Fibronectin splice variation in human knee cartilage, meniscus and synovial membrane: observations in osteoarthritic knee

Get Spliced: Uniting Alternative Splicing and Arthritis

Immune responses demand the rapid and precise regulation of gene protein expression. Splicing is a crucial step in this process; ~95% of protein-coding gene transcripts are spliced during mRNA maturation. Alternative splicing allows for distinct functional regulation, as it can affect transcript degradation and can lead to alternative functional protein isoforms. There is increasing evidence that splicing can directly regulate immune responses. For several genes, immune cells display dramatic changes in isoform-level transcript expression patterns upon activation. Recent advances in long-read RNA sequencing assays have enabled an unbiased and complete description of transcript isoform expression patterns. With an increasing amount of cell types and conditions that have been analyzed with such assays, thousands of novel transcript isoforms have been identified. Alternative splicing has been associated with autoimmune diseases, including arthritis. Here, GWASs revealed that SNPs associated with arthritis are enriched in splice sites. In this review, we will discuss how alternative splicing is involved in immune responses and how the dysregulation of alternative splicing can contribute to arthritis pathogenesis. In addition, we will discuss the therapeutic potential of modulating alternative splicing, which includes examples of spliceform-based biomarkers for disease severity or disease subtype, splicing manipulation using antisense oligonucleotides, and the targeting of specific immune-related spliceforms using antibodies.

Identification and functional characterization of imbalanced osteoarthritis-associated fibronectin splice variants

OBJECTIVE

To identify FN1 transcripts associated with OA pathophysiology and investigate the downstream effects of modulating FN1 expression and relative transcript ratio.

METHODS

FN1 transcriptomic data was obtained from our previously assessed RNA-seq dataset of lesioned and preserved OA cartilage samples from the Research osteoArthritis Articular Cartilage (RAAK) study. Differential transcript expression analysis was performed on all 27 FN1 transcripts annotated in the Ensembl database. Human primary chondrocytes were transduced with lentiviral particles containing short hairpin RNA (shRNA) targeting full-length FN1 transcripts or non-targeting shRNA. Subsequently, matrix deposition was induced in our 3D in vitro neo-cartilage model. Effects of changes in the FN1 transcript ratio on sulphated glycosaminoglycan (sGAG) deposition were investigated by Alcian blue staining and dimethylmethylene blue assay. Moreover, gene expression levels of 17 cartilage-relevant markers were determined by reverse transcription quantitative polymerase chain reaction.

RESULTS

We identified 16 FN1 transcripts differentially expressed between lesioned and preserved cartilage. FN1-208, encoding migration-stimulating factor, was the most significantly differentially expressed protein coding transcript. Downregulation of full-length FN1 and a concomitant increased FN1-208 ratio resulted in decreased sGAG deposition as well as decreased ACAN and COL2A1 and increased ADAMTS-5, ITGB1 and ITGB5 gene expression levels.

CONCLUSION

We show that full-length FN1 downregulation and concomitant relative FN1-208 upregulation was unbeneficial for deposition of cartilage matrix, likely due to decreased availability of the classical RGD (Arg-Gly-Asp) integrin-binding site of fibronectin.

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.

Targeted transcriptomic analyses of RNA isolated from formalin-fixed and paraffin-embedded human menisci

Formalin-fixed and paraffin-embedded (FFPE) biospecimens are a valuable and widely-available resource for diagnostic and research applications. With biobanks of tissue samples available in many institutions, FFPE tissues could prove to be a valuable resource for translational orthopaedic research. The purpose of this study was to characterize the molecular profiles and degree of histologic degeneration on archival fragments of FFPE human menisci obtained during arthroscopic partial meniscectomy. We used FFPE menisci for multiplexed gene expression analysis using the NanoString nCounter® platform, and for histological assessment using a quantitative scoring system. In total, 17 archival specimens were utilized for integrated histologic and molecular analyses. The median patient age was 22 years (range: 14-62). We found that the genes with the highest normalized counts were those typically expressed in meniscal fibrocartilage. Gene expression differences were identified in patient cohorts based on age (≤40 years), including genes associated with the extracellular matrix and tissue repair. The majority of samples showed mild to moderate histologic degeneration. Based on these data, we conclude that FFPE human menisci can be effectively utilized for molecular evaluation following a storage time as long as 11 years. Statement of Clinical Significance: The integration of histological and transcriptomic analyses described in this study will be useful for future studies investigating the basis for biological classification of meniscus specimens in patients. Further exploration into the genes and pathways uncovered by this study may suggest targets for biomarker discovery and identify patients at greater risk for osteoarthritis once the meniscus is torn.

