Single-cell RNA sequencing analysis of human chondrocytes reveals cell-cell communication alterations mediated by interactive signaling pathways in osteoarthritis

Theranostics of osteoarthritis: Applications and prospects of precision targeting nanotechnology

Osteoarthritis (OA), a complex degenerative joint disease driven by cartilage degeneration, synovial inflammation, and subchondral bone remodeling, lacks effective disease-modifying therapies. Precision-targeted nanotechnology has emerged as a breakthrough strategy, offering enhanced drug delivery, reduced toxicity, and synergistic diagnostic-therapeutic capabilities. This review summarizes OA pathogenesis, focusing on dysregulated immune networks and self-perpetuating synovial microenvironmental interactions. We discuss advanced nanomedicine approaches, which leverage OA-specific pathological cues for localized treatment. Innovations in cytokine modulation, photothermal therapy, and integrated theranostics (photoacoustic/fluorescence imaging) are highlighted as transformative tools for real-time diagnosis and personalized intervention. Despite progress, challenges such as biocompatibility optimization, clinical translation barriers, OA heterogeneity necessitate further development of multifunctional nanocarriers and rationaldesigns. This work underscores the potential of nanotechnology to advance OA therapeutics, bridging preclinical innovation with clinical applicability in pharmaceutical sciences.

Integrative analysis of bulk and single-cell RNA sequencing data reveals increased arachidonic acid metabolism in osteoarthritic chondrocytes

Background

Abnormal lipid metabolism in chondrocytes, especially arachidonic acid (AA) metabolism, has attracted considerable attention in promoting osteoarthritis (OA) progression. However, the metabolic regulation of chondrocytes in OA remains to be investigated.

Methods

Bulk RNA sequencing (RNA-seq) data and single-cell RNA sequencing (scRNA-seq) data of human knee cartilage were downloaded from public databases. Gene set variation analysis (GSVA) and weighted correlation network analysis (WGCNA) were used to explore functional regulation and gene expression characterization. A reference gene set from the Kyoto Encyclopedia of Genes and Genomes (KEGG) database was used to validate metabolic changes. CellChat analysis was performed to investigate the communication among osteoarthritic chondrocytes. Human immortalized chondrocytes were stimulated with macrophage migration inhibitory factor (MIF), then quantitative real-time PCR (qPCR) and western blot (WB) analysis were used to detect transcription or translation levels of genes. Enzyme linked immunosorbent assay (ELISA) was used to measure AA content. Cartilage from OA patients was collected for immunohistochemistry (IHC) to validate protein expression.

Results

Functional analysis revealed significant activation of the AA metabolic pathway was significantly enriched in the cluster of proliferative chondrocytes (ProCs). CellChat analysis indicated that the incoming signals of MIF increased in ProCs, and the expressions of extracellular signal-regulated kinase (ERK) and phospholipase A2 group IVA (PLA2G4A) were upregulated. Moreover, functional analysis showed that the ERK pathway was enriched in ProCs. Cell experiments indicated MIF stimulation elevated phospho-ERK (p-ERK) and PLA2G4A expression and AA content. IHC showed p-ERK and PLA2G4A were significantly activated in OA cartilage. MIF also upregulated interleukin 1β (IL1B) and matrix metalloproteinase 13 (MMP13) expression.

Conclusion

Our study shows that MIF stimulation of chondrocytes can activate the ERK/PLA2G4A signaling pathway and increase AA production. ProCs located in the proliferative layer of cartilage are likely the main cells executing this mechanism. Therefore, targeting and inhibiting MIF signaling in chondrocytes, especially in ProCs, could be a novel strategy for the prevention and treatment of OA.

