Ceramide-induced enhancement of secretory phospholipase A₂ expression via generation of reactive oxygen species in tumor necrosis factor-α-stimulated mesangial cells

Since prostanoids such as prostaglandin E₂ play a pivotal role in modulating renal function, we investigated the involvement of ceramide in expression of secretory phospholipase A₂ (sPLA₂) and cyclooxygenase-2 (COX-2) in tumor necrosis factor-α (TNF-α)- stimulated mesangial cells. TNF-α stimulation increased ceramide generation in parallel with a decrease in sphingomyelin. Pretreatment with exogenous sphingomyelinase (SMase) dose-dependently enhanced TNF-α-stimulated increases in COX-2 protein and sPLA₂ activity. SMase also augmented TNF-α-mediated nuclear factor κB (NF-κB) activation. N-acetylcysteine (NAC), an antioxidant, completely inhibited the SMase-induced increase in sPLA₂ activity, whereas NAC inhibited partially the activity stimulated with TNF-α alone. Under the conditions, NAC completely inhibited reactive oxygen species (ROS) production induced by SMase followed by TNF-α. These results suggest that ceramide elicits up-regulation of NF-κB through ROS production, which, in turn, leads to stimulation of COX-2 and sPLA₂ expression. Therefore, ceramide may be implicated in the pathogenesis of renal abnormalities.