Effects of light and food schedules on liver and tumor molecular clocks in mice

Abstract

Background: Disrupted circadian coordination accelerates malignant growth, but the molecular mechanism is unclear. Methods: Healthy or Glasgow osteosarcoma-bearing mice (n = 162) were synchronized with light and darkness over 2-3 weeks, submitted to an 8-hour advance onset of light every 2 days (chronic jet lag) to disrupt circadian coordination, or submitted to chronic jet lag and meal timing to prevent molecular clock alteration. The expression of molecular clock genes and of the cell cycle genes c-Myc and p53 in liver and tumor was determined with quantitative reverse transcription-polymerase chain reaction at six circadian times over a 24-hour period of light and darkness and analyzed with analysis of variance and cosinor. Tumor weight was measured daily over the course of the experiment. All statistical tests were two-sided. Results: In synchronized mice, mean mRNA levels of clock genes Rev-erbα, Per2, and Bmal1 varied by 206-, four-, and 26-fold, respectively, over the 24 hours in healthy mouse liver; by 36-, 35-, and 32-fold in the livers of tumor-bearing mice; and by 9.4-, 5.5-, and sixfold in tumor tissue (P = .046 to