Identification of epistatic interaction involved in obesity using the KK/Ta mouse as a Type 2 diabetes model: is Zn-alpha2 glycoprotein-1 a candidate gene for obesity?

Genome-wide association study reveals genetic loci and candidate genes for meat quality traits in a four-way crossbred pig population

Meat quality traits (MQTs) have gained more attention from breeders due to their increasing economic value in the commercial pig industry. In this genome-wide association study (GWAS), 223 four-way intercross pigs were genotyped using the specific-locus amplified fragment sequencing (SLAF-seq) and phenotyped for PH at 45 min post mortem (PH45), meat color score (MC), marbling score (MA), water loss rate (WL), drip loss (DL) in the longissimus muscle, and cooking loss (CL) in the psoas major muscle. A total of 227, 921 filtered single nucleotide polymorphisms (SNPs) evenly distributed across the entire genome were detected to perform GWAS. A total of 64 SNPs were identified for six meat quality traits using the mixed linear model (MLM), of which 24 SNPs were located in previously reported QTL regions. The phenotypic variation explained (PVE) by the significant SNPs was from 2.43% to 16.32%. The genomic heritability estimates based on SNP for six meat-quality traits were low to moderate (0.07-0.47) being the lowest for CL and the highest for DL. A total of 30 genes located within 10 kb upstream or downstream of these significant SNPs were found. Furthermore, several candidate genes for MQTs were detected, including pH45 (GRM8), MC (ANKRD6), MA (MACROD2 and ABCG1), WL (TMEM50A), CL (PIP4K2A) and DL (CDYL2, CHL1, ABCA4, ZAG and SLC1A2). This study provided substantial new evidence for several candidate genes to participate in different pork quality traits. The identification of these SNPs and candidate genes provided a basis for molecular marker-assisted breeding and improvement of pork quality traits.

Differential Gene Expression Associated with Soybean Oil Level in the Diet of Pigs

Simple Summary

Findings from the analysis of the pig transcriptome may help to better understand the biological mechanisms that can be modulated by the diet. Thus, the aim of this study was to identify the differentially expressed genes from the skeletal muscle and liver samples of pigs fed diets with two different levels of soybean oil (1.5 or 3%). The FA profile in the tissues was modified by the diet mainly related to monounsaturated (MUFA) and polyunsaturated (PUFA). This nutrigenomics study verified the effect of different levels of soybean oil in the pig diet on the transcriptome profile of skeletal muscle and liver, where the higher level of soybean oil added to the diet led to a higher expression of genes targeting biological processes related to lipid oxidation and consequently to metabolic diseases and inflammation.

Abstract

The aim of this study was to identify the differentially expressed genes (DEG) from the skeletal muscle and liver samples of animal models for metabolic diseases in humans. To perform the study, the fatty acid (FA) profile and RNA sequencing (RNA-Seq) data of 35 samples of liver tissue (SOY1.5, n = 17 and SOY3.0, n = 18) and 36 samples of skeletal muscle (SOY1.5, n = 18 and SOY3.0, n = 18) of Large White pigs were analyzed. The FA profile of the tissues was modified by the diet, mainly those related to monounsaturated (MUFA) and polyunsaturated (PUFA) FA. The skeletal muscle transcriptome analysis revealed 45 DEG (FDR 10%), and the functional enrichment analysis identified network maps related to inflammation, immune processes, and pathways associated with oxidative stress, type 2 diabetes, and metabolic dysfunction. For the liver tissue, the transcriptome profile analysis revealed 281 DEG, which participate in network maps related to neurodegenerative diseases. With this nutrigenomics study, we verified that different levels of soybean oil in the pig diet, an animal model for metabolic diseases in humans, affected the transcriptome profile of skeletal muscle and liver tissue. These findings may help to better understand the biological mechanisms that can be modulated by the diet.

Construction and Analysis of a Joint Diagnosis Model of Random Forest and Artificial Neural Network for Obesity

Obesity is a significant global health concern since it is connected to a higher risk of several chronic diseases. As a consequence, obesity may be described as a condition that reduces human life expectancy and significantly impacts life quality. Because traditional obesity diagnosis procedures have several flaws, it is vital to design new diagnostic models to enhance current methods. More obesity-related markers have been discovered in recent years as a result of improvements and enhancements in gene sequencing technology. Using current gene expression profiles from the Gene Expression Omnibus (GEO) collection, we identified differentially expressed genes (DEGs) associated with obesity and found 12 important genes (CRLS1, ANG, ALPK3, ADSSL1, ABCC1, HLF, AZGP1, TSC22D3, F2R, FXN, PEMT, and SPTAN1) using a random forest classifier. ALPK3, HLF, FXN, and SPTAN1 are the only genes that have never been linked to obesity. We also used an artificial neural network to build a novel obesity diagnosis model and tested its diagnostic effectiveness using public datasets.

Associations of zinc-α-2-glycoprotein with metabolic syndrome and its components among adult Arabs

Epidemiological studies suggest that the Zinc-α-2-glycoprotein (ZAG) plays significant physiological roles. In this study we investigate whether ZAG could be considered as a clinical biomarker in the diagnosis and prognosis of metabolic syndrome (MetS) in Saudi population. As such insights urgently required for management of MetS. Thus, we have determined serum levels of ZAG in patients with MetS and normal individuals. We have also assessed the correlation between ZAG and different components of MetS. In this case–control study, clinical information of 200 Saudi male and female subjects (age range 30–65) with MetS (n = 100) and healthy controls (n = 100) were extracted from the database of the Chair of Biomarkers of Chronic Disease (CBCD) in King Saud University (KSU), Riyadh, Saudi Arabia. MetS was screened according to NCEP ATP III criteria (National Cholesterol Education Program Adult Treatment Panel III). Fasting glucose and lipid profile levels were measured using Konelab. Serum TNF-α, IL- 6, CRP and ZAG levels were measured using commercially available assays. There was an age-dependent significant increase in ZAG level among MetS subjects than controls (43.8 ± 19.5 vs 48.1 ± 14.8; P = 0.04). A significant inverse correlation between ZAG and serum HDL-cholesterol (r = − 0.20, P < 0.05) was observed. Whereas, triglycerides (r = 0.25, P < 0.01), waist circumference (WHR) (r = 0.17, P < 0.05) and CRP (r = 0.24, P < 0.01) were all significantly and positively associated with ZAG. Circulating ZAG is associated with MetS in an age-dependent manner. Serum ZAG is a potential biomarker for MetS.

Zinc and the Innovative Zinc-α2-Glycoprotein Adipokine Play an Important Role in Lipid Metabolism: A Critical Review

Numerous studies indicate that zinc and the new zinc-related adipokine, zinc-α2-glycoprotein (ZAG), are involved in lipid metabolism. Excess body fat lowers blood concentrations of Zn and ZAG, leading not only to the development of obesity but also to other components of the metabolic syndrome. Zinc homeostasis disorders in the body negatively affect the lipid profile and cytokine secretion. Zinc appears to be a very important ZAG homeostasis regulator. The physiological effects of ZAG are related to lipid metabolism, but studies show that ZAG also affects glucose metabolism and is linked to insulin resistance. ZAG has a zinc binding site in its structure, which may indicate that ZAG mediates the effect of zinc on lipid metabolism. The review aimed to verify the available studies on the effects of zinc and ZAG on lipid metabolism. A literature review within the scope of this research area was conducted using articles available in PubMed (including MEDLINE), Web of Science and Cochrane Library databases. An analysis of available studies has shown that zinc improves hepatic lipid metabolism and has an impact on the lipid profile. Numerous studies have found that zinc supplementation in overweight individuals significantly reduced blood levels of total cholesterol, LDL (Low-density lipoprotein)cholesterol and triglycerides, potentially reducing cardiovascular morbidity and mortality. Some results also indicate that it increases HDL-C (High-density lipoprotein) cholesterol levels. ZAG has been shown to play a significant role in reducing obesity and improving insulin sensitivity, both in experimental animal model studies and in human studies. Furthermore, ZAG at physiologically relevant concentrations increases the release of adiponectin from human adipocytes. In addition, ZAG has been shown to inhibit in vitro leptin production. Further studies are needed to provide more data on the role of zinc and zinc-α2-glycoprotein.

