Environmental pollution as a trigger of reactive astrogliosis and neurovascular dysfunction in Alzheimer's disease

Abstract

To date, the general understanding concerning the influence of environmental factors on the development and progression of Alzheimer's disease (AD) remains largely unclear. Given the capacity of certain urban pollutants to permeate the air pathways and, through a variety of mechanisms, translocate into the brain parenchyma, assessing the potential cytotoxic properties of these xenobiotic compounds is vital towards elucidating the homeostatic resilience of the blood-brain barrier (BBB). In this respect, astrocytes play key roles within the neurovascular unit (NVU) as cell types sensitive to chemical changes in the extracellular environment as well as active effectors of intercellular communication across neuronal, vascular, and immune cell types. Therefore, this work aims to approach environmentally-induced neurovascular stress through reactive changes in astrocytes associated with the strongest genetic risk factor for sporadic AD, APOE status. For this purpose, an in vitro 2D platform was generated from both primary and human induced pluripotent stem cell (iPSC)-derived astrocytes in which fine particulate matter (PM2.5), a major constituent of urban pollution, could be assessed for its cytotoxic and proinflammatory potential. Additionally, a neurovascular co-culture model composed of astrocytes and brain endothelial cells (BMECs) was employed within a static Transwell system to monitor the effect of PM2.5 exposure on endothelial barrier integrity. Finally, ApoE-dependent changes in reactive astrogliosis following PM2.5 exposure were analysed at the transcriptomic level through RNA sequencing, providing evidence for a genetic, molecular, and functional effect of environmental pollution on ApoE4 astrocytes. Both primary and iPSC-derived astrocytes stained positively for canonical astroglial markers GFAP, CD44 and AQP4 and secreted increased amounts of proinflammatory cytokine IL-6 following PM2.5 exposure, an effect which was significantly enhanced for ApoE4 astrocytes. This susceptibility of ApoE4 cell types to PM2.5 was further demonstrated to affect maintenance of endothelial barrier integrity in iPSC-derived BMECs as determined through transendothelial electrical resistance (TEER) values. Transcriptomic analysis of ApoE4 astrocytes exposed to PM2.5 revealed alterations in proinflammatory pathways associated with reactive astrogliosis, as well as dysregulation of neurovascular maintenance. Overall, this work demonstrates an inflammatory effect of PM2.5 on human astrocytes and adjacent vascular cell types as determined through an in vitro NVU model while also providing molecular and cellular insight into the effects of environmental pollution on neurovascular cells and, thus, into the potential pathogenesis of AD.

Date of Award	6 Jan 2025
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Tao Wang (Supervisor), Nigel Hooper (Supervisor) & Marco Domingos (Supervisor)