MRNA expression profiling in the spinal nerve ligation model of neuropathic pain in rats
ABSTRACT: Expression profiling of L4 and L5 Dorsal Root Ganglion (DRG) in the spinal nerve ligation model of neuropathic pain. The goal of the study was to identify genes involved in neuropathic pain Overall design: This series of samples comprises of contralateral and ipsilateral L4 and L5 DRG tissue collected 4 weeks after rats underwent a L5 spinal nerve ligation (SNL) or a sham operation with no L5 spinal nerve ligation. This defines 8 groups (i) contralateral L4 DRG from the sham cohort (n=5), (ii) ipsilateral L4 DRG from sham cohort (n=5), (iii) contralateral L4 DRG from SNL cohort (n=5), (iv) ipsilateral L4 DRG from the SNL chort (n=5), (v) contralateral L5 DRG from the sham cohort (n=5), (vi) ipsilateral L5 DRG from sham cohort (n=5), (vii) contralateral L5 DRG from SNL cohort (n=5), (viii) ipsilateral L5 DRG from the SNL cohort (n=5)
INSTRUMENT(S): [Rat230_2] Affymetrix Rat Genome 230 2.0 Array
Project description:Expression profiling of L4 and L5 Dorsal Root Ganglion (DRG) in the spinal nerve ligation model of neuropathic pain. The goal of the study was to identify genes involved in neuropathic pain This series of samples comprises of contralateral and ipsilateral L4 and L5 DRG tissue collected 4 weeks after rats underwent a L5 spinal nerve ligation (SNL) or a sham operation with no L5 spinal nerve ligation. This defines 8 groups (i) contralateral L4 DRG from the sham cohort (n=5), (ii) ipsilateral L4 DRG from sham cohort (n=5), (iii) contralateral L4 DRG from SNL cohort (n=5), (iv) ipsilateral L4 DRG from the SNL chort (n=5), (v) contralateral L5 DRG from the sham cohort (n=5), (vi) ipsilateral L5 DRG from sham cohort (n=5), (vii) contralateral L5 DRG from SNL cohort (n=5), (viii) ipsilateral L5 DRG from the SNL cohort (n=5)
Project description:Nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are two major members of the neurotrophin family. Using immunohistochemistry and in situ hybridization histochemistry, we examined the effect of L5 spinal nerve ligation (SPNL), a neuropathic pain model, on the expression of BDNF in the uninjured L4 dorsal root ganglion (DRG). After L5 SPNL, both immunoreactivity for BDNF and the hybridization intensity for BDNF mRNA increased mainly in the small- and medium-sized neurons. The percentage of BDNF mRNA-expressing neurons increased in the ipsilateral L4 DRG compared with the contralateral DRG from the third to 28th day after ligation. A significantly greater number of BDNF-immunoreactive neurons were observed in the ipsilateral L4 DRG than contralateral side 14 d after ligation. To test the contribution of BDNF to the thermal hyperalgesia produced in this model, we intrathecally injected anti-BDNF antibody at third day after ligation. This treatment clearly attenuated thermal hyperalgesia for a few hours. Almost all BDNF mRNA-expressing neurons coexpressed trkA, a high-affinity NGF receptor, mRNA. The percentage of BDNF mRNA-expressing cells of trkA cells significantly increased in the ipsilateral L4 DRG 14 d after ligation. Furthermore, we examined the contribution of NGF on this phenotypic change using ELISA, Northern blot analysis, and anti-NGF antibody. NGF content in the ipsilateral L4 DRG linearly increased and reached a statistical significant level 14 d after L5 SPNL. Moreover, at this time point, the increase in NGF mRNA was observed in the ipsilateral L5 DRG and sciatic nerve, but not in the ipsilateral L4 DRG or L4 spinal nerve. Local application of anti-NGF antibody to the L4 spinal nerve beside the L5 spinal nerve-ligation site prevented the development of thermal hyperalgesia for 5 d after ligation. Our data suggest that BDNF, which increased in the uninjured L4 DRG neurons, acts as a sensory neuromodulator in the dorsal horn and contributes to thermal hyperalgesia in this neuropathic pain model. The contribution of locally synthesized NGF to thermal hyperalgesia was also demonstrated. These dynamic alterations in the expression and content of BDNF and NGF in the uninjured DRG neurons might be involved in the pathomechanisms of neuropathic pain.
