LRP5, SLC6A3, and SOX10 Expression in Conventional Ameloblastoma

Cell proliferation and invasion are characteristic of many tumors, including ameloblastoma, and are important features to target in possible future therapeutic applications.

OBJECTIVE

The objective of this study was the identification of key genes and inhibitory drugs related to the cell proliferation and invasion of ameloblastoma using bioinformatic analysis.

METHODS

The H10KA_07_38 gene profile database was analyzed by Rstudio and ShinyGO Gene Ontology enrichment. String, Cytoscape-MCODE, and Kaplan-Meier plots were generated, which were subsequently validated by RT-qPCR relative expression and immunoexpression analyses. To propose specific inhibitory drugs, a bioinformatic search using Drug Gene Budger and DrugBank was performed.

RESULTS

A total of 204 significantly upregulated genes were identified. Gene ontology enrichment analysis identified four pathways related to cell proliferation and cell invasion. A total of 37 genes were involved in these pathways, and 11 genes showed an MCODE score of ≥0.4; however, only SLC6A3, SOX10, and LRP5 were negatively associated with overall survival (HR = 1.49 (p = 0.0072), HR = 1.55 (p = 0.0018), and HR = 1.38 (p = 0.025), respectively). The RT-qPCR results confirmed the significant differences in expression, with overexpression of >2 for SLC6A3 and SOX10. The immunoexpression analysis indicated positive LRP5 and SLC6A3 expression. The inhibitory drugs bioinformatically obtained for the above three genes were parthenolide and vorinostat.

CONCLUSIONS

We identify LRP5, SLC6A3, and SOX10 as potentially important genes related to cell proliferation and invasion in the pathogenesis of ameloblastomas, along with both parthenolide and vorinostat as inhibitory drugs that could be further investigated for the development of novel therapeutic approaches against ameloblastoma.

LRPs in WNT Signalling

The WNT/β-catenin signalling pathway is a rich and complex network of cellular proteins that orchestrates diverse short-range cell-to-cell communication in metazoans and is essential for both embryonic development and adult homeostasis. Due to its fundamental importance in controlling cell behaviour at multiple levels, its deregulation is associated with a wide range of diseases in humans and identification of drugs targeting the pathway has attracted strong interest in the pharmaceutical sector. Transduction of WNT signals across the plasma membrane of cells involves a staggering degree of complexity and variety with respect to ligand-receptor, receptor-receptor and receptor-co-receptor interactions (Niehrs, Nat Rev Mol Cell Biol 13:767-779, 2012). Although the low-density-lipoprotein-receptor-related-protein (LRP) family is best known for its role in binding and endocytosis of lipoproteins, specific members appear to have additional roles in cellular communication. Indeed, for WNT/β-catenin signalling one apparently universal requirement is the presence of either LRP5 or LRP6 in combination with one of the ten Frizzled (FZD) WNT receptors (FZD_1-10). In the 20 years since their discovery as WNT/FZD co-receptors, research on the LRP family has contributed greatly to our understanding of WNT signalling and LRPs have emerged as central players in WNT/β-catenin signalling. LRP5/6 are highly similar and represent the least redundant class of WNT receptor that transduce WNT/β-catenin signalling from a wide range of different WNT and FZD subtypes. This apparent simplicity however belies the complex arrangement of binding sites in the extracellular domain (ECD) of LRP5/6, which regulate interaction not only with WNTs but also with several inhibitors of WNT signalling. This chapter provides a historical overview, chronologically charting this remarkable progress in the field during the last 20 years of research on LRPs and their role in WNT/-catenin signalling. A more focused overview of the structural, functional and mechanistic aspects of LRP biology is also provided, together with the implications this has for pharmacological targeting of this notoriously intractable pathway.

Light-Controlled BMSC Sheet-Implant Complexes with Improved Osteogenesis via an LRP5/β-Catenin/Runx2 Regulatory Loop

The combination of bone marrow mesenchymal stem cell (BMSC) sheets and titanium implants (BMSC sheet-implant complexes) can accelerate osseointegration. However, methods of fabricating BMSC sheet-implant complexes are quite limited, and the survival of BMSC sheet-implant complexes is one of the key barriers. Here, we show that a light-controlled fabricating system can generate less injured BMSC sheet-implant complexes with improved viability and osteogenesis and that noninvasive monitoring of the viability of BMSC sheet-implant complexes using a lentiviral delivery system is feasible. Enhanced green fluorescent protein- and luciferase-expressing BMSC sheets were used to track the viability of BMSC sheet-implant complexes in vivo. The experiments of micro-computed tomography analysis and hard tissue slices were performed to evaluate the osteogenic ability of BMSC sheet-implant complexes in vivo. The results showed that BMSC sheet-implant complexes survived for almost 1 month after implantation. Notably, BMSC sheet-implant complexes fabricated by the light-controlled fabricating system had upregulating expression levels of low-density lipoprotein-receptor-related protein 5 (LRP5), β-catenin, and runt-related transcription factor 2 (Runx2) compared to the complexes fabricated by mechanical scraping. Furthermore, we found that Runx2 directly bound to the rat LRP5 promoter and the LRP5/β-catenin/Runx2 regulatory loop contributed to the enhancement of the osseointegrating potentials. In this study, we successfully fabricated BMSC sheet-implant complexes with improved viability and osteogenesis and established a feasible, noninvasive, and continuous method for tracking BMSC sheet-implant complexes in vivo. Our findings lay the foundation for the application of BMSC sheet-implant complexes in vivo and open new avenues for engineered BMSC sheet-implant complexes.

[Genetics of osteoporosis]

Osteoporosis is characterized by low bone mineral density (BMD) and microarchitectural deterioration of bone tissue, with a consequent increase in the fragility of bones and susceptibility to fractures. Over the last five years, genome-wide association studies (GWAS) have identified the single-nucleotide polymorphisms(SNPs) associated with osteoporosis, BMD and other determinants of fracture risk. These SNPs were mapped close to or within the genes, such as LRP5, RANKL, SOST and ESR1. In the future, the novel important bone loss susceptibility genes may be uncovered by the GWAS.

Mechanical loading activates β-catenin signaling in periodontal ligament cells

OBJECTIVE

To determine whether β-catenin signaling is responsive to mechanical loading in periodontal ligament (PDL) cells.

MATERIALS AND METHODS

To determine whether Wnt/β-catenin signaling pathway components are present and functional, PDL cells were treated with lithium chloride or Wnt3a-conditioned media. To determine whether mechanical strain activates β-catenin signaling, PDL cells were subjected to compressive loading. Activation of the β-catenin signaling pathway was determined by immunofluorescence, Western immunoblotting, and TOPflash assay.

RESULTS

Mimicking Wnt signaling stimulates β-catenin nuclear translocation and T-cell factor/lymphoid enhancer binding factor-dependent transcriptional activation in PDL cells. Mechanical loading stimulates a transient accumulation of dephosphorylated β-catenin in the cytoplasm and its translocation to the nucleus. This effect of strain acts through activation of protein kinase B and phosphorylation of glycogen synthase kinase-3 beta. These strain-related changes do not involve the low-density lipoprotein receptor-related protein 5/Wnt receptor.

CONCLUSIONS

The Wnt/β-catenin signaling pathway components are functional and activated by mechanical loading in PDL cells. β-catenin serves as an effector of mechanical signals in PDL cells.

