ALS: a disease of motor neurons and their nonneuronal neighbors.

https://www.cell.com/cell-reports/pdf/S2211-1247(14)00197-1.pdf

Intrinsic Membrane Hyperexcitability of Amyotrophic Lateral Sclerosis Patient-Derived Motor Neurons

Amyotrophic lateral sclerosis (ALS) is a devastating and fatal neurodegenerative disease of adults which preferentially attacks the neuromotor system Riluzole has been used as the only approved treatment for amyotrophic lateral sclerosis since 1995, but its mechanism(s) of action in slowing the progression of this disease remain obscure Searching PubMed for "riluzole" found 705 articles published between January 1996 and June 2009 A systematic review of this literature found that riluzole had a wide range of effects on factors influencing neural activity in general, and the neuromotor system in particular These effects occurred over a large dose range ( 1 mM) Reported neural effects of riluzole included (in approximate ascending order of dose range): inhibition of persistent Na+ current = inhibition of repetitive firing < potentiation of calcium-dependent K+ current < inhibition of neurotransmitter release < inhibition of fast Na+ current < inhibition of voltage-gated Ca2+ current = promotion of neuronal survival or growth factors < inhibition of voltage-gated K+ current = modulation of two-pore K+ current = modulation of ligand-gated neurotransmitter receptors = potentiation of glutamate transporters Only the first four of these effects commonly occurred at clinically relevant concentrations of riluzole (plasma levels of 1-2 mu M with three- to four-fold higher concentrations in brain tissue) Treatment of human ALS patients or transgenic rodent models of ALS with riluzole most commonly produced a modest but significant extension of lifespan Riluzole treatment was well tolerated in humans and animals In animals, despite in vitro evidence that riluzole may inhibit rhythmic motor behaviors, in vivo administration of riluzole produced relatively minor effects on normal respiration parameters, but inhibited hypoxia-induced gasping This effect may have implications for the management of hypoventilation and sleep-disordered breathing during end-stage ALS in humans

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A Review of the Neural Mechanisms of Action and Clinical Efficiency of Riluzole in Treating Amyotrophic Lateral Sclerosis: What have we Learned in the Last Decade?

The mechanisms of human mutant superoxide dismutase-1 (mSOD1) toxicity to motor neurons (MNs) are unresolved. We show that MNs in G93A-mSOD1 transgenic mice undergo slow degeneration lacking similarity to apoptosis structurally and biochemically. It is characterized by somal and mitochondrial swelling and formation of DNA single-strand breaks prior to double-strand breaks occurring in nuclear and mitochondrial DNA. p53 and p73 are activated in degenerating MNs, but without nuclear import. The MN death is independent of activation of caspases-1, -3, and -8 or apoptosis-inducing factor within MNs, with a blockade of apoptosis possibly mediated by Aven up-regulation. MN swelling is associated with compromised Na,K-ATPase activity and aggregation. mSOD1 mouse MNs accumulate mitochondria from the axon terminals and generate higher levels of superoxide, nitric oxide, and peroxynitrite than MNs in control mice. Nitrated and aggregated cytochrome c oxidase subunit-I and α-synuclein as well as nitrated SOD2 accumulate in mSOD1 mouse spinal cord. Mitochondria in mSOD1 mouse MNs accumulate NADPH diaphorase and inducible nitric oxide synthase (iNOS)-like immunoreactivity, and iNOS gene deletion extends significantly the life span of G93A-mSOD1 mice. Prior to MN loss, spinal interneurons degenerate. These results identify novel mechanisms for mitochondriopathy and MN degeneration in amyotrophic lateral sclerosis (ALS) mice involving blockade of apoptosis, accumulation of MN mitochondria with enhanced toxic potential from distal terminals, NOS localization in MN mitochondria and peroxynitrite damage, and early degeneration of α-synuclein+ interneurons. The data support roles for oxidative stress, protein nitration and aggregation, and excitotoxicity as participants in the process of MN degeneration caused by mSOD1. J. Comp. Neurol. 500:20–46, 2007. © 2006 Wiley-Liss, Inc.

Motor neuron degeneration in amyotrophic lateral sclerosis mutant superoxide dismutase-1 transgenic mice: mechanisms of mitochondriopathy and cell death.

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease for which a greater understanding of early disease mechanisms is needed to reveal novel therapeutic targets. We report the use of human induced pluripotent stem cell (iPSC)-derived motoneurons (MNs) to study the pathophysiology of ALS. We demonstrate that MNs derived from iPSCs obtained from healthy individuals or patients harbouring TARDBP or C9ORF72 ALS-causing mutations are able to develop appropriate physiological properties. However, patient iPSC-derived MNs, independent of genotype, display an initial hyperexcitability followed by progressive loss of action potential output and synaptic activity. This loss of functional output reflects a progressive decrease in voltage-activated Na(+) and K(+) currents, which occurs in the absence of overt changes in cell viability. These data implicate early dysfunction or loss of ion channels as a convergent point that may contribute to the initiation of downstream degenerative pathways that ultimately lead to MN loss in ALS.

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Human iPSC-derived motoneurons harbouring TARDBP or C9ORF72 ALS mutations are dysfunctional despite maintaining viability

Altered excitability of motor neurons in a transgenic mouse model of familial amyotrophic lateral sclerosis.

α-amino-3-hydroxy-5-methyl-isoxazole-4-propionate receptors in spinal cord motor neurons are altered in transgenic mice overexpressing human Cu,Zn superoxide dismutase (Gly93→Ala) mutation

The action of the neuroprotective and anticonvulsant agent riluzole on kainate-induced currents was studied in rat cortical neurons in primary culture by using the whole-cell configuration of the patch-clamp technique. Kainate elicited macroscopic, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX)-sensitive inward currents in all the patched cells and the amplitude of the current was concentration-dependent (EC50= 106 μM). Riluzole decreased the inward currents induced by 100 μM kainate at all holding potentials and the reduction was dose-dependent (IC50= 101 μM). The maximal response to kainate decreased in the presence of 50 μM riluzole, without changing its EC50, indicating a noncompetitive mechanism of inhibition. The amplitude of the responses induced by kainate under control conditions and during riluzole was a linear function of the membrane potential and the reversal potential of the currents was not significantly different in the two experimental conditions. Instead, the total conductance of the cell membrane for the currents induced by 100 μM kainate was significantly reduced in the presence of 50 μM riluzole (P < 0.05). The analysis of the kainate membrane current noise performed under control conditions and during perfusion of 100 μM riluzole revealed that riluzole reduced the probability of kainate-activated ionic channels to be in the open state. Conversely, the unitary conductance of channels, as well as their characteristic time constant, seemed to be unchanged. These results reveal an additional mechanism by which riluzole can interact with glutamatergic neurotransmission and provides further support for the idea that riluzole may prove beneficial in the treatment of central nervous system injuries involving the excitotoxic actions of glutamate. Synapse 43:244–251, 2002. © 2002 Wiley-Liss, Inc.

Chiara Gaetti

Papers

Altered excitability of motor neurons in a transgenic mouse model of familial amyotrophic lateral sclerosis.

α-amino-3-hydroxy-5-methyl-isoxazole-4-propionate receptors in spinal cord motor neurons are altered in transgenic mice overexpressing human Cu,Zn superoxide dismutase (Gly93→Ala) mutation

Kainate-induced currents in rat cortical neurons in culture are modulated by riluzole.