Basic calcium phosphate crystals induce matrix metalloproteinase-1 through the Ras/mitogen-activated protein kinase/c-Fos/AP-1/metalloproteinase 1 pathway. Involvement of transcription factor binding sites AP-1 and PEA-3

The interleukin-1α stimulated expression of the wrinkle-inducing elastase neprilysin in adult human dermal fibroblasts is mediated via the intracellular signaling axis of ERK/JNK/c-Jun/c-Fos/AP-1

Neprilysin is a skin wrinkle-inducing membrane bound elastase that is expressed abundantly in UV-exposed and in aged dermal fibroblasts. The overexpression of neprilysin is closely associated with enhanced epithelial-mesenchymal cytokine interactions mainly via interleukin (IL)-1α, which has the distinct potential to stimulate the expression of neprilysin by human dermal fibroblasts (HDFs). The over-expression of neprilysin also accelerates the formation of wrinkles, accompanied by disruptions of the three-dimensional architecture of dermal elastic fibers that are responsible for the loss of skin elasticity. Because the signaling pathway(s) that lead to the IL-1α-stimulated expression of neprilysin in HDFs remain unclear, we characterized the signaling pathway involved, including their related transcription factors, in IL-1α-treated HDFs. Since qRT-PCR analysis revealed that the mRNA expression level of neprilysin is stimulated to a stronger extent in adult HDFs (aHDFs) by IL-1α than in neonatal HDFs, we used aHDFs for the signaling analysis. Western blotting analysis of the phosphorylation of signaling factors revealed that IL-1α significantly stimulated the phosphorylation of ERK1/2, RSK, JNK, p38, MSK1, NFkB, c-Jun, ATF-2, CREB, and STAT3. Analysis using various signaling inhibitors demonstrated that inhibiting ERK and JNK but not p38, MSK1, NFkB, or STAT3 significantly abrogated the IL-1α stimulated expression of neprilysin at the mRNA, protein, and enzyme activity levels. Furthermore, silencing c-Fos significantly down-regulated the IL-1α-increased expression of neprilysin at the protein and enzyme activity levels. These findings strongly suggest that the IL-1α-stimulated expression of neprilysin in aHDFs is mediated via the intracellular signaling axis of ERK/JNK/c-Jun/c-Fos/AP-1.

Discovery of calcite as a new pro-inflammatory calcium-containing crystal in human osteoarthritic synovial fluid

OBJECTIVE

We aimed to characterize calcium-containing crystals present in synovial fluid from patients with knee osteoarthritis (OA) using Raman spectroscopy, and specifically investigate the biological effects of calcite crystals.

DESIGN

Thirty-two synovial fluid samples were collected pre-operatively from knee OA patients undergoing total joint arthroplasty. An integrated Raman polarized light microscope was used for identification of crystals in synovial fluid. Human peripheral blood mononuclear cells (PBMC's), human OA articular chondrocytes (HACs) and fibroblast-like synoviocytes (FLSs) were exposed to calcite crystals. Expression of relevant cytokines and inflammatory genes were measured using enzyme-linked immuno sorbent assay (ELISA) and real-time polymerase chain reaction (PCR).

RESULTS

Various calcium-containing crystals were identified, including calcium pyrophosphate (37.5 %) and basic calcium phosphate (21.8 %), but they were never found simultaneously in the same OA synovial fluid sample. For the first time, we discovered the presence of calcite crystals in 93.8 % of the samples, while dolomite was detected in 25 % of the cases. Characterization of the cellular response to calcite crystal exposure revealed increased production of innate immune-derived cytokines by PBMC's, when co-stimulated with lipopolysaccharide (LPS). Additionally, calcite crystal stimulation of HACs and FLSs resulted in enhanced secretion of pro-inflammatory molecules and alterations in the expression of extracellular matrix remodeling enzymes.

CONCLUSIONS

This study highlights the unique role of Raman spectroscopy in OA crystal research and identified calcite as a novel pro-inflammatory crystal type in OA synovial fluid. Understanding the role of specific crystal species in the OA joint may open new avenues for pharmacological interventions and personalized approaches to treating OA.

Unravelling the Basic Calcium Phosphate crystal-dependent chondrocyte protein secretome; a role for TGF-β signaling

OBJECTIVE

Basic Calcium Phosphate (BCP) crystals play an active role in the progression of osteoarthritis (OA). However, the cellular consequences remain largely unknown. Therefore, we characterized for the first time the changes in the protein secretome of human OA articular chondrocytes as a result of BCP stimulation using two unbiased proteomic analysis methods.

METHOD

Isolated human OA articular chondrocytes were stimulated with BCP crystals and examined by Quantitative Reverse Transcription PCR (RT-qPCR) and enzyme-linked immune sorbent assay (ELISA) after twenty-four and forty-eight hours. Forty-eight hours conditioned media were analyzed by label-free liquid chromatography-tandem mass spectrometry (LC-MS/MS) and an antibody array. The activity of BCP dependent Transforming Growth Factor Beta (TGF-β) signaling was analyzed by RT-qPCR and luciferase reporter assays. The molecular consequences regarding BCP-dependent TGF-β signaling on BCP-dependent Interleukin 6 (IL-6) were investigated using specific pathway inhibitors.

RESULTS

Synthesized BCP crystals induced IL-6 expression and secretion upon stimulation of human articular chondrocytes. Concomitant induction of catabolic gene expression was observed. Analysis of conditioned media revealed a complex and diverse response with a large number of proteins involved in TGF-β signaling, both in activation of latent TGF-β and TGF-β superfamily members, which were increased compared to non-stimulated OA chondrocytes. Activity of this BCP driven TGF-β signaling was confirmed by increased activity of expression of TGF-β target genes and luciferase reporters. Inhibition of BCP driven TGF-β signaling resulted in decreased IL-6 expression and secretion with a moderate effect on catabolic gene expression.

CONCLUSION

BCP crystal stimulation resulted in a complex and diverse chondrocyte protein secretome response. An important role for BCP-dependent TGF-β signaling was identified in development of a pro-inflammatory environment.

Cartilage calcification in osteoarthritis: mechanisms and clinical relevance

Pathological calcification of cartilage is a hallmark of osteoarthritis (OA). Calcification can be observed both at the cartilage surface and in its deeper layers. The formation of calcium-containing crystals, typically basic calcium phosphate (BCP) and calcium pyrophosphate dihydrate (CPP) crystals, is an active, highly regulated and complex biological process that is initiated by chondrocytes and modified by genetic factors, dysregulated mitophagy or apoptosis, inflammation and the activation of specific cellular-signalling pathways. The links between OA and BCP deposition are stronger than those observed between OA and CPP deposition. Here, we review the molecular processes involved in cartilage calcification in OA and summarize the effects of calcium crystals on chondrocytes, synovial fibroblasts, macrophages and bone cells. Finally, we highlight therapeutic pathways leading to decreased joint calcification and potential new drugs that could treat not only OA but also other diseases associated with pathological calcification.

The Hallmarks of Flavonoids in Cancer

Flavonoids represent an important group of bioactive compounds derived from plant-based foods and beverages with known biological activity in cells. From the modulation of inflammation to the inhibition of cell proliferation, flavonoids have been described as important therapeutic adjuvants against several diseases, including diabetes, arteriosclerosis, neurological disorders, and cancer. Cancer is a complex and multifactor disease that has been studied for years however, its prevention is still one of the best known and efficient factors impacting the epidemiology of the disease. In the molecular and cellular context, some of the mechanisms underlying the oncogenesis and the progression of the disease are understood, known as the hallmarks of cancer. In this text, we review important molecular signaling pathways, including inflammation, immunity, redox metabolism, cell growth, autophagy, apoptosis, and cell cycle, and analyze the known mechanisms of action of flavonoids in cancer. The current literature provides enough evidence supporting that flavonoids may be important adjuvants in cancer therapy, highlighting the importance of healthy and balanced diets to prevent the onset and progression of the disease.

