LAUSR

Abstract The pathobiology of in situ pulmonary thrombosis in acute respiratory distress syndrome (ARDS) due to severe acute respiratory syndrome coronavirus‐2 (SARS‐CoV‐2) infection is incompletely characterized. In human pulmonary artery endothelial cells (HPAECs), hypoxia increases neural precursor cell expressed, developmentally downregulated 9 (NEDD9) and induces expression of a prothrombotic NEDD9 peptide (N9P) on the extracellular plasma membrane surface. We hypothesized that the SARS‐CoV‐2–ARDS pathophenotype involves increased pulmonary endothelial N9P. Paraffin‐embedded autopsy lung specimens were acquired from patients with SARS‐CoV‐2–ARDS (n = 13), ARDS from other causes (n = 10), and organ donor controls (n = 5). Immunofluorescence characterized the expression of N9P, fibrin, and transcription factor 12 (TCF12), a putative binding target of SARS‐CoV‐2 and known transcriptional regulator of NEDD9. We performed RNA‐sequencing on normal HPAECs treated with normoxia or hypoxia (0.2% O2) for 24 h. Immunoprecipitation‐liquid chromatography‐mass spectrometry (IP‐LC‐MS) profiled protein–protein interactions involving N9P relevant to thrombus stabilization. Hypoxia increased TCF12 messenger RNA significantly compared to normoxia in HPAECs in vitro (+1.19‐fold, p = 0.001; false discovery rate = 0.005), and pulmonary endothelial TCF12 expression was increased threefold in SARS‐CoV‐2–ARDS versus donor control lungs (p < 0.001). Compared to donor controls, pulmonary endothelial N9P‐fibrin colocalization was increased in situ in non‐SARS‐CoV‐2–ARDS and SARS‐CoV‐2–ARDS decedents (3.7 ± 1.2 vs. 10.3 ± 3.2 and 21.8 ± 4.0 arb. units, p < 0.001). However, total pulmonary endothelial N9P was increased significantly only in SARS‐CoV‐2–ARDS versus donor controls (15 ± 4.2 vs. 6.3 ± 0.9 arb. units, p < 0.001). In HPAEC plasma membrane isolates, IP‐LC‐MS identified a novel protein–protein interaction between NEDD9 and the β3‐subunit of the αvβ3‐integrin, which regulates fibrin anchoring to endothelial cells. In conclusion, lethal SARS‐CoV‐2–ARDS is associated with increased pulmonary endothelial N9P expression and N9P‐fibrin colocalization in situ. Further investigation is needed to determine the pathogenetic and potential therapeutic relevance of N9P to the thrombotic pathophenotype of SARS‐CoV‐2–ARDS.