Upregulation Of Regeneration-associated Genes Research Articles

Transcription factor network analysis identifies REST/NRSF as an intrinsic regulator of CNS regeneration in mice

The inability of neurons to regenerate long axons within the CNS is a major impediment to improving outcome after spinal cord injury, stroke, and other CNS insults. Recent advances have uncovered an intrinsic program that involves coordinate regulation by multiple transcription factors that can be manipulated to enhance growth in the peripheral nervous system. Here, we use a systems genomics approach to characterize regulatory relationships of regeneration-associated transcription factors, identifying RE1-Silencing Transcription Factor (REST; Neuron-Restrictive Silencer Factor, NRSF) as a predicted upstream suppressor of a pro-regenerative gene program associated with axon regeneration in the CNS. We validate our predictions using multiple paradigms, showing that mature mice bearing cell type-specific deletions of REST or expressing dominant-negative mutant REST show improved regeneration of the corticospinal tract and optic nerve after spinal cord injury and optic nerve crush, which is accompanied by upregulation of regeneration-associated genes in cortical motor neurons and retinal ganglion cells, respectively. These analyses identify a role for REST as an upstream suppressor of the intrinsic regenerative program in the CNS and demonstrate the utility of a systems biology approach involving integrative genomics and bio-informatics to prioritize hypotheses relevant to CNS repair.

The longitudinal transcriptomic response of the substantia nigra to intrastriatal 6-hydroxydopamine reveals significant upregulation of regeneration-associated genes.

We hypothesized that the study of gene expression at 1, 2, 4, 6 and 16 weeks in the substantia nigra (SN) after intrastriatal 6-OHDA in the Sprague-Dawley rat (rattus norvegicus) would identify cellular responses during the degenerative process that could be axoprotective. Specifically, we hypothesized that genes expressed within the SN that followed a profile of being highly upregulated early after the lesion (during active axonal degeneration) and then progressively declined to baseline over 16 weeks as DA neurons died are indicative of potential protective responses to the striatal 6-OHDA insult. Utilizing a κ-means cluster analysis strategy, we demonstrated that one such cluster followed this hypothesized expression pattern over time, and that this cluster contained several interrelated transcripts that are classified as regeneration-associated genes (RAGs) including Atf3, Sprr1a, Ecel1, Gadd45a, Gpnmb, Sox11, Mmp19, Srgap1, Rab15,Lifr, Trib3, Tgfb1, and Sema3c. All exemplar transcripts tested from this cluster (Sprr1a, Ecel1, Gadd45a, Atf3 and Sox11) were validated by qPCR and a smaller subset (Sprr1a, Gadd45a and Sox11) were shown to be exclusively localized to SN DA neurons using a dual label approach with RNAScope in situ hybridization and immunohistochemistry. Upregulation of RAGs is typically associated with the response to axonal injury in the peripheral nerves and was not previously reported as part of the axodegenerative process for DA neurons of the SN. Interestingly, as part of this cluster, other transcripts were identified based on their expression pattern but without a RAG provenance in the literature. These "RAG-like" transcripts need further characterization to determine if they possess similar functions to or interact with known RAG transcripts. Ultimately, it is hoped that some of the newly identified axodegeneration-reactive transcripts could be exploited as axoprotective therapies in PD and other neurodegenerative diseases.

Chronically CNS-Injured Adult Sensory Neurons Gain Regenerative Competence upon a Lesion of Their Peripheral Axon

Several experimental manipulations result in axonal regeneration in the central nervous system (CNS) when applied before or at the time of injury but not when initiated after a delay, which would be clinically more relevant. As centrally injured neurons show signs of atrophy and degeneration, it raises the question whether chronically injured neurons are able to regenerate. To address this question, we used adult rodent primary sensory neurons that regenerate their central axon when their peripheral axon is cut (called conditioning) beforehand but not afterwards. We found that primary sensory neurons express regeneration-associated genes and efficiently regrow their axon in cell culture two months after a central lesion upon conditioning. Moreover, conditioning enables central axons to regenerate through a fresh lesion independent of a previous central lesion. Using in vivo imaging we demonstrated that conditioned neurons rapidly regrow their axons through a fresh central lesion. Finally, when single sensory axons were cut with a two-photon laser, they robustly regenerate within days after attaining growth competence through conditioning. We conclude that sensory neurons can acquire the intrinsic potential to regenerate their axons months after a CNS lesion, which they implement in the absence of traumatic tissue.