Morphological and molecular characterization of GALNT2-mediated adipogenesis.

3T3L1 mouse pre-adipocytes develop into adipocytes differently in response to GALNT2 overexpression or to stimulation with rosiglitazone, a reference inducer of adipogenesis. To investigate the biology of alternative pathways of adipogenesis, we studied lipid droplets (LD) morphology, chromatin organization, and gene expression in GALNT2- versus rosiglitazone-induced 3T3L1 adipogenesis. 3T3L1 overexpressing either GALNT2 (GALNT2) or GFP and treated with rosiglitazone (GFPR) were differentiated into adipocytes. LD and nuclei were profiled measuring their morphological features. The expression of adipogenesis-related genes was measured by RT-PCR. As compared to GFPR, GALNT2 showed smaller and more clustered LD, more nuclei with condensed chromatin and several gene expression changes (P < 0.001 for all). As compared to those stimulated by rosiglitazone, GALNT2 overexpressing cells show differences in the most established readouts of adipogenesis. Characterizing alternative pathways of adipogenesis may help tackle those diseases which are secondary to increased dysfunctional mass of adipose tissue.

GALNT2 as a novel modulator of adipogenesis and adipocyte insulin signaling.

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.

Serum resistin is causally related to mortality risk in patients with type 2 diabetes: preliminary evidences from genetic data.

Resistin has been firmly associated with all-cause mortality. We investigated, whether, in patients with type 2 diabetes (T2D), this association is sustained by a cause-effect relationship. A genotype risk score (GRS), created by summing the number of resistin increasing alleles of two genome-wide association studies (GWAS)-derived single nucleotide polymorphisms (SNPs), serum resistin measurements and all-cause death records were obtained in 1,479 (403 events/12,454 person-years), patients with T2D from three cohorts, Gargano Heart Study-prospective design (n = 350), Gargano Mortality Study (n = 698) and Foggia Mortality Study (n = 431), from Italy. GRS was strongly associated with serum resistin in a non-linear fashion (overall p = 3.5 * 10-7) with effect size modest for GRS = 1 and 2 and much higher for GRS >3, with respect to GRS = 0. A significant non-linear association was observed also between GRS and all-cause mortality (overall p = 3.3 * 10-2), with a low effect size for GRS = 1 and 2, and nearly doubled for GRS ≥ 3, with respect to GRS = 0. Based on the above-reported associations, each genetic equivalent SD increase in log-resistin levels showed a causal hazard ratio of all-cause mortality equal to 2.17 (95%CI: 1.22-3.87), thus providing evidence for a causal role of resistin in shaping the risk of mortality in diabetic patients.

Suggestive evidence of a multi-cytokine resistin pathway in humans and its role on cardiovascular events in high-risk individuals.

In cells and tissues resistin affects IL-1ß, IL-6, IL-8, IL-12 and TNF-α expression, thus suggesting the existence of a multi-cytokine "resistin pathway". We investigated whether such pathway does exist in humans and, if so, if it is associated with cardiovascular risk factors and with major adverse cardiovascular events (MACE). Serum cytokines were measured in 280 healthy subjects from the Gargano Study 2 (GS2) whose BMI, waist circumference, HOMAIR, triglycerides, HDL-cholesterol, systolic and diastolic blood pressure data were available and in 353 patients with type 2 diabetes and coronary artery disease from the Gargano Heart Study (GHS)-prospective design (follow-up 5.4 ± 2.5 years; 71 MACE). In GS2, cytokines mRNA levels in white blood cells were also measured. In GS2, resistin mRNA was correlated with all cytokines expression (all p < 0.001), but IL-12B. Consistently, serum resistin was correlated with all serum cytokines (all p < 0.001), but IL-12. Expression (eRPS) and serum (sRPS) resistin pathway scores (excluding IL-12) were each other correlated (p < 0.001) and both associated with cardiovascular risk factors (all p < 0.01). In GHS, sRPS was independently associated with MACE (HR = 1.44, 95% CI = 1.10-1.90). Our data indicate the existence of a resistin pathway, which is associated with cardiovascular risk factors and which strongly and independently predicts MACE.

The combined effect of adiponectin and resistin on all-cause mortality in patients with type 2 diabetes: Evidence of synergism with abdominal adiposity.

