A Role for Nitric Oxide in Muscle Repair: Nitric Oxide–mediated Activation of Muscle Satellite Cells

Abstract

Muscle satellite cells are quiescent precursors interposed between myofibers and a sheath of external lamina. Although their activation and recruitment to cycle enable muscle repair and adaptation, the activation signal is not known. Evidence is presented that nitric oxide (NO) mediates satellite cell activation, including morphological hypertrophy and decreased adhesion in the fiber-lamina complex. Activation in vivo occurred within 1 min after injury. Cell isolation and histology showed that pharmacological inhibition of nitric oxide synthase (NOS) activity prevented the immediate injury-induced myogenic cell release and delayed the hypertrophy of satellite cells in that muscle. Transient activation of satellite cells in contralateral muscles 10 min later suggested that a circulating factor may interact with NO-mediated signaling. Interestingly, satellite cell activation in muscles of mdx dystrophic mice and NOS-I knockout mice quantitatively resembled NOS-inhibited release of normal cells, in agreement with reports of displaced and reduced NOS expression in dystrophin-deficient mdx muscle and the complete loss of NOS-I expression in knockout mice. Brief NOS inhibition in normal and mdx mice during injury produced subtle alterations in subsequent repair, including apoptosis in myotube nuclei and myotube formation inside laminar sheaths. Longer NOS inhibition delayed and restricted the extent of repair and resulted in fiber branching. A model proposes the hypothesis that NO release mediates satellite cell activation, possibly via shear-induced rapid increases in NOS activity that produce "NO transients." INTRODUCTIONAfter muscle injury, satellite cells are activated and recruited to cycle as precursors for new muscle formation. Between injury and proliferation in vivo, satellite cells express immediate early genes after 3-6 h (Weiss, 1994;Kami et al., 1995) and muscle regulatory genes after 6 h (Grounds et al., 1992) in concert with proliferating cell nuclear antigen (Chambers and McDermott, 1996). The expression of these genes, release of growth factors such as bFGF, and DNA synthesis 24 -30 h later are used to characterize muscle regeneration in injured and dystrophic muscle (Grounds and McGeachie, 1989;Anderson et al., 1995;Floss et al., 1997 Floss et al., , 1998. The timing and sequence of events are specific to those of repair (Megeney et al., 1996;Li et al., 1997;McIntosh et al., 1998) but similar to those of development (Rudnicki and Jaenisch, 1995;Yun and Wold, 1996).The fine structure of satellite cells, positioned intimately between the fiber sarcolemma and the external lamina (Mauro, 1961;Ishikawa, 1966), changes during their transition from quiescence to activation. Nuclei enlarge and become euchromatic. The typical attenuated organelle-poor cytoplasm expands, and organelles such as mitochondria and rough endoplasmic reticulum hypertrophy (Schultz, 1976;Snow, 1977;Schultz et al., 1978Schultz et al., , 1985. However, although activation is recognized as essential to repair and defined as precursor s...

Release of Hepatocyte Growth Factor from Mechanically Stretched Skeletal Muscle Satellite Cells and Role of pH and Nitric Oxide

“…In myotube cultures, cyclical stretch for 2 d was reported to increase NO production and nNOS concentration in a calcium-dependent manner (Tidball et al, 1998), and the same study showed that resumption of weight bearing after muscle unloading restored normal nNOS expression and NO release, as did electric stimulation and passive stretch of excised muscle. It is interesting in this regard that in dystrophic muscle without dystrophin, nNOS was absent from the subsarcolemmal region (Brenman et al, 1995(Brenman et al, , 1996 and that dysregulation of satellite cell activation in vivo was reportedly very similar to that occurring as a result of absent nNOS expression or NOS inhibition (Anderson, 2000).…”

“…Anderson (2000) demonstrated that NO mediated the rapid morphological changes associated with satellite cell activation after crush injury, including cell hypertrophy and detachment from the adjacent fiber. At the cellular level, shear forces generated by contraction or re-traction of damaged fibers within the basal lamina are thought to stimulate nitric-oxide synthase (NOS) to produce bursts of NO synthesis.…”

“…The first is hepatocyte growth factor (HGF); HGF can activate quiescent rat muscle satellite cells in vitro and in vivo (Allen et al, 1995;Tatsumi et al, 1998). HGF is a heparin-binding growth factor that has been localized in the extracellular domain of uninjured skeletal muscle fibers, and after injury HGF quickly associates with satellite cells (Tatsumi et al, 1998;Anderson, 2000). Furthermore, quiescent and activated satellite cells have been shown to express the c-met receptor, which mediates the intracellular signaling response of HGF (Cornelison and Wold, 1997;Allen et al, 1998;Tatsumi et al, 1998), which is consistent with the proposed role of HGF in activating quiescent satellite cells.…”

“…At the cellular level, shear forces generated by contraction or re-traction of damaged fibers within the basal lamina are thought to stimulate nitric-oxide synthase (NOS) to produce bursts of NO synthesis. Such bursts of NO were hypothesized by Anderson (2000) to provide the initial signal for activating satellite cells. Consequently, there is a strong hypothetical link between mechanical changes in muscle, NO synthesis, and satellite cell activation.…”

Hypoxia and Resistance Exercise: A Comparison of Localized and Systemic Methods

“…via nitrogen dilution hypoxic generators) does not [131]. Nitric oxide is a potent reactive species and has been proposed to mediate the activation of skeletal muscle satellite cells and subsequent hypertrophy [132]. It is therefore possible that the type of hypoxia employed during IHRT may influence the subsequent physiological responses.…”