PTEN regulates matrix synthesis in adult human chondrocytes under oxidative stress

2D MXene Nanosheets with ROS Scavenging Ability Effectively Delay Osteoarthritis Progression

MXenes nanosheets with high conductivity, hydrophilicity, and excellent reactive oxygen species (ROS) scavenging ability have shown promise in treating various degenerative diseases correlated with abnormal ROS accumulation. Herein, the therapeutic potential of Ti3C2Tx nanosheets, which is the most widely investigated MXene material, in delaying osteoarthritis (OA) progression is demonstrated. In vitro experiments indicate the strong ROS scavenging capacity of Ti3C2Tx nanosheets and their acceptable biocompatibility. Ti3C2Tx nanosheets effectively protect chondrocytes from cell death induced by oxidative stress. In addition, Ti3C2Tx nanosheets demonstrate a prominent anti-inflammatory effect and the ability to restore homeostasis between anabolic activities and catabolic activities in chondrocytes. Furthermore, RNA sequencing reveals the potential mechanism underlying the Ti3C2Tx nanosheet-mediated therapeutic effect. Finally, the in vivo curative effect of Ti3C2Tx nanosheets is verified using a rat OA model. Histological staining and immunohistochemical analyses indicate that Ti3C2Tx nanosheets effectively ameliorate OA progression. Conclusively, the in vitro and in vivo experiments suggest that Ti3C2Tx nanosheets could be a promising and effective option for OA treatment.

Intra-Articular Injection of PLGA/Polydopamine Core-Shell Nanoparticle Attenuates Osteoarthritis Progression

Osteoarthritis (OA) is a common joint disease characterized by progressive cartilage degeneration. Unfortunately, currently available clinical drugs are mainly analgesics and cannot alleviate the development of OA. Kartogenin (KGN) has been found to promote the differentiation of bone marrow mesenchymal stem cells (BMSCs) into chondrocytes for the treatment of cartilage damage in early OA. However, KGN, as a small hydrophobic molecule, is rapidly cleared from the synovial fluid after intra-articular injection. This study synthesized a KGN-loaded nanocarrier based on PLGA/polydopamine core/shell structure to treat OA. The fluorescence signal of KGN@PLGA/PDA-PEG-E7 nanoparticles lasted for 4 weeks, ensuring long-term sustained release of KGN from a single intra-articular injection. In addition, the polyphenolic structure of PDA enables it to effectively scavenge reactive oxygen species, and the BMSC-targeting peptide E7 (EPLQLKM) endows KGN@PLGA/PDA-PEG-E7 NPs with an effective affinity for BMSCs. As a result, the KGN@PLGA/PDA-PEG-E7 nanoparticles could effectively induce cartilage in vitro and protect the cartilage and subchondral bone in a rat ACLT model. This therapeutic strategy could also be extended to the delivery of other drugs, targeting other tissues to treat joint diseases.

Extracellular Vesicles from Hypoxic Pretreated Urine-Derived Stem Cells Enhance the Proliferation and Migration of Chondrocytes by Delivering miR-26a-5p

OBJECTIVE

Stem-cell therapy is a promising treatment for cartilage defects. The newly identified urine-derived stem cells (USCs), which have multipotency and sufficient proliferative ability, are promising candidates for several tissue engineering therapies. In this study, we investigated the role of USC extracellular vehicles (EVs) in promoting the proliferation and migration of chondrocytes.

DESIGN

USCs were characterized by measuring induced multipotent differentiation and flow cytometry analysis of surface marker expression. The EVs were isolated from USCs under normoxic conditions (nor-EVs) and hypoxic conditions (hypo-EVs). Transmission electron microscopy and western blot analysis characterized the EVs. The chondrocytes were cultured in the USC-EVs. CCK-8 assay and EdU staining detected the proliferation of chondrocytes, and transwell assay detected their migration. miR-26a-5p expression in EVs was detected by quantitative real-time polymerase chain reaction (qRT-PCR). The target relationship of miR-26a-5p and phosphatase and tensin homolog (PTEN) was predicted and confirmed. The roles of EVs-miR-26a-5p and PTEN on the proliferation and migration of chondrocytes were also investigated.

RESULTS

Hypo-EVs showed a superior effect in promoting the proliferation and migration of chondrocytes than nor-EVs. Mechanistically, USC-EVs delivered miR-26a-5p into chondrocytes to overexpress miR-26a-5p. PTEN was identified as an miR-26a-5p target in chondrocytes. The effects of EVs-miR-26a-5p on promoting the proliferation and migration of chondrocytes were mediated by its regulation of PTEN.

CONCLUSION

Our study suggested that hypoxic USC-EVs may represent a promising strategy for osteoarthritis by promoting the proliferation and migration of chondrocytes via miR-26a-5p transfer.

Vaspin promotes chondrogenic differentiation of BMSCs via Akt activation in osteoarthritis

Background

The aim of this study was to investigate the role of Vaspin on the chondrogenic differentiation of bone mesenchymal stem cells (BMSCs), and its effect on chondrocyte survival and ECM secretion. We also assessed whether the Akt activation participates in these processes.

Methods

In vivo, immunohistochemistry was used to examine the positive rate of the protein expressions of Akt in Wistar rat articular cartilage and subchondral bone after Vaspin intraperitoneal injection for 14 days. In vitro, we isolated and expanded BMSCs from Wistar rats, and further cultured BMSCs as pellets in a chondrogenic-differentiation medium supplemented with different concentrations of Vaspin. After 21 days, the pellets were processed for cell counting kit assay. The mRNA level of Akt, SOX9 and COL2A1 in the pellets were investigated using quantitative Real-Time polymerase chain reaction, and the protein level of COMP was detected using western blot.

Results

During the chondrogenic differentiation of BMSCs, Vaspin promoted the chondrogenic differentiation of BMSCs and chondrocyte survival by activating the Akt pathway. These effects were significantly reduced by treatment with an Akt inhibitor. Moreover, Vaspin promoted chondrogenic differentiation of BMSCs by increasing the expression of markers in cartilage formation and extracellular matrix secretion. Furthermore, our study also found that Vaspin could increase Akt expression in cartilage cavities and subchondral bone in vivo.

Conclusion

These findings demonstrate that Vaspin can promote the chondrogenic differentiation of BMSCs and chondrocyte survival via Akt activation. Our study provides new insights into the potential ability of Vaspin to ameliorate the chondrogenic differentiation of BMSCs and chondrocyte survival in OA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-022-05295-9.

Protein tyrosine phosphatases in skeletal development and diseases

Skeletal development and homeostasis in mammals are modulated by finely coordinated processes of migration, proliferation, differentiation, and death of skeletogenic cells originating from the mesoderm and neural crest. Numerous molecular mechanisms are involved in these regulatory processes, one of which is protein posttranslational modifications, particularly protein tyrosine phosphorylation (PYP). PYP occurs mainly through the action of protein tyrosine kinases (PTKs), modifying protein enzymatic activity, changing its cellular localization, and aiding in the assembly or disassembly of protein signaling complexes. Under physiological conditions, PYP is balanced by the coordinated action of PTKs and protein tyrosine phosphatases (PTPs). Dysregulation of PYP can cause genetic, metabolic, developmental, and oncogenic skeletal diseases. Although PYP is a reversible biochemical process, in contrast to PTKs, little is known about how this equilibrium is modulated by PTPs in the skeletal system. Whole-genome sequencing has revealed a large and diverse superfamily of PTP genes (over 100 members) in humans, which can be further divided into cysteine (Cys)-, aspartic acid (Asp)-, and histidine (His)-based PTPs. Here, we review current knowledge about the functions and regulatory mechanisms of 28 PTPs involved in skeletal development and diseases; 27 of them belong to class I and II Cys-based PTPs, and the other is an Asp-based PTP. Recent progress in analyzing animal models that harbor various mutations in these PTPs and future research directions are also discussed. Our literature review indicates that PTPs are as crucial as PTKs in supporting skeletal development and homeostasis.

Effects of ibuprofen on gene expression in chondrocytes from patients with osteoarthritis as determined by RNA-Seq

Non-steroidal anti-inflammatory drugs are a widely used symptomatic treatment in osteoarthritis (OA), but their effects on cartilage remain controversial. We studied the effects of ibuprofen on gene expression in chondrocytes from patients with OA using RNA-Seq. Chondrocytes were isolated from cartilage samples of patients with OA undergoing knee replacement surgery, cultured with ibuprofen, and total mRNA was sequenced. Differentially expressed genes were identified with edgeR using pairwise comparisons. Functional analysis was performed using ingenuity pathway analysis (IPA). Ibuprofen did not induce statistically significant changes in chondrocyte transcriptome when the cells were cultured in the absence of added cytokines. In inflammatory conditions (when the cells were exposed to the OA-related cytokine interleukin (IL)-1β), 51 genes were upregulated and 42 downregulated by ibuprofen with fold change >1.5 in either direction. The upregulated genes included anti-inflammatory factors and genes associated with cell adhesion, while several mediators of inflammation were among the downregulated genes. IPA analysis revealed ibuprofen having modulating effects on inflammation-related pathways such as integrin, IL-8, ERK/MAPK and cAMP-mediated signalling pathways. In conclusion, the effects of ibuprofen on primary OA chondrocyte transcriptome appear to be neutral in normal conditions, but ibuprofen may shift chondrocyte transcriptome towards anti-inflammatory phenotype in inflammatory environments.

Prolidase expression in knee osteoarthritis and healthy controls: Observational study

Prolidase enzyme activity is important for collagen resynthesis. In late stages of osteoarthritis (OA) its activity is decreased.To evaluate prolidase expression in knees of patients undergoing total arthroplasty for OA, and compare with young people undergoing knee arthroscopy due to traumatic injuries.In this cross-sectional study we included 20 patients with OA grade IV who underwent total knee arthroplasty and 20 controls of young patients who underwent arthroscopy for another reason besides OA. All participants were evaluated by knee ultrasound before the procedure. During the procedure, synovial tissue biopsies were taken and analyzed by immunofluorescence to search inflammation. Measures of central tendency, dispersion measures and position measures were used for the case of quantitative variables. Student t test or Mann-Whitney U test, and the logistic regression of Cox, was used.Prolidase expression in the synovial biopsy was significantly lower in the OA group than in the controls (0.017 ± 0.009 vs 0.062 ± 0.094, P < .05). Power Doppler (PD) signal was present in the synovitis of all knee recesses of the OA group in grayscale and in 17 (85%) of knees. The mean of the micro-vessel count in patients with OA was significantly higher vs controls (11 + 5.3 vs 4 + 2.1, P = .001). The neovascularization correlated significantly with the presence of PD signal in patients with OA (1.16, 95% CI, 1.02-1.34, P = .02).The prolidase expression in the synovial membrane evaluated by immunofluorescence, in patients with late stages of knee OA, is low, which may be interpreted as an evidence of decreased collagen resynthesis.

