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.