ORAI1 inhibition as an efficient preclinical therapy for tubular aggregate myopathy and Stormorken syndrome
Roberto Silva-Rojas, Laura Pérez-Guàrdia, Alix Simon, Sarah Djeddi, Susan Treves, Agnès Ribes, Lorenzo Silva-Hernández, Céline Tard, Jocelyn Laporte, Johann Böhm
Roberto Silva-Rojas, Laura Pérez-Guàrdia, Alix Simon, Sarah Djeddi, Susan Treves, Agnès Ribes, Lorenzo Silva-Hernández, Céline Tard, Jocelyn Laporte, Johann Böhm
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Research Article Muscle biology Therapeutics

ORAI1 inhibition as an efficient preclinical therapy for tubular aggregate myopathy and Stormorken syndrome

Abstract

Tubular aggregate myopathy (TAM) and Stormorken syndrome (STRMK) are clinically overlapping disorders characterized by childhood-onset muscle weakness and a variable occurrence of multisystemic signs, including short stature, thrombocytopenia, and hyposplenism. TAM/STRMK is caused by gain-of-function mutations in the Ca2+ sensor STIM1 or the Ca2+ channel ORAI1, both of which regulate Ca2+ homeostasis through the ubiquitous store-operated Ca2+ entry (SOCE) mechanism. Functional experiments in cells have demonstrated that the TAM/STRMK mutations induce SOCE overactivation, resulting in excessive influx of extracellular Ca2+. There is currently no treatment for TAM/STRMK, but SOCE is amenable to manipulation. Here, we crossed Stim1R304W/+ mice harboring the most common TAM/STRMK mutation with Orai1R93W/+ mice carrying an ORAI1 mutation partially obstructing Ca2+ influx. Compared with Stim1R304W/+ littermates, Stim1R304W/+Orai1R93W/+ offspring showed a normalization of bone architecture, spleen histology, and muscle morphology; an increase of thrombocytes; and improved muscle contraction and relaxation kinetics. Accordingly, comparative RNA-Seq detected more than 1,200 dysregulated genes in Stim1R304W/+ muscle and revealed a major restoration of gene expression in Stim1R304W/+Orai1R93W/+ mice. Altogether, we provide physiological, morphological, functional, and molecular data highlighting the therapeutic potential of ORAI1 inhibition to rescue the multisystemic TAM/STRMK signs, and we identified myostatin as a promising biomarker for TAM/STRMK in humans and mice.

Authors

Roberto Silva-Rojas, Laura Pérez-Guàrdia, Alix Simon, Sarah Djeddi, Susan Treves, Agnès Ribes, Lorenzo Silva-Hernández, Céline Tard, Jocelyn Laporte, Johann Böhm

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Figure 3

Resolved myofiber degeneration and ER stress in Stim1R304W/+Orai1R93W/+ muscle.

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Resolved myofiber degeneration and ER stress in Stim1R304W/+Orai1R93W/+ ...
(A) H&E staining of tibialis anterior sections from 4-month-old Stim1R304W/+ mice revealed internalized nuclei (blue arrow), regenerating fibers (green arrow), and immune cell infiltrations (black arrow), while the Stim1R304W/+Orai1R93W/+ histology was indistinguishable from that of the WT and Orai1R93W/+ controls (representative images, n = 5–7). Immunofluorescence detected prominent embryonic myosin (eMHC) signals, indicating regenerating fibers in Stim1R304W/+ muscle sections and, to a much lesser extent, in WT, Orai1R93W/+, and Stim1R304W/+Orai1R93W/+ myofibers. Scale bar: 50 μm (representative images, n = 5–7). (B) Quantification of myofibers with internal nuclei showed an increased ratio in Stim1R304W/+ tibialis anterior compared with WT, Orai1R93W/+, and Stim1R304W/+Orai1R93W/+ muscle sections (n = 5–8, 1-way ANOVA and Tukey’s post hoc test). (C) Serum creatine kinase levels were significantly reduced in 4-month-old Stim1R304W/+Orai1R93W/+ blood compared with Stim1R304W/+ samples (n = 4–6, 1-way ANOVA and Tukey’s post hoc test). (D) Quantification of eMHC signals disclosed an enhanced proportion of regenerating myofibers in Stim1R304W/+ mice and a complete normalization in Stim1R304W/+Orai1R93W/+ mice (n = 6–8, Kruskal-Wallis and Dunn’s multiple comparison test). (E) The expression of the UPR markers Hspa5 and Hsp90b1 and the ratio of spliced/unspliced Xbp1 were comparable in muscle extracts from Stim1R304W/+Orai1R93W/+ mice and healthy WT and Orai1R93W/+ controls (n = 5–7, 1-way ANOVA and Tukey’s post hoc test). Data are shown as the mean ± SEM. Significant differences are indicated as *,α,$P < 0.05, **,αα,$$P < 0.01, ααα,$$$P < 0.001, and ****,αααα,$$$$P < 0.0001, with * reflecting comparison of Stim1R304W/+ with the WT group, α comparison with the Orai1R93W/+ group, and $ the comparison with Stim1R304W/+Orai1R93W/+ group.