Injured Peripheral Nervous System Research Articles

Machine Learning Integrated Workflow for Predicting Schwann Cell Viability on Conductive MXene Biointerfaces.

Severe injuries to the peripheral nervous system (PNS) require Schwann cells to aid in neuronal regeneration. Low-frequency electrical stimulation is known to induce the cogrowth of neurons and Schwann cells in an injured PNS. However, the correlations between electrical stimulation and Schwann cell viability are complex and not well understood. In this work, we develop a machine learning (ML)-integrated workflow that uses conductive hydrogel biointerfaces to evaluate the impacts of fabrication parameters and electrical stimulation on the Schwann cell viability. First, a hydrogel array with varying MXene and peptide loadings is fabricated, which serves as conductive biointerfaces to incubate Schwann cells and introduce various electrical stimulation (at different voltages and frequencies). Upon specific fabrication parameters and stimulation, the cell viability is evaluated and input into an artificial neural network model to train the model. Additionally, a data augmentation method is applied to synthesize 1000-fold virtual data points, enabling the construction of a high-accuracy prediction model (with a testing mean absolute error ≤11%). By harnessing the model's predictive power, we can accurately predict Schwann cell viability based on a given set of fabrication/stimulation parameters. Finally, the SHapley Additive exPlanations model interpretation provides several data-scientific insights that are validated by microscopic cellular observations. Our hybrid approach, involving conductive biointerface fabrication, ML algorithms, and data analysis, offers an unconventional platform to construct a preclinical prediction model at the cellular level.

Study on antibacterial activity and repair of peripheral nervous system injury by Zno nanocomposites

In this paper, three samples of ZnO/PPy, ZnO/CNTs and ZnO/PPy/CNTs nano- composites were studied in the aspects of antimicrobial properties, cell imaging and tumor targeting. Firstly, Escherichia coli strains were selected and controlled test method was used. Colony data showed that the inhibition rate of ZnO/PPy was 73.06%, the inhibition rate of ZnO /CNTs was 99.44%, and the inhibition rate of ZnO/PPy/CNTs composite was 99.99%. The results showed that the three kinds of composites had certain antibacterial effect. At the same time, in order to optimize the application of nano-sized zinc oxide (ZnOs), ZnOs nanocomposite microspheres were prepared by emulsification and dispersion method with polypyrrole and carbon nanotubes as microballoon walls, and the animal model of peripheral nervous system (PNS) injury was established. ZnOs nanocomposite microspheres and control samples were implanted into the injured peripheral nervous system (sciatic nerve was used as the site). The experimental results show that ZnOs nanocomposite microspheres can repair peripheral nervous system injury in animals.

Driving axon regeneration by orchestrating neuronal and non-neuronal innate immune responses via the IFNγ-cGAS-STING axis

The coordination mechanism of neural innate immune responses for axon regeneration is not well understood. Here, we showed that neuronal deletion of protein tyrosine phosphatase non-receptor type 2 sustains the IFNγ-STAT1 activity in retinal ganglion cells (RGCs) to promote axon regeneration after injury, independent of mTOR or STAT3. DNA-damage-induced cGAMP synthase (cGAS)-stimulator of interferon genes (STINGs) activation is the functional downstream signaling. Directly activating neuronal STING by cGAMP promotes axon regeneration. In contrast to the central axons, IFNγ is locally translated in the injured peripheral axons and upregulates cGAS expression in Schwann cells and infiltrating blood cells to produce cGAMP, which promotes spontaneous axon regeneration as an immunotransmitter. Our study demonstrates that injured peripheral nervous system (PNS) axons can direct the environmental innate immune response for self-repair and that the neural antiviral mechanism can be harnessed to promote axon regeneration in the central nervous system (CNS).

Neuroimmune interactions and immunoengineering strategies in peripheral nerve repair.

