Deciphering the function of obesity-associated regulatory elements within FTO

• Main Author: Laber, Samantha
• Other Authors: Cantley, James ; Cox, Roger
• Published: University of Oxford 2017
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.740866

Genome-wide association studies have repeatedly shown that the strongest association with obesity arises from variants in the first intron of FTO. The intronic FTO variant rs1421085 is within an adipocyte-specific enhancer and that risk allele carriers have increased IRX3 and IRX5 expression in early adipogenesis (Claussnitzer et al., 2015). Additionally, the same human risk variant was linked to decreased AKTIP, RPGRIP1L and FTO expression in iPSC-derived neurons (Stratigopoulos et al., 2016). These data point towards several likely causal transcripts and tissues at the FTO locus and essentially, several likely mechanisms. Importantly, whether any of the high-risk variants at the FTO locus has any effect on the organismal level has not been addressed so far. The aim of my DPhil project was to use novel gene manipulation strategies in vivo to mechanistically dissect the Fto regulatory circuitry in mouse to pinpoint causal transcripts their effector tissues and to unravel their physiological role in body weight regulation . Using publicly available as well as my own genomic data (ATAC-seq) revealed that the intronic FTO regulatory element in human adipocytes is conserved in mouse pre-adipocytes. Manipulation of the corresponding motif in mouse (by deleting 82 nucleotides at the mouse orthologous region around rs1421085) resulted in depot- and sex-specific alteration of target genes Irx3 and Irx5 in pre-adipocytes. In addition to recapitulating many of the human findings in mouse, my results further unravelled a new level of regulatory complexity at the FTO/Fto locus. When these mutant mice were put on a high fat diet, I found a reduction on overall fat-mass that could be linked to altered mRNA levels of Irx3 and Irx5 in pre-adipocytes. Using a number of genetic techniques, I further showed that Irx3 regulates several processes during adipocyte development, amongst which is modulation of mitochondrial function. In summary, my findings provide new insight into how variants in FTO intron 1 affect adipocyte development and more specifically how IRX3 affects early adipocyte differentiation.