CircRNA_0092516 regulates chondrocyte proliferation and apoptosis in osteoarthritis through the miR-337-3p/PTEN axis

The dysregulation of circular RNAs (circRNAs) has been identified in various human diseases. Here, we probed into the potential mechanism of circRNA_0092516 in osteoarthritis (OA). The expression of circRNA_0092516 was tested by quantitative real-time PCR. MTT, flow cytometry and western blot were applied to confirm the functions of circRNA_0092516 in vitro. Besides, RNA pull-down and dual-luciferase reporter gene experiments were applied to probe into the mechanism. circRNA_0092516 was raised in the tissues of OA patients and chondrocytes stimulated by IL-1β. The potential mechanism analysis expounded that circRNA_0092516 bound to miR-337-3p, and the interference with circRNA_0092516 boosted chondrocyte proliferation and restrained cell apoptosis through the miR-337-3p/phosphatase and tensin homolog (PTEN) axis, thereby improving OA. In-vivo experiments expounded that circRNA_0092516 regulated cartilage production through miR-337-3p. Overall, our data expounded that the interference with circRNA_0092516 boosted chondrocyte proliferation and restrained cell apoptosis through the miR-337-3p/PTEN axis, eventually slowed down the progress of OA.

Per2 attenuates LPS-induced chondrocyte injury through the PTEN/PI3K/Akt signalling pathway

This research aimed to explore the role of period circadian clock 2 (Per2) in the evolution of osteoarthritis (OA) and the relevant mechanisms. Per2 messenger RNA (mRNA) and protein levels were markedly reduced in NHAC-kn cells treated with 5 µg/ml lipopolysaccharide (LPS) for 12 h. Then, pcDNA3.1-Per2 and si-Per2 were recruited to boost and reduce the expression of Per2, respectively. MTT assay, apoptosis analysis and enzyme-linked immunosorbent assay (ELISA) results showed that Per2 increased cell proliferation, while inhibited apoptosis and inflammation. Furthermore, the PTEN/PI3K/Akt signalling pathway was activated by Per2 overexpression; the CO-IP data confirmed that Per2 specifically bound to PTEN. Through employing IGF-1, a PI3K activator, we determined that Per2-mediated inflammation response in LPS-stimulated NHAC-kn cells through the PTEN/PI3K/Akt signalling pathway. In summary, the present study indicates that Per2 may serve as a novel therapeutic target through activating the PTEN/PI3K/Akt signalling pathway.

Critical implication of the PTEN/PI3K/AKT pathway during BMP2-induced heterotopic ossification

Heterotopic ossification (HO) is characterized by extraskeletal ossification in soft tissue. Thus far, there is a lack of effective drug therapy against HO. Loss of PTEN in osteoblasts has been reported to accumulate bone mass in skeletal development and promote fracture healing in association with the activation of the PI3K/AKT pathway. However, the role of the PTEN/PI3K/AKT signaling in HO pathogenesis remains unknown. The present study investigated the implication of this pathway during BMP2-induced osteogenic differentiation and ectopic bone formation. It was shown that overexpression of PTEN inhibited proliferation but stimulated apoptosis in mesenchymal pluripotent C3H10T1/2 cells. PTEN also inhibited BMP2-induced osteoblast differentiation, whereas BMP2 repressed PTEN expression and subsequently activated PI3K/AKT. The PI3K inhibitor, LY294002, blocked BMP2-induced osteoblastogenesis, suggesting that the PI3K/AKT pathway is critically required for BMP2 to initiate osteoblastogenesis. In vivo, implantation of BMP2 in muscle induced ectopic endochondral ossification. Strikingly, this bone-forming capacity was notably suppressed by the PI3K inhibitor LY294002. Hence, the results of the present study demonstrated that the PI3K/AKT signaling activity is indispensable for BMP2 to induce ectopic new bone. Targeting the PI3K/AKT pathway using inhibitor(s) may represent a potential molecular therapy for the treatment against HO.

Identification and Analysis of Key Genes Driving Gastric Cancer Through Bioinformatics

Objective: The aim of this study was to use bioinformatic analyses to identify key genes and pathways driving gastric cancer (GC). Materials and Methods: The gene expression profiles, from human gastric tissue samples were downloaded from the Gene Expression Omnibus (GSE)29272 dataset. These data revealed 284 differentially expressed genes (DEGs) that included a group upregulated in cancer tissues (n = 142) and another group that were downregulated in cancer tissues. (n = 142). These DEGs were identified using the GEO2R. We used multiple online analysis tools, including, Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), protein-protein interaction networks, gene expression profiling interactive analysis (GEPIA), and the cBio Cancer Genomics Portal (cBioportal) database. Next, we identified the most significant DEGs using the Kaplan-Meier plotter (KM-plotter) database. Multiple bioinformatic platforms were used to identify candidate prognostic marker genes. We then analyzed freshly frozen GC tissues for the expression of these marker genes to validate the informatic findings. Results: We identified three DEGs related to overall survival from our analyses of the GEO data. Next, we analyzed these three DEGs in GEPIA and the cBioportal database and found that the biglycan (BGN) gene was related to invasion and metastases of GCs. This finding of differential gene expression was confirmed in a separate laboratory analysis of normal and GC tissues. In this analysis we found that high levels of BGN expression were correlated with GC clinicopathological characteristics, including microvascular tumor thrombus (p = 0.018), lymph node metastases (p = 0.013), and vessel invasion (p = 0.004). Conclusions: BGN expression levels appear to be an independent prognostic factor for predicting the survival times of GC patients.

Histological Evaluation and Gene Expression Profiling of Autophagy-Related Genes for Cartilage of Young and Senescent Rats

Autophagy is a cellular mechanism that protects cells from stress by digesting non-functional cellular components. In the cartilage, chondrocytes depend on autophagy as a principal mechanism to maintain cellular homeostasis. This protective role diminishes prior to the structural damage that normally occurs during aging. Considering that aging is the main risk factor for osteoarthritis, evaluating the expression of genes associated with autophagy in senescent cartilage might allow for the identification of potential therapeutic targets for treatment. Thus, we studied two groups of young and senescent rats. A histological analysis of cartilage and gene expression quantification for autophagy-related genes were performed. In aged cartilage, morphological changes were observed, such as an increase in cartilage degeneration as measured by the modified Mankin score, a decrease in the number of chondrocytes and collagen II (Col2a1), and an increase in matrix metalloproteinase 13 (Mmp13). Moreover, 84 genes associated with autophagy were evaluated by a PCR array analysis, and 15 of them were found to be significantly decreased with aging. Furthermore, an in silico analysis based on by two different bioinformatics software tools revealed that several processes including cellular homeostasis, autophagosome assembly, and aging—as well as several biological pathways such as autophagy, insulin-like growth factor 1 (IGF-1) signaling, PI3K (phosphoinositide 3-kinase)/AKT (serine/threonine kinase) signaling, and mammalian target of rapamycin (mTOR) signaling—were enriched. In conclusion, the analysis identified some potential targets for osteoarthritis treatment that would allow for the development of new therapeutic strategies for this chronic disease.

Circular RNA CircCDH13 contributes to the pathogenesis of osteoarthritis via CircCDH13/miR-296-3p/PTEN axis

Circular RNAs (circRNAs) are involved in a variety of human diseases; however, the function of circRNAs in osteoarthritis (OA) remains largely unknown. In this study, we investigated the role of CircCDH13 in OA and its underlying mechanisms. CircRNA expression profiles in OA and normal cartilage tissues were detected by microarray. The expression pattern, functional role, and mechanisms of CircCDH13 in OA were studied in vitro and in vivo. Gain-of-function and loss-of-function approaches were used to demonstrate the participation of CircCDH13 in OA. The regulatory relationship between CircCDH13 and miR-296-3p and miR-296-3p and phosphatase and tensin homolog (PTEN) was predicted by bioinformatics and verified by RNA pulldown and luciferase assay. Adeno-associated virus was also used to reveal the role and mechanisms of CircCDH13 in destabilization of medial meniscus (DMM)-induced OA mice. The upregulation of CircCDH13 in OA cartilage tissues significantly induces chondrocyte apoptosis, promotes extracellular matrix (ECM) catabolism, and inhibits ECM anabolism. Mechanistically, CircCDH13 contributes to OA pathogenesis by functioning as a sponge of miR-296-3p and regulating the miR-296-3p-PTEN pathway. Silencing of CircCDH13 in vivo markedly alleviated DMM-induced OA in mice. Our study revealed an important role of CircCDH13 in OA pathogenesis. Silencing of CircCDH13 could reduce chondrocyte apoptosis, inhibit ECM catabolism, and promote ECM anabolism through the miR-296-3p-PTEN pathway. It provides a potential target for developing effective interventions in treating OA.

Long-chain non-coding RNA HOTAIR promotes the progression of osteoarthritis via sponging miR-20b/PTEN axis

AIMS

Cumulative evidence suggests that long-chain non-coding RNA (lncRNA) is involved in the pathogenesis of osteoarthritis (OA). The present study aimed to explore the regulatory role and related mechanisms of HOX transcript antisense intergenic RNA (HOTAIR) in OA.

MATERIAL AND METHODS

The OA mouse model was constructed by the medial meniscus (DMM) method, and Interleukin (IL)-1β-induced chondrocytes were used to simulate OA in vitro.

