Peripheral Insulin Regulates A Broad Network of Gene Expression in Brain

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. Overall design: Three month-old male C57BL/6J mice were anestethized and had an indwelling catheter placed in the right internal jugular vein. After recovery (4-5 days), conscious mice were continuously perfused with either 4 or 12 mU/kg/min insulin or saline as control. Blood glucose was verified every 5-30 min and adjusted with infusion of a 20% glucose solution. After 3 h of clamp, mice were euthanized by cervical dislocation, and brain tissues were harvested, snap frozen in liquid nitrogen and kept at -80C. Total RNA was isolated from hypothalamus, hippocampus and nucleus accumbens. Stranded cDNA libraries with unique index tags for each sample (48 multiplexed) were made using a directional RNA-seq kit (Wafergen). Sequencing was performed on an Illumina HiSeq 2500 run on rapid mode (2x50).