Identification in human osteoarthritic chondrocytes of proteins binding to the novel regulatory site AGRE in the human matrix metalloprotease 13 proximal promoter

DDB1 binds histone reader BRWD3 to activate the transcriptional cascade in adipogenesis and promote onset of obesity

Obesity has become a global pandemic. Identification of key factors in adipogenesis helps to tackle obesity and related metabolic diseases. Here, we show that DDB1 binds the histone reader BRWD3 to promote adipogenesis and diet-induced obesity. Although typically recognized as a component of the CUL4-RING E3 ubiquitin ligase complex, DDB1 stimulates adipogenesis independently of CUL4. A DDB1 mutant that does not bind CUL4A or CUL4B fully restores adipogenesis in DDB1-deficient cells. Ddb1+/- mice show delayed postnatal development of white adipose tissues and are protected from diet-induced obesity. Mechanistically, by interacting with BRWD3, DDB1 is recruited to acetylated histones in the proximal promoters of ELK1 downstream immediate early response genes and facilitates the release of paused RNA polymerase II, thereby activating the transcriptional cascade in adipogenesis. Our findings have uncovered a CUL4-independent function of DDB1 in promoting the transcriptional cascade of adipogenesis, development of adipose tissues, and onset of obesity.

Transplantation of Human Umbilical Cord Blood-Derived Mesenchymal Stem Cells Improves Cartilage Repair in a Rabbit Model

The aim of this study was to investigate the therapeutic efficacy and safety of transplanting human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) in the treatment of cartilage injury. First, the articular cartilage defect model in rabbits was constructed. Then, the identified hUCB-MSCs and rabbit bone marrow stem cells (rBM-MSCs) were transplanted into the bone defect, respectively, and the cartilage repair effect was observed by hematoxylin-eosin (HE) staining and immunohistochemistry. Besides, the glycosaminoglycan (GAG) content and biomechanics of the restoration area were also evaluated. In our study, hUCB-MSCs and rBM-MSCs exhibited typical MSC characteristics, with positive expressions of CD73, CD105, and CD90 and negative for CD45, CD34, CD14, and HLA-DR. After the transplantation of hUCB-MSCs and rBM-MSCs, the overall quality of cartilage tissue was significantly improved, and the recipients did not show significant side effects in general. However, the expression of matrix metalloproteinase-13 (MMP-13) in the de novo tissues of the hUCB-MSCs and rBM-MSCs groups was both increased, indicating that the novel tissues may have some potential osteoarthritic changes. In conclusion, our results suggest the therapeutic effect of hUCB-MSCs transplantation in cartilage regeneration, providing a promising future in the clinical treatment of cartilage injury.

The unfolded protein response genes in human osteoarthritic chondrocytes: PERK emerges as a potential therapeutic target

BACKGROUND

The unfolded protein response (UPR) is activated following an endoplasmic reticulum (ER) stress. The aim of this study was to investigate the global expression of UPR genes in human OA chondrocytes in induced (I)-UPR conditions, and to explore the regulation and role of the UPR genes in homeostatic (H)-UPR conditions in human normal and OA chondrocytes.

METHODS

Gene expression was determined by PCR array and qPCR. Protein production in cartilage was determined by immunohistochemistry, gene silencing by specific siRNAs, and gene regulation by treating chondrocytes with cytokines and growth factors associated with cartilage pathobiology.

RESULTS

Several UPR genes, among them ERN1, PERK, and CREB3L2 were downregulated in OA compared to normal chondrocytes at both the mRNA and protein levels, but the ER stress response triggered by thapsigargin or tunicamycin treatment was similar in normal and OA chondrocytes. The activation of ER stress sensors (phosphorylated PERK, cleavage of ATF6B, and the spliced mRNA forms of XBP1) was not significantly increased in OA chondrocytes/cartilage. PDGF-BB and IL-6 significantly downregulated the expression of ERN1, PERK, and CREB3L2, but not that of ATF6B. Silencing experiments done under conditions of no ER stress (physiological conditions) revealed that decreasing ERN1 expression led to decreased COL2a1, MMP-13, ADAMTS4 and ADAMTS5 expression, while decreasing CREB3L2 and ATF6B led to decreased ADAMTS5 and ADAMTS4 expression, respectively. Importantly, the downregulation of PERK expression increased COL1a1 and suppressed COL2a1 expression.

