Neutrophil apoptosis associated with the pathogenesis of asthma

Abstract

Asthma is an inflammatory airway disease and is characterized by the releases of inflammatory mediators including chemokines. Chemokines are mainly associated with the recruitment, activation and dysregulation of specific inflammatory cells, especially mast cells, monocytes, T cells, eosinophils, and neutrophils in asthma. In various inflammatory cells, neutrophils play an important role in the pathogenesis of severe asthma. In this study, the effects of CC chemokine ligand 2 (CCL2) on constitutive apoptosis of neutrophils isolated from the peripheral blood of healthy subjects were investigated. CCL2 blocked the constitutive apoptosis of neutrophils through CC chemokine receptor 2 (CCR2). CCL2 also induced elevation of the cytosolic Ca2+ concentration, but had no effect on normal neutrophil chemotaxis. Anti-apoptotic signaling mediated by CCL2 was found to be associated with the PI3K/Akt/ERK/NF-B cascade in neutrophils. The supernatant collected from CCL2-treated normal neutrophils inhibited the constitutive apoptosis of neutrophils. Both the cleavage of procaspase 3 and procaspase 9, and the decrease in Mcl-1 expression were delayed by CCL2 stimulation. For confirmation of the anti-apoptotic effect induced by CCL2 on asthma pathogenesis, these effects of CCL2 on normal neutrophils were compared to the effect of CCL2 on neutrophils of asthmatic patients. Although asthmatic neutrophils were not affected by constitutive apoptosis, calcium influx or cell migration following CCL2 stimulation, and the inhibition of NF-B blocked constitutive apoptosis of neutrophils from asthmatic patients via inhibition of the cleavage of procaspase 3 and procaspase 9. The anti-apoptotic effect of BAY 11-7985 on neutrophils of severe asthma was stronger than that on neutrophils of mild or moderate asthma. NF-B was involved in CCL2-induced anti-apoptotic signaling in normal

neutrophils, whereas it functioned as a basal pro-apoptotic factor in asthmatic neutrophils. A better understanding of the difference in the regulation of neutrophil apoptosis mediated by CCL2 between normal subjects and asthmatics will enable to elucidate the role of CC chemokine in neutrophils and build a framework for understanding the pathogenesis of asthma.