I04 Reduction of glutamate dehydrogenase increases autophagy and ameliorate motility and survival in a drosophila model for huntington’s disease

Autophagy is a fundamental cellular pathway involved in the clearance of protein aggregates, and it is particularly important in neurons. The toxic aggregates derived from the mutated Huntingtin have been shown to interfere with the physiological autophagic flux, resulting in neuronal death. Glutamate Dehydrogenase (GDH) is an evolutionary conserved enzyme that catalyses the conversion of glutamate and ammonia to α-ketoglutarate and vice versa and is also member of the Glutamate-Glutamine Cycle (GGC), a physiological process between glia and neurons that controls glutamate homeostasis. Through a genetic screen using a Drosophila model for Huntington’s disease (HD), we identified that reduction of GDH ameliorates animal motility and decreases the size of mutated Huntingtin’s (mHTT) aggregates in brains. The aim of our project is to analyze how GDH downregulation induces autophagy in neurons. We modeled HD phenotype in Drosophila by expressing mHTT with 93-CAG repetition (HTTQ93) in neurons. To investigate the effect of GDH we used motility and viability assay, while western blots and immunofluorescence analysis were used to investigate changes in mHTT aggregates. We found the reduction of GDH inhibits the accumulation of p62/Ref(2)P, an autophagic adaptor that abnormally increases in mHTT-expressing neurons. Reduction of GDH also leads to a substantial decrease in essential aminoacids in heads of adult flies. In particular we focused on Leucine and Glutamine, two major activators of TOR pathway. Leucine binds to its sensor Sestrin, while Glutamine enters the cell through specific receptors including LAT1/SCLA7/Minidisc, a Glutamine/Leucine antiporter. We are currently exploiting whether these sensors modulate TOR activity in the mechanism through which GDH downregulation induces autophagy. The goal of our work is also to design pharmacological inhibitors of GDH to be tested in vivo in flies to ameliorate HD pathology in humans.