Neurodegenerative disorders are characterized by a selective loss of neuronal subtypes that is often irreversible due to the failure of the adult huma brain to generate new neurons. To date, several options to ameliorate some of the symptoms exist, but none of these treatments successfully replace the lost neurons in humans. Thus, new avenues for brain repair are necessary. A method to replenish lost cells by giving rise to new neurons from adult stem cells or from existing neurons could potentially ameliorate the degenerative phenotype. While most mammalian neurons do not readily regenerate or reprogram without external manipulation, several species of salamanders naturally exhibit these feats. The axolotl is one such species with an increasing array of experimental tools. Intriguingly, recent studies have demonstrated that the various axolotl organs with regenerative potential - limb, spinal cord, heart - undergo natural reprogramming in order to replace lost tissue. Though the general mechanism is still unclear, this coupling of regeneration and reprogramming seem to be necessary for the regenerative potential of various organs in the axolotl. The axolotl brain is another organ with great regenerative ability. One-third of the telencephalon can be completely removed and the brain will repopulate the lost tissue within a few months with new neurons. However, the research of axolotl brain regeneration has only been performed before the 1960's when molecular and cellular biological tools were limited. Broadly, the goal of this proposal is to understand the regenerative process of the axolotl brain. Three specific questions drive this goal: 1) Do the specific neuronal subtypes and their respective circuits reconstruct with fidelity upon injury? 2) Where do the new neurons come from? Is it possible that existing neurons dedifferentiate to form a blastema, which subsequently differentiates into new neurons? 3) What molecular changes are associated with the regenerative process? Answering these questions would not only reveal the mechanism of brain regeneration in the axolotl, but it also may give clues to what molecules may be used to induce neurogenesis and nuclear reprogramming in an adult human brain. The combination of the lab of Dr. Paola Arlotta and the surrounding labs and institutes provide the necessary tools to answer these questions. The methods of completing the goal include immunofluorescence, in situ hybridization, RNA-seq, retrograde tracing, viral injection, and BrdU birthdating. The animal facility has the capacity to hold over one hundred axolotls in a free-flowing water system and a dedicated animal care team. These resources and tools that were unavailable fifty years ago will greatly facilitate the understanding of the brain regeneration process in the axolotl as well as th means to translate the regenerative process to a mammalian system and eventually towards therapy in humans.

Public Health Relevance

Neuronal loss resulting from neurological disorders and mental illnesses are often irreversible, and treatments for these debilitating diseases are currently limited. Using the salamander, axolotl, as a model of brain regeneration, we propose to elucidate the cellular and molecular mechanism of natural neuronal regeneration in a non-mammalian vertebrate, with the hope that this understanding will eventually translate to additional human therapies.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Predoctoral Individual National Research Service Award (F31)
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Special Emphasis Panel (ZRG1)
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Riddle, Robert D
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Harvard Medical School
Schools of Medicine
United States
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Amamoto, Ryoji; Huerta, Violeta Gisselle Lopez; Takahashi, Emi et al. (2016) Adult axolotls can regenerate original neuronal diversity in response to brain injury. Elife 5: