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Beta-cell failure in diet-induced obese mice stratified according to body weight gain: secretory dysfunction and altered islet lipid metabolism without steatosis or reduced beta-cell mass.

Peyot ML, Pepin E, Lamontagne J, Latour MG, Zarrouki B, Lussier R, Pineda M, Jetton TL, Madiraju SR, Joly E, Prentki M - Diabetes (2010)

Bottom Line: The glucose-induced rise in ATP was reduced in both DIO groups, and the glucose-induced rise in Ca(2+) was reduced in HDR islets relatively to LDR.Glucose-stimulated lipolysis was decreased in LDR and HDR islets, whereas fat oxidation was increased in HDR islets only.Fatty acid esterification processes were markedly diminished, and free cholesterol accumulated in HDR islets. beta-Cell failure in HDR mice is not due to reduced beta-cell mass and glucose metabolism or steatosis but to a secretory dysfunction that is possibly due to altered ATP/Ca(2+) and lipid signaling, as well as free cholesterol deposition.

View Article: PubMed Central - PubMed

Affiliation: Montreal Diabetes Research Center and CRCHUM, Montreal, QC, Canada. marie-line.peyot@crchum.qc.ca.

ABSTRACT

Objective: C57Bl/6 mice develop obesity and mild hyperglycemia when fed a high-fat diet (HFD). Although diet-induced obesity (DIO) is a widely studied model of type 2 diabetes, little is known about beta-cell failure in these mice.

Research design and methods: DIO mice were separated in two groups according to body weight gain: low- and high-HFD responders (LDR and HDR). We examined whether mild hyperglycemia in HDR mice is due to reduced beta-cell mass or function and studied islet metabolism and signaling.

Results: HDR mice were more obese, hyperinsulinemic, insulin resistant, and hyperglycemic and showed a more altered plasma lipid profile than LDR. LDR mice largely compensated insulin resistance, whereas HDR showed perturbed glucose homeostasis. Neither LDR nor HDR mice showed reduced beta-cell mass, altered islet glucose metabolism, and triglyceride deposition. Insulin secretion in response to glucose, KCl, and arginine was impaired in LDR and almost abolished in HDR islets. Palmitate partially restored glucose- and KCl-stimulated secretion. The glucose-induced rise in ATP was reduced in both DIO groups, and the glucose-induced rise in Ca(2+) was reduced in HDR islets relatively to LDR. Glucose-stimulated lipolysis was decreased in LDR and HDR islets, whereas fat oxidation was increased in HDR islets only. Fatty acid esterification processes were markedly diminished, and free cholesterol accumulated in HDR islets.

Conclusions: beta-Cell failure in HDR mice is not due to reduced beta-cell mass and glucose metabolism or steatosis but to a secretory dysfunction that is possibly due to altered ATP/Ca(2+) and lipid signaling, as well as free cholesterol deposition.

