A physiologically relevant blood-cerebrospinal fluid barrier model to study the permeability of neurodegenerative biomarkers.

The blood-cerebrospinal fluid barrier (BCSFB) is formed by the choroid plexus and represents the interface between the blood and cerebrospinal fluid (CSF). Several in vitro models have been developed to establish an active cellular barrier and to study the functional and molecular properties of the BCSFB. These models are suitable for simulating disease processes and evaluating drug permeability into brain tissue. Here we have established and optimized a protocol for the high-yield isolation of primary epithelial cells from rat choroid plexus. The addition of cytosine arabinoside suppressed the growth of contaminating cells (fibroblasts and astrocytes), and epithelial culture was grown into a confluent impermeable monolayer within 5-6 days after seeding. To characterize functional and structural properties of our BCSFB model, we employed immunocytochemical and biochemical techniques. Using this model, we assessed the permeability of small molecules as well as proteins associated with neurodegenerative disorders, including tau protein and neurofilament light chain (NfL). The cells were able to secrete cerebrospinal fluid (CSF) actively and the epithelial secretome was enriched in growth factors, cell-matrix proteins, proteases, carrier proteins, and inflammation-related proteins. The novelty of our model lies in its ability to mimic the structural and functional characteristics of the BCSFB while also expressing transporters that are important for pharmaceutical research. The model is suitable for in vitro investigations of the BCSFB, preclinical drug discovery, and for studying the mechanisms by which CNS biomarkers cross from the CSF to the blood during disease.