Effects of adipocyte-specific Dkk1 deletion on bone homeostasis and obesity-induced bone loss in male mice

The link between obesity and low bone strength has become a significant medical concern. The canonical Wnt signaling pathway is a key regulator of mesenchymal stem cell differentiation into either osteoblasts or adipocytes with active Wnt signaling promoting osteoblastogenesis. Our previous research indicated that Dickkopf-1 (Dkk1), a Wnt inhibitor, is upregulated in bone tissue in obesity and that osteoblast-derived Dkk1 drives obesity-induced bone loss. However, Dkk1 is also produced by adipocytes, but the impact of adipogenic Dkk1 on bone remodeling and its role in obesity-induced bone loss remain unclear. Thus, in this study, we investigated the influence of adipogenic Dkk1 on bone homeostasis and obesity-induced bone loss in mice. To that end, deletion of Dkk1 in adipocytes was induced by tamoxifen administration into 8-week-old male Dkk1fl/fl;AdipoQcreERT2 mice. Bone and fat mass were analyzed at 12 and 20 weeks of age. Obesity was induced in 8-week-old male Dkk1fl/fl;AdipoQcre mice with a high-fat diet (HFD) rich in saturated fats for 12 weeks. We observed that 12-week-old male mice without adipogenic Dkk1 had a significant increase in trabecular bone volume in the vertebrae and femoral bones. While histological and serological bone formation markers were not different, the number of osteoclasts and adipocytes was decreased in the vertebral bones of Dkk1fl/fl;AdipoQcre-positive mice. Despite the increased bone mass in 12-week-old male mice, at 20 weeks of age, there was no difference in the bone volume between the controls and Dkk1fl/fl;AdipoQcre-positive mice. Also, Dkk1fl/fl;AdipoQcre-positive mice were not protected from HFD-induced bone loss. Even though mRNA expression levels of Sost, another important Wnt inhibitor, in bone from Dkk1-deficient mice fed with HFD were decreased compared to Dkk1-sufficient mice on an HFD, this did not prevent the HFD-induced suppression of bone formation. In conclusion, adipogenic Dkk1 may play a transient role in bone mass regulation during adolescence, but it does not contribute to bone homeostasis or obesity-induced bone loss later in life.

Serum sclerostin level is positively associated with endothelial dysfunction measured by digital thermal monitoring in patients with type 2 diabetes: A prospective cross-sectional study

Sclerostin and dickkopf-1 (DKK1), extracellular inhibitors of the canonical Wnt/β-catenin signaling pathway, have been associated with vascular aging and atherosclerosis. This study aimed to assess the correlation of sclerostin and DKK1 concentrations with endothelial function measured using vascular reactivity index (VRI) in patients with type 2 diabetes mellitus (T2DM). Fasting blood samples were collected from 100 patients with T2DM. Endothelial function and VRI were measured using digital thermal monitoring and circulating sclerostin and DKK1 levels by enzyme-linked immunosorbent assays. VRI values < 1.0, 1.0-1.9, and > 2.0 indicated poor, intermediate, and good vascular reactivity, respectively. Overall, 30, 38, and 32 patients had poor, intermediate, and good vascular reactivity, respectively. Older age, higher serum glycated hemoglobulin, urinary albumin-to-creatinine ratio, and sclerostin as well as lower hypertension prevalence, systolic blood pressure, and diastolic blood pressure (DBP) were associated with poor VRI. Multivariable forward stepwise linear regression analysis showed that DBP (β = 0.294, adjusted R2 change = 0.098, P < .001), log-glycated hemoglobin (β = -0.235, adjusted R2 change = 0.050, P = .002), log-urine albumin-to-creatinine ratio (β = -0.342, adjusted R2 change = 0.227, P < .001), and log-sclerostin level (β = -0.327, adjusted R2 change = 0.101, P < .001) were independently associated with VRI. Serum sclerostin, along with glycated hemoglobin and albumin-to-creatinine ratio, exhibited a negative correlation with VRI, while DBP showed a positive correlation with VRI. These factors can independently predict endothelial dysfunction in patients with T2DM.

A Synergistic Effect between Plasma Dickkopf-1 and Obstructive Coronary Artery Disease on the Prediction of Major Adverse Cardiac Events in Patients with Angina: An Observational Study

The canonical β-catenin-dependent wingless (Wnt) pathway is associated with endothelial function. We examined the effect of plasma dickkopf-1 (DKK-1), an inhibitor of the Wnt pathway, on the prediction of major adverse cardiac events (MACEs). We enrolled patients who had undergone selective coronary angiography for angina. DKK-1 levels were determined using plasma collected at the outpatient visit after fasting. MACEs served as the primary endpoint. All 470 enrolled patients were divided into four groups according to their median plasma DKK-1 levels and the presence of obstructive coronary artery disease (CAD). Forty-eight patients reached the primary endpoint during a median follow-up time of 4.8 years. Kaplan–Meier survival analysis indicated that the group with high DKK-1 and obstructive CAD had a significantly higher mortality rate than the other three groups (log-rank test p = 0.001). Compared with the low plasma DKK-1 without significant coronary obstruction group, the high DKK-1 with obstructive CAD group had a hazard ratio of 10.640 (95% confidence interval: 1.350–83.874) for MACEs, as determined by multivariable Cox proportional hazard regression analysis. In conclusion, we observed a synergistic effect between high plasma DKK-1 and obstructive CAD on the prediction of MACEs in patients with angina.

Effects of periodontal and bisphosphonate treatment on the gingival crevicular levels of sclerostin and dickkopf-1 in postmenopausal osteoporosis with and without periodontitis

OBJECTIVE AND BACKGROUND

Both periodontitis and osteoporosis are associated with osteoclast-related bone resorption. Bone metabolism is regulated by wingless-type MMTV integration site family (WNT), and WNT/β-catenin signals are controlled by physiological antagonists including dickkopf-1 (DKK-1) and sclerostin (SOST). This study examined the effects of periodontal and bisphosphonate (BP) treatment on the gingival crevicular fluid (GCF) sclerostin (SOST) and dickkopf-related protein-1 (DKK-1) levels in osteoporotic and systemically healthy postmenopausal women with and without periodontitis.

