Literature context: RRID:AB_2258513 1:3000
Neuropathic pain resulting from nerve injury can become persistent and difficult to treat but the molecular signaling responsible for its development remains poorly described. Here, we identify the neuronal stress sensor dual leucine zipper kinase (DLK; Map3k12) as a key molecule controlling the maladaptive pathways that lead to pain following injury. Genetic or pharmacological inhibition of DLK reduces mechanical hypersensitivity in a mouse model of neuropathic pain. Furthermore, DLK inhibition also prevents the spinal cord microgliosis that results from nerve injury and arises distant from the injury site. These striking phenotypes result from the control by DLK of a transcriptional program in somatosensory neurons regulating the expression of numerous genes implicated in pain pathogenesis, including the immune gene Csf1. Thus, activation of DLK is an early event, or even the master regulator, controlling a wide variety of pathways downstream of nerve injury that ultimately lead to chronic pain.
Literature context: z, RRID:AB_2258513; NFH, 1:1000; Aves Labs, RRID:
Stress and glucocorticoid (GC) release are common behavioral and hormonal responses to injury or disease. In the brain, stress/GCs can alter neuron structure and function leading to cognitive impairment. Stress and GCs also exacerbate pain, but whether a corresponding change occurs in structural plasticity of sensory neurons is unknown. Here, we show that in female mice (Mus musculus) basal GC receptor (Nr3c1, also known as GR) expression in dorsal root ganglion (DRG) sensory neurons is 15-fold higher than in neurons in canonical stress-responsive brain regions (M. musculus). In response to stress or GCs, adult DRG neurite growth increases through mechanisms involving GR-dependent gene transcription. In vivo, prior exposure to an acute systemic stress increases peripheral nerve regeneration. These data have broad clinical implications and highlight the importance of stress and GCs as novel behavioral and circulating modifiers of neuronal plasticity.
Literature context: AB_10699016), ATF2 (AB_630885), ATF3 (AB_2258513), Bax (AB_2227995), Bcl2 (AB_206
The c-Jun N-terminal kinases (JNKs) are important mediators of cell viability and structural integrity in postmitotic neurons, which is required for maintaining synaptic connections and neural plasticity. In the present study, we chose differentiated PC12 cells as a well-characterised neuronal model system to selectively examine the regulation of basal JNK activity by extracellular signal-regulated kinase 1/2 (ERK1/2) and Akt. We detected a complex interaction between the kinases to prevent cell death and neurite loss. Especially the appropriate level of JNK activation determined cellular survival. Basal activity of ERK1/2 attenuated the potentiation of JNK phosphorylation and thereby the induction of apoptosis. Importantly, when JNK activity was too low, cell viability and the number of neurite-bearing cells also decreased, even though the activation of ERK1/2 was enhanced. In this case, the JNK-mediated survival signals via activating transcription factor-3 (ATF3) were inhibited. Furthermore, the phosphorylation of ERK1/2 induced by the JNK inhibitor SP600125 inhibited the basal activity of Akt, which normally supported cell viability. Thus, controlling JNK activity is crucial to promote survival and neurite stability of differentiated neuronal cells.
Literature context: (C-19) Santa Cruz Cat# sc-188, RRID:AB_2258513 Sheep anti-CGRP Enzo Life Scien
Human autoantibodies to contactin-associated protein-like 2 (CASPR2) are often associated with neuropathic pain, and CASPR2 mutations have been linked to autism spectrum disorders, in which sensory dysfunction is increasingly recognized. Human CASPR2 autoantibodies, when injected into mice, were peripherally restricted and resulted in mechanical pain-related hypersensitivity in the absence of neural injury. We therefore investigated the mechanism by which CASPR2 modulates nociceptive function. Mice lacking CASPR2 (Cntnap2-/-) demonstrated enhanced pain-related hypersensitivity to noxious mechanical stimuli, heat, and algogens. Both primary afferent excitability and subsequent nociceptive transmission within the dorsal horn were increased in Cntnap2-/- mice. Either immune or genetic-mediated ablation of CASPR2 enhanced the excitability of DRG neurons in a cell-autonomous fashion through regulation of Kv1 channel expression at the soma membrane. This is the first example of passive transfer of an autoimmune peripheral neuropathic pain disorder and demonstrates that CASPR2 has a key role in regulating cell-intrinsic dorsal root ganglion (DRG) neuron excitability.
