Hepatitis delta virus (HDV) infection causes the most severe form of viral hepatitis, but little is known about the molecular mechanisms involved. We have recently developed an HDV mouse model based on the delivery of HDV replication-competent genomes using adeno-associated vectors (AAV), which developed a liver pathology very similar to the human disease and allowed us to perform mechanistic studies. We have generated different AAV-HDV mutants to eliminate the expression of HDV antigens (HDAgs), and we have characterized them both in vitro and in vivo. We confirmed that S-HDAg is essential for HDV replication and cannot be replaced by L-HDAg or host cellular proteins, and that L-HDAg is essential to produce the HDV infectious particle and inhibits its replication. We have also found that lack of L-HDAg resulted in the increase of S-HDAg expression levels and the exacerbation of liver damage, which was associated with an increment in liver inflammation but did not require T cells. Interestingly, early expression of L-HDAg significantly ameliorated the liver damage induced by the mutant expressing only S-HDAg. In summary, the use of AAV-HDV represents a very attractive platform to interrogate in vivo the role of viral components in the HDV life cycle and to better understand the mechanism of HDV-induced liver pathology.

Hepatitis delta virus (HDV) infection causes the most severe form of viral hepatitis but little is known about the molecular mechanisms involved. The recently developed HDV mouse model based on the delivery of HDV replication-competent genomes using adeno-associated vectors (AAV) develop a liver pathology very similar to the human disease, and allowed us to perform mechanistic studies. We have generated different AAV-HDV mutants to eliminate the expression HDV antigens (HDAgs), characterized them both in vitro and in vivo. We confirmed that S-HDAg is essential for HDV replication and cannot be replaced by L-HDAg or host cellular proteins, and the L-HDAg is essential for HDV infectious particle production. We have also found that the lack of L-HDAg resulted in the increase of of S-HDAg expression levels and the exacerbation of liver damage which is T cell independent but is associated with an increment in liver inflammation. Interestingly, early expression of L-HDAg significantly ameliorated the liver damage induced by the mutant expressing only the S-HDAg. In summary, the use of AAV-HDV represents a very attractive platform to interrogate in vivo the role of viral components in the HDV life cycle and to better understand the mechanism of HDV-induced liver pathology.

Hepatitis D virus (HDV) infection represents the most severe form of chronic viral hepatitis. We have shown that the delivery of HDV replication-competent genomes to the hepatocytes using adeno-associated virus (AAV-HDV) as gene delivery vehicles offers a unique platform to investigate the molecular aspects of HDV and associated liver damage. For the purpose of this study, we generated HDV genomes modified by site-directed mutagenesis aimed to (i) prevent some post-translational modifications of HDV antigens (HDAgs) such as large-HDAg (L-HDAg) isoprenylation or short-HDAg (S-HDAg) phosphorylation; (ii) alter the localization of HDAgs within the subcellular compartments; and (iii) inhibit the right conformation of the delta ribozyme. First, the different HDV mutants were tested in vitro using plasmid-transfected Huh-7 cells and then in vivo in C57BL/6 mice using AAV vectors. We found that Ser177 phosphorylation and ribozymal activity are essential for HDV replication and HDAg expression. Mutations of the isoprenylation domain prevented the formation of infectious particles and increased cellular toxicity and liver damage. Furthermore, altering HDAg intracellular localization notably decreased viral replication, though liver damage remained unchanged versus normal HDAg distribution. In addition, a mutation in the nuclear export signal impaired the formation of infectious viral particles. These findings contribute valuable insights into the intricate mechanisms of HDV biology and have implications for therapeutic considerations.

Hepatitis D virus (HDV) infection represents the most severe form of chronic viral hepatitis. We have shown that the delivery of HDV replication-competent genomes to the hepatocytes using adenoassociated virus (AAV-HDV) as gene delivery vehicles offers a unique platform to investi-gate the molecular aspects of HDV and associated liver damage. Here, we generated HDV ge-nomes modified by site directed mutagenesis aimed to: i) prevent some post-translational modi-fications of HDV antigens (HDAgs) such as Large-HDAg (L-HDAg) isoprenylation or Short-HDAg (S-HDAg) phosphorylation ii) alter the localization of HDAgs within the subcellular compartments and iii) inhibit the right conformation of the delta ribozyme. First, the different HDV mutants were tested in vitro using plasmid-transfected Huh-7 cells and then in vivo in C57BL/6 mice using AAV vectors. We found that Ser 177 phosphorylation and the ribozymal ac-tivity are essential for HDV replication and HDAg expression. Mutation of the isoprenylation domain prevent the formation of infectious particles and increase cellular toxicity and liver dam-age. Finally, altering the intracellular localization od HDAg have a profound on viral replication in vivo but liver toxicity is maintained. Mutation in the nuclear export signal impair the for-mation of infectious viral particles. These findings contribute valuable insights into the intricate mechanisms of HDV biology and have implications for therapeutic considerations