SPEG Activation to Regulate Sarcoplasmic Reticulum in Muscle Disease

Authors

Lauren Nguyen, Rice UniversityFollow
Sara Kondamadugula, University of HoustonFollow
Ting Chang, Baylor College of MedicineFollow
Susan Hamilton, Baylor College of MedicineFollow

Abstract

Sarcoplasmic reticulum (SR) Ca²⁺ leak contributes to many muscle diseases, including Duchenne Muscle Dystrophy (DMD) and Malignant Hyperthermia (MH) with enhanced sensitivity to heat stroke. Recently, we demonstrated that the striated muscle preferentially expressed protein kinase, SPEG, decreases SR Ca²⁺ leak by phosphorylating Ser2902 on the Ca²⁺ release channel (also known as the ryanodine receptor 1, RYR1). While SPEG is activated in response to increased leak, the mechanisms of this activation are unknown. In addition, this compensatory mechanism is overwhelmed in the disease states associated with excessive Ca²⁺ leak. Increasing SPEG activation could potentially be beneficial for treating these muscle disorders. However, the mechanisms of SPEG activation remain to be fully elucidated. PURPOSE: The goal of this study was to identify the mechanism of activation of the SPEG pathway to shut down Ca²⁺ leak. SR Ca²⁺ leak activates various Ca²⁺ -dependent kinases (CaMKII) and increases muscle metabolism (increased AMP/ATP). METHODS: To determine if the metabolic changes activate SPEG, we used 2-deoxy-D-glucose (2-DOG), a glycolytic inhibitor, to further increase the AMP/ATP ratio. Wild-type mice were incubated in vitro with 2-DOG. Muscle lysates were analyzed by immunoblotting for RyR1 phosphorylation at Ser2902, total RyR1, and SPEG protein abundance. We also treated a mouse model (Y524S mutation in RYR1, YS) of enhanced sensitivity to heat stroke and MH with 2-DOG to determine if this decreased their heat sensitivity. RESULTS: In vitro exposure to 2-DOG in WT mice significantly increased SPEG protein levels (↑359%, p2+/metabolic rate and serves to limit SR Ca²⁺ leak. Drugs that further activate or stabilize SPEG may be able to prolong its protective effects and be useful for treating these RYR1 Ca²⁺ leak-mediated myopathies. CONCLUSION: These findings demonstrate that glycolytic inhibition with 2-DOG activates SPEG, increases SPEG levels, and increases RyR1 phosphorylation in skeletal muscle. 2-DOG also decreases the sensitivity of YS mice to heat stroke. Ongoing ex vivo studies will be used to identify the muscle-specific mechanisms upstream of SPEG activation.

Recommended Citation

Nguyen, Lauren; Kondamadugula, Sara; Chang, Ting; and Hamilton, Susan (2026) "SPEG Activation to Regulate Sarcoplasmic Reticulum in Muscle Disease," International Journal of Exercise Science: Conference Proceedings: Vol. 2: Iss. 18, Article 95.
Available at: https://digitalcommons.wku.edu/ijesab/vol2/iss18/95