Ceramide-induced enhancement of secretory phospholipase A2 expression via generation of reactive oxygen species in tumor necrosis factor-alpha-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-alpha (TNF-alpha)-stimulated mesangial cells. TNF-alpha stimulation increased ceramide generation in parallel with a decrease in sphingomyelin. Pretreatment with exogenous sphingomyelinase (SMase) dose-dependently enhanced TNF-alpha-stimulated increases in COX-2 protein and sPLA) activity. SMase also augmented TNF-alpha-mediated nuclear factor kappaB (NF-kappaB) activation. N-acetylcysteine (NAC), an antioxidant, completely inhibited the SMase-induced increase in sPLA2 activity, whereas NAC inhibited partially the activity stimulated with TNF-alpha alone. Under the conditions, NAC completely inhibited reactive oxygen species (ROS) production induced by SMase followed by TNF-alpha. These results suggest that ceramide elicits up-regulation of NF-kappaB 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.