Endoplasmic reticulum stress and the ER mitochondria calcium cycle in amyotrophic lateral sclerosis

Abstract

The endoplasmic reticulum (ER) is a multifunctional organelle involved in protein synthesis, processing and folding, in intracellular transport and calcium signalling. ER stress can be triggered by depletion of ER calcium content and the accumulation of un- and mis-folded proteins, and relays stress signals to the ER mitochondria calcium cycle (ERMCC) and to the nucleus and protein translation machinery. The ensuing unfolded protein response (UPR) helps to cope with ER stress. Total protein synthesis is inhibited to keep protein load low, while the synthesis of ER chaperones, which assist protein folding, is induced. If cell integrity cannot be restored, signal cascades mediating cell death are activated. This review focuses on the role of ER stress and the UPR in the pathology of amyotrophic lateral sclerosis (ALS). The triggers for ER stress are as yet unclear, but induction of UPR sensor proteins, up-regulation of chaperones and induction of cell death proteins have been described in human post mortem ALS tissue and in mutant superoxide dismutase-1 (SOD1) expressing models of ALS. TDP-43 and VAPB seem to be involved in UPR signalling as well. Recent reports raise hope that UPR sensor proteins become effective therapeutic targets in the treatment of ALS.

Key words::

• Amyotrophic lateral sclerosis
• ER stress
• unfolded protein response
• calcium dysregulation
• TDP-43

Acknowledgements

This research is supported by a BMBF (the Bundesministerium für Bildung und Forschung) grant to JG (ERMCC-NDEG) in the framework of the ERANET-NEURON program of the European Union, and a grant from the interdisciplinary centre of clinical research (IZKF) of the University Hospital Jena to TP.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.