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 Ca(2+) concentration ([Ca(2+)]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 (PS1M146V). The ATP-evoked ANP discharge from single vesicles was less efficient in 3xTg-AD and PS1M146V-expressing astrocytes than in respective wt controls (P < 0.05). Purinergic stimulation evoked biphasic and oscillatory [Ca(2+)]i responses; the latter were less frequent (P < 0.001) in 3xTg-AD astrocytes. Expression of PS1M146V in astrocytes impairs vesicle dynamics and reduces evoked secretion of the signaling molecule ANP; both may contribute to the development of AD.

High-mobility group box-1 protein and ß-amyloid oligomers promote neuronal differentiation of adult hippocampal neural progenitors via receptor for advanced glycation end products/nuclear factor-κB axis: relevance for Alzheimer's disease.

Dysregulated hippocampal neurogenesis has been associated with neurodegenerative disorders, including Alzheimer's disease (AD), in which it may potentially represent an auto-reparatory mechanism that could counteract neuronal loss and cognitive impairment. We evaluated hippocampal neurogenesis in TgCRND8 mice and reported that, at 32 weeks of age, corresponding to an advanced AD-like neuropathology stage, increased numbers of proliferating cells, doublecortin-expressing progenitors/neuroblasts, and early postmitotic calretinin-expressing neurons were present compared with wild-type (WT) littermates. When hippocampal neural progenitor cells (NPCs) were isolated from TgCRND8 mice, we demonstrated that (1) their neurogenic potential was higher compared with WT NPCs; (2) medium conditioned by TgCRND8 NPC promoted neuronal differentiation of WT NPCs; and (3) the proneurogenic effect of TgCRND8-conditioned medium was counteracted by blockade of the receptor for advanced glycation end products (RAGE)/nuclear factor-κB (NF-κB) axis. Furthermore, we showed that ß-amyloid 1-42 (Aß(1-42)) oligomers, but not monomers and fibrils, and the alarmin high-mobility group box-1 protein (HMGB-1) could promote neuronal differentiation of NPCs via activation of the RAGE/NF-κB axis. Altogether, these data suggest that, in AD brain, an endogenous proneurogenic response could be potentially triggered and involve signals (Aß(1-42) oligomers and HMGB-1) and pathways (RAGE/NF-κB activation) that also contribute to neuroinflammation/neurotoxicity. A more detailed analysis confirmed no significant increase of new mature neurons in hippocampi of TgCRND8 compared with WT mice, suggesting reduced survival and/or integration of newborn neurons. Therapeutic strategies in AD should ideally combine the ability of sustaining hippocampal neurogenesis as well as of counteracting an hostile brain microenvironment so to promote survival of vulnerable cell populations, including adult generated neurons.

Glutamine synthetase in astrocytes from entorhinal cortex of the triple transgenic animal model of Alzheimer's disease is not affected by pathological progression.

Astrocytes are fundamental for brain physiology and pathology, including Alzheimer's disease (AD). Among their functions, the maintenance of glutamate balance via the glutamate-glutamine (Glu-Gln) shuttle is critical for both normal cognitive functions and excitotoxicity relevant for AD progression. Astroglial glutamine synthetase (GS), converting glutamate to glutamine, is a key element in the Glu-Gln cycle. The entorhinal cortex (EC) is the brain area earliest affected in human AD. We have recently reported an early astrocytic atrophy in the EC in triple transgenic animal model of AD (3×Tg-AD). Here, we studied and analysed whether the changes in astrocytic morphology coincides with alterations of the Glu-Gln cycle by determining astrocytic GS. We found that the numerical density of GS-immunoreactive (GS-IR) cells as well as GS content (measured by optical density, OD) remained constant between 1 and 12 months of age, independent of the presence of senile plaques. Dual labelling images revealed GS-IR, GFAP-IR, GS/GFAP-IR subsets of astroglia. Despite the evident decrease in GFAP-IR surface and volume, the surface and volume of GS-IR and GS/GFAP-IR cells remained unchanged. Therefore, reduced GFAP presence obvious in the progression of AD from early stages does not impair upon glutamate homeostasis in the EC of 3×Tg-AD mice. Our data also indicate distinct functional populations of astrocytes, which may undergo specific remodelling during AD progression.

Complex and region-specific changes in astroglial markers in the aging brain.

Morphological aging of astrocytes was investigated in entorhinal cortex (EC), dentate gyrus (DG), and cornu ammonis 1 (CA1) regions of hippocampus of male SV129/C57BL6 mice of different age groups (3, 9, 18, and 24 months). Astroglial profiles were visualized by immunohistochemistry by using glial fibrillary acidic protein (GFAP), glutamine synthetase (GS), and s100ß staining; these profiles were imaged using confocal or light microscopy for subsequent morphometric analysis. GFAP-positive profiles in the DG and the CA1 of the hippocampus showed progressive age-dependent hypertrophy, as indicated by an increase in surface, volume, and somata volume at 24 months of age compared with 3-month-old mice. In contrast with the hippocampal regions, aging induced a decrease in GFAP-positive astroglial profiles in the EC: the surface, volume, and cell body volume of astroglial cells at 24 months of age were decreased significantly compared with the 3-month group. The GS-positive astrocytes displayed smaller cellular surface areas at 24 months compared with 3-month-old animals in both areas of hippocampus, whereas GS-positive profiles remained unchanged in the EC of old mice. The morphometry of s100ß-immunoreactive profiles revealed substantial increase in the EC, more moderate increase in the DG, and no changes in the CA1 area. Based on the morphological analysis of 3 astroglial markers, we conclude that astrocytes undergo a complex age-dependent remodeling in a brain region-specific manner.