The pro-inflammatory cytokine 14-3-3ε is a ligand of CD13 in cartilage.

Osteoarthritis is a whole-joint disease characterized by the progressive destruction of articular cartilage involving abnormal communication between subchondral bone and cartilage. Our team previously identified 14-3-3ε protein as a subchondral bone soluble mediator altering cartilage homeostasis. The aim of this study was to investigate the involvement of CD13 (also known as aminopeptidase N, APN) in the chondrocyte response to 14-3-3ε. After identifying CD13 in chondrocytes, we knocked down CD13 with small interfering RNA (siRNA) and blocking antibodies in articular chondrocytes. 14-3-3ε-induced MMP-3 and MMP-13 was significantly reduced with CD13 knockdown, which suggests that it has a crucial role in 14-3-3ε signal transduction. Aminopeptidase N activity was identified in chondrocytes, but the activity was unchanged after stimulation with 14-3-3ε. Direct interaction between CD13 and 14-3-3ε was then demonstrated by surface plasmon resonance. Using labeled 14-3-3ε, we also found that 14-3-3ε binds to the surface of chondrocytes in a manner that is dependent on CD13. Taken together, these results suggest that 14-3-3ε might directly bind to CD13, which transmits its signal in chondrocytes to induce a catabolic phenotype similar to that observed in osteoarthritis. The 14-3-3ε-CD13 interaction could be a new therapeutic target in osteoarthritis.

Protective role of frizzled-related protein B on matrix metalloproteinase induction in mouse chondrocytes.

INTRODUCTION: Our objective was to investigate whether a lack of frizzled-related protein B (FrzB), an extracellular antagonist of the Wnt signaling pathways, could enhance cartilage degradation by facilitating the expression, release and activation of matrix metalloproteinases (MMPs) by chondrocytes in response to tissue-damaging stimuli. METHODS: Cartilage explants from FrzB-/- and wild-type mice were challenged by excessive dynamic compression (0.5 Hz and 1 MPa for 6 hours). Load-induced glycosaminoglycan (GAG) release and MMP enzymatic activity were assessed. Interleukin-1ß (IL-1ß) (10, 100 and 1000 pg/mL for 24 hours) was used to stimulate primary cultures of articular chondrocytes from FrzB-/- and wild-type mice. The expression and release of MMP-3 and -13 were determined by RT-PCR, western blot and ELISA. The accumulation of ß-catenin was assessed by RT-PCR and western blot. RESULTS: Cartilage degradation, as revealed by a significant increase in GAG release (2.8-fold, P = 0.014) and MMP activity (4.5-fold, P = 0.014) by explants, was induced by an excessive load. Load-induced MMP activity appeared to be enhanced in FrzB-/- cartilage explants compared to wild-type (P = 0.17). IL-1ß dose-dependently induced Mmp-13 and -3 gene expression and protein release by cultured chondrocytes. IL-1ß-mediated increase in MMP-13 and -3 was slightly enhanced in FrzB-/- chondrocytes compared to wild-type (P = 0.05 and P = 0.10 at gene level, P = 0.17 and P = 0.10 at protein level, respectively). Analysis of Ctnn1b and Lef1 gene expression and ß-catenin accumulation at protein level suggests that the enhanced catabolic response of FrzB-/- chondrocytes to IL-1ß and load may be associated with an over-stimulation of the canonical Wnt/ß-catenin pathway. CONCLUSIONS: Our results suggest that FrzB may have a protective role on cartilage degradation and MMP induction in mouse chondrocytes by attenuating deleterious effects of the activation of the canonical Wnt/ß-catenin pathway.

Induction of nerve growth factor expression and release by mechanical and inflammatory stimuli in chondrocytes: possible involvement in osteoarthritis pain.

