Macrophage SAMSN1 protects against sepsis-induced acute lung injury in mice

OBJECTIVE: Inflammation and oxidative stress contribute to the progression of sepsis-induced acute lung injury (ALI). SAM domain, SH3 domain and nuclear localization signals 1 (SAMSN1) is a signaling adaptor protein, and mainly regulates inflammatory response of various immune cells. The present study generates macrophage-specific SAMSN1-knockout (Samsn1(MKO)) and SAMSN1-transgenic (Samsn1(MTG)) mice to investigate its role and mechanism in sepsis-induced ALI. METHODS: Samsn1(MKO) and Samsn1(MTG) mice were exposed to lipopolysaccharide (LPS) instillation or cecal ligation and puncture (CLP) surgery to induce sepsis-induced ALI. Bone marrow transplantation, cellular depletion and non-invasive adoptive transfer of bone marrow-derived macrophages (BMDMs) were performed to validate the role of macrophage SAMSN1 in sepsis-induced ALI in vivo. Meanwhile, BMDMs were isolated from Samsn1(MKO) or Samsn1(MTG) mice to further clarify the role of SAMSN1 in vitro. RESULTS: Macrophage SAMSN1 expression was increased in response to LPS stimulation, and negatively correlated with LPS-induced ALI in mice. Macrophage SAMSN1 deficiency exacerbated, while macrophage SAMSN1 overexpression ameliorated LPS-induced inflammation, oxidative stress and ALI in mice and in BMDMs. Mechanistically, we found that macrophage SAMSN1 overexpression prevented LPS-induced ALI though activating AMP-activated protein kinase α2 (AMPKα2) in vivo and in vitro. Further studies revealed that SAMSN1 directly bound to growth factor receptor bound protein 2-associated protein 1 (GAB1) to prevent its protein degradation, and subsequently enhanced protein kinase A (PKA)/AMPKα2 activation in a protein tyrosine phosphatase, non-receptor type 11 (PTPN11, also known as SHP2)-dependent manner. Moreover, we observed that macrophage SAMSN1 overexpression diminished CLP-induced ALI in mice. CONCLUSION: Our study documents the protective role of macrophage SAMSN1 against sepsis-induced inflammation, oxidative stress and ALI through activating AMPKα2 in a GAB1/SHP2/PKA pathway, and defines it as a promising biomarker and therapeutic target to treat sepsis-induced ALI.