Zinc-α2-Glycoprotein Knockout Influenced Genes Expression Profile in Adipose Tissue and Decreased the Lipid Mobilizing After Dexamethasone Treatment in Mice

Zinc-α2-glycoprotein (ZAG), as an adipokine, plays an important role in lipid metabolism. However, its influence on whole gene expression profile in adipose tissue is not known. Under stress condition, how ZAG affects the lipid metabolism is also unclear. Therefore, in this study ZAG systemic knockout (KO) mice were used as a model to reveal the genes expression profile in visceral fat tissues of ZAG KO mice and wild-type mice by genome-wide microarray screening. Then dexamethasone (DEX) was used to explore the effect of ZAG deletion on body fat metabolism under stress. Our results showed that 179 genes were differentially expressed more than 1.5 times between ZAG KO mice and wild type mice, of which 26 genes were upregulated dramatically and 153 genes were significantly downregulated. Under DEX simulated stress, ZAG systemic knockout in vivo resulted in a markedly decrease of triglycerides (TG) and nonesterified fatty acid (NEFA) content in in plasma. Similarly, for lipid catabolism, ZAG KO led to a significant increase of phosphorylated HSL (p-HSL) protein and a rising tendency of adipose triglyceride lipase (ATGL) protein relative to those of the DEX group. For lipid anabolism, fatty acid synthase (FAS) and adiponectin protein expression in visceral fat rose notably in ZAG KO mice after DEX treatment. In conclusion, ZAG knockout can affect the gene expression profile of adipose tissue, reduce elevated TG and NEFA levels in plasma, and alter lipid metabolism under DEX treatment. These findings provide new insights into the mechanism of lipid metabolic disorders in response to stress.

The Construction and Analysis of the Aberrant lncRNA-miRNA-mRNA Network in Adipose Tissue from Type 2 Diabetes Individuals with Obesity

BACKGROUND

The prevalence of obesity and type 2 diabetes mellitus (T2DM) has become the most serious global public health issue. In recent years, there has been increasing attention to the role of long noncoding RNAs (lncRNAs) in the occurrence and development of obesity and T2DM. The aim of this work was to find new lncRNAs as potential predictive biomarkers or therapeutic targets for obesity and T2DM.

METHODS

In this study, we identified significant differentially expressed mRNAs (DEmRNAs) and differentially expressed lncRNAs (DElncRNAs) between adipose tissue of individuals with obesity and T2DM and normal adipose tissue (absolute log₂FC ≥ 1 and FDR < 0.05). Then, the lncRNA-miRNA interactions predicted by miRcode were further screened with a threshold of MIC > 0.2. Simultaneously, the mRNA-miRNA interactions were explored by miRWalk 2.0. Finally, a ceRNA network consisting of lncRNAs, miRNAs, and mRNAs was established by integrating lncRNA-miRNA interactions and mRNA-miRNA interactions.

RESULTS

Upon comparing adipose tissue from individuals with obesity and T2DM and normal adipose tissues, 364 significant DEmRNAs, including 140 upregulated and 224 downregulated mRNAs, were identified in GSE104674; in addition, 231 significant DEmRNAs, including 146 upregulated and 85 downregulated mRNAs, were identified in GSE133099. GO and KEGG analyses have shown that downregulated DEmRNAs in GSE104674 and GSE133099 were associated with obesity- and T2DM-related biological pathways, such as lipid metabolism, AMPK signaling, and insulin resistance. Furthermore, 28 significant DElncRNAs, including 14 upregulated and 14 downregulated lncRNAs, were found. Based on the predicted lncRNA-miRNA and mRNA-miRNA relationships, we constructed a competitive endogenous RNA (ceRNA) network, including five lncRNAs, ten miRNAs, and 15 mRNAs. KEGG-GSEA analysis revealed that four lncRNAs (FLG-AS1, SNAI3-AS1, AC008147.0, and LINC02015) in the ceRNA network were related to the biological pathways of metabolic diseases.

CONCLUSIONS

Through ceRNA network analysis, our study identified four new lncRNAs that may be used as potential biomarkers and therapeutic targets of obesity and T2DM, thus laying a foundation for future clinical studies.

Effects of Azgp1-/-on mammary gland, adipose tissue and liver gene expression and milk lipid composition in lactating mice

The expression of Azgp1 gene, an adipokine involved in the mobilization of body reserves, was observed in mammary gland of ruminants. Its regulation by different dietary conditions suggests a potential role in the mechanisms controlling the composition of milk fat. The aim of this study was to evaluate the role of Azgp1 during lactation. Azgp1^-/- mice were compared to wild-type to determine its effects on milk fatty acid composition and offspring growth. To determine its effects on mammary gland, adipose tissue and liver gene expression, gene expression was analyzed using RT-qPCR via TLDA analyses. The body weight of Azgp1^-/- mothers was slightly higher after parturition and at 10 days of lactation compared to the wild type. The milk polyunsaturated fatty acid content was increased in Azgp1^-/- mice. Among the 40 genes studied, Azgp1^-/- modified the expression of 9, 10 and 3 genes in mammary gland, adipose tissue and liver, respectively. These genes, involved in fatty acid synthesis, transport and triglyceride synthesis, were downregulated in Azgp1^-/- mice showing a particularity during lactation. Changes in mammary gland gene expression may explain the modifications observed in milk fatty acid composition. This study supports a role of Azgp1 on lipid metabolism, in particular in mammary gland, during lactation function.

Serum ZAG Levels Were Associated with eGFR Mild Decrease in T2DM Patients with Diabetic Nephropathy

Objective. To investigate the changes of serum zinc-α2-glycoprotein (ZAG) in type 2 diabetes mellitus (T2DM) with eGFR mild decrease. Subjects and Methods. A total of 438 T2DM patients (61.3 ± 4.0 y) were recruited and the demographic, anthropometric, and biochemical parameters were all collected. Serum ZAG levels were determined by commercially available ELISA kits. Results. The proportion of T2DM patients with the high tertile ZAG levels was 11.9% higher in patients with mildly decreased estimated glomerular filtration rate (eGFR) (<90 mL/min/1.73 m²) than those with the low tertile ZAG levels (P = 0.038). The probability of the eGFR < 90 mL/min/1.73 m² in patients with the high ZAG levels was 94% higher than those with the low serum ZAG levels after adjusting for age, gender, and education [OR = 1.94, 95% CI (1.17-3.23), P = 0.0094]. This phenomenon was more likely to be observed in the condition of uACR ≥ 2.7 mg/mmol, WC ≥ 90 cm for men, or WC ≥ 85 cm for women. Conclusion. Serum ZAG levels were firstly found to be related with eGFR in T2DM patients. The patients with the high tertile ZAG levels were more likely to have mildly eGFR decrease, especially for female patients with higher uACR and bigger WC.

Short term exendin-4 treatment reduces markers of metabolic disorders in female offspring of obese rat dams

OBJECTIVES

Maternal obesity imposes significant health risks in the offspring including diabetes and dyslipidemia. We previously showed that the hypoglycaemic agent exendin-4 (Ex-4) administered from weaning can reverse the maternal impact of 'transmitted disorders' in such offspring. However daily injection for six-weeks was required and the beneficial effect may lapse upon drug withdrawal. This study aimed to investigate whether short term Ex-4 treatment during suckling period in a rodent model can reverse transmitted metabolic disorders due to maternal obesity.

METHODS

Maternal obesity was induced in female Sprague Dawley rats by high-fat diet feeding for 6 weeks, throughout gestation and lactation. Female offspring were treated with Ex-4 (5μg/kg/day) between postnatal day (P) 4 and 14. Female offspring were harvested at weaning (P20). Lipid and glucose metabolic markers were measured in the liver and fat. Appetite regulators were measured in the plasma and hypothalamus.

RESULTS

Maternal obesity significantly increased body weight, fat mass, and liver weight in the offspring. There was an associated inhibition of peroxisomal proliferator activated receptor gamma coactivator 1α (PGC1α), increased fatty acid synthase (FASN) expression in the liver, and reduced adipocyte triglyceride lipase (ATGL) expression. It also increased the plasma gut hormone ghrelin and reduced glucagon-like peptide-1. Ex-4 treatment partially reversed the maternal impact on adiposity and impaired lipid metabolism in the offspring, with increased liver PGC1α and inhibition of FASN mRNA expression. Ex-4 treatment also increased the expression of a novel fat depletion gene a2-zinc-glycoprotein 1 in the fat tissue.

