Interleukin-1β induced Stress Granules Sequester COX-2 mRNA and Regulates its Stability and Translation in Human OA Chondrocytes

The regulatory role and mechanism of TRPV3 on apoptosis and inflammation in osteoarthritis

Osteoarthritis (OA) is one of the most common forms of degenerative joint disease characterized by persistent pain, inflammation of the joints, and restricted range of motion among the elderly worldwide. Interleukin-1 beta (IL-1β) is increased in the injured joints and contributes to the OA pathobiology by inducing chondrocyte apoptosis and inflammation. Transient receptor potential (TRP) ion channels have recently been reported as potential players in the modulation of apoptosis and inflammation. Here, we aimed to understand the regulatory role and effect of TRPV3 on apoptosis and inflammation in osteoarthritis by using C28/I2 chondrocyte cells as a model. Chondrocytes were transfected with TRPV3-specific siRNA for 24 hours and then stimulated with IL-1β in vitro. Cell cycle progression and apoptosis were evaluated with flow cytometry. The levels of TRPV3, apoptotic (Bax, Caspase-3, and Bcl-2), and inflammatory (iNOS, COX-2) genes were measured by quantitative real-time polymerase chain reaction (qRT-PCR) and confirmed with western blot. Treatment of the C28/I2 chondrocyte cells with IL-1β resulted in the over-expression of TRPV3, induction of apoptosis, and over-expression of inflammation indices. Knockdown of TRPV3 significantly reduced the expression of Bax and Caspase 3 proapoptotic factors while increasing the expression of the Bcl-2 antiapoptotic factor in the mRNA and protein levels in the IL-1β-stimulated cells. Its knockdown also decreased the expression of the inflammatory factors iNOS and COX-2 in mRNA and protein levels, confirming that TRPV3 knockdown hinders apoptosis and inflammation in IL-1β-stimulated chondrocytes. In conclusion, we demonstrated that si-TRPV3 treatment significantly mitigates IL-1β-related effects on the C28/I2 chondrocyte cells. These findings suggested that TRPV3 could be an effective target for the treatment of OA. See also the graphical abstract(Fig. 1).

Deciphering the Role of LncRNAs in Osteoarthritis: Inflammatory Pathways Unveiled

Long non-coding RNA (LncRNA), with transcripts over 200 nucleotides in length, play critical roles in numerous biological functions and have emerged as significant players in the pathogenesis of osteoarthritis (OA), an inflammatory condition traditionally viewed as a degenerative joint disease. This review comprehensively examines the influence of LncRNA on the inflammatory processes driving OA progression, focusing on their role in regulating gene expression, cellular activities, and inflammatory pathways. Notably, LncRNAs such as MALAT1, H19, and HOTAIR are upregulated in OA and exacerbate the inflammatory milieu by modulating key signaling pathways like NF-κB, TGF-β/SMAD, and Wnt/β-catenin. Conversely, LncRNA like MEG3 and GAS5, which are downregulated in OA, show potential in dampening inflammatory responses and protecting against cartilage degradation by influencing miRNA interactions and cytokine production. By enhancing our understanding of LncRNA' roles in OA inflammation, we can better leverage them as potential biomarkers for the disease and develop innovative therapeutic strategies for OA management. This paper aims to delineate the mechanisms by which LncRNA influence inflammatory responses in OA and propose them as novel targets for therapeutic intervention.

Mechanisms of chondrocyte cell death in osteoarthritis: implications for disease progression and treatment

Osteoarthritis (OA) is a chronic joint disease characterized by the degeneration, destruction, and excessive ossification of articular cartilage. The prevalence of OA is rising annually, concomitant with the aging global population and increasing rates of obesity. This condition imposes a substantial and escalating burden on individual health, healthcare systems, and broader social and economic frameworks. The etiology of OA is multifaceted and not fully understood. Current research suggests that the death of chondrocytes, encompassing mechanisms such as cellular apoptosis, pyroptosis, autophagy, ferroptosis and cuproptosis, contributes to both the initiation and progression of the disease. These cell death pathways not only diminish the population of chondrocytes but also exacerbate joint damage through the induction of inflammation and other deleterious processes. This paper delineates the morphological characteristics associated with various modes of cell death and summarizes current research results on the molecular mechanisms of different cell death patterns in OA. The objective is to review the advancements in understanding chondrocyte cell death in OA, thereby offering novel insights for potential clinical interventions.

Whole-Transcriptome Sequencing of Knee Joint Cartilage from Kashin-Beck Disease and Osteoarthritis Patients

The aim of this study was to provide a comprehensive understanding of similarities and differences in mRNAs, lncRNAs, and circRNAs within cartilage for Kashin-Beck disease (KBD) compared to osteoarthritis (OA). We conducted a comparison of the expression profiles of mRNAs, lncRNAs, and circRNAs via whole-transcriptome sequencing in eight KBD and ten OA individuals. To facilitate functional annotation-enriched analysis for differentially expressed (DE) genes, DE lncRNAs, and DE circRNAs, we employed bioinformatic analysis utilizing Gene Ontology (GO) and KEGG. Additionally, using quantitative reverse transcriptase polymerase chain reaction (qRT-PCR), we validated the expression levels of four cartilage-related genes in chondrocytes. We identified a total of 43 DE mRNAs, 1451 DE lncRNAs, and 305 DE circRNAs in KBD cartilage tissue compared to OA (q value < 0.05; |log2FC| > 1). We also performed competing endogenous RNA network analysis, which identified a total of 65 lncRNA-mRNA interactions and 4714 miRNA-circRNA interactions. In particular, we observed that circRNA12218 had binding sites for three miRNAs targeting ACAN, while circRNA12487 had binding sites for seven miRNAs targeting COL2A1. Our results add a novel set of genes and non-coding RNAs that could potentially serve as candidate diagnostic biomarkers or therapeutic targets for KBD patients.

Protective effects of ectoine on articular chondrocytes and cartilage in rats for treating osteoarthritis

Osteoarthritis (OA) is a chronic degenerative disease that primarily includes articular cartilage destruction and inflammatory reactions, and effective treatments for this disease are still lacking. The present study aimed to explore the protective effects of ectoine, a compatible solute found in nature, on chondrocytes in rats and its possible application in OA treatment. In the in vitro studies, the morphology of the chondrocytes after trypsin digestion for 2 min and the viability of the chondrocytes at 50°C were observed after ectoine treatment. The reactive oxygen species (ROS) levels in chondrocytes pretreated with ectoine and post-stimulated with H2O2 were detected using an ROS assay. Chondrocytes were pretreated with ectoine before IL-1β stimulation. RT‒qPCR was used to measure the mRNA levels of cyclooxygenase-2 (COX-2), metallomatrix proteinase-3, -9 (MMP-3, -9), and collagen type II alpha 1 (Col2A1). In addition, immunofluorescence was used to assess the expression of type II collagen. The in vivo effect of ectoine was evaluated in a rat OA model induced by the modified Hulth method. The findings revealed that ectoine significantly increased the trypsin tolerance of chondrocytes, maintained the viability of the chondrocytes at 50°C, and improved their resistance to oxidation. Compared with IL-1β treatment alone, ectoine pretreatment significantly reduced COX-2, MMP-3, and MMP-9 expression and maintained type II collagen synthesis in chondrocytes. In vivo, the cartilage of ectoine-treated rats exhibited less degeneration and lower Osteoarthritis Research Society International (OARSI) scores. The results of this study suggest that ectoine exerts protective effects on chondrocytes and cartilage and can, therefore, be used as a potential therapeutic agent in the treatment of OA.

Therapeutic targets and potential delivery systems of melatonin in osteoarthritis

Osteoarthritis (OA) is a highly prevalent age-related musculoskeletal disorder that typically results in chronic pain and disability. OA is a multifactorial disease, with increased oxidative stress, dysregulated inflammatory response, and impaired matrix metabolism contributing to its onset and progression. The neurohormone melatonin, primarily synthesized by the pineal gland, has emerged as a promising therapeutic agent for OA due to its potential to alleviate inflammation, oxidative stress, and chondrocyte death with minimal adverse effects. The present review provides a comprehensive summary of the current understanding regarding melatonin as a promising pharmaceutical agent for the treatment of OA, along with an exploration of various delivery systems that can be utilized for melatonin administration. These findings may provide novel therapeutic strategies and targets for inhibiting the advancement of OA.

