The bone marrow neutrophil reserve is regulated by serpinB1 and cathepsin G through a cell autonomous and caspase-independent death pathway (172.32)

Abstract

Abstract The bone marrow (BM) neutrophil reserve is a large pool of mature neutrophils that can be rapidly mobilized to the circulation and recruited to tissues in response to danger signals. We have previously shown that serpinB1-/- mature neutrophils have a survival defect that leads to a considerable reduction of the BM reserve and failure to clear bacterial infection. SerpinB1 is one of the best inhibitors of neutrophil serine proteases including elastase (NE) and cathepsin G (CG). Here, BM chimera showed that serpinB1 deficiency in hematopoietic cells was necessary and sufficient to reproduce the bone marrow neutropenia of serpinB1-/- mice. We found that CG, but not NE, was responsible for the BM neutropenia of serpinB1-/- mice. Mice deficient in both CG and serpinB1 had a normal neutrophil reserve, whereas NE-deficiency did not rescue the BM defect of serpinB1-/- mice. Neutrophil survival was increased by pan-caspase inhibitor Q-VD-OPh in both wild-type and serpinB1-/- neutrophils in vitro compared to untreated cells. However, survival was significantly lower in serpinB1-/- neutrophils (35%) vs. wild type (80%) after 72hr. This survival defect in vitro was rescued by CG deficiency. Furthermore, neither transgenic over expression of anti-apoptotic factor BCL-2 nor G-CSF treatment of serpinB1-/- mice rescued CG-mediated neutrophil death. We conclude that CG and serpinB1 regulate neutrophil survival through a proteolytic process distinct from classical apoptotic pathways.