Differential effects of diet composition and timing of feeding behavior on rat brown adipose tissue and skeletal muscle peripheral clocks.

The effects of feeding behavior and diet composition,as well as their possible interactions,on daily (clock) gene expression rhythms have mainly been studied in the liver, and to a lesser degree in white adipose tissue(WAT), but hardly in other metabolic tissues such as skeletal muscle (SM) and brown adipose tissues (BAT). We therefore subjected male Wistar rats to a regular chow or free choice high-fat-high sugar (fcHFHS) diet in combination with time restricted feeding (TRF) to either the light or dark phase. InSM,all tested clock geneslost their rhythmicexpressioninthe chow light fed group.In the fcHFHS light fed group rhythmic expression for some, but not all, clock genes was maintained, but shifted by several hours. In BATthedaily rhythmicity of clock genes was maintained for the light fed groups, but expression patterns were shiftedas compared with ad libitumand dark fed groups,whilst thefcHFHS diet made the rhythmicity of clock genes become more pronounced.Most of the metabolic genesin BAT tissuetested didnot show any rhythmic expression ineither the chow or fcHFHS groups.In SM Pdk4and Ucp3were phase-shifted, butremained rhythmically expressed inthe chow light fed groups.Rhythmicexpressionwas lost for Ucp3whilst on the fcHFHS diet during the light phase.In summary, both feeding at the wrong time of dayand diet compositiondisturbthe peripheral clocks in SM and BAT, but to different degreesand thereby result in a further desynchronization between metabolically active tissuessuch as SM, BAT, WAT and liver.