Wntless spatially regulates bone development through β-catenin-dependent and independent mechanisms

Inhibiting WNT secretion reduces high bone mass caused by Sost loss-of-function or gain-of-function mutations in Lrp5

Proper regulation of Wnt signaling is critical for normal bone development and homeostasis. Mutations in several Wnt signaling components, which increase the activity of the pathway in the skeleton, cause high bone mass in human subjects and mouse models. Increased bone mass is often accompanied by severe headaches from increased intracranial pressure, which can lead to fatality and loss of vision or hearing due to the entrapment of cranial nerves. In addition, progressive forehead bossing and mandibular overgrowth occur in almost all subjects. Treatments that would provide symptomatic relief in these subjects are limited. Porcupine-mediated palmitoylation is necessary for Wnt secretion and binding to the frizzled receptor. Chemical inhibition of porcupine is a highly selective method of Wnt signaling inhibition. We treated three different mouse models of high bone mass caused by aberrant Wnt signaling, including homozygosity for loss-of-function in Sost, which models sclerosteosis, and two strains of mice carrying different point mutations in Lrp5 (equivalent to human G171V and A214V), at 3 months of age with porcupine inhibitors for 5-6 weeks. Treatment significantly reduced both trabecular and cortical bone mass in all three models. This demonstrates that porcupine inhibition is potentially therapeutic for symptomatic relief in subjects who suffer from these disorders and further establishes that the continued production of Wnts is necessary for sustaining high bone mass in these models.

Integrated Analysis of Transcriptome Expression Profiles Reveals miRNA-326-NKX3.2-Regulated Porcine Chondrocyte Differentiation

The porcine body length trait is an essential factor affecting meat production and reproductive performance. It is evident that the development/lengthening of individual vertebrae is one of the main reasons for increases in body length; however, the underlying molecular mechanism remains unclear. In this study, RNA-seq analysis was used to profile the transcriptome (lncRNA, mRNA, and miRNA) of the thoracic intervertebral cartilage (TIC) at two time points (1 and 4 months) during vertebral column development in Yorkshire (Y) and Wuzhishan pigs (W). There were four groups: 1- (Y1) and 4-month-old (Y4) Yorkshire pigs and 1- (W1) and 4-month-old (W4) Wuzhishan pigs. In total, 161, 275, 86, and 126 differentially expressed (DE) lncRNAs, 1478, 2643, 404, and 750 DE genes (DEGs), and 74,51, 34, and 23 DE miRNAs (DE miRNAs) were identified in the Y4 vs. Y1, W4 vs. W1, Y4 vs. W4, and Y1 vs. W1 comparisons, respectively. Functional analysis of these DE transcripts (DETs) demonstrated that they had participated in various biological processes, such as cellular component organization or biogenesis, the developmental process, the metabolic process, bone development, and cartilage development. The crucial bone development-related candidate genes NK3 Homeobox 2 (NKX3.2), Wnt ligand secretion mediator (WLS), gremlin 1 (GREM1), fibroblast growth factor receptor 3 (FGFR3), hematopoietically expressed homeobox (HHEX), (collagen type XI alpha 1 chain (COL11A1), and Wnt Family Member 16 (WNT16)) were further identified by functional analysis. Moreover, lncRNA, miRNA, and gene interaction networks were constructed; a total of 55 lncRNAs, 6 miRNAs, and 7 genes formed lncRNA-gene, miRNA-gene, and lncRNA-miRNA-gene pairs, respectively. The aim was to demonstrate that coding and non-coding genes may co-regulate porcine spine development through interaction networks. NKX3.2 was identified as being specifically expressed in cartilage tissues, and it delayed chondrocyte differentiation. miRNA-326 regulated chondrocyte differentiation by targeting NKX3.2. The present study provides the first non-coding RNA and gene expression profiles in the porcine TIC, constructs the lncRNA-miRNA-gene interaction networks, and confirms the function of NKX3.2 in vertebral column development. These findings contribute to the understanding of the potential molecular mechanisms regulating pig vertebral column development. They expand our knowledge about the differences in body length between different pig species and provide a foundation for future studies.

