Enhanced hepatitis E virus (HEV) replication in the presence of placental lactogen utilizing an optimized in vitro system for genotype 3 

Kush Kumar Yadav
Category: 
Graduate (PhD)
Advisor: 
Scott P. Kenney
Department: 
Center for Food Animal Health
Abstract: 

Hepatitis E virus (HEV), a zoonotic enteric pathogen, is the leading cause of acute viral hepatitis in humans worldwide. HEV infection is most dangerous to immunocompromised and pregnant women, producing up to 30% pregnancy mortality during the third trimester. Mechanisms behind pregnancy related pathology are still understudied due to inadequate virus replication and insufficient animal models. Recently, open reading frame (ORF4) was discovered in genotype (gt) 1 HEV. ORF4 protein expression is regulated via an IRES-like RNA element. We sought to validate whether HEV gt3 contained a similar ORF4 to gt1 HEV and whether ORF4-mediated replication enhancement could function in non-genotype 1 HEV by providing ORF4 in trans and observing replication in genotype 3 HEV (P1 and P6 strains). Recently, rabbits were shown to recapitulate the pregnancy mortality found in humans which suggests a similar host factor could be enhancing viral pathogenesis. Rabbits and humans share a similar hemochorial placenta and produce placental lactogen (PL) in increasing concentration throughout pregnancy. We hypothesize that PL induced lipolysis results in increased fatty acid synthesis, which is then utilized by HEV to replicate more efficiently during pregnancy. Human hepatoma cells (Huh7) constitutively expressing ORF4 were created and used to assess the replication of the gt3 via transfection with HEV RNA. Virus stocks from transfected Huh7 cells with or without ORF4 were harvested and infectivity assessed via infection of HepG2/C3A cells. In addition, ORF4 expressing cells were treated with PL on day 0, 2, 4 and fatty acid concentration was measured. Furthermore, the PL treated ORF4+ expressing Huh7 cells were transfected with gt3 HEV RNA. Flow cytometry analysis and immunofluorescence microscopy to detect ORF2 protein was performed after harvesting cells at 5 days post transfection. We found high levels of HEV protein in ectopically expressed ORF4 cell lines for cell culture adapted gt3 HEV. PL treatment increased fatty acid concentrations in ORF4+ expressing Huh7 cells. Gt3 HEV replication enhanced in the presence of PL. We developed a more efficient HEV cell culture system and demonstrated PL is one factor responsible for enhanced replication whose detail role on pregnancy mortality is warranted.