Functional repair after axonal damage requires disparate responses in the proximal and distal parts of the damaged axon. The proximal axon must initiate new axonal growth, however in many cases this fails to occur, particularly in the adult mammalian CNS. In addition, the distal axonal stump must be cleared out of the way. This occurs via a cell-autonomously initiated axonal fragmentation process termed `Wallerian degeneration'. While this degeneration plays a beneficial role in clearing irreparably damaged axons, the loss of axons is generally a deleterious feature of neuropathies and neurodegenerative diseases. The long term goals of this project are to understand the cellular mechanisms that detect axonal damage and facilitate the dichotomous outcomes of degeneration verses repair. Previous work in the lab, using a Drosophila model, has delineated a conserved molecular pathway that regulates both the regeneration and degeneration of damaged axons. The current grant focuses upon two important components of this pathway: (1) Wnd/DLK, a conserved axonal kinase whose can mediate either regenerative or degenerative responses to axonal injury, hence has been coined a `dual-edged sword', and (2) the NAD+ biosynthetic enzyme, Nmnat [2, 3], whose rapid turnover in distal axons appears to play an important role in initiating degeneration, however the cellular mechanism for Nmnat's protective function(s) is not known.
Aim 1 tests a hypothesis, raised by preliminary data, that both Wnd and its DLK homologue in mammals are regulated directly by PKA downstream of cAMP signaling. Because elevated cAMP signaling correlates with successful regeneration in the PNS, this mechanism may yield insight into how pro-regenerative outcomes of Wnd/DLK's activation can be specifically biased.
Aim 2 tests a new hypothesis for the protective mechanism in axons, specifically that Nmnat attenuates intracellular Ca2+ influx from ER stores that are triggered by injury, and further links calcium homeostasis to ATP rundown and mitochondrial trafficking in damaged axons. The approaches take advantage of genetic and live imaging techniques in Drosophila larvae which allow for subcellular events (including changes in intracellular Ca2+, ATP, and mitochondrial trafficking) to be manipulated and tracked within injured axons and synapses in live animals. In addition, the project initiates complementary studies in mouse DRG cultures to study axonal regeneration in the context of individual cellular events regulated by DLK. This work is expected to reveal important cellular mechanisms that influence both regenerative and degenerative responses to axonal damage.

Public Health Relevance

Axons form connections between neurons over great distances in the brain and body, hence are vulnerable to damage. This grant studies a molecular pathway that coordinates multiple responses to axonal damage in neurons, including the choice of whether to regrow (regenerate) or degenerate. The findings from this work will be relevant for developing future treatments of spinal cord injuries and potentially other injuries to the central nervous system, as well as a wide range of neurodegenerative diseases (including ALS, Alzheimer's Disease and Parkinson's Disease) and neuropathies (including neuropathies induced by diabetes and chemotherapy), which involve axonal damage.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS069844-06
Application #
9133475
Study Section
Neurodifferentiation, Plasticity, and Regeneration Study Section (NDPR)
Program Officer
Jakeman, Lyn B
Project Start
2010-04-01
Project End
2020-06-30
Budget Start
2016-07-01
Budget End
2017-06-30
Support Year
6
Fiscal Year
2016
Total Cost
Indirect Cost
Name
University of Michigan Ann Arbor
Department
Biochemistry
Type
Schools of Arts and Sciences
DUNS #
073133571
City
Ann Arbor
State
MI
Country
United States
Zip Code
48109
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Hao, Yan; Collins, Catherine (2017) Intrinsic mechanisms for axon regeneration: insights from injured axons in Drosophila. Curr Opin Genet Dev 44:84-91
Li, Jiaxing; Zhang, Yao V; Asghari Adib, Elham et al. (2017) Restraint of presynaptic protein levels by Wnd/DLK signaling mediates synaptic defects associated with the kinesin-3 motor Unc-104. Elife 6:
Chaudhury, Amrita Ray; Insolera, Ryan; Hwang, Ran-Der et al. (2017) On chip cryo-anesthesia of Drosophila larvae for high resolution in vivo imaging applications. Lab Chip 17:2303-2322
Chen, Li; Nye, Derek M; Stone, Michelle C et al. (2016) Mitochondria and Caspases Tune Nmnat-Mediated Stabilization to Promote Axon Regeneration. PLoS Genet 12:e1006503
Hao, Yan; Frey, Erin; Yoon, Choya et al. (2016) An evolutionarily conserved mechanism for cAMP elicited axonal regeneration involves direct activation of the dual leucine zipper kinase DLK. Elife 5:
Wong, Ching-On; Palmieri, Michela; Li, Jiaxing et al. (2015) Diminished MTORC1-Dependent JNK Activation Underlies the Neurodevelopmental Defects Associated with Lysosomal Dysfunction. Cell Rep 12:2009-20
Siebert, Matthias; Böhme, Mathias A; Driller, Jan H et al. (2015) A high affinity RIM-binding protein/Aplip1 interaction prevents the formation of ectopic axonal active zones. Elife 4:
Mishra, Bibhudatta; Ghannad-Rezaie, Mostafa; Li, Jiaxing et al. (2014) Using microfluidics chips for live imaging and study of injury responses in Drosophila larvae. J Vis Exp :e50998
Wang, Adrienne M; Miyata, Yoshinari; Klinedinst, Susan et al. (2013) Activation of Hsp70 reduces neurotoxicity by promoting polyglutamine protein degradation. Nat Chem Biol 9:112-8

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