Developing a Nasal Organotypic Model to Investigate the Effects of the Nasal Microbiome on the Susceptibility to Pathogens

The nasal mucosa is colonized by diverse bacteria, however, the influence of the nasal microbiome on the susceptibility of respiratory pathogens in adults is poorly understood. Defining the complex relationship requires a relevant in vitro model, but current nasal models fail to differentiate into a pseudostratified columnar epithelium that mimicsthe nasal milieu. Hence, these models can not support the investigation of these aspects concurrently. In this study, we established an in vitro human primary nasal epithelial model using the air-liquid interface (ALI) condition. Commercially available and locally isolated nasal cells were successfully differentiated into pseudostratified columnar epithelia. The differentiated epithelium included goblet and ciliated cells as indicated by an enzyme-linked immunosorbent assay and immunofluorescence imaging. Notably, I have identified visual ciliary beating (viewed under light microscopy) as a simple and accessible method of indicating cell differentiation and polarization. This finding is further supported by reverse transcription-quantitative polymerase chain reaction results on angiotensinconverting enzyme 2 (ACE2) and transmembrane serine protease 2 (TMPRSS2) expression and by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral challenges. Compared to the ALI model with no ciliary motion (ALI-N), the ALI model with ciliary beating (ALI-C) demonstrated an increased expression of ACE2 and TMPRSS2. The increased gene expression resulted in greater permissiveness to SARS-CoV-2 infection observed as greater luciferase intensity. Interestingly, the submerged undifferentiated model exhibited phenotypes and functional characteristics comparable to the ALI-N. However, both conditions failed to differentiate and support viral infection. Our results highlight the importance of primary nasal cells to develop a differentiated model to support viral challenges Thus, this study provides a fundamental model for future viral-microbiota-host interaction studies