SRA

The circadian clock is a cell-autonomous transcription-translation feedback mechanism that anticipates and adapts physiology and behavior to different phases of the day. A variety of factors including hormones, temperature, food-intake, and exercise can act on tissue-specific peripheral clocks to alter the expression of genes that influence metabolism, all in a time-of-day dependent manner. The aim of this study was to elucidate the effects of exercise timing on adipose tissue metabolism. We performed RNA sequencing on inguinal adipose tissue of mice immediately following maximal exercise or sham treatment at the early rest or early active phase. Only during the early active phase did exercise elicit an immediate increase in serum non-esterified fatty acids. Furthermore, early active phase exercise increased expression of markers of thermogenesis and mitochondrial proliferation in inguinal adipose tissue. In vitro, synchronized 3T3-L1 adipocytes showed a timing-dependent difference in Adrb2 expression, as well as a greater lipolytic activity. Thus, the response of adipose tissue to exercise is time- of-day sensitive and may be partly driven by the circadian clock. To determine the influence of feeding state on the time-of-day response to exercise, we replicated the experiment in 10- hour-fasted early rest phase mice to mimic the early active phase metabolic status. A 10-hour fast led to a similar lipolytic response as observed after active phase exercise, but did not replicate the transcriptomic response, suggesting that the observed changes in gene expression are not driven by feeding status. In conclusion, acute exercise elicits timing-specific effects on adipose tissue to maintain metabolic homeostasis. Overall design: For the exercise intervention, 10- to 11-week-old mice were separated into sham- or exercise- treatment at the early rest (ZT3) or early active (ZT15) phase. Exercised mice were exposed to a 1-hour exercise bout (ZT3 with lights on; ZT15 in the dark with the use of a red-light lamp) while sham-exercise counterparts were placed on an artificial treadmill for 1 hour. Following the exercise bout, mice were sacrificed under isoflurane anesthesia and samples of inguinal white adipose tissue, epididymal white adipose tissue, intrascapular brown adipose tissue, and serum were collected at 0h, 4h, 8h, 12h, 16h, and 20h (n=6 per group). RNA concentration and purity were assessed by absorbance at 260 and 280 nm using NanoDrop One (Thermo Fisher Scientific, Waltham, MA). RNA was checked for quality using the Agilent RNA 600 nano kit and Bioanalyser instrument (Agilent Technologies, Santa Clara, CA). Aliquots of RNA (1000 ng) were analyzed using the Illumina TruSeq Stranded Total RNA with Ribo-Zero Gold protocol (Illumina). Samples were cleaned and validated for DNA concentration using the Qubit dsDNA HS assay kit (Invitrogen) and for base pair size and purity using the Agilent High Sensitivity DNA chip and Bioanalyzer instrument. The libraries were subjected to 38-bp paired-end sequencing on a NextSeq500 (Illumina).