Identification and validation of up-regulated TNFAIP6 in osteoarthritis with type 2 diabetes mellitus

Lines of evidence have indicated that type 2 diabetes mellitus (T2DM) is an independent risk factor for osteoarthritis (OA) progression. However, the study focused on the relationship between T2DM and OA at the transcriptional level remains empty. We downloaded OA- and T2DM-related bulk RNA-sequencing and single-cell RNA sequencing data from the Gene Expression Omnibus (GEO) dataset. Differential expression analysis and weighted gene co-expression network analysis (WGCNA) were performed to screen out hub genes between OA and T2DM, and functional enrichment was done. Single-cell sequencing analysis was further used to screen key genes on OA and T2DM datasets. Rat chondrocytes and human articular cartilage were used to validate biomarkers among OA and T2DM. Sixty-eight hub genes were obtained, which were mainly enriched in the inflammatory response. We found that the hub gene TNFAIP6 is not only closely related to OA and T2DM but also a marker of prehypertrophic chondrocytes, which are closely related to the progression of OA. TNFAIP6 was found to be significantly elevated in CD14 + monocytes in T2DM patients, and this group of cells can promote inflammation. Validation on rat chondrocytes and human cartilage showed that TNFAIP6 was highly expressed in OA and further increased in the presence of T2DM or high glucose. Our study identified several characteristic modules and hub genes in the pathogenesis of T2DM-induced OA, which may facilitate further investigation of its molecular mechanisms. Up-regulated TNFAIP6 may contribute to OA in patients with T2DM by the recruitment of pro-inflammatory CD14 + monocytes in the OA synovium, which provides a potential target for the diagnosis and treatment of T2DM-associated OA.

Single-cell RNA transcriptomics reveals Du-Zhong-Wan promotes osteoporotic fracture healing via YAP/β-catenin/VEGF axis in BMSCs

BACKGROUND

Our previous study demonstrated that Du-Zhong-Wan (DZW) promoted osteoporotic fracture (OPF) healing by enhancing osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) and angiogenesis of endothelial cells (ECs). However, the heterogeneity of BMSCs and ECs, as well as the specific molecular mechanism underlying these effects, still require further evaluation.

PURPOSE

The primary objective of this study was to elucidate the heterogeneity of BMSCs and ECs, as well as the cellular-level mechanism of DZW against OPF through single-cell RNA sequencing.

METHODS

In this study, we presented a single-cell atlas of mouse femoral callus, comparing samples with and without DZW treatment, utilizing single-cell RNA sequencing. Variable genes were identified using the FindVariableGenes (FVG) and principal component analysis (PCA) analysis. Additionally, uniform manifold approximation and projection (U-MAP) was employed to reduce and visualize the distinct subclusters. The CellPhoneDB2 method was employed to analyze intercellular communication and quantify the interaction between ligands and receptors within distinct cell clusters. The osteogenic differentiation capacity of BMSCs was assessed by micro-CT, alkaline phosphatase (ALP), and alizarin red S (ARS) assay. The scratch wound assay and tube formation assay were utilized to assess the angiogenic capabilities of ECs in vitro. Additionally, western blot and immunofluorescence experiments were utilized to elucidate the related protein expression.

RESULTS

Consistent with our previous studies, DZW obviously promoted osteoporotic fracture healing. Moreover, this study discovered 14 cell clusters at the femoral fracture callus, where the BMSCs most actively interacted with ECs, through single-cell sequencing. Notably, DZW significantly elevated the proportion of Lepr+ BMSCs and Podxl+ ECs subgroup, which were respectively considered essential cells for osteoblastogenesis and angiogenesis of arteriolar vessels. The increased proportion of Podxl+ ECs was partially attributed to vascular endothelial growth factor (VEGF), secreted by BMSCs, which were able to be reversed by YAP pharmacological inhibitor verteporfin. Furthermore, the western blot assay revealed elevated expression levels of YAP/β-catenin, VEGF, RUNX2, and OCN in BMSCs treated with DZW, which were counteracted by verteporfin.

CONCLUSION

The data above indicates that DZW elevates the proportion of LEPR+ BMSCs and Podxl+ ECs, therefore contributing for the osteogenic ability of BMSCs and BMSCs-mediated angiogenesis via activation of the YAP/β-catenin/VEGF axis, which provides novel potential targets and mechanism for DZW in treating OPF in sub-clusters and molecular level.