Literature context: logy Sc-188 RRID:AB_2258513 GAP43 1:10,000 Atlas Antibodies
Injury to the peripheral axons of sensory neurons strongly enhances the regeneration of their central axons in the spinal cord. It remains unclear on what molecules that initiate such conditioning effect. Because ATP is released extracellularly by nerve and other tissue injury, we hypothesize that injection of ATP into a peripheral nerve might mimic the stimulatory effect of nerve injury on the regenerative state of the primary sensory neurons. We found that a single injection of 6 μl of 150 μm ATP into female rat sciatic nerve quadrupled the number of axons growing into a lesion epicenter in spinal cord after a concomitant dorsal column transection. A second boost ATP injection 1 week after the first one markedly reinforced the stimulatory effect of a single injection. Single ATP injection increased expression of phospho-STAT3 and GAP43, two markers of regenerative activity, in sensory neurons. Double ATP injections sustained the activation of phospho-STAT3 and GAP43, which may account for the marked axonal growth across the lesion epicenter. Similar studies performed on P2X7 or P2Y2 receptor knock-out mice indicate P2Y2 receptors are involved in the activation of STAT3 after ATP injection or conditioning lesion, whereas P2X7 receptors are not. Injection of ATP at 150 μm caused little Wallerian degeneration and behavioral tests showed no significant long-term adverse effects on sciatic nerve functions. The results in this study reveal possible mechanisms underlying the stimulation of regenerative programs and suggest a practical strategy for stimulating axonal regeneration following spinal cord injury.SIGNIFICANCE STATEMENT Injury of peripheral axons of sensory neurons has been known to strongly enhance the regeneration of their central axons in the spinal cord. In this study, we found that injection of ATP into a peripheral nerve can mimic the effect of peripheral nerve injury and significantly increase the number of sensory axons growing across lesion epicenter in the spinal cord. ATP injection increased expression of several markers for regenerative activity in sensory neurons, including phospho-STAT3 and GAP43. ATP injection did not cause significant long-term adverse effects on the functions of the injected nerve. These results may lead to clinically applicable strategies for enhancing neuronal responses that support regeneration of injured axons.
Literature context: 188; RRID:AB_2258513 Rabbit anti-PGP9.5 AbD Serotec
N6-methyladenosine (m6A) affects multiple aspects of mRNA metabolism and regulates developmental transitions by promoting mRNA decay. Little is known about the role of m6A in the adult mammalian nervous system. Here we report that sciatic nerve lesion elevates levels of m6A-tagged transcripts encoding many regeneration-associated genes and protein translation machinery components in the adult mouse dorsal root ganglion (DRG). Single-base resolution m6A-CLIP mapping further reveals a dynamic m6A landscape in the adult DRG upon injury. Loss of either m6A methyltransferase complex component Mettl14 or m6A-binding protein Ythdf1 globally attenuates injury-induced protein translation in adult DRGs and reduces functional axon regeneration in the peripheral nervous system in vivo. Furthermore, Pten deletion-induced axon regeneration of retinal ganglion neurons in the adult central nervous system is attenuated upon Mettl14 knockdown. Our study reveals a critical epitranscriptomic mechanism in promoting injury-induced protein synthesis and axon regeneration in the adult mammalian nervous system.
Literature context: Santa Cruz Biotechnology Inc., RRID:AB_2258513), activated caspase 3 (1 : 200;
N-myc downstream-regulated gene 2 (NDRG2) is a differentiation- and stress-associated molecule that is predominantly expressed in astrocytes in the central nervous system. In this study, we examined the expression and role of NDRG2 in experimental autoimmune encephalomyelitis (EAE), which is an animal model of multiple sclerosis. Western blot and immunohistochemical analysis revealed that the expression of NDRG2 was observed in astrocytes of spinal cord, and was enhanced after EAE induction. A comparative analysis of wild-type and Ndrg2-/- mice revealed that deletion of Ndrg2 ameliorated the clinical symptoms of EAE. Although Ndrg2 deficiency only slightly affected the inflammatory response, based on the results of flow cytometry, qRT-PCR, and immunohistochemistry, it significantly reduced demyelination in the chronic phase, and, more importantly, neurodegeneration both in the acute and chronic phases. Further studies revealed that the expression of astrocytic glutamate transporters, including glutamate aspartate transporter (GLAST) and glutamate transporter 1, was more maintained in the Ndrg2-/- mice compared with wild-type mice after EAE induction. Consistent with these results, studies using cultured astrocytes revealed that Ndrg2 gene silencing increased the expression of GLAST, while NDRG2 over-expression decreased it without altering the expression of glial fibrillary acidic protein. The effect of NDRG2 on GLAST expression was associated with the activation of Akt, but not with the activation of nuclear factor-kappa B. These findings suggest that NDRG2 plays a key role in the pathology of EAE by modulating glutamate metabolism. Cover Image for this Issue: doi: 10.1111/jnc.14173.
