Mitogen-activated protein kinase pathway mediates hyperoxia-induced apoptosis in cultured macrophage cells

We have previously demonstrated that the lungs of mice can exhibit increase d programmed cell death or apoptosis after hyperoxic exposure in vivo. In t his report, we show that hyperoxic exposure in vitro can also induce apopto sis in cultured murine macrophage cells (RAW 264.7) as assessed by DNA-ladd ering, terminal deoxynucleotidyltransferase dUTP nick end-labeling, and nuc leosomal assays. To further delineate the signaling pathway of hyperoxia-in duced apoptosis in RAW 264.7 macrophages, we first show that hyperoxia can activate the mitogen-activated protein kinase (MAPK) pathway, the extracell ular signal-regulated kinases (ERKs) p42/p44, in a time-dependent manner as assessed by increased phosphorylation of ERK1/ERK2 by Western blot analyse s. Neither the c-Jun NH2-terminal kinase/stress-activated protein kinase no r the p38 MAPK was activated by hyperoxia in these cells. Chemical or genet ic inhibition of the ERK p42/p44 MAPK pathway by PD-98059, a selective inhi bitor of MAPK kinase, and dominant negative mutants of ERK, respectively, a ttenuated hyperoxia-induced apoptosis as assessed by DNA laddering and nucl eosomal ELISAs. Taken together, our data suggest that hyperoxia can induce apoptosis in cultured murine macrophages and that the MAPK pathway mediates hyperoxia-induced apoptosis.