Project description:Two out-bred rat selection lines were separated to produce different hypersensitivity phenotypes following nerve injury. These lines were termed High Pain and Low Pain (HP or LP). Each sub-strain was either subject to a Sham surgery or a Spinal Nerve Ligation (SNL) surgery to the L4 and L5 spinal nerves. Three days following surgery L4/L5 Dorsal Root Ganglia (DRG) were dissected from these animals. For the rat line separation protocol see: Devor M, Raber P (1990) Heritability of symptoms in an experimental model of neuropathic pain. Pain 42:51-67. 12 Hybridizations, 3 per condition; Sham HP DRG; 3 day SNL HP DRG; Sham LP DRG; 3 day SNL LP DRG.
Project description:Parvalbumin (PV) is a calcium binding protein that identifies a subpopulation of proprioceptive dorsal root ganglion (DRG) neurons. Calcitonin gene-related peptide (CGRP) is also expressed in a high proportion of muscle afferents but its relationship to PV is unclear. Little is known of the phenotypic responses of muscle afferents to nerve injury. Sciatic nerve axotomy or L5 spinal nerve ligation and section (SNL) lesions were used to explore these issues in adult rats using immunocytochemistry.In naive animals, the mean PV expression was 25 % of L4 or L5 dorsal root ganglion (DRG) neurons, and this was unchanged 2 weeks after sciatic nerve axotomy. Colocalization studies with the injury marker activating transcription factor 3 (ATF3) showed that approximately 24 % of PV neurons expressed ATF3 after sciatic nerve axotomy suggesting that PV may show a phenotypic switch from injured to uninjured neurons. This possibility was further assessed using the spinal nerve ligation (SNL) injury model where injured and uninjured neurons are located in different DRGs. Two weeks after L5 SNL there was no change in total PV staining and essentially all L5 PV neurons expressed ATF3. Additionally, there was no increase in PV-ir in the adjacent uninjured L4 DRG cells. Co-labelling of DRG neurons revealed that less than 2 % of PV neurons normally expressed CGRP and no colocalization was seen after injury.These experiments clearly show that axotomy does not produce down regulation of PV protein in the DRG. Moreover, this lack of change is not due to a phenotypic switch in PV immunoreactive (ir) neurons, or de novo expression of PV-ir in uninjured neurons after nerve injury. These results further illustrate differences that occur when muscle afferents are injured as compared to cutaneous afferents.
Project description:Neuropathic pain is a complex chronic condition occurring post-nervous system damage. The transcriptional reprogramming of injured dorsal root ganglia (DRGs) drives neuropathic pain. However, few comparative analyses using high-throughput platforms have investigated uninjured DRG in neuropathic pain, and potential interactions among differentially expressed genes (DEGs) and pathways were not taken into consideration. The aim of this study was to identify changes in genes and pathways associated with neuropathic pain in uninjured L4 DRG after L5 spinal nerve ligation (SNL) by using bioinformatic analysis.The microarray profile GSE24982 was downloaded from the Gene Expression Omnibus database to identify DEGs between DRGs in SNL and sham rats. The prioritization for these DEGs was performed using the Toppgene database followed by gene ontology and pathway enrichment analyses. The relationships among DEGs from the protein interactive perspective were analyzed using protein-protein interaction (PPI) network and module analysis. Real-time polymerase chain reaction (PCR) and Western blotting were used to confirm the expression of DEGs in the rodent neuropathic pain model.A total of 206 DEGs that might play a role in neuropathic pain were identified in L4 DRG, of which 75 were upregulated and 131 were downregulated. The upregulated DEGs were enriched in biological processes related to transcription regulation and molecular functions such as DNA binding, cell cycle, and the FoxO signaling pathway. Ctnnb1 protein had the highest connectivity degrees in the PPI network. The in vivo studies also validated that mRNA and protein levels of Ctnnb1 were upregulated in both L4 and L5 DRGs.This study provides insight into the functional gene sets and pathways associated with neuropathic pain in L4 uninjured DRG after L5 SNL, which might promote our understanding of the molecular mechanisms underlying the development of neuropathic pain.
