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

Abstract

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 iPLA2with 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 iPLA2in development of inflammation in brain. We suggest that this enzyme might be a possible target for treatment of pathologies related to brain inflammation.