Julie Anne Côté

Circulating interleukin-6 concentrations during and after gestational diabetes mellitus.

Objective. Recent studies have shown that high interleukin‐6 (IL‐6) secretion may aggravate insulin resistance in pregnancy and participate in the pathogenesis of gestational diabetes mellitus (GDM). The aim of this study was to determine whether the presence of GDM is associated with elevated IL‐6 concentrations and whether this association remains after delivery, independent of body mass index. Design. Longitudinal study. Setting. Hospital‐based. Sample. Forty‐seven women were screened for GDM with a 75g oral glucose tolerance test at 26.1±3.7 weeks of pregnancy following the Canadian Diabetes Association guidelines (20 GDM, 27 control subjects). Main outcome measures. Interleukin‐6 levels were measured by ELISA at the time of GDM screening and two months post‐partum. Results. Interleukin‐6 concentrations were significantly higher in women with GDM compared with control women at the time of GDM screening (1.47±0.72 vs. 0.90±0.32pg/mL, p≤0.01). Similar results were obtained two months post‐partum, where IL‐6 levels remained significantly higher in women with GDM compared with control women (1.88±0.85 vs. 1.41±0.87pg/mL, p≤0.05). Interleukin‐6 concentrations were significantly correlated with the Matsuda insulin sensitivity index, measured at the two time points (r=–0.60, p≤0.01 and r=–0.34, p≤0.05). The Matsuda insulin sensitivity index was an independent and significant predictor of IL‐6 concentrations at the time of GDM screening, explaining 35.6% of the variance (p≤0.0001) in this variable. IL‐6 concentration measured at GDM screening was identified as an independent and significant predictor of post‐partum IL‐6 concentrations, explaining 28.6% of the variance (p≤0.001). Conclusions. These results show that GDM is associated with elevated IL‐6 levels independent of obesity levels, both during pregnancy and after delivery.

Visceral/epicardial adiposity in nonobese and apparently healthy young adults: Association with the cardiometabolic profile

OBJECTIVE We investigate associations of regional adipose tissues with cardiometabolic profile of nonobese and apparently healthy young adults. METHODS Four hundred twenty-five nonobese and apparently healthy individuals were assessed for blood pressure and fasting lipid profile, blood glucose and adiponectin. Subcutaneous abdominal adipose tissue (SAT) and ectopic fat depots (visceral abdominal adipose tissue [VAT], epicardial adipose tissue [EAT] and hepatic fat fraction [HFF]) were quantified by magnetic resonance imaging. RESULTS According to anthropometric measurements, blood pressure and blood markers, the population (18-35 years, 54% women) had a low cardiometabolic risk. Compared to women, men had more VAT, EAT and HFF, but less SAT. Regional adipose tissues were positively correlated with each other. VAT and EAT carried significant correlations with all markers of cardiometabolic risk, while SAT and HFF correlated variably with these markers. While taking into account age and gender, SAT, VAT and EAT were associated with most cardiometabolic markers, while HFF was only associated with total cholesterol/high-density lipoprotein ratio (TC/HDL-C) and triglycerides (TG). When comparing SAT, VAT and EAT head-to-head, VAT was the only adipose tissue location maintaining significant association with most markers of cardiometabolic risk. Greater VAT (≥50th percentile) was associated with a worse cardiometabolic profile, whether individuals were overweight or normal weight. CONCLUSION Even in nonobese and apparently healthy young women and men, accumulation of ectopic visceral adiposity in general, and of VAT in particular, is associated with a worse cardiometabolic profile whether individuals were overweight or normal weight.

