Lack of SOCS3 increases LPS-induced murine acute lung injury through modulation of Ly6C(+) macrophages

BACKGROUND: SOCS3 (suppressor of cytokine signaling 3) is a negative regulator of JAK/STAT3 signaling pathway and participates in the regulation of lung inflammation in a mouse model with acute lung injury (ALI). However, it is not well understood how SOCS3 regulates lung inflammation in the ALI mouse model. METHOD: In the present study, we investigated the effects of SOCS3 on modulation of Ly6C(+) monocyte phenotypes in a mouse model with lipopolysaccharide (LPS)-induced ALI. Conditional SOCS3(Lyz2cre) mice with myeloid cell-restricted depletion of SOCS3 gene were created by breeding transgenic Lyz2Cre mice with SOCS3(fl/fl) mice. Wilde-type (WT) and SOCS3(Lyz2cre) mice were intratracheal instilled with 5 mg/kg LPS for 2 days. Lung, bronchoalveolar lavage (BAL) and blood were collected for analysis by flow cytometry, ELISA, qRT-PCR and Western blot analysis. RESULTS: The studies in the ALI mouse model revealed that myeloid cell-restricted SOCS3 deficiency exacerbated the severity of ALI as compared to the WT mice. The increased severity of ALI in SOCS3-deficient mice was associated with higher populations of neutrophils, T lymphocytes and Ly6C(+) monocytes in the inflamed lung tissues. In addition, CCR2 and CXCL15 were elevated, and accompanied by greater expression and activation of STAT3 in the lung of SOCS3-deficient mice. SOCS3-deficient bone marrow-derived macrophages (BMDMs) expressed a higher amount of TNF-alpha, and adoptive transfer of the SOCS3-deficient Ly6C(+) BMDMs into WT mice enhanced the severity of ALI than adoptive transfer of WT control BMDMs. However, depletion of Ly6C(+) circulating monocytes by anti-Ly6C(+) neutralizing antibody moderately attenuated neutrophil infiltration and resulted in lower prevalence of Ly6C(+) cells in the lung of treated mice. CONCLUSION: Myeloid cell-restricted lack of SOCS3 induced more severe ALI through modulation of Ly6C(+) subtype macrophages. The results provide insight into a new role of SOCS3 in modulation of Ly6C(+) monocyte phenotypes and provide a novel therapeutic strategy for ALI by molecular intervention of macrophages subtypes.