Project description:The brain is now recognized as an insulin sensitive tissue, however, the role of insulin on gene expression in the brain is largely unknown. Here, we show that increases in peripheral insulin within the physiological range regulate expression of a broad network of gene expression, with the most robust effect in the hypothalamus followed by the hippocampus then nucleus accumbens. In hypothalamus, insulin regulates many genes involved in neurotransmission, including up-regulating expression of GABA-A receptor components, differentially modulating glutamate receptors, and suppressing multiple neuropeptides. Insulin also strongly modulates brain metabolism by suppressing genes involved in the glycolysis and pentose phosphate pathways while increasing expression of genes regulating pyruvate dehydrogenase complex, long-chain fatty acyl-CoA and cholesterol biosynthesis, rerouting carbon substrates to the biogenesis of plasma membrane for neuronal and glial function and synaptic remodeling. Thus, peripheral insulin acutely and potently regulates expression of genes involved in neurotransmission, neuromodulation and brain metabolism.
Project description:The brain plays a key role in energy homeostasis, detecting circulating hormones from peripheral organs, nutrients, and metabolites, and integrating this information to control food intake and energy expenditure. However, the signals mediating communication between peripheral organs and brain are largely unknown. Here, we show that a group of neurons in the Drosophila larval brain expressing the adiponectin receptor (AdipoR) control systemic growth and metabolism. We identify glucose-regulated protein 78 (Grp78) as a circulating ligand for AdipoR. Grp78 is produced by fat cells in response to dietary sugar and modulates the activity of AdipoR-positive neurons. The terpenoid juvenile hormone (JH) serves as an effector for brain AdipoR signaling, reducing the levels of insulin signaling in peripheral organs. In conclusion, we identify a neuroendocrine axis whereby AdipoR neurons control systemic insulin responses by modulating peripheral JH function.
Project description:Skeletal muscle insulin resistance is the earliest defect in type 2 diabetes (T2D), preceding and predicting disease development. Whether this represents the underlying primary defect in T2D or effects of changes in hormones or circulating metabolites is unknown. To address this question, we have developed a “disease-in-a-dish” model by differentiating iPS cells from T2D patients and controls into myoblasts (iMyo) and studied their function in vitro. We find that T2D iMyos exhibit multiple defects mirroring human disease including altered insulin signaling through the IRS/AKT pathway, decreased insulin-stimulated glucose uptake, and reduced mitochondrial oxidation. In addition, using global phosphoproteomics we find that T2D alters phosphorylation of a large network of targets of mTOR, S6K, PKC and other kinases including proteins involved in regulation of Rho-GTPases, mRNA splicing/processing, vesicular trafficking, gene transcription and chromatin remodeling. This cell-autonomous dysregulated phosphorylation network reveals a new dimension in the mechanism underlying insulin resistance in T2D.
Project description:Insulin-stimulated glucose uptake is known to involve microtubules, although the function of microtubules and the microtubule-regulating proteins involved in insulin action are poorly understood. CLASP2, a plus-end tracking microtubule-associated protein (+TIP) that controls microtubule dynamics, was recently implicated as the first +TIP associated with insulin-regulated glucose uptake. Here, using protein-specific targeted quantitative phosphoproteomics within 3T3-L1 adipocytes, we discovered that insulin regulates phosphorylation of the CLASP2 network members G2L1, MARK2, CLIP2, AGAP3 and CKAP5 as well as EB1, revealing the existence of a previously unknown microtubule-associated protein system that responds to insulin. To further investigate, G2L1 interactome studies within 3T3-L1 adipocytes revealed that G2L1 co-immunoprecipitates CLASP2 and CLIP2 as well as the master integrators of +TIP assembly, the end binding (EB) proteins. Live-cell total internal reflection fluorescence microscopy in adipocytes revealed G2L1 and CLASP2 colocalize on microtubule plus-ends. We found that while insulin increases the number of CLASP2-containing plus-ends, insulin treatment simultaneously decreases CLASP2-containing plus-end velocity. In addition, we discovered that insulin stimulates re-distribution of CLASP2 and G2L1 from exclusive plus-end tracking to “trailing” behind the growing tip of the microtubule. Insulin treatment increases -tubulin Lysine 40 acetylation, a mechanism that was observed to be regulated by a counterbalance between GSK3 and mTOR, and also led to microtubule stabilization. Our studies introduce insulin-stimulated microtubule stabilization and plus-end trailing of +TIPs as new modes of insulin action and reveal the likelihood that a network of microtubule-associated proteins synergize to coordinate insulin-regulated microtubule dynamics.
