Basic researchLoss of Fas ligand-function improves survival in G93A-transgenic ALS mice
Introduction
ALS is the most common motor neuron disease in adults with an incidence of two to three per 100,000 leading to rapidly progressive paralysis and muscular wasting due to motor neuron loss in the brain and spinal cord. Ten percent of cases are familial; 10–20% of these are due to mutations in the superoxide dismutase (SOD) 1 gene [1]. Mice overexpressing a human SOD1 mutation, where a glycine is substituted by an alanine at amino acid position 93, show a phenotype closely mimicking human ALS, and serve as a widely used animal model for the disease [2]. The precise molecular mechanisms causing the selective vulnerability of motor neurons in familial as well as sporadic ALS still remain unclear.
Raoul et al. demonstrated a motor neuron-specific pathway triggered by activation of the Fas receptor [3]. Fas (Apo-1/CD95) is a type I membrane protein of the death receptor family which activates the FADD/caspase 8 cascade [3], [4], [5]. Besides the classical FADD/caspase 8 cascade, motor neurons display a second cell death pathway downstream of Fas: binding of FasL which activates a cascade involving Daxx, apoptosis signal-regulating kinase 1 (ASK1), p38 kinase, activation of nNOS and subsequent peroxynitrite formation. This motor neuron specific cell-autonomous pathway is upregulated in motor neurons from transgenic ALS mice overexpressing different SOD1 mutations (G37R, G85A, G93A) [3]. The components of this pathway (ASK1, p38 kinase, nNOS), are also upregulated in vivo in early disease stages in ALS transgenic mice [6], [7], [8]. FasL, Fas and Daxx immunoreactivity are increased in presymptomatic G93A and G85R SOD1 transgenic mice [9]. Therefore, motor neuron degeneration stimulated by Fas-signaling may play a role in mutant SOD1-related familial ALS. Furthermore, in 25% of sporadic ALS-patients, upregulation of serum anti-Fas antibodies has been described [10], and in the spinal cord of ALS patients nNOS immunoreactivity was increased [11].
In the present study, we investigated whether the reduction of endogenous Fas receptor activation via its ligand FasL would have a beneficial effect on motor neuron degeneration in the G93A ALS mouse model. We, therefore, crossed G93A mice with mice carrying a null function mutation in the FasL gene [12] and evaluated if this improved survival, motor performance, cell loss or the levels of components of the Fas-activated cell death pathway.
Section snippets
Transgenic mice
Mice homozygous for a mutation of the FasL gene (B6Smn.C3-Fasl/Jgld) were obtained by the Jackson Laboratories. The FasLgld mutation is a point mutation in the C-terminal region of the Fas ligand gene resulting in loss of function [12]. Their phenotype consists in lymphadenopathy and systemic autoimmunity with significant enlargement of all lymph nodes to 50 times the control weight, an enlarged spleen, greatly increased numbers of T, B, and null lymphocytes and a tendency to develop immune
Results
The average lifespan of mice carrying a high copy number of the human mutant G93A allele with a C57black background was 160 ± 9 days, heterozygous expression of the FasLgld allele (FasL+/−) had no significant effect on the lifespan (the mean survival of this group was 159 ± 9 days), homozygous expression of the FasLgld mutation (FasL−/−) led to a small but statistically significant extension of the survival to 170 ± 17 days (7%) (p < 0.05, Mantel-Cox Logrank) (Fig. 1).
The motor performance was not
Discussion
In the present study, we present evidence that the Fas pathway plays a role in the death of motor neurons in G93A SOD1 transgenic mice. There is a large body of evidence implicating Fas ligand (FasL) and activation of Fas receptors in death of motor neurons. Studies of cultured motor neurons show that they co-express the death receptor Fas and its ligand FasL at the stage of which programmed cell death is about to begin [14]. In the absence of trophic factors, approximately 50% of the motor
Acknowledgements
This work was supported in part by grants from Muscular Dystrophy Association and the Amyotrophic Lateral Sclerosis Association, by NIH grants to MFB, MK and by a grant of the Deutsche Forschungsgemeinschaft to SP.
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2015, International Review of Cell and Molecular BiologyCitation Excerpt :Fas activation has an additive effect to IFNγ, which induces selective MN death (Aebischer et al., 2011). In an attempt to block Fas-induced MN death in ALS, Petri et al., crossed mSOD1 mice with a mutation in FasL, and showed a reduction in MN loss and prolonged survival (Petri et al., 2006). Furthermore, silencing of Fas by RNAi promotes the survival of both wild-type and mSOD1 motor neurons in vitro, while treatment of SOD1 animals with the same RNAi improved their motor function and survival (Locatelli et al., 2007).
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2011, Free Radical Biology and MedicineCitation Excerpt :AKRCs are valuable in the study of activation of Nrf2 because of their enzymatic reductase activity [50]. An important proinflammatory cytokine receptor is Fas, which plays a role in ALS pathogenesis [10,51,52]. Nrf2 directly inhibits Fas-mediated apoptosis [53].
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2011, Brain Research ReviewsCitation Excerpt :In contrast, treatments resulting in the extension of disease progression imply that the cell death inhibition is downstream of denervation and weakness and therefore a downstream process of MN disease. With respect to members of the extrinsic apoptotic pathway, deletion of FasL and p38 MAPK both delayed progression but not onset of disease (Dewil, 2007; Petri et al., 2006), whereas this distinction was not reported after iNOS deletion (Martin et al., 2007). In contrast, overexpression of Bcl-2 or deletion of Bax, BIM or PUMA all extend disease onset, suggesting that the intrinsic pathway may be involved in disease pathogenesis (Gould et al., 2006; Kostic et al., 1997; Kieran et al., 2007; Hetz et al., 2007).