MKP-1 Deficiency Exacerbates Skin Fibrosis in a Mouse Model of Scleroderma.

Scleroderma is a chronic fibrotic disease, where proinflammatory and profibrotic events precede collagen accumulation. MKP-1 [mitogen-activated protein kinase (MAPK) phosphatase-1] downregulates inflammatory MAPK pathways suppressing inflammation. MKP-1 also supports Th1 polarization, which could shift Th1/Th2 balance away from profibrotic Th2 profile prevalent in scleroderma. In the present study, we investigated the potential protective role of MKP-1 in scleroderma. We utilized bleomycin-induced dermal fibrosis model as a well-characterized experimental model of scleroderma. Dermal fibrosis and collagen deposition as well as the expression of inflammatory and profibrotic mediators were analyzed in the skin samples. Bleomycin-induced dermal thickness and lipodystrophy were increased in MKP-1-deficient mice. MKP-1 deficiency enhanced collagen accumulation and increased expression of collagens, 1A1 and 3A1, in the dermis. Bleomycin-treated skin from MKP-1-deficient mice also showed enhanced expression of inflammatory and profibrotic factors IL-6, TGF-ß1, fibronectin-1 and YKL-40, and chemokines MCP-1, MIP-1α and MIP-2, as compared to wild-type mice. The results show, for the first time, that MKP-1 protects from bleomycin-induced dermal fibrosis, suggesting that MKP-1 favorably modifies inflammation and fibrotic processes that drive the pathogenesis of scleroderma. Compounds enhancing the expression or activity of MKP-1 could thus prevent fibrotic processes in scleroderma and possess potential as a novel immunomodulative drug.

TRPA1 as a potential factor and drug target in scleroderma: dermal fibrosis and alternative macrophage activation are attenuated in TRPA1-deficient mice in bleomycin-induced experimental model of scleroderma.

BACKGROUND: Systemic sclerosis is a rheumatoid disease best known for its fibrotic skin manifestations called scleroderma. Alternatively activated (M2-type) macrophages are normally involved in the resolution of inflammation and wound healing but also in fibrosing diseases such as scleroderma. TRPA1 is a non-selective cation channel, activation of which causes pain and neurogenic inflammation. In the present study, we investigated the role of TRPA1 in bleomycin-induced skin fibrosis mimicking scleroderma. METHODS: Wild type and TRPA1-deficient mice were challenged with intradermal bleomycin injections to induce a scleroderma-mimicking disease. Macrophages were investigated in vitro to evaluate the underlying mechanisms. RESULTS: Bleomycin induced dermal thickening and collagen accumulation in wild type mice and that was significantly attenuated in TRPA1-deficient animals. Accordingly, the expression of collagens 1A1, 1A2, and 3A1 as well as pro-fibrotic factors TGF-beta, CTGF, fibronectin-1 and YKL-40, and M2 macrophage markers Arg1 and MRC1 were lower in TRPA1-deficient than wild type mice. Furthermore, bleomycin was discovered to significantly enhance M2-marker expression particularly in the presence of IL-4 in wild type macrophages in vitro, but not in macrophages harvested from TRPA1-deficient mice. IL-4-induced PPARγ-expression in macrophages was increased by bleomycin, providing a possible mechanism behind the phenomenon. CONCLUSIONS: In conclusion, the results indicate that interfering TRPA1 attenuates fibrotic and inflammatory responses in bleomycin-induced scleroderma. Therefore, TRPA1-blocking treatment could potentially alleviate M2 macrophage driven diseases like systemic sclerosis and scleroderma.

Inflammation in Health and Disease: New Insights and Therapeutic Avenues.

The inflammatory response is an adaptive mechanism that evolved to fight against infections and tissue damage [...].

mtDNA variability determines spontaneous joint aging damage in a conplastic mouse model.

