LEF1 mediates osteoarthritis progression through circRNF121/miR-665/MYD88 axis via NF-кB signaling pathway

Kongensin A targeting PI3K attenuates inflammation-induced osteoarthritis by modulating macrophage polarization and alleviating inflammatory signaling

The inflammatory microenvironment, polarization of macrophages towards the M1 phenotype, and consequent matrix degradation and senescence of chondrocytes are primary contributors to the degeneration of knee joint cartilage, further exacerbating the progression of osteoarthritis (OA). Kongensin A (KA) is a recently identified natural plant extract exhibiting anti-necrotic apoptosis and anti-inflammatory properties, but the potential efficacy in alleviating OA remains uncertain. The current research lucubrated the effect of KA on the inflammatory microenvironment and macrophage polarization, as well as its regulatory function in extracellular matrix (ECM) metabolism and chondrocyte senescence. Our findings demonstrated that KA can suppress inflammatory signaling, maintain homeostasis between ECM anabolism and catabolism, and suppress chondrocytes senescence. Further investigation elucidated that the mechanism involves the suppression of the PI3K/AKT/NF-κB axis in chondrocytes under inflammatory conditions. Moreover, KA impeded M1 polarization of macrophages via inhibiting PI3K/AKT/NF-κB axis. Subsequently, we treated chondrocytes with macrophages-derived conditioned medium (CM) and revealed that KA can promote ECM anabolism and alleviate chondrocytes senescence by reprogramming macrophage polarization. Consistent with in vitro experiments, in vivo administration of KA demonstrated alleviated cartilage degeneration and delayed progression of OA. Collectively, through obstructing the PI3K/AKT/NF-κB axis, KA can reprogram macrophage polarization, promote matrix metabolism equilibrium, and alleviate chondrocytes senescence, thereby attenuating the pathology of OA. In conclusion, KA may emerge as a promising therapy for OA.

DNM3OS/miR-127-5p/CDH11, activates Wnt3a/β-catenin/LEF-1 pathway to form a positive feedback and aggravate spine facet joint osteoarthritis

Spinal facet joint osteoarthritis (FJOA) is an OA disease with pathogenesis and progression uncovered. Our present study was performed to elucidate the role of DNM3OS on spinal FJOA. In this study, spine facet joint tissue of patients were collected. In vitro and in vivo models were constructed with SW1353 cells and rats. Hematoxylin and eosin (HE) staining, Safranin O-fast Green, Alcian blue staining, and Tolueine blue O (TBO) staining were employed for histology analyses. Quantitative PCR, western blotting, and Immunofluorescence were performed to evaluate the expression of genes. The levels of inflammatory cytokines were measured by enzyme-linked immunosorbent assay analysis. Cell Counting Kit-8 and flow cytometry were used for cell activity and apoptosis evaluation. The targeting sites between microRNA (miR)-127-5p and cadherin 11 (CDH11) were predicted TargetScan and miRbase database and confirmed by Dual-luciferase reporter assays. CHIP and EMS assay were employed to confirm the binding of LEF1and DNM3OS promoter. Our results showed that DNM3OS was found to upregulated, while miR-127-5p was downregulated in severe FJOA patients and inflammation-induced chondrosarcoma SW1353 cells. DNM3OS reduced cell activity, induced cell apoptosis and extracellular matrix (ECM) degradation by sponging miR-127-5p in vitro. miR-127-5p targeted CDH11 and inhibited wnt3a/β-catenin pathway to regulate OA in vitro. LEF1 promoted DNM3OS transcription to form a positively feedback in activated wnt3a/β-catenin pathway. In vivo rat model also confirmed that DNM3OS aggravated FJOA. In summary, DNM3OS/miR-127-5p/CDH11 enhanced Wnt3a/β-Catenin/LEF-1 pathway to form a positive feedback and aggravate spinal FJOA.

SP2-induced circPUM1 modulates chemoresistance and nature killer cell toxicity in oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) is a type of tumour found in the cavity that is characterized by differentiation and metastasis to the lymph nodes. Although diagnosis strategy and clinical treatment have recently improved, the outcomes for OSCC patients remain unsatisfactory. This study verified the characteristics of circPUM1 in OSCC cells, subsequently generating dysregulated circPUM1 cell models, showing that circPUM1 promoted chemoresistance and natural killer (NK) cell toxicity. Furthermore, the transcription factor SP2 regulated the expression of circPUM1 in OSCC cells, circPUM1 acted as a molecular sponge for miR-770-5p. Moreover, Nucleosome Assembly Protein 1 Like 1 (NAP1L1) is a downstream target for miR-770-5p and essential for circPUM1-mediated cisplatin resistance and NK cell cytotoxicity in OSCC cells. The network composed of SP2, circPUM1, miR-770-5p and NAP1L1 in OSCC appears to be a promising avenue for the development of novel targets for diagnosing or treating OSCC.

MiR-203a-3p attenuates apoptosis and pyroptosis of chondrocytes by regulating the MYD88/NF-κB pathway to alleviate osteoarthritis progression

BACKGROUND

Osteoarthritis (OA) is a degenerative joint disease that imposes a significant socioeconomic burden worldwide. Our previous studies revealed a down-regulation of miR-203a-3p in the knee tissues of OA patients. However, the underlying mechanism through which miR-203a-3p mediates the pathological process of OA remains unknown. Thus, we aimed to determine the effects of miR-203a-3p in the progression of OA.

