Cell Stress and risk of COVID-19

It is now well established that certain pre-existing conditions (including cancer, hypertension, obesity, lung disease, and diabetes) greatly increase the risk of severe disease and death from COVID-19. However, the causal link between these co-morbidities and COVID-19 severity remains poorly understood. Most proposed explanations have focused on these conditions causing chronic organ dysfunction and therefore limited physiological reserve. Here we propose an alternative hypothesis: that chronic cellular endoplasmic reticulum (ER) stress, resulting from these diseases, pre-disposes patients to SARS-CoV-2 infection and heightened viral replication.
All the aforementioned co-morbidities are characterised by chronic, elevated ER stress. In normal cells, when ER stress is induced by external stimuli, ER proteins are upregulated to allow cells to halt translation, resolve protein misfolding and restore cellular homeostasis. However, this balance is perturbed where cells under long term, chronic ER stress. To protect cells from apoptosis, key ER stress response proteins remain upregulated and, as we have demonstrated in cancers, the cells become "addicted" to these proteins for their survival.
We have shown, by both immunoprecipitation and immunofluorescence, that the nucleocapsid (N) protein of SARS-CoV-2 binds to cellular ER stress proteins. We have also shown that cells increase their expression of these proteins following infection by SARS-CoV-2. We therefore aim to determine the role played by ER stress in the viral life cycle, specifically in viral replication. We propose that in diseases involving chronic ER stress, SARS-CoV-2 hijacks the cellular dependency on the ER stress response to promote its own replication and ensure the preferential translation of viral proteins. We hypothesise that chronic medical conditions associated with ER stress have COVID-19 predisposition because they have higher cellular and circulating levels of ER stress proteins, which facilitate viral replication and worse outcome. Furthermore, this may implicate circulating ER stress proteins as potential biomarkers for COVID-19 risk, even in the absence of a diagnosed condition. We will determine if pre-existing ER stress allows increased replication of SARS-CoV-2 and, by depleting key ER proteins, will determine if they play a mechanistic role in the viral replication cycle.
The second aim of this project is to determine whether the release of viral proteins and RNA into exosomes can promote the spread of SARS-CoV-2 between cells. Several viruses are known to utilise this mechanism as it can shield viral components from recognition by the immune system, and can prime cells for more efficient infection by virions. We have shown previously that certain ER proteins are released within exosomes upon exposure to stress. As we have also demonstrated binding of these proteins to SARS-CoV-2 N protein, there is a strong likelihood that N protein and viral RNA are also packaged into the exosomes of infected cells. We will determine (1) if viral components are packaged into exosomes, (2) if ER proteins are required for this process and (3) whether these viral exosomes promote the spread of SARS-CoV-2 between cells.