Alexander Chang

Statin therapies, used to lower high blood cholesterol, have been proposed to cause skeletal muscle side effects including myalgia and rhabdomyolysis. The ryanodine receptor 1 (RyR1)/Ca²⁺ release channel in skeletal muscle has recently been identified as an off-target binder of statins. Here, we report the cryo-electron microscopy structure of RyR1 in complex with rosuvastatin. Rosuvastatin occupies a single binding site in the pore region of RyR1 stabilizing the open conformation. In the closed conformation, the rosuvastatin binding site is occupied by the RyR1 auxiliary transmembrane helices (TMx1-2). Structural comparison indicates steric overlap of rosuvastatin with simvastatin (at Sim-1) but not with atorvastatin on RyR1, while all these statins may interfere with the conformational stability of the TMx1-2 helices. In contrast to simvastatin and atorvastatin, rosuvastatin does not exhibit multiple binding sites on RyR1 while similarly promoting RyR1 activation, indicating its potential as a preferable lead structure for developing statins that minimizes adverse side effects on RyR1.

Statins lower cholesterol, reducing the risk of heart disease, and are among the most frequently prescribed drugs. Approximately 10% of individuals develop statin-associated muscle symptoms (SAMS; myalgias, rhabdomyolysis, and muscle weakness), often rendering them statin intolerant. The mechanism underlying SAMS remains poorly understood. Patients with mutations in the skeletal muscle ryanodine receptor 1 (RyR1)/calcium release channel can be particularly intolerant of statins. High-resolution structures revealed simvastatin binding sites in the pore region of RyR1. Simvastatin stabilized the open conformation of the pore and activated the RyR1 channel. In a mouse expressing a mutant RyR1-T4709M found in a patient with profound statin intolerance, simvastatin caused muscle weakness associated with leaky RyR1 channels. Cotreatment with a Rycal drug that stabilizes the channel closed state prevented simvastatin-induced muscle weakness. Thus, statin binding to RyR1 can cause SAMS, and patients with RyR1 mutations may represent a high-risk group for statin intolerance.

BACKGROUND: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a rare inherited arrhythmia, with pathogenic variants in the RYR2 gene responsible for 60% of clinically well-defined CPVT cases. Diagnosis of CPVT often occurs after a major cardiac event, posing a severe threat to the patient’s life. A data set of patients with CPVT would improve the diagnosis and treatment of patients with CPVT. METHODS: This review cataloged clinical data on patients with RYR2 -related CPVT variants from articles published up to October 2020 from PubMed, Scopus, and Embase. Variants were mapped to the structural domains of RYR2. Differences in the age of onset based on variant location and incidence of CPVT symptoms, and differences in treatment strategies were analyzed. RESULTS: In 221 publications analyzed, 964 patients with CPVT (351 male, 463 female) were identified with 263 RYR2 protein-coding variants and a median age of onset of CPVT of 11 years (interquartile range, 7–14 years). A web app was developed to allow users to query the database and is available at https://markslab-cpvtdb.org . The proportion of patients requiring treatments in addition to β-blockers varied between variants. The age of onset of CPVT differed significantly between RYR2 variants located in different exons, domains, and subdomains. Patients with variants in the core solenoid at the domain level, and the core solenoid (exEF-hand) and channel pore at the subdomain level, tended to have a lower age of onset compared with other regions. CONCLUSIONS: This study compiled a comprehensive data set of CPVT-associated RYR2 variants and their clinical phenotypes. The age of onset in certain domains (core solenoid) and subdomains (core solenoid[exEF-hand], channel pore) tended to be lower compared with other regions. Variability in patient phenotypes, such as age of onset and treatment efficacy, along with structural information on variants, suggests that patients may benefit from personalized interventions based on their variant.

S100A1, a small homodimeric EF-hand Ca²⁺-binding protein (~21 kDa), plays an important regulatory role in Ca²⁺signaling pathways involved in various biological functions including Ca²⁺cycling and contractile performance in skeletal and cardiac myocytes. One key target of the S100A1 interactome is the ryanodine receptor (RyR), a huge homotetrameric Ca²⁺release channel (~2.3 MDa) of the sarcoplasmic reticulum. Here, we report cryoelectron microscopy structures of S100A1 bound to RyR1, the skeletal muscle isoform, in absence and presence of Ca²⁺. Ca²⁺-free apo-S100A1 binds beneath the bridging solenoid (BSol) and forms contacts with the junctional solenoid and the shell-core linker of RyR1. Upon Ca²⁺-binding, S100A1 undergoes a conformational change resulting in the exposure of the hydrophobic pocket known to serve as a major interaction site of S100A1. Through interactions of the hydrophobic pocket with RyR1, Ca²⁺-bound S100A1 intrudes deeper into the RyR1 structure beneath BSol than the apo-form and induces sideways motions of the C-terminal BSol region toward the adjacent RyR1 protomer resulting in tighter interprotomer contacts. Interestingly, the second hydrophobic pocket of the S100A1-dimer is largely exposed at the hydrophilic surface making it prone to interactions with the local environment, suggesting that S100A1 could be involved in forming larger heterocomplexes of RyRs with other protein partners. Since S100A1 interactions stabilizing BSol are implicated in the regulation of RyR-mediated Ca²⁺release, the characterization of the S100A1 binding site conserved between RyR isoforms may provide the structural basis for the development of therapeutic strategies regarding treatments of RyR-related disorders.