Fasting and postprandial regulation of the intracellular localization of adiponectin and of adipokines secretion by dietary fat in rats.

V Olivares-García,I Torre-Villalvazo,G Alemán,N Lara,P López-Romero,L Velázquez-Villegas,A Díaz-Villaseñor,N Torres,A R Tovar

doi:10.1038/nutd.2015.34

Abstract

Background/Objective:Dietary fat sources modulate fasting serum concentration of adipokines, particularly adiponectin. However, previous studies utilized obese animals in which adipose tissue function is severely altered. Thus, the present study aimed to assess the postprandial regulation of adipokine secretion in nonobese rats that consumed high-fat diet (HFD) composed of different types of fat for a short time.Methods:The rats were fed a control diet or a HFD containing coconut, safflower or soybean oil (rich in saturated fatty acid, monounsaturated fatty acid or polyunsaturated fatty acid, respectively) for 21 days. The serum concentrations of adiponectin, leptin, retinol, retinol-binding protein-4 (RBP-4), visfatin and resistin were determined at fasting and after refeeding. Adiponectin multimerization and intracellular localization, as well as the expression of endoplasmic reticulum (ER) chaperones and transcriptional regulators, were evaluated in epididymal white adipose tissue.Results:In HFD-fed rats, serum adiponectin was significantly decreased 30 min after refeeding. With coconut oil, all three multimeric forms were reduced; with safflower oil, only the high-molecular-weight (HMW) and medium-molecular-weight (MMW) forms were decreased; and with soybean oil, only the HMW form was diminished. These reductions were due not to modifications in mRNA abundance or adiponectin multimerization but rather to an increment in intracellular localization at the ER and plasma membrane. Thus, when rats consumed a HFD, the type of dietary fat differentially affected the abundance of endoplasmic reticulum resident protein 44 kDa (ERp44), sirtuin 1 (SIRT1) and peroxisome proliferator-activated receptor-γ (PPARγ) mRNAs, all of which are involved in the post-translational processing of adiponectin required for its secretion.Leptin, RBP-4, resistin and visfatin serum concentrations did not change during fasting, whereas modest alterations were observed after refeeding.Conclusions:The short-term consumption of a HFD affected adiponectin localization in adipose tissue, thereby decreasing its secretion to a different magnitude depending on the dietary fat source. Evaluating the fasting serum concentration of adipokines was not sufficient to identify alterations in their secretion, whereas postprandial values provided additional information as dynamic indicators.

Highlights

Adipose tissue acts as an endocrine organ by secreting hormones and cytokines called adipokines that exert their physiological effects in autocrine and paracrine manners
We reported that the type and amount of dietary fat modulated the circulating levels of adiponectin and other relevant adipokines in rats, during the postprandial period, before the onset of significant weight gain and the development of obesity-related insulin resistance
We found that adiponectin secretion was sensitive to the composition and amount of dietary fat

Summary

Introduction

Adipose tissue acts as an endocrine organ by secreting hormones and cytokines called adipokines that exert their physiological effects in autocrine and paracrine manners. Adiponectin has strong insulinsensitizing, anti-diabetic and anti-inflammatory activities.[2] In particular, adiponectin reduces the plasma levels of free fatty acids and fat accumulation in the liver, muscle and visceral adipose tissue and prevents pancreatic β-cell apoptosis. It increases hepatic insulin action, mitochondrial function and the rate of glucose-stimulated insulin secretion, all of which improve glucose tolerance.[3,4]. In the rats that consumed a HFD or CD rich in soybean oil, the peak occurred at 90 min after refeeding (Figure 1a).

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