Janine McMillan

Decorin is a secreted protein associated with obesity and type 2 diabetes

Objective:To characterize the expression of the small leucine-rich glycoprotein decorin in adipose tissue.Design:Real-time PCR was used to measure decorin gene expression in adipose tissue from normal glucose tolerant (NGT), impaired glucose tolerant and type 2 diabetic (T2D) Psammomys obesus. Adipose tissue was fractionated to determine which cells were responsible for decorin expression. The location of decorin protein expression in adipose tissue was determined using immunohistochemistry. Real-time PCR was used to measure decorin mRNA levels in human adipose tissue from 16 insulin-sensitive, 16 insulin-resistant and 6 T2D human subjects. Circulating plasma decorin concentrations were measured by enzyme-linked immunosorbent assay in 145 NGT and 141 T2D human individuals from a large-scale epidemiological study in Mauritius.Results:Decorin mRNA was found to be highly expressed in adipose tissue, and decorin gene expression was significantly higher in visceral than that in subcutaneous adipose tissue depots in both P. obesus and human subjects (P=0.002 and P=0.001, respectively). Decorin mRNA was predominantly expressed by stromal/vascular cells of adipose tissue, and decorin protein in adipose tissue was primarily detected adjacent to blood vessels. Circulating plasma decorin levels in humans were elevated by 12% in T2D (P=0.049) compared to NGT subjects. There was a significant independent correlation between plasma decorin levels and waist-to-hip ratio (WHR, P=0.024). In male subjects, plasma decorin levels were significantly correlated with WHR (P=0.006), and fasting and 2-h glucose levels in an oral glucose tolerance test (P=0.027 and P=0.001, respectively).Conclusions:Decorin expression in adipose tissue was markedly upregulated in the obese state and may therefore play a role in adipose tissue homeostasis or in pathophysiology associated with obesity.

Calpain 3 gene expression in skeletal muscle is associated with body fat content and measures of insulin resistance.

OBJECTIVE: To investigate whether skeletal muscle gene expression of calpain 3 is related to obesity and insulin resistance.DESIGN: Cross-sectional studies in 27 non-diabetic human subjects and in Psammomys obesus, a polygenic animal model of obesity and type 2 diabetes.MEASUREMENTS: Expression of CAPN3 in skeletal muscle was measured using Taqman fluorogenic PCR. In the human subjects, body composition was assessed by DEXA and insulin sensitivity was measured by euglycemic–hyperinsulinemic clamp. In Psammomys obesus, body composition was determined by carcass analysis, and substrate oxidation rates, physical activity and energy expenditure were measured by whole-body indirect calorimetry.RESULTS: In human subjects, calpain 3 gene expression was negatively correlated with total (P=0.022) and central abdominal fat mass (P=0.034), and with blood glucose concentration in non-obese subjects (P=0.017). In Psammomys obesus, calpain 3 gene expression was negatively correlated with circulating glucose (P=0.013) and insulin (P=0.034), and with body fat mass (P=0.049). Indirect calorimetry revealed associations between calpain 3 gene expression and carbohydrate oxidation (P=0.009) and energy expenditure (P=0.013).CONCLUSION/INTERPRETATION: Lower levels of expression of calpain 3 in skeletal muscle were associated with reduced carbohydrate oxidation and elevated circulating glucose and insulin concentrations, and also with increased body fat and in particular abdominal fat. Therefore, reduced expression of calpain 3 in both humans and Psammomys obesus was associated with phenotypes related to obesity and insulin resistance.

Identification of secreted proteins associated with obesity and type 2 diabetes in Psammomys obesus.

Objective:Skeletal muscle produces a variety of secreted proteins that have important roles in intercellular communication and affects processes such as glucose homoeostasis. The objective of this study was to develop a novel Signal Sequence Trap (SST) in conjunction with cDNA microarray technology to identify proteins secreted from skeletal muscle of Psammomys obesus that were associated with obesity and type 2 diabetes (T2D).Design:Secreted proteins that were differentially expressed between lean, normal glucose tolerant (NGT), overweight and impaired glucose tolerant (IGT) and obese, T2D P. obesus were isolated using SST in conjunction with cDNA microarray technology. Subsequent gene expression was measured in tissues from P. obesus by real-time PCR (RT-PCR).Results:The SST yielded 1600 positive clones, which were screened for differential expression. A total of 91 (∼6%) clones were identified by microarray to be differentially expressed between NGT, IGT and T2D P. obesus. These clones were sequenced to identify 51 genes, of which only 27 were previously known to encode secreted proteins. Three candidate genes not previously associated with obesity or type 2 diabetes, sushi domain containing 2, collagen and calcium-binding EGF domains 1 and periostin (Postn), as well as one gene known to be associated, complement component 1, were shown by RT-PCR to be differentially expressed in skeletal muscle of P. obesus. Further characterization of the secreted protein Postn revealed it to be predominantly expressed in adipose tissue, with higher expression in visceral compared with subcutaneous adipose depots.Conclusion:SST in conjunction with cDNA microarray technology is a powerful tool to identify differentially expressed secreted proteins involved in complex diseases such as obesity and type 2 diabetes. Furthermore, a number of candidate genes were identified, in particular, Postn, which may have a role in the development of obesity and type 2 diabetes.

