Biomedical subjects

F M Gregoire

Publications and source records attributed to F M Gregoire.

10 recordsLinked to original sources

PubMed2001

Adipocyte differentiation: from fibroblast to endocrine cell.

Recent advances regarding the biology of adipose tissue have demonstrated that white adipose tissue (WAT) plays a central role in the regulation of energy balance and acts as a secretory/endocrine organ that mediates numerous physiological and pathological processes. Dysregulation of WAT mass causes obesity or lipoatrophy, two disorders associated with life-threatening pathologies, including cardiovascular diseases and diabetes. Alterations in WAT mass result from changes in adipocyte size and/or number. Change in adipocyte number is achieved through a complex interplay between proliferation and differentiation of preadipocytes. Adipocyte differentiation or adipogenesis is a highly controlled process that has been extensively studied for the last 25 years. In vitro preadipocyte culture systems that recapitulate most of the critical aspects of fat cell formation in vivo have allowed a meticulous dissection of the cellular and molecular events involved in the adipogenesis process. The adipogenic transcription factors peroxisome proliferator-activated receptor-gamma and CCAAT/enhancer binding protein-alpha play a key role in the complex transcriptional cascade that occurs during adipogenesis. Hormonal and nutritional signaling affects adipocyte differentiation in a positive or negative manner, and components involved in cell-cell or cell-matrix interactions are also pivotal in regulating the differentiation process. This knowledge provides a basis for understanding the physiological and pathophysiological mechanisms that underlie adipose tissue formation and for the development of novel and sound therapeutic approaches to treat obesity and its related diseases.

Adipocytes↗

PubMed1999

T(3) stimulates resting metabolism and UCP-2 and UCP-3 mRNA but not nonphosphorylating mitochondrial respiration in mice.

The molecular basis for variations in resting metabolic rate (RMR) within a species is unknown. One possibility is that variations in RMR occur because of variations in uncoupling protein 2 (UCP-2) and uncoupling protein 3 (UCP-3) expression, resulting in mitochondrial proton leak differences. We tested the hypothesis that UCP-2 and -3 mRNAs positively correlate with RMR and proton leak. We treated thyroidectomized and sham-operated mice with triiodothyronine (T(3)) or vehicle and measured RMR, liver, and skeletal muscle mitochondrial nonphosphorylating respiration and UCP-2 and -3 mRNAs. T(3) stimulated RMR and liver UCP-2 and gastrocnemius UCP-2 and -3 expression. Mitochondrial respiration was not affected by T(3) and did not correlate with UCP-2 and -3 mRNAs. Gastrocnemius UCP-2 and -3 expression did correlate with RMR. We conclude 1) T(3) did not influence intrinsic mitochondrial properties such as membrane structure and composition, and 2) variations in UCP-2 and -3 expression may partly explain variations in RMR. One possible explanation for these data is that T(3) stimulates the leak in vivo but not in vitro because a posttranslational regulator of UCP-2 and -3 is not retained in the mitochondrial fraction.

Animals↗

PubMed1998

Cloning and developmental regulation of a novel member of the insulin-like gene family in Caenorhabditis elegans.

Aging, metabolism and fat accumulation in Caenorhabditis elegans (C. elegans) are influenced by mutations in DAF-2, a putative insulin-like receptor. Ten putative insulin-like genes have been recently identified from the C. elegans genome database. However, it is unclear if these genes are orthologues of human insulin since they lack the C-peptide dibasic amino acid proteolysis sites. We have identified and measured mRNA expression during development of two novel members of the C. elegans insulin-like gene family. We also report the sequence characterization and gene structure for one of these, the insulin-like protein-1 (ILP1). We focused on ILP1 characterization because it has structural features consistent with its being a candidate insulin ligand for the DAF-2 insulin-like receptor. For example, ILP1 has a putative C-peptide flanked by dibasic amino acids, exhibits conserved cysteine residues that could provide disulfide bonds between the A and B chains, and has two introns. Northern blot analysis revealed that ILP1 mRNA is expressed at very high levels in embryos and is downregulated very early during postnatal development, suggesting that it may influence embryonic development, but not Dauer formation. We also identified a novel insulin-like growth factor-1-like protein (T28B8/IGF-I) that exhibits a very different developmental expression profile than ILP1. Our results are consistent with the hypothesis that members of the unusually large and complex C. elegans insulin-like protein family exhibit complex and perhaps redundant roles.