KEY FINDINGS

Results found that HOTAIR was significantly up-regulated in articular cartilage tissues of OA mice and IL-1β-induced chondrocytes, accompanied by down-regulation of miR-20b and increased expression of the phosphatase and tensin homolog (PTEN). HOTAIR silencing improved cartilage tissue damage in OA mice, and promoted the expression of collagen II and aggrecan in cartilage tissue, while inhibited the expression of matrix metalloproteinases (MMP)-13 and ADAMTS-5. Overexpression of HOTAIR inhibited the proliferation of IL-1β-induced chondrocytes and promoted apoptosis and extracellular matrix (ECM) degradation, whereas the effect of HOTAIR knockdown was reversed. Bioinformatics software and luciferase reporter experiments confirmed that HOTAIR could negatively regulate miR-20b, and PTEN was a target gene of miR-20b. An increase in PTEN expression induced by HOTAIR overexpression could be reversed by the introduction of miR-20b mimic. HOTAIR overexpression significantly reversed miR-20 mimic-mediated inhibition of apoptosis and ECM degradation in IL-1β-induced chondrocytes, whereas the introduction of si-HOTAIR eliminated anti-miR-20b-mediated apoptosis and ECM degradation.

SIGNIFICANCE

HOTAIR can participate in OA by promoting chondrocyte apoptosis and ECM degradation, which may be related to its targeted regulation of miR-20b/PTEN axis.

Identification of DNA hydroxymethylation associated genes in osteoarthritis by combined analysis of hydroxymethylation and gene expression

BACKGROUND

Our study aimed to explore more mechanistic insights into the epigenetic regulation of osteoarthritis (OA).

METHODS

The expression profiles (accession number: GSE64393 and GSE64394) were downloaded from the Gene Expression Omnibus database. The differentially hydroxymethylated regions (DhMRs) and differentially expressed genes (DEGs) between OA and control groups were identified. The distribution of DhMRs in the whole genome and the correlation between DhMRs and DEGs were analyzed. Functional module mining for the DEGs and DhMRs was conducted, followed by protein-protein interaction (PPI) analysis. The transcriptional factor (TF) was predicted.

RESULTS

Total 52,282 DhMRs were obtained, among which 31,452 ones were annotated to 9726 genes. Additionally, 1806 DEGs were selected. Hydroxymethylation mainly occurred in gene body region. Correlation analysis revealed that more than 70% of DhMRs were uncorrelated with DEGs expression. Functional module mining for the DEGs and DhMRs identified 2 functional modules, which were involved in pathways of regulation of actin cytoskeleton, and TGF-β signaling pathway. A PPI network was constructed, and ITGB3 had the highest degree. Furthermore, 7 TFs were predicted, which regulated 12 candidate genes, such as HES1-PTEN.

CONCLUSIONS

The onset and progression of OA may be associated with the upregulated hydroxymethylation in gene body region of PTEN. HES1 may be important TF in the pathogenesis of OA. Additionally, pathways of regulation of actin cytoskeleton, and TGF-beta signaling pathway may also play important roles in OA progression.

Anti-Inflammatory and Chondroprotective Effects of Vanillic Acid and Epimedin C in Human Osteoarthritic Chondrocytes

In osteoarthritis (OA), inhibition of excessively expressed pro-inflammatory cytokines in the OA joint and increasing the anabolism for cartilage regeneration are necessary. In this ex-vivo study, we used an inflammatory model of human OA chondrocytes microtissues, consisting of treatment with cytokines (interleukin 1β (IL-1β)/tumor necrosis factor α (TNF-α)) with or without supplementation of six herbal compounds with previously identified chondroprotective effect. The compounds were assessed for their capacity to modulate the key catabolic and anabolic factors using several molecular analyses. We selectively investigated the mechanism of action of the two most potent compounds Vanillic acid (VA) and Epimedin C (Epi C). After identification of the anti-inflammatory and anabolic properties of VA and Epi C, the Ingenuity Pathway Analysis showed that in both treatment groups, osteoarthritic signaling pathways were inhibited. In the treatment group with VA, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling was inhibited by attenuation of the nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor alpha (IκBα) phosphorylation. Epi C showed a significant anabolic effect by increasing the expression of collagenous and non-collagenous matrix proteins. In conclusion, VA, through inhibition of phosphorylation in NF-κB signaling pathway and Epi C, by increasing the expression of extracellular matrix components, showed significant anti-inflammatory and anabolic properties and might be potentially used in combination to treat or prevent joint OA.

MiR-455-3p reduces apoptosis and alleviates degeneration of chondrocyte through regulating PI3K/AKT pathway

AIMS

This study aimed to explore the functions of miR-455-3p, PTEN, and PI3K/AKT pathway in osteoarthritis.

MATERIALS AND METHODS

We used the human bone marrow stem cell (BMSC), healthy chondrocytes, osteoarthritis chondrocytes (OA), and the IL-1β/TNF-α-treated chondrocyte model to explore the relationship between miR-455-3p and PTEN. Mimic or inhibitor was used to transfect chondrocytes to determine whether miR-455-3p can regulate PTEN and influence COL2A1 and MMP13. Apoptosis was detected by flow cytometry. A luciferase report was applied to verify the targeted binding. KO mice were applied to investigate PTEN and pAKT expression and the effect on chondrocytes in vivo.

