Dysregulation of Ca signaling in astrocytes from mice lacking amyloid precursor protein

Linde CI, Baryshnikov SG, Mazzocco-Spezzia A, Golovina VA. Dysregulation of Ca signaling in astrocytes from mice lacking amyloid precursor protein. Am J Physiol Cell Physiol 300: C1502–C1512, 2011. First published March 2, 2011; doi:10.1152/ajpcell.00379.2010.—The relationship between altered metabolism of the amyloidprecursor protein (APP) and Alzheimer’s disease is well established but the physiological roles of APP still remain unclear. Here, we studied Ca signaling in primary cultured and freshly dissociated cortical astrocytes from APP knockout (KO) mice and from Tg5469 mice overproducing by fiveto sixfold wild-type APP. Resting cytosolic Ca (measured with fura-2) was not altered in cultured astrocytes from APP KO mice. The stored Ca evaluated by measuring peak amplitude of cyclopiazonic acid [CPA, endoplasmic reticulum (ER) Ca ATPase inhibitor]-induced Ca transients in Ca -free medium was significantly smaller in APP KO astrocytes than in wild-type cells. Store-operated Ca entry (SOCE) activated by ER Ca store depletion with CPA was also greatly reduced in APP KO astrocytes. This reflected a downregulated expression in APP KO astrocytes of TRPC1 (C-type transient receptor potential) and Orai1 proteins, essential components of store-operated channels (SOCs). Indeed, silencer RNA (siRNA) knockdown of Orai1 protein expression in wild-type astrocytes significantly attenuated SOCE. SOCE was also essentially reduced in freshly dissociated APP KO astrocytes. Importantly, knockdown of APP with siRNA in cultured wild-type astrocytes markedly attenuated ATPand CPA-induced ER Ca release and extracellular Ca influx. The latter correlated with downregulation of TRPC1. Overproduction of APP in Tg5469 mice did not alter, however, the stored Ca level, SOCE, and expression of TRPC1/4/5 in cultured astrocytes from these mice. The data demonstrate that the functional role of APP in astrocytes involves the regulation of TRPC1/Orai1-encoded SOCs critical for Ca signaling.