Human-Derived Blood-Brain Barrier In Vitro Models as Reliable Tools for Research and Therapeutics

Abstract

The blood-brain barrier (BBB) serves as a crucial interface between the bloodstream and the brain, regulating molecular exchange to maintain brain homeostasis. Comprising endothelial cells, astrocytes, pericytes and neurons, the BBB allows selective passage of molecules whilst restricting others. Dysfunction of the BBB is implicated in various neurodegenerative and neurodevelopmental diseases, including amyotrophic lateral sclerosis (ALS) and Rett syndrome (RTT), although its precise role remains unclear. Brain microvascular endothelial cells (BMECs) are key components of the BBB, featuring unique characteristics such as tight junctions and specialised transporters. Astrocytes also play a vital role in BBB regulation, forming a protective network around brain vasculature. Dysregulation of astrocyte function is linked to several neurological disorders, but the exact contribution of BBB dysfunction to disease progression is uncertain. While some studies suggest that BBB breakdown may be secondary to neurodegeneration, others propose a direct role in disease pathogenesis. To address this gap, my research utilised both human C9ORF72 and MECP2 patient-derived cells to model the BBB, thus revealing autonomous endothelial cell dysfunction in both ALS and RTT. Human induced pluripotent stem cells (hi-PSCs) have shown promise due to their patient-specific origin, making them more relevant for personalised medicine research compared to other models. Protocols for differentiating hi-PSCs into BMEC-like cells were applied, demonstrating the expression of key BBB markers and functional characteristics, including transendothelial electrical resistance (TEER) values exceeding 4000 Ω x cm².