Axonal damage to the central nervous system (CNS) do not spontaneously regenerate because of the inherent low repair capacity and cannot currently be repaired or replaced by any treatment, resulting in devastating and permanent loss of neurophysiological function. By contrast, spontaneous axon regeneration occurs following injury of peripheral nerves, although the regenerative capacity declines as the PNS neurons get maturate. Distinguishing the differences between these and finding the key regulators and related target genes responsible for successful regeneration will bring key insight into the reasons why CNS neurons fail to regenerate. The long-term goal of my research is to understand the molecular mechanisms that induce regenerative response in PNS neurons and to develop new therapeutic strategies for CNS nerve regeneration. Injury to axons in PNS induces rapid and local regenerative responses for which local protein synthesis in axons is essential to initiate damage repair, to form a new growth cone and to generate retrogradely transporting injury signal. Small non-coding RNAs, including microRNAs (miRNA), have recently been recognized as a prominent player in post-transcriptional regulation of local protein synthesis. Although it is now certain that the miRNAs localize into axons and play a role in the coordinated regulation of local protein synthesis in regenerating axons, how these non-coding RNAs translocate into distal process of neurons is completely unknown to date. Interestingly, several recent studies show the presence of Dicer and components of the miRNA-induced silencing complex (miRISC) that are required for processing precursor miRNAs (pre- miRNAs) to mature functional miRNAs both in dendrites and axons. Processing of a pre-miRNA to mature miRNA locally in neuronal processes could confer a unique advantage for coordinately altering the population of proteins generated in growth cones by targeting mRNA cohorts. Here, we propose to characterize the population of pre-miRNAs transported into axons and to determine the RNA structures and the trans-acting factor(s) underlying this transport of pre-miRNA into distal process of sensory neurons.
The specific aims of this proposal are: (1) to profile changes of the precursor and mature miRNA expression levels in the axonal compartments following sciatic nerve injury;(2) To identify the cis-acting region(s) of precursor miRNAs and trans-acting factor(s) that are required for localization. On completion of these studies, we will have characterized a novel set of neuronal miRNAs that regulate local protein synthesis in distal axons to promote nerve regeneration. In addition, the proposed work will, for the first time, demonstrate mRNA-independent localization of precursor miRNAs into distal axons and a subsequent local maturation to the mature functional miRNA upon a signal arrival. We also anticipate that these studies should identify new targets that could be manipulated to promote axonal regrowth in various neurological disorders including spinal cord injury and demyelinating neuropathies.

Public Health Relevance

Axons injured in the central nervous system do not generally regenerate and there are currently no effective treatments, resulting in devastating and permanent neurophysiological dysfunction. The goal of this proposed study is to understand neuroregnerative mechanisms in the peripheral nervous system that enable PNS axons to spontaneously regenerate. A detailed understanding of the neuroregenerative mechanisms will lead us to develop strategies for much-needed treatment for CNS injury.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Exploratory/Developmental Grants (R21)
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Neurodifferentiation, Plasticity, and Regeneration Study Section (NDPR)
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Jakeman, Lyn B
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Alfred I. Du Pont Hosp for Children
United States
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Phay, Monichan; Kim, Hak Hee; Yoo, Soonmoon (2018) Analysis of piRNA-Like Small Non-coding RNAs Present in Axons of Adult Sensory Neurons. Mol Neurobiol 55:483-494
Merianda, Tanuja T; Coleman, Jennifer; Kim, Hak Hee et al. (2015) Axonal amphoterin mRNA is regulated by translational control and enhances axon outgrowth. J Neurosci 35:5693-706
Sampson, Valerie B; Yoo, Soonmoon; Kumar, Asmita et al. (2015) MicroRNAs and Potential Targets in Osteosarcoma: Review. Front Pediatr 3:69
Kim, Hak Hee; Lee, Seung Joon; Gardiner, Amy S et al. (2015) Different motif requirements for the localization zipcode element of ?-actin mRNA binding by HuD and ZBP1. Nucleic Acids Res 43:7432-46
Kim, Hak Hee; Kim, Paul; Phay, Monichan et al. (2015) Identification of precursor microRNAs within distal axons of sensory neuron. J Neurochem 134:193-9
Phay, Monichan; Kim, Hak Hee; Yoo, Soonmoon (2015) Dynamic Change and Target Prediction of Axon-Specific MicroRNAs in Regenerating Sciatic Nerve. PLoS One 10:e0137461