Abstract
The circadian clock maintains synchrony between biological processes and light/dark cycles by integrating environmental cues. How the clock adapts to seasonal variations in the environment is incompletely understood. We found that a high-fat diet increased phosphorylation of the clock protein PERIOD2 (PER2) on serine 662 (S662), which was necessary and sufficient for regulating phase shifting of daily locomotor activity to entrain to seasonal light cycles. PER2-S662 phosphorylation correlated with genome-wide expression pathways that regulate polyunsaturated fatty acid (PUFA) conversion into oxylipins in the hypothalamus. Partial hydrogenation of dietary PUFAs increased hypothalamic PER2-S662 phosphorylation and entrainment to a summer photoperiod in control mice, but not in mice for which PER2-S662 could not be phosphorylated. PER2-S662 phosphorylation is influenced by, and alters the regulation of, unsaturated fat to control circadian phase shifting across the seasons.