Literature context: z, CA, USA, order numb. sc-188, RRID:AB_2258513). Appropriate Alexa Fluor-coupl
The extent of remyelination in multiple sclerosis lesions is often incomplete. Injury to oligodendrocyte progenitor cells can be a contributing factor for such incomplete remyelination. The precise mechanisms underlying insufficient repair remain to be defined, but oxidative stress appears to be involved. Here, we used immortalized oligodendrocyte cell lines as model systems to investigate a causal relation of oxidative stress and endoplasmic reticulum stress signaling cascades. OLN93 and OliNeu cells were subjected to chemical hypoxia by blocking the respiratory chain at various levels. Mitochondrial membrane potential and oxidative stress levels were quantified by flow cytometry. Endoplasmic reticulum stress was monitored by the expression induction of activating transcription factor 3 and 4 (Atf3, Atf4), DNA damage-inducible transcript 3 protein (Ddit3), and glucose-regulated protein 94. Lentiviral silencing of nuclear factor (erythroid-derived 2)-like 2 or kelch-like ECH-associated protein 1 was applied to study the relevance of NRF2 for endoplasmic reticulum stress responses. We demonstrate that inhibition of the respiratory chain induces oxidative stress in cultured oligodendrocytes which is paralleled by the expression induction of distinct mediators of the endoplasmic reticulum stress response, namely Atf3, Atf4, and Ddit3. Atf3 and Ddit3 expression induction is potentiated in kelch-like ECH-associated protein 1-deficient cells and absent in cells lacking the oxidative stress-related transcription factor NRF2. This study provides strong evidence that oxidative stress in oligodendrocytes activates endoplasmic reticulum stress response in a NRF2-dependent manner and, in consequence, might regulate oligodendrocyte degeneration in multiple sclerosis and other neurological disorders.
Literature context: (C-19) Santa Cruz Cat#sc-188x; RRID:AB_2258513 Mouse monoclonal anti-CSA (D-2)
Cockayne syndrome (CS) is caused by mutations in CSA and CSB. The CSA and CSB proteins have been linked to both promoting transcription-coupled repair and restoring transcription following DNA damage. We show that UV stress arrests transcription of approximately 70% of genes in CSA- or CSB-deficient cells due to the constitutive presence of ATF3 at CRE/ATF sites. We found that CSB, CSA/DDB1/CUL4A, and MDM2 were essential for ATF3 ubiquitination and degradation by the proteasome. ATF3 removal was concomitant with the recruitment of RNA polymerase II and the restart of transcription. Preventing ATF3 ubiquitination by mutating target lysines prevented recovery of transcription and increased cell death following UV treatment. Our data suggest that the coordinate action of CSA and CSB, as part of the ubiquitin/proteasome machinery, regulates the recruitment timing of DNA-binding factors and provide explanations about the mechanism of transcription arrest following genotoxic stress.
Literature context: RID:RRID:AB_2258513). Paw sections were double-labe
Chemotherapy-induced peripheral neuropathy (CIPN) arises from collateral damage to peripheral afferent sensory neurons by anticancer pharmacotherapy, leading to debilitating neuropathic pain. No effective treatment for CIPN exists, short of dose-reduction which worsens cancer prognosis. Here, we report that stimulation of nicotinamide phosphoribosyltransferase (NAMPT) produced robust neuroprotection in an aggressive CIPN model utilizing the frontline anticancer drug, paclitaxel (PTX). Daily treatment of rats with the first-in-class NAMPT stimulator, P7C3-A20, prevented behavioral and histologic indicators of peripheral neuropathy, stimulated tissue NAD recovery, improved general health, and abolished attrition produced by a near maximum-tolerated dose of PTX. Inhibition of NAMPT blocked P7C3-A20-mediated neuroprotection, whereas supplementation with the NAMPT substrate, nicotinamide, potentiated a subthreshold dose of P7C3-A20 to full efficacy. Importantly, P7C3-A20 blocked PTX-induced allodynia in tumored mice without reducing antitumoral efficacy. These findings identify enhancement of NAMPT activity as a promising new therapeutic strategy to protect against anticancer drug-induced peripheral neurotoxicity.
