Senescent cell population with ZEB1 transcription factor as its main regulator promotes osteoarthritis in cartilage and meniscus

Overexpression of RAD54L attenuates osteoarthritis by suppressing the HIF-1α/VEGF signaling pathway: Bioinformatics analysis and experimental validation

Osteoarthritis (OA) is a widespread chronic, progressive, degenerative joint disease that causes pain and disability. Current treatments for OA have limited effectiveness and new biomarkers need to be identified. Bioinformatics analysis was conducted to explore differentially expressed genes and DNA repair/recombination protein 54 L (RAD54L) was selected. We firstly overexpressed RAD54L in interleukin-1β (IL-1β)-induced human articular chondrocytes or in OA rats to investigate its effect on OA. Chondrocyte viability and apoptotic rate were measured by Cell Counting Kit-8 and flow cytometry, respectively. Then we evaluated OA severity in vivo by Hematoxylin-eosin staining and Osteoarthritis Research Society International standards. The expression of inflammatory mediators was tested by enzyme-linked immunosorbent assay. Finally, western blot was performed to determine the relative expression level of hypoxia-inducible factors 1α (HIF-1α) and vascular endothelial growth factor (VEGF). Overexpression of RAD54L promoted cell viability and attenuated apoptosis in IL-1β-induced human chondrocytes. A lower Osteoarthritis Research Society International score and a remarkable alleviation of chondrocyte disordering and infiltration of inflammatory cells were found in cartilage tissues of OA rats after overexpressing RAD54L. The inflammatory response induced by OA was decreased by RAD54L overexpression in vitro and in vivo. In addition, RAD54L overexpression decreased the relative expression level of HIF-1α and VEGF. Overexpression of RAD54L could attenuate OA by suppressing the HIF-1α/VEGF signaling pathway, indicating that RAD54L may be a potential treatment target for OA.

Graphene oxide activates canonical TGFβ signalling in a human chondrocyte cell line via increased plasma membrane tension

Graphene Oxide (GO) has been shown to increase the expression of key cartilage genes and matrix components within 3D scaffolds. Understanding the mechanisms behind the chondroinductive ability of GO is critical for developing articular cartilage regeneration therapies but remains poorly understood. The objectives of this work were to elucidate the effects of GO on the key chondrogenic signalling pathway - TGFβ and identify the mechanism through which signal activation is achieved in human chondrocytes. Activation of canonical signalling was validated through GO-induced SMAD-2 phosphorylation and upregulation of known TGFβ response genes, while the use of a TGFβ signalling reporter assay allowed us to identify the onset of GO-induced signal activation which has not been previously reported. Importantly, we investigate the cell-material interactions and molecular mechanisms behind these effects, establishing a novel link between GO, the plasma membrane and intracellular signalling. By leveraging fluorescent lifetime imaging (FLIM) and a membrane tension probe, we reveal GO-mediated increases in plasma membrane tension, in real-time for the first time. Furthermore, we report the activation of mechanosensory pathways which are known to be regulated by changes in plasma membrane tension and reveal the activation of endogenous latent TGFβ in the presence of GO, providing a mechanism for signal activation. The data presented here are critical to understanding the chondroinductive properties of GO and are important for the implementation of GO in regenerative medicine.

Tolerant and Rapid Endochondral Bone Regeneration Using Framework-Enhanced 3D Biomineralized Matrix Hydrogels

Tissue-engineered bone has emerged as a promising alternative for bone defect repair due to the advantages of regenerative bone healing and physiological functional reconstruction. However, there is very limited breakthrough in achieving favorable bone regeneration due to the harsh osteogenic microenvironment after bone injury, especially the avascular and hypoxic conditions. Inspired by the bone developmental mode of endochondral ossification, a novel strategy is proposed for tolerant and rapid endochondral bone regeneration using framework-enhanced 3D biomineralized matrix hydrogels. First, it is meticulously designed 3D biomimetic hydrogels with both hypoxic and osteoinductive microenvironment, and then integrated 3D-printed polycaprolactone framework to improve their mechanical strength and structural fidelity. The inherent hypoxic 3D matrix microenvironment effectively activates bone marrow mesenchymal stem cells self-regulation for early-stage chondrogenesis via TGFβ/Smad signaling pathway due to the obstacle of aerobic respiration. Meanwhile, the strong biomineralized microenvironment, created by a hybrid formulation of native-constitute osteogenic inorganic salts, can synergistically regulate both bone mineralization and osteoclastic differentiation, and thus accelerate the late-stage bone maturation. Furthermore, both in vivo ectopic osteogenesis and in situ skull defect repair successfully verified the high efficiency and mechanical maintenance of endochondral bone regeneration mode, which offers a promising treatment for craniofacial bone defect repair.