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β-Cell mass and proliferation, islet cell cytosolic free calcium, ATP, proinsulin, insulin and protein contents, and glucose metabolism of DIO mice. (A) β-Cell mass and (B) proliferation as indicated by the number of Ki-67 positive β-cells/islet. Means ± SE of six animals for normal diet (ND) and LDR and seven for HDR. Normal diet versus LDR or HDR, *P < 0.05. One-way ANOVA with Dunnett post hoc test. (C) Protein, (D and E) insulin expressed per islet (D) or per islet protein content (E), and (F) total islet proinsulin contents. Means ± SE of 83, 35, and 9 animals per group for (C), (D and E), and (F), respectively. Normal diet versus LDR or HDR, *P < 0.05, **P < 0.01, and ***P < 0.001; LDR versus HDR, §§P < 0.01. One-way ANOVA with Bonferroni post hoc test. Glucose utilization (G) and oxidation (H) were measured in islets incubated in KRBH at 3, 8, and 16 mmol/l glucose (G) with d-[U-14C]glucose and d-[5-3H]glucose. Means ± SE of 13–15 determinations from islets of 9 normal diet, 8 LDR, and 10 HDR mice in three separate experiments. ###P < 0.001 versus 3 mmol/l glucose for the same group. One-way ANOVA–Bonferroni multiple comparison test. I: Total ATP content was determined in islets incubated for 15 min in KRBH at 3 or 16 mmol/l glucose (G). Means ± SE of 13–15 determinations from islets of 9 normal diet, 9 LDR, and 9 HDR mice in three separate experiments. #P < 0.05 versus 3 mmol/l glucose for the same group. One-way ANOVA–Bonferroni multiple comparison test. J: Cytosolic free calcium was measured by confocal microscopy using Fluo-4 AM dye in dispersed-islet cells of normal diet, LDR, and HDR mice. Cells were perifused for 3 min at 3 mmol/l glucose, then at 16 mmol/l glucose for 10 min, and finally at 3 mmol/l glucose + 35 mmol/l KCl for 2 min. Fluorescence level is expressed in arbitrary units. For clarity purposes, only the mean of six independent experiments from six mice per group is represented. Of note, SE was no more than 15% at all times. One-way ANOVA with repeated measures, Tukey post test. ***P < 0.001 normal diet versus LDR and §§§P < 0.001 LDR versus HDR.
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Figure 4: β-Cell mass and proliferation, islet cell cytosolic free calcium, ATP, proinsulin, insulin and protein contents, and glucose metabolism of DIO mice. (A) β-Cell mass and (B) proliferation as indicated by the number of Ki-67 positive β-cells/islet. Means ± SE of six animals for normal diet (ND) and LDR and seven for HDR. Normal diet versus LDR or HDR, *P < 0.05. One-way ANOVA with Dunnett post hoc test. (C) Protein, (D and E) insulin expressed per islet (D) or per islet protein content (E), and (F) total islet proinsulin contents. Means ± SE of 83, 35, and 9 animals per group for (C), (D and E), and (F), respectively. Normal diet versus LDR or HDR, *P < 0.05, **P < 0.01, and ***P < 0.001; LDR versus HDR, §§P < 0.01. One-way ANOVA with Bonferroni post hoc test. Glucose utilization (G) and oxidation (H) were measured in islets incubated in KRBH at 3, 8, and 16 mmol/l glucose (G) with d-[U-14C]glucose and d-[5-3H]glucose. Means ± SE of 13–15 determinations from islets of 9 normal diet, 8 LDR, and 10 HDR mice in three separate experiments. ###P < 0.001 versus 3 mmol/l glucose for the same group. One-way ANOVA–Bonferroni multiple comparison test. I: Total ATP content was determined in islets incubated for 15 min in KRBH at 3 or 16 mmol/l glucose (G). Means ± SE of 13–15 determinations from islets of 9 normal diet, 9 LDR, and 9 HDR mice in three separate experiments. #P < 0.05 versus 3 mmol/l glucose for the same group. One-way ANOVA–Bonferroni multiple comparison test. J: Cytosolic free calcium was measured by confocal microscopy using Fluo-4 AM dye in dispersed-islet cells of normal diet, LDR, and HDR mice. Cells were perifused for 3 min at 3 mmol/l glucose, then at 16 mmol/l glucose for 10 min, and finally at 3 mmol/l glucose + 35 mmol/l KCl for 2 min. Fluorescence level is expressed in arbitrary units. For clarity purposes, only the mean of six independent experiments from six mice per group is represented. Of note, SE was no more than 15% at all times. One-way ANOVA with repeated measures, Tukey post test. ***P < 0.001 normal diet versus LDR and §§§P < 0.001 LDR versus HDR.

Mentions: HDR mice showed a 1.7- and 2-fold increase in β-cell mass (Fig. 4A) and proliferation (Fig. 4B), respectively. There was a trend for β-cell mass and proliferation to be increased in the LDR group. Islet protein contents were increased by 24 and 44% in LDR and HDR mice, respectively (Fig. C). Total insulin content per islet was similar in all groups (Fig. 4D); however, islet content corrected per protein content decreased by 20 and 24% in LDR and HDR islets, respectively (Fig. 4E). The islet proinsulin content per protein was similar in all groups (Fig. 4F).


