Identification of Blood–Brain Barrier-Associated Proteins in the Human Brain

The blood–brain barrier (BBB)
is essential for cerebral
homeostasis and controls the selective passage of molecules traveling
in and out of the brain. Despite the crucial role of the BBB in a
variety of brain diseases and its relevance for the development of
drugs, there is little known about its molecular architecture. In
particular, the composition of the basal lamina between the astrocytic
end-feet and the endothelial cells is only partly known. Here, we
present a proteomic analysis of the basal lamina of the human BBB.
We combined laser capture microdissection with shotgun proteomics
for selective enrichment and identification of specific proteins present
in the cerebral microvasculature and arachnoidal vessels collected
from normal human brain tissue specimens. Proteins found to be associated
with the blood–brain barrier were validated by immunohistochemistry.
Expression of membrane protein MLC1 was found in all brain barriers.
Phosphoglucomutase-like protein 5 appeared to be variably present
along the outer part of intracerebral vessels, and multidrug resistance
protein 1 was identified in both intracerebral, as well as arachnoidal
blood vessels. The results demonstrate the presence of so far unidentified
proteins in the human BBB and illustrate topic differences in their
expression. In conclusion, we showed that sample purification by microdissection
followed by shotgun proteomics provides a list of proteins identified
in the BBB. Subsequent immunohistochemistry detailed the respective
expression sites of membrane protein MLC1 and phosphoglucomutase-related
protein 5. The role of the identified proteins in the functioning
of the BBB needs further investigations.