Dysfunctional O-glycosylation exacerbates LPS-induced ARDS in mice through impairment of podoplanin expression on alveolar macrophages.

O-glycosylation is one of the most common post-translational modifications of proteins, which participates in immune cell recognition, activation, and surveillance. Alveolar macrophage (AM) is closely involved in the pathogenesis of acute respiratory distress syndrome (ARDS), which is associated with excessive, uncontrolled inflammatory response. It is unclear whether and how O-glycosylation affects AM activation as well as ARDS. Here, we administrated experimental mice with an O-glycosylation inhibitor (benzyl-α-GalNAc) at 5 or 10 mg/kg 24 h before intratracheal instillation of LPS (1 mg/kg). At 6 h and 12 h after LPS challenge, mice were sacrificed to collect samples for further analysis. The results showed that benzyl-α - GalNAc induced abundant expression of the Tn antigen, which is a typical marker for abnormal O-glycosylation. Benzyl-α-GalNAc pretreatment significantly exacerbated LPS-induced inflammatory damage in lungs, evidenced by more severe histological signs and drastic elevation of multiple inflammatory cytokines. Mechanistically, benzyl-α-GalNAc impaired podoplanin expression on AMs in mice, which is a heavily O-glycosylated protein that mediates anti-inflammation responses, whereas adoptive transfer of podoplanin-expressing macrophages alleviated LPS-induced ARDS in mice. This study demonstrated that benzyl-α-GalNAc-induced inhibition of O-glycosylation aggravated LPS-induced ARDS in mice, which may be due to down-regulation of podoplanin expression on AMs. We therefore suggest that podoplanin on AMs is essential for lung protection.