IVV-11 Pan-neuronal expression of human SOD1 mutations in Drosophila induces early neuroinflammation

Background: Superoxide Dismutase 1 (SOD1), coding for the antioxidant enzyme SOD1, is the second most common ALSassociated gene, with more than 200 identified point mutations. Since most of the mutant proteins retain their enzymatic function, SOD1-associated pathogenicity is thought to be due to a toxic gain-of-function leading to motor neuron death. Several causes sustain ALS neurodegeneration when a certain, still undefined, threshold of damage is exceeded and generates a pathogenic cascade culminating in motor neurons depletion. Despite the generation of many in vitro and in vivo models and the huge effort of research (1), our knowledge about the events that precede this neurodegenerative cascade remains elusive. Objectives: Based on these premises, our main objective was to better characterize the very early cellular mechanisms thatare deregulated in SOD1-ALS and induce motor neuron degeneration with clinically evident symptomatology. Methods: Drosophila is a well-established model for studying ALS, not only because transgenic flies recapitulate several symptoms, but also because they can be easily adopted for screening disease progression and novel therapeutic compounds (2). Here we took advantage of two Drosophila models expressing different mutant human SOD1 transgenes (hSOD1-A4V or hSOD1-G85R) (3). We expressed the transgenes pan-neuronally and performed: qRT-PCR, immunofluorescence and western blot analysis to assess the expression of several inflammatory and antioxidant markers; cytological preparations to score chromosomal aberrations; flow cytometry to quantify global ROS measurement; finally climbing and survival assays. Results: Our results show that pan-neuronal expression of mutant SOD1 induces a strong neuroinflammatory phenotype in Drosophila, resulting in glial activation, innate immunity stimulation, antimicrobial peptides up-regulation and oxidative stress, in turn sustaining genomic instability and impaired motor performance. Interestingly, the observed phenotypes manifest in the very early stages of adult life when neuronal depletion is not still detected. However, at later time points, ALS flies show reduced survival respect to healthy controls. Discussion: Taken together, our results reinforce the concept that SOD1-ALS pathogenesis is characterized by a very precocious neuroinflammatory component that precedes, and maybe sustains, the progressive cascade of motor neuron damage, overall leading to the typical ALS symptoms.