METHODS

Rat primary chondrocytes were stimulated with 10 μg/mL lipopolysaccharide (LPS) for 24 hours, followed by transfection with 50 nM miR-203a-3p mimic, inhibitor, and siRNA for MYD88 or consistent negative controls for 48 hours. To evaluate the effects of miR-203a-3p on cartilage matrix degradation, oxidative stress, apoptosis, and pyroptosis in chondrocytes, various techniques such as immunofluorescence staining, biochemical analysis, Western blotting, and the TUNEL staining were utilized. In the rat OA model, all rats were randomly divided into four groups: Sham, OA, OA+Agomir negative control (NC), and OA+Agomir. They received intra-articular injections of 25 nmol miR-203a-3p agomir, agomir NC, or normal saline twice a week for the duration of 8 weeks after OA induction. Immunofluorescence staining was performed to evaluate the effects of miR-203a-3p on cartilage matrix degradation in rats.

RESULTS

MiR-203a-3p was down-regulated in LPS-treated rat chondrocytes and OA cartilage, and directly targeted MYD88. Moreover, miR-203a-3p significantly inhibited LPS-induced cartilage matrix degradation, oxidative stress, apoptosis, and pyroptosis of chondrocytes via targeting MYD88. Mechanistically, miR-203a-3p exerted protective effects via the inhibition of the MYD88/NF-κB pathway. In the rat OA model, intra-articular injections of miR-203a-3p agomir also significantly inhibited cartilage matrix degradation, thereby alleviating OA progression. Furthermore, the miR-203a-3p agomir-treated arthritic rat dramatically exhibited better articular tissue morphology and lower OARSI scores.

CONCLUSIONS

MiR-203a-3p plays a role in alleviating the progression of OA by regulating the MYD88/NF-κB pathway, thereby inhibiting cartilage matrix degradation, oxidative stress, apoptosis, and pyroptosis of chondrocytes. It highlights the potential significance of miR-203a-3p as an important regulator of OA.

Role of non‑coding RNAs in cartilage endplate (Review)

Cartilage endplate (CEP) degeneration is considered one of the major causes of intervertebral disc degeneration (IDD), which causes non-specific neck and lower back pain. In addition, several non-coding RNAs (ncRNAs), including long ncRNAs, microRNAs and circular RNAs have been shown to be involved in the regulation of various diseases. However, the particular role of ncRNAs in CEP remains unclear. Identifying these ncRNAs and their interactions may prove to be is useful for the understanding of CEP health and disease. These RNA molecules regulate signaling pathways and biological processes that are critical for a healthy CEP. When dysregulated, they can contribute to the development disease. Herein, studies related to ncRNAs interactions and regulatory functions in CEP are reviewed. In addition, a summary of the current knowledge regarding the deregulation of ncRNAs in IDD in relation to their actions on CEP cell functions, including cell proliferation, apoptosis and extracellular matrix synthesis/degradation is presented. The present review provides novel insight into the pathogenesis of IDD and may shed light on future therapeutic approaches.

CircRNAs in osteoarthritis: research status and prospect

Osteoarthritis (OA) is the most common joint disease globally, and its progression is irreversible. The mechanism of osteoarthritis is not fully understood. Research on the molecular biological mechanism of OA is deepening, among which epigenetics, especially noncoding RNA, is an emerging hotspot. CircRNA is a unique circular noncoding RNA not degraded by RNase R, so it is a possible clinical target and biomarker. Many studies have found that circRNAs play an essential role in the progression of OA, including extracellular matrix metabolism, autophagy, apoptosis, the proliferation of chondrocytes, inflammation, oxidative stress, cartilage development, and chondrogenic differentiation. Differential expression of circRNAs was also observed in the synovium and subchondral bone in the OA joint. In terms of mechanism, existing studies have mainly found that circRNA adsorbs miRNA through the ceRNA mechanism, and a few studies have found that circRNA can serve as a scaffold for protein reactions. In terms of clinical transformation, circRNAs are considered promising biomarkers, but no large cohort has tested their diagnostic value. Meanwhile, some studies have used circRNAs loaded in extracellular vesicles for OA precision medicine. However, there are still many problems to be solved in the research, such as the role of circRNA in different OA stages or OA subtypes, the construction of animal models of circRNA knockout, and more research on the mechanism of circRNA. In general, circRNAs have a regulatory role in OA and have particular clinical potential, but further studies are needed in the future.

CircRNA-mediated ceRNA mechanism in Osteoarthritis: special emphasis on circRNAs in exosomes and the crosstalk of circRNAs and RNA methylation

Osteoarthritis (OA) is an age-related joint disease with chronic inflammation, progressive articular cartilage destruction and subchondral bone sclerosis. CircRNAs (circRNAs) are a class of non-coding RNA with a circular structure that participate in a series of important pathophysiological processes of OA, especially its ceRNA mechanisms, and play an important role in OA. CircRNAs may be potential biomarkers for the diagnosis and prognosis of OA. Additionally, differentially expressed circRNAs were found in patients with OA, indicating that circRNAs are involved in the pathogenesis of OA. Experiments have shown that the intra-articular injection of modified circRNAs can effectively relieve OA. Exosomal circRNAs and methylated circRNAs also provide new ideas for the treatment of OA. Clarifying the important roles of circRNAs in OA will deepen people's understanding of the pathogenesis of OA. CircRNAs may be developed as new biomarkers or drug targets for the diagnosis of OA and provide new methods for the treatment of OA.

