Osteoporosis is a common disorder, affecting hundreds of millions of people worldwide, and characterized by decreased bone mineral density and increased fracture risk. Known nonheritable risk factors ...for primary osteoporosis include advanced age, sex-steroid deficiency and increased oxidative stress. Age is a nonmodifiable risk factor, but the influence of a person's lifestyle (diet and physical activity) on their bone structure and density is modifiable to some extent. Heritable factors influencing bone fragility can be monogenic or polygenic. Osteogenesis imperfecta, juvenile osteoporosis and syndromes of decreased bone density are discussed as examples of monogenic disorders associated with bone fragility. So far, the factors associated with polygenic osteoporosis have been investigated mainly in genome-wide association studies. However, epigenetic mechanisms also contribute to the heritability of polygenic osteoporosis. Identification of these heritable and nonheritable risk factors has already led to the discovery of therapeutic targets for osteoporosis, which emphasizes the importance of research into the pathogenetic mechanisms of osteoporosis. Accordingly, this article discusses the many heritable and nonheritable factors that contribute to the pathogenesis of primary osteoporosis. Although osteoporosis can also develop secondary to many other diseases or their treatment, a discussion of the factors that contribute only to secondary osteoporosis is beyond the scope of this Review.
Genetic control of bone mass Boudin, Eveline; Fijalkowski, Igor; Hendrickx, Gretl ...
Molecular and cellular endocrinology,
09/2016, Letnik:
432
Journal Article
Recenzirano
Bone mineral density (BMD) is a quantitative traits used as a surrogate phenotype for the diagnosis of osteoporosis, a common metabolic disorder characterized by increased fracture risk as a result ...of a decreased bone mass and deterioration of the microarchitecture of the bone. Normal variation in BMD is determined by both environmental and genetic factors. According to heritability studies, 50–85% of the variance in BMD is controlled by genetic factors which are mostly polygenic. In contrast to the complex etiology of osteoporosis, there are disorders with deviating BMD values caused by one mutation with a large impact. These mutations can result in monogenic bone disorders with either an extreme high (sclerosteosis, Van Buchem disease, osteopetrosis, high bone mass phenotype) or low BMD (osteogenesis imperfecta, juvenile osteoporosis, primary osteoporosis). Identification of the disease causing genes, increased the knowledge on the regulation of BMD and highlighted important signaling pathways and novel therapeutic targets such as sclerostin, RANKL and cathepsin K. Genetic variation in genes involved in these pathways are often also involved in the regulation of normal variation in BMD and osteoporosis susceptibility. In the last decades, identification of genetic factors regulating BMD has proven to be a challenge. Several approaches have been tested such as linkage studies and candidate and genome wide association studies. Although, throughout the years, technological developments made it possible to study increasing numbers of genetic variants in populations with increasing sample sizes at the same time, only a small fraction of the genetic impact can yet be explained. In order to elucidate the missing heritability, the focus shifted to studying the role of rare variants, copy number variations and epigenetic influences. This review summarizes the genetic cause of different monogenic bone disorders with deviating BMD and the knowledge on genetic factors explaining normal variation in BMD and osteoporosis risk.