INTRODUCTION: Nerve growth factor (NGF) level is increased in osteoarthritis (OA) joints and is involved in pain associated with OA. Stimuli responsible for NGF stimulation in chondrocytes are unknown. We investigated whether mechanical stress and proinflammatory cytokines may influence NGF synthesis by chondrocytes. METHODS: Primary cultures of human OA chondrocytes, newborn mouse articular chondrocytes or cartilage explants were stimulated by increasing amounts of IL-1ß, prostaglandin E2 (PGE2), visfatin/nicotinamide phosphoribosyltransferase (NAMPT) or by cyclic mechanical compression (0.5 Hz, 1 MPa). Before stimulation, chondrocytes were pretreated with indomethacin, Apo866, a specific inhibitor of NAMPT enzymatic activity, or transfected by siRNA targeting visfatin/NAMPT. mRNA NGF levels were assessed by real-time quantitative PCR and NGF released into media was determined by ELISA. RESULTS: Unstimulated human and mouse articular chondrocytes expressed low levels of NGF (19.2 ± 8.7 pg/mL, 13.5 ± 1.0 pg/mL and 4.4 ± 0.8 pg/mL/mg tissue for human and mouse articular chondrocytes and costal explants, respectively). Mechanical stress induced NGF release in conditioned media. When stimulated by IL-1ß or visfatin/NAMPT, a proinflammatory adipokine produced by chondocytes in response to IL-1ß, a dose-dependent increase in NGF mRNA expression and NGF release in both human and mouse chondrocyte conditioned media was observed. Visfatin/NAMPT is also an intracellular enzyme acting as the rate-limiting enzyme of the generation of NAD. The expression of NGF induced by visfatin/NAMPT was inhibited by Apo866, whereas IL-1ß-mediated NGF expression was not modified by siRNA targeting visfatin/NAMPT. Interestingly, PGE2, which is produced by chondrocytes in response to IL-1ß and visfatin/NAMPT, did not stimulate NGF production. Consistently, indomethacin, a cyclooxygenase inhibitor, did not counteract IL-1ß-induced NGF production. CONCLUSIONS: These results show that mechanical stress, IL-1ß and extracellular visfatin/NAMPT, all stimulated the expression and release of NGF by chondrocytes and thus suggest that the overexpression of visfatin/NAMPT and IL-1ß in the OA joint and the increased mechanical loading of cartilage may mediate OA pain via the stimulation of NGF expression and release by chondrocytes.

Identification of soluble 14-3-3∊ as a novel subchondral bone mediator involved in cartilage degradation in osteoarthritis.

OBJECTIVE: Mechanical stress plays an important role in cartilage degradation and subchondral bone remodeling in osteoarthritis (OA). The remodeling of the subchondral bone could initiate cartilage loss in OA through the interplay of bone and cartilage. The aim of this study was to identify soluble mediators released by loaded osteoblasts/osteocytes that could induce the release of catabolic factors by chondrocytes. METHODS: Murine osteoblasts/osteocytes were subjected to cyclic compression, and then conditioned medium from either compressed (CCM) or uncompressed (UCM) cells was used to stimulate mouse chondrocytes. Chondrocyte expression of matrix metalloproteinase 3 (MMP-3), MMP-13, type II collagen, and aggrecan was assessed by reverse transcription-polymerase chain reaction, Western blotting, and enzyme-linked immunosorbent assay. Soluble mediators released by compressed osteoblasts/osteocytes were identified using iTRAQ (isobaric tags for relative and absolute quantification), a differential secretome analysis. Subchondral bone and cartilage samples were isolated from OA patients, and culture medium conditioned with OA subchondral bone or cartilage was used to stimulate human chondrocytes. RESULTS: Stimulation of mouse chondrocytes with CCM strongly induced the messenger RNA (mRNA) expression and protein release of MMP-3 and MMP-13 and inhibited the mRNA expression of type II collagen and aggrecan. Differential secretome analysis revealed that 10 proteins were up-regulated in compressed osteoblasts/osteocytes. Among them, soluble 14-3-3∊ (s14-3-3∊) dose-dependently induced the release of catabolic factors by chondrocytes, mimicking the effects of cell compression. Addition of a 14-3-3∊ blocking antibody greatly attenuated the CCM-mediated induction of MMP-3 and MMP-13 expression. Furthermore, in human OA subchondral bone, s14-3-3∊ was strongly released, and in cultures of human OA chondrocytes, s14-3-3∊ stimulated MMP-3 expression. CONCLUSION: The results of this study identify s14-3-3∊ as a novel soluble mediator critical in the communication between subchondral bone and cartilage in OA. Thus, s14-3-3∊ may be a potential target for future therapeutic or prognostic applications in OA.

