The effects of β/A4-amyloid and its fragments on calcium homeostasis, glial fibrillary acidic protein and S100β staining, morphology and survival of cultured hippocampal astrocytes

Abstract

Aggregated β/A4-amyloid is known to increase intraneuronal calcium by various mechanisms and to lead eventually to the death of the cultured neuron. This study deals with the role of β/A4-amyloid and several of its fragments in calcium homeostasis, glial fibrillary acid protein and S100β staining, morphology and survival of cultured rat hippocampal astrocytes as determined by Fura imaging, indirect immunofluorescence and life/death assays. In contrast to cultured neurons, none of the 12 different β/A4 fragments tested caused an increase in intra-astrocytic free calcium. However, among the compounds evaluated, the fragments 10–20mer, 25–35mer and the full-length peptides (1–40, 1–42 and 1–43mer), at 5 and 10 μM, decreased free intra-astrocytic calcium statistically significantly after the cells had been incubated for 48 and 72 h. This occurred both for astrocytes treated with vehicle alone or the reversed sequence of the 1–40mer, i.e. the 40-1mer. However, survival was not altered under the conditions examined, even when there was a change in free intracellular calcium. Concomitant with the decrease in intracellular free calcium, the shape of the astrocytes became more spider-like, normally an indication of activated astrocytes, and markedly more intense anti-S100β and anti-glial fibrillary acidic protein staining was seen. The functional relevance of altered calcium homeostasis for apolipoprotein E secretion, potentially relevant for neuronal plasticity in general and in Alzheimer's disease, is discussed.