Assembly of a perivascular astrocyte protein scaffold at the mammalian blood-brain barrier is dependent on alpha-syntrophin.

alpha-Syntrophin, a member of the dystrophin-associated protein complex, is required for proper localization of the water channel aquaporin-4 at the blood-brain barrier. Mice lacking alpha-syntrophin have reduced levels of aquaporin-4 in perivascular astroglial endfeet. Consequently, they exhibit reduced edema and infarct volume in brain trauma models and reduced K+ clearance from the neuropil, leading to increased seizure susceptibility. We have used the alpha-syntrophin null mice to investigate whether alpha-syntrophin is required for proper localization of other components of the dystrophin complex at the blood-brain barrier. We find that alpha-syntrophin is required for the full recruitment of gamma2-syntrophin and alpha-dystrobrevin-2 to glial endfeet in adult cerebellum. In contrast, the localization of beta1- and beta2-syntrophin and alpha-dystrobrevin-1 at the blood-brain barrier is not dependent on the presence of alpha-syntrophin. The localization patterns of alpha-dystrobrevin-1 and -2 in wild type cerebellum are strikingly different; while alpha-dystrobrevin-1 is present in glial endfeet throughout the cerebellum, alpha-dystrobrevin-2 is restricted to glial endfeet in the granular layer alone. Finally, we show that the enrichment of dystrophin in glial endfeet depends on the presence of alpha-syntrophin. This finding is the first demonstration that dystrophin localization is dependent on syntrophin. Since the localization of gamma2-syntrophin, alpha-dystrobrevin-2, and dystrophin is contingent on alpha-syntrophin, we conclude that alpha-syntrophin is a central organizer of the astrocyte dystrophin complex, an important molecular scaffold for localization of aquaporin-4 at the blood-brain barrier.