Decreased Peli1 expression attenuates osteoarthritis by protecting chondrocytes and inhibiting M1-polarization of macrophages

Peli1, regulated by m6A modification, suppresses NLRP3 inflammasome activation in atherosclerosis by inhibiting YB-1

The activation of pyrin domain-containing-3 (NLRP3) inflammasome in macrophages is a risk factor accelerating the progression of atherosclerosis (AS). Here, the function of pellino 1 (Peli1) in regulating the activation of NLRP3 inflammasome during the development of AS was investigated. Our results showed that Y-box binding protein 1 (YB-1) knockdown could inhibit the progression of AS in vivo, and YB-1 silencing repressed oxidized low-density lipoprotein (ox-LDL)-mediated lipid accumulation and inflammation in macrophages by inactivating NLRP3 inflammasome. E3 ubiquitination ligase Peli1 mediated ubiquitination-dependent degradation of YB-1 during AS progression. Moreover, it was found that YTH domain-containing 2 (YTHDC2) recognized methyltransferase-like 3 (METTL3)-mediated Peli1 N6-methyladenosine (m6A) modification and mediated Peli1 mRNA degradation. Rescue studies revealed that YB-1 upregulation abrogated the repressive effect of Peli1 upregulation on AS progression both in vitro and in vivo. Taken together, Peli1, regulated by m6A modification, inhibited YB-1-mediated activation of NLRP3 inflammasome in macrophages by promoting YB-1 ubiquitination to suppress the progression of AS.

Mechanical compression induces chondrocyte hypertrophy by regulating Runx2 O-GlcNAcylation during temporomandibular joint condyle degeneration

Aims

Excessive chondrocyte hypertrophy is a common feature in cartilage degeneration which is susceptible to joint overloading, but the relationship between mechanical overloading and chondrocyte hypertrophy still remains elusive. The aim of our study was to explore the mechanism of mechanical compression-induced chondrocyte hypertrophy.

Methods

In this study, the temporomandibular joint (TMJ) degeneration model was built through forced mandibular retrusion (FMR)-induced compression in TMJ. Chondrocytes were also mechanically compressed in vitro. The role of O-GlcNAcylation in mechanical compression-induced chondrocyte hypertrophy manifested through specific activator Thiamet G and inhibitor OSMI-1.

Results

Both in vivo and in vitro data revealed that chondrocyte hypertrophic differentiation is promoted by compression. Immunofluorescent and immunoblotting results showed that protein pan-O-GlcNAcylation levels were elevated in these hypertrophic chondrocytes. Pharmacologically inhibiting protein pan-O-GlcNAcylation by OSMI-1 partially mitigated the compression-induced hypertrophic differentiation of chondrocytes. Specifically, runt-related transcription factor 2 (Runx2) and SRY-Box 9 transcription factor (Sox9) were subjected to modification of O-GlcNAcylation under mechanical compression, and pharmacological activation or inhibition of O-GlcNAcylation affected the transcriptional activity of Runx2 but not Sox9. Furthermore, compression-induced protein pan-O-GlcNAcylation in chondrocytes was induced by enhanced expression of glucose transporter 1 (GLUT1), and depletion of GLUT1 by WZB117 dampened the effect of compression on chondrocyte hypertrophy.

Conclusion

Our study proposes a novel function of GLUT1-mediated protein O-GlcNAcylation in driving compression-induced hypertrophic differentiation of chondrocytes by O-GlcNAc modification of Runx2, which promoted its transcriptional activity and strengthened the expressions of downstream hypertrophic marker.

eIF5A downregulated by mechanical overloading delays chondrocyte senescence and osteoarthritis by regulating the CREBBP-mediated Notch pathway

Aims

To examine how eukaryotic translation initiation factor 5A (eIF5A) regulates osteoarthritis (OA) during mechanical overload and the specific mechanism.

Methods

Histological experiments used human bone samples and C57BL/6J mice knee samples. All cell experiments were performed using mice primary chondrocytes. Messenger RNA (mRNA) sequencing was performed on chondrocytes treated with 20% cyclic tensile strain for 24 hours. Western blot (WB) and quantitative polymerase chain reaction were employed to detect relevant indicators of cartilage function in chondrocytes. We created the destabilization of the medial meniscus (DMM) model and the mechanical overload-induced OA model and injected with overexpressing eIF5A adenovirus (eIF5A-ADV). Cartilage degeneration was evaluated using Safranin O/Fast Green staining. Relative protein levels were ascertained by immunohistochemistry (IHC) and immunofluorescence (IF) staining.

Results

After OA initiation, eIF5A caused an upregulation of type II collagen (COL2) and a downregulation of matrix metalloproteinase 13 (MMP13), P16, and P21, which postponed the aggravation of OA. Further sequencing and experimental findings revealed that eIF5A knockdown accelerated the progression of OA by boosting the expression of histone acetyltransferase cyclic-adenosine monophosphate response element binding protein (CREB)-binding protein (CREBBP) to mediate activation of the Notch pathway.

