Neurotoxic Ca2+ Signaling Induced by Amyloid-β Oligomers in Aged Hippocampal Neurons In Vitro

Novel Algorithm of Network Calcium Dynamics Analysis for Studying the Role of Astrocytes in Neuronal Activity in Alzheimer's Disease Models

Accumulated experimental data strongly suggest that astrocytes play an important role in the pathogenesis of neurodegeneration, including Alzheimer's disease (AD). The effect of astrocytes on the calcium activity of neuron-astroglia networks in AD modelling was the object of the present study. We have expanded and improved our approach's capabilities to analyze calcium activity. We have developed a novel algorithm to construct dynamic directed graphs of both astrocytic and neuronal networks. The proposed algorithm allows us not only to identify functional relationships between cells and determine the presence of network activity, but also to characterize the spread of the calcium signal from cell to cell. Our study showed that Alzheimer's astrocytes can change the functional pattern of the calcium activity of healthy nerve cells. When healthy nerve cells were cocultivated with astrocytes treated with Aβ42, activation of calcium signaling was found. When healthy nerve cells were cocultivated with 5xFAD astrocytes, inhibition of calcium signaling was observed. In this regard, it seems relevant to further study astrocytic-neuronal interactions as an important factor in the regulation of the functional activity of brain cells during neurodegenerative processes. The approach to the analysis of streaming imaging data developed by the authors is a promising tool for studying the collective calcium dynamics of nerve cells.

Evolutionary Origin of Insulin-Degrading Enzyme and Its Subcellular Localization and Secretion Mechanism: A Study in Microglial Cells

The insulin-degrading enzyme (IDE) is a zinc-dependent metalloendopeptidase that belongs to the M16A metalloprotease family. IDE is markedly expressed in the brain, where it is particularly relevant due to its in vitro amyloid beta (Aβ)-degrading activity. The subcellular localization of IDE, a paramount aspect to understand how this enzyme can perform its proteolytic functions in vivo, remains highly controversial. In this work, we addressed IDE subcellular localization from an evolutionary perspective. Phylogenetic analyses based on protein sequence and gene and protein structure were performed. An in silico analysis of IDE signal peptide suggests an evolutionary shift in IDE exportation at the prokaryote/eukaryote divide. Subcellular localization experiments in microglia revealed that IDE is mostly cytosolic. Furthermore, IDE associates to membranes by their cytoplasmatic side and further partitions between raft and non-raft domains. When stimulated, microglia change into a secretory active state, produces numerous multivesicular bodies and IDE associates with their membranes. The subsequent inward budding of such membranes internalizes IDE in intraluminal vesicles, which later allows IDE to be exported outside the cells in small extracellular vesicles. We further demonstrate that such an IDE exportation mechanism is regulated by stimuli relevant for microglia in physiological conditions and upon aging and neurodegeneration.

Xestospongin C, a Reversible IP3 Receptor Antagonist, Alleviates the Cognitive and Pathological Impairments in APP/PS1 Mice of Alzheimer's Disease

Exaggerated Ca2+ signaling might be one of primary causes of neural dysfunction in Alzheimer's disease (AD). And the intracellular Ca2+ overload has been closely associated with amyloid-β (Aβ)-induced endoplasmic reticulum (ER) stress and memory impairments in AD. Here we showed for the first time the neuroprotective effects of Xestospongin C (XeC), a reversible IP3 receptor antagonist, on the cognitive behaviors and pathology of APP/PS1 AD mice. Male APP/PS1-AD mice (n = 20) were injected intracerebroventricularly with XeC (3μmol) via Alzet osmotic pumps for four weeks, followed by cognition tests, Aβ plaque examination, and ER stress-related protein measurement. The results showed that XeC pretreatment significantly improved the cognitive behavior of APP/PS1-AD mice, raising the spontaneous alteration accuracy in Y maze, decreasing the escape latency and increasing the target quadrant swimming time in Morris water maze; XeC pretreatment also reduced the number of Aβ plaques and the overexpression of ER stress proteins 78 kDa glucose-regulated protein (GRP-78), caspase-12, and CAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP) in the hippocampus of APP/PS1 mice. In addition, in vitro experiments showed that XeC effectively ameliorated Aβ1 - 42-induced early neuronal apoptosis and intracellular Ca2+ overload in the primary hippocampal neurons. Taken together, IP3R-mediated Ca2+ disorder plays a key role in the cognitive deficits and pathological damages in AD mice. By targeting the IP3 R, XeC might be considered as a novel therapeutic strategy in AD.

Brain-Derived Neurotrophic Factor (BDNF) Preserves the Functional Integrity of Neural Networks in the β-Amyloidopathy Model in vitro

Alzheimer’s disease (AD) is a widespread chronic neurodegenerative pathology characterized by synaptic dysfunction, partial neuronal death, cognitive decline and memory impairments. The major hallmarks of AD are extracellular senile amyloid plaques formed by various types of amyloid proteins (Aβ) and the formation and accumulation of intracellular neurofibrillary tangles. However, there is a lack of relevant experimental models for studying changes in neural network activity, the features of intercellular signaling or the effects of drugs on the functional activity of nervous cells during AD development. In this work, we examined two experimental models of amyloidopathy using primary hippocampal cultures. The first model involves the embryonic brains of 5xFAD mice; the second uses chronic application of amyloid beta 1-42 (Aβ1-42). The model based on primary hippocampal cells obtained from 5xFAD mice demonstrated changes in spontaneous network calcium activity characterized by a decrease in the number of cells exhibiting Ca²⁺ activity, a decrease in the number of Ca²⁺ oscillations and an increase in the duration of Ca²⁺ events from day 21 of culture development in vitro. Chronic application of Aβ1-42 resulted in the rapid establishment of significant neurodegenerative changes in primary hippocampal cultures, leading to marked impairments in neural network calcium activity and increased cell death. Using this model and multielectrode arrays, we studied the influence of amyloidopathy on spontaneous bioelectrical neural network activity in primary hippocampal cultures. It was shown that chronic Aβ application decreased the number of network bursts and spikes in a burst. The spatial structure of neural networks was also disturbed that characterized by reduction in both the number of key network elements (hubs) and connections between network elements. Moreover, application of brain-derived neurotrophic factor (BDNF) recombinant protein and BDNF hyperexpression by an adeno-associated virus vector partially prevented these amyloidopathy-induced neurodegenerative phenomena. BDNF maintained cell viability and spontaneous bioelectrical and calcium network activity in primary hippocampal cultures.