Morphological and biochemical features of obesity are associated with mineralization genes' polymorphisms

Peripheral and central control of obesity by primary cilia

Primary cilia are hair-like structures that protrude from the cell surface. They are capable of sensing external cues and conveying a vast array of signals into cells to regulate a variety of physiological activities. Mutations in cilium-associated genes are linked to a group of diseases with overlapping clinical manifestations, collectively known as ciliopathies. A significant proportion of human ciliopathy cases are accompanied by metabolic disorders such as obesity and type 2 diabetes. Nevertheless, the mechanisms through which dysfunction of primary cilia contributes to obesity are complex. In this article, we present an overview of primary cilia and highlight obesity-related ciliopathies. We also discuss the potential role of primary cilia in peripheral organs, with a focus on adipose tissues. In addition, we emphasize the significance of primary cilia in the central regulation of obesity, especially the involvement of ciliary signaling in the hypothalamic control of feeding behavior. This article therefore proposes a framework of both peripheral and central regulation of obesity by primary cilia, which may benefit further exploration of the ciliary role in metabolic regulation.

From Myricetin to the Discovery of Novel Natural Human ENPP1 Inhibitors: A Virtual Screening, Molecular Docking, Molecular Dynamics Simulation, and MM/GBSA Study

It was recently revealed that naturally occurring myricetin can inhibit ectonucleotidase ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1), which, in turn, can treat ischemic cardiac injury. However, due to myricetin’s poor druggability, its further developments are relatively limited, which necessitates the discovery of novel ENPP1-inhibiting myricetin analogs as alternatives. In this study, the binding model of myricetin with ENPP1 was elucidated by molecular docking and molecular dynamics studies. Subsequently, virtual screening on the self-developed flavonoid natural product database (FNPD), led to the identification of two flavonoid glycosides (Cas No: 1397173-50-0 and 1169835-58-8), as potential ENPP1 inhibitors. Docking scores and MM/GBSA binding energies predicted that they might have higher inhibitory effects than myricetin. This study provides a strong foundation for the future development of ischemic cardiac injury drugs.

A new perspective on the function of Tissue Non-Specific Alkaline Phosphatase: from bone mineralization to intra-cellular lipid accumulation

Tissue-nonspecific alkaline phosphatase (TNAP) is one of four isozymes, which include germ cell, placental and intestinal alkaline phosphatases. The TNAP isozyme has 3 isoforms (liver, bone and kidney) which differ by tissue expression and glycosylation pattern. Despite a long history of investigation, the exact function of TNAP in many tissues is largely unknown. Only the bone isoform has been well characterised during mineralization where the enzyme hydrolyses pyrophosphate to inorganic phosphate, which combines with calcium to form hydroxyapatite crystals deposited as new bone. The inorganic phosphate also increases gene expression of proteins that support tissue mineralization. Recent studies have shown that TNAP is expressed in preadipocytes from several species, and that inhibition of TNAP activity causes attenuation of intracellular lipid accumulation in these and other lipid-storing cells. The mechanism by which TNAP stimulates lipid accumulation is not known; however, proteins that are important for controlling phosphate levels in bone are also expressed in adipocytes. This review examines the evidence that inorganic phosphate generated by TNAP promotes transcription that enhances the expression of the regulators of lipid storage and consequently, that TNAP has a major function of lipid metabolism.

Cilia signaling and obesity

An emerging number of rare genetic disorders termed ciliopathies are associated with pediatric obesity. It is becoming clear that the mechanisms associated with cilia dysfunction and obesity in these syndromes are complex. In addition to ciliopathic syndromic forms of obesity, several cilia-associated signaling gene mutations also lead to morbid obesity. While cilia have critical and diverse functions in energy homeostasis including their roles in centrally mediated food intake as well as in peripheral tissues, many questions remain. Here, we briefly discuss the syndromic ciliopathies and monoallelic cilia signaling gene mutations associated with obesity. We also describe potential ways cilia may be involved in common obesity. We discuss how neuronal cilia impact food intake potentially through leptin signaling and changes in ciliary G protein-coupled receptor (GPCR) signaling. We highlight several recent studies that have implicated the potential for cilia in peripheral tissues such as adipose and the pancreas to contribute to metabolic dysfunction. Then we discuss the potential for cilia to impact energy homeostasis through their roles in both development and adult tissue homeostasis. The studies discussed in this review highlight how a comprehensive understanding of the requirement of cilia for the regulation of diverse biological functions will contribute to our understanding of common forms of obesity.