Fibronectin in development and wound healing

Fibronectin structure and composition regulate contextual cell signaling. Recent advances have been made in understanding fibronectin and its role in tissue organization and repair. This review outlines fibronectin splice variants and their functions, evaluates potential therapeutic strategies targeting or utilizing fibronectin, and concludes by discussing potential future directions to modulate fibronectin function in development and wound healing.

Forkhead box C1 promotes the pathology of osteoarthritis by upregulating β-catenin in synovial fibroblasts

Osteoarthritis (OA) is a joint disease characterized by articular cartilage degeneration, and no effective treatment is available. The OA classification has shifted from a cartilage-only disease to a whole-joint disease, and the synovial membrane plays an important role. Therefore, studies are needed to identify additional genes that regulate the pathological changes in the synovial membrane to develop a promising therapeutic strategy for OA. Here, we validated that the expression of forkhead box protein C1 (FoxC1) and β-catenin was upregulated in OA synovial membranes and synovial fibroblasts (SFs). Gain- and loss-of-function studies revealed that FoxC1 overexpression promoted, whilst silencing inhibited OA synovial fibroblast (OASF) proliferation and pro-inflammatory cytokine [interleukin 6 (IL-6), interleukin 8 (IL-8) and tumour necrosis factor-α (TNF-α)] production. FoxC1 overexpression increased β-catenin mRNA, total and nuclear protein expression in OASFs and upregulated a disintegrin and metalloproteinase with thrombospondin motif 5 (ADAMTS-5), fibronectin, matrix metalloproteinase 3 (MMP3) and matrix metalloproteinase 13 (MMP13) mRNA and total protein expression in OASFs. Conversely, FoxC1 knockdown reduced β-catenin mRNA, total and nuclear protein expression in OASFs and reduced ADAMTS-5, fibronectin, MMP3 and MMP13 mRNA and total protein expression in OASFs. β-catenin mediates FoxC1-induced pathological changes (proliferation, catabolic regulation and inflammation) in OASFs. MicroRNA-200a-3p (miR-200a-3p) binds to the 3'-UTR of FoxC1 and mediates FoxC1 expression. Intra-articular FoxC1-specific siRNA transfection hindered OA development in mice. Therefore, our results demonstrate the key role FoxC1 plays in vivo and in vitro in OA synovial pathology, possibly identifying a potential novel therapeutic target for OA.

Profile of Matrix-Remodeling Proteinases in Osteoarthritis: Impact of Fibronectin

The extracellular matrix (ECM) is a complex and specialized three-dimensional macromolecular network, present in nearly all tissues, that also interacts with cell surface receptors on joint resident cells. Changes in the composition and physical properties of the ECM lead to the development of many diseases, including osteoarthritis (OA). OA is a chronic degenerative rheumatic disease characterized by a progressive loss of synovial joint function as a consequence of the degradation of articular cartilage, also associated with alterations in the synovial membrane and subchondral bone. During OA, ECM-degrading enzymes, including urokinase-type plasminogen activator (uPA), matrix metalloproteinases (MMPs), and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTSs), cleave ECM components, such as fibronectin (Fn), generating fibronectin fragments (Fn-fs) with catabolic properties. In turn, Fn-fs promote activation of these proteinases, establishing a degradative and inflammatory feedback loop. Thus, the aim of this review is to update the contribution of ECM-degrading proteinases to the physiopathology of OA as well as their modulation by Fn-fs.

