Sigma 1 receptor activation modifies intracellular calcium exchange in the G93A^hSOD1 ALS model

Aberrations in intracellular calcium (Ca²⁺) have been well established within amyotrophic lateral sclerosis (ALS), a severe motor neuron disease. Intracellular Ca²⁺ concentration is controlled in part through the endoplasmic reticulum (ER) mitochondria Ca²⁺ cycle (ERMCC). The ER supplies Ca²⁺ to the mitochondria at close contacts between the two organelles, i.e. the mitochondria-associated ER membranes (MAMs). The Sigma 1 receptor (Sig1R) is enriched at MAMs, where it acts as an inter-organelle signaling modulator. However, its impact on intracellular Ca²⁺ at the cellular level remains to be thoroughly investigated. Here, we used cultured embryonic mice spinal neurons to investigate the influence of Sig1R activation on intracellular Ca²⁺ homeostasis in the presence of G93A^hSOD1 (G93A), an established ALS-causing mutation. Sig1R expression was increased in G93A motor neurons relative to non-transgenic (nontg) controls. Furthermore, we demonstrated significantly reduced bradykinin-sensitive intracellular Ca²⁺ stores in G93A spinal neurons, which were normalized by the Sig1R agonist SA4503. Moreover, SA4503 accelerated cytosolic Ca²⁺ clearance following a) AMPAR activation by kainate and b) IP₃R–mediated ER Ca²⁺ release following bradykinin stimulation in both genotypes. PRE-084 (another Sig1R agonist) did not exert any significant effects on cytosolic Ca²⁺. Both Sig1R expression and functionality were altered by the G93A mutation, indicating the centrality of Sig1R in ALS pathology. Here, we showed that intracellular Ca²⁺ shuttling can be manipulated by Sig1R activation, thus demonstrating the value of using the pharmacological manipulation of Sig1R to understand Ca²⁺ homeostasis.