Hypothalamic inflammation and the development of an obese phenotype induced by high-fat diet consumption is exacerbated in alpha7 nicotinic cholinergic receptor knockout mice.

Hypothalamic inflammation and metabolic changes resulting from the consumption of high-fat diets have been linked to low grade inflammation and obesity. Inflammation impairs the hypothalamic expression of α7 nicotinic acetylcholine receptor (α7nAChR). The α7nAChR is described as the main component of the anti-inflammatory cholinergic pathway in different inflammation models. To assess whether the reduction in α7nAChR expression exacerbates hypothalamic inflammation induced by a high-fat diet (HFD), were used male and female global α7nAChR knockout mouse line in normal or high-fat diet for 4 weeks. Body weight gain, adiposity, glucose homeostasis, hypothalamic inflammation, food intake, and energy expenditure were evaluated. Insulin sensitivity was evaluated in neuronal cell culture. Consumption of an HFD for 4 weeks resulted in body weight gain and adiposity in male Chrna7-/- mice and the hypothalamus of male Chrna7-/- mice showed neuroinflammatory markers, with increased gene expression of pro-inflammatory cytokines and dysregulation in the nuclear factor kappa B pathway. Moreover, male Chrna7-/- mice consuming an HFD showed alterations in glucose homeostasis and serum of Chrna7-/- mice that consumed an HFD impaired insulin signalling in neuronal cell culture experiments. In general, female Chrna7-/- mice that consumed an HFD did not show the phenotypic and molecular changes found in male mice, indicating that there is sexual dimorphism in the analysed parameters. Thus, receptor deletion resulted in increased susceptibility to hypothalamic inflammation and metabolic damage associated with HFD consumption in male mice.

Time-restricted feeding combined with aerobic exercise training can prevent weight gain and improve metabolic disorders in mice fed a high-fat diet.

KEY POINTS: Time-restricted feeding (TRF, in which energy intake is restricted to 8 h/day during the dark phase) alone or combined with aerobic exercise (AE) training can prevent weight gain and metabolic disorders in Swiss mice fed a high-fat diet. The benefits of TRF combined with AE are associated with improved hepatic metabolism and decreased hepatic lipid accumulation. TRF combined with AE training increased fatty acid oxidation and decreased expression of lipogenic and gluconeogenic genes in the liver of young male Swiss mice. TRF combined with AE training attenuated the detrimental effects of high-fat diet feeding on the insulin signalling pathway in the liver. ABSTRACT: Time-restricted feeding (TRF) or physical exercise have been shown to be efficient in the prevention and treatment of metabolic disorders; however, the additive effects of TRF combined with aerobic exercise (AE) training on liver metabolism have not been widely explored. In this study TRF (8 h in the active phase) and TRF combined with AE (TRF+Exe) were compared in male Swiss mice fed a high-fat diet, with evaluation of the effects on insulin sensitivity and expression of hepatic genes involved in fatty acid oxidation, lipogenesis and gluconeogenesis. As in previous reports, we show that TRF alone (eating only between zeitgeber time 16 and 0) was sufficient to reduce weight and adiposity gain, increase fatty acid oxidation and decrease lipogenesis genes in the liver. In addition, we show that mice of the TRF+Exe group showed additional adaptations such as increased oxygen consumption ( V̇O2${\dot V_{{{\rm{O}}_{\rm{2}}}}}$ ), carbon dioxide production ( V̇CO2${\dot V_{{\rm{C}}{{\rm{O}}_{\rm{2}}}}}$ ) and production of ketone bodies (ß-hydroxybutyrate). Also, TRF+Exe attenuated the negative effects of high-fat diet feeding on the insulin signalling pathway (insulin receptor, insulin receptor substrate, Akt), and led to increased fatty acid oxidation (Ppara, Cpt1a) and decreased gluconeogenic (Fbp1, Pck1, Pgc1a) and lipogenic (Srebp1c, Cd36) gene expression in the liver. These molecular results were accompanied by increased glucose metabolism, lower serum triglycerides and reduced hepatic lipid content in the TRF+Exe group. The data presented in this study show that TRF alone has benefits but TRF+Exe has additive benefits and can mitigate the harmful effects of consuming a high-fat diet on body adiposity, liver metabolism and glycaemic homeostasis in young male Swiss mice.

Acute effects of fatty acids on autophagy in NPY neurones.

High-fat diet (HFD) feeding is deleterious to hypothalamic tissue, leading to inflammation and lipotoxicity, as well as contributing to central insulin resistance. Autophagy is a process that restores cellular homeostasis by degrading malfunctioning organelles and proteins. Chronic HFD-feeding down-regulates hypothalamic autophagy. However, the effects of short-term HFD-feeding and the saturated fatty acid palmitate (PA) on hypothalamic autophagy and in neurones that express neuropeptide Y (NPY) and agouti-related peptide remains unknown. Therefore, we assessed hypothalamic autophagy after 1 and 3 days of HFD-feeding. We also injected PA i.c.v and analysed the modulation of autophagy in hypothalamic tissue. Both interventions resulted in changes in autophagy-related gene profiles without significant differences in protein content of p62 and LC3B-II, markers of the autophagy pathway. When we assessed native NPY neurones in brain slices from PA-treated animals, we observed increased levels of Atg7 and LC3B protein in response to PA treatment, indicating the induction of autophagy. We then tested the direct effects of fatty acids using the immortalised hypothalamic NPY-expressing neuronal cell model mHypoE-46. We found that PA, but not palmitoleate (PO) (a monounsaturated fatty acid), was able to induce autophagy. Co-treatment with PA and PO was able to block the PA-mediated induction of autophagy, as assessed by flow cytometry. When the de novo ceramide synthesis pathway was blocked with myriocin pre-treatment, we observed a decrease in PA-mediated induction of autophagy, although there was no change with the toll-like receptor 4 inhibitor, TAK-242. Taken together, these findings provide evidence that saturated and unsaturated fatty acids can differentially regulate hypothalamic autophagy and that ceramide synthesis may be an important mediator of those effects. Understanding the mechanisms by which dietary fats affect autophagy in neurones involved in the control of energy homeostasis will provide potential new pathways for targeting and containing the obesity epidemic.