Chronic Obstructive Pulmonary Disease (COPD) is a neutrophil-associated pulmonary condition that is accompanied by chronic inflammation. Neutrophil lifespan is typically controlled by constitutive apoptosis, but their prolonged persistence at inflammatory sites is implicated in COPD pathology. However, current COPD therapies are inadequate at targeting neutrophilia.
Prostaglandin E2 (PGE2) is a potent pro-survival mediator in neutrophils that is increased in COPD. Therefore, PGE2 may contribute to neutrophilic accumulation in COPD lungs and the resolution of inflammation may be achieved by decreasing neutrophil lifespan. Specifically, it was hypothesised that PGE2 modulates protein kinase A (PKA)-dependent neutrophil lifespan through a specific prostaglandin (EP) receptor subtype, and that the nuclear receptors NR4A2 or NR4A3 are downstream effectors of PKA-mediated neutrophil survival.
Human polymorphonuclear neutrophils (PMN) were isolated from the blood of healthy volunteers and COPD patients. Cellular apoptosis was assessed by light microscopy and phosphatidyl serine exposure. Gene expression of PGE2 and NR4A receptors was measured by RT-PCR and qPCR. Additionally, a novel approach uses murine neutrophils (mNØ) derived from cultures of bone-marrow progenitors, conditionally immortalised by expression of a chimeric Hoxb8 protein. RNAi strategies to knock down NR4A2 and NR4A3 in mNØ were undertaken.
PGE2 and a pharmacological EP2 receptor agonist induced PKA-dependent PMN survival and NR4A2 expression by qPCR. Likewise, PGE2-induced PKA survival was blocked by EP2 receptor antagonism. Interestingly, the inflammatory mediator LPS increased EP2 and EP4 expression by qPCR in healthy control and COPD PMN. Consistently, LPS induced early PKA-dependent survival and enhanced late PGE2 survival. Additionally, RNAi-mediated knockdown of NR4A2 in mNØ decreased cell numbers during mNØ differentiation.
In conclusion, EP2 is the dominant receptor subtype in PGE2/PKA survival in PMN. In the context of COPD, LPS further enhances PGE2 survival through increased prostaglandin receptor expression. Moreover, this study links the nuclear receptor NR4A2 to neutrophil survival induced by the PGE2/PKA signalling axis, potentially providing a novel, specific molecular target for neutrophilia in COPD
