Cellular tropism, transmission and pathogenesis of Middle East respiratory syndrome coronavirus

Abstract

MERS-CoV has caused over 2000 human infections with a high case-fatality rate over 35% since 2012. Most MERS patients developed acute pneumonia with respiratory distress syndrome or multiorgan failure resulting in the fatal outcome. Although the MERS epidemic has persisted for six years, important issues related to MERS-CoV infection including the pathogenesis, virus-host interaction, extrapulmonary involvement, mode of virus transmission and infection route remain poorly understood. In addition, there is no effective drugs and vaccines tested in randomized control trials for MERS-CoV treatment and prevention. Therefore, it is important to elucidate the pathogenesis and mechanism of transmission, as well as to identify potential antiviral agents against MERS-CoV. Macrophage and dendritic cells are at the frontline of host response against invading pathogens. To understand the pathogenesis of MERS-CoV, we studied viral replication, proinflammatory and antiviral cytokine/chemokine response in MERS-CoV-infected human monocyte-derived macrophages (MDMs) and monocyte-derived-dendritic cells (Mo-DCs) in comparison with SARS-CoV infected cells. Our findings suggested that MDMs and Mo-DCs were exploited by MERS-CoV for viral replication and became vehicles for virus dissemination, instead of virus restriction. MERS-CoV infection in these cells resulted in the exuberant production of an array of cytokines and chemokines, and modulated innate immune response differently from that of SARS-CoV infection. The aberrant induction of inflammatory cytokines/chemokines may contribute to the high pathogenicity of MERS-CoV. Our findings also help to explain the distinct pathogenicity and clinical manifestations of MERS-CoV and SARS-CoV. MERS primarily manifested as a respiratory infection. However, epidemiological studies, biological evaluation of the virus and bioinformatics prediction collectively suggested that human may also acquire MERS-CoV infection via the gastrointestinal tract. To test the hypothesis, we performed a series of in vitro and in vivo studies. Firstly, we demonstrated that human primary intestinal epithelial cells were highly susceptible to MERS-CoV. MERS-CoV infection and replication were further verified in ex vivo culture of the human small intestine. Secondly, we further characterized MERS-CoV infection and replication in human intestinoids. Thirdly, the direct intragastric MERS-CoV inoculation initiated an infection in the intestinal mucosa, leading to progressive inflammation and epithelial degeneration in hDPP4 transgenic mice. Importantly, with the progression of intestinal MERS-CoV infection, a sequential respiratory infection occurred. Taken together, we demonstrated that the human intestinal tract could serve as an alternative infection route of MERS-CoV. Lastly, we sought to dissect the host factors involved in MERS-CoV replication. Heat shock protein 90 (Hsp90), a multi-functional chaperone protein, plays essential roles in a variety of physiological processes. In addition, accumulating evidence has demonstrated the involvement of Hsp90 in the growth of multiple viruses. We found that an Hsp90 inhibitor could reduce MERS-CoV replication in multiple human cell lines and human small intestinal organoids. In addition, the Hsp90 inhibitor inhibited MERS-CoV replication in a dose-dependent manner. We further demonstrated that siRNA depletion of Hsp90β, but not Hsp90α, inhibit viral growth. The preliminary results indicated MERS-CoV nucleoprotein as a potential interacting partner of Hsp90β. Thus, we concluded that Hsp90β is an essential cellular protein for MERS-CoV infection and replication through its interaction with MERS-CoV NP protein.