Hereditary congenital defects that impair lysosomal degradation often affect the nervous system before other organs, suggesting an increased or specialized neuronal demand for lysosomal function. The objective of our work is to understand and manipulate lysosomal degradation in order to improve neuronal function by utilizing a Drosophila model for Charcot-Marie-Tooth type 2B (CMT 2B) disease. CMT 2B is an autosomal dominant sensory neuropathy caused by mutations in the late endosomal GTPase rab7. In a systematic characterization of all rab GTPases, we discovered that rab7 is expressed in neurons at elevated levels prior to other cell types. We have generated the first null mutants in rab7 in Drosophila; to our knowledge rab7 knock-outs in mouse or zebrafish have not been characterized. Loss of rab7 in Drosophila causes late developmental defects in neurons and postnatal progressive degeneration of sensory nerve terminals that can be rescued by neuron-specific rab7 cDNA expression. In further similarity to the human disease, rab7 mutant nerve terminals are characterized by endolysosomal degradation and protein accumulation defects. Overexpression of classical dominant negative (GDP-bound) or constitutively active (GTP-bound) Rab7 does not mimic the null mutant and disease phenotypes in vivo. Nonetheless, human CMT 2B mutations have been proposed to represent dominant gain-of-function alleles. In contrast, based on our preliminary data, we hypothesize that the human disease mutations are partial loss-of-function alleles that may cause a dominant phenotype through haploinsufficiency in heterozygous patients. We will genetically and mechanistically test this hypothesis in Drosophila. We will further elucidate the precise degradation defects associated with loss of rab7 in neuronal and non-neuronal cell types by analyzing the null mutant and known human disease mutations in Drosophila. We will thereby establish the first animal model for CMT 2B disease. In addition, we will utilize this model as a genetic inroad to study the cell biological mechanisms underlying the increased neuronal sensitivity to endolysosomal defects. Finally, we seek to establish methods to manipulate the degradative capacity of neurons affected by endolysosomal dysfunction.

Public Health Relevance

The proposed project has direct and substantial relevance for public health, because we present the first genetic model for the sensory neuropathy Charcot-Marie-Tooth type 2B disease. The experiments described in this grant are aimed at understanding the cell biological cause of pathology in this neuropathy as well as a class of related lysosomal dysfunction disorders and will have an impact on the choice of therapeutic approaches to developing potential treatment.

Agency
National Institute of Health (NIH)
Institute
National Eye Institute (NEI)
Type
Research Project (R01)
Project #
7R01EY023333-03
Application #
9033164
Study Section
Synapses, Cytoskeleton and Trafficking Study Section (SYN)
Program Officer
Neuhold, Lisa
Project Start
2013-05-01
Project End
2018-04-30
Budget Start
2015-07-01
Budget End
2016-04-30
Support Year
3
Fiscal Year
2015
Total Cost
Indirect Cost
Name
Free University of Berlin
Department
Type
DUNS #
313311078
City
Berlin
State
Country
Germany
Zip Code
14195
Kiral, Ferdi Ridvan; Kohrs, Friederike Elisabeth; Jin, Eugene Jennifer et al. (2018) Rab GTPases and Membrane Trafficking in Neurodegeneration. Curr Biol 28:R471-R486
Jin, Eugene Jennifer; Kiral, Ferdi Ridvan; Ozel, Mehmet Neset et al. (2018) Live Observation of Two Parallel Membrane Degradation Pathways at Axon Terminals. Curr Biol 28:1027-1038.e4
Jin, Eugene Jennifer; Kiral, Ferdi Ridvan; Hiesinger, Peter Robin (2018) The where, what, and when of membrane protein degradation in neurons. Dev Neurobiol 78:283-297
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Langen, Marion; Agi, Egemen; Altschuler, Dylan J et al. (2015) The Developmental Rules of Neural Superposition in Drosophila. Cell 162:120-33
Hassan, Bassem A; Hiesinger, P Robin (2015) Beyond Molecular Codes: Simple Rules to Wire Complex Brains. Cell 163:285-91
Zschätzsch, Marlen; Oliva, Carlos; Langen, Marion et al. (2014) Regulation of branching dynamics by axon-intrinsic asymmetries in Tyrosine Kinase Receptor signaling. Elife 3:e01699
Wang, Dong; Epstein, Daniel; Khalaf, Ossama et al. (2014) Ca2+-Calmodulin regulates SNARE assembly and spontaneous neurotransmitter release via v-ATPase subunit V0a1. J Cell Biol 205:21-31
Agi, Egemen; Langen, Marion; Altschuler, Steven J et al. (2014) The evolution and development of neural superposition. J Neurogenet 28:216-32
Cherry, Smita; Jin, Eugene Jennifer; Ozel, Mehmet Neset et al. (2013) Charcot-Marie-Tooth 2B mutations in rab7 cause dosage-dependent neurodegeneration due to partial loss of function. Elife 2:e01064

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