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Influence of Depot Origin on the Susceptibility of Adipose Progenitor Cells to Cell Death
Abstracts / Can J Diabetes 37 (2013) S13eS84
that are best associated with the standard measure derived from the insulin-glucose clamp and with central adiposity. Methods: Sixteen men and 10 women, aged 20 to 35 years, without any disease or family history of type 2 diabetes, underwent a 75 g OGTT and a 2-step euglycemic clamp with low- and highdose insulin infusions (10 and 40 mU/kg/min). OGTT indices of NEFA suppressibility were: area under the curve (AUC) of NEFA, AUCNEFAAUCinsulin, NEFA T50, insulin concentration at T50 (EC50) and negative slope of the log-linear portion of NEFA suppression curve corrected by AUCinsulin (NegSlopeLnNEFA/AUCIns). NEFA insulin suppression during the clamp was calculated by DNEFA/Dinsulin at low-dose insulin (from baseline¼positive results). Central adiposity was estimated mainly by the waist-to-hip ratio (WHR) and glucose insulin sensitivity, by the M/I value (clamp, high-dose insulin). Results: OGTT-derived indices of insulin-induced NEFA suppression significantly associated with clamp DNEFA/Dinsulin: AUCNEFAAUCinsulin (r¼0.54), EC50 (r¼0.50), NegSlopeLnNEFA/AUCIns (r¼e0.44) and %reductionNEFA/AUCinsulin (r¼e0.42). The only index significantly associated with WHR: AUCNEFAAUCinsulin (r¼0.55). Based on a step-wise regression analysis, the variables significantly and independently associated with WHR were: AUCNEFAAUCinsulin (p¼0.002) and AUCglucose (p¼0.01) (model R2¼0.49). Conclusions: AUCNEFAAUCinsulin may represent the best OGTTderived parameter to estimate sensitivity to insulin suppression of lipolysis because, in our sample, it was the only one significantly correlated with central adiposity. Moreover, among all metabolic parameters measured in our study, AUCNEFAAUCinsulin and AUCglucose were the two main factors independently associated with central adiposity.
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193 Erythropoietin Signalling in Adipocytes is Not Essential for Regulation of Metabolism In Vivo CYNTHIA T. LUK*, SALLY Y. SHI, DIANA CHOI, ERICA P. CAI, STEPHANIE A. SCHROER, MINNA WOO Toronto, ON Erythropoietin (EPO) has increasingly been shown to have extraerythropoietic and cytoprotective roles. Exogenous administration has recently been shown to have beneficial effects on obesity and diabetes in mouse models and we have previously shown that EPO protects against diabetes through direct effects on pancreatic b-cells. EPO can directly modulate adipogenesis and insulin signalling in 3T3-L1 adipocytes; however, its physiological role in vivo has not been identified. To study the role of erythropoietin signalling in adipocytes, we used an adipocyte protein 2 (aP2) CRE-loxP recombination system to generate adipose tissue-specific erythropoietin receptor (EpoR) knockout mice. Knockout mice did not display any differences in weight gain compared to wild-type littermate controls on either control chow diet (p¼0.65, n¼5 males; p¼0.46, n¼5 females) or high-fat diet (HFD) (p¼0.79, n¼10 males; p¼0.76, n¼10 females) up to 8 months of age. Similarly, even with HFD, disruption of EpoR did not significantly alter body composition, adipose tissue morphology or energy homeostasis, including energy expenditure, respiratory expenditure ratio or activity level. Furthermore, disruption of EPO signalling in adipocytes did not alter glucose tolerance (p0.05, n¼14) or insulin sensitivity (p0.05, n¼14) in vivo, and did not alter adipocyte inflammation or expression of genes involved in angiogenesis. In summary, we determine that adipocyte EPO signalling is not essential for maintenance of energy homeostasis or glucose metabolism. In contrast to the pharmacological effects of EPO, we demonstrate that physiological EPO signalling is not essential for adipose tissue regulation of metabolism.