MATERIALS AND METHODS

A total of 48 postmenopausal women were divided into 4 groups (n = 12) according to periodontal health and osteoporosis status, as follows: Group OP/P: subjects with both osteoporosis and periodontitis; Group P: systemically healthy subjects with periodontitis; Group OP: periodontally healthy subjects with osteoporosis; Group H: systemically and periodontally healthy controls. Clinical data and GCF SOST and DKK-1 levels of the participants were collected at baseline and at 6 and 12 months following the initiation of periodontal and/or BP treatment in the experimental groups. GCF SOST and DKK-1 data were obtained by ELISA.

RESULTS

Clinical improvements were observed in all experimental groups. GCF SOST and DKK1 baseline levels varied significantly between groups due to periodontal disease (p < .001). Following treatment, significant increases in SOST and DKK-1 concentrations and significant decreases in total amounts of SOST were observed in both periodontitis groups (OP/P, P). However, while total amounts of DKK-1 decreased in Group OP/P, in Group P, these amounts had significantly increased at 12 months post-treatment (p < .05). At both 6 and 12 months post-treatment, SOST and DDK1 total amounts in Groups OP/P, OP, and H were similar (p > .05), whereas significant differences were observed between Groups H and P, indicating a deviation from periodontal health in Group P (p < .01).

CONCLUSIONS

Significant changes in GCF SOST and DKK-1 levels were observed among women with osteoporosis who received both periodontal and BP treatment. A more detailed examination of how these treatment protocols can be combined may lead to new therapeutic approaches towards periodontal disease.

Effects of a Watercress Extract Fraction on R-spondin 1-Mediated Growth of Human Hair

OBJECTIVE

Hair loss and greying affect men and women of all ages, often causing psychosocial difficulties. Dickkopf-1 (DKK1), a major hair loss factor secreted from dermal papilla (DP) cells in response to the secretion of dihydrotestosterone (DHT), has been reported to induce and accelerate androgenetic alopecia (AGA). In addition, DKK1 acts as a potent suppressor of melanogenesis and is closely related to hair colour. R-spondin 1 (RSPO1) is a secretory agonist of Wnt signalling known to antagonize the effects of DKK1, including DKK1-mediated hair follicle suppression. In this study, we investigated the effect of watercress extract (WCE) on the secretion of RSPO1 and DKK1 from DP cells as well as its anti-hair loss effect in human hair follicles and patients.

METHODS

The in vitro secretion of RSPO1 and DKK1 was measured by ELISA. Human hair follicles were collected from the scalp of a female donor and used for ex vivo organ culture to investigate the effects of WCE on human hair loss. Finally, a 6-month human clinical trial was conducted to examine the effect of WCE-containing lotion on hair growth in a male panel.

RESULTS

WCE significantly upregulated RSPO1 secretion and suppressed DKK1 secretion in a dose-dependent manner, even in the presence of DHT. WCE-treated hair follicles elongated 1.6-fold compared to the control, and the level of RSPO1 production in DP as well as RSPO1 bound to the outer root sheath (ORS) increased. In the clinical trial, the hair lotion containing 2% WCE increased hair thickness and density to improve against hair loss symptoms.

CONCLUSION

WCE exhibited a strong anti-androgenic effect through its ability to suppress DKK1 secretion and antagonize DKK1 via RSPO1. These findings highlighted the potential use of WCE for the treatment of hair loss. These results also showed that WCE might have an effect on hair colour since DKK1 is a suppressor of melanogenesis.

Decreased Serum Dickkopf-1 Levels After Hypoglycemic Therapy in Patients with Type 2 Diabetes Mellitus

AIM

Dickkopf-1 (DKK-1) is a major inhibitor of Wingless protein signaling pathway, which is involved in glucose metabolism and cardiovascular diseases. The aim of the study was to investigate the changes of serum DKK-1 levels after hypoglycemic treatments and the relationship between DKK-1 and clinical parameters.

MATERIALS AND METHODS

The study was a sub-study of a previously published clinical trial (the effect of Acarbose on glycemic variability in patients with type 2 diabetes mellitus using premixed insulin compared to metformin). All subjects underwent anthropometric and biochemical assessments at baseline and endpoint. Serum DKK-1 levels of 92 subjects were measured at baseline and after 12-week hypoglycemic treatment.

RESULTS

DKK-1 levels were significantly decreased after hypoglycemic treatment for 12 weeks (P < 0.001). ΔDKK-1 levels were not correlated with improvement of metabolic parameters (all P > 0.05) but were negatively correlated with baseline DKK-1 levels (r = -0.263, P = 0.011). Spearman correlation showed that baseline DKK-1 levels were positively related to baseline total cholesterol (r = 0.226, P = 0.030) and low-density lipoprotein cholesterol (LDL-C) (r = 0.277, P = 0.007). Compared with the higher baseline DKK-1 group (≥3700 pg/mL), subjects in the lower baseline DKK-1 group (<3700 pg/mL) had significantly lower baseline glycated hemoglobin A1c levels (P = 0.008) and LDL-C levels (P = 0.048). Systolic and diastolic pressure were decreased more significantly in the lower baseline DKK-1 group than that in the higher baseline DKK-1 group (both P < 0.05).

CONCLUSION

Serum DKK-1 levels were decreased after hypoglycemic treatments. Patients with lower baseline DKK-1 levels were featured by more favorable cardiometabolic factors.

New Insights to the Crosstalk between Vascular and Bone Tissue in Chronic Kidney Disease-Mineral and Bone Disorder

Vasculature plays a key role in bone development and the maintenance of bone tissue throughout life. The two organ systems are not only linked in normal physiology, but also in pathophysiological conditions. The chronic kidney disease–mineral and bone disorder (CKD-MBD) is still the most serious complication to CKD, resulting in increased morbidity and mortality. Current treatment therapies aimed at the phosphate retention and parathyroid hormone disturbances fail to reduce the high cardiovascular mortality in CKD patients, underlining the importance of other factors in the complex syndrome. This review will focus on vascular disease and its interplay with bone disorders in CKD. It will present the very late data showing a direct effect of vascular calcification on bone metabolism, indicating a vascular-bone tissue crosstalk in CKD. The calcified vasculature not only suffers from the systemic effects of CKD but seems to be an active player in the CKD-MBD syndrome impairing bone metabolism and might be a novel target for treatment and prevention.

