Identification and association analysis of single nucleotide polymorphisms in the human noggin (NOG) gene and osteoporosis phenotypes

The roles and regulatory mechanisms of TGF-β and BMP signaling in bone and cartilage development, homeostasis and disease

Transforming growth factor-βs (TGF-βs) and bone morphometric proteins (BMPs) belong to the TGF-β superfamily and perform essential functions during osteoblast and chondrocyte lineage commitment and differentiation, skeletal development, and homeostasis. TGF-βs and BMPs transduce signals through SMAD-dependent and -independent pathways; specifically, they recruit different receptor heterotetramers and R-Smad complexes, resulting in unique biological readouts. BMPs promote osteogenesis, osteoclastogenesis, and chondrogenesis at all differentiation stages, while TGF-βs play different roles in a stage-dependent manner. BMPs and TGF-β have opposite functions in articular cartilage homeostasis. Moreover, TGF-β has a specific role in maintaining the osteocyte network. The precise activation of BMP and TGF-β signaling requires regulatory machinery at multiple levels, including latency control in the matrix, extracellular antagonists, ubiquitination and phosphorylation in the cytoplasm, nucleus-cytoplasm transportation, and transcriptional co-regulation in the nuclei. This review weaves the background information with the latest advances in the signaling facilitated by TGF-βs and BMPs, and the advanced understanding of their diverse physiological functions and regulations. This review also summarizes the human diseases and mouse models associated with disordered TGF-β and BMP signaling. A more precise understanding of the BMP and TGF-β signaling could facilitate the development of bona fide clinical applications in treating bone and cartilage disorders.

BMP Signaling Pathway in Dentin Development and Diseases

BMP signaling plays an important role in dentin development. BMPs and antagonists regulate odontoblast differentiation and downstream gene expression via canonical Smad and non-canonical Smad signaling pathways. The interaction of BMPs with their receptors leads to the formation of complexes and the transduction of signals to the canonical Smad signaling pathway (for example, BMP ligands, receptors, and Smads) and the non-canonical Smad signaling pathway (for example, MAPKs, p38, Erk, JNK, and PI3K/Akt) to regulate dental mesenchymal stem cell/progenitor proliferation and differentiation during dentin development and homeostasis. Both the canonical Smad and non-canonical Smad signaling pathways converge at transcription factors, such as Dlx3, Osx, Runx2, and others, to promote the differentiation of dental pulp mesenchymal cells into odontoblasts and downregulated gene expressions, such as those of DSPP and DMP1. Dysregulated BMP signaling causes a number of tooth disorders in humans. Mutation or knockout of BMP signaling-associated genes in mice results in dentin defects which enable a better understanding of the BMP signaling networks underlying odontoblast differentiation and dentin formation. This review summarizes the recent advances in our understanding of BMP signaling in odontoblast differentiation and dentin formation. It includes discussion of the expression of BMPs, their receptors, and the implicated downstream genes during dentinogenesis. In addition, the structures of BMPs, BMP receptors, antagonists, and dysregulation of BMP signaling pathways associated with dentin defects are described.

Clinical and Molecular Study of the NOG Gene in Families with Mandibular Micrognathism

Objectives Previous studies showed that noggin gene ( NOG ) sequence alterations, as well as epigenetic factors, could influence mandibular development. The aim of this study was to analyze clinical characteristics, NOG gene sequences, and promoter methylation sites in patients with mandibular micrognathism.

Materials and Methods A total of 35 individuals of five Colombian families were subject to clinical and cephalometric analysis for mandibular micrognathism. One nonaffected individual of each family was included as a control. DNA was isolated from whole blood sample from all individuals by salting out method. Nine NOG gene fragments were amplified by polymerase chain reaction (PCR) and sequenced. Identification of CpG islands for methylation analysis at the NOG gene promoter was performed by MSP-PCR kit (Qiagen R).

Statistical Analysis A descriptive statistical analysis was carried out evaluating the presence or absence of genetics variants and the methylation sites in the NOG gene.

