P4‐025: SMases increase BACE1 levels in primary neurons through palmitate astrocyte‐conditioned media

Abstract

Astrocytes play a critical role in Alzheimer's disease. Previously, we showed that saturated free-fatty acid, palmitate (PA), upregulates BACE1 level in primary rat neurons mediated by astrocytes. However, the molecular mechanisms by which conditioned media from PA-treated astrocytes upregulates BACE1 level in neurons are unknown. Western blot, Quantitative real time polymerase chain reaction, Enzyme-linked immunosorbent assay (ELISA) and quantitative mass spectrometry were performed. This study demonstrates that neural and acidic sphingomyelinase (N-SMase and A-SMase) are activated in neurons cultured with palmitate-astrocyte conditioned media, which in turn increase BACE1 level in the primary neurons. Silencing the SMases in neurons decreased the upregulation in BACE1 level. Further studies indicate that increased serine palmitoyltransferase (SPT) level in PA-treated astrocytes in turn enhanced cytokine, namely TNFa and IL-1b, secretions into the media. The cytokines in the conditioned media activate N-SMase and A-SMase in the neurons to propagate the deleterious effects of BACE1 upregulation. Neutralizing the cytokines in the PA-treated astrocyte conditioned media reduced BACE1 upregulation. Notably, decreasing TNFa and IL-1b levels in the conditioned media by inhibiting SPT in the astrocytes also reduced the SMase activities and BACE1 level in the neurons. In summary, our data suggest the activation of astrocytes by PA is mediated by SPT, and in turn, the activated astrocytes increased BACE1 level in neurons mediated by SMases.