Human coronavirus-host interactions: Patogenesis and antiviral response

Abstract

Coronaviruses (CoVs) are emerging pathogens causing life-threatening diseases in humans. MERS-CoV emerged during the summer of 2012 in Saudi Arabia, and the virus is still circulating causing a mortality rate around 35%. In December 2019, SARS-CoV-2 emerged in Wuhan, China. This virus is causing the current coronavirus disease-19 (COVID-19) pandemic. As of April 20th 2022, there have been 502,313,498 confirmed cases of COVID-19 and 6,197,928 deaths in more than 200 countries around the world with a mortality rate of about 2%. Analysis of virus-host interactions will help to understand the molecular basis of emergent CoVs pathogenesis and to develop novel therapeutic strategies. In this thesis, a mouse-adapted MERS-CoV infectious cDNA was engineered, leading to a recombinant mouse-adapted virus (rMERS-MA) virulent in hDPP4-KI mice. The role of genus-specific protein 5 was analyzed by engineering viruses expressing a full-length gene 5 (rMERS-MA-5FL), or containing a full-length gene 5 deletion (rMERS-MA-Δ5). rMERS-MA-5FL virus was unstable, as deletions appeared during early passage in tissue culture cells, highlighting MERS-CoV instability. Unexpectedly, rMERS-MA-Δ5 virus was more virulent than the parental one in a sublethal hDPP4-KI mouse model. Interferon (IFN) and pro-inflammatory cytokine expression was delayed and dysregulated in the lungs of rMERS-MA-Δ5 infected mice. Similar results were obtained with the human MERS-CoV, including or lacking gene 5, in transgenic TghDPP4 mice, and provide identified novel activities on IFN modulation by gene 5 in the context of infection. In addition, the interaction between cellular RNA helicase MOV10 and N protein from several human CoVs was analyzed. Both MOV10 proviral and antiviral activities have been described in a limited number of viruses, but not in CoVs. Using MERS-CoV as a model, it was shown that MOV10 antiviral activity was mediated by viral RNA sequestration in cytoplasmic ribonucleoprotein structures. It was also found that MOV10 antiviral activity may be specifically activated in highly pathogenic human CoVs, but not in the attenuated ones, suggesting a role for MOV10 in modulating CoVs pathogenesis. The data obtained uncovered a complex network of interactions between viral and cellular RNAs and proteins, modulating the antiviral response against CoVs. SARS-CoV-2 emerged during the development of this thesis. We engineered an infectious cDNA clone and a replicon expressing a reporter gene for this virus. Cell systems and animal models were constructed to study SARS-CoV-2 genetic stability and in vivo virulence mechanism, respectively. A SARS-CoV-2 variant with S protein D614G mutation became prevalent globally early in the pandemic. Preliminary studies on the effect of D614G variant were also performed