Investigating peripheral inflammation induced neuroinflammation in the absence of blood-brain barrier breakdown in relation to Alzheimer’s disease

Abstract

Neuroinflammation is important in Alzheimer’s disease (AD) pathogenesis, with microglia and astrocytes contributing to both inflammatory signalling and neurodegeneration. Peripheral inflammation is increasingly implicated as a potential driver of cognitive decline and accelerated pathology, yet the mechanisms by which peripheral signals influence the brain, particularly when the blood-brain barrier (BBB) remains intact, remain poorly understood.

To investigate how peripheral inflammatory signals can propagate to the neurovascular unit (NVU), an in vitro BBB model was developed using brain endothelial cells, pericytes, and astrocytes cultured above a secondary compartment containing astrocytes, neurons, and microglia. An acute peripheral inflammatory stimulus (LPS; 250 ng/ml), at a dose that did not reduce TEER or allow LPS translocation to the central compartment of the barrier, induced strong microglia-dependent inflammatory transcriptional changes across all NVU cell types downstream of endothelial cells.

Conditioned media from the abluminal (central) side of the barrier activated primary microglia in an NFκB-dependent manner, and mass spectrometry highlighted Von Willebrand factor (VWF) as a candidate endothelial-derived mediator.

Recombinant VWF reproduced microglial inflammatory activation via NFκB signalling.

To further assess these mechanisms in vivo, FIRE KO mice lacking microglia and wild-type controls were treated with systemic LPS (0.5 mg/kg). RNA-seq from FACS-isolated endothelial cells and astrocytes revealed that endothelial transcriptional responses were largely microglia-independent, whereas astrocytic inflammatory responses were largely microglia-dependent, supporting microglia as intermediaries that amplify endothelial derived signals.

Together, these findings demonstrate that peripheral inflammation can promote neuroinflammation without overt disruption of the BBB, with endothelial cells acting as early sensors and microglia as intermediaries that amplify CNS inflammatory signalling. VWF has emerged as a novel mediator of endothelial-to-microglial communication. These results highlight a mechanistic pathway by which systemic inflammation may contribute to neuroinflammation in AD, and highlight endothelial-microglial signalling, including VWF and NFκB pathways, as potential therapeutic targets.