ABSTRACT
Purpose of Study: COVID pneumonia caused by SARS-CoV-2 can result in a depletion of surfactant & lung injury, which resembles neonatal respiratory distress syndrome. Exogenous surfactant has shown promise as a therapeutic option in intubated hospitalized patients. Our preliminary data in human lung organoids (LOs) with a deficiency of surfactant protein B (SP-B) showed an increased viral load compared to normal LOs. Single cell RNA sequencing (scRNAseq) revealed that SP-B-deficient cells showed increased viral entry genes (ACE2 receptor) & dysregulated inflammatory markers emanating from the lung cells themselves. Our objective was to determine: (1) cell-specific transcriptional differences between normal & SP-B deficient human lung cells after infection with SARS-CoV-2 and (2) a therapeutic role of SP-B protein & surfactant in COVID-19 pneumonia. Methods Used: We used normal and SP-B mutant (homozygous, frameshift, loss of function mutation p.Pro133GlnfsTer95, previously known as 121ins2) human induced pluripotent stem cells (hiPSC) and differentiated them into 3D proximal lung organoids. The organoids were infected with the delta variant of SARS-CoV-2 for 24 hours at an MOI of 1. Infected and uninfected organoids were fixed in trizol in triplicate and underwent processing for bulk RNA sequencing. We tested for differentially expressed genes using the program DEseq. We also plated normal iPSC derived lung organoids as a monolayer and pre-treated them with 1mg/ml of Poractant alfa or 5 uM of recombinant SP-B protein. The delta strain of SARS-CoV-2 was added to the 96 wells at an MOI of 0.1 for one hour with shaking, then an overlay with DMEM/CMC/FBS was added and left on for 23 hours. The plate was fixed and stained for nucleocapsid (NC) protein. Summary of Results: Bioinformatic analysis of the bulk RNA sequencing data showed an increase in the multiple cytokines and chemokines in the SP-B mutant LOs compared to control. We also saw differential gene expression patterns in the SP-B mutant LOs including a reduction in SFTPC, FOXA2, and NKX2-1 and an increase in IL1A, VEGFA, PPARG and SMAD3. In the exogenous surfactant experiments, there was a decrease in total expression of viral NC in the Poractant alfa & rSP-B-treated cells compared to SARS-CoV-2 infection alone (p<0.001). Conclusion(s): Surfactant modulates the viral load of SARS-CoV-2 infection in the human lung. Deficiency in SP-B results in the dysregulation of the lung epithelial inflammatory signaling pathways resulting in worsening infections.