Implications and theragnostic potentials of circular RNAs in rheumatic diseases

Circular RNAs (circRNAs), a class of non-coding RNAs (ncRNAs), are highly stable and ubiquitous molecules that exhibit tissue-specific expression. Accumulating evidence has shown that aberrant expression of circRNAs can play a role in the pathogenesis of several diseases. Rheumatic diseases are a varied group of autoimmune and inflammatory disorders affecting mainly the musculoskeletal system. Notably, circRNAs, which are essential immune system gene modulators, are strongly linked to the occurrence and progression of autoimmune disorders. Here, we present and discuss the current findings concerning the roles, implications and theragnostic potentials of circRNAs in common rheumatic diseases, including ankylosing spondylitis (AS), osteoarthritis (OA), osteoporosis (OP), rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), Crohn's disease (CD), and gout. This review aims to provide new insights to support the development of novel diagnostic and therapeutic strategies for these disabling diseases.

Regulatory mechanism of circular RNA involvement in osteoarthritis

Osteoarthritis (OA) causes joint pain, stiffness, and dysfunction in middle-aged and older adults; however, its pathogenesis remains unclear. Circular RNAs (circRNAs) are differentially expressed in patients with OA and participate in a multigene, multitarget regulatory network. CircRNAs are involved in the development of OA through inflammatory responses, including proliferation, apoptosis, autophagy, differentiation, oxidative stress, and mechanical stress. Most circRNAs are used as intracellular miRNA sponges in chondrocytes, endplate chondrocytes, mesenchymal stem cells, synoviocytes, and macrophages to promote the progression of OA. However, a small portion of circRNAs participates in the pathogenesis of OA by intracellular mechanisms, such as protein binding, methylation, or intercellular exosome pathways. In this sense, circRNAs might serve as potential novel biomarkers and therapeutic targets for OA.

Circular RNAs: typical biomarkers for bone-related diseases

Bone is a connective tissue that has important functions in the human body. Cells and the extracellular matrix (ECM) are key components of bone and are closely related to bone-related diseases. However, the outcomes of conventional treatments for bone-related diseases are not promising, and hence it is necessary to elucidate the exact regulatory mechanisms of bone-related diseases and identify novel biomarkers for diagnosis and therapy. Circular RNAs (circRNAs) are single-stranded RNAs that form closed circular structures without a 5' cap or 3' tail and polycyclic adenylate tails. Due to their high stability, circRNAs have the potential to be typical biomarkers. Accumulating evidence suggests that circRNAs are involved in bone-related diseases, including osteoarthritis, osteoporosis, osteosarcoma, multiple myeloma, intervertebral disc degeneration, and rheumatoid arthritis. Herein, we summarize the recent research progress on the characteristics and functions of circRNAs, and highlight the regulatory mechanism of circRNAs in bone-related diseases.

The emerging power and promise of non-coding RNAs in chronic pain

Chronic pain (CP) is an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage lasting longer than 3 months. CP is the main reason why people seek medical care and exerts an enormous economic burden. Genome-wide expression analysis has revealed that diverse essential genetic elements are altered in CP patients. Although many possible mechanisms of CP have been revealed, we are still unable to meet all the analgesic needs of patients. In recent years, non-coding RNAs (ncRNAs) have been shown to play essential roles in peripheral neuropathy and axon regeneration, which is associated with CP occurrence and development. Multiple key ncRNAs have been identified in animal models of CP, such as microRNA-30c-5p, ciRS-7, and lncRNA MRAK009713. This review highlights different kinds of ncRNAs in the regulation of CP, which provides a more comprehensive understanding of the pathogenesis of the disease. It mainly focuses on the contributions of miRNAs, circRNAs, and lncRNAs to CP, specifically peripheral neuropathic pain (NP), diabetic NP, central NP associated with spinal cord injury, complex regional pain syndrome, inflammatory pain, and cancer-induced pain. In addition, we summarize some potential ncRNAs as novel biomarkers for CP and its complications. With an in-depth understanding of the mechanism of CP, ncRNAs may provide novel insight into CP and could become new therapeutic targets in the future.

circFOXO3 Induced by KLF16 Modulates Clear Cell Renal Cell Carcinoma Growth and Natural Killer Cell Cytotoxic Activity through Sponging miR-29a-3p and miR-122-5p

Renal cell carcinoma (RCC) is one of the most common urological malignancies with high incidence and metastatic relapse. Clear cell RCC (ccRCC) comprises nearly 70% of all RCC cases and is responsible for the majority of morbidity and mortality of RCC. Due to the poor diagnosis strategy and unsatisfactory clinical intervention, ccRCC causes a huge economic burden and poor patient quality of life; therefore, novel diagnostic or therapeutic targets for ccRCC are urgently needed. This study investigated the biological role of circFOXO3 in ccRCC development, showing that circFOXO3 is highly expressed in RCC cells and tissues and inhibits the viability of ccRCC cells. circFOXO3 dysregulation regulates NK cell cytotoxicity towards RCC cells by directly sponging miR-29a-3p and miR-122-5p. Overexpression of miR-29a-3p or miR-122-5p attenuated NK cell toxicity towards RCC cells and the transcriptional factor Kruppel-Like Factor 16 (KLF16) regulates circFOXO3 expression in RCC cells. In conclusion, this study has partially elucidated the function of circFOXO3 in ccRCC development, providing potential novel therapeutic targets for ccRCC.

