Tumor necrosis factor-alpha induces apoptosis in immortalized hypothalamicneurons: Involvement of ceramide-generating pathways

To investigate possible effects that may contribute, together with a direct action on neurohormone secretion, to the impairment of gonadal axis functi on during inflammation, we evaluated the effect of TNF alpha on the growth and viability of GT1-7 hypothalamic neurons and the intracellular transduct ion pathways involved in these effects. TNF alpha caused a reduction of cel l number and an induction of apoptotic death. These effects were mimicked b y cell-permeable analogs of ceramide and by neutral or acidic sphingomyelin ase. Exposure to acidic sphingomyelinase induced a persistent (up to 48 h) reduction of cell growth and apoptosis, whereas the effect of neutral sphin gomyelinase was time limited. The involvement of acidic sphingomyelinase in TNF alpha action was demonstrated by the partial prevention of ceramide ge neration, apoptosis, and reduced cell growth by the inhibitor of the acidic sphingomyelinase-generating pathway, D609, whereas the involvement of cera mide was proved by complete prevention of TNF alpha-induced effects by trea tment with okadaic acid at concentrations inhibiting ceramide-dependent pro tein phosphatase. The present data indicate that TNF alpha, through activat ion of ceramide-generating pathways, is able to affect GT1-7 cell viability , suggesting an additional effect that may contribute to the global action of this cytokine on neuroendocrine activities.