Apolipoprotein E, a Crucial Cellular Protein in the Lifecycle of Hepatitis Viruses

International audienceApolipoprotein E (ApoE) is a multifunctional protein expressed in several tissues, including those of the liver. This lipoprotein component is responsible for maintaining lipid content homeostasis at the plasma and tissue levels by transporting lipids between the liver and peripheral tissues. The ability of ApoE to interact with host-cell surface receptors and its involvement in several cellular pathways raised questions about the hijacking of ApoE by hepatotropic viruses. Hepatitis C virus (HCV) was the first hepatitis virus reported to be dependent on ApoE for the completion of its lifecycle, with ApoE being part of the viral particle, mediating its entry into host cells and contributing to viral morphogenesis. Recent studies of the hepatitis B virus (HBV) lifecycle have revealed that this virus and its subviral envelope particles also incorporate ApoE. ApoE favors HBV entry and is crucial for the morphogenesis of infectious particles, through its interaction with HBV envelope glycoproteins. This review summarizes the data highlighting the crucial role of ApoE in the lifecycles of HBV and HCV and discusses its potential role in the lifecycle of other hepatotropic viruses

Apolipoprotein E, a Crucial Cellular Protein in the Lifecycle of Hepatitis Viruses

Apolipoprotein E (ApoE) is a multifunctional protein expressed in several tissues, including those of the liver. This lipoprotein component is responsible for maintaining lipid content homeostasis at the plasma and tissue levels by transporting lipids between the liver and peripheral tissues. The ability of ApoE to interact with host-cell surface receptors and its involvement in several cellular pathways raised questions about the hijacking of ApoE by hepatotropic viruses. Hepatitis C virus (HCV) was the first hepatitis virus reported to be dependent on ApoE for the completion of its lifecycle, with ApoE being part of the viral particle, mediating its entry into host cells and contributing to viral morphogenesis. Recent studies of the hepatitis B virus (HBV) lifecycle have revealed that this virus and its subviral envelope particles also incorporate ApoE. ApoE favors HBV entry and is crucial for the morphogenesis of infectious particles, through its interaction with HBV envelope glycoproteins. This review summarizes the data highlighting the crucial role of ApoE in the lifecycles of HBV and HCV and discusses its potential role in the lifecycle of other hepatotropic viruses

Endoplasmic Reticulum Detergent-Resistant Membranes Accommodate Hepatitis C Virus Proteins for Viral Assembly

During Hepatitis C virus (HCV) morphogenesis, the non-structural protein 2 (NS2) brings the envelope proteins 1 and 2 (E1, E2), NS3, and NS5A together to form a complex at the endoplasmic reticulum (ER) membrane, initiating HCV assembly. The nature of the interactions in this complex is unclear, but replication complex and structural proteins have been shown to be associated with cellular membrane structures called detergent-resistant membranes (DRMs). We investigated the role of DRMs in NS2 complex formation, using a lysis buffer combining Triton and n-octyl glucoside, which solubilized both cell membranes and DRMs. When this lysis buffer was used on HCV-infected cells and the resulting lysates were subjected to flotation gradient centrifugation, all viral proteins and DRM-resident proteins were found in soluble protein fractions. Immunoprecipitation assays demonstrated direct protein−protein interactions between NS2 and E2 and E1 proteins, and an association of NS2 with NS3 through DRMs. The well-folded E1E2 complex and NS5A were not associated, instead interacting separately with the NS2-E1-E2-NS3 complex through less stable DRMs. Core was also associated with NS2 and the E1E2 complex through these unstable DRMs. We suggest that DRMs carrying this NS2-E1-E2-NS3-4A-NS5A-core complex may play a central role in HCV assembly initiation, potentially as an assembly platform

Comparison of the innate immune response to infection by mycobacteria and SARS-CoV-2 in humans using an ex vivo physiological lung model

The recent emergence of the new coronavirus SARS-Cov-2 reminds us the importance of research on emerging and zoonotic pathogens. Most of the models used to study respiratory pathogens rely on cells lines, which do not represent the diversity of lung cells nor their tissular organization or cell-cell interactions 1,2.We validated a model of Precision Cut Lung Slices (PCLS) to study the early steps of infection by Mycobacterium bovis (Mb) and tuberculosis (Mtb), respectively causing bovine and human tuberculosis. While Mb is zoonotic, Mtb is restricted to Humans but host specificities are not understood yet. The bovine PCLS study showed that type I interferon pathway was activated by Mb and not Mtb, with a significant contribution of resident alveolar macrophages3. By adapting the bovine protocol, we used biopsies obtained from surgical resection from lung adenocarcinoma, to obtain human PCLS. This enabled ex vivo infections in a preserved and functional lung micro-environment.First, we set up the infection conditions (strains, timepoint, detection methods). We validated mycobacteria protocols but faced difficulty with SRAS-Cov-2 detection. We were able to observe infected cells with a neon green recombinant virus. Then we investigated which cell types were infected by our pathogens, by imaging (TEM, confocal microscopy). We focused on alveolar macrophage, a cell which play a key role in the development of both infections. Alveolar macrophages were numerously recruited in infected alveoli 48h after Mtb or Mb infection. The analysis of the transcriptomic signature of infected PCLS is ongoing. Our project will improve our understanding of the pathophysiology of top two deadliest respiratory diseases worldwide, COVID-19 and tuberculosis