Final Report Summary - MODIFALS (From zebrafish to manModifying amyotrophic lateral sclerosis (ALS): translation of biology into therapy)
This project aimed to develop novel models for Amyotrophic Lateral Sclerosis (ALS), identify new targets for intervention, and translate these into validated options for drug development in ALS. We have followed a longitudinal paradigm to reveal effective therapeutic targets, from the (unbiased) screening for targets in a small animal model (zebrafish), to the elucidation of their pathogenic mechanism, the exploration of their therapeutic potential for patients.
We first generated a novel zebrafish model for ALS expressing the expansion mutation of the GGGGCC repeat sequence in the C9orf72 gene, the most frequent cause of ALS. This model allowed us to detect direct toxicity of RNA, independent of the formation of unusual peptides formed by non-conventional translation (called DPRs). Interestingly, a genetic screen in this model identified the RNA binding proteins Pur-alpha to be a strong suppressor of toxicity, probably through an effect on autophagy. In addition, we also generated a Drosophila model that overexpressed arguinine-containing DPRs. Several genes involved in the transport of molecules between the cellular cytoplasm and nucleus were found to be critical for the toxicity of these DPRs.
Previous work by our lab identified Id2, Elp3 and EphA4 as potential modifiers for ALS in a mutant SOD1 zebrafish model. We next validated these targets by using mouse models. We first deleted a detrimental factor for oligodendrocyte differentiation, Id2, selectively from oligodendrocytes and their progenitor cells in the SOD1G93A mouse model of ALS. By doing so, we aimed to improve the motor neuron supporting function of oligodendrocytes. However, we were not able to improve disease outcome nor oligodendrocyte function. Our results therefore indicate that we should rethink our strategies in order to modulate oligodendrocyte pathology in ALS. Intervening with a single pathogenic mechanism within oligodendrocytes might not be sufficient to modulate the course of disease in ALS. We next determined whether an increase in ELp3 levels would be of benefit in ALS. Several findings suggest that loss of function of ELP3 affects the nervous system. In ALS patients, increased risk to develop the disease was associated with lower brain expression levels of ELP3. Confirming our hypothesis, reduction of Elp3 levels accelerated disease onset in SOD1G93A mice, whereas increasing its levels delayed disease onset and prolonged their survival. Finally, the axonal guidance molecule EphA4 was already validated in a mouse model by our lab, by reducing EphA4 levels from developmental stages onwards in the SOD1G93A mouse model. We aimed to go one step further and validate the therapeutic potential of EphA4 by deleting it from an adult stage onwards. Unfortunately, we did not see any beneficial effect in the mouse model, indicating that although EphA4 is an ALS modifier, its potential as therapeutic strategy for patients might be low. In parallel we have generated small antibodies called Nanobodies that specifically bind EphA4 and block it.
As factors identified to modify ALS, may be generic in action and may also modify the course of other neurodegenerative disorders, we studied the role of EphA4 in spinal muscular atrophy (SMA) and Alzheimer’s disease (AD). SMA is an autosomal recessive neurodegenerative disorder, which affects the spinal motor neurons within the central nervous system. Although loss of EphA4 rescued the axonal deficits in a zebrafish model for SMA, it did not improve neuromuscular junction innervation, motor function and survival in a severe mouse model for SMA. AD is a devastating neurodegenerative disorder, characterized by progressive decline in memory, together with multiple cognitive impairments compromising the patient’s daily life. Reduction of EphA4 in cortical and hippocampal brain areas, improved social memory without affecting other cognitive functions. We found altered synaptic strength and altered microglial activation to be associated with this improved outcome. These data show it may be worthwhile to further explore the ephrin system as a possible therapeutic target in Alzheimer’s.
We first generated a novel zebrafish model for ALS expressing the expansion mutation of the GGGGCC repeat sequence in the C9orf72 gene, the most frequent cause of ALS. This model allowed us to detect direct toxicity of RNA, independent of the formation of unusual peptides formed by non-conventional translation (called DPRs). Interestingly, a genetic screen in this model identified the RNA binding proteins Pur-alpha to be a strong suppressor of toxicity, probably through an effect on autophagy. In addition, we also generated a Drosophila model that overexpressed arguinine-containing DPRs. Several genes involved in the transport of molecules between the cellular cytoplasm and nucleus were found to be critical for the toxicity of these DPRs.
Previous work by our lab identified Id2, Elp3 and EphA4 as potential modifiers for ALS in a mutant SOD1 zebrafish model. We next validated these targets by using mouse models. We first deleted a detrimental factor for oligodendrocyte differentiation, Id2, selectively from oligodendrocytes and their progenitor cells in the SOD1G93A mouse model of ALS. By doing so, we aimed to improve the motor neuron supporting function of oligodendrocytes. However, we were not able to improve disease outcome nor oligodendrocyte function. Our results therefore indicate that we should rethink our strategies in order to modulate oligodendrocyte pathology in ALS. Intervening with a single pathogenic mechanism within oligodendrocytes might not be sufficient to modulate the course of disease in ALS. We next determined whether an increase in ELp3 levels would be of benefit in ALS. Several findings suggest that loss of function of ELP3 affects the nervous system. In ALS patients, increased risk to develop the disease was associated with lower brain expression levels of ELP3. Confirming our hypothesis, reduction of Elp3 levels accelerated disease onset in SOD1G93A mice, whereas increasing its levels delayed disease onset and prolonged their survival. Finally, the axonal guidance molecule EphA4 was already validated in a mouse model by our lab, by reducing EphA4 levels from developmental stages onwards in the SOD1G93A mouse model. We aimed to go one step further and validate the therapeutic potential of EphA4 by deleting it from an adult stage onwards. Unfortunately, we did not see any beneficial effect in the mouse model, indicating that although EphA4 is an ALS modifier, its potential as therapeutic strategy for patients might be low. In parallel we have generated small antibodies called Nanobodies that specifically bind EphA4 and block it.
As factors identified to modify ALS, may be generic in action and may also modify the course of other neurodegenerative disorders, we studied the role of EphA4 in spinal muscular atrophy (SMA) and Alzheimer’s disease (AD). SMA is an autosomal recessive neurodegenerative disorder, which affects the spinal motor neurons within the central nervous system. Although loss of EphA4 rescued the axonal deficits in a zebrafish model for SMA, it did not improve neuromuscular junction innervation, motor function and survival in a severe mouse model for SMA. AD is a devastating neurodegenerative disorder, characterized by progressive decline in memory, together with multiple cognitive impairments compromising the patient’s daily life. Reduction of EphA4 in cortical and hippocampal brain areas, improved social memory without affecting other cognitive functions. We found altered synaptic strength and altered microglial activation to be associated with this improved outcome. These data show it may be worthwhile to further explore the ephrin system as a possible therapeutic target in Alzheimer’s.