CONCLUSION

Short term Ex-4 treatment during the suckling period significantly improved the metabolic profile in the offspring from the obese mothers at weaning. Long-term studies are needed to follow such offspring to adulthood to examine the sustained effects of Ex-4 in preventing the development of metabolic disease.

Omics technologies provide new insights into the molecular physiopathology of equine osteochondrosis

Background

Osteochondrosis (OC(D)) is a juvenile osteo-articular disorder affecting several mammalian species. In horses, OC(D) is considered as a multifactorial disease and has been described as a focal disruption of endochondral ossification leading to the development of osteoarticular lesions. Nevertheless, OC(D) physiopathology is poorly understood. Affected horses may present joint swelling, stiffness and lameness. Thus, OC(D) is a major concern for the equine industry. Our study was designed as an integrative approach using omics technologies for the identification of constitutive defects in epiphyseal cartilage and/or subchondral bone associated with the development of primary lesions to further understand OC(D) pathology. This study compared samples from non-affected joints (hence lesion-free) from OC(D)-affected foals (n = 5, considered predisposed samples) with samples from OC-free foals (n = 5) considered as control samples. Consequently, results are not confounded by changes associated with the evolution of the lesion, but focus on altered constitutive molecular mechanisms. Comparative proteomics and micro computed tomography analyses were performed on predisposed and OC-free bone and cartilage samples. Metabolomics was also performed on synovial fluid from OC-free, OC(D)-affected and predisposed joints.

Results

Two lesion subtypes were identified: OCD (lesion with fragment) and OC (osteochondral defects). Modulated proteins were identified using omics technologies (2-DE proteomics) in cartilage and bone from affected foals compare to OC-free foals. These were associated with cellular processes including cell cycle, energy production, cell signaling and adhesion as well as tissue-specific processes such as chondrocyte maturation, extracellular matrix and mineral metabolism. Of these, five had already been identified in synovial fluid of OC-affected foals: ACTG1 (actin, gamma 1), albumin, haptoglobin, FBG (fibrinogen beta chain) and C4BPA (complement component 4 binding protein, alpha).

Conclusion

This study suggests that OCD lesions may result from a cartilage defect whereas OC lesions may be triggered by both bone and cartilage defects, suggesting that different molecular mechanisms responsible for the equine osteochondrosis lesion subtypes and predisposition could be due to a defect in both bone and cartilage. This study will contribute to refining the definition of OC(D) lesions and may improve diagnosis and development of therapies for horses and other species, including humans.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-947) contains supplementary material, which is available to authorized users.

Proteomic profiling for peritoneal dialysate: differential protein expression in diabetes mellitus

Peritoneal dialysis (PD) is an increasingly accepted modality of renal replacement therapy. It provides the advantages of having a flexible lifestyle, stable hemodynamics, and better preservation of residual renal function. To enhance our understanding of the peritoneal dialysate of diabetes mellitus (DM), peritoneal dialysate proteins were identified by two-dimensional gel electrophoresis (2DE) combined with reverse-phase nano-ultra performance liquid chromatography electrospray ionization tandem mass spectrometry (RP-nano-UPLC-ESI-MS/MS) followed by peptide fragmentation patterning. To validate the differential proteins, ELISA and Western blotting analyses were applied to detect candidate proteins that may be related to DM. We performed 2DE on the peritoneal dialysate samples, with detection of more than 300 spots. From this, 13 spots were excised, in-gel digested, and identified by RP-nano-UPLC-ESI-MS/MS. Ten of these showed significant differential expression between the DM and chronic glomerulonephritis (CGN) peritoneal dialysate samples. In this study, we conducted a comparative proteomic study on these two groups of dialysate that may provide evidence for understanding the different peritoneal protein changes. These proteins may not be new biomarkers; however, they may indicate a situation for possible drug treatment and can be the predictors of peritonitis for a validation study in the future.

Zinc-α2-glycoprotein is associated with insulin resistance in humans and is regulated by hyperglycemia, hyperinsulinemia, or liraglutide administration: cross-sectional and interventional studies in normal subjects, insulin-resistant subjects, and subjects with newly diagnosed diabetes

OBJECTIVE

Zinc-α2-glycoprotein (ZAG) has been proposed to play a role in the pathogenesis of insulin resistance. Previous studies in humans and in rodents have produced conflicting results regarding the link between ZAG and insulin resistance. The objective of this study was to examine the relationships between ZAG and insulin resistance in cross-sectional and interventional studies.

RESEARCH DESIGN AND METHODS

Serum ZAG (determined with ELISA) was compared with various parameters related to insulin resistance in subjects with normal glucose tolerance, impaired glucose tolerance (IGT), and newly diagnosed type 2 diabetes mellitus (T2DM), and in women with or without polycystic ovary syndrome (PCOS). Euglycemic-hyperinsulinemic clamps were performed in healthy and PCOS women. Real-time RT-PCR and Western blotting were used to assess mRNA and protein expression of ZAG. The effect of a glucagon-like peptide-1 agonist on ZAG was studied in a 12-week liraglutide treatment trial.

RESULTS

Circulating ZAG was lower in patients with IGT and newly diagnosed T2DM than in controls. Circulating ZAG correlated positively with HDL cholesterol and adiponectin, and correlated inversely with BMI, waist-to-hip ratio, body fat percentage, triglycerides, fasting blood glucose, fasting insulin, HbA1c, and homeostasis model assessment of insulin resistance (HOMA-IR). On multivariate analysis, ZAG was independently associated with BMI, HOMA-IR, and adiponectin. ZAG mRNA and protein were decreased in adipose tissue of T2DM patients. Moreover, circulating ZAG levels were lower in women with PCOS than in women with high insulin sensitivity. Liraglutide treatment for 12 weeks significantly increased circulating ZAG levels.

CONCLUSIONS

We conclude that ZAG may be an adipokine associated with insulin resistance.

Genotype and haplotype analysis of the AZGP1 gene in cattle

Zinc-a2-glycoprotien (AZGP1) involved in lipid metabolism and associated with adipose tissue atrophy in cachexia. And it also related to sperm motility and in turn fertilization. To ascertain whether there were mutations in the bovine AZGP1 gene, this study investigated variation of the AZGP1 gene through PCR-SSCP and sequencing. Four missense mutations were identified in 649 cattle from six independent populations. Haplotype frequencies and linkage disequilibrium (LD) coefficients of these SNPs in three Chinese indigenous cattle breeds were analyzed. One LD block was found in three cattle breeds. The statistical analyses indicated that AC genotype of Z4 locus was associated with the high body weight, body length and chest girth in Jiaxian cattle breed (P < 0.05). Our results provided evidence that polymorphisms in the AZGP1 gene were associated with growth traits, and may be used for marker-assisted selection and management in cattle breeding program.

Serum levels of the adipokine zinc-α2-glycoprotein are increased in preeclampsia

BACKGROUND

Preeclampsia (PE) is associated with facets of the metabolic syndrome and an increased future metabolic and cardiovascular risk for mother and newborn. Recently, zinc-α2-glycoprotein (ZAG) has been proposed as a new adipokine involved in the pathogenesis of obesity.

AIM

In the current study, we investigated ZAG serum levels in PE patients as compared to healthy gestational age-matched controls.

SUBJECTS AND METHODS

We quantified serum concentrations of ZAG in patients with PE (no.=37) as compared to healthy gestational age-matched controls (no.=37) by enzyme-linked immunosorbent assay. Furthermore, association of this adipokine with renal function, glucose and lipid metabolism, as well as inflammation was studied.

RESULTS

Median serum ZAG levels were 1.4-fold higher in PE patients (58.8 mg/l) as compared to controls (41.9 mg/l) (p<0.01). Furthermore, circulating ZAG was positively correlated to systolic and diastolic blood pressure, creatinine, triglycerides, and leptin in univariate analyses. In multiple regression analysis, creatinine remained independently associated with ZAG.

CONCLUSIONS

We demonstrate that maternal ZAG serum concentrations are significantly increased in PE. Furthermore, renal function is an independent predictor of circulating ZAG.

Zinc-alpha 2-glycoprotein gene expression in adipose tissue is related with insulin resistance and lipolytic genes in morbidly obese patients

Objective

Zinc-α₂ glycoprotein (ZAG) stimulates lipid loss by adipocytes and may be involved in the regulation of adipose tissue metabolism. However, to date no studies have been made in the most extreme of obesity. The aims of this study are to analyze ZAG expression levels in adipose tissue from morbidly obese patients, and their relationship with lipogenic and lipolytic genes and with insulin resistance (IR).