RNA-binding proteins that are highly expressed and enriched in healthy cartilage but suppressed in osteoarthritis

Objectives: RNA-binding proteins (RBPs) have diverse and essential biological functions, but their role in cartilage health and disease is largely unknown. The objectives of this study were (i) map the global landscape of RBPs expressed and enriched in healthy cartilage and dysregulated in osteoarthritis (OA); (ii) prioritize RBPs for their potential role in cartilage and in OA pathogenesis and as therapeutic targets. Methods: Our published bulk RNA-sequencing (RNA-seq) data of healthy and OA human cartilage, and a census of 1,542 RBPs were utilized to identify RBPs that are expressed in healthy cartilage and differentially expressed (DE) in OA. Next, our comparison of healthy cartilage RNA-seq data to 37 transcriptomes in the Genotype-Tissue Expression (GTEx) database was used to determine RBPs that are enriched in cartilage. Finally, expression of RBPs was analyzed in our single cell RNA-sequencing (scRNA-seq) data from healthy and OA human cartilage. Results: Expression of RBPs was higher than nonRBPs in healthy cartilage. In OA cartilage, 188 RBPs were differentially expressed, with a greater proportion downregulated. Ribosome biogenesis was enriched in the upregulated RBPs, while splicing and transport were enriched in the downregulated. To further prioritize RBPs, we selected the top 10% expressed RBPs in healthy cartilage and those that were cartilage-enriched according to GTEx. Intersecting these criteria, we identified Tetrachlorodibenzodioxin (TCDD) Inducible Poly (ADP-Ribose) Polymerase (TIPARP) as a candidate RBP. TIPARP was downregulated in OA. scRNA-seq data revealed TIPARP was most significantly downregulated in the "pathogenic cluster". Conclusion: Our global analyses reveal expression patterns of RBPs in healthy and OA cartilage. We also identified TIPARP and other RBPs as novel mediators in OA pathogenesis and as potential therapeutic targets.

Stress granules affect the sensitivity of renal cancer cells to sorafenib by sequestering and stabilizing COX‑2 mRNA

Most patients with renal cancer will develop resistance to sorafenib therapy and will therefore exhibit disease progression. Effective therapies for these patients are extremely limited. Cyclooxygenase-2 (COX-2) promotes the malignant transformation of cancer cells and drug resistance. The potential of COX-2 inhibitor (celecoxib) administration in combination with sorafenib for the treatment of renal cancer is unclear. The present study demonstrated that sorafenib rapidly increased the expression of COX-2 in renal cancer cells, as determined using reverse transcription-quantitative PCR and western blotting. The results of the MTT assay and cell apoptosis experiment demonstrated that the cytotoxicity of sorafenib was also affected by COX-2 expression and celecoxib enhanced the cytotoxicity of sorafenib against renal cell carcinoma. Immunofluorescence analysis indicated that sorafenib induced the formation of stress granules (SGs) in renal cancer cells. In addition, COX-2 expression was associated with the formation of SGs, and SGs could capture and stabilize COX-2 mRNAs in renal cancer cells; this was confirmed using RNA fluorescence in situ hybridization and an actinomycin D chase experiment. The protective effect of SGs was further demonstrated in cell experiments and xenograft tumor models. Thus, the present study indicated that the use of celecoxib may significantly enhance the sensitivity of renal cancer cells to sorafenib and improve efficacy. Sorafenib-induced SGs may contribute to critical events that promote COX-2 expression and survival in renal cancer cells. Therefore, the present study may provide novel ideas for the treatment of renal cancer.

Natural Compounds: Potential Therapeutics for the Inhibition of Cartilage Matrix Degradation in Osteoarthritis

Osteoarthritis (OA) is the most common degenerative joint disease characterized by enzymatic degradation of the cartilage extracellular matrix (ECM) causing joint pain and disability. There is no disease-modifying drug available for the treatment of OA. An ideal drug is expected to stop cartilage ECM degradation and restore the degenerated ECM. The ECM primarily contains type II collagen and aggrecan but also has minor quantities of other collagen fibers and proteoglycans. In OA joints, the components of the cartilage ECM are degraded by matrix-degrading proteases and hydrolases which are produced by chondrocytes and synoviocytes. Matrix metalloproteinase-13 (MMP-13) and a disintegrin and metalloproteinase with thrombospondin motifs 4 and 5 (ADAMTS5) are the major collagenase and aggrecanase, respectively, which are highly expressed in OA cartilage and promote cartilage ECM degradation. Current studies using various in vitro and in vivo approaches show that natural compounds inhibit the expression and activity of MMP-13, ADAMTS4, and ADAMTS5 and increase the expression of ECM components. In this review, we have summarized recent advancements in OA research with a focus on natural compounds as potential therapeutics for the treatment of OA with emphasis on the prevention of cartilage ECM degradation and improvement of joint health.

RNA binding proteins in osteoarthritis

Osteoarthritis (OA) is a common chronic degenerative joint disease worldwide. The pathological features of OA are the erosion of articular cartilage, subchondral bone sclerosis, synovitis, and metabolic disorder. Its progression is characterized by aberrant expression of genes involved in inflammation, proliferation, and metabolism of chondrocytes. Effective therapeutic strategies are limited, as mechanisms underlying OA pathophysiology remain unclear. Significant research efforts are ongoing to elucidate the complex molecular mechanisms underlying OA focused on gene transcription. However, posttranscriptional alterations also play significant function in inflammation and metabolic changes related diseases. RNA binding proteins (RBPs) have been recognized as important regulators in posttranscriptional regulation. RBPs regulate RNA subcellular localization, stability, and translational efficiency by binding to their target mRNAs, thereby controlling their protein expression. However, their role in OA is less clear. Identifying RBPs in OA is of great importance to better understand OA pathophysiology and to figure out potential targets for OA treatment. Hence, in this manuscript, we summarize the recent knowledge on the role of dysregulated RBPs in OA and hope it will provide new insight for OA study and targeted treatment.

Mitochonic Acid-5 Inhibits Reactive Oxygen Species Production and Improves Human Chondrocyte Survival by Upregulating SIRT3-Mediated, Parkin-dependent Mitophagy

Mitochondrial dysfunction is related to the pathogenesis of osteoarthritis (OA); however, there are no effective drugs to treat OA for maintaining mitochondrial homeostasis. Studies have shown that mitochonic acid-5 (MA-5) has a protective effect against mitochondrial damage and plays a role in mitophagy. However, it is not clear whether MA-5 has a beneficial effect on inflammatory articular cartilage. Here, human OA cartilage was obtained from patients undergoing total joint replacement. Interleukin-1β (IL-1β) was used to stimulate chondrocytes and induce inflammatory injury. Cell Counting Kit-8, TUNEL, and flow cytometry assays were used to assess apoptosis. Gene expression was examined using quantitative reverse transcription-polymerase chain reaction. Mitochondrial function was evaluated using immunoblotting, mitochondrial membrane potential assay, JC-1 staining, and immunofluorescence analysis. Mitophagy was detected using immunoblotting and immunofluorescence. 3-(1H-1,2,3-triazol-4-yl) pyridine (3-TYP), a specific inhibitor of Sirtuin 3 (SIRT3), was used to block the SIRT3/Parkin pathway. Mitophagy in the cartilage sections was evaluated via immunohistochemistry. IL-1β was found to induce chondrocyte apoptosis by inhibiting SIRT3 expression and mitophagy. In addition, inflammatory damage reduced the mitochondrial membrane potential and promoted the production of intracellular reactive oxygen species (ROS), leading to increased mitochondrial division, mitochondrial fusion inhibition, and the consequent mitochondrial damage. In contrast, the MA-5 treatment inhibited excessive ROS production by upregulating mitophagy, maintaining the mitochondrial membrane potential, and reducing mitochondrial apoptosis. After chemically blocking SIRT3 with 3-TYP, Parkin-related mitophagy was also inhibited, an effect that was prevented by pretreatment of the chondrocytes with MA-5, thereby suggesting that SIRT3 is upstream of Parkin. Overall, MA-5 was found to enhance the activity of SIRT3, promote Parkin-dependent mitophagy, eliminate depolarized/damaged mitochondria in chondrocytes, and protect cartilage cells. In conclusion, MA-5 inhibits IL-1β-induced oxidative stress and protects chondrocytes by upregulating the SIRT3/Parkin-related autophagy signaling pathway.