Knockdown of Circ_0037658 Alleviates IL-1β-Induced Osteoarthritis Progression by Serving as a Sponge of miR-665 to Regulate ADAMTS5

Background: Osteoarthritis (OA) is a chronic musculoskeletal degeneration disease which brings great pain to patients and a tremendous burden on the world’s medical resources. Previous reports have indicated that circular RNAs (circRNAs) are involved in the pathogenesis of OA. The purpose of this study was to explore the role and mechanism of circ_0037658 in the OA cell model.

Methods: The content of interleukin-6 (IL-6) and tumor necrosis factor α (TNF-α) was measured using enzyme-linked immunosorbent assay (ELISA). Cell proliferation ability and apoptosis were detected using Cell Counting Kit-8 (CCK-8), 5-ethynyl-2′-deoxyuridine (EDU), and flow cytometry assays. Western blot assay was used to measure the protein levels of Bcl-2-related X protein (Bax), cleaved-caspase-3, MMP13, Aggrecan, and ADAMTS5. The expression of circ_0037658, microRNA-665 (miR-665), and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) 5 was detected using real-time quantitative polymerase chain reaction (RT-qPCR). Dual-luciferase reporter assay and RNA Immunoprecipitation (RIP) assay were manipulated to analyze the relationships of circ_0037658, miR-665, and ADAMTS5.

Results: Human chondrocytes (CHON-001 cells) were treated with interleukin-1β (IL-1β) to establish an OA cell model. Circ_0037658 and ADAMTS5 levels were increased, and miR-665 was decreased in OA cartilage samples and IL-1β-treated chondrocyte cells. Moreover, circ_0037658 silencing promoted proliferation and impaired inflammation, apoptosis, and ECM degradation in IL-1β-treated CHON-001 cells. Mechanically, circ_0037658 acted as a sponge for miR-665 to regulate ADAMTS5 expression.

Conclusion: Circ_0037658 knockdown relieved IL-1β-triggered chondrocyte injury via regulating the miR-665/ADAMTS5 axis, promising an underlying therapeutic strategy for OA.

Reversal of Epigenetic Peroxisome Proliferator-Activated Receptor-γ Suppression by Diacerein Alleviates Oxidative Stress and Osteoarthritis in Mice

Aims: The pathogenesis of osteoarthritis (OA) is characterized by oxidative stress (OS) and sustained inflammation that are substantially associated with epigenetic DNA methylation alterations of osteogenic gene expression. Diacerein as an anthraquinone anti-OA drug exhibits multiple chondroprotective properties, but less clarified pharmacological actions. Since anthraquinone contain an epigenetic modulating property, in this study we investigate whether the anti-OA functions of diacerein involve DNA methylation modulation and antioxidant signaling. Results: The OA mice incurred by destabilization of medial meniscus exhibited marked suppression of peroxisome proliferator-activated receptor-gamma (PPARγ), a chondroprotective transcription factor with anti-inflammation and OS-balancing properties, aberrant upregulations of DNA methyltransferase (DNMT)1/3a, and PPARγ promoter hypermethylation in knee joint cartilage. Diacerein treatment mitigated the cartilage damage and significantly inhibited the DNMT1/3a upregulation, the PPARγ promoter hypermethylation, and the PPARγ loss, and it effectively corrected the adverse expression of antioxidant enzymes and inflammatory cytokines. In cultured chondrocytes, diacerein reduced the interleukin-1β-induced PPARγ suppression and the abnormal expression of its downstream antioxidant enzymes in a gain of DNMT and PPARγ inhibition-sensitive manner, and in PPARγ knockout mice, the anti-OA effects of diacerein were significantly reduced. Innovation: Our work reveals a novel anti-OA pharmacological property of diacerein and identifies the aberrant DNMT elevation and the resultant PPARγ suppression as an important epigenetic pathway that mediates diacerein's anti-OA activities. Conclusion: DNA methylation aberration and the resultant PPARγ suppression contribute significantly to epigenetic OA pathogenesis, and targeting PPARγ suppression via DNA demethylation is an important component of diacerein's anti-OA functions. Antioxid. Redox Signal. 37, 40-53.

