DKK1 expression by synovial fibroblasts in very early rheumatoid arthritis associates with lymphocyte adhesion in an in vitro flow co-culture system

Dual drug nanoparticle synergistically induced apoptosis, suppressed inflammation, and protected autophagic response in rheumatoid arthritis fibroblast-like synoviocytes

Rheumatoid arthritis (RA) is a chronic immune-mediated joint inflammatory disorder associated with aberrant activation of fibroblast-like synoviocytes (FLS). Recently, FLS gained importance due to its crucial role in RA pathogenesis, and thus, targeting FLS is suggested as an attractive treatment strategy for RA. FLS-targeted approaches may be combined with disease-modifying antirheumatic drugs (DMARDs) and natural phytochemicals to improve efficacy in RA control and negate immunosuppression. In this study, we assessed the therapeutic effectiveness of DD NP HG in primary RA-FLS cells isolated from the synovial tissue of FCA-induced RA rats. We observed that DD NP HG had good biosafety for healthy FLS cells and, at higher concentrations, a mild inhibitory effect on RA-FLS. The combination therapy (DD NP HG) of MTX NP and PEITC NE in RA-FLS showed a higher rate of apoptosis with significantly reduced LPS-induced expression of pro-inflammatory cytokines (TNF-α, IL-17A, and IL-6) in arthritic FLS. Further, the gene expression studies showed that DD NP HG significantly down-regulated the mRNA expression of IL-1β, RANKL, NFATc1, DKK1, Bcl-xl, Mcl-1, Atg12, and ULK1, and up-regulated the mRNA expression of OPG, PUMA, NOXA and SQSTM1 in LPS-stimulated RA-FLS cells. Collectively, our results demonstrated that DD NP HG significantly inhibited the RA-FLS proliferation via inducing apoptosis, down-regulating pro-inflammatory cytokines, and further enhancing the expression of genes associated with bone destruction in RA pathogenesis. A nanotechnology approach is a promising strategy for the co-delivery of dual drugs to regulate the RA-FLS function and achieve synergistic treatment of RA.

Serum concentration of dickkopf-related protein 1 (DKK1) in psoriatic arthritis in the context of bone remodelling

Psoriatic arthritis (PsA) is a chronic inflammatory disease, characterised by the pathological occurrence of two opposite phenomena-osteoresorption and osteogenesis. Dickkopf-related protein 1 (DKK1) which inhibits the Wingless protein (Wnt) signalling pathway has been shown to be a master regulator of bone remodeling in inflammatory rheumatic diseases. However, the exact relationship between DKK1 serum level and bone remodelling is not clear. The goal of this study is to review state-of-the-art knowledge on the association of serum DKK1 with a bone remodelling in PsA. The MEDLINE-PubMed, EMBASE, Scopus, Web of Science and DOAJ databases were searched for appropriate papers. The English terms: 'DKK1', 'Dickkopf-1' 'Dickkopf related protein 1', 'psoriatic arthritis' and 'PsA' were used for search purposes. Eight original articles and two reviews were identified up to August 2023. In four out of 8 discussed studies DKK1 serum level was higher in PsA patients than in healthy controls [Dalbeth, p < 0.01; Diani, p < 0.001; Chung, p < 0.01; Abd el Hamid, p < 0.001)], it was comparable in another (Daousiss, p = 0.430) and was lower in two (Fassio2017, p < 0.05; Fassio2019, p < 0.05). In one study, the comparative groups included patients with axial spondyloarthritis, where DKK1 serum levels were lower in PsA groups [Jadon, peripheral PsA, p = 0.01]. The true relative serum concentration of DKK1 in PsA, as well as its influence on osteogenesis and osteoresorption, is still equivocal. Further studies on this matter with consistent and stringent methodology are warranted.

