Spatial and episodic memory loss are the main hallmarks of Alzheimer's disease (AD), often occurring before any amyloid-β (Aβ) plaque deposition is detected. These symptoms appear to arise from the progressive degeneration of two main hippocampal pathways: place cells in the CA1 of hippocampus, which encode spatial maps, allowing the learning and recall of position in space during navigation and their dopaminergic (DA) inputs from the ventral tegmental area (VTA), which convey signals of novelty, reward and synaptic plasticity, crucial for memory formation and associations. However, this perspective is mainly centered on neuronal pathways and has overlooked the role of astrocytes and their important role in spatial learning and memory consolidation. Hippocampal astrocytes control or facilitate different forms of synaptic plasticity that can support spatial memory. Additionally, they may receive DAergic inputs that can trigger plasticity in response to reward. Recent findings have proved functional impairments in astrocytes in a mouse model of familial AD (fAD, PS2APP). These findings also suggest that aged PS2APP mice exhibit long-term memory impairment, mirroring AD symptoms when trained in behavioural spatial memory tasks. Therefore, our research aims to understand if the progression of Aβ plaque accumulation correlates with astrocytes activity, by analysing changes in Ca²⁺ signalling and dopaminergic response across the developmental stages of AD. To that end, we used the PS2-APP mouse model of familial AD at 3, 6 and 8 months of age. After mice underwent behavioural tests to evaluate their cognitive performance and spatial memory deficits, their brains were collected and processed by means of immunohistochemistry, in order to quantify and analyse: 1) the progression of Aβ plaques accumulations, 2) the alterations in astrocytic Ca²⁺ signalling through the expression of STIM1 receptor, and 3) the impairment of astrocytes dopaminergic activity via the expression of D1 and D2-like receptors, specifically in the CA1 of hippocampus. Our findings showed that the accumulation of Aβ plaques starts at 6 months of age and drastically and significantly increases throughout the progression of the disease when comparing fAD mice to age matched wild type (WT) mice. Additionally, the expression of astrocytic STIM1 receptors also appears to be lower in fAD mice at the age of 6 months compared to WT mice, and significantly decreases throughout the progression of the disease. Also, in PS2-APP mice the expression of D1-like dopaminergic receptors is already significantly lower than what observed in WT mice at 3 months of age, and progressively decreased from 6 to 8 months of age. On the other hand, the expression of D2-like receptors in PS2-APP mice was similar to WT at all ages and stayed stable across time. These results, together with preliminary data on spatial memory deficit available from the lab, suggest that the drastic decrease in the STIM1 and in D1-like dopaminergic receptors in CA1 hippocampal astrocytes between the age of 3 to 6 months, could precede the memory impairments observed starting from 8 months of age, and can be predictive and therefore contribute to the cognitive impairments including the spatial memory deficits typical of AD. Moreover, we plan to apply further analysis using the RNAscope technique, in order to understand if the biomarkers of AD, such as plaque deposition, DAergic and STIM1 receptor reduction are occurring at the RNA level, the protein level or both. These analysis will help clarify whether these impairment in AD arises from disruptions in the transcriptional or post-transcriptional mechanisms, providing a deeper understanding of AD pathology.
La perdita della memoria spaziale ed episodica è uno dei principali segnali di Alzheimer (AD), che spesso compare prima della formazione di placche di amiloide-β (Aβ). Tali sintomi sembrano coinvolgere anche l’ippocampo tramite la degenerazione di due vie neuronali principali: una include le cellule di posizione della regione CA1 dell’ippocampo, le quali codificano per mappe spaziali utili per apprendere e ricordare posizioni durante la navigazione; l’altra riguarda gli input dopaminergici (DAergici) provenienti dall’area tegmentale ventrale (VTA), che trasmettono segnali legati a novità, ricompensa e plasticità sinaptica, fondamentali per la formazione della memoria spaziale. Tuttavia, queste osservazioni si concentrano principalmente sul ruolo dei neuroni, trascurando il contributo degli astrociti e il loro ruolo nell’apprendimento e consolidamento della memoria. Gli astrociti ippocampali infatti regolano o facilitano vari tipi di plasticità sinaptica, e questo suggerisce un loro possibile coinvolgimento anche nella memoria spaziale. Inoltre, possono ricevere input DAergici, innescando meccanismi plastici legati alla ricompensa. Recenti ricerche hanno rivelato alterazioni funzionali negli astrociti in un modello murino di AD familiare (fAD, PS2APP). Inoltre, dati preliminari dal laboratorio in cui ho svolto il tirocinio, indicano che i topi PS2APP di 8 mesi presentano deficit di memoria a lungo termine in compiti comportamentali spaziali, riflettendo i sintomi della patologia. Il nostro studio intende quindi verificare se la progressione dell’accumulo di Aβ sia correlata all’attività astrocitaria, esaminando le modifiche nella segnalazione del Ca²⁺ e nella risposta dopaminergica degli astrociti durante le fasi dello sviluppo dell’AD. A tale scopo, abbiamo utilizzato il modello murino PS2APP a 3, 6 e 8 mesi di età. Dopo aver esaminato il comportamento di questi topi per valutare le prestazioni cognitive e i possibili deficit di memoria spaziale quando confrontati con topi wild-type (WT), gli stessi cervelli i sono stati analizzati tramite immunoistochimica