USP13 mediates PTEN to ameliorate osteoarthritis by restraining oxidative stress, apoptosis and inflammation via AKT-dependent manner

LncRNA FRMD6-AS1/miR-491-5p/USP13 pathway attenuated ferroptosis and contributed to liver fibrosis

Liver fibrosis is an invertible pathophysiologic process featured by excessive accumulation of extracellular matrix (ECM) which injures liver cells and activates hepatic stellate cells (HSCs). Besides, inducing ferroptosis in activated HSCs can alleviate liver fibrosis. LncRNAs modulate ferroptosis in activated HSCs and ECM deposition in liver fibrosis. However, the role of lncRNA FRMD6-AS1 in liver fibrosis is not discovered. In this study, lncRNA FRMD6-AS1 was dramatically up-regulated in activated HSCs. Knockdown of FRMD6-AS1 markedly increased iron ion, ROS and MDA levels, decreased GSH level, SLC7A11 and GPX4 protein expressions in activated HSCs. In addition, HSCs activation markers α-SMA and COL1α1 expressions were up-regulated in activated HSCs; knockdown of FRMD6-AS1 markedly down-regulated α-SMA and COL1α1 expressions in HSCs. Besides, lncRNA FRMD6-AS1 could interact with miR-491-5p, and negatively modulate miR-491-5p expression. USP13 was a target of miR-491-5p, and could be negatively modulated by miR-491-5p. Moreover, FRMD6-AS1 knockdown increased iron ion and ROS levels, decreased SLC7A11 and GPX4 protein expressions, facilitated HSCs viability, and up-regulated α-SMA and COL1α1 expressions via miR-491-5p/USP13 pathway. Finally, FRMD6-AS1 knockdown restored liver tissue structure and abrogated fibrosis in livers in a CCL4 liver fibrosis mouse model. Hence, lncRNA FRMD6-AS1/miR-491-5p/USP13 pathway repressed ferroptosis, promoted ECM deposition and facilitated liver fibrosis in vitro and in vivo models.

PTEN: an emerging target in rheumatoid arthritis?

Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is a critical tumor suppressor protein that regulates various biological processes such as cell proliferation, apoptosis, and inflammatory responses by controlling the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PI3K/AKT) signaling pathway. PTEN plays a crucial role in the pathogenesis of rheumatoid arthritis (RA). Loss of PTEN may contribute to survival, proliferation, and pro-inflammatory cytokine release of fibroblast-like synoviocytes (FLS). Also, persistent PI3K signaling increases myeloid cells' osteoclastic potential, enhancing localized bone destruction. Recent studies have shown that the expression of PTEN protein in the synovial lining of RA patients with aggressive FLS is minimal. Experimental upregulation of PTEN protein expression could reduce the damage caused by RA. Nonetheless, a complete comprehension of aberrant PTEN drives RA progression and its interactions with other crucial molecules remains elusive. This review is dedicated to promoting a thorough understanding of the signaling mechanisms of aberrant PTEN in RA and aims to furnish pertinent theoretical support for forthcoming endeavors in both basic and clinical research within this domain.

Subchondral osteoclasts and osteoarthritis: new insights and potential therapeutic avenues

Osteoarthritis (OA) is the most common joint disease, and good therapeutic results are often difficult to obtain due to its complex pathogenesis and diverse causative factors. After decades of research and exploration of OA, it has been progressively found that subchondral bone is essential for its pathogenesis, and pathological changes in subchondral bone can be observed even before cartilage lesions develop. Osteoclasts, the main cells regulating bone resorption, play a crucial role in the pathogenesis of subchondral bone. Subchondral osteoclasts regulate the homeostasis of subchondral bone through the secretion of degradative enzymes, immunomodulation, and cell signaling pathways. In OA, osteoclasts are overactivated by autophagy, ncRNAs, and Rankl/Rank/OPG signaling pathways. Excessive bone resorption disrupts the balance of bone remodeling, leading to increased subchondral bone loss, decreased bone mineral density and consequent structural damage to articular cartilage and joint pain. With increased understanding of bone biology and targeted therapies, researchers have found that the activity and function of subchondral osteoclasts are affected by multiple pathways. In this review, we summarize the roles and mechanisms of subchondral osteoclasts in OA, enumerate the latest advances in subchondral osteoclast-targeted therapy for OA, and look forward to the future trends of subchondral osteoclast-targeted therapies in clinical applications to fill the gaps in the current knowledge of OA treatment and to develop new therapeutic strategies.

