Heterotrimeric guanine nucleotide-binding proteins (G-proteins) transmit signals from G protein-coupled receptors (GPCRs) to intracellular effector systems that are disrupted in Alzheimer’s disease (AD). However, there is limited information on the specific changes in Gα subunits related to amyloidosis and tauopathy at the subcellular level. Here, we aimed to detect potential alterations in the protein levels and localization of Gα o in the brains of 5xFAD, APP/PS1, and P301S mice using histoblot and quantitative immunoelectron microscopic techniques. Histoblot analysis revealed that Gα o is widely distributed throughout the brain. We observed a significant downregulation of Gα o protein levels in the hippocampus of 5xFAD, APP/PS1, and P301S mice, particularly in the dendritic layers of the CA1 region, which was less pronounced in the context of tau pathology. Additionally, a reduction in Gα o was noted in the caudate putamen and cortex of 5xFAD mice. At the subcellular level, immunoelectron microscopy showed a significant decrease in the postsynaptic localization of Gα o along the extrasynaptic plasma membrane of dendritic spines and shafts in CA1 pyramidal cells across the three AD mouse models. However, the distribution of Gα o protein relative to glutamate release sites in dendritic spines was altered in 5xFAD and APP/PS1 mice, but not in P301S mice. Presynaptically, Gα o immunolabeling in axon terminals was significantly reduced in the three AD transgenic mouse models. These reductions in Gα o at both postsynaptic and presynaptic sites suggest potential alterations in G protein-mediated signalling within hippocampal pyramidal cells, which may contribute to the cognitive dysfunctions observed in those transgenic mice. • Significant hippocampal reduction of Gαo in AD models : All three Alzheimer’s disease (AD) mouse models studied (5xFAD, APP/PS1, and P301S) show a marked decrease in Gαo protein levels in the hippocampus, particularly in dendritic layers of the CA1 region. • Stronger effect in amyloid pathology than tau pathology : The reduction of Gαo is more pronounced in amyloid-based models (5xFAD and APP/PS1) than in the tauopathy model (P301S). • Loss of membrane-bound Gαo : Immunoelectron microscopy reveals a significant decrease of Gαo associated with the plasma membrane at both postsynaptic (dendritic spines and shafts) and presynaptic (axon terminals) sites in all AD models. • Intracellular accumulation of Gαo : The reduction at the membrane is accompanied by increased intracellular localization of Gαo, suggesting protein redistribution rather than simple loss. • Altered nanoscale organization in amyloid pathology : In 5xFAD and APP/PS1 mice, Gαo loses its preferential perisynaptic localization near excitatory synapses, a change not observed in P301S mice. • Presynaptic signaling disruption : Gαo is significantly reduced at presynaptic active zones and extrasynaptic membranes, potentially impairing GPCR-mediated control of neurotransmitter release. • Implications for synaptic dysfunction : The combined pre- and postsynaptic loss and mislocalization of Gαo suggest disrupted G protein–mediated signaling that may contribute to hippocampal hyperexcitability and cognitive deficits in AD. • Novel mechanistic insight : This study provides the first ultrastructural, quantitative evidence linking amyloid and tau pathology to altered subcellular organization of a key G-protein subunit in the hippocampus.
Aguado et al. (Sun,) studied this question.