NFAT1 protects articular cartilage against osteoarthritic degradation by directly regulating transcription of specific anabolic and catabolic genes

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

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

RNF125, transcriptionally regulated by NFATC2, alleviates osteoarthritis via inhibiting the Wnt/β-catenin signaling pathway through degrading TRIM14

Osteoarthritis (OA) is a chronic joint disease characterized by the progressive degradation of articular cartilage. In this study, as determined by histological staining, the cartilage surface of the OA rats was damaged, defective and broken, and chondrocytes and proteoglycan were reduced. While moderate physical exercise showed protective effects on the cartilage. Besides, RNA-seq was performed to select a target protein and RNF125 (an E3 ubiquitin ligase) was decreased in the cartilage tissues of OA rats and increased after physiological exercise. However, the precise role of RNF125 in OA is still unknown. This work aimed to investigate the involvement and underlying mechanism of RNF125 in OA pathogenesis. Our results defined that adenovirus-mediated overexpression of RNF125 inhibited the degradation of extracellular matrix of chondrocytes induced by IL-1β, as revealed by increased chondrocyte viability, upregulated COL2A1 and ACAN levels, and downregulated MMP1, MMP13 and ADAMTS5 levels, which was abrogated by NR4A2 knockdown. In vivo, RNF125 relieved OA, manifested as reduced cartilage injury and increased chondrocytes. Mechanically, NFATC2 bound to the RNF125 promoter and directly regulated RNF125 transcription, as illustrated by luciferase reporter, Ch-IP and DNA pull-down assays. Furthermore, RNF125 overexpression inhibited the nuclear translocation of β-catenin, thus suppressing activation of the Wnt/β-catenin signaling pathway. Also, RNF125 as E3 ubiquitin ligase led to the ubiquitination and degradation of TRIM14 protein, and TRIM14 overexpression efficiently reversed the effects of RNF125 overexpression on OA progression. Totally, this study provides new insights into OA pathogenesis regulated by RNF125. RNF125 may be a novel biomarker for OA therapy.

Regulatory role of NFAT1 signaling in articular chondrocyte activities and osteoarthritis pathogenesis

Osteoarthritis (OA), the most common form of joint disease, is characterized clinically by joint pain, stiffness, and deformity. OA is now considered a whole joint disease; however, the breakdown of the articular cartilage remains the major hallmark of the disease. Current treatments targeting OA symptoms have a limited impact on impeding or reversing the OA progression. Understanding the molecular and cellular mechanisms underlying OA development is a critical barrier to progress in OA therapy. Recent studies by the current authors' group and others have revealed that the nuclear factor of activated T cell 1 (NFAT1), a member of the NFAT family of transcription factors, regulates the expression of many anabolic and catabolic genes in articular chondrocytes of adult mice. Mice lacking NFAT1 exhibit normal skeletal development but display OA in both appendicular and spinal facet joints as adults. This review mainly focuses on the recent advances in the regulatory role of NFAT1 transcription factor in the activities of articular chondrocytes and its implication in the pathogenesis of OA.

A whole-joint histopathologic grading system for murine knee osteoarthritis

This study aims to develop a comprehensive and easily executable histopathologic grading scheme for murine knee osteoarthritis (OA) using specific scoring criteria for both cartilage and periarticular changes, which may overcome important limitations of the existing grading systems. The new grading scheme was developed based on mouse knee OA models with observation periods up to 24 months of age (spontaneous OA) or 24-week post-injury (posttraumatic OA). Semi-quantitative assessments of the histopathologic OA changes were applied to all four quadrants per femorotibial joint for 50 joints (200 quadrants) using specific scoring criteria rather than mild to severe grades. Scoring elements per quadrant were as follows: cartilage lesion (0-7), osteophyte (0-3), subchondral bone change (0-3), synovitis (0-3), and ectopic periarticular soft-tissue chondrogenesis and ossification (0-3). The new histopathologic grading scheme had high intra- and interobserver reproducibility (correlation coefficients r > 0.95) across experienced and novice observers. Sensitivity and reliability analyses confirmed the ability of the new scheme to detect minimal but significant OA progression (p < 0.01) within a 2-week interval and to accurately identify tissue- and quadrant-specific OA severity within the joints. In conclusion, this study presents the first whole-joint histopathologic grading scheme for murine knee OA that covers all-stage osteoarthritic changes in all major joint tissues, including periarticular soft-tissue ossification that is not included in any of the existing OA grading systems. This reproducible scheme is easy to execute and sensitive to minimal OA progression without using computer software, suitable for quick OA severity assessments of the entire femorotibial joint.

