The Acute Effects of Morning Bright Light on the Human White Adipose Tissue Transcriptome

The circadian rhythm of the central brain clock in the suprachiasmatic nucleus (SCN) is synchronized by light. White adipose tissue (WAT) is one of the metabolic endocrine organs containing a molecular clock, and it is synchronized by the SCN. Excess WAT is a risk factor for health issues including type 2 diabetes mellitus (DM2). We hypothesized that bright-light exposure would affect the human WAT transcriptome. Therefore, we analyzed WAT biopsies from two previously performed randomized cross-over trials (trial 1: n = 8 lean, healthy men, and trial 2: n = 8 men with obesity and DM2). From 7:30 h onwards, all the participants were exposed to either bright or dim light. Five hours later, we performed a subcutaneous abdominal WAT biopsy. RNA-sequencing results showed major group differences between men with obesity and DM2 and lean, healthy men as well as a differential effect of bright-light exposure. For example, gene sets encoding proteins involved in oxidative phosphorylation or respiratory chain complexes were down-regulated under bright-light conditions in lean, healthy men but up-regulated in men with obesity and DM2. In addition to evident group differences between men with obesity and DM2 and healthy lean subjects, autonomic or neuroendocrine signals resulting from bright-light exposure also differentially affect the WAT transcriptome.