Expression and Biological Functions of miRNAs in Chronic Pain: A Review on Human Studies

Chronic pain is a major public health problem and an economic burden worldwide. However, its underlying pathological mechanisms remain unclear. MicroRNAs (miRNAs) are a class of small noncoding RNAs that post-transcriptionally regulate gene expression and serve key roles in physiological and pathological processes. This review aims to synthesize the human studies examining miRNA expression in the pathogenesis of chronic primary pain and chronic secondary pain. Additionally, to understand the potential pathophysiological impact of miRNAs in these conditions, an in silico analysis was performed to reveal the target genes and pathways involved in primary and secondary pain and their differential regulation in the different types of chronic pain. The findings, methodological issues and challenges of miRNA research in the pathophysiology of chronic pain are discussed. The available evidence suggests the potential role of miRNA in disease pathogenesis and possibly the pain process, eventually enabling this role to be exploited for pain monitoring and management.

Lef1 ablation alleviates cartilage mineralization following posttraumatic osteoarthritis induction

Cartilage mineralization is imperative in various processes such as skeletal growth and fracture repair. However, this process may also be pathological, as in the case of the degenerative joint disease, osteoarthritis (OA). Using a posttraumatic OA model (PTOA), we find that cartilage-specific Sirt1 genetic nulls caused severe synovitis and mineralization of the lateral joint compartment, due to augmented Lef1 gene expression. Conversely, cartilage-specific Lef1 nulls exhibited impaired synovitis and mineralization of the lateral joint, accompanied by a reduction of local pain. Consistently, transcriptomic profiles of Lef1-ablated chondrocytes exhibited enhanced anabolism, yet impaired pathways related to calcification and inflammation. Accordingly, cartilage mineralization of the lateral joint compartment relies on amplified inflammatory pathways, contributing to articular damage following PTOA.

Cartilage mineralization is a tightly controlled process, imperative for skeletal growth and fracture repair. However, in osteoarthritis (OA), cartilage mineralization may impact the joint range of motion, inflict pain, and increase chances for joint effusion. Here we attempt to understand the link between inflammation and cartilage mineralization by targeting Sirtuin 1 (SIRT1) and lymphoid enhancer binding factor 1 (LEF1), both reported to have contrasting effects on cartilage. We find that inflammatory-dependent cleavage of SIRT1 or its cartilage-specific genetic ablation, directly enhanced LEF1 expression accompanied by a catabolic response. Applying a posttraumatic OA (PTOA) model to cartilage-specific Sirt1 nulls displayed severe OA, which was accompanied by synovitis, meniscal mineralization, and osteophyte formation of the lateral joint compartment. Alternatively, cartilage-specific Lef1 nulls presented reduced lateral mineralization, OA severity, and local pain. Differential gene expression analysis revealed that Lef1 ablation reduced nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and Toll-like receptor (Tlr) pathways, while enhancing SRY-Box transcription factor 9 (Sox9) and cartilaginous extracellular matrix genes. The results support a link between inflammation and Lef1-dependent cartilage mineralization, mediated by the inactivation of Sirt1. By ablating Lef1 in a PTOA model, the structural and pain-related phenotypes of OA were reduced, in part, by preventing cartilage mineralization of the lateral joint compartment, partially manifested by meniscal tissue mineralization. Overall, these data provide a molecular axis to link between inflammation and cartilage in a PTOA model.

Rhoifolin ameliorates osteoarthritis via the Nrf2/NF-κB axis: in vitro and in vivo experiments

OBJECTIVE

Osteoarthritis (OA) is an age-related degenerative disease accompanied by an increasing number of senescent cells and chronic low-grade inflammation. Rhoifolin (ROF) showed considerable inhibition to inflammation, but its role in chondrocyte senescence and OA progress has not been fully characterized. We aimed to evaluate the protective effects of ROF on OA through a series of in vitro and in vivo experiments.

METHODS

The role of ROF in the expression of senescence-associated secretory phenotype (SASP) factors was investigated using RT-qPCR, western blotting, and ELISA. Chondrocyte senescence was assessed by SA-β-gal staining. We applied molecular docking to screen candidate proteins regulated by ROF. Meanwhile, SASP factors and cellular senescence were further assessed after the transfection of Nrf2 siRNA. In the anterior cruciate ligament transection (ACLT) rat model, X-ray, hematoxylin-eosin (HE), and Masson's staining were performed to evaluate the therapeutic effects of ROF on OA.

RESULTS

We found that ROF inhibited SASP factors expression and senescence phenotype in IL-1β-treated chondrocytes. Furthermore, ROF suppressed IL-1β-induced activation of the NF-κB pathway cascades. Also, molecular docking and knock-down studies demonstrated that ROF might bind to Nrf2 to suppress the NF-κB pathway. In vivo, ROF ameliorated the OA process in the ACLT rat model.

CONCLUSIONS

ROF inhibits SASP factors expression and senescence phenotype in chondrocytes and ameliorates the progression of OA via the Nrf2/NF-κB axis, which supports ROF as a potential therapeutic agent for the treatment of OA.

Epigenetic Regulation of Chondrocytes and Subchondral Bone in Osteoarthritis

The aim of this review is to provide an updated review of the epigenetic factors involved in the onset and development of osteoarthritis (OA). OA is a prevalent degenerative joint disease characterized by chronic inflammation, ectopic bone formation within the joint, and physical and proteolytic cartilage degradation which result in chronic pain and loss of mobility. At present, no disease-modifying therapeutics exist for the prevention or treatment of the disease. Research has identified several OA risk factors including mechanical stressors, physical activity, obesity, traumatic joint injury, genetic predisposition, and age. Recently, there has been increased interest in identifying epigenetic factors involved in the pathogenesis of OA. In this review, we detail several of these epigenetic modifications with known functions in the onset and progression of the disease. We also review current therapeutics targeting aberrant epigenetic regulation as potential options for preventive or therapeutic treatment.

