Calcium dysregulation in amyotrophic lateral sclerosis

In the fatal neurodegenerative disease amyotrophic lateral sclerosis (ALS), motor neurons degenerate with signs of organelle fragmentation, free radical damage, mitochondrial Ca²⁺ overload, impaired axonal transport and accumulation of proteins in intracellular inclusion bodies. Subgroups of motor neurons of the brainstem and the spinal cord expressing low amounts of Ca²⁺ buffering proteins are particularly vulnerable. In ALS, chronic excitotoxicity mediated by Ca²⁺-permeable AMPA type glutamate receptors seems to initiate a self-perpetuating process of intracellular Ca²⁺ dysregulation with consecutive endoplasmic reticulum Ca²⁺ depletion and mitochondrial Ca²⁺ overload. The only known effective treatment, riluzole, seems to reduce glutamatergic input. This review introduces the hypothesis of a "toxic shift of Ca²⁺" within the endoplasmic reticulum-mitochondria Ca²⁺ cycle (ERMCC) as a key mechanism in motor neuron degeneration, and discusses molecular targets which may be of interest for future ERMCC modulating neuroprotective therapies.