Presenting Author Western University London, Ontario, Canada
Rachel Wilson (Western University)| Yun Jin Chen (Western University)| Ashley Domingues (Western University)| Richard Zhang (Western University)| Cynthia Sawyez (Western University)| Brian Sutherland (Western University)| John Kennelly (University of Alberta)| Kelly-Ann Leonard (University of Alberta)| René Jacobs (University of Alberta)| Nica Borradaile (Western University)
Non-alcoholic fatty liver disease (NAFLD) is characterized by hepatocyte lipid accumulation, which can cause hepatocyte injury through lipotoxicity. Eukaryotic elongation factor 1A1 (EEF1A1), which is a component of the protein synthetic machinery and regulates actin cytoskeleton turnover, is induced in human hepatocyte-like HepG2 cells undergoing lipotoxicity, in association with ER stress. Moreover, EEF1A1 has been identified in the lipid droplet (LD) proteome in various cell and tissue types, suggesting that it may have a role in LD biology. Partial inhibition of EEF1A1 peptide elongation activity with the marine compound didemnin B (DB) decreases lipotoxic HepG2 cell death. However, the effects of EEF1A1 inhibition on cellular lipid accumulation are unclear. Based on the potential association of EEF1A1 with LDs, and its apparent roles in responding to ER stress and in regulating cytoskeleton dynamics, we hypothesized that inhibition of EEF1A1 with DB would alter hepatocyte LD accumulation. Male 129S6 mice were fed a western diet for 26 weeks to induce NAFLD, followed by intervention with DB (50 μg/kg, i.p.) once every 3 days for 14 days. Treatment with DB decreased liver lipid accumulation, as determined by biochemical and histological analyses, and upregulated expression of genes involved in fatty acid oxidation (Cpt1a, Fgf21). Assessments of LD size in mouse liver revealed a significant decrease in median size upon treatment with DB, suggesting that DB promotes the formation of smaller LDs. To explore whether this effect was conserved in human hepatocyte-like cells, HepG2 cells were treated for 6 h with DB (80 nM) under lipotoxic conditions (1 mM palmitate plus oleate) and LDs were visualized by confocal microscopy. Cells exposed to lipotoxic conditions exhibited increased LD area, and treatment with DB appeared to decrease the formation of large LDs (-63%, p=0.11). This occurred alongside upregulation of CPT1A mRNA, which was consistent with the upregulation of genes involved in fatty acid oxidation observed in mouse liver. Finally, a Chinese hamster ovary cell line that harbors a mutation leading to reduced EEF1A1 expression accumulated less triglyceride under high fatty acid conditions compared to wild-type cells. Together, these findings suggest that that disruption of EEF1A1 activity may diminish LD accumulation and channel excess fatty acids toward oxidation, which could have implications for the treatment of NAFLD.