Reduced Nogo expression inhibits diet-induced metabolic disorders by regulating ChREBP and insulin activity.

ABSTRACT

BACKGROUND & AIMS: Chronic overconsumption of a high-carbohydrate diet leads to steatosis and its associated metabolic disorder and, eventually, to non-alcoholic fatty liver disease. Carbohydrate-responsive element binding protein (ChREBP) and insulin regulate de novo lipogenesis from glucose. Herein, we studied the effect of reticulon-4 (Nogo) expression on diet-induced metabolic disorders in mice. METHODS: Nogo-deficient (Nogo-/-) and littermate control [wild-type (WT)] mice were fed a high-glucose or high-fructose diet (HGD/HFrD) to induce metabolic disorders. The effects of Nogo small interfering (si) RNA (siRNA) on HFrD-induced metabolic disorders were investigated in C57BL/6J mice. RESULTS: HGD/HFrD induced steatosis and its associated metabolic disorders in WT mice by activating ChREBP and impairing insulin sensitivity. They also activated Nogo-B expression, which in turn inhibited insulin activity. In response to HGD/HFrD feeding, Nogo deficiency enhanced insulin sensitivity and energy metabolism to reduce the expression of ChREBP and lipogenic molecules, activated AMP-activated catalytic subunit α, peroxisome proliferator activated receptor α and fibroblast growth factor 21, and reduced endoplasmic reticulum (ER) stress and inflammation, thereby blocking HGD/HFrD-induced hepatic lipid accumulation, insulin resistance and other metabolic disorders. Injection of Nogo siRNA protected C57BL/6J mice against HFrD-induced metabolic disorders by ameliorating insulin sensitivity, ChREBP activity, ER stress and inflammation. CONCLUSIONS: Our study identified Nogo as an important mediator of insulin sensitivity and ChREBP activity. Reduction of Nogo expression is a potential strategy for the treatment of high-carbohydrate diet-induced metabolic complications. LAY SUMMARY: Nogo deficiency blocks high-carbohydrate diet-induced glucose intolerance and insulin resistance, while increasing glucose/lipid utilisation and energy expenditure. Thus, reduction of Nogo expression protects against high-carbohydrate diet-induced body-weight gain, hepatic lipid accumulation and the associated metabolic disorders, indicating that approaches inhibiting Nogo expression can be applied for the treatment of diseases associated with metabolic disorders.