Protein Secretion From Liver Ex Vivo Reveals Regulation of Hepatokines by Sex and Circadian Rhythm.

Despite the importance of liver secreted proteins in health and disease, an understanding of their regulation by biological variables such as sex and circadian time is lacking. Here, we validated a well-maintained, dynamic, and unbiased ex vivo assay of liver protein secretion, revealing novel findings. Proteomic analyses uncovered hundreds of sex-dependent hepatokines involved in lipid metabolism, sulfation, and serine protease inhibition, as well as time-dependent hepatokines. Many apolipoproteins and well-characterized plasma proteins were secreted more during daytime, whereas several carboxylesterases and proteins with unconventional secretion tended to be secreted more during nighttime. Time-dependent secreted proteins were transcriptionally regulated by the molecular clock and dysregulated by chronic jet lag-induced circadian misalignment. Finally, we showed that the clock-dependent liver secreted protein endostatin tunes the expression of metabolic genes in white adipose tissue during daytime in female mice. Together, these findings provide key insights into circadian control and sexual dimorphism of liver secreted proteins, which serve as clinical biomarkers and novel therapeutic targets.