Wnt signaling pathway in rheumatoid arthritis, with special emphasis on the different roles in synovial inflammation and bone remodeling

Rheumatoid arthritis (RA) is a chronic symmetrical autoimmune disease of unknown etiology that affects primarily the diarthrodial joints. Characteristic features of RA pathogenesis are synovial inflammation and proliferation accompanied by cartilage erosion and bone loss. Fibroblast-like synoviocytes (FLS) display an important role in the pathogenesis of RA. Several lines of evidence show that the Wnt signaling pathway significantly participates in the RA pathogenesis. The Wnt proteins are glycoproteins that bind to the Fz receptors on the cell surface, which leads to several important biological functions, such as cell differentiation, embryonic development, limb development and joint formation. Accumulated evidence has suggested that this signaling pathway plays a key role in the FLS activation, bone resorption and joint destruction during RA development. Greater knowledge of the role of the Wnt signaling pathway in RA could improve understanding of the RA pathogenesis and the differences in RA clinical presentation and prognosis. In this review, new advances of the Wnt signaling pathway in RA pathogenesis are discussed, with special emphasis on its different roles in synovial inflammation and bone remodeling. Further studies are needed to reveal the important role of the members of the Wnt signaling pathway in the RA pathogenesis and treatment.

Etanercept Promotes Bone Formation via Suppression of Dickkopf-1 Expression in Rats with Collagen-Induced Arthritis

BACKGROUND

Various clinical reports suggest etanercept (ETN) has some efficacy in bone formation in rheumatoid arthritis (RA). To examine this effect, we investigated the gene expression of cytokines relevant to osteoblast/osteoclast differentiation, and evaluated histomorphometric findings in mature rats with collagen-induced arthritis (CIA).

METHODS

Total RNA was extracted from knee joints with CIA after ETN or placebo administration. Subsequently, realtime-PCR was carried out to quantify the mRNAs encoding Wnt-1, Dickkopf-1 (DKK-1), receptor activator of nuclear factor kappa-B ligand (RANKL), osteoprotegelin (OPG) and TNF (tumor necrosis factor)-alpha. In histomorphometric analysis, the infiltrating pannus volume and pannus surface, and the following items in contact with pannus surface were measured: osteoclast number, osteoid surface, osteoid volume and labeling surface. These were evaluated in the distal femur with CIA with or without ETN administration.

RESULTS

TNF-alpha, RANKL and OPG mRNA expressions, linked to osteoclastogenesis, were not significantly different with or without ETN administration. ETN administration significantly increased Wnt-1 mRNA expression, the osteoblast promoter, and decreased DKK-1 mRNA expression, the Wnt signal inhibitor. In histomorphometric analysis, pannus volume, pannus surface and osteoclast number, parameters of bone destruction, were not significantly different among groups. Osteoid volume, osteoid surface and labeling surface, parameters of bone formation, increased significantly with ETN administration.

CONCLUSION

Our results suggest that ETN suppresses DDK-1 expression, and, as a result, Wnt expression is promoted and osteoblastogenesis becomes more active, independent of the regulation of osteoclast activity. Marked bone formation is attributed to the fact that ETN directly promotes osteoblastogenesis, not as a result of suppressing osteoclastogenesis.

A novel biomarker of coronary atherosclerosis: serum DKK1 concentration correlates with coronary artery calcification and atherosclerotic plaques

DKK1 modulates Wnt signaling, which is involved in the atherosclerosis. However, no data exist regarding the usefulness of measuring serum DKK1 concentration in predicting coronary atherosclerosis. A total of 270 consecutive patients (62.8 ± 11.2 yr; 70% male) were included. A contrast-enhanced 64-slice coronary MDCT was performed to identify the presence of atherosclerotic plaques. Agatston calcium scores (CS) were calculated to quantify the coronary artery calcification (CAC). DKK1 concentrations were measured by enzyme-linked immunosorbent assay. For each subsequent DKK1 quartile, there was a significant increase in CAC (P = 0.004) and the number of segments with coronary atherosclerosis (P < 0.001). In addition, DKK1 concentration was significantly higher in patients with atherosclerotic plaques, regardless of plaque composition (P = 0.01). Multivariate analysis identified DKK1 as an independent risk factor for the presence of coronary atherosclerotic plaque. The adjusted odds ratio for coronary atherosclerotic plaque was 4.88 (95% CI, 1.67 to 14.25) for highest versus lowest quartile of the DKK1 levels. Furthermore, patients with DKK1 concentrations ≥ 68.6 pg/mL demonstrated coronary atherosclerotic plaques even when they had low CS. Serum DKK1 concentrations correlate with the coronary atherosclerosis and play an independent role in predicting the presence of coronary atherosclerosis.

Anti-colon carcinoma mechanism of cloned Dickkopf-1

AIM: To clone the cDNA of Dickkopf-1 (Dkk1) and to investigate its anti-colon carcinoma activity.

METHODS: Dkk1 cDNA was retrived from Mouse Embryo 9 dpc, DH10B cDNA library, and eukaryotic expression vector pcDNA3.1(+) Dkk1 was constructed. Transfected CT26 colon carcinoma cells served as the experimental group, transfection empty vector pcDNA3.1(+) cells served as the empty vector group, and non-transfected cells as the non-transfected group. Proliferation of the CT26 colon carcinoma cells was measured by MTT assay. Expression of Dkk1, p53, Bcl-2 and Bax was detected by Western blotting.

RESULTS: Absorbance at 570 nm in the experimental group was lower than that in the empty vector and non-transfected groups (0.779 ± 0.025 vs 0.968 ± 0.016 and 0.973 ± 0.016, P < 0.05). Compared with the empty vector and non-transfected groups, the level of p53 and Bcl-2 in CT26 cells was lower, and the level of Dkk1 and Bax was higher.

CONCLUSION: Inhibition of CT26 cell proliferation by Dkk1 expression may be mediated by Dkk1 blocking mutant p53, decreasing Bcl-2 and enhancing Bax expression.

Analysis of cellular changes resulting from forced expression of Dickkopf-1 in hepatocellular carcinoma cells

PURPOSE

Recent studies have shown that Dickkopf-1 (DKK-1) is overexpressed in some tumors, including hepatocellular carcinoma. However, the role of increased DKK-1 in these tumors is not known. In this study, the DKK-1 expression in hepatocellular carcinoma (HCC) cell lines was evaluated and the effect of DKK-1 overexpression in HCC cell lines was studied.

MATERIALS AND METHODS

The expression of DKK-1 in hepatocellular carcinoma cell lines was evaluated by RT-PCR. Stable cell lines that overexpressed DKK-1 were established. Cell growth, adhesion, migration and invasion assays were performed.

RESULTS

RT-PCR analysis showed that 5 out of 8 HCC cell lines expressed DKK-1. The forced expression of DKK-1 suppressed the growth of cells and increased the population of cells in the sub-G1 phase. In addition, DKK-1 reduced the cellular adhesion capacity to collagen type I and fibronectin, and it increased migratory capacity. However, overexpression of DKK-1 did not increase the invasion capacity of the HCC cell line.

CONCLUSION

Collectively, our data suggest that overexpression of DKK-1 affects the biology of HCC cells.