Role of Sp1 transcription factor in Interleukin-1-induced ADAMTS-4 (aggrecanase-1) gene expression in human articular chondrocytes

Identification and validation of hub genes and pathways associated with mitochondrial dysfunction in hypertrophy of ligamentum flavum

Background: Lumbar spinal stenosis which can lead to irreversible neurologic damage and functional disability, is characterized by hypertrophy of ligamentum flavum (HLF). Recent studies have indicated that mitochondrial dysfunction may contribute to the development of HLF. However, the underlying mechanism is still unclear. Methods: The dataset GSE113212 was obtained from the Gene Expression Omnibus database, and the differentially expressed genes were identified. The intersection of DEGs and mitochondrial dysfunction-related genes were identified as mitochondrial dysfunction-related DEGs. Gene Ontology analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, and Gene Set Enrichment Analysis were performed. Protein-protein interaction network was constructed, and miRNAs and transcriptional factors of the hub genes were predicted via the miRNet database. Small molecule drugs targeted to these hub genes were predicted via PubChem. Immune infiltration analysis was performed to evaluate the infiltration level of immune cells and their correlation with the hub genes. In final, we measured the mitochondrial function and oxidative stress in vitro and verified the expression of hub genes by qPCR experiments. Results: In total, 43 genes were identified as MDRDEGs. These genes were mainly involved in cellular oxidation, catabolic processes, and the integrity of mitochondrial structure and function. The top hub genes were screened, including LONP1, TK2, SCO2, DBT, TFAM, MFN2. The most significant enriched pathways include cytokine-cytokine receptor interaction, focal adhesion, etc. Besides, SP1, PPARGC1A, YY1, MYC, PPARG, and STAT1 were predicted transcriptional factors of these hub genes. Additionally, increased immune infiltration was demonstrated in HLF, with a close correlation between hub genes and immune cells found. The mitochondrial dysfunction and the expression of hub genes were validated by evaluation of mitochondrial DNA, oxidative stress markers and quantitative real-time PCR. Conclusion: This study applied the integrative bioinformatics analysis and revealed the mitochondrial dysfunction-related key genes, regulatory pathways, TFs, miRNAs, and small molecules underlying the development of HLF, which improved the understanding of molecular mechanisms and the development of novel therapeutic targets for HLF.

Noggin Inhibits IL-1β and BMP-2 Expression, and Attenuates Cartilage Degeneration and Subchondral Bone Destruction in Experimental Osteoarthritis

Osteoarthritis (OA) is a chronic inflammatory and progressive joint disease that results in cartilage degradation and subchondral bone remodeling. The proinflammatory cytokine interleukin 1 beta (IL-1β) is abundantly expressed in OA and plays a crucial role in cartilage remodeling, although its role in the activity of chondrocytes in cartilage and subchondral remodeling remains unclear. In this study, stimulating chondrogenic ATDC5 cells with IL-1β increased the levels of bone morphogenetic protein 2 (BMP-2), promoted articular cartilage degradation, and enhanced structural remodeling. Immunohistochemistry staining and microcomputed tomography imaging of the subchondral trabecular bone region in the experimental OA rat model revealed that the OA disease promotes levels of IL-1β, BMP-2, and matrix metalloproteinase 13 (MMP-13) expression in the articular cartilage and enhances subchondral bone remodeling. The intra-articular injection of Noggin protein (a BMP-2 inhibitor) attenuated subchondral bone remodeling and disease progression in OA rats. We also found that IL-1β increased BMP-2 expression by activating the mitogen-activated protein kinase (MEK), extracellular signal-regulated kinase (ERK), and specificity protein 1 (Sp1) signaling pathways. We conclude that IL-1β promotes BMP-2 expression in chondrocytes via the MEK/ERK/Sp1 signaling pathways. The administration of Noggin protein reduces the expression of IL-1β and BMP-2, which prevents cartilage degeneration and OA development.

