The secreted protein augurin is a novel modulator of canonical Wnt signalling involved in osteoblast differentiation

Background ECRG4/C2ORF40 is a tumour suppressor gene downregulated in several cancer types, which encodes the secreted protein augurin. A wide number of functions in health and disease have been assigned to augurin, but the signalling pathways it regulates are still poorly characterized. Augurin expression is strongly upregulated during in vitro differentiation of neonatal mouse osteoblasts. Methods In vitro differentiation assays of calvarial osteoblasts isolated from Ecrg4 -/- and wild-type mice; transient transfection assays using reporters activated by Wnt signalling and other signal transduction pathways; Real-time quantitative polymerase chain reaction for measurement of gene expression; protein expression in Chinese hamster ovary cells and Escherichia coli; in situ binding assays of proteins expressed as fusions to alkaline phosphatase with cells expressing various membrane receptors. Results Osteoblasts from Ecrg4 -/- mice have an accelerated differentiation compared to wild-type and upregulation of Wnt markers. Augurin is a specific repressor of Wnt-stimulated transcriptional activity, both when coexpressed together with the reporter and when added to the culture medium as a soluble protein. We confirmed the previously described binding of augurin to LOX1, a scavenger receptor, but an inhibitor of this molecule did not impair augurin repression of Wnt-stimulated transcription specifically. Genome-wide association studies showed an association of ECRG4 genomic variation with body height and osteoarthritis. Conclusions Our study sheds new light on the wide spectrum of functions previously ascribed to augurin in brain function, stem cell biology, inflammation/immunity and cancer. Furthermore, our discovery paves the way to further characterization of the mechanisms involved in augurin repression of Wnt signalling and the development of agonists and antagonists for this protein, which have a wide array of potential applications in the clinic

Identification of 153 new loci associated with heel bone mineral density and functional involvement of GPC6 in osteoporosis

Osteoporosis is a common disease diagnosed primarily by measurement of bone mineral density (BMD). We undertook a genome-wide association study in 142,487 individuals from the UK Biobank to identify loci associated with BMD estimated by quantitative ultrasound of the heel (“eBMD”). We identified 307 conditionally independent SNPs attaining genome-wide significance at 203 loci, explaining approximately 12% of the phenotypic variance. These included 153 novel loci, and several rare variants with large effect sizes. To investigate underlying mechanisms we undertook: 1) bioinformatic, functional genomic annotation and human osteoblast expression studies; 2) gene function prediction; 3) skeletal phenotyping of 120 knockout mice with deletions of genes adjacent to lead independent SNPs; and 4) analysis of gene expression in mouse osteoblasts, osteocytes and osteoclasts. These studies strongly implicate GPC6 as a novel determinant of BMD and also identify abnormal skeletal phenotypes in knockout mice for a further 100 prioritized genes.This part of the work was supported by Genome Quebec, Genome Canada and the Canadian Institutes of Health Research (CIHR). This work was supported by the Medical Research Council (Programme Grant MC_UU_12013/4 to D.M.E.), the Wellcome Trust (Strategic Award grant number 101123; project grant 094134; to G.R.W., J.H.D.B. and P.I.C.), the Netherlands Organization for Health Research and Development ZonMw VIDI 016.136.367 (funding to F.R., C.M.-G. and K.T.), the mobility stimuli plan of the European Union Erasmus Mundus Action 2: ERAWEB (programme funding to K.T.), NIAMS, NIH (AR060981 and AR060234 to C.L.A.-B.), the National Health and Medical Research Council (Early Career Fellowship APP1104818 to N.M.W.), the Swedish Research Council (funding to E.G.), the Réseau de Médecine Génétique Appliquée (RMGA; J.A.M.), the Fonds de Recherche du Québec–Santé (FRQS; J.A.M. and J.B.R.), the Natural Sciences and Engineering Research Council of Canada (C.M.T.G.), the J. Gibson and the Ernest Heine Family Foundation (P.I.C.), Arthritis Research UK (ref. 20000; to C.L.G.), the Canadian Institutes of Health Research (J.B.R.), the Jewish General Hospital (J.B.R.), and the Australian Research Council (Future Fellowship FT130101709 to D.M.E.). This research was conducted using the UK Biobank Resource (application number 12703). Access to the UK Biobank study data was funded by the University of Queensland (Early Career Researcher Grant 2014002959 to N.M.W.)

Osteocyte transcriptome mapping identifies a molecular landscape controlling skeletal homeostasis and susceptibility to skeletal disease

Osteocytes are master regulators of the skeleton. We mapped the transcriptome of osteocytes from different skeletal sites, across age and sexes in mice to reveal genes and molecular programs that control this complex cellular-network. We define an osteocyte transcriptome signature of 1239 genes that distinguishes osteocytes from other cells. 77% have no previously known role in the skeleton and are enriched for genes regulating neuronal network formation, suggesting this programme is important in osteocyte communication. We evaluated 19 skeletal parameters in 733 knockout mouse lines and reveal 26 osteocyte transcriptome signature genes that control bone structure and function. We showed osteocyte transcriptome signature genes are enriched for human orthologs that cause monogenic skeletal disorders (P = 2.4 × 10−22) and are associated with the polygenic diseases osteoporosis (P = 1.8 × 10−13) and osteoarthritis (P = 1.6 × 10−7). Thus, we reveal the molecular landscape that regulates osteocyte network formation and function and establish the importance of osteocytes in human skeletal disease

Identification of 153 new loci associated with heel bone mineral density and functional involvement of GPC6 in osteoporosis

Osteoporosis is a common disease diagnosed primarily by measurement of bone mineral density (BMD). We undertook a genome-wide association study (GWAS) in 142,487 individuals from the UK Biobank to identify loci associated with BMD as estimated by quantitative ultrasound of the heel. We identified 307 conditionally independent single-nucleotide polymorphisms (SNPs) that attained genome-wide significance at 203 loci, explaining approximately 12% of the phenotypic variance. These included 153 previously unreported loci, and several rare variants with large effect sizes. To investigate the underlying mechanisms, we undertook (1) bioinformatic, functional genomic annotation and human osteoblast expression studies; (2) gene-function prediction; (3) skeletal phenotyping of 120 knockout mice with deletions of genes adjacent to lead independent SNPs; and (4) analysis of gene expression in mouse osteoblasts, osteocytes and osteoclasts. The results implicate GPC6 as a novel determinant of BMD, and also identify abnormal skeletal phenotypes in knockout mice associated with a further 100 prioritized genes