Rab5 Endosomal Overactivation Linked to Oxytocin Receptor Signalling Defects in Early Alzheimer’s Models

Endosomal dysfunction has long been suspected as an early player in Alzheimer’s disease, but a new open-access study in Cell Communication and Signaling adds a specific molecular link: hyperactivation of the small GTPase Rab5, a master regulator of early endosomes, appears to disrupt the trafficking of the oxytocin receptor and blunt the receptor-associated signalling that depends on it. The work, published on 21 October 2026, was conducted in early Alzheimer’s disease-relevant settings rather than in late-stage disease, and its authors emphasise that the connection between receptor mistrafficking and downstream brain phenotypes still requires further testing.

The researchers used two complementary models. First, they examined young APP/PS1 mice, an amyloid-producing model of Alzheimer’s pathology, and found that the hippocampus of these animals contained enlarged Rab5-positive early endosomal structures. These structures showed increased overlap with Rab7, a late endosome marker, and with LAMP1, a lysosomal marker, indicating that endosomes were maturing or being trafficked abnormally. The oxytocin receptor itself showed an abnormal intracellular redistribution, and phosphorylation of the signalling proteins ERK and CREB, readouts of oxytocin receptor-associated downstream signalling, was reduced in the hippocampus.

To test whether sustained Rab5 activation alone could drive these changes, the team delivered an AAV vector carrying constitutively active Rab5Q79L into the hippocampus of otherwise healthy animals. This overactivation model reproduced the Rab5-associated endosomal abnormalities seen in the APP/PS1 mice. It was also accompanied by altered association of the oxytocin receptor with endosomes, impaired recovery of oxytocin receptors at the plasma membrane, and reduced ERK and CREB phosphorylation in response to oxytocin. Complementary experiments in HEK293T cells, including receptor internalisation and recycling assays, membrane protein western blotting, oxytocin rechallenge, and oxytocin receptor antagonist experiments, supported the conclusion that Rab5 overactivation compromises plasma-membrane recovery of the receptor and the oxytocin-responsive ERK and CREB phosphorylation that follows.

The consequences extended well beyond receptor trafficking. RNA sequencing revealed disruption of transcriptional programmes related to neuronal signalling, and synaptic marker analysis showed loss of both excitatory and inhibitory synapses. Resting-state functional magnetic resonance imaging detected reduced spontaneous brain activity and weakened functional connectivity between the hippocampus and the medial prefrontal cortex, while structural imaging showed hippocampal atrophy. Behavioural testing confirmed cognitive impairment. These multi-level phenotypes were observed across the two models, although the study design cannot yet establish that oxytocin receptor mistrafficking directly causes them; the authors explicitly note that further work is needed to determine whether OTR trafficking mediates the downstream effects.

A therapeutic angle emerged from testing MW150, a p38alpha inhibitor. Across both models, MW150 treatment was associated with partial improvement in endosomal abnormalities, oxytocin receptor-associated signalling readouts, and behavioural measures. In the Rab5-overactivation model specifically, additional improvements were seen in synaptic measures and imaging outcomes. The authors interpret this as evidence that the p38alpha–Rab5/endosomal axis is modifiable, while stressing that the improvement was partial rather than complete. Because the study is being shared early as a peer-reviewed accepted manuscript, it remains subject to further editorial edits before the final version of record.

Methodologically, the study relied on confocal immunofluorescence and western blotting to track receptor localisation, endosomal marker colocalisation, and signalling readouts, with group comparisons analysed by one-way analysis of variance followed by Tukey’s post hoc test. The hippocampus-targeted Rab5 overactivation model was established by stereotaxic delivery of AAV-hSyn-EGFP-Rab5Q79L, allowing the researchers to separate the effects of Rab5 hyperactivation itself from the broader amyloid pathology of the APP/PS1 background.

The findings fit a growing body of evidence that endosomal abnormalities arise early in Alzheimer’s disease, before extensive neurodegeneration. By connecting Rab5 hyperactivation to a specific receptor system, the oxytocin receptor, whose signalling depends on proper receptor trafficking between endosomes and the plasma membrane, the study offers a mechanistic account of how endosomal dysfunction could erode neuronal communication. The observed loss of excitatory and inhibitory synapses, weakened hippocampal-prefrontal connectivity, and cognitive impairment in the models provide a circuit-level and functional context for these molecular changes, though all of these results come from animal and cellular models rather than human patients.

Limitations remain clear. The work was carried out in young APP/PS1 mice and an artificially induced Rab5 overactivation model, so the extent to which the same mechanisms operate in human Alzheimer’s disease is not established. The partial rescue by MW150 suggests that blocking p38alpha signalling upstream of Rab5 can soften, but not eliminate, the endosomal and downstream phenotypes. Whether restoring oxytocin receptor trafficking specifically would restore signalling and cognition is a question the authors leave open for future research, alongside the broader task of defining how Rab5-driven endo-lysosomal mistrafficking interacts with other early Alzheimer’s disease mechanisms.

Subject of Research: Rab5-mediated endo-lysosomal trafficking abnormalities and oxytocin receptor signalling in early Alzheimer's disease models

Article Title: Rab5-mediated endo-lysosomal mistrafficking associated with impaired oxytocin receptor signalling in early Alzheimer’s disease

Article References: Wang, S., Chen, Y., Miao, Y., Xie, J., Yang, F., Ye, C., Qi, J., Liu, Y., Zhang, Q., Dou, Y., & Wang, J. (2026). Rab5-mediated endo-lysosomal mistrafficking associated with impaired oxytocin receptor signalling in early Alzheimer’s disease. Cell Communication and Signaling. https://doi.org/10.1186/s12964-026-03315-y

Image Credits: AI Generated

DOI: 10.1186/s12964-026-03315-y

Keywords: Alzheimer's disease, Rab5, endosomes, oxytocin receptor, ERK, CREB, p38alpha, MW150, hippocampus, synapses, APP/PS1 mice, functional connectivity