Peripheral nerve injuries result in disrupted cellular communication between the central nervous system and somatic distal end targets. The peripheral nervous system is capable of independent and extensive regeneration; however, meaningful target muscle reinnervation and functional recovery remain limited and may result in chronic neuropathic pain and diminished quality of life. Macrophages, the primary innate immune cells of the body, are critical contributors to regeneration of the injured peripheral nervous system. However, in some clinical scenarios, macrophages may fail to provide adequate support with optimal timing, duration, and location. Here, we review the history of immunosuppressive and immunomodulatory strategies to treat nerve injuries. Thereafter, we enumerate the ways in which macrophages contribute to successful nerve regeneration. We argue that implementing macrophage-based immunomodulatory therapies is a promising treatment strategy for nerve injuries across a wide range of clinical presentations.

Polycomb Group Protein Ezh2 Supports Mammalian Axon Regeneration in Peripheral and Central Nervous System

In mammals, neurons in the central nervous system (CNS) lose their axon growth ability as they mature. On the contrary, mature neurons in the peripheral nervous system (PNS) still possess such an ability and can spontaneously regenerate axons upon axonal injury by initiating a regenerative response. Emerging evidence suggests that the transition from a non-regenerative state to a regenerative state of injured PNS neurons largely involves epigenetic regulation of chromatin accessibility. Here we investigated the role of Ezh2, a histone methyltransferase that adds methyl groups onto lysine 27 on histone H3 (H3K27) to suppress gene transcription, in mammalian axon regeneration. Western blot results showed that Ezh2 level was significantly upregulated in mouse lumbar 4 and 5 dorsal root ganglia (L4/5 DRGs) 3 days following sciatic nerve axotomy. Functionally, Ezh2 knockdown or knockout in cultured DRG neurons impaired axon growth in vitro. In consistence, knockdown or knockout of Ezh2 in L4/5 DRGs by in vivo electroporation or conditional knockout of Ezh2 in sensory neurons impaired sensory axon regeneration after sciatic nerve crush. More importantly, using optic nerve regeneration model, we found that overexpressing Ezh2 in retinal ganglion cells (RGCs) by intravitreal injection of AAV2-Ezh2 virus significantly promoted axon regeneration after optic nerve crush. RNA-seq analysis of RGCs enriched by fluorescence-activated cell sorting revealed that the transcription of a large number of genes involved in synaptic transmission were downregulated by Ezh2 overexpression, indicating that Ezh2 supports axon regeneration by rejuvenating adult neurons to a younger state. Using optic nerve regeneration model again, we showed that overexpression of Slc6a13 (encoding Gat2), a gene suppressed by Ezh2, partially blocked RGC axon regeneration induced by Ezh2 overexpression. Our study demonstrated that Ezh2 was required for the successful spontaneous axon regeneration in the PNS, and that Ezh2 gain-of-function could promote axon regeneration in the CNS by silencing synaptic transmission-associated genes.

Micropatterned biodegradable polyesters clicked with CQAASIKVAV promote cell alignment, directional migration, and neurite outgrowth

The interplay of microstructures and biological cues is critical to regulate the behaviors of Schwann cells (SCs) in terms of cellular spatial arrangement and directional migration as well as neurite orientation for bridging the proximal and distal stumps of the injured peripheral nervous system. In this study, stripe micropatterns having ridges/grooves of width 20/20 and 20/40 μm were fabricated on the surface of maleimide-functionalized biodegradable poly(ester carbonate) (P(LLA-MTMC)) films by the polydimethylsiloxane mold-pressing method, respectively. The laminin-derived CQAASIKVAV peptides end-capped with an SH group were then grafted by the thiol-ene click reaction under mild conditions to obtain micropatterned and peptide-grafted films. SCs cultured on these films, especially on the 20/40-μm film, displayed faster and aligned adhesion as well as a larger number of elongated cells with a higher length-to-width (L/W) ratio along the stripe direction than those on the flat-pep film. The migration rate of SCs was significantly enhanced in parallel to the stripe direction with a large net displacement. The micropatterned and peptide-grafted films, especially the 20/40-μm film, could promote SC proliferation and nerve growth factor (NGF) secretion in a manner similar to that of the peptide-grafted planar film. Moreover, the neurites of rat pheochromocytoma 12 (PC12) cells sprouted along the ridges with a longer average length on the micropatterned and peptide-grafted films. The synergistic effect of physical patterns and biological cues was evaluated by considering the results of cell adhesion force; immunofluorescence staining of vinculin; fluorescence staining of F-actin and the nucleus; as well as gene expression of neural cadherin (NCAD), neurocan (NCAN), and myelin protein zero (P0). Statement of SignificanceThe interplay of microstructures and biological cues is critical to regulate the behaviors of Schwann cells (SCs) and nerve cells, and thereby the regeneration of peripheral nerve system. In this study, the combined micropatterning and CQAASIKVAV grafting endowed the modified P(LLA-MTMC) films with both contact guidance and bioactive chemical cues to enhance cell proliferation, directional alignment and migration, longer net displacement and larger NGF secretion, and stronger neurite outgrowth of SCs and PC12 cells. Hence, the integration of physical micropatterns and bioactive molecules is an effective way to obtain featured biomaterials for the regeneration of nerves and other types of tissues.