Gsmtx4 Alleviated Osteoarthritis through Piezo1/Calcineurin/NFAT1 Signaling Axis under Excessive Mechanical Strain

Excessive mechanical strain is the prominent risk factor for osteoarthritis (OA), causing cartilage destruction and degeneration. However, the underlying molecular mechanism contributing to mechanical signaling transduction remains unclear in OA. Piezo type mechanosensitive ion channel component 1 (Piezo1) is a calcium-permeable mechanosensitive ion channel and provides mechanosensitivity to cells, but its role in OA development has not been determined. Herein, we found up-regulated expression of Piezo1 in OA cartilage, and that its activation contributes to chondrocyte apoptosis. The knockdown of Piezo1 could protect chondrocytes from apoptosis and maintain the catabolic and anabolic balance under mechanical strain. In vivo, Gsmtx4, a Piezo1 inhibitor, markedly ameliorated the progression of OA, inhibited the chondrocyte apoptosis, and accelerated the production of the cartilage matrix. Mechanistically, we observed the elevated activity of calcineurin (CaN) and the nuclear transfection of nuclear factor of activated T cells 1 (NFAT1) under mechanical strain in chondrocytes. Inhibitors of CaN or NFAT1 rescued the pathologic changes induced by mechanical strain in chondrocytes. Overall, our findings revealed that Piezo1 was the essential molecule response to mechanical signals and regulated apoptosis and cartilage matrix metabolism via the CaN/NFAT1 signaling axis in chondrocytes, and that Gsmtx4 could be an attractive therapeutic drug for OA treatment.

Intergenic Interactions of SBNO1, NFAT5 and GLT8D1 Determine the Susceptibility to Knee Osteoarthritis among Europeans of Russia

This study was conducted to examine the associations between genome-wide association studies (GWAS)-important single nucleotide polymorphisms (SNPs) and knee osteoarthritis (KOA) among Europeans of Russia. The present replicative study ("patient-control" design has been used) was carried out on 1000 DNA samples from KOA (n = 500) and KOA-free (n = 500) participants. Ten GWAS-important for KOA SNPs of eight candidate genes (LYPLAL1, GNL3, GLT8D1, SBNO1, WWP2, NFAT5, TGFA, GDF5) were studied. To assess the link between SNPs and KOA susceptibility, logistic regression (to establish independent SNP effects) and MB-MDR (to identify SNP-SNP interactions) were used. As a result of this genetic analysis, the associations of individual SNPs with KOA have not been proven. Eight loci out of ten tested SNPs interacted with each other (within twelve genetic models) and determined susceptibility to KOA. The greatest contribution to the disease development were made by three polymorphisms/genes such as rs6976 (C>T) GLT8D1, rs56116847 (G>A) SBNO1, rs6499244 (T>A) NFAT5 (each was included in 2/3 [8 out 12] KOA-responsible genetic interaction models). A two-locus epistatic interaction of rs56116847 (G >A) SBNO1 × rs6499244 (T>A) NFAT5 determined the maximum percentage (0.86%) of KOA entropy. KOA-associated SNPs are regulatory polymorphisms that affect the expression/splicing level, epigenetic modification of 72 genes in KOA-pathogenetically significant organs such as skeletal muscles, tibial arteries/nerves, thyroid, adipose tissue, etc. These putative KOA-effector genes are mainly involved in the organization/activity of the exoribonuclease complex and antigen processing/presentation pathways. In conclusion, KOA susceptibility among Europeans of Russia is mediated by intergenic interactions (but not the main effects) of GWAS-important SNPs.