KEY FINDINGS

MiR-455-3p and PTEN were reverse in chondrogenesis and healthy cartilage versus OA cartilage. Similar trends were noted in IL-1β model. PTEN and MMP13 decreased and COL2A1 increased after overexpressing miR-455-3p, whereas the inhibition showed opposite results. Flow cytometry showed that miR-455-3p could reduce the apoptosis of chondrocytes. The results of luciferase revealed that miR-455-3p could affect fluorescence activity of PTEN by targeting its 3'-UTR. Finally, we found a marked increased in the expression of PTEN in KO mice relative to WT mice, while pAKT levels decreased.

SIGNIFICANCE

It can be supported that miR-455-3p can reduce the apoptosis of chondrocytes and alleviate OA through regulating PI3K/AKT pathway, which may be expected to be a target for the treatment of osteoarthritis.

The PI3K/AKT/mTOR signaling pathway in osteoarthritis: a narrative review

Osteoarthritis (OA) is a complicated degenerative disease that affects whole joint tissue. Currently, apart from surgical approaches to treat late stage OA, effective treatments to reverse OA are not available. Thus, the mechanisms leading to OA, and more effective approaches to treat OA should be investigated. According to available evidence, the PI3K/AKT/mTOR signaling pathway is essential for normal metabolism of joint tissues, but is also involved in development of OA. To provide a wide viewpoint to roles of PI3K/AKT/mTOR signaling pathway in osteoarthritis, a comprehensive literature search was performed using PubMed terms 'PI3K OR AKT OR mTOR' and 'osteoarthritis'. This review highlights the role of PI3K/AKT/mTOR signaling in cartilage degradation, subchondral bone dysfunction, and synovial inflammation, and discusses how this signaling pathway affects development of the disease. We also summarize recent evidences of therapeutic approaches to treat OA by targeting the PI3K/AKT/mTOR pathway, and discuss potential challenges in developing these strategies for clinical treatment of OA.

Astaxanthin protects against osteoarthritis via Nrf2: a guardian of cartilage homeostasis

Scope: Osteoarthritis (OA) is a progressive disease characterized by cartilage degradation. Astaxanthin (Ast), a natural compound with remarkable antioxidant activity and multiple medical applications due to its activation of Nrf2 signaling, has been studied for application to various degenerative diseases. Currently, however, little is known about its efficacy in treating OA. This study reports the effects of Ast on cartilage homeostasis in OA progression.

Methods: IL-1β, TNF-α, and tert-butyl hydroperoxide (TBHP) were used to impair cartilage homeostasis. Modulating effects of Ast on the Nrf2 signaling pathway, and damage-associated events including extracellular matrix (ECM) degradation, inflammation, oxidative stress, chondrocyte apoptosis, and in vivo cartilage degradation were examined.

Results: Ast attenuated ECM degradation of OA chondrocytes through the Nrf2 signaling, and ameliorated the IL-1β-induced inflammatory response and ECM degradation via blockade of MAPK signaling. Additionally, Ast alleviated TNF-α-induced ECM degradation and chondrocyte apoptosis by inhibiting the NF-κB signaling, suppressed TBHP-induced oxidative stress, and subsequently reduced chondrocyte apoptosis. In vitro results were finally corroborated in vivo by demonstrating that Ast attenuates the severity of cartilage destruction in a mouse model of OA.

Conclusions: Ast could protect against osteoarthritis via the Nrf2 signaling, suggesting Ast might be a potential therapeutic supplement for OA treatment.

PTEN promotes intervertebral disc degeneration by regulating nucleus pulposus cell behaviors

Intervertebral disc degeneration (IDD) is induced by multiple factors including increased apoptosis, decreased survival, and reduced extracellular matrix (ECM) synthesis in the nucleus pulposus (NP) cells. The tumor suppressor phosphatase and tensin homolog deleted from chromosome 10 (PTEN) is the only known lipid phosphatase counteracting the PI3K/AKT pathway. Loss of PTEN leads to activated PI3K/AKT signaling, which plays a key role in a variety of cancers. However, the role of PTEN/PI3K/AKT signaling nexus in IDD remains unknown. Here, we report that PTEN is overexpressed in degenerative NP, which correlates with inactivated AKT. Using the PTEN knockdown approach by lentivirus-mediated short interfering RNA gene transfer technique, we report that PTEN decreases survival but induces apoptosis and senescence of NP cells. PTEN also inhibits expression and production of ECM components including collagen II, aggrecan, and proteoglycan. Furthermore, PTEN modulates the expression of ECM regulatory molecules SOX-9 and matrix metalloproteinase-3 (MMP-3). Using small-molecule AKT inhibitor GDC-0068, we confirm that PTEN regulates NP cell behaviors through its direct targeting of PI3K/AKT. These findings demonstrate for the first time that PTEN/PI3K/AKT signaling axis plays an important role in the pathogenesis of IDD. Targeting PTEN using gene therapy may represent a promising therapeutic approach against disc degenerative diseases.

