Pathophysiological Effects of Overactive STIM1 on Murine Muscle Function and Structure.

Roberto Silva-Rojas,Anne-Laure Charles,Sarah Djeddi,Johann Böhm,Jocelyn Laporte,Bernard Geny

doi:10.3390/cells10071730

Abstract

Store-operated Ca2+ entry (SOCE) is a ubiquitous mechanism regulating extracellular Ca2+ entry to control a multitude of Ca2+-dependent signaling pathways and cellular processes. SOCE relies on the concerted activity of the reticular Ca2+ sensor STIM1 and the plasma membrane Ca2+ channel ORAI1, and dysfunctions of these key factors result in human pathologies. STIM1 and ORAI1 gain-of-function (GoF) mutations induce excessive Ca2+ influx through SOCE over-activation, and cause tubular aggregate myopathy (TAM) and Stormorken syndrome (STRMK), two overlapping disorders characterized by muscle weakness and additional multi-systemic signs affecting growth, platelets, spleen, skin, and intellectual abilities. In order to investigate the pathophysiological effect of overactive SOCE on muscle function and structure, we combined transcriptomics with morphological and functional studies on a TAM/STRMK mouse model. Muscles from Stim1R304W/+ mice displayed aberrant expression profiles of genes implicated in Ca2+ handling and excitation-contraction coupling (ECC), and in vivo investigations evidenced delayed muscle contraction and relaxation kinetics. We also identified signs of reticular stress and abnormal mitochondrial activity, and histological and respirometric analyses on muscle samples revealed enhanced myofiber degeneration associated with reduced mitochondrial respiration. Taken together, we uncovered a molecular disease signature and deciphered the pathomechanism underlying the functional and structural muscle anomalies characterizing TAM/STRMK.

Highlights

Calcium (Ca2+) is a ubiquitous second messenger implicated in the regulation of fundamental adaptive and developmental processes in all cell types
In order to determine the sequence of events leading to the muscle phenotype in Stim1R304W/+ mice, we performed transcriptomic analyses on fast-twitch and slow-twitch muscles, and we identified major dysregulations of genes implicated in intracellular Ca2+ handling, excitation-contraction coupling (ECC), unfolded protein response (UPR), and mitochondrial dynamics
To shed light on the molecular pathways affected by overactive STIM1 and to decipher the sequence of events leading to the muscle phenotype, we generated gene expression profiles through RNAseq on tibialis anterior muscle extracts from Stim1R304W/+ mice and WT littermates

Summary

Introduction

Calcium (Ca2+) is a ubiquitous second messenger implicated in the regulation of fundamental adaptive and developmental processes in all cell types. TAM/STRMK arises from dominant gain-of-function (GoF) mutations in the Ca2+ sensor STIM1 and the Ca2+ channel ORAI1, and milder adult-onset cases with exclusive muscle involvement have been associated with mutations in the Ca2+ buffer calsequestrin (CASQ1) [8,9,10,11]. Functional investigations in the cellular model have shown that the STIM1 and ORAI1 mutations lead to excessive cytosolic Ca2+ levels through SOCE over-activation [9,11,13,14,15,16,17,18,19], and a recently reported TAM/STRMK mouse model harboring the most common STIM1 mutation p.Arg304Trp (R304W) was shown to exhibit elevated cytosolic Ca2+ levels in skeletal muscle and to recapitulate the main clinical signs of the human disorder including muscle weakness, thrombocytopenia, smaller size, and eye, skin, and spleen anomalies [20]. The precise molecular and cellular effect of overactive STIM1 and the associated Ca2+ excess on muscle function and structure remain elusive

Methods

Results

Discussion

Conclusion