Coordinated action of CK1 isoforms in canonical Wnt signaling

Activation of the Wnt pathway promotes the progressive phosphorylation of coreceptor LRP5/6 (low-density lipoprotein receptor-related proteins 5 and 6), creating a phosphorylated motif that inhibits glycogen synthase kinase 3β (GSK-3β), which in turn stabilizes β-catenin, increasing the transcription of β-catenin target genes. Casein kinase 1 (CK1) kinase family members play a complex role in this pathway, either as inhibitors or as activators. In this report, we have dissected the roles of CK1 isoforms in the early steps of Wnt signaling. CK1ε is constitutively bound to LRP5/6 through its interaction with p120-catenin and E-cadherin or N-cadherin and is activated upon Wnt3a stimulation. CK1α also associates with the LRP5/6/p120-catenin complex but, differently from CK1ε, only after Wnt3a addition. Binding of CK1α is dependent on CK1ε and occurs in a complex with axin. The two protein kinases function sequentially: whereas CK1ε is required for early responses to Wnt3a stimulation, such as recruitment of Dishevelled 2 (Dvl-2), CK1α participates in the release of p120-catenin from the complex, which activates p120-catenin for further actions on this pathway. Another CK1, CK1γ, acts at an intermediate level, since it is not necessary for Dvl-2 recruitment but for LRP5/6 phosphorylation at Thr1479 and axin binding. Therefore, our results indicate that CK1 isoforms work coordinately to promote the full response to Wnt stimulus.

[Bone metabolism in dyslipidemia and metabolic syndrome]

Dyslipidemia and osteoporosis are etiologically related to each other. Experiments show that oxidized LDL suppresses the differentiation of bone marrow stromal cells to osteoblasts, while it promotes that to adipocytes, which may result in fatty marrow and bone mass reduction. Inactivation of LRP5÷6 is linked to hypercholesterolemia as well as bone mass reduction, indicating the involvement of Wnt signaling in both disorders. A few clinical studies suggest that high serum triglyceride levels may lower the risk of vertebral fractures. Metabolic syndrome, especially visceral fat accumulation, may have a beneficial effect on bone possibly through mechanical stress from gravity, as long as patients are devoid of advanced type 2 diabetes and are less affected by hyperglycemia or oxidative stress.

[Adipocytes and bone metabolism]

Adipocytes, osteoblasts and chondrocytes derive from common mesenchymal stem cells. A number of factors were reported to regulate differentiation of multiple cell types among adipocytes, osteoblasts and chondrocytes. Thiazolidinediones are prescribed to treat diabetes in obese subjects, but recent clinical data suggested that it increases a risk of bone fracture especially in postmenopausal women. Here, we will review recent advances in the researches of mutual connection between adipocytes and bone metabolism.

Differentiation generates paracrine cell pairs that maintain basaloid mouse mammary tumors: proof of concept

There is a paradox offered up by the cancer stem cell hypothesis. How are the mixed populations that are characteristic of heterogeneous solid tumors maintained at constant proportion, given their high, and different, mitotic indices? In this study, we evaluate a well-characterized mouse model of human basaloid tumors (induced by the oncogene Wnt1), which comprise mixed populations of mammary epithelial cells resembling their normal basal and luminal counterparts. We show that these cell types are substantially inter-dependent, since the MMTV LTR drives expression of Wnt1 ligand in luminal cells, whereas the functional Wnt1-responsive receptor (Lrp5) is expressed by basal cells, and both molecules are necessary for tumor growth. There is a robust tumor initiating activity (tumor stem cell) in the basal cell population, which is associated with the ability to differentiate into luminal and basal cells, to regenerate the oncogenic paracrine signaling cell pair. However, we found an additional tumor stem cell activity in the luminal cell population. Knowing that tumors depend upon Wnt1-Lrp5, we hypothesized that this stem cell must express Lrp5, and found that indeed, all the stem cell activity could be retrieved from the Lrp5-positive cell population. Interestingly, this reflects post-transcriptional acquisition of Lrp5 protein expression in luminal cells. Furthermore, this plasticity of molecular expression is reflected in plasticity of cell fate determination. Thus, in vitro, Wnt1-expressing luminal cells retro-differentiate to basal cell types, and in vivo, tumors initiated with pure luminal cells reconstitute a robust basal cell subpopulation that is indistinguishable from the populations initiated by pure basal cells. We propose this is an important proof of concept, demonstrating that bipotential tumor stem cells are essential in tumors where oncogenic ligand-receptor pairs are separated into different cell types, and suggesting that Wnt-induced molecular and fate plasticity can close paracrine loops that are usually separated into distinct cell types.

The structure of MESD45-184 brings light into the mechanism of LDLR family folding

Mesoderm development (MESD) is a 224 amino acid mouse protein that acts as a molecular chaperone for the low-density lipoprotein receptor (LDLR) family. Here, we provide evidence that the region 45-184 of MESD is essential and sufficient for this function and suggest a model for its mode of action. NMR studies reveal a β-α-β-β-α-β core domain with an α-helical N-terminal extension that interacts with the β sheet in a dynamic manner. As a result, the structural ensemble contains open (active) and closed (inactive) forms, allowing for regulation of chaperone activity through substrate binding. The mutant W61R, which is lethal in Drosophila, adopts only the open state. The receptor motif recognized by MESD was identified by in vitro-binding studies. Furthermore, in vivo functional evidence for the relevance of the identified contact sites in MESD is provided.

[Animal models for bone and joint disease. The genetically-modified mice as a tool for osteoporosis research]

Recent advances of molecular genetics made it possible to generate genetically-modified mice. Furthermore, the discovery and application of Cre-loxP recombination system into mouse genetics led to study the function of a gene in a tissue-specific manner. Analyses of these mutant mice advanced our understanding of the molecular physiology and pathophisiology of skeletal tissue.

Wnt receptors, bone mass, and fractures: gene-wide association analysis of LRP5 and LRP6 polymorphisms with replication

OBJECTIVE

Genes explaining the susceptibility to osteoporosis have not been fully elucidated. Our objective was to explore the association of polymorphisms capturing common variations of the lipoprotein receptor-related protein (LRP) 5 and 6 genes, encoding two Wnt receptors, with femoral neck bone mineral density (BMD) and osteoporotic fractures of the spine and the hip.

DESIGN

Cross-sectional, case-control, and replication genetic association study.

METHODS

Thirty-nine tagging and functional single nucleotide polymorphisms (SNPs) were analyzed in a group of 1043 postmenopausal women and 394 women with hip fractures. The results were replicated in a different group of 342 women.

RESULTS

Three SNPs of the LRP6 gene were associated with BMD (nominal uncorrected P values <0.05) in the discovery cohort. One showed a significant association after multiple test correction; two of them were also associated in the replication cohort, with a combined standardized mean difference of 0.51 (P=0.009) and 0.47 (P<0.003) across rs11054704 and rs2302685 genotypes. In the discovery cohort, several LRP5 SNPs were associated with vertebral fractures (odds ratio (OR) 0.67; P=0.01), with hip fractures (unadjusted ORs between 0.59 and 1.21; P=0.005-0.033, but not significant after multiple test adjustment or age adjustment), and with height and the projected femoral neck area, but not with BMD. Transcripts of LRP5 and LRP6 were similarly abundant in bone samples.