ERK1/2-mediated activation of DRP1 regulates mitochondrial dynamics and apoptosis in chondrocytes

OBJECTIVE

To determine the Dynamin-related protein 1 (DRP1) regulation of mitochondrial fission in chondrocytes under pathological conditions, an area which is underexplored in osteoarthritis pathogenesis.

DESIGN

DRP1 protein expression was determined by immunohistochemistry (IHC) or immunofluorescence (IF) staining of cartilage sections. IL-1β-induced DRP1 mRNA expression in chondrocytes was quantified by qPCR and protein expression by immunoblotting. Mitochondrial fragmentation in chondrocytes was visualized by MitoTracker staining or IF staining of mitochondrial marker proteins or by transient expression of mitoDsRed. Mitochondrial reactive oxygen species (ROS) levels were determined by MitoSOX staining. Apoptosis was determined by lactate dehydrogenase (LDH) release assay, Caspase 3/7 activity assay, propidium iodide (PI), and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining and IF staining of cleaved caspase 3. Cytochrome c release was determined by confocal microscopy. Surgical destabilization of the medial meniscus (DMM) was used to induce osteoarthritis (OA) in mice.

RESULTS

Expression of DRP1 and mitochondrial damage was high in human OA cartilage and in the joints of mice subjected to DMM surgery which also showed increased chondrocytes apoptosis. IL-1β-induced mitochondrial network fragmentation and chondrocyte apoptosis via modulation of DRP1 expression and activity and induce apoptosis via Bax-mediated release of Cytochrome c. Pharmacological inhibition of DRP1 activity by Mdivi-1 blocked IL-1β-induced mitochondrial damage and apoptosis in chondrocytes. Additionally, IL-1β-induced activation of extracellular signal-regulated kinase 1/2 (ERK1/2) is crucial for DRP1 activation and induction of mitochondrial network fragmentation in chondrocytes as these were blocked by inhibiting ERK1/2 activation.

CONCLUSIONS

These findings demonstrate that ERK1/2 is a critical player in DRP1-mediated induction of mitochondrial fission and apoptosis in IL-1β-stimulated chondrocytes.

Drug delivery approaches for HuR-targeted therapy for lung cancer

Lung cancer (LC) is often diagnosed at an advanced stage and conventional treatments for disease management have limitations associated with them. Novel therapeutic targets are thus avidly sought for the effective management of LC. RNA binding proteins (RBPs) have been convincingly established as key players in tumorigenesis, and their dysregulation is linked to multiple cancers, including LC. In this context, we review the role of Human antigen R (HuR), an RBP that is overexpressed in LC, and further associated with various aspects of LC tumor growth and response to therapy. Herein, we describe the role of HuR in LC progression and outline the evidences supporting various pharmacologic and biologic approaches for inhibiting HuR expression and function. These approaches, including use of small molecule inhibitors, siRNAs and shRNAs, have demonstrated favorable results in reducing tumor cell growth, invasion and migration, angiogenesis and metastasis. Hence, HuR has significant potential as a key therapeutic target in LC. Use of siRNA-based approaches, however, have certain limitations that prevent their maximal exploitation as cancer therapies. To address this, in the conclusion of this review, we provide a list of nanomedicine-based HuR targeting approaches currently being employed for siRNA and shRNA delivery, and provide a rationale for the immense potential therapeutic benefits offered by nanocarrier-based HuR targeting and its promise for treating patients with LC.

Oroxin B alleviates osteoarthritis through anti-inflammation and inhibition of PI3K/AKT/mTOR signaling pathway and enhancement of autophagy

BACKGROUND

Osteoarthritis (OA) is a common aging-related degenerative joint disease with chronic inflammation as its possible pathogenesis. Oroxin B (OB), a flavonoid isolated from traditional Chinese herbal medicine, possesses anti-inflammation properties which may be involved in regulating the pathogenesis of OA, but its mechanism has not been elucidated. Our study was the first to explore the potential chondroprotective effect and elucidate the underlying mechanism of OB in OA.

METHODS

In vitro, primary mice chondrocytes were stimulated with IL-1β along with or without the administration of OB or autophagy inhibitor 3-methyladenine (3-MA). Cell viability assay was measured with a cell counting kit-8 (CCK-8). The phenotypes of anabolic-related (Aggrecan and Collagen II), catabolic-related (MMP3, MMP13, and ADAMTS5), inflammation-related (iNOS, COX-2, TNF-α, IL-6, and IL-1β), and markers of related signaling pathways in chondrocytes with different treatment were detected through western blot, RT-qPCR, and immunofluorescent staining. In vivo, the destabilized medial meniscus (DMM) operation was performed to establish the OA mice model. After knee intra-articular injection with OB for 8 weeks, the mice's knee joints were obtained for subsequent histological staining and analysis.

RESULTS

OB reversed the expression level of anabolic-related proteins (Aggrecan and Collagen II) and catabolic-related (MMP3, MMP13, and ADAMTS5) in IL-1β-induced chondrocytes. Mechanistically, OB suppressed the inflammatory response stimulated by IL-1β, as the inflammation-related (iNOS, COX-2, TNF-α, IL-6, and IL-1β) markers were downregulated after the administration of OB in IL-1β-induced chondrocytes. Besides, the activation of PI3K/AKT/mTOR signaling pathway induced by IL-1β could be inhibited by OB. Additionally, the autophagy process impaired by IL-1β could be rescued by OB. What's more, the introduction of 3-MA to specifically inhibit the autophagic process impairs the protective effect of OB on cartilage. In vivo, histological staining revealed that intra-articular injection of OB attenuated the cartilage degradation, as well as reversed the expression level of anabolic and catabolic-related proteins such as Aggrecan, Collagen II, and MMP13 induced in DMM-induced OA models.

CONCLUSIONS

The study verified that OB exhibited the chondroprotective effect by anti-inflammatory, inhibiting the PI3K/AKT/mTOR signaling pathway, and enhancing the autophagy process, indicating that OB might be a promising agent for the treatment of OA.

HuR drives lung fibroblast differentiation but not metabolic reprogramming in response to TGF-β and hypoxia

Background

Pulmonary fibrosis is thought to be driven by recurrent alveolar epithelial injury which leads to the differentiation of fibroblasts into α-smooth muscle actin (α-SMA)-expressing myofibroblasts and subsequent deposition of extracellular matrix (ECM). Transforming growth factor beta-1 (TGF-β1) plays a key role in fibroblast differentiation, which we have recently shown involves human antigen R (HuR). HuR is an RNA binding protein that also increases the translation of hypoxia inducible factor (HIF-1α) mRNA, a transcription factor critical for inducing a metabolic shift from oxidative phosphorylation towards glycolysis. This metabolic shift may cause fibroblast differentiation. We hypothesized that under hypoxic conditions, HuR controls myofibroblast differentiation and glycolytic reprogramming in human lung fibroblasts (HLFs).

Methods

Primary HLFs were cultured in the presence (or absence) of TGF-β1 (5 ng/ml) under hypoxic (1% O₂) or normoxic (21% O₂) conditions. Evaluation included mRNA and protein expression of glycolytic and myofibroblast/ECM markers by qRT-PCR and western blot. Metabolic profiling was done by proton nuclear magnetic resonance (¹H- NMR). Separate experiments were conducted to evaluate the effect of HuR on metabolic reprogramming using siRNA-mediated knock-down.

Results

Hypoxia alone had no significant effect on fibroblast differentiation or metabolic reprogramming. While hypoxia- together with TGFβ1- increased mRNA levels of differentiation and glycolysis genes, such as ACTA2, LDHA, and HK2, protein levels of α-SMA and collagen 1 were significantly reduced. Hypoxia induced cytoplasmic translocation of HuR. Knockdown of HuR reduced features of fibroblast differentiation in response to TGF-β1 with and without hypoxia, including α-SMA and the ECM marker collagen I, but had no effect on lactate secretion.