Engineering Closed-Loop, Autoregulatory Gene Circuits for Osteoarthritis Cell-Based Therapies

PURPOSE OF REVIEW

Genetic engineering offers the possibility to simultaneously target multiple cellular pathways in the joints affected by osteoarthritis (OA). The purpose of this review is to summarize the ongoing efforts to develop disease-modifying osteoarthritis drugs (DMOADs) using genetic engineering, including targeting approaches, genome editing techniques, and delivery methods.

RECENT FINDINGS

Several gene circuits have been developed that reprogram cells to autonomously target inflammation, and their efficacy has been demonstrated in chondrocytes and stem cells. Gene circuits developed for metabolic disorders, such as those targeting insulin resistance and obesity, also have the potential to mitigate the impact of these conditions on OA onset and/or progression. Despite the strides made in characterizing the inflammatory environment of the OA joint, our incomplete understanding of how the multiple regulators interact to control signal transduction, gene transcription, and translation to protein limits the development of targeted disease-modifying therapeutics. Continuous advances in targeted genome editing, combined with online toolkits that simplify the design and production of gene circuits, have the potential to accelerate the discovery and clinical application of multi-target gene circuits with disease-modifying properties for the treatment of OA.

circPhc3 sponging microRNA‑93‑3p is involved in the regulation of chondrocyte function by mechanical instability in osteoarthritis

Cartilage extracellular matrix (ECM) metabolism disorder caused by mechanical instability is a leading cause of osteoarthritis (OA), but the exact mechanisms have not been fully elucidated. Recent studies have suggested an important role of circular RNAs (circRNAs/circs) in OA. The present study aimed to investigate whether circRNAs might have a role in mechanical instability‑regulated chondrocyte matrix metabolism in OA. The expression levels of circPhc3 in human and mouse OA cartilage samples were measured using reverse transcription‑quantitative PCR and fluorescence in situ hybridization. The effects of circPhc3 on chondrocyte ECM metabolism were further investigated by overexpressing and knocking down circPhc3 in OA chondrocytes. The downstream target of circPhc3 was examined by performing a luciferase reporter assay. The results showed that the expression of circPhc3 was reduced in human and mouse OA cartilage. Moreover, circPhc3 was involved in mechanical loading‑regulated production of ECM and cartilage‑degrading enzymes. Further studies showed that circPhc3 regulated chondrocyte matrix metabolism primarily by binding to microRNA (miR)‑93‑3p, and mechanistic studies found that miR‑93‑3p targeting of FoxO1 was involved in chondrocyte matrix metabolism. Taken together, these results indicated that circPhc3 may serve an important role in the progression of OA and may be a good target for the treatment of OA.

The circRAB3IP Mediated by eIF4A3 and LEF1 Contributes to Enzalutamide Resistance in Prostate Cancer by Targeting miR-133a-3p/miR-133b/SGK1 Pathway

An increasing number of studies have shown that circRNAs are closely related to the carcinogenesis and development of prostate cancer (PCa). However, little is known about the effect of the biological functions of circRNAs on the enzalutamide resistance of PCa. Through bioinformatic analysis and experiments, we investigated the expression pattern of circRNAs in enzalutamide-resistant PCa cells. Quantitative real-time PCR was used to detect the expression of circRAB3IP, and plasmids that knock down or overexpress circRAB3IP were used to evaluate its effect on the enzalutamide sensitivity of PCa cells. Mechanistically, we explored the potential regulatory effects of eIF4A3 and LEF1 on the biogenesis of circRAB3IP. Our in vivo and in vitro data indicated that increased expression of circRAB3IP was found in enzalutamide-resistant PCa, and knockdown of circRAB3IP significantly enhanced enzalutamide sensitivity in PCa cells. However, upregulation of circRAB3IP resulted in the opposite effects. Further mechanistic research demonstrated that circRAB3IP could regulate the expression of serum and glucocorticoid-regulated kinase 1 (SGK1) by serving as a sponge that directly targets miR-133a-3p/miR-133b. Then, we showed that circRAB3IP partially exerted its biological functions via SGK1 signaling. Furthermore, we discovered that eIF4A3 and LEF1 might increase circRAB3IP expression in PCa.

