P044 HIF1A IS A SWITCH IN THE PRO- VS ANTI-INFLAMMATORY FOXP3 GENE CIRCUITRY NETWORKS IMPLICATED IN INFLAMMATORY BOWEL DISEASE

Abstract Background We have published data sets revealing the majority of FOXP3 gene targets in CD4+ lymphocytes isolated from Crohn's lesions are significantly up-regulated. FOXP3 gene target status in the disease state is incongruent with FOXP3 and its associated complex functioning as an established gene repressor/silencer. This finding of up-regulated gene expression is best explained by the gain of a co-activation complex in addition to loss of repression. A putative FOXP3 co-activator complex associated with Crohn's disease is unknown. We employed tertiary bioinformatic analysis tools utilizing the FOXP3/EZH2 up-regulated gene sets and found HIF1a to be a consistent and significant pathway/protein of interest. Methods FOXP3 complex composition was assessed by immunoprecipitation +/- HIF1a. Treg or Jurkat cellular phenotyping and FOXP3 target gene expression was performed by flow cytometry. FOXP3 gene target promoter histone and histone modifying enzyme status was assessed by ChIP. A FOXP3-cre driven, EZH2fl/fl, animal model was utilized to assess FOXP3/EZH2 repressor function with HIF1a modulation on colitis. Results The FOXP3/p300 activation complex was more abundant in the absence of HIF1a, whereas the FOXP3/EZH2 repressor complex was reciprocally more abundant in the presence of HIF1a. Using IFNg as a model gene for FOXP3 transcriptional regulation, we demonstrated that HIF1a regulates FOXP3 dependent IFNg gene activation by histone modifications at the IFNg promoter. We demonstrated that HIF1a restores repression of the master lineage markers TBET and RORgT in in-vitro derived Tregs lacking FOXP3/EZH2 repressor function. Finally, the use of a HIF1a activator rescues colitis through HIF1a stabilization in the FOXP3 driven EZH2 null animals. Conclusions We demonstrated functional and biochemical preliminary data in both in-vitro and in-vivo models demonstrating that HIF1a modulates FOXP3 activator/repressor function.