Saturated Fat Impairs Circadian Transcriptomics through Histone Modification of Enhancers

Aims/hypothesis: Obesity and elevated circulating lipids may impair metabolism by disrupting the molecular circadian clock. We tested the hypothesis that lipid-overload may interact with the circadian clock and alter the rhythmicity of gene expression through epigenetic mechanisms. Methods: We determined the effect of the saturated fatty acid palmitate on circadian transcriptomics and examined the impact on histone H3 lysine K27 acetylation (H3K27ac) and the regulation of circadian rhythms in primary human skeletal muscle myotubes. Total H3 abundance and histone H3K27ac was assessed in vastus lateralis muscle biopsies from men with either obesity or normal weight. Results: Palmitate reprogrammed the circadian transcriptome in myotubes without altering the mRNA rhythm of core clock genes. Genes with enhanced cycling in response to palmitate were associated with post-translational modification of histones. Cycling of histone 3 lysine 27 acetylation (H3K27ac), a marker of active gene enhancers, was modified by palmitate treatment in myotubes. Chromatin immunoprecipitation and sequencing confirmed that palmitate altered the cycling of DNA regions associated with H3K27ac. Overlap of mRNA and DNA regions associated with H3K27ac and pharmacological inhibition of histone acetyl transferases revealed novel cycling genes associated to lipid exposure in human myotubes. Conclusion/interpretation: Palmitate disrupts transcriptomic rhythmicity and modifies histone H3K27ac in circadian manner, suggesting acute lipid-overload alters the circadian chromatin landscape and reprograms circadian gene expression of skeletal muscle. Human primary skeletal myotubes were synchronized with serum shock and exposed to 0.4 mM of palmitate of BSA-conjugated palmitate. DNA was extracted 24h, 32h, 40h and 48h after the beginning of treatment and analyzed by ChIPseq for histone 3 lyzine 27 acetylation.