Fisetin suppresses chondrocyte senescence and attenuates osteoarthritis progression by targeting sirtuin 6

Osteoarthritis (OA) is the most common type of arthritis and is an age-related joint disease that is particularly prevalent in subjects over 65 years old. The chronic rise of senescent cells has a close correlation with age-related diseases such as OA, and the senescence-associated secretory phenotype (SASP) is implicated in OA cartilage degeneration pathogenesis. Sirtuin 6 (SIRT6) is likely to be a key senescence-related regulator. Fisetin (FST) is a natural flavonol of the flavonoid family that is recommended as a senolytic drug to extend health and lifespan. However, the potential chondroprotective effects of FST on OA rats are largely unclarified. The aim of this study is to investigate the ameliorative effects of FST on OA joint cartilage and the relationship with SIRT6 and the detailed mechanisms from anti-inflammatory and anti-senescent perspectives. Rats were subjected to destabilization of the medial meniscus (DMM) surgery as a means of inducing the experimental OA model in vivo. Chondrocytes treated with IL-1β were utilized for mimicking the OA cell model in vitro. Intra-articular injection of FST, OSS_128,167 (OSS, SIRT6 inhibitor), and MDL800 (MDL, SIRT6 agonist) in vivo or administering them in IL-1β-induced rat chondrocytes in vitro were performed in order to determine the effects FST has on OA and the link with SIRT6. This study found SIRT6 level to be negatively correlated with OA severity. SIRT6 downregulation was validated in the joint cartilages of DMM rats and IL-1β-treated chondrocytes. It was also notably demonstrated that FST can activate SIRT6. Both the administration of FST and activation of SIRT6 using MDL were found to rescue cartilage erosion, decrease extracellular matrix (ECM) degradation, prevent cartilage from apoptosis, and improve detrimental senescence-related phenotype. The alleviative effects of FST against inflammation, ECM degradation, apoptosis, and senescence in IL-1β-stimulated chondrocytes were also confirmed. SIRT6 loss occurs in articular cartilage in OA pathogenesis, which is linked to aging. FST attenuates injury-induced aging-related phenotype changes in chondrocytes through the targeting of SIRT6.

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.

vSPACE: Exploring Virtual Spatial Representation of Articular Chondrocytes at the Single-Cell Level

Single cell RNA sequencing technology has been dramatically changing how gene expression studies are performed. However, its use has been limited to identifying subtypes of cells by comparing cells' gene expression levels in an unbiased manner to produce a 2D plot (e.g., UMAP/tSNE). We developed a new method of placing cells in 2D space. This system, called vSPACE, shows a virtual spatial representation of scRNAseq data obtained from human articular cartilage by emulating the concept of spatial transcriptomics technology, but virtually. This virtual 2D plot presentation of human articular cartage cells generates several zonal distribution patterns, in one or multiple genes at a time, reveling patterns that scientists can appreciate as imputed spatial distribution patterns along the zonal axis. The discovered patterns are explainable and remarkably consistent across all six healthy doners despite their respectively different clinical variables (age and sex), suggesting the confidence of the discovered patterns.

PDK4 inhibits osteoarthritis progression by activating the PPAR pathway

BACKGROUND

Osteoarthritis (OA) is a degenerative joint disease caused by the deterioration of cartilage. However, the underlying mechanisms of OA pathogenesis remain elusive.

METHODS

Hub genes were screened by bioinformatics analysis based on the GSE114007 and GSE169077 datasets. The Sprague-Dawley (SD) rat model of OA was constructed by intra-articular injection of a mixture of papain and L-cysteine. Hematoxylin-eosin (HE) staining was used to detect pathological changes in OA rat models. Inflammatory cytokine levels in serum were measured employing the enzyme-linked immunosorbent assay (ELISA). The reverse transcription quantitative PCR (RT-qPCR) was implemented to assess the hub gene expressions in OA rat models. The roles of PDK4 and the mechanism regulating the PPAR pathway were evaluated through western blot, cell counting kit-8 (CCK-8), ELISA, and flow cytometry assays in C28/I2 chondrocytes induced by IL-1β.

