Characterizing the Role of TDG in FXR-dependent Signaling

Oladapo A. Onabote, The University of Western Ontario

Abstract

Thymine DNA Glycosylase (TDG) plays a key role in active demethylation by excising intermediates of 5-methylcytosine. The function of TDG is required for embryonic development, as Tdg-null embryos die at E11.5. To bypass this embryonic lethality, our lab generated conditional Tdg knockout (TDG_CKO) mice. These mice develop late-onset hepatocellular carcinoma (HCC), partly due to impaired Farnesoid X Receptor (FXR) signaling. Interestingly, Fxr-knockout mice display a similar phenotype and transcriptional profile to TDG_CKO mice, prompting us to investigate a role for TDG in FXR signaling. To this end, we generated Tdg/Fxr double-knockout (DKO) mice. We also generated a novel Fxr-null mouse model using CRISPR/Cas9, which facilitated the knockout of FXR through a 47-bp deletion event. We demonstrated that 3-week-old Fxr-null mice display impaired bile acid and glucose metabolism. Moreover, we demonstrated a novel interaction between TDG and FXR in vivo. Collectively, these findings implicate TDG as a coactivator of FXR signaling.