Mitochondria and mtDNA variations contribute to specific aspects of the aging process. Here, we aimed to investigate the influence of mtDNA variation on joint damage in a model of aging using conplastic mice. A conplastic (BL/6NZB) mouse strain was developed with the C57BL/6JOlaHsd nuclear genome and NZB/OlaHsd mtDNA, for comparison with the original C57BL/6JOlaHsd strain (BL/6C57). Conplastic (BL/6NZB) and BL/6C57 mice were sacrificed at 25, 75, and 90 weeks of age. Hind knee joints were processed for histological analysis and joint pathology graded using the Mankin scoring system. By immunohistochemistry, cartilage expression of markers of autophagy (LC3, Beclin-1, and P62) and markers of senescence (MMP13, beta-Galactosidase, and p16) and proliferation (Ki67) were analyzed. We also measured the expression of 8-oxo-dG and cleaved caspase-3. Conplastic (BL/6NZB) mice presented lower Mankin scores at 25, 75, and 90 weeks of age, higher expression of LC3 and Beclin-1 and lower of P62 in cartilage than the original strain. Moreover, the downregulation of MMP13, beta-Galactosidase, and p16 was detected in cartilage from conplastic (BL/6NZB) mice, whereas higher Ki67 levels were detected in these mice. Finally, control BL/6C57 mice showed higher cartilage expression of 8-oxo-dG and cleaved caspase-3 than conplastic (BL/6NZB) mice. This study demonstrates that mtDNA genetic manipulation ameliorates joint aging damage in a conplastic mouse model, suggesting that mtDNA variability is a prognostic factor for aging-related osteoarthritis (OA) and that modulation of mitochondrial oxidative phosphorylation (OXPHOS) could be a novel therapeutic target for treating OA associated with aging.

WISP-2 modulates the induction of inflammatory mediators and cartilage catabolism in chondrocytes.

Wnt-1 inducible signaling pathway protein 2 (WISP-2/CCN5) is a recently identified adipokine that has been described as an important mediator of canonical Wnt activation in adipogenic precursor cells. In osteoarthritis (OA), the most common form of arthritis, chondrocytes exhibit aberrant and increased production of pro-inflammatory mediators and matrix degrading enzymes such as IL-1ß and MMP-13. Although recent evidence suggests a role for Wnt signaling in OA physiopathology, little is known about the involvement of WISP-2 in cartilage degradation. In the present study, we determined the expression of WISP-2 in healthy and OA human chondrocytes. WISP-2 expression is modulated along chondrocyte differentiation and downregulated at the onset of hypertrophy by inflammatory mediators. We also investigated the effect of WISP-2 on cartilage catabolism and performed WISP-2 loss-of-function experiments using RNA interference technology in human T/C-28a2 immortalized chondrocytes. We demonstrated that recombinant human WISP-2 protein reduced IL-1ß-mediated chondrocyte catabolism, that IL-1ß and WNT/b-catenin signaling pathways are involved in rhWISP-2 protein and IL-1ß effects in human chondrocytes, and that WISP-2 has a regulatory role in attenuating the catabolic effects of IL-1ß in chondrocytes. Gene silencing of WISP-2 increased the induction of the catabolic markers MMP-13 and ADAMTS-5 and the inflammatory mediators IL-6 and IL-8 triggered by IL-1ß in human primary OA chondrocytes in a Wnt/ß-catenin dependent manner. In conclusion, here we have shown for the first time that WISP-2 may have relevant roles in modulating the turnover of extracellular matrix in the cartilage and that its downregulation may detrimentally alter the inflammatory environment in OA cartilage. We also proved the participation of Wnt/ß-catenin signaling pathway in these processes. Thus, targeting WISP-2 might represent a potential therapeutical approach for degenerative and/or inflammatory diseases of musculoskeletal system, such as osteoarthritis.

Activation of Hypothalamic AMP-Activated Protein Kinase Ameliorates Metabolic Complications of Experimental Arthritis.