Wingless-type mouse mammary tumor virus integration site regulation of bovine theca cells

Ovarian paracrine mediation by components of the wingless-type mouse mammary tumor virus integration site ligands (WNT1 to 11) and their receptors, frizzled family members (FZD1 to 10), has been proposed. Secreted truncated forms of FZD proteins (e.g., secreted frizzled-related protein 4 [SFRP4]) block the action of WNT ligands. Dickkopf-1 (DKK1) is another WNT antagonist, and R-spondin-1 (RSPO1) is one of a group of four secreted proteins that enhance WNT/β-catenin signaling. Our hypothesis was that granulosa cells signal theca cells (TCs) via SFRP4, DKK1, RSPO1, and WNT secretion to regulate TC differentiation and proliferation. Therefore, in vitro experiments were conducted to study the effects of WNT family member 3A (WNT3A), WNT5A, RSPO1, DKK1, insulin-like growth factor 1 (IGF1), bone morphogenetic protein 7 (BMP7), Indian hedgehog (IHH), and fibroblast growth factor 9 (FGF9) on bovine TC proliferation and steroidogenesis. TCs of large (8 to 20 mm) and small (3 to 6 mm) follicles were collected from bovine ovaries; TC monolayers were established in vitro and treated with various doses of recombinant human WNT3A, WNT5A, RSPO1, DKK1, IGF1, FGF9, BMP7, IHH, and/or ovine luteinizing hormone (LH) in serum-free medium for 48 h. In experiment 1, using LH-treated TC, IGF1, IHH, and WNT3A increased (P < 0.05) cell numbers and androstenedione production, whereas WNT3A and BMP7 inhibited (P < 0.05) progesterone production. In experiment 2, FGF9 blocked (P < 0.05) the WNT3A-induced increase in androstenedione production in LH plus IGF1-treated TC. In experiment 3, RSPO1 further increased (P < 0.05) LH plus IGF1-induced progesterone and androstenedione production. In experiment 4, SFRP4 and DKK1 alone had no significant effect on TC proliferation or progesterone production of large-follicle TC but both blocked the inhibitory effect of WNT5A on androstenedione production. In contrast, DKK1 alone inhibited (P < 0.05) small-follicle TC androstenedione production whereas SFRP4 was without effect. We conclude that the ovarian TC WNT system is functional in cattle, with WNT3A increasing proliferation and androstenedione production of TC.

Dickkopf-1 promotes Vascular Smooth Muscle Cell proliferation and migration through upregulating UHRF1 during Cyclic Stretch application

Dickkopf-1 (DKK1) was recently shown to play an important role in cardiovascular disease. The aim of this work was to assess the role of DKK1 in the regulation of smooth muscle cell function by mechanical stretch and the mechanisms underlying this process.

Methods: Wild-type C57BL/6J mice were subjected to sham or abdominal aortic constriction (AAC) surgery. The expression level of DKK1 was examined by immunohistochemical staining and Western blotting. Analyses of DKK1 function in vascular smooth muscle cell (VSMC) proliferation and migration were performed. Transcriptome sequencing analysis was performed to identify the differentially expressed genes and pathways regulated by DKK1. Smooth muscle-specific Dkk1 knockout mice were used to confirm the function of DKK1 in vivo. Chromatin immunoprecipitation (ChIP) was used to confirm DNA-protein interactions. Promoter luciferase analysis was used to detect transcription factor activity.

Results: We found that AAC significantly increased DKK1 protein levels in the thoracic aorta and coronary artery in vivo. In vitro, high-level stretch (18%) induced the expression of DKK1 in VSMCs. Knocking down DKK1 inhibited VSMC proliferation and migration under high-level stretch (18%). We identified ubiquitin-like containing PHD and RING finger domains 1 (UHRF1) as a target gene of DKK1. Knockdown of UHRF1 with small interfering RNAs partially reversed the regulatory effect of recombinant DKK1 on VSMCs. Specific deletion of DKK1 in VSMCs was sufficient to attenuate the AAC-induced upregulation of UHRF1, thickening of arterial media and increase in VSMC proliferation. Furthermore, we found that DKK1 regulated UHRF1 expression through the YAP-TEAD pathway. TEAD1 and TEAD4 bound directly to the promoter of UHRF1, and blocking the YAP-TEAD interaction inhibited UHRF1 upregulation due to DKK1.

Conclusions: This study reveals that DKK1 mediates the mechanical stretch regulation of smooth muscle cell function by modulating UHRF1 expression through the YAP-TEAD pathway.

Changes in bone formation regulator biomarkers in early axial spondyloarthritis

OBJECTIVE

The hallmark of advanced axial SpA (axSpA) is spine ankylosis due to excessive ectopic bone formation. This prospective study aimed to describe the changes in serum levels of different regulators [sclerostin, dickkopf-1 (DKK-1)] and markers of bone formation [bone morphogenetic protein 7 (BMP-7)] over 5 years in early axSpA patients and to assess determinants of such changes.

METHODS

The DEvenir des Spondyloarthropathies Indifférenciées Récentes cohort is a prospective, multicentre French study of 708 patients with early (>3 months-<3 years) inflammatory back pain suggestive of axSpA. Serum levels of BMP-7, sclerostin and DKK-1 were assessed at baseline and after 2 and 5 years. Changes in bone formation regulators over time were analysed using mixed linear models.

RESULTS

Serum BMP-7 significantly increased over time, with a median relative change of 223.7% [interquartile range (IQR) 0-10 700 (0.17 pg/ml/month), P < 0.001]. Serum sclerostin significantly increased over time, with a median relative change of 14.8% [IQR -7.9-41.4% (0.001 ng/ml/month), P < 0.001]. Serum DKK-1 did not significantly change over time. Serum BMP-7 increased over time in active disease (Ankylosing Spondylitis Disease Activity Score with CRP ≥1.3, P = 0.01), but the increase was less pronounced with TNF inhibitor (TNFi) use (P < 0.001). No determinant was associated with serum sclerostin change.

CONCLUSION

Serum BMP-7 change over 5 years was related with inflammation; it was increased in active disease, but the increase was low with TNFi use. Serum sclerostin levels significantly increased over time, but to a lesser degree than for serum BMP-7.

CLINICAL TRIAL REGISTRATION

https://clinicaltrials.gov/, NCT01648907.

