Expression of Familial Alzheimer Disease Presenilin 1 Gene Attenuates Vesicle Traffic and Reduces Peptide Secretion in Cultured Astrocytes Devoid of Pathologic Tissue Environment

In the brain, astrocytes provide metabolic and trophic support to neurones. Failure in executing astroglial homeostatic functions may contribute to the initiation and propagation of diseases, including Alzheimer disease (AD), characterized by a progressive loss of neurones over years. Here, we examined whether astrocytes from a mice model of AD isolated in the presymptomatic phase of the disease exhibit alterations in vesicle traffic, vesicular peptide release and purinergic calcium signaling. In cultured astrocytes isolated from a newborn wild-type (wt) and 3xTg-AD mouse, secretory vesicles and acidic endosomes/lysosomes were labeled by transfection with plasmid encoding atrial natriuretic peptide tagged with mutant green fluorescent protein (ANP.emd) and by LysoTracker, respectively. The intracellular Ca2+ concentration ([Ca2+](i)) was monitored with Fluo-2 and visualized by confocal microscopy. In comparison with controls, spontaneous mobility of ANP- and LysoTracker-labeled vesicles was diminished in 3xTg-AD astrocytes; the track length (TL), maximal displacement (MD) and directionality index (DI) were all reduced in peptidergic vesicles and in endosomes/lysosomes (P < 0.001), as was the ATP-evoked attenuation of vesicle mobility. Similar impairment of peptidergic vesicle trafficking was observed in wt rat astrocytes transfected to express mutated presenilin 1 (PS1(M146V)). The ATP-evoked ANP discharge from single vesicles was less efficient in 3xTg-AD and PS1(M146V)-expressing astrocytes than in respective wt controls (P < 0.05). Purinergic stimulation evoked biphasic and oscillatory [ Ca2+](i) responses; the latter were less frequent (P < 0.001) in 3xTg-AD astrocytes. Expression of PS1(M146V) in astrocytes impairs vesicle dynamics and reduces evoked secretion of the signaling molecule ANP; both may contribute to the development of AD.