CONCLUSIONS

In this study, we found common polymorphisms of LRP5 associated with osteoporotic fractures, and polymorphisms of the LRP6 gene associated with BMD, thus suggesting them as likely candidates to contribute to the explaination of the hereditary influence on osteoporosis.

Intrinsic material properties of cortical bone

The G171V mutation (high bone mass, HBM) is autosomal dominant and is responsible for high bone mass in humans. Transgenic HBM mice in which the human LRP5 G171V gene is inserted also show a similar phenotype with greater bone mass and biomechanical performance than wild-type mice, as determined by whole bone testing. Whole bone mechanics, however, depend jointly on bone mass, architecture, and intrinsic bone tissue mechanical properties. To determine whether the HBM mutation affects tissue-level biomechanical performance, we performed nano-indentation testing of unembedded cortical bone from HBM mice and their nontransgenic (NTG) littermates. Femora from 17-week-old mice (female, 8 mice/genotype) were subjected to nano-indentation using a Triboscope (Hysitron, Minneapolis, MN, USA). For each femoral specimen, approximately 10 indentations were made on the midshaft anterior surface with a target force of either 3 or 9 mN at a constant loading rate of 400 mN/s. The load-displacement data from each test were used to calculate indentation modulus and hardness for bone tissue. The intrinsic material property that reflected the bone modulus was greater (48%) in the HBM as compared to the NTG mice. Our results of intrinsic properties are consistent with the published structural and material properties of the midshaft femur in HBM and NTG mice. The greater intrinsic modulus in HBM reflects greater bone mineral content as compared to NTG (wild-type, WT) mice. This study suggests that the greater intrinsic property of cortical bone is derived from the greater bone mineral content and BMD, resulting in greater bone strength in HBM as compared to NTG (WT) mice.

[Control of bone remodeling by nervous system. The role of serotonin in the regulation of bone metabolism]

There is increasing evidence for a contribution of serotonin to the regulation of bone metabolism. In the periphery, gut derived serotonin (GDS) regulates osteoblast proliferation and bone formation. In the brain, brain derived serotonin regulates bone mass through sympathetic nervous system. In addition, inhibition of GDS biosynthesis can treat osteoporosis in ovariectomized rodents by increasing bone formation. The emerging evidence has suggested that inhibiting GDS biosynthesis could become a new anabolic treatment for osteoporosis in humans.

[Cytokines in bone diseases. Wnt signal and excessive bone formation]

Wnt signal has been known to play various roles in many organ from the beginning of embryogensis. Its role in bone metabolism has also been investigated and established. Lipoprotein receptor-related protein 5 (LRP5) is one of the important molecules in wnt signal pathway whose point mutations are related to both bone loss and excessive bone formation. Wnt signal is involved in the action of sclerostin which was found as a gene for osteosclerosis, one of the diseases of excessive bone formation. Wnt signal is keeping the position as an important research target for normal and pathological bone formation.

[Cytokines in bone diseases. Wnt signaling and osteoporosis-pseudoglioma syndrome]

Wnt signaling system plays essential roles in development, cancer and bone metabolism. Canonical wnt signaling, which involves wnt ligands, receptor named frizzled and co-receptors LRP5/6, beta-catenin and transcription factors named LEF/TCF is well characterized and its defect causes bone abnormalities. The loss-of-function type of the LRP5 gene mutation is responsible for osteoporosis-pseudoglioma syndrome. In addition, the LRP6 gene mutation leads to osteoporosis and metabolic syndrome. Thus, wnt signaling system is one of determinant factors for bone mineral density.

Update in serotonin and bone

CONTEXT

Serotonin (5-HT) may be an important regulatory agent in bone, and agents that modify 5-HT signaling, such as selective serotonin reuptake inhibitors (SSRIs), are in widespread clinical use.

EVIDENCE ACQUISITION

Evidence was obtained by PubMed search and the author's knowledge of the field.

EVIDENCE SYNTHESIS

Recent data suggest that gut-derived 5-HT may mediate the skeletal effects of LDL receptor-related protein 5, stimulating intense interest in a novel mechanism for regulating bone mass. However, the specific biochemical nature of serotonergic pathways influencing bone and their direct and/or indirect effects on bone metabolism are still unclear. The weight of epidemiological evidence suggests that SSRIs are associated with reduced bone mass, increased bone loss, and increased risk of fractures. Interpretation of these studies is complicated by the confounding effects of depression, the usual indication for treatment with SSRIs. The mechanisms for putative SSRI-induced deleterious effects on the skeleton are unknown, and are likely multifactorial.

CONCLUSIONS

5-HT may have regulatory effects on bone. Initial preclinical data suggest that its effects may be deleterious and may be regulated by low-density lipoprotein receptor-related protein 5. These studies need confirmation, as well as elucidation, of the biochemical pathways utilized and the feedback loops involved among bone, gut, and perhaps brain. Paradoxically, targeting of 5-HT synthesis and/or signaling in selective tissues may hold promise as an anabolic intervention for bone. Epidemiological data suggest that clinicians should be vigilant about detection of bone disease in patients who are using SSRIs.

Effects of glucocorticoid treatment on bone strength

Glucocorticoids (GCs) are prescribed for the treatment of several diseases, but their long-term use causes osteoporosis. Current research suggests that GCs suppress the canonical Wnt/beta pathway, resulting in decreased expression of critical bone proteins. This study examined how bone structure and strength of high bone mass (HBM) mice and low density lipoprotein receptor-related protein 5 (LRP5) knockout (KO+/-) mice are affected by GC treatment in comparison to wild-type (WT) mice, and if changes were specific to either trabecular or cortical bone. Mice were treated with either prednisone or placebo. The femurs and L4 vertebral bodies were analyzed by micro-CT for structure and mechanically tested to determine strength and apparent material strength properties. Differences in all measured variables corresponding to GC treatment and genotype were tested using two-way ANOVA. GC treatment caused decreased structural strength parameters, weakened apparent material strength properties, and disruption of bone structure in HBM, but not LRP5+/- or WT, mice. Despite treatment-related loss, trabecular bone structure and strength remained elevated as compared to LRP5+/- and WT mice. In HBM femurs, both cortical and trabecular structure, but not strength parameters, were negatively affected by treatment. In HBM vertebral bodies, both structural and strength parameters were negatively affected by treatment.

LRP5 gene polymorphism and cortical bone

BACKGROUND AND AIMS

There is evidence that distinct genetic polymorphisms of LRP5 are associated with low Bone Mineral Density (BMD) and the risk of fracture. However, relationships between LRP5 polymorphisms and micro- and macro architectural bone characteristics assessed by pQCT have not been studied. The aim of the present study was to investigate the association of Ala1330Val and Val667Met polymorphisms in LRP5 gene with volumetric BMD (vBMD) and macro-architectural bone parameters in a population-based sample of men and women.

METHODS

We studied 959 participants of the InCHIANTI study (451 men and 508 women, age range: 21-94 yrs). Trabecular vBMD (vBMDt, mg/cm3), cortical vBMD (vBMDc, mg/cm3), cortical bone area (CBA, mm2) and cortical thickness (Ct.Th, mm) at the level of the tibia were assessed by peripheral quantitative computed tomography (pQCT). Ala1330Val and Val667Met genotypes were determined on genomic DNA by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP).