Expression and Role of Dickkopf-1 (Dkk1) in Tumors: From the Cells to the Patients

Dickkopf-1 (Dkk1) is a secretory antagonist of the classical Wnt signaling pathway. Many studies have reported that Dkk1 is abnormally expressed in tumor cells, and abnormal expression of Dkk1 can inhibit cell proliferation or induce apoptosis through pro-apoptotic factors, However, due to the differences in tumor environment and the complex regulatory mechanisms in different tumors, Dkk1 has different effects on the progression of different tumors. In many tumors, high expression of Dkk1 may promote tumor metastasis. However, Dkk1, which is highly expressed in other tumors, can inhibit tumor invasion and metastasis. More and more evidence shows that Dkk1 plays a complex and different role in tumor occurrence, development and metastasis in different tumor environments and through a variety of complex regulatory mechanisms. Therefore, Dkk1 may not only be a useful biomarker of metastasis, but also a target for studying the metabolic mechanism of tumor cells and treating tumors in many tumor types. Therefore, this article reviews the research progress on the expression, mechanism and function of Dkk1 in different tumors, and at the same time, based on the public database data, we made a further analysis of the expression of Dkk1 in different tumors.

Expression and methylation of Dickkopf-1 in the pathogenesis and malignant transformation of oral submucous fibrosis

BACKGROUND

Dickkopf-1 is an inhibitor of the Wnt/β-catenin pathway, but the role of Dickkopf-1 in oral submucous fibrosis remains unclear. We evaluated the protein expression and gene methylation levels of dickkopf-1 to determine the mechanism underlying abnormal Wnt/β-catenin pathway activation.

METHODS

Healthy mucosa, oral submucous fibrosis, oral squamous cell carcinoma, and cancer-adjacent tissues were collected. The expression and promoter methylation levels of dickkopf-1 were analyzed.

RESULTS

The expression levels of dickkopf-1 in oral submucous fibrosis and oral squamous cell carcinoma tissues were lower than those in healthy and cancer-adjacent tissues. The methylation levels of the dickkopf-1 gene in oral submucous fibrosis and oral squamous cell carcinoma tissues were higher than those in healthy and cancer-adjacent tissues. Dickkopf-1 expression was negatively correlated with dickkopf-1 gene methylation.

CONCLUSIONS

High dickkopf-1 methylation levels in oral submucous fibrosis and oral squamous cell carcinoma tissues may decrease dickkopf-1 expression, which may induce an abnormal activation of the Wnt/β-catenin pathway and oral submucous fibrosis pathogenesis.

Prognostic role of dickkopf-1 in patients with cancer

As an antagonist for the WNT signal passway, dickkopf-1(DKK1) have a great important role in the occurence and development of various type cancer. The present paper performed a meta-analysis to evaluate the predictive significance of DKK1 in cancer.To assess the relationship between the expression of DKK1 and prognostic role in human cancers, a total of 16 articals were screened from the multiple online databases (Pubmed, EMBASE, CNKI, Web of Science and Google Scholar) in our study. By using the STATA soft,pooled hazard ratio and 95% confidence intervals of overall survival (OS), progression-free survival, disease-free survival and time to recurrence were used to evaluate the strength of this relationship.The meta-analysis showed that higher expression of DKK1 was significantly associated with shorter OS in cancer patients. In stratified analyzes, the higher expression of DKK1 could reduced the OS in patients with breast cancer,digestive system cancer and urogenital system cancer, but not patients with the lung cancer. It also showed that higher expression of DKK1 was significantly associated with shorter progression-free survival, disease-free survival and time to recurrence in cancer patients.The present study indicate that higher expression of DKK1 predict an unfavorable clinical outcome in patients with breast cancer, digestive system cancer and urogenital system cancer.

Serum Dkk-1 (Dickkopf-1) Is a Potential Biomarker in the Prediction of Clinical Outcomes Among Patients With Acute Ischemic Stroke

Objective- Serum Dkk-1 (dickkopf-1) level has been shown to be elevated in patients with ischemic stroke, but its impact on clinical outcomes of ischemic stroke remains unclear. The aim of this study is to investigate the association between serum Dkk-1 and prognosis of ischemic stroke. Approach and Results- We measured serum Dkk-1 levels in 3178 patients with ischemic stroke from CATIS (China Antihypertensive Trial in Acute Ischemic Stroke). The primary outcome was a combination of all-cause mortality and major disability (modified Rankin scale score, ≥3) at 1 year after stroke. Secondary outcomes were stroke recurrence and vascular events. After multivariate adjustment, elevated Dkk-1 levels were associated with an increased risk of primary outcome (odds ratio, 1.40; 95% CI, 1.03-1.89; P_trend=0.015) when 2 extreme quartiles were compared. Each SD increase of log-transformed Dkk-1 was associated with 12% (95% CI, 1%-24%) increased risk of primary outcome. Multiple-adjusted spline regression model showed a linear association between serum Dkk-1 and risk of primary outcome ( P for linearity, 0.039). Subgroup analyses further confirmed these associations. The addition of serum Dkk-1 to conventional risk factors improved the predictive power for primary outcome (net reclassification improvement: 10.11%, P=0.029; integrated discrimination improvement: 0.21%, P=0.028). Conclusions- High serum Dkk-1 levels at baseline were associated with poor prognosis at 1 year after ischemic stroke, suggesting that serum Dkk-1 may be a potential prognostic biomarker for ischemic stroke. Further studies from other samples of patients with ischemic stroke are needed to replicate our findings and to clarify the potential mechanisms.

Long noncoding RNA TTN-AS1 enhances the malignant characteristics of osteosarcoma by acting as a competing endogenous RNA on microRNA-376a thereby upregulating dickkopf-1

The expression levels and detailed functions of TTN-AS1 in osteosarcoma (OS) have not yet been explored. This study aimed to measure TTN-AS1 expression in OS tissues and cell lines, investigate its specific roles in the aggressive characteristics of OS cells in vitro and in vivo, and elucidate the regulatory mechanisms of TTN-AS1 action. TTN-AS1 expression was high in OS tissue samples and cell lines; TTN-AS1 overexpression correlated with the clinical stage, distant metastasis, and shorter overall survival of the patients. A TTN-AS1 knockdown inhibited OS cell proliferation, migration, and invasion and induced apoptosis in vitro and slowed tumor growth in vivo. Mechanism investigation revealed that TTN-AS1 acts as a competing endogenous RNA on microRNA-376a-3p (miR-376a) in OS cells. Dickkopf-1 (DKK1) mRNA was identified as a direct target of miR-376a in OS cells. Resumption of DKK1 expression reversed the tumor-suppressive activities of miR-376a overexpression in OS cells. The knockdown of miR-376a counteracted the reduction in the malignant characteristics of OS cells by the downregulation of TTN-AS1. In conclusion, TTN-AS1 functions as a competing endogenous RNA targeting miR-376a and increases the malignancy of OS cells in vitro and in vivo by upregulating DKK1.