Project description:Here we employed phosphoproteomics to delineate insulin signal transduction in adipocyte cells and adipose tissue. Across a range of insults triggering insulin resistance, we observed marked rewiring of the insulin signaling network. This included both attenuated insulin-responsive phosphorylation, and the emergence of phosphorylation uniquely insulin-regulated in insulin resistance. Identifying dysregulated phosphosites common to multiple insults revealed subnetworks containing novel regulators of insulin action, such as MARK2/3, and causal drivers of insulin resistance. The presence of several GSK3 substrates among these phosphosites led us to establish a pipeline for identifying context-specific kinase substrates. This revealed widespread dysregulation of GSK3 signaling. Pharmacological inhibition of GSK3 partially reversed insulin resistance in cells and tissue explants. These data highlight that insulin resistance is multi-nodal signaling defect that includes dysregulated GSK3 activity.
Project description:Using mass spectrometry-based phosphoproteomics, we quantified 23,126 phosphosites in the skeletal muscle of five genetically distinct inbred mouse strains exposed to two controlled dietary environments, with and without acute insulin treatment. Almost half of the insulin-regulated phosphoproteome was altered by genetic background independently of diet, and high-fat high-sugar feeding also affected insulin signalling in a strain-dependent manner. Our data illuminated signalling network organisation principles, including the uncoupling of phosphosites targeted by the same kinase. Associating diverse signalling responses with insulin-stimulated glucose uptake uncovered regulators of muscle insulin responsiveness, including the regulatory phosphosite S469 on Pfkfb2, a key glycolytic enzyme.
Project description:Global energy balance in mammals is controlled by the actions of circulating hormones that coordinate fuel production and utilization in metabolically active tissues. Bone-derived osteocalcin, in its undercarboxylated, hormonal form, regulates fat deposition and is a potent insulin secretagogue. Here, we show that insulin receptor (IR) signaling in osteoblasts controls osteoblast development and osteocalcin expression by suppressing the Runx2 inhibitor Twist-2. Mice lacking IR in osteoblasts have low circulating undercarboxylated osteocalcin and reduced bone acquisition due to decreased bone formation and deficient numbers of osteoblasts. With age, these mice develop marked peripheral adiposity and hyperglycemia accompanied by severe glucose intolerance and insulin resistance. The metabolic abnormalities in these mice are improved by infusion of exogenous under-carboxylated osteocalcin. These results indicate the existence of a bone-pancreas endocrine loop through which insulin signaling in the osteoblast ensures osteoblast differentiation and stimulates osteocalcin production, which in turn regulates insulin sensitivity and pancreatic insulin secretion to control glucose homeostasis. We used microarrays to detail the global gene expression changes in response to insulin acting through insulin receptor in osteoblasts and identified distinct genes specifically involved in bone remodeling process. 4 groups and 3 time points (0h as a control, 6h, 12h, and 24h)
Project description:Global energy balance in mammals is controlled by the actions of circulating hormones that coordinate fuel production and utilization in metabolically active tissues. Bone-derived osteocalcin, in its undercarboxylated, hormonal form, regulates fat deposition and is a potent insulin secretagogue. Here, we show that insulin receptor (IR) signaling in osteoblasts controls osteoblast development and osteocalcin expression by suppressing the Runx2 inhibitor Twist-2. Mice lacking IR in osteoblasts have low circulating undercarboxylated osteocalcin and reduced bone acquisition due to decreased bone formation and deficient numbers of osteoblasts. With age, these mice develop marked peripheral adiposity and hyperglycemia accompanied by severe glucose intolerance and insulin resistance. The metabolic abnormalities in these mice are improved by infusion of exogenous under-carboxylated osteocalcin. These results indicate the existence of a bone-pancreas endocrine loop through which insulin signaling in the osteoblast ensures osteoblast differentiation and stimulates osteocalcin production, which in turn regulates insulin sensitivity and pancreatic insulin secretion to control glucose homeostasis. We used microarrays to detail the global gene expression changes in response to insulin acting through insulin receptor in osteoblasts and identified distinct genes specifically involved in bone remodeling process.
Project description:Systems genetics has begun to tackle the complexity of insulin resistance by capitalising on computational advances to study high-diversity populations. “Diversity Outbred in Australia (DOz)” is a population of genetically unique mice with profound metabolic heterogeneity. We leveraged this variance to explore skeletal muscle’s contribution to whole-body insulin action through metabolic phenotyping and skeletal muscle proteomics of 215 DOz mice. Linear modelling identified 553 proteins that associated with whole-body insulin sensitivity (Matsuda Index) including regulators of endocytosis and muscle proteostasis. To enrich for causality, we refined this network by focussing on negatively associated, genetically regulated proteins, resulting in a 76-protein fingerprint of insulin resistance. We sought to perturb this network and restore insulin action with small molecules by integrating the Broad Institute Connectivity Map platform and in vitro assays of insulin action using the Prestwick chemical library. These complimentary approaches identified the antibiotic thiostrepton as an insulin resistance reversal agent. Subsequent validation in ex vivo insulin resistant mouse muscle, and palmitate induced insulin resistant myotubes demonstrated potent insulin action restoration, potentially via up-regulation of glycolysis. This work demonstrates the value of a drug-centric framework to validate systems level analysis by identifying potential therapeutics for insulin resistance.