Genetic abrogation of the fibronectin-α5β1 integrin interaction in articular cartilage aggravates osteoarthritis in mice

Tropoelastin-Pretreated Exosomes from Adipose-Derived Stem Cells Improve the Synthesis of Cartilage Matrix and Alleviate Osteoarthritis

Mesenchymal stem cells (MSCs) have recently been widely used to treat osteoarthritis (OA). Our prior research shows that tropoelastin (TE) increases MSC activity and protects knee cartilage from OA-related degradation. The underlying mechanism might be that TE regulates the paracrine of MSCs. Exosomes (Exos), the paracrine secretion of MSCs, have been found to protect chondrocytes, reduce inflammation, and preserve the cartilage matrix. In this study, we used Exos derived from TE-pretreated adipose-derived stem cells (ADSCs) (TE-Exo^ADSCs) as an injection medium, and compared it with Exos derived from unpretreated ADSCs (Exo^ADSCs). We found that TE-Exo^ADSCs could effectively enhance the matrix synthesis of chondrocytes in vitro. Moreover, TE pretreatment increased the ability of ADSCs to secrete Exos. In addition, compared with Exo^ADSCs, TE-Exo^ADSCs exhibited therapeutic effects in the anterior cruciate ligament transection (ACLT)-induced OA model. Further, we observed that TE altered the microRNA expression in Exo^ADSCs and identified one differentially upregulated microRNA: miR-451-5p. In conclusion, TE-Exo^ADSCs helped maintain the chondrocyte phenotype in vitro, and promoted cartilage repair in vivo. These therapeutic effects might be related with the altered expression of miR-451-5p in the Exo^ADSCs. Thus, the intra-articular delivery of Exos derived from ADSCs with TE pretreatment could be a new approach to treat OA.

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.

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.

Molecular crosstalk between articular cartilage, meniscus, synovium, and subchondral bone in osteoarthritis

AIMS

Osteoarthritis (OA) is a common degenerative joint disease worldwide, which is characterized by articular cartilage lesions. With more understanding of the disease, OA is considered to be a disorder of the whole joint. However, molecular communication within and between tissues during the disease process is still unclear. In this study, we used transcriptome data to reveal crosstalk between different tissues in OA.

METHODS

We used four groups of transcription profiles acquired from the Gene Expression Omnibus database, including articular cartilage, meniscus, synovium, and subchondral bone, to screen differentially expressed genes during OA. Potential crosstalk between tissues was depicted by ligand-receptor pairs.

RESULTS

During OA, there were 626, 97, 1,060, and 2,330 differentially expressed genes in articular cartilage, meniscus, synovium, and subchondral bone, respectively. Gene Ontology enrichment revealed that these genes were enriched in extracellular matrix and structure organization, ossification, neutrophil degranulation, and activation at different degrees. Through ligand-receptor pairing and proteome of OA synovial fluid, we predicted ligand-receptor interactions and constructed a crosstalk atlas of the whole joint. Several interactions were reproduced by transwell experiment in chondrocytes and synovial cells, including TNC-NT5E, TNC-SDC4, FN1-ITGA5, and FN1-NT5E. After lipopolysaccharide (LPS) or interleukin (IL)-1β stimulation, the ligand expression of chondrocytes and synovial cells was upregulated, and corresponding receptors of co-culture cells were also upregulated.

CONCLUSION

Each tissue displayed a different expression pattern in transcriptome, demonstrating their specific roles in OA. We highlighted tissue molecular crosstalk through ligand-receptor pairs in OA pathophysiology, and generated a crosstalk atlas. Strategies to interfere with these candidate ligands and receptors may help to discover molecular targets for future OA therapy.Cite this article: Bone Joint Res 2022;11(12):862-872.

Assessment of functional roles and therapeutic potential of integrin receptors in osteoarthritis: A systematic review and meta-analysis of preclinical studies

BACKGROUND

Integrins are heterodimeric transmembrane receptors that mediate a variety of biological function and plays a critical role in osteoarthritis (OA) pathogenesis, which may provide new targets for the development of OA therapies. However, the roles of integrins in different stages of OA remain elusive.

