Common and rare variants of WNT16, DKK1 and SOST and their relationship with bone mineral density

Regulation of WNT16 in bone may involve upstream enhancers within CPED1

WNT16 stands up as an essential gene for bone homeostasis. Here, we present new evidence of the functional role of a particular region within WNT16. Performing 4 C chromatin conformation analysis in three osteoblast-related cells (the human fetal osteoblast hFOB 1.19 cell line, Saos 2 osteosarcoma cell line and mesenchymal Stem Cells -MSC-), we identify physical interactions between the proximal part of WNT16 intron 2, shown here to be an active promoter in Saos 2 osteosarcoma cells, and several putative regulatory regions within CPED1. Analysis of previously published RNA-seq data from hFOB cells disclosed low expression of a region located downstream of this promoter. Our results suggest a novel regulatory mechanism of WNT16 in bone, mediated by physical interaction with various enhancer regions within CPED1.

Wnt16 Promotes Vascular Smooth Muscle Contractile Phenotype and Function via Taz (Wwtr1) Activation in Male LDLR-/- Mice

Wnt16 is expressed in bone and arteries, and maintains bone mass in mice and humans, but its role in cardiovascular physiology is unknown. We show that Wnt16 protein accumulates in murine and human vascular smooth muscle (VSM). WNT16 genotypes that convey risk for bone frailty also convey risk for cardiovascular events in the Dallas Heart Study. Murine Wnt16 deficiency, which causes postnatal bone loss, also reduced systolic blood pressure. Electron microscopy demonstrated abnormal VSM mitochondrial morphology in Wnt16-null mice, with reductions in mitochondrial respiration. Following angiotensin-II (AngII) infusion, thoracic ascending aorta (TAA) dilatation was greater in Wnt16-/- vs Wnt16+/+ mice (LDLR-/- background). Acta2 (vascular smooth muscle alpha actin) deficiency has been shown to impair contractile phenotype and worsen TAA aneurysm with concomitant reductions in blood pressure. Wnt16 deficiency reduced expression of Acta2, SM22 (transgelin), and other contractile genes, and reduced VSM contraction induced by TGFβ. Acta2 and SM22 proteins were reduced in Wnt16-/- VSM as was Ankrd1, a prototypic contractile target of Yap1 and Taz activation via TEA domain (TEAD)-directed transcription. Wnt16-/- VSM exhibited reduced nuclear Taz and Yap1 protein accumulation. SiRNA targeting Wnt16 or Taz, but not Yap1, phenocopied Wnt16 deficiency, and Taz siRNA inhibited contractile gene upregulation by Wnt16. Wnt16 incubation stimulated mitochondrial respiration and contraction (reversed by verteporfin, a Yap/Taz inhibitor). SiRNA targeting Taz inhibitors Ccm2 and Lats1/2 mimicked Wnt16 treatment. Wnt16 stimulated Taz binding to Acta2 chromatin and H3K4me3 methylation. TEAD cognates in the Acta2 promoter conveyed transcriptional responses to Wnt16 and Taz. Wnt16 regulates cardiovascular physiology and VSM contractile phenotype, mediated via Taz signaling.

Genetic variation in WNT16 and its association with bone mineral density, fractures and osteoporosis in children with bone fragility

Several genome-wide association studies (GWAS), GWAS meta-analyses, and mouse studies have demonstrated that wingless-related integration site 16 (WNT16) gene is associated with bone mineral density (BMD), cortical bone thickness, bone strength and fracture risk. Practically no data exist regarding the significance of WNT16 in childhood-onset osteoporosis and related fractures. We hypothesized that pathogenic variants and genetic variations in WNT16 could explain skeletal fragility in affected children. We screened the WNT16 gene by Sanger sequencing in three pediatric cohorts: 35 with primary osteoporosis, 59 with multiple fractures, and in 95 healthy controls. Altogether, we identified 12 variants in WNT16. Of them one was a rare 5′UTR variant rs1386898215 in genome aggregate and medical trans-omic databases (GnomAD, TOPMED; minor allele frequency (MAF) 0.00 and 0.000008, respectively). One variant rs1554366753, overrepresented in children with osteoporosis (MAF = 0.06 vs healthy controls MAF = 0.01), was significantly associated with lower BMD. This variant was found associated with increased WNT16 gene expression at mRNA level in fibroblast cultures. None of the other identified variants were rare (MAF < 0.001) or deemed pathogenic by predictor programs. WNT16 may play a role in childhood osteoporosis but genetic WNT16 variation is not a common cause of skeletal fragility in childhood.