Differential Expression of Sox11 and Bdnf mRNA Isoforms in the Injured and Regenerating Nervous Systems.

In both the central nervous system (CNS) and the peripheral nervous system (PNS), axonal injury induces changes in neuronal gene expression. In the PNS, a relatively well-characterized alteration in transcriptional activation is known to promote axonal regeneration. This transcriptional cascade includes the neurotrophin Bdnf and the transcription factor Sox11. Although both molecules act to facilitate successful axon regeneration in the PNS, this process does not occur in the CNS. The present study examines the differential expression of Sox11 and Bdnf mRNA isoforms in the PNS and CNS using three experimental paradigms at different time points: (i) the acutely injured CNS (retina after optic nerve crush) and PNS (dorsal root ganglion after sciatic nerve crush), (ii) a CNS regeneration model (retina after optic nerve crush and induced regeneration); and (iii) the retina during a chronic form of central neurodegeneration (the DBA/2J glaucoma model). We find an initial increase of Sox11 in both PNS and CNS after injury; however, the expression of Bdnf isoforms is higher in the PNS relative to the CNS. Sustained upregulation of Sox11 is seen in the injured retina following regeneration treatment, while the expression of two Bdnf mRNA isoforms is suppressed. Furthermore, two isoforms of Sox11 with different 3′UTR lengths are present in the retina, and the long isoform is specifically upregulated in later stages of glaucoma. These results provide insight into the molecular cascades active during axonal injury and regeneration in mammalian neurons.

The Role of Peripheral Myelin Protein 2 in Remyelination

The protein component of the myelin layer is essential for all aspects of peripheral nerves, and its deficiency can lead to structural and functional impairment. The presence of peripheral myelin protein 2 (P2, PMP2, FABP8, M-FABP) in Schwann cells has been known for decades and shown recently to be involved in the lipid homeostasis in the peripheral neural system. However, its precise role during de- and remyelination has yet to be elucidated. To this end, we assessed remyelination after sciatic nerve crush injury in vivo, and in an experimental de/remyelination ex vivo myelinating culture model in P2-deficient (P2 -/- ) and wild-type (WT) animals. In vivo, the nerve crush paradigm revealed temporal structural and functional changes in P2 -/- mice as compared to WT animals. Concomitantly, P2 -/- DRG cultures demonstrated the presence of shorter internodes and enlarged nodes after ex vivo de/remyelination. Together, these data indicate that P2 may play a role in remyelination of the injured peripheral nervous system, presumably by affecting the nodal and internodal configuration.

AlphaB-crystallin expression correlates with aging deficits in the peripheral nervous system

In an effort to identify factors that contribute to age-related deficits in the undamaged and injured peripheral nervous system (PNS), we noted that Brady and colleagues found that mice null for a small heat shock protein called alphaB-crystallin (αBC) developed abnormalities early in life that are reminiscent of aging pathologies. Because of our observation that αBC protein levels markedly reduce as wild-type mice age, we investigated whether the crystallin plays a role in modulating age-related deficits in the uninjured and damaged PNS. We show here that the presence of αBC correlates with maintenance of myelin sheath thickness, reducing macrophage presence, sustaining lipid metabolism, and promoting remyelination following peripheral nerve injury in an age-dependent manner. More specifically, animals null for αBC displayed a higher frequency of thinly myelinated axons, enhanced presence of Iba1+ macrophages, and fewer immunoreactive profiles of the cholesterol biosynthesis enzyme, squalene monooxygenase, before and after sciatic nerve crush injury. These findings thus suggest that αBC plays a protective and beneficial role in the aging PNS.

