FOXO6 activation promotes hepatic steatosis via PPARα inhibition in aged male rats

Aging contributes to hepatic steatosis by increasing de novo lipogenesis. The Forkhead box O6 (FOXO6) transcription factor links insulin signaling to lipid metabolism. Activated FOXO6 induces hyperlipidemia and decreases peroxisome proliferator-activated receptor alpha (PPARα), thereby promoting hepatic lipogenesis. In this paper, we describe the role of FOXO6 in hepatic steatosis in aged male rats and liver cells, and examine the relationship between FOXO6 and PPARα, and the functional consequences of their altered interaction. We find that FOXO6 induces lipid accumulation by inhibiting PPARα in aged male rat livers. Our data show that AKT signaling negatively regulates FOXO6-induced hepatic lipid accumulation, and that a key β-oxidation gene, PPARα, is decreased in aged livers. We further demonstrate that FOXO6 activation decreases PPARα expression and increases lipid accumulation. Furthermore, interaction between FOXO6 and PPARα promotes hepatic steatosis in aged males. Also, high glucose upregulates Foxo6, reduces β-oxidation gene expression, and increases cellular TG-mediated lipid accumulation. Transcriptional activation of FOXO6 by aging and high glucose cause lipid accumulation by downregulating PPARα and hyperglycemia-responsive genes in aged male rats and liver cell cultures. We provide evidence that age-related insulin resistance suppresses β-oxidation through interaction between FOXO6 and PPARα, thereby promoting hepatic lipid accumulation in aged male rats.