The role of Angptl4/Fiaf in exercise-induced skeletal muscle AMPK activation.

Angiopoietin-like protein 4 (Angptl4)/fasting-induced adipose factor (Fiaf) expression levels are increased by exercise in skeletal muscle. We have previously shown that Angptl4 regulates food intake and energy expenditure via modulation of hypothalamic AMP-activated protein kinase (AMPK) activity. AMPK is an important signaling molecule that integrates skeletal muscle metabolism during exercise. Therefore, we investigated the involvement of Angptl4 in exercise-induced AMPK activation in skeletal muscle. Angptl4 protein and mRNA expression levels were significantly increased in the gastrocnemius and soleus muscles of mice following a 50-min running bout. Treatment of C2C12 myotubes with Angptl4 increased phosphorylation of AMPK and acetyl-CoA carboxylase (ACC), which were markers of AMPK activation, and the mitochondrial maximum respiratory capacity. Treadmill exercise increased AMPK and ACC phosphorylation in the gastrocnemius of normal mice; this phosphorylation increase was attenuated in mice lacking Angptl4. Endurance to swimming and hanging was also reduced in Angptl4 knockout mice. Taken together, our current data demonstrate that exercise-induced upregulation of skeletal muscle Angptl4 is critical for AMPK activation and exercise tolerance. These findings unveil a new role for skeletal muscle Angptl4 in exercise physiology. NEW & NOTEWORTHY 1) Angiopoietin-like protein 4 (Angptl4) treatment activates AMP-activated protein kinase (AMPK) signaling in skeletal muscle cells. 2) Angptl4 increases the maximum mitochondrial oxidative capacity through AMPK activation in skeletal muscle cells. 3) Lack of Angptl4 mitigates exercise-induced skeletal muscle AMPK activation. 4) Angptl4-deficient mice show a lower endurance to exercise.