Circulating 5α-dihydrotestosterone, abdominal obesity and adipocyte characteristics in women

Abstract Background: The association between circulating androgen levels and fat distribution in women has been widely inconsistent among existing studies. Objective: We sought to investigate the relation between plasma adrenal and gonadal androgen levels and body fat distribution, as well as abdominal adipocyte characteristics. Methods: Paired omental and subcutaneous adipose tissue samples were surgically obtained from 60 women (age, 47±5 years; body mass index, 26±5 kg/m2) undergoing gynecological surgery. Body composition and fat distribution were measured by dual-energy X-ray absorptiometry and computed tomography, respectively. Adipocyte diameter, basal lipolysis, and heparin-releasable lipoprotein lipase activity were measured. Steroids were quantified using high-performance gas chromatography and mass spectrometry. Results: Significant negative associations were found between plasma dihydrotestosterone (DHT) levels and total adiposity (body mass index, r=–0.35, p<0.05; fat mass, r=–0.31, p<0.05) as well as computed tomography assessments of abdominal adiposity (r=–0.30, p<0.05 and r=–0.44, p<0.005 for subcutaneous and visceral adipose tissue area, respectively). The association between DHT levels and visceral adipose tissue area was independent of total body fat mass. A significant negative association was also observed between plasma DHT and omental adipocyte diameter (r=–0.27, p<0.05). When expressed as the omental/subcutaneous ratio, heparin-releasable lipoprotein lipase activity was negatively and significantly related to plasma DHT, androstenedione, and dehydroepiandrosterone (DHEA) levels. Conclusion: Abdominally obese women with large, metabolically active omental adipocytes appear to be characterized by reduced endogenous levels of DHT. The assumption that high androgen levels are associated with an android body fat distribution pattern in women should be critically re-examined.

Adipose tissue diacylglycerol acyltransferase activity and blood lipoprotein triglyceride enrichment in women with abdominal obesity.

UNLABELLED Previous studies have suggested altered triglyceride (TG) storage in patients with abdominal obesity and blood lipid disorders. OBJECTIVE We hypothesized that women with abdominal obesity and a dysmetabolic profile have low DGAT activity in their abdominal fat compartments. METHODS Paired omental (OM) and subcutaneous (SC) adipose tissue samples were obtained surgically from 39 women undergoing abdominal hysterectomies. Body composition and fat distribution were measured by dual energy x-ray absorptiometry and computed tomography. DGAT activity was measured by acylation of sn-l,2-diacylglycerol with [(14)C] oleoyl-CoA in microsomal fractions isolated from whole adipose tissue homogenates. DGAT activity was calculated on the basis of picomoles (pmol) TG synthesized in the assay per min per mg lipid, per μg protein or per 1000 cells. RESULTS No depot differences were found when DGAT activity was reported per μg microsomal protein or per 1000 cells. DGAT activity in either depot was not associated with adipocyte diameters and blood lipid profile variables. DGAT activity per mg lipid was higher in OM than in abdominal SC adipose tissue (0.43 ± 0.20 vs. 0.34 ± 0.18 pmol/min/mg lipid, p < 0.05). OM DGAT activity was negatively correlated with OM adipocyte diameter and visceral adipose tissue area (r = -0.43, p < 0.01 and r = -0.38, p < 0.05 respectively). Plasma total, LDL and HDL TG levels were negatively associated with OM DGAT activity independent of total body fat mass (r = -0.39, p < 0.05, r = -0.46, p < 0.001 and r = -0.40, p < 0.05 respectively). CONCLUSION A defect in adipose tissue DGAT activity is predictive of adiposity and blood lipoprotein TG enrichment only when considering activity per tissue lipid mass.

Temporal Changes in Gene Expression Profile during Mature Adipocyte Dedifferentiation

Objective. To characterize changes in gene expression profile during human mature adipocyte dedifferentiation in ceiling culture. Methods. Subcutaneous (SC) and omental (OM) adipose tissue samples were obtained from 4 participants paired for age and BMI. Isolated adipocytes were dedifferentiated in ceiling culture. Gene expression analysis at days 0, 4, 7, and 12 of the cultures was performed using Affymetrix Human Gene 2.0 STvi arrays. Hierarchical clustering according to similarity of expression changes was used to identify overrepresented functions. Results. Four clusters gathered genes with similar expression between day 4 to day 7 but decreasing expression from day 7 to day 12. Most of these genes coded for proteins involved in adipocyte functions (LIPE, PLIN1, DGAT2, PNPLA2, ADIPOQ, CEBPA, LPL, FABP4, SCD, INSR, and LEP). Expression of several genes coding for proteins implicated in cellular proliferation and growth or cell cycle increased significantly from day 7 to day 12 (WNT5A, KITLG, and FGF5). Genes coding for extracellular matrix proteins were differentially expressed between days 0, 4, 7, and 12 (COL1A1, COL1A2, and COL6A3, MMP1, and TGFB1). Conclusion. Dedifferentiation is associated with downregulation of transcripts encoding proteins involved in mature adipocyte functions and upregulation of genes involved in matrix remodeling, cellular development, and cell cycle.

Role of the TGF‐β pathway in dedifferentiation of human mature adipocytes

Dedifferentiation of adipocytes contributes to the generation of a proliferative cell population that could be useful in cellular therapy or tissue engineering. Adipocytes can dedifferentiate into precursor cells to acquire a fibroblast‐like phenotype using ceiling culture, in which the buoyancy of fat cells is exploited to allow them to adhere to the inner surface of a container. Ceiling culture is usually performed in flasks, which limits the ability to test various culture conditions. Using a new six‐well plate ceiling culture approach, we examined the relevance of TGF‐β signaling during dedifferentiation. Adipose tissue samples from patients undergoing bariatric surgery were digested with collagenase, and cell suspensions were used for ceiling cultures. Using the six‐well plate approach, cells were treated with SB431542 (an inhibitor of TGF‐β receptor ALK5) or human TGF‐β1 during dedifferentiation. Gene expression was measured in these cultures and in whole adipose tissue, the stromal–vascular fraction (SVF), mature adipocytes, and dedifferentiated fat (DFAT) cells. TGF‐β1 and collagen type I alpha 1 (COL1A1) gene expression was significantly higher in DFAT cells compared to whole adipose tissue samples and SVF cells. TGF‐β1, COL1A1, and COL6A3 gene expression was significantly higher at day 12 of dedifferentiation compared to day 0. In the six‐well plate model, treatment with TGF‐β1 or SB431542, respectively, stimulated and inhibited the TGF‐β pathway as shown by increased TGF‐β1, TGF‐β2, COL1A1, and COL6A3 gene expression and decreased expression of TGF‐β1, COL1A1, COL1A2, and COL6A3, respectively. Treatment of DFAT cells with TGF‐β1 increased the phosphorylation level of SMAD 2 and SMAD 3. Thus, a new six‐well plate model for ceiling culture allowed us to demonstrate a role for TGF‐β in modulating collagen gene expression during dedifferentiation of mature adipocytes.

Generation of human adipose stem cells through dedifferentiation of mature adipocytes in ceiling cultures.

Mature adipocytes have been shown to reverse their phenotype into fibroblast-like cells in vitro through a technique called ceiling culture. Mature adipocytes can also be isolated from fresh adipose tissue for depot-specific characterization of their function and metabolic properties. Here, we describe a well-established protocol to isolate mature adipocytes from adipose tissues using collagenase digestion, and subsequent steps to perform ceiling cultures. Briefly, adipose tissues are incubated in a Krebs-Ringer-Henseleit buffer containing collagenase to disrupt tissue matrix. Floating mature adipocytes are collected on the top surface of the buffer. Mature cells are plated in a T25-flask completely filled with media and incubated upside down for a week. An alternative 6-well plate culture approach allows the characterization of adipocytes undergoing dedifferentiation. Adipocyte morphology drastically changes over time of culture. Immunofluorescence can be easily performed on slides cultivated in 6-well plates as demonstrated by FABP4 immunofluorescence staining. FABP4 protein is present in mature adipocytes but down-regulated through dedifferentiation of fat cells. Mature adipocyte dedifferentiation may represent a new avenue for cell therapy and tissue engineering.