BACKGROUND AND AIMS: While elevated serum adiponectin and resistin levels have been singly associated with all-cause mortality in patients with type 2 diabetes (T2D), their combined effect has never been studied. We investigated such joint effect in patients with T2D and its possible modulation by several demographic and clinical conditions, known to affect per se mortality rate. METHODS: Patients with T2D from the Gargano Mortality Study (GMS; N = 895, follow-up = 10.5 ± 3.7 years; 290 events) and the Foggia Mortality Study (FMS; N = 519, follow-up = 7.1 ± 2.5 years; 140 events) were examined. RESULTS: As singly considered, adiponectin and resistin were independently associated with mortality rate in GMS and FMS (p < 0.0001 for both). The two studies were then pooled, for investigating the nature of the joint effect of the two adipokines. In such sample, both adipokines were associated with death, independent of each other and of several additional covariates (p = 0.01-4.58 × 10(-12)). Of note, no adiponectin-by-resistin interaction was observed (p = 0.40), thus pointing to an additive effect of the two adipokines. As compared to individuals with low levels of both adiponectin and resistin (i.e. below median values), those with high levels of both adipokines had an HR (95%CI) for death of 3.02 (2.26-4.03). Such increased risk was more pronounced in individuals with relatively low abdominal adiposity (p for HR heterogeneity below or above the median value of waist circumference = 0.03). CONCLUSIONS: Adiponectin and resistin show an additive independent effect on all-cause mortality in patients with T2D. Such effect is modified by abdominal adiposity.

Evidence of a causal relationship between high serum adiponectin levels and increased cardiovascular mortality rate in patients with type 2 diabetes.

BACKGROUND: Despite its beneficial role on insulin resistance and atherosclerosis, adiponectin has been repeatedly reported as an independent positive predictor of cardiovascular mortality. METHODS: A Mendelian randomization approach was used, in order to evaluate whether such counterintuitive association recognizes a cause-effect relationship. To this purpose, single nucleotide polymorphism rs822354 in the ADIPOQ locus which has been previously associated with serum adiponectin at genome-wide level, was used as an instrument variable. Our investigation was carried out in the Gargano Heart Study-prospective design, comprising 356 patients with type 2 diabetes, in whom both total and high molecular weight (HMW) adiponectin were measured and cardiovascular mortality was recorded (mean follow-up = 5.4 ± 2.5 years; 58 events/1922 person-year). RESULTS: The A allele of rs822354 was associated with both total and HMW adiponectin [ß (SE) = 0.10 (0.042), p = 0.014 and 0.17 (0.06), p = 0.003; respectively]. In a Poisson model comprising age, sex, smoking habits, BMI, HbA1c, total cholesterol, HDL-cholesterol, triglycerides, insulin therapy and hypertension, both rs822354 (IRR = 1.94, 95 % CI 1.23-3.07; p = 0.005), as well as the genetic equivalent of total adiponectin change (IRR = 1.07, 95 % CI 1.02-1.12; p = 0.003) were significantly associated with cardiovascular mortality. The observed genetic effect was significantly greater than that exerted by the genetic equivalent change of serum adiponectin (p for IRR heterogeneity = 0.012). In the above-mentioned adjusted model, very similar results were obtained when HMW, rather than total, adiponectin was used as the exposure variable of interest. CONCLUSIONS: Our data suggest that the paradoxical association between high serum adiponectin levels and increased cardiovascular mortality rate is based on a cause-effect relationship, thus pointing to an unexpected deleterious role of adiponectin action/metabolism on atherosclerotic processes.

The paradoxical association of adiponectin with mortality rate in patients with type 2 diabetes: evidence of synergism with kidney function.

BACKGROUND: The paradoxical relationship between high adiponectin and increased mortality, described in several clinical subsets, has been reported only once in type 2 diabetes (T2D) and only in selected elderly patients. We investigated this relationship in unselected patients with T2D and, then, addressed its possible modulation by several demographic and clinical conditions, known to affect per se mortality rate. METHODS: Patients from the Gargano Mortality Study (GMS; N = 897, follow-up = 10.5 ± 3.7 years; 290 events) and the Foggia Mortality Study (FMS; N = 529, follow-up = 7.1 ± 2.5 years; 143 events), were investigated. RESULTS: For each SD adiponectin increase, HRs (95% CI) for all-cause mortality were 1.30 (1.19-1.43) in GMS, 1.43 (1.26-1.64) in FMS and 1.34 (1.24-1.45) in the combined studies. This association was independent of the possible confounding effect of demographics, adiposity measures, diabetes-related features, kidney function-related parameters and medications (p = 9.34 × 10(-9)). While no interaction was observed between adiponectin and sex, age, smoking habits, BMI, waist circumference, HbA1c, diabetes duration, micro-/macro-albuminuria and medications, a strong interaction was observed with GFR, with a significant adiponectin-mortality association observed in individuals with GFR ≥ but not those with GFR < 60 ml/min/1.73 m(2); p for adiponectin-by-GFR status interaction = 2.13 × 10(-6)). CONCLUSION: This is the first study reporting a paradoxical association of adiponectin with all-cause mortality in a large sample of unselected diabetic patients and indicating that such counterintuitive effect is observed only among patients with preserved kidney function. Further studies are needed to address if the strong interwoven effect of adiponectin and GFR turns to be useful in improving previously validated tools for predicting mortality in T2D.