MiR-17-5p-engineered sEVs Encapsulated in GelMA Hydrogel Facilitated Diabetic Wound Healing by Targeting PTEN and p21

Delayed wound healing is a major complication of diabetes, and is associated with impaired cellular functions. Current treatments are unsatisfactory. Based on the previous reports on microRNA expression in small extracellular vesicles (sEVs), miR-17-5p-engineered sEVs (sEVs17-OE) and encapsulated them in gelatin methacryloyl (GelMA) hydrogel for diabetic wounds treatment are fabricated. SEVs17-OE are successfully fabricated with a 16-fold increase in miR-17-5p expression. SEVs17-OE inhibited senescence and promoted the proliferation, migration, and tube formation of high glucose-induced human umbilical vein endothelial cells (HG-HUVECs). Additionally, sEVs17-OE also performs a promotive effect on high glucose-induced human dermal fibroblasts (HG-HDFs). Mechanism analysis showed the expressions of p21 and phosphatase and tensin homolog (PTEN), as the target genes of miR-17-5p, are downregulated significantly by sEVs17-OE. Accordingly, the downstream genes and pathways of p21 and PTEN, are activated. Next, sEVs17-OE are loaded in GelMA hydrogel to fabricate a novel bioactive wound dressing and to evaluate their effects on diabetic wound healing. Gel-sEVs17-OE effectively accelerated wound healing by promoting angiogenesis and collagen deposition. The cellular mechanism may be associated with local cell proliferation. Therefore, a novel bioactive wound dressing by loading sEVs17-OE in GelMA hydrogel, offering an option for chronic wound management is successfully fabricated.

MiR-29a-3p mediates phosphatase and tensin homolog and inhibits osteoarthritis progression

Despite substantial progress in clinical trials of osteoarthritis (OA) gene therapy, the prevalence of OA is still on the rise. MiRNAs have a potential biomarker and therapeutic target for OA. OA cartilage and chondrosarcoma cells were studied to determine the role of miR-29a-3p and PTEN. OA cartilage and human chondrosarcoma cells (SW1353) were obtained. miR-29a-3p and PTEN signature expression was determined by RT-qPCR. The binding relationship between miR-29a-3p and PTEN was investigated by dual-luciferase reporter gene and western blot assay. TUNEL, immunohistochemistry, CCK-8, and flow cytometry were utilized to determine the proliferation and apoptosis of SW1353 cells. This study indicated downregulation of miR-29a-3p expression and upregulation of PTEN expression in human OA primary chondrocytes or OA tissue samples, compared with the normal cartilage cells or tissues. PTEN expression was negatively correlated with miR-29a-3p expression, and miR-29a-3p targeted PTEN mechanistically. miR-29a-3p reduced SW1353 cell activity and proliferation and promoted cell apoptosis. However, the aforementioned effects could be reversed by downregulating PTEN. miR-29a-3p can stimulate chondrocyte proliferation and inhibit apoptosis by inhibiting PTEN expression.

PTEN-mediated FOXO signaling affects autophagy, migration and invasion of rheumatoid arthritis fibroblast-like synoviocytes

Rheumatoid arthritis (RA) is a chronic, progressive, systemic autoimmune disease. Among them, abnormal proliferation, migration and vascularization of fibroblast-like synoviocytes (FLS) are the main pathological basis of persistent synovitis and bone destruction in RA. In the current study, we attempted to find effective molecular mechanisms for the treatment of RA by investigating RA-FLS. Firstly, the study was conducted to identify the potential target gene PTEN and its related signaling pathway through bioinformatics analysis. Subsequently, the target gene PTEN overexpression was regulated by cell transfection. The expression of FOXO signaling factors and autophagy-related proteins were detected by western blotting assay. Cell proliferation was measured by CCK-8 and EdU assays. Inflammation level was detected by ELISA. Cell migration and invasion were detected using wound healing assay and transwell chamber assay, respectively. Cell apoptosis was detected using flow cytometry. The results showed that overexpression of PTEN activated FOXO1 signaling in RA-FLS, and regulated autophagy, proliferation, invasion, migration, and the levels of pro-inflammatory factors in the disease. In conclusion, PTEN might provide an effective therapeutic strategy for rheumatoid arthritis by mediating the FOXO1 signaling pathway.

