The research, led by the Institute for Bioengineering of Catalonia, reveals that the blood–brain barrier is defined not only by the proteins it expresses, but by how it uses them, through a dynamic property known as endocytic turnover rate (ETOR). This discovery shows that brain endothelial cells have a unique molecular behaviour that distinguishes them from other blood vessels and can be disrupted during inflammation. The results provide new insight into how the barrier functions and fails in disease which may help identify novel therapeutic strategies to restore neurovascular health.
A study led by researchers at the Institute for Bioengineering of Catalonia (IBEC) in collaboration with the Proteomics Platform of the Institute for Research in Biomedicine (IRB Barcelona) has uncovered a key mechanism that helps define how the blood–brain barrier functions — not just based on which proteins are present, but on how dynamically they are used.
We asked whether blood–brain barrier specialization arises not only from the proteins it expresses, but also from how it uses them.
Daniel Gonzalez-Carter
The research, published in iScience, shows that brain endothelial cells, which form the BBB, possess a unique “endocytic profile”, describing how quickly proteins are internalised, recycled, or degraded. In other words, how long they remain active at the cell surface. This property, known as the endocytic turnover rate (ETOR), emerges as a critical driver of the blood–brain barrier specialization and is disrupted under inflammatory conditions.
“Through a collaboration bringing together cell biology, proteomics, bioinformatics and mathematics, we asked whether blood–brain barrier specialization arises not only from the proteins it expresses, but also from how it uses them,” says Daniel Gonzalez-Carter, senior research fellow in the Molecular Bionics Group at IBEC and leader of the study.
“These findings may help identify novel therapeutic strategies to restore neurovascular health,” adds Giuseppe Battaglia, ICREA research professor at IBEC, principal investigator at the Molecular Bionics Group and co-author of the study.
The blood–brain barrier is a highly selective interface that protects the brain while allowing essential nutrients and signals to pass. Traditionally, its function has been explained by the identity and abundance of proteins on the surface of endothelial cells.
However, it remains unclear whether the dynamic regulation of these proteins, the so-called ETOR profile, contributes to the unique properties of brain endothelial cells. Furthermore, it is unknown whether this dynamic regulation changes in disease to affect the blood–brain barrier.
These findings may help identify novel therapeutic strategies to restore neurovascular health.
Giuseppe Battaglia
Using advanced proteomics, the team tracked how nearly 1,000 membrane proteins behave over time in rat endothelial cells from the brain and other organs. They found that how long proteins remain on the cell surface provides an additional, independent layer of regulation.
The researchers identified a distinct ETOR profile in brain endothelial cells that clearly differentiates them from endothelial cells in other organs, even when protein composition is relatively similar.
More specifically, proteins involved in transport showed high turnover rates, which likely supports efficient nutrient delivery to the brain. In contrast, junction proteins, essential for maintaining the barrier’s tightness, displayed low turnover, ensuring structural stability.
Crucially, these dynamics were not correlated with protein abundance, demonstrating that ETOR represents an independent regulatory feature of endothelial function.
Inflammation rewires barrier behaviour
The research also shows that pathology alters these dynamics. When exposed to inflammatory signals, brain endothelial cells retained a similar overall protein composition, but their behaviour changed: their ETOR profile was significantly altered.
“We found that brain endothelial cells handle proteins in a very specific way that sets them apart from blood vessels in the rest of the body. Importantly, this specialised behaviour is disrupted during inflammation, making them behave more like typical peripheral blood vessels and potentially weakening their ability to protect the brain,” explains Gonzalez-Carter.
Importantly, the researchers found that changes in protein abundance primarily reflected immune responses. In contrast,changes in ETOR revealed processes linked to vascular remodelling. This suggests that focusing only on protein levels may overlook key disease mechanisms.
Implications for brain health and therapy
The findings open new avenues for understanding how the BBB is regulated in health and disease. Since the barrier plays a central role in neurological disorders — including Alzheimer’s disease, consequences of a stroke, and neuroinflammation, among others — identifying the mechanisms that control its integrity is crucial.
By highlighting ETOR as a key regulatory dimension, the study could also inform strategies to restore BBB function, improve drug delivery to the brain, and identify new therapeutic targets to protect or restore brain health.
Referenced paper:
Alba Tomás-Sitjes, Gianluca Arauz-Garofalo, Marina Gay, Sònia Jarió, Marta Vilaseca, Valentina Schastlivaia, Maaike Kessen, Nicola Manicardi, Giuseppe Battaglia, Daniel Gonzalez-Carter. Endocytic turnover of endothelial cell-membrane proteins as a driver of rat blood-brain barrier specialization and dysfunction. iScience (2026). DOI: https://doi.org/10.1016/j.isci.2026.116231
