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Normal hematopoiesis and lack of ?-catenin activation in osteoblasts of patients and mice harboring Lrp5 gain-of-function mutations.

ABSTRACT: Osteoblasts are emerging regulators of myeloid malignancies since genetic alterations in them, such as constitutive activation of ?-catenin, instigate their appearance. The LDL receptor-related protein 5 (LRP5), initially proposed to be a co-receptor for Wnt proteins, in fact favors bone formation by suppressing gut-serotonin synthesis. This function of Lrp5 occurring in the gut is independent of ?-catenin activation in osteoblasts. However, it is unknown whether Lrp5 can act directly in osteoblast to influence other functions that require ?-catenin signaling, particularly, the deregulation of hematopoiesis and leukemogenic properties of ?-catenin activation in osteoblasts, that lead to development of acute myeloid leukemia (AML). Using mice with gain-of-function (GOF) Lrp5 alleles (Lrp5(A214V)) that recapitulate the human high bone mass (HBM) phenotype, as well as patients with the T253I HBM Lrp5 mutation, we show here that Lrp5 GOF mutations in both humans and mice do not activate ?-catenin signaling in osteoblasts. Consistent with a lack of ?-catenin activation in their osteoblasts, Lrp5(A214V) mice have normal trilinear hematopoiesis. In contrast to leukemic mice with constitutive activation of ?-catenin in osteoblasts (Ctnnb1(CAosb)), accumulation of early myeloid progenitors, a characteristic of AML, myeloid-blasts in blood, and segmented neutrophils or dysplastic megakaryocytes in the bone marrow, are not observed in Lrp5(A214V) mice. Likewise, peripheral blood count analysis in HBM patients showed normal hematopoiesis, normal percentage of myeloid cells, and lack of anemia. We conclude that Lrp5 GOF mutations do not activate ?-catenin signaling in osteoblasts. As a result, myeloid lineage differentiation is normal in HBM patients and mice. This article is part of a Special Issue entitled: Tumor Microenvironment Regulation of Cancer Cell Survival, Metastasis, Inflammation, and Immune Surveillance edited by Peter Ruvolo and Gregg L. Semenza.

SUBMITTER: Galan-Diez M

PROVIDER: S-EPMC4924618 | biostudies-literature | 2016 Mar

REPOSITORIES: biostudies-literature

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Normal hematopoiesis and lack of β-catenin activation in osteoblasts of patients and mice harboring Lrp5 gain-of-function mutations.

Galán-Díez Marta M Isa Adiba A Ponzetti Marco M Nielsen Morten Frost MF Kassem Moustapha M Kousteni Stavroula S

Biochimica et biophysica acta 20151208 3

Osteoblasts are emerging regulators of myeloid malignancies since genetic alterations in them, such as constitutive activation of β-catenin, instigate their appearance. The LDL receptor-related protein 5 (LRP5), initially proposed to be a co-receptor for Wnt proteins, in fact favors bone formation by suppressing gut-serotonin synthesis. This function of Lrp5 occurring in the gut is independent of β-catenin activation in osteoblasts. However, it is unknown whether Lrp5 can act directly in osteobl ...[more]

PMID: 26681532

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Project description:Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease characterized by chronic synovitis, bone erosion, and bone loss. Erzhi Pill (EZP), a classic Chinese patent medicine, is often used to treat osteoporosis and shows a capacity for bone metabolism regulation. Methotrexate (MTX), an essential drug for RA treatment, has been reported to inhibit generalized bone loss in RA patients. However, the combined therapeutic effects and mechanism of EZP and MTX in RA have not been fully elucidated. The aim of this study was to investigate the synergistic effect of EZP and MTX on RA and to explore the underlying mechanism through network pharmacological prediction and experimental verification. Chemical compounds of EZP, human target proteins of EZP and MTX, and RA-related human genes were identified in the Encyclopedia of Traditional Chinese Medicine database, PubChem database, and NCBI database, respectively. The molecular network of EZP and MTX in RA was generated and analyzed with Ingenuity Pathway Analysis software according to the datasets. Then, MTX monotherapy, EZP monotherapy, and combined MTX and EZP therapy were administered to collagen-induced arthritis rats, followed by assessment of pathological score, bone damage, bone alkaline phosphatases (BALP), and tartrate-resistant acid phosphatase (TRACP), and of gene levels related to the Wnt1/LRP5/?-catenin pathway according to network pharmacological analysis. Finally, serum samples from MTX-, EZP- and MTX+EZP-treated rats were used to treat the rat osteoblast (OB)-like UMR-106 cell line to evaluate gene levels related to Wnt1/LRP5/?-catenin. Network pharmacological analysis showed that the Wnt/?-catenin signaling pathway was the top signaling pathway shared among MTX, EZP, and RA. The results from in vivo experiments indicated that EZP combined with MTX reduced arthritis severity, alleviated ankle bone damage, increased BALP and decreased TRACP serum levels, and regulated the mRNA expression of Wnt1, LRP5, ?-catenin, Runx2, BALP, and BGP in the ankles. In vitro experiments showed that EZP combined with MTX could also improve the expression of genes related to the Wnt1/LRP5/?-catenin pathway. This study demonstrated that EZP in combination with MTX played a synergistic role in regulating OBs in RA, which was connected to the modulatory effect of EZP and MTX on the Wnt1/LRP5/?-catenin signaling pathway.