The role of Evi/Wntless in exporting Wnt proteins

Intercellular communication by Wnt proteins governs many essential processes during development, tissue homeostasis and disease in all metazoans. Many context-dependent effects are initiated in the Wnt-producing cells and depend on the export of lipidated Wnt proteins. Although much focus has been on understanding intracellular Wnt signal transduction, the cellular machinery responsible for Wnt secretion became better understood only recently. After lipid modification by the acyl-transferase Porcupine, Wnt proteins bind their dedicated cargo protein Evi/Wntless for transport and secretion. Evi/Wntless and Porcupine are conserved transmembrane proteins, and their 3D structures were recently determined. In this Review, we summarise studies and structural data highlighting how Wnts are transported from the ER to the plasma membrane, and the role of SNX3-retromer during the recycling of its cargo receptor Evi/Wntless. We also describe the regulation of Wnt export through a post-translational mechanism and review the importance of Wnt secretion for organ development and cancer, and as a future biomarker.

Single-cell transcriptomic signatures and gene regulatory networks modulated by Wls in mammalian midline facial formation and clefts

Formation of highly unique and complex facial structures is controlled by genetic programs that are responsible for the precise coordination of three-dimensional tissue morphogenesis. However, the underlying mechanisms governing these processes remain poorly understood. We combined mouse genetic and genomic approaches to define the mechanisms underlying normal and defective midfacial morphogenesis. Conditional inactivation of the Wnt secretion protein Wls in Pax3-expressing lineage cells disrupted frontonasal primordial patterning, cell survival and directional outgrowth, resulting in altered facial structures, including midfacial hypoplasia and midline facial clefts. Single-cell RNA sequencing revealed unique transcriptomic atlases of mesenchymal subpopulations in the midfacial primordia, which are disrupted in the conditional Wls mutants. Differentially expressed genes and cis-regulatory sequence analyses uncovered that Wls modulates and integrates a core gene regulatory network, consisting of key midfacial regulatory transcription factors (including Msx1, Pax3 and Pax7) and their downstream targets (including Wnt, Shh, Tgfβ and retinoic acid signaling components), in a mesenchymal subpopulation of the medial nasal prominences that is responsible for midline facial formation and fusion. These results reveal fundamental mechanisms underlying mammalian midfacial morphogenesis and related defects at single-cell resolution.

Crosstalk between the gut microbiota and postmenopausal osteoporosis: Mechanisms and applications

Postmenopausal osteoporosis (PMO) results from a reduction in bone mass and microarchitectural deterioration in bone tissue due to estrogen deficiency, which may increase the incidence of fragility fractures. The number of people suffering from PMO has increased over the years because of the rapidly aging population worldwide. However, several pharmacological agents for the treatment of PMO have many safety risks and impose a heavy financial burden to patients and society. In recent years, the "gut-bone" axis has been proposed as a new approach in the prevention and treatment of PMO. This paper reviews the relationship between the gut microbiota and PMO, which mainly includes the underlying mechanisms between hormones, immunity, nutrient metabolism, metabolites of the gut microbiota and intestinal permeability, and explores the possible role of the gut microbiota in these processes. Finally, we discuss the therapeutic effects of diet, prebiotics, probiotics, and fecal microbiota transplantation on the gut microbiota.

Parkinson's in the bone

Patients with Parkinson’s disease (PD) exhibit systemic deficits, including arthritis and osteoporosis-like symptoms. However, the questions, how the deficits in periphery organs or tissues occur in PD patients, and what are the relationship (s) of the periphery tissue deficits with the brain pathology (e.g., dopamine neuron loss), are at the beginning stage to be investigated. Notice that both PD and osteoporosis are the products of a complex interaction of genetic and environmental risk factors. Genetic mutations in numerous genes have been identified in patients either with recessive or autosomal dominant PD. Most of these PD risk genes are ubiquitously expressed; and many of them are involved in regulation of bone metabolism. Here, we review the functions of the PD risk genes in regulating bone remodeling and homeostasis. The knowledge gaps in our understanding of the bone-to-brain axis in PD development are also outlined.