Transcription factor EGR-1 transactivates the MMP1 gene promoter in response to TNFα in HaCaT keratinocytes

Matrix metalloproteinase 1 (MMP-1), a calcium-dependent zinc- containing collagenase, is involved in the initial degradation of native fibrillar collagen. Tissue necrosis factor-alpha (TNFα) is a pro-inflammatory cytokine that is rapidly produced by dermal fibroblasts, monocytes/macrophages, and keratinocytes and regulates inflammation and damaged-tissue remodeling. MMP-1 is induced by TNFα and plays a critical role in tissue remodeling and skin aging processes. However, the regulation of the MMP1 gene by TNFα is not fully understood. We aimed to find additional cis-acting elements involved in the regulation of TNFα-induced MMP1 gene transcription in addition to the nuclear factor-kappa B (NF-kB) and activator protein 1 (AP1) sites. Assessments of the 5’-regulatory region of the MMP1 gene, using a series of deletion constructs, revealed the requirement of the early growth response protein 1 (EGR-1)-binding sequence (EBS) in the proximal region for proper transcription by TNFα. Ectopic expression of EGR-1, a zinc-finger transcription factor that binds to G-C rich sequences, stimulated MMP1 promoter activity. The silencing of EGR-1 by RNA interference reduced TNFα-induced MMP-1 expression. EGR-1 directly binds to the proximal region and transactivates the MMP1 gene promoter. Mutation of the EBS within the MMP1 promoter abolished EGR-1-mediated MMP-1 promoter activation. These data suggest that EGR-1 is required for TNFα-induced MMP1 transcriptional activation. In addition, we found that all three MAPKs, ERK1/2, JNK, and p38 kinase, mediate TNFα-induced MMP-1 expression via EGR-1 upregulation. These results suggest that EGR-1 may represent a good target for the development of pharmaceutical agents to reduce inflammation-induced MMP-1 expression.

Inhibition of EGR-1-dependent MMP1 transcription by ethanol extract of Ageratum houstonianum in HaCaT keratinocytes

Matrix metalloproteinase 1 (MMP-1) initiates the breakdown of matrix networks by cleaving fibrillar collagen during the pathophysiological progression of skin aging. Ageratum houstonianum ethanol extract (AHE) has been used as a traditional herbal medicine to treat external wounds and skin diseases. However, the mechanism of action underlying A. houstonianum-mediated modulation of skin aging has not been investigated. In this study, we evaluated the effect of AHE on MMP-1 expression in HaCaT keratinocytes. Gene expression was analyzed by Reverse transcription-PCR (RT-PCR), Quantitative real-time PCR (Q-PCR), gene promoter-reporter assay, and immunoblotting. We found that AHE abrogated TNFα-induced MMP1 expression at the transcriptional level via the suppression of ERK1/2 mitogen-activated protein kinase (MAPK)-mediated Early Growth Response 1 (EGR1) expression. We also demonstrated that β-caryophyllene, a cannabinoid receptor 2 (CB2) agonist, is a functional component of the AHE that inhibits TNFα-induced EGR-1 and MMP1 expression. AHE exerts inhibitory activity on TNFα-induced MMP1 expression at the transcription level through EGR-1 downregulation in keratinocytes. β-Caryophyllene is a bioactive ingredient of AHE that is responsible for the inhibition of TNFα-induced EGR1 expression. β-Caryophyllene can be used as a potential agent to prevent inflammation-induced skin aging.

Cytokine-induced cysteine- serine-rich nuclear protein-1 (CSRNP1) selectively contributes to MMP1 expression in human chondrocytes

Irreversible cartilage collagen breakdown by the collagenolytic matrix metalloproteinases (MMPs)-1 and MMP-13 represents a key event in pathologies associated with tissue destruction such as arthritis. Inflammation is closely associated with such pathology and occurs in both rheumatoid and osteoarthritis making it highly relevant to the prevailing tissue damage that characterises these diseases. The inflammation-induced activating protein-1 (AP-1) transcription factor is an important regulator of both MMP1 and MMP13 genes with interplay between signalling pathways contributing to their expression. Here, we have examined the regulation of MMP1 expression, and using in vivo chromatin immunoprecipitation analyses we have demonstrated that cFos bound to the AP-1 cis element within the proximal MMP1 promoter only when the gene was transcriptionally silent as previously observed for MMP13. Subsequent small interfering RNA-mediated silencing confirmed however, that cFos significantly contributes to MMP1 expression. In contrast, silencing of ATF3 (a prime MMP13 modulator) did not affect MMP1 expression whilst silencing of the Wnt-associated regulator cysteine- serine-rich nuclear protein-1 (CSRNP1) resulted in substantial repression of MMP1 but not MMP13. Furthermore, following an early transient peak in expression of CSRNP1 at the mRNA and protein levels similar to that seen for cFOS, CSRNP1 expression subsequently persisted unlike cFOS. Finally, DNA binding assays indicated that the binding of CSRNP1 to the AP-1 consensus-like sequences within the proximal promoter regions of MMP1 and MMP13 was preferentially selective for MMP1 whilst activating transcription factor 3 (ATF3) binding was exclusive to MMP13. These data further extend our understanding of the previously reported differential regulation of these MMP genes, and strongly indicate that although cFos modulates the expression of MMP1/13, downstream factors such as CSRNP1 and ATF3 ultimately serve as transcriptional regulators in the context of an inflammatory stimulus for these potent collagenolytic MMPs.

Scopoletin downregulates MMP‑1 expression in human fibroblasts via inhibition of p38 phosphorylation

Irradiation of keratinocytes by ultraviolet B induces cytokine production, which in turn activates fibroblasts to produce cytokines and increase matrix metallopeptidase (MMP)‑1 protein expression. The present study investigated the effect and potential mechanisms of scopoletin on the regulation of MMP‑1 expression in fibroblasts. Scopoletin was isolated from Artemisia capillaris crude extract. Treatment of fibroblasts with scopoletin resulted in a decrease in the protein expression of MMP‑1 following stimulation with human keratinocyte (HaCaT) conditioned medium. To further explore the mechanism underlying this effect, the expression levels of proteins in the mitogen‑activated protein kinase (MAPK) and nuclear factor‑κB (NF‑κB) signaling pathways were evaluated via western blot analysis. The mRNA expression levels of interleukin (IL)‑1α and tumor necrosis factor (TNF) α were evaluated via reverse transcription‑quantitative polymerase chain reaction. The effect of scopoletin on cell viability was assessed with the MTT assay. The results demonstrated that scopoletin treatment markedly decreased MMP‑1, IL‑1α and TNFα mRNA expression in fibroblasts stimulated with HaCaT conditioned medium (40 mJ/cm2), without any apparent cell cytotoxicity, and in a dose‑dependent manner. In addition, western blot analysis demonstrated that scopoletin reduced the phosphorylation of p38 MAPK in fibroblasts. In summary, the present study demonstrated that scopoletin inhibited MMP‑1 and proinflammatory cytokine expression by inhibiting p38 MAPK phosphorylation. These findings suggest that scopoletin may have potential as a therapeutic agent to prevent and treat photoaging of the skin.

Biological Effects of Phosphocitrate on Osteoarthritic Articular Chondrocytes

BACKGROUND

Phosphocitrate (PC) inhibits osteoarthritis (OA) in Hartley guinea pigs. However, the underlying molecular mechanisms remain poorly understood.

OBJECTIVE

This study sought to examine the biological effect of PC on OA chondrocytes and test the hypothesis that PC may exert its OA disease modifying effect, in part, by inhibiting the expression of genes implicated in OA disease process and stimulating the production of extracellular matrices.

METHOD

OA chondrocytes were cultured in the absence or presence of PC. Total RNA was extracted and subjected to microarray analyses. The effect of PC on proliferation and chondrocyte-mediated calcification were examined in monolayer culture. The effect of PC on the production of extracellular matrices was examined in micromass culture.

RESULTS

PC downregulated the expression of numerous genes classified in proliferation and apoptosis while upregulating the expression of many genes classified in transforming growth factor-β (TGF-β) receptor signaling pathway and ossification. PC also downregulated the expressions of many genes classified in inflammatory response and Wnt receptor signaling pathways. Consistent with its effect on the expression of genes classified in proliferation, ossification, and skeletal development, PC inhibited the proliferation of OA chondrocytes and chondrocyte-mediated calcification while stimulating the production of extracellular matrices.

CONCLUSION

PC may exert its OA disease modifying effect, in part, through a crystal-independent mechanism or by inhibiting the expressions of many genes implicated in OA disease process, and at the same time, stimulating the expression of genes implicated in chondroprotection and production of extracellular matrices.