Effects of Biological/Targeted Therapies on Bone Mineral Density in Inflammatory Arthritis

Inflammatory arthritis has been reported to be associated with the development of osteoporosis. Recent research has investigated the mechanisms of bone metabolism in chronic inflammatory arthritis such as rheumatoid arthritis (RA) and spondyloarthritis (SpA). Progress in both animal and clinical studies has provided a better understanding of the osteoclastogenesis-related pathways regarding the receptor activator of nuclear factor-κB ligand (RANKL), anti-citrullinated protein antibodies (ACPAs), and Wnt signaling and Dickkopf-related protein 1 (Dkk-1). The complex interplay between inflammatory cytokines and bone destruction has been elucidated, especially that in the interleukin-17/23 (IL-17/23) axis and Janus kinase and signal transducer and activator of transcription (JAK-STAT) signaling. Moreover, advances in biological and targeted therapies have achieved essential modifications to the bone metabolism of these inflammatory arthritis types. In this narrative review, we discuss recent findings on the pathogenic effects on bone in RA and SpA. Proinflammatory cytokines, autoantibodies, and multiple signaling pathways play an essential role in bone destruction in RA and SpA patients. We also reviewed the underlying pathomechanisms of bone structure in biological and targeted therapies of RA and SpA. The clinical implications of tumor necrosis factor inhibitors, abatacept, rituximab, tocilizumab, Janus kinase inhibitors, and inhibitors of the IL-17/23 axis are discussed. Since these novel therapeutics provide new options for disease improvement and symptom control in patients with RA and SpA, further rigorous evidence is warranted to provide a clinical reference for physicians and patients.

Bridging Insights From Lymph Node and Synovium Studies in Early Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease of unknown etiology characterized by inflammation of the peripheral synovial joints leading to pannus formation and bone destruction. Rheumatoid Factor (RF) and anti-citrullinated protein antibodies (ACPA) are present years before clinical manifestations and are indicative of a break in tolerance that precedes chronic inflammation. The majority of studies investigating disease pathogenesis focus on the synovial joint as target site of inflammation while few studies explore the initial break in peripheral tolerance which occurs within secondary lymphoid organs such as lymph nodes. If explored during the earliest phases of RA, lymph node research may provide innovative drug targets for disease modulation or prevention. RA research largely centers on the role and origin of lymphocytes, such as pro-inflammatory T cells and macrophages that infiltrate the joint, as well as growing efforts to determine the role of stromal cells within the synovium. It is therefore important to explore these cell types also within the lymph node as a number of mouse studies suggest a prominent immunomodulatory role for lymph node stromal cells. Synovium and proximal peripheral lymph nodes should be investigated in conjunction with one another to gain understanding of the immunological processes driving RA progression from systemic autoimmunity toward synovial inflammation. This perspective seeks to provide an overview of current literature concerning the immunological changes present within lymph nodes and synovium during early RA. It will also propose areas that warrant further exploration with the aim to uncover novel targets to prevent disease progression.

Association of Serum and Crevicular Fluid Dickkopf-1 Levels with Disease Activity and Periodontitis in Patients with Early Rheumatoid Arthritis

BACKGROUND

The aim of this study was to assess DKK-1 levels, in Gingival Crevicular Fluid (GCF) and serum, as a biomarker for bone loss and disease activity in periodontitis and early RA (eRA).

METHODS

In this cross-sectional study, we obtained serum and GCF from 10 interproximal sites (Distal Buccal I/S, Mesio Buccal I/S, Distal Palatal/Lingual, Mesio Palatal/Lingual) according to the highest degree of inflammation by a patient for 240 sites from eRA patients. Patients received a periodontal assessment, a radiographic evaluation, tomography of interproximal sites, and DKK1 levels were determined by ELISA. Comparisons were performed by the Mann-Whitney U test and analysis by Chi2 test, and a logistic regression model was applied.