Serum Adiponectin and Glomerular Filtration Rate in Patients with Type 2 Diabetes.

High serum adiponectin has been increased in several conditions of kidney disease. Only sparse and conflicting results have been reported in patients with type 2 diabetes (T2D), a subgroup of individuals who are at high risk for renal dysfunction. The aim of this study was to fill up this gap of knowledge by investigating such association in a large sample of Italian diabetic patients. The association between serum adiponectin levels and estimated glomerular filtration rate (eGFR by Chronic Kidney Disease-Epidemiology Collaboration CKD-EPI equation) was investigated in 1,243 patients with T2D from two cross-sectional Italian studies: 878 from San Giovanni Rotondo (SGR) and 365 from Foggia (FG). Serum adiponectin was inversely associated with eGFR in SGR [ß (standard error, SE) for 1 standard deviation (SD) of adiponectin = -3.26 (0.64)] and in FG [ß(SE)=-5.70(1.28)] sample, as well as in the two studies combined [ß(SE)=-3.99(0.59)];(p<0.0001 for all). In this combined analysis, the association was still significant after adjusting for sex, smoking habits, body mass index (BMI), waist circumference, diabetes duration, glycated hemoglobin (HbA1c), albumin creatinine ratio (ACR) and anti-hyperglycemic, anti-hypertensive and anti-dyslipidemic treatments [ß (SE)= -2.19 (0.59), p = 0.0001]. A stronger association between each SD adiponectin increment and low eGFR was observed among patients with micro-/macro-albuminuria, as compared to those with normo-albuminuria [adjusted ß(SE)=-4.42(1.16) ml/min/1.73m2 vs. -1.50 (0.67) ml/min/1.73m2, respectively; p for adiponectin-by-albuminuric status = 0.022]. For each adiponectin SD increment, the odds of having eGFR < 60 ml/min/1.73m2 increased by 41% (odds ratio, OR = 1.41; 95% confidence interval, CI 1.21-1.64) in SGR sample, 53% (OR = 1.53; 95% CI 1.21-1.94) in FG sample, and 44% (OR = 1.44; 95%CI 1.27-1.64) in the two studies considered together (p<0.0001 for all). In the combined sample, further adjustment for the above mentioned covariates did not change the observed association (OR = 1.36; 95%CI 1.16-1.60; p<0.0001). Our study, so far the largest addressing the relationship between serum adiponectin and GFR in T2D, strongly suggests that the paradoxical inverse association, previously reported in different clinical sets, is also observed in diabetic patients. Further studies are needed to unravel the biology underlying this counterintuitive relationship.

Serum resistin and glomerular filtration rate in patients with type 2 diabetes.

