Bone mass is inversely proportional to Dkk1 levels in mice. Bone 41(3) : 331-339

Harvard University, Cambridge, Massachusetts, United States
Bone (Impact Factor: 3.97). 10/2007; 41(3):331-9. DOI: 10.1016/j.bone.2007.05.009
Source: PubMed


The Wnt/beta-catenin signaling pathway has emerged as a key regulator in bone development and bone homeostasis. Loss-of-function mutations in the Wnt co-receptor LRP5 result in osteoporosis and "activating" mutations in LRP5 result in high bone mass. Dickkopf-1 (DKK1) is a secreted Wnt inhibitor that binds LRP5 and LRP6 during embryonic development, therefore it is expected that a decrease in DKK1 will result in an increase in Wnt activity and a high bone mass phenotype. Dkk1-/- knockout mice are embryonic lethal, but mice with hypomorphic Dkk1d (doubleridge) alleles that express low amounts of Dkk1 are viable. In this study we generated an allelic series by crossing Dkk1+/- and Dkk1+/d mice resulting in the following genotypes with decreasing Dkk1 expression levels: +/+, +/d, +/- and d/-. Using muCT imaging we scanned dissected left femora and calvariae from 8-week-old mice (n=60). We analyzed the distal femur to represent trabecular bone and the femur diaphysis for cortical endochondral bone. A region of the parietal bones was used to analyze intramembranous bone of the calvaria. We found that trabecular bone volume is increased in Dkk1 mutant mice in a manner that is inversely proportional to the level of Dkk1 expression. Trabeculae number and thickness were significantly higher in the low Dkk1 expressing genotypes from both female and male mice. Similar results were found in cortical bone with an increase in cortical thickness and cross sectional area of the femur diaphysis that correlated with lower Dkk1 expression. No consistent differences were found in the calvaria measurements. Our results indicate that the progressive Dkk1 reduction increases trabecular and cortical bone mass and that even a 25% reduction in Dkk1 expression could produce significant increases in trabecular bone volume fraction. Thus DKK1 is a negative regulator of normal bone homeostasis in vivo. Our study suggests that manipulation of DKK1 function or expression may have therapeutic significance for the treatment of low bone mass disorders.

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Available from: Bryan T Macdonald
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    • "Dickkopf-1 (DKK1) is a soluble inhibitor of Wingless type Wnt/β-catenin signaling and is implicated in the regulation of osteoblast differentiation. It is a negative regulator of normal bone homeostasis in vivo [17]. DKK1 overexpression in osteoblasts causes osteopenia and inhibits fracture repair [18], while DKK1 activation in osteoblasts seems to participate in the pathogenesis of estrogen deficiency-mediated osteoporosis [19]. "
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    ABSTRACT: Objective. To assess serum level of Dickkopf-1 in postmenopausal females and its correlation with bone mineral density and serum biochemical markers. Methods. Bone densitometry, serum Dickkopf-1, calcium, phosphorus, and alkaline phosphatase were done in sixty postmenopausal females. Patients were divided according to T score into osteoporosis (group I), osteopenia (group II), and normal bone mineral density that served as controls. Results. There was highly significant increase in serum Dickkopf-1 levels in postmenopausal females with abnormal T score versus controls (P < 0.001). Serum DKK-1 levels correlated negatively with both lumbar T score (r = −0.69, P < 0.001) and femur T score (r = −0.64, P < 0.001) and correlated positively with duration of menopause (r = 0.61, P < 0.001), while there was no significant correlation between serum levels of either calcium, phosphorus or alkaline phosphatase, and both serum Dickkopf-1 levels and the level of bone mineral density (P > 0.05). Conclusion. Postmenopausal females may suffer from osteoporosis as evidenced by bone densitometry. Postmenopausal women with significantly increased serum Dickkopf-1 had more significant osteoporosis. Prolonged duration of menopause and increased serum Dickkopf-1 are important risk factors for the development and severity of osteoporosis.
    Full-text · Article · Jun 2013 · Journal of Osteoporosis
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    • "This is consistent with findings from mouse models deficient of Dkk-1. A single allele deletion of Dkk-1 in mice showed increased bone mass and greater bone formation activity [Morvan et al. 2006], as did mice with hypomorphic alleles (doubleridge) of Dkk-1 [MacDonald et al. 2007]. However, transgenic overexpression of Dkk-1 in osteoblasts of mice led to osteopenia and skeletal defects [Li et al. 2006]. "
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    ABSTRACT: The Wnt signaling pathway plays an important role not only in embryonic development but also in the maintenance and differentiation of the stem cells in adulthood. In particular, Wnt signaling has been shown as an important regulatory pathway in the osteogenic differentiation of mesenchymal stem cells. Induction of the Wnt signaling pathway promotes bone formation while inactivation of the pathway leads to osteopenic states. Our current understanding of Wnt signaling in osteogenesis elucidates the molecular mechanisms of classic osteogenic pathologies. Activating and inactivating aberrations of the canonical Wnt signaling pathway in osteogenesis results in sclerosteosis and osteoporosis respectively. Recent studies have sought to target the Wnt signaling pathway to treat osteogenic disorders. Potential therapeutic approaches attempt to stimulate the Wnt signaling pathway by upregulating the intracellular mediators of the Wnt signaling cascade and inhibiting the endogenous antagonists of the pathway. Antibodies against endogenous antagonists, such as sclerostin and dickkopf-1, have demonstrated promising results in promoting bone formation and fracture healing. Lithium, an inhibitor of glycogen synthase kinase 3β, has also been reported to stimulate osteogenesis by stabilizing β catenin. Although manipulating the Wnt signaling pathway has abundant therapeutic potential, it requires cautious approach due to risks of tumorigenesis. The present review discusses the role of the Wnt signaling pathway in osteogenesis and examines its targeted therapeutic potential.
    Full-text · Article · Feb 2013 · Therapeutic advances in musculoskeletal disease
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    • "The inhibition of Wnt signaling by DKK1 has been related to bone degeneration processes and reduced bone mass [22]. "
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    ABSTRACT: Background. DKK1 antagonizes canonical Wnt signalling through high-affinity binding to LRP5/6, an essential component of the Wnt receptor complex responsible for mediating downstream canonical Wnt signalling. DKK1 overexpression is known for its pathological implications in osteoporosis, cancer, and neurodegeneration, suggesting the interaction with LRP5/6 as a potential therapeutic target. Results. We show that the small-molecule NCI8642 can efficiently displace DKK1 from LRP6 and block DKK1 inhibitory activity on canonical Wnt signalling, as shown in binding and cellular assays, respectively. We further characterize NCI8642 binding activity on LRP6 by Surface Plasmon Resonance (SPR) technology. Conclusions. This study demonstrates that the DKK1-LRP6 interaction can be the target of small molecules and unlocks the possibility of new therapeutic tools for diseases associated with DKK1 dysregulation.
    Full-text · Article · Jan 2012
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