RESULTS

Six hub genes were identified, of which COL1A1, POSTN, FAP, and CDH11 expressions were elevated, while PDK4 and ANGPTL4 were reduced in OA. Overexpression of PDK4 inhibited apoptosis, inflammatory cytokine levels (TNF-α, IL-8, and IL-6), and extracellular matrix (ECM) degradation protein expressions (MMP-3, MMP-13, and ADAMTS-4) in IL-1β-induced chondrocytes. Further investigation revealed that PDK4 promoted the expression of PPAR signaling pathway-related proteins: PPARA, PPARD, and ACSL1. Additionally, GW9662, an inhibitor of the PPAR pathway, significantly counteracted the inhibitory effect of PDK4 overexpression on IL-1β-induced chondrocytes.

CONCLUSION

PDK4 inhibits OA development by activating the PPAR pathway, which provides new insights into the OA management.

Osteoarthriris year in review 2023: genetics, genomics, and epigenetics

OBJECTIVE

To elucidate the scientific advances made in the last 12 months within the realm of osteoarthritis genetics, genomics, and epigenetics. This review paper highlights major research publications that enhance our current understanding of the role of genetics, genomics, and epigenetics in osteoarthritis.

METHODS

A systematic literature search was conducted on pubmed.ncbi.nlm.nih.gov on "March 17, 2023", using the following keywords: "osteoarthritis" in combination with any of these terms: "genetic(s)", "mutation(s)", "genomic(s)", "epigenetic(s)", "DNA methylation", "noncoding RNA", "lncRNA", "circular RNA", "microRNA", "transcriptomic(s)", "RNA sequencing", "single cell RNA sequencing", or "single nucleus RNA sequencing". The selection comprised original research articles published in the English language between the OARSI congresses of 2022 and 2023.

RESULTS

A total of 2178 research articles were identified, which subsequently reduced to 67 unique articles relevant to the field. Current trends in osteoarthritis genetics research involve meta-analyses of various cohorts to explore the impact of gene variants on osteoarthritis-related outcomes, such as pain. Early developmental changes within the joint were also found to influence osteoarthritis through genetic variations. Researchers also prioritize testing the mechanisms and functions of miRNAs, circRNAs, and lncRNAs. Potential drug targets began to emerge; however, independent validation studies are lacking. Single cell RNA sequencing studies revealed unique immune cell populations in the knee; however, no study reported single nucleus RNA sequencing analysis.

CONCLUSIONS

This review focused on recent advances in the above-mentioned themes within the field of osteoarthritis. These advances improve our understanding of the disease's complexity and guide us toward functional assessments of genetic/epigenetic outcomes and toward their translational and clinical applications.

Osteoarthritis year in review 2023: Biology

Great progress continues to be made in our understanding of the multiple facets of osteoarthritis (OA) biology. Here, we review the major advances in this field and progress towards therapy development over the past year, highlighting a selection of relevant published literature from a PubMed search covering the year from the end of April 2022 to the end of April 2023. The selected articles have been arranged in themes. These include 1) molecular regulation of articular cartilage and implications for OA, 2) mechanisms of subchondral bone remodelling, 3) role of synovium and inflammation, 4) role of age-related changes including cartilage matrix stiffening, cellular senescence, mitochondrial dysfunction, metabolic dysfunction, and impaired autophagy, and 5) peripheral mechanisms of OA pain. Progress in the understanding of the cellular and molecular mechanisms responsible for the multiple aspects of OA biology is unravelling novel therapeutic targets for disease modification.