BACKGROUND: High serum levels of the pro-inflammatory adipokine resistin have been associated with decreased renal function in the general population. The goal of this study was to investigate whether such association is also present among diabetic subjects, who are at increased risk of renal function loss. METHODS: The cross-sectional association between serum resistin levels and estimated glomerular filtration rate (eGFR) was investigated in 1,560 type 2 diabetic (T2D) patients of European ancestry comprised in two different cohorts: 762 patients from San Giovanni Rotondo (SGR; Italy) and 798 patients from Boston (US). RESULTS: Serum resistin was inversely associated with eGFR in SGR [ß (SE) for one SD of resistin increment = -1.01 (0.70) ml/min/1.73 m(2), p = 0.019] and in Boston [ß (SE) = -5.31 (0.74) ml/min/1.73 m(2), p < 0.001] samples, as well as in the two studies combined [ß (SE) = -3.42 (0.52) ml/min/1.73 m(2), p < 0.001]. The association was unaffected by adjustment for smoking habits, BMI, waist circumference, diabetes duration, HbA1c, insulin treatment, hypertension and lipid-lowering therapy: ß (SE) for one SD of resistin increment = -1.07 (0.70), p = 0.02; -5.50 (0.88), p < 0.001; and -2.81 (0.55) ml/min/1.73 m(2), p < .001, in SGR, Boston and the two studies combined, respectively. The association was significantly stronger in men than in women (p for resistin-by-gender interaction = 0.003). For each resistin SD increment, the odds of having eGFR < 0 ml/min/1.7 3m(2) increased by 22% (OR = 1.22; 95% CI 1.02-1.44; p = 0.025) in SGR sample, 69% (OR = 1.69; 95% CI 1.38-2.07; p < 0.001) in Boston sample, and 47% (OR = 1.47; 95% CI 1.29-1.68; p < 0.001) in the two studies considered together. Similar associations were observed in the adjusted model: OR 95% CI for each SD resistin increment being 1.23 (1.03-1.46), p = 0.021; 1.52 (1.20-1.92), p < 0.001; 1.33 (1.16-1.53), p < 0.001, in SGR, Boston and the two studies combined, respectively. CONCLUSIONS: This is the first report of an association between high serum resistin and low eGFR in patients with T2D of European ancestry.

Circulating adiponectin and cardiovascular mortality in patients with type 2 diabetes mellitus: evidence of sexual dimorphism.

BACKGROUND: The pathogenesis of cardiovascular (CV) mortality, whose rate is increased in type 2 diabetes, is poorly understood. METHODS: Three prospective cohorts were analyzed: 1) Gargano Heart Study (GHS; 359 patients, 58 events/1,934 person-years; py); 2) Health Professional Follow-up Study (HPFS; 833 men, 146 events/10,024 py); 3) Nurses' Health Study (NHS; 902 women, 144 events/15,074 py). RESULTS: In GHS serum adiponectin predicted CV mortality in men (hazard ratio, HR, and 95% CI per standard deviation, SD, increment = 1.54, 1.19-2.01), but not women (HR = 0.98, 0.48-2.01). CONCLUSIONS: This is the first report showing that high circulating adiponectin predicts increased CV mortality in men, but not in women with type 2 diabetes. Further studies are necessary to unravel the mechanisms through which adiponectin influences CV mortality in a sex-specific manner.

Serum resistin, cardiovascular disease and all-cause mortality in patients with type 2 diabetes.

BACKGROUND: High serum resistin has been associated with increased risk of cardiovascular disease in the general population, Only sparse and conflicting results, limited to Asian individuals, have been reported, so far, in type 2 diabetes. We studied the role of serum resistin on coronary artery disease, major cardiovascular events and all-cause mortality in type 2 diabetes. METHODS: We tested the association of circulating resistin concentrations with coronary artery disease, major cardiovascular events (cardiovascular death, non-fatal myocardial infarction and non-fatal stroke) and all-cause mortality in 2,313 diabetic patients of European ancestry from two cross-sectional and two prospective studies. In addition, the expression of resistin gene (RETN) was measured in blood cells of 68 diabetic patients and correlated with their serum resistin levels. RESULTS: In a model comprising age, sex, smoking habits, BMI, HbA1c, and insulin, antihypertensive and antidyslipidemic therapies, serum resistin was associated with coronary artery disease in both cross-sectional studies: OR (95%CI) per SD increment = 1.35 (1.10-1.64) and 1.99 (1.55-2.55). Additionally, serum resistin predicted incident major cardiovascular events (HR per SD increment = 1.31; 1.10-1.56) and all-cause mortality (HR per SD increment = 1.16; 1.06-1.26). Adjusting also for fibrinogen levels affected the association with coronary artery disease and incident cardiovascular events, but not that with all cause-mortality. Finally, serum resistin was positively correlated with RETN mRNA expression (rho = 0.343). CONCLUSIONS: This is the first study showing that high serum resistin (a likely consequence, at least partly, of increased RETN expression) is a risk factor for cardiovascular disease and all-cause mortality in diabetic patients of European ancestry.

Serum resistin and kidney function: a family-based study in non-diabetic, untreated individuals.

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 (ß±SE = 0.049±0.023, p = 0.035) and inversely related to eGFR (ß±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.

Novel locus FER is associated with serum HMW adiponectin levels.

