Peripheral Monocyte-Derived Extracellular Vesicles Establish an Immune-Brain Communication Pathway in Alzheimer's Disease

Alzheimer's disease (AD) is increasingly being viewed as a disorder affecting both the central and peripheral immune systems. The way peripheral immune cells impact neurodegeneration is not well understood. This study identifies a biological pathway through which peripheral monocytes communicate with neurons via extracellular vesicles (EVs), shedding light on how AD-associated changes in monocytes can turn this communication into a mechanism that causes neuronal damage.

Genetic tracking in mice shows that EVs released by specific types of peripheral immune cells, including monocytes, can reach the healthy brain and attach to neurons. EVs taken from monocytes of mice genetically engineered to exhibit features of AD show an increased presence of inflammatory substances, including IL-1β, which significantly hampers the growth of neuron branches.

By blocking the action of this substance, the research found that neuron growth can be partially restored, highlighting IL-1β as a crucial mediator of EV-induced harm to neurons. Additionally, stimulation with a key component of AD, Aβ, produces similar characteristics of this harmful EV behavior in macrophages and triggers metabolic problems and heightened inflammatory responses in peripheral monocytes.

The repeated use of EVs from AD-activated cells worsens cognitive decline and reduces the integrity of synapses in the hippocampus of 5xFAD mice, even without increasing the accumulation of amyloid plaques. This study suggests that the communication between peripheral monocytes and neurons via EVs can become harmful under normal conditions and can be manipulated in a way that promotes pathogenic signaling in AD.

Targeting this EV-mediated communication pathway could potentially serve as a new therapeutic approach, complementing existing strategies that target Aβ.