Differential expression and methylation patterns of NFATC1, NADSYN1 and JAK3 gene in equine chondrocytes expanded in monolayer culture

Ex vivo expansion of chondrocytes in monolayer (ML) culture for therapeutic purposes is burdened with difficulties related to the loss of cartilaginous phenotype. Epigenetic mechanisms responsible for regulation of gene expression are believed to underlie chondrocyte dedifferentiation. We have inspected the relevance of DNA methylation alterations for passage-related differential expression of NFATC1 gene involved in hard connective tissue turnover and development, NADSYN1 influencing redox metabolism, and JAK3 - an important driver of inflammation. We have assessed relative amount of transcript abundance and performed DNA bisulfite sequencing of upstream located elements. It seems that anabolic-like effects of chondrogenic differentiation were observed in form of NFATC1 and NADSYN1 upregulation in chondrocytes at the earlier stages of passaging whereas JAK3 upregulation at the 11th passage was the sign of chondrocytes dedifferentiation. Summarizing the inversely correlated DNA methylation and expression patterns in NFATC1 and JAK3 locus might be relevant for cellular dedifferentiation during chondrocyte expansion in monolayer. Obtained results are supportive for further studies on the role of encoded proteins in regenerative biology of articular cartilage using in vitro expanded chondrocytes.

Spontaneous Facet Joint Osteoarthritis in NFAT1-Mutant Mice: Age-Dependent Histopathologic Characteristics and Molecular Mechanisms

BACKGROUND

Facet joint (FJ) osteoarthritis (FJOA) is a widely prevalent spinal disorder but its pathogenesis remains unclear, largely due to the difficulties in conducting longitudinal human studies and lack of spontaneous-FJOA animal models for mechanistic investigations. This study aimed to investigate whether spontaneous FJOA occurs in mice bearing mutant NFAT1 (nuclear factor of activated T cells 1) transcription factor.

METHODS

The lumbar FJs of 50 NFAT1-mutant mice and of 50 wild-type control mice, of both sexes, were examined by histopathology, quantitative gene expression analysis, semiquantitative immunohistochemistry, and a novel FJOA scoring system for semiquantitative assessment of the histopathologic changes at 2, 6, 12, and 18 months of age. Age-dependent and tissue-specific histopathologic and gene or protein expression changes were analyzed statistically.

RESULTS

FJs in NFAT1-mutant mice displayed significantly increased expression of specific catabolic genes (p < 0.05) and proteins (p < 0.001) in cartilage and synovium as early as 2 months of age, followed by early osteoarthritic structural changes such as articular surface fissuring and chondro-osteophyte formation at 6 months. More severe cartilage lesions, osteophytes, subchondral bone changes, synovitis, and tissue-specific molecular alterations in FJs of NFAT1-mutant mice were observed at 12 and 18 months. Osteoarthritic structural changes were not detected in FJs of wild-type mice at any ages, although age-related cartilage degeneration was observed at 18 months. The novel FJOA scoring system had high intraobserver and interobserver reproducibility (correlation coefficients: r > 0.97). Whole-joint FJOA scoring showed significantly higher OA scores in FJs of NFAT1-mutant mice compared with wild-type mice at all time points (p = 0.0033 at 2 months, p = 0.0001 at 6 months, p < 0.0001 at 12 and 18 months).

CONCLUSIONS

This study has identified the NFAT1-mutant mouse as a novel animal model of spontaneous FJOA with age-dependent and slowly progressing osteoarthritic features, developed the first FJOA scoring system, and elucidated the molecular mechanisms of NFAT1 mutation-induced FJOA.

CLINICAL RELEVANCE

This murine FJOA model resembles the features of human FJOA and may provide new insights into the pathogenesis of and therapeutic strategies for FJOA in humans.