Epidermal growth factor receptor and HER-3 restrict cell response to sorafenib in hepatocellular carcinoma cells.

BACKGROUND & AIMS: Sorafenib is the standard of care for the treatment of advanced hepatocellular carcinoma (HCC). However, primary and acquired resistance is observed in patients. We examined whether gefitinib, which inhibits both epidermal growth factor receptor (EGFR) and HER-3 phosphorylation, could improve HCC cell response to sorafenib. METHODS: Sorafenib and gefitinib were tested in HCC tumor xenografts and in sorafenib-sensitive and sorafenib-resistant HCC cell lines. Biomarkers relevant to the HER system were analyzed by Western blotting and ELISA. RNA interference was used to downregulate the HER system. Amphiregulin concentrations were measured by ELISA in sera from patients under sorafenib treatment. RESULTS: Sorafenib combined with gefitinib significantly inhibited tumor growth in mice and reduced cell viability in vitro compared to single agents. In cell lines cultured in 10% serum or treated with EGF, sorafenib alone inhibited phospho-STAT3 while it maintained or even increased phospho-ERK and/or phospho-AKT. The paradoxical effects of sorafenib were prevented by gefitinib or by downregulation of EGFR and HER-3 expression. In cells with acquired resistance to sorafenib, aberrant activation of EGFR/HER-3 receptors as well as overexpression of several EGFR ligands were observed. These enhanced autocrine/paracrine loops led to the constitutive activation of ERK and AKT and conferred increased sensitivity to gefitinib. Increased serum concentrations of amphiregulin were observed in 10 out of 14 patients under sorafenib treatment compared to baselines. CONCLUSIONS: Signaling pathways controlled by EGFR and HER-3 restrict sorafenib effects both in naive and sorafenib-resistant HCC cells. Consequently, gefitinib cooperates with sorafenib to increase antiproliferative response and to prevent resistance.

Induction of the chemokine IL-8/Kc by the articular cartilage: possible influence on osteoarthritis.

PURPOSE: IL-8 and its murine equivalent keratinocyte chemoattractant (Kc), chemokines produced by chondrocytes, contribute to the pathophysiology of osteoarthritis. However, the mechanisms leading to their production are poorly known. We aimed to investigate whether mechanical (compression), inflammatory (IL-1ß) and metabolic (visfatin) stresses may induce the release of Kc when applied on murine cartilage. METHODS: Mouse cartilage explants were subjected to intermittent compression for 4, 6 and 24h. Primary cultures of immature murine articular chondrocytes were obtained by enzymatic digestion of articular cartilage from 6-days-old newborns mice. The effect of compression, IL-1ß (10, 50, 100pg/mL) and of visfatin (5µg/mL) on the release of Kc was assessed by ELISA. IL-8 levels in conditioned media from human OA joint tissues (cartilage or synovium) were also assessed. RESULTS: In comparison with non-compressed explants, loading increased Kc release of 3.2-, 1.9- and 2.0-fold at 4, 6 and 24h respectively (P<0.004, n=9). IL-1ß triggered an increase of Kc release by primary cultured chondrocytes of 4.1-, 15.5- and 35.2-fold at 10, 50 and 100pg/mL of IL-1ß respectively (P<0.05, n=4). Likewise, visfatin (5µg/mL) induced an increase in Kc release of 56.5±25.2 fold (P=0.002, n=6). IL-8 was released in conditioned media by synovium as well as by cartilage. CONCLUSION: We show for the first time that IL-8/Kc is highly responsive to mechanical, inflammatory and metabolic stresses, strengthening the hypothesis that IL-8/Kc could be added to the cytokines which may have a deleterious impact in osteoarthritis.