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Background/objectives: A better understanding of adipose tissue biology is crucial to tackle insulin resistance and eventually coronary heart disease and diabetes, leading causes of morbidity and mortality worldwide. GALNT2, a GalNAc-transferase, positively modulates insulin signaling in human liver cells by down-regulating ENPP1, an insulin signaling inhibitor. GALNT2 expression is increased in adipose tissue of obese as compared to that of non-obese individuals. Whether this association is secondary to a GALNT2-insulin sensitizing effect exerted also in adipocytes is unknown. We then investigated in mouse 3T3-L1 adipocytes the GALNT2 effect on adipogenesis, insulin signaling and expression levels of both Enpp1 and 72 adipogenesis-related genes. Methods: Stable over-expressing GALNT2 and GFP preadipocytes (T0) were generated. Adipogenesis was induced with (R+) or without (R−) rosiglitazone and investigated after 15 days (T15). Lipid accumulation (by Oil Red-O staining) and intracellular triglycerides (by fluorimetric assay) were measured. Lipid droplets (LD) measures were analyzed at confocal microscope. Gene expression was assessed by RT-PCR and insulin-induced insulin receptor (IR), IRS1, JNK and AKT phosphorylation by Western blot. Results: Lipid accumulation, triglycerides and LD measures progressively increased from T0 to T15R- and furthermore to T15R+. Such increases were significantly higher in GALNT2 than in GFP cells so that, as compared to T15R+GFP, T15R- GALNT2 cells showed similar (intracellular lipid and triglycerides accumulation) or even higher (LD measures, p < 0.01) values. In GALNT2 preadipocytes, insulin-induced IR, IRS1 and AKT activation was higher than that in GFP cells. GALNT2 effect was totally abolished during adipocyte maturation and completely reversed at late stage maturation. Such GALNT2 effect trajectory was paralleled by coordinated changes in the expression of Enpp1 and adipocyte-maturation key genes. Conclusions: GALNT2 is a novel modulator of adipogenesis and related cellular phenotypes, thus becoming a potential target for tackling the obesity epidemics and its devastating sequelae.

Obesity is a major predisposing risk factor for the development of insulin resistance. Recently, a sexual dimorphism in the relationship between body mass index (BMI) and insulin resistance has been reported, with the deleterious effect of increasing BMI being more evident in men than in women [1]. To the best of our knowledge, the biology underlying this sex-specific association has never been addressed. By inhibiting insulin signaling, TNF-a overexpression is the main mechanism responsible for the deleterious effect of obesity on insulin resistance [2]. It is, therefore, reasonable to address the role of TNF-a as a mediator of the sex-specific response of insulin sensitivity to the insult of increasing BMI. Accordingly, we measured both the HOMA-IR insulin resistance index and TNF-a mRNA levels (in peripheral whole blood cells; PWBC) from healthy subjects with a wide range of BMI and then looked for BMI-by-sex interaction in modulating these two variables.

OBJECTIVE Insulin resistance (IR) and cardiovascular disease may share a common genetic background. We investigated the role of IR-associated ENPP1 K121Q polymorphism (rs1044498) on cardiovascular disease in high-risk individuals. RESEARCH DESIGN AND METHODS A prospective study (average follow-up, 37 months) was conducted for major cardiovascular events (myocardial infarction [MI], stroke, cardiovascular death) from the Gargano Heart Study (GHS; n = 330 with type 2 diabetes and coronary artery disease), the Tor Vergata Atherosclerosis Study (TVAS; n = 141 who had MI), and the Cardiovascular Risk Extended Evaluation in Dialysis (CREED) database (n = 266 with end-stage renal disease). Age at MI was investigated in cross-sectional studies of 339 type 2 diabetic patients (n = 169 from Italy, n = 170 from the U.S.). RESULTS Incidence of cardiovascular events per 100 person--years was 4.2 in GHS, 10.8 in TVAS, and 11.7 in CREED. Hazard ratios (HRs) for KQ+QQ versus individuals carrying the K121/K121 genotype (KK) individuals were 1.47 (95% CI 0.80–2.70) in GHS, 2.31 (95% CI 1.22–4.34) in TVAS, and 1.36 (95% CI 0.88–2.10) in CREED, and 1.56 (95% CI 1.15–2.12) in the three cohorts combined. In the 395 diabetic patients, the Q121 variant predicted cardiovascular events among obese but not among nonobese individuals (HR 5.94 vs. 0.62, P = 0.003 for interaction). A similar synergism was observed in cross-sectional studies, with age at MI being 3 years younger in Q121 carriers than in KK homozygotes among obese but not among nonobese patients (P = 0.035 for interaction). CONCLUSIONS The ENPP1 K121Q polymorphism is an independent predictor of major cardiovascular events in high-risk individuals. In type 2 diabetes, this effect is exacerbated by obesity. Future larger studies are needed to confirm our finding.

