Late Breaking Abstract - Epithelial CLEC2 protects against acute lung injury

<bold>Background:</bold> C-type lectin-like receptor 2 (CLEC2) is a transmembrane receptor expressed on platelets which regulates platelet aggregation and immune response. Yet, the role of CLEC2 in lung epithelium in the development of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is unclear. <bold>Aims:</bold> To elucidate the role of epithelial CLEC2 in ALI/ARDS. <bold>Methods:</bold> An inducible lung epithelial-specific CLEC2 knockout mouse (<italic>Clec1b^AT2-KO</italic>) was generated and performed for lipopolysaccharide (LPS)- or hydrochloric acid (HCl)-induced murine ALI model. <bold>Results:</bold> In two murine models of LPS- and acid-induced lung injury, which mimic the clinical development of ARDS following sepsis and gastric aspiration, respectively, the ALI signs of <italic>Clec1b^AT2-KO</italic> mice were further exacerbated. The therapeutic application of CLEC2 overexpression using AAV6.2-CLEC2 or CLEC2 activation using recombinant podoplanin (PDPN) served as a lung epithelial protective agent in the setting of ALI. Mechanistically, transcriptomic analyses showed that CLEC2-regulated genes are highly enriched in chemotaxis, cytokine activity, and extracellular matrix (ECM) components. Lung injury was partially attenuated in chemokine/cytokine knockout mice (<italic>Ccl5^−/−</italic>, <italic>Csf3^−/−</italic> and <italic>Cxcl1^−/−</italic>) pretreated with AAV-si-CLEC2, followed by LPS challenge. In both human epithelial cells and isolated primary mouse AT-II cells, loss of CLEC2 led to cell morphology alteration and ECM degradation, which could be resorted by exogenous transforming growth factor (TGF)-β. <bold>Conclusions:</bold> Our results demonstrated that downregulation of epithelial CLEC2 exacerbates ALI through cytokine and chemokine-mediated signaling and TGF-β–mediated epithelial cell morphology alteration and ECM degradation.