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Int. J. Mol. Sci. 2017, 18(7), 1431; doi:10.3390/ijms18071431

LPS-Induced Low-Grade Inflammation Increases Hypothalamic JNK Expression and Causes Central Insulin Resistance Irrespective of Body Weight Changes

1
Department of Physiology, Ribeirao Preto Medical School, University of Sao Paulo, Sao Paulo 14049-900, Brazil
2
Department of Physiological Sciences, State University of Londrina, Londrina 86057-970, Brazil
3
Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI 48109-5622, USA
These authors contribute equally to this study.
*
Authors to whom correspondence should be addressed.
Received: 26 April 2017 / Revised: 22 June 2017 / Accepted: 27 June 2017 / Published: 4 July 2017
(This article belongs to the Special Issue Lipopolysaccharides (LPSs))
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Abstract

Metabolic endotoxemia contributes to low-grade inflammation in obesity, which causes insulin resistance due to the activation of intracellular proinflammatory pathways, such as the c-Jun N-terminal Kinase (JNK) cascade in the hypothalamus and other tissues. However, it remains unclear whether the proinflammatory process precedes insulin resistance or it appears because of the development of obesity. Hypothalamic low-grade inflammation was induced by prolonged lipopolysaccharide (LPS) exposure to investigate if central insulin resistance is induced by an inflammatory stimulus regardless of obesity. Male Wistar rats were treated with single (1 LPS) or repeated injections (6 LPS) of LPS (100 μg/kg, IP) to evaluate the phosphorylation of the insulin receptor substrate-1 (IRS1), Protein kinase B (AKT), and JNK in the hypothalamus. Single LPS increased the expression of pIRS1, pAKT, and pJNK, whereas the repeated LPS treatment failed to recruit pIRS1 and pAKT. The 6 LPS treated rats showed increased total JNK and pJNK. The 6 LPS rats became unresponsive to the hypophagic effect induced by central insulin administration (12 μM/5 μL, ICV). Prolonged exposure to LPS (24 h) impaired the insulin-induced AKT phosphorylation and the translocation of the transcription factor forkhead box protein O1 (FoxO1) from the nucleus to the cytoplasm of the cultured hypothalamic GT1-7 cells. Central administration of the JNK inhibitor (20 μM/5 μL, ICV) restored the ability of insulin to phosphorylate IRS1 and AKT in 6 LPS rats. The present data suggest that an increased JNK activity in the hypothalamus underlies the development of insulin resistance during prolonged exposure to endotoxins. Our study reveals that weight gain is not mandatory for the development of hypothalamic insulin resistance and the blockade of proinflammatory pathways could be useful for restoring the insulin signaling during prolonged low-grade inflammation as seen in obesity. View Full-Text
Keywords: LPS tolerance; hypothalamic inflammation; insulin resistance; pJNK LPS tolerance; hypothalamic inflammation; insulin resistance; pJNK
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MDPI and ACS Style

Rorato, R.; Borges, B.C.; Uchoa, E.T.; Antunes-Rodrigues, J.; Elias, C.F.; Elias, L.L.K. LPS-Induced Low-Grade Inflammation Increases Hypothalamic JNK Expression and Causes Central Insulin Resistance Irrespective of Body Weight Changes. Int. J. Mol. Sci. 2017, 18, 1431.

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