Increased susceptibility of circadian clock mutant mice to metabolic diseases has led to the idea that a molecular clock is necessary for metabolic homeostasis. However, these mice often lack a normal feeding-fasting cycle. We tested whether time-restricted feeding (TRF) could prevent obesity and metabolic syndrome in whole-body Cry1;Cry2 and in liver-specific Bmal1 and Rev-erbα/β knockout mice. When provided access to food ad libitum, these mice rapidly gained weight and showed genotype-specific metabolic defects. However, when fed the same diet under TRF (food access restricted to 10 hr during the dark phase) they were protected from excessive weight gain and metabolic diseases. Transcriptome and metabolome analyses showed that TRF reduced the accumulation of hepatic lipids and enhanced cellular defenses against metabolic stress. These results suggest that the circadian clock maintains metabolic homeostasis by sustaining daily rhythms in feeding and fasting and by maintaining balance between nutrient and cellular stress responses.

SUMMARY The AMP-activated protein kinase (AMPK) is a highly conserved master regulator of metabolism, whose activation has been proposed to be therapeutically beneficial for the treatment of several metabolic diseases, including nonalcoholic fatty liver disease (NAFLD). NAFLD, characterized by excessive accumulation of hepatic lipids, is the most common chronic liver disease and a major risk factor for development of nonalcoholic steatohepatitis, type 2 diabetes, and other metabolic conditions. To assess the therapeutic potential of AMPK activation, we have generated a genetically engineered mouse model, termed iAMPKCA, where AMPK can be inducibly activated in vivo in mice in a spatially and temporally restricted manner. Using this model, we show that liver-specific AMPK activation reprograms lipid metabolism, reduces liver steatosis, decreases expression of inflammation and fibrosis genes, and leads to significant therapeutic benefits in the context of diet-induced obesity. These findings further support AMPK as a target for the prevention and treatment of NAFLD.

Highlights d TRF protects against body weight gain in young and old male mice but not in female mice d TRF protects from fatty liver regardless of sex or age d TRF preserves whole-body glucose regulation in males and females irrespective of age d TRF extends muscle performance, motor coordination, and survival to sepsis in old mice

No abstract

Diabetes represents a spectrum of disease in which metabolic dysfunction damages multiple organ systems including liver, kidneys and peripheral nerves1,2. Although the onset and progression of these co-morbidities are linked with insulin resistance, hyperglycaemia and dyslipidaemia3–7, aberrant non-essential amino acid (NEAA) metabolism also contributes to the pathogenesis of diabetes8–10. Serine and glycine are closely related NEAAs whose levels are consistently reduced in patients with metabolic syndrome10–14, but the mechanistic drivers and downstream consequences of this metabotype remain unclear. Low systemic serine and glycine are also emerging as a hallmark of macular and peripheral nerve disorders, correlating with impaired visual acuity and peripheral neuropathy15,16. Here we demonstrate that aberrant serine homeostasis drives serine and glycine deficiencies in diabetic mice, which can be diagnosed with a serine tolerance test that quantifies serine uptake and disposal. Mimicking these metabolic alterations in young mice by dietary serine or glycine restriction together with high fat intake markedly accelerates the onset of small fibre neuropathy while reducing adiposity. Normalization of serine by dietary supplementation and mitigation of dyslipidaemia with myriocin both alleviate neuropathy in diabetic mice, linking serine-associated peripheral neuropathy to sphingolipid metabolism. These findings identify systemic serine deficiency and dyslipidaemia as novel risk factors for peripheral neuropathy that may be exploited therapeutically.