Choroid plexus organoids predict CNS drug permeability and reveal human CSF proteins produced by specialized cell types

The choroid plexus (ChP) is a protective epithelial barrier that filters blood and secretes cerebrospinal fluid (CSF), an important fluid for nutrient maintenance in the brain and transport of signalling molecules. Here, we establish human ChP organoids with a selective epithelial barrier that secrete CSF-like fluid in self-contained compartments. We show that this in vitro barrier exhibits the same selectivity to small molecules as the in vivo counterpart, and that ChP-CSF organoids can predict CNS permeability of novel compounds. Characterization of the transcriptomic signature of ChP organoids and the proteomic make-up of the CSF-like fluid demonstrate a high degree of similarity to the in vivo counterpart. We leverage the fact that these organoids represent the tissue in isolation to examine their cellular make-up, and explore the specialized epithelial subtypes involved in de novo production of key CSF components. This reveals the presence of heterogeneous epithelial ChP populations, including a newly identified myoepithelial cell type, and uncovers human-specific factors secreted by these specialized cell types. Overall design: 3 samples of 2 pooled human choroid plexus organoids each along with 1 sample of 2 pooled telencaphalic organoids were dissociated with Accumax and run through the 10X pipeline and then analysed in Seurat and compared with existing in vivo datasets (available through the USCS cell browser: cortex-dev.cells.ucsc.edu and mouse-organogenesis.cells.ucsc.edu).