RESULTS

In age-adjusted analyses both LRP 1330-valine and LRP 667-metionin variants were associated with lower vBMDt in men (p<0.05), and lower vBMDt (p<0.05), Ct.Th (p<0.05) and CBA (p<0.05) in women. After adjusting for multiple confounders, only the association of LRP5 1330-valine and 667-metionin with CBA remained statistically significant (p=0.04 and p=0.01, respectively) in women.

CONCLUSION

These findings suggest that both Ala1330Val and Val667Met LRP5 polymorphisms may affect the determination of geometric bone parameters in women.

Genetic analysis of Lrp5 function in osteoblast progenitors

The low-density lipoprotein receptor-related protein (Lrp)-5 regulates osteoblast proliferation and bone formation through its expression in duodenum by modifying the gut serotonin-bone endocrine axis. However, its direct role, if any, in osteoblast progenitor cells has not been studied thus far. Here, we show that mice with a Dermo1-Cre-mediated disruption of Lrp5 in osteoblast progenitor cells have normal embryonic skeletogenesis and normal skeletal growth and development postnatally. Histomorphometric analysis of 3-month-old adult mice revealed normal osteoblast numbers, bone formation rate, and bone mass in Lrp5(Dermo)(-/-) mice. In addition, analysis of two osteoporosis pseudoglioma (OPPG) patients revealed a three- to fivefold increase in their serum serotonin levels compared to age-matched controls. These results rule out a direct function of Lrp5 in osteoblast progenitor cells and add further support to the notion that dysregulation of serotonin synthesis is involved in bone mass abnormalities observed in OPPG patients.

Low density lipoprotein receptor-related protein 5 (LRP5) mutations and osteoporosis, impaired glucose metabolism and hypercholesterolaemia

OBJECTIVE

Mutations in the low-density lipoprotein receptor-related protein 5 gene (LRP5) underlie osteoporosis-pseudoglioma syndrome. Animal models implicate a role for LRP5 in lipid and glucose homeostasis. The objective was to evaluate metabolic consequences of LRP5 mutations in humans.

DESIGN AND PATIENTS

Thirteen Finnish individuals with homozygous or heterozygous LRP5 mutations were assessed for bone health, glucose and lipid metabolism, and for serum serotonin concentration. Results were compared with findings in family members without mutations.

MEASUREMENTS

Bone mineral density (BMD), vertebral morphology, oral and intravenous glucose tolerance tests, lipid profile and serum serotonin concentrations.

RESULTS

Two individuals were homozygous for R570W, one compound heterozygous for R570W and R1036Q, and 10 were heterozygous (six for R570W, three for R1036Q and one for R925C). Subjects with two LRP5 mutations had multiple spinal fractures and low BMD. Subjects with one mutation had significantly lower median lumbar spine (P = 0.004) and femoral neck (P = 0.005) BMD Z-scores, and more often vertebral fractures than the 18 individuals without mutations. Of the 12 subjects with LRP5 mutation six had diabetes and one had impaired glucose tolerance. Intravenous glucose tolerance tests suggested impaired beta-cell function; no insulin resistance was observed. Prevalence of hypercholesterolaemia was similar in mutation positive and negative subjects. Serum serotonin concentrations showed a trend towards higher concentrations in subjects with LRP5 mutation.

CONCLUSIONS

We found high prevalence of osteoporosis and abnormal glucose metabolism in subjects with LRP5 mutation(s). Further studies are needed to establish the role of LRP5 in glucose and lipid metabolism.

Low-density lipoprotein receptor-related protein 5 (LRP5) variation in fracture prone children

OBJECTIVE

Recent studies have confirmed that the low-density lipoprotein receptor-related protein 5 gene (LRP5), plays a role in bone mass accrual and in susceptibility to osteoporotic fractures in adults. This study evaluated whether LRP5 variation is implicated in childhood fractures.

PATIENTS AND METHODS

During an epidemiological study on childhood fractures, comprising 1390 consecutive Finnish children with an acute fracture, we recruited fracture-prone 4-16 years old children, who had a history of at least two low-energy long bone fractures before age 10 years or three low-energy long bone fractures before age 16 years, and/or at least one low-energy vertebral compression fracture. A total of 72 (5.2%) children fulfilled these inclusion criteria; DNA samples were obtained for 66 of them. All 23 exons and exon-intron boundaries of the LRP5 gene were sequenced; the identified variants were analyzed in 235 healthy Finnish control samples.

RESULTS

Sequencing revealed 15 coding region missense or silent variants with unknown functional consequences. No obvious loss-of-function mutations such as deletions, insertions, or changes resulting in premature termination codon or altered splicing were identified. Phenotyping of the proband and parents, and genotyping of the parents, in 9 families with novel or rare variants showed no obvious correlation between any of the LRP5 variants and fractures.

CONCLUSIONS

Our study shows that in children LRP5 mutations are not a common cause of increased fractures. The observed rare LRP5 variants may together with unfavorable environmental and other genetic factors contribute to childhood fractures, but further studies are needed to confirm their functional significance and biological pathways through which this may occur. Our findings suggest that systematic LRP5 screening is not indicated in children with recurrent fractures.

The role of cigarette smoking and statins in the development of postmenopausal osteoporosis: a pilot study utilizing the Marshfield Clinic Personalized Medicine Cohort

SUMMARY

A cohort of postmenopausal osteoporotic females and controls with normal bone mineral density, the interleukin 6 (IL6) -634G > C (rs1800796) C allele of the promoter region showed association with osteoporosis. The lipoprotein receptor-related protein 5 (LRP5) gene showed association between C135242T C/T alleles and osteoporosis only in smokers, suggesting a role for environmental interaction.

INTRODUCTION

A nested case-control study within a population-based cohort was undertaken to assess the relative impact of cigarette smoking, statin use, genetic polymorphisms, and one-way interaction of these factors on development of osteoporosis in postmenopausal women.

METHODS

Genotyping of 14 single-nucleotide polymorphisms (SNPs) corresponding to vitamin D receptor gene, estrogen receptor 1, collagen type 1 alpha 1, IL6, transcription growth factor beta, apolipoprotein E, and LRP5 genes was performed in cases (n = 309) with osteoporosis and controls (n = 293) with normal bone mineral density drawn from a homogeneous Caucasian population. SNPs were chosen based on known functional consequences or prior evidence for association and genotyped using matrix-assisted laser desorption ionization time-of-flight technology.

RESULTS

Cases differed from controls relative to body mass index, age, and smoking but not statin use. After adjusting for age, the IL6 -634G > C (rs1800796) allele showed association with osteoporosis (odds ratio (OR) for CC + CG = 2.51, p = 0.0047)), independent of statin use or smoking status. On stratification for smoking, association with LRP5 C135242T (rs545382) and osteoporosis emerged (OR 2.8 in smokers for CT alleles, p = 0.03)), suggestive of potential environmental interaction.

CONCLUSION

Evidence suggested a role for genetic variation in IL6 and LRP5 in conferring risk for osteoporosis in Caucasian women, with the latter manifest only in smokers.