The Transcription Factor-microRNA Regulatory Network during hESC-chondrogenesis

Human embryonic stem cells (ESCs) offer a promising therapeutic approach for osteoarthritis (OA). The unlimited source of cells capable of differentiating to chondrocytes has potential for repairing damaged cartilage or to generate disease models via gene editing. However their use is limited by the efficiency of chondrogenic differentiation. An improved understanding of the transcriptional and post-transcriptional regulation of chondrogenesis will enable us to improve hESC chondrogenic differentiation protocols. Small RNA-seq and whole transcriptome sequencing was performed on distinct stages of hESC-directed chondrogenesis. This revealed significant changes in the expression of several microRNAs including upregulation of known cartilage associated microRNAs and those transcribed from the Hox complexes, and the downregulation of pluripotency associated microRNAs. Integration of miRomes and transcriptomes generated during hESC-directed chondrogenesis identified key functionally related clusters of co-expressed microRNAs and protein coding genes, associated with pluripotency, primitive streak, limb development and extracellular matrix. Analysis identified regulators of hESC-directed chondrogenesis such as miR-29c-3p with 10 of its established targets identified as co-regulated 'ECM organisation' genes and miR-22-3p which is highly co-expressed with ECM genes and may regulate these genes indirectly by targeting the chondrogenic regulators SP1 and HDAC4. We identified several upregulated transcription factors including HOXA9/A10/D13 involved in limb patterning and RELA, JUN and NFAT5, which have targets enriched with ECM associated genes. We have developed an unbiased approach for integrating transcriptome and miRome using protein-protein interactions, transcription factor regulation and miRNA target interactions and identified key regulatory networks prominent in hESC chondrogenesis.

Fibronectin fragment inhibits xylosyltransferase-1 expression by regulating Sp1/Sp3- dependent transcription in articular chondrocytes

OBJECTIVE

We investigated the effects of 29-kDa amino-terminal fibronectin fragment (29-kDa FN-f) on xylosyltransferase-1 (XT-1), an essential anabolic enzyme that catalyzes the initial and rate-determining step in glycosaminoglycan chain synthesis, in human primary chondrocytes.

METHODS

Proteoglycan and XT-1 expression in cartilage tissue was analyzed using safranin O staining and immunohistochemistry. The effects of 29-kDa FN-f on XT-1 expression and its relevant signaling pathway were analyzed by quantitative real-time-PCR, immunoblotting, chromatin immunoprecipitation, and immunoprecipitation assays. The receptors for 29-kDa FN-f were investigated using small interference RNA and blocking antibodies.

RESULTS

The expression of XT-1 was significantly lower in human osteoarthritis cartilage than in normal cartilage. Intra-articular injection of 29-kDa FN-f reduced proteoglycan levels and XT-1 expression in murine cartilage. In addition, in 29-kDa FN-f-treated cells, XT-1 expression was significantly suppressed at both the mRNA and protein levels, modulated by the transcription factors specificity protein 1 (Sp1), Sp3, and activator protein 1 (AP-1). The 29-kDa FN-f suppressed the binding of Sp1 to the promoter region of XT-1 and enhanced the binding of Sp3 and AP-1. Inhibition of mitogen-activated protein kinase and nuclear factor kappa B signaling pathways restored the 29-kDa FN-f-inhibited XT-1 expression, along with the altered expression of Sp1 and Sp3. Blockading toll-like receptor 2 (TLR-2) and integrin α5β1 via siRNA and blocking antibodies revealed that the effects of 29-kDa FN-f on XT-1 expression were mediated through the TLR-2 and integrin α5β1 signaling pathways.

CONCLUSION

These results demonstrate that 29-kDa FN-f negatively affects cartilage anabolism by regulating glycosaminoglycan formation through XT-1.