Free fatty acids provide an important energy source as nutrients, and act as signalling molecules in various cellular processes. Several G-protein-coupled receptors have been identified as ...free-fatty-acid receptors important in physiology as well as in several diseases. GPR120 (also known as O3FAR1) functions as a receptor for unsaturated long-chain free fatty acids and has a critical role in various physiological homeostasis mechanisms such as adipogenesis, regulation of appetite and food preference. Here we show that GPR120-deficient mice fed a high-fat diet develop obesity, glucose intolerance and fatty liver with decreased adipocyte differentiation and lipogenesis and enhanced hepatic lipogenesis. Insulin resistance in such mice is associated with reduced insulin signalling and enhanced inflammation in adipose tissue. In human, we show that GPR120 expression in adipose tissue is significantly higher in obese individuals than in lean controls. GPR120 exon sequencing in obese subjects reveals a deleterious non-synonymous mutation (p.R270H) that inhibits GPR120 signalling activity. Furthermore, the p.R270H variant increases the risk of obesity in European populations. Overall, this study demonstrates that the lipid sensor GPR120 has a key role in sensing dietary fat and, therefore, in the control of energy balance in both humans and rodents.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Summary
Obesity is a highly heritable multifactorial disease that places an enormous burden on human health. Its increasing prevalence and the concomitant‐reduced life expectancy has intensified the ...search for new analytical methods that can reduce the knowledge gap between genetic susceptibility and functional consequences of the disease pathology. Although the influence of genetics and epigenetics has been studied independently in the past, there is increasing evidence that genetic variants interact with environmental factors through epigenetic regulation. This suggests that a combined analysis of genetic and epigenetic variation may be more effective in characterizing the obesity phenotype. To date, limited genome‐wide integrative analyses have been performed. In this review, we provide an overview of the latest findings, advantages, and challenges and discuss future perspectives.
Throughout life, bone is continuously remodelled to be able to fulfil its multiple functions. The importance of strictly regulating the bone remodelling process, which is defined by the sequential ...actions of osteoclasts and osteoblasts, is shown by a variety of disorders with abnormalities in bone mass and strength. The best known and most common example of such a disorder is osteoporosis, which is marked by a decreased bone mass and strength that consequently results in an increased fracture risk. As osteoporosis is a serious health problem, a large number of studies focus on elucidating the aetiology of the disease as well as on the identification of novel therapeutic targets for the treatment of osteoporotic patients. These studies have demonstrated that a large amount of variation in bone mass and strength is often influenced by genetic variation in genes encoding important regulators of bone homeostasis. Throughout the years, studies into the genetic causes of osteoporosis as well as several rare monogenic disorders with abnormal high or low bone mass and strength have largely increased the knowledge on regulatory pathways important for bone resorption and formation. This review gives an overview of genes and pathways that are important for the regulation of bone formation and that are identified through their involvement in monogenic and complex disorders with abnormal bone mass. Furthermore, novel bone-forming strategies for the treatment of osteoporosis that resulted from these discoveries, such as antibodies against sclerostin, are discussed as well.
Abstract Objectives The Wnt signaling pathway is a key pathway in various processes, including bone metabolism. In this review, current knowledge of all extracellular modulators of the canonical Wnt ...signaling in bone metabolism is summarized and discussed. Methods The PubMed database was searched using the following keywords: canonical Wnt signaling, β-catenin bone metabolism, BMD, osteoblast, osteoporosis, Wnt, LRPs, Frizzleds, sFRPs, sclerostin or SOST , dickkopfs, Wif1, R-spondins, glypicans, SOST-dc1 and kremen, all separately as well as in different combinations. Results Canonical Wnt signaling is considered to be one of the major pathways regulating bone formation. Consequently, a large number of studies were performed to elucidate the role of numerous proteins in canonical Wnt signaling and bone metabolism. These studies led to the identification of novel modulators of the pathway like the R-spondin and glypican protein families. Furthermore novel insights are gained in the regulatory role of the different Wnt proteins. Finally, due to its function in bone formation, the pathway is an interesting target for the development of therapeutics for osteoporosis and other bone diseases. In this review, we discuss the promising results of the Wnt modulators sclerostin, Dkk1 and sFRP1 as targets for osteoporosis treatment. Conclusion The increasing number of studies into the exact function of all proteins in the canonical Wnt pathway in general and in bone metabolism already led to novel insights in the regulation of the canonical Wnt pathway. In this review we covered the current knowledge of all extracellular modulators of canonical Wnt signaling.