Evidence of nigericin as a potential therapeutic candidate for cancers: A review

Emerging studies have shown that nigericin, an H⁺, K⁺ and Pb²⁺ ionophore, has exhibited a promising anti-cancer activity in various cancers. However, its anti-cancer mechanisms have not been fully elucidated. In this review, the recent progresses on the use of nigericin in human cancers have been summarized. By exchanging H⁺ and K⁺ across cell membranes, nigericin shows promising anti-cancer activities in in vitro and in vivo as a single agent or in combination with other anti-cancer drugs through decreasing intracellular pH (pHi). The underlying mechanisms of nigericin also include the inactivation of Wnt/β-catenin signals, blockade of Androgen Receptor (AR) signaling, and activation of Stress-Activated Protein Kinase/c-Jun N-terminal Kinase (SAPK/JNK) signaling pathways. In many cancers, nigericin is proved to specifically target putative Cancer Stem Cells (CSCs), and its synergistic effects on photodynamic therapy are also reported. Other mechanisms of nigericin including influencing the mitochondrial membrane potentials, inducing an increase in drug accumulation and autophagy, controlling insulin accumulation in nuclei, and increasing the cytotoxic activity of liposome-entrapped drugs, are also discussed. Notably, the potential adverse effects such as teratogenic effects, insulin resistance and eryptosis shall not be ignored. Taken together, these reports suggest that treatment of cancer cells with nigericin may offer a novel therapeutic strategy and future potential of translation to clinics.

YJ5 as an immunohistochemical marker of osteogenic lineage

Overexpression of WLS, an upstream protein in the Wnt pathway, has been implicated in several non-osteogenic tumours. This study represents the first attempt at evaluating WLS expression in various bone and soft tissue tumours using YJ5, a monoclonal antibody specific to WLS, with the aim of elucidating its utility in discerning tumours with aberrant Wnt signalling and as a marker of osteogenic lineage in challenging cases. Tumour tissue sections of 144 bone mass lesions and 63 soft tissue mass lesions were immunostained with the YJ5 antibody following standardised protocols. Subsequent assessment of immunoreactivity segregated cases into one of three groups: absent/weak, moderate, or strong YJ5 immunoreactivity. For the bone tumours, strong YJ5 immunoreactivity was seen in almost all osteosarcomas and chondroblastomas, all osteoblastomas and osteoid osteomas. In contrast, all other cartilaginous tumours, chordomas, aneurysmal bone cysts, chondromyxoid fibromas, most fibrous dysplasias and most giant cell tumours exhibited absent/weak YJ5 immunostaining. For the soft tissue tumours, a more heterogeneous pattern of YJ5 immunoreactivity was observed. Because diffuse and strong YJ5 expression is identified in almost all benign and malignant bone tumours with osteoblastic activity, it can be potentially utilised as an immunohistochemical marker to support osteogenic lineage. If interpreted in the appropriate context, this marker is useful in determining whether a malignant bone tumour is an osteosarcoma, particularly in those subtypes with no or minimal osteoid or unusual morphological features. This marker can also complement SATB2 to denote osteogenic lineage.