OBJECTIVES

This study aimed to synthesize all published preclinical evidence on the roles of integrin receptors in different stages of OA to identify the potential target for drug development in alleviating OA pathogenesis.

METHODS

Major electronic databases were used to identify related original articles. The methodological quality of all included studies was appraised using the SYRCLE risk of bias tool. We used the generic inverse variance with random effects model to calculate standardized mean differences (SMDs) and 95% confidence interval (CI).

RESULTS

Seventeen studies were included in this systematic review. Integrin α5β1 activation increases the histopathological score both in early [SMD, 6.39; 95%CI (2.90, 9.87); p = 0.0003] and late [SMD, 3.41; 95%CI (2.44, 4.38); p < 0.00001] stage of OA. Integrin α5β1 also increased the core catabolic factors like MMP-3, IL-1β, and TNF-α. Interestingly, the inactivation of α5β1 integrin did not change the histopathological score (p = 0.84). Similarly, β1 integrin notably increased histopathological score at both stages of OA [early; SMD, 7.13; 95%CI (2.01, 12.24); p = 0.006]; [late; SMD, 10.25; 95%CI (5.11, 15.39); p < 0.0001], and increased the MMP-13 levels. However, integrin β1 was upregulated at the early stage and downregulated at the late stage of OA. Furthermore, α2β1 integrin significantly increased histopathological score [SMD, 3.14; 95%CI (2.18, 4.10); p < 0.00001] and MMP-13 [SMD, 2.24; 95%CI (0.07, 4.41); p = 0.04]. Deactivating integrin α1β1 increased histopathological score in late [SMD, 1.53; 95%CI (0.80, 2.26); p < 0.0001], but not in early [SMD, 0.90; 95%CI (-1.65, 3.45); p = 0.49] stage of OA.

CONCLUSION

This study provides evidence that α5β1, α2β1, and α1β1 integrin might be the potential target for future drug development in alleviating OA pathogenesis. Further work is required to establish our findings through activating/deactivating these receptors in different stages of OA.

Roles of focal adhesion proteins in skeleton and diseases

The skeletal system, which contains bones, joints, tendons, ligaments and other elements, plays a wide variety of roles in body shaping, support and movement, protection of internal organs, production of blood cells and regulation of calcium and phosphate metabolism. The prevalence of skeletal diseases and disorders, such as osteoporosis and bone fracture, osteoarthritis, rheumatoid arthritis, and intervertebral disc degeneration, increases with age, causing pain and loss of mobility and creating a huge social and economic burden globally. Focal adhesions (FAs) are macromolecular assemblies that are composed of the extracellular matrix (ECM), integrins, intracellular cytoskeleton and other proteins, including kindlin, talin, vinculin, paxillin, pinch, Src, focal adhesion kinase (FAK) and integrin-linked protein kinase (ILK) and other proteins. FA acts as a mechanical linkage connecting the ECM and cytoskeleton and plays a key role in mediating cell-environment communications and modulates important processes, such as cell attachment, spreading, migration, differentiation and mechanotransduction, in different cells in skeletal system by impacting distinct outside-in and inside-out signaling pathways. This review aims to integrate the up-to-date knowledge of the roles of FA proteins in the health and disease of skeletal system and focuses on the specific molecular mechanisms and underlying therapeutic targets for skeletal diseases.

High-impact FN1 mutation decreases chondrogenic potential and affects cartilage deposition via decreased binding to collagen type II

Osteoarthritis is the most prevalent joint disease worldwide, yet progress in development of effective disease-modifying treatments is slow because of lack of insight into the underlying disease pathways. Therefore, we aimed to identify the causal pathogenic mutation in an early-onset osteoarthritis family, followed by functional studies in human induced pluripotent stem cells (hiPSCs) in an in vitro organoid cartilage model. We demonstrated that the identified causal missense mutation in the gelatin-binding domain of the extracellular matrix protein fibronectin resulted in significant decreased binding capacity to collagen type II. Further analyses of formed hiPSC-derived neo-cartilage tissue highlighted that mutated fibronectin affected chondrogenic capacity and propensity to a procatabolic osteoarthritic state. Together, we demonstrate that binding of fibronectin to collagen type II is crucial for fibronectin downstream gene expression of chondrocytes. We advocate that effective treatment development should focus on restoring or maintaining proper binding between fibronectin and collagen type II.

