Repercussions of the high fat diet chronic intake on the mechanisms of nutrients transport of enterocytes: evaluation of the involvement of thyroid hormones in these processes

Abstract

Although the mechanisms of the nutrients transport regulation across the intestinal epithelium are very important, few studies have addressed this issue. This call our attention considering some aspects of the contemporary world characterized by consumption of high-fat and high-carbohydrate diets, leading to an increase in obesity and its comorbidities, as cardiovascular diseases, diabetes mellitus and cancer. PPAR alpha, a transcription factor for genes that regulate metabolism and transport of lipids, appears to interfere with the expression of nutrient transporters in the enterocytes. It is worth noting that PPAR alpha is activated by fatty acids, whose concentration in the current diet has increased significantly, which reinforces their role on the biological process induced by lipids. Similarly, it is our interest to assess thyroid hormones (THs) effects on the nutrients carriers, since: they exert important effects on carbohydrate, lipid and protein metabolism; little is known about their effects on the gastrointestinal tract (GIT) and that PPAR alpha is a target gene of THs. Therefore, it is extremely significant to evaluate the molecular mechanisms involved on the regulation of the nutrients transport in enterocytes after chronic ingestion of high-fat diet, as well as the impact of thyroid hormones (THs) on this process. It will be carried out both studies, in vivo and in vitro. C57BL/6 mice fed a standard diet (10%) or hyperlipidic (60%) for 12 weeks will be used in this study, as well as, Caco-2 cells lineage, which will be also maintained in the presence of saturated fatty acids. Hypo and hyperthyroidism will be induced in the animals and cell culture, in order to evaluate whether THs affect the nutrients transport after chronic high-fat exposure. The following proteins will be evaluated: PPAR alpha, SGLT1, GLUT2, GLUT5, PEPT1, NHE2, NHE3, FATP4, FAT/CD36 and NPC1L1. Since there is an association between dietary fat and the establishment of inflammatory processes in some tissues, the protein contents of proinflammatory cytokines, such as IL-1b, IL-6, IFN gamma and TNF-alpha, will be also evaluated. Immunofluorescence and Western blotting techniques will be used to analyze the protein expression. The analysis of intestinal barrier integrity will be made by hematoxylin and eosin staining. These results may contribute to clarify the molecular mechanisms involved in the nutrients transport regulation in conditions of excessive chronic lipid intake, as well as to characterize THs actions on the GIT, which are little known, compared to their impact on the metabolic rate and lipid metabolism. (AU)