Roles of ubiquitin‑specific protease 13 in normal physiology and tumors (Review)

Ubiquitin-specific protease 13 (USP13) is one of the most important deubiquitinases involved in various diseases. As deubiquitinases are components of the deubiquitination process, a significant post-translational modification, they are potential treatment targets for different diseases. With recent technological developments, the structure of USP13 and its pathological and physiological functions have been investigated. However, USP13 expression and function differ in various diseases, especially in tumors, and the associated mechanisms are complex and remain to be fully investigated. The present review summarized the recent discoveries and the current understanding of the USP13 function in tumors.

USP13 deubiquitinates p62/SQSTM1 to induce autophagy and Nrf2 release for activating antioxidant response genes

SQSTM1/p62 (sequestosome 1) is a multifunctional protein that serves as a receptor for selective autophagy and scaffold. In selective autophagy, p62 functions as a bridge between polyubiquitinated proteins and autophagosomes. Further, p62 acts as a signaling hub for many cellular pathways including mTORC1, NF-κB, and Keap1-Nrf2. Post-translational modifications of p62, such as ubiquitination and phosphorylation, are known to determine its binding partners and regulate their intracellular functions. However, the mechanism of p62 deubiquitination remains unclear. In this study, we found that ubiquitin-specific protease 13 (USP13), a member of the USP family, directly binds p62 and removes ubiquitin at Lys7 (K7) of the PB1 domain. USP13-mediated p62 deubiquitination enhances p62 protein stability and facilitates p62 oligomerization, resulting in increased autophagy and degradation of Keap1, which is a negative regulator of the antioxidant response that promotes Nrf2 activation. Thus, USP13 can be considered a therapeutic target as a deubiquitination enzyme of p62 in autophagy-related diseases.

Ubiquitin-specific peptidase 25 exacerbated osteoarthritis progression through facilitating TXNIP ubiquitination and NLRP3 inflammasome activation

Several members of the ubiquitin-specific proteases (USPs) family have been revealed to regulate the progression of osteoarthritis (OA). The current study aimed to investigate the role and the underlying mechanism of USP25 in IL-1β-induced chondrocytes and OA rat model. It was discovered that IL-1β stimulation upregulated USP25, increased ROS level, and suppressed cell viability in rat chondrocytes. Besides, USP25 knockdown alleviated IL-1β-induced injury by decreasing ROS level, attenuating pyroptosis, and downregulating the expression of IL-18, NLRP3, GSDMD-N, active caspase-1, MMP-3, and MMP-13. Furthermore, we discovered that USP25 affected the IL-1β-induced injury in chondrocytes in a ROS-dependent manner. Moreover, USP25 was revealed to interact with TXNIP, and USP25 knockdown increased the ubiquitination of TXNIP. The pro-OA effect of USP25 abundance could be overturned by TXNIP suppression in IL-1β-induced chondrocytes. Finally, in vivo experiment results showed that USP25 inhibition alleviated cartilage destruction in OA rats. In conclusion, we demonstrated that USP25 stimulated the overproduction of ROS to activate the NLRP3 inflammasome via regulating TXNIP, resulting in increased pyroptosis and inflammation in OA.

