SHIP-1, a target of miR-155, regulates endothelial cell responses in lung fibrosis

Src Homology 2-containing Inositol Phosphatase-1 (SHIP-1) is a target of miR-155, a pro-inflammatory factor. Deletion of the SHIP-1 gene in mice caused spontaneous lung inflammation and fibrosis. However, the role and function of endothelial miR-155 and SHIP-1 in lung fibrosis remain unknown. Using whole-body miR-155 knockout mice and endothelial cell-specific conditional miR-155 (VEC-Cre-miR-155 or VEC-miR-155) or SHIP-1 (VEC-SHIP-1) knockout mice, we assessed endothelial-mesenchymal transition (EndoMT) and fibrotic responses in bleomycin (BLM) induced lung fibrosis models. Primary mouse lung endothelial cells (MLEC) and human umbilical vein endothelial cells (HUVEC) with SHIP-1 knockdown were analyzed in TGF-beta 1 or BLM, respectively, induced fibrotic responses. Fibrosis and EndoMT were significantly reduced in miR-155KO mice and changes in EndoMT markers in MLEC after TGF-beta 1 stimulation confirmed the in vivo findings. Furthermore, lung fibrosis and EndoMT responses were reduced in VEC-miR-155 mice but significantly enhanced in VEC-SHIP-1 mice after BLM challenge. SHIP-1 knockdown in HUVEC cells resulted in enhanced EndoMT induced by BLM. Meanwhile, these changes involved the PI3K/AKT, JAK/STAT3, and SMAD/STAT signaling pathways. These studies demonstrate that endothelial miR-155 plays an important role in fibrotic responses in the lung through EndoMT. Endothelial SHIP-1 is essential in controlling fibrotic responses and SHIP-1 is a target of miR-155. Endothelial cells are an integral part in lung fibrosis.