Identification of key biomarkers related to fibrocartilage chondrocytes for osteoarthritis based on bulk, single-cell transcriptomic data

Introduction

Osteoarthritis (OA) is a prevalent joint disease that severely impacts patients' quality of life. Due to its unclear pathogenesis and lack of effective therapeutic targets, discovering new biomarkers for OA is essential. Recently, the role of chondrocyte subpopulations in OA progression has gained significant attention, offering potential insights into the disease. This study aimed to explore the role of fibrocartilage chondrocytes (FC) in the progression of OA and identify key biomarkers related to FC.

Methods

We analyzed single-cell ribonucleic acid sequencing (scRNA-seq) data from samples of OA and normal cartilage, focusing on FC. Microarray data were integrated to identify differentially expressed genes (DEGs). We conducted functional-enrichment analyses, including Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO), and used weighted gene co-expression network analysis (WGCNA) and the least absolute shrinkage and selection operator (LASSO) algorithm to select biomarkers. A novel risk model for OA was constructed using these biomarkers. We then built a transcription factor (TF)-gene interaction network and performed immunohistochemistry (IHC) to validate protein expression levels of these biomarkers in cartilage samples.

Results

The study identified 545 marker genes associated with FC in OA. GO and KEGG analyses revealed their biological functions; microarray analysis identified 243 DEGs on which functional-enrichment analysis were conducted. Using WGCNA and LASSO, we identified six hub genes, on the basis of which we constructed a risk model for OA. In addition, correlation analysis revealed a close association between Forkhead Box (FoxO)-mediated transcription and these these biomarkers. IHC showed significantly lower protein levels of ABCA5, ABCA6 and SLC7A8 in OA samples than in normal samples.

Conclusion

This study used a multi-omics approach to identify six FC-related OA biomarkers (BCL6, ABCA5, ABCA6, CITED2, NR1D1, and SLC7A8) and developed an exploratory risk model. Functional enrichment analysis revealed that the FoxO pathway may be linked to these markers, particularly implicating ABCA5 and ABCA6 in cholesterol homeostasis within chondrocytes. These findings highlight ABCA family members as novel contributors to OA pathogenesis and suggest new therapeutic targets.

Advancing skeletal health and disease research with single-cell RNA sequencing

Orthopedic conditions have emerged as global health concerns, impacting approximately 1.7 billion individuals worldwide. However, the limited understanding of the underlying pathological processes at the cellular and molecular level has hindered the development of comprehensive treatment options for these disorders. The advent of single-cell RNA sequencing (scRNA-seq) technology has revolutionized biomedical research by enabling detailed examination of cellular and molecular diversity. Nevertheless, investigating mechanisms at the single-cell level in highly mineralized skeletal tissue poses technical challenges. In this comprehensive review, we present a streamlined approach to obtaining high-quality single cells from skeletal tissue and provide an overview of existing scRNA-seq technologies employed in skeletal studies along with practical bioinformatic analysis pipelines. By utilizing these methodologies, crucial insights into the developmental dynamics, maintenance of homeostasis, and pathological processes involved in spine, joint, bone, muscle, and tendon disorders have been uncovered. Specifically focusing on the joint diseases of degenerative disc disease, osteoarthritis, and rheumatoid arthritis using scRNA-seq has provided novel insights and a more nuanced comprehension. These findings have paved the way for discovering novel therapeutic targets that offer potential benefits to patients suffering from diverse skeletal disorders.

Collagen and Alginate Hydrogels Support Chondrocytes Redifferentiation In Vitro without Supplementation of Exogenous Growth Factors