Conclusion

Our findings identified a crucial functional mechanism for the onset of OA, and suggest that intra-articular eIF5A injections might be a useful therapeutic strategy for OA treatment.

Knockdown of PELI1 promotes Th2 and Treg cell differentiation in juvenile idiopathic arthritis

Pellino1 (PELI1) is a key regulator of inflammatory and autoimmune diseases. The role of PELI1 in juvenile idiopathic arthritis (JIA) is unclear. The correlation between serum PELI1 mRNA levels and clinical indicators of JIA patients was evaluated by Pearson correlation analysis. The percentage of Th1, Th2, Th17 and Treg cells was analyzed by flow cytometry. ELISA kits were used to detect cytokine levels in serum and cell supernatants. Co-immunoprecipitation experiments were performed to validate PELI1 and TCF-1 interactions. The protein and ubiquitination levels of TCF-1 were detected by western blot. The results showed that JIA patients have high serum PELI1 levels. PELI1 levels were positively correlated with erythrocyte sedimentation rate, C-reactive protein levels and JADAS27 scores in JIA patients. Interfering with PELI1 promoted naïve CD4+ T cell differentiation to Th2 and Treg cells and increased IL-4 and IL-10 levels, while inhibiting their differentiation to Th1 and Th17 cells and decreasing IFN-γ and IL-17 levels. PELI1 increased TCF-1 ubiquitination levels and accelerated its degradation. Inhibition of TCF-1 reduced the effects of interfering with PELI1 on cell differentiation and cytokine levels. In conclusion, Silencing of PELI1 facilitated the naïve CD4+ T cell differentiation into Th2 and Treg cells by TCF-1.

Emerging Roles of Macrophage Polarization in Osteoarthritis: Mechanisms and Therapeutic Strategies

Osteoarthritis (OA) is the most common chronic degenerative joint disease in middle-aged and elderly people, characterized by joint pain and dysfunction. Macrophages are key players in OA pathology, and their activation state has been studied extensively. Various studies have suggested that macrophages might respond to stimuli in their microenvironment by changing their phenotypes to pro-inflammatory or anti-inflammatory phenotypes, which is called macrophage polarization. Macrophages accumulate and become polarized (M1 or M2) in many tissues, such as synovium, adipose tissue, bone marrow, and bone mesenchymal tissues in joints, while resident macrophages as well as other stromal cells, including fibroblasts, chondrocytes, and osteoblasts, form the joint and function as an integrated unit. In this study, we focus exclusively on synovial macrophages, adipose tissue macrophages, and osteoclasts, to investigate their roles in the development of OA. We review recent key findings related to macrophage polarization and OA, including pathogenesis, molecular pathways, and therapeutics. We summarize several signaling pathways in macrophage reprogramming related to OA, including NF-κB, MAPK, TGF-β, JAK/STAT, PI3K/Akt/mTOR, and NLRP3. Of note, despite the increasing availability of treatments for osteoarthritis, like intra-articular injections, surgery, and cellular therapy, the demand for more effective clinical therapies has remained steady. Therefore, we also describe the current prospective therapeutic methods that deem macrophage polarization to be a therapeutic target, including physical stimulus, chemical compounds, and biological molecules, to enhance cartilage repair and alleviate the progression of OA.

TonEBP: A Key Transcription Factor in Microglia Following Intracerebral Hemorrhage Induced-Neuroinflammation

Transcription factors within microglia contribute to the inflammatory response following intracerebral hemorrhage (ICH). Therefore, we employed bioinformatics screening to identify the potential transcription factor tonicity-responsive enhancer-binding protein (TonEBP) within microglia. Inflammatory stimuli can provoke an elevated expression of TonEBP in microglia. Nevertheless, the expression and function of microglial TonEBP in ICH-induced neuroinflammation remain ambiguous. In our recent research, we discovered that ICH instigated an increased TonEBP in microglia in both human and mouse peri-hematoma brain tissues. Furthermore, our results indicated that TonEBP knockdown mitigates lipopolysaccharide (LPS)-induced inflammation and the activation of NF-κB signaling in microglia. In order to more deeply comprehend the underlying molecular mechanisms of how TonEBP modulates the inflammatory response, we sequenced the transcriptomes of TonEBP-deficient cells and sought potential downstream target genes of TonEBP, such as Pellino-1 (PELI1). PELI has been previously reported to mediate nuclear factor-κB (NF-κB) signaling. Through the utilization of CUT & RUN, a dual-luciferase reporter, and qPCR, we confirmed that TonEBP is the transcription factor of Peli1, binding to the Peli1 promoter. In summary, TonEBP may enhance the LPS-induced inflammation and activation of NF-κB signaling via PELI1.

