Esser-Nobis, K. | Search bioRxiv

bioRxiv2022

Comparison of HAV and HCV infections in vivo and in vitro reveals distinct patterns of innate immune evasion and activation

ObjectiveHepatitis A virus (HAV) infections are considered not to trigger an innate immune response in vivo, in contrast to hepatitis C virus (HCV). This lack of immune induction has been imputed to strong immune counteraction by HAV proteases 3CD and 3ABC. We aimed at elucidating the mechanisms of innate immune induction and counteraction by HAV and HCV in vivo and in vitro. DesignuPA-SCID mice with humanized liver were infected with HAV and HCV. Hepatic cell culture models were used to assess HAV and HCV sensing by TLR3 and RIG-I/MDA5, respectively. Cleavage of the adaptor proteins TRIF and MAVS was analyzed by transient and stable expression of HAV and HCV proteases and virus infection. ResultsWe detected similar levels of Interferon stimulated genes (ISGs) induction in hepatocytes of HAV and HCV infected human liver chimeric mice. In cell culture, HAV induced ISGs exclusively upon sensing by MDA5 and dependent on LGP2. TRIF and MAVS were only partially cleaved by HAV 3ABC and 3CD, not sufficiently to abrogate signalling. In contrast, HCV NS3-4A efficiently degraded MAVS, as previously reported, whereas TRIF was not cleaved. ConclusionsHAV induces an innate immune response in hepatocytes via MDA5/LGP2, with limited control of both pathways by proteolytic cleavage. HCV activates TLR3 and lacks TRIF cleavage, suggesting that this pathway mainly contributes to HCV induced antiviral response in hepatocytes. Our results shed new light on induction and counteraction of innate immunity by HAV and HCV and their potential contribution to clearance and persistence. SIGNIFICANCE OF THIS STUDYO_ST_ABSWhat is already known on this topic?C_ST_ABS-- Despite sharing biological and molecular similarities, HAV infections are always cleared while HCV infections persist in most cases. -- In infected chimpanzees HAV does not trigger a strong innate immune response, as opposed to HCV. This has been imputed to the action of HAV proteases abrogating the signalling pathways. -- Physiological in vitro and in vivo models, based on human hepatocytes, to assess HAV and HCV mechanisms of induction and interference of innate immunity are still missing. What this study adds-- HAV induces an innate immune response in vitro and in vivo, in systems with intact signalling pathways and devoid of adaptive immunity. -- HAV 3ABC and 3CD proteases do not abolish the host innate immune response. -- HCV NS3-4A protease disrupts the RLRs pathways, but cannot cleave TRIF and has no impact on TLR3 response. How this study might affect research, practice or policy-- This study offers a comprehensive, side-by-side investigation on HAV and HCV infections in physiological models which recapitulate a cytokine response in the human liver, and allows a precise assessment of the viral interference related to the function of the respective signalling pathways. -- Our results elucidate mechanisms, so far controversial or poorly investigated, thus contributing to our understanding of HAV clearance and HCV persistence.

immunology↗

bioRxiv2021

Endomembrane targeting of human OAS1 p46 augments antiviral activity

Many host RNA sensors are positioned in the cytosol to detect viral RNA during infection. However, most positive-strand RNA viruses replicate within a modified organelle co-opted from intracellular membranes of the endomembrane system, which shields viral products from host cell innate immune sensors. Targeting innate RNA sensors to the endomembrane system may enhance their ability to sense viral RNA generated by viruses that use these compartments for replication. Here, we reveal that an isoform of oligoadenylate synthetase 1, OAS1 p46, is prenylated and targeted to the endomembrane system. Membrane localization of OAS1 p46 confers enhanced access to viral replication sites and results in increased antiviral activity against a subset of RNA viruses including flavivirus, picornavirus, and SARS-CoV-2. Finally, our human genetic analysis shows that the OAS1 splice-site SNP responsible for production of the OAS1 p46 isoform strongly associates with COVID-19 severity. This study highlights the importance of endomembrane targeting for the antiviral specificity of OAS1 and suggests early control of SARS-CoV-2 replication through OAS1-p46 is an important determinant of COVID-19 severity.

immunology↗

bioRxiv2020

De novo design of ACE2 protein decoys to neutralize SARS-CoV-2

There is an urgent need for the ability to rapidly develop effective countermeasures for emerging biological threats, such as the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes the ongoing coronavirus disease 2019 (COVID-19) pandemic. We have developed a generalized computational design strategy to rapidly engineer de novo proteins that precisely recapitulate the protein surface targeted by biological agents, like viruses, to gain entry into cells. The designed proteins act as decoys that block cellular entry and aim to be resilient to viral mutational escape. Using our novel platform, in less than ten weeks, we engineered, validated, and optimized de novo protein decoys of human angiotensin-converting enzyme 2 (hACE2), the membrane-associated protein that SARS-CoV-2 exploits to infect cells. Our optimized designs are hyperstable de novo proteins ([~]18-37 kDa), have high affinity for the SARS-CoV-2 receptor binding domain (RBD) and can potently inhibit the virus infection and replication in vitro. Future refinements to our strategy can enable the rapid development of other therapeutic de novo protein decoys, not limited to neutralizing viruses, but to combat any agent that explicitly interacts with cell surface proteins to cause disease.

biochemistry↗