SP1-mediated downregulation of ADAMTS3 gene expression in osteosarcoma models

ADAMTS3 is a member of procollagen N-proteinase subfamily of ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) gene family. It has an important function in the procollagen maturation process. The removal of N-peptidases is required for the accurate processing of fibrillar collagens. Otherwise, several disorders can occur that is related with the collagenous tissues. ADAMTS3 mainly maturates type II collagen molecule which is the main component of the bone and cartilage. There are several expression studies about ADAMTS3 gene however its transcriptional regulation has not been lightened up, yet. Here we first time cloned and functionally analyzed the promoter region of ADAMTS3 gene, approximately 1380 bp upstream of the transcription start site. Transient transfection experiments showed that all truncated promoter constructs are active and 171 bp fragment is sufficient to activate gene expression in both Saos-2 and MG63 cells. In silico analysis showed that ADAMTS3 has a TATA-less promoter and contains several SP1/GC box binding motifs and a CpG island. Therefore we mainly investigated the SP1 dependent regulation of ADAMTS3 promoter. SP1 downregulated ADAMTS3 transcriptional activity. As consistent with the transcriptional activity, mRNA, and protein expression levels were also decreased by SP1. On the other hand, functional binding of the SP1 on multiple regions of ADAMTS3 promoter was confirmed by EMSA studies. As ADAMTS3 is responsible for the collagen maturation and biosynthesis, further we investigated the effect of SP1 on type I-II and III collagen gene expressions. We point out that SP1 increased type II and III collagen expression and in contrast decreased type I collagen expression levels in Saos-2 cells. mRNA expression level was decreased for all collagen types in MG63 model. Decrease in the type II collagen expression was also demonstrated at the protein level by SP1. Collectively these results provide first findings for the SP1-related transcriptional regulation of ADAMTS3 and collagen genes in osteosarcoma cell lines.

Mithramycin A Alleviates Osteoarthritic Cartilage Destruction by Inhibiting HIF-2α Expression

Osteoarthritis (OA) is the most common and increasing joint disease worldwide. Current treatment for OA is limited to control of symptoms. The purpose of this study was to determine the effect of specificity protein 1 (SP1) inhibitor Mithramycin A (MitA) on chondrocyte catabolism and OA pathogenesis and to explore the underlying molecular mechanisms involving SP1 and other key factors that are critical for OA. Here, we show that MitA markedly inhibited expressions of matrix-degrading enzymes induced by pro-inflammatory cytokine interleukin-1β (IL-1β) in mouse primary chondrocytes. Intra-articular injection of MitA into mouse knee joint alleviated OA cartilage destruction induced by surgical destabilization of the medial meniscus (DMM). However, modulation of SP1 level in chondrocyte and mouse cartilage did not alter catabolic gene expression or cartilage integrity, respectively. Instead, MitA significantly impaired the expression of HIF-2α known to be critical for OA pathogenesis. Such reduction in expression of HIF-2α by MitA was caused by inhibition of NF-κB activation, at least in part. These results suggest that MitA can alleviate OA pathogenesis by suppressing NF-κB-HIF-2α pathway, thus providing insight into therapeutic strategy for OA.

Effects of sesamin on chondroitin sulfate proteoglycan synthesis induced by interleukin-1beta in human chondrocytes

Background

Numerous studies have reported on the health benefits of sesamin, a major lignin found in sesame (S. indicum) seeds. Recently, sesamin was shown to have the ability to promote chondroitin sulfate proteoglycan synthesis in normal human chondrocytes. This study assesses the anti-inflammatory effect of sesamin on proteoglycans production in 3D chondrocyte cultures.

Methods

To evaluate the effects of sesamin on IL-1β-treated human articular chondrocytes (HAC) pellets, the pellets were pre-treated with IL-1β then cultured in the presence of various concentrations of sesamin for 21 days. During that period, the expression of IL-1β, glycosaminoglycans (GAGs) content and Chondroitin sulfate proteoglycans (CSPGs) synthesis genes (ACAN, XT-1, XT-2, CHSY1 and ChPF) was measured. The GAGs accumulation in the extracellular matrix was determined on day 21 by histological analysis.

Results

There was clear evidence that sesamin upregulated expression of all the CSPGs synthesis genes, in contrast to the down-regulation of IL-1β expression both in genes and in protein levels. The level of release and matrix accumulation of GAGs in IL-1β pre-treated HAC pellets in the presence of sesamin was recovered. These results correlate with the histological examination which showed that sesamin enhanced matrix CSPGs accumulation.

Conclusions

Sesamin enhances CSPGs synthesis, suppresses IL-1β expression and ameliorates IL-1β induced inflammation in human chondrocytes. Sesamin could have therapeutic benefits for treating inflammation in osteoarthritis.