Insulin resistance is associated with reduced serum adiponectin and increased albuminuria levels. Thus, one would anticipate an inverse relationship between circulating adiponectin and albuminuria. However, several studies have described a 'paradoxical' elevation of serum adiponectin in patients with elevated albuminuria. These findings may have been confounded by the presence of diseases and related treatments known to affect circulating adiponectin and albuminuria. We therefore studied the relationship between circulating adiponectin and albuminuria in the absence of such confounders.To this purpose, the relationship between adiponectin isoforms and albumin:creatinine ratio (ACR) was investigated in a family-based sample of 634 non-diabetic untreated white individuals with normal kidney function. We also investigated whether the two variables share a common genetic background and addressed the specific role of the gene encoding adiponectin on that background by genotyping several ADIPOQ single nucleotide polymorphisms (SNPs).ACR was directly associated with high molecular weight (HMW) adiponectin isoform (p = 0.024). The two variables shared some genetic correlation (ρ(g) = 0.38, p = 0.04). ADIPOQ promoter SNP rs17300539 was associated with HMW adiponectin (p = 4.8 × 10(-5)) and ACR (p =0.0027). The genetic correlation between HMW adiponectin and ACR was no longer significant when SNP rs17300539 was added to the model, thus reinforcing the role of this SNP in determining both traits.Our study shows a positive, independent correlation between HWM adiponectin and ACR. ADIPOQ variability is associated with HMW adiponectin and ACR, and explains some of the common genetic background shared by these traits, thus suggesting that ADIPOQ and HMW adiponectin modulate albuminuria levels.

Reduced circulating adiponectin levels contribute to the aetiology of insulin resistance. Adiponectin circulates in three different isoforms: high molecular weight (HMW), medium molecular weight (MMW) and low molecular weight (LMW) isoforms. The genetics of adiponectin isoforms is mostly unknown. Our aim was to investigate whether and to which extent circulating adiponectin isoforms are heritable and whether they share common genetic backgrounds with insulin resistance-related traits.In a family-based sample of 640 nondiabetic White Caucasians from Italy, serum adiponectin isoforms concentrations were measured by ELISA. Three single nucleotide polymorphisms (SNPs) in the ADIPOQ gene previously reported to affect total adiponectin levels (rs17300539, rs1501299 and rs677395) were genotyped. The heritability of adiponectin isoform levels was assessed by variance component analysis. A linear mixed effects model was used to test the association between SNPs and adiponectin isoforms. Bivariate analyses were conducted to study genetic correlations between adiponectin isoforms levels and other insulin resistance-related traits.All isoforms were highly heritable (h(2) = 0.60-0.80, P = 1.0 x 10(-13)-1.0 x 10(-23)). SNPs rs17300539, rs1501299 and rs6773957 explained a significant proportion of HMW variance (2-9%, P = 1.0 x 10(-3)-1.0 x 10(-5)). In a multiple-SNP model, only rs17300539 and rs1501299 remained associated with HMW adiponectin (P = 3.0 x 10(-4) and 2.0 x 10(-2)). Significant genetic correlations (P = 1.0 x 10(-2)-1.0 x 10(-5)) were observed between HMW adiponectin and fasting insulin, homeostasis model assessment of insulin resistance, HDL cholesterol and the metabolic syndrome score. Only rs1501299 partly accounted for these genetic correlations.Circulating levels of adiponectin isoforms are highly heritable. The genetic control of HMW adiponectin is shared in part with insulin resistance-related traits and involves, but is not limited to, the ADIPOQ locus.