Project description:LRP5 loss-of-function mutations have been shown to cause profound osteoporosis and have been associated with impaired insulin sensitivity and dysregulated lipid metabolism. We hypothesized that gain-of-function mutations in LRP5 would also affect these parameters. We therefore studied individuals with LRP5 gain-of-function mutations exhibiting high bone mass (HBM) phenotypes and found that while there was no detected change in insulin sensitivity, there was a significant reduction in serum LDL.IntroductionWnt signaling through LRP5 represents a newly appreciated metabolic pathway, which potentially represents a target for drug discovery in type 2 diabetes and hyperlipidemia. Studies in animal models suggest a physiologic link between LRP5 and glucose and lipid homeostasis; however, whether it plays a similar role in humans is unclear. As current literature links loss-of-function LRP5 to impaired glucose and lipid metabolism, we hypothesized that individuals with an HBM-causing mutation in LRP5 would exhibit improved glucose and lipid homeostasis. Since studies in animal models have suggested that Wnt signaling augments insulin secretion, we also examined the effect of Wnt signaling on glucose-stimulated insulin secretion on human pancreatic islets.MethodsThis was a matched case-control study. We used several methods to assess glucose and lipid metabolism in 11 individuals with HBM-causing mutations in LRP5. Affected study participants were recruited from previously identified kindreds with HBM-causing LRP5 mutations and included 9 males and 2 females. Two subjects that were being treated with insulin for type 2 diabetes were excluded from our analysis, as this would have obscured our ability to determine the impact of gain-of-function LRP5 mutations on glucose metabolism. The mean age of the evaluated study subjects was 55 ± 7 with a mean BMI of 27.2 ± 2.0. Control subjects were matched and recruited from the general community at an equivalent ratio, with 18 males and 4 females (mean age 56 ± 4; mean BMI 27.2 ± 1.0). Study testing was conducted at an academic medical center.ResultsThere were no statistically significant differences between affected and matched control populations for HbA1c (p = 0.06), eAG (p = 0.06), insulin (p = 0.82), HOMA-B (p = 0.34), or HOMA-IR (p = 0.66). The mean Insulin Sensitivity Index (ISI) was also similar between control and affected individuals. Total cholesterol (p = 0.43), triglycerides (TG) (p = 0.56), and HDL (p = 0.32) were not different between the same two groups. In a small subset of studied subjects, intramyocellular and hepatic lipid content were similar in the affected individuals and controls when quantified by proton magnetic resonance spectroscopy (MRS). However, the mean value for serum LDL was significantly lower (p = 0.04) in affected individuals. In primary human islets, there were no differences between control and Wnt treatment groups for insulin secretion measured as area under the curve (AUC) for first phase (p = 0.17) or second phase (p = 0.33) insulin secretion.ConclusionsAlthough our sample size was small, our data do not support the hypothesis that HBM-causing LRP5 mutations, associated with increased Wnt signaling, improve glucose metabolism in humans. However, it does appear that LRP5 variants may affect LDL metabolism, a major risk factor for coronary artery disease. The molecular mechanisms underpinning this effect warrant further study.

Dataset Information

Normal hematopoiesis and lack of ?-catenin activation in osteoblasts of patients and mice harboring Lrp5 gain-of-function mutations.

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Normal hematopoiesis and lack of β-catenin activation in osteoblasts of patients and mice harboring Lrp5 gain-of-function mutations.

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