Amyotrophic lateral sclerosis (ALS) is a devastating, neurodegenerative disorder characterized by muscle weakness progressing to paralysis as a consequence of dysfunction and death of motor neurons. A striking number of genes implicated in pathogenesis encode proteins with functions in RNA metabolism. To address the mechanisms involved and identify common therapeutic targets, we have formed a unique transnational consortium of investigators with expertise in clinical neurology and pathology, RNA metabolism, motor neuron cell biology and experimental modeling. The specific aims build on strong preliminary evidence that miRNAs, regulators of protein-encoding RNAs, are aberrantly expressed in motor neurons in ALS and that neurofilaments are a disease-relevant target. We will characterise and determine the relative role of the miRNAs regulating stability of mRNAs encoding the neurofilament-forming proteins. How their expression is affected in ALS will be defined using autopsy tissue from sporadic and familial ALS patients relative to controls. The function of ALS-relevant miRNAs and consequences of their disruption will be investigated by manipulating their expression in spinal motor neurons in culture, in adult mice and in zebrafish models, and by assessing the impact on multiple functional measures. Finally, we will determine if manipulating key miRNAs is neuroprotective in primary motor neuron culture and zebrafish models of familial ALS. These experiments will establish models and relevant endpoints for future studies to identify novel therapeutics for ALS.

Hereditary spastic paraplegia (HSP) defines a genetically heterogeneous group of disorders characterized by weakness and spasticity of the lower limbs, owing to retrograde degeneration of corticospinal axons. Recently, both genetic and functional studies, largely contributed by research from members of this consortium, have revealed a pathogenic link of HSP with lipid metabolism, pointing to defects in cholesterol (SPG5), fatty acid (SPG49), phospholipid (SPG28, SPG39, SPG54), sphingolipid (SPG26, SPG35, SPG46) metabolism, and lipid droplet turnover (SPG3, SPG4, SPG17, SPG20, SPG31). These data open the way to the identification of novel biomarkers for this pathology, and suggest that therapeutic approaches aiming at restoring normal lipid profiles may prove beneficial in HSP. Lipid composition of biological membranes affects several physiological processes of crucial relevance in neurons, such as endo- and exocytosis, trafficking, and dynamics of organelles. Moreover, lipid molecules may act as direct signalling effectors. Our proposal brings together four groups with complementary expertise with the object to: 1) Establish frequency, natural history, and genotype/phenotype correlations of HSP forms linked to lipid metabolism; 2) Perform lipidomic studies on cell lines and tissues derived from HSP patients and animal models to identify novel biomarkers; 3) Assess cellular consequences of changes in lipid composition and lipid droplets in these forms of HSP; 4) Develop mouse and Drosophila models for a subset of these genes to be used for future preclinical trials.