CONCLUSIONS

Although the level of ER stress is not significantly increased in OA chondrocytes, these cells respond strongly to an acute ER stress despite the decreased expression of ERN1, PERK, and CREB3L2. Emerging findings revealed for the first time that these genes play a role in cartilage biology in conditions where an acute ER stress response is not triggered and OA is not characterized by an overall basal activation of the ER stress response. Importantly, these findings identify PERK as a potential target for new OA treatment avenues.

The Transcription Factor NMP4 Binds to the AQP5 Promoter and Is a Novel Transcriptional Regulator of the AQP5 Gene

Aquaporin 5 (AQP5) is a water channel that regulates water transport, cell migration, and proliferation. Therefore, knowledge of its genetic regulation could be relevant to study these mechanisms. The AQP5 promoter region containing the AQP5-1364 A/C single-nucleotide polymorphism (SNP) might be an important regulatory region because the SNP is associated with the etiopathology of several diseases. The aim of this study was to identify a transcription factor that binds to this AQP5 promoter region and to investigate its potential impact upon AQP5 expression. In silico analysis revealed nuclear matrix protein 4 (NMP4) as a putative candidate. Electrophoretic mobility shift assays showed specific binding of NMP4 to the AQP5 promoter region of nt -1370 to nt -1329. Overexpression of NMP4 increased AQP5 promoter activity of the analyzed promoter constructs from nt -469 to nt -1979. Furthermore, an additional NMP4 binding site at position nt -592/nt -602 of the AQP5 promoter was identified. NMP4 overexpression increased AQP5 mRNA expression by 2.5-fold in HEK293 cells. Summarizing, we identified NMP4 as a novel transcriptional regulator of AQP5 expression, which binds to two AQP5 promoter regions. Both regions appear to impact AQP5 expression significantly.

NFAT3 and TGF-β/SMAD3 regulate the expression of miR-140 in osteoarthritis

Introduction

MicroRNAs (miRNAs) down-regulate their target genes. The intronic miR-140, present in the WW domain containing E3 ubiquitin protein ligase 2 (WWP2) gene, decreases the expression of genes that play detrimental roles in osteoarthritis (OA). As the expression level of miR-140 is significantly decreased in human OA chondrocytes, we investigated its regulation in those cells.

Methods

Gene expression in human chondrocytes was determined by quantitative polymerase chain reaction (qPCR) and gene silencing was done in OA chondrocytes by transient transfection with specific small interfering RNAs (siRNAs). Binding sites of the miR-140 regulatory sequence (rsmiR-140) were identified by mutagenesis and chromatin immunoprecipitation (ChIP) in OA chondrocytes. The effects of translocation on OA chondrocytes were determined by immunocytochemistry and qPCR.

Results

In contrast to miR-140, the expression of WWP2 was similar in both normal and OA cells, suggesting that miR-140 has an additional level of regulation. rsmiR-140 showed activity and predicted binding sites for nuclear matrix transcription factor 4 (NMP4), myc-associated zinc (MAZ), nuclear factor of activated T-cells (NFAT), and mothers against decapentaplegic homolog 3 (SMAD3). Silencing NFAT3 (P ≤0.01) and SMAD3 (P ≤0.05) differentially regulated miR-140 independently of WWP2. Silencing NFAT5 decreased both miR-140 and WWP2 (P ≤0.003 and P ≤0.05, respectively). NFAT3 activation increased and transforming growth factor-β (TGF-β) decreased rsmiR-140 activity. Mutagenesis of rsmiR-140 and ChIP assays identified binding sites at which NFAT3 (activator) and SMAD3 (repressor) directly regulated miR-140. TGF-β interfered with NFAT3 translocation, and subsequently with miR-140 expression.