RESULTS

The mean age was 46.33 ± 12.0 years, the Disease Activity Score (DAS-28-ESR) was 4.08 ± 1.4. Periodontitis was present in 65.2% of the patients, and 59.6% of these patients had bone loss in interproximal sites. Higher GCF-DKK1 levels were associated with serum-DKK1 (OR:2.41 IC95% 1.14-5.09, p=0.021) and were related with DAS28-ESR (p=0.001), Routine Assessment of Patient Index Data 3 (RAPID 3) (p=0.001), and tender joints (p=0.040). Foot bone erosion and juxta-articular osteopenia were associated with high levels of serum-DKK1 (p=0.009 and 0.001, respectively). Serum-DKK1 were associated with SDAI (OR: 2.38 IC95% 1.03-5.52, p=0.043), RAPID 3 (p=0.001), and rheumatoid factor (p=0.018). The GCF-DKK1 levels were associated with periodontal bone loss (p=0.011), periodontitis (p=0.070) and its severity (OR: 2.58 IC95% 2.28-7.28, p=0.001). Bone loss was more frequent in buccal sites (73.5%) and was associated with increased levels of DKK1 (p=0.033).

CONCLUSION

In the early stages of the eRA disease, serum and GCF-DKK1 could be a biomarker for clinical disease activity and periodontal and articular bone erosion.

Identification of biological pathways specific to phases preceding rheumatoid arthritis development through gene expression profiling

The etiopathogenesis of rheumatoid arthritis is partially understood; however, it is believed to result from a multi-step process. The immune onset followed by pre-clinical phases will eventually lead to the development of symptomatic disease. We aim at identifying differentially expressed genes in order to highlight pathways involved in the pre-clinical stages of rheumatoid arthritis development. The study population consisted of first-degree relatives of patients with rheumatoid arthritis, known to have an increased risk of developing disease as compared to the general population. Whole transcriptome analysis was performed in four groups: asymptomatic without autoantibodies or symptoms associated with possible rheumatoid arthritis (controls); having either clinically suspect arthralgias, undifferentiated arthritis or autoimmunity associated with RA (pre-clinical stages of RA: Pcs-RA); having subsequently developed classifiable RA (pre-RA); and early untreated rheumatoid arthritis patients (RA). Differentially expressed genes were determined, and enrichment analysis was performed. Functional enrichment analysis revealed 31 pathways significantly enriched in differentially expressed genes for Pcs-RA, pre-RA and RA compared to the controls. Osteoclast pathway is among the seven pathways specific for RA. In Pcs-RA and in pre-RA, several enriched pathways include TP53 gene connections, such as P53 and Wnt signalling pathways. Analysis of whole transcriptome for phenotypes related to rheumatoid arthritis allows highlighting which pathways are requested in the pre-clinical stages of disease development. After validation in replication studies, molecules belonging to some of these pathways could be used to identify new specific biomarkers for individuals with impending rheumatoid arthritis.

Activity of fibroblast-like synoviocytes in rheumatoid arthritis was impaired by dickkopf-1 targeting siRNA

BACKGROUND

Fibroblast-like synoviocytes (FLSs), resident mesenchymal cells of synovial joints, play an important role in the pathogenesis of rheumatoid arthritis (RA). Dickkopf-1 (DKK-1) has been proposed to be a master regulator of bone remodeling in inflammatory arthritis. Here, potential impairation on the activity of FLSs derived from RA to small interfering RNAs (siRNAs) targeting DKK-1 was investigated.

METHODS

siRNAs targeting DKK-1 were transfected into FLSs of patients with RA. Interleukin (IL)-1β, IL-6, IL-8, matrix metalloproteinase (MMP) 2, MMP3, MMP9, transforming growth factor (TGF)-β1, TGF-β2 and monocyte chemoattractant protein (MCP)-1 levels in the cell culture supernatant were detected by enzyme-linked immunosorbent assay (ELISA). Invasion assay and H incorporation assay were utilized to investigate the effects of siRNAs targeting DKK-1 on FLSs invasion and cell proliferation, respectively. Western blotting was performed to analyze the expression of nuclear factor (NF)-κB, interleukin-1 receptor-associated kinase (IRAK)1, extracellular regulated protein kinases (ERK)1, Jun N-terminal kinase (JNK) and β-catenin in FLSs.