Focal cartilage defects are a prevalent knee problem affecting people of all ages. Articular cartilage (AC) possesses limited healing potential, and osteochondral defects can lead to pain and long-term complications such as osteoarthritis. Autologous chondrocyte implantation (ACI) has been a successful surgical approach for repairing osteochondral defects over the past two decades. However, a major drawback of ACI is the dedifferentiation of chondrocytes during their in vitro expansion. In this study, we isolated ovine chondrocytes and cultured them in a two-dimensional environment for ACI procedures. We hypothesized that 3D scaffolds would support the cells' redifferentiation without the need for growth factors so we encapsulated them into soft collagen and alginate (col/alg) hydrogels. Chondrocytes embedded into the hydrogels were viable and proliferated. After 7 days, they regained their original rounded morphology (aspect ratio 1.08) and started to aggregate. Gene expression studies showed an upregulation of COL2A1, FOXO3A, FOXO1, ACAN, and COL6A1 (37, 1.13, 22, 1123, and 1.08-fold change expression, respectively) as early as day one. At 21 days, chondrocytes had extensively colonized the hydrogel, forming large cell clusters. They started to replace the degrading scaffold by depositing collagen II and aggrecan, but with limited collagen type I deposition. This approach allows us to overcome the limitations of current approaches such as the dedifferentiation occurring in 2D in vitro expansion and the necrotic formation in spheroids. Further studies are warranted to assess long-term ECM deposition and integration with native cartilage. Though limitations exist, this study suggests a promising avenue for cartilage repair with col/alg hydrogel scaffolds.

PTH treatment before cyclic joint loading improves cartilage health and attenuates load-induced osteoarthritis development in mice

Osteoarthritis (OA) treatment is limited by the lack of effective nonsurgical interventions to slow disease progression. Here, we examined the contributions of the subchondral bone properties to OA development. We used parathyroid hormone (PTH) to modulate bone mass before OA initiation and alendronate (ALN) to inhibit bone remodeling during OA progression. We examined the spatiotemporal progression of joint damage by combining histopathological and transcriptomic analyses across joint tissues. The additive effect of PTH pretreatment before OA initiation and ALN treatment during OA progression most effectively attenuated load-induced OA pathology. Individually, PTH directly improved cartilage health and slowed the development of cartilage damage, whereas ALN primarily attenuated subchondral bone changes associated with OA progression. Joint damage reflected early transcriptomic changes. With both treatments, the structural changes were associated with early modulation of immunoregulation and immunoresponse pathways that may contribute to disease mechanisms. Overall, our results demonstrate the potential of subchondral bone-modifying therapies to slow the progression of OA.

Probing the communication patterns of different chondrocyte subtypes in osteoarthritis at the single cell level using pattern recognition and manifold learning

The patterns of communication among different chondrocyte subtypes in human cartilage degeneration and regeneration help us understand the microenvironment of osteoarthritis and optimize cell-targeted therapies. Here, a single-cell transcriptome dataset of chondrocytes is used to explore the synergistic and communicative patterns of different chondrocyte subtypes. We collected 1600 chondrocytes from 10 patients with osteoarthritis and analyzed the active communication patterns for the first time based on network analysis and pattern recognition at the single-cell level. Manifold learning and quantitative contrasts were performed to analyze conserved and specific communication pathways. We found that ProCs (Proliferative chondrocytes), ECs (Effector chondrocytes), preHTCs (Prehypertrophic chondrocytes), HTCs (Hypertrophic chondrocytes), and FCs (Fibrocartilage chondrocytes) are more active in incoming and outgoing signaling patterns, which is consistent with studies on their close functional cooperation. Among them, preHTCs play multiple roles in chondrocyte communication, and ProCs and preHTCs have many overlapping pathways. These two subtypes are the most active among all chondrocyte subtypes. Interestingly, ECs and FCs are a pair of "mutually exclusive" subtypes, of which ECs are predominant in incoming patterns and FCs in outgoing patterns. The active signaling pathways of ECs and FCs largely do not overlap. COLLAGEN and LAMININ are the main pivotal pathways, which means they are very important in the repair and expansion of joint homeostasis. Notably, only preHTCs assume multiple roles (including sender, receiver, mediator, and influencer) and are involved in multiple communication pathways. We have examined their communication patterns from the perspective of cellular interactions, revealed the relationships among different chondrocyte subtypes, and, in particular, identified a number of active subtypes and pathways that are important for targeted therapy in the osteoarthritic microenvironment. Our findings provide a new research paradigm and new insights into understanding chondrocyte activity patterns in the osteoarthritic microenvironment.