Translational Regulation in Initial Stages of the Neuronal Injury Response
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ABSTRACT: Transcriptional events leading to outgrowth of neuronal axons have been intensively studied, but the role of translational regulation in this process is not well understood. Here we use translatome analyses by ribosome pull-down and protein synthesis characterization by metabolic isotopic labeling to study nerve injury and axon outgrowth proteomes in rodent dorsal root ganglia (DRG) and sensory neurons. We identify over 1600 gene products that are primarily translationally regulated in DRG neurons after nerve injury, many of which contain a 5’UTR CERT motif, implicating the translation initiation factor Eif4e in the injury response. We further identified approximately 200 proteins that undergo robust de novo synthesis in the initial stages of axon growth. ApoE is one of the highly synthesized proteins in neurons, and inhibition of its signaling affects axon outgrowth. These findings suggest prominent roles for translational regulation in initial stages of the neuronal injury response and axon extension.
Project description:Axon regeneration is a necessary step toward functional recovery after spinal cord injury. The AP-1 transcription factor c-Jun has long been known to play an important role in directing the transcriptional response of Dorsal Root Ganglion (DRG) neurons to peripheral axotomy that results in successful axon regeneration. Here we performed ChIPseq for Jun in mouse DRG neurons after a sciatic nerve crush or sham surgery in order to measure the changes in Jun’s DNA binding in response to peripheral axotomy. We found that the majority of Jun’s injury-responsive changes in DNA binding occur at putative enhancer elements, rather than proximal to transcription start sites. We also used a series of single polypeptide chain tandem transcription factors to test the effects of different Jun-containing dimers on neurite outgrowth in cortical and hippocampal neurons. These experiments demonstrated that dimers composed of Jun and Atf3 promoted neurite outgrowth in rat CNS neurons. Our work provides new insight into the mechanisms underlying Jun’s role in axon regeneration.
Project description:Primary sensory neurons with cell soma in dorsal root ganglia (DRG) project axons in both the peripheral nervous system and the spinal cord. Whereas the peripheral axon can regenerate after injury, the central axon cannot, providing an opportunity to identify the mechanisms that promote axon regeneration. Using this system, multiple intrinsic mechanisms operating in sensory neurons have been shown to promote axon regeneration. Peripheral sensory neurons also benefit from a supportive environment. In particular, macrophages play important roles in nerve regeneration by clearing debris and regulating Schwann cell function at the site of injury in the nerve. Nerve macrophages have been characterized at the molecular level and derive for the most part from infiltrating monocytes. However, the role and origin of macrophages in the DRG remains poorly understood. Following a 14-days treatment with a CSF1R inhibitor, less than 10% of macrophages remained in the DRG. Recovery from this treatment resulted in a dramatic macrophage repopulation, with the number of DRG macrophages reaching level similar to untreated mice three days post injury. These repopulated DRG macrophages contribute to promote axon regeneration. Our scRNA-seq analysis allow in-depth characterization of the repopulated DRG macrophages in response to nerve injury. These data will provide a better understanding of DRG macrophages and the molecular mechanisms by which they contribute to peripheral nerve repair. These studies may lead to new potential targets to promote axon regeneration.
Project description:Axon regeneration in the central nervous system (CNS) requires reactivating injured neurons’ intrinsic growth state and enabling growth in an inhibitory environment. Using an inbred mouse neuronal phenotypic screen, we find that CAST/Ei mouse adult dorsal root ganglion neurons extend axons more on CNS myelin than the other eight strains tested, especially when pre-injured. Injury-primed CAST/Ei neurons also regenerate markedly in the spinal cord and optic nerve more than those from C57BL/6 mice and show greater spouting following ischemic stroke. Heritability estimates indicate that extended growth in CAST/Ei neurons on myelin is genetically determined, and two whole-genome expression screens yield the Activin transcript Inhba as most correlated with this ability. These screens are presented here. Biological quadruplicate - Mouse tissue - Naïve Dorsal Root Ganglia (DRG) and 5 day post sciatic nerve crush DRG - x9 strains.
Project description:We generated whole-genome gene expression profiles of dorsal root ganglion (DRG) neurons following nerve damage. DRG neurons extend one peripheral axon into the spinal nerve and one central axon into the dorsal root. The peripheral axon regenerates vigorously, while in contrast the central axon has little regenerative capacity. For this study, two groups of animals were subjected either to sciatic nerve (SN) or dorsal root (DR) crush, and at 12, 24, 72 hours and 7 days after the crush, lumbar DRGs L4, L5 and L6 were dissected and total RNA was extracted. For each time point after lesion, three biological replicate RNA samples were hybridized together with the common reference sample consisting of labeld RNA pooled from three unlesioned animals.