Engineering approaches for RNA-based and cell-based osteoarthritis therapies

Osteoarthritis (OA) is a chronic, debilitating disease that substantially impairs the quality of life of affected individuals. The underlying mechanisms of OA are diverse and are becoming increasingly understood at the systemic, tissue, cellular and gene levels. However, the pharmacological therapies available remain limited, owing to drug delivery barriers, and consist mainly of broadly immunosuppressive regimens, such as corticosteroids, that provide only short-term palliative benefits and do not alter disease progression. Engineered RNA-based and cell-based therapies developed with synthetic chemistry and biology tools provide promise for future OA treatments with durable, efficacious mechanisms of action that can specifically target the underlying drivers of pathology. This Review highlights emerging classes of RNA-based technologies that hold potential for OA therapies, including small interfering RNA for gene silencing, microRNA and anti-microRNA for multi-gene regulation, mRNA for gene supplementation, and RNA-guided gene-editing platforms such as CRISPR-Cas9. Various cell-engineering strategies are also examined that potentiate disease-dependent, spatiotemporally regulated production of therapeutic molecules, and a conceptual framework is presented for their application as OA treatments. In summary, this Review highlights modern genetic medicines that have been clinically approved for other diseases, in addition to emerging genome and cellular engineering approaches, with the goal of emphasizing their potential as transformative OA treatments.

The matrix microenvironment influences but does not dominate tissue-specific stem cell lineage differentiation

Mesenchymal stem cells (MSCs) play a pivotal role in tissue engineering and regenerative medicine, with their clinical application often hindered by cell senescence during ex vivo expansion. Recent studies suggest that MSC-deposited decellularized extracellular matrix (dECM) offers a conducive microenvironment that fosters cell proliferation and accentuates stem cell differentiation. However, the ability of this matrix environment to govern lineage differentiation of tissue-specific stem cells remains ambiguous. This research employs human adipose-derived MSCs (ADSCs) and synovium-derived MSCs (SDSCs) as models for adipogenesis and chondrogenesis differentiation pathways, respectively. Genetically modified dECM (GMdECM), produced by SV40LT-transduced immortalized cells, was studied for its influence on cell differentiation. Both types of immortalized cells displayed a reduction in chondrogenic ability but an enhancement in adipogenic potential. ADSCs grown on ADSC-deposited dECM showed stable chondrogenic potential but increased adipogenic capacity; conversely, SDSCs expanded on SDSC-generated dECM displayed elevated chondrogenic capacity and diminished adipogenic potential. This cell-dependent response was confirmed through GMdECM expansion, with SDSCs showing enhanced chondrogenesis. However, ADSCs did not exhibit improved chondrogenic potential on GMdECM, suggesting that the matrix microenvironment does not dictate the final differentiation path of tissue-specific stem cells. Potential molecular mechanisms, such as elevated basement membrane protein expression in GMdECMs and dynamic TWIST1 expression during expansion and chondrogenic induction, may underpin the strong chondrogenic differentiation of GMdECM-expanded SDSCs.

A roadmap for delivering a human musculoskeletal cell atlas

Advances in single-cell technologies have transformed the ability to identify the individual cell types present within tissues and organs. The musculoskeletal bionetwork, part of the wider Human Cell Atlas project, aims to create a detailed map of the healthy musculoskeletal system at a single-cell resolution throughout tissue development and across the human lifespan, with complementary generation of data from diseased tissues. Given the prevalence of musculoskeletal disorders, this detailed reference dataset will be critical to understanding normal musculoskeletal function in growth, homeostasis and ageing. The endeavour will also help to identify the cellular basis for disease and lay the foundations for novel therapeutic approaches to treating diseases of the joints, soft tissues and bone. Here, we present a Roadmap delineating the critical steps required to construct the first draft of a human musculoskeletal cell atlas. We describe the key challenges involved in mapping the extracellular matrix-rich, but cell-poor, tissues of the musculoskeletal system, outline early milestones that have been achieved and describe the vision and directions for a comprehensive musculoskeletal cell atlas. By embracing cutting-edge technologies, integrating diverse datasets and fostering international collaborations, this endeavour has the potential to drive transformative changes in musculoskeletal medicine.