Methods

mRNA expression levels of PPARγ, IRS-1, IRS-2, lipogenic and lipolytic genes and ZAG were quantified in visceral (VAT) and subcutaneous adipose tissue (SAT) of 25 nondiabetic morbidly obese patients, 11 with low IR and 14 with high IR. Plasma ZAG was also analyzed.

Results

The morbidly obese patients with low IR had a higher VAT ZAG expression as compared with the patients with high IR (p = 0.023). In the patients with low IR, the VAT ZAG expression was greater than that in SAT (p = 0.009). ZAG expression correlated between SAT and VAT (r = 0.709, p<0.001). VAT ZAG expression was mainly predicted by insulin, HOMA-IR, plasma adiponectin and expression of adiponectin and ACSS2. SAT ZAG expression was only predicted by expression of ATGL.

Conclusions

ZAG could be involved in modulating lipid metabolism in adipose tissue and is associated with insulin resistance. These findings suggest that ZAG may be a useful target in obesity and related disorders, such as diabetes.

rs4215 SNP in zinc-α2-glycoprotein gene is associated with obesity in Chinese north Han population

OBJECTIVE

Zinc-α2-glycoprotein (ZAG) has been identified recently as a novel adipokine due to its close link with lipid and glucose metabolism, as well as regulation of body weight. The aim of our present study is to investigate the ZAG genetic polymorphism association with obesity in Chinese north Han population.

DESIGN AND METHODS

Five SNPs of ZAG gene including rs2247607 (A>T), rs4727442 (G>T), rs4215 (A>G), rs2527923 (C>T) and rs2527882 (C>T) were genotyped in 648 overweight/obese patients and 313 healthy controls by TaqMan-PCR methods. Crosstabs statistical analysis method with subjects stratifying by age (≦ 30 y, 31-45 y, ≧ 46 y) and gender was used.

RESULTS

The results showed the constitution of three genotype frequencies in rs4215 (A>G) site significantly differs in male subgroup (aged 31-45 y) between overweight/obese and healthy control group (χ(2)=6.401, P=0.041). GG genotype frequency in overweight/obese group is 19.3% which is much higher than 6.1% in healthy control group. Further statistical analysis under a recessive inheritance model demonstrated odd ratio (OR) for GG vs. AA+AG in overweight/obese group was 3.674 (95% CI 1.049-12.866; P=0.035). Among three genotypes of rs4215, the subjects with GG genotype have much more higher body weight, BMI, waist circumference and SBP.

CONCLUSION

Our data, for the first time, suggest the genotypes of rs4215 in ZAG gene are significantly associated with obesity in Chinese north Han population. GG genotype subjects in rs4215 site have an increased susceptibility to obesity when compared with the AA+AG genotype subjects.

Is zinc-α2-glycoprotein a cardiovascular protective factor for patients undergoing hemodialysis?

BACKGROUND

Zinc-α2-glycoprotein (ZAG) is a lipid mobilizing factor. Its anti-inflammatory action and expression pattern suggest that ZAG could act by protecting against the obesity-associated disorders. In hemodialysis (HD) patients, ZAG levels were described to be elevated but its effects on markers of inflammation and LDL oxidation are still unclear. We investigated the relationship between ZAG and markers of systemic inflammation and LDL atherogenic modification profile in HD patients.

METHODS

Forty-three patients regularly on HD were studied and compared to 20 healthy subjects. Plasma ZAG, adiponectin, electronegative LDL [LDL(-)], an atherosclerotic negatively charged LDL subfraction, and anti-LDL(-) autoantibodies levels were measured by ELISA. Markers of inflammation and atherogenic cell recruitment (TNF-α, interleukin-6, VCAM-1, ICAM-1, MCP-1 and PAI-1) were also determined.

RESULTS

Inflammatory markers and atherogenic cell recruitment were higher in HD patients when compared to healthy subjects. ZAG levels were also higher in HD patients (151.5 ± 50.1 mg/l vs 54.6 ± 23.0 mg/l; p<0.0001) and its levels were negatively correlated with TNF-α (r=-0.39; p=0.001) and VCAM-1 (r=-0.52; p<0.0001) and, positively correlated with anti-LDL(-) autoantibodies (r=0.38; p=0.016). On multivariate analyses, plasma ZAG levels were independently associated with VCAM-1 (p=0.01).

CONCLUSION

ZAG is inversely associated with markers of pro-atherogenic factors linked to systemic inflammation and oxidative stress. Thus, this adipokine may constitute a novel marker of a favorable metabolic profile regarding cardiovascular risk factors in HD population.

Weight loss precedes cancer-specific symptoms in pancreatic cancer-associated diabetes mellitus

OBJECTIVES

New-onset diabetes mellitus (DM) may herald pancreatic cancer (PaC). We determined whether changes in body weight distinguished PaC-associated DM (PaCDM) from type 2 DM.

METHODS

Among Olmsted County residents, we identified 29 PaCDM and 43 type 2 DM subjects who had serial fasting blood glucose measurements, new-onset DM, and no cancer-specific symptoms at DM onset. We compared body weight (kg) and fasting blood glucose (mg/dL) at DM onset, 1 to 2 years before and at index date in the 2 groups.

RESULTS

Fasting blood glucose values were similar before and at the onset of DM. Before onset of DM, PaCDM and type 2 DM subjects had similar body weight (P = 0.80). However, at onset of DM, 59% of PaCDM subjects lost weight versus 30% of type 2 DM subjects (P = 0.02). At onset of DM, 56% of type 2 DM subjects gained weight versus 31% of PaCDM subjects (P = 0.04). By index date, PaCDM subjects lost more weight than type 2 DM subjects did (8.3 ± 8.3 vs 0.8 ± 4.8 kg, P < 0.01).

CONCLUSIONS

Although new-onset primary type 2 DM is typically associated with weight gain, weight loss frequently precedes onset of PaCDM. The paradoxical development of diabetes in the face of ongoing weight loss may be an important clue to understanding the pathogenesis of PaCDM.

Plasma proteome analysis in diet-induced obesity-prone and obesity-resistant rats

One of the major issues in the field of obesity is why some humans become obese and others resist development of obesity when exposed to high-calorie diets. Despite the same genetic background, namely obesity-prone (OP) and -resistant (OR) rats, differing responses have been demonstrated in a high fat diet-induced rodent model. The aim of the present study was to discover novel obesity-related biomarkers for susceptibility and/or resistance to obesity by proteomic analysis of OP and OR rat plasma. After feeding of high fat diet, OP rats gained approximately 25% more body weight than OR rats and were used for proteomic analysis using 2-DE combined with MALDI-TOF-MS. We categorized identified proteins into three groups by analysis of both average spot density in each group and individual spot density of six rats as a function of body weight. Consequently, category (1) included inter-α-inhibitor H4 heavy chain and fetuin B precursor, which can be used as novel plasma biomarkers for risk of obesity. Nine proteins of category (2) and (3) can also be plausible plasma markers in the study of obesity. This proteomic study is an important advancement over the previous steps needed for identification of OP and OR rats.

Studies on the anti-obesity activity of zinc-α2-glycoprotein in the rat

OBJECTIVE

To investigate the anti-obesity effect of the adipokine zinc-α(2)-glycoprotein (ZAG) in rats and the mechanism of this effect.

SUBJECTS

Mature male Wistar rats (540 ± 83 g) were administered human recombinant ZAG (50 μg per 100 g body weight given intravenously daily) for 10 days, while control animals received an equal volume of phosphate-buffered saline (PBS).

RESULTS

Animals treated with ZAG showed a progressive decrease in body weight, without a decrease in food and water intake, but with a 0.4 °C rise in body temperature. Body composition analysis showed loss of adipose tissue, but an increase in lean body mass. The loss of fat was due to an increase in lipolysis as shown by a 50% elevation of plasma glycerol, accompanied by increased utilization of non-esterified fatty acids, as evidenced by the 55% decrease in plasma levels. Plasma levels of glucose and triglycerides were also reduced by 36-37% and there was increased expression of the glucose transporter 4 in both skeletal muscle and adipose tissue. Expression of the lipolytic enzymes adipose triglyceride lipase and hormone-sensitive lipase in the white adipose tissue (WAT) were increased twofold after ZAG administration. There was almost a twofold increased expression of uncoupling proteins 1 and 3 in brown adipose tissue and WAT, which would contribute to increased substrate utilization. Administration of ZAG increased ZAG expression twofold in the gastrocnemius muscle, BAT and WAT, which was probably necessary for its biological effect.