Low-density Lipoprotein Receptor-related Proteins in a Novel Mechanism of Axon Guidance and Peripheral Nerve Regeneration

The low-density lipoprotein receptor-related protein receptors 1 and 2 (LRP1 and LRP2) are emerging as important cell signaling mediators in modulating neuronal growth and repair. We examined whether LRP1 and LRP2 are able to mediate a specific aspect of neuronal growth: axon guidance. We sought to identify LRP1 and LRP2 ligands that could induce axonal chemoattraction, which might have therapeutic potential. Using embryonic sensory neurons (rat dorsal root ganglia) in a growth cone turning assay, we tested a range of LRP1 and LRP2 ligands for the ability to guide growth cone navigation. Three ligands were chemorepulsive: α-2-macroglobulin, tissue plasminogen activator, and metallothionein III. Conversely, only one LRP ligand, metallothionein II, was found to be chemoattractive. Chemoattraction toward a gradient of metallothionein II was calcium-dependent, required the expression of both LRP1 and LRP2, and likely involves further co-receptors such as the tropomyosin-related kinase A (TrkA) receptor. The potential for LRP-mediated chemoattraction to mediate axonal regeneration was examined in vivo in a model of chemical denervation in adult rats. In these in vivo studies, metallothionein II was shown to enhance epidermal nerve fiber regeneration so that it was complete within 7 days compared with 14 days in saline-treated animals. Our data demonstrate that both LRP1 and LRP2 are necessary for metallothionein II-mediated chemotactic signal transduction and that they may form part of a signaling complex. Furthermore, the data suggest that LRP-mediated chemoattraction represents a novel, non-classical signaling system that has therapeutic potential as a disease-modifying agent for the injured peripheral nervous system.

Role of macrophages in Wallerian degeneration and axonal regeneration after peripheral nerve injury.

The peripheral nervous system (PNS) has remarkable regenerative abilities after injury. Successful PNS regeneration relies on both injured axons and non-neuronal cells, including Schwann cells and immune cells. Macrophages are the most notable immune cells that play key roles in PNS injury and repair. Upon peripheral nerve injury, a large number of macrophages are accumulated at the injury sites, where they not only contribute to Wallerian degeneration, but also are educated by the local microenvironment and polarized to an anti-inflammatory phenotype (M2), thus contributing to axonal regeneration. Significant progress has been made in understanding how macrophages are educated and polarized in the injured microenvironment as well as how they contribute to axonal regeneration. Following the discussion on the main properties of macrophages and their phenotypes, in this review, we will summarize the current knowledge regarding the mechanisms of macrophage infiltration after PNS injury. Moreover, we will discuss the recent findings elucidating how macrophages are polarized to M2 phenotype in the injured PNS microenvironment, as well as the role and underlying mechanisms of macrophages in peripheral nerve injury, Wallerian degeneration and regeneration. Furthermore, we will highlight the potential application by targeting macrophages in treating peripheral nerve injury and peripheral neuropathies.

Aucubin promotes neurite outgrowth in neural stem cells and axonal regeneration in sciatic nerves.

Aucubin is an iridoid glycoside with a wide range of biological activities, including anti-inflammatory, anti-microbial, anti-algesic as well as anti-tumor activities. Recently, it has been shown that aucubin prevents neuronal death in the hippocampal CA1 region in rats with diabetic encephalopathy. In addition, it has protective effects on H2O2-induced apoptosis in PC12 cells. We have shown here that aucubin promotes neuronal differentiation and neurite outgrowth in neural stem cells cultured primarily from the rat embryonic hippocampus. We also investigated whether aucubin facilitates axonal elongation in the injured peripheral nervous system. Aucubin promoted lengthening and thickness of axons and re-myelination at 3 weeks after sciatic nerve injury. These results indicate that administration of aucubin improved nerve regeneration in the rat model of sciatic nerve injury, suggesting that aucubin may be a useful therapeutic compound for the human peripheral nervous system after various nerve injuries.