Conclusions

Hypoxia reduced myofibroblasts differentiation and lactate secretion in conjunction with TGF-β. HuR is an important protein in the regulation of myofibroblast differentiation but does not control glycolysis in HLFs in response to hypoxia. More research is needed to understand the functional implications of HuR in IPF pathogenesis.

Aberrant Post-Transcriptional Regulation of Protein Expression in the Development of Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is an incurable and prevalent respiratory disorder that is characterized by chronic inflammation and emphysema. COPD is primarily caused by cigarette smoke (CS). CS alters numerous cellular processes, including the post-transcriptional regulation of mRNAs. The identification of RNA-binding proteins (RBPs), microRNAs (miRNAs), and long non-coding RNAs (lncRNAs) as main factors engaged in the regulation of RNA biology opens the door to understanding their role in coordinating physiological cellular processes. Dysregulation of post-transcriptional regulation by foreign particles in CS may lead to the development of diseases such as COPD. Here we review current knowledge about post-transcriptional events that may be involved in the pathogenesis of COPD.

A retrotransposon gag-like-3 gene RTL3 and SOX-9 co-regulate the expression of COL2A1 in chondrocytes

PURPOSE

Transposable elements are known to remodel gene structure and provide a known source of genetic variation. Retrotransposon gag-like-3 (RTL3) is a mammalian retrotransposon-derived transcript (MART) whose function in the skeletal tissue is unknown. This study aimed to elucidate the biological significance of RTL3 in chondrogenesis and type-II collagen (COL2A1) gene expression in chondrocytes.

MATERIALS AND METHODS

Expression of RTL3, SOX-9 and COL2A1 mRNAs was determined by TaqMan assays and the protein expression by immunoblotting. RTL3 and Sox-9 depletion in human chondrocytes was achieved using validated siRNAs. An RTL3 mutant (∆RTL3) lacking the zinc finger domain was created using in vitro mutagenesis. Forced expression of RTL3, ∆RTL3, and SOX-9 was achieved using CMV promoter containing expression plasmids. CRISPR-Cas9 was utilized to delete Rtl3 and create a stable ATDC5^Rlt3-/- cell line. Matrix deposition and Col2a1 quantification during chondrogenesis were determined by Alcian blue staining and Sircol™ Soluble Collagen Assay, respectively.

RESULTS

RTL3 is not ubiquitously expressed but showed strong expression in cartilage, chondrocytes and synoviocytes but not in muscle, brain, or other tissues analyzed. Loss-of-function and gain-of-function studies demonstrated a critical role of RTL3 in the regulation of SOX-9 and COL2A1 expression and matrix synthesis during chondrogenesis. Both RTL3 and SOX-9 displayed co-regulated expression in chondrocytes. Gene regulatory activity of RTL3 requires the c-terminal CCHC zinc-finger binding domain.

CONCLUSIONS

Our results identify a novel regulatory mechanism of COL2A1 expression in chondrocytes that may help to further understand the skeletal development and the pathogenesis of diseases with altered COL2A1 expression.

Genetic association scan of 32 osteoarthritis susceptibility genes identified TP63 associated with an endemic osteoarthritis, Kashin-Beck disease

BACKGROUND

Kashin-Beck disease (KBD) is an endemic chronic osteochondropathy. The clinical manifestations and radiographic features of adult KBD were similar to those of osteoarthritis (OA).

METHODS

We first performed a genetic association scan of 32 OA susceptibility genes with KBD in 898 Han Chinese subjects. The MassARRAY genotyping system (Agena) was used for SNP genotyping. PLINK 1.9 was used for quality control and association testing. Using articular cartilage specimens from 7 adult KBD patients and 4 control subjects, lentivirus-mediated RNA interference (RNAi), qRT-PCR, Western blot and immunohistochemistry were employed to explore the functional relevance of TP63 to KBD chondrocyte.

RESULTS

SNP genotyping and association analysis identified TP63 (rs12107036, P = 0.005, OR = 0.71) and OARD1 (rs11280, P = 0.004, OR = 1.51) were significantly associated with KBD. It was also found that TP63 was significantly up-regulated in KBD articular cartilage in both mRNA and protein level compared with the controls (P < 0.05). TP63 suppression by lentivirus-mediated RNAi notably decreased the abundance of Caspase3 and SOX9 in chondrocytes. Most importantly, compared with the scrambled sequence (shControl) group, the protein level of ACAN was increased in the shTP63 group. The mRNA expression of chondrocyte marker genes (COL2A1 and ACAN) was not significantly changed after TP63 knockdown relative to shControl group.

CONCLUSION

Our study identifies TP63 as a novel susceptibility gene for KBD, and demonstrates that the inhibition of TP63 suppresses chondrocyte apoptosis and partly facilitates chondrogenesis. The combination of SNP genotyping and molecular biology techniques provides a useful tool for understanding the biological mechanism and differential diagnosis studies of KBD and OA.

TDP-43 maintains chondrocyte homeostasis and alleviates cartilage degradation in osteoarthritis

OBJECTIVE

Osteoarthritis (OA) is the most prevalent age-related disorder due to cartilage degradation. Previous studies have identified aberrant chondrocyte homeostasis under extracellular stress as a key pathological mechanism behind cartilage degradation in OA. TDP-43, a DNA/RNA-binding protein has been demonstrated to participate in processing many extracellular stress responses; however, understanding of the role of TDP-43 in OA is limited. This study aims to investigate the role of TDP-43 in chondrocyte homeostasis and cartilage degradation in OA.

METHODS

The role of TDP-43 during degradation of cartilage is examined by experimental posttraumatic OA animal models and human cartilage specimens. Cartilage degradation is assessed by histological analysis, qPCR, and Western blot. The molecular mechanisms are investigated in vitro using human primary chondrocytes.

RESULTS

TDP-43 decreases significantly in degenerated cartilage. TDP-43 concentration is positively correlated with IL-1β concentration in synovial fluid derived from OA patients (Pearson r = 0.95, CI (95%) [0.80, 0.99], P < 0.0001). Intra-articular injection of recombinant TDP-43 significantly alleviates cartilage degradation and subchondral bone remodeling in vivo. In vitro mechanistic analyses show that TDP-43 maintains chondrocyte homeostasis under oxidative stress through regulating stress granule dynamics via G3BP1.

CONCLUSION

The present study indicates that TDP-43 maintains chondrocyte homeostasis under oxidative stress and alleviates cartilage degeneration in osteoarthritis, identifying TDP-43 as a potential target for the diagnosis and treatment of knee OA.

Primary Osteoarthritis Early Joint Degeneration Induced by Endoplasmic Reticulum Stress Is Mitigated by Resveratrol

Increasing numbers of people are living with osteoarthritis (OA) due to aging and obesity, creating an urgent need for effective treatment and preventions. Two top risk factors for OA, age and obesity, are associated with endoplasmic reticulum (ER) stress. The I-ERS mouse, an ER stress-driven model of primary OA, was developed to study the role of ER stress in primary OA susceptibility. The I-ERS mouse has the unique ability to induce ER stress in healthy adult articular chondrocytes and cartilage, driving joint degeneration that mimics early primary OA. In this study, ER stress-induced damage occurred gradually and stimulated joint degeneration with OA characteristics including increased matrix metalloproteinase activity, inflammation, senescence, chondrocyte death, decreased proteoglycans, autophagy block, and gait dysfunction. Consistent with human OA, intense exercise hastened and increased the level of ER stress-induced joint damage. Notably, loss of a critical ER stress response protein (CHOP) largely ameliorated ER stress-stimulated OA outcomes including preserving proteoglycan content, reducing inflammation, and relieving autophagy block. Resveratrol diminished ER stress-induced joint degeneration by decreasing CHOP, TNFα, IL-1β, MMP-13, pS6, number of TUNEL-positive chondrocytes, and senescence marker p16 INK4a. The finding, that a dietary supplement can prevent ER stressed-induced joint degeneration in mice, provides a preclinical foundation to potentially develop a prevention strategy for those at high risk to develop OA.