Sp1 downregulates proinflammatory cytokine‑induced catabolic gene expression in nucleus pulposus cells

During the pathogenesis of intervertebral disc degeneration, pro‑inflammatory cytokines, including tumor necrosis factor‑α (TNF‑α), stimulate the degradation of the extracellular matrix (ECM) of intervertebral discs via the activity of catabolic enzymes including matrix metalloproteinases (MMPs), disintegrins and metalloproteinases with thrombospondin motifs (ADAMTSs), and cyclooxygenase 2 (Cox2). The transcriptional promoters of the human catabolic enzymes MMPs, ADAMTS, Cox2 and Syndecan 4 contain at least one specificity protein‑1 (Sp1) transcription factor‑binding site. The present study investigated the role of Sp1 in the regulation of the mRNA and protein expression of the aforementioned catabolic enzyme genes in nucleus pulposus cells, using reverse transcription‑quantitative polymerase chain reaction, western blot, transfection and RNA interference. The data demonstrated that Sp1 transcription factor protein expression is induced by TNF‑α and interleukin‑1β. Specific inhibitors of Sp1 DNA binding to its GC‑rich consensus site, WP631 and mithramycin A, partially suppressed TNF‑α‑induced catabolic enzyme expression and activity. Genetic inhibition of Sp1 by small interfering RNA‑mediated Sp1 knockdown partially inhibited catabolic enzyme induction by TNF‑α. In addition, Sp1 transcription factor inhibitors decreased the activity of MMP3, ADAMTS4 and ADAMTS5 promoters. Furthermore, chromatin immunoprecipitation revealed functional Sp1 binding sites at ‑577/‑567 bp within the ADAMTS4 promoter and ‑718/‑708 bp within the ADAMTS5 promoter. These results provide pharmacological and genetic evidence of the importance of Sp1 in catabolic enzyme gene regulation during TNF‑α stimulation. Thus, Sp1 may represent an effective target in reducing intervertebral disc‑associated ECM loss.

MicroRNA-124 inhibits the progression of adjuvant-induced arthritis in rats

Objective

MicroRNAs (miRNAs) are small endogenous, non-coding RNAs that act as post-transcriptional regulators. We analysed the in vivo effect of miRNA-124 (miR-124, the rat analogue of human miR-124a) on adjuvant-induced arthritis (AIA) in rats.

Methods

AIA was induced in Lewis rats by injecting incomplete Freund's adjuvant with heat-killed Mycobacterium tuberculosis. Precursor (pre)-miR-124 was injected into the right hind ankle on day 9. Morphological changes in the ankle joint were assessed by micro-CT and histopathology. Cytokine expression was examined by western blotting and real-time RT-PCR. The effect of miR-124 on predicted target messenger RNAs (mRNAs) was examined by luciferase reporter assays. The effect of pre-miR-124 or pre-miR-124a on the differentiation of human osteoclasts was examined by tartrate-resistant acid phosphatase staining.

Results

We found that miR-124 suppressed AIA in rats, as demonstrated by decreased synoviocyte proliferation, leucocyte infiltration and cartilage or bone destruction. Osteoclast counts and expression level of receptor activator of the nuclear factor κB ligand (RANKL), integrin β1 (ITGB1) and nuclear factor of activated T cells cytoplasmic 1 (NFATc1) were reduced in AIA rats treated with pre-miR-124. Luciferase analysis showed that miR-124 directly targeted the 3′UTR of the rat NFATc1, ITGB1, specificity protein 1 and CCAAT/enhancer-binding protein α mRNAs. Pre-miR-124 also suppressed NFATc1 expression in RAW264.7 cells. Both miR-124 and miR-124a directly targeted the 3′-UTR of human NFATc1 mRNA, and both pre-miR-124 and pre-miR-124a suppressed the differentiation of human osteoclasts.

Conclusions

We found that miR-124 ameliorated AIA by suppressing critical prerequisites for arthritis development, such as RANKL and NFATc1. Thus, miR-124a is a candidate for therapeutic use for human rheumatoid arthritis.