Harpagoside suppresses IL-6 expression in primary human osteoarthritis chondrocytes

There is growing evidence in support of the involvement of inflammatory response in the pathogenesis of osteoarthritis (OA). Harpagoside, one of the bioactive components of Harpagophytum procumbens (Hp), has been shown to possess anti-inflammatory properties. Here we used an in vitro model of inflammation in OA to investigate the potential of harpagoside to suppress the production of inflammatory cytokines/chemokines such as IL-6 and matrix degrading proteases. We further investigated the likely targets of harpagoside in primary human OA chondrocytes. OA chondrocytes were pre-treated with harpagoside before stimulation with IL-1β. mRNA expression profile of 92 cytokines/chemokines was determined using TaqMan Human Chemokine PCR Array. Expression levels of selected mRNAs were confirmed using TaqMan assays. Protein levels of IL-6 and MMP-13 were assayed by ELISA and immunoblotting. Total protein levels and phosphorylation of signaling proteins were determined by immunoblotting. Cellular localization of IL-6 and c-Fos was performed by immunofluorescence and confocal microscopy. DNA binding activity of c-FOS/AP-1 was determined by ELISA. Harpagoside significantly altered the global chemokine expression profile in IL-1β-stimulated OA chondrocytes. Expression of IL-6 was highly induced by IL-1β, which was significantly inhibited by pre-treatment of OA chondrocytes with harpagoside. Harpagoside did not inhibit the IL-1β-induced activation of NF-κB and C/EBPβ transcription factors but suppressed the IL-1β-triggered induction, phosphorylation, and DNA binding activity of c-FOS, one of the main components of AP-1 transcription factors. Further, harpagoside significantly inhibited the expression of MMP-13 in OA chondrocytes under pathological conditions. siRNA-mediated knockdown of IL-6 resulted in suppressed expression and secretion of MMP-13 directly linking the role of IL-6 with MMP-13 expression. Taken together, the present study suggests that harpagoside exerts a significant anti-inflammatory effect by inhibiting the inflammatory stimuli mediated by suppressing c-FOS/AP-1 activity in OA chondrocytes under pathological conditions. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:311-320, 2017.

Pathophysiology of colorectal peritoneal carcinomatosis: Role of the peritoneum

Colorectal cancer (CRC) is the third most common cancer and the fourth most common cause of cancer-related death worldwide. Besides the lymphatic and haematogenous routes of dissemination, CRC frequently gives rise to transcoelomic spread of tumor cells in the peritoneal cavity, which ultimately leads to peritoneal carcinomatosis (PC). PC is associated with a poor prognosis and bad quality of life for these patients in their terminal stages of disease. A loco-regional treatment modality for PC combining cytoreductive surgery and hyperthermic intraperitoneal peroperative chemotherapy has resulted in promising clinical results. However, this novel approach is associated with significant morbidity and mortality. A comprehensive understanding of the molecular events involved in peritoneal disease spread is paramount in avoiding unnecessary toxicity. The emergence of PC is the result of a molecular crosstalk between cancer cells and host elements, involving several well-defined steps, together known as the peritoneal metastatic cascade. Individual or clumps of tumor cells detach from the primary tumor, gain access to the peritoneal cavity and become susceptible to the regular peritoneal transport. They attach to the distant peritoneum, subsequently invade the subperitoneal space, where angiogenesis sustains proliferation and enables further metastatic growth. These molecular events are not isolated events but rather a continuous and interdependent process. In this manuscript, we review current data regarding the molecular mechanisms underlying the development of colorectal PC, with a special focus on the peritoneum and the role of the surgeon in peritoneal disease spread.

A Qualitative Model of the Differentiation Network in Chondrocyte Maturation: A Holistic View of Chondrocyte Hypertrophy

Differentiation of chondrocytes towards hypertrophy is a natural process whose control is essential in endochondral bone formation. It is additionally thought to play a role in several pathophysiological processes, with osteoarthritis being a prominent example. We perform a dynamic analysis of a qualitative mathematical model of the regulatory network that directs this phenotypic switch to investigate the influence of the individual factors holistically. To estimate the stability of a SOX9 positive state (associated with resting/proliferation chondrocytes) versus a RUNX2 positive one (associated with hypertrophy) we employ two measures. The robustness of the state in canalisation (size of the attractor basin) is assessed by a Monte Carlo analysis and the sensitivity to perturbations is assessed by a perturbational analysis of the attractor. Through qualitative predictions, these measures allow for an in silico screening of the effect of the modelled factors on chondrocyte maintenance and hypertrophy. We show how discrepancies between experimental data and the model’s results can be resolved by evaluating the dynamic plausibility of alternative network topologies. The findings are further supported by a literature study of proposed therapeutic targets in the case of osteoarthritis.

Sodium Thiosulfate Prevents Chondrocyte Mineralization and Reduces the Severity of Murine Osteoarthritis

Objectives

Calcium-containing crystals participate in the pathogenesis of OA. Sodium thiosulfate (STS) has been shown to be an effective treatment in calcification disorders such as calciphylaxis and vascular calcification. This study investigated the effects and mechanisms of action of STS in a murine model of OA and in chondrocyte calcification.

Methods

Hydroxyapatite (HA) crystals-stimulated murine chondrocytes and macrophages were treated with STS. Mineralization and cellular production of IL-6, MCP-1 and reactive oxygen species (ROS) were assayed. STS's effects on genes involved in calcification, inflammation and cartilage matrix degradation were studied by RT-PCR. STS was administered in the menisectomy model of murine OA, and the effect on periarticular calcific deposits and cartilage degeneration was investigated by micro-CT-scan and histology.

Results

In vitro, STS prevented in a dose-dependent manner calcium crystal deposition in chondrocytes and inhibited Annexin V gene expression. In addition, there was a reduction in crystal-induced IL-6 and MCP-1 production. STS also had an antioxidant effect, diminished HA-induced ROS generation and abrogated HA-induced catabolic responses in chondrocytes. In vivo, administration of STS reduced the histological severity of OA, by limiting the size of new periarticular calcific deposits and reducing the severity of cartilage damage.

Conclusions

STS reduces the severity of periarticular calcification and cartilage damage in an animal model of OA via its effects on chondrocyte mineralization and its attenuation of crystal-induced inflammation as well as catabolic enzymes and ROS generation. Our study suggests that STS may be a disease-modifying drug in crystal-associated OA.

Interleukin-6 and chondrocyte mineralisation act in tandem to promote experimental osteoarthritis

OBJECTIVES

Basic calcium phosphate (BCP) crystal and interleukin 6 (IL-6) have been implicated in osteoarthritis (OA). We hypothesise that these two factors may be linked in a reciprocal amplification loop which leads to OA.

METHODS

Primary murine chondrocytes and human cartilage explants were incubated with hydroxyapatite (HA) crystals, a form of BCP, and the modulation of cytokines and matrix-degrading enzymes assayed. The ability of IL-6 to stimulate chondrocyte calcification was assessed in vitro. The mechanisms underlying the effects of HA on chondrocytes were investigated using chemical inhibitors, and the pathways mediating IL-6-induced calcification characterised by quantifying the expression of genes involved in chondrocyte mineralisation. The role of calcification in vivo was studied in the meniscectomy model of murine OA (MNX), and the link between IL-6 and cartilage degradation investigated by histology.

RESULTS

In chondrocytes, BCP crystals stimulated IL-6 secretion, further amplified in an autocrine loop, through signalling pathways involving Syk and PI3 kinases, Jak2 and Stat3 molecules. Exogenous IL-6 promoted calcium-containing crystal formation and upregulation of genes involved in calcification: the pyrophosphate channel Ank, the calcium channel Annexin5 and the sodium/phosphate cotransporter Pit-1. Treatment of chondrocytes with IL-6 inhibitors significantly inhibited IL-6-induced crystal formation. In meniscectomised mice, increasing deposits of BCP crystals were observed around the joint and correlated with cartilage degradation and IL-6 expression. Finally, BCP crystals induced proteoglycan loss and IL-6 expression in human cartilage explants, which were reduced by an IL-6 inhibitor.

CONCLUSIONS

BCP crystals and IL-6 form a positive feedback loop leading to OA. Targeting calcium-containing crystal formation and/or IL-6 are promising therapeutic strategies in OA.

Disease-modifying effects of phosphocitrate and phosphocitrate-β-ethyl ester on partial meniscectomy-induced osteoarthritis

Background

It is believed that phosphocitrate (PC) exerts its disease-modifying effects on osteoarthritis (OA) by inhibiting the formation of crystals. However, recent findings suggest that PC exerts its disease-modifying effect, at least in part, through a crystal-independent action. This study sought to examine the disease-modifying effects of PC and its analogue PC-β-ethyl ester (PC-E) on partial meniscectomy-induced OA and the structure-activity relationship.

Methods

Calcification- and proliferation-inhibitory activities were examined in OA fibroblast-like synoviocytes (FLSs) culture. Disease-modifying effects were examined using Hartley guinea pigs undergoing partial meniscectomy. Cartilage degeneration was examined with Indian ink, safranin-O, and picrosirius red. Levels of matrix metalloproteinase-13 (MMP-13), ADAM metallopeptidase with thrombospondin type 1 motif 5 (ADAMTS5), chemokine (C-C motif) ligand 5 (CCL5), and cyclooxygenase-2 (Cox-2) were examined with immunostaining. The effects of PC-E and PC on gene expressions in OA FLSs were examined with microarray. Results are expressed as mean ± standard deviation and analyzed using Student’s t test or Wilcoxon rank sum test.