Chromatin accessibility landscape of articular knee cartilage reveals aberrant enhancer regulation in osteoarthritis

Osteoarthritis (OA) is a common joint disorder with increasing impact in an aging society. While genetic and transcriptomic analyses have revealed some genes and non-coding loci associated to OA, the pathogenesis remains incompletely understood. Chromatin profiling, which provides insight into gene regulation, has not been reported in OA mainly due to technical difficulties. Here, we employed Assay for Transposase-Accessible Chromatin with high throughput sequencing (ATAC-seq) to map the accessible chromatin landscape in articular knee cartilage of OA patients. We identified 109,215 accessible chromatin regions for cartilages, of which 71% were annotated as enhancers. By overlaying them with genetic and DNA methylation data, we have determined potential OA-relevant enhancers and their putative target genes. Furthermore, through integration with RNA-seq data, we characterized genes that are altered both at epigenomic and transcriptomic levels in OA. These genes are enriched in pathways regulating ossification and mesenchymal stem cell (MSC) differentiation. Consistently, the differentially accessible regions in OA are enriched for MSC-specific enhancers and motifs of transcription factor families involved in osteoblast differentiation. In conclusion, we demonstrate how direct chromatin profiling of clinical tissues can provide comprehensive epigenetic information for a disease and suggest candidate genes and enhancers of translational potential.

Depletion of aquaporin 1 decreased ADAMTS‑4 expression in human chondrocytes

Inflammation serves an important role in the progression of osteoarthritis (OA), and IL-1β may act as a catabolic factor on cartilage, reducing the synthesis of primary cartilage components type II collagen and aggrecan. Aquaporin 1 (AQP1) is a 28-kDa water channel formed of six transmembrane domains on the cell membrane. AQP1 is highly expressed in the anus, gallbladder and liver, and is moderately expressed in the hippocampus, ependymal cells of the central nervous system and articular cartilage. It was hypothesized that AQP1 may be highly expressed in OA cartilage and that it may increase the expression of catabolic factors during inflammatory OA progression. Therefore, the present study evaluated AQP1 functions in human OA articular chondrocytes. Primary chondrocytes were isolated from human hip and knee cartilage tissues, cultured and transfected with AQP1-specific small interfering RNA with or without subsequent IL-1β treatment. In vitro explant culture from hip cartilages were also prepared. Reverse transcription-polymerase chain reaction (RT-PCR) was performed to assess the expression of AQP genes in human articular cartilage, AQP1 immunohistochemistry of the cartilages and explant culture, as well as RT-quantitative PCR, western blotting and immunocytochemistry/immunofluorescence of OA chondrocytes to evaluate the expression of AQP1, and catabolic and anabolic factors. RT-PCR results demonstrated that AQP0, 1, 3, 7, 9, and 11 were expressed in OA chondrocytes. Immunohistochemistry revealed that AQP1 was highly expressed in the superficial to middle zones of OA articular cartilages. Additionally, AQP1 mRNA was significantly higher in OA cartilage and IL-1β treatment significantly increased AQP1 expression in hip explant cartilage. Furthermore, AQP1 downregulation decreased a disintegrin and metalloprotease with thrombospondin motifs (ADAMTS)-4 expression in OA chondrocytes, though it did not affect other associated genes. Immunofluorescence showed that AQP1 and ADAMTS-4 were co-localized. These findings indicated that AQP1 depletion may decrease ADAMTS-4 expression in human OA chondrocytes. Therefore, regulating AQP1 expression may be a strategy to suppress catabolic factors during OA progression.

Up-regulation of Biglycan is Associated with Poor Prognosis and PTEN Deletion in Patients with Prostate Cancer

Biglycan (BGN), a proteoglycan of the extracellular matrix, is included in mRNA signatures for prostate cancer aggressiveness. To understand the impact of BGN on prognosis and its relationship to molecularly defined subsets, we analyzed BGN expression by immunohistochemistry on a tissue microarray containing 12,427 prostate cancers. Seventy-eight percent of 11,050 interpretable cancers showed BGN expression, which was considered as low intensity in 47.7% and as high intensity in 31.1% of cancers. BGN protein expression rose with increasing pathological tumor stage, Gleason grade, lymph node metastasis and early PSA recurrence (P<.0001 each). Comparison with our molecular database attached to the TMA revealed that BGN expression was linked to presence of TMPRRS2:ERG fusion and PTEN deletion (P<.0001 each). In addition, BGN was strongly linked to androgen-receptor (AR) levels (P<.0001), suggesting a hormone-depending regulation of BGN. BGN up-regulation is a frequent feature of prostate cancer that parallels tumor progression and may be useful to estimate tumor aggressiveness particularly if combined with other molecular markers.

Gene expression analysis of growth factor receptors in human chondrocytes in monolayer and 3D pellet cultures

The main goal of cartilage repair is to create functional tissue by enhancing the in vitro conditions to more physiological in vivo conditions. Chondrogenic growth factors play an important role in influencing cartilage homeostasis. Insulin‑like growth factor (IGF)‑1 and transforming growth factor (TGF)‑β1 affect the expression of collagen type II (Col2) and glycosaminoglycans (GAGs) and, therefore, the targeted use of growth factors could make chondrogenic redifferentiation more efficient. In the present study, human chondrocytes were postmortally isolated from healthy articular cartilage and cultivated as monolayer or 3D pellet cultures either under normoxia or hypoxia and stimulated with IGF‑1 and/or TGF‑β1 to compare the impact of the different growth factors. The mRNA levels of the specific receptors (IGF1R, TGFBR1, TGFBR2) were analyzed at different time points. Moreover, gene expression rates of collagen type 1 and 2 in pellet cultures were observed over a period of 5 weeks. Additionally, hyaline‑like Col2 protein and sulphated GAG (sGAG) levels were quantified. Stimulation with IGF‑1 resulted in an enhanced expression of IGF1R and TGFBR2 whereas TGF‑β1 stimulated TGFBR1 in the monolayer and pellet cultures. In monolayer, the differences reached levels of significance. This effect was more pronounced under hypoxic culture conditions. In pellet cultures, increased amounts of Col2 protein and sGAGs after incubation with TGF‑β1 and/or IGF‑1 were validated. In summary, constructing a gene expression profile regarding mRNA levels of specific growth factor receptors in monolayer cultures could be helpful for a targeted application of growth factors in cartilage tissue engineering.

