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Updated: Jul 21, 2026
Modeling Charcot-Marie-Tooth Disease In Vitro by Transfecting Mouse Primary Motoneurons
Published on: January 7, 2019
Chronic activation in presymptomatic amyotrophic lateral sclerosis (ALS) mice of a feedback loop involving Fas, Daxx,
1Ecole Polytechnique Fédérale de Lausanne (EPFL), Integrative Biosciences Institute, SV IBI LEN, AAB 1 32, CH-1015 Lausanne, Switzerland.
Abstract:
The reasons for the cellular specificity and slow progression of motoneuron diseases such as ALS are still poorly understood. We previously described a motoneuron-specific cell death pathway downstream of the Fas death receptor, in which synthesis of nitric oxide (NO) is an obligate step. Motoneurons from ALS model mice expressing mutant SOD1 showed increased susceptibility to exogenous NO as compared with controls. Here, we report a signaling mechanism whereby NO leads to death of mutant, but not control, motoneurons. Unexpectedly, exogenous NO triggers expression of Fas ligand (FasL) in cultured motoneurons. In mutant SOD1(G93A) and SOD1(G85R), but not in control motoneurons, this up-regulation results in activation of Fas, leading through Daxx to phosphorylation of p38 and further NO synthesis. This Fas/NO feedback amplification loop is required for motoneuron death in vitro. In vivo, mutant SOD1(G93A) and SOD1(G85R) mice show increased numbers of positive motoneurons and Daxx nuclear bodies weeks before disease onset. Moreover, FasL up-regulation is reduced in the presence of transgenic dominant-negative Daxx. We propose that chronic low-level activation of the Fas/NO feedback loop may underlie the motoneuron loss that characterizes familial ALS and may help to explain its slowly progressive nature.
Insights
Nitric oxide (NO) triggers a death pathway in mutant SOD1 motoneurons by upregulating Fas ligand (FasL). This Fas/NO feedback loop, involving Daxx and p38, causes motoneuron death and may explain familial ALS progression.
Area of Science:
- Neuroscience
- Cell Biology
- Molecular Biology
Background:
- Motoneuron diseases like Amyotrophic Lateral Sclerosis (ALS) exhibit cellular specificity and slow progression, with underlying mechanisms poorly understood.
- A previously identified motoneuron-specific cell death pathway involves the Fas death receptor and nitric oxide (NO) synthesis.
- Motoneurons from ALS model mice with mutant SOD1 are more susceptible to exogenous NO compared to controls.
Purpose of the Study:
- To elucidate the signaling mechanism by which NO induces death in mutant motoneurons.
- To investigate the role of the Fas/NO pathway in motoneuron degeneration in vitro and in vivo.
- To explore the potential contribution of this pathway to the pathogenesis of familial ALS.
Main Methods:
- Cultured motoneurons from wild-type and mutant SOD1 (G93A, G85R) mice were treated with exogenous NO.
- Expression of Fas ligand (FasL) and activation of downstream signaling molecules (Daxx, p38) were assessed.
- In vivo studies involved analyzing motoneurons and Daxx nuclear bodies in mutant SOD1 mice before disease onset.
- The effect of dominant-negative Daxx on FasL up-regulation was examined.
Main Results:
- Exogenous NO unexpectedly triggered FasL expression in cultured motoneurons.
- This up-regulation led to Fas activation, Daxx involvement, p38 phosphorylation, and subsequent NO synthesis specifically in mutant SOD1 motoneurons.
- A Fas/NO feedback amplification loop was identified as essential for motoneuron death in vitro.
- Mutant SOD1 mice exhibited increased FasL and Daxx nuclear bodies weeks before clinical signs of disease.
- Dominant-negative Daxx expression reduced FasL up-regulation in vivo.
Conclusions:
- A novel signaling mechanism reveals that NO induces death in mutant SOD1 motoneurons via a Fas/NO feedback loop.
- This loop, involving FasL, Daxx, p38, and NO synthesis, is crucial for motoneuron degeneration.
- Chronic, low-level activation of this Fas/NO feedback loop is proposed as a key factor in motoneuron loss and slow progression in familial ALS.