Deciphering the Relationship between Obesity and Various Diseases from a Network Perspective

The number of obesity cases is rapidly increasing in developed and developing countries, thereby causing significant health problems worldwide. The pathologic factors of obesity at the molecular level are not fully characterized, although the imbalance between energy intake and consumption is widely recognized as the main reason for fat accumulation. Previous studies reported that obesity can be caused by the dysfunction of genes associated with other diseases, such as myocardial infarction, hence providing new insights into dissecting the pathogenesis of obesity by investigating its associations with other diseases. In this study, we investigated the relationship between obesity and diseases from Online Mendelian Inheritance in Man (OMIM) databases on the protein–protein interaction (PPI) network. The obesity genes and genes of one OMIM disease were mapped onto the network, and the interaction scores between the two gene sets were investigated on the basis of the PPI of individual gene pairs, thereby inferring the relationship between obesity and this disease. Results suggested that diseases related to nutrition and endocrine are the top two diseases that are closely associated with obesity. This finding is consistent with our general knowledge and indicates the reliability of our obtained results. Moreover, we inferred that diseases related to psychiatric factors and bone may also be highly related to obesity because the two diseases followed the diseases related to nutrition and endocrine according to our results. Numerous obesity–disease associations were identified in the literature to confirm the relationships between obesity and the aforementioned four diseases. These new results may help understand the underlying molecular mechanisms of obesity–disease co-occurrence and provide useful insights for disease prevention and intervention.

The role of alkaline phosphatase in intracellular lipid accumulation in the human hepatocarcinoma cell line, HepG2

Inhibition of tissue non-specific alkaline phosphatase (TNALP) decreases intracellular lipid accumulation in human preadipocytes and the murine preadipocyte cell line, 3T3-L1. Therefore, the current study was performed to determine if TNALP is required for intracellular lipid deposition in the human hepatocyte cell line, HepG2. Intracellular lipid accumulation, TNALP activity and peroxisome proliferator activated receptor (PPAR) γ gene expression were measured in HepG2 and 3T3-L1 cells in the presence and absence of the TNALP inhibitors levamisole and histidine. Sub-cellular TNALP activity was localized using cytochemical analysis. Both PPARγ gene expression and TNALP activity increased during intracellular lipid accumulation in HepG2 and 3T3-L1 cells. Inhibition of TNALP blocked intracellular lipid accumulation but did not alter expression of the PPARγ gene. In HepG2 cells, TNALP co-localized with adipophilin on the lipid droplet membrane. These data suggest a role for TNALP in lipid droplet formation, possibly downstream from PPARγ, within HepG2 and 3T3-L1 cells.

Quantitative genetics of circulating Dickkopf-related protein 1 (DKK1) in community-based sample of UK twins

Dickkopf-related protein 1 (DKK1) is a major inhibitor of Wnt signalling pathway but also plays an important role in bone formation. Its circulating levels appear to correlate significantly with plasma levels of inflammatory factors, fractalkine and IL-6. This study, using a large sample of UK twins, showed that the variation of each of these factors and correlation between them was explained by the genetic factors, and indicated possible association with DKK1 gene variants.

INTRODUCTION

DKK1 is involved in the development of several inflammatory conditions related to bone and joint degradation. Our objectives were to explore the genetic contribution (heritability) to circulating DKK1 variation and its correlation with other inflammatory cytokines, interleukin 6 (IL-6) and fractalkine, and to test whether the DKK1 heritability could be attributable to single nucleotide polymorphisms (SNPs) mapped to DKK1, IL-6 and FRCT genes.

METHODS

The study included a large community-based sample of 4939 women drawn from the general UK population. Plasma samples were analysed for circulating levels of DKK1, IL-6 and fractalkine (FRCT); 65 SNPs of DKK1, IL-6 and FRCT candidate genes, with MAF >0.1, were examined. We applied variance component analysis to evaluate contribution of putative genetic (including above SNPs) and environmental factors to variation of DKK1, and its correlation with IL-6 and FRCT.

RESULTS

Putative genetic factors explained 42.2 ± 2 % of the total variation of circulating DKK1 levels, and were also significant for fractalkine and IL-6 variations. Most importantly, we report significant phenotypic (0.208 ± 0.006-0.459 ± 0.007) and genetic (0.338 ± 0.069-0.617 ± 0.033) correlations between these molecules. We found evidence suggestive of association between the DKK1 and its structural genes variants.

CONCLUSIONS

Circulating DKK1 levels correlated significantly with levels of IL-6 and FRCT, known risk factors for several inflammatory processes suggesting a potential role of DKK1 in inflammation and tissue injury. Our results suggest the contribution of genetic factors in inter-individual variation of DKK1 levels in human population. However, further studies are required to determine genetic polymorphisms affecting DKK1 variation and its correlation with IL-6 and FRCT.