Results

PC-E was slightly less powerful than PC as a calcification inhibitor but as powerful as PC in the inhibition of OA FLSs proliferation. PC significantly inhibited cartilage degeneration in the partial meniscectomied right knee. PC-E was less powerful than PC as a disease-modifying drug, especially in the inhibition of cartilage degeneration in the non-operated left knee. PC significantly reduced the levels of ADAMTS5, MMP-13 and CCL5, whereas PC-E reduced the levels of ADAMTS5 and CCL5. Microarray analyses revealed that PC-E failed to downregulate the expression of many PC-downregulated genes classified in angiogenesis and inflammatory response.

Conclusions

PC is a disease-modifying drug for posttraumatic OA therapy. PC exerts its disease-modifying effect through two independent actions: inhibiting pathological calcification and modulating the expression of many genes implicated in OA. The β-carboxyl group of PC plays an important role in the inhibition of cartilage degeneration, little role in the inhibition of FLSs proliferation, and a moderate role in the inhibition of FLSs-mediated calcification.

Interplay between TAp73 Protein and Selected Activator Protein-1 (AP-1) Family Members Promotes AP-1 Target Gene Activation and Cellular Growth

Unlike p53, which is mutated at a high rate in human cancers, its homologue p73 is not mutated but is often overexpressed, suggesting a possible context-dependent role in growth promotion. Previously, we have shown that co-expression of TAp73 with the proto-oncogene c-Jun can augment cellular growth and potentiate transactivation of activator protein (AP)-1 target genes such as cyclin D1. Here, we provide further mechanistic insights into the cooperative activity between these two transcription factors. Our data show that TAp73-mediated AP-1 target gene transactivation relies on c-Jun dimerization and requires the canonical AP-1 sites on target gene promoters. Interestingly, only selected members of the Fos family of proteins such as c-Fos and Fra1 were found to cooperate with TAp73 in a c-Jun-dependent manner to transactivate AP-1 target promoters. Inducible expression of TAp73 led to the recruitment of these Fos family members to the AP-1 target promoters on which TAp73 was found to be bound near the AP-1 site. Consistent with the binding of TAp73 and AP-1 members on the target promoters in a c-Jun-dependent manner, TAp73 was observed to physically interact with c-Jun specifically at the chromatin via its carboxyl-terminal region. Furthermore, co-expression of c-Fos or Fra1 was able to cooperate with TAp73 in potentiating cellular growth, similarly to c-Jun. These data together suggest that TAp73 plays a vital role in activation of AP-1 target genes via direct binding to c-Jun at the target promoters, leading to enhanced loading of other AP-1 family members, thereby leading to cellular growth.

A positive role of DBC1 in PEA3-mediated progression of estrogen receptor-negative breast cancer

Deleted in Breast Cancer 1 (DBC1), a negative regulator of deacetylase SIRT1, has been shown to act as an estrogen receptor α (ER) coactivator that has a key role in ER transcription complex assembly and estrogen-dependent breast cancer cell proliferation. However, little is known about its physiological role and mechanism of action in ER-negative breast cancer cells. Here we report that DBC1 functions as a coactivator for the oncogenic ETS transcription factor PEA3 to promote ER-negative breast cancer progression. DBC1 is required for the expression of PEA3 target genes and for recruitment of PEA3 and RNA polymerase II to PEA3 target promoters. We also demonstrated that acetylation of PEA3 stimulates its DNA binding and association with DBC1 by disrupting the intramolecular interaction of PEA3. The molecular mechanism underlying DBC1 function in PEA3-mediated transcription involves inhibition of SIRT1 interaction with PEA3 and of SIRT1-mediated deacetylation of PEA3. Moreover, DBC1 depletion inhibited the tumorigenic properties of ER-negative breast cancer cells in vitro and in vivo. Importantly, increased DBC1 expression correlated with shorter relapse-free survival of ER-negative breast cancer patients. Our results firmly established DBC1 as a critical coactivator of PEA3 and as a key player in PEA3-mediated breast cancer progression.

Small molecule inhibitors targeting activator protein 1 (AP-1)

Activator protein 1 (AP-1) is a pivotal transcription factor that regulates a wide range of cellular processes including proliferation, apoptosis, differentiation, survival, cell migration, and transformation. Accumulating evidence supports that AP-1 plays an important role in several severe disorders including cancer, fibrosis, and organ injury, as well as inflammatory disorders such as asthma, psoriasis, and rheumatoid arthritis. AP-1 has emerged as an actively pursued drug discovery target over the past decade. Excitingly, a selective AP-1 inhibitor T-5224 (51) has been investigated in phase II human clinical trials. Nevertheless, no effective AP-1 inhibitors have yet been approved for clinical use. Despite significant advances achieved in understanding AP-1 biology and function, as well as the identification of small molecules modulating AP-1 associated signaling pathways, medicinal chemistry efforts remain an urgent need to yield selective and efficacious AP-1 inhibitors as a viable therapeutic strategy for human diseases.

Fibroblast-like synoviocytes induce calcium mineral formation and deposition

Calcium crystals are present in the synovial fluid of 65%–100% patients with osteoarthritis (OA) and 20%–39% patients with rheumatoid arthritis (RA). This study sought to investigate the role of fibroblast-like synoviocytes (FLSs) in calcium mineral formation. We found that numerous genes classified in the biomineral formation process, including bone gamma-carboxyglutamate (gla) protein/osteocalcin, runt-related transcription factor 2, ankylosis progressive homolog, and parathyroid hormone-like hormone, were differentially expressed in the OA and RA FLSs. Calcium deposits were detected in FLSs cultured in regular medium in the presence of ATP and FLSs cultured in chondrogenesis medium in the absence of ATP. More calcium minerals were deposited in the cultures of OA FLSs than in the cultures of RA FLSs. Examination of the micromass stained with nonaqueous alcoholic eosin indicated the presence of birefringent crystals. Phosphocitrate inhibited the OA FLSs-mediated calcium mineral deposition. These findings together suggest that OA FLSs are not passive bystanders but are active players in the pathological calcification process occurring in OA and that potential calcification stimuli for OA FLSs-mediated calcium deposition include ATP and certain unidentified differentiation-inducing factor(s). The OA FLSs-mediated pathological calcification process is a valid target for the development of disease-modifying drug for OA therapy.

The oxygen free radicals control MMP-9 and transcription factors expression in the spontaneously hypertensive rat

Oxygen free radical and matrix metalloproteinases-9 (MMP-9) play an important pathophysiological role in the development of chronic hypertension. MMP-9 activities are regulated at different levels. We hypothesize that as mediators of the expression of MMP-9 the transcription factors like nuclear factor kappa B (NF-κB), c-fos and retinoic acid receptors-α (RAR-α) with binding sites to the MMP-9 promoter are overexpressed in the spontaneously hypertensive rat (SHR) in a process that is regulated by oxygen free radicals. Transcription factor NF-κB, c-fos and RAR-α expression levels were determined by immunohistochemistry in renal, cardiac and mesentery microcirculation of the SHR and its normotensive control, the Wistar Kyoto (WKY) rat. The animals were treated with a superoxide scavenger (Tempol) for eight weeks. The elevated plasma levels of thiobarbituric acid reactive substances and MMP-9 levels in the SHR were significantly decreased by Tempol treatment (P<0.05). The NF-κB, c-fos and RAR-α expression levels in renal glomerular, heart and mesentery microvessels were enhanced in the SHR and could also be reduced by Tempol compared to untreated animals (P<0.05). The enhanced MMP-9 levels in SHR microvessels co-express with transcription factors. These results suggest that elevated NF-κB, c-fos and RAR-α expressions and MMP-9 activity in the SHR are superoxide-dependent.

Phosphocitrate is potentially a disease-modifying drug for noncrystal-associated osteoarthritis

Phosphocitrate (PC), a calcification inhibitor, inhibits the development of crystal-associated osteoarthritis (OA) in Hartley guinea pigs. However, the molecular mechanisms underlying its disease-modifying effect remain elusive. This study sought to test the hypothesis that PC has calcium crystal-independent biological activities which are, at least in part, responsible for its disease-modifying activity. We found that PC inhibited the proliferation of OA fibroblast-like synoviocytes in the absence of calcium crystals. Consistent with its effect on cell proliferation, PC downregulated the expression of numerous genes classified in cell proliferation. PC also downregulated the expression of many genes classified in angiogenesis and inflammatory response including prostaglandin-endoperoxide synthase 2, interleukin-1 receptor, type I, and chemokine (C-C motif) ligand 2. In contrast, PC upregulated the expression of many genes classified in musculoskeletal tissue development, including aggrecan, type I collagen, and insulin-like growth factor binding protein 5. These findings suggest that PC is not only a promising disease-modifying drug for crystal-associated OA but also for noncrystal-associated OA.

