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. 2014 Feb 5;9(2):e86815.
doi: 10.1371/journal.pone.0086815. eCollection 2014.

Alterations of Pancreatic Islet Structure, Metabolism and Gene Expression in Diet-Induced Obese C57BL/6J Mice

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Free PMC article

Alterations of Pancreatic Islet Structure, Metabolism and Gene Expression in Diet-Induced Obese C57BL/6J Mice

Regan Roat et al. PLoS One. .
Free PMC article

Abstract

The reduction of functional β cell mass is a key feature of type 2 diabetes. Here, we studied metabolic functions and islet gene expression profiles of C57BL/6J mice with naturally occurring nicotinamide nucleotide transhydrogenase (NNT) deletion mutation, a widely used model of diet-induced obesity and diabetes. On high fat diet (HF), the mice developed obesity and hyperinsulinemia, while blood glucose levels were only mildly elevated indicating a substantial capacity to compensate for insulin resistance. The basal serum insulin levels were elevated in HF mice, but insulin secretion in response to glucose load was significantly blunted. Hyperinsulinemia in HF fed mice was associated with an increase in islet mass and size along with higher BrdU incorporation to β cells. The temporal profiles of glucose-stimulated insulin secretion (GSIS) of isolated islets were comparable in HF and normal chow fed mice. Islets isolated from HF fed mice had elevated basal oxygen consumption per islet but failed to increase oxygen consumption further in response to glucose or carbonyl cyanide-4-trifluoromethoxyphenylhydrazone (FCCP). To obtain an unbiased assessment of metabolic pathways in islets, we performed microarray analysis comparing gene expression in islets from HF to normal chow-fed mice. A few genes, for example, those genes involved in the protection against oxidative stress (hypoxia upregulated protein 1) and Pgc1α were up-regulated in HF islets. In contrast, several genes in extracellular matrix and other pathways were suppressed in HF islets. These results indicate that islets from C57BL/6J mice with NNT deletion mutation develop structural, metabolic and gene expression features consistent with compensation and decompensation in response to HF diet.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. In vivo glucose homeostasis and insulin secretion in BL6J on high fat diet.
(A–C) Male Bl6J mice were weaned to regular rodent chow (NC, 4.5% kcal fat diet) or high fat diet (HF, 45% kcal fat diet) and allowed free access to food. Body weight (BW, A), tail blood glucose (B), and blood insulin levels (C) were determined at indicated time. (D–F) I.P. Glucose Tolerance Test was performed in Bl6J mice on NC or HF diet for 3 months. (D) Blood glucose levels and (E) insulin levels during the test. (F) The increase in serum insulin levels was expressed taking the value at the time 0 as 100%. Data are mean ± s.e.m., (A–B) both n = 7, a repeated measures ANOVA p<0.005. (C) n = 10–14. (D) n = 7, a repeated measures ANOVA p<0.005. (E) n = 4–5, a repeated measures ANOVA p<0.05. (F) n = 4–5. * p<0.05, ** p<0.01, *** p<0.005 vs. control.
Figure 2
Figure 2. Morphometric analysis assessed islets from HF fed BL6J.
(A) Total β cell area per pancreas, (B) β cell mass, and (C) average area of an individual islet in pancreatic sections from mice on normal rodent chow (NC) and high fat (HF) diet were compared The distribution of area of an individual islet is shown in (D). 6 sections for NC and 5 sections for HF fed mice were analyzed for (A–B). 4 sections per group from NC and HF fed mice with total of 448 islets for NC and 653 islets for HF were analyzed for (C–D). (E–H) The percentage of β cells positive for anti BrdU antibody was compared between NC and HF fed mice labeled with BrdU at 1 month of age (E), and 4 month of age (F). 4 sections per group were analyzed for (E) and 5 sections per group were analyzed for (F). Representative photos from an islet labeled at 1 month of age on NC (G) and HF (H) are shown. Green staining: BrdU. Red staining: insulin. Scale bars indicate 50 µm. Data are mean ± s.e.m., n = 4–5 for (E) and (F). ** p<0.01 vs. NC, *** p<0.005 vs. NC.
Figure 3
Figure 3. Changes in secretory and metabolic functions, and gene expression in islets from HF fed BL6J.
(A) Glucose–stimulated insulin secretion (GSIS) was compared ex vivo between islets from mice on NC versus HF diets. Profiles of insulin secretion, area under the curve (AUC) of insulin secretion, and the ratio of first and second peak of insulin secretion are shown. (B) Oxygen consumption was compared between islets from NC and HF incubated without glucose (0), followed by treatment with 25 mM glucose (Glu), and then with carbonyl cyanide-4-trifluoromethoxyphenylhydrazone (FCCP). (C) rtPCR compared hypoxia up-regulated protein 1 (Hyou1), peroxisome proliferator-activated receptor gamma coactivator 1-alpha, (Ppargc1a), collagen, type I, alpha 1, (Col1a1), and asporin (Aspn) expression between islets from NC and HF groups. The results were expressed using 36B4 gene expression as an internal. Data are mean ± s.e.m., n = 4–5. * p<0.05, ** p<0.01, *** p<0.005 vs. control.

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