Primary sensory axons injured by dorsal root injuries fail to regenerate into the spinal cord, leading to chronic pain and permanent sensory loss. The mechanisms that prevent regeneration at the CNS-PNS interface, the dorsal root entry zone (DREZ), are unknown. The present approaches for overcoming this regeneration failure have had only limited success. Over the past few years, we have pioneered in applying in vivo imaging to directly monitor sensory axons arriving at the DREZ in living mice. These studies lead us to hypothesize that the regeneration failure and the limited success with current interventions might be because regenerating axons undergo rapid and aberrant synaptic differentiation that causes growth to cease prematurely at the DREZ. To test this idea, we will apply advanced techniques, including in vivo imaging, inducible transgenic mice, and targeted electron microscopy.
In Aim 1, we will identify postsynaptic mechanisms by testing whether NG2 glia induce presynaptic differentiation and/or growth arrest.
In Aim 2, we will identify presynapti mechanisms by testing whether targeting calcium channel alpha2delta subunits and their interaction with thrombospondins will promote regeneration.
In Aim 3, we will promote robust regeneration by combining treatment with gabapentin (GBP) and pregabalin (PG), which prevent synaptogenesis, with conventional interventions targeting intrinsic and extrinsic growth barriers, which individually elicit little regeneration. The proposed work has the potential to revise the prevailing explanation for the regeneration failure of primary sensory neurons and may also be applicable to spinal cord injury. In addition, GBP and PG are commonly prescribed anti-neuropathic pain medications already approved by the FDA. Our work therefore can be quickly applied to patients with brachial plexus, lumbosacral plexus and cauda equina injuries, which are common and debilitating and have no effective treatment.

Public Health Relevance

We propose to study why injured sensory axons fail to regenerate into the spinal cord. In contrast to the prevailing view in the field, we postulate that axons stop regeneration because they form inappropriate connections with incorrect partners. Our studies will also develop new treatments for patients with extremely debilitating types of spinal root injuries that presently have no effective treatment.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Research Project (R01)
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Clinical Neuroplasticity and Neurotransmitters Study Section (CNNT)
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Jakeman, Lyn B
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Temple University
Schools of Medicine
United States
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Han, Seung Baek; Kim, Hyukmin; Lee, Hyunkyoung et al. (2017) Postinjury Induction of Activated ErbB2 Selectively Hyperactivates Denervated Schwann Cells and Promotes Robust Dorsal Root Axon Regeneration. J Neurosci 37:10955-10970
Grove, Matthew; Kim, Hyukmin; Santerre, Maryline et al. (2017) YAP/TAZ initiate and maintain Schwann cell myelination. Elife 6:
Liu, Yingpeng; Kelamangalath, Lakshmi; Kim, Hyukmin et al. (2016) NT-3 promotes proprioceptive axon regeneration when combined with activation of the mTor intrinsic growth pathway but not with reduction of myelin extrinsic inhibitors. Exp Neurol 283:73-84
Son, Young-Jin (2015) Synapsing with NG2 cells (polydendrocytes), unappreciated barrier to axon regeneration? Neural Regen Res 10:346-8
Skuba, Andrew; Manire, Meredith Ann; Kim, Hyukmin et al. (2014) Time-lapse in vivo imaging of dorsal root nerve regeneration in mice. Methods Mol Biol 1162:219-32
O'Donovan, Kevin J; Ma, Kaijie; Guo, Hengchang et al. (2014) B-RAF kinase drives developmental axon growth and promotes axon regeneration in the injured mature CNS. J Exp Med 211:801-14
Niu, Jingwen; Ding, Long; Li, Jian J et al. (2013) Modality-based organization of ascending somatosensory axons in the direct dorsal column pathway. J Neurosci 33:17691-709