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Highlights • Oleate and low glucose hyperpolarize and inhibit GT1-7 and mouse GE neurons by activation of KATP. • Oleate inhibition of GT1-7 neuron activity is not mediated by AMPK or fatty acid oxidation. • Activation of KATP by oleate requires ATP hydrolysis but does not reduce the levels ATP or the ATP:ADP ratio. • GT1-7 hyperpolarization by oleate is not dependent on UCP2. • Oleate and low glucose depolarize a subpopulation of hypothalamic GI neurons., The unsaturated fatty acid, oleate exhibits anorexigenic properties reducing food intake and hepatic glucose output. However, its mechanism of action in the hypothalamus has not been fully determined. This study investigated the effects of oleate and glucose on GT1-7 mouse hypothalamic cells (a model of glucose-excited (GE) neurons) and mouse arcuate nucleus (ARC) neurons. Whole-cell and perforated patch-clamp recordings, immunoblotting and cell energy status measures were used to investigate oleate- and glucose-sensing properties of mouse hypothalamic neurons. Oleate or lowered glucose concentration caused hyperpolarization and inhibition of firing of GT1-7 cells by the activation of ATP-sensitive K+ channels (KATP). This effect of oleate was not dependent on fatty acid oxidation or raised AMP-activated protein kinase activity or prevented by the presence of the UCP2 inhibitor genipin. Oleate did not alter intracellular calcium, indicating that CD36/fatty acid translocase may not play a role. However, oleate activation of KATP may require ATP metabolism. The short-chain fatty acid octanoate was unable to replicate the actions of oleate on GT1-7 cells. Although oleate decreased GT1-7 cell mitochondrial membrane potential there was no change in total cellular ATP or ATP/ADP ratios. Perforated patch and whole-cell recordings from mouse hypothalamic slices demonstrated that oleate hyperpolarized a subpopulation of ARC GE neurons by KATP activation. Additionally, in a separate small population of ARC neurons, oleate application or lowered glucose concentration caused membrane depolarization. In conclusion, oleate induces KATP-dependent hyperpolarization and inhibition of firing of a subgroup of GE hypothalamic neurons without altering cellular energy charge.

Funding: Supported by grants MR/J001465/1 (JDH, MLJA, JFD and RJMcC) and MR/N009851/1 (JDH, MLJA, ATD-K and DJH) from the Medical Research Council of the UK and grants from Stony Brook Foundation and Reata Pharmaceuticals, Inc. (TH) Background & Aims: Nonalcoholic steatohepatitis (NASH) is associated with oxidative stress. We surmised that pharmacological activation of NF-E2 p45-related factor 2 (Nrf2) using the acetylenic tricyclic bis(cyano-enone) TBE-31 would suppress NASH because Nrf2 is a transcriptional master regulator of intracellular redox homeostasis. Methods: Nrf2+/+ and Nrf2-/- C57BL/6 mice were fed a high-fat plus fructose (HFFr) or regular chow (RC) diet for 16 weeks or 30 weeks, and then treated for the final 6 weeks, whilst still being fed the same HFFr or RC diets, with either TBE-31 or DMSO vehicle control. Measures of whole body glucose homeostasis, histological assessment of liver, and biochemical and molecular measurements of steatosis, endoplasmic reticulum (ER) stress, inflammation, apoptosis, fibrosis and oxidative stress were performed in livers from these animals. Results: TBE-31−treatment reversed insulin resistance in HFFr-fed wild-type mice, but not in HFFr-fed Nrf2-null mice. TBE-31−treatment of HFFr-fed wild-type mice substantially decreased liver steatosis and expression of lipid synthesis genes, whilst increasing hepatic expression of fatty acid oxidation and lipoprotein assembly genes. Also, TBE-31−treatment decreased ER stress, expression of inflammation genes, and markers of apoptosis, fibrosis and oxidative stress in the livers of HFFr-fed wild-type mice. By comparison, TBE-31 did not decrease steatosis, ER stress, lipogenesis, inflammation, fibrosis or oxidative stress in livers of HFFr-fed Nrf2-null mice. Conclusions: Pharmacological activation of Nrf2 in mice that had already been rendered obese and insulin resistant reversed insulin resistance, suppressed hepatic steatosis, and mitigated against NASH and liver fibrosis, effects that we principally attribute to inhibition of ER, inflammatory and oxidative stress. Publisher PDF