ResultsNOG sequence results of affected individuals with mandibular micrognathism for one of the families studied demonstrated that they were heterozygous for 672 C/A (new mutation). For a second family, individuals were heterozygous for 567 G/C (single nucleotide polymorphism [SNP] RS116716909). For DNA analyzed from all patients studied, no methylations were observed at the NOG gene promoter region.

Conclusion Our results suggested that 672 C/A and 567 G/C variants could be involved in the presence of mandibular micrognathism. Moreover, lack of methylation sites at the NOG gene promoter region of all individuals studied suggests possibly other epigenetic factors could modulate mandibular growth. The search of genetic variants related with mandibular micrognathism will allow to predict in an integral way the development patterns of the patients and therefore establish a better clinical treatment.

IL-17F promotes osteoblastic osteogenesis via the MAPK/ERK1/2 signaling pathway

Osteoimmunology is a field that focuses on the interactions between the skeletal and immune systems, and has become a focus of research over the years. The role of interleukin (IL)-17F, a proinflammatory cytokine, in bone regeneration and its signal transduction are not completely understood. The aim of the present study was to evaluate the function of IL-17F and the possible mechanisms underlying IL-17F in osteoblasts in vitro. Osteoblasts derived from newborn rats were treated with various concentrations of IL-17F. The pro-osteogenic effects of IL-17F were assessed at the cellular and molecular level. The results demonstrated that IL-17F promoted osteoblast proliferation, differentiation and mineralization. Reverse transcription-quantitative PCR and western blotting indicated that IL-17F treatment upregulated osteogenesis-related factors, including bone morphogenetic protein-2, Runt-related transcription factor-2 (Runx2) and Osterix, and downregulated Noggin compared with the control group. Subsequently, whether the IL-17F receptors, IL-17 receptor (IL-17R) A and IL-17RC, served a role in the effects of IL-17F on osteoblasts was investigated. The mRNA expression levels of IL-17RA and IL-17RC were upregulated in IL-17F-treated osteoblasts compared with control osteoblasts. Furthermore, U0126, a MAPK/ERK1/2 inhibitor, was utilized to investigate the mechanisms underlying IL-17F. The results indicated that compared with the control group, IL-17F increased the protein expression of phosphorylated-ERK1/2, Runx2 and Osterix, whereas U0126 reversed IL-17F-mediated effects. Collectively, the results of the present study suggested that IL-17F promoted osteoblastic osteogenesis via the MAPK/ERK1/2-mediated signaling pathway. IL-17F promoted osteogenesis, including proliferation, differentiation and mineralization activity, indicating that IL-17F may serve as a potential therapeutic target for osteoblast-mediated bone loss disease.

Sp1 promotes dental pulp stem cell osteoblastic differentiation through regulating noggin

Based on the high self-renewal ability and osteoblastic differentiation capacity, dental pulp stem cells (DPSCs) are suggested to be promising cell source for osteogenesis. Therefore, illustrating the mechanism of osteoblastic differentiation of DPSCs is required. This current study aims to illustrate the role and mechanism of Sp1 in regulating osteoblastic differentiation of DPSCs. In this study, we downregulated Sp1 in DPSCs and evaluated the osteoblastic differentiation by measuring Runx2 and OCN expression with Western blot analysis and by Alizarin red staining. Furthermore, we investigated the mechanism of Sp1 regulating noggin with Firefly luciferase reporter gene assay and ChIP assay, and correspondingly evaluated the function of noggin in Sp1-regulated osteoblastic differentiation of DPSCs. We found that knockdown of Sp1 inhibits the expression of ALP, Runx2, COL1A1 and OCN, and decreases ALP staining, Alizarin red staining. Sp1 binds to noggin promoter and inhibits noggin expression, thus correspondingly regulates DPSCs osteoblastic differentiation. In conclusion, our study revealed that Sp1 regulates DPSCs osteoblastic differentiation through noggin and that Sp1/noggin can provide new perspective for enhancing DPSCs osteogenesis.