We describe a diabetic child and her relatives carrying the HNF4A R311H mutation. The proband was diagnosed with insulin-dependent diabetes when 9.1 year-old. Three weeks later, a complete remission occurred. She underwent genetic testing showing the HNF4A-R311H mutation, which was found also in the brother (with impaired glucose tolerance), the mother (with gestational diabetes), and the maternal uncle (with type 2 diabetes). This case suggests that the HNF4A R311H mutation may play a role on hyperglycaemia since childhood and may be associated with clinical heterogeneity of abnormal glucose homeostasis. Transient diabetes might warrant the screening for MODY when indicated.

Impaired insulin action plays a major role in the pathogenesis of type 2 diabetes, a chronic metabolic disorder which imposes a tremendous burden to morbidity and mortality worldwide. Unraveling the molecular mechanisms underlying insulin resistance would improve setting up preventive and treatment strategies of type 2 diabetes. Down-regulation of GALNT2, an UDPN-acetyl-alpha-D-galactosamine polypeptideN-acetylgalactosaminyltransferase-2 (ppGalNAc-T2), causes impaired insulin signaling and action in cultured human liver cells. In addition, GALNT2 mRNA levels are down-regulated in liver of spontaneously insulin resistant, diabetic Goto-Kakizaki rats. To investigate the role of GALNT2 in human hyperglycemia, we measured GALNT2 mRNA expression levels in peripheral whole blood cells of 84 non-obese and 46 obese non-diabetic individuals as well as of 98 obese patients with type 2 diabetes. We also measured GALNT2 mRNA expression in human U937 cells cultured under different glucose concentrations. In vivo studies indicated that GALNT2 mRNA levels were significantly reduced from non obese control to obese non diabetic and to obese diabetic individuals (p

Background High serum resistin levels have been associated with kidney dysfunction. Most of these studies have been carried out in individuals with severe kidney impairment, diabetes, cardiovascular disease and related treatments. Thus, the observed association might have been influenced by these confounders. Our aim was to study the relationship between serum resistin, urinary albumin/creatinine ratio (ACR) and glomerular filtration rate (GFR) in a family-based sample, the Gargano Family Study (GFS) of 635 non diabetic, untreated Whites. Methods A linear mixed effects model and bivariate analyses were used to evaluate the phenotypic and genetic relations between serum resistin and both ACR and eGFR. All analyses were adjusted for sex, age, age squared, BMI, systolic blood pressure, smoking habits and physical exercise. Results After adjustments, resistin levels were slightly positively associated with ACR (β±SE = 0.049±0.023, p = 0.035) and inversely related to eGFR (β±SE = −1.43±0.61, p = 0.018) levels. These associations remained significant when either eGFR or ACR were, reciprocally, added as covariates. A genetic correlation (ρg = −0.31±0.12; adjusted p = 0.013) was observed between resistin and eGFR (but not ACR) levels. Conclusion Serum resistin levels are independently associated with ACR and eGFR in untreated non-diabetic individuals. Serum resistin and eGFR share also some common genetic background. Our data strongly suggest that resistin plays a role in modulating kidney function.

Insulin resistance (IR) is pathogenic for type 2 diabetes and coronary artery disease (CAD). The K121Q polymorphism of the ENPP1/PC-1 gene is associated with IR. Our aim was to investigate the role of the 121Q variant on the risk of type 2 diabetes and CAD. Nondiabetic control subjects (n = 638), type 2 diabetic patients without CAD (n = 535), and type 2 diabetic patients with CAD (n = 434) from Italy and the U.S. were studied. The proportion of 121Q carriers progressively increased in the three groups (27.4, 28.8, and 33.2%, respectively; adjusted P value = 0.027). Among diabetic patients (n = 969), 121Q carriers had an increased risk of developing type 2 diabetes before the age of 65 years (adjusted odds ratio [OR] 2.26, 95% CI 1.26–4.03; P = 0.006) and having a myocardial infarction (MI) (n = 156) by 50 years of age (3.17, 1.46–6.88, P = 0.007). The 121Q variant was also associated with an increased risk for CAD (1.47, 1.01–2.18; P = 0.049) in diabetic patients who did not smoke (n = 546). In conclusion, the ENPP1/PC-1 121Q variant is associated with a progressive deterioration of the IR-atherogenic phenotype; among diabetic individuals, it is also associated with earlier onset of type 2 diabetes and MI.