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Reduced insulin action in muscle of high fat diet rats over the diurnal cycle is not associated with defective insulin signaling.

ABSTRACT: OBJECTIVE:Energy metabolism and insulin action follow a diurnal rhythm. It is therefore important that investigations into dysregulation of these pathways are relevant to the physiology of this diurnal rhythm. METHODS:We examined glucose uptake, markers of insulin action, and the phosphorylation of insulin signaling intermediates in muscle of chow and high fat, high sucrose (HFHS) diet-fed rats over the normal diurnal cycle. RESULTS:HFHS animals displayed hyperinsulinemia but had reduced systemic glucose disposal and lower muscle glucose uptake during the feeding period. Analysis of gene expression, enzyme activity, protein abundance and phosphorylation revealed a clear diurnal regulation of substrate oxidation pathways with no difference in Akt signaling in muscle. Transfection of a constitutively active Akt2 into the muscle of HFHS rats did not rescue diet-induced reductions in insulin-stimulated glucose uptake. CONCLUSIONS:These studies suggest that reduced glucose uptake in muscle during the diurnal cycle induced by short-term HFHS-feeding is not the result of reduced insulin signaling.

SUBMITTER: Small L

PROVIDER: S-EPMC6600078 | biostudies-literature | 2019 Jul

REPOSITORIES: biostudies-literature

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Reduced insulin action in muscle of high fat diet rats over the diurnal cycle is not associated with defective insulin signaling.

Small Lewin L Brandon Amanda E AE Parker Benjamin L BL Deshpande Vinita V Samsudeen Azrah F AF Kowalski Greg M GM Reznick Jane J Wilks Donna L DL Preston Elaine E Bruce Clinton R CR James David E DE Turner Nigel N Cooney Gregory J GJ

Molecular metabolism 20190412

<h4>Objective</h4>Energy metabolism and insulin action follow a diurnal rhythm. It is therefore important that investigations into dysregulation of these pathways are relevant to the physiology of this diurnal rhythm.<h4>Methods</h4>We examined glucose uptake, markers of insulin action, and the phosphorylation of insulin signaling intermediates in muscle of chow and high fat, high sucrose (HFHS) diet-fed rats over the normal diurnal cycle.<h4>Results</h4>HFHS animals displayed hyperinsulinemia b ...[more]

PMID: 31029696

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Project description:AimTo investigate the effects of mitofusin-2 (MFN2) on insulin sensitivity and its potential targets in the liver of rats fed with a high-fat diet (HFD).MethodsRats were fed with a control or HFD for 4 or 8 wk, and were then infected with a control or an MFN2 expressing adenovirus once a week for 3 wk starting from the 9(th) wk. Blood glucose (BG), plasma insulin and insulin sensitivity of rats were determined at end of the 4(th) and 8(th) wk, and after treatment with different amounts of MFN2 expressing adenovirus (10(8), 10(9) or 10(10) vp/kg body weight). BG levels were measured by Accu-chek Active Meter. Plasma insulin levels were analyzed by using a Rat insulin enzyme-linked immunosorbent assay kit. Insulin resistance was evaluated by measuring the glucose infusion rate (GIR) using a hyperinsulinemic euglycemic clamp technique. The expression or phosphorylation levels of MFN2 and essential molecules in the insulin signaling pathway, such as insulin receptor (INSR), insulin receptor substrate 2 (IRS2), phosphoinositide-3-kinase (PI3K), protein kinase beta (AKT2) and glucose transporter type 2 (GLUT2) was assayed by quantitative real-time polymerase chain reaction and Western-blotting.ResultsAfter the end of 8 wk, the body weight of rats receiving the normal control diet (ND) and the HFD was not significantly different (P > 0.05). Compared with the ND group, GIR in the HFD group was significantly decreased (P < 0.01), while the levels of BG, triglycerides (TG), total cholesterol (TC) and insulin in the HFD group were significantly higher than those in the ND group (P < 0.05). Expression of MFN2 mRNA and protein in liver of rats was significantly down-regulated in the HFD group (P < 0.01) after 8 wk of HFD feeding. The expression of INSR, IRS2 and GLUT2 were down-regulated markedly (P < 0.01). Although there were no changes in PI3K-P85 and AKT2 expression, their phosphorylation levels were decreased significantly (P < 0.01). After intervention with MFN2 expressing adenovirus for 3 wk, the expression of MFN2 mRNA and protein levels were up-regulated (P < 0.01). There was no difference in body weight of rats between the groups. The levels of BG, TG, TC and insulin in rats were lower than those in the Ad group (P < 0.05), but GIR in rats infected with Ad-MFN2 was significantly increased (P < 0.01), compared with the Ad group. The expression of INSR, IRS2 and GLUT2 was increased, while phosphorylation levels of PI3K-P85 and AKT2 were increased (P < 0.01), compared with the Ad group.ConclusionHFDs induce insulin resistance, and this can be reversed by MFN2 over-expression targeting the insulin signaling pathway.

Project description:Background:Gut microbiota dysbiosis has been linked to obesity-associated chronic inflammation. Microbiota manipulation may therefore affect obesity-related comorbidities. Blueberries are rich in anthocyanins, which have anti-inflammatory properties and may alter the gut microbiota. Objective:We hypothesized that blueberry supplementation would alter the gut microbiota, reduce systemic inflammation, and improve insulin resistance in high-fat (HF)-diet-fed rats. Methods:Twenty-four male Wistar rats (260-270 g; n = 8/group) were fed low-fat (LF; 10% fat), HF (45% fat), or HF with 10% by weight blueberry powder (HF_BB) diets for 8 wk. LF rats were fed ad libitum, whereas HF and HF_BB rats were pair-fed with diets matched for fiber and sugar contents. Glucose tolerance, microbiota composition (16S ribosomal RNA sequencing), intestinal integrity [villus height, gene expression of mucin 2 (Muc2) and ?-defensin 2 (Defb2)], and inflammation (gene expression of proinflammatory cytokines) were assessed. Results:Blueberry altered microbiota composition with an increase in Gammaproteobacteria abundance (P < 0.001) compared with LF and HF rats. HF feeding led to an ?15% decrease in ileal villus height compared with LF rats (P < 0.05), which was restored by blueberry supplementation. Ileal gene expression of Muc2 was ?150% higher in HF_BB rats compared with HF rats (P < 0.05), with expression in the LF group not being different from that in either the HF or HF_BB groups. Tumor necrosis factor ? (Tnfa) and interleukin 1? (Il1b) gene expression in visceral fat was increased by HF feeding when compared with the LF group (by 300% and 500%, respectively; P < 0.05) and normalized by blueberry supplementation. Finally, blueberry improved markers of insulin sensitivity. Hepatic insulin receptor substrate 1 (IRS1) phosphorylation at serine 307:IRS1 ratio was ?35% higher in HF rats compared with LF rats (P < 0.05) and HF_BB rats. Conclusion:In HF-diet-fed male rats, blueberry supplementation led to compositional changes in the gut microbiota associated with improvements in systemic inflammation and insulin signaling.

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Reduced insulin action in muscle of high fat diet rats over the diurnal cycle is not associated with defective insulin signaling.

Publications

Reduced insulin action in muscle of high fat diet rats over the diurnal cycle is not associated with defective insulin signaling.

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