Background: Astrocytes constitute about 20~40% of glial cells, making up the central nervous system. Astrocytes usually maintain homeostasis in the extracellular environment, changing their morphology to the activated state in neurodegenerative diseases and releasing inflammatory cytokines. Sphingolipids, one of the lipids, have been reported as a molecule associated with astrocyte activation. Here, we evaluated astrocyte activity by changing sphingomyelin (SM) levels using HASTR/ci35, a conditionally immortalized human astrocyte.
Results＆Discussion: Increasing endogenous SM levels by inhibiting neutral sphingomyelinase and the external addition of SM increased protein and mRNA expression of astrocyte activation markers by IL-1α/TNF-αtreatment. On the other hand, decreasing intercellular SM by the knockdown of sphingomyelin synthase and ceramide transport protein (CERT) reduced protein and mRNA expression of astrocyte activation markers by IL-1α/TNF-α treatment. We analyzed the NF-κB pathway to elucidate how reducing intracellular SM levels suppresses astrocyte activation. We found that CERT knockdown did not alter phospho-IκB, phospho-p65 expression, and p65 nuclear translocation. Interestingly, protein expression of HDAC3, which negatively regulates the NF-κB pathway, was significantly increased. These results suggest that reducing intracellular SM levels suppress astrocyte activation by inhibiting the NF-κB pathway through the induction of HDAC3 expression.