Choline mediated hepatic lipid homeostasis in yellow catfish: Unravelling choline's lipotropic and methyl donor functions and significance of ire-1α signalling pathway.

Choline plays a crucial role in hepatic lipid homeostasis by acting as a major methyl-group donor. However, despite this well-accepted fact, no study has yet explored how choline's methyl-donor function contributes to preventing hepatic lipid dysregulation. Moreover, the potential regulatory role of Ire-1α, an ER-transmembrane transducer for the unfolded protein response (UPRer), in choline-mediated hepatic lipid homeostasis remains unexplored. To address these gaps, this study was conducted to investigate the mechanism by which choline prevents hepatic lipid dysregulation, focusing on its role as a methyl-donor and the involvement of Ire-1α in this process. To this end, a model animal for lipid metabolism, yellow catfish ( Pelteobagrus fulvidraco ), were fed two different diets (adequate or deficient choline diets) in vivo for 10 weeks, and in vitro experiments were conducted to intercept the methyl-donor function of choline in isolated hepatocytes by transfecting them with si-choline dehydrogenase ( chdh ). The key findings of studies are as follows: 1. Dietary choline downregulated the gene and protein expression of fatty acid synthase and transcription of other lipid biosynthetic genes. Consequently, dietary choline, upregulated selected lipolytic and fatty acid β-oxidation transcripts promoting hepatic lipid homeostasis. 2. Dietary choline ameliorated UPRer and prevented hepatic lipid dysregulation mainly through ire-1α signalling, not perk or atf-6α signalling. 3. Choline inhibited the transcriptional expression level of ire-1α by activating site-specific DNA methylations in the promoter of ire-1α . 4. Choline-mediated ire-1α methylations reduced Ire-1α/Fas interactions, thereby further inhibiting Fas activity and reducing lipid droplet deposition. These results offer a novel insight into the direct and indirect regulation of choline on lipid metabolism genes and suggests a potential crosstalk between ire-1α signalling and choline-deficiency-induced hepatic lipid dysregulation, highlighting the critical contribution of choline as a methyl-donor in maintaining hepatic lipid homeostasis.