OBJECTIVE: To investigate whether thermogenesis and the hypothalamus may be involved in the physiopathology of experimental arthritis (EA). METHODS: EA was induced in male Lewis rats by intradermal injection of Freund's complete adjuvant (CFA). Food intake, body weight, plasma cytokines, thermographic analysis, gene and protein expression of thermogenic markers in brown adipose tissue (BAT) and white adipose tissue (WAT), and hypothalamic AMP-activated protein kinase (AMPK) were analyzed. Virogenetic activation of hypothalamic AMPK was performed. RESULTS: We first demonstrated that EA was associated with increased BAT thermogenesis and browning of subcutaneous WAT leading to elevated energy expenditure. Moreover, rats experiencing EA showed inhibition of hypothalamic AMPK, a canonical energy sensor modulating energy homeostasis at the central level. Notably, specific genetic activation of AMPK in the ventromedial nucleus of the hypothalamus (a key site modulating energy metabolism) reversed the effect of EA on energy balance, brown fat, and browning, as well as promoting amelioration of synovial inflammation in experimental arthritis. CONCLUSION: Overall, these data indicate that EA promotes a central catabolic state that can be targeted and reversed by the activation of hypothalamic AMPK. This might provide new therapeutic alternatives to treat rheumatoid arthritis (RA)-associated metabolic comorbidities, improving the overall prognosis in patients with RA.

Mitochondrial DNA impact on joint damaged process in a conplastic mouse model after being surgically induced with osteoarthritis.

It has been suggested that mitochondrial dysfunction and mtDNA variations may contribute to osteoarthritis (OA) pathogenesis. However, the causative link to support this claim is lacking. Here, we surgically-induced OA in conplastic mice in order to evaluate the functional consequences of mtDNA haplotypes in their joint degeneration. BL/6NZB strain was developed with C57BL/6JOlaHsd nuclear genome and NZB/OlaHsdmtDNA while BL/6C57, which is the original, was developed with C57BL/6JOlaHsd nuclear genome and C57/OlaHsdmtDNA for comparison. The surgical DMM OA model was induced in both strains. Their knees were processed and examined for histopathological changes. Cartilage expression of markers of autophagy, apoptosis, oxidative stress and senescence were also analyzed by immunohistochemistry. The joints of BL/6NZB mice that were operated presented more cellularity together with a reduced OARSI histopathology score, subchondral bone, menisci score and synovitis compared to those of BL/6C57 mice. This was accompanied with higher autophagy and a lower apoptosis in the cartilage of BL/6NZB mice that were operated. Therefore, the study demonstrates the functional impact of non-pathological variants of mtDNA on OA process using a surgically-induced OA model. Conplastic (BL/6NZB ) mice develop less severe OA compared to the BL/6C57original strain. These findings demonstrate that mitochondria and mtDNA are critical targets for potential novel therapeutic approaches to treat osteoarthritis.

Dickkopf-3 (DKK3) Signaling in IL-1α-Challenged Chondrocytes: Involvement of the NF-κB Pathway.

OBJECTIVE: Osteoarthritis (OA) is an age-related biomechanical and low-grade inflammometabolic disease of the joints and one of the costliest and disabling forms of arthritis. Studies on matrix-degrading enzymes such as metalloproteases, which are implicated in the increased catabolism of extracellular matrix, are of paramount relevance. DKK3 is a member of DKK family and is best known for its role in cancer. Although there is some information about the participation of DKK3 in cartilage pathophysiology and on metalloproteases regulation, in particular, little is known about DKK3 signaling mechanisms. Thus, the aim of this study is to explore how DKK3 regulates matrix metalloproteinase-13 (MMP-13) expression. DESIGN: Gene, protein expression and protein phosphorylation in primary human chondrocytes and ATDC5 mouse cells were assessed by RT-qPCR and Western blot analysis. Further studies on DKK3 activity were performed by targeting DKK3 gene with a specific siRNA. RESULTS: DKK3 expression was found to be higher in OA human chondrocytes than healthy cells, being its expression decreased in interleukin-1α (IL-1α)-stimulated cells. DKK3 knockdown increased the induction of MMP-13 elicited by IL-1α in human and mouse chondrocytes and after the analysis of different signalling pathways, we observed that NF-κB pathway was involved in the regulation of MMP-13 expression by DKK3. CONCLUSIONS: Herein we have demonstrated, for the first time, that DKK3 gene silencing exacerbated NF-κB activation, resulting in an increased IL-1α-driven induction of MMP-13. Our results further confirm that DKK3 may play a protective role in OA by attenuating NF-κB activation and the subsequent production of metalloproteases.