Integrins, cadherins and channels in cartilage mechanotransduction: perspectives for future regeneration strategies

Articular cartilage consists of hyaline cartilage, is a major constituent of the human musculoskeletal system and has critical functions in frictionless joint movement and articular homoeostasis. Osteoarthritis (OA) is an inflammatory disease of articular cartilage, which promotes joint degeneration. Although it affects millions of people, there are no satisfying therapies that address this disease at the molecular level. Therefore, tissue regeneration approaches aim at modifying chondrocyte biology to mitigate the consequences of OA. This requires appropriate biochemical and biophysical stimulation of cells. Regarding the latter, mechanotransduction of chondrocytes and their precursor cells has become increasingly important over the last few decades. Mechanotransduction is the transformation of external biophysical stimuli into intracellular biochemical signals, involving sensor molecules at the cell surface and intracellular signalling molecules, so-called mechano-sensors and -transducers. These signalling events determine cell behaviour. Mechanotransducing ion channels and gap junctions additionally govern chondrocyte physiology. It is of great scientific and medical interest to induce a specific cell behaviour by controlling these mechanotransduction pathways and to translate this knowledge into regenerative clinical therapies. This review therefore focuses on the mechanotransduction properties of integrins, cadherins and ion channels in cartilaginous tissues to provide perspectives for cartilage regeneration.

From the Matrix to the Nucleus and Back: Mechanobiology in the Light of Health, Pathologies, and Regeneration of Oral Periodontal Tissues

Among oral tissues, the periodontium is permanently subjected to mechanical forces resulting from chewing, mastication, or orthodontic appliances. Molecularly, these movements induce a series of subsequent signaling processes, which are embedded in the biological concept of cellular mechanotransduction (MT). Cell and tissue structures, ranging from the extracellular matrix (ECM) to the plasma membrane, the cytosol and the nucleus, are involved in MT. Dysregulation of the diverse, fine-tuned interaction of molecular players responsible for transmitting biophysical environmental information into the cell's inner milieu can lead to and promote serious diseases, such as periodontitis or oral squamous cell carcinoma (OSCC). Therefore, periodontal integrity and regeneration is highly dependent on the proper integration and regulation of mechanobiological signals in the context of cell behavior. Recent experimental findings have increased the understanding of classical cellular mechanosensing mechanisms by both integrating exogenic factors such as bacterial gingipain proteases and newly discovered cell-inherent functions of mechanoresponsive co-transcriptional regulators such as the Yes-associated protein 1 (YAP1) or the nuclear cytoskeleton. Regarding periodontal MT research, this review offers insights into the current trends and open aspects. Concerning oral regenerative medicine or weakening of periodontal tissue diseases, perspectives on future applications of mechanobiological principles are discussed.

Mechanisms linking mitochondrial mechanotransduction and chondrocyte biology in the pathogenesis of osteoarthritis

Mechanical loading is essential for chondrocyte health. Chondrocytes can sense and respond to various extracellular mechanical signals through an integrated set of mechanisms. Recently, it has been found that mitochondria, acting as critical mechanotransducers, are at the intersection between extracellular mechanical signals and chondrocyte biology. Much attention has been focused on identifying how mechanical loading-induced mitochondrial dysfunction contributes to the pathogenesis of osteoarthritis. In contrast, little is known regarding the mechanisms underlying functional alterations in mitochondria induced by mechanical stimulation. In this review, we describe how chondrocytes perceive environmental mechanical signals. We discuss how mechanical load induces mitochondrial functional alterations and highlight the major unanswered questions in this field. We speculate that AMP-activated protein kinase (AMPK), a master regulator of energy homeostasis, may play an important role in coupling force transmission to mitochondrial health and intracellular biological responses.