Project description:BACKGROUND: Dysregulation of voltage-gated sodium channels (Na(v)s) is believed to play a major role in nerve fiber hyperexcitability associated with neuropathic pain. A complete transcriptional characterization of the different isoforms of Na(v)s under normal and pathological conditions had never been performed on mice, despite their widespread use in pain research. Na(v)s mRNA levels in mouse dorsal root ganglia (DRG) were studied in the spared nerve injury (SNI) and spinal nerve ligation (SNL) models of neuropathic pain. In the SNI model, injured and non-injured neurons were intermingled in lumbar DRG, which were pooled to increase the tissue available for experiments. RESULTS: A strong downregulation was observed for every Na(v)s isoform expressed except for Na(v)1.2; even Na(v)1.3, known to be upregulated in rat neuropathic pain models, was lower in the SNI mouse model. This suggests differences between these two species. In the SNL model, where the cell bodies of injured and non-injured fibers are anatomically separated between different DRG, most Na(v)s were observed to be downregulated in the L5 DRG receiving axotomized fibers. Transcription was then investigated independently in the L3, L4 and L5 DRG in the SNI model, and an important downregulation of many Na(v)s isoforms was observed in the L3 DRG, suggesting the presence of numerous injured neurons there after SNI. Consequently, the proportion of axotomized neurons in the L3, L4 and L5 DRG after SNI was characterized by studying the expression of activating transcription factor 3 (ATF3). Using this marker of nerve injury confirmed that most injured fibers find their cell bodies in the L3 and L4 DRG after SNI in C57BL/6 J mice; this contrasts with their L4 and L5 DRG localization in rats. The spared sural nerve, through which pain hypersensitivity is measured in behavioral studies, mostly projects into the L4 and L5 DRG. CONCLUSIONS: The complex regulation of Na(v)s, together with the anatomical rostral shift of the DRG harboring injured fibers in C57BL/6 J mice, emphasize that caution is necessary and preliminary anatomical experiments should be carried out for gene and protein expression studies after SNI in mouse strains.
Project description:The study pursued dual goals: To advance mRNA-seq bioinformatics towards unbiased transcriptome capture and to demonstrate its potential for discovery in neuroscience by applying the approach to an in vivo model of neurological disease. We found that 12.4% of known genes were induced and 7% were suppressed in the dysfunctional (but anatomically intact) L4 dorsal root ganglion (DRG) 2 weeks after L5 spinal Nerve Ligation (SNL). A new algorithm for agnostic mapping of pre-mRNA splice junctions (SJ) achieved a precision of 97%. mRNA-seq of L4 DRG 2 weeks and 2 months after L5 spinal nerve ligation. CONTROL and SNL were used to identify differential gene expression between chronic pain and standard conditions in Rattus norvegicus. CONTROL and SNL and PILOT were used to perform 'agnostic splice site discovery' in the nervous system transcriptome in Rattus norvegicus
Project description:The study pursued dual goals: To advance mRNA-seq bioinformatics towards unbiased transcriptome capture and to demonstrate its potential for discovery in neuroscience by applying the approach to an in vivo model of neurological disease. We found that 12.4% of known genes were induced and 7% were suppressed in the dysfunctional (but anatomically intact) L4 dorsal root ganglion (DRG) 2 weeks after L5 spinal Nerve Ligation (SNL). A new algorithm for agnostic mapping of pre-mRNA splice junctions (SJ) achieved a precision of 97%. Overall design: mRNA-seq of L4 DRG 2 weeks and 2 months after L5 spinal nerve ligation. CONTROL and SNL were used to identify differential gene expression between chronic pain and standard conditions in Rattus norvegicus. CONTROL and SNL and PILOT were used to perform 'agnostic splice site discovery' in the nervous system transcriptome in Rattus norvegicus