Novel adipokine associated with OA: retinol binding protein 4 (RBP4) is produced by cartilage and is correlated with MMPs in osteoarthritis patients.

OBJECTIVE: Retinol binding protein 4 (RBP4) is a member of the lipocalin family and a vitamin A carrier in the blood. More recently, RBP4 has been described as an adipokine that is involved in insulin resistance and metabolic syndrome (MetS). As obesity, MetS and some adipokines contribute to the pathogenesis of osteoarthritis (OA), we investigated RBP4 in patients with OA. MATERIALS AND METHODS: Cartilage, synovial fluid and blood samples were collected from 100 OA patients undergoing total knee replacement surgery. Primary chondrocytes and cartilage tissue were cultured to measure the RBP4 expression. The concentrations of RBP4, other adipokines (adipsin, adiponectin, leptin and resistin) and biomarkers of OA (COMP, MMP-1, MMP-3 and YKL-40) were measured by immunoassay, and gene expression was measured by next-generation RNA sequencing. RESULTS: The OA cartilage samples released RBP4 into the culture medium, and the levels correlated positively with the expression of the adipokines adipsin, adiponectin, leptin and resistin. RBP4 was the most prominently expressed of these adipokines in the OA chondrocytes, and the expression of the RBP4 receptors STRA6 (stimulated by retinoic acid gene homologue 6) and TLR4 (Toll-like receptor 4) was also detected. Within the cartilage culture medium, RBP4 showed a positive correlation with MMP-1, MMP-3 and YKL-40. RBP4 was also present in the synovial fluid from the OA patients and correlated positively with the concentrations of RBP4 found in the plasma and the cartilage culture medium. Plasma RBP4 concentrations also showed a positive correlation with MMP-3 and adipsin. CONCLUSIONS: We show here, for the first time, that RBP4 is produced within OA joints and that it is associated with increased levels of adipokines and MMPs. The results suggest a role for RBP4 in the pathogenesis of OA and as a possible target for the disease-modifying drugs for the treatment of OA.

Natural Molecules for Healthy Lifestyles: Oleocanthal from Extra Virgin Olive Oil.

Extra virgin olive oil (EVOO) is the main source of fat in the Mediterranean diet. Phenolic compounds of EVOO, in particular, secoiridoids, are minor components that have generated special interest due to their positive effects on human health, supported by several clinical trials. This review summarizes the most recent findings on the pharmacological properties and action's mechanisms of secoiridoid oleocanthal, focusing attention on inflammation, oxidative stress, cancer, neurodegenerative processes, and rheumatic diseases. Being of relevance to the clinical effects of EVOO intake, the bioavailability and biotransformation of EVOO polyphenols are addressed. Moreover, this review summarizes the factors that may influence the oleocanthal concentration in EVOO. With the growing incidence of age- and lifestyle-related diseases, the current data indicated that the administration of EVOO rich in secoiridoids may be helpful in the prevention or treatment of different pathologies with an inflammatory component. Although promising, the future raises several questions and challenges, which are discussed here. The real beneficial effects of olive oil phenols on human health need to be clarified in new, well-designed clinical studies.

Attenuating Effects of Nortrachelogenin on IL-4 and IL-13 Induced Alternative Macrophage Activation and on Bleomycin-Induced Dermal Fibrosis.

Excessive alternative macrophage activation contributes to fibrosis. We studied the effects of nortrachelogenin, the major lignan component of Pinus sylvestris knot extract, on alternative (M2) macrophage activation. J774 murine and THP-1 human macrophages were cultured with IL-4+IL-13 to induce alternative activation, together with the extract and its components. Effects of nortrachelogenin were also studied in bleomycin-induced murine dermal fibrosis model. Knot extract significantly decreased the expression of alternative activation markers-arginase 1 in murine macrophages (97.4 ± 1.3% inhibition at 30 µg/mL) and CCL13 and PDGF in human macrophages-as did nortrachelogenin (94.9 ± 2.4% inhibition of arginase 1 at 10 µM). Nortrachelogenin also decreased PPARγ expression but had no effect on STAT6 phosphorylation. In vivo, nortrachelogenin reduced bleomycin-induced increase in skin thickness as well as the expression of collagens COL1A1, COL1A2, and COL3A1 (all by >50%). In conclusion, nortrachelogenin suppressed IL-4+IL-13-induced alternative macrophage activation and ameliorated bleomycin-induced fibrosis, indicating therapeutic potential in fibrosing conditions.