Elucidating the role of ubiquitination and deubiquitination in osteoarthritis progression

Osteoarthritis is non-inflammatory degenerative joint arthritis, which exacerbates disability in elder persons. The molecular mechanisms of osteoarthritis are elusive. Ubiquitination, one type of post-translational modifications, has been demonstrated to accelerate or ameliorate the development and progression of osteoarthritis via targeting specific proteins for ubiquitination and determining protein stability and localization. Ubiquitination process can be reversed by a class of deubiquitinases via deubiquitination. In this review, we summarize the current knowledge regarding the multifaceted role of E3 ubiquitin ligases in the pathogenesis of osteoarthritis. We also describe the molecular insight of deubiquitinases into osteoarthritis processes. Moreover, we highlight the multiple compounds that target E3 ubiquitin ligases or deubiquitinases to influence osteoarthritis progression. We discuss the challenge and future perspectives via modulation of E3 ubiquitin ligases and deubiquitinases expression for enhancement of the therapeutic efficacy in osteoarthritis patients. We conclude that modulating ubiquitination and deubiquitination could alleviate the osteoarthritis pathogenesis to achieve the better treatment outcomes in osteoarthritis patients.

Ubiquitin-specific peptidases: Players in bone metabolism

Osteoporosis is an ageing-related disease, that has become a major public health problem and its pathogenesis has not yet been fully elucidated. Substantial evidence suggests a strong link between overall age-related disease progression and epigenetic modifications throughout the life cycle. As an important epigenetic modification, ubiquitination is extensively involved in various physiological processes, and its role in bone metabolism has attracted increasing attention. Ubiquitination can be reversed by deubiquitinases, which counteract protein ubiquitination degradation. As the largest and most structurally diverse cysteinase family of deubiquitinating enzymes, ubiquitin-specific proteases (USPs), comprising the largest and most structurally diverse cysteine kinase family of deubiquitinating enzymes, have been found to be important players in maintaining the balance between bone formation and resorption. The aim of this review is to explore recent findings highlighting the regulatory functions of USPs in bone metabolism and provide insight into the molecular mechanisms governing their actions during bone loss. An in-deep understanding of USPs-mediated regulation of bone formation and bone resorption will provide a scientific rationale for the discovery and development of novel USP-targeted therapeutic strategies for osteoporosis.

USP13 promotes breast cancer metastasis through FBXL14-induced Twist1 ubiquitination

PURPOSE

Epithelial-to-mesenchymal transition (EMT) is an important cause of high mortality in breast cancer. Twist1 is one of the EMT transcription factors (EMT-TFs) with a noticeably short half-life, which is regulated by proteasome degradation pathways. Recent studies have found that USP13 stabilizes several specific oncogenic proteins. As yet, however, the relationship between Twist1 and USP13 has not been investigated.

METHODS

Co-Immunoprecipitation, GST-pulldown, Western blot, qRT-PCR and immunofluorescence assays were used to investigate the role of USP13 in de-ubiquitination of Twist1. Chromatin immunoprecipitation and Luciferase reporter assays were used to investigate the role of Twist1 in inhibiting USP13 reporter transcription. Scratch wound healing, cell migration and invasion assays, and a mouse lung metastases assay were used to investigate the roles of USP13 and Twist1 in promoting breast cancer metastasis.

RESULTS

We found that Twist1 can be de-ubiquitinated by USP13. In addition, we found that the protein levels of Twist1 dose-dependently increased with USP13 overexpression, while USP13 knockdown resulted in a decreased expression of endogenous Twist1. We also found that USP13 can directly interact with Twist1 and specifically cleave the K48-linked polyubiquitin chains of Twist1 induced by FBXL14. We found that the effect of USP13 in promoting the migration and invasion capacities of breast cancer cells can at least partly be achieved through its regulation of Twist1, while Twist1 can inhibit the transcriptional activity of USP13.

CONCLUSIONS

Our data indicate that an interplay between Twist1 and USP13 can form a negative physiological feedback loop. Our findings show that USP13 may play an essential role in breast cancer metastasis by regulating Twist1 and, as such, provide a potential target for the clinical treatment of breast cancer.

USP13 reduces septic mediated cardiomyocyte oxidative stress and inflammation by inducing Nrf2

BACKGROUND

Sepsis is a common cardiovascular complication that can cause heart damage. The regulatory role of ubiquitin-specific peptidase 13 (USP13) on erythroid 2-related factor 2 (Nrf2) has been reported, but its regulatory role in septic cardiomyopathy remains unclear.