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No pathogenic WNT16 variants were found associated with pediatric osteoporosis or fracture-prone patients

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Altogether, twelve WNT16 variants were found in pediatric osteoporosis or fracture-prone patients

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The genetic variation rs1554366753 in the WNT16 gene is associated with bone mineral density and primary osteoporosis

Genetic analysis in a familial case with high bone mineral density suggests additive effects at two loci

Osteoporosis is the most common bone disease, characterized by a low bone mineral density (BMD) and increased risk of fracture. At the other end of the BMD spectrum, some individuals present strong, fracture‐resistant, bones. Both osteoporosis and high BMD are heritable and their genetic architecture encompasses polygenic inheritance of common variants and some cases of monogenic highly penetrant variants in causal genes. We have investigated the genetics of high BMD in a family segregating this trait in an apparently Mendelian dominant pattern. We searched for rare causal variants by whole‐exome sequencing in three affected and three nonaffected family members. Using this approach, we have identified 38 rare coding variants present in the proband and absent in the three individuals with normal BMD. Although we have found four variants shared by the three affected members of the family, we have not been able to relate any of these to the high‐BMD phenotype. In contrast, we have identified missense variants in two genes, VAV3 and ADGRE5, each shared by two of out of three affected members, whose loss of function fits with the phenotype of the family. In particular, the proband, a woman displaying the highest BMD (sum Z‐score = 7), carries both variants, whereas the other two affected members carry one each. VAV3 encodes a guanine‐nucleotide‐exchange factor with an important role in osteoclast activation and function. Although no previous cases of VAV3 mutations have been reported in humans, Vav3 knockout (KO) mice display dense bones, similarly to the high‐BMD phenotype present in our family. The ADGRE5 gene encodes an adhesion G protein‐coupled receptor expressed in osteoclasts whose KO mouse displays increased trabecular bone volume. Combined, these mouse and human data highlight VAV3 and ADGRE5 as novel putative high‐BMD genes with additive effects, and potential therapeutic targets for osteoporosis. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Wnt16 signaling in bone homeostasis and osteoarthristis

Wnts are secreted cysteine-rich glycoproteins involved in joint development and skeletal homeostasis and have been implicated in the occurrence of osteoarthritis. Over the past decade, Wnt16, a member of the Wnt family, has received widespread attention for its strong association with bone mineral density, cortical bone thickness, bone strength, and osteoporotic fracture risk. In recent years, further studies have shed light on the role of Wnt16 a positive regulator of bone mass and protective regulator of osteoarthritis progression. Transduction mechanisms and crosstalk involving Wnt16 signaling have also been illustrated. More importantly, local Wnt16 treatment has been shown to ease osteoarthritis, inhibit bone resorption, and promote new bone formation in bone defect models. Thus, Wnt16 is now a potential therapeutic target for skeletal diseases and osteoarthritis. This paper reviews our current understanding of the mechanisms by which Wnt16 signaling regulates bone homeostasis and osteoarthritis.

Genotypic Analyses of the Sclerostin rs851056 and Dickkopf rs1569198 Polymorphisms in Mexican-Mestizo Postmenopausal Osteoporosis: A Case-Control Study

Background: The Wnt/β catenin pathway promotes bone mineralization stimulating proliferation, differentiation, and survival of osteoblasts; it also inhibits osteoclast differentiation and osteocyte activity. Sclerostin (SOST) and Dickkopf 1 (DKK1) are Wnt/β catenin pathway inhibitors. Genetic variability in the expression of SOST and DKK1 might be involved in the development of postmenopausal osteoporosis (OP). Aim: To determine whether the SOST rs851056 and DKK1 rs1569198 polymorphisms are associated with OP in Mexican-Mestizo postmenopausal women. Materials and Methods: Two hundred and eighty Mexican-Mestizo postmenopausal women were assessed for their bone mineral density by dual-energy X-ray absorptiometry (DXA). Patients were classified as OP or non-OP. Genomic DNA was extracted from peripheral blood leukocytes. Genetic polymorphisms were analyzed by quantitative polymerase chain reaction using TaqMan probes. Results: The frequency of OP was 40% among the study population. Osteoporotic patients were older (p < 0.001), had a higher frequency of smoking (p = 0.01), and lower body mass index (p < 0.001) compared with the non-osteoporotic patients. The genotypic frequencies of the rs851056 locus of the SOST gene were GG 19%, GC 45%, and CC 35%, whereas the genotypic frequencies of the rs1569198 locus of the DKK1 gene were GG 15%, GA 40%, and AA 44%. In relation to rs851056 locus of the SOST gene, no differences were observed between the OP and non-OP cohorts in the frequencies of the GC polymorphism (48.7% vs. 43.1%). Similarly, analyses of the DKK1 rs1569198 does not demonstrate differences in the GA genotypic frequencies between the OP and non-OP cohorts (42.5% vs. 38.9%). Conclusion: Polymorphisms SOST rs851056 and DKK1 rs1569198 polymorphisms are not associated with OP in Mexican-Mestizo postmenopausal women.

