PHOTOACTIVATED ADENYLYL CYCLASE IN HIPPOCAMPAL ASTROCYTES BUT NOT NEURONS MITIGATE Β-AMYLOID AND INFLAMMATORY ALZHEIMER PATHOLOGY IN 5XFAD MICE

Alzheimer’s disease (AD) is characterized by amyloid-β (Aβ) plaque deposition, neuroinflammation, and neuronal dysfunction. AD pathology is also associated with disrupted cyclic adenosine monophosphate (cAMP) signalling, contributing to impaired synaptic plasticity and memory deficits. Here, whether selectively increasing cAMP levels in hippocampal neurons or astrocytes could alleviate AD-related pathological alterations in 5xFAD mice. A red-light-sensitive Photoactivable Adenylate Cyclase (DdPAC) was expressed in hippocampal neurons or astrocytes using AAV9 vectors under CamKII or GFAP promoters in eight-month-old 5xFAD and wild-type (WT) mice. After four weeks, mice were stimulated with 685 nm light for 10 minutes, and brain tissue was analysed 24 hours later using immunofluorescence and proteomic approaches.
Astrocytic DdPAC activation significantly reduced Aβ plaque burden and GFAP expression in 5xFAD mice, indicating decreased astrocyte reactivity, whereas neuronal stimulation produced minimal effects. Astrocyte and microglia morphology was distinctly modulated by both neuronal or astrocytic DdPAC activation. Proteomic analyses revealed cell-type- and disease-specific responses. In WT mice, astrocytic cAMP activation predominantly affected immune-related pathways and synaptic transmission at both pre- and post-synaptic levels, while neuronal stimulation mainly influenced post-synaptic proteins. In 5xFAD mice, astrocytic stimulation activated diverse immune pathways, whereas neuronal stimulation affected cell adhesion and junctional processes. Interestingly, modulation of actin dynamics was common across all groups, yet the PKA interactome differ between DdPAC stimulation in neurons or astrocytes.
These findings highlight distinct roles of cAMP signalling in neurons and astrocytes and suggest that astrocyte-targeted cAMP activation may represent a promising therapeutic strategy for AD.