Literature context: y; RRID:AB_2258513), 4.1B (generated against a fus
Axons must withstand mechanical forces, including tension, torsion, and compression. Spectrins and actin form a periodic cytoskeleton proposed to protect axons against these forces. However, because spectrins also participate in assembly of axon initial segments (AISs) and nodes of Ranvier, it is difficult to uncouple their roles in maintaining axon integrity from their functions at AIS and nodes. To overcome this problem and to determine the importance of spectrin cytoskeletons for axon integrity, we generated mice with αII spectrin-deficient peripheral sensory neurons. The axons of these neurons are very long and exposed to the mechanical forces associated with limb movement; most lack an AIS, and some are unmyelinated and have no nodes. We analyzed αII spectrin-deficient mice of both sexes and found that, in myelinated axons, αII spectrin forms a periodic cytoskeleton with βIV and βII spectrin at nodes of Ranvier and paranodes, respectively, but that loss of αII spectrin disrupts this organization. Avil-cre;Sptan1f/f mice have reduced numbers of nodes, disrupted paranodal junctions, and mislocalized Kv1 K+ channels. We show that the density of nodal βIV spectrin is constant among axons, but the density of nodal αII spectrin increases with axon diameter. Remarkably, Avil-cre;Sptan1f/f mice have intact nociception and small-diameter axons, but severe ataxia due to preferential degeneration of large-diameter myelinated axons. Our results suggest that nodal αII spectrin helps resist the mechanical forces experienced by large-diameter axons, and that αII spectrin-dependent cytoskeletons are also required for assembly of nodes of Ranvier.SIGNIFICANCE STATEMENT A periodic axonal cytoskeleton consisting of actin and spectrin has been proposed to help axons resist the mechanical forces to which they are exposed (e.g., compression, torsion, and stretch). However, until now, no vertebrate animal model has tested the requirement of the spectrin cytoskeleton in maintenance of axon integrity. We demonstrate the role of the periodic spectrin-dependent cytoskeleton in axons and show that loss of αII spectrin from PNS axons causes preferential degeneration of large-diameter myelinated axons. We show that nodal αII spectrin is found at greater densities in large-diameter myelinated axons, suggesting that nodes are particularly vulnerable domains requiring a specialized cytoskeleton to protect against axon degeneration.
Literature context: Cruz, RRID:AB_2258513) or anti-Î²-actin/actin primary
Fish oil (FO) is the main source of long chain omega-3 polyunsaturated fatty acids (ω-3 PUFAs), which display relevant analgesic and anti-inflammatory properties. Peripheral nerve injury is driven by degeneration, neuroinflammation, and neuronal plasticity which results in neuropathic pain (NP) symptoms such as allodynia and hyperalgesia. We tested the preventive effect of an EPA/DHA-concentrate fish oil (CFO) on NP development and regenerative features. Swiss mice received daily oral treatment with CFO 4.6 or 2.3 g/kg for 10 days after NP was induced by partial sciatic nerve ligation. Mechanical allodynia and thermal hypernociception were assessed 5 days after injury. CFO 2.3 g/kg significantly prevented mechanical and thermal sensitization, reduced TNF levels in the spinal cord, sciatic MPO activity, and ATF-3 expression on DRG cells. CFO improved Sciatic Functional Index (SFI) as well as electrophysiological recordings, corroborating the increased GAP43 expression and total number of myelinated fibers observed in sciatic nerve. No locomotor activity impairment was observed in CFO treated groups. These results point to the regenerative and possibly protective properties of a combined EPA and DHA oral administration after peripheral nerve injury, as well as its anti-neuroinflammatory activity, evidencing ω-3 PUFAs promising therapeutic outcomes for NP treatment.
Literature context: z sc-188; RRID:AB_2258513 Rabbit ant
Mature neurons in the adult peripheral nervous system can effectively switch from a dormant state with little axonal growth to robust axon regeneration upon injury. The mechanisms by which injury unlocks mature neurons' intrinsic axonal growth competence are not well understood. Here, we show that peripheral sciatic nerve lesion in adult mice leads to elevated levels of Tet3 and 5-hydroxylmethylcytosine in dorsal root ganglion (DRG) neurons. Functionally, Tet3 is required for robust axon regeneration of DRG neurons and behavioral recovery. Mechanistically, peripheral nerve injury induces DNA demethylation and upregulation of multiple regeneration-associated genes in a Tet3- and thymine DNA glycosylase-dependent fashion in DRG neurons. In addition, Pten deletion-induced axon regeneration of retinal ganglion neurons in the adult CNS is attenuated upon Tet1 knockdown. Together, our study suggests an epigenetic barrier that can be removed by active DNA demethylation to permit axon regeneration in the adult mammalian nervous system.