The predictive values of serum dickkopf-1 and circulating tumor cells in evaluating the efficacy of transcatheter arterial chemoembolization treatment on hepatocellular carcinoma

In this study, we aim to explore the values of serum dickkopf-1 (DKK1) and circulating tumor cells (CTCs) in predicting the efficacy and prognosis of transcatheter arterial chemoembolization (TACE) treatment on patients with hepatocellular carcinoma (HCC). We did a retrospective analysis on 155 HCC patients who underwent TACE treatment. The patients were divided into response group (complete response and partial response) and nonresponse group (stable disease and progressive disease), and their changes in serum DKK1 and CTCs after TACE were recorded. Receiver operating characteristic curve and survival analysis were used to assess the predictive values of DKK1 and CTCs for TACE efficacy and long-term prognosis of HCC. We found that the levels of preoperative DKK1 and CTCs in patients with HCC had a moderate positive correlation (r = 0.54). After TACE treatment, the serum DKK1 and CTCs in the response group were significantly decreased compared to pretreatment levels (P < .05), whereas the nonresponse group showed significantly increased serum DKK1 and CTCs levels (P < .05). The largest area under the curve (AUC) was achieved when using >0.02 μg/L reduction in DKK1 level after 4 weeks of TACE to predict the efficacy of TACE treatment (AUC = 0.913, 95% confidence interval: 0.856-0.952, P < .001), with the sensitivity of 78.26% and the specificity of 88.07%. The overall survival, disease-free survival, and 5-year survival rates were all significantly lower in the patients with positive preoperative levels of serum DKK1 and CTCs. COX multivariate regression analysis showed that Eastern Cooperative Oncology Group score, and preoperative levels of serum DKK1 and CTCs are independent influencing factors for the prognosis of patients with HCC. Overall, our results demonstrated that serum DKK1 and CTCs levels were good biomarkers for predicting the efficacy and prognosis of TACE treatment in patients with HCC. Moreover, these parameters exhibited different characteristics, and might have different potential applications.

Strong immunoexpression of dickkopf-1 is associated with response to bortezomib in multiple myeloma

The predictive significance of osteolysis-related proteins was evaluated in bortezomib-treated multiple myeloma. The clinicopathological characteristics were collected retrospectively. Immunohistochemistry was performed for analyzing receptor activator of NF-κB ligand (RANKL), osteoprotegerin (OPG), macrophage inflammatory protein 1 alpha (MIP1α), and dickkopf-1 (DKK1) expression. Among clinicopatholgical characteristics, osteolytic lesion was associated with higher response to bortezomib treatment (79% vs. 46%). High DKK1 expression was significantly correlated with osteolytic lesion (p = .003), whereas RANKL, OPG, and MIP1α were not. In high DKK1 expression, higher response to bortezomib was observed (84% vs. 44%). In multivariate analysis, high DKK1 expression was associated with better response to bortezomib (p = .005). Patients with high DKK1 expression had longer median progression-free survival (PFS) and overall survival (OS) after bortezomib treatment. In multivariate analysis, high DKK1 expression was an independent prognostic factor of favorable PFS (p = .027) and OS (p = .035). In multiple myeloma treated with bortezomib, expression status of DKK1 may be a useful predictive marker.

The role of sclerostin/dickkopf-1 and receptor activator of nuclear factor kB ligand/osteoprotegerin signalling pathways in the development of osteoporosis in patients with haemophilia A and B: A cross-sectional study

AIM

Haemophilia A and B are associated with reduced bone mineral density (BMD). The aim of this study was to assess circulating sclerostin and dickkopf-1 (Dkk-1), (inhibitors of osteoblastic differentiation), as well as the receptor activator of nuclear factor kB ligand (RANKL)/osteoprotegerin (OPG) system (the major regulator of osteoclastogenesis), in patients with haemophilia (PWH), their possible correlations with clinical risk factors and the effect of ibandronate on these markers.

METHODS

Eighty-nine male PWH (mean age 45.9 ± 15.3 years) and 30 age-matched healthy male controls participated. BMD was assessed by DXA. Sclerostin, Dkk-1, RANKL and OPG were measured in serum of patients, controls, as well as in ten patients receiving oral ibandronate (150 mg/mo), at baseline and after 12 months.

RESULTS

Patients with haemophilia had lower circulating sclerostin (median ± IQR: 47.4 ± 26.93 vs 250 ± 250 pmol/L, P < .001), Dkk-1 (21.24 ± 17.18 vs 26.16 ± 15.32pg/mL, P = .04) and higher levels of RANKL (0.23 ± 0.03 vs 0.04 ± 0.03 pmol/L, P = .001), RANKL/OPG ratio (0.063 ± 0.25 vs 0.005 ± 0.11, P = .001) compared with controls. Patients with low BMD had higher OPG concentrations compared to those with normal BMD. Sclerostin and RANKL/OPG correlated positively with BMD. Patients with severe haemophilia had lower sclerostin concentrations compared with those with mild or moderate disease. The degree of arthropathy negatively correlated with sclerostin and Dkk-1 levels. PWH who received ibandronate showed a decrease in serum Dkk-1 without any significant effect on sclerostin and RANKL/OPG.

CONCLUSIONS

Patients with haemophilia present increased osteoclastic activity coupled with compensatory increased osteoblastic activity. Ibandronate did not affect RANKL/OPG ratio, but it decreased Dkk-1.

