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A new target for blood–brain barrier transport

Written by Charlotte Harrison, Science Writer

Getting large-molecule drugs across the blood–brain barrier (BBB) is challenging, largely because of our limited knowledge of the mechanisms and targets involved in blood–brain transport.

Now, a study published in Science Advances has identified new potential targets in humans, including carbonic anhydrase IV. The discovery could enable the rational design of gene-delivery vectors and drugs that cross the BBB for central nervous system disorders. 

Target screening

To identify BBB transport targets, the authors used previously identified adenovirus vectors (AVVs) that are known to cross the BBB in mice. These AAVs were tested against many receptors found on the BBB in a cell-based infectivity screen. This process identified two targets: LY6C1, which is only found in mice, and carbonic anhydrase IV, which is found across species.

The role of carbonic anhydrase IV in BBB transport was confirmed in studies using knockout mice.

Binding models

The researchers then used AlphaFold-based in-silico methods to generate capsid–BBB receptor binding models to learn more about the specific interactions that mediate the binding of the AVVs to target proteins.

Then they focused on the binding of one AVV (the PHP.eB insertion peptide) to the LY6A receptor complex. Because of the large size of AAV capsids and weak binding interactions, the authors could not use standard modelling tools, so devised an ‘integrative structure modelling pipeline’, dubbed APPRAISE-AAV. This enabled them to decipher a binding model that until now could not be characterized at high resolution. The researchers noted that APPRAISE-AAV could be used for other large proteins.

Surprising target

Carbonic anhydrase IV is a previously unrecognised target for enhancing BBB receptor-mediated transport, which the authors found surprising:

“To say that an enzyme that regulates blood pH and lets us taste the fizz in soda is an unintuitive target for helping viruses through the BBB would be an understatement,” said lead author Viviana Gradinaru in a press release.