Neutrophil Elastase Activates Macrophage MMPs, Promotes Cell Adhesion And Cytokine Production Via Integrin-Src Kinases Pathway

There are a number of diseases characterized by the presence of neutrophil elastase (NE) activity in tissues including cystic fibrosis and alpha-1-antitrypsin deficiency induced lung destruction. It is generally accepted that NE actively contributes to this pathological process, but the precise mechanisms has yet to be determined. We hypothesized that NE activates the macrophages (Mϕ) pro-inflammatory program. We demonstrate that following NE exposure, monocyte-derived Mϕ release proteolytic activity composed of several matrix metalloproteinases (MMPs) which could contribute to extracellular matrix (ECM) degradation. NE upregulates expression of Mϕ derived pro-inflammatory cytokines including TNFα, IL-1β, and IL-8. Thus, NE-activated Mϕ can contribute to tissue destruction through the proteolytic activity of metalloproteinases and by supporting chronic inflammation through expression of pro-inflammatory cytokines. We also demonstrate that NE increases Mϕ adhesion that is attenuated by antibodies specific to integrin subunits. We show that the effects of NE on Mϕ can be mediated through an activation of integrin pathways. In support of integrin involvement, we demonstrate that NE activates the Src kinase family, a hallmark of integrin signaling activation. Moreover, pretreatment of macrophages with a specific Src kinase inhibitor, PP2, completely prevents NE-induced inflammatory cytokine production. Taken together these findings indicate that NE has effect on lung destruction that extends beyond direct proteolytic degradation of matrix proteins.