Calcium deposition in osteoarthritic meniscus and meniscal cell culture

INTRODUCTION

Calcium crystals exist in the knee joint fluid of up to 65% of osteoarthritis (OA) patients and the presence of these calcium crystals correlates with the radiographic evidence of hyaline cartilaginous degeneration. This study sought to examine calcium deposition in OA meniscus and to investigate OA meniscal cell-mediated calcium deposition. The hypothesis was that OA meniscal cells may play a role in pathological meniscal calcification.

METHODS

Studies were approved by our human subjects Institutional Review Board. Menisci were collected during joint replacement surgeries for OA patients and during limb amputation surgeries for osteosarcoma patients. Calcium deposits in menisci were examined by alizarin red staining. Expression of genes involved in biomineralization in OA meniscal cells was examined by microarray and real-time RT-PCR. Cell-mediated calcium deposition in monolayer culture of meniscal cells was examined using an ATP-induced (45)calcium deposition assay.

RESULTS

Calcium depositions were detected in OA menisci but not in normal menisci. The expression of several genes involved in biomineralization including ENPP1 and ANKH was upregulated in OA meniscal cells. Consistently, ATP-induced calcium deposition in the monolayer culture of OA meniscal cells was much higher than that in the monolayer culture of control meniscal cells.

CONCLUSIONS

Calcium deposition is common in OA menisci. OA meniscal cells calcify more readily than normal meniscal cells. Pathological meniscal calcification, which may alter the biomechanical properties of the knee meniscus, is potentially an important contributory factor to OA.

Adapted Boolean network models for extracellular matrix formation

BACKGROUND

Due to the rapid data accumulation on pathogenesis and progression of chronic inflammation, there is an increasing demand for approaches to analyse the underlying regulatory networks. For example, rheumatoid arthritis (RA) is a chronic inflammatory disease, characterised by joint destruction and perpetuated by activated synovial fibroblasts (SFB). These abnormally express and/or secrete pro-inflammatory cytokines, collagens causing joint fibrosis, or tissue-degrading enzymes resulting in destruction of the extra-cellular matrix (ECM).We applied three methods to analyse ECM regulation: data discretisation to filter out noise and to reduce complexity, Boolean network construction to implement logic relationships, and formal concept analysis (FCA) for the formation of minimal, but complete rule sets from the data.

RESULTS

First, we extracted literature information to develop an interaction network containing 18 genes representing ECM formation and destruction. Subsequently, we constructed an asynchronous Boolean network with biologically plausible time intervals for mRNA and protein production, secretion, and inactivation. Experimental gene expression data was obtained from SFB stimulated by TGFbeta1 or by TNFalpha and discretised thereafter. The Boolean functions of the initial network were improved iteratively by the comparison of the simulation runs to the experimental data and by exploitation of expert knowledge. This resulted in adapted networks for both cytokine stimulation conditions. The simulations were further analysed by the attribute exploration algorithm of FCA, integrating the observed time series in a fine-tuned and automated manner. The resulting temporal rules yielded new contributions to controversially discussed aspects of fibroblast biology (e.g., considerable expression of TNF and MMP9 by fibroblasts stimulation) and corroborated previously known facts (e.g., co-expression of collagens and MMPs after TNFalpha stimulation), but also revealed some discrepancies to literature knowledge (e.g., MMP1 expression in the absence of FOS).

CONCLUSION

The newly developed method successfully and iteratively integrated expert knowledge at different steps, resulting in a promising solution for the in-depth understanding of regulatory pathways in disease dynamics. The knowledge base containing all the temporal rules may be queried to predict the functional consequences of observed or hypothetical gene expression disturbances. Furthermore, new hypotheses about gene relations were derived which await further experimental validation.

Advances in understanding calcium-containing crystal disease

PURPOSE OF REVIEW

Calcium pyrophosphate dihydrate and basic calcium phosphate crystals are the two most common calcium-containing crystals involved in rheumatic diseases. Recent literature concerning their role in the pathogenesis of osteoarthritis is reviewed.

RECENT FINDINGS

In some instances, these calcium crystals might worsen osteoarthritis cartilage destruction. Laboratory investigations have identified determinants of cartilage calcification, especially a better characterization of matrix vesicle content and a better understanding of the regulation of inorganic pyrophosphate and phosphate concentration. In-vitro studies have highlighted new pathogenic mechanisms of calcium crystal-induced cell activation. Several intracellular signalling pathways are activated by calcium crystals. Recent studies suggested the implication of the inflammasome complex and a pivotal role for IL-1 in pseudogout attacks and chondrocyte apoptosis in basic calcium phosphate crystal-related arthropathies.

SUMMARY

Animal models of osteoarthritis and in-vitro studies using calcium pyrophosphate dihydrate and basic calcium phosphate crystals will improve our knowledge of these common crystals and could suggest new targets for drugs, as these common diseases are 'orphan' with respect to therapy.

Adaptor proteins and Ras synergistically regulate IL-1-induced ADAMTS-4 expression in human chondrocytes

Aggrecanases (a disintegrin [corrected] and metalloproteinase with thrombospondin motif, ADAMTSs) are principal proteases involved in cartilage extracellular matrix aggrecan degradation. The role and relative contribution of MyD88, IRAK1, and TRAF6 adaptor proteins in IL-1beta regulation of aggrecanase-1 (ADAMTS-4) is unknown. By small interfering RNAs-mediated knockdown, we show that IL-1beta-induced up-regulation of ADAMTS-4 in chondrocytes requires MyD88, IRAK1, and TRAF6 adaptor proteins. However, partial inhibition of ADAMTS-4 induction by their knockdown suggested the involvement of additional signaling proteins. Because IL-1beta is also known to induce reactive oxygen species (ROS) through Ras-mediated activation of NADPH oxidase, we investigated the implication of Ras in ADAMTS-4 regulation. Ras knockdown, or inhibition of ROS by antioxidants along with the ablation of MyD88, IRAK1, or TRAF6 more potently down-regulated IL-1beta-induced ADAMTS-4. In addition, IL-1beta-induced phosphorylation of downstream effectors, IkappaB kinase alphabeta, IkappaBalpha, and activation of transcription factor NF-kappaB was significantly reduced in the MyD88-, IRAK1-, TRAF6-, or Ras-deficient cells. The combined knockdown of Ras and individual adaptor proteins strongly blocked the activation of IKKalphabeta, IkappaBalpha, and NF-kappaB. These findings suggest that Ras, ROS along with MyD88, IRAK1, or TRAF6 synergistically mediate ADAMTS-4 regulation by IL1-beta. Thus, complete ablation of ADAMTS-4 induction could be achieved by combined inhibition of Ras and individual adaptor proteins, which may be of therapeutic value in arthritis.

Mechanism of basic calcium phosphate crystal-stimulated matrix metalloproteinase-13 expression by osteoarthritic synovial fibroblasts: inhibition by prostaglandin E2

OBJECTIVE

To determine the mechanism of matrix metalloproteinase (MMP)-13 upregulation in osteoarthritic synovial fibroblasts (OASF) in response to stimulation with basic calcium phosphate (BCP) crystals and to investigate the effect of prostaglandin (PG)E2 on BCP crystal-stimulated MMP expression.

METHODS

Primary OASF were stimulated with BCP crystals; mRNA expression was measured by real-time reverse transcription-polymerase chain reaction and protein levels were assessed by Western blotting.

RESULTS

BCP crystals upregulated MMP-13 mRNA expression over 20-fold and increased MMP-13 protein production in OASF. BCP crystal-stimulated MMP-13 mRNA expression was blocked by inhibition of the extracellular regulated kinase (ERK1/2) and p38 mitogen activated protein kinase (MAPK) pathways and inhibition of the activation of nuclear factor kappaB. Addition of exogenous PGE2 downregulated BCP crystal-stimulated MMP-13 expression. In contrast, PGE2 upregulated, and had no effect, on BCP crystal stimulated MMP-3 and MMP-1 mRNA expression, respectively. These effects of PGE2 were diminished by L-161,982, a selective EP4 receptor antagonist, and mimicked by CAY10399, a selective EP2 receptor agonist, and forskolin, an adenylate cyclase activator.