192 Influence of Depot Origin on the Susceptibility of Adipose Progenitor Cells to Cell Death AMANDA BIERNACKA-LAROCQUE*, ANNEMARIE GAGNON, ALEXANDER SORISKY Ottawa, ON Nutrient excess and a sedentary lifestyle lead to an accumulation of adipose tissue (obesity) through an increase in adipocyte size (hypertrophy) and number (hyperplasia). Hypertrophic obesity results in dysfunctional adipocytes associated with adipose tissue inflammation and insulin resistance. On the other hand, hyperplastic adipose tissue expansion is linked to preservation of insulin sensitivity. Metabolically functional adipose tissue expansion via hyperplasia may require an adequate number of responsive adipose progenitor cells. Distinct adipose tissue depots vary with respect to functional responses, such as lipolysis and adipogenesis. The aim of this study was to investigate the influence of depot origin on the susceptibility of adipose progenitor cells to cell death. Using serum deprivation alone or in the presence of 25nM tumor necrosis factor (TNF) a, visceral omental (OM) versus abdominal subcutaneous (SC) adipose progenitor cells displayed a 3- and 1.7-fold increase in cell death, as assessed by by Hoechst staining, respectively (p<0.05, n¼3 or 4). Similar results were obtained when cell death rates were evaluated by cell enumeration. The ratio of OM/SC cell death in response to serum deprivation was positively correlated with body mass index (r¼0.96; p<0.01, n¼5). The depot-specific difference in apoptosis susceptibility observed was lost when a stronger apoptotic stimulus (TNFa with cycloheximide) was used. Depot-related differences in apoptotic susceptibility of adipose progenitor cells may influence regional cellular remodelling during adipose tissue expansion and alter metabolic functionality in obesity.
194 Assessing Energy Expenditure in Obese Adolescents in a Clinical Setting: Is the Handheld Indirect Calorimeter Valid and Accurate? PAULA P.W. WOO*, GAYATHRI MURTHY*, CINDY WONG, JEAN-PIERRE CHANOINE, RAJAVEL ELANGO Vancouver, BC As energy balance is dependent on caloric consumption and expenditure, providing food recommendations based on individualized energy assessment could optimize pediatric weight management. Resting energy expenditure (REE), which contributes 70% to 80% of total energy expenditure, is key to meaningful energy prescriptions. Standard open-circuit indirect calorimeter carts (VMax, VM), used as a gold standard, measure valid REE but are not easily accessible. Recently, a handheld indirect calorimeter (MedGem, MG) has become available in the pediatric outpatient clinic. Its validity, however, has never been assessed in the obese adolescent ambulatory population. Objective: To validate REE measured by MG against VM in obese adolescents and to compare measured REE with those estimated by predictive equations. Methods: Eighteen adolescents (7:11, M:F), aged 14.71.8 years, participated in the study after an overnight fast. Anthropometric measurements were performed. REE were measured with both MG (upright, 7 to 13 mins) and VM (supine, 20 to 25 mins) in random order. Results: Body mass index was 31.34.7 kg/m2. Measured average REE using MG and VM were 1608331 kcal/day (19.6 kcal/kg) and 1666335 kcal/day (20.3 kcal/kg), respectively. Data show significant correlation (R2¼0.89) between the 2 methods. Predictive equations overestimate REE by 25% of indirect calorimeters.
that are best associated with the standard measure derived from the insulin-glucose clamp and with central adiposity. Methods: Sixteen men and 10 women, aged 20 to 35 years, without any disease or family history of type 2 diabetes, underwent a 75 g OGTT and a 2-step euglycemic clamp with low- and highdose insulin infusions (10 and 40 mU/kg/min). OGTT indices of NEFA suppressibility were: area under the curve (AUC) of NEFA, AUCNEFAAUCinsulin, NEFA T50, insulin concentration at T50 (EC50) and negative slope of the log-linear portion of NEFA suppression curve corrected by AUCinsulin (NegSlopeLnNEFA/AUCIns). NEFA insulin suppression during the clamp was calculated by DNEFA/Dinsulin at low-dose insulin (from baseline¼positive results). Central adiposity was estimated mainly by the waist-to-hip ratio (WHR) and glucose insulin sensitivity, by the M/I value (clamp, high-dose insulin). Results: OGTT-derived indices of insulin-induced NEFA suppression significantly associated with clamp DNEFA/Dinsulin: AUCNEFAAUCinsulin (r¼0.54), EC50 (r¼0.50), NegSlopeLnNEFA/AUCIns (r¼e0.44) and %reductionNEFA/AUCinsulin (r¼e0.42). The only index significantly associated with WHR: AUCNEFAAUCinsulin (r¼0.55). Based on a step-wise regression analysis, the variables significantly and independently associated with WHR were: AUCNEFAAUCinsulin (p¼0.002) and AUCglucose (p¼0.01) (model R2¼0.49). Conclusions: AUCNEFAAUCinsulin may represent the best OGTTderived parameter to estimate sensitivity to insulin suppression of lipolysis because, in our sample, it was the only one significantly correlated with central adiposity. Moreover, among all metabolic parameters measured in our study, AUCNEFAAUCinsulin and AUCglucose were the two main factors independently associated with central adiposity.