Oleocanthal Inhibits Catabolic and Inflammatory Mediators in LPS-Activated Human Primary Osteoarthritis (OA) Chondrocytes Through MAPKs/NF-κB Pathways.

BACKGROUND/AIMS: Oleocanthal (OC), a phenolic compound present in extra virgin olive oil (EVOO), has attracted attention since its discovery for its relevant pharmacological properties in different pathogenic processes, including inflammation. Here, we investigated the involvement of OC in LPS-activated osteoarthritis (OA) human primary chondrocytes. METHODS: Human primary chondrocytes were harvested from articular cartilage samples obtained from OA patients. The effects of OC on the viability of chondrocytes were tested by MTT assay. Protein and mRNA expression of several catabolic and pro-inflammatory factors after OC treatment were measured by RT-qPCR and western blot respectively. Moreover, we analysed the NO production by Griess reaction. Finally, several pathways mediators were analysed by western blot. RESULTS: We demonstrated that OC did not have any cytotoxic effect. Oleocanthal inhibited NO production and strongly decreased NOS2 and COX-2 protein and mRNA expression in LPS-activated human primary OA chondrocytes. Interestingly, OC also inhibits MMP-13 and ADAMTS-5. In addition, OC downregulates several pro-inflammatory factors, such as IL-6, IL-8, CCL3, LCN2 and TNF-α induced by LPS in human primary OA chondrocytes. Finally, we demonstrated that OC exerts its effects through the MAPK/P38/NF-kB pathways. CONCLUSION: These data show that OC is able to block LPS-mediated inflammatory response and MMP-13 and ADAMTS-5 induction in human primary OA chondrocytes via MAPKs/NF-kB pathways, suggesting that OC may be a promising agent for the treatment of inflammation in cartilage and a potential molecule to prevent disease progression by inhibiting metalloproteases and aggrecanases.

E74-Like Factor (ELF3) and Leptin, a Novel Loop Between Obesity and Inflammation Perpetuating a Pro-Catabolic State in Cartilage.

BACKGROUND/AIMS: The E74-like factor 3 (ELF3) is an inflammatory mediator that participates in cartilage destruction in osteoarthritis. Leptin and other adipokines negatively impact articular cartilage, triggering catabolic and inflammatory responses in chondrocytes. Here, we investigated whether leptin induces ELF3 expression in chondrocytes and the signaling pathway involved in this process. METHODS: We determined mRNA and protein levels of ELF3 by RT-qPCR and Western blotting using cultured human primary chondrocytes and the human T/C-28a2 chondrocyte cell line. Further, we measured luciferase activities of different reporter constructs, and we assessed the contribution of leptin to the induction of ELF3 mRNA by knocking down hLEPR gene expression using siRNA technology. RESULTS: Leptin synergizes with IL-1ß in inducing ELF3 expression in chondrocytes. We also found that PI3K, p38, and JAK2 signaling pathways are at play in the leptin-driven induction of ELF3. Moreover, we confirm the participation of NFΚB in the leptin/IL-1ß synergistic induction of ELF3. CONCLUSION: Here we show, for the first time, the regulation of ELF3 expression by leptin, suggesting that this transcription factor likely mediates the inflammatory responses triggered by leptin in articular chondrocytes.

Progranulin as a biomarker and potential therapeutic agent.

Progranulin is a cysteine-rich secreted protein with diverse pleiotropic actions and participates in several processes, such as inflammation or tumorigenesis. Progranulin was first identified as a growth factor and, recently, it was characterised as an adipokine implicated in obesity, insulin resistance and rheumatic disease. At a central level, progranulin acts as a neurotropic and neuroprotective factor and protects from neural degeneration. In this review, we summarise the most recent research advances concerning the potential role of progranulin as a therapeutic target and biomarker in cancer, neurodegenerative and inflammatory diseases.

Leptin in the interplay of inflammation, metabolism and immune system disorders.