Effects of beacon administration on energy expenditure and substrate utilisation in Psammomys obesus (Israeli sand rats)

OBJECTIVE: To investigate whether beacon administration affects substrate utilisation, physical activity levels or energy expenditure in Psammomys obesus.DESIGN: Pairs of age- and sex-matched Psammomys obesus were randomly assigned to either beacon-treated (15 μg/day for 7 days (i.c.v.)) or control (i.c.v. saline) groups.MEASUREMENTS: Indirect calorimetry on day 0 and day 7 to measure oxygen consumption and carbon dioxide production, which were used to calculate fat oxidation, carbohydrate oxidation and total energy expenditure. Physical activity in the calorimeter was measured using an infrared beam system. Food intake and body weight were measured daily.RESULTS: The administration of beacon significantly increased body weight compared to saline-treated control animals. This body weight gain was primarily due to increased body fat content. Average daily food intake tended to be higher in beacon-treated Psammomys obesus, but no effect of beacon administration on substrate oxidation, activity or energy expenditure was detected.CONCLUSION: The effects of beacon on body weight are due to increased food intake, with no detectable effect on nutrient partitioning, physical activity or energy expenditure.

AGT-121, a novel hypothalamic gene implicated in the development of obesity

High prevalence of foot ulceration in the Balkan region a multicenter study from the BALKANDIAB network. C. N. Manes1, C. Ionescu-Tirgoviste2, L. Koeva3, D. Koev4, F. Agaci5, P. Djordjevic6, M. Bogoev7; 1Diabetes Unit, „Papageorgiou“ Gen. Hospital, Thessaloniki, Greece, 2N. Paulescu, Bucharest, Romania, 3University of Varna, Varna, Bulgaria, 4Bulgarian Society of Endocrinology, Sofia, Bulgaria, 5“Mother Teresa“, University Hospital Center, Tirana, Albania, 6Diabetes Unit, Institute of Endocrinology, Belgrade, Yugoslavia, 7Clinic of Endocrinology, Skopje, The former Yugoslav Republic of Macedonia.

Periostin, a novel secreted protein involved in the pathogenesis of obesity and type 2 diabetes.

Insulin resistance of glucose and fat metabolism in T2DM is firmly established whereas that of protein remains controversial. We addressed this in nine lean (L), 11 overweight/obese (O/O) non-diabetic and 10 T2DM male subjects using the hyperinsulinemic (40 mU/m min), euglycemic (5.5 mM), isoaminoacidemic (maintaining post-absorptive plasma amino acids) clamp. [3-3H]glucose and [1-13C]leucine kinetics were measured. BMI in L (21 ± 0.4) was <O/O and T2DM (both 29 ± 1 kg/m, P < 0.001) but FFM did not differ, nor did waist circumference between O/O and T2DM. Fasting glycemia was 10.4 ± 0.5 mM in T2DM, and insulin was higher (126 ± 17) vs. O/O (75 ± 7) and L (63 ± 3 pM, P < 0.05). Clamp insulin was higher in T2DM (663 ± 23) and O/O (647 ± 22) than L (552 ± 30 pM, P < 0.05). The response of protein synthesis (S) to hyperinsulinemia was markedly blunted in T2DM vs. L (P < 0.001), and <O/O. S was stimulated 23 ± 4% in L, only 6 ± 2% in O/O, but not in T2DM (-2 ± 2%), P < 0.001. Breakdown (B) was inhibited comparably in all. Increase in net balance (S-B) was greater in L (48 ± 2) than in O/O (40 ± 2) and T2DM (36 ± 3 lmol/min), P < 0.05. Clamp glucose disposal (Rd) was lower in T2DM (232 ± 19 vs. 486 ± 48 mg/min, in O/O (P < 0.001), vs. 550 ± 48 in L (P < 0.001). Clamp glucose Rd correlated with S (r = 0.408, P = 0.028, n = 30, controlled for FFM) and S-B (r = 0.678, P < 0.001) and anabolic response (DS-B), (r = 0.604, P < 0.001). Thus, (i) T2DM in men is associated with diminished insulin-stimulated protein synthesis and is dramatically impaired compared to L; (ii) Whereas resistance of protein anabolism to insulin parallels that of glucose, sensitivity of breakdown suppression does not appear to be impaired; and (iii) Insulin resistance of protein metabolism in T2DM and its correction have important therapeutic implications.