CONCLUSIONS

These data suggest that BCP crystal induction of MMP-13 expression may involve the ERK1/2 and p38 MAPK pathways and activation of nuclear factor kappaB; this upregulation of MMP-13 may contribute to the accelerated cartilage breakdown in BCP crystal-associated osteoarthritis. PGE2 had contrasting effects on BCP crystal-stimulated MMP-3 and MMP-13 mRNA expression, mediated in an EP2/EP4/cAMP-dependent manner, suggesting that PGE2 may have beneficial as well as deleterious effects in BCP crystal-associated osteoarthritis.

Annexin 5 overexpression increased articular chondrocyte apoptosis induced by basic calcium phosphate crystals

OBJECTIVES

Basic calcium phosphate (BCP) crystals (octacalcium phosphate (OCP), carbapatite (CA) and hydroxyapatite (HA)) are associated with severe forms of osteoarthritis. In advanced osteoarthritis, cartilage shows chondrocyte apoptosis, overexpression of annexin 5 (A5) and BCP crystal deposition within matrix vesicles. We assessed in vitro whether BCP crystals and overexpression of A5 increased chondrocyte apoptosis.

METHODS

Apoptosis was induced by BCP crystals, tumour necrosis factor (TNF)-alpha (20 ng/ml) and Fas ligand (20 ng/ml) in normal articular chondrocytes (control) and in A5 overexpressed chondrocytes, performed by adenovirus infection. Apoptosis was assessed by caspase 3 (Cas3) activity, and DNA fragmentation.

RESULTS

All BCP crystals, TNF-alpha and Fas ligand induced chondrocyte apoptosis as demonstrated by decreased cell viability and increased Cas3 activity and DNA fragmentation. TUNEL (terminal deoxyribonucleotide transferase-mediated dUTP nick end-labelling)-positive staining chondrocytes were increased by OCP (12.4 (5.2)%), CA (9.6 (2.6)%) and HA (9.2 (3.0)%) crystals and TNF-alpha (9.6 (2.4)%) stimulation compared with control (3.1 (1.9)%). BCP crystals increased Cas3 activity in a dose-dependent fashion. BCP-crystal-induced chondrocyte apoptosis was independent from TNF-alpha and interleukin-1beta pathways but required cell-crystal contact and intralysosomal crystal dissolution. Indeed, preincubation with ammonium chloride, a lysosomal inhibitor of BCP crystal dissolution, significantly decreased BCP-crystal-induced Cas3 activity. Finally, overexpression of A5 enhanced BCP crystal- and TNF-alpha-induced chondrocyte apoptosis.

CONCLUSIONS

Overexpression of A5 and the presence of BCP crystals observed in advanced osteoarthritis contributed to chondrocyte apoptosis. Our results suggest a new pathophysiological mechanism for calcium-containing crystal arthropathies.

Treatment of arthritis with a selective inhibitor of c-Fos/activator protein-1

To inhibit arthritis upstream of inflammatory cytokine release and matrix metalloproteinase (MMP) action, we designed de novo a small-molecule inhibitor of c-Fos/activator protein-1 (AP-1) using three-dimensional (3D) pharmacophore modeling. This model was based on the 3D structure of the basic region-leucine zipper domain of AP-1-DNA complex. Administration of this inhibitor prevented type II collagen-induced arthritis from day 21, before the onset of arthritis, or from day 27, resolved arthritis after its onset. Suppression of disease was accomplished by reducing the amounts of inflammatory cytokines and MMPs in vivo in sera and joints and in vitro in synovial cell and chondrocyte cultures. The primary action of this molecule was the inhibition of matrix-degrading MMPs and inflammatory cytokines including interleukin 1beta; this molecule also synergized with anti-tumor necrosis factor alpha to inhibit arthritis. Thus, selective inhibition of c-Fos/AP-1 resolves arthritis in a preclinical model of the disease.

Matrine inhibits PMA-induced MMP-1 expression in human dermal fibroblasts

Matrix metalloproteinase-1 (MMP-1) plays an important role in the maintenance and turnover of extracellular matrix (ECM) macromolecules. Remodelling of extracellular matrix by MMPs is a hallmark feature of physiological and pathological processes. In this study, in order to establish the therapeutic potential of matrine, we investigated its effect on MMP-1 expression in human dermal fibroblast cells. We found that matrine inhibited both MMP-1 mRNA and protein expression induced by PMA (phorbol myristate acetate). Therefore, we characterized the inhibitory mechanism of matrine on PMA-induced MMP-1 expression. Matrine inhibited PMA-induced activation of the AP-1 promoter, an important nuclear transcription factor in MMP-1 expression. Additionally, we detected that matrine suppressed the PMA-induced phosphorylation of two mitogen-activated protein kinases, extracellular signal-regulated protein kinase and c-Jun N-terminal kinase, but did not suppress the PMA-induced phosphorylation of p38 kinase. These results suggest that matrine suppresses PMA-induced MMP-1 expression through inhibition of the AP-1 signaling pathway and also may be beneficial for treatment of some inflammatory skin disorders.

Link between the early calcium deposition in placenta and nanobacterial-like infection

The placenta is a vitally important organ in the regulation of embryonic development. That is why extensive calcium deposition [also named as pathological placental calcification (PPC)] could have serious negative consequences for the adequate growth of embryos. The nature and mechanism of PPC development has not been defined as yet. In the present investigation, we have tested the hypothesis that the molecular basis of PPC development consists of nanobacteria-induced calcification in infected female placenta. Electron microscopy findings support this hypothesis. The initial stage of micro-calcification may originate from the external surface of individual nanobacteria-like particles found mainly in placental extracellular matrix, where initial calcium deposition occurs as a needle surface deposition or as an amorphous-like surface precipitate. Further calcific propagation in placenta takes place in the newly formed macro-cavities, which are characterized by low electron density, possibly reflecting its liquid content around calcium deposition. The micro-cavities contain free nanobacterial-like particles, which may relate to atypical Gram-negative bacteria but not to apoptotic bodies by morphological characters and DNA/RNA distribution. We hypothesize that the increased placental calcification might be caused, at least in part, by nanobacterial infection.

Basic calcium phosphate crystals activate c-fos expression through a Ras/ERK dependent signaling mechanism

Diseases caused by calcium pyrophosphate dihydrate (CPPD) and basic calcium phosphate (BCP) crystals occur frequently in osteoarthritic joints. Both crystals induce mitogenesis, metalloproteinase synthesis and secretion by fibroblasts and chondrocytes, promoting degradation of articular tissue. We investigated the mechanism by which BCP activates the c-fos proto-oncogene, which has been shown to activate various matrix metalloproteinases (MMPs). We demonstrate that BCP crystals induce c-fos expression primarily through a Ras/ERK-dependent signaling mechanism targeting two highly conserved regulatory binding sites, the serum response element (SRE) and the cAMP response element (CRE). These results establish a calcium crystal induced, calcium/calmodulin independent, signaling pathway in which BCP crystals activate Ras/MAPK, which can directly target an SRF-containing transcription factor complex, to induce fibroblasts to secrete metalloproteinases.

Prostaglandin E2 downregulates TNF-α-induced production of matrix metalloproteinase-1 in HCS-2/8 chondrocytes by inhibiting Raf-1/MEK/ERK cascade through EP4 prostanoid receptor activation

Matrix metalloproteinase-1 (MMP-1, collagenase-1) plays a pivotal role in the process of joint destruction in degenerative joint diseases. We have examined the regulation of MMP-1 production in human chondrocytic HCS-2/8 cells stimulated by tumor necrosis factor-alpha (TNF-alpha). In response to TNF-alpha, MMP-1 is induced and actively released from HCS-2/8 cells. The induction of MMP-1 expression correlates with activation of ERK1/2, MEK, and Raf-1, and is potently prevented by U0126, a selective inhibitor of MEK1/2 activation. In contrast, SB203580, a selective p38 mitogen-activated protein kinases (MAPK) inhibitor, had no effects on TNF-alpha-induced MMP-1 release. A serine/threonine kinase, Akt was not activated in TNF-alpha-stimulated HCS-2/8 cells. TNF-alpha stimulated the production of PGE(2) in addition to MMP-1 in HCS-2/8 cells. Exogenously added PGE(2) potently inhibited TNF-alpha-induced both MMP-1 production and activation of ERK1/2. The effects of PGE(2) were mimicked by ONO-AE1-329, a selective EP4 receptor agonist but not by butaprost, a selective EP2 agonist. In contrast, blockade of endogenously produced PGE(2) signaling by ONO-AE3-208, a selective EP4 receptor antagonist, enhanced TNF-alpha-induced MMP-1 production. Furthermore, the suppression of MMP-1 production by exogenously added PGE(2) was reversed by ONO-AE3-208. Activation of EP4 receptor resulted in cAMP-mediated phosphorylation of Raf-1 on Ser259, a negative regulatory site, and blocked activation of Raf-1/MEK/ERK cascade. Taken together, these findings indicate that Raf-1/MEK/ERK signaling pathway plays a crucial role in the production of MMP-1 in HCS-2/8 cells in response to TNF-alpha, and that the produced PGE(2) downregulates the expression of MMP-1 by blockage of TNF-alpha-induced Raf-1 activation through EP4-PGE(2) receptor activation.

