Postdevelopmental knockout of Orai1 improves muscle pathology in a mouse model of Duchenne muscular dystrophy

Abstract

Duchenne muscular dystrophy (DMD), an X-linked disorder caused by loss-of-function mutations in the dystrophin gene, is characterized by progressive muscle degeneration and weakness. Enhanced store-operated Ca2+ entry (SOCE), a Ca2+ influx mechanism coordinated by STIM1 sensors of luminal Ca2+ within the sarcoplasmic reticulum (SR) and Ca2+-permeable Orai1 channels in the sarcolemma, is proposed to contribute to Ca2+-mediated muscle damage in DMD. To directly determine the impact of Orai1-dependent SOCE on the dystrophic phenotype, we crossed mdx mice with tamoxifen-inducible, muscle-specific Orai1 knockout mice (mdx-Orai1 KO mice). Both constitutive and SOCE were significantly increased in flexor digitorum brevis fibers from mdx mice, while SOCE was absent in fibers from both Orai1 KO and mdx-Orai1 KO mice. Compared with WT mice, fibers from mdx mice exhibited (1) increased resting myoplasmic Ca2+ levels, (2) reduced total releasable Ca2+ store content, and (3) a prolonged rate of electrically evoked Ca2+ transient decay. These effects were partially normalized in fibers from mdx-Orai1 KO mice. Intact extensor digitorum longus muscles from mdx mice exhibited a significant reduction of maximal specific force, which was rescued in muscles from mdx-Orai1 KO mice. Finally, during exposure to consecutive eccentric contractions, muscles from mdx mice displayed a more pronounced decline in specific force compared with that of WT mice, which was also significantly attenuated by Orai1 ablation. Together, these results indicate that enhanced Orai1-dependent SOCE exacerbates the dystrophic phenotype and that Orai1 deficiency improves muscle pathology by both normalizing Ca2+ homeostasis and promoting sarcolemmal integrity/stability.

Constitutive assembly of Ca2+ entry units in soleus muscle from calsequestrin knockout mice

“…Thus, a three- to fourfold increase in Orai1 expression could result in an increase in SOCE function even in the absence of a detectable change in STIM1 expression. Consistent with this, using a murine model of Duchenne muscular dystrophy in which SOCE activity is increased, several studies showed that this increase in SOCE correlates with a significant increment of Orai1 expression in the absence of a change in STIM1 expression ( Edwards et al, 2010 ; Zhao et al, 2012 ; Goonasekera et al, 2014 ; García-Castañeda et al, 2022 ). However, other studies have reported a significant increase in STIM1S expression in muscles from mdx mice ( Edwards et al, 2010 ; Cully et al, 2012 ).…”

Loss of calpain 3 dysregulates store-operated calcium entry and its exercise response in mice

“…Resting cytosolic Ca 2+ levels were significantly higher in FDB fibers isolated from 6 month old C3KO mice (Fig. 1A), suggesting intracellular Ca 2+ overload as a mechanism contributing to the dystrophic pathology in LGMD2A, as it was shown with other types of muscular dystrophies (25)(26)(27). This difference was age-dependent, as there were no differences in resting cytosolic Ca 2+ levels at 8 weeks of age (Indo-1 Ratio405/485: C3KO 0.4±0.01; WT 0.4±0.01; mean ± SEM for N=4-6 mice; P=0.94, unpaired t test), paralleling the late-onset and progressive nature of…”

Ion Channels of the Sarcolemma and Intracellular Organelles in Duchenne Muscular Dystrophy: A Role in the Dysregulation of Ion Homeostasis and a Possible Target for Therapy

“…In addition, breeding transgenic mice expressing the dominant-negative mutant Orai1 (dnOrai1) with mdx mice resulted in a significant improvement in mouse skeletal muscle histopathology, further supporting the involvement of STIM1-Orai1 in the progression of DMD [74]. A recent study also showed that crossing mdx mice with muscle-specific Orai1 knockout mdx mice (mdx-Orai1 KO mice) also resulted in normalizing Ca 2+ homeostasis and promoting sarcolemmal integrity/stability [76].…”