IL-1α Reversibly Inhibits Skeletal Muscle Ryanodine Receptor A Novel Mechanism for Critical Illness Myopathy?

Critical illness myopathies in patients with sepsis or sustained mechanical ventilation prolong intensive care treatment and threaten both patients and health budgets; no specific therapy is available. Underlying pathophysiological mechanisms are still patchy. We characterized IL-1 alpha action on muscle performance in skinned muscle fibers using force transducers and confocal Ca2+ fluorescence microscopy for force/Ca2+ transients and Ca2+ sparks. Association of IL-1 alpha with sarcoplasmic reticulum (SR) release channel, ryanodine receptor (RyR) 1, was investigated with coimmunoprecipitation and confocal immunofluorescence colocalization. Membrane integrity was studied in single, intact fibers challenged with IL-1 alpha. IL-1 alpha reversibly stabilized Mg2+ inhibition of Ca2+ release. Low Mg2+-induced force and Ca2+ transients were reversibly abolished by IL-1 alpha. At normal Mg2+, IL-1 alpha reversibly increased caffeine-induced force and Ca2+ transients. IL-1 alpha reduced SR Ca2+ leak via RyR1, as judged by (1) increased SR Ca2+ retention, (2) increased IL-1 alpha force transients being reproduced by 25 mu M tetracaine, and (3) reduced Ca2+ spark frequencies by IL-1 alpha or tetracaine. Coimmunoprecipitation confirmed RyR1/IL-1 association. RyR1/IL-1 immunofluorescence patterns perfectly colocalized. Long-term, 8-hour IL-1 alpha challenge of intact muscle fibers compromised membrane integrity in approximately 50% of fibers, and confirmed intracellular IL-1 alpha deposition. IL-1 alpha exerts a novel, specific, and reversible interaction mechanism with the skeletal muscle RyR1 macromolecular release complex without the need to act via its membrane IL-1 receptor, as IL-1R membrane expression levels were not detectable in Western blots or immunostaining of single fibers. We present a potential explanation of how the inflammatory mediator, IL-1 alpha, may contribute to muscle weakness in critical illness.