Emodin inhibits TNF alpha-induced MMP-1 expression through suppression of activator protein-1 (AP-1)

Matrix metalloproteinases (MMPs) are the proteases involved in the degradation of the extracellular matrix. MMP-1 is thought to be one of the key enzymes acting in fibrolysis, a process closely related to tissue remodeling. In this study, we found that emodin, an anthraquinone which has been isolated from the rhizome of Rheum palmatum, significantly inhibited TNF alpha-induced MMP-1 gene expression in a concentration-dependent manner. Therefore, we have attempted to characterize the inhibitory mechanism of emodin in TNF alpha-induced MMP-1 expression. Emodin was determined to inhibit TNF alpha-induced activation of AP-1 promoter, an important nuclear transcription factor in MMP-1 expression. Additionally, we detected that emodin suppressed the TNF alpha-induced phosphorylation of two mitogen-activated protein kinases, extracellular signal-regulated protein kinase and c-Jun N-terminal kinase, but it did not suppress the TNF alpha-induced phosphorylation of p38 kinase. In a consistent result, the TNF alpha-induced MMP-1 expression was inhibited by PD98059 (MEK/ERK inhibitor) and SP600125 (JNK inhibitor), but was not inhibited by SB203580, a p38 MAPK inhibitor. Taken together, these results show that emodin suppresses TNF alpha-induced MMP-1 expression through the inhibition of the AP-1 signaling pathway.

Acceleration of matrix metalloproteinase-1 production and activation of platelet-derived growth factor receptor β in human coronary smooth muscle cells by oxidized LDL and 4-hydroxynonenal

Increases in matrix metalloproteinases (MMPs) at atherosclerotic lesions are involved in the migration of smooth muscle cells (SMCs) into the intima and to the rupture of plaques, being implicated in the progression of atherosclerosis. The present study examined the mechanisms underlying the production of MMP-1, interstitial collagenase-1, induced by oxidized low-density lipoprotein (oxLDL) and 4-hydroxynonenal (4-HNE), factors proposed to play a pivotal role in atherogenesis, in human coronary SMCs. oxLDL promoted the production of MMP-1 with the preceding phosphorylation of extracellular signal-regulated kinase (ERK) 1/2. Immunoprecipitation of platelet-derived growth factor receptor beta (PDGFR-beta) revealed that oxLDL induced tyrosine phosphorylation of the receptor. Inhibition of the activation of PDGFR-beta and ERK1/2 resulted in a suppression of the production of MMP-1. Consistently, 4-HNE also elicited the production of MMP-1 with the preceding phosphorylation of PDGFR-beta and ERK1/2. The 4-HNE-induced production of MMP-1 was prevented when the activation of PDGFR-beta and ERK1/2 was inhibited. The present results suggest that the activation of PDGFR-beta and ERK1/2 is involved in the production of MMP-1 in oxLDL- and 4-HNE-stimulated human coronary SMCs.

Calcium crystal deposition diseases: update on pathogenesis and manifestations

Basic calcium phosphate (BCP) and calcium pyrophosphate dihydrate crystals are the most common types of pathologic calcium-containing crystals. Although these crystals long have been associated with a variety of rheumatic syndromes, recent evidence implicates BCP crystals in the pathogenesis of breast cancer and atherosclerosis. Although understanding of molecular mechanisms involved in generating these pathologic effects has been advanced significantly in recent years, they still are understood incompletely. Such advances are essential to the ongoing search for effective therapies for crystal-associated diseases.

Soya isoflavones suppress phorbol 12-myristate 13-acetate-induced COX-2 expression in MCF-7 cells

Epidemiological studies indicate that Asian women have a lower incidence of breast cancer compared with their counterparts in the West, and soya consumption has been suggested as a contributory factor. Clinical and animal studies have revealed that cyclooxygenase-2 (COX-2) expression is associated with a risk of breast cancer. In the present study, we investigated the effect of soya isoflavones on the expression of COX-2 in the breast cell line MCF-7. Genistein, daidzein and equol were found to inhibit COX-2 expression induced by phorbol 12-myristate 13-acetate (PMA). Similar findings were observed in the COX-2 protein analysis. In order to study transcriptional control, a fragment of the 5'-flanking region of the hCOX-2 gene was amplified and inserted into a firefly luciferase reporter plasmid. The reporter assay indicated that the transactivation of the hCOX-2 promoter was induced by PMA, and activity was inhibited with the co-administration of genistein, daidzein or equol. An activator protein-1 (AP-1)/cyclic AMP response element binding protein (CREB) binding site (-59/-53) was identified in hCOX-2 promoter, and this could be critical in PMA-induced COX-2 expression. Truncation reporter plasmids with (-70/-36) and without (-51/-36) AP-1/CREB were constructed for subsequent analysis. The results revealed that the hCOX-2 promoter transactivation suppressed by isoflavone could be dependent on AP-1/CREB binding. Nonetheless, this study illustrated that the soya isoflavones reduced COX-2 expression, which could be important in the post-initiation events of breast carcinogenesis.

Balance between polyoma enhancing activator 3 and activator protein 1 regulates Helicobacter pylori-stimulated matrix metalloproteinase 1 expression

Helicobacter pylori infection and elevated expression of tissue matrix metalloproteinase 1 (MMP-1) are both associated with gastric cancer. We investigated the regulation of MMP-1 expression during H. pylori infection. Real-time reverse transcription-PCR was used to examine mucosal MMP-1 mRNA levels in 55 patients with gastric cancers and 61 control patients. Increased MMP-1 mRNA levels in the gastric mucosa and epithelial cells were observed in H. pylori infections in which both the cag pathogenicity island (PAI) and outer inflammatory protein A (OipA) were expressed. The combined induction of c-fos, c-jun, and polyoma enhancing activator-3 (pea-3) by H. pylori caused maximal increase in MMP-1 expression. Activation of the MMP-1 promoter by H. pylori involved occupation of the activator protein 1 (AP-1) sites at -72 and -181 and, surprisingly, vacancy of the -88 PEA-3 site. Electrophoretic mobility shift, supershift, and chromatin immunoprecipitation assays showed increased binding of c-Fos and c-Jun to the -72 and -181 AP-1 sites during H. pylori infection. Importantly, during wild-type H. pylori infection, we detected increased PEA-3 binding to the -72AP-1 site and decreased PEA-3 binding to the -88 PEA-3 site. However, during infection with the cag PAI and oipA mutants, PEA-3 binding to the -88 site was detected. MMP-1 and pea-3 activities are increased in gastric cancers. Maximal activation of MMP-1 transcription requires the cag PAI and OipA, which regulate AP-1 and PEA-3 binding. Thus, cag PAI and OipA provide a possible link between bacterial virulence factors and important host factors related to disease pathogenesis.

Basic calcium phosphate crystals: pathways to joint degeneration

PURPOSE OF REVIEW

Basic calcium phosphate crystals have long been associated with rheumatic syndromes. Although an understanding of the molecular mechanisms involved in generating these pathological effects has been significantly advanced in recent years, it is still incomplete.

RECENT FINDINGS

Basic calcium phosphate crystals have been shown to increase prostaglandin E(2) production in human fibroblasts, mediated by the induction of both cyclooxygenases 1 and 2. Basic calcium phosphate crystals have also been found to upregulate IL-1beta in fibroblasts and chondrocytes. The upregulation of inducible nitric oxide synthase and stimulation of nitric oxide production in chondrocytes by octacalcium phosphate crystals has been demonstrated. The involvement of protein kinase C isoforms in basic calcium phosphate crystal-mediated matrix metalloproteinase 1 and 3 expression in human fibroblasts has been clarified. Two pathways are involved: protein kinase Calpha mediates the calcium-dependent pathway, whereas protein kinase Cmu activates the extracellular-regulated kinase pathway in a calcium-independent cascade. In addition, basic calcium phosphate crystals activate the transcription factor Egr-1, an effect that may contribute to the mitogenic effect of these crystals on fibroblasts.

SUMMARY

Recent findings have emphasized the potential for basic calcium phosphate crystals to stimulate the production of a variety of inflammatory mediators such as prostaglandin E(2), nitric oxide, IL-1beta and matrix metalloproteinases, and have helped to elucidate the mechanisms of these effects. Such advances are essential for the ongoing search for effective therapies for basic calcium phosphate crystal-associated diseases.

