SPINELLI, ROSA (2017) Epigenetic Silencing of Ankrd26 Gene Contributes to Adipose Tissue Inflammation in Obesity. [Tesi di dottorato]

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Environmental factors interact with the genome to influence gene expression, tissue function and also disease risk. External stimuli may affect the phenotype through epigenetic mechanisms that provide an interface with the genome. Indeed, epigenetic modifications represent a mechanism through which both genetic and environmental cues, including dietary factors, are integrated at specific genomic loci and affect individual phenotypes, contributing to susceptibility to obesity and type 2 diabetes. Recently, alterations of Ankyrin repeat domain 26 (Ankrd26) gene expression and function have been associated with the onset of these metabolic disorders. However, whether external cues can affect its expression remains unclear. Therefore, the aim of this study is to evaluate whether the administration of a high fat diet (HFD) in mice could affect Ankrd26 expression and function, and whether chromatin remodeling and epigenetic modifications take part in this regulation. Particularly, I examined the correlation between obesity and inflammation with defective regulation of Ankrd26 gene in visceral adipose tissue (VAT) depots, aiming at identifying epigenetic mechanism that might underpin the development of VAT dysfunctions induced by overnutrition. Using the HFD-induced obesity mouse model, I reported evidence of detailed epigenetic changes of Ankrd26 promoter. Indeed, I demonstrated that the HFD-induced Ankrd26 down-regulation in VAT was directly caused by specific hyper-methylation of -436 and -431 cytosine residues at its promoter region, that was followed by chromatin reorganization. Indeed, DNA methylation of these specific CpG sites impaired binding of the histone acetyltransferase/transcriptional coactivator p300 to this region, both in vitro and in vivo, causing hypo-acetylation of histone H4 at the Ankrd26 promoter and loss of binding of RNA Pol II at the Ankrd26 Transcription Start Site in obese mice. Furthermore, the HFD treatment increased binding of DNA methyl-transferases 3a and 3b and methyl-CpG-binding domain protein 2 to the Ankrd26 promoter. To evaluate the functional consequences of these changes, the HFD-induced Ankrd26 down-regulation was mimicked by silencing Ankrd26 gene expression in vitro in 3T3-L1 adipocytes. This silencing caused enhanced secretion of the pro-inflammatory chemokines KC/IL-8, Eotaxin, MCP1 and Rantes. The relevance of these observations to humans is supported by other findings in obese individuals, revealing that the reduction of ANKRD26 expression in VAT negatively correlates with serum concentrations of inflammatory markers. Taken together, my data provide evidence for environmentally induced DNA changes at Ankrd26 promoter and, for the first time, highlight a role for Ankrd26 epigenetic silencing in raising and/or sustaining VAT inflammation following unhealthy dieting and in development of obesity-related insulin resistance. Since direct evidence linking specific environmental cues and metabolic disorders are still limited, addressing this issue will provide new insight into the molecular basis of obesity as well as create novel translational perspective.

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