α1-Syntrophin Gene Disruption Results in the Absence of Neuronal-type Nitric-oxide Synthase at the Sarcolemma but Does Not Induce Muscle Degeneration

Abstract α1-Syntrophin is a member of the family of dystrophin-associated proteins and is strongly expressed in the sarcolemma and the neuromuscular junctions. All three syntrophin isoforms have a PDZ domain that appears to participate in protein-protein interactions at the plasma membrane. α1-Syntrophin has additionally been shown to associate with neuronal nitric-oxide synthase (nNOS) through PDZ domains in vitro. These observations suggest that α1-syntrophin may work as a modular adaptor protein that can link nNOS or other signaling enzyme to the sarcolemmal dystrophin complex. In the sarcolemma, nNOS regulates the homeostasis of reactive free radical species and may contribute to the oxidative damage to muscle protein in muscle disease such as Duchenne muscular dystrophy. In this study, we generated α1-syntrophin knock-out mice to clarify the interaction between α1-syntrophin and nNOS in the skeletal muscle. We observed that nNOS, normally expressed in the sarcolemma, was largely absent from the sarcolemma, but considerably remained in the cytosol of the knock-out mice. Even though the distribution of nNOS was altered, the knock-out mice displayed no gross histological changes in the skeletal muscle. We also discovered that muscle contractile properties have not been influenced in the knock-out mice.