Stress granules safeguard against MAPK signaling hyperactivation by sequestering PKC/Pck2: new findings and perspectives

Stress granule (SG) assembly is a conserved cellular strategy that copes with stress-related damage and promotes cell survival. SGs form through a process of liquid-liquid phase separation. Cellular signaling also appears to employ SG assembly as a mechanism for controlling cell survival and cell death by spatial compartmentalization of signal-transducing factors. While several lines of evidence highlight the importance of SGs as signaling hubs, where protein components of signaling pathways can be temporarily sequestered, shielded from the cytoplasm, the regulation and physiological significance of SGs in this aspect remain largely obscure. A recent study of the heat-shock response in the fission yeast Schizosaaccharomyces pombe provides an unexpected answer to this question. Recently, we demonstrated that the PKC orthologue Pck2 in fission yeast translocates into SGs through phase separation in a PKC kinase activity-dependent manner upon high-heat stress (HHS). Importantly, the downstream MAPK Pmk1 promotes Pck2 recruitment into SGs, which intercepts MAPK hyperactivation and cell death, thus posing SGs as a negative feedback circuit in controlling MAPK signaling. Intriguingly, HHS, but not modest-heat stress targets Pck2 to SGs, independent of canonical SG machinery. Finally, cells fail to activate MAPK signaling when Pck2 is sequestrated into SGs. In this review, we will discuss how SGs have a role as signaling hubs beyond serving as a repository for non-translated mRNAs during acute stress.

Small Noncoding RNAs in Knee Osteoarthritis: The Role of MicroRNAs and tRNA-Derived Fragments

Knee osteoarthritis (OA) is a degenerative knee joint disease that results from the breakdown of joint cartilage and underlying bone, affecting about 3.3% of the world's population. As OA is a multifactorial disease, the underlying pathological process is closely associated with genetic changes in articular cartilage and bone. Many studies have focused on the role of small noncoding RNAs in OA and identified numbers of microRNAs that play important roles in regulating bone and cartilage homeostasis. The connection between other types of small noncoding RNAs, especially tRNA-derived fragments and knee osteoarthritis is still elusive. The observation that there is limited information about small RNAs different than miRNAs in knee OA was very surprising to us, especially given the fact that tRNA fragments are known to participate in a plethora of human diseases and a portion of them are even more abundant than miRNAs. Inspired by these findings, in this review we have summarized the possible involvement of microRNAs and tRNA-derived fragments in the pathology of knee osteoarthritis.

Xanthohumol Attenuated Inflammation and ECM Degradation by Mediating HO-1/C/EBPβ Pathway in Osteoarthritis Chondrocytes

Osteoarthritis (OA) is the most frequent and disabling disease in developed countries. The progressive degeneration of articular cartilage characterized as thinner and erosive. Inflammation is well-known to be involved in OA development. However, there are no effective therapeutic strategies to cure it. Xanthohumol (XH) is a natural prenylflavonoid isolated from hops and beer. The protective activity of XH against OA chondrocytes inflammation and ECM degradation is unclear. In this article, we found that XH significantly inhibited inflammatory responses, attenuated catabolic enzymes expression, and ameliorated ECM degradation, as showed by decreased production of NO, PGE2, TNFα, and IL-6, decreased expression of MMP-3/-13 and ADAMTS-4/-5, and increased expression of collagen-II and aggrecan. In addition, XH activated HO-1 signaling and attenuated IL-1β-induced C/EBPβ. XH promoted the interaction between HO-1 and C/EBPβ, inhibiting the nuclear translocation of C/EBPβ. HO-1 knockdown could abrogate the protective effects of XH in IL-1β-treated chondrocytes. Collectively, XH attenuated inflammatory responses and ECM degradation by mediating HO-1 and C/EBPβ signaling pathways in osteoarthritis chondrocytes.

Stress granules: regulators or by-products?

Cells have to deal with conditions that can cause damage to biomolecules and eventually cell death. To protect against these adverse conditions and promote recovery, cells undergo dramatic changes upon exposure to stress. This involves activation of signaling pathways, cell cycle arrest, translational reprogramming, and reorganization of the cytoplasm. Notably, many stress conditions cause a global inhibition of mRNA translation accompanied by the formation of cytoplasmic condensates called stress granules (SGs), which sequester mRNA together with RNA-binding proteins, translation initiation factors, and other components. SGs are highly conserved in eukaryotes, suggesting that they perform an important function during the stress response. Over the years, many different roles have been assigned to SGs, including translational control, mRNA storage, regulation of mRNA decay, antiviral innate immune response, and modulation of signaling pathways. Most of our understanding, however, has been deduced from correlative data based upon the composition of SGs and only recently have technological innovations allowed hypotheses for SG function to be directly tested. Here, we discuss these challenges and explore the evidence related to the function of SGs.

Lysosomal dysfunction in osteoarthritis and aged cartilage triggers apoptosis in chondrocytes through BAX mediated release of Cytochrome c

OBJECTIVE

Lysosomes are the major catabolic organelle of the cell and regulate the macromolecular and organelle turnover and programmed cell death. Here, we investigated the lysosome dysfunction in cartilage and its role in chondrocytes apoptosis and the associated mechanism.

DESIGN

Lysosomal acidification in Osteoarthritis (OA) and aged cartilage was determined by LysoSensor staining. Lysosomal function in chondrocytes was blocked by siRNA mediated depletion of Lysosomal Associated Membrane Protein 2 (LAMP2) or with lysosome inhibitors. Chondrocyte apoptosis was determined by LDH release, Caspase-3/7 activation, TUNEL and PI uptake assays. Loss of mitochondrial membrane potential (MMP/ΔΨM) and mitochondrial superoxide level was determined by JC-1 and MitoSOX staining, respectively. Colocalization of mitochondria with BCL2 associated X (BAX) and Cytochrome c was determined by immunostaining. Destabilization of medial meniscus (DMM) was performed to induce OA in mice.

RESULTS

Lysosomal acidification was found to be significantly decreased in aged mouse and human and mouse OA cartilage which also showed increased chondrocyte apoptosis. Inhibition of lysosomal function resulted in increased oxidative stress, accumulation of dysfunctional mitochondria and apoptosis in chondrocytes in monolayer and in cartilage explant cultures. Depletion of LAMP2 expression or treatment of chondrocytes with lysosomal function inhibitors increased the expression and mitochondrial translocation of BAX leading to Cytochrome c release. Lysosomal dysfunction-induced apoptosis in chondrocytes was not blocked by antioxidants MitoTempo or Diphenyleneiodonium (DPI) but was abrogated by inhibiting BAX.

CONCLUSION

Lysosomal dysfunction induce apoptosis in chondrocytes through BAX-mediated mitochondrial damage and release of Cytochrome c. Our data points to lysosomal function restoration and/or BAX inhibition in chondrocytes as a therapeutic approach for OA.

Mitochondrial dysfunction triggers a catabolic response in chondrocytes via ROS-mediated activation of the JNK/AP1 pathway

Mitochondrial function is impaired in osteoarthritis (OA) but its impact on cartilage catabolism is not fully understood. Here, we investigated the molecular mechanism of mitochondrial dysfunction-induced activation of the catabolic response in chondrocytes. Using cartilage slices from normal and OA cartilage, we showed that mitochondrial membrane potential was lower in OA cartilage, and that this was associated with increased production of mitochondrial superoxide and catabolic genes [interleukin 6 (IL-6), COX-2 (also known as PTGS2), MMP-3, -9, -13 and ADAMTS5]. Pharmacological induction of mitochondrial dysfunction in chondrocytes and cartilage explants using carbonyl cyanide 3-chlorophenylhydrazone increased mitochondrial superoxide production and the expression of IL-6, COX-2, MMP-3, -9, -13 and ADAMTS5, and cartilage matrix degradation. Mitochondrial dysfunction-induced expression of catabolic genes was dependent on the JNK (herein referring to the JNK family)/activator protein 1 (AP1) pathway but not the NFκB pathway. Scavenging of mitochondrial superoxide with MitoTEMPO, or pharmacological inhibition of JNK or cFos and cJun, blocked the mitochondrial dysfunction-induced expression of the catabolic genes in chondrocytes. We demonstrate here that mitochondrial dysfunction contributes to OA pathogenesis via JNK/AP1-mediated expression of catabolic genes. Our data shows that AP1 could be used as a therapeutic target for OA management.This article has an associated First Person interview with the first author of the paper.