RESULTS

DKK-1 targeting siRNAs inhibited the expression of DKK-1 in FLSs (P < 0.01). siRNAs induced a significant reduction of the levels of IL-6, IL-8, MMP2, MMP3 and MMP9 in FLSs compared to the control group (P < 0.05). DKK-1 targeting siRNAs inhibited the proliferation and invasion of FLSs (P < 0.05). Important molecules of pro-inflammatory signaling in FLSs, including IRAK1 and ERK1, were decreased by the inhibition of DKK-1 in FLSs. In contrast, β-catenin, a pivotal downstream molecule of the Wnt signaling pathway was increased.

CONCLUSIONS

By inhibiting DKK-1, we were able to inhibit the proliferation, invasion and pro-inflammatory cytokine secretion of FLSs derived from RA, which was mediated by the ERK or the IRAK-1 signaling pathway. These data indicate the application of DKK-1 silencing could be a potential therapeutic approach to RA.

Blockade of Discoidin Domain Receptor 2 as a Strategy for Reducing Inflammation and Joint Destruction in Rheumatoid Arthritis Via Altered Interleukin-15 and Dkk-1 Signaling in Fibroblast-Like Synoviocytes

OBJECTIVE

This study was undertaken to uncover the pathophysiologic role of discoidin domain receptor 2 (DDR-2), a putative fibrillar collagen receptor, in inflammation promotion and joint destruction in rheumatoid arthritis (RA).

METHODS

In synovial tissue from patients with RA and from mice with collagen antibody-induced arthritis (CAIA) (using Ddr2^-/- and DBA/1 mice), gene and protein expression levels of DDR-2, interleukin-15 (IL-15), and Dkk-1 were measured by quantitative reverse transcription-polymerase chain reaction, Western blotting, and immunohistochemistry. Gene knockdown of DDR2 in human RA fibroblast-like synoviocytes (FLS) was conducted via small interfering RNA. Interaction between the long noncoding RNA H19 and microRNA 103a (miR-103a) was assessed in RA FLS using RNA pulldown assays. Cellular localization of H19 was examined using fluorescence in situ hybridization assays. Chromatin immunoprecipitation and dual luciferase reporter assays were applied to verify H19 transcriptional and posttranscriptional regulation by miR-103a.

RESULTS

DDR2 messenger RNA (mRNA) expression was significantly associated with the levels of IL-15 and Dkk-1 mRNA in the synovial tissue of RA patients (r² = 0.2022-0.3293, all P < 0.05; n = 33) and with the serum levels of IL-15 and Dkk-1 in mice with CAIA (P < 0.05). In human RA FLS, activated DDR-2 induced the expression of H19 through c-Myc. Moreover, H19 directly interacted with and promoted the degradation of miR-103a.

CONCLUSION

These results indicate a novel role for activated DDR-2 in RA FLS, showing that DDR-2 is responsible for regulating the expression of IL-15 and Dkk-1 in RA FLS and is involved in the promotion of inflammation and joint destruction during pathophysiologic development of RA. Moreover, DDR-2 inhibition, acting through the H19-miR-103a axis, leads to reductions in the inflammatory reaction and severity of joint destruction in mice with CAIA, suggesting that inhibition of DDR-2 may be a potential therapeutic strategy for RA.