Axonal degeneration in dorsal columns of spinal cord does not induce recruitment of hematogenous macrophages

It is generally accepted that there are two populations of macrophages that respond to neural injuries and successful recruitment of hematogenous macrophages has been shown to help the process of nerve repair in the peripheral nervous system (PNS). Meanwhile, the recruitment of circulating macrophages after central nerve system (CNS) injuries is considered mild and delayed. We compared the recruitment of circulating macrophages in the peripheral nerves and spinal cord after dorsal root ganglionectomies, which induce selective and approximately similar extent of sensory fiber degeneration in PNS and CNS, in bone marrow chimeric mice. Our results showed that circulating macrophages were efficiently recruited in PNS but virtually no recruitment in CNS despite degeneration of peripheral and central sensory projections emanating from the same dorsal root ganglion (DRG) neurons. The mechanisms that prevent recruitment of circulating macrophages in CNS after injury remain poorly elucidated.

Peptide Mimetic of the S100A4 Protein Modulates Peripheral Nerve Regeneration and Attenuates the Progression of Neuropathy in Myelin Protein P0 Null Mice

We recently found that S100A4, a member of the multifunctional S100 protein family, protects neurons in the injured brain and identified two sequence motifs in S100A4 mediating its neurotrophic effect. Synthetic peptides encompassing these motifs stimulated neuritogenesis and survival in vitro and mimicked the S100A4-induced neuroprotection in brain trauma. Here, we investigated a possible function of S100A4 and its mimetics in the pathologies of the peripheral nervous system (PNS). We found that S100A4 was expressed in the injured PNS and that its peptide mimetic (H3) affected the regeneration and survival of myelinated axons. H3 accelerated electrophysiological, behavioral and morphological recovery after sciatic nerve crush while transiently delaying regeneration after sciatic nerve transection and repair. On the basis of the finding that both S100A4 and H3 increased neurite branching in vitro, these effects were attributed to the modulatory effect of H3 on initial axonal sprouting. In contrast to the modest effect of H3 on the time course of regeneration, H3 had a long-term neuroprotective effect in the myelin protein P0 null mice, a model of dysmyelinating neuropathy (Charcot-Marie-Tooth type 1 disease), where the peptide attenuated the deterioration of nerve conduction, demyelination and axonal loss. From these results, S100A4 mimetics emerge as a possible means to enhance axonal sprouting and survival, especially in the context of demyelinating neuropathies with secondary axonal loss, such as Charcot-Marie-Tooth type 1 disease. Moreover, our data suggest that S100A4 is a neuroprotectant in PNS and that other S100 proteins, sharing high homology in the H3 motif, may have important functions in PNS pathologies.

Reduced BACE1 Activity Enhances Clearance of Myelin Debris and Regeneration of Axons in the Injured Peripheral Nervous System

β-Site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1) is an aspartyl protease best known for its role in generating the amyloid-β peptides that are present in plaques of Alzheimer's disease. BACE1 has been an attractive target for drug development. In cultured embryonic neurons, BACE1-cleaved N-terminal APP is further processed to generate a fragment that can trigger axonal degeneration, suggesting a vital role for BACE1 in axonal health. In addition, BACE1 cleaves neuregulin 1 type III, a protein critical for myelination of peripheral axons by Schwann cells during development. Here, we asked whether axonal degeneration or axonal regeneration in adult nerves might be affected by inhibition or elimination of BACE1. We report that BACE1 knock-out and wild-type nerves degenerated at a similar rate after axotomy and to a similar extent in the experimental neuropathies produced by administration of paclitaxel and acrylamide. These data indicate N-APP is not the sole culprit in axonal degeneration in adult nerves. Unexpectedly, however, we observed that BACE1 knock-out mice had markedly enhanced clearance of axonal and myelin debris from degenerated fibers, accelerated axonal regeneration, and earlier reinnervation of neuromuscular junctions, compared with littermate controls. These observations were reproduced in part by pharmