Acid sphingomyelinase activity regulates in vitro CREB activation in murine primary neurons

The pathogenesis of major depressive disorder (MDD) is not elucidated so far. The pathophysiology of MDD implies dysregulations in both the acid sphingomyelinase (ASM)/ceramide system and the activity of the transcription factor CREB. MDD was found to be associated with an increase in ASM activity and ceramide levels, and a decrease in CREB activation. Antidepressant treatment is able to reverse both effects. This study investigated in vitro the interconnection between both targets, namely the impact of ASM activity on CREB activation in cell lines and murine primary cells using reporter assays, immuno-staining and immuno-blotting. ASM activity and CREB activation were negatively correlated in murine primary hippocampal and cortical cells: Increased ASM activity resulted in a decrease in CREB activation, whereas decreased ASM activity resulted in an increased CREB activation. Under neuronal activated conditions induced by high external potassium (KCl) levels (25 mM instead of 5 mM), distinct results emerged for both cell types. In hippocampal cells, high amounts of KCl levels abolished the impact of ASM activity on CREB phosphorylation, which might fulfill a protective function. In contrast, high amounts of KCl levels on cortical cells reversed the impact of ASM activity on CREB phosphorylation with increased ASM activity resulting in increased CREB activation, similar to our neuronal cell line experiments. This in vitro study shows for the first time that the ASM/ceramide system and the CREB signaling pathway are interconnected. The ASM/ceramide system impacts CREB phosphorylation and transcriptional activity in a cell type- specific and activation- dependent way.