Denosumab effects on serum levels of the bone morphogenetic proteins antagonist noggin in patients with transfusion-dependent thalassemia and osteoporosis

INTRODUCTION

Noggin is an antagonist of bone morphogenetic proteins (BMPs) and has a strong effect on osteogenesis. Osteoporosis is a common complication of transfusion dependent beta-thalassemia (TDT) and denosumab has been recently emerged as a promising therapeutic option. This was a post hoc investigation of serum noggin levels among TDT patients with osteoporosis who participated in a randomized, placebo-control, phase 2b study.

METHODS

Patients received either 60 mg denosumab (n = 32) or placebo (n = 31) every 6 months for 12 months. Noggin was measured, for the first time in thalassemia patients, at baseline and at 12 months, using a recently developed high sensitivity fluorescent immunoassay.

RESULTS

Both groups showed a significant increase in noggin serum levels (denosumab p < 0.001; placebo p < 0.0001). Interestingly, the increase was higher in the placebo group. Furthermore, we observed a strong correlation between noggin and wrist bone mineral density (r = -0.641, p = 0.002) only in the denosumab group.

CONCLUSION

In conclusion, higher noggin levels reflected more BMP inhibition, since our assay detects free bioactive noggin, which in turn impaired bone formation in placebo group. Therefore, denosumab possibly regulates noggin and favours bone turnover in TDT patients with osteoporosis through a novel mechanism of action.

Osteoporosis: the current status of mesenchymal stem cell-based therapy

Osteoporosis, or bone loss, is a progressive, systemic skeletal disease that affects millions of people worldwide. Osteoporosis is generally age related, and it is underdiagnosed because it remains asymptomatic for several years until the development of fractures that confine daily life activities, particularly in elderly people. Most patients with osteoporotic fractures become bedridden and are in a life-threatening state. The consequences of fracture can be devastating, leading to substantial morbidity and mortality of the patients. The normal physiologic process of bone remodeling involves a balance between bone resorption and bone formation during early adulthood. In osteoporosis, this process becomes imbalanced, resulting in gradual losses of bone mass and density due to enhanced bone resorption and/or inadequate bone formation. Several growth factors underlying age-related osteoporosis and their signaling pathways have been identified, such as osteoprotegerin (OPG)/receptor activator of nuclear factor B (RANK)/RANK ligand (RANKL), bone morphogenetic protein (BMP), wingless-type MMTV integration site family (Wnt) proteins and signaling through parathyroid hormone receptors. In addition, the pathogenesis of osteoporosis has been connected to genetics. The current treatment of osteoporosis predominantly consists of antiresorptive and anabolic agents; however, the serious adverse effects of using these drugs are of concern. Cell-based replacement therapy via the use of mesenchymal stem cells (MSCs) may become one of the strategies for osteoporosis treatment in the future.

Bone morphogenetic protein signaling in bone homeostasis

Bone morphogenetic proteins (BMPs) are cytokines belonging to the transforming growth factor-β (TGF-β) superfamily. They play multiple functions during development and tissue homeostasis, including regulation of the bone homeostasis. The BMP signaling pathway consists in a well-orchestrated manner of ligands, membrane receptors, co-receptors and intracellular mediators, that regulate the expression of genes controlling the normal functioning of the bone tissues. Interestingly, BMP signaling perturbation is associated to a variety of low and high bone mass diseases, including osteoporosis, bone fracture disorders and heterotopic ossification. Consistent with these findings, in vitro and in vivo studies have shown that BMPs have potent effects on the activity of cells regulating bone function, suggesting that manipulation of the BMP signaling pathway may be employed as a therapeutic approach to treat bone diseases. Here we review the recent advances on BMP signaling and bone homeostasis, and how this knowledge may be used towards improved diagnosis and development of novel treatment modalities. This article is part of a Special Issue entitled "Muscle Bone Interactions".

The "bone morphogenic proteins" pathways in bone and joint diseases: translational perspectives from physiopathology to therapeutic targets

A large body of evidence supports an important role of bone morphogenic proteins (BMPs) pathways in skeletal development in the embryo. BMPs are also involved in skeletal homeostasis and diseases in the adult. They were first identified as major bone anabolic agents and recent advances indicate that they also regulate osteoclastogenesis and joint components via multiple cross-talks with other signaling pathways. This review attempts to integrate these data in the pathogenesis of bone and joints diseases, such as osteoporosis, fracture healing, osteoarthritis, inflammatory arthritis, or bone metastasis. The use of recombinant BMPs in bone tissue engineering and in the treatment of skeletal diseases, or future therapeutic strategies targeting BMPs signal and its regulators, will be discussed based on these considerations.