Clinical evaluation after matrix-associated autologous chondrocyte transplantation : a comparison of four different graft types

Aims

The aim of this retrospective study was to determine if there are differences in short-term clinical outcomes among four different types of matrix-associated autologous chondrocyte transplantation (MACT).

Methods

A total of 88 patients (mean age 34 years (SD 10.03), mean BMI 25 kg/m² (SD 3.51)) with full-thickness chondral lesions of the tibiofemoral joint who underwent MACT were included in this study. Clinical examinations were performed preoperatively and 24 months after transplantation. Clinical outcomes were evaluated using the International Knee Documentation Committee (IKDC) Subjective Knee Form, the Brittberg score, the Tegner Activity Scale, and the visual analogue scale (VAS) for pain. The Kruskal-Wallis test by ranks was used to compare the clinical scores of the different transplant types.

Results

The mean defect size of the tibiofemoral joint compartment was 4.28 cm² (SD 1.70). In total, 11 patients (12.6%) underwent transplantation with Chondro-Gide (matrix-associated autologous chondrocyte implantation (MACI)), 40 patients (46.0%) with Hyalograft C (HYAFF), 21 patients (24.1%) with Cartilage Regeneration System (CaReS), and 15 patients (17.2%) with NOVOCART 3D. The mean IKDC Subjective Knee Form score improved from 35.71 (SD 6.44) preoperatively to 75.26 (SD 18.36) after 24 months postoperatively in the Hyalograft group, from 35.94 (SD 10.29) to 71.57 (SD 16.31) in the Chondro-Gide (MACI) group, from 37.06 (SD 5.42) to 71.49 (SD 6.76) in the NOVOCART 3D group, and from 45.05 (SD 15.83) to 70.33 (SD 19.65) in the CaReS group. Similar improvements were observed in the VAS and Brittberg scores.

Conclusion

Two years postoperatively, there were no significant differences in terms of outcomes. Our data demonstrated that MACT, regardless of the implants used, resulted in good clinical improvement two years after transplantation for localized tibiofemoral defects.

Cite this article: Bone Joint Res 2021;10(7):370–379.

The function of lncRNAs in the pathogenesis of osteoarthritis

Osteoarthritis (OA), one of the most common motor system disorders, is a degenerative disease involving progressive joint destruction caused by a variety of factors. At present, OA has become the fourth most common cause of disability in the world. However, the pathogenesis of OA is complex and has not yet been clarified. Long non-coding RNA (lncRNA) refers to a group of RNAs more than 200 nucleotides in length with limited protein-coding potential, which have a wide range of biological functions including regulating transcriptional patterns and protein activity, as well as binding to form endogenous small interference RNAs (siRNAs) and natural microRNA (miRNA) molecular sponges. In recent years, a large number of lncRNAs have been found to be differentially expressed in a variety of pathological processes of OA, including extracellular matrix (ECM) degradation, synovial inflammation, chondrocyte apoptosis, and angiogenesis. Obviously, lncRNAs play important roles in regulating gene expression, maintaining the phenotype of cartilage and synovial cells, and the stability of the intra-articular environment. This article reviews the results of the latest research into the role of lncRNAs in a variety of pathological processes of OA, in order to provide a new direction for the study of OA pathogenesis and a new target for prevention and treatment. Cite this article: Bone Joint Res 2021;10(2):122-133.

Transcription Factors in Cartilage Homeostasis and Osteoarthritis

Osteoarthritis (OA) is the most common degenerative joint disease, and it is characterized by articular cartilage loss. In part, OA is caused by aberrant anabolic and catabolic activities of the chondrocyte, the only cell type present in cartilage. These chondrocyte activities depend on the intra- and extracellular signals that the cell receives and integrates into gene expression. The key proteins for this integration are transcription factors. A large number of transcription factors exist, and a better understanding of the transcription factors activated by the various signaling pathways active during OA can help us to better understand the complex etiology of OA. In addition, establishing such a profile can help to stratify patients in different subtypes, which can be a very useful approach towards personalized therapy. In this review, we discuss crucial transcription factors for extracellular matrix metabolism, chondrocyte hypertrophy, chondrocyte senescence, and autophagy in chondrocytes. In addition, we discuss how insight into these factors can be used for treatment purposes.