Osteoblastic Wntless deletion differentially regulates the fate and functions of bone marrow-derived stem cells in relation to age

Although functional association between Wnt signaling and bone homeostasis has been well described through genetic ablation of Wntless (Wls), the mechanisms of how osteoblastic Wls regulates the fate of bone marrow stromal cells (BMSCs) and hematopoietic stem cells (HSCs) in relation to age are not yet understood. Here, we generated Col2.3-Cre;Wls^fl/fl mice that were free from premature lethality and investigated age-related impacts of osteoblastic Wls deficiency on hematopoiesis, BM microenvironment, and maintenance of BMSCs (also known as BM-derived mesenchymal stem/stromal cells) and HSCs. Ablation of osteoblastic Wls deteriorated BM microenvironment and bone mass accrual along with age-independent effects on functions of BMSCs. Osteoblastic Wls deletion impaired HSC repopulation and progeny with skewing toward myeloid lineage cells only at old stage. As proven by hallmarks of stem cell senescence, osteoblastic Wls ablation differentially induced senescence of BMSCs and HSCs in relation to age without alteration in their BM frequency. Our findings support that deletion of Wls in Col2.3-expressing cells induces senescence of BMSCs and impairs BM microenvironment in age-independent manner. Overall, long-term deterioration in BM microenvironment contributes to age-related HSC senescence with impaired progeny and hematopoiesis, which also suggests possible roles of osteoblastic Wls on the maintenance of BM HSCs.

Identifying Pleiotropic SNPs Associated With Femoral Neck and Heel Bone Mineral Density

Background

Genome-wide association studies (GWASs) routinely identify loci associated with risk factors for osteoporosis. However, GWASs with relatively small sample sizes still lack sufficient power to ascertain the majority of genetic variants with small to modest effect size, which may together truly influence the phenotype. The loci identified only account for a small percentage of the heritability of osteoporosis. This study aims to identify novel genetic loci associated with DXA-derived femoral neck (FNK) bone mineral density (BMD) and quantitative ultrasound of the heel calcaneus estimated BMD (eBMD), and to detect shared/causal variants for the two traits, to assess whether the SNPs or putative causal SNPs associated with eBMD were also associated with FNK-BMD.

Methods

Novel loci associated with eBMD and FNK-BMD were identified by the genetic pleiotropic conditional false discovery rate (cFDR) method. Shared putative causal variants between eBMD and FNK-BMD and putative causal SNPs for each trait were identified by the colocalization method. Mendelian randomization analysis addresses the causal relationship between eBMD/FNK-BMD and fracture.

Results

We identified 9,500 (cFDR < 9.8E-6), 137 (cFDR < 8.9E-4) and 124 SNPs associated with eBMD, FNK-BMD, and both eBMD and FNK-BMD, respectively, with 37 genomic regions where there was a SNP that influences both eBMD and FNK-BMD. Most genomic regions only contained putative causal SNPs associated with eBMD and 3 regions contained two distinct putative causal SNPs influenced both traits, respectively. We demonstrated a causal effect of FNK-BMD/eBMD on fracture.

Conclusion

Most of SNPs or putative causal SNPs associated with FNK-BMD were also associated with eBMD. However, most of SNPs or putative causal SNPs associated with eBMD were not associated with FNK-BMD. The novel variants we identified may help to account for the additional proportion of variance of each trait and advance our understanding of the genetic mechanisms underlying osteoporotic fracture.

The Function of Wnt Ligands on Osteocyte and Bone Remodeling

Bone homeostasis is continually maintained by the process of bone remodeling throughout life. Recent studies have demonstrated that Wnt signaling pathways play a fundamental role in the process of bone homeostasis and remodeling. Intracellular Wnt signaling cascades are initially triggered by a Wnt ligand-receptor complex formation. In previous studies, the blocking of Wnt ligands from different osteoblastic differentiation stages could cause defective bone development at an early stage. Osteocytes, the most abundant and long-lived type of bone cell, are a crucial orchestrator of bone remodeling. However, the role of Wnt ligands on osteocyte and bone remodeling remains unclear. In our present study, we found that, besides osteoblasts, osteocytes also express multiple Wnt ligands in the bone environment. Then, we used a Dmp1-Cre mouse line, in which there is expression in a subset of osteoblasts but mainly osteocytes, to study the function of Wnt ligands on osteocyte and bone remodeling in vivo. Furthermore, we explored the role of Wnt ligands on osteocytic mineralization ability, as well as the regulatory function of osteocytes on the process of osteoblastic differentiation and osteoclastic migration and maturity in vitro. We concluded that Wnt proteins play an important regulatory role in 1) the process of perilacunar/canalicular remodeling, as mediated by osteocytes, and 2) the balance of osteogenesis and bone resorption at the bone surface, as mediated by osteoblasts and osteoclasts, at least partly through the canonical Wnt/β-catenin signaling pathway and the OPG/RANKL signaling pathway.

