Intracellular calcium leak as a therapeutic target for RYR1-related myopathies

Area of Science:

• Muscle Physiology
• Molecular Biology
• Genetics

Background:

• RYR1 gene mutations cause rare neuromuscular disorders known as RYR1-related myopathies (RYR1-RM).
• These mutations can lead to abnormal calcium release (leak) from the sarcoplasmic reticulum (SR) in skeletal muscle, potentially causing myopathy.
• The direct impact of RyR1 leak in RYR1-RM patients and the correlation between variant location and disease severity remain unclear.

Purpose of the Study:

• To investigate whether individuals with RYR1-RM exhibit pathological RyR1 calcium leak.
• To determine if the location of RYR1 variants within the channel structure can predict pathogenicity.
• To explore the therapeutic potential of RyR1-stabilizing molecules.

Main Methods:

• Skeletal muscle biopsies from 17 RYR1-RM patients were analyzed.
• RyR1 calcium leak and protease activity were measured.
• Ex-vivo treatment with S107, a Rycal molecule, was used to assess its effect on RyR1 function.
• A predictive tool was developed using cryo-EM structures and a large dataset of RYR1 variants to assign pathogenicity probabilities.

Main Results:

• Mutant RyR1 in RYR1-RM patients demonstrated pathological SR calcium leak and increased calcium-activated protease activity.
• Ex-vivo treatment with S107 successfully normalized both the calcium leak and protease activity.
• A novel method was established to predict RYR1 variant pathogenicity based on 3D structural localization.

Conclusions:

• Pathological RyR1 calcium leak is a key feature in RYR1-related myopathies.
• Rycal molecules, like S107, show promise in stabilizing RyR1 and normalizing its function.
• The developed predictive tool can aid in understanding the significance of RYR1 variants of uncertain significance and guide clinical trials.