CONCLUSION

These results show that ZAG produces increased lipid mobilization and utilization in the rat.

Preliminary report: Zn-alpha2-glycoprotein genotype and serum levels are associated with serum lipids

Zn-alpha2-glycoprotein (ZAG) is a serum protein implicated in cancer cachexia and lipolysis. Our aim was to investigate serum levels of ZAG and polymorphisms in the ZAG gene in relation to serum lipids in man. Serum levels of ZAG correlated with serum levels of cholesterol (P = .00088) in healthy subjects and during weight loss (P = .059). The ZAG genotype was associated with total cholesterol (P = .014) and low-density lipoprotein cholesterol (P = .026) in healthy subjects, and the associations were replicated in an additional cohort (P = .0017 and P = .060, respectively). Our data indicate that ZAG plays a role in lipid metabolism.

Studies on the antiobesity effect of zinc-α2-glycoprotein in the ob/ob mouse

OBJECTIVE

To investigate the mechanism of the lipid depletion by zinc-α(2)-glycoprotein (ZAG).

DESIGN

Studies were conducted in the ob/ob mouse, or on isolated adipocytes from these animals or their lean counterparts.

RESULTS

Treatment of these animals for 15 days with ZAG (100  μg, intravenously, daily) resulted in a reduction of body weight of 6.55  g compared with phosphate-buffered saline-treated controls, without a change in food or water intake, but with a 0.4 °C rise in rectal temperature. ZAG-treated mice had a 30% reduction in carcass fat mass and a twofold increase in weight of brown adipose tissue. Epididymal adipocytes from ZAG-treated mice showed an increased expression of ZAG and hormone-sensitive lipase (HSL), and this was maintained for a further 3 days in the absence of ZAG. There was an increased lipolytic response to isoproterenol, which was retained for 3 days in vitro in the absence of ZAG. Expression of HSL was also increased in subcutaneous and visceral adipose tissue, as was also adipose triglyceride lipase (ATGL). There was a rapid loss of labelled lipid from epididymal adipose tissue of ZAG-treated mice, but not from the other depots, reflecting the difference in sensitivity to lipolytic stimuli. The increased expression of HSL and ATGL may involve the extracellular signal-regulated kinase (ERK) pathway, as the active (phospho) form was upregulated in all adipose depots after ZAG administration, whereas in vitro studies showed induction of HSL and ATGL by ZAG to be attenuated by PD98059, an inhibitor of the ERK pathway.

CONCLUSION

These results suggest that ZAG not only induces direct lipolysis, but also sensitizes adipose tissue to other lipolytic stimuli.

Zinc-α2-glycoprotein: an adipokine modulator of body fat mass?

The importance of white adipose tissue in the control of energy balance is now firmly recognized. In addition to fuel storage, adipocytes secrete an array of proteins factors (adipokines), which regulate multiple physiological and metabolic processes as well as influence body fat accumulation. Zinc-α2-glycoprotein (ZAG), a lipid mobilizing factor initially characterized as a tumor product associated with cachexia, has recently been identified as a novel adipokine. Although the exact role of ZAG in adipose tissue remains to be clarified, there is evidence that ZAG expression appears to be inversely related to adiposity, being upregulated in cachexia whereas reduced in obesity. Investigations on the regulation of ZAG give insights into its potential function in adipose tissue with a link to lipid mobilization and an anti-inflammatory action. Recent work shows that ZAG stimulates adiponectin secretion by human adipocytes. Data from genetic studies suggest that ZAG may be a candidate gene for body weight regulation; this is supported by the demonstration that ZAG-knockout mice are susceptible to weight gain, whereas transgenic mice overexpressing ZAG exhibit weight loss. The present review summarizes these new perspectives of ZAG and the potential mechanisms by which it might modulate adipose tissue mass and function.

The adipokine zinc-alpha2-glycoprotein (ZAG) is downregulated with fat mass expansion in obesity

INTRODUCTION

Zinc-alpha2-glycoprotein (ZAG) is a novel adipokine, which may act locally to influence adipocyte metabolism. This study assessed the effect of increased adiposity on ZAG expression in adipose tissue in human subjects. The study also examined the association between ZAG and adiponectin expression in human adipose tissue, and whether ZAG modulates adiponectin secretion by human adipocytes.

METHODS

Adipose tissue (visceral and subcutaneous) was collected from human subjects with a wide range of BMIs. Human Simpson-Golabi-Behmel syndrome (SGBS) adipocytes were used for in vitro studies. ZAG mRNA levels were quantified by real-time PCR and protein by Western blotting.

RESULTS

In human subjects, ZAG mRNA level was negatively correlated with BMI (r = -0.61, P < 0.001, n = 23, visceral; r = -0.6, P < 0.05, n = 14, subcutaneous) and fat mass (r = -0.62, P < 0.01, visceral; r = -0.6, P < 0.05, subcutaneous). Negative associations were also found between ZAG mRNA and insulin resistance parameters including plasma insulin (r = -0.65, P < 0.001, visceral; r = -0.55, P < 0.05, subcutaneous) and homeostasis model of insulin resistance (HOMA-IR) (r = -0.65, P < 0.001, visceral; r = -0.52, P = 0.055, subcutaneous), and C reactive protein (CRP) (r = -0.46, P < 0.05, visceral; r = -0.53, P < 0.05, subcutaneous). However, ZAG mRNA was positively correlated with adiponectin (r = 0.5, P < 0.05, visceral; r = 0.82, P < 0.001, subcutaneous) but negatively associated with leptin mRNA (r = -0.42, P < 0.05, visceral; r = -0.54, P < 0.05, subcutaneous). ZAG secretion by differentiated human adipocytes was abundant. Addition of recombinant ZAG stimulated adiponectin release from human adipocytes.

CONCLUSION

ZAG gene expression in adipose tissue is downregulated with increased adiposity and circulating insulin. ZAG mRNA is positively correlated with adiponectin mRNA, and ZAG enhances adiponectin production by human adipocytes. We suggest that ZAG is linked to obesity and obesity-related insulin resistance.

Antidiabetic properties of zinc-alpha2-glycoprotein in ob/ob mice

Zinc-alpha(2)-glycoprotein (ZAG) is an adipokine associated with fat loss in cancer cachexia. The purpose of this study was to evaluate the ability of recombinant human ZAG to attenuate type 2 diabetes in the ob/ob mouse model. ZAG (50 microg daily, iv) induced a progressive loss of body weight (3.5 g in 5 d), without an effect on food or water intake but with a 0.4 C rise in body temperature, suggesting an increased energy expenditure. Despite an increased plasma glycerol, indicative of increased lipolysis, levels of glucose, triglycerides, and nonesterified fatty acids were decreased by 17, 25, and 62%, respectively, due to an increased use of both glucose and lipids by muscle and brown adipose tissue. The weight of the latter increased 2-fold, and there was increased expression of uncoupling proteins-1 and -3. Plasma insulin levels were reduced by 36%, whereas pancreatic insulin was increased 4-fold, and there was a 53% decrease in the total area under the glucose curve in the glucose tolerance test and reduced insulin requirement. There was an increase in skeletal muscle mass due to an increase in protein synthesis and a decrease in protein degradation. These results suggest that ZAG may potentially be effective in the treatment of type 2 diabetes.

Zinc-alpha2-glycoprotein in cachexia and obesity

PURPOSE OF REVIEW

Control of adipose mass is important in the treatment of both cachexia and obesity. This review focuses on a novel adipokine, zinc-alpha2-glycoprotein (ZAG), which plays an important role in the mobilization and utilization of stored lipids.

RECENT FINDINGS

An increased lipolysis is responsible for the loss of adipose tissue in cachexia, through an increased lipolytic response to catecholamines, arising from an increased expression of hormone-sensitive lipase. In obesity, there is a decreased response of adipocytes to catecholamines and reduced expression of hormone-sensitive lipase. ZAG was identified as a lipolytic factor produced by certain cachexia-inducing tumours, and subsequently adipose tissue (both white and brown), the expression of which was found to increase in cachexia. In contrast, ZAG expression is low in obesity. ZAG not only increases lipolysis in white adipose tissue through the classical cyclic AMP pathway, but also stimulates an increase in expression of uncoupling protein-1 in brown adipose tissue, which would stimulate utilization of the release lipid to generate heat. Homozygous ZAG null mice show an increase in body weight, especially when fed a high-fat diet, whereas adipocytes from such animals show a resistance to lipolysis by catecholamines and agents that increase cyclic AMP levels.