METHODS

The Sprague Dawley (SD) rat model of septic myocardial injury was constructed by lipopolysaccharides (LPS). The serum lactate dehydrogenase (LDH) and creatine kinase (CK) levels were detected, the mRNA and protein expression levels of Nrf2 and USP13 in tissues were detected by real-time quantitative reverse transcription PCR (qRT-PCR) and western blot (WB), and the expression of USP13 at the treatment time of 3 h, 6 h, and 12 h was also detected. The cell viability and USP13, Nrf-2 and heme oxygenase-1 (HO-1) expression levels of H9C2-treated cells by LPS and the oxidative stress level and inflammatory response of H9C2 cells were detected by enzyme-linked immunosorbent assay (ELISA) and WB.

RESULTS

The results showed that USP13 was downregulated in septic myocardial injury tissues, and the Nrf2 level was increased in vitro after the cells were treated with LPS. Overexpression of USP13 further induced Nrf2 to reduce apoptosis, oxidative stress, and expression of inflammatory factors.

CONCLUSION

In conclusion, this study demonstrated that USP13 was downregulated in septic myocardial injury tissues, and USP13 overexpression increased Nrf2 levels and reduced apoptosis. Further studies showed that USP13 reduced LPS-induced oxidative stress and inflammation by inducing Nrf2.

The deubiquitinating enzyme 13 retards non-alcoholic steatohepatitis via blocking inactive rhomboid protein 2-dependent pathway

Nowadays potential preclinical drugs for the treatment of nonalcoholic steatohepatitis (NASH) have failed to achieve expected therapeutic efficacy because the pathogenic mechanisms are underestimated. Inactive rhomboid protein 2 (IRHOM2), a promising target for treatment of inflammation-related diseases, contributes to deregulated hepatocyte metabolism-associated nonalcoholic steatohepatitis (NASH) progression. However, the molecular mechanism underlying Irhom2 regulation is still not completely understood. In this work, we identify the ubiquitin-specific protease 13 (USP13) as a critical and novel endogenous blocker of IRHOM2, and we also indicate that USP13 is an IRHOM2-interacting protein that catalyzes deubiquitination of Irhom2 in hepatocytes. Hepatocyte-specific loss of the Usp13 disrupts liver metabolic homeostasis, followed by glycometabolic disorder, lipid deposition, increased inflammation, and markedly promotes NASH development. Conversely, transgenic mice with Usp13 overexpression, lentivirus (LV)- or adeno-associated virus (AAV)-driven Usp13 gene therapeutics mitigates NASH in 3 models of rodent. Mechanistically, in response to metabolic stresses, USP13 directly interacts with IRHOM2 and removes its K63-linked ubiquitination induced by ubiquitin-conjugating enzyme E2N (UBC13), a ubiquitin E2 conjugating enzyme, and thus prevents its activation of downstream cascade pathway. USP13 is a potential treatment target for NASH therapy by targeting the Irhom2 signaling pathway.

Role of USP13 in physiology and diseases

Ubiquitin specific protease (USP)-13 is a deubiquitinase that removes ubiquitin from substrates to prevent protein degradation by the proteasome. Currently, the roles of USP13 in physiology and pathology have been reported. In physiology, USP13 is highly associated with cell cycle regulation, DNA damage repair, myoblast differentiation, quality control of the endoplasmic reticulum, and autophagy. In pathology, it has been reported that USP13 is important in the pathogenesis of infection, inflammation, idiopathic pulmonary fibrosis (IPF), neurodegenerative diseases, and cancers. This mini-review summarizes the most recent advances in USP13 studies involving its pathophysiological roles in different conditions and provides new insights into the prevention and treatment of relevant diseases, as well as further research on USP13.

Geniposide restricts angiogenesis in experimentary arthritis via inhibiting Dnmt1-mediated PTEN hypermethylation