The role of GPCRs in bone diseases and dysfunctions

The superfamily of G protein-coupled receptors (GPCRs) contains immense structural and functional diversity and mediates a myriad of biological processes upon activation by various extracellular signals. Critical roles of GPCRs have been established in bone development, remodeling, and disease. Multiple human GPCR mutations impair bone development or metabolism, resulting in osteopathologies. Here we summarize the disease phenotypes and dysfunctions caused by GPCR gene mutations in humans as well as by deletion in animals. To date, 92 receptors (5 glutamate family, 67 rhodopsin family, 5 adhesion, 4 frizzled/taste2 family, 5 secretin family, and 6 other 7TM receptors) have been associated with bone diseases and dysfunctions (36 in humans and 72 in animals). By analyzing data from these 92 GPCRs, we found that mutation or deletion of different individual GPCRs could induce similar bone diseases or dysfunctions, and the same individual GPCR mutation or deletion could induce different bone diseases or dysfunctions in different populations or animal models. Data from human diseases or dysfunctions identified 19 genes whose mutation was associated with human BMD: 9 genes each for human height and osteoporosis; 4 genes each for human osteoarthritis (OA) and fracture risk; and 2 genes each for adolescent idiopathic scoliosis (AIS), periodontitis, osteosarcoma growth, and tooth development. Reports from gene knockout animals found 40 GPCRs whose deficiency reduced bone mass, while deficiency of 22 GPCRs increased bone mass and BMD; deficiency of 8 GPCRs reduced body length, while 5 mice had reduced femur size upon GPCR deletion. Furthermore, deficiency in 6 GPCRs induced osteoporosis; 4 induced osteoarthritis; 3 delayed fracture healing; 3 reduced arthritis severity; and reduced bone strength, increased bone strength, and increased cortical thickness were each observed in 2 GPCR-deficiency models. The ever-expanding number of GPCR mutation-associated diseases warrants accelerated molecular analysis, population studies, and investigation of phenotype correlation with SNPs to elucidate GPCR function in human diseases.

Strontium inhibits osteoclastogenesis by enhancing LRP6 and β-catenin-mediated OPG targeted by miR-181d-5p

Strontium is a drug with the bone formation and anti-resorption effects on bone. The underlying mechanisms for the dual effect of strontium on bone metabolism, especially for the anti-resorption effects remain unknown. Thus, we aim to investigate the mechanisms of effects of strontium on osteoclastogenesis. Firstly, we found that strontium decreased the levels of important biomarkers of receptor activator of nuclear factor kappa-B ligand (RANKL) which induced osteoclast differentiation, indicating that strontium might directly inhibit osteoclast differentiation. Next, we revealed that strontium enhanced Low Density Lipoprotein Receptor-Related Protein 6 (LRP6)/β-catenin/osteoprotegerin (OPG) signaling pathway in MC3T3-E1 cells. The signaling pathway may negatively regulate osteoclastogenesis. Thus, strontium indirectly inhibited RANKL induced osteoclast differentiation. Finally, we revealed that OPG was targeted by miR-181d-5p as determined by luciferase reporter assay and downregulated by miR-181d-5p at both mRNA and protein levels as determined by western blot.

