The relevance of lipid droplet biogenesis to the hepatitis C virus replication organelle

• Applicant: Gabrielle Vieyres, Ph.D.
• Subject Area: Virology ; Cell Biology
• Term: from 2019 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 417852234

All plus-strand RNA viruses investigated so far remodel host intracellular membranes into a replication organelle, where they multiply their genome. Although replication organelles are pleiomorphic and derive from different subcellular compartments, the mechanisms for their biogenesis are often conserved. Hepatitis C virus (HCV) is a human liver-tropic virus that exquisitely depends on the host lipid metabolism for its replication. Hepatitis C is also associated in vitro and in patients with important dysregulations of the lipid metabolism. This includes lipid droplet accumulation, a phenomenom called steatosis. The virus replicates in modified endoplasmic reticulum-derived membranes, the so-called « membranous web » and in direct proximity to lipid droplets, which are necessary for progeny virion production and maturation.With this project, we will examine the link between lipid droplet synthesis and HCV RNA replication. Lipid droplets are the main intracellular fat storage organelle and energy source. Diacylglycerol acyltransferases (DGAT) 1 and 2 are the two critical enzymes for triglyceride synthesis and lipid droplet biogenesis. We found that DGAT2 expression causes lipid droplet accumulation and strongly limits HCV RNA replication. On the contrary, DGAT1 is a known HCV assembly cofactor. This suggests that HCV might use DGAT1- rather than DGAT2-originating lipid droplets for its multiplication. To test this hypothesis, we will compare the roles of DGAT1 and DGAT2 in HCV genome replication and in the formation of distinct lipid droplet subsets. We will also unravel the mechanism of DGAT2 antiviral activity. We believe that lipid droplet synthesis locally affects the ER lipid landscape and thereby the membranous web formation as well as the anchoring and function of the replication complexes. Finally, we will identify viral determinants that determine HCV sensitivity to DGAT2 and modulate the interplay between viral replicase and intracellular membranes. Altogether, this project will provide a new insight into the hepatic lipid droplet heterogeneity and its contribution to HCV infection. More globally, this has important implications to understand liver steatosis, whose incidence is rapidly growing in industrialized countries, and to design more specific therapeutic strategies targeting this crucial organelle. Finally, this project will shed light on connections and lipid transfers between lipid droplets and the endoplasmic reticulum or, from the virus perspective, between HCV assembly and replication sites. These new information will add up to our understanding of the role of lipids in the membrane-bound replication of plus-strand RNA viruses.

• DFG Programme: Research Grants