Ceramide-induced apoptosis in cortical neurons is mediated by an increase in p38 phosphorylation and not by the decrease in ERK phosphorylation

Ceramide, the central molecule of the sphingomyelin pathway, serves as a second messenger for cellular functions ranging from proliferation and differentiation to growth arrest and apoptosis. In this study we show that c(2)-ceramide induces apoptosis in primary cortical neuron cultures and that this effect correlates with differential modulation of mitogen-activated protein kinase (MAPK) cascades. Phosphorylation of extracellular signal-regulated kinases (ERKs) and their upstream activators MAPK kinases (MEKs), as measured by immunoblotting is rapidly decreased by c(2)-ceramide. However, the MEK inhibitor PD98059 alone does not induce apoptosis and in combination with c(2)-ceramide it does not modify c(2)-ceramide-induced apoptosis. Treatment with c(2)-ceramide increases p38 and c-jun N-terminal kinase (JNK) phosphorylation before and during caspase-3 activation. The p38 inhibitor SB203580 partially protects cortical neurons against ca-ceramide-induced apoptosis, implicating the p38 pathway in this process. The c(2)-ceramide treatment also increases levels of c-jun, c-fos and p53 mRNA in primary cortical neuron cultures, but this is independent of p38 activation. Our study further elucidates the time-courses of MAPK cascade modulation, acid of c-jun, c-fos and p53 activation during c(2)-ceramide-induced neuronal apoptosis. It reveals that one of the activated kinases, p38, is necessary for this apoptosis.