The UIP honeycomb airway cells are the site of mucin biogenesis with deranged cilia

Honeycombing (HC) is a histological pattern consistent with Usual Interstitial Pneumonia (UIP). HC refers to cystic airways (HC airways) located at sites of dense fibrosis with marked mucus accumulation. Utilizing laser capture microdissection coupled mass spectrometry (LCM-MS), we interrogated the fibrotic HC airway cells and fibrotic uninvolved airway cells (distant from sites of UIP and morphologically intact) in 10 UIP specimens; 6 non-fibrotic airway cell specimens served as controls. Furthermore, we performed LCM-MS on the mucus plugs found in 6 UIP and 6 mucinous adenocarcinoma (MA) specimens. The mass spectrometry data were subject to both qualitative and quantitative analysis and validated by immunohistochemistry. Surprisingly, fibrotic uninvolved airway cells share a similar protein profile to HC airway cells, showing deregulation of SLITs and ROBO pathway as the strongest category. We find that BPIFB1 is the most significantly increased secretome-associated protein in UIP, whereas MUC5AC is the most significantly increased in MA. We conclude that spatial proteomics demonstrates that the fibrotic uninvolved airway cells are abnormal. In addition, fibrotic HC airway cells are enriched in mucin biogenesis proteins with a marked derangement in proteins essential for ciliogenesis. This unbiased spatial proteomic approach will generate novel and testable hypotheses to decipher fibrosis progression. ### Competing Interest Statement The authors have declared no competing interest.