Nigericin Exerts Anticancer Effects on Human Colorectal Cancer Cells by Inhibiting Wnt/β-catenin Signaling Pathway

Nigericin, an antibiotic derived from Streptomyces hygroscopicus, which works by acting as an H⁺, K⁺, and Pb²⁺ ionophore, has exhibited promising anticancer activity. The main purpose of this study is to investigate its inhibitory effects on Wnt/β-catenin signaling pathway in colorectal cancer cells and clarify the underlying mechanism. We exposed two colorectal cancer lines (SW620 and KM12) to increasing concentrations of nigericin for different time periods and the 50% inhibiting concentration (IC₅₀) values were evaluated. Our data showed that nigericin treatment significantly reduced tumor cell proliferation in dose- and time-dependent manners in colorectal cancer cells. The subsequent experiments in vitro and in vivo implied that nigericin could significantly suppress the tumor growth, migration, and invasion, and induce the apoptosis of colorectal cancer cells. Our results of Western blot and immunofluorescence assay showed that nigericin could suppress the Wnt/β-catenin signaling pathway in colorectal cancer cells with dose-dependent increased expressions of downstream effectors and target proteins. To further elucidate the inhibitory effects of nigericin via a β-catenin-dependent signaling mechanism, we established the stably β-catenin overexpression colorectal cancer cells. Western blot, SuperTOPFlash luciferase reporter, and immunoprecipitation assays all confirmed β-catenin as a critical intermediary and player in Wnt/β-catenin pathway, and nigericin exerted anticancer effects on colorectal cancer cells by directly targeting the β-catenin destruction complex. These results suggested that Wnt/β-catenin signaling might have an essential role in colorectal cancer progression. Nigericin targeting Wnt/β-catenin signaling might provide new insight into the molecular mechanism of nigericin toward cancer cells, and suggest possible clinical application in colorectal cancer. Mol Cancer Ther; 17(5); 952-65. ©2018 AACR.

Sex-Dependent, Osteoblast Stage-Specific Effects of Progesterone Receptor on Bone Acquisition

The role of the progesterone receptor (PR) in the regulation of sexual dimorphism in bone has yet to be determined. Here we utilized genetic fate mapping and Western blotting to demonstrate age-dependent PR expression in the mouse femoral metaphysis and diaphysis. To define sex-dependent and osteoblast stage-specific effects of PR on bone acquisition, we selectively deleted PR at different stages of osteoblast differentiation. We found that when Prx1-Cre mice were crossed with PR floxed mice to generate a mesenchymal stem cell (MSC) conditional KO model (Prx1; PRcKO), the mutant mice developed greater trabecular bone volume with higher mineral apposition rate and bone formation. This may be explained by increased number of MSCs and greater osteogenic potential, particularly in males. Age-related trabecular bone loss was similar between the Prx1; PRcKO mice and their WT littermates in both sexes. Hormone deficiency during the period of rapid bone growth induced rapid trabecular bone loss in both the WT and the Prx1; PRcKO mice in both sexes. No differences in trabecular bone mass was observed when PR was deleted in mature osteoblasts using osteocalcin-Cre (Bglap-Cre). Also, there were no differences in cortical bone mass in all three PRcKO mice. In conclusion, PR inactivation in early osteoprogenitor cells but not in mature osteoblasts influenced trabecular bone accrual in a sex-dependent manner. PR deletion in osteoblast lineage cells did not affect cortical bone mass. © 2017 American Society for Bone and Mineral Research.

FOXP1 controls mesenchymal stem cell commitment and senescence during skeletal aging

A hallmark of aged mesenchymal stem/progenitor cells (MSCs) in bone marrow is the pivot of differentiation potency from osteoblast to adipocyte coupled with a decrease in self-renewal capacity. However, how these cellular events are orchestrated in the aging progress is not fully understood. In this study, we have used molecular and genetic approaches to investigate the role of forkhead box P1 (FOXP1) in transcriptional control of MSC senescence. In bone marrow MSCs, FOXP1 expression levels declined with age in an inverse manner with those of the senescence marker p16INK4A. Conditional depletion of Foxp1 in bone marrow MSCs led to premature aging characteristics, including increased bone marrow adiposity, decreased bone mass, and impaired MSC self-renewal capacity in mice. At the molecular level, FOXP1 regulated cell-fate choice of MSCs through interactions with the CEBPβ/δ complex and recombination signal binding protein for immunoglobulin κ J region (RBPjκ), key modulators of adipogenesis and osteogenesis, respectively. Loss of p16INK4A in Foxp1-deficient MSCs partially rescued the defects in replication capacity and bone mass accrual. Promoter occupancy analyses revealed that FOXP1 directly represses transcription of p16INK4A. These results indicate that FOXP1 attenuates MSC senescence by orchestrating their cell-fate switch while maintaining their replicative capacity in a dose- and age-dependent manner.

