Golgi and sarcolemmal neuronal NOS differentially regulate contraction-induced fatigue and vasoconstriction in exercising mouse skeletal muscle

Abstract

Signaling via the neuronal NOS (nNOS) splice variant nNOSμ is essential for skeletal muscle health and is commonly reduced in neuromuscular disease. nNOSμ is thought to be the predominant source of NO in skeletal muscle. Here we demonstrate the existence of what we believe to be a novel signaling pathway, mediated by the nNOS splice variant nNOSβ, localized at the Golgi complex in mouse skeletal muscle cells. In contrast to muscles lacking nNOSμ alone, muscles missing both nNOSμ and nNOSβ were severely myopathic, exhibiting structural defects in the microtubule cytoskeleton, Golgi complex, and mitochondria. Skeletal muscles lacking both nNOSμ and nNOSβ were smaller in mass, intrinsically weak, highly susceptible to fatigue, and exhibited marked postexercise weakness. Our data indicate that nNOSβ is a critical regulator of the structural and functional integrity of skeletal muscle and demonstrate the existence of 2 functionally distinct nNOS microdomains in skeletal muscle, created by the differential targeting of nNOSμ to the sarcolemma and nNOSβ to the Golgi. We have previously shown that sarcolemmal nNOSμ matches the blood supply to the metabolic demands of active muscle. We now demonstrate that nNOSβ simultaneously modulates the ability of skeletal muscle to maintain force production during and after exercise. We conclude therefore that nNOS splice variants are critical regulators of skeletal muscle exercise performance.

nNOS regulation of skeletal muscle fatigue and exercise performance

“…While nNOSμ-deficient muscles in a B6/129 strain were found to be susceptible to fatigue, the nNOSμ-deficient muscles from mice on a C57/Bl6 background exhibited normal fatigue resistance (Percival et al 2010). These data suggest an important role for strain-specific genetic modifiers that modulate fatigue in the absence of nNOSμ.…”

“…One explanation arises from recent reports that both nNOSμ and nNOSβ play a pivotal role in promoting skeletal muscle fatigue resistance. The nNOS regulation of fatigue has been studied using a minimally invasive in situ approach that preserves muscle innervation, vascularization, temperature, and tissue O 2 concentrations (Percival et al , 2010. This approach is widely considered to be the most physiologically relevant method for measuring skeletal muscle fatigue and is especially useful given the known vasomodulatory function and exquisite oxygen sensitivity of nNOS enzymatic activity (Thomas et al 1998;Eu et al 2003;Stuehr et al 2004;Allen et al 2008).…”

“…nNOSμ association and regulation of the ryanodine receptor is also seen in the heart (Gonzalez et al 2007). nNOSβ associates with the subsarcolemmal Golgi complex (Percival et al 2010), suggesting the presence of a high concentration of nNOS-derived NO from both nNOSμ and nNOSβ just under the plasma membrane.…”

“…nNOS splice variants in skeletal muscle nNOS is the major source of NO in skeletal muscle cells Percival et al 2010 (Bredt and Snyder 1990;Bredt et al 1991). The Ca 2+ / calmodulin sensitivity of nNOS facilitates its coupling to muscle contraction.…”

“…The increases in intracellular Ca 2+ that occur upon muscle excitation increase basal nNOS activity several fold during contraction . Skeletal muscles express two alternatively spliced nNOS isoforms, nNOSμ and nNOSβ, both of which are expressed in fast and slow muscle types (Silvagno et al 1996;Stamler and Meissner 2001;Percival et al 2010, Figure 1). nNOSμ is scaffolded to the subsarcolemmal dystrophin glycoprotein complex (DGC) and neuromuscular junction (Brenman et al 1995(Brenman et al , 1996Adams et al 2000).…”