Molecular mechanisms of mechanical load-induced osteoarthritis

INTRODUCTION

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Comprehensive evaluation of differential long non-coding RNA and gene expression in patients with cartilaginous endplate degeneration of cervical vertebra

Long non-coding RNAs (lncRNAs) are emerging as key regulators in gene expression; however, little is currently known regarding their role in cartilaginous endplate (CE) degeneration (CED) of cervical vertebra. The present study aimed to investigate the expression levels of lncRNAs and analyze their potential functions in CED of cervical vertebra in patients with cervical fracture and cervical spondylosis. Human competitive endogenous RNA (ceRNA) array was used to analyze lncRNA and mRNA expression levels in CE samples from patients with cervical fracture and cervical spondylosis, who received anterior cervical discectomy and fusion. Differentially expressed lncRNAs (DELs) or differentially expressed genes (DEGs) were identified and functionally analyzed, using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses. An lncRNA-microRNA(miRNA)-mRNA ceRNA regulatory network was constructed based on the DELs and DEGs, and the ceRNA network was visualized using Cytoscape 3.7.2 software. In total, one downregulated mRNA, one upregulated miRNA and five downstream regulated lncRNAs were identified using reverse transcription-quantitative PCR in CED and healthy CE samples. A total of 369 lncRNAs and 246 mRNAs were identified as differentially expressed in CE. The GO and KEGG analyses demonstrated that the majority of GO and KEGG enrichments were associated with CED. Furthermore, a ceRNA network was established, including 168 putative miRNA response elements, 189 upregulated and 37 downregulated lncRNAs and 47 upregulated and 10dow regulated DEGs. The present study analyzed the function of DEGs in the ceRNA network and filtered out the same items as in DEG-function enrichment analysis. These results provide a new perspective for an improved understanding of ceRNA-mediated gene regulation in cervical spondylosis, and provide a novel theoretical basis for further studies on the function of lncRNA in cervical spondylosis. However, further experiments are required to validate the results of the present study.

Biomaterial Stiffness Guides Cross-talk between Chondrocytes: Implications for a Novel Cellular Response in Cartilage Tissue Engineering

The exquisite cartilage architecture maintains an orderly dynamic equilibrium as a result of the interplay between chondrocyte functions and the unique extracellular matrix (ECM) microenvironment. Numerous studies have demonstrated that extracellular cues, including topological, mechanical, and biochemical properties of the underlying substrates, dictate the chondrocyte behaviors. Consequently, developing advanced biomaterials with the desired characteristics which could achieve the biointerface between cells and the surrounded matrix close to the physiological conditions becomes a great hotspot in bioengineering. However, how the substrate stiffness influences the intercellular communication among chondrocytes is still poorly reported. We used polydimethylsiloxane with varied stiffnesses as a cell culture substrate to elucidate a novel cell-to-cell communication in a collective of chondrocytes. First, morphological images collected using scanning electron microscopy revealed that the tunable substrate stiffnesses directed the changes in intercellular links among chondrocytes. Next, fibronectin, which played a vital role in the connection of ECM components or linkage of ECM to chondrocytes, was shown to be gathered along cell-cell contact areas and was changed with the tunable substrate stiffnesses. Furthermore, transmembrane junctional proteins including connexin 43 (Cx43) and pannexin 1 (Panx1), which are responsible for gap junction formation in cell-to-cell communication, were mediated by the tunable substrate stiffnesses. Finally, through a scrape loading/dye transfer assay, we revealed cell-to-cell communication changes in a living chondrocyte population in response to the tunable substrate stiffnesses via cell-to-cell fluorescent molecule transport. Taken together, this novel cell-to-cell communication regulated by biomaterial stiffness could help us to increase the understanding of cell behaviors under biomechanical control and may ultimately lead to refining cell-based cartilage tissue engineering.