miR-375-3p negatively regulates osteogenesis by targeting and decreasing the expression levels of LRP5 and β-catenin

Wnt signaling pathways are essential for bone formation. Previous studies showed that Wnt signaling pathways were regulated by miR-375. Thus, we aim to explore whether miR-375 could affect osteogenesis. In the present study, we investigated the roles of miR-375 and its downstream targets. Firstly, we revealed that miR-375-3p negatively modulated osteogenesis by suppressing positive regulators of osteogenesis and promoting negative regulators of osteogenesis. In addition, the results of TUNEL cell apoptosis assay showed that miR-375-3p induced MC3T3-E1 cell apoptosis. Secondly, miR-375-3p targeted low-density lipoprotein receptor-related protein 5 (LRP5), a co-receptor of the Wnt signaling pathways, and β-catenin as determined by luciferase activity assay, and it decreased the expression levels of LRP5 and β-catenin. Thirdly, the decline of protein levels of β-catenin was determined by immunocytochemistry and immunofluorescence. Finally, silence of LRP5 in osteoblast precursor cells resulted in diminished cell viability and cell proliferation as detected by WST-1-based colorimetric assay. Additionally, all the parameters including the relative bone volume from μCT measurement suggested that LRP5 knockout in mice resulted in a looser and worse-connected trabeculae. The mRNA levels of important negative modulators relating to osteogenesis increased after the functions of LRP5 were blocked in mice. Last but not least, the expression levels of LRP5 increased during the osteogenesis of MC3T3-E1, while the levels of β-catenin decreased in bone tissues from osteoporotic patients with vertebral compression fractures. In conclusion, we revealed miR-375-3p negatively regulated osteogenesis by targeting LRP5 and β-catenin. In addition, loss of functions of LRP5 damaged bone formation in vivo. Clinically, miR-375-3p and its targets might be used as diagnostic biomarkers for osteoporosis and might be also as novel therapeutic agents in osteoporosis treatment. The relevant products of miR-375-3p might be developed into molecular drugs in the future. These molecules could be used in translational medicine.

Genetically engineered mouse models to evaluate the role of Wnt secretion in bone development and homeostasis

Alterations in components of the Wnt signaling pathway are associated with altered bone development and homeostasis in several human diseases. We created genetically engineered mouse models (GEMMs) that mimic the cellular defect associated with the Porcupine mutations in patients with Goltz Syndrome/Focal Dermal Hypoplasia. These GEMMs were established by utilizing mice containing a conditionally inactivatable allele of Wntless/GPR177 (a gene encoding a protein required for the transport of Porcupine-modified ligand to the plasma membrane for secretion). We crossed this strain to another which drives cre-mediated gene deletion in mature osteoblasts (Osteocalcin-cre) resulted in mice lacking the ability to secrete Wnt ligands in this cell type. These mice displayed severely reduced bone mass and provide a model to understand the effects of disrupting the ability to secrete Wnt ligands on the skeletal system.

Characterization of genetically engineered mouse models carrying Col2a1-cre-induced deletions of Lrp5 and/or Lrp6

Mice carrying Collagen2a1-cre-mediated deletions of Lrp5 and/or Lrp6 were created and characterized. Mice lacking either gene alone were viable and fertile with normal knee morphology. Mice in which both Lrp5 and Lrp6 were conditionally ablated via Collagen2a1-cre-mediated deletion displayed severe defects in skeletal development during embryogenesis. In addition, adult mice carrying Collagen2a1-cre-mediated deletions of Lrp5 and/or Lrp6 displayed low bone mass suggesting that the Collagen2a1-cre transgene was active in cells that subsequently differentiated into osteoblasts. In both embryonic skeletal development and establishment of adult bone mass, Lrp5 and Lrp6 carry out redundant functions.

