Deletion of Arntl, a component of the molecular clock, in adipocytes leads to cellular hypertrophy by increasing insulin sensitivity via FGF21

Brain and muscle Arnt-like protein 1 (BMAL1), encoded by Aryl hydrocarbon receptor nuclear translocator like 1 (Arntl) gene, is a transcription factor that regulates the circadian rhythm of the expressions of several genes. The link between the loss of BMAL1 function in adipose tissue and obesity has been reported. Although these previous studies have suggested that dysregulation of lipolysis is a contributing factor, but the detailed mechanism has not been fully understood. This study aimed to elucidate the role of BMAL1 in adipocytes using adipocyte-specific Arntl deficient (AAKO) mice. Deletion of Arntl in adipocytes leads to increased cellular insulin sensitivity, which in turn, inhibited lipolysis in adipocytes and caused cellular hypertrophy. The expression levels of Fgf21 in adipose tissue were significantly elevated in AAKO mice compared to Arntl ^flox/flox mice. Double knockout of Arntl and Fgf21 in adipocytes abolished metabolic phenotypes such as decreased circulating non-esterified fatty acid levels, adipocyte hypertrophy, and increased insulin sensitivity in AAKO mice. These results indicated that BMAL1 regulates fat mobilization and insulin signaling in adipocytes via FGF21 during the stationary phase. This is the possible mechanism by which disruption of circadian rhythm induces obesity.