Relationship between changes of bone mineral density over seven years and A1330V polymorphism of the low-density lipoprotein receptor-related protein 5 gene or lifestyle factors in Japanese female workers

A longitudinal study was conducted to investigate the relation between the changes of bone mineral density (BMD) over a seven-year period and A1330V polymorphism of the low-density lipoprotein receptor-related protein 5 (LRP5) gene or lifestyle factors. The subjects were 113 premenopausal female employees from a large-scale integrated manufacturing facility in Japan aged 25.6 ± 4.2 years (mean ± standard deviation) at baseline. BMD was measured at the radius by dual energy X-ray absorptiometry. Lifestyle information was obtained by a questionnaire. The genotype frequencies of LRP5 gene polymorphism were 52%, 39%, and 9% for AA, AV, and VV, respectively. After seven years, BMD showed a significant decrease (from 0.463 ± 0.045 to 0.456 ± 0.046 g/m²) in subjects with the AV or VV genotypes, but not in subjects with the AA genotype. Analysis of covariance with adjustment for age and body mass index showed that subjects who drank alcohol displayed a significantly greater change of BMD if they had the AV or VV genotype than if they had the AA genotype (F=4.547, p=0.036). Investigation of LRP5 A1330V polymorphism may be useful for identifying individuals who are susceptible to osteoporosis, allowing early preventive measures to be provided.

The emerging role of serotonin (5-hydroxytryptamine) in the skeleton and its mediation of the skeletal effects of low-density lipoprotein receptor-related protein 5 (LRP5)

Novel molecular pathways obligatory for bone health are being rapidly identified. One pathway recently revealed involves gut-derived 5-hydroxytryptamine (5-HT) mediation of the complete skeletal effects of low-density lipoprotein receptor-related protein 5 (LRP5). Mounting evidence supports 5-HT as an important regulatory compound in bone with previous evidence demonstrating that bone cells possess functional pathways for responding to 5-HT. In addition, there is growing evidence that potentiation of 5-HT signaling via inhibition of the 5-HT transporter (5-HTT) has significant skeletal effects. The later is clinically significant as the 5-HTT is a popular target of pharmaceutical agents, such as selective serotonin reuptake inhibitors (SSRIs), used for the management of major depressive disorder and other affective conditions. The observation that 5-HT mediates the complete skeletal effects of LRP5 represents a significant paradigm shift from the traditional view that LRP5 located on the cell surface membrane of osteoblasts exerts direct skeletal effects via Wnt/beta-catenin signaling. This paper discusses the mounting evidence for skeletal effects of 5-HT and the ability of gut-derived 5-HT to satisfactorily explain the skeletal effects of LRP5.

Analysis of association of LRP5, LRP6, SOST, DKK1, and CTNNB1 genes with bone mineral density in a Slovenian population

The Wnt pathway has a bifunctional role in bone mass regulation, influencing osteoblasts and osteoclasts. The Wnt pathway genes are therefore candidate genes for susceptibility to osteoporosis. In our study, we focused on the effects of polymorphisms in selected Wnt pathway genes: low-density lipoprotein receptor-related proteins 5 and 6 (LRP5 and LRP6), Dickkopf1 (DKK1), sclerostin (SOST), and beta-catenin (CTNNB1). We genotyped 652 subjects for the following polymorphisms: A1330V in LRP5; I1062V in LRP6; E232K in DKK1; D32Y, G34V, and N287S in CTNNB1; and -1397_-1396insGGA in SOST. Bone mineral density (BMD) was also measured. The allele frequencies were as follows: for A1330V C:T = 87%:13%, for I1062V C:T = 20%:80%, and for -1397_-1396insGGA-:GGA = 64%:36%. The studied nucleotide changes in the DKK1 and CTNNB1 genes were shown not to be polymorphic. In a Slovenian population, no association was shown between lumbar spine and femoral neck BMD in A1330V (P = 0.151 and 0.243) and in I1062V (P = 0.209 and 0.405). We observed a difference between SOST genotypes, corresponding to an allele dose effect, which was borderline significant for lumbar spine and femoral neck BMD (P = 0.047 and 0.085); but this did not survive the adjustment for multiple testing. These results indicate that a larger sample size would be necessary to detect these subtle effects. Our results suggest that A1330V in LRP5, I1062V in LRP6, and -1397_-1396insGGA in SOST are not associated with BMD in the Slovenian population.

Norrin, frizzled-4, and Lrp5 signaling in endothelial cells controls a genetic program for retinal vascularization

Disorders of vascular structure and function play a central role in a wide variety of CNS diseases. Mutations in the Frizzled-4 (Fz4) receptor, Lrp5 coreceptor, or Norrin ligand cause retinal hypovascularization, but the mechanisms by which Norrin/Fz4/Lrp signaling controls vascular development have not been defined. Using mouse genetic and cell culture models, we show that loss of Fz4 signaling in endothelial cells causes defective vascular growth, which leads to chronic but reversible silencing of retinal neurons. Loss of Fz4 in all endothelial cells disrupts the blood brain barrier in the cerebellum, whereas excessive Fz4 signaling disrupts embryonic angiogenesis. Sox17, a transcription factor that is upregulated by Norrin/Fz4/Lrp signaling, plays a central role in inducing the angiogenic program controlled by Norrin/Fz4/Lrp. These experiments establish a cellular basis for retinal hypovascularization diseases due to insufficient Frizzled signaling, and they suggest a broader role for Frizzled signaling in vascular growth, remodeling, maintenance, and disease.

Body composition and bone mineral density in children with premature adrenarche and the association of LRP5 gene polymorphisms with bone mineral density

CONTEXT

Precocious increase in adrenal androgen production is the hallmark of premature adrenarche (PA). Adrenal androgens have anabolic properties.

OBJECTIVE

The objective of the study was to test whether body composition and bone mineral density (BMD) are altered in PA and study whether genetic variation in low-density lipoprotein receptor-related protein 5 (LRP5) affects BMD in PA.

DESIGN

This was a cross-sectional study.

SETTING

The study was conducted at a university hospital.

SUBJECTS AND MEASURES

The study included 126 prepubertal children (64 with PA, 10 boys; 62 non-PA controls, 10 boys). Femoral neck and lumbar spine areal and calculated volumetric BMD (dual energy X-ray absorptiometry), body composition (bioimpedance), serum 25-hydroxyvitamin D, and markers of bone turnover and calcium homeostasis were compared between the PA and control groups. Single-nucleotide polymorphisms of LRP5 were determined and associated with BMD.

RESULTS

Children with PA had higher femoral neck and lumbar spine BMD(areal) than the controls (Z-score 0.56 vs. -0.09, P < 0.001, and 0.20 vs. -0.31, P = 0.009, respectively). However, the mean BMDs did not differ significantly between the groups when adjusted for height or bone size. BMD(areal) correlated strongly with height sd score in both groups. Among the PA children, LRP5 single-nucleotide polymorphism E644E minor variant was associated with lower and F549F minor variant with higher BMD. Total body fat mass, fat percent, serum PTH, and alkaline phosphatase concentrations were higher and 25-hydroxyvitamin D lower in the PA group.

CONCLUSIONS

Prepubertal children with PA had higher BMD(areal) compared with healthy controls. This was mainly explained by their increased height. LRP5 polymorphisms may contribute to bone mass accrual in prepubertal PA children.

The Wnt receptor, Lrp5, is expressed by mouse mammary stem cells and is required to maintain the basal lineage

BACKGROUND

Ectopic Wnt signaling induces increased stem/progenitor cell activity in the mouse mammary gland, followed by tumor development. The Wnt signaling receptors, Lrp5/6, are uniquely required for canonical Wnt activity. Previous data has shown that the absence of Lrp5 confers resistance to Wnt1-induced tumor development.