Biology of Pellino1: a potential therapeutic target for inflammation in diseases and cancers

Pellino1 (Peli1) is a highly conserved E3 Ub ligase that exerts its biological functions by mediating target protein ubiquitination. Extensive evidence has demonstrated the crucial role of Peli1 in regulating inflammation by modulating various receptor signaling pathways, including interleukin-1 receptors, Toll-like receptors, nuclear factor-κB, mitogen-activated protein kinase, and phosphoinositide 3-kinase/AKT pathways. Peli1 has been implicated in the development of several diseases by influencing inflammation, apoptosis, necrosis, pyroptosis, autophagy, DNA damage repair, and glycolysis. Peli1 is a risk factor for most cancers, including breast cancer, lung cancer, and lymphoma. Conversely, Peli1 protects against herpes simplex virus infection, systemic lupus erythematosus, esophageal cancer, and toxic epidermolysis bullosa. Therefore, Peli1 is a potential therapeutic target that warrants further investigation. This comprehensive review summarizes the target proteins of Peli1, delineates their involvement in major signaling pathways and biological processes, explores their role in diseases, and discusses the potential clinical applications of Peli1-targeted therapy, highlighting the therapeutic prospects of Peli1 in various diseases.

The role of EDIL3 in maintaining cartilage extracellular matrix and inhibiting osteoarthritis development

Aims

Therapeutic agents that prevent chondrocyte loss, extracellular matrix (ECM) degradation, and osteoarthritis (OA) progression are required. The expression level of epidermal growth factor (EGF)-like repeats and discoidin I-like domains-containing protein 3 (EDIL3) in damaged human cartilage is significantly higher than in undamaged cartilage. However, the effect of EDIL3 on cartilage is still unknown.

Methods

We used human cartilage plugs (ex vivo) and mice with spontaneous OA (in vivo) to explore whether EDIL3 has a chondroprotective effect by altering OA-related indicators.

Results

EDIL3 protein prevented chondrocyte clustering and maintained chondrocyte number and SOX9 expression in the human cartilage plug. Administration of EDIL3 protein prevented OA progression in STR/ort mice by maintaining the number of chondrocytes in the hyaline cartilage and the number of matrix-producing chondrocytes (MPCs). It reduced the degradation of aggrecan, the expression of matrix metalloproteinase (MMP)-13, the Osteoarthritis Research Society International (OARSI) score, and bone remodelling. It increased the porosity of the subchondral bone plate. Administration of an EDIL3 antibody increased the number of matrix-non-producing chondrocytes (MNCs) in cartilage and exacerbated the serum concentrations of OA-related pro-inflammatory cytokines, including monocyte chemotactic protein-3 (MCP-3), RANTES, interleukin (IL)-17A, IL-22, and GROα. Administration of β1 and β3 integrin agonists (CD98 protein) increased the expression of SOX9 in OA mice. Hence, EDIL3 might activate β1 and β3 integrins for chondroprotection. EDIL3 may also protect cartilage by attenuating the expression of IL-1β-enhanced phosphokinase proteins in chondrocytes, especially glycogen synthase kinase 3 alpha/beta (GSK-3α/β) and phospholipase C gamma 1 (PLC-γ1).

Conclusion

EDIL3 has a role in maintaining the cartilage ECM and inhibiting the development of OA, making it a potential therapeutic drug for OA.

Classification of distinct osteoarthritis subtypes with different knee joint tissues by gene expression profiles

Aims

Knee osteoarthritis (OA) involves a variety of tissues in the joint. Gene expression profiles in different tissues are of great importance in order to understand OA.

Methods

First, we obtained gene expression profiles of cartilage, synovium, subchondral bone, and meniscus from the Gene Expression Omnibus (GEO). Several datasets were standardized by merging and removing batch effects. Then, we used unsupervised clustering to divide OA into three subtypes. The gene ontology and pathway enrichment of three subtypes were analyzed. CIBERSORT was used to evaluate the infiltration of immune cells in different subtypes. Finally, OA-related genes were obtained from the Molecular Signatures Database for validation, and diagnostic markers were screened according to clinical characteristics. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) was used to verify the effectiveness of markers.

Results

C1 subtype is mainly concentrated in the development of skeletal muscle organs, C2 lies in metabolic process and immune response, and C3 in pyroptosis and cell death process. Therefore, we divided OA into three subtypes: bone remodelling subtype (C1), immune metabolism subtype (C2), and cartilage degradation subtype (C3). The number of macrophage M0 and activated mast cells of C2 subtype was significantly higher than those of the other two subtypes. COL2A1 has significant differences in different subtypes. The expression of COL2A1 is related to age, and trafficking protein particle complex subunit 2 is related to the sex of OA patients.

Conclusion

This study linked different tissues with gene expression profiles, revealing different molecular subtypes of patients with knee OA. The relationship between clinical characteristics and OA-related genes was also studied, which provides a new concept for the diagnosis and treatment of OA.

Disease-modifying agents in osteoarthritis: where are we now and what does the future hold?

Cite this article: Bone Joint Res  2023;12(10):654–656.