Neovascularization in rheumatoid arthritis (RA) is a key bridge between malignant proliferative synovial tissue and pannus. In view of previous studies on the efficacy of Geniposide (GE) in experimentary arthritis, the purpose of this study was to investigate the possible mechanism of GE inhibiting angiogenesis by regulating the gene of phosphate and tension homology deleted on chromosome ten (PTEN). In this study, human umbilical vein endothelial cells (HUVEC) and adjuvant arthritis (AA) rat models were performed to research in vitro and in vivo. The results showed that GE treatment significantly reduced synovitis and angiogenesis in AA rats, which may be associated with the increased expression of PTEN with GE treatment. Meanwhile, the hypermethylation of PTEN accompanied by the over-expression of DNA methyltransferases (Dnmts) was demonstrated in TNF-α-induced HUVEC and AA rats. Knockdown of Dnmt1 by Dnmt1- siRNA significantly inhibited the tube formation of HUVEC in vitro. GE significantly restricted the angiogenesis of HUVEC by inhibiting DNA methylation, which was attributed to the down-regulation of Dnmt1 rather than Dnmt3a and Dnmt3b. The anti-angiogenesis effect of GE was further verified in AA model by the inhibition of Dnmt1. These results indicate that GE exhibited anti-angiogenesis effects in experimentary arthritis by inhibiting Dnmt1-mediated PTEN gene hypermethylation, which may brings new insights for the prevention and research of RA.

Mesenchymal stem cells-derived small extracellular vesicles alleviate diabetic retinopathy by delivering NEDD4

Background

As a leading cause of vision decline and severe blindness in adults, diabetic retinopathy (DR) is characterized by the aggravation of retinal oxidative stress and apoptosis in the early stage. Emerging studies reveal that mesenchymal stem cells-derived small extracellular vesicles (MSC-sEV) treatment represents a promising cell-free approach to alleviate ocular disorders. However, the repairing effects of MSC-sEV in DR remain largely unclear. This study aimed at exploring the role and the underlying mechanism of MSC-sEV in hyperglycemia-induced retinal degeneration.

Methods

In vivo, we used streptozotocin (STZ) to establish diabetic rat model, followed by the intravitreal injection of MSC-sEV to determine the curative effect. The cell viability and antioxidant capacity of retinal pigment epithelium (RPE) cells stimulated with high-glucose (HG) medium after MSC-sEV treatment were analyzed in vitro. By detecting the response of cell signaling pathways in MSC-sEV-treated RPE cells, we explored the functional mechanism of MSC-sEV. Mass spectrometry was performed to reveal the bioactive protein which mediated the role of MSC-sEV.

Results

The intravitreal injection of MSC-sEV elicited antioxidant effects and counteracted retinal apoptosis in STZ-induced DR rat model. MSC-sEV treatment also reduced the oxidative level and enhanced the proliferation ability of RPE cells cultured in HG conditions in vitro. Further studies showed that the increased level of phosphatase and tensin homolog (PTEN) inhibited AKT phosphorylation and nuclear factor erythroid 2-related factor 2 (NRF2) expression in RPE cells stimulated with HG medium, which could be reversed by MSC-sEV intervention. Through mass spectrometry, we illustrated that MSC-sEV-delivered neuronal precursor cell-expressed developmentally downregulated 4 (NEDD4) could cause PTEN ubiquitination and degradation, activate AKT signaling and upregulate NRF2 level to prevent DR progress. Moreover, NEDD4 knockdown impaired MSC-sEV-mediated retinal therapeutic effects.

Conclusions

Our findings indicated that MSC-sEV ameliorated DR through NEDD4-induced regulation on PTEN/AKT/NRF2 signaling pathway, thus revealing the efficiency and mechanism of MSC-sEV-based retinal protection and providing new insights into the treatment of DR.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02983-0.

Synovial mesenchymal stem cell-derived extracellular vesicles containing microRN555A-26a-5p ameliorate cartilage damage of osteoarthritis

BACKGROUND

Osteoarthritis (OA) is a degenerative disease characterized by cartilage damage. We aimed to improve the understanding of the protective mechanism of synovial mesenchymal stem cell (SMSC)-derived extracellular vesicles (EVs) in cartilage damage of OA.