Human osteoarthritic cartilage shows reduced in vivo expression of IL-4, a chondroprotective cytokine that differentially modulates IL-1β-stimulated production of chemokines and matrix-degrading enzymes in vitro

Background

In osteoarthritis (OA), an inflammatory environment is responsible for the imbalance between the anabolic and catabolic activity of chondrocytes and, thus, for articular cartilage derangement. This study was aimed at providing further insight into the impairment of the anabolic cytokine IL-4 and its receptors in human OA cartilage, as well as the potential ability of IL-4 to antagonize the catabolic phenotype induced by IL-1β.

Methodology/Principal Findings

The in vivo expression of IL-4 and IL-4 receptor subunits (IL-4R, IL-2Rγ, IL-13Rα1) was investigated on full thickness OA or normal knee cartilage. IL-4 expression was found to be significantly lower in OA, both in terms of the percentage of positive cells and the amount of signal per cell. IL-4 receptor type I and II were mostly expressed in mid-deep cartilage layers. No significant difference for each IL-4 receptor subunit was noted. IL-4 anti-inflammatory and anti-catabolic activity was assessed in vitro in the presence of IL-1β and/or IL-4 for 24 hours using differentiated high density primary OA chondrocyte also exhibiting the three IL-4 R subunits found in vivo. Chemokines, extracellular matrix degrading enzymes and their inhibitors were evaluated at mRNA (real time PCR) and protein (ELISA or western blot) levels. IL-4 did not affect IL-1β-induced mRNA expression of GRO-α/CXCL1, IL-8/CXCL8, ADAMTS-5, TIMP-1 or TIMP-3. Conversely, IL-4 significantly inhibited RANTES/CCL5, MIP-1α/CCL3, MIP-1β/CCL4, MMP-13 and ADAMTS-4. These results were confirmed at protein level for RANTES/CCL5 and MMP-13.

Conclusions/Significance

Our results indicate for the first time that OA cartilage has a significantly lower expression of IL-4. Furthermore, we found differences in the spectrum of biological effects of IL-4. The findings that IL-4 has the ability to hamper the IL-1β-induced release of both MMP-13 and CCL5/RANTES, both markers of OA chondrocytes, strongly indicates IL-4 as a pivotal anabolic cytokine in cartilage whose impairment impacts on OA pathogenesis.

Silencing of microRNA-101 prevents IL-1β-induced extracellular matrix degradation in chondrocytes

Introduction

Extracellular matrix (ECM) degradation leads to malfunction of the cartilage in osteoarthritis (OA). Inflammatory cytokine interleukin-1 beta (IL-1β) functions in ECM degradation and prevents ECM synthesis by down-regulating the key transcription factor, Sox9, and consequently inhibiting ECM gene expression. Evidence reveals that microRNAs (miRNA) have been associated with OA, but little is known of their function in chondrocyte ECM degradation. This study aimed to identify possible miRNAs that mediate IL-1β-induced down-regulation of Sox9 as well as its known down-stream genes, collagen type II and aggrecan.

Methods

The miRNAs were predicted based on three classical databases. The expression levels of the predicted miRNAs were assessed in IL-1β stimulated chondrocytes by real-time PCR. A luciferase reporter was used to test the binding of the miRNAs to the 3' untranslated regions (3'UTR) of Sox9. The predicted miRNAs were transfected into chondrocytes to validate their relationship with Sox9. Functional analysis of the miRNAs on chondrocytes ECM degradation was performed at both the mRNA and protein levels after miRNA transfection and IL-1β treatment.

Results

Six miRNAs were predicted to target Sox9, and their expression in IL-1β-stimulated chondrocytes was revealed by real-time PCR. The luciferase reporter assay indicated that only miR-101 could bind to the 3'UTR of Sox9. The expression of Sox9 was likewise negatively regulated by miR-101 in rat chondrocytes. Functional analysis showed that miR-101 could aggravate chondrocyte ECM degradation, whereas miR-101 inhibition could reverse IL-1β-induced ECM degradation.

Conclusion

miR-101 participates in IL-1β-induced chondrocyte ECM degradation. Down-regulating miR-101 expression can prevent the IL-1β-induced ECM degradation in chondrocytes. miR-101 probably functions by directly targeting Sox9 mRNA.