OBJECTIVE: High molecular weight (HMW) adiponectin is a predominant isoform of circulating adiponectin and has been related to type 2 diabetes. Previous linkage studies suggest that different genetic components might be involved in determining HMW and total adiponectin levels. RESEARCH DESIGN AND METHODS: We performed a genome-wide association study (GWAS) of serum HMW adiponectin levels in individuals of European ancestry drawn from the Nurses' Health Study (NHS) (N = 1,591). The single nucleotide polymorphisms (SNPs) identified in the GWAS analysis were replicated in an independent cohort of Europeans (N = 626). We examined the associations of the identified variations with diabetes risk and metabolic syndrome. RESULTS: We identified a novel locus near the FER gene (5q21) at a genome-wide significance level, best represented by SNP rs10447248 (P = 4.69 × 10(-8)). We also confirmed that variations near the adiponectin-encoding ADIPOQ locus (3q27) were related to serum HMW adiponectin levels. In addition, we found that FER SNP rs10447248 was related to HDL cholesterol levels (P = 0.009); ADIPOQ variation was associated with fasting glucose (P = 0.04), HDL cholesterol (P = 0.04), and a metabolic syndrome score (P = 0.002). CONCLUSIONS: Our results suggest that different loci may be involved in regulation of circulating HMW adiponectin levels and provide novel insight into the mechanisms that affect HMW adiponectin homeostasis.

Akt2 Gene common allelic variants in insulin resistance and the metabolic syndrome.

BACKGROUND AND AIM: Several lines of evidence indicate that glucose homeostasis may be under the control of Akt2 and it can therefore be seen as a candidate gene for human insulin resistance (IR) and related phenotypes. The aim of our study was the identification of Akt2 common allelic variants that might modulate susceptibility to IR and related metabolic abnormalities. METHODS AND RESULTS: The Akt2 gene (exons, 5' and 3' regulatory regions) was re-sequenced in samples of 50 blood donors from the Gargano region. Two single nucleotide polymorphisms (SNPs) in 5' (rs11669332 and rs969531) and two in 3' (rs2304186 and C1658T) regulatory regions were exploited in an association study using 661 healthy unrelated Caucasian individuals from the same region. Individuals being homozygous for the T allele of rs11669332 (an Akt2 promoter) showed lower systolic blood pressure (p=0.04), total/HDL cholesterol ratio (p=0.02) and the metabolic syndrome score (p=0.04), while carriers of the A allele of rs969531 (in 5'-UTR) showed higher systolic blood pressure (p=0.027). The association between phenotypic traits and possible haplotypes was tested as well. However, no haplotype affecting the risk of metabolic abnormalities was found. CONCLUSIONS: Two variants in 5' regulatory region of Akt2 gene are associated and may modulate susceptibility to IR and related metabolic abnormalities.

The -318 C>G single-nucleotide polymorphism in GNAI2 gene promoter region impairs transcriptional activity through specific binding of Sp1 transcription factor and is associated with high blood pressure in Caucasians from Italy.

Inhibiting Galpha subunit 2 protein, which is encoded by the GNAI2 gene, is suggested to be pathogenic for essential hypertension and/or insulin resistance. The aim of this study was to determine whether GNAI2 variations modulate the risk for these abnormalities. Seven single-nucleotide polymorphisms (SNP) at the GNAI2 locus were identified. Because of either low allelic frequency or unlikely biologic relevance (i.e., synonymous or intronic), six SNP were not studied further. The -318C>G SNP (allelic frequency 6%) in the promoter region was studied for association with adiposity, systolic BP (SBP) and diastolic BP, fasting insulin and glucose, and lipids levels in 655 nondiabetic Caucasians from Italy. As compared with individuals who carry the C/C genotype, G carriers (i.e., individuals who carry either the G/G or the C/G genotype) had higher SBP (117.8 +/- 16 versus 113.6 +/- 12.6 mmHg; P = 0.010) and were at increased risk for hypertension (odds ratio 2.2; 95% confidence interval 1.1 to 4.5). Compared with the C, the G allele had 2.5-fold reduced transcriptional activity in transfected HEK293 cells. As predicted by the TRANSFAC database, competition with YY1 or Sp1 transcription factors specifically reduced the binding of HeLa cell nuclear proteins to -318C or -318G allele, respectively, as indicated by shifted electrophoretic mobility. A "supershift" of the nuclear proteins/-318G allele complex was observed after anti-Sp1 was added but not anti-YY1 antibody. The GNAI2 -318 C>G SNP impairs transcriptional activity through specific binding of Sp1 and is associated with high SBP in Caucasians from Italy.