Beta-cell failure in diet-induced obese mice stratified according to body weight gain: secretory dysfunction and altered islet lipid metabolism without steatosis or reduced beta-cell mass.

Peyot ML, Pepin E, Lamontagne J, Latour MG, Zarrouki B, Lussier R, Pineda M, Jetton TL, Madiraju SR, Joly E, Prentki M - Diabetes (2010)

β-Cell mass and proliferation, islet cell cytosolic free calcium, ATP, proinsulin, insulin and protein contents, and glucose metabolism of DIO mice. (A) β-Cell mass and (B) proliferation as indicated by the number of Ki-67 positive β-cells/islet. Means ± SE of six animals for normal diet (ND) and LDR and seven for HDR. Normal diet versus LDR or HDR, *P < 0.05. One-way ANOVA with Dunnett post hoc test. (C) Protein, (D and E) insulin expressed per islet (D) or per islet protein content (E), and (F) total islet proinsulin contents. Means ± SE of 83, 35, and 9 animals per group for (C), (D and E), and (F), respectively. Normal diet versus LDR or HDR, *P < 0.05, **P < 0.01, and ***P < 0.001; LDR versus HDR, §§P < 0.01. One-way ANOVA with Bonferroni post hoc test. Glucose utilization (G) and oxidation (H) were measured in islets incubated in KRBH at 3, 8, and 16 mmol/l glucose (G) with d-[U-14C]glucose and d-[5-3H]glucose. Means ± SE of 13–15 determinations from islets of 9 normal diet, 8 LDR, and 10 HDR mice in three separate experiments. ###P < 0.001 versus 3 mmol/l glucose for the same group. One-way ANOVA–Bonferroni multiple comparison test. I: Total ATP content was determined in islets incubated for 15 min in KRBH at 3 or 16 mmol/l glucose (G). Means ± SE of 13–15 determinations from islets of 9 normal diet, 9 LDR, and 9 HDR mice in three separate experiments. #P < 0.05 versus 3 mmol/l glucose for the same group. One-way ANOVA–Bonferroni multiple comparison test. J: Cytosolic free calcium was measured by confocal microscopy using Fluo-4 AM dye in dispersed-islet cells of normal diet, LDR, and HDR mice. Cells were perifused for 3 min at 3 mmol/l glucose, then at 16 mmol/l glucose for 10 min, and finally at 3 mmol/l glucose + 35 mmol/l KCl for 2 min. Fluorescence level is expressed in arbitrary units. For clarity purposes, only the mean of six independent experiments from six mice per group is represented. Of note, SE was no more than 15% at all times. One-way ANOVA with repeated measures, Tukey post test. ***P < 0.001 normal diet versus LDR and §§§P < 0.001 LDR versus HDR.
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Figure 4: β-Cell mass and proliferation, islet cell cytosolic free calcium, ATP, proinsulin, insulin and protein contents, and glucose metabolism of DIO mice. (A) β-Cell mass and (B) proliferation as indicated by the number of Ki-67 positive β-cells/islet. Means ± SE of six animals for normal diet (ND) and LDR and seven for HDR. Normal diet versus LDR or HDR, *P < 0.05. One-way ANOVA with Dunnett post hoc test. (C) Protein, (D and E) insulin expressed per islet (D) or per islet protein content (E), and (F) total islet proinsulin contents. Means ± SE of 83, 35, and 9 animals per group for (C), (D and E), and (F), respectively. Normal diet versus LDR or HDR, *P < 0.05, **P < 0.01, and ***P < 0.001; LDR versus HDR, §§P < 0.01. One-way ANOVA with Bonferroni post hoc test. Glucose utilization (G) and oxidation (H) were measured in islets incubated in KRBH at 3, 8, and 16 mmol/l glucose (G) with d-[U-14C]glucose and d-[5-3H]glucose. Means ± SE of 13–15 determinations from islets of 9 normal diet, 8 LDR, and 10 HDR mice in three separate experiments. ###P < 0.001 versus 3 mmol/l glucose for the same group. One-way ANOVA–Bonferroni multiple comparison test. I: Total ATP content was determined in islets incubated for 15 min in KRBH at 3 or 16 mmol/l glucose (G). Means ± SE of 13–15 determinations from islets of 9 normal diet, 9 LDR, and 9 HDR mice in three separate experiments. #P < 0.05 versus 3 mmol/l glucose for the same group. One-way ANOVA–Bonferroni multiple comparison test. J: Cytosolic free calcium was measured by confocal microscopy using Fluo-4 AM dye in dispersed-islet cells of normal diet, LDR, and HDR mice. Cells were perifused for 3 min at 3 mmol/l glucose, then at 16 mmol/l glucose for 10 min, and finally at 3 mmol/l glucose + 35 mmol/l KCl for 2 min. Fluorescence level is expressed in arbitrary units. For clarity purposes, only the mean of six independent experiments from six mice per group is represented. Of note, SE was no more than 15% at all times. One-way ANOVA with repeated measures, Tukey post test. ***P < 0.001 normal diet versus LDR and §§§P < 0.001 LDR versus HDR.
Mentions: HDR mice showed a 1.7- and 2-fold increase in β-cell mass (Fig. 4A) and proliferation (Fig. 4B), respectively. There was a trend for β-cell mass and proliferation to be increased in the LDR group. Islet protein contents were increased by 24 and 44% in LDR and HDR mice, respectively (Fig. C). Total insulin content per islet was similar in all groups (Fig. 4D); however, islet content corrected per protein content decreased by 20 and 24% in LDR and HDR islets, respectively (Fig. 4E). The islet proinsulin content per protein was similar in all groups (Fig. 4F).

