PROJECT SUMMARY A decline in neuronal function occurs with age and is the hallmark of neurodegenerative diseases (NDs). Neurodegenerative diseases (NDs), characterized by the functional loss of discrete neuronal populations due to complex sources of cellular dysfunction, reduce the quality and duration of life for millions of individuals. Once considered two quite different NDs: frontotemporal dementia (FTD), affecting neurons of the frontal and temporal lobes, and amyotrophic lateral sclerosis (ALS), typified by death of upper and/or lower motor neurons, are now known to share a genetic basis, with clinical and pathological overlap. One of the most efficient and effective means for elucidating the molecular mechanisms underlying complex cellular processes, like ALS/FTD, is by the identification of genetic modifiers that restore function. We have identified genetic variants that alleviate a loss of motor function and neurodegeneration associated with different models of ALS/FTD. The modifying genes act in carbohydrate metabolism and nucleotide biosynthesis, with the gene encoding Transketolase (Tkt), a central enzyme in the pentose phosphate pathways (PPP), playing a critical role in regulating flux through glycolysis, nucleotide biosynthesis, and oxidative PPP, to meet the cell’s energy demands and counteract oxidative stress. These metabolic pathways are highly conserved across evolution, so the powerful genetics of Drosophila will enable the elucidation of the genetic interactions that regulate these metabolic pathways. Our research program aims to elucidate the mechanistic basis of tkt-meditated suppression of neurodegeneration. Our experimental design makes use of two newly generated patient allele CRISPR-Cas9 knock-in models in the endogenous Drosophila dSod1 locus, and the controlled expression of GGGGCC (G4C2)- repeats whose expansion in the human C9orf72 gene is the most common cause of familial ALS. Since biological systems respond to perturbations by modulating system homeostasis, the complex genetic basis of ALS/FTD will likely not be obtained by studying a single genetic mutation related to the disease. Therefore, we will study multiple models of ALS/FTD and combine an unbiased approach of functional assessments of genetic perturbations, with specific molecular readouts such as, redox state, autophagy, as well as comparative metabolite profiling, transcriptomics, and chromatin state to obtain a global, biomarker readout of disease versus suppressed state. This comprehensive understanding of the molecular landscape will identify the changes that correlate with restoration of neuronal function and motor activity in ALS/FTD. The resulting data will accelerate progress towards a translational goal by highlighting targets where therapeutics could intervene to restore, or even prevent, the loss of neuronal function responsible for the devastating motor and cognitive decline associated with ALS/FTD.