Skeletal dysplasias are a diverse group of heritable diseases affecting bone and cartilage growth. Throughout the years, the molecular defect underlying many of the diseases has been identified. ...These identifications led to novel insights in the mechanisms regulating bone and cartilage growth and homeostasis. One of the pathways that is clearly important during skeletal development and bone homeostasis is the Wingless and int-1 (WNT) signaling pathway. So far, three different WNT signaling pathways have been described, which are all activated by binding of the WNT ligands to the Frizzled (FZD) receptors. In this review, we discuss the skeletal disorders that are included in the latest nosology of skeletal disorders and that are caused by genetic defects involving the WNT signaling pathway. The number of skeletal disorders caused by defects in WNT signaling genes and the clinical phenotype associated with these disorders illustrate the importance of the WNT signaling pathway during skeletal development as well as later on in life to maintain bone mass. The knowledge gained through the identification of the genes underlying these monogenic conditions is used for the identification of novel therapeutic targets. For example, the genes underlying disorders with altered bone mass are all involved in the canonical WNT signaling pathway. Consequently, targeting this pathway is one of the major strategies to increase bone mass in patients with osteoporosis. In addition to increasing the insights in the pathways regulating skeletal development and bone homeostasis, knowledge of rare skeletal dysplasias can also be used to predict possible adverse effects of these novel drug targets. Therefore, this review gives an overview of the skeletal and extra-skeletal phenotype of the different skeletal disorders linked to the WNT signaling pathway.
In the past years, WNT16 became an interesting target in the field of skeletal research, as it was identified as an essential regulator of the cortical bone compartment, with the ability to increase ...both cortical and trabecular bone mass and strength in vivo. Even though there are indications that these advantageous effects are coming from canonical and non-canonical WNT-signalling activity, a clear model of WNT signalling by WNT16 is not yet depicted. We, therefore, investigated the modulation of canonical (WNT/β-catenin) and non-canonical WNT/calcium, WNT/planar cell polarity (PCP) signalling in human embryonic kidney (HEK) 293 T and SaOS2 cells. Here, we demonstrated that WNT16 activates all WNT-signalling pathways in osteoblasts, whereas only WNT/calcium signalling was activated in HEK293T cells. In osteoblasts, we therefore, additionally investigated the role of Gα subunits as intracellular partners in WNT16′s mechanism of action by performing knockdown of Gα12, Gα13 and Gαq. These studies point out that the above-mentioned Gα subunits might be involved in the WNT/β-catenin and WNT/calcium-signalling activity by WNT16 in osteoblasts, and for Gα12 in its WNT/PCP-signalling activity, illustrating a novel possible mechanism of interplay between the different WNT-signalling pathways in osteoblasts. Additional studies are needed to demonstrate whether this mechanism is specific for WNT16 signalling or relevant for all other WNT ligands as well. Altogether, we further defined WNT16′s mechanism of action in osteoblasts that might underlie the well-known beneficial effects of WNT16 on skeletal homeostasis. These findings on WNT16 and the activity of specific Gα subunits in osteoblasts could definitely contribute to the development of novel therapeutic approaches for fragility fractures in the future.
Camurati–Engelmann Disease Van Hul, Wim; Boudin, Eveline; Vanhoenacker, Filip M. ...
Calcified tissue international,
05/2019, Letnik:
104, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Camurati–Engelmann disease or progressive diaphyseal dysplasia is a rare autosomal dominant sclerosing bone dysplasia. Mainly the skull and the diaphyses of the long tubular bones are affected. ...Clinically, the patients suffer from bone pain, easy fatigability, and decreased muscle mass and weakness in the proximal parts of the lower limbs resulting in gait disturbances. The disease-causing mutations are located within the
TGFβ-1
gene and expected to or thought to disrupt the binding between TGFβ1 and its latency-associated peptide resulting in an increased signaling of the pathway and subsequently accelerated bone turnover. In preclinical studies, it was shown that targeting the type I receptor ameliorates the high bone turnover. In patients, treatment options are currently mostly limited to corticosteroids that may relieve the pain, and improve the muscle weakness and fatigue. In this review, the clinical and radiological characteristics as well as the molecular genetics of this condition are discussed.
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.
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