Bottom Line: The glucose-induced rise in ATP was reduced in both DIO groups, and the glucose-induced rise in Ca(2+) was reduced in HDR islets relatively to LDR.Glucose-stimulated lipolysis was decreased in LDR and HDR islets, whereas fat oxidation was increased in HDR islets only.Fatty acid esterification processes were markedly diminished, and free cholesterol accumulated in HDR islets. beta-Cell failure in HDR mice is not due to reduced beta-cell mass and glucose metabolism or steatosis but to a secretory dysfunction that is possibly due to altered ATP/Ca(2+) and lipid signaling, as well as free cholesterol deposition.

View Article: PubMed Central - PubMed

Affiliation: Montreal Diabetes Research Center and CRCHUM, Montreal, QC, Canada. marie-line.peyot@crchum.qc.ca.

ABSTRACT

Objective: C57Bl/6 mice develop obesity and mild hyperglycemia when fed a high-fat diet (HFD). Although diet-induced obesity (DIO) is a widely studied model of type 2 diabetes, little is known about beta-cell failure in these mice.

Research design and methods: DIO mice were separated in two groups according to body weight gain: low- and high-HFD responders (LDR and HDR). We examined whether mild hyperglycemia in HDR mice is due to reduced beta-cell mass or function and studied islet metabolism and signaling.

Results: HDR mice were more obese, hyperinsulinemic, insulin resistant, and hyperglycemic and showed a more altered plasma lipid profile than LDR. LDR mice largely compensated insulin resistance, whereas HDR showed perturbed glucose homeostasis. Neither LDR nor HDR mice showed reduced beta-cell mass, altered islet glucose metabolism, and triglyceride deposition. Insulin secretion in response to glucose, KCl, and arginine was impaired in LDR and almost abolished in HDR islets. Palmitate partially restored glucose- and KCl-stimulated secretion. The glucose-induced rise in ATP was reduced in both DIO groups, and the glucose-induced rise in Ca(2+) was reduced in HDR islets relatively to LDR. Glucose-stimulated lipolysis was decreased in LDR and HDR islets, whereas fat oxidation was increased in HDR islets only. Fatty acid esterification processes were markedly diminished, and free cholesterol accumulated in HDR islets.

Conclusions: beta-Cell failure in HDR mice is not due to reduced beta-cell mass and glucose metabolism or steatosis but to a secretory dysfunction that is possibly due to altered ATP/Ca(2+) and lipid signaling, as well as free cholesterol deposition.

Show MeSH
Related in: MedlinePlus