Serinc2 deficiency causes susceptibility to sepsis-associated acute lung injury

Severe sepsis and its subsequent complications cause high morbidity and mortality rates worldwide. The lung is one of the most vulnerable organs sensitive to the sepsis-associated inflammatory storm and usually develops into acute respiratory distress syndrome (ARDS)/acute lung injury (ALI). The pathogenesis of sepsis-associated ALI is accompanied by coordinated transmembrane signal transduction and subsequent programmed cell death; however, the underlying mechanism remains largely unclear.

Here we find that the expression of serine incorporator 2 (Serinc2), a protein involved in phosphatidylserine synthesis and membrane incorporation, is upregulated in cecal ligation and puncture (CLP)-induced ALI. Furthermore, the Serinc2-knockout (KO) mouse line is generated by the CRISPR-cas9 approach. Compared with wild-type mice, the Serinc2-KO mice exhibit exacerbated ALI-related pathologies after CLP. The expressions of pro-inflammatory factors, including IL1β, IL6, TNFα, and MCP1, are significantly enhanced by Serinc2 deficiency, concurrent with over-activation of STAT3, p38 and ERK pathways. Conversely, Serinc2 overexpression in RAW264.7 cells significantly suppresses the inflammatory responses induced by lipopolysaccharide (LPS). Serinc2 KO aggravates CLP-induced apoptosis as evidenced by increases in TUNEL-positive staining, Bax expression, and cleaved caspase-3 and decreases in BCL-2 expression and Akt phosphorylation, whereas these changes are suppressed by Serinc2 overexpression in LPS-treated RAW264.7 cells. Moreover, the administration of AKTin, an inhibitor of Akt, abolishes the protective effects of Serinc2 overexpression against inflammation and apoptosis.

Our findings demonstrate a protective role of Serinc2 in the lung through activating the Akt pathway, and provide novel insight into the pathogenesis of sepsis-induced ALI.