Literature context: Anti-ATF3 RRID:AB_2258513 Santa Cruz Biotechnology sc-188
This study evaluates the pathological role of the stress sensor activating transcription factor-3 (ATF3) in ischemic neurotoxicity. Upregulation of the transcript and protein for ATF3 was seen 2-10 hr after reperfusion in the ipsilateral cerebral hemisphere of mice with transient middle cerebral artery occlusion for 2 hr. Immunohistochemical analysis confirmed the expression of ATF3 by cells immunoreactive for a neuronal marker in neocortex, hippocampus, and striatum within 2 hr after reperfusion. In murine neocortical neurons previously cultured under ischemic conditions for 2 hr, transient upregulation of both Atf3 and ATF3 expression was similarly found during subsequent culture for 2-24 hr under normoxia. Lentiviral overexpression of ATF3 ameliorated the neurotoxicity of glutamate (Glu) in cultured murine neurons along with a slight but statistically significant inhibition of both Fluo-3 and rhodamine-2 fluorescence increases by N-methyl-D-aspartate. Similarly, transient upregulation was seen in Atf3 and ATF3 expression during the culture for 48 hr in neuronal Neuro2A cells previously cultured under ischemic conditions for 2 hr. Luciferase reporter analysis with ATF3 promoter together with immunoblotting revealed the possible involvement of several transcription factors responsive to extracellular and intracellular stressors in the transactivation of the Atf3 gene in Neuro2A cells. ATF3 could be upregulated to play a role in mechanisms underlying mitigation of the neurotoxicity mediated by the endogenous neurotoxin Glu at an early stage after ischemic signal inputs.
Literature context: uz SC-188 RRID:AB_2258513), or rabbi
BACKGROUND: 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. RESULTS: 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. CONCLUSION: 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.
Mice with high numbers of the Cu/Zn superoxide dismutase-1 G93A transgene (SOD1(G93A) G1H) have become the most commonly used animal model to study amyotrophic lateral sclerosis. This study investigated changes in size, numbers, and cell stress/death markers of motor neuron numbers in G1H mice that re-express the common p75 neurotrophin receptor (p75NTR). SOD1(G93A) G1H mice and age-matched C57BL/6J controls at 60, 80, 100, 120 days and end stage/140 days were analyzed for p75NTR, choline acetyltransferase (ChAT), activating transcription factor 3 (ATF3), and cleaved caspase-3. In addition, motor neuron counts and soma sizes were recorded. Motor neurons re-expressing p75NTR in SOD1(G93A) G1H mice were first observed at 80 days, and this continued to 140 days, peaking at 100-120 days at ∼5%. The soma area of motor neurons re-expressing p75NTR was always 600-800 µm(2) , suggesting that these are alpha motor neurons, which was confirmed after examination of somas post injection of a retrogradely transported antibody to p75NTR in 110-day-old SOD1(G93A) G1H mice. In motor neurons not re-expressing p75NTR, the frequency of small soma 200-400 µm2 motor neurons increased, whereas the larger 600-900 µm2 motor neurons decreased with progression, indicating that large motor neurons were dying off and shrinking in the process. There was minimal coexpression of p75NTR with ATF3, a marker for cell stress, but 85% coexpressed the apoptotic marker cleaved caspase-3. These findings indicate that in SOD1(G93A) G1H mice, p75NTR re-expression is detectable from 80 days in a small population of large motor neurons that represent 5% of the total motor neurons. Furthermore, p75NTR re-expression occurs in larger alpha motor neurons that express cleaved caspsase-3 and are destined to die.