METHODOLOGY/PRINCIPAL FINDINGS

Here, we show that all basal mammary cells express Lrp5, and co-express Lrp6 in a similar fashion. Though Wnt dependent transcription of key target genes is relatively unchanged in mammary epithelial cell cultures, the absence of Lrp5 specifically depletes adult regenerative stem cell activity (to less than 1%). Stem cell activity can be enriched by >200 fold (over 80% of activity), based on high Lrp5 expression alone. Though Lrp5 null glands have apparent normal function, the basal lineage is relatively reduced (from 42% basal/total epithelial cells to 22%) and Lrp5-/- mammary epithelial cells show enhanced expression of senescence-associated markers in vitro, as measured by expression of p16(Ink4a) and TA-p63.

CONCLUSIONS/SIGNIFICANCE

This is the first single biomarker that has been demonstrated to be functionally involved in stem cell maintenance. Together, these results demonstrate that Wnt signaling through Lrp5 is an important component of normal mammary stem cell function.

Low‐density lipoprotein receptor‐related protein 5 variant Q89R is associated with hypertension in Japanese females

We examined the influence of the Q89R variant in low-density lipoprotein receptor-related protein 5 on hypertension in a large Japanese cohort. We used multivariate logistic regression analysis to adjust for the effects of other factors known to influence hypertension such as age, body mass index, blood chemistry and lifestyle. Our cohort consisted of 1444 males and 1161 females selected from 3834 male and 2591 female workers in a single company. Hypertension was defined as systolic blood pressure 140 mmHg and/or diastolic blood pressure 90 mmHg or the use of antihypertensive medication. Because the RR genotype was so rare (three normotensive males and three normotensive females), they were excluded from analyses. Genotype distributions for Q89R in hypertensive females (QR = 14, QQ = 60) were significantly different (p = 0.033) from normotensive females (QR = 113, QQ = 971). In contrast, those in hypertensive males (QR = 26, QQ = 230) and in normotensive males (QR = 145, QQ = 1040) were similar. Allele distributions were not significantly different in either gender. In females, multivariate logistic regression showed that the QR genotype was associated with hypertension with odds ratio of 2.1 compared to the QQ genotype. This study indicates that the Q89R polymorphism is an independent factor for hypertension in Japanese females.

The Wnt co-receptor Lrp6 is required for normal mouse mammary gland development

Canonical Wnt signals are transduced through a Frizzled receptor and either the LRP5 or LRP6 co-receptor; such signals play central roles during development and in disease. We have previously shown that Lrp5 is required for ductal stem cell activity and that loss of Lrp5 delays normal mammary development and Wnt1-induced tumorigenesis. Here we show that canonical Wnt signals through the Lrp6 co-receptor are also required for normal mouse mammary gland development. Loss of Lrp6 compromises Wnt/beta-catenin signaling and interferes with mammary placode, fat pad, and branching development during embryogenesis. Heterozygosity for an inactivating mutation in Lrp6 is associated with a reduced number of terminal end buds and branches during postnatal development. While Lrp6 is expressed in both the basal and luminal mammary epithelium during embryogenesis, Lrp6 expression later becomes restricted to cells residing in the basal epithelial layer. Interestingly, these cells also express mammary stem cell markers. In humans, increased Lrp6 expression is associated with basal-like breast cancer. Taken together, our results suggest both overlapping and specific functions for Lrp5 and Lrp6 in the mammary gland.

LRP5 in premature adrenarche and in metabolic characteristics of prepubertal children

OBJECTIVE

Premature adrenarche (PA) is associated with unfavourable metabolic characteristics. We hypothesized that genetic variation in low density lipoprotein (LDL) receptor-related protein 5 (LRP5), which is involved in Wnt signalling in the adrenal cortex and in cholesterol metabolism, plays a role in the pathogenesis of PA.

DESIGN AND PATIENTS

We performed a cross-sectional association study in 73 Finnish children with PA and 97 age- and gender-matched healthy controls.

MEASUREMENTS

LRP5 genotypes were determined by direct sequencing. Single-marker associations with clinical-metabolic characteristics, including adrenocortical function, glucose tolerance and lipid profile, were examined with age and gender as covariates.

RESULTS

Nineteen single nucleotide polymorphisms (SNPs) in LRP5 were found in the 170 children. No significant differences in the genotype distributions were observed between the PA and control groups. SNPs A1330V and N740N were associated with higher serum dehydroepiandrosterone sulphate (DHEAS) levels in the control subjects (A/A vs. A/a; mean 0.8 vs. 1.4 micromol/l, P = 0.01). They were also associated with higher plasma levels of total (4.2 vs. 4.7 mmol/l, P = 0.02) and LDL cholesterol (2.4 vs. 2.9 mmol/l, P = 0.02) in the control group, as was SNP V1119V (P = 0.04 and P = 0.03, respectively). SNPs F549F and V1119V were associated with higher systolic blood pressure (P = 0.04 and P = 0.02, respectively). There were no differences in the parameters of glucose metabolism between the genotype groups.

CONCLUSIONS

Genetic variation in LRP5 did not predispose to PA but was associated with metabolic characteristics, especially lipid profile, in healthy prepubertal children.

No association between hip geometry and four common polymorphisms associated with fracture: the Danish osteoporosis prevention study

Both osteoporosis and hip geometry are independently associated with fracture risk. There is a significant genetic contribution to the risk of osteoporosis, and evidence provided by twin studies has suggested that hip geometry may also in part be genetically programmed. Polymorphisms in a number of genes, including those coding for methylene-tetrahydrofolate reductase (MTHFR c.677C > T), the purinergic P2X(7) receptor (Glu496Ala and Ile568Asn), and the low-density lipoprotein receptor-related protein 5 (LRP5 exon 9 [c.266A > G]), have been associated with an increased fracture incidence and/or reduced bone mineral density (BMD). The aim of the present study was to test whether these polymorphisms influence hip structural geometry in perimenopausal women. The four polymorphisms were genotyped in 800 healthy recently perimenopausal women never using hormone replacement therapy. BMD of the femoral neck was measured using a Hologic QDR-2000 densitometer and femoral neck axis length, neck width, neck shaft angle, and femoral head diameter were measured from the screen images. Genotype frequencies were compatible with Hardy-Weinberg equilibrium. No significant differences between homozygotes for the minor allele and carriers of the common allele regarding parameters of hip geometry were demonstrated. According to the anthropometric characteristics of the subjects, only body height in the MTHFR TT genotype group was significantly different from the combined CT/CC genotype group (P < 0.05). The geometric dimensions of the proximal femur in perimenopausal women are not associated with the MTHFR c.677C > T, P2X(7) (Glu496Ala), P2X(7) (Ile568Asn), and LRP5 exon 9 (c.266A > G) polymorphisms.