PSD95 as a New Potential Therapeutic Target of Osteoarthritis: A Study of the Identification of Hub Genes through Self-Contrast Model

Osteoarthritis (OA) is a worldwide joint disease. However, the precise mechanism causing OA remains unclear. Our primary aim was to identify vital biomarkers associated with the mechano-inflammatory aspect of OA, providing potential diagnostic and therapeutic targets for OA. Thirty OA patients who underwent total knee arthroplasty were recruited, and cartilage samples were obtained from both the lateral tibial plateau (LTP) and medial tibial plateau (MTP). GO and KEGG enrichment analyses were performed, and the protein-protein interaction (PPI) assessment was conducted for hub genes. The effect of PSD95 inhibition on cartilage degeneration was also conducted and analyzed. A total of 1247 upregulated and 244 downregulated DEGs were identified. Significant differences were observed between MTP and LTP in mechanical stress-related genes and activated sensory neurons based on a self-contrast model of human knee OA. Cluster analysis identified DLG4 as the hub gene. Cyclic loading stress increased PSD95 (encoded by DLG4) expression in LTP cartilage, and PSD95 inhibitors could alleviate OA progression. This study suggests that inhibiting PSD95 could be a potential therapeutic strategy for preventing articular cartilage degradation.

RNA-binding proteins that are highly expressed and enriched in healthy cartilage but suppressed in osteoarthritis

Objectives: RNA-binding proteins (RBPs) have diverse and essential biological functions, but their role in cartilage health and disease is largely unknown. The objectives of this study were (i) map the global landscape of RBPs expressed and enriched in healthy cartilage and dysregulated in osteoarthritis (OA); (ii) prioritize RBPs for their potential role in cartilage and in OA pathogenesis and as therapeutic targets. Methods: Our published bulk RNA-sequencing (RNA-seq) data of healthy and OA human cartilage, and a census of 1,542 RBPs were utilized to identify RBPs that are expressed in healthy cartilage and differentially expressed (DE) in OA. Next, our comparison of healthy cartilage RNA-seq data to 37 transcriptomes in the Genotype-Tissue Expression (GTEx) database was used to determine RBPs that are enriched in cartilage. Finally, expression of RBPs was analyzed in our single cell RNA-sequencing (scRNA-seq) data from healthy and OA human cartilage. Results: Expression of RBPs was higher than nonRBPs in healthy cartilage. In OA cartilage, 188 RBPs were differentially expressed, with a greater proportion downregulated. Ribosome biogenesis was enriched in the upregulated RBPs, while splicing and transport were enriched in the downregulated. To further prioritize RBPs, we selected the top 10% expressed RBPs in healthy cartilage and those that were cartilage-enriched according to GTEx. Intersecting these criteria, we identified Tetrachlorodibenzodioxin (TCDD) Inducible Poly (ADP-Ribose) Polymerase (TIPARP) as a candidate RBP. TIPARP was downregulated in OA. scRNA-seq data revealed TIPARP was most significantly downregulated in the "pathogenic cluster". Conclusion: Our global analyses reveal expression patterns of RBPs in healthy and OA cartilage. We also identified TIPARP and other RBPs as novel mediators in OA pathogenesis and as potential therapeutic targets.

Diagnostic efficiency of [68 Ga]Ga-DOTA-FAPI-04 in differentiating periprosthetic hip joint infection and aseptic failure

PURPOSE

To assess the efficiency of [68 Ga]Ga-DOTA-FAPI-04 in diagnosing periprosthetic hip joint infection and establish a diagnostic standard of clinical significance based on uptake pattern.

METHODS

[68 Ga]Ga-DOTA-FAPI-04 PET/CT was performed in patients with symptomatic hip arthroplasty from December 2019 to July 2022. The reference standard was based on the 2018 Evidence-Based and Validation Criteria. Two diagnostic criteria, SUVmax and uptake pattern, were used to diagnose PJI. Meanwhile, original data were imported into IKT-snap to draw the view of interest, A.K. was used to extract features of clinical cases, and unsupervised clustering analysis was applied according to the groups.

RESULTS

A total of 103 patients were included, 28 of whom had PJI. The area under the curve of SUVmax was 0.898, which was better than that of all of the serological tests. The cutoff value of SUVmax was 7.53, and the sensitivity and specificity were 100 and 72%, respectively. The sensitivity, specificity and accuracy of the uptake pattern were 100, 93.1 and 95%, respectively. In radiomics analysis, the features of PJI were significantly different from those of aseptic failure.

CONCLUSION

The efficiency of [68 Ga]Ga-DOTA-FAPI-04 PET/CT in diagnosing PJI showed promising results, and the diagnostic criteria of the uptake pattern were more clinically instructive. Radiomics also showed certain application prospects in the field of PJI.

TRIAL REGISTRATION NUMBER

Trial registration: ChiCTR2000041204. Registered 24 September 2019.