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Molecular phenotyping of multiple mouse strains under metabolic challenge uncovers Elovl2 as a novel regulator of glucose-induced insulin secretion

ABSTRACT: Defective insulin secretion by pancreatic β cells underlies the development of type 2 diabetes (T2D). High fat diet-fed mice are commonly used to study diabetes progression, but studies are usually limited to a single strain, such as C57Bl/6J. Here, we use a systems biology approach to integrate large phenotypic and islet transcriptomic data sets from six commonly used strains fed a high fat or regular chow diet to identify genes associated with glucose intolerance and insulin secretion. One of these genes is Elovl2, encoding very long chain fatty acid elongase 2. ELOVL2 is responsible for the synthesis of the polyunsaturated fatty acid, docosahexaenoic acid (DHA). We show that DHA rescues glucose-induced insulin secretion and cytosolic Ca2+ influx impaired by glucolipotoxicity, and that Elovl2 over-expression is able to restore the insulin secretion defect under these conditions. We propose that increased endogenous DHA levels resulting from Elovl2 up-regulation counteracts the insulin secretion defect associated with glucolipotoxicity. Although we focus our experimental validation on Elovl2, the comprehensive data set and integrative network model we used to identify this candidate gene represents an important novel resource to dissect the molecular aetiology of β cell failure in murine models.

ORGANISM(S): Mus musculus

PROVIDER: GSE78183 | GEO | 2017/04/28

SECONDARY ACCESSION(S): PRJNA312845

REPOSITORIES: GEO

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Project description:Impaired resistance to insulin, the key defect in type 2 diabetes (T2D), is associated with a low capacity to adapt fuel oxidation to fuel availability, i.e., metabolic inflexibility. The hampered metabolic adaptability triggers a further damage of insulin signaling. Since skeletal muscle is the main site of glucose uptake, effectiveness of T2D treatment depends in large on the improvement of insulin sensitivity and metabolic adaptability of the muscle. We have shown previously in mice fed an obesogenic high-fat diet that a combination treatment using n-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA) and thiazolidinedione (TZD) anti-diabetic drugs preserved metabolic health and synergistically improved muscle insulin sensitivity. We investigated here whether TZD rosiglitazone could elicit the additive beneficial effects on metabolic flexibility when combined with n-3 LC-PUFA. Adult male C57BL/6J mice were fed an obesogenic corn oil-based high-fat diet (cHF) for 8 weeks, or randomly assigned to various dietary treatments: (i) cHF+F, cHF with n-3 LC-PUFA concentrate replacing 15% of dietary lipids; (ii) cHF+ROSI, cHF with 10 mg rosiglitazone/kg diet; and (iii) cHF+F+ROSI, or chow-fed. Indirect calorimetry demonstrated superior preservation of metabolic flexibility to carbohydrates in response to the combination treatment. Metabolomic and gene expression analyses in the muscle suggested distinct and complementary effects of the single treatments, with rosiglitazone augmenting insulin sensitivity by the modulation of branched-chain amino acid metabolism, and n-3 LC PUFA supporting complete oxidation of fatty acids in mitochondria. These beneficial metabolic effects were associated with the activation of the switch between glycolytic and oxidative muscle fibers, especially in the cHF+F+ROSI mice. Our results further support the idea that the combination treatment using n-3 LC-PUFA and TZDs could improve the efficacy of the treatment of obese and diabetic patients. Male C57BL/6N mice had free access to water and Chow. Three-month-old mice were randomly assigned (8 animals per group) to cHF+ROSI diet (lipid content ~35% wt/wt) supplemented with 10 mg rosiglitazone/kg diet, or cHF+F+ROSI in which n-3 LC-PUFA concentrate (46% DHA, 14% EPA, wt/wt, as triglycerides; product EPAX 1050 TG) replaced 15% wt/wt of dietary lipids. The treatment lasted for 8 weeks, whereafter the animals were first fasted for 10 hours during the light phase of the day (between 8.00hr and 18.00hr), than re-fed Chow (starting at 18.00hr), and killed the following day by cervical dislocation under pentobarbital anesthesia (between 9.00hr and 11.00hr); the so-called 'diet-switch protocol'. Gastrocnemius muscle was isolated and used for total RNA isolation.

Project description:Maternal low-protein diet increases the susceptibility of offspring to type 2 diabetes. An insult to the pancreas during development can have long-term consequences on ?-cell mass and function. Because nutrients and growth factors signaling converge on mTOR, we hypothesized that mTOR plays a central role in ?-cell programming during fetal development. In this study, we revealed that newborns of dams exposed to low-protein diet (LP0.5) throughout pregnancy exhibited decreased insulin levels, ?-cell fraction, and mTOR signaling. Adult LP0.5 offspring demonstrated enhanced insulin sensitivity but remained glucose intolerant due to an insulin secretory defect and not reduced ?-cell mass. The insulin secretory defect was distal to Ca2+ influx, at the level of proinsulin biosynthesis and insulin content. LP0.5 islets exhibited reduced mTOR protein and increased expression of specific microRNAs. The reductions in mTOR protein and insulin secretion in LP0.5 islets were restored to normal by blockade of microRNAs 199a-3p and 342. Finally, transient activation of mTORC1 signaling in ?-cells during the last week of pregnancy rescued the neonatal ?-cell fraction defect and metabolic abnormalities in LP0.5 mice. These findings identify a major role of microRNAs and mTOR in ?-cell programing by maternal low-protein diet. To investigate which microRNAs are altered in islets isolated from 2-3 months old male offspring of dams fed low-protein diet (LP0.5) or control diet throughout pregnancy Pancreatic islets were isolated from 2-3 months old male offspring of dams fed low-protein diet (LP0.5) or control diet throughout pregnancy. Islets were isolated by collagenase digestion. The pancreas was perfused via the common duct with 1 mg/ml collagenase XI (Sigma-Aldrich) in HBSS (Life Technologies). Pancreatic digestion was carried out at 37 °C for 15 min, after which cold HBSS with 2.5% FBS (Life Technologies) was added. The suspension was centrifuged at 1000 rpm for 30s, washed 3 times with HBSS with 2.5% FBS, resuspended in RPMI complete media (RPMI 1640 with 5 mM Glucose, 10% FBS,100 IU/ml penicillin, 100 g/ml streptomycin) and poured onto a 70 µm cell strainer (BD Falcon, BD Biosciences). Islets were rinsed and handpicked. Islets were allowed to recover overnight in RPMI complete media before RNA isolation using MirVana Kit (Life Technologies).

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Molecular phenotyping of multiple mouse strains under metabolic challenge uncovers Elovl2 as a novel regulator of glucose-induced insulin secretion

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