Liver-Specific Expression of Dominant-Negative Transcription Factor 7-Like 2 Causes Progressive Impairment in Glucose Homeostasis

Abstract

Investigations on the metabolic role of the Wnt signaling pathway and hepatic transcription factor 7-like 2 (TCF7L2) have generated opposing views. While some studies demonstrated a repressive effect of TCF7L2 on hepatic gluconeogenesis, a recent study using liver-specific Tcf7l2 2/2 mice suggested the opposite. As a consequence of redundant and bidirectional actions of transcription factor (TCF) molecules and other complexities of the Wnt pathway, knockout of a single Wnt pathway component may not effectively reveal a complete metabolic picture of this pathway. To address this, we generated the liver-specific dominant-negative (DN) TCF7L2 (TCF7L2DN) transgenic mouse model LTCFDN. These mice exhibited progressive impairment in response to pyruvate challenge. Importantly, LTCFDN hepatocytes displayed elevated gluconeogenic gene expression, gluconeogenesis, and loss of Wnt-3a-mediated repression of gluconeogenesis. In C57BL/6 hepatocytes, adenovirus-mediated expression of TCF7L2DN, but not wild-type TCF7L2, increased gluconeogenesis and gluconeogenic gene expression. Our further mechanistic exploration suggests that TCF7L2DN-mediated inhibition of Wnt signaling causes preferential interaction of b-catenin (b-cat) with FoxO1 and increased binding of b-cat/FoxO1 to the Pck1 FoxO binding site, resulting in the stimulation of Pck1 expression and increased gluconeogenesis. Together, our results using TCF7L2DN as a unique tool revealed that the Wnt signaling pathway and its effector b-cat/TCF serve a beneficial role in suppressing hepatic gluconeogenesis.

Curcumin represses mouse 3T3-L1 cell adipogenic differentiation via inhibiting miR-17-5p and stimulating the Wnt signalling pathway effector Tcf7l2

“…The possession of HA-tagged adenovirus vehicles for wild type TCF7L2 and TCF7L2DN 16 allowed us to assess the effect of their expression on 3T3-L1 differentiation (Figure 3c). Figure 3d shows that 48 h after the virus infection in 3T3-L1 cells, we were able to detect the expression of HA-tagged exogenous TCF7L2 or TCF7L2DN.…”

“…The generation of Ad-TCF7L2, Ad-TCF7L2DN and miR-17 over-expression plasmid has been previously presented. 16, 47, 48 miR-17 lentivirus construct was generated by inserting two copies of miR-17 precursor into the plv vector (Biosettia, CA, USA). RNA extraction and real-time PCR were performed as previously described, 16 with actin or U6 as the correspondent normalization controls.…”

“…Western blotting was performed as previously described. 16 Supplementary Tables 1 and 2 list primers and antibodies utilized in this study.…”

Cross-species gene expression analysis identifies a novel set of genes implicated in human insulin sensitivity

“…52,53 However, subsequent studies have found that TCF7L2 principally functions as a regulator of insulin action in liver and possibly other tissues. 54,55 This is important, as overall most SNPs associated with T2D are thought to principally have a role in beta cell dysfunction and very few SNPs have been found in genes that control insulin action in tissue such as muscle. As we observed β-catenin to be a major regulatory node in a GEM associated with IR we speculate that this pathway may represent a major biomarker for defects in insulin action.…”

Nuclear Mechanisms of Insulin Resistance

“…In response to oxidative stress, β-catenins also directly interact with FOXO1 to increase its transcriptional activity (Almeida et al, 2007, Essers et al, 2005). Such β-catenin/FOXO1 interactions in liver have been shown to contribute to regulation of gluconeogenic gene expression and glucose homeostasis (Ip et al, 2015). …”