Activated Polymorphonuclear Neutrophil Induces Apoptosis In Cultured Rat Neonatal Cardiomyocyte And Analysis Of Its Mechanisms

Objective: Previous studies suggest that polymorphonuclear neutrophils (PMNs) may be involved in triggering reperfusion-induced cardiomyocyte apoptosis through release of reactive oxidant substances, yet there is no evidence showing that activated PMNs could directly elicit apoptotic cell death due to the method limitation for differentiation of cell types in in vivo study. The aim of the present study, therefore, was to examine whether isolated PMNs could directly induce apoptosis in cultured cardiomyocyte. Methods: Neonatal rat cardiomyocytes were co-cultured with rat PMNs activated by platelet activating factor (PAF). Cardiomyocyte apoptosis was detected using the terminal transferase UTP nick end labeling (TUNEL) assay and confirmed by both DNA ladders on agarose gel electrophoresis and flow cytometry. The type of cell death was also examined by transmission electron microscopy. Results: Activated PMNs significantly induced cardiomyocyte apoptosis after 48 h of co-incubation. The number of apoptotic cells detected by both TUNEL and flow cytometry increased in proportion to the concentration of activated PMNs. These findings were further supported by the appearance of DNA ladders and the typical apoptotic characteristics under electron microscopic analysis. Conclusion: These results suggest that PMNs, when activated by PAF, candirectly induce cardiomyocyte apoptosis.