Nico Olegario

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes a range of symptoms in infected individuals, from mild respiratory illness to acute respiratory distress syndrome. A systematic understanding of host factors influencing viral infection is critical to elucidate SARS-CoV-2-host interactions and the progression of Coronavirus disease 2019 (COVID-19). Here, we conducted genome-wide CRISPR knockout and activation screens in human lung epithelial cells with endogenous expression of the SARS-CoV-2 entry factors ACE2 and TMPRSS2. We uncovered proviral and antiviral factors across highly interconnected host pathways, including clathrin transport, inflammatory signaling, cell-cycle regulation, and transcriptional and epigenetic regulation. We further identified mucins, a family of high molecular weight glycoproteins, as a prominent viral restriction network that inhibits SARS-CoV-2 infection in vitro and in murine models. These mucins also inhibit infection of diverse respiratory viruses. This functional landscape of SARS-CoV-2 host factors provides a physiologically relevant starting point for new host-directed therapeutics and highlights airway mucins as a host defense mechanism.

Airway mucus clearance from the lungs occurs by 2 widely recognized mechanisms: cilia-mediated clearance and high-velocity airflow-mediated cough clearance. However, a potentially important third mechanism of mucus clearance, referred to as cilia-independent gas-liquid transport (GLT), was proposed based on in vitro model systems to occur during normal tidal breathing but has largely been overlooked. We conducted in vitro and in vivo studies to investigate the role of tidal breathing airflow rates in mucus clearance. An in vitro airway culture bead-tracking model demonstrated airflow-dependent mucus transport at tidal breathing flow rates. As with other modes of mucus clearance, GLT was critically dependent on mucus concentration. In vivo studies in cilial beat-deficient mice demonstrated that GLT-mediated mucus clearance occurs during tidal breathing in the absence of cough, and the rate of GLT mucus clearance was dependent on breathing frequency and body orientation. These studies demonstrated that GLT is a third mechanism of mucus clearance and likely represents a significant mode of clearance in persons with cilial dysfunction. These findings indicate that increasing breathing rates through exercise, using mucus rehydrating agents or mucolytics, or combining these approaches may restore clinically and physiologically meaningful airway clearance in these patients.