DHA inhibits ER Ca2+release and ER stress in astrocytes following in vitro ischemia

Docosahexaenoic acid (DHA) has neuroprotective effects in several neurodegenerative disease conditions. However, the underlying mechanisms are not well understood. In the present study, we investigated the effects of DHA on astrocyte Ca2+ signaling under in vitro ischemic conditions (oxygen/glucose deprivation and reoxygenation, OGD/REOX). OGD (2 h) triggered a Ca2+ER store overload (similar to 1.9-fold). Ca2+ uptake by the Ca2+ER stores was further augmented during REOX and Ca2+ER was elevated by similar to 4.7-fold at 90 min REOX. Interestingly, Ca2+ER stores abruptly released Ca2+ at similar to 120 min REOX and emptied at 160 min REOX. Depletion of Ca2+ER stores led to delayed elevation of intracellular Ca2+ concentration (Ca2+cyt) and cell death. Activation of the purinergic receptor P2Y1 was responsible for the release of Ca2+ER. Most importantly, DHA blocked the initial Ca2+ER store overload, the delayed depletion of Ca2+ER, and rise in Ca2+cyt, which was in part via inhibiting d-myo-inositol 1,4,5-triphosphate receptors. The DHA metabolite DiHDoHE exhibited similar effects. DHA also attenuated expression of phosphorylated eukaryotic initiation factor 2a and activating transcription factor-4, two ER stress markers, following in vitro ischemia. Taken together, these findings suggest that DHA has protective effects in astrocytes following in vitro ischemia, in part, by inhibiting Ca2+ dysregulation and ER stress.