Strategies to prevent motoneuron degeneration in models of Amyotrophic Lateral Sclerosis
Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disorder, characterised by progressive motoneuron degeneration in the spinal cord, motor cortex and brainstem. The pathogenic mechanisms underlying selective motoneuron degeneration are unclear and currently there is no effective treatment. In this Thesis, strategies designed to prevent motoneuron degeneration are investigated in both in vivo and in vitro models of ALS. Furthermore, interaction between motoneurons and astrocytes is studied to examine the influence of astrocytes on disease progression. In the SODlG93A mouse model of ALS, the glial cell genotype influences the susceptibility of motoneurons to degeneration (Gong et al., 2000 Clement et al., 2003). In this Thesis, the effect of mutant SOD1 expression in astrocytes on motoneuron properties is examined in an in vitro co-culture system using confocal microscopy. Cannabinoids exert anti-excitotoxic, anti-inflammatory and anti-oxidant actions, all of which may contribute to ALS pathogenesis. In these experiments, the potential neuroprotective effect of manipulating the endocannabinoid system is investigated in vivo in SODl093* mice. Augmentation of the endocannabinoid system, by pharmacological and genetic manipulation, ameliorates disease symptoms in SOD1 mice. Furthermore, genetic ablation of the CBi receptor significantly extends lifespan in SOD 1093A mice. Finally, the effect of ablating the expression of mutant SOD1 protein in vitro in primary motoneurons using viral delivery of targeted small interfering RNA (siRNA) is assessed. The successful transfection and ablation of the mutant protein in vitro, as shown in this Thesis, has since been tested successfully in vivo. The results of this Thesis show that manipulation of the endocannabinoid system and siRNA technology may be successful therapeutic approaches in ALS. The results also indicate that mutant SOD1 expression in astrocytes has a deleterious influence on mitochondrial function in motoneurons even under resting conditions. Therefore, specific targeting of astrocytes may also be an appropriate strategy to prevent motoneuron degeneration in ALS.