Time-of-day-dependent variation of the hepatic transcriptome and metabolome is disrupted in non-alcoholic fatty liver disease patients

Abstract

ABSTRACTLiver homeostasis is ensured in part by time-of-day-dependent processes, many of them being paced by the molecular circadian clock. Liver functions are compromised in non-alcoholic fatty liver (NAFL) and non-alcoholic steatohepatitis (NASH), and clock disruption increases susceptibility to non-alcoholic fatty liver disease (NAFLD) progression in rodent models. We therefore investigated whether time-of-day-dependent transcriptome and metabolome are significantly altered in human NAFL and NASH livers. Liver biopsies, collected within an 8 hour- window from a carefully phenotyped cohort of 290 patients and histologically diagnosed to be either normal, NAFL or NASH hepatic tissues, were analyzed by RNA sequencing and unbiased metabolomic approaches. Time-of-day-dependent gene expression patterns and metabolomes were identified and compared between histologically normal, NAFL and NASH livers. We provide here a first-of-its-kind report of a daytime-resolved human liver transcriptome-metabolome and associated alterations in NAFLD. Transcriptomic analysis showed a robustness of core molecular clock components in NAFL and NASH livers. It also revealed stage-specific, time-of-day- dependent alterations of hundreds of transcripts involved in cell-to-cell communication, intra- cellular signaling and metabolism. Similarly, rhythmic amino acid and lipid metabolomes were affected in pathological livers. Both TNFa and PPARγ signaling are predicted as important contributors to altered rhythmicity. NAFLD progression to NASH perturbs time-of-day-dependent processes in human livers, while core molecular clock component differential expression is maintained.