Genome-wide association study using family-based cohorts identifies the WLS and CCDC170/ESR1 loci as associated with bone mineral density

Background

Osteoporosis is a common and debilitating bone disease that is characterised by a low bone mineral density (BMD), a highly heritable trait. Genome-wide association studies (GWAS) have proven to be very successful in identifying common genetic variants associated with BMD adjusted for age, gender and weight, however a large portion of the genetic variance for this trait remains unexplained. There is evidence to suggest significant genetic correlation between body size traits and BMD. It has also recently been suggested that unintended bias can be introduced as a result of adjusting a phenotype for a correlated trait. We performed a GWAS meta-analysis in two populations (total n = 6,696) using BMD data adjusted for only age and gender, in an attempt to identify genetic variants associated with BMD including those that may have potential pleiotropic effects on BMD and body size traits.

Results

We observed a single variant, rs2566752, associated with spine BMD at the genome-wide significance level in the meta-analysis (P = 3.36 × 10⁻⁰⁹). Logistic regression analysis also revealed an association between rs2566752 and fracture rate in one of our study cohorts (P = 0.017, n = 5,654). This is an intronic variant located in the wntless Wnt ligand secretion mediator (WLS) gene (1p31.3), a known BMD locus which encodes an integral component of the Wnt ligand secretion pathway. Bioinformatics analyses of variants in moderate LD with rs2566752 produced strong evidence for a regulatory role for the variants rs72670452, rs17130567 and rs1430738. Expression quantitative trait locus (eQTL) analysis suggested that the variants rs12568456 and rs17130567 are associated with expression of the WLS gene in whole blood, cerebellum and temporal cortex brain tissue (P = 0.034–1.19 × 10⁻²³). Gene-wide association testing using the VErsatile Gene-based Association Study 2 (VEGAS2) software revealed associations between the coiled-coil domain containing 170 (CCDC170) gene, located adjacent to the oestrogen receptor 1 (ESR1) gene, and BMD at the spine, femoral neck and total hip sites (P = 1.0 × 10⁻⁰⁶, 2.0 × 10⁻⁰⁶ and 2.0 × 10⁻⁰⁶ respectively).

Conclusions

Genetic variation at the WLS and CCDC170/ESR1 loci were found to be significantly associated with BMD adjusted for only age and gender at the genome-wide level in this meta-analysis.

Wnt signaling in cartilage development and diseases: lessons from animal studies

Cartilage not only plays essential roles in skeletal development and growth during pre- and postnatal stages but also serves to provide smooth movement of skeletons throughout life. Thus, dysfunction of cartilage causes a variety of skeletal disorders. Results from animal studies reveal that β-catenin-dependent canonical and independent non-canonical Wnt signaling pathways have multiple roles in regulation of cartilage development, growth, and maintenance. β-Catenin-dependent signaling is required for progression of endochondral ossification and growth of axial and appendicular skeletons, while excessive activation of this signaling can cause severe inhibition of initial cartilage formation and growth plate organization and function in mice. In contrast, non-canonical Wnt signaling is important in columnar organization of growth plate chondrocytes. Manipulation of Wnt signaling causes or ameliorates articular cartilage degeneration in rodent osteoarthritis models. Human genetic studies indicate that Wnt/β-catenin signaling is a risk factor for osteoarthritis. Accumulative findings from analysis of expression of Wnt signaling molecules and in vivo and in vitro functional experiments suggest that Wnt signaling is a therapeutic target for osteoarthritis. The target tissues of Wnt signaling may be not only articular cartilage but also synovium and subchondral bone.