Conclusions

This is the first study to provide evidence of a regulatory mechanism of miR-140 independent of WWP2, and new and differential roles for NFAT3 and SMAD3 in the OA process in the regulation of miR-140 transcription. Such knowledge could advance therapeutic strategies targeting OA.

IKKα/CHUK regulates extracellular matrix remodeling independent of its kinase activity to facilitate articular chondrocyte differentiation

Background

The non-canonical NF-κB activating kinase IKKα, encoded by CHUK (conserved-helix-loop-helix-ubiquitous-kinase), has been reported to modulate pro- or anti- inflammatory responses, cellular survival and cellular differentiation. Here, we have investigated the mechanism of action of IKKα as a novel effector of human and murine chondrocyte extracellular matrix (ECM) homeostasis and differentiation towards hypertrophy.

Methodology/Principal Findings

IKKα expression was ablated in primary human osteoarthritic (OA) chondrocytes and in immature murine articular chondrocytes (iMACs) derived from IKKα^f/f:CreERT2 mice by retroviral-mediated stable shRNA transduction and Cre recombinase-dependent Lox P site recombination, respectively. MMP-10 was identified as a major target of IKKα in chondrocytes by mRNA profiling, quantitative RT-PCR analysis, immunohistochemistry and immunoblotting. ECM integrity, as assessed by type II collagen (COL2) deposition and the lack of MMP-dependent COL2 degradation products, was enhanced by IKKα ablation in mice. MMP-13 and total collagenase activities were significantly reduced, while TIMP-3 (tissue inhibitor of metalloproteinase-3) protein levels were enhanced in IKKα-deficient chondrocytes. IKKα deficiency suppressed chondrocyte differentiation, as shown by the quantitative inhibition of.Alizarin red staining and the reduced expression of multiple chondrocyte differentiation effectors, including Runx2, Col10a1 and Vegfa,. Importantly, the differentiation of IKKα-deficient chondrocytes was rescued by a kinase-dead IKKα protein mutant.

Conclusions/Significance

IKKα acts independent of its kinase activity to help drive chondrocyte differentiation towards a hypertrophic-like state. IKKα positively modulates ECM remodeling via multiple downstream targets (including MMP-10 and TIMP-3 at the mRNA and post-transcriptional levels, respectively) to maintain maximal MMP-13 activity, which is required for ECM remodeling leading to chondrocyte differentiation. Chondrocytes are the unique cell component in articular cartilage, which are quiescent and maintain ECM integrity during tissue homeostasis. In OA, chondrocytes reacquire the capacity to proliferate and differentiate and their activation results in pronounced cartilage degeneration. Τηυσ, our findings are also of potential relevance for defining the onset and/or progression of OA disease.

Regulated transcription of human matrix metalloproteinase 13 (MMP13) and interleukin-1β (IL1B) genes in chondrocytes depends on methylation of specific proximal promoter CpG sites

The role of DNA methylation in the regulation of catabolic genes such as MMP13 and IL1B, which have sparse CpG islands, is poorly understood in the context of musculoskeletal diseases. We report that demethylation of specific CpG sites at -110 bp and -299 bp of the proximal MMP13 and IL1B promoters, respectively, detected by in situ methylation analysis of chondrocytes obtained directly from human cartilage, strongly correlated with higher levels of gene expression. The methylation status of these sites had a significant impact on promoter activities in chondrocytes, as revealed in transfection experiments with site-directed CpG mutants in a CpG-free luciferase reporter. Methylation of the -110 and -299 CpG sites, which reside within a hypoxia-inducible factor (HIF) consensus motif in the respective MMP13 and IL1B promoters, produced the most marked suppression of their transcriptional activities. Methylation of the -110 bp CpG site in the MMP13 promoter inhibited its HIF-2α-driven transactivation and decreased HIF-2α binding to the MMP13 proximal promoter in chromatin immunoprecipitation assays. In contrast to HIF-2α, MMP13 transcriptional regulation by other positive (RUNX2, AP-1, ELF3) and negative (Sp1, GATA1, and USF1) factors was not affected by methylation status. However, unlike the MMP13 promoter, IL1B was not susceptible to HIF-2α transactivation, indicating that the -299 CpG site in the IL1B promoter must interact with other transcription factors to modulate IL1B transcriptional activity. Taken together, our data reveal that the methylation of different CpG sites in the proximal promoters of the human MMP13 and IL1B genes modulates their transcription by distinct mechanisms.