LRP5 Polymorphisms and response to risedronate treatment in osteoporotic men

Genetic factors are important in the pathogenesis of osteoporosis, but little is known about the genetic determinants of treatment response. Previous studies have shown that polymorphisms of the LRP5 gene are associated with bone mineral density (BMD), but the relationship between LRP5 polymorphisms and response to bisphosphonate treatment in osteoporosis has not been studied. In this study we investigated LRP5 polymorphisms in relation to treatment response in a group of 249 osteoporotic or osteopenic men who participated in a 24-month randomized double blind placebo-controlled trial of risedronate treatment. BMD and biochemical markers of bone turnover were measured at baseline and after 6, 12, and 24 months of follow-up. We analyzed two coding polymorphisms of LRP5, which have previously been associated with BMD, V667M (rs4988321) and A1330V (rs3736228), and found a significant association between the A1330V polymorphism and hip BMD at baseline. Subjects with the 1330 Val/Val genotype had 8.4% higher total-hip BMD compared with the other genotype groups (P = 0.009), and similar associations were observed at the femoral neck (P = 0.01) and trochanter (P = 0.002). There was no association between A1330V and spine BMD, however, or between the V667M polymorphism and BMD at any site. The difference in hip BMD between A1330V genotype groups remained significant throughout the study, but there was no evidence of a genotype-treatment interaction in either risedronate- or placebo-treated patients. In conclusion, the LRP5 A1330V polymorphism is associated with hip BMD in osteoporotic men, but allelic variations in LRP5 do not appear to be associated with response to bisphosphonate treatment.

Gene expression profiling of peripheral blood in patients with abdominal aortic aneurysm

OBJECT

Abdominal aortic aneurysm (AAA) pathogenesis remains poorly understood. This study investigated the gene expression profile of peripheral blood from patients with AAA using microarray technology.

METHODS AND RESULTS

We determined gene expression profiles in pooled RNA from 10 AAA patients and 10 matched controls with arrays representing 14,000 transcripts. Microarray data for selected genes were confirmed by real-time PCR in two different AAA (n=36) and control (n=36) populations and integrated with biochemical data. We identified 91 genes which were differentially expressed in AAA patients. Gene Ontology analysis indicated a significant alteration of oxygen transport (increased hemoglobin gene expression) and lipid metabolism [including monoglyceride lipase and low density lipoprotein receptor-related protein 5 (LRP5) gene]. LRP5 expression was associated inversely with serum lipoprotein(a) [Lp(a)] concentration.

CONCLUSIONS

Increased expression of hemoglobin chain genes as well as of genes involved in erythrocyte mechanical stability were observed in the AAA RNA pools. The association between low levels of LRP5 gene expression and increased levels of Lp(a) in AAA patients suggests a potential role of LRP5 in Lp(a) catabolism. Our data underline the power of microarrays in identifying further molecular perturbations associated with AAA.

Where Wnts went: the exploding field of Lrp5 and Lrp6 signaling in bone

Wnt signaling has emerged as a central regulator of skeletal modeling and remodeling. Loss- or gain-of-function mutations in two Wnt co-receptors, Lrp5 and (more recently) Lrp6, have drawn attention to the importance of the Wnt pathway in bone biology. This review summarizes our current understanding of how the Wnt pathway operates on bone and the implications this has for skeletal physiology and drug discovery. Over the past 9 yr, rapid advances have been made in our understanding of the cellular targets for Wnt signaling and of the important regulatory molecules in this metabolic pathway. Both canonical and noncanonical signaling pathways seem to be important for mediating the effects of Wnt in bone. A rapidly expanding catalog of genetically engineered mice has been used to establish the importance of downstream effector molecules (such as beta-catenin) in the Wnt pathway, as well as the critical role of endogenous inhibitors of Wnt signaling (such as Dkk1 and sclerostin) in bone metabolism. Indeed, regulation of sclerostin in osteocytes is emerging as an important final pathway for regulating bone anabolism in response to diverse trophic stimuli, from mechnotransduction to the anabolic actions of PTH. From the outset, it had been assumed that the effects of Wnt signaling in bone were caused by direct actions in osteoblast precursors, osteoblasts, and osteocytes. However, startling recent findings have challenged this view and suggest that a key target, at least in mice, is the duodenal enterochromaffin cell. There, Wnt signaling transduced by Lrp5 regulates serotonin synthesis, which acts in an endocrine fashion to regulate bone cell metabolism. It will take time to reconcile this new information with the considerable body of information we already have regarding the actions of Wnt in bone. The Wnt pathway has rapidly emerged as a therapeutic target for drug discovery. Neutralizing antibodies and small-molecule inhibitors of endogenous Wnt inhibitors have shown early promise as bone anabolic agents. However, given the central role of the Wnt pathway in regulating growth and development in extraskeletal tissues, as well as our still rudimentary understanding of how this signaling cascade actually affects bone metabolism, considerable work will be needed to ensure the safety of these new therapies.

The internally truncated LRP5 receptor presents a therapeutic target in breast cancer

Background

Breast cancer is a common malignant disease, which may be caused by a number of genes deregulated by genomic or epigenomic events. Deregulated WNT/β-catenin signaling with accumulation of β-catenin is common in breast tumors, but mutations in WNT signaling pathway components have been rare. An aberrantly spliced internally truncated LRP5 receptor (LRP5Δ666–809, LRP5Δ) was shown recently to be resistant to DKK1 inhibition, and was required for β-catenin accumulation in hyperparathyroid tumors and parathyroid tumor growth.

Methodology/Principal Findings

Here we show, by reverse transcription PCR and Western blot analysis, that LRP5Δ is frequently expressed in breast tumors of different cancer stage (58–100%), including carcinoma in situ and metastatic carcinoma. LRP5Δ was required in MCF7 breast cancer cells for the non-phosphorylated active β-catenin level, transcription activity of β-catenin, cell growth in vitro, and breast tumor growth in a xenograft SCID mouse model. WNT3 ligand, but not WNT1 and WNT3A augmented the endogenous β-catenin activity of MCF7 cells in a DKK1-insensitive manner. Furthermore, an anti-LRP5 antibody attenuated β-catenin activity, inhibited cell growth, and induced apoptosis in LRP5Δ-positive MCF7 and T-47D breast cancer cells, but not in control cells.

Conclusions/Significance

Our results suggest that the LRP5Δ receptor is strongly implicated in mammary gland tumorigenesis and that its aberrant expression present an early event during disease progression. LRP5 antibody therapy may have a significant role in the treatment of breast cancer.

A1330V variant of the low-density lipoprotein receptor-related protein 5 (LRP5) gene decreases Wnt signaling and affects the total body bone mineral density in Japanese women

Wnt signaling is an important regulator of bone homeostasis. The Wnt co-receptor, namely, low-density lipoprotein receptor-related protein 5 (LRP5), initiates Wnt signal transduction. Recently, we and several other groups have shown that there is a single nucleotide polymorphism (SNP) located in the exon 18 of the LRP5 gene that leads to an amino acid change (3989C > T, A1330V), and is associated with lumbar spine, femoral neck, and radial bone mineral density (BMD), and incidence of fracture. These data suggest that the A1330V variation in the LRP5 gene may affect the pathogenesis of osteoporosis. However, the functional basis of the A1330V variation remains unclear. In the present study, we analyzed the effect of the A1330V variation on Wnt activity. We also investigated the association between this LRP5 SNP and total body BMD using 739 postmenopausal women. LRP5 with the A1330V SNP were transiently coexpressed with Wnt3a in 293T cells and their activity was evaluated by the TCF-Lef reporter assay. In vitro, the TCF-Lef activity in presence of Wnt3a in cells expressing LRP5 and carrying the T allele (Valine at 1330 (V1330)) of exon 18 was significantly reduced as compared to the wild-type allele. The association between the A1330V SNP and total body BMD were replicated in 739 postmenopausal Japanese women (AA vs. VV; P = 0.0026). These data suggest that the V1330 variant in the LRP5 gene decreases Wnt activity, which in turn decreases the BMD.