Literature context: one C-19, RRID:AB_2258513 0.0 5 Î¼g/m
The mechanisms underlying rheumatoid arthritis (RA)-induced pain are still not fully elucidated, and accumulating data indicate that peripheral inflammation is not the only factor driving pain in these patients. The focus of our work is to investigate the molecular basis for long-term alterations in nociceptive pathways induced by polyarthritis using the collagen antibody-induced arthritis (CAIA) mouse model. In this model, mechanical hypersensitivity outlasts the joint inflammation by weeks. Here we examined expression levels of neuropeptides, ion channels, and nerve injury markers associated with neuropathic and/or inflammatory pain in dorsal root ganglia (DRGs) and spinal cord both during the peak of inflammation (day 15) and when the inflammation has resolved but the hypersensitivity persists (days 45-47). No apparent differences were observed in substance P, calcitonin gene-related peptide, or neuropeptide Y protein expression in DRGs and spinal cord of CAIA mice. However, the neuropeptide galanin, the ATP-gated ion channel P2X3, and calcium channel subunit α2δ1 were significantly increased in the CAIA DRGs as compared to controls, both 15 and 47 days after induction of arthritis. On day 15 there was an increase in expression of two factors associated with nerve injury and cell stress, activating transcription factor 3 and growth-associated protein 43 in DRGs, whereby the latter was still dramatically upregulated after 47 days. In conclusion, this study suggests that long-term joint inflammation has an impact on DRG neurons that resembles both inflammation and nerve injury-induced pain states. Thus, antibody-driven inflammation generates a pain state with a unique neurochemical profile.
Literature context: # sc-188, RRID:AB_2258513), goat ant
Molecular and cellular mechanisms underlying the peripheral conditioning lesion remain unsolved. We show here that injection of a chemical demyelinating agent, ethidium bromide, into the sciatic nerve induces a similar set of regeneration-associated genes and promotes a 2.7-fold greater extent of sensory axon regeneration in the spinal cord than sciatic nerve crush. We found that more severe peripheral demyelination correlates with more severe functional and electrophysiological deficits, but more robust central regeneration. Ethidium bromide injection does not activate macrophages at the demyelinated sciatic nerve site, as observed after nerve crush, but briefly activates macrophages in the dorsal root ganglion. This study provides a new method for investigating the underlying mechanisms of the conditioning response and suggests that loss of the peripheral myelin may be a major signal to change the intrinsic growth state of adult sensory neurons and promote regeneration.
The L1 family of cell adhesion molecules (L1-CAMs) is known to be involved in various neuronal functions such as cell adhesion, axon guidance, and synaptic plasticity. We investigated the detailed expression/changes of a close homolog of the L1 cell adhesion molecule (CHL1) after nerve injury and the possible role on neuropathic pain using the rat spared nerve injury (SNI) model. SNI induced the expression of CHL1 in L4/5 DRG neurons, particularly in small-size injured neurons and in satellite cells. In the spinal cord, CHL1 immunoreactivity increased mainly in laminae I-II of the dorsal horn on the side ipsilateral to the nerve injury. Ultrastructural study clarified the fine localization of CHL1 in axons of primary afferents in the dorsal horn. CHL1 immunoreactivities were localized in the adherence such as axon-axon, axon-dorsal horn neurons (dendrite, soma), and axon-glial cells (astrocyte and microglia). Experimental inhibition of CHL1 adhesion by intrathecal administration of the antibody for CHL1 extracellular domain significantly prevented and reversed SNI-induced mechanical allodynia. Thus, alterations of CHL1 may be involved in the structural plasticity after peripheral nerve injury and have important roles in neuropathic pain.
Small proline-rich repeat protein 1A (SPRR1A) is expressed in dorsal root ganglion (DRG) neurons following peripheral nerve injury but it is not known whether SPRR1A is differentially expressed following injury to peripheral versus central DRG projections and a detailed characterization of expression in sensory neuron subpopulations and spinal cord has not been performed. Here we use immunocytochemical techniques to characterize SPRR1A expression following sciatic nerve, dorsal root, and dorsal column injury in adult mice. SPRR1A was not detected in naïve spinal cord, DRG, or peripheral nerves and there was minimal expression following injury to the centrally projecting branches of DRG neurons. However, following peripheral (sciatic) nerve injury, intense SPRR1A immunoreactivity was observed in the dorsal horn and motoneurons of the spinal cord, in L4/5 DRG neurons, and in the injured nerve. A time-course study comparing expression following sciatic nerve crush and transection revealed maximum SPRR1A levels at day 7 in both models. However, while SPRR1A was downregulated to baseline by 30 days postlesion following crush injury, it remained elevated 30 days after transection. Cell-size and double-labeling studies revealed that SPRR1A was expressed by DRG cells of all sizes and colocalized with classical markers of DRG subpopulations and their primary afferent terminals. High coexpression of SPRR1A with activating transcription factor-3 and growth-associated protein-43 was observed, indicating that it is expressed by injured and regenerating neurons. This study supports the hypothesis that SPRR1A is a regeneration-associated gene and that SPRR1A provides a valuable marker to assess the regenerative potential of injured neurons.