Dickkopf-1 induces angiogenesis via VEGF receptor 2 regulation independent of the Wnt signaling pathway

Tumor angiogenesis is essential for invasive tumor growth and metastasis. Dickkopf-1 (DKK-1), an antagonist of Wnt signaling, participates in tumor development and progression. We evaluated whether DKK-1 stimulation induces angiogenesis and the endothelial-mesenchymal transition (EnMT). Human umbilical vein endothelial cells (HUVECs) were stimulated with recombinant DKK-1 (rDDK-1) or conditioned medium from a culture of DKK-1-transfected 293 cells. Following stimulation, the expression levels of angiogenesis-related factors and EnMT related markers were determined by immunoblot assays. In addition, the effects of exogenous DKK-1 on angiogenesis and EnMT were assessed by tube-formation, cell invasion, and wound-healing assays. Human hepatoma cells, such as Hep3B and Huh-7, showed high levels of DKK-1 expression, whereas 293 cells and HUVECs showed little or no DKK-1 expression. Increased endothelial cell tube formation and invasiveness were observed in HUVECs treated with concentrated conditioned medium from DKK-1-overexpressing 293 cells or rDKK-1. DKK-1-stimulated HUVECs also exhibited increased motility in wound-healing assays. Furthermore, the expression levels of angiogenesis-related factors, including vascular endothelial growth factor receptor 2 and vascular endothelial-cadherin, were increased in DKK-1-stimulated HUVECs. The expression of EnMT markers, such as vimentin and Twist, was also increased in DKK-1-stimulated HUVECs. However, no significant change in β-catenin or GSK3β expression was observed. Our in vitro data suggest that DKK-1 can enhance angiogenesis and EnMT by HUVECs independent of the Wnt signaling pathway. Modulation of DKK-1 expression may facilitate development of novel strategies to control tumor angiogenesis and metastasis.

Combined detection of dickkopf-1 subtype classification autoantibodies as biomarkers for the diagnosis and prognosis of non-small cell lung cancer

Purpose

This study aims to identify the clinical significance of serum autoantibodies against dickkopf-1 (DKK1) and evaluate their feasibility in the immunodiagnosis and prognosis of non-small cell lung cancer (NSCLC).

Experimental design

Epitope mapping by peptide microarray-based serum screening of NSCLC patients (n=72) and healthy controls (n=16) was performed. Indirect ELISA with peptides was used to measure the serum levels of autoantibodies in 206 NSCLC patients and 99 healthy controls. A 3-year follow-up was monitored to evaluate the correlation between serological levels of autoantibodies and overall survival (OS) and progression-free survival (PFS).

Results

Four highly reactive epitopes were identified, which included peptides 67–84 (Pep A), 37–54 (Pep B), 145–156 (Pep C) and 247–261 (Pep D). The autoantibodies levels were considerably higher in sera of NSCLC patients compared with controls (P<0.001), and a highly significant correlation with distant metastases was observed (Pep A: P=0.09, Pep B: P<0.01, Pep C: P<0.01 and Pep D: P<0.01). High levels of antibody subtype to Pep B were remarkably associated with better OS (P=0.004) and PFS (P=0.006). Subsequent Cox regression analysis disclosed that antibody to Pep B was an independent prognostic factor for NSCLC (OS: P=0.008, HR =0.435, 95% CI 0.236–0.802; PFS: P=0.032, HR =0.533, 95% CI 0.322–0.950).

Conclusion

Identified linear epitopes of antigens by peptide microarray are easily available, and subtype classification of DKK1 autoantibodies as novel biomarkers for the diagnosis and prognosis of NSCLC. Our results also highlight the antibody subtype to Pep B as the most valuable biomarker for favorable prognosis of NSCLC.

Serum dickkopf-1 as a clinical and prognostic factor in non-small cell lung cancer patients with bone metastases

Background

The study was designed to evaluate the association between serum dickkopf-1 (DKK1) and non-small cell lung cancer (NSCLC) bone metastases.

Materials and Methods

Serum DKK1 levels were quantified in 470 NSCLC patients, 140 with osseous metastases, 178 with extraosseous metastases, and 152 with early stage in complete remission. The Receiver Operating Characteristic (ROC) curve enabled us to identify a threshold value to distinguish patients with bone metastases.

Results

Serum DKK1 levels in patients with osseous metastases were significantly higher than in the other 2 groups (P < 0.001). ROC curves showed that the optimum cutoff was 311.8 pg/ml (area under curve 0.791, 95% confidence interval 0.739–0.843, sensitivity 77.1% and specificity 71.4%). Of interest, serum DKK1 correlated with the number of bone lesions (P = 0.042) and associated with the poor survival in NSCLC patients with osseous metastases (P = 0.029).

Conclusions

Our data shows that serum DKK1 can be used for the detection of NSCLC bone metastases. More importantly this is the first report to show that serum DKK1 is a good predictor of poor prognosis in NSCLC patients with bone metastases.

Factors associated with serum soluble inhibitors of Wnt-β-catenin signaling (sclerostin and dickkopf-1) in patients undergoing peritoneal dialysis

AIM

Sclerostin and dickkopf-1 (Dkk-1) are soluble inhibitors of Wnt-β-catenin signaling and are involved in decreased bone formation and bone volume in patients with various bone diseases. The clinical characteristics of sclerostin and Dkk-1 and their impacts on mineral and bone metabolism remain undetermined in patients undergoing peritoneal dialysis (PD).

METHODS

This cross-sectional study investigated the association between serum sclerostin and Dkk-1 levels and mineral disorders in 74 outpatients under PD treatment. Levels of sclerostin and Dkk-1 in serum, urine, and peritoneal dialysate were determined using enzyme-linked immunosorbent assay kits. The associations between serum sclerostin and Dkk-1 levels and biochemical parameters were evaluated by linear regression analyses.

RESULTS

Median serum sclerostin and Dkk-1 levels were 138 pmol/L (range, 98.3-195.9 pmol/L) and 38.8 pmol/L (range, 28.5-47.1 pmol/L), respectively. Both sclerostin and Dkk-1 were excreted into urine and peritoneal dialysate. Multivariable linear regression analyses showed that serum sclerostin level was significantly associated with age, sex, parathyroid hormone level, and renal Kt/V. In contrast, serum Dkk-1 level was associated with platelet count and serum fibroblast growth factor 23 level but not with any of the bone metabolic markers.