Amino Acid Sequence↗

PubMed1998

Understanding adipocyte differentiation.

The adipocyte plays a critical role in energy balance. Adipose tissue growth involves an increase in adipocyte size and the formation of new adipocytes from precursor cells. For the last 20 years, the cellular and molecular mechanisms of adipocyte differentiation have been extensively studied using preadipocyte culture systems. Committed preadipocytes undergo growth arrest and subsequent terminal differentiation into adipocytes. This is accompanied by a dramatic increase in expression of adipocyte genes including adipocyte fatty acid binding protein and lipid-metabolizing enzymes. Characterization of regulatory regions of adipose-specific genes has led to the identification of the transcription factors peroxisome proliferator-activated receptor-gamma (PPAR-gamma) and CCAAT/enhancer binding protein (C/EBP), which play a key role in the complex transcriptional cascade during adipocyte differentiation. Growth and differentiation of preadipocytes is controlled by communication between individual cells or between cells and the extracellular environment. Various hormones and growth factors that affect adipocyte differentiation in a positive or negative manner have been identified. In addition, components involved in cell-cell or cell-matrix interactions such as preadipocyte factor-1 and extracellular matrix proteins are also pivotal in regulating the differentiation process. Identification of these molecules has yielded clues to the biochemical pathways that ultimately result in transcriptional activation via PPAR-gamma and C/EBP. Studies on the regulation of the these transcription factors and the mode of action of various agents that influence adipocyte differentiation will reveal the physiological and pathophysiological mechanisms underlying adipose tissue development.

Adipocytes↗

PubMed1998

Evidence that glucose metabolism regulates leptin secretion from cultured rat adipocytes.

Circulating leptin secreted from adipocytes is correlated with fat mass and plasma insulin concentrations in humans and rodents. Plasma leptin, insulin, and glucose decrease during fasting and increase after refeeding; however, the underlying mechanisms regulating the changes of leptin secretion are not known. To investigate the role of insulin-stimulated glucose metabolism in the regulation of leptin secretion, we examined the effects of insulin and inhibitors of glucose transport and metabolism on leptin secretion from rat adipocytes in primary culture. Insulin (0.16-16 nM) increased leptin secretion over 96 h; however, the increase in leptin was more closely related to the amount of glucose taken up by the adipocytes (r = 0.64; P < 0.0001) than to the insulin concentration per se (r = 0.20; P < 0.28), suggesting a role for glucose transport and/or metabolism in regulating leptin secretion. 2-Deoxy-D-glucose (2-DG), a competitive inhibitor of glucose transport and phosphorylation, caused a concentration-dependent (2-50 mg/dl) inhibition of leptin release in the presence of 1.6 nM insulin. The inhibitory effect of 2-DG was reversed by high concentrations of glucose. Two other inhibitors of glucose transport, phloretin (0.05-0.25 mM) and cytochalasin-B (0.5-50 microM), also inhibited leptin secretion. Inhibition of leptin secretion by these agents was proportional to the inhibition of glucose uptake (r = 0.60 to 0.86; all P < 0.01). Two inhibitors of glycolysis, iodoacetate (0.005-1.0 mM) and sodium fluoride (0.1-5 mM), produced concentration-dependent inhibition of leptin secretion in the presence of 1.6 nM insulin. In addition, both 2-DG and sodium fluoride markedly decreased the leptin (ob) messenger RNA content of cultured adipocytes, but did not affect 18S ribosomal RNA content. We conclude that glucose transport and metabolism are important factors in the regulation of leptin expression and secretion and that the effect of insulin to increase adipocyte glucose utilization is likely to contribute to insulin-stimulated leptin secretion. Thus, in vivo, decreased adipose glucose metabolism may be one mechanism by which fasting decreases circulating leptin, whereas increased adipose glucose metabolism would increase leptin after refeeding.