Ethnic differences in pre-adipocyte intracellular lipid accumulation and alkaline phosphatase activity

Alkaline phosphatase (ALP) increases lipid accumulation in human pre-adipocytes. This study was performed to assess whether ethnic differences in the prevalence of obesity in African and European females are related to differences in pre-adipocyte lipid accretion and ALP activity. Pre-adipocytes were isolated from 13 black and 14 white females. Adipogenesis was quantified using the lipid dye, Oil red O, whilst ALP activity was assayed in cell extracts on day zero and 12days after initiating adipogenesis. Lipid levels (OD units/mg protein) were lower in pre-adipocytes from white than black females on day 0 (0.36±0.05 versus 0.44±0.03, respectively; p<0.0005) and day 12 (1.18±0.14 versus 1.80±0.22, respectively; p<0.0005), as was ALP activity (mU/mg protein) on day zero (36.5±5.8 versus 136.4±10.9, respectively; p<0.0005) and day 12 (127±16 versus 278±27, respectively; p<0.0005). Treatment of pre-adipocytes with histidine, an ALP inhibitor, blocked lipid accumulation. Thus, lipid uptake is higher in pre-adipocytes isolated from black compared to white females which parallels the obesity prevalence rates in these population groups. The reason for higher fat accumulation in pre-adipocytes isolated from black females may be related to higher ALP activity.

Genome-wide association study on serum alkaline phosphatase levels in a Chinese population

BACKGROUND

Serum alkaline phosphatase (ALP) is a complex phenotype influenced by both genetic and environmental factors. Recent Genome-Wide Association Studies (GWAS) have identified several loci affecting ALP levels; however, such studies in Chinese populations are limited. We performed a GWAS analyzing the association between 658,288 autosomal SNPs and serum ALP in 1,461 subjects, and replicated the top SNPs in an additional 8,830 healthy Chinese Han individuals. The interactions between significant locus and environmental factors on serum ALP levels were further investigated.

RESULTS

The association between ABO locus and serum ALP levels was replicated (P = 2.50 × 10⁻²¹, 1.12 × 10⁻⁵⁶ and 2.82 × 10⁻²⁷ for SNP rs8176720, rs651007 and rs7025162 on ABO locus, respectively). SNP rs651007 accounted for 2.15% of the total variance of serum ALP levels independently of the other 2 SNPs. When comparing our findings with previously published studies, ethnic differences were observed across populations. A significant interaction between ABO rs651007 and overweight and obesity was observed (FDR for interaction was 0.036); for individuals with GG genotype, those with normal weight and those who were overweight or obese have similar serum ALP concentrations; minor allele A of rs651007 remarkably reduced serum ALP levels, but this effect was attenuated in overweight and obese individuals.

CONCLUSIONS

Our findings indicate that ABO locus is a major determinant for serum ALP levels in Chinese Han population. Overweight and obesity modifies the effect of ABO locus on serum ALP concentrations.

Common FSNP variants of fourteen Bardet-Biedl syndrome genes and adult body mass

OBJECTIVE

Bardet-Biedl syndrome (BBS) is a rare monogenic multi-systemic disorder manifesting with marked obesity. Fourteen BBS genes have been identified to date and additional loci are expected. Mutations of several BBS genes were shown to affect fat cell differentiation. The purpose was to Investigate the association between common polymorphisms in all 14 genes as a group and body weight.

DESIGN AND METHODS

We investigated association between tagging single nucleotide polymorphisms (tSNPs) located between 10 kb upstream and downstream from the transcribed sequences of each of 14 BBS genes, and body weight and fat in 2462 adult women from the UK Twins study. Significant results were further tested in a confirmation sample of 2003 women from the same cohort and additionally in the GIANT consortium population (n = 123,865).

RESULTS

105 SNPs in 14 BBS genes were selected and tested in the first cohort of women for association with the body weight and fat related phenotypes, i.e. weight, body mass index (BMI), total body fat (assessed by DEXA), total fat/height(2), and total fat/weight. We used principal component (PC) derived using the latter five traits as a primary phenotype for this study. Of the 105 SNPs, 3 variants in BBS9 and BBS11 showed evidence of nominally significant association with elevated body weight and fat. However, none of the associations survived multiple-testing correction.

CONCLUSIONS

The results suggest that common variation in 14 BBS genes (within or adjacent to the genes) are unlikely to have a substantial effect on body weight and fat in the European population.

