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

Strokin M, Sergeeva M, Reiser G. Proinflammatory treatment of astrocytes with lipopolysaccharide results in augmented Ca2+ signaling through increased expression of VIA phospholipase A(2) (iPLA(2)). Am J Physiol Cell Physiol 300: C542-C549, 2011. First published December 22, 2010; doi:10.1152/ajpcell.00428.2010.-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 proin-flammatory 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 A(2) (VIA iPLA(2)). Indeed, both gene silencing with specific small interfering RNA and pharmacological inhibition of VIA iPLA(2) 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 iPLA(2) in development of inflammation in brain. We suggest that this enzyme might be a possible target for treatment of pathologies related to brain inflammation.