Osteogenic Dkk1 Mediates Glucocorticoid-Induced but Not Arthritis-Induced Bone Loss

Dickkopf-1 (Dkk1) is a negative regulator of bone formation and bone mass and is deregulated in bone loss induced by arthritis and glucocorticoid (GC) exposure. However, the role of Dkk1 in these pathological processes is still unknown. Here, we used conditional Dkk1 knock-out mice to determine the role of Dkk1 produced by osteolineage cells in the development of arthritis and GC-induced bone loss. Osteoprogenitor (Osx-Cre)- and osteocyte (Dmp1-Cre)-specific knock-out mice and their Cre-negative controls were subjected to two arthritis models, K/BxN and antigen-induced arthritis. Disease induction and progression were assessed. GC-induced bone loss was induced in 25-week-old female mice by implanting prednisolone (7.5 mg) slow-release pellets for 4 weeks. Dkk1^fl/fl ;Osx-Cre mice subjected to K/BxN arthritis showed mildly reduced disease severity with reduced infiltration of neutrophils and T cells into affected joints and reduced bone erosions compared with Cre-negative controls. Osteocyte-specific Dkk1 deletion did not affect disease severity or local bone erosions. However, systemic bone loss at the spine was less severe in both mouse lines. In contrast to arthritis, both lines were protected from GC-induced bone loss. Although the Cre-negative controls lost about 26% and 31% bone volume potentially caused by decreased bone formation, Cre-positive mice did not exhibit such alterations. Dkk-1 deficiency in osteolineage cells protects against GC-induced bone loss, whereas it had only minor effects in arthritis. Therefore, Dkk1 may be a promising therapeutic target especially for bone diseases in which inhibition of bone formation represents the predominant mechanism. © 2019 American Society for Bone and Mineral Research.

MiR-613 inhibits proliferation and invasion and induces apoptosis of rheumatoid arthritis synovial fibroblasts by direct down-regulation of DKK1

BACKGROUND

This study aimed to investigate the effects of miR-613 on the proliferation, invasion and apoptosis of rheumatoid arthritis synovial fibroblasts (RASFs).

METHODS

Synovial tissue samples were collected from 20 rheumatoid arthritis (RA) patients and 10 patients with joint trauma undergoing joint replacement surgery. The RASFs were isolated and cultured. MiR-613 and DKK1 expression in both synovial tissues and cells was detected using quantitative real-time PCR (qRT-PCR). Dual luciferase reporter gene assay was employed to evaluate the effect of miR-613 on the luciferase activity of DKK1. Then RASFs were transfected with miR-613 mimics, si-DKK1 and pcDNA-DKK1. Changes in cellular proliferation, invasion and apoptosis were detected through BrdU assay, Transwell invasion assay and flow cytometry analysis, respectively.

RESULTS

MiR-613 was significantly down-regulated in RA tissues and RASFs compared to normal tissues and cells, whereas DKK1 was up-regulated in RA tissues and RASFs. Dual luciferase reporter gene assay showed that miR-613 could specifically bind to the 3'UTR of DKK1 and significantly inhibit the luciferase activity. Moreover, miR-613 significantly reduced the expression of DKK1. Overexpression of miR-613 or knockdown of DKK1 suppressed proliferation and invasion of RASFs, and induced RASF apoptosis. The reverse results were observed when DKK1 was up-regulated in miR-613-overexpressing RASFs.

CONCLUSIONS

MiR-613 can inhibit proliferation and invasion and induce apoptosis of RASFs by directly targeting DKK1 expression.

Macrophage proliferation distinguishes 2 subgroups of knee osteoarthritis patients

Osteoarthritis (OA) is a leading cause of disability, globally. Despite an emerging role for synovial inflammation in OA pathogenesis, attempts to target inflammation therapeutically have had limited success. A better understanding of the cellular and molecular processes occurring in the OA synovium is needed to develop novel therapeutics. We investigated macrophage phenotype and gene expression in synovial tissue of OA and inflammatory-arthritis (IA) patients. Compared with IA, OA synovial tissue contained higher but variable proportions of macrophages (P < 0.001). These macrophages exhibited an activated phenotype, expressing folate receptor-2 and CD86, and displayed high phagocytic capacity. RNA sequencing of synovial macrophages revealed 2 OA subgroups. Inflammatory-like OA (iOA) macrophages are closely aligned to IA macrophages and are characterized by a cell proliferation signature. In contrast, classical OA (cOA) macrophages display cartilage remodeling features. Supporting these findings, when compared with cOA, iOA synovial tissue contained higher proportions of macrophages (P < 0.01), expressing higher levels of the proliferation marker Ki67 (P < 0.01). These data provide new insight into the heterogeneity of OA synovial tissue and suggest distinct roles of macrophages in pathogenesis. Our findings could lead to the stratification of OA patients for suitable disease-modifying treatments and the identification of novel therapeutic targets.