Adipocytes↗

PubMed1997

Changes of islet size and islet size distribution resulting from protein-malnutrition in lean (Fa/Fa) and obese (fa/fa) Zucker rats.

Potential alterations in islet size and islet size distribution resulting from protein malnutrition were studied in lean (Fa/Fa) and obese (fa/fa) Zucker rats. The purpose was to investigate whether the distribution of enlarged islets in obese rats was altered by low-protein feeding. Four-week-old, male, lean and obese Zucker rats were fed either a diet containing 20% (w/w) protein (control diet) or a diet containing 5% (w/w) protein (low-protein diet) for 3 weeks. Pancreata were dissected at autopsy and immunostained for insulin. Islet size and distribution were determined by morphometric analysis. Bodyweight gain, food intake, and serum insulin and glucose were also measured. After 3 weeks on the diets, serum insulin was significantly lower in both lean (-75%) and obese (-54%) rats fed low protein compared with that in controls. However, obese rats were still hyperinsulinemic compared with lean rats. Protein malnutrition resulted in a shift in distribution of islets to smaller size both in lean and in obese rats, with an increase in the population of small islets (< or = 100 microns2) and a decrease in the population of large islets (> 20,000 microns2). In lean and obese rats fed low protein, beta-cell weight was significantly lower, beta cell volume fraction tended to decrease, and islet number per section area was significantly elevated when compared with controls. Taken together, these results show that protein deficiency alters the endocrine pancrease in both lean and obese Zucker rats. Although the decrease in islet size and the shift in distribution to smaller islets most likely contribute to the decrease in serum insulin concentration, these changes appear insufficient to normalize hyperinsulinemia in the obese Zucker rat.

Animals↗

PubMed1995

A low protein diet lowers islet insulin secretion but does not alter hyperinsulinemia in obese Zucker (fa/fa) rats.

The effects of feeding a low protein diet on pancreatic insulin secretion early in life in genetically lean and obese Zucker rats were studied. Four-week-old lean (Fa/Fa) and obese (fa/fa) Zucker rats were fed either a 5% protein or a 20% protein diet for 3 wk. Rats were killed at 7 wk of age. Pancreatic islets were isolated and insulin response of islets was measured in a 60-min static incubation under one of the following conditions: 2.7 mmol/L glucose +/- 10 mmol/L arginine, 8.3 mmol/L glucose +/- 10 mmol/L arginine, and 16.7 mmol/L glucose. Serum insulin was significantly lower (P < or = 0.05) in lean, but not in obese rats fed low protein compared with those fed the normal protein diet. Interestingly, obese rats fed the low protein diet had the highest plasma glucose concentrations (P < or = 0.05) among the four groups. Feeding the low protein diet reduced insulin secretion of islets from lean rats by 70%, and from obese rats by 30 to 50% compared with rats fed the normal protein diet. Insulin content of islets was reduced significantly in lean rats fed the low protein diet (by 70%) and in obese rats (by 50%). A short-term protein deficiency early in life reduced in vitro insulin secretion of islets from both lean and obese rats. However, reductions in insulin content and insulin release from islets resulting from low protein feeding were not sufficient to alter hyperinsulinemia in genetically obese Zucker rats.

Animals↗

PubMed1994

Positive modulation of the adipoconversion of adipoblasts derived from genetically obese rats by sodium butyrate.

