Remodeling of ryanodine receptor complex causes “leaky” channels: A molecular mechanism for decreased exercise capacity

Abstract

During exercise, defects in calcium (Ca 2؉ ) release have been proposed to impair muscle function. Here, we show that during exercise in mice and humans, the major Ca 2؉ release channel required for excitationcontraction coupling (ECC) in skeletal muscle, the ryanodine receptor (RyR1), is progressively PKA-hyperphosphorylated, S-nitrosylated, and depleted of the phosphodiesterase PDE4D3 and the RyR1 stabilizing subunit calstabin1 (FKBP12), resulting in ''leaky'' channels that cause decreased exercise tolerance in mice. Mice with skeletal musclespecific calstabin1 deletion or PDE4D deficiency exhibited significantly impaired exercise capacity. A small molecule (S107) that prevents depletion of calstabin1 from the RyR1 complex improved force generation and exercise capacity, reduced Ca 2؉ -dependent neutral protease calpain activity and plasma creatine kinase levels. Taken together, these data suggest a possible mechanism by which Ca 2؉ leak via calstabin1-depleted RyR1 channels leads to defective Ca 2؉ signaling, muscle damage, and impaired exercise capacity. muscle fatigue ͉ calcium channel ͉ calstabin ͉ exitation-contraction coupling ͉ rycals

nNOS regulation of skeletal muscle fatigue and exercise performance

“…Bellinger et al (2008) observed that depletion of both PDE4D3 and FKBP12 led to impaired exercise performance. Exercise led to a progressive increase in RyR1 nitrosylation that was thought to promote FKBP12 disassociation, correlating well with expected increases in nNOSμ expression and activity.…”

“…The cytoplasmic amino terminus of RyR1 acts as a scaffold for regulatory proteins such as calstabin1, also known as FK506 binding protein 12 (FKBP12) (Kushnir et al 2010). FKBP12 is required for normal exercise performance and is thought to stabilize RyR1 by increasing its closed state probability, thereby preventing "Ca 2+ leak" (Bellinger et al 2008). Pathogenic RyR1 Ca 2+ release or a "Ca 2+ leak" can lead to global perturbation of muscle Ca 2+ handling, including depletion of SR Ca 2+ stores and muscle damage and fatigue (Wang et al 2005;Bellinger et al 2008, Figure 1).…”

“…Exercise led to a progressive increase in RyR1 nitrosylation that was thought to promote FKBP12 disassociation, correlating well with expected increases in nNOSμ expression and activity. Reduction of the RyR1-associated FKBP12 association was suggested to destabilize RyR1, leading to the Ca 2+ leak and resulting in protease-mediated muscle damage, weakness, and impaired exercise performance (Aracena et al 2005;Bellinger et al 2008, Figure 1). Although S-nitrosylation of RyR1 reduced the binding affinity of FKBP12 (calstabin1) for RyR1 in vitro, it did not prevent FKBP12 reassociation with the RyR1 complex in vivo (Aracena et al 2005;Bellinger et al 2008).…”

“…Reduction of the RyR1-associated FKBP12 association was suggested to destabilize RyR1, leading to the Ca 2+ leak and resulting in protease-mediated muscle damage, weakness, and impaired exercise performance (Aracena et al 2005;Bellinger et al 2008, Figure 1). Although S-nitrosylation of RyR1 reduced the binding affinity of FKBP12 (calstabin1) for RyR1 in vitro, it did not prevent FKBP12 reassociation with the RyR1 complex in vivo (Aracena et al 2005;Bellinger et al 2008). Interestingly, both RyR2 hyponitrosylation resulting from nNOSμ deficiency and RyR1 hypernitrosylation resulting from excessive nNOS activity promote Ca 2+ leakage (Gonzalez et al 2007;Durham et al 2008).…”

“…During normal exercise, nNOS may be required to appropriately S-nitrosylate RyR1, thus promoting normal Ca 2+ release and fatigue resistance. However, over-training exercise or pathophysiological stress (e.g., chronic activation of the fight-or-flight response or disease) results in excessive RyR1 complex destabilization, causing the Ca 2+ leak (Bellinger et al 2008). Abnormal Ca 2+ release or leakage may also inappropriately lead to pathogenic nNOS activation, causing further oxidative and nitrosative stress including RyR1 hypernitrosylation, which in turn causes more Ca 2+ leakage (in a feed-forward loop), leading to muscle damage, weakness, and exaggerated fatigue (Durham et al 2008, Figure 1).…”