Project description:Analysis of gene expression in injured primary DRG with or without camptothecin (CPT) treatment after sciatic nerve crushing may help us identify critical molecular pathways related to axon regeneration. We performed RNA-sequencing of (i) Naive primary DRG tissues without injury, (ii) Primary DRG tissues with vehicle treatment different time-points (18, 24, 36 hours) after sciatic nerve injury, and (iii) Primary DRG tissues with camptothecin treatment different time-points (18, 24, 36 hours) after sciatic nerve injury.
Project description:We generated whole-genome gene expression profiles of dorsal root ganglion (DRG) neurons following nerve damage. DRG neurons extend one peripheral axon into the spinal nerve and one central axon into the dorsal root. The peripheral axon regenerates vigorously, while in contrast the central axon has little regenerative capacity. For this study, two groups of animals were subjected either to sciatic nerve (SN) or dorsal root (DR) crush, and at 12, 24, 72 hours and 7 days after the crush, lumbar DRGs L4, L5 and L6 were dissected and total RNA was extracted.
Project description:Preconditioning nerve injury drives pro-regenerative perineuronal macrophage activation in dorsal root ganglia (DRG). The present study reports that oncomodulin (ONCM) is produced from the regeneration-associated macrophages (RAMs) and strongly influences regeneration of DRG sensory axons. ONCM in macrophages was necessary to produce RAMs in the in vitro model of neuron-macrophage interaction and played an essential role in for preconditioning-induced neurite outgrowth. In order to gain insight on potential mechanisms downstream of ONCM for potent neurite outgrowth activity, we performed RNA-seq using cultured DRG neurons treated with ONCM.
Project description:The goal of this study was to compare the transcriptional effects of sciatic nerve injury and spinal cord injury on lumbar dorsal root ganglion (DRG) and FACS-sorted dorsal column (DC) sensory neurons. We performed RNA-seq of whole DRG from naïve and spinal cord-injured (SCI) mice (1dpi) and compared this with previously published data for sciatic nerve transection. In order to assess changes specifically in DC neurons, we performed RNA-seq from FACS-sorted DC neurons from Thy1-YFP16 transgenic mice in naïve, sciatic nerve injured (SNI), and SCI (1 and 3dpi). We found that DC neurons alter their transcriptome after SCI, but that gene changes after SCI mostly differ from SNI. These transcriptional differences may reflect both growth promoting and growth inhibitory effects on axon regeneration after SCI.
Project description:Retrograde signaling from axon to soma activates intrinsic regeneration mechanisms in lesioned peripheral sensory neurons; however, the links between axonal injury signaling and the cell body response are not well understood. Here, we used phosphoproteomics and microarrays to implicate ~900 phosphoproteins in retrograde injury signaling in rat sciatic nerve axons in vivo and ~4500 transcripts in the in vivo response to injury in the dorsal root ganglia. Computational analyses of these data sets identified ~400 redundant axonal signaling networks connected to 39 transcription factors implicated in the sensory neuron response to axonal injury. Experimental perturbation of individual overrepresented signaling hub proteins, including Abl, AKT, p38, and protein kinase C, affected neurite outgrowth in sensory neurons. Paradoxically, however, combined perturbation of Abl together with other hub proteins had a reduced effect relative to perturbation of individual proteins. Our data indicate that nerve injury responses are controlled by multiple regulatory components, and suggest that network redundancies provide robustness to the injury response Microarrays were run on mRNA extracted from adult rat L4 and L5 DRGs cells after 1,3,8,12,16,18,24, and 28 hours after a sciatic nerve (proximal and distal) lesion.
Project description:Dorsal root ganglion (DRG) neurons provide connectivity between peripheral tissues and spinal cord. Transcriptional plasticity within DRG sensory neurons after peripheral nerve injury contributes to nerve repair but also leads to maladaptive plasticity, including the development of neuropathic pain. This study presents tissue and neuron specific expression profiling of both known and novel Long Non-Coding RNAs (LncRNAs) in rodent DRG following nerve injury. We have identified a large number of novel LncRNAs expressed within rodent DRG, a minority of which were syntenically conserved between mouse and rat and which including both- intergenic and antisense LncRNAs. We have also identified neuron type-specific LncRNAs in mouse DRG, and LncRNAs that are expressed in human IPS cell-derived sensory neurons. We show significant plasticity in LncRNA expression following nerve injury, which in mouse is strain dependant. This resource is publicly available and will aid future studies of DRG neuron identity and the transcriptional landscape in both naïve and injured DRG.