Therapeutic Effect of IL1β Priming Tonsil Derived-Mesenchymal Stem Cells in Osteoporosis

BACKGROUND

Stem cell therapies can be a new therapeutic strategy that may rebalance anabolic and anti-resorptive effects in osteoporosis patients. Tonsil-derived mesenchymal stem cells (TMSCs) can be an alternative therapeutic source for chronic degenerative diseases including osteoporosis. MSCs acquire immune regulatory function under the inflammatory cytokines. Since interleukin (IL) 1β is known to be one of inflammatory cytokines involved in osteoporosis progression, treatment of IL1β with TMSCs may enhance immunomodulatory function and therapeutic effects of TMSCs in osteoporosis.

METHODS

For IL1β priming, TMSCs were cultured in the presence of the medium containing IL1β for 1 day. Characteristics of IL1β priming TMSCs such as multipotent differentiation properties, anti-inflammatory potential, and suppression of osteoclast differentiation were assessed in vitro. For in vivo efficacy study, IL1β priming TMSCs were intravenously infused twice with ovariectomized (OVX) osteoporosis mouse model, and blood serum and bone parameters from micro computed tomography images were analyzed.

RESULTS

IL1β priming TMSCs had an enhanced osteogenic differentiation and secreted factors that regulate both osteoclastogenesis and osteoblastogenesis. IL1β priming TMSCs also suppressed proliferation of peripheral blood mononuclear cells (PBMCs) and decreased expression of Receptor activator of nuclear factor kappa-Β ligand (RANKL) in PHA-stimulated PBMCs. Furthermore, osteoclast specific genes such as Nuclear factor of activated T cells c1 (NFATc1) were effectively down regulated when co-cultured with IL1β priming TMSCs in RANKL induced osteoclasts. In OVX mice, IL1β priming TMSCs induced low level of serum RANKL/osteoprotegerin (OPG) ratio on the first day of the last administration. Four weeks after the last administration, bone mineral density and serum Gla-osteocalcin were increased in IL1β priming TMSC-treated OVX mice. Furthermore, bone formation and bone resorption markers that had been decreased in OVX mice with low calcium diet were recovered by infusion of IL1β priming TMSCs.

CONCLUSION

IL1β priming can endow constant therapeutic efficacy with TMSCs, which may contribute to improve bone density and maintain bone homeostasis in postmenopausal osteoporosis. Therefore, IL1β priming TMSCs can be a new therapeutic option for treating postmenopausal osteoporosis.

FAM3C: an emerging biomarker and potential therapeutic target for cancer

FAM3C is a member of the FAM3 family. Recently, overexpression of FAM3C has been reported in numerous types of cancer, including breast and colon cancer. Increasing evidence suggests that elevated FAM3C and its altered subcellular localization are closely associated with tumor formation, invasion, metastasis and poor survival. Moreover, FAM3C has been found to be the regulator of various proteins that associate with cancer, including Ras, STAT3, TGF-β and LIFR. This review summarizes the current knowledge regarding FAM3C, including its structure, expression patterns, regulation, physiological roles and regulatory functions in various malignancies. These findings highlight the importance of FAM3C in cancer development and provide evidence that FAM3C is a novel biomarker and potential therapeutic target for various cancers.

Genetics and Genomics of SOST: Functional Analysis of Variants and Genomic Regulation in Osteoblasts

SOST encodes the sclerostin protein, which acts as a key extracellular inhibitor of the canonical Wnt pathway in bone, playing a crucial role in skeletal development and bone homeostasis. The objective of this work was to assess the functionality of two variants previously identified (the rare variant rs570754792 and the missense variant p.Val10Ile) and to investigate the physical interactors of the SOST proximal promoter region in bone cells. Through a promoter luciferase reporter assay we show that the minor allele of rs570754792, a variant located in the extended TATA box motif, displays a significant decrease in promoter activity. Likewise, through western blot studies of extracellular and intracellular sclerostin, we observe a reduced expression of the p.Val10Ile mutant protein. Finally, using a circular chromosome conformation capture assay (4C-seq) in 3 bone cell types (MSC, hFOB, Saos-2), we have detected physical interactions between the SOST proximal promoter and the ECR5 enhancer, several additional enhancers located between EVT4 and MEOX1 and a distant region containing exon 18 of DHX8. In conclusion, SOST presents functional regulatory and missense variants that affect its expression and displays physical contacts with far reaching genomic sequences, which may play a role in its regulation within bone cells.