Leptin is one of the most relevant factors secreted by adipose tissue and the forerunner of a class of molecules collectively called adipokines. Initially discovered in 1994, its crucial role as a central regulator in energy homeostasis has been largely described during the past 20 years. Once secreted into the circulation, leptin reaches the central and peripheral nervous systems and acts by binding and activating the long form of leptin receptor (LEPR), regulating appetite and food intake, bone mass, basal metabolism, reproductive function and insulin secretion, among other processes. Research on the regulation of different adipose tissues has provided important insights into the intricate network that links nutrition, metabolism and immune homeostasis. The neuroendocrine and immune systems communicate bi-directionally through common ligands and receptors during stress responses and inflammation, and control cellular immune responses in several pathological situations including immune-inflammatory rheumatic diseases. This Review discusses the latest findings regarding the role of leptin in the immune system and metabolism, with particular emphasis on its effect on autoimmune and/or inflammatory rheumatic diseases, such as rheumatoid arthritis and osteoarthritis.

Adipokines induce pro-inflammatory factors in activated Cd4+ T cells from osteoarthritis patient.

Osteoarthritis (OA) is a chronic systemic musculoskeletal disorder involving inflammation, immunity, and metabolic alterations. OA is commonly regarded as non-inflammatory disease; still inflammation is recognized as contributing to the symptoms and progression of OA. New evidence suggests that adipokines are involved in the pathophysiology of OA and might modulate the production of inflammatory mediators including in immune cells. However, the role of immune component in osteoarthritis is still poorly investigated. To gain further insights into the interaction of immune cells in OA and the role of adipokines on these cells, we performed experiments aimed to determine the cytokine profile in activated CD4+ T cells from OA patients. For completeness, we also explored the cross talk between T lymphocytes and chondrocytes in OA by co-culturing human primary chondrocytes with activated CD4+ T cells in two ways: the first by incubating the cells by direct contact (D.C.) or by transwell system. Our results show that the exposure of activated CD4+ T cells to adipokines modulates IL-6, IL-8, and CCL-3 production. In addition, the production of key macromolecules of ECM (aggrecan and collagen-2) and matrix metalloproteinase 13 (MMP-13) in co-cultured chondrocytes with activated CD4+ T cells was altered. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1299-1303, 2017.

Pollutants make rheumatic diseases worse: Facts on polychlorinated biphenyls (PCBs) exposure and rheumatic diseases.

BACKGROUND: Polychlorinated biphenyls (PCBs) are persistent organic pollutants that bioaccumulate in adipose tissue, disturbing its metabolism and the balance of adipokines, related to obesity. The altering secretion pattern of adipokines from the adipose tissue and the increasing mechanical load in weight-bearing joints presented in obesity condition, are risk factors for osteoarthritis development. The most prevalent rheumatic diseases, osteoarthritis and rheumatoid arthritis, are chronic conditions that target the whole joints, leading to increasing disability and health care cost. The goal of this focused review is to summarize the current knowledge on the role of PCBs in osteoarthritis and rheumatoid arthritis pathogenesis. SEARCH STRATEGY: A PubMed search was managed using keywords as "rheumatic diseases", "polychlorinated biphenyls", "obesity" and "endocrine disruption". MAIN RESULTS OF THE REVIEW: The incidence of rheumatoid arthritis has been reported to be increased especially in urban areas in industrialized countries, emphasizing the importance of environment in the pathogenesis of rheumatic diseases. Analysis of two cohorts exposed to PCBs food contamination showed high incidence of arthritis. In addition, PCBs in serum correlated positively with the prevalence of self-reported arthritis. Few studies support the hypothesis that osteoarthritis development could be related to PCBs induction of chondrocytes apoptosis. CONCLUSION: Evidences have emerged for a relationship between PCBs and development of several types of arthritis. Further research is encouraged to determine the correlation between PCBs exposure and the development of rheumatic diseases.

E74-like factor 3 and nuclear factor-κB regulate lipocalin-2 expression in chondrocytes.