CONCLUSION

Serum sclerostin was associated with serum intact parathyroid hormone, while Dkk-1 was associated with serum fibroblast growth factor 23 in patients undergoing PD. The utility of determining soluble Wnt-β-catenin inhibitors levels in patients undergoing PD requires further investigation.

Downregulation of dickkopf-1 enhances the proliferation and osteogenic potential of fibroblasts isolated from ankylosing spondylitis patients via the Wnt/β-catenin signaling pathway in vitro

BACKGROUND

Heterotopic ossification of the entheses is one of the most distinctive features in ankylosing spondylitis (AS). Fibroblasts are potential target cells for heterotopic ossification. The Wnt/β-catenin pathway and its inhibitor dickkopf-1 (DKK-1) regulate bone formation. DKK-1 expression in human AS tissues has not been documented.

OBJECTIVE

The purpose of the current study was to investigate the expression of DKK-1 in AS tissues and to elucidate its role in fibroblasts proliferation and osteogenesis in AS.

METHODS

DKK-1 expression was assessed by western blotting, real time-polymerase chain reaction (RT-PCR), and immunohistochemistry analysis of hip synovial tissues obtained from AS and control patients. Fibroblasts were isolated, cultured, and transfected with lentiviral vectors for overexpressing human DKK-1 or an shRNA for silencing DKK-1. MTS [(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl) 2-(4-sulfophenyl)-2H-tetrazolium] and a 5-ethynyl-2'-deoxyuridine (EdU) incorporation assay were used to detect AS fibroblasts proliferation after transfection. The expression levels of β-catenin, phosphorylated β-catenin, c-Myc, cyclin D1, and the osteogenesis markers alkaline phosphatase (ALP), osteocalcin (OCN), and Runt-related transcription factor 2 (Runx2) were then examined by western blot analysis. Alizarin red staining (ARS) was also used to observe biomineralization activity.

RESULTS

DKK-1 was downregulated in hip synovial tissues from AS patients compared to that observed in controls. AS fibroblasts exhibited excessive proliferation, a higher growth rate, and a decreased apoptotic rate. EdU assay demonstrated that DKK-1 suppressed the growth of AS fibroblasts. Downregulation of DKK-1 decreased the phosphorylation of β-catenin and upregulated the expression of β-catenin, c-Myc, cyclin D1, and osteogenesis markers. Overexpression of DKK-1 had the opposite effect, resulting in the inhibition of the Wnt/β-catenin pathway. ARS showed an increase in biomineralization activity after the inhibition of DKK-1.

CONCLUSIONS

AS fibroblasts are characterized by an imbalance between proliferation and apoptosis. DKK-1 may play a role in switching to new bone formation in AS progression.

Activation of dickkopf-1 and focal adhesion kinase pathway by tumour necrosis factor α induces enhanced migration of fibroblast-like synoviocytes in rheumatoid arthritis

OBJECTIVE

The objective of this study was to investigate the roles of dickkopf-1 (DKK-1) and integrin-related focal adhesion kinase (FAK) by TNF-α on the migration of fibroblast-like synoviocytes (FLSs) in RA.

METHODS

Wound scratch assays were performed to assess FLS migration. Western blotting was used to measure the levels of DKK-1, Wnt signalling molecules and FAK signalling molecules. Quantitative real-time PCR was used to measure the expression levels of DKK-1, integrin αv, laminin, fibronectin, E-cadherin, MMP-8 and MMP-13. The concentrations of DKK-1, TNF-α and GSK-3β were measured by ELISA. Genetic silencing of TNF-α was achieved by the transfection of small interfering RNA into cells.

RESULTS

Migrating RA FLSs exhibited higher levels of DKK-1 and TNF-α expression compared with those in OA FLSs and/or stationary RA FLSs. Moreover, migrating FLSs exhibited significantly higher levels of FAK, p-JNK, paxillin and cdc42 expression, whereas the level of cytosolic β-catenin was lower. WAY-262611, Wnt pathway agonist via inhibition of DKK-1, markedly inhibited cell migration of RA FLSs through the accumulation of cytosolic β-catenin and suppression of FAK-related signalling pathways. TNF-α treatment to RA FLSs up-regulated expression of DKK-1, integrin αv, fibronectin, laminin and MMP-13. TNF-α stimulation also suppressed cytosolic β-catenin and E-cadherin expression in a time-dependent manner. Moreover, TNF-α small interfering RNA-transfected migrating FLSs exhibited decreased activation of integrin-related FAK, paxillin, p-JNK and cdc42 signalling pathways.

CONCLUSION

This study demonstrates that the activation of DKK-1 and the integrin-related FAK signalling pathway stimulated by TNF-α induces the dissociation of β-catenin/E-cadherin, thus promoting RA FLS migration.

Serum dickkopf-1 as a biomarker in screening gastrointestinal cancers: a systematic review and meta-analysis

OBJECTIVE

Despite advances in the early diagnosis of gastrointestinal (GI) cancers, these cancers are often being detected rather late in their course. Emerging published data on the accuracy of dickkopf-1 (DKK1) for diagnosing GI cancers are inconsistent. The purpose of this systematic review and meta-analysis was to evaluate the diagnostic value of DKK1 in the diagnosis of GI cancers.

METHODS

A systematic literature search of PubMed, Web of Science, Embase, Chinese National Knowledge Infrastructure, and WANFANG databases was conducted to identify the related studies published before May 1, 2015, which investigated the diagnostic value of serum DKK1 for GI cancers. The methodological quality of each study was assessed according to the Quality Assessment of Diagnostic Accuracy Studies 2 checklist. The diagnostic performance was pooled and analyzed using a bivariate model. Publication bias was evaluated with the Deeks' funnel test.

RESULTS

A total of 15 studies with 5,076 participants were finally identified for the meta-analysis. The pooled results of sensitivity (SEN), specificity (SPE), positive likelihood ratio, negative likelihood ratio, and diagnostic odds ratio for DKK1 test were 0.72 (95% confidence interval [CI]: 0.70-0.74), 0.90 (95% CI: 0.89-0.91), 7.72 (95% CI: 4.90-12.14), 0.29 (95% CI: 0.22-0.39), and 28.95 (95% CI: 16.25-51.65) for diagnosis of GI cancers, respectively. The area under the summary receiver-operating characteristic curve was 0.8901. The SEN of DKK1 in diagnosis of gastric cancer and pancreatic cancer may be higher than hepatocellular carcinoma, and the SPE in pancreatic cancer subgroup was lower than hepatocellular carcinoma and gastric cancer subgroups.

