytes. Chondrocytes from both zones were sensitive to changes in the structural and mechanical properties of gelatin scaffolds. Of interest, although all chondrocytes better retained chondrocyte phenotype in stiffer scaffolds, those from the lesion and remote zones, respectively, preferred scaffolds with larger and smaller pores. Distinct variations exist in cartilage and chondrocyte characteristics in the lesion and remote zones of knee OA. Cells in these two zones respond differently to variations in the physical and mechanical microenvironment. Understanding and manipulating these differences will facilitate the development of more efficient and precise diagnostic and therapeutic approaches for knee OA.

Widespread regulation of gene expression by glucocorticoids in chondrocytes from patients with osteoarthritis as determined by RNA-Seq

Background

Intra-articular glucocorticoid (GC) injections are widely used as a symptomatic treatment for osteoarthritis (OA). However, there are also concerns about their potentially harmful effects, and their detailed effects on chondrocyte phenotype remain poorly understood.

Methods

We studied the effects of dexamethasone on gene expression in OA chondrocytes with RNA-Seq. Chondrocytes were isolated from the cartilage from OA patients undergoing knee replacement surgery and cultured with or without dexamethasone for 24 h. Total RNA was isolated and sequenced, and functional analysis was performed against the Gene Ontology (GO) database. Results for selected genes were confirmed with RT-PCR. We also investigated genes linked to OA in recent genome-wide expression analysis (GWEA) studies.

Results

Dexamethasone increased the expression of 480 and reduced that of 755 genes with a fold change (FC) 2.0 or greater. Several genes associated with inflammation and cartilage anabolism/catabolism as well as lipid and carbohydrate metabolism were among the most strongly affected genes. In the GO analysis, genes involved in the extracellular matrix organization, cell proliferation and adhesion, inflammation, and collagen synthesis were enriched among the significantly affected genes. In network analysis, NGF, PI3KR1, and VCAM1 were identified as central genes among those most strongly affected by dexamethasone.

Conclusions

This is the first study investigating the genome-wide effects of GCs on the gene expression in OA chondrocytes. In addition to clear anti-inflammatory and anticatabolic effects, GCs affect lipid and glucose metabolism in chondrocytes, an observation that might be particularly important in the metabolic phenotype of OA.

Masseter response to long-term experimentally induced anterior crossbite in Sprague-Dawley rats

OBJECTIVE

To detect the long-term response to unilateral anterior crossbite (UAC) in masticatory muscles and in molecular biomarkers of peripheral blood leukocytes.

DESIGN

Fifty-six six-week-old Sprague-Dawley rats were used. The gene-fold changes in peripheral blood leukocytes were detected by the microarray analysis to compare the rats that received 20-week UAC treatment with age-matched controls (n = 4). Muscle atrophy-related gene Fbxo32 was selected based on the data of the microarray analysis verified by using real-time PCR. The remaining 36 rats were randomly separated in the UAC and control groups at 12 and 20 weeks (n = 12). The protein expression of Fbxo32 and the muscle injury and myogenesis-related markers, αB-crystallin and desmin, were detected in the masseter and lateral pterygoid muscles by western blot assay.

RESULTS

In the 20-week UAC group, the masseter muscle weight was lower than that in the age-matched control group, and the expression level of Fbxo32 gene in peripheral blood leukocytes was increased according to the microarray analysis confirmed by real-time PCR detection. The increased protein expression levels of Fbxo32 were detected in the masseter in the 20-week UAC group, and the protein expression levels of desmin and αB-crystallin were decreased at this time point. No similar changes were detected in the lateral pterygoid muscle.

CONCLUSIONS

Masseter atrophy is induced by long-term stimulation of UAC. The increased expression of the Fbxo32 gene in peripheral blood leukocytes may be a candidate biological marker of masseter atrophy.

OATargets: a knowledge base of genes associated with osteoarthritis joint damage in animals

Objectives

To collate the genes experimentally modulated in animal models of osteoarthritis (OA) and compare these data with OA transcriptomics data to identify potential therapeutic targets.

Methods

PubMed searches were conducted to identify publications describing gene modulations in animal models. Analysed gene expression data were retrieved from the SkeletalVis database of analysed skeletal microarray and RNA-Seq expression data. A network diffusion approach was used to predict new genes associated with OA joint damage.

Results

A total of 459 genes were identified as having been modulated in animal models of OA, with ageing and post-traumatic (surgical) models the most prominent. Ninety-eight of the 143 genes (69%) genetically modulated more than once had a consistent effect on OA joint damage severity. Several discrepancies between different studies were identified, providing lessons on interpretation of these data. We used the data collected along with OA gene expression data to expand existing annotations and prioritise the most promising therapeutic targets, which we validated using the latest reported associations. We constructed an online database OATargets to allow researchers to explore the collated data and integrate it with existing OA and skeletal gene expression data.

Conclusions

We present a comprehensive survey and online resource for understanding gene regulation of animal model OA pathogenesis.