Cell Culture Models for Hepatitis E Virus

Abstract

Despite a growing awareness, hepatitis E virus (HEV) remains understudied and investigations have been historically hampered by the absence of efficient cell culture systems. As a result, the pathogenesis of HEV infection and basic steps of the HEV life cycle are poorly understood. Major efforts have recently been made through the development of HEV infectious clones and cellular systems that significantly advanced HEV research. Here, we summarize these systems, discussing their advantages and disadvantages for HEV studies. We further capitalize on the need for HEV-permissive polarized cell models to better recapitulate the entire HEV life cycle and transmission.

Keywords: cell culture systems; hepatitis E virus; hepatocyte polarization; stem cells.

Figure 1

Hepatitis E virus (HEV) life cycle and transmission. (1) Supposedly naked HEV (nHEV) particles reach the liver and infect hepatocytes through their basolateral membrane. (2) Replication of the HEV genome (green) mediated by HEV nonstructural proteins occurs in a yet uncharacterized cellular compartment. (3) Translation of the subgenomic RNA leads to the translation of open reading frame 2 (ORF2) capsid protein (grey) and ORF3 protein (purple). The assembly site of infectious HEV particles is unknown. (4) Progeny HEV particles bud into multivesicular buddies mediated by the interaction of ORF3 with the ESCRT machinery of the host cell. (5) Basolaterally secreted HEV particles are quasi-enveloped (eHEV) and circulate in this form in the bloodstream. (6) Apically secreted particles supposedly bud as eHEV particles and are then matured into nHEV particles. While exact modes of nHEV entry (1) are unknown, (7) eHEV particles enter through clathrin-dependent endocytosis. Cell-to-cell transmission or (8) transmission between neighboring apical domains have not been described yet.

Figure 2

Cell polarity and hepatitis E virus (HEV) secretion. HEV particle release from hepatocytes with (A) complex hepatocyte or (B) columnar polarity. Blue boxes are tight junctions separating apical and basal membranes. Adapted from the work of [22].