Fibroblast-like synovial cell production of extra domain A fibronectin associates with inflammation in osteoarthritis

Background

The pathophysiology of osteoarthritis (OA) involves wear and tear, and a state of low-grade inflammation. Tissue repair responses include transforming growth factor beta (TGFβ)-induced myofibroblast production of extracellular matrix. Fibronectins are an essential part of the extracellular matrix, and injection of fibronectin fragments into rabbit joints is a previously established animal model of OA. Fibronectin containing the ED-A domain is currently being used as drug delivery target in the development of anti-inflammatory drugs (e.g. Dekavil).

Methods

In this study, samples of synovial membrane were obtained from patients with knee OA undergoing joint replacement surgery. Immunostaining for ED-A fibronectin and the myofibroblast marker alpha smooth muscle actin (αSMA) was performed on fibroblast-like synovial cells (FLS) and synovial membranes. RAW 264.7 macrophages were incubated with recombinant ED-A fibronectin.

Results

The staining of ED-A fibronectin in OA FLS was increased by TGFβ but not by TNFα, lipopolysaccharide, or IL-6 (n = 3). ED-A fibronectin co-stained with the myofibroblast marker αSMA in both the OA FLS (n = 3) and in the OA synovial membranes (n = 8). ED-A fibronectin staining was associated with both number of lining layer cells (rho = 0.85 and p = 0.011) and sublining cells (rho = 0.88 and p = 0.007) in the OA synovium (n = 8), and co-distributed with TNFα (n = 5). Recombinant ED-A fibronectin increased the production of TNFα by RAW 264.7 macrophages (n = 3).

Conclusions

The disease process in OA shares features with the chronic wound healing response. Our findings support utilizing ED-A fibronectin for drug delivery or therapeutic targeting to reduce pro-inflammatory responses in OA.

Noninvasive imaging of tumor progression, metastasis, and fibrosis using a nanobody targeting the extracellular matrix

Extracellular matrix (ECM) deposition is a hallmark of many diseases, including cancer and fibroses. To exploit the ECM as an imaging and therapeutic target, we developed alpaca-derived libraries of "nanobodies" against disease-associated ECM proteins. We describe here one such nanobody, NJB2, specific for an alternatively spliced domain of fibronectin expressed in disease ECM and neovasculature. We showed by noninvasive in vivo immuno-PET/CT imaging that NJB2 detects primary tumors and metastatic sites with excellent specificity in multiple models of breast cancer, including human and mouse triple-negative breast cancer, and in melanoma. We also imaged mice with pancreatic ductal adenocarcinoma (PDAC) in which NJB2 was able to detect not only PDAC tumors but also early pancreatic lesions called pancreatic intraepithelial neoplasias, which are challenging to detect by any current imaging modalities, with excellent clarity and signal-to-noise ratios that outperformed conventional 2-fluorodeoxyglucose PET/CT imaging. NJB2 also detected pulmonary fibrosis in a bleomycin-induced fibrosis model. We propose NJB2 and similar anti-ECM nanobodies as powerful tools for noninvasive detection of tumors, metastatic lesions, and fibroses. Furthermore, the selective recognition of disease tissues makes NJB2 a promising candidate for nanobody-based therapeutic applications.

Autologous Bone Marrow Concentrate in a Sheep Model of Osteoarthritis: New Perspectives for Cartilage and Meniscus Repair

INTRODUCTION

Cell-based therapies are becoming a valuable tool to treat osteoarthritis (OA). This study investigated and compared the regenerative potential of bone marrow concentrate (BMC) and mesenchymal stem cells (MSC), both engineered with Hyaff(®)-11 (HA) for OA treatment in a sheep model.

METHODS

OA was induced via unilateral medial meniscectomy. Bone marrow was aspirated from the iliac crest, followed by concentration processes or cell isolation and expansion to obtain BMC and MSC, respectively. Treatments consisted of autologous BMC and MSC seeded onto HA. The regenerative potential of bone, cartilage, menisci, and synovia was monitored using macroscopy, histology, immunohistochemistry, and micro-computed tomography at 12 weeks post-op. Data were analyzed using the general linear model with adjusted Sidak's multiple comparison and Spearman's tests.