Circular RNA circ_0023404 serves as a miR-636 sponge to promote malignant behaviors in cervical cancer cells through upregulation of CYP2S1

Cervical cancer is the most common malignant gynecological tumor. Circular RNA (circRNA) circ_0023404 is reported to be upregulated in cervical cancer cells. This aim is to explore the role and mechanism of circ_0023404 in cervical cancer. circ_0023404, microRNA-636 (miR-636), and cytochrome P450 2S1 (CYP2S1) levels were detected by real-time quantitative polymerase chain reaction (RT-qPCR). Cell proliferation, migration, invasion, and apoptosis were detected by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) assay, 5-ethynyl-2'-deoxyuridine (EDU) assay, colony formation assay, transwell assay, and cytometry assay. Protein levels of cyclin D1, matrix metallopeptidase 9 (MMP9), Bcl-2-associated X protein (Bax), and CYP2S1 were examined by western blot assay. The binding relationship between miR-636 and circ_0023404 or CYP2S1 was predicted by Circinteractome or targetscan, and then verified by a dual-luciferase reporter assay and RNA pull-down assay. circ_0023404 and CYP2S1 expression were increased, and miR-636 was decreased in cervical cancer tissues and cells. Moreover, circ_0023404 knockdown could repress proliferation, migration, invasion, and promote apoptosis of cervical cancer cells in vitro. Mechanically, circ_0023404 could regulate CYP2S1 expression by sponging miR-636. circ_0023404 silencing could attenuate the progression of cervical cancer cells partly by targeting the miR-636/CYP2S1 axis, hinting at a promising therapeutic target for cervical cancer.

Circ_SPG11 plays contributing effects on IL-1β-induced chondrocyte apoptosis and ECM degradation via miR-665 inhibition-mediated GREM1 upregulation

The dysregulation of circular RNA (circRNA) has been monitored in osteoarthritis (OA) cartilage, hinting that circRNA deregulation modulates OA progression. We thus aimed to unveil the role of circRNA spastic paraplegia 11 (circ_SPG11) in OA conditions. The upregulation of circ_SPG11 was observed in OA cartilage and IL-1β-treated chondrocytes. Knockdown of circ_SPG11 restored IL-1β-depleted cell proliferation and alleviated IL-1β-induced cell apoptosis and ECM degradation. Circ_SPG11 bound to miR-665 and negatively regulated miR-665 expression. Inhibition of miR-665 reversed the inhibitory effect on IL-1β-induced chondrocyte injury caused by circ_SPG11 knockdown. GREM1 was a target of miR-665, and circ_SPG11 knockdown depleted GREM1 expression by enriching miR-665. Overexpression of GREM1 also reversed the inhibitory effect on IL-1β-induced chondrocyte injury caused by miR-665 enrichment. Circ_SPG11 might promote IL-1β-induced chondrocyte apoptosis and ECM degradation via increasing GREM1 expression by decoying miR-665.

The non-coding RNA interactome in joint health and disease

Non-coding RNAs have distinct regulatory roles in the pathogenesis of joint diseases including osteoarthritis (OA) and rheumatoid arthritis (RA). As the amount of high-throughput profiling studies and mechanistic investigations of microRNAs, long non-coding RNAs and circular RNAs in joint tissues and biofluids has increased, data have emerged that suggest complex interactions among non-coding RNAs that are often overlooked as critical regulators of gene expression. Identifying these non-coding RNAs and their interactions is useful for understanding both joint health and disease. Non-coding RNAs regulate signalling pathways and biological processes that are important for normal joint development but, when dysregulated, can contribute to disease. The specific expression profiles of non-coding RNAs in various disease states support their roles as promising candidate biomarkers, mediators of pathogenic mechanisms and potential therapeutic targets. This Review synthesizes literature published in the past 2 years on the role of non-coding RNAs in OA and RA with a focus on inflammation, cell death, cell proliferation and extracellular matrix dysregulation. Research to date makes it apparent that 'non-coding' does not mean 'non-essential' and that non-coding RNAs are important parts of a complex interactome that underlies OA and RA.

Mesenchymal Stem Cell-Derived Exosomes and MicroRNAs in Cartilage Regeneration: Biogenesis, Efficacy, miRNA Enrichment and Delivery

Exosomes are the small extracellular vesicles secreted by cells for intercellular communication. Exosomes are rich in therapeutic cargos such as microRNA (miRNA), long non-coding RNA (lncRNA), small interfering RNA (siRNA), DNA, protein, and lipids. Recently, many studies have focused on miRNAs as a promising therapeutic factor to support cartilage regeneration. Exosomes are known to contain a substantial amount of a variety of miRNAs. miRNAs regulate the post-transcriptional gene expression by base-pairing with the target messenger RNA (mRNA), leading to gene silencing. Several exosomal miRNAs have been found to play a role in cartilage regeneration by promoting chondrocyte proliferation and matrix secretion, reducing scar tissue formation, and subsiding inflammation. The exosomal miRNA cargo can be modulated using techniques such as cell transfection and priming as well as post-secretion modifications to upregulate specific miRNAs to enhance the therapeutic effect. Exosomes are delivered to the joints through direct injection or via encapsulation within a scaffold for sustained release. To date, exosome therapy for cartilage injuries has yet to be optimized as the ideal cell source for exosomes, and the dose and method of delivery have yet to be identified. More importantly, a deeper understanding of the role of exosomal miRNAs in cartilage repair is paramount for the development of more effective exosome therapy.

Studies on the Role of circRNAs in Osteoarthritis

Objective

Provide a reference to elucidate the mechanism of circRNAs regulating osteoarthritis (OA) and the clinical treatment.

Methods

Herein, articles about circRNAs (hsa-circ) and osteoarthritis in the recent 5 years have been reviewed and the differential expression and regulatory effect of circRNAs in OA deduced. Based on these conclusions and Protein-Protein Interaction (PPI), Gene Ontology (GO), and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses of the acquired circRNAs, the potential functions and interactions of circRNAs in OA and the involved signaling pathways are discussed.