E74-like factor 3 (ELF3) impacts on matrix metalloproteinase 13 (MMP13) transcriptional control in articular chondrocytes under proinflammatory stress

Matrix metalloproteinase (MMP)-13 has a pivotal, rate-limiting function in cartilage remodeling and degradation due to its specificity for cleaving type II collagen. The proximal MMP13 promoter contains evolutionarily conserved E26 transformation-specific sequence binding sites that are closely flanked by AP-1 and Runx2 binding motifs, and interplay among these and other factors has been implicated in regulation by stress and inflammatory signals. Here we report that ELF3 directly controls MMP13 promoter activity by targeting an E26 transformation-specific sequence binding site at position -78 bp and by cooperating with AP-1. In addition, ELF3 binding to the proximal MMP13 promoter is enhanced by IL-1β stimulation in chondrocytes, and the IL-1β-induced MMP13 expression is inhibited in primary human chondrocytes by siRNA-ELF3 knockdown and in chondrocytes from Elf3(-/-) mice. Further, we found that MEK/ERK signaling enhances ELF3-driven MMP13 transactivation and is required for IL-1β-induced ELF3 binding to the MMP13 promoter, as assessed by chromatin immunoprecipitation. Finally, we show that enhanced levels of ELF3 co-localize with MMP13 protein and activity in human osteoarthritic cartilage. These studies define a novel role for ELF3 as a procatabolic factor that may contribute to cartilage remodeling and degradation by regulating MMP13 gene transcription.

Hypoxia differentially affects IL-1β-stimulated MMP-1 and MMP-13 expression of fibroblast-like synoviocytes in an HIF-1α-dependent manner

OBJECTIVES

To further understand the expression regulation of MMP-1 and MMP-13 under physiological and pathological conditions, we investigated the combined effects of hypoxia and pro-inflammatory stimuli on the expression of MMP-1 and MMP-13 in rheumatoid synovial fibroblasts.

METHODS

Synovial fibroblasts were cultured under either hypoxic or normoxic conditions in the presence of IL-1β stimulation. The culture supernatant was analysed for secreted levels of VEGF, MMP-1 and MMP-13. Their gene expression was quantified with real-time and semi-quantitative PCR. Another group of cells was transfected with small-interfering RNA (siRNA) specific for hypoxia-inducible factor-1 α (HIF-1α). The protein levels of HIF-1α were detected by western blot analysis.

RESULTS

In response to 10 ng/ml of IL-1β under normoxia, the levels of MMP-1 and MMP-13 increased compared with the levels observed under hypoxia. IL-1β stimulation under hypoxia induced a 2-fold increase in the level of MMP-1 and a 2-fold decrease in the level of MMP-13 compared with cells cultured under normoxia. A similar pattern of differential expression for MMP-1 and MMP-13 was observed with 1 and 5 ng/ml IL-1β, but not at 0.1 ng/ml. The differential expression of MMPs under the combined effect of IL-1β and hypoxia was significantly attenuated by silencing HIF-1α with siRNA.

CONCLUSIONS

Hypoxia in arthritic joints may differentially affect the IL-1β-stimulated expression of MMP-1 and MMP-13 in rheumatoid synovial fibroblasts. This effect is dependent on HIF-1α expression. This hypoxia-mediated differential effect should be taken into consideration when testing the efficiency of therapies that target HIF-1α.