Integration of transcriptome-wide association study and messenger RNA expression profile to identify genes associated with osteoarthritis

Aims

Osteoarthritis (OA) is the most prevalent joint disease. However, the specific and definitive genetic mechanisms of OA are still unclear.

Methods

Tissue-related transcriptome-wide association studies (TWAS) of hip OA and knee OA were performed utilizing the genome-wide association study (GWAS) data of hip OA and knee OA (including 2,396 hospital-diagnosed hip OA patients versus 9,593 controls, and 4,462 hospital-diagnosed knee OA patients versus 17,885 controls) and gene expression reference to skeletal muscle and blood. The OA-associated genes identified by TWAS were further compared with the differentially expressed genes detected by the messenger RNA (mRNA) expression profiles of hip OA and knee OA. Functional enrichment and annotation analysis of identified genes was performed by the DAVID and FUMAGWAS tools.

Results

We detected 33 common genes, eight common gene ontology (GO) terms, and one common pathway for hip OA, such as calcium and integrin-binding protein 1 (CIB1) (P_TWAS = 0.025, FC_mRNA = -1.575 for skeletal muscle), adrenomedullin (ADM) (P_TWAS = 0.022, FC_mRNA = -4.644 for blood), Golgi apparatus (P_TWAS <0.001, P_mRNA = 0.012 for blood), and phosphatidylinositol 3' -kinase-protein kinase B (PI3K-Akt) signalling pathway (P_TWAS = 0.033, P_mRNA = 0.005 for blood). For knee OA, we detected 24 common genes, eight common GO terms, and two common pathways, such as histocompatibility complex, class II, DR beta 1 (HLA-DRB1) (P_TWAS = 0.040, FC_mRNA = 4.062 for skeletal muscle), Follistatin-like 1 (FSTL1) (P_TWAS = 0.048, FC_mRNA = 3.000 for blood), cytoplasm (P_TWAS < 0.001, P_mRNA = 0.005 for blood), and complement and coagulation cascades (P_TWAS = 0.017, P_mRNA = 0.001 for skeletal muscle).

Conclusion

We identified a group of OA-associated genes and pathways, providing novel clues for understanding the genetic mechanism of OA.

Cite this article:Bone Joint Res. 2020;9(3):130–138.

Regulatory mechanisms and clinical manifestations of musculoskeletal aging

Aging is the strongest risk factor for degenerative bone and joint diseases. Clinical therapies for age-related musculoskeletal disorders face significant challenges as their pathogenic mechanisms remain largely unclear. This review article focuses on the recent advances in the understanding of regulatory mechanisms of musculoskeletal aging and their clinical relevance. We begin with the prevalence and socioeconomic impacts of major age-related musculoskeletal disorders such as sarcopenia, osteoporosis, osteoarthritis, and degenerative tendinopathy. The current understanding of responsible biological mechanisms involved in general aging is then summarized. Proposed molecular, cellular, and biomechanical mechanisms relevant to the clinical manifestations of aging in the musculoskeletal system are discussed in detail, with a focus on the disorders affecting muscle, bone, articular cartilage, and tendon. Although musculoskeletal aging processes share many common pathways with the aging of other body systems, unique molecular and cellular mechanisms may be involved in the aging processes of musculoskeletal tissues. Advancements in the understanding of regulatory mechanisms of musculoskeletal aging may promote the development of novel treatments for age-related musculoskeletal disorders. Finally, future research directions for major musculoskeletal tissues including functional interaction between the tissues and their clinical relevance to age-related musculoskeletal disorders are highlighted in the Future Prospects section. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1475-1488, 2019.