METHODS

SMSCs and SMSC-EVs were isolated from synovial biopsies of patients without OA and then identified. The pathological microenvironment of chondrocytes in OA was simulated by inducing SW1353 cells with interleukin (IL)-1β, followed by SMSC-EV treatment to assess SW1353 cell proliferation, apoptosis and inflammation. Endocytosis of Dil-labeled EVs by SW1353 cells was observed. microRNA (miR)-26a-5p expression in EVs and EV-treated SW1353 cells was assessed. The effect of miR-26a-5p was evaluated after it was down-regulated in SMSCs, followed by extraction of EVs, which acted on SW1353 cells. The target relationship of miR-26a-5p and phosphatase and tensin homologue (PTEN) was predicted and confirmed. The role of PTEN in OA was evaluated after it was overexpressed. Functional assays were implemented in vivo to certify the role of SMSC-EVs in OA.

RESULTS

SMSC-EVs enhanced IL-1β-induced SW1353 cell proliferation, whereas they inhibited apoptosis and inflammation. EVs were endocytosed by SW1353 cells and delivered miR-26a-5p into SW1353 cells to overexpress miR-26a-5p. Down-regulation of miR-26a-5p in EVs attenuated the protection of EVs against IL-1β-induced cell damage. miR-26a-5p targeted PTEN, for which overexpression spoiled the protection of EVs against IL-1β-induced cell damage. SMSC-EVs carrying miR-26a-5p repaired cartilage damage of OA.

CONCLUSIONS

SMSC-EVs carried miR-26a-5p into chondrocytes to up-regulate miR-26a-5p and inhibit PTEN, thereby inhibiting apoptosis and inflammation and ameliorating cartilage damage of OA.

Synovial Fibrosis Involvement in Osteoarthritis

Bone changes have always been the focus of research on osteoarthritis, but the number of studies on synovitis has increased only over the last 10 years. Our current understanding is that the mechanism of osteoarthritis involves all the tissues that make up the joints, including nerve sprouting, pannus formation, and extracellular matrix environmental changes in the synovium. These factors together determine synovial fibrosis and may be closely associated with the clinical symptoms of pain, hyperalgesia, and stiffness in osteoarthritis. In this review, we summarize the consensus of clinical work, the potential pathological mechanisms, the possible therapeutic targets, and the available therapeutic strategies for synovial fibrosis in osteoarthritis to gain insight and provide a foundation for further study.

Positive feedback regulation between USP15 and ERK2 inhibits osteoarthritis progression through TGF-β/SMAD2 signaling

Background

The transforming growth factor-β (TGF-β) signaling pathway plays an essential role in maintaining homeostasis in joints affected by osteoarthritis (OA). However, the specific mechanism of non-SMAD and classical SMAD signaling interactions is still unclear, which needs to be further explored.

Methods

In ATDC5 cells, USP15 overexpression and knockout were performed using the transfected lentivirus USP15 and Crispr/Cas9. Western blotting and immunofluorescence staining were used to test p-SMAD2 and cartilage phenotype-related molecular markers. In rat OA models, immunohistochemistry, hematoxylin and eosin (HE)/Safranin-O fast green staining, and histology were used to examine the regulatory activity of USP15 in TGF-β/SMAD2 signaling and the cartilage phenotype. Then, ERK2 overexpression and knockout were performed. The expressions of USP15, p-SMAD2, and the cartilage phenotype were evaluated in vitro and in vivo. To address whether USP15 is required for ERK2 and TGF-β/SMAD2 signaling, we performed rescue experiments in vitro and in vivo. Immunoprecipitation and deubiquitination assays were used to examine whether USP15 could bind to ERK2 and affect the deubiquitination of ERK2. Finally, whether USP15 regulates the level of p-ERK1/2 was evaluated by western blotting, immunofluorescence staining, and immunohistochemistry in vitro and in vivo.

Results

Our results indicated that USP15 stimulated TGF-β/SMAD2 signaling and the cartilage phenotype. Moreover, ERK2 required USP15 to influence TGF-β/SMAD2 signaling for regulating the cartilage phenotype in vivo and in vitro. And USP15 can form a complex with ERK2 to regulate ubiquitination of ERK2. Interestingly, USP15 did not regulate the stability of ERK2 but increased the level of p-ERK1/2 to further enhance the TGF-β/SMAD2 signaling pathway.

Conclusions

Taken together, our study revealed positive feedback regulation between USP15 and ERK2, which played a critical role in TGF-β/SMAD2 signaling to inhibit OA progression. Therefore, this specific mechanism can guide the clinical treatment of OA.