Results

A total of 33 studies meeting the inclusion criteria were included in this study, and 27 circRNAs were upregulated and 8 circRNAs were downregulated in OA. A total of 31 circRNAs were finally included in the PPI, GO, and KEGG analyses. From PPI, 12 map nodes and 7 map edges were interrelated. VWF had the biggest node and edge size. From GO, VWF showed a majority of the functions. From KEGG, circRNAs are enriched in PI3K/AKT, human papillomavirus infection (HPI), and focal adhesion (FA) pathways, and VWF was involved in major pathways.

Conclusion

We found that most articles about circRNAs regulating OA in the recent 5 years focused on the mechanism, especially the absorption effect of circ-miRNA as sponges in the recent 2 years, while most of the articles about their functions addressed ECM and PI3K, AKT, and mTOR signaling pathways. Future studies might focus on the functions of circRNAs, and circRNA VWF, with preferable functions, interactions, and involvement, can be used as a biological indicator to detect OA in clinical practice.

Circular RNA hsa_circ_0032463 Acts as the Tumor Promoter in Osteosarcoma by Regulating the MicroRNA 498/LEF1 Axis

Several studies have examined the relationship between osteosarcoma (OS) and microRNAs (miRNAs). However, only a few researchers have investigated the underlying mechanism of circular RNAs (circRNAs) in OS development. Our paper aimed to assess how hsa_circ_0032463 (abbreviated “circ_0032463” here) initiates and regulates OS progression. We detected circ_0032463 expression in OS tissues and cell lines by using reverse transcription-quantitative PCR (RT-qPCR) analysis and then investigated the interaction between circ_0032463, miRNA 489 (miR-498), and LEF1 using RNA pulldown, RNA immunoprecipitation (RIP), and luciferase assays. The effect of the circ_0032463/miR-498/LEF1 axis on the migration, proliferation, and apoptosis levels of OS cells was explored using CCK-8, bromodeoxyuridine (BrdU), wound healing, and fluorescein isothiocyanate (FITC) assays. Our findings revealed that circ_0032463 expression was upregulated in OS tissues and cell lines. We also found that circ_0032463 interacted with miR-498, thereby reducing the expression of miR-498 in OS cells. Experimental results indicated that miR-498 could directly target LEF1 in OS cells and that circ_0032463 could abrogate the tumor-inhibitory effect of miR-498 by upregulating LEF1 in OS. More specifically, by binding to miR-498 and inhibiting LEF1 expression, circ_0032463 promoted the migration and proliferation abilities of OS cells and suppressed the apoptosis ability of OS cells. Overall, this research suggested that circ_0032463 could promote OS development by regulating the miR-498/LEF1 axis.

Biological roles and therapeutic potential of circular RNAs in osteoarthritis

Osteoarthritis (OA) is a common and disabling joint disorder that is mainly characterized by cartilage degeneration and narrow joint spaces. The regulatory functions of non-coding RNAs (long non-coding RNAs, microRNAs [miRNAs], and circular RNAs [circRNAs]) in OA progression have attracted considerable attention, and the function of circular RNAs in the context of OA has been an increasingly popular research topic in the last 6 years. Recent studies have reported that various circRNAs can delay or aggravate diverse aspects of the OA process, including extracellular matrix formation, apoptosis, proliferation, inflammation, and autophagy, via circRNA/miRNA/mRNA pathways. Thus, circRNAs and related pathways are potential therapeutic targets for OA. Our review provides comprehensive information about circRNAs, including their biogenesis, functions, and characteristics, and it reveals their critical roles in the pathogenesis of OA via a large regulatory network of sponges. Considering their regulatory functions and characteristics, we hypothesize that circRNAs not only can be transferred through bodily fluids to serve as diagnostic biomarkers, but they can also be released from mesenchymal stem cell-derived exosomes and delivered to OA chondrocytes acting as therapeutic circRNAs. Further investigations of the in-depth molecular mechanisms of action of circRNAs in OA are expected to provide effective and safe OA treatment strategies.

Promising diagnostic and therapeutic circRNAs for skeletal and chondral disorders

Circular RNAs (circRNAs) belong to a highly conserved subtype of non-coding RNAs, produced by the back-splicing of specific regions of pre-mRNA. CircRNAs have wide-ranging effects on eukaryotic physiology and pathology by acting as transcription regulators, miRNA sponges, protein sponges, and templates for translation. Skeletal and chondral disorders are the leading causes of pain and disability, especially for elders, affecting hundreds of millions of people worldwide. Plenty of evidence have shown that circRNAs are dysregulated and play vital roles in the occurrence and progression of skeletal and chondral disorders. Herein, we systematically summarize the emerging roles and underlying molecular mechanisms of hub circRNAs in the pathogenesis of several representative skeletal and chondral disorders. Our findings may provide further insight into the mechanistic details of the role of circRNA in bone or cartilage metabolism, and highlight the promising application of circRNAs in serving as potential diagnostic or therapeutic targets for the prevention and treatment of skeletal and chondral disorders.