The interrelationship between bone and fat: from cellular see-saw to endocrine reciprocity

The number of mature osteoblasts and marrow adipocytes in bone is influenced by the differentiation of the common mesenchymal progenitor cell towards one phenotype and away from the other. Consequently, factors which promote adipogenesis not only lead to fatty marrow but also inhibit osteoblastogenesis, resulting in decreased osteoblast numbers, diminished bone formation and, potentially, inadequate bone mass and osteoporosis. In addition to osteoblast and bone adipocyte numbers being influenced by this skewing of progenitor cell differentiation towards one phenotype, mature osteoblasts and adipocytes secrete factors which may evoke changes in the cell fate and function of each other. This review examines the endogenous factors, such as PPAR-γ2, Wnt, IGF-1, GH, FGF-2, oestrogen, the GP130 signalling cytokines, vitamin D and glucocorticoids, which regulate the selection between osteoblastogenesis and adipogenesis and the interrelationship between fat and bone. The role of adipokines on bone, such as adiponectin and leptin, as well as adipose-derived oestrogen, is reviewed and the role of bone as an energy regulating endocrine organ is discussed.

Significant association between body composition phenotypes and the osteocalcin genomic region in normative human population

Osteocalcin, a major inorganic component of bone matrix and marker of bone formation, is also involved in regulation of glucose and fat mass metabolism. However, much uncertainty remains about whether the above effect on fat mass has a genetic component. Our main aim was to test whether a variation of body composition phenotypes is associated with BGLAP genomic region variants. To achieve this aim, we used an ethnically homogeneous discovery sample of 230 families consisting of 1112 apparently healthy individuals (561 males and 551 females) of European origin. We conducted association analysis between six SNPs and five obesity-related phenotypes: plasma levels of leptin, anthropometrical fat mass (FM), principal component scores of eight skinfold (SK_PC) and nine circumference (CR_PC) measurements, and body mass index (BMI). Two powerful and robust tools were applied: the pedigree disequilibrium test and variance component models, taking into account both familial and genetic effects. Significant association results were observed for all phenotypes. The most significant results were observed between the haplotype composed of three SNPs (rs2758605-rs1543294-rs2241106) and BMI (p=8.07(-7)), and CR_PC (p=5.29(-5)). The association with BMI was tested and confirmed in our replication study, including 2244 unrelated adult US Caucasians, who were previously assessed for whole genome SNP data. In addition, we obtained an evidence of potential non-additive interactions between the above three SNPs concerning their association with BMI. Bioinformatics sources suggest that the aforementioned interaction could originate from different genetic loci in this region; however, ascertaining the exact circumstances requires a detailed molecular-genetic study.

Association of FTO gene variants with body composition in UK twins

The association of FTO gene variants with body mass index (BMI) and other obesity characteristics is well established. However, uncertainties remain whether the association is present only in young populations and whether it is attributable to body fat mass specifically. We aimed to clarify these two questions in a large sample (N= 4,523 individuals) of middle-aged and older (range 40–80 years) British female twins. The women were assessed for BMI, waist and hip circumference, total lean (LBM) and fat (FBM) body mass. Since the majority of FTO association signals have been reported in a haploblock bordering 52,355–52,408 kb (on chromosome 16q12.2), we examined five genotyped and 43 imputed SNPs mapped to this block. Canonical correlation and other association analyses showed significant and consistent association between the selected SNP and studied body composition phenotypes, with p-values reaching p= 0.000004. Of particular interest, in addition to the expected significant associations between FTO variants and FBM, we also identified significant associations with LBM. These results suggest that the association between FTO variants and body composition phenotypes is present across a wide range of ages, and that FTO appears primarily to affect the amount of body soft tissue, influencing both fat and lean mass.

A significant association exists between receptor tyrosine kinase-like orphan receptor 2 gene variants and the OPG/RANKL ratio in human plasma

SUMMARY

There is a paucity of studies investigating association between ROR2 gene variants and osteoporosis and osteoarthritis-related phenotypes. The published literature suggests that osteoprotegerin (OPG) and receptor activator of nuclear factor-kB ligand (RANKL) are essential for bone metabolism and correlate with osteoarthritis manifestation and progression. The present study provides evidence of the significant association between ROR2 variants and the OPG/RANKL ratio in human plasma. The present results also suggest significant association between ROR2 polymorphisms and severity of radiographic hand osteoarthritis.

INTRODUCTION

Despite the importance of the ROR-2 in skeletal physiology, there is a paucity of studies investigating the potential association of ROR2 gene variants with phenotypes relevant to osteoporosis and osteoarthritis. On the other hand, there is a considerable body of literature suggesting that OPG and RANKL and their ratio (OPG/RANKL) are essential for regulating bone resorption. This is also correlated with osteoarthritis manifestation and progression. The present study therefore examines whether ROR2 polymorphisms may be associated with the OPG/RANKL ratio and hand osteoarthritis (HOA).

