Steroids induce acetylcholine receptors on cultured human muscle: implications for myasthenia gravis.

Abstract

Antibodies to the acetylcholine receptor (AChR), which are diagnostic of the human autoimmune disease myasthenia gravis, block AChR function and increase the rate of AChR degradation leading to impaired neuromuscular transmission. Steroids are frequently used to alleviate symptoms of muscle fatigue and weakness in patients with myasthenia gravis because of their well-documented immunosuppressive effects. We show here that the steroid dexamethasone significantly increases total surface AChRs on cultured human muscle exposed to myasthenia gravis sera. Our results suggest that the clinical improvement observed in myasthenic patients treated with steroids is due not only to an effect on the immune system but also to a direct effect on muscle. We propose that the identification and development of pharmacologic agents that augment receptors and other proteins that are reduced by human genetic or autoimmune disease will have broad therapeutic applications.Myasthenia gravis (MG) is a human autoimmune disorder that affects neuromuscular function by impairing synaptic transmission. MG patients have circulating autoantibodies directed against nicotinic acetylcholine receptors (AChRs) concentrated on skeletal muscle at neuromuscular junctions (1-3). These antibodies reduce the sensitivity of muscle to acetylcholine by blocking ligand binding sites and by increasing the rate of AChR degradation (4-10). Glucocorticoids used in conjunction with acetylcholinesterase (AChE) inhibitors are currently among the most effective pharmacologic treatments of the debilitating clinical symptoms of MG and may be responsible for the 50% reduction in mortality in the past two decades (11). The recovery of motor strength after glucocorticoid therapy is thought to result from the welldocumented immunosuppressive effects of steroids (12, 13). However, the titer of anti-AChR antibodies in MG patients treated with steroids often does not correlate with the severity of the disease or incidence of death (11, 14). We demonstrate here that the glucocorticoid dexamethasone (Dex) directly affects cultured human myotubes by inducing AChR synthesis and increasing total surface AChRs 2-fold. In contrast, Dex has no effect on other parameters of muscle differentiation such as fusion index, AChE activity, and sarcomeric actin transcript accumulation. The effect of Dex on AChR levels is evident in the presence of sera from MG patients, indicating that the therapeutic benefits of corticosteroid therapy are likely to derive from effects not only on the immune system but also on muscle tissue. These results suggest that therapeutic strategies directed at promoting tissue-specific gene expression will prove useful in MG as well as other human genetic and autoimmune disorders characterized by reduced levels of proteins including cell surface receptors. MATERIALS AND METHODSMuscle Cultures. Individual muscle clones were isolated as described (15) from the vastus lateralis muscle of three individuals (XXVI, XXXII, and XXVIII aged 2, 7, and 63 years, respect...

Modulation by prednisolone of calcium handling in skeletal muscle cells

“…In mdx mice, however, Weller et al (1991) found that PDN did not change the in vivo prevalence of fibre necrosis and regeneration. (2) A direct effect on myogenesis has been noted (Guerriero & Florini, 1980;Askanas et al, 1986;Misra & Entrikin, 1988;Braun et al, 1989;Kaplan et al, 1990;Sklar & Brown, 1991;Passaquin et al, 1993;; an acceleration of the rate of fusion of quiescent myoblasts, so-called satellite cells (Bischoff, 1990), with DMD muscle fibres would therefore enhance muscle regeneration. (3) Protection of the newly formed myotubes by antioxidant action and/or inhibition of myotube apoptosis (Sklar & Brown, 1991).…”

“…It was clinically demonstrated that the glucocorticoid a-methylprednisolone (PDN) is able to improve or sustain muscular strength and function in DMD boys for at least three years (Fenichel et al, 1991). We and others have already shown that PDN and other glucocorticoids are able to enhance in vitro differentiation of skeletal muscle cells derived from normal (Guerriero & Florini, 1980;Braun et al, 1989;Kaplan et al, 1990;Sklar & Brown, 1991;Vilquin et al, 1992;Passaquin et al, 1994) and dystrophin-deficient muscle Passaquin et al, 1993 Passaquin et al, 1993) and lazaroids 45Ca2+ efflux measurements 45Ca2" loading and subsequent efflux measurements were performed on cells that had been washed twice with 0.5 ml PSS (containing 0.12 mM CaCl2) and incubated for 20 min in 0.2 ml PSS (containing 0.12 mM CaCl2) and 2 MCi of 45Ca2+ at 370C. After loading, cells were rapidly washed four times with 0.5 ml of ice-cold PSS (containing 1.2 mM CaCd2).…”

Different magnitude of resistance to non-depolarizing muscle relaxants in dexamethasone-treated rat diaphragm associated with altered acetylcholine receptor expression

“…Braun et al (1993) observed that long-term treatment with glucocorticoids (hydrocortisone, prednisolone or Dex) decreased degradation and increased synthesis of junctional nicotinic acetylcholine receptor (nAChRs). Kaplan et al (1990) found that Dex significantly increases total surface nAChRs in cultured human muscle exposed to myasthenia gravis serum. Furthermore, with the single channel patch-clamp technique, Maestrone et al (1995) proved that Dex-upregulated nAChRs were functional and that their electrophysiological parameters were similar to those found in control myotubes.…”

“…The beneficial effect of corticosteroids in deficient neuromuscular transmission (e.g., in myasthenia gravis) is due not only to an effect on the immune system but also to a direct effect on muscle (Kaplan et al, 1990). Braun et al (1993) observed that long-term treatment with glucocorticoids (hydrocortisone, prednisolone or Dex) decreased degradation and increased synthesis of junctional nicotinic acetylcholine receptor (nAChRs).…”

Myasthenia Gravis and Its Comorbidities

“…Acute disease and the use of steroids affect thyroid function, but steroids have a beneficial effect on MG and are used as treatment [20] due to its immunoregulator function and associated proliferation of Ach receptors [21].…”