Damage-specific DNA binding protein 1 (DDB1): a protein with a wide range of functions

Damage-specific DNA binding protein 1 (DDB1) is a multifunctional protein that was first isolated as a subunit of a heterodimeric complex that recognises the UV-induced DNA lesions in the nucleotide excision repair pathway. DDB1 and DDB2 form a complex that promotes the global genome repair (GG-NER), whereas DDB1 and Cockayne syndrome group A protein (CSA) form a complex that contributes to the transcription-coupled repair (TC-NER) pathway. DDB1 is also a component of an ubiquitin-E3 ligase complex and functions as substrate or adapter protein between Cullin 4A (Cul4A) and CUL4-associated factors (DCAFs) to target substrates for ubiquitination. CUL4-DDB1 E3-ligase complex regulates the selective proteolysis of key proteins in DNA repair, replication and transcription. In addition, DDB1 plays a role in transcriptional regulation of UV-induced genes. It is conceivable that DDB1 acts as a sensor of damage to maintain the balance between genome integrity and cell cycle progression. However, the temporal order between these two events remains to be established.

Effect of taurine chloramine on the production of matrix metalloproteinases (MMPs) in adiponectin- or IL-1beta-stimulated fibroblast-like synoviocytes

BACKGROUND

Adiponectin greatly stimulated the expression of matrix metalloproteinases (MMPs) in fibroblast-like synoviocytes (FLSs) as did IL-1beta. We wondered whether taurine chloramine (TauCl) inhibits the production of MMPs stimulated by adiponectin in the same pattern as by IL-1beta stimulation in vitro

METHODS

Synovial cells from rheumatoid arthritis (RA) patients were treated with adiponectin or interleukin (IL)-1beta for 24 hr in the presence or absence of TauCl. The culture supernatant was collected and the levels of MMPs were measured by enzyme-linked immunosorbent assay (ELISA). The IkappaB signaling pathways stimulated by adiponectin were studied and the levels of NF-kappaB in the nuclei of the cells were analyzed by ELISA.

RESULTS

TauCl (600 microM) inhibited MMP-13, but not MMP-1, expression in IL-1beta-stimulated RA FLSs. However, TauCl at the same concentration significantly inhibited the production of both adiponectin-stimulated MMP-1 and MMP-13 expression. TauCl inhibited the degradation of IkappaB-alpha stimulated by adiponectin, but not by IL-1beta. Similarly, the level of NF-kappaB in the nucleus was increased by adiponectin stimulation and was inhibited by 600 microM TauCl. However, the levels of NF-kappaB increased by IL-1beta stimulation were not inhibited by 600 microM TauCl.

CONCLUSIONS

TauCl more effectively inhibited MMPs expression induced by adiponectin than that by IL-1beta in RA FLS, suggesting that TauCl plays an important role in down-regulating the expression of MMPs in arthritic joints.

Defining the roles of inflammatory and anabolic cytokines in cartilage metabolism

In osteoarthritis (OA), adult articular chondrocytes undergo phenotypic modulation in response to alterations in the environment owing to mechanical injury and inflammation. These processes not only stimulate the production of enzymes that degrade the cartilage matrix but also inhibit repair. With the use of in vitro and in vivo models, new genes, not known previously to act in cartilage, have been identified and their roles in chondrocyte differentiation during development and in dysregulated chondrocyte function in OA have been examined. These new genes include growth arrest and DNA damage (GADD)45beta and the epithelial-specific ETS (ESE)-1 transcription factor, induced by bone morphogenetic protein (BMP)-2 and inflammatory cytokines, respectively. Both genes are induced by NF-kappaB, suppress COL2A1 and upregulate matrix meatalloproteinase-13 (MMP-13) expression. These genes have also been examined in mouse models of OA, in which discoidin domain receptor 2 is associated with MMP-13-mediated remodelling, in order to understand their roles in physiological cartilage homoeostasis and joint disease.

Cartilage in normal and osteoarthritis conditions

The preservation of articular cartilage depends on keeping the cartilage architecture intact. Cartilage strength and function depend on both the properties of the tissue and on their structural parameters. The main structural macromolecules are collagen and proteoglycans (aggrecan). During life, cartilage matrix turnover is mediated by a multitude of complex autocrine and paracrine anabolic and catabolic factors. These act on the chondrocytes and can lead to repair, remodeling or catabolic processes like those that occur in osteoarthritis. Osteoarthritis is characterized by degradation and loss of articular cartilage, subchondral bone remodeling, and, at the clinical stage of the disease, inflammation of the synovial membrane. The alterations in osteoarthritic cartilage are numerous and involve morphologic and metabolic changes in chondrocytes, as well as biochemical and structural alterations in the extracellular matrix macromolecules.

