Many defects in lysosomal degradation affect the nervous system before other organs, suggesting an increased or specialized neuronal demand for endomembrane degradation. I have generated the first null mutant for the ubiquitous endolysosomal rab GTPase rab7 in Drosophila. Partial or complete loss of rab7 causes neuropathy-like phenotypes in sensory neurons before other cell types. Moreover, four point mutations in human rab7 cause the autosomal dominant sensory neuropathy Charcot-Marie-Tooth type 2B (CMT 2B) through a partial loss-of-function mechanism. Both the Drosophila rab7 null mutant and the CMT 2B disease in human highlight the neuronal sensitivity to defects in endolysosomal degradative capacity. Based on my preliminary findings, I hypothesize that neurons have a specialized or increased requirement for endolysosomal degradation. I will test this hypothesis by combining fly genetics and novel live imaging approaches to quantitatively measure cargo-specificity and dynamics of rab7-dependent degradation at neuronal synapses compared to cell bodies and other cell types. Next, I will use genetic interaction experiments combined with imaging and electrophysiological read-outs to investigate the cellular mechanism of rab7 function in the context of ubiquitous autophagy and neuron-specific endolysosomal degradation mechanism. Finally, together with my Co-Sponsor, I will characterize rab7 function in mouse neuronal culture to test the generality of my findings from the Drosophila model. Together, my findings will elucidate the cellular mechanism of rab7-dependent degradation and its role in neuronal maintenance and longevity, with a potential therapeutic application in the establishment of methods to manipulate the degradative capacity of neurons affected by endolysosomal dysfunction.
The proposed project is aimed to characterize the mechanism and the role of rab7-dependent endolysosomal degradation in neuronal maintenance and longevity. The findings will have direct and substantial relevance for public health by impacting the choice of therapeutic approaches to develop potential treatments for the sensory neuropathy Charcot-Marie-Tooth Type 2B and other related lysosomal dysfunction disorders.