Lrp5 controls bone formation by inhibiting serotonin synthesis in the duodenum

Loss- and gain-of-function mutations in the broadly expressed gene Lrp5 affect bone formation, causing osteoporosis and high bone mass, respectively. Although Lrp5 is viewed as a Wnt coreceptor, osteoblast-specific disruption of beta-Catenin does not affect bone formation. Instead, we show here that Lrp5 inhibits expression of Tph1, the rate-limiting biosynthetic enzyme for serotonin in enterochromaffin cells of the duodenum. Accordingly, decreasing serotonin blood levels normalizes bone formation and bone mass in Lrp5-deficient mice, and gut- but not osteoblast-specific Lrp5 inactivation decreases bone formation in a beta-Catenin-independent manner. Moreover, gut-specific activation of Lrp5, or inactivation of Tph1, increases bone mass and prevents ovariectomy-induced bone loss. Serotonin acts on osteoblasts through the Htr1b receptor and CREB to inhibit their proliferation. By identifying duodenum-derived serotonin as a hormone inhibiting bone formation in an Lrp5-dependent manner, this study broadens our understanding of bone remodeling and suggests potential therapies to increase bone mass.

Replication of associations between LRP5 and ESRRA variants and bone density in premenopausal women

Replication is a critical step to validate positive genetic associations. In this study, we tested two previously reported positive associations. The low density lipoprotein receptor-related protein 5 (LRP5) Val667Met and lumbar spine bone density are replicated. This result is in line with results from large consortiums such as Genomos. However, the estrogen-related receptor alpha (ESRRA) repeat in the promoter is not replicated although the polymorphism studied was functional and could have been a causative variant.

INTRODUCTION

We sought to validate associations previously reported between LRP5 V667M polymorphism and lumbar spine (LS, p = 0.013) and femoral neck (FN, p = 0.0002) bone mineral density (BMD), and between ESRRA 23 base pair repeat polymorphism and LS BMD (p = 0.0036) in a sample of premenopausal Caucasian women using an independent sample.

METHODS

For the replication sample, we recruited 673 premenopausal women from the Toronto metropolitan area. All women were Caucasian and had BMD measured. LRP5 V667M was genotyped by allele-specific PCR and ESRRA repeats by sizing of PCR products on agarose gels.

RESULTS

We reproduced the same association as we reported previously between LRP5 V667M and LS BMD (p = 0.015) but not with FN BMD (p = 0.254). The combined data from the two populations indicate an effect size of 0.28SD for LS BMD (p = 0.00048) and an effect size of 0.26 SD for FN BMD (p = 0.00037). In contrast, the association we reported earlier between ESRRA repeats and LS BMD was not replicated in the sample from Toronto (p = 0.645).

CONCLUSIONS

The association between LRP5 V667M and LS BMD is confirmed but not that between ESRRA repeats and LS BMD. This result indicates that it is imperative to validate any positive association in an independent sample.

Lack of association of LRP5 and LRP6 polymorphisms with type 2 diabetes mellitus in the Japanese population

AIMS

A missense mutation in the low density lipoprotein receptor-related protein 6 gene (LRP6) was recently shown to be responsible for a disorder characterized by early-onset coronary artery disease as well as diabetes mellitus (DM), hyperlipidemia, hypertension, and osteoporosis. Mice deficient in LRP5, a closely related paralog of LRP6, manifest a marked impairment in glucose tolerance. The aim of the present study was to examine whether common variants of LRP5 and LRP6 are associated with Type 2 DM or dyslipidemia in Japanese individuals.

METHODS

Thirteen single nucleotide polymorphisms (SNPs) of LRP6 and nine SNPs of LRP5 were genotyped in a total of 608 Type 2 DM patients and 366 nondiabetic control subjects (initial study). An association analysis was then performed for each SNP and for haplotypes. For some of the SNPs, we provided another sample panel of 576 cases and 576 controls for the replication study. The relation to clinical characteristics was also examined in diabetic subjects.

RESULTS

In the initial study, three SNPs of LRP6 were found to be associated with susceptibility to Type 2 DM. However, this association was not detected in the replication panel. None of SNPs in LRP5 were associated with Type 2 DM in the initial panel. Neither LRP6 nor LRP5 was associated with body mass index, HOMA-beta, HOMA-IR or serum lipid concentrations.

CONCLUSIONS

We found no evidence for a substantial effect of LRP5 or LRP6 SNPs on susceptibility to type 2 diabetes or clinical characteristics of diabetic subjects in Japanese population.

The binding between sclerostin and LRP5 is altered by DKK1 and by high-bone mass LRP5 mutations

Low-density lipoprotein receptor-related protein 5 (LRP5), a Wnt coreceptor, plays an important role in bone metabolism as loss-of-function and gain-of-function mutations in LRP5 result in the autosomal recessive osteoporosis-pseudoglioma syndrome and autosomal dominant high-bone mass (HBM) phenotypes, respectively. Prior studies suggested that the presence of HBM-associated LRP5 mutations results in decreased antagonism of LRP5-mediated Wnt signaling. In the present study, we investigated six different HBM-LRP5 mutations and confirm that neither Dickkopf1 (DKK1) nor sclerostin efficiently inhibits HBM-LRP5 signaling. In addition, when coexpressed, DKK1 and sclerostin do not inhibit HBM-LRP5 mutants better than either inhibitor by itself. Also, DKK1 and sclerostin do not simultaneously bind to wild-type LRP5, and DKK1 is able to displace sclerostin from previously formed sclerostin-LRP5 complexes. In conclusion, our results indicate that DKK1 and sclerostin are independent, and not synergistic, regulators of LRP5 signaling and that the function of each is impaired by HBM-LRP5 mutations.

Large-scale association study between two coding LRP5 gene polymorphisms and bone phenotypes and fractures in men

Herein we investigated the association between polymorphisms in the LRP5 gene and bone phenotypes and fractures in three large male cohorts based on the rationale that mutations in LRP5 cause severe bone phenotypes. Results showed an association of the Val667Met SNP with spine BMD in 3,800 young and elderly men.

INTRODUCTION

The low-density lipoprotein receptor-related protein 5 (LRP5)-Wnt signalling system is of importance for regulating osteoblastic activity, which became clear after findings that inactivating mutations in LRP5 cause osteoporosis. The overall aim of this study was to investigate the association between polymorphisms in the LRP5 gene and bone mineral density (BMD) in three large cohorts of young and elderly men.

METHODS

The cohorts used were MrOS Sweden (n = 3014, aged 69-81 years) and MrOs Hong Kong (n = 2000, aged > 65 years) and the Swedish GOOD study (n = 1068, aged 18-20 years). The polymorphisms Val667Met and Ala1330Val were genotyped using a TaqMan assay.

RESULTS

When combining the data from the Swedish cohorts in a meta-analysis (n = 3,800), men carrying the 667Met-allele had 3% lower BMD at lumbar spine compared with non-carriers (p < 0.05). The Val667Met SNP was not polymorphic in the Hong Kong population and thus were not included. There were no associations between the Ala1330Val SNP and bone phenotypes in the study populations. No associations between the LRP5 polymorphisms and self-reported fractures were seen in MrOs Sweden.

CONCLUSIONS

Results from these three large cohorts indicate that the Val667Met polymorphism but not the Ala1330Val contributes to the observed variability in BMD in the Swedish populations.