Project description:Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) decodes neuronal activity by translating cytoplasmic Ca(2+) signals into kinase activity that regulates neuronal functions including excitability, gene expression, and synaptic transmission. Four genes lead to developmental and differential expression of CaMKII isoforms (α, β, γ, δ). We determined mRNA levels of these isoforms in the dorsal root ganglia (DRG) of adult rats with and without nerve injury in order to determine if differential expression of CaMKII isoforms may contribute to functional differences that follow injury. DRG neurons express mRNA for all four isoforms, and the relative abundance of CaMKII isoforms was γ>α>β=δ, based on the CT values. Following ligation of the 5th lumbar (L5) spinal nerve (SNL), the β isoform did not change, but mRNA levels of both the γ and α isoforms were reduced in the directly injured L5 neurons, and the α isoform was reduced in L4 neurons, compared to their contemporary controls. In contrast, expression of the δ isoform mRNA increased in L5 neurons. CaMKII protein decreased following nerve injury in both L4 and L5 populations. Total CaMKII activity measured under saturating Ca(2+)/CaM conditions was decreased in both L4 and L5 populations, while autonomous CaMKII activity determined in the absence of Ca(2+) was selectively reduced in axotomized L5 neurons 21days after injury. Thus, loss of CaMKII signaling in sensory neurons after peripheral nerve injury may contribute to neuronal dysfunction and pain.
Project description:The sigma-1 receptor (σ1R), an endoplasmic reticulum chaperone protein, is widely distributed and regulates numerous intracellular processes in neurons. Nerve injury alters the structure and function of axotomized dorsal root ganglion (DRG) neurons, contributing to the development of pain. The σ1R is enriched in the spinal cord and modulates pain after peripheral nerve injury. However, σ1R expression in the DRG has not been studied. We therefore characterized σ1R expression in DRGs at baseline and following spinal nerve ligation (SNL) in rats.Immunohistochemical (IHC) studies in DRG sections show σ1R in both neuronal somata and satellite glial cells. The punctate distribution of σ1R in the neuronal cytoplasm suggests expression in the endoplasmic reticulum. When classified by neuronal size, large neurons (>1300 μm) showed higher levels of σ1R staining than other groups (700-1300 μm, <700 μm). Comparing σ1R expression in neuronal groups characterized by expression of calcitonin gene-related peptide (CGRP), isolectin-B4 (IB4) and neurofilament-200 (NF-200), we found σ1R expression in all three neuronal subpopulations, with highest levels of σ1R expression in the NF-200 group. After SNL, lysates from L5 DRGs that contains axotomized neurons showed decreased σ1R protein but unaffected transcript level, compared with Control DRGs. IHC images also showed decreased σ1R protein expression, in SNL L5 DRGs, and to a lesser extent in the neighboring SNL L4 DRGs. Neurons labeled by CGRP and NF-200 showed decreased σ1R expression in L5 and, to a lesser extent, L4 DRGs. In IB4-labeled neurons, σ1R expression decreased only in axotomized L5 DRGs. Satellite cells also showed decreased σ1R expression in L5 DRGs after SNL.Our data show that σ1R is present in both sensory neurons and satellite cells in rat DRGs. Expression of σ1R is down-regulated in axotomized neurons as well as in their accompanying satellite glial cells, while neighboring uninjured neurons show a lesser down-regulation. Therefore, elevated σ1R expression in neuropathic pain is not an explanation for pain relief after σ1R blockade. This implies that increased levels of endogenous σ1R agonists may play a role, and diminished neuroprotection from loss of glial σ1R may be a contributing factor.