Requirement of a4b1 and a5b1 Integrin Expression in Bone‐Marrow Derived Progenitor Cells in Preventing Endotoxin‐Induced Lung Vascular Injury and Edema in Mice

Abstract

The goal of this study was to address the hypothesis that integrin‐mediated cell adhesion is a critical requirement for the endothelial barrier protection induced by bone marrow derived progenitor cells (BMPCs). Bone marrow (BM)‐derived mononuclear cells (MNCs) from donor C57BL mice were used as a source for BMPCs and characterized for BMPCs marker and integrin expression. To test the efficacy of BMPCs treatment and to address the mechanisms of the benefit, we used a mouse model of endotoxin‐induced ALI. We noted robust expression of α4 and α5 integrins in donor BMPCs. The adhesion of BMPCs onto purified extracellular matrix not only induced Fak phosphorylation, but also the formation of branching point structures in an α4 and α5 integrin‐dependent manner. BMPCs expressing red fluorescent protein (RFP) were administered via the retro‐orbital venous route in mice treated intraperitonially with LPS. These mice received either control endothelial cells (ECs) or BMPC or BMPCs incubated with specific anti‐integrin monoclonal antibodies, or BMPCs tranduced with a specific shRNA integrin construct. BMPCs afforded a 50% survival and reduced extravascular fluid content. Blocking or silencing the α4 and α5 integrins in donor BMPCs failed to protect these mice from injury or to reduce extravascular fluid content. In these mice, we also noted an increased retention of RFP+, Flk1+ and CD34+ BMPCs (20%) for the next 8 weeks, as well as overall improved lung architecture. Collectively, our data showed that BMPCs play a critical role in mounting lung microvessel repair through the expression of α4β1 and α5β1 integrins, causing restoration of lung fluid balance and increased survival rates in a mouse model of ALI.This study was supported by NIH‐RO1, HL079356 and R01HL090152.