Epidermal growth factor affects the synthesis and degradation of type I collagen in cultured human dermal fibroblasts

EGF and type I collagen are known to play important roles in wound healing. In the present study, we demonstrated that EGF down-regulates the expression of type I procollagen protein as well as alpha2(I) collagen mRNA in cultured human dermal fibroblasts. EGF induced the degradation of type I procollagen protein in conditioned medium through the up-regulation of MMP-1 expression. EGF down-regulated alpha2(I) mRNA expression partially at the post-transcriptional level by reducing the mRNA stability. In contrast, EGF up-regulated MMP-1 mRNA expression mostly at the transcriptional level, in that it had a stimulatory effect on MMP-1 promoter activity, but no effect on MMP-1 mRNA stability. The MEK/ERK signaling pathway was shown to be involved in EGF-mediated type I collagen and MMP-1 expression.

Fos/AP-1 proteins in bone and the immune system

The skeleton and the immune system share a variety of different cytokines and transcription factors, thereby mutually influencing each other. These interactions are not confined to the bone marrow cavity where bone cells and hematopoietic cells exist in proximity but also occur at locations that are target sites for inflammatory bone diseases. The newly established research area termed 'osteoimmunology' attempts to unravel these skeletal/immunological relationships. Studies towards a molecular understanding of inflammatory bone diseases from an immunological as well as a bone-centered perspective have been very successful and led to the identification of several signaling pathways that are causally involved in inflammatory bone loss. Induction of receptor activator of nuclear factor (NF)-kappaB ligand (RANKL) signals by activated T cells and subsequent activation of the key transcription factors Fos/activator protein-1 (AP-1), NF-kappaB, and NF for activation of T cells c1 (NFATc1) are in the center of the signaling networks leading to osteoclast-mediated bone loss. Conversely, nature has employed the interferon system to antagonize excessive osteoclast differentiation, although this counteracting activity appears to be overruled under pathological conditions. Here, we focus on Fos/AP-1 functions in osteoimmunology, because this osteoclastogenic transcription factor plays a central role in inflammatory bone loss by regulating genes like NFATc1 as well as the interferon system. We also attempt to put potential therapeutic strategies for inflammatory bone diseases in perspective.

Inflammation-responsive transcription factors SAF-1 and c-Jun/c-Fos promote canine MMP-1 gene expression

Matrix metalloproteinase-1 (MMP-1) has been implicated in the pathogenesis of osteoarthritis (OA) due to its ability to degrade extracellular matrix component of the joint cartilage tissue that cushions the bone from frictional damage. Canine hip dysplasia, a developmental orthopedic disease which results in arthritic condition as is seen in human OA is an excellent system to study the involvement of MMP-1 in the pathogenesis of OA. To date, however, no report is available regarding canine MMP-1 promoter and the regulatory mechanism by which increased synthesis of MMP-1 protein might be regulated. To gain an insight, we have investigated the promoter region of canine MMP-1. MMP-1 synthesis in the resident cells of arthritic joints is regulated via two major cytokines, IL-1beta and TNF-alpha. By using a series of progressively deleted reporter constructs, multiple cytokine-responsive elements were identified in the proximal promoter region of canine MMP-1. These include DNA-binding elements of AP-1 and SAF-1 transcription factors. Mutation of AP-1 or SAF-1 element resulted in marked reduction in the cytokine responsiveness of MMP-1 promoter. We show that AP-1 and SAF-1 DNA-binding activities are increased in cytokine-stimulated cells as well as in osteoarthritic cartilage tissues. In correlation, immunohistochemical analysis indicated higher levels of MMP-1, SAF-1 and AP-1 proteins in osteoarthritic but not in the normal cartilage tissue. These results show that induction and activation of AP-1 and SAF-1 transcription factors are involved in the regulation of MMP-1 expression in the chondrocytes which could be used as therapeutic targets to combat pathogenesis of OA.

Regulation of interleukin-6 promoter activation in gastric epithelial cells infected with Helicobacter pylori

The regulation of Helicobacter pylori induced interleukin (IL)-6 in the gastric epithelium remains unclear. Primary gastric epithelial cells and MKN28 cells were cocultured with H. pylori and its isogenic cag pathogenicity island (PAI) mutant and/or oipA mutants. H. pylori infection-induced IL-6 mRNA expression and IL-6 protein production, which was further enhanced by the cag PAI and OipA. Luciferase reporter gene assays and electrophoretic mobility shift assays showed that full IL-6 transcription required binding sites for nuclear factor-kappaB (NF-kappaB), cAMP response element (CRE), CCAAT/enhancer binding protein (C/EBP), and activator protein (AP)-1. The cag PAI and OipA were involved in binding to NF-kappaB, AP-1, CRE, and C/EBP sites. The cag PAI activated the extracellular signal-regulated kinase (ERK) and Jun N-terminal kinase (JNK) pathways; OipA activated the p38 pathway. Transfection of dominant negative G-protein confirmed roles for Raf, Rac1, and RhoA in IL-6 induction. Overall, the cag PAI-related IL-6 signal transduction pathway involved the Ras/Raf/MEK1/2/ERK/AP-1/CRE pathway and the JNK/AP-1/CRE pathway; the OipA-related pathway is p38/AP-1/CRE and both the cag PAI and OipA appear to be involved in the RhoA/Rac1/NF-kappaB pathway. Combination of different pathways by the cag PAI and OipA will lead to the maximum IL-6 induction.

Octacalcium phosphate crystals directly stimulate expression of inducible nitric oxide synthase through p38 and JNK mitogen-activated protein kinases in articular chondrocytes

Basic calcium phosphate (BCP) crystals, including hydroxyapatite, octacalcium phosphate (OCP) and carbonate-apatite, have been associated with severe osteoarthritis and several degenerative arthropathies. Most studies have considered the chondrocyte to be a bystander in the pathogenesis of calcium crystal deposition disease, assuming that synovial cell cytokines were the only triggers of chondrocyte activation. In the present study we identified direct activation of articular chondrocytes by OCP crystals, which are the BCP crystals with the greatest potential for inducing inflammation. OCP crystals induced nitric oxide (NO) production and inducible nitric oxide synthase (NOS) mRNA expression by isolated articular chondrocytes and cartilage fragments, in a dose-dependent manner and with variations over time. OCP crystals also induced IL-1β mRNA expression. Using pharmacological and cytokine inhibitors, we observed that OCP crystals induced NO production and inducible NOS mRNA activation were regulated at both the transcriptional and the translational levels; were independent from IL-1β gene activation; and involved p38 and c-Jun amino-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) pathways, as further confirmed by OCP crystal-induced p38 and JNK MAPK phosphorylation. Taken together, our data suggest that the transcriptional inducible NOS response to OCP crystals involved both the p38 and the JNK MAPK pathways, probably under the control of activator protein-1. NO, a major mediator of cartilage degradation, can be directly produced by BCP crystals in chondrocytes. Together with synovial activation, this direct mechanism may be important in the pathogenesis of destructive arthropathies triggered by microcrystals.

Biologic effects of calcium-containing crystals

PURPOSE OF REVIEW

Calcium-containing crystals can cause the degeneration of articular tissues in two separate pathways. In the direct pathway, crystals directly induce synoviocytes to proliferate and produce metalloproteinases and prostaglandins. The other pathway, the paracrine pathway, involves the interaction between crystals and macrophages/monocytes, which leads to the synthesis and release of cytokines, which can reinforce the action of crystals on synoviocytes and/or induce chondrocytes to secrete enzymes and which eventually causes the degeneration of articular tissues. The purpose of this review is to highlight the recent findings of the biologic effect of these crystals.

RECENT FINDINGS

In the past few years, major advances in the understanding of the biologic effect of crystals and the signal transduction pathway of crystal-induced cell activation offer a unique opportunity to examine the role of crystal in osteoarthritis and cartilage degeneration.

SUMMARY

Evidence for a causal role of crystals in cartilage degeneration in osteoarthritis is primarily inferential and is based on correlative data. Clinical observations indicate that exaggerated and uniquely distributed cartilage degeneration is associated with these deposits. Measurements of putative markers of cartilage breakdown suggest that these crystals magnify the degenerative process. Studies have shown two potential mechanisms by which crystals cause degeneration. These involve the stimulation of mitogenesis in synovial fibroblasts and the secretion of metalloproteinases by cells that subject these crystals to phagocytosis. New information on how crystals form and how they exert their biologic effects will help in the design of an effective therapeutic approach.