Chondroprotective effects of alpha-lipoic acid in a rat model of osteoarthritis

OBJECTIVE

The purpose of this study was to investigate whether alpha-lipoic acid (ALA) confers a chondroprotective effect on articular cartilage in rats with monosodium iodoacetate (MIA)-induced osteoarthritis (OA).

METHODS

Fifty male SD rats were divided into five groups, including SHAM-operated, MIA-induced OA, and three experimental groups treated with 50-, 100-, or 200-mg/kg ALA. After 14 d of ALA treatment, rats were sacrificed for joint macroscopic and histology assessments. The gene and protein expressions of markers related to chondrocyte phenotype, caspase proteins, NADPH oxidase 4 (Nox4), p22(phox), activation of nuclear factor-κB (NF-κB), and endoplasmic reticulum (ER) stress were measured by Western blot analyses or qRT-PCR.

RESULTS

The results showed that MIA injection successfully induced OA by causing cartilage degeneration. Morphological and histological examinations demonstrated that ALA treatment, especially 200 mg/kg of ALA, significantly ameliorated cartilage degeneration in rats with MIA-induced OA. ALA could effectively increase the levels of the collagen type II and aggrecan genes and inhibit apoptosis-related proteins expression. ALA reduced biomakers of oxidative damage and over-expression levels of Nox4 and p22(phox). ALA also suppressed ER stress and inhibited the activation of NF-κB pathway. Moreover, ALA obviously inhibited TNF-α secretion and Wnt/β-catenin signaling way.

CONCLUSION

These findings indicated that ALA might be a potential therapeutic agent for the protection of articular cartilage against progression of OA through inhibition of oxidative stress, ER stress, inflammatory cytokine secretion, and Wnt/β-catenin activation.

Consequences of metabolic and oxidative modifications of cartilage tissue

A hallmark of chronic metabolic diseases, such as diabetes and metabolic syndrome, and oxidative stress, as occurs in chronic inflammatory and degenerative conditions, is the presence of extensive protein post-translational modifications, including glycation, glycoxidation, carbonylation and nitrosylation. These modifications have been detected on structural cartilage proteins in joints and intervertebral discs, where they are known to affect protein folding, induce protein aggregation and, ultimately, generate microanatomical changes in the proteoglycan-collagen network that surrounds chondrocytes. Many of these modifications have also been shown to promote oxidative cleavage as well as enzymatically-mediated matrix degradation. Overall, a general picture starts to emerge indicating that biochemical changes in proteins constitute an early event that compromises the anatomical organization and viscoelasticity of cartilage, thereby affecting its ability to sustain pressure and, ultimately, impeding its overall bio-performance.

Emerging targets in osteoarthritis therapy

Osteoarthritis (OA) is a destructive joint disease in which the initiation may be attributed to direct injury and mechanical disruption of joint tissues, but the progressive changes are dependent on active cell-mediated processes that can be observed or inferred during the generally long time-course of the disease. Based on clinical observations and experimental studies, it is now recognized a that it is possible for individual patients to exhibit common sets of symptoms and structural abnormalities due to distinct pathophysiological pathways that act independently or in combination. Recent research that has focused on the underlying mechanisms involving biochemical cross talk among the cartilage, synovium, bone, and other joint tissues within a background of poorly characterized genetic factors will be addressed in this review.

Oxidative stress-induced apoptosis and matrix loss of chondrocytes is inhibited by eicosapentaenoic acid

Eicosapentaenoic acid (EPA) is an antioxidant and n-3 polyunsaturated fatty acid that reduces the production of inflammatory cytokines. We evaluated the role of EPA in chondrocyte apoptosis and degeneration. Normal human chondrocytes were treated with EPA and sodium nitroprusside (SNP). Expression of metalloproteinases (MMPs) was detected by real-time polymerase chain reaction (PCR) and that of apoptosis-related proteins was detected by western blotting. Chondrocyte apoptosis was detected by flow cytometry. C57BL/6J mice were used for the detection of MMP expression by immunohistochemistry and for investigation of chondrocyte apoptosis. EPA inhibited SNP-induced chondrocyte apoptosis, caspase 3 and poly(ADP-ribose) polymerase cleavage, phosphorylation of p38 MAPK and p53, and expression of MMP3 and MMP13. Intra-articular injection of EPA prevented the progression of osteoarthritis (OA) by inhibiting MMP13 expression and chondrocyte apoptosis. EPA treatment can control oxidative stress-induced OA progression, and thus may be a new approach for OA therapy.