SUMMARY

These results suggest that ZAG may play an important role in the regulation of adipose mass in obesity and cachexia.

Circulating and adipose tissue gene expression of zinc-alpha2-glycoprotein in obesity: its relationship with adipokine and lipolytic gene markers in subcutaneous and visceral fat

CONTEXT

Zinc-alpha2-glycoprotein (ZAG) is a soluble protein similar to the class I major histocompatibility complex heavy chain, which has been implicated in lipid catabolism. We hypothesized that ZAG mRNA expression in adipose tissue may be linked with lipolytic and adipokine gene expression and have a close relationship with clinical phenotype.

OBJECTIVES

The objective of the study was to analyze ZAG gene expression in human adipose tissue from lean and obese subjects. ZAG circulating plasma levels and its relationship with cardiometabolic risk factors were also studied.

DESIGN

Seventy-three Caucasian (43 male and 30 female) subjects were included. Plasma and adipose tissue [sc (SAT) and visceral (VAT)] from the same patient were studied. mRNA of PPARgamma, hormone-sensitive lipase (HSL), adipose triglyceride lipase, adiponectin, omentin, visfatin, and ZAG were quantified. Plasma concentrations of ZAG were determined with ELISA.

RESULTS

ZAG plasma levels showed a negative correlation with insulin (r = -0.39; P = 0.008) and the homeostasis model assessment for insulin resistance index (r = -0.36; P = 0.016). No differences in ZAG circulating levels according to body mass index classification were observed. ZAG expression in SAT was significantly reduced in overweight and obese individuals compared with lean subjects (P < 0.001 and P = 0.007, respectively). ZAG mRNA expression in both SAT and VAT depots were negatively correlated with many clinical and metabolic cardiovascular risk factors. After multiple linear regression analysis, SAT ZAG was mainly predicted by adiponectin mRNA expression (B = 0.993; P < 0.0001) and plasma triglyceride levels (B = -0.565; P = 0.006). VAT ZAG expression was predicted by adiponectin expression (B = 0.449; P < 0.0001), and HSL VAT expression (B = 0.180; P = 0.023).

CONCLUSIONS

The present study provides evidence of a role of ZAG gene in adipose tissue metabolism, with a close association with adiponectin gene expression in sc and visceral fat.

Lower zinc-alpha2-glycoprotein production by adipose tissue and liver in obese patients unrelated to insulin resistance

CONTEXT

Zinc-alpha2 glycoprotein (ZAG) has been proposed as a new candidate in the pathogenesis of obesity, but most of the information stems from studies performed in rodents and in vitro assays.

OBJECTIVE

The main aim of the study was to compare serum levels of ZAG and its expression (mRNA levels and protein) in adipose tissue and the liver between obese and nonobese subjects. The relationship between ZAG and insulin resistance was also explored.

DESIGN

This was a case-control study.

SETTING

The study was conducted at a university referral center.

PATIENTS AND METHODS

Samples of serum, sc adipose tissue (SAT), visceral adipose tissue (VAT), and liver were obtained from 20 obese subjects during bariatric surgery. Samples from 10 nonobese patients matched by age and gender were used as a control group. Serum ZAG levels were determined by ELISA. ZAG mRNA levels were measured by real-time PCR and protein content by Western blot. The effect of insulin on liver production of ZAG was assessed using HepG2 cultures.

RESULTS

Serum concentration of ZAG (micrograms per milliliter) was significantly lower in obese subjects (40.87 +/- 10.45 vs. 63.26 +/- 16.40; P = 0.002). ZAG expression was significantly lower in the adipose tissue (SAT and VAT) and liver of obese patients than in control subjects. Significant negative correlations between body mass index and circulating ZAG (r = -0.65, P < 0.001) as well as between body mass index and mRNA ZAG levels in SAT (r = -0.68, P < 0.001) and VAT were detected (r = -0.64, P < 0.001). No relationship was found between ZAG and homeostasis model assessment for insulin resistance and insulin had no effect on ZAG production in vitro.

CONCLUSION

A down-regulation of ZAG in SAT, VAT, and liver exists in obese patients but seems unrelated to insulin resistance.

Serum zinc-alpha2-glycoprotein correlates with adiposity, triglycerides, and the key components of the metabolic syndrome in Chinese subjects

CONTEXT

Zinc-alpha2-glycoprotein (ZAG) is a 40-kDa circulating glycoprotein secreted from the liver and adipose tissues. Animal studies have demonstrated the role of ZAG as a lipid-mobilizing factor involved in regulating lipid metabolism and adiposity. However, the clinical relevance of these findings remains to be established.

OBJECTIVE

This study aimed to address the relationship of serum ZAG levels with adiposity and cardiometabolic risk factors in humans.

DESIGN AND SETTING

A total of 258 Chinese subjects [aged 55.1 +/- 12.5 yr; 120 males, 138 females; body mass index (BMI), 25.4 +/- 4.1 kg/m(2)] were randomly selected from the population-based Hong Kong Cardiovascular Risk Factor Prevalence Study, based on their BMI. Serum ZAG levels were determined with ELISA. The relationship between serum ZAG levels and cardiometabolic parameters was assessed.

RESULTS

Serum ZAG levels were higher in men (P < 0.001 vs. women). Serum ZAG correlated positively with age, parameters of adiposity (waist circumference and BMI), fasting insulin, insulin resistance indices, serum triglycerides, adipocyte-fatty acid-binding protein, and C-reactive protein, and diastolic blood pressure (all P < 0.005, age- and sex-adjusted), and inversely with high-density lipoprotein-cholesterol levels (P = 0.008, age- and sex-adjusted). It was also elevated progressively with an increasing number of components of the metabolic syndrome (P for trend < 0.001). On multivariate analysis, serum ZAG was independently associated with male sex, the metabolic syndrome (or type 2 diabetes and serum triglycerides), and C-reactive protein (all P <or= 0.002).

CONCLUSIONS

ZAG might be involved in the pathogenesis of obesity-related metabolic disorders in humans and thus warrants further investigation.

ZAG, a lipid mobilizing adipokine, is downregulated in human obesity

The main goal of this study was to compare the expression of Zinc-alpha2-glycoprotein (ZAG), a recently described adipokine, in obese and lean subjects. ZAG expression was determined by Real-time PCR analysis in subcutaneous abdominal adipose tissue of eighteen young men, 9 lean (BMI = 23.1 +/- 0.4 kg/m2) and 9 obese (34.7 +/- 1.2 kg/m2) with a similar habitual dietary intake of fat and physical activity, which were assessed by validated methods. Our data revealed that ZAG gene was downregulated (-70%; p < 0.05) in subcutaneous adipose tissue of obese compared to lean subjects. Moreover, statistically significant positive correlations between ZAG gene expression and serum adiponectin (r = 0.89; p < 0.01) and a negative correlation with the plasma levels of leptin (r = -0.82; p < 0.05) and waist circumference (r = -0.64; p < 0.05) were found in obese subjects. Our data suggest that this novel adipokine could play a role in human susceptibility to obesity related disorders and that upregulation of ZAG could be a promising therapeutic target for metabolic syndrome treatment.

Zinc alpha 2-glycoprotein: a multidisciplinary protein

Zinc alpha 2-glycoprotein (ZAG) is a protein of interest because of its ability to play many important functions in the human body, including fertilization and lipid mobilization. After the discovery of this molecule, during the last 5 decades, various studies have been documented on its structure and functions, but still, it is considered as a protein with an unknown function. Its expression is regulated by glucocorticoids. Due to its high sequence homology with lipid-mobilizing factor and high expression in cancer cachexia, it is considered as a novel adipokine. On the other hand, structural organization and fold is similar to MHC class I antigen-presenting molecule; hence, ZAG may have a role in the expression of the immune response. The function of ZAG under physiologic and cancerous conditions remains mysterious but is considered as a tumor biomarker for various carcinomas. There are several unrelated functions that are attributed to ZAG, such as RNase activity, regulation of melanin production, hindering tumor proliferation, and transport of nephritic by-products. This article deals with the discussion of the major aspects of ZAG from its gene structure to function and metabolism.