A comprehensive review of reported heritable noggin-associated syndromes and proposed clinical utility of one broadly inclusive diagnostic term: NOG-related-symphalangism spectrum disorder (NOG-SSD)

The NOG gene encodes noggin, a secreted polypeptide that is important for regulating multiple signaling pathways during human development, particularly in cartilage and bone. The hallmark of NOG-related syndromes is proximal symphalangism, defined by abnormal fusion of the proximal interphalangeal joints of the hands and feet. Many additional features secondary to NOG mutations are commonly but inconsistently observed, including a characteristic facies with a hemicylindrical nose, congenital conductive hearing loss due to stapes fixation, and hyperopia. The variable clinical presentations led to the designation of five different autosomal dominant syndromes, all subsequently found to have resulted from NOG mutations. These include (1) proximal symphalangism; (2) multiple synostoses syndrome 1; (3) stapes ankylosis with broad thumbs and toes; (4) tarsal-carpal coalition syndrome; and (5) brachydactyly type B2. Herein, we review the phenotypic features associated with mutations in the NOG gene, demonstrating the overlapping characteristics of these syndromes. Due to the variable phenotypic spectrum within families and among families with the same mutation, we propose a unifying term, NOG-related symphalangism spectrum disorder (NOG-SSD), to aid in the clinical recognition and evaluation of all affected individuals with these phenotypes. These NOG gene variants are available in a new locus-specific database (https://NOG.lovd.nl).

Molecular genetic studies of gene identification for osteoporosis: the 2009 update

Osteoporosis is a complex human disease that results in increased susceptibility to fragility fractures. It can be phenotypically characterized using several traits, including bone mineral density, bone size, bone strength, and bone turnover markers. The identification of gene variants that contribute to osteoporosis phenotypes, or responses to therapy, can eventually help individualize the prognosis, treatment, and prevention of fractures and their adverse outcomes. Our previously published reviews have comprehensively summarized the progress of molecular genetic studies of gene identification for osteoporosis and have covered the data available to the end of September 2007. This review represents our continuing efforts to summarize the important and representative findings published between October 2007 and November 2009. The topics covered include genetic association and linkage studies in humans, transgenic and knockout mouse models, as well as gene-expression microarray and proteomics studies. Major results are tabulated for comparison and ease of reference. Comments are made on the notable findings and representative studies for their potential influence and implications on our present understanding of the genetics of osteoporosis.

Genetics of osteoporosis: accelerating pace in gene identification and validation

Osteoporosis is characterized by low bone mineral density and structural deterioration of bone tissue, leading to an increased risk of fractures. It is the most common metabolic bone disorder worldwide, affecting one in three women and one in eight men over the age of 50. In the past 15 years, a large number of genes have been reported as being associated with osteoporosis. However, only in the past 4 years we have witnessed an accelerated pace in identifying and validating osteoporosis susceptibility loci. This increase in pace is mostly due to large-scale association studies, meta-analyses, and genome-wide association studies of both single nucleotide polymorphisms and copy number variations. A comprehensive review of these developments revealed that, to date, at least 15 genes (VDR, ESR1, ESR2, LRP5, LRP4, SOST, GRP177, OPG, RANK, RANKL, COLIA1, SPP1, ITGA1, SP7, and SOX6) can be reasonably assigned as confirmed osteoporosis susceptibility genes, whereas, another >30 genes are promising candidate genes. Notably, confirmed and promising genes are clustered in three biological pathways, the estrogen endocrine pathway, the Wnt/beta-catenin signaling pathway, and the RANKL/RANK/OPG pathway. New biological pathways will certainly emerge when more osteoporosis genes are identified and validated. These genetic findings may provide new routes toward improved therapeutic and preventive interventions of this complex disease.