Proinflarnrnatory treatment of astrocytes with lipopolysaccharide results in augmented Ca2+ signaling through increased expression of VIA phospholipase A2 (iPLA2).

Many Ca²⁺-regulated intracellular processes are involved in the development of neuroinflammation. However, the changes of Ca²⁺ signaling in the brain under inflammatory conditions were hardly studied. ATP-induced Ca²⁺ signaling is a central event of signal transmission in astrocytic networks. We investigated primary astrocytes after proinflammatory stimulation with lipopolysaccharide (LPS; 100 ng/ml) for 6-24 h. We reveal that Ca²⁺ responses to purinergic ATP stimulation are significantly increased in amplitude and duration after stimulation with LPS. We detected that increased amplitudes of Ca²⁺ responses to ATP in LPS-treated astrocytes can be explained by substantial increase of Ca²⁺ load in stores in endoplasmic reticulum. The mechanism implies enhanced Ca²⁺ store refilling due to the amplification of capacitative Ca²⁺ entry. The reason for the increased duration of Ca²⁺ responses in LPS-treated cells is also the amplified capacitative Ca²⁺ entry. Next, we established that the molecular mechanism for the LPS-induced amplification of Ca²⁺ responses in astrocytes is increased expression and activity of VIA phospholipase A₂ (VIA iPLA₂). Indeed, both gene silencing with specific small interfering RNA and pharmacological inhibition of VIA iPLA₂ with S-bromoenol lactone reduced the load of the Ca²⁺ stores and caused a decrease in the amplitudes of Ca²⁺ responses in LPS-treated astrocytes to values, which were comparable with those in untreated cells. Our findings highlight a novel regulatory role of VIA iPLA₂ in development of inflammation in brain. We suggest that this enzyme might be a possible target for treatment of pathologies related to brain inflammation. [ABSTRACT FROM AUTHOR]