KEY POINTS: E74-like factor 3 (ELF3) is a transcription factor regulated by inflammation in different physio-pathological situations. Lipocalin-2 (LCN2) emerged as a relevant adipokine involved in the regulation of inflammation. In this study we showed for the first time the involvement of ELF3 in the control of LCN2 expression and its cooperation with nuclear factor-κB (NFκB). Our results will help to better understand of the role of ELF3, NFκB and LCN2 in the pathophysiology of articular cartilage. ABSTRACT: E74-like factor 3 (ELF3) is a transcription factor induced by inflammatory cytokines in chondrocytes that increases gene expression of catabolic and inflammatory mediators. Lipocalin 2 (LCN2) is a novel adipokine that negatively impacts articular cartilage, triggering catabolic and inflammatory responses in chondrocytes. Here, we investigated the control of LCN2 gene expression by ELF3 in the context of interleukin 1 (IL-1)-driven inflammatory responses in chondrocytes. The interaction of ELF3 and nuclear factor-κB (NFκB) in modulating LCN2 levels was also explored. LCN2 mRNA and protein levels, as well those of several other ELF3 target genes, were determined by RT-qPCR and Western blotting. Human primary chondrocytes, primary chondrocytes from wild-type and Elf3 knockout mice, and immortalized human T/C-28a2 and murine ATDC5 cell lines were used in in vitro assays. The activities of various gene reporter constructs were evaluated by luciferase assays. Gene overexpression and knockdown were performed using specific expression vectors and siRNA technology, respectively. ELF3 overexpression transactivated the LCN2 promoter and increased the IL-1-induced mRNA and protein levels of LCN2, as well as the mRNA expression of other pro-inflammatory mediators, in human and mouse chondrocytes. We also identified a collaborative loop between ELF3 and NFκB that amplifies the induction of LCN2. Our findings show a novel role for ELF3 and NFκB in the induction of the pro-inflammatory adipokine LCN2, providing additional evidence of the interaction between ELF3 and NFκB in modulating inflammatory responses, and a better understanding of the mechanisms of action of ELF3 in chondrocytes.

The novel adipokine progranulin counteracts IL-1 and TLR4-driven inflammatory response in human and murine chondrocytes via TNFR1.

Progranulin (PGRN) is a recently identified adipokine that is supposed to have anti-inflammatory actions. The proinflammatory cytokine interleukin-1ß (IL1ß) stimulates several mediators of cartilage degradation. Toll like receptor-4 (TLR4) can bind to various damage-associated molecular patterns, leading to inflammatory condition. So far, no data exist of PGRN effects in inflammatory conditions induced by IL1ß or lipopolysaccharide (LPS). Here, we investigated the anti-inflammatory potential of PGRN in IL1ß- or LPS-induced inflammatory responses of chondrocytes. Human osteoarthritic chondrocytes and ATDC-5 cells were treated with PGRN in presence or not of IL1ß or LPS. First, we showed that recombinant PGRN had no effects on cell viability. We present evidence that PGRN expression was increased during the differentiation of ATDC-5 cell line. Moreover, PGRN mRNA and protein expression is increased in cartilage, synovial and infrapatellar fat pad tissue samples from OA patients. PGRN mRNA levels are upregulated under TNFα and IL1ß stimulation. Our data showed that PGRN is able to significantly counteract the IL1ß-induced expression of NOS2, COX2, MMP13 and VCAM-1. LPS-induced expression of NOS2 is also decreased by PGRN. These effects are mediated, at least in part, through TNFR1. Taken together, our results suggest that PGRN has a clear anti-inflammatory function.

The potential of lipocalin-2/NGAL as biomarker for inflammatory and metabolic diseases.

Lipocalin-2 (LCN2), also known as neutrophil gelatinase-associated lipocalin (NGAL), is a secreted glycoprotein that belongs to a group of transporters of small lipophilic molecules in circulation. LCN2 has been recently characterized as an adipose-derived cytokine. This adipokine is believed to bind small substances, such as steroids and lipopolysaccharides, and has been reported to have roles in the induction of apoptosis in hematopoietic cells, transport of fatty acids and iron, modulation of inflammation, and metabolic homeostasis. Recently, LCN2 has emerged as a useful biomarker and rheumatic diseases. This review provides an overview of LCN2 in inflammation, immunity, and metabolism.