Resumen de Epigenetics of adipose tissue and its related disorders
Obesity and metabolic syndrome are increasing epidemic worldwide, especially in developed countries. Obesity and metabolic disease increase the risk of suffering certain diseases such as diabetes, cardiovascular disease, NASH, neurodegenerative disorders or some type of cancers like colorectal cancer. Adipose tissue is nowadays considered as an important organ that can regulate body homeostasis and modulate other tissues function through the delivery of a wide range of molecules. It has been shown that in obesity and metabolic disease context an adipose tissue dysfunction exists, producing changes in the adipokine secretion profile that in turn can prone to the disorders usually associated to these conditions. Besides, metabolic disease and obesity development are closely related to environmental factors such as food, smoking, sedentary habits, etc. However, obesity and metabolic syndrome also have a genetic and an epigenetic component, being regarded the epigenetic landscape as a mediator between environmental and genetic factors.
In this sense, epigenetics mechanisms can be shaped by nutrition, smoking or exercise among other lifestyle factors. There are two main epigenetics mechanism: 1) DNA methylation, which occurs in the C5 of a cytosine pyrimidine near to a guanine (position called CpG); and 2) histone modifications, which mainly occurs in the N terminal of histone proteins and that have a more diverse nature (acetylation, methylation, phosphorylation, sumoylation, ubiquitination, glycosylation,…). Both mechanism have been shown to be deregulated in metabolic syndrome and obesity, and could be implied in the etiology and associated risks observed in these conditions.
Thus, the hypothesis of this thesis is that visceral adipose tissue (VAT) epigenetics could be de-regulated in obese, metabolic syndrome and colorectal cancer subjects contributing to the etiology of these disorders. To answer this hypothesis, the objective was to study the DNA methylation and histone H3K4me3 modification in VAT from Obese and Metabolic Syndrome Subjects as well as DNA methylation from VAT of Colorectal Cancer patients.
Two main techniques were used: DNA methylation was measured by DNA bisulfite conversion and pyrosequencing using the Pyromark Q96 system (Qiagen, Corea); and to study histone modifications, a chromatin immunoprecipitation (ChIP) protocol was first established. After that we apply this ChIP method to quantify tri-methylation at lysine 4 of histone 3 (H3K4me3) modifications. Moreover, standard molecular technics were used such as qPCR for the quantification of mRNA and enriched DNA after chromatin immunoprecipitation, western blot for protein quantification or ELISA assays.
We observed differences in some studied CpG islands in metabolic syndrome, extreme obese subjects and colorectal cancer subjects such as LPL, TNF, C3, VDR or NFκB1 promoters. Besides, some of these marks presented negative correlations with mRNA levels suggesting an epigenetic control of the transcriptional activity. These marks were also associated to variables related to the etiology of obesity as well as the metabolic syndrome worsening, and to inflammation in colorectal cancer. Besides, H3K4me3 was positively associated to the body mass index and to insulin resistance states, being higher the promoter enrichment for most of the studied genes in extreme obese people with glucose intolerance. Furthermore, some of these marks were positively related to mRNA levels, fact that could suggest that these mRNA levels could be regulated by this histone mark.
Thus, this thesis dissertation shows that adipose tissue epigenetics might be contributing to adipose tissue function and to the etiology of obesity, metabolic syndrome and colorectal cancer.
