p38 MAPK mediates renal tubular cell TNF-alpha production and TNF-alpha-dependent apoptosis during simulated ischemia

Ischemia causes renal tubular cell loss through apoptosis; however, the mec hanisms of this process remain unclear. Using the renal tubular epithelial cell line LLC-PK1, we developed a model of simulated ischemia (SI) to inves tigate the role of p38 MAPK (mitogen-activated protein kinase) in renal cel l tumor necrosis factor-alpha (TNF-alpha) mRNA production, protein bioactiv ity, and apoptosis. Results demonstrate that 60 min of SI induced maximal T NF-alpha mRNA production and bioactivity. Furthermore, 60 min of ischemia i nduced renal tubular cell apoptosis at all substrate replacement time point s examined, with peak apoptotic cell death occurring after either 24 or 48 h. p38 MAPK inhibition abolished TNF-alpha mRNA production and TNF-alpha bi oactivity, and both p38 MAPK inhibition and TNF-alpha neutralization (anti- porcine TNF-alpha antibody) prevented apoptosis after 60 min of SI. These r esults constitute the initial demonstration that 1) renal tubular cells pro duce TNF-alpha mRNA and biologically active TNF-alpha and undergo apoptosis in response to SI, and 2) p38 MAPK mediates renal tubular cell TNF-alpha p roduction and TNF-alpha -dependent apoptosis after SI.