Determination of serum zinc-alpha-2-glycoprotein in patients with metabolic syndrome by a new ELISA

OBJECTIVES

To develop an assay for the determination of ZAG in human serum, and to investigate its clinical relevance as a marker of metabolic syndrome.

DESIGN AND METHODS

A new sandwich ELISA was introduced and clinically tested.

RESULTS

ZAG serum level did not differentiate healthy subjects (27.4+/-8.3 mg/L; N=132) from patients with metabolic syndrome (24.9+/-8.1; N=92). ZAG correlated with glucose, creatinine and uric acid.

CONCLUSION

The immunoassay offers a new research tool for glucose metabolism.

Proteomic analysis of human vitreous fluid by fluorescence-based difference gel electrophoresis (DIGE): a new strategy for identifying potential candidates in the pathogenesis of proliferative diabetic retinopathy

AIMS/HYPOTHESIS

The aim of this study was to compare the protein profile of vitreous fluid from diabetic patients with proliferative diabetic retinopathy (PDR) with that from non-diabetic patients with idiopathic macular holes (MH). The mRNA of proteins differentially produced was also assessed in the retinas from diabetic and non-diabetic donors.

MATERIALS AND METHODS

Vitreous humour from type 1 diabetic patients with PDR (n = 8) and from non-diabetic patients with MH (n = 10) closely matched in terms of age were studied. The comparative proteomic analysis was performed using fluorescence-based difference gel electrophoresis (DIGE). Differentially produced proteins (abundance ratio >1.4, p < 0.05) were identified by mass spectrometry. Expressions of mRNA were measured by real-time RT-PCR in retinas from ten human eyes obtained at post-mortem (five eyes from diabetic subjects and five eyes from non-diabetic subjects).

RESULTS

Eight proteins were highly produced in PDR patients in comparison with non-diabetic subjects: zinc-alpha(2)-glycoprotein (ZAG), apolipoprotein (apo) A1, apoH, fibrinogen A, and the complement factors C3, C4b, C9 and factor B). We found three proteins that were underproduced in PDR subjects: pigment epithelial derived factor (PEDF), interstitial retinol-binding protein (IRBP) and inter-alpha-trypsin inhibitor heavy chain (ITIH2). There was no overlap in the vitreous levels of the above-mentioned proteins between PDR patients and non-diabetic control subjects. The differential production of ZAG, C3, factor B, PEDF and IRBP was further confirmed by western blot, and was in agreement with mRNA levels detected in the retina.

CONCLUSIONS/INTERPRETATION

Proteomic analysis by DIGE, which permits an accurate quantitative comparison, was useful in identifying new potential candidates involved in the pathogenesis of PDR.

Lipolysis is altered in MHC class I zinc-α2-glycoprotein deficient mice

Non-conventional major histocompatibility complex class I molecules are involved in a variety of physiological functions, most at the periphery of the immune system per se. Zinc-alpha(2)-glycoprotein (ZAG), the sole soluble member of this superfamily has been implicated in cachexia, a poorly understood yet life-threatening, severe wasting syndrome. To further ascertain the role of ZAG in lipid metabolism and perhaps the immune system, we inactivated both ZAG alleles by gene targeting in mice. Subjecting these ZAG deficient animals to standard or lipid rich food regimens led to increased body weight in comparison to identically treated wild-type mice. This phenotype appeared to correlate with a significant decrease in adipocytic lipolysis that could not be rescued by several pharmacological agents including beta(3)-adrenoreceptor agonists. Furthermore, in contrast to previously reported data, ZAG was found to be ubiquitously and constitutively expressed, with an especially high level in the mouse liver. No overt immunological phenotype was identified in these animals.

A strong association between body fat mass and protein profiles in nipple aspirate fluid of healthy premenopausal non-lactating women

Fluid can be aspirated from the nipples of most non-lactating women. This nipple aspirate fluid (NAF) is a potential source for the discovery of new breast cancer biomarkers. NAF has two distinct protein profiles. Type I NAF is similar to the fluid associated with cystic disease of the breast, whereas type II NAF is enriched in milk-associated proteins. The prevalence of these two profiles differs in healthy women and in breast cancer patients. This study investigated the relationship of these two NAF profiles to reproductive history, body composition, diet, and levels of lipids, steroids and thyroid hormones in healthy premenopausal women (age 30-40 years) who had regular menstrual cycles and normal mammograms and were not taking contraceptive medications. On average, women with the type I NAF profile were older, had more years since last childbirth, were less likely to have breastfed their babies and had higher dietary saturated fat intake, body mass index, body fat mass, and levels of plasma low density lipoproteins than women with the type II profile (P <0.05). Using multiple logistic regression, type I NAF was predicted independently (P <0.05) by higher body fat mass [Odds Ratio (OR) = 3.0; 95% Confidence Interval (CI): 1.5-6.1], more years since last childbirth (OR = 2.6; 95% CI: 1.3-5.2) and a higher percentage of calories from saturated fat (OR = 4.1; 95% CI: 1.1-14.6). These results suggest that protein profiles of NAF might be influenced by amounts or types of dietary and body fat, but further study of the relationship of the two profiles to breast cancer risk is needed.

Minor gene effect of leptin receptor variant on the body weight in KK/Ta mice

OBJECTIVE

Leptin is an adipocyte-derived hormone involved in body weight regulation that acts through the leptin receptor. Previous studies exploring potential association between the leptin receptor (Lepr) variant and obesity have reported conflicting results. The objectives of the present study are to evaluate (1) whether the Lepr variant contributes to type 2 diabetes and its related disorders such as obesity and (2) whether the gene interaction between Lepr and Zn-alpha(2) glycoprotein1 (Azgp1) genes is recognized using genetically homogeneous type 2 diabetic KK/Ta mice.

METHODS

The levels of leptin (Lep) and Lepr mRNA in adipose tissues and brain were measured by relative quantitative RT-PCR. The levels of leptin protein in sera were measured by enzyme-linked immunosorbent assay. Genotyping of backcross mice was performed using a mismatch primer.

RESULTS

Leptin protein and its mRNA levels were increased in KK/Ta mice. Lepr mRNA levels of KK/Ta mice did not differ from those of BALB/c mice. Sequence analysis revealed that the coding region of Lep in KK/Ta mice was identical to that in BALB/c mice. Six nucleotide polymorphisms were observed in the coding region of Lepr. In KK/Ta x (BALB/c x KK/Ta) F1 backcross mice, the Lepr variant of KK/Ta mice failed to alter any of the variables of obesity except for body weight at 20 weeks of age. However, it enhanced the effect of Azgp1 on body weight.

CONCLUSION

It is concluded that the Lepr variant contributes to obesity to some degree in KK/Ta mice.

The human obesity gene map: the 2005 update

This paper presents the 12th update of the human obesity gene map, which incorporates published results up to the end of October 2005. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTL) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2005, 176 human obesity cases due to single-gene mutations in 11 different genes have been reported, 50 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 244 genes that, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 408. The number of human obesity QTLs derived from genome scans continues to grow, and we now have 253 QTLs for obesity-related phenotypes from 61 genome-wide scans. A total of 52 genomic regions harbor QTLs supported by two or more studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably, with 426 findings of positive associations with 127 candidate genes. A promising observation is that 22 genes are each supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. The electronic version of the map with links to useful publications and relevant sites can be found at http://obesitygene.pbrc.edu.

Genetic susceptibility to type 2 diabetic nephropathy in human and animal models

Diabetic nephropathy is the most common cause of end-stage renal disease (ESRD) in Japan, Western Europe, and the United States. Mega studies such as Diabetes Control and Complication Trial (DCCT), Epidemiology of Diabetes Interventions and Complications (EDIC), and the United Kingdom Prospective Diabetes Study (UKPDS) clarified that poor glycemic and blood pressure control are undoubtedly involved in the development of nephropathy. However, these factors are not sufficient to predict which diabetic patients will develop renal disease, because not all patients with poor glycemic and blood pressure control develop renal disease. Since ethnic variations and familial clustering of diabetic nephropathy have been observed, genetic factors might contribute to susceptibility to this disease. Several methods such as (genome wide) association studies, sib-pair analysis, and quantitative trait loci (QTLs) analysis are available to examine polygenic diseases. However, no mutations that could explain the majority of nephropathy cases have been identified so far. The development of most diabetic nephropathy might be explained by the polygenic effect (i.e. many minor gene-gene interactions might be very important in the development of nephropathy). Identification of candidate genes of nephropathy enables targeting of therapy in patients at risk and development of novel therapeutic agents.