Functional Assessment of Coding and Regulatory Variants From the DKK1 Locus

The DKK1 gene encodes an extracellular inhibitor of the Wnt pathway with an important role in bone tissue development, bone homeostasis, and different critical aspects of bone biology. Several BMD genome‐wide association studies (GWASs) have consistently found association with SNPs in the DKK1 genomic region. For these reasons, it is important to assess the functionality of coding and regulatory variants in the gene. Here, we have studied the functionality of putative regulatory variants, previously found associated with BMD in different studies by others and ourselves, and also six missense variants present in the general population. Using a Wnt‐pathway‐specific luciferase reporter assay, we have determined that the variants p.Ala41Thr, p.Tyr74Phe, p.Arg120Leu, and p.Ser157Ile display a reduced DKK1 inhibitory capacity as compared with WT. This result agrees with the high‐bone‐mass (HBM) phenotype of two women from our cohort who carried mutations p.Tyr74Phe or p.Arg120Leu. On the other hand, by means of a circularized chromosome conformation capture‐ (4C‐) sequencing experiment, we have detected that the region containing 24 BMD‐GWA variants, located 350‐kb downstream of DKK1, interacts both with DKK1 and the LNCAROD (LncRNA‐activating regulator of DKK1, AKA LINC0148) in osteoblastic cells. In conclusion, we have shown that some rare coding variants are partial loss‐of‐function mutations that may lead to a HBM phenotype, whereas the common SNPs associated with BMD in GWASs belong to a putative long‐range regulatory region, through a yet unknown mechanism involving LNCAROD. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Bone development and remodeling in metabolic disorders

There are many metabolic disorders that present with bone phenotypes. In some cases, the pathological bone symptoms are the main features of the disease whereas in others they are a secondary characteristic. In general, the generation of the bone problems in these disorders is not well understood and the therapeutic options for them are scarce. Bone development occurs in the early stages of embryonic development where the bone formation, or osteogenesis, takes place. This osteogenesis can be produced through the direct transformation of the pre-existing mesenchymal cells into bone tissue (intramembranous ossification) or by the replacement of the cartilage by bone (endochondral ossification). In contrast, bone remodeling takes place during the bone's growth, after the bone development, and continues throughout the whole life. The remodeling involves the removal of mineralized bone by osteoclasts followed by the formation of bone matrix by the osteoblasts, which subsequently becomes mineralized. In some metabolic diseases, bone pathological features are associated with bone development problems but in others they are associated with bone remodeling. Here, we describe three examples of impaired bone development or remodeling in metabolic diseases, including work by others and the results from our research. In particular, we will focus on hereditary multiple exostosis (or osteochondromatosis), Gaucher disease, and the susceptibility to atypical femoral fracture in patients treated with bisphosphonates for several years.

Polymorphisms of FDPS, LRP5, SOST and VKORC1 genes and their relation with osteoporosis in postmenopausal Romanian women

OBJECTIVES

This study aimed to assess the relationship between bone mineral density and genotypes of four polymorphisms in previously detected osteoporosis-candidate genes (FDPS rs2297480, LRP5 rs3736228, SOST rs1234612, VKORC1 rs9934438) in postmenopausal Romanian women with primary osteoporosis.

METHODS

An analytical, prospective, transversal, observational, case-control study on 364 postmenopausal Romanian women was carried out between June 2016 and August 2017 in Cluj Napoca, Romania. Clinical data and blood samples were collected from all study participants. Four polymorphisms were genotyped using TaqMan SNP Genotyping assays, run on a QuantStudio 3 real-time PCR machine.

RESULTS

Women with TT genotype in FDPS rs2297480 had significantly lower bone mineral density values in the lumbar spine and total hip, and the presence of the T allele was significantly associated with the osteoporosis. Women carrying the CC genotype in LRP5 rs3736228 tend to have lower bone mineral density values in the femoral neck and total hip. No significant association was found for the genotypes of SOST rs1234612 or VKORC1 rs9934438.

CONCLUSIONS

Our study showed a strong association between bone mineral density and polymorphisms in the FDPS gene, and a borderline association with LRP5 and SOST polymorphisms in postmenopausal Romanian women with osteoporosis. No association was found for VKORC1.