Dickkopf-related protein 1 and gremlin 1 show different response than frizzled-related protein in human synovial fluid following knee injury and in patients with osteoarthritis

OBJECTIVE

To explore the involvement of the wingless-type MMTV integration site (WNT) and bone morphogenetic protein (BMP) antagonists dickkopf-related protein 1 (DKK1), frizzled-related protein (FRZB) and gremlin 1 (GREM1) in knee injury and osteoarthritis (OA).

DESIGN

The antagonists were immunoassayed in synovial fluid from a cross-sectional cohort of nine knee healthy reference subjects, patients with recent (0-77 days, n = 158) or old (1-37 years, n = 50) knee injuries, and OA (n = 22). Cartilage (ARGS-aggrecan, cartilage oligomeric matrix protein and C2C type II collagen) and other biomarkers were assessed in synovial fluid in a subset of samples. Statistical analysis was by Kendall's tau (τ) correlation, Mann-Whitney U test, and linear regression analysis.

RESULTS

Compared to references, median concentration of GREM1 (but not DKK1 and FRZB) was elevated 1.5-fold immediately after injury, and FRZB was reduced 1000-folds in OA. All three antagonists decreased with increasing time after injury as well as with increasing age, but the temporal change after injury was less accentuated for FRZB (peaked 8-22 days after injury) compared to that of DKK1 and GREM1 (peaked immediately after injury). In the recent injury group, there was a correlation between GREM1 and DKK1 (τ = 0.172); FRZB concentrations correlated with concentrations of cartilage biomarkers (τ between 0.257 and 0.369), while DKK1 and GREM1 were inversely correlated (τ between -0.177 and -0.217) with these markers.

CONCLUSIONS

Our results indicate separate roles for the antagonists, where DKK1 and GREM1 had similarities in response to injury and in OA, with a different response for FRZB.

Analysis of early changes in DNA methylation in synovial fibroblasts of RA patients before diagnosis

DNA methylation is an important epigenetic modification that is known to be altered in rheumatoid arthritis synovial fibroblasts (RASF). Here, we compared the status of promoter DNA methylation of SF from patients with very early RA with SF from patients with resolving arthritis, fully established RA and from non-arthritic patients. DNA was hybridized to Infinium Human methylation 450k and 850k arrays and differential methylated genes and pathways were identified. We could identify a significant number of CpG sites that differed between the SF of different disease stages, showing that epigenetic changes in SF occur early in RA development. Principal component analysis confirmed that the different groups of SF were separated according to their DNA methylation state. Furthermore, pathway analysis showed that important functional pathways were altered in both very early and late RASF. By focusing our analysis on CpG sites in CpG islands within promoters, we identified genes that have significant hypermethylated promoters in very early RASF. Our data show that changes in DNA methylation differ in RASF compared to other forms of arthritis and occur at a very early, clinically yet unspecific stage of disease. The identified differential methylated genes might become valuable prognostic biomarkers for RA development.

Dkk1: A key molecule in joint remodelling and fibrosis

Dickkopf-1 (Dkk-1) is a Wnt signaling pathway inhibitor that has been shown to play an important role in joint remodeling, in experimental models of arthritis and in humans. Recent data suggest that this molecule is involved in the fibrotic process as well.

Identification of a transitional fibroblast function in very early rheumatoid arthritis

OBJECTIVES

Synovial fibroblasts actively regulate the inflammatory infiltrate by communicating with neighbouring endothelial cells (EC). Surprisingly, little is known about how the development of rheumatoid arthritis (RA) alters these immunomodulatory properties. We examined the effects of phase of RA and disease outcome (resolving vs persistence) on fibroblast crosstalk with EC and regulation of lymphocyte recruitment.