Taurine chloramine differentially inhibits matrix metalloproteinase 1 and 13 synthesis in interleukin-1beta stimulated fibroblast-like synoviocytes

It has been suggested that taurine chloramine (TauCl) plays an important role in the downregulation of proinflammatory mediators. However, little is known about its effect on the expression of matrix metalloproteinases (MMPs). In this study, we investigated the effects of TauCl on synovial expression of MMPs. The effects of TauCl on MMP expression in IL-1β stimulated fibroblast-like synoviocytes (FLSs) were studied using the following techniques. Real-time PCR and semi-quantitative PCR were employed to analyze the mRNA expression of MMPs. ELISA was used to determine protein levels of MMPs. Western blot analyses were performed to analyze the mitogen-activated protein kinase and inhibitor of nuclear factor-κB (IκB) kinase signalling pathways. Finally, electrophoretic mobility shift assay and immunohistochemistry were used to assess localization of transcription factors. IL-1β increased the transcriptional and translational levels of MMP-1 and MMP-13 in rheumatoid arthritis FLSs, whereas the levels of MMP-2 and MMP-9 were unaffected. TauCl at a concentration of 400 to 600 μmol/l greatly inhibited the transcriptional and translational expression of MMP-13, but the expression of MMP-1 was significantly inhibited at 800 μmol/l. At a concentration of 600 μmol/l, TauCl did not significantly inhibit phosphorylation of mitogen-activated protein kinase or IκB degradation in IL-1β stimulated rheumatoid arthritis FLSs. The degradation of IκB was significantly inhibited at a TauCl concentration of 800 μmol/l. The inhibitory effect of TauCl on IκB degradation was confirmed by electrophoretic mobility shift assay and immunochemical staining for localization of nuclear factor-κB. TauCl differentially inhibits the expression of MMP-1 and MMP-13, and inhibits expression of MMP-1 primarily through the inhibition of IκB degradation, whereas it inhibits expression of MMP-13 through signalling pathways other than the IκB pathway.

Nmp4/CIZ contributes to fluid shear stress induced MMP-13 gene induction in osteoblasts

The expression of matrix metalloproteinase-13 (MMP-13), involved in bone turnover, is elevated in stretched MC3T3-E1 osteoblast-like cells. Strain-mediated forces impact bone remodeling due in large part to the movement of fluid through the canalicular-lacunar network. The resulting fluid shear stress (FSS) over the surface membranes of bone cells initiates bone remodeling. Although the nuclear events mediating putative FSS-induced changes in osteoblast MMP-13 transcription are unknown, previous studies with bone cells suggest an overlap between osteoblast FSS- and PTH-induced signal response pathways. MMP-13 PTH response is regulated by a 110 bp 5' regulatory region, conserved across the mouse, rat, and human genes, that supports the binding of numerous transcription factors including Runx2, c-fos/c-jun, Ets-1, and nuclear matrix protein 4/cas interacting zinc finger protein (Nmp4/CIZ) a nucleocytoplasmic shuttling trans-acting protein that attenuates PTH-driven transcription. Nmp4/CIZ also binds p130(cas), an adaptor protein implicated in mechanotransduction. Here we sought to determine whether Nmp4/CIZ contributes to FSS-induced changes in MMP-13 transcription. FSS (12 dynes/cm(2), 3-5 h) increased MMP-13 promoter-reporter activity approximately two-fold in MC3T3-E1 osteoblast-like cells attended by a comparable increase in mRNA expression. This was accompanied by a decrease in Nmp4/CIZ binding to its cis-element within the PTH response region, the mutation of which abrogated the MMP-13 response to FSS. Interestingly, FSS enhanced Nmp4/CIZ promoter activity and induced p130(cas) nuclear translocation. We conclude that the PTH regulatory region of MMP-13 also contributes to FSS response and that Nmp4/CIZ plays similar but distinct roles in mediating hormone- and FSS-driven induction of MMP-13 in bone cells.