From Axon Damage to Disease: Common Pathways in Neurodegeneration
- Claire E. Le Pichon, PhD, Head, Unit on the Development of Neurodegeneration
- Hanna Silberberg, MA, Biologist
- Jorge Gomez Deza, PhD, Postdoctoral Visiting Fellow
- Sangeetha Hareendran, PhD, Postdoctoral Visiting Fellow
- Mor Alkaslasi, BS, Graduate Student
- Zoe Piccus, MA, Graduate Student
- Josette J. Wlaschin, MSc, Graduate Student
- Austin Gable, BA, Postbaccalaureate Fellow
- Matthew Nebiyou, BS, Postbaccalaureate Fellow
- Aditya Santoki, BA, Postbaccalaureate Fellow
Our work is dedicated to advancing our understanding of common molecular and cellular mechanisms of neurodegeneration, with the ultimate goal of developing treatments for neurodegenerative diseases and even preventing them. The hypothesis driving our work is that common mechanisms are responsible for neurodegeneration during development and in aging. One focus is on mechanisms of stress-response pathways in neurons, such as the evolutionarily conserved axon-damage signaling pathway under the control of DLK (dual leucine zipper kinase; MAP3K12). Another theme is to understand fundamental differences between vulnerable and resilient populations of neurons in models of acute injury and in chronic disease. The lab uses the mouse and human iPSC–derived neurons as model systems.
Elucidation of mechanisms of axon damage signaling in human neurons
DLK is an essential player in the axonal response to neuronal injury. It promotes axon degeneration, neuronal cell death, and regeneration, depending on the neuronal cell type. To elucidate regulators and substrates of DLK function, about which relatively little is known, we study DLK localization, trafficking, and interactors in a human iPSC (induced pluripotent stem cells)–derived neuron model (i3neurons; Fernandopulle MS et al., Curr Protoc Cell Biol 2018;79: e51). Importantly, very few studies have examined DLK function in human neurons, despite DLK inhibitors being considered in clinical trials. Almost all we know comes from studies in model organisms (worm, fly, mouse).
Understanding fundamental differences between vulnerable and resilient populations of spinal motor neurons in disease
We are individually profiling transcriptomes of spinal-cord motor neurons in healthy mice and disease models to track the transcriptomic alterations that such cells undergo during disease progression. Last year, we published a single-cell transcriptomic atlas of adult mouse spinal motor neurons [Reference 1]. Previously, very few spinal motor neurons (MNs) had been resolved at the single-cell level, both because they are relatively rare among all spinal cells, and because they do not survive single-cell isolation protocols well. Our success relied on two strategies: (1) enriching for spinal MNs using a Chat-Cre line; and (2) capturing single nuclei, which are more robust than whole cells. We were able to collect single-nucleus RNA sequencing data from 16,000 cholinergic nuclei, define the full heterogeneity of these neurons at the single-cell level, and provide a comprehensive transcriptomic description of the lower MNs that selectively degenerate in ALS and other motor neuron diseases. We observed three main classes of skeletal MNs: alpha, gamma, and a third type potentially corresponding to beta MNs. Within each skeletal MN class, we identified previously uncharacterized subtypes corresponding to anatomical and functional specializations. The data from this study can be browsed at www.spinalcordatlas.org and will soon also be available at seqseek.ninds.nih.gov.
Having laid this important groundwork, we are currently obtaining data from mouse models of motor neuron disease and will compare the transcriptomes of resilient with those of vulnerable MN types across several time points in disease.
- Alkaslasi MR, Piccus ZE, Silberberg H, Chen L, Zhang Y, Petros TJ, Le Pichon CE. Single nucleus RNA-sequencing defines unexpected diversity of cholinergic neuron types in the adult mouse spinal cord. Nat Commun 2021;12:2471.
- Nguyen E, Smith KM, Cramer N, Holland RA, Bleimeister IH, Flores-Felix K, Silberberg H, Keller A, Le Pichon CE, Ross SE. Medullary kappa-opioid receptor neurons inhibit pain and itch through a descending circuit. Brain 2022 145(7):2586–2601.
- Ariel Levine, MD, PhD, Spinal Circuits and Plasticity Unit, NINDS, Bethesda, MD
- Michael E. Ward, MD, PhD, Inherited Neurodegenerative Diseases Unit, NINDS, Bethesda, MD