METHODS

Fibroblasts were isolated from patients without synovitis, with resolving arthritis, very early RA (VeRA; symptom ≤12 weeks) and established RA undergoing joint replacement (JRep) surgery. Endothelial-fibroblast cocultures were formed on opposite sides of porous filters. Lymphocyte adhesion from flow, secretion of soluble mediators and interleukin 6 (IL-6) signalling were assessed.

RESULTS

Fibroblasts from non-inflamed and resolving arthritis were immunosuppressive, inhibiting lymphocyte recruitment to cytokine-treated endothelium. This effect was lost very early in the development of RA, such that fibroblasts no longer suppressed recruitment. Changes in IL-6 and transforming growth factor beta 1 (TGF-β₁) signalling appeared critical for the loss of the immunosuppressive phenotype. In the absence of exogenous cytokines, JRep, but not VeRA, fibroblasts activated endothelium to support lymphocyte.

CONCLUSIONS

In RA, fibroblasts undergo two distinct changes in function: first a loss of immunosuppressive responses early in disease development, followed by the later acquisition of a stimulatory phenotype. Fibroblasts exhibit a transitional functional phenotype during the first 3 months of symptoms that contributes to the accumulation of persistent infiltrates. Finally, the role of IL-6 and TGF-β₁ changes from immunosuppressive in resolving arthritis to stimulatory very early in the development of RA. Early interventions targeting 'pathogenic' fibroblasts may be required in order to restore protective regulatory processes.

The role of stromal cells in inflammatory bone loss

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation, local and systemic bone loss and a lack of compensatory bone repair. Fibroblast-like synoviocytes (FLS) are the most abundant cells of the stroma and a key population in autoimmune diseases such as RA. An increasing body of evidence suggests that these cells play not only an important role in chronic inflammation and synovial hyperplasia, but also impact bone remodelling. Under inflammatory conditions FLS release inflammatory cytokines, regulate bone destruction and formation and communicate with immune cells to control bone homeostasis. Other stromal cells, such as osteoblasts and terminally differentiated osteoblasts, termed osteocytes, are also involved in the regulation of bone homeostasis and are dysregulated during inflammation. This review highlights our current understanding of how stromal cells influence the balance between bone formation and bone destruction. Increasing our understanding of these processes is critical to enable the development of novel therapeutic strategies with which to treat bone loss in RA.

Dickkopf-1 Is a Biomarker for Systemic Lupus Erythematosus and Active Lupus Nephritis

An early diagnosis of lupus nephritis (LN) has an important clinical implication in guiding treatments of systemic lupus erythematosus (SLE) in clinical settings. In this study, the concentrations of Wnt-3A, Frizzled-8 (FZD-8), and Dickkopf-1 (DKK-1) of Wnt signaling, as well as their diagnostic values for accessing LN, were evaluated by ELISA in sera and urine of 111 SLE patients (31 with LN and 80 without LN) and 70 healthy cohorts. Significantly more abundances of DKK-1 protein were determined in both of sera and urine of SLE patients compared to healthy cohorts (p < 0.0001); in particular the serum DKK-1 concentration was even higher in LN-SLE patients relative to non-LN SLE subjects (p < 0.0001). Intriguingly, concentrations of above examined proteins in SLE patients showed no correlation between serum and urine. Moreover, a combination of DKK-1 with anti-dsDNA and/or levels of complement C3 and C4 could not increase the specificity and/or sensitivity for identification of patients with LN diseases, but both ROC curve and multiple-factor nonconditional logistic regression analysis showed that serum DKK-1 was considered better positive biomarker for identification of LN in SLE patients. These results imply that serum and/or urine DKK-1 may be a valuable and independent biomarker for identification of SLE patients with LN.