Oxidative stress and inflammation in osteoarthritis pathogenesis: Role of polyphenols

Osteoarthritis (OA) is the most prevalent joint degenerative disease leading to irreversible structural and functional changes in the joint and is a major cause of disability and reduced life expectancy in ageing population. Despite the high prevalence of OA, there is no disease modifying drug available for the management of OA. Oxidative stress, a result of an imbalance between the production of reactive oxygen species (ROS) and their clearance by antioxidant defense system, is high in OA cartilage and is a major cause of chronic inflammation. Inflammatory mediators, such as interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) are highly upregulated in OA joints and induce ROS production and expression of matrix degrading proteases leading to cartilage extracellular matrix degradation and joint dysfunction. ROS and inflammation are interdependent, each being the target of other and represent ideal target/s for the treatment of OA. Plant polyphenols possess potent antioxidant and anti-inflammatory properties and can inhibit ROS production and inflammation in chondrocytes, cartilage explants and in animal models of OA. The aim of this review is to discuss the chondroprotective effects of polyphenols and modulation of different molecular pathways associated with OA pathogenesis and limitations and future prospects of polyphenols in OA treatment.

tRNA-derived fragments (tRFs) regulate post-transcriptional gene expression via AGO-dependent mechanism in IL-1β stimulated chondrocytes

OBJECTIVES

Recent studies have shown that tRNA-derived RNA fragments (tRFs) are novel regulators of post-transcriptional gene expression. However, the expression profiles and their role in post-transcriptional gene regulation in chondrocytes is unknown. Here, we determined tRFs expression profile and explored tRF-3003a role in post-transcriptional gene regulation in IL-1β stimulated chondrocytes.

METHODS

We used qPCR arrays to determine tRNAs and tRFs expression in age- and sex-matched primary human OA chondrocytes and TC28/I2 cells stimulated with IL-1β. Chondrocytes were transfected with tRNA-Cys^GCA overexpression plasmid or tRF-3003a mimic and 3'UTR luciferase reporter plasmids of mRNAs harboring predicted tRF target "seed sequence". The AGO-RNA-induced silencing complex (AGO-RISC)-dependent repressive activity of tRF-3003a was determined by siRNA-mediated knockdown of AGO2.

RESULTS

IL-1β increased the expression levels of specific tRNAs and of tRF-3003a, a type 3 tRF produced by the cleavage of tRNA-Cys^GCA. tRF-3003a "seed sequence" was identified in the 3'UTR of JAK3 mRNA and tRNA-Cys^GCA overexpression or transfection of a tRF-3003a mimic in chondrocytes downregulated JAK3 expression and significantly reduced the activity of the 3'UTR reporter. RIP assay showed enrichment of tRF-3003a into AGO2/RISC in IL-1β treated chondrocytes. The suppressive effect of tRF-3003a on JAK3 3'UTR reporter was abrogated with siRNA-mediated depletion of AGO2.

CONCLUSIONS

We demonstrate that under pathological conditions chondrocytes display perturbations in the expression profile of specific tRNAs and tRFs. Furthermore, a specific tRF namely tRF-3003a can post-transcriptionally regulate JAK3 expression via AGO/RISC formation in chondrocytes. Identification of this novel mechanism may be of value in the design of precision therapies for OA.

Aminoguanidine inhibits IL-1β-induced protein expression of iNOS and COX-2 by blocking the NF-κB signaling pathway in rat articular chondrocytes

Osteoarthritis is a chronic joint disease which has a serious impact on the health and quality of life of affected humans and animals. As an inhibitor of inducible nitric oxide synthase (iNOS), aminoguanidine (AG) displays anti-inflammatory effects. The purpose of the present study was to investigate the effect of AG on the expression of iNOS and cyclooxygenase-2 (COX-2), and the activity of the NF-κB signaling pathway in rat chondrocytes stimulated by interleukin-1β (IL-1β). The viability of chondrocytes treated with AG (0.3, 1 or 3 mM) alone was determined using a Cell Counting Kit-8 assay. Subsequently, the chondrocytes were treated with either 10 ng/ml IL-1β alone, or co-treated with increasing concentrations of AG (0.3, 1 or 3 mM) and 10 ng/ml IL-1β. The protein levels of COX-2, iNOS, phosphorylated (p)-p65, p65, p-NF-κβ inhibitor α (IκBα), IκBα, p-inhibitor of NF-κβ-β (IKKβ) and IKKβ were evaluated by western blotting. NF-κB translocation was determined by immunofluorescence analysis. Western blotting and reverse transcription-quantitative PCR were used to detect expression levels of relevant proteins/genes. The results suggested that the inhibitory effect of AG on the protein and gene expression levels of iNOS and COX-2 in IL-1β-treated chondrocytes was dose-dependent. In addition, AG decreased the level of phosphorylation of IKKβ, IκBα and NF-κB p65, the degradation of IKKβ, IκBα and p65, and the translocation of NF-κB in IL-1β-stimulated chondrocytes. The most significant inhibitory effect of AG was observed at a concentration of 1 mM. Therefore, the present study suggested that AG may serve as a potential agent to reduce the inflammatory response of chondrocytes stimulated by IL-1β.

Imperatorin suppresses IL-1β-induced iNOS expression via inhibiting ERK-MAPK/AP1 signaling in primary human OA chondrocytes

Joint inflammation is a key player in the pathogenesis of osteoarthritis (OA). Imperatorin, a plant-derived small molecule has been reported to have anti-inflammatory properties; however, its effect on chondrocytes is not known. Here, we investigated the effects of Imperatorin on interleukin-1β (IL-1β) induced expression of inducible nitric oxide synthase (iNOS) and nitric oxide production in primary human OA chondrocytes and cartilage explants culture under pathological conditions and explored the associated signaling pathways. We pretreated chondrocytes or explants with Imperatorin (50 μM) followed by IL-1β (1 ng/ml), and the culture supernatant was used to determine the levels of nitrite production by Griess assay and chondrocytes were harvested to prepare cell lysate or RNA for gene expression analysis of iNOS by Western blot or qPCR and in explants by immunohistochemistry (IHC). Pretreatment of primary chondrocytes and cartilage explants with Imperatorin suppressed IL-1β induced expression of iNOS and NO production. Imperatorin blocked the IL-1β-induced phosphorylation of ERK-MAPK/AP1 signaling pathway to suppress iNOS expression. The role of ERK in the regulation of iNOS expression was verified by using ERK inhibitor. Interestingly, we also found that Imperatorin binds to iNOS protein and inhibits its activity in vitro. Our data demonstrated that Imperatorin possess strong anti-inflammatory activity and may be developed as a therapeutic agent for the management of OA.

Theobromine mitigates IL-1β-induced oxidative stress, inflammatory response, and degradation of type II collagen in human chondrocytes

Osteoarthritis is one of the major causes of disability in elderly adults. Chondrocytes are responsible for the formation and remodeling of articular cartilage in joint tissue. The dysfunction of chondrocytes is a significant factor in the development of osteoarthritis. In the current study, we found that theobromine, a constituent of the cacao plant, possesses a preventive effect against interleukin (IL)-1β-induced chondrocyte dysfunction. Theobromine ameliorates IL-1β-induced production of cellular reactive oxygen species (ROS) and inflammatory mediators including cyclooxygenase-2 (COX-2) and prostaglandin E2 (PGE2). The presence of theobromine suppresses IL-1β-induced inducible nitro oxide synthase (iNOS) expression and cellular nitro oxide (NO) production. Theobromine also suppresses IL-1β-induced production of the pro-inflammatory cytokines tumor necrosis factor-α (TNF-α) and monocyte chemoattractant protein-1 (MCP-1), as well as matrix metalloproteinases (MMP)-3 and MMP-13. Additionally, theobromine mitigates IL-1β-induced type II collagen degradation. Mechanistically, we show that theobromine inhibits IL-1β-induced IκBα activation, nuclear factor-κB (NF-κB) protein p65 accumulation, and transfected NF-κB promoter activity, indicating that theobromine suppresses the NF-κB pathway in chondrocytes. Collectively, our study demonstrates that the natural molecule theobromine has a protective effect to counter cytokine-induced chondrocyte dysfunction, implying its beneficial effect in the prevention of osteoarthritis.

Regulation of Stress Granule Formation by Inflammation, Vascular Injury, and Atherosclerosis

OBJECTIVE

Stress granules (SGs) are dynamic cytoplasmic aggregates containing mRNA, RNA-binding proteins, and translation factors that form in response to cellular stress. SGs have been shown to contribute to the pathogenesis of several human diseases, but their role in vascular diseases is unknown. This study shows that SGs accumulate in vascular smooth muscle cells (VSMCs) and macrophages during atherosclerosis. Approach and Results: Immunohistochemical analysis of atherosclerotic plaques from LDLR^-/- mice revealed an increase in the stress granule-specific markers Ras-G3BP1 (GTPase-activating protein SH3 domain-binding protein) and PABP (poly-A-binding protein) in intimal macrophages and smooth muscle cells that correlated with disease progression. In vitro, PABP+ and G3BP1+ SGs were rapidly induced in VSMC and bone marrow-derived macrophages in response to atherosclerotic stimuli, including oxidized low-density lipoprotein and mediators of mitochondrial or oxidative stress. We observed an increase in eIF2α (eukaryotic translation initiation factor 2-alpha) phosphorylation, a requisite for stress granule formation, in cells exposed to these stimuli. Interestingly, SG formation, PABP expression, and eIF2α phosphorylation in VSMCs is reversed by treatment with the anti-inflammatory cytokine interleukin-19. Microtubule inhibitors reduced stress granule accumulation in VSMC, suggesting cytoskeletal regulation of stress granule formation. SG formation in VSMCs was also observed in other vascular disease pathologies, including vascular restenosis. Reduction of SG component G3BP1 by siRNA significantly altered expression profiles of inflammatory, apoptotic, and proliferative genes.

CONCLUSIONS

These results indicate that SG formation is a common feature of the vascular response to injury and disease, and that modification of inflammation reduces stress granule formation in VSMC.

Genetic Inactivation of ZCCHC6 Suppresses Interleukin-6 Expression and Reduces the Severity of Experimental Osteoarthritis in Mice

OBJECTIVE

Cytokine expression is tightly regulated posttranscriptionally, but high levels of interleukin-6 (IL-6) in patients with osteoarthritis (OA) indicate that regulatory mechanisms are disrupted in this disorder. The enzyme ZCCHC6 (zinc-finger CCHC domain-containing protein 6; TUT-7) has been implicated in posttranscriptional regulation of inflammatory cytokine expression, but its role in OA pathogenesis is unknown. The present study was undertaken to investigate whether ZCCHC6 directs the expression of IL-6 and influences OA pathogenesis in vivo.

METHODS

Human and mouse chondrocytes were stimulated with recombinant IL-1β. Expression of ZCCHC6 in human chondrocytes was knocked down using small interfering RNAs. IL-6 transcript stability was determined by actinomycin D chase, and 3'-uridylation of microRNAs was determined by deep sequencing. Zcchc6^-/- mice were produced by gene targeting. OA was surgically induced in the knee joints of mice, and disease severity was scored using a semiquantitative grading system.

RESULTS

ZCCHC6 was markedly up-regulated in damaged cartilage from human OA patients and from wild-type mice with surgically induced OA. Overexpression of ZCCHC6 induced the expression of IL-6, and its knockdown reduced IL-6 transcript stability and IL-1β-induced IL-6 expression in chondrocytes. Reintroduction of Zcchc6 in Zcchc6^-/- mouse chondrocytes rescued the IL-1β-induced IL-6 expression. Knockdown of ZCCHC6 reduced the population of micro-RNA 26b (miR-26b) with 3'-uridylation by 60%. Zcchc6^-/- mice with surgically induced OA produced low levels of IL-6 and exhibited reduced cartilage damage and synovitis in the joints.

CONCLUSION

These findings indicate that ZCCHC6 enhances IL-6 expression in chondrocytes through transcript stabilization and by uridylating miR-26b, which abrogates repression of IL-6. Inhibition of IL-6 expression and significantly reduced OA severity in Zcchc6^-/- mice identify ZCCHC6 as a novel therapeutic target to inhibit disease pathogenesis.

15-Deoxy-Δ12,14-prostaglandin J2 promotes phosphorylation of eukaryotic initiation factor 2α and activates the integrated stress response

Stress granules (SGs) are cytoplasmic RNA–protein aggregates formed in response to inhibition of translation initiation. SGs contribute to the stress response and are implicated in a variety of diseases, including cancer and some forms of neurodegeneration. Neurodegenerative diseases often involve chronic phosphorylation of eukaryotic initiation factor 2α (eIF2α), with deletions of eIF2α kinases or treatment with eIF2α kinase inhibitors being protective in some animal models of disease. However, how and why the integrated stress response (ISR) is activated in different forms of neurodegeneration remains unclear. Because neuroinflammation is common to many neurodegenerative diseases, we hypothesized that inflammatory factors contribute to ISR activation in a cell-nonautonomous manner. Using fluorescence microscopy and immunoblotting, we show here that the endogenously produced product of inflammation, 15-deoxy-Δ^12,14-prostaglandin J2 (15-d-PGJ2), triggers eIF2α phosphorylation, thereby activating the ISR, repressing bulk translation, and triggering SG formation. Our findings define a mechanism by which inflammation activates the ISR in a cell-nonautonomous manner and suggest that inhibition of 15-d-PGJ2 production might be a useful therapeutic strategy in some neuroinflammatory contexts.

Salidroside attenuates interleukin-1β-induced inflammation in human osteoarthritis chondrocytes

Salidroside, a bioactive constituent isolated from Rhodiola rosea, has been reported to have anti-inflammatory effects. However, the effects of salidroside on interleukin (IL)-1β-stimulated osteoarthritis (OA) chondrocytes remain to be elucidated. Thus, this study aimed to evaluate the anti-inflammatory effects of salidroside on IL-1β-stimulated human OA chondrocytes and explore its underlying mechanisms. Our results showed that salidroside significantly inhibited the production of nitric oxide and prostaglandin E-2, as well as suppressed the expression of inducible nitric oxide synthase and cyclooxygenase-2 in IL-1β-stimulated chondrocytes ( P < .05). In addition, salidroside also suppressed IL-1β-induced matrix metalloproteinases production in human OA chondrocytes ( P < .05). Furthermore, pretreatment with salidroside prevented IL-1β-induced NF-κB activation in OA chondrocytes ( P < .05). In conclusion, the current study demonstrated that salidroside inhibited the IL-1β-induced inflammatory response in OA chondrocytes via inhibition of NF-κB activation.

Potential antitumor activity of nonsteroidal anti-inflammatory drugs against Ehrlich ascites carcinoma in experimental animals

OBJECTIVES

Although there is evidence that nonsteroidal anti-inflammatory drugs (NSAID) (e.g., celecoxib [Cxb]) can reduce the occurrence of cancer, the precise mechanism remains under study. The current study aimed to investigate the possible antitumor activity of a selective cyclooxygenase-2 inhibitor on solid tumors, its effect on antioxidant status, and ability to prevent angiogenesis.

MATERIALS AND METHODS

Solid carcinomas were induced in female Swiss albino mice. Fifty adult female mice were randomly selected and categorized into five groups. The effects of Cxb on hepatic oxidative parameters and the serum level of vascular endothelial growth factors (VEGF) were investigated in parallel to liver histopathological examinations. Biochemical measurements of hepatic malondialdehyde, superoxide dismutase (SOD) activity, hepatic catalase (CAT) activity, and reduced glutathione (GSH) were estimated in liver homogenates prepared from mice in each study group.