CONCLUSION

The currently available evidence suggests that serum DKK1 is a potential biomarker with high SEN and SPE for screening GI cancers. To better elucidate the usefulness of serum DKK1, further studies are needed.

Molecular signalling in hepatocellular carcinoma: Role of and crosstalk among WNT/ß-catenin, Sonic Hedgehog, Notch and Dickkopf-1

Hepatocellular carcinoma is the sixth most common cancer worldwide. In the majority of cases, there is evidence of existing chronic liver disease from a variety of causes including viral hepatitis B and C, alcoholic liver disease and nonalcoholic steatohepatitis. Identification of the signalling pathways used by hepatocellular carcinoma cells to proliferate, invade or metastasize is of paramount importance in the discovery and implementation of successfully targeted therapies. Activation of Wnt/β-catenin, Notch and Hedgehog pathways play a critical role in regulating liver cell proliferation during development and in controlling crucial functions of the adult liver in the initiation and progression of human cancers. β-catenin was identified as a protein interacting with the cell adhesion molecule E-cadherin at the cell-cell junction, and has been shown to be one of the most important mediators of the Wnt signalling pathway in tumourigenesis. Investigations into the role of Dikkopf-1 in hepatocellular carcinoma have demonstrated controversial results, with a decreased expression of Dickkopf-1 and soluble frizzled-related protein in various cancers on one hand, and as a possible negative prognostic indicator of hepatocellular carcinoma on the other. In the present review, the authors focus on the Wnt⁄β-catenin, Notch and Sonic Hedgehog pathways, and their interaction with Dikkopf-1 in hepatocellular carcinoma.

Heritability and genetics of serum dickkopf 1 levels in African ancestry families

The aim of the study was to determine the heritability of serum dickkopf-1 (DKK1) and its association with DKK1 polymorphisms in African ancestry subjects. Serum DKK1 was measured in 422 Afro-Caribbean men and women aged 18+ from 7 large, multi-generational families (mean family size: 60; 3,215 relative pairs). Twenty-four common single nucleotide polymorphisms (SNPs) were genotyped within an 80 kilobase-pair region encompassing the DKK1 gene. Heritability was estimated and SNPs were tested for association with serum DKK1 using variance components analysis. DKK1 mRNA expression was tested in peripheral blood of 16 individuals from each of the rs7069912 genotypes. Mean serum DKK1 was 1724.1 pg/mL and was significantly lower in women than men (P = 0.043). Residual genetic heritability of serum DKK1 was 0.4460 (P < 0.0001). Six SNPs reached nominal significance with DKK1, with rs7069912 being significant after adjustment for multiple comparisons. Two of these six SNPs represented independent association signals (rs7069912 and rs16928725), which accounted for 4.6% of the phenotypic variation in DKK1. Additionally, carriers of the rs7069912 variant had significantly greater DKK1 expression than non-carriers (P = 0.036). Serum DKK1 levels are highly heritable in the African ancestry families. Two SNPs within the DKK1 region accounted for nearly 5% of the variation in serum DKK1.

Clusterin regulates β-amyloid toxicity via Dickkopf-1-driven induction of the wnt-PCP-JNK pathway

Although the mechanism of Aβ action in the pathogenesis of Alzheimer's disease (AD) has remained elusive, it is known to increase the expression of the antagonist of canonical wnt signalling, Dickkopf-1 (Dkk1), whereas the silencing of Dkk1 blocks Aβ neurotoxicity. We asked if clusterin, known to be regulated by wnt, is part of an Aβ/Dkk1 neurotoxic pathway. Knockdown of clusterin in primary neurons reduced Aβ toxicity and DKK1 upregulation and, conversely, Aβ increased intracellular clusterin and decreased clusterin protein secretion, resulting in the p53-dependent induction of DKK1. To further elucidate how the clusterin-dependent induction of Dkk1 by Aβ mediates neurotoxicity, we measured the effects of Aβ and Dkk1 protein on whole-genome expression in primary neurons, finding a common pathway suggestive of activation of wnt-planar cell polarity (PCP)-c-Jun N-terminal kinase (JNK) signalling leading to the induction of genes including EGR1 (early growth response-1), NAB2 (Ngfi-A-binding protein-2) and KLF10 (Krüppel-like factor-10) that, when individually silenced, protected against Aβ neurotoxicity and/or tau phosphorylation. Neuronal overexpression of Dkk1 in transgenic mice mimicked this Aβ-induced pathway and resulted in age-dependent increases in tau phosphorylation in hippocampus and cognitive impairment. Furthermore, we show that this Dkk1/wnt-PCP-JNK pathway is active in an Aβ-based mouse model of AD and in AD brain, but not in a tau-based mouse model or in frontotemporal dementia brain. Thus, we have identified a pathway whereby Aβ induces a clusterin/p53/Dkk1/wnt-PCP-JNK pathway, which drives the upregulation of several genes that mediate the development of AD-like neuropathologies, thereby providing new mechanistic insights into the action of Aβ in neurodegenerative diseases.

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.

Induction of Dickkopf-1, a negative modulator of the Wnt pathway, is associated with neuronal degeneration in Alzheimer's brain

We used primary cultures of cortical neurons to examine the relationship between beta-amyloid toxicity and hyperphosphorylation of the tau protein, the biochemical substrate for neurofibrillary tangles of Alzheimer's brain. Exposure of the cultures to beta-amyloid peptide (betaAP) induced the expression of the secreted glycoprotein Dickkopf-1 (DKK1). DKK1 negatively modulates the canonical Wnt signaling pathway, thus activating the tau-phosphorylating enzyme glycogen synthase kinase-3beta. DKK1 was induced at late times after betaAP exposure, and its expression was dependent on the tumor suppressing protein p53. The antisense induced knock-down of DKK1 attenuated neuronal apoptosis but nearly abolished the increase in tau phosphorylation in betaAP-treated neurons. DKK1 was also expressed by degenerating neurons in the brain from Alzheimer's patients, where it colocalized with neurofibrillary tangles and distrophic neurites. We conclude that induction of DKK1 contributes to the pathological cascade triggered by beta-amyloid and is critically involved in the process of tau phosphorylation.