METHODS

The study was conducted in a family-based sample of 1,515 Caucasian individuals, assessed for radiographic hand osteoarthritis, using the Kellgren/Lawrence score. Of these, 865 individuals were genotyped for 19 SNPs, relatively equally covering the ROR2 locus, and their plasma levels of OPG and RANKL were assayed. The association between the selected SNPs and OPG, along with the OPG/RANKL ratio and HOA, was explored using the pedigree disequilibrium test.

RESULTS

Of the total of 57 tests, 16 nominally significant results (p < 0.05) were obtained, which is considerably more than the three normally expected for type I error. The significant association signals for all three phenotypes were mapped to the intron 1 region. The most significant results were detected between OPG/RANKL and rs7048756 (p < 0.0005) and between adjacent rs4744107 and Kellgren/Lawrence score (p = 0.006).

CONCLUSIONS

The present study provides evidence of the significant association between ROR2 variants and the OPG/RANKL ratio in human plasma and also suggests ROR2 association with HOA.

Quantitative genetic study of the circulating osteopontin in community-selected families

The study assessed contribution of genetic factors to variability of osteopontin (OPN) levels. Evidence of association of OPN levels with polymorphisms in its structural gene and integrin-binding sialoprotein gene loci was obtained. The results motivate research of OPN-related proteins and genes with respect to biomineralization and other biological processes.

INTRODUCTION

OPN is a major phosphoprotein in bone, which plays key role in regulation of bone mineralization process. It is considered as a promising biomarker for osteoarthritis and osteoporosis, and various other pathological conditions. However, the contribution of genetics and other confounding factors to OPN circulating levels variation in general population has never been specifically determined. The main aims of the present study included (1) evaluation of the putative genetic and familial factors' effect on OPN variability and (2) testing the hypothesis that OPN plasma levels are associated with the genetic polymorphisms in its structural gene locus (SPP1) and in integrin-binding sialoprotein gene locus (IBSP).

METHODS

To address these questions, we used a family-based sample of 925 apparently healthy Caucasian individuals. Association of OPN levels with three SNPs in each of the two selected gene loci was explored using pedigree disequilibrium tests.

RESULTS

Some 58% and 13% of the OPN levels variability were attributable to genetic factors and common spouse environment, respectively. Three SNPs showed nominally significant association with OPN (p < 0.05). Of these, rs2616262 linked to IBSP promoter region remained significant after correction for multiple testing (p = 0.003). Significant association of this SNP and rs10516799 (distal segment of SPP1) with OPN was confirmed in several statistical tests. Using a special modification of variance component analysis, we examined gene-gene and gene-sex interaction effects, but found non-significant confirmation for these hypotheses.

CONCLUSIONS

Further studies are required to confirm the observed results and to explore the underlying molecular and physiological mechanisms.

Quantitative genetic study of amphiregulin and fractalkine circulating levels--potential markers of arthropathies

OBJECTIVE

Amphiregulin (AREG) and Fractalkine (FRACT), are involved in a variety of normal and pathological processes, and are both suggested to be relevant to joint degeneration. The aims of the present study included (1) testing association between circulating levels of these biomarkers and joint pathologies, (2) evaluation of the putative genetic and familial factors' effect on AREG and FRACT variability.

DESIGN

The study was conducted in the family-based sample of 923 Caucasian individuals. Variance component analysis was used to assess contribution of genetic and environmental factors to variability of AREG and FRACT concentration.

RESULTS

The mean levels of FRACT were significantly higher in the affected group with arthropathies (synovial joints osteoarthritis (OA) and disc degenerative disease, DDD) then in the control group (P<0.0004). Circulating AREG levels were higher in DDD (P=0.0272). Genetic factors constituted the main source of the interindividual differences of the AREG and FRACT levels in our sample, and explained 29.68% and 41.68% of the total variation, respectively. The phenotypic correlation between AREG and FRACT was substantial (r=0.55, P=0.0001) and was associated with both common genetic and environmental factors. Specifically, 30% of the phenotypic correlation between AREG and FRACT was due to common genetic effects.

CONCLUSIONS

Further studies are required to assess relevancy of FRACT to clinical diagnosis and prognosis of arthropathies, to investigate the mechanisms behind the observed phenotypic and genetic covariation among the studied biomarkers, and to explore specific genetic polymorphisms affecting AREG and FRACT variation.