S67
193 Erythropoietin Signalling in Adipocytes is Not Essential for Regulation of Metabolism In Vivo CYNTHIA T. LUK*, SALLY Y. SHI, DIANA CHOI, ERICA P. CAI, STEPHANIE A. SCHROER, MINNA WOO Toronto, ON Erythropoietin (EPO) has increasingly been shown to have extraerythropoietic and cytoprotective roles. Exogenous administration has recently been shown to have beneficial effects on obesity and diabetes in mouse models and we have previously shown that EPO protects against diabetes through direct effects on pancreatic b-cells. EPO can directly modulate adipogenesis and insulin signalling in 3T3-L1 adipocytes; however, its physiological role in vivo has not been identified. To study the role of erythropoietin signalling in adipocytes, we used an adipocyte protein 2 (aP2) CRE-loxP recombination system to generate adipose tissue-specific erythropoietin receptor (EpoR) knockout mice. Knockout mice did not display any differences in weight gain compared to wild-type littermate controls on either control chow diet (p¼0.65, n¼5 males; p¼0.46, n¼5 females) or high-fat diet (HFD) (p¼0.79, n¼10 males; p¼0.76, n¼10 females) up to 8 months of age. Similarly, even with HFD, disruption of EpoR did not significantly alter body composition, adipose tissue morphology or energy homeostasis, including energy expenditure, respiratory expenditure ratio or activity level. Furthermore, disruption of EPO signalling in adipocytes did not alter glucose tolerance (p0.05, n¼14) or insulin sensitivity (p0.05, n¼14) in vivo, and did not alter adipocyte inflammation or expression of genes involved in angiogenesis. In summary, we determine that adipocyte EPO signalling is not essential for maintenance of energy homeostasis or glucose metabolism. In contrast to the pharmacological effects of EPO, we demonstrate that physiological EPO signalling is not essential for adipose tissue regulation of metabolism.
192 Influence of Depot Origin on the Susceptibility of Adipose Progenitor Cells to Cell Death AMANDA BIERNACKA-LAROCQUE*, ANNEMARIE GAGNON, ALEXANDER SORISKY Ottawa, ON Nutrient excess and a sedentary lifestyle lead to an accumulation of adipose tissue (obesity) through an increase in adipocyte size (hypertrophy) and number (hyperplasia). Hypertrophic obesity results in dysfunctional adipocytes associated with adipose tissue inflammation and insulin resistance. On the other hand, hyperplastic adipose tissue expansion is linked to preservation of insulin sensitivity. Metabolically functional adipose tissue expansion via hyperplasia may require an adequate number of responsive adipose progenitor cells. Distinct adipose tissue depots vary with respect to functional responses, such as lipolysis and adipogenesis. The aim of this study was to investigate the influence of depot origin on the susceptibility of adipose progenitor cells to cell death. Using serum deprivation alone or in the presence of 25nM tumor necrosis factor (TNF) a, visceral omental (OM) versus abdominal subcutaneous (SC) adipose progenitor cells displayed a 3- and 1.7-fold increase in cell death, as assessed by by Hoechst staining, respectively (p<0.05, n¼3 or 4). Similar results were obtained when cell death rates were evaluated by cell enumeration. The ratio of OM/SC cell death in response to serum deprivation was positively correlated with body mass index (r¼0.96; p<0.01, n¼5). The depot-specific difference in apoptosis susceptibility observed was lost when a stronger apoptotic stimulus (TNFa with cycloheximide) was used. Depot-related differences in apoptotic susceptibility of adipose progenitor cells may influence regional cellular remodelling during adipose tissue expansion and alter metabolic functionality in obesity.
194 Assessing Energy Expenditure in Obese Adolescents in a Clinical Setting: Is the Handheld Indirect Calorimeter Valid and Accurate? PAULA P.W. WOO*, GAYATHRI MURTHY*, CINDY WONG, JEAN-PIERRE CHANOINE, RAJAVEL ELANGO Vancouver, BC As energy balance is dependent on caloric consumption and expenditure, providing food recommendations based on individualized energy assessment could optimize pediatric weight management. Resting energy expenditure (REE), which contributes 70% to 80% of total energy expenditure, is key to meaningful energy prescriptions. Standard open-circuit indirect calorimeter carts (VMax, VM), used as a gold standard, measure valid REE but are not easily accessible. Recently, a handheld indirect calorimeter (MedGem, MG) has become available in the pediatric outpatient clinic. Its validity, however, has never been assessed in the obese adolescent ambulatory population. Objective: To validate REE measured by MG against VM in obese adolescents and to compare measured REE with those estimated by predictive equations. Methods: Eighteen adolescents (7:11, M:F), aged 14.71.8 years, participated in the study after an overnight fast. Anthropometric measurements were performed. REE were measured with both MG (upright, 7 to 13 mins) and VM (supine, 20 to 25 mins) in random order. Results: Body mass index was 31.34.7 kg/m2. Measured average REE using MG and VM were 1608331 kcal/day (19.6 kcal/kg) and 1666335 kcal/day (20.3 kcal/kg), respectively. Data show significant correlation (R2¼0.89) between the 2 methods. Predictive equations overestimate REE by 25% of indirect calorimeters.