The Syntrophin-Dystrobrevin Subcomplex in Human Neuromuscular Disorders

The syntrophins and α-dystrobrevin form a subcomplex with dystrophin at the skeletal muscle membrane, and are also highly concentrated at the neuromuscular synapse. Here we demonstrate that the different syntrophins and α-dystrobrevin isoforms have distinct expression patterns during human skeletal muscle development, and are differentially affected by loss of dystrophin anchorage and denervation in human neuromuscular disease. During normal fetal development, and in Duchenne muscular dystrophy and denervation disorders, α1-syntrophin and α-dystrobrevin are absent or markedly reduced at the sarcolemmal membrane. β1-Syntrophin is the predominant syntrophin isoform expressed at the muscle membrane during development, and it undergoes upregulation in response to loss of α1-syntrophin in Duchenne muscular dystrophy and in denervation. Upregulation of β1-syntrophin in neuromuscular disorders is associated with re-expression of the fetal nicotinic acetylcholine receptor γ-subunit, cardiac actin, and neonatal myosin, suggesting reversion of muscle fibers to an immature phenotype. We show that denervation specifically affects expression of the syntrophin-dystrobrevin subcomplex and does not affect levels or localization of other members of the dystrophin-associated protein complex. Our results confirm that dystrophin is required for anchorage of the syntrophin-dystrobrevin subcomplex and suggest that expression of the syntrophin-dystrobrevin complex may be independently regulated through neuromuscular transmission.