The assembly of the dystrophin-associated protein complex at the blood-brain barrier is dependent upon the presence of α-syntrophin [16
]. Specifically, α-syntrophin is required for the localization of γ2-syntrophin, α-dystrobrevin-2, and dystrophin to the perivascular astrocyte endfoot membrane. Since localization of αDB-2, but not αDB-1, requires α-syntrophin, we questioned how the DAPC would be affected by the loss of α-dystrobrevin isoforms. We performed immunolocalization for α-syntrophin on brains from α-dystrobrevin null animals [; 22
] and wild-type littermates (). The merged image in indicates that, in wild type mice, α-syntrophin co-localizes with α-dystrobrevin 1 in perivascular astrocyte endfeet, as reported previously. Furthermore, we observed a striking decrease in the level of α-syntrophin immunofluorescence in the α-dystrobrevin-null mice (compare 1E to 1B).
α-Syntrophin is Reduced at the Blood-Brain Barrier in the Absence of α-Dystrobrevin
We have previously shown that the localization of γ2-syntrophin to perivascular endfeet is dependent on α-syntrophin [16
]. Since we find that expression of α-syntrophin at glial endfeet is dependent on the presence of α-dystrobrevin, we determined whether the localization of γ2-syntrophin was disrupted by the loss of α-dystrobrevin. We compared γ2-syntrophin immunolocalization (green, ) in wild-type () and α-dystrobrevin-null () cerebellum. γ2-Syntrophin immunofluorescence was reduced in the surrounding cerebellar vasculature in the absence of α-dystrobrevin (compare 2E to 2B). As in the α-syntrophin null animals [16
], γ2-syntrophin expression is unaffected in neurons (see arrows, ). Taken together, these data indicate that expression of γ2-syntrophin in non-neuronal cells is dependent on both α-syntrophin and α-dystrobrevin.
γ2-Syntrophin is Reduced at the Blood-Brain Barrier in the Absence of α-Dystrobrevin
Dystrophin colocalizes with α-syntrophin in both the granular layer and the molecular layer of the cerebellum. The α-Db-1 and -2 isoforms exhibit discrete distributions in the vasculature of these layers but both colocalize with α-sybtrophin. Thus, dystrophin and a form of α-dystrobrevin are colocalized in the vasculature throughout the cerebellum. Dystrophin localization at the blood-brain barrier is contingent on the presence of α-syntrophin [16
]. Since α-syntrophin localization is disrupted in the α-dystrobrevin-null mice, the localization of dystrophin might also be affected. We assessed immunofluorescence for dystrophin (green, ) and αDb-2 (red, ) in cerebellum from wild type () and α-dystrobrevin-null mice (). As shown previously, αDb-2 is present in the granular layer of cerebellar cortex (, see arrows). As expected, the α-dystrobrevin-null cerebellum is negative for α-Db2 (). Dystrophin is associated with the blood-brain barrier throughout the cerebellar cortex (), and its expression levels are substantially reduced in the α-dystrobrevin-null mouse (compare 3E to 3B).
Dystrophin is Reduced at the Blood-Brain Barrier in the Absence of α-Dystrobrevin