Endocrine and signalling role of adipose tissue: new perspectives on fat

White adipose tissue (WAT) is now recognized as a major endocrine and secretory organ, releasing a wide range of protein factors and signals termed adipokines - in addition to fatty acids and other lipid moieties. A paradigm shift came with the discovery of leptin, a pleiotropic hormone which is a critical signal to the hypothalamus in the control of appetite and energy balance. A number of adipokines, including adiponectin, tumour necrosis factor-alpha, interleukin (IL)-1beta, IL-6, IL-8, IL-10, monocyte chemoattractant protein-1, macrophage migration inhibitory factor, nerve growth factor, vascular endothelial growth factor, plasminogen activator inhibitor-1 and haptoglobin, are linked to inflammation and the inflammatory response. Obesity is characterized by a state of mild inflammation, and the expression and release of inflammation-related adipokines generally rises as adipose tissue expands; a notable exception is adiponectin, with its anti-inflammatory action, the levels of which fall. WAT may be the main site of inflammation in obesity, increased circulating levels of inflammatory markers reflecting spillover from an 'inflamed' tissue, leading to the obesity-associated pathologies of type 2 diabetes and the metabolic syndrome. From the wide range of adipokines now identified, it is evident that WAT is highly integrated into overall physiological regulation, involving extensive crosstalk with other organs and multiple metabolic systems. Whether major changes in adipokine production in obesity, particularly of those factors linked to inflammation, are unique to this condition, or are a feature of all situations in which there are substantial increases in adipose mass (such as pregnancy, and pre-hibernatory and pre-migratory fattening) requires consideration.

Animal models of diabetes mellitus

Animal models have been used extensively in diabetes research. Early studies used pancreatectomised dogs to confirm the central role of the pancreas in glucose homeostasis, culminating in the discovery and purification of insulin. Today, animal experimentation is contentious and subject to legal and ethical restrictions that vary throughout the world. Most experiments are carried out on rodents, although some studies are still performed on larger animals. Several toxins, including streptozotocin and alloxan, induce hyperglycaemia in rats and mice. Selective inbreeding has produced several strains of animal that are considered reasonable models of Type 1 diabetes, Type 2 diabetes and related phenotypes such as obesity and insulin resistance. Apart from their use in studying the pathogenesis of the disease and its complications, all new treatments for diabetes, including islet cell transplantation and preventative strategies, are initially investigated in animals. In recent years, molecular biological techniques have produced a large number of new animal models for the study of diabetes, including knock-in, generalized knock-out and tissue-specific knockout mice.

Zinc-alpha2-glycoprotein, a lipid mobilizing factor, is expressed and secreted by human (SGBS) adipocytes

Zinc-alpha2-glycoprotein (ZAG), a lipid mobilizing factor, is expressed in mouse adipose tissue and is markedly upregulated in mice with cancer cachexia. We have explored whether ZAG is expressed and secreted by human adipocytes, using SGBS cells, and examined the regulation of ZAG expression. ZAG mRNA was detected by RT-PCR in mature human adipocytes and in SGBS cells post-, but not pre-, differentiation to adipocytes. Relative ZAG mRNA levels increased rapidly after differentiation of SGBS cells, peaking at day 8 post-induction. ZAG protein was evident in differentiated adipocytes (by day 3) and also detected in the culture medium (by day 6) post-induction. The PPARgamma agonist rosiglitazone induced a 3-fold increase in ZAG mRNA level, while TNF-alpha led to a 4-fold decrease. Human adipocytes express and secrete ZAG, with ZAG expression being regulated particularly through TNF-alpha and the PPARgamma nuclear receptor. ZAG is a novel adipokine, which may be involved in the local regulation of adipose tissue function.

Altered mouse cholinephosphotransferase gene expression in kidneys of type 2 diabetic KK/TA mouse

It is generally considered that genetic factors may contribute to the susceptibility of type 2 diabetic nephropathy. The purpose of the present study is to identify molecules that contribute to the development and/or progression of this disease. Differential display was performed to isolate genes in the kidney using the KK/Ta mouse model of type 2 diabetes. The differential expression of 8 randomly chosen candidate genes (DN1-8) were verified by reverse-transcriptase polymerase chain reaction (RT-PCR) or Northern blot analysis. DN1-3 (Zn-alpha2-glycoprotein, vascular endothelial growth factor receptor [VEGFR]-2, and lactate dehydrogenase [LDH]) were overexpressed and DN7-8 (peroxisome proliferator-activated receptor [PPAR]-interacting protein [PRIP], unknown) were underexpressed in the KK/Ta mouse kidney. DN4-6 (Ezrin, transcobalamin 2, aldo-ketoreductase) did not differ between KK/Ta and control (BALB/c) mice. DN8 only showed no significant sequence similarity to previously reported genes. Molecular cloning revealed that full-length DN8 shares 89% identity with human cholinephosphotransferase 1 (hCHPT1), and we designated it as "putative" mouse cholinephosphotransferase 1 (mCHPT1). The putative mCHPT1 gene was most closely mapped to the D10Mit94 locus with the highest logarithm of odds (lod) score. In situ hybridization revealed the levels of glomerular putative mCHPT1 in BALB/c mice tended to be slightly higher than those in KK/Ta mice. The altered renal mRNA expression of these genes may be involved in the development and/or progression of diabetic nephropathy.

Zinc-alpha2-glycoprotein, a lipid mobilizing factor, is expressed in adipocytes and is up-regulated in mice with cancer cachexia

Zinc-alpha2-glycoprotein (ZAG), a 43-kDa protein, is overexpressed in certain human malignant tumors and acts as a lipid-mobilizing factor to stimulate lipolysis in adipocytes leading to cachexia in mice implanted with ZAG-producing tumors. Because white adipose tissue (WAT) is an endocrine organ secreting a wide range of protein factors, including those involved in lipid metabolism, we have investigated whether ZAG is produced locally by adipocytes. ZAG mRNA was detected by RT-PCR in the mouse WAT depots examined (epididymal, perirenal, s.c., and mammary gland) and in interscapular brown fat. In WAT, ZAG gene expression was evident in mature adipocytes and in stromal-vascular cells. Using a ZAG Ab, ZAG protein was located in WAT by Western blotting and immunohistochemistry. Mice bearing the MAC16-tumor displayed substantial losses of body weight and fat mass, which was accompanied by major increases in ZAG mRNA and protein levels in WAT and brown fat. ZAG mRNA was detected in 3T3-L1 cells, before and after the induction of differentiation, with the level increasing progressively after differentiation with a peak at days 8-10. Both dexamethasone and a beta3 agonist, BRL 37344, increased ZAG mRNA levels in 3T3-L1 adipocytes. ZAG gene expression and protein were also detected in human adipose tissue (visceral and s.c.). It is suggested that ZAG is a new adipose tissue protein factor, which may be involved in the modulation of lipolysis in adipocytes. Overexpression in WAT of tumor-bearing mice suggests a local role for adipocyte-derived ZAG in the substantial reduction of adiposity of cancer cachexia.

Induction of lipolysis in vitro and loss of body fat in vivo by zinc-α2-glycoprotein

Loss of adipose tissue in cancer cachexia has been associated with tumour production of a lipid-mobilizing factor (LMF) which has been shown to be homologous with the plasma protein zinc-alpha(2)-glycoprotein (ZAG). The aim of this study was to compare the ability of human ZAG with LMF to stimulate lipolysis in vitro and induce loss of body fat in vivo, and to determine the mechanisms involved. ZAG was purified from human plasma using a combination of Q Sepharose and Superdex 75 chromatography, and was shown to stimulate glycerol release from isolated murine epididymal adipocytes in a dose-dependent manner. The effect was enhanced by the cyclic AMP phosphodiesterase inhibitor Ro20-1724, and attenuated by freeze/thawing and the specific beta3-adrenoreceptor antagonist SR59230A. In vivo ZAG caused highly significant, time-dependent, decreases in body weight without a reduction in food and water intake. Body composition analysis showed that loss of body weight could be attributed entirely to the loss of body fat. Loss of adipose tissue may have been due to the lipolytic effect of ZAG coupled with an increase in energy expenditure, since there was a dose-dependent increase in expression of uncoupling protein-1 (UCP-1) in brown adipose tissue. These results suggest that ZAG may be effective in the treatment of obesity.