Activating ATF6 in spinal muscular atrophy promotes SMN expression and motor neuron survival through the IRE1α‐XBP1 pathway

• Published in: Neuropathology and applied neurobiology 2022-08, Vol.48 (5), p.e12816-n/a
• Main Authors: D'Amico, Domenico, Biondi, Olivier, Januel, Camille, Bezier, Cynthia, Sapaly, Delphine, Clerc, Zoé, El Khoury, Mirella, Sundaram, Venkat Krishnan, Houdebine, Léo, Josse, Thibaut, Della Gaspera, Bruno, Martinat, Cécile, Massaad, Charbel, Weill, Laure, Charbonnier, Frédéric
• Format: Article
• Language: English
• Subjects: Animal models; Atrophy; Cell culture; Degeneration; Fibroblasts; Gene therapy; IRE1α; Life Sciences; Myoblasts; Neuromuscular diseases; Neuroprotection; Patients; Protein folding; SMN; SMN protein; Spinal muscular atrophy; unfolded protein response; Western blotting; XBP1
• ISSN: 0305-1846; 1365-2990
• DOI: 10.1111/nan.12816

Aim Spinal muscular atrophy (SMA) is a neuromuscular disease caused by survival of motor neuron (SMN) deficiency that induces motor neuron (MN) degeneration and severe muscular atrophy. Gene therapies that increase SMN have proven their efficacy but not for all patients. Here, we explored the unfolded protein response (UPR) status in SMA pathology and explored whether UPR modulation could be beneficial for SMA patients. Methods We analysed the expression and activation of key UPR proteins by RT‐qPCR and by western blots in SMA patient iPSC‐derived MNs and one SMA cell line in which SMN expression was re‐established (rescue). We complemented this approach by using myoblast and fibroblast SMA patient cells and SMA mouse models of varying severities. Finally, we tested in vitro and in vivo the effect of IRE1α/XBP1 pathway restoration on SMN expression and subsequent neuroprotection. Results We report that the IRE1α/XBP1 branch of the unfolded protein response is disrupted in SMA, with a depletion of XBP1s irrespective of IRE1α activation pattern. The overexpression of XBP1s in SMA fibroblasts proved to transcriptionally enhance SMN expression. Importantly, rebalancing XBP1s expression in severe SMA‐like mice, induced SMN expression and spinal MN protection. Conclusions We have identified XBP1s depletion as a contributing factor in SMA pathogenesis, and the modulation of this transcription factor proves to be a plausible therapeutic avenue in the context of pharmacological interventions for patients. We investigated the statue of UPR in SMA and show a decrease of XPB1s expression despite IREα overactivation. The activation ATF6 with AA147 increases the transcription of XBP1u mRNA, the substrate of IREα. This increase compensates the ineffective splicing of XPB1s in SMA despite IREα overactivation and enhances the XBP1s expression. Therefore, XBP1s translocates in the nucleus and activates directly SMN2 gene. Heightening SMN expression leads therefore to MN protection and motor behaviour improving.