RESULTS

The induction of solid tumors in female albino mice was associated with a significant elevation in hepatic lipid peroxidation, whereas the activity of antioxidant enzyme NSAID and CAT was significantly decreased. The level of reduced GSH was decreased. Serum levels of VEGF were significantly increased in tumor-bearing mice compared with normal control mice. These changes were ameliorated when mice were treated with Cxb either before or after the induction of tumors. Antioxidant enzymes were significantly increased, and the serum level of VEGF was significantly reduced compared with the levels in tumor-bearing mice.

CONCLUSION

Cxb exerts antitumor activity through antioxidative and antiangiogenic activities.

Parkin clearance of dysfunctional mitochondria regulates ROS levels and increases survival of human chondrocytes

OBJECTIVE

Mitochondrial dysfunction, oxidative stress and chondrocyte death are important contributors to the development and pathogenesis of osteoarthritis (OA). In this study, we determined the expression and role of Parkin in the clearance of damaged/dysfunctional mitochondria, regulation of reactive oxygen species (ROS) levels and chondrocyte survival under pathological conditions.

METHODS

Human chondrocytes were from the unaffected area of knee OA cartilage (n = 12) and were stimulated with IL-1β to mimic pathological conditions. Mitochondrial membrane depolarization and ROS levels were determined using specific dyes and flow cytometry. Autophagy was determined by Western blotting for ATG5, Beclin1, immunofluorescence staining and confocal microscopy. Gene expression was determined by RT-qPCR. siRNA, wild-type and mutant Parkin plasmids were transfected using Amaxa system. Apoptosis was determined by PI staining of chondrocytes and TUNEL assay.

RESULTS

IL-1β-stimulated OA chondrocytes showed high levels of ROS generation, mitochondrial membrane damage, accumulation of damaged mitochondria and higher incidence of apoptosis. IL-1β stimulation of chondrocytes with depleted Parkin expression resulted in sustained high levels of ROS, accumulation of damaged/dysfunctional mitochondria and enhanced apoptosis. Parkin translocation to depolarized/damaged mitochondria and recruitment of p62/SQSTM1 was required for the elimination of damaged/dysfunctional mitochondria in IL-1β-stimulated OA chondrocytes. Importantly we demonstrate that Parkin elimination of depolarized/damaged mitochondria required the Parkin ubiquitin ligase activity and resulted in reduced ROS levels and inhibition of apoptosis in OA chondrocytes under pathological conditions.

CONCLUSIONS

Our data demonstrates that Parkin functions to eliminate depolarized/damaged mitochondria in chondrocytes which is necessary for mitochondrial quality control, regulation of ROS levels and chondrocyte survival under pathological conditions.

The Role of RNA in Biological Phase Separations

Phase transitions that alter the physical state of ribonucleoprotein particles contribute to the spacial and temporal organization of the densely packed intracellular environment. This allows cells to organize biologically coupled processes as well as respond to environmental stimuli. RNA plays a key role in phase separation events that modulate various aspects of RNA metabolism. Here, we review the role that RNA plays in ribonucleoprotein phase separations.

Comparative Immune- and Stress-Related Transcript Response Induced by Air Exposure and Vibrio anguillarum Bacterin in Rainbow Trout (Oncorhynchus mykiss) and Gilthead Seabream (Sparus aurata) Mucosal Surfaces

Fish have to face various environmental challenges that may compromise the efficacy of the immune response in mucosal surfaces. Since the effect of acute stress on mucosal barriers in fish has still not been fully elucidated, we aimed to compare the short-term mucosal stress and immune transcriptomic responses in a freshwater (rainbow trout, Oncorhynchus mykiss) and a marine fish (gilthead seabream, Sparus aurata) to bacterial immersion (Vibrio anguillarum bacterin vaccine) and air exposure stress in skin, gills, and intestine. Air exposure and combined (vaccine + air) stressors exposure were found to be inducers of the cortisol secretion in plasma and skin mucus on both species in a time-dependent manner, while V. anguillarum bacterin exposure induced cortisol release in trout skin mucus only. This was coincident with a marked differential increase in transcriptomic patterns of stress- and immune-related gene expression profiles. Particularly in seabream skin, the expression of cytokines was markedly enhanced, whereas in gills the response was mainly suppressed. In rainbow trout gut, both air exposure and vaccine stimulated the transcriptomic response, whereas in seabream, stress and immune responses were mainly induced by air exposure. Therefore, our comparative survey on the transcriptomic mucosal responses demonstrates that skin and gut were generally more reactive in both species. However, the upregulation of immune transcripts was more pronounced in gills and gut of vaccinated trout, whereas seabream appeared to be more stress-prone and less responsive to V. anguillarum bacterin in gills and gut. When fish were subjected to both treatments no definite pattern was observed. Overall, the results indicate that (1) the immune response was not homogeneous among mucosae (2), it was greatly influenced by the specific traits of each stressor in each surface and (3) was highly species-specific, probably as a result of the adaptive life story of each species to the microbial load and environmental characteristics of their respective natural habitats.

Suberanilohydroxamic acid prevents TGF-β1-induced COX-2 repression in human lung fibroblasts post-transcriptionally by TIA-1 downregulation

Cyclooxygenase-2 (COX-2), with its main antifibrotic metabolite PGE₂, is regarded as an antifibrotic gene. Repressed COX-2 expression and deficient PGE₂ have been shown to contribute to the activation of lung fibroblasts and excessive deposition of collagen in pulmonary fibrosis. We have previously demonstrated that COX-2 expression in lung fibroblasts from patients with idiopathic pulmonary fibrosis (IPF) is epigenetically silenced and can be restored by epigenetic inhibitors. This study aimed to investigate whether COX-2 downregulation induced by the profibrotic cytokine transforming growth factor-β1 (TGF-β1) in normal lung fibroblasts could be prevented by epigenetic inhibitors. We found that COX-2 protein expression and PGE₂ production were markedly reduced by TGF-β1 and this was prevented by the pan-histone deacetylase inhibitor suberanilohydroxamic acid (SAHA) and to a lesser extent by the DNA demethylating agent Decitabine (DAC), but not by the G9a histone methyltransferase (HMT) inhibitor BIX01294 or the EZH2 HMT inhibitor 3-deazaneplanocin A (DZNep). However, chromatin immunoprecipitation assay revealed that the effect of SAHA was unlikely mediated by histone modifications. Instead 3′-untranslated region (3′-UTR) luciferase reporter assay indicated the involvement of post-transcriptional mechanisms. This was supported by the downregulation by SAHA of the 3′-UTR mRNA binding protein TIA-1 (T-cell intracellular antigen-1), a negative regulator of COX-2 translation. Furthermore, TIA-1 knockdown by siRNA mimicked the effect of SAHA on COX-2 expression. These findings suggest SAHA can prevent TGF-β1-induced COX-2 repression in lung fibroblasts post-transcriptionally through a novel TIA-1-dependent mechanism and provide new insights into the mechanisms underlying its potential antifibrotic activity.

Abbreviations

Unlabelled Table

SAHA	suberanilohydroxamic acid
TGF-β1	transforming growth factor-β1
COX-2	cyclooxygenase-2
TIA-1	T-cell intracellular antigen-1
PGE2	prostaglandin E2
IPF	idiopathic pulmonary fibrosis
DAC	Decitabine
HMT	histone methyltransferase
EZH2	enhancer of zeste homolog 2
DZNep	3-deazaneplanocin A
3′-UTR	3′-untranslated region
α-SMA	α-smooth muscle actin
ECM	extracellular matrix
COL1	collagen 1
DNMT	DNA methyltransferase
HAT	histone acetyltransferase
HDAC	histone deacetylase
H3K9me3	histone H3 lysine 9 trimethylation
ARE	AUUUA-rich element
HuR	human antigen R
ELAV1	ELAV-like RNA binding protein 1
TTP	Tristetraprolin
CUGBP2	CUG triplet repeat, RNA binding protein 2
F-NL	fibroblast from non-fibrotic lung
FCS	fetal calf serum

•

The HDAC inhibitor SAHA upregulates the expression of the antifibrotic gene COX-2 post-transcriptionally.

•

The mechanism relies on the downregulation of TIA-1, a negative regulator of COX-2 translation.

•

SAHA has a therapeutic potential by preventing COX-2 repression induced by TGF-β1 in human lung fibroblasts.