RESULTS

BMC-HA treatment showed a greater repair ability in inhibiting OA progression compared to MSC-HA, leading to a reduction of inflammation in cartilage, meniscus, and synovium. Indeed, the decrease of inflammation positively contributed to counteract the progression of fibrotic and hypertrophic processes, known to be involved in tissue failure. Moreover, the treatment with BMC-HA showed the best results in allowing meniscus regeneration. Minor healing effects were noticed at bone level for both cell strategies; however, a downregulation of subchondral bone thickness (Cs.Th) was found in both cell treatments compared to the OA group in the femur.

CONCLUSION

The transplantation of BMC-HA provided the best effects in supporting regenerative processes in cartilage, meniscus, and synovium and at less extent in bone. On the whole, both MSC and BMC combined with HA reduced inflammation and contributed to switch off fibrotic and hypertrophic processes. The observed regenerative potential by BMC-HA on meniscus could open new perspectives, suggesting its use not only for OA care but also for the treatment of meniscal lesions, even if further analyses are necessary to confirm its healing potential at long-term follow-up.

Brief Report: Alternative Splicing of Extra Domain A (EIIIA) of Fibronectin Plays a Tissue-Specific Role in Hematopoietic Homeostasis

Fibronectin (FN) is a major extracellular matrix protein implicated in cell adhesion and differentiation in the bone marrow (BM) environment. Alternative splicing of FN gene results in the generation of protein variants containing an additional EIIIA domain that sustains cell proliferation or differentiation during physiological or pathological tissue remodeling. To date its expression and role in adult hematopoiesis has not been explored. In our research, we demonstrate that during physiological hematopoiesis a small fraction of BM derived FN contains the EIIIA domain and that mice constitutively including (EIIIA(+/+) ) or excluding (EIIIA(-/-) ) the EIIIA exon present comparable levels of hematopoietic stem cells, myeloid and lymphoid progenitors within BM. Moreover, only minor alterations were detected in blood parameters and in hematopoietic frequencies of BM granulocytes/monocytes and B cells. As opposed to other tissues, unique compensatory mechanisms, such as increased FN accumulation and variable expression of the EIIIA receptors, Toll like receptor-4 and alpha9 integrin subunit, characterized the BM of these mice. Our data demonstrate that FN is a fundamental component of the hematopoietic tissue and that the EIIIA exon may play a key role in modulating hematopiesis in conditions of BM stress or diseases. Stem Cells 2016;34:2263-2268.

Detecting new microRNAs in human osteoarthritic chondrocytes identifies miR-3085 as a human, chondrocyte-selective, microRNA

OBJECTIVE

To use deep sequencing to identify novel microRNAs (miRNAs) in human osteoarthritic cartilage which have a functional role in chondrocyte phenotype or function.

DESIGN

A small RNA library was prepared from human osteoarthritic primary chondrocytes using in-house adaptors and analysed by Illumina sequencing. Novel candidate miRNAs were validated by northern blot and qRT-PCR. Expression was measured in cartilage models. Targets of novel candidates were identified by microarray and computational analysis, validated using 3'-UTR-luciferase reporter plasmids. Protein levels were assessed by western blot and functional analysis by cell adhesion.

RESULTS

We identified 990 known miRNAs and 1621 potential novel miRNAs in human osteoarthritic chondrocytes, 60 of the latter were expressed in all samples assayed. MicroRNA-140-3p was the most highly expressed microRNA in osteoarthritic cartilage. Sixteen novel candidate miRNAs were analysed further, of which six remained after northern blot analysis. Three novel miRNAs were regulated across models of chondrogenesis, chondrocyte differentiation or cartilage injury. One sequence (novel #11), annotated in rodents as microRNA-3085-3p, was preferentially expressed in cartilage, dependent on chondrocyte differentiation and, in man, is located in an intron of the cartilage-expressed gene CRTAC-1. This microRNA was shown to target the ITGA5 gene directly (which encodes integrin alpha5) and inhibited adhesion to fibronectin (dependent on alpha5beta1 integrin).

CONCLUSION

Deep sequencing has uncovered many potential microRNA candidates expressed in human cartilage. At least three of these show potential functional interest in cartilage homeostasis and osteoarthritis (OA). Particularly, novel #11 (microRNA-3085-3p) which has been identified for the first time in man.