per quantificare: 1) l’accumulo progressivo di Aβ, 2) le variazioni della segnalazione del Ca²⁺ astrocitario tramite l’espressione del recettore STIM1, e 3) l’attività DAergica astrocitaria mediante l’espressione dei recettori D1- e D2-like nella regione CA1 dell’ippocampo. I nostri risultati mostrano che le placche Aβ iniziano ad accumularsi già a 6 mesi di età nei topi fAD, aumentando in modo significativo a 8 mesi rispetto ai WT della stessa età. Inoltre, l’espressione del recettore astrocitario STIM1 risulta già ridotta nei topi fAD a 6 mesi rispetto ai WT e continua a diminuire durante la progressione della malattia. L’espressione dei recettori dopaminergici D1-like è anch’essa significativamente più bassa nei PS2APP rispetto ai WT già a 3 mesi, con ulteriore calo tra i 6 e gli 8 mesi. Al contrario, i recettori D2-like mostrano livelli simili nei due gruppi a tutte le età, rimanendo stabili. Questi risultati, insieme ai dati preliminari sui deficit di memoria spaziale disponibili nel nostro laboratorio, suggeriscono che la marcata riduzione dei recettori STIM1 e D1-like tra i 3 e i 6 mesi negli astrociti dell’ippocampo possa precedere i deficit spaziali osservati con gli esperimenti comportamentali a 8 mesi, risultando potenzialmente predittiva dei sintomi cognitivi, inclusi quelli della memoria spaziale, caratteristici dell’AD. Infine, prevediamo di applicare ulteriori analisi tramite RNAscope per verificare se la riduzione dei recettori DAergici e di STIM1 e l’accumulo di Aβ avvengano anche a livello trascrizionale (RNA), proteico o in entrambi. Queste analisi chiariranno se i deficit osservati derivino da alterazioni trascrizionali o post-trascrizionali, facendo luce sui meccanismi molecolari alla base della patofisiologia dell’AD.
Studio dei meccanismi molecolari astrocitari coinvolti nella perdita della memoria spaziale ippocampale in un modello murino di Alzheimer familiare.
ARABI, ANAHITA
2024/2025
Abstract
Spatial and episodic memory loss are the main hallmarks of Alzheimer's disease (AD), often occurring before any amyloid-β (Aβ) plaque deposition is detected. These symptoms appear to arise from the progressive degeneration of two main hippocampal pathways: place cells in the CA1 of hippocampus, which encode spatial maps, allowing the learning and recall of position in space during navigation and their dopaminergic (DA) inputs from the ventral tegmental area (VTA), which convey signals of novelty, reward and synaptic plasticity, crucial for memory formation and associations. However, this perspective is mainly centered on neuronal pathways and has overlooked the role of astrocytes and their important role in spatial learning and memory consolidation. Hippocampal astrocytes control or facilitate different forms of synaptic plasticity that can support spatial memory. Additionally, they may receive DAergic inputs that can trigger plasticity in response to reward. Recent findings have proved functional impairments in astrocytes in a mouse model of familial AD (fAD, PS2APP). These findings also suggest that aged PS2APP mice exhibit long-term memory impairment, mirroring AD symptoms when trained in behavioural spatial memory tasks. Therefore, our research aims to understand if the progression of Aβ plaque accumulation correlates with astrocytes activity, by analysing changes in Ca²⁺ signalling and dopaminergic response across the developmental stages of AD. To that end, we used the PS2-APP mouse model of familial AD at 3, 6 and 8 months of age. After mice underwent behavioural tests to evaluate their cognitive performance and spatial memory deficits, their brains were collected and processed by means of immunohistochemistry, in order to quantify and analyse: 1) the progression of Aβ plaques accumulations, 2) the alterations in astrocytic Ca²⁺ signalling through the expression of STIM1 receptor, and 3) the impairment of astrocytes dopaminergic activity via the expression of D1 and D2-like receptors, specifically in the CA1 of hippocampus. Our findings showed that the accumulation of Aβ plaques starts at 6 months of age and drastically and significantly increases throughout the progression of the disease when comparing fAD mice to age matched wild type (WT) mice. Additionally, the expression of astrocytic STIM1 receptors also appears to be lower in fAD mice at the age of 6 months compared to WT mice, and significantly decreases throughout the progression of the disease. Also, in PS2-APP mice the expression of D1-like dopaminergic receptors is already significantly lower than what observed in WT mice at 3 months of age, and progressively decreased from 6 to 8 months of age. On the other hand, the expression of D2-like receptors in PS2-APP mice was similar to WT at all ages and stayed stable across time. These results, together with preliminary data on spatial memory deficit available from the lab, suggest that the drastic decrease in the STIM1 and in D1-like dopaminergic receptors in CA1 hippocampal astrocytes between the age of 3 to 6 months, could precede the memory impairments observed starting from 8 months of age, and can be predictive and therefore contribute to the cognitive impairments including the spatial memory deficits typical of AD. Moreover, we plan to apply further analysis using the RNAscope technique, in order to understand if the biomarkers of AD, such as plaque deposition, DAergic and STIM1 receptor reduction are occurring at the RNA level, the protein level or both. These analysis will help clarify whether these impairment in AD arises from disruptions in the transcriptional or post-transcriptional mechanisms, providing a deeper understanding of AD pathology.| File | Dimensione | Formato | |
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https://hdl.handle.net/20.500.14239/30154