Using a new serum-free primary culture system, we have previously reported genotypic differences between adipoblasts derived from the epididymal adipose deposit of lean and obese 8-week-old Zucker and Wistar Diabetic Fatty (WDF) rats (15). In these strictly controlled culture conditions, obese-derived adipoblasts expressed low levels of the late markers of differentiation (lipid accumulation, GPDH). In order to further characterize obese-derived adipoblasts and analyze the critical relationship between growth and differentiation, growth arrest was induced in lean- and obese-derived cultures using sodium butyrate treatment. Addition of 2.5 mM sodium butyrate to the serum-free medium from day 1 reduced markedly the growth of lean as well as obese-derived cells. Adipoconversion of lean-derived adipoblasts was not altered, similar levels of LPL and GPDH activities being obtained in control and butyrate-treated groups. By contrast, a marked increase in both activities was observed in obese-derived cultures, restoring the level of both markers of differentiation to the lean level. Similar results were obtained with adipoblasts derived from subcutaneous inguinal (ING) fat pad of obese Zucker as well as adipoblasts derived from ING and EPI fat deposits from obese WDF rats. Taken together, these results suggest that adipose deposits of these genetically obese rats contain a specific adipoblast population which differs from lean-derived adipoblasts in respect to its adipoconversion capacity and/or its stage of commitment to differentiation.

Adipocytes↗

PubMed1990

[Prevention of aspiration pneumonia in obstetrical anesthesia with the effervescent combination of cimetidine and sodium citrate].

The effect of an oral effervescent formulation combining 200 mg cimetidine and 1.8 g sodium citrate on gastric pH and volume were studied in patients undergoing caesarean section. Seventy-four patients undergoing elective (group 1) or emergency caesarean section (group 2) were included. Before entering the operating theater (5 to 60 min before intubation), they were given the tablet dissolved in 15 ml of water. Induction and maintenance of anaesthesia were carried out with conventional techniques. The patient's gastric content was aspirated just after endotracheal intubation, and before extubation. its pH and volume were measured at both times. Mean pH was similar in the two groups after intubation (6.07 +/- 1.13 in group 1; 5.52 +/- 1.14 in group 2) and before extubation (6.32 +/- 1.08 vs. 5.85 +/- 1.02 respectively). Gastric pH was therefore greater than 2.5 in all 74 patients at both times. Mean volumes of gastric content after intubation were greater in group 2 (32.7 +/- 23.9 ml vs. 21.6 +/- 15.8 ml; p less than 0.02). However, just before extubation, these were similar (15.0 +/- 15.4 ml in group 1, 20.1 +/- 14.9 ml in group 2). The percentage of patients in the 2 groups with gastric volumes greater than 25 ml at the time of intubation were not significantly different (29.7% vs. 45.9% respectively). No patient was at risk of developing pneumonitis in case of aspiration (gastric content pH less than 2.5 and volume greater than 25 ml), either during endotracheal intubation or extubation.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗

PubMed1990

Aspiration pneumonitis prophylaxis in obstetric anaesthesia: comparison of effervescent cimetidine-sodium citrate mixture and sodium citrate.

One hundred and forty-seven patients undergoing elective or emergency Caesarean section under general anaesthesia were allocated randomly to three groups: group 1 (n = 28) received no premedication; group 2 (n = 58) received 0.3-molar sodium citrate 15 ml (sodium citrate 1.16 g); group 3 (n = 61) received effervescent cimetidine-sodium citrate combination (cimetidine 400 mg with sodium citrate 0.9 g) after entering the operating room. Gastric pH was measured at tracheal intubation (pH1) and extubation (pH2). Mean pH1 and mean pH2 values in group 1 were, respectively, 2.25 (SD 1.35) and 2.83 (1.64). Mean pH1 and pH2 values in group 2 were, respectively, 4.38 (1.44) and 4.57 (1.51). In group 3 mean pH1 and pH2 values were, respectively, 5.07 (1.13) and 5.37 (1.30). Percentages of patients with pH1 less than or equal to 2.5 in groups 1, 2 and 3 were, respectively, 75, 13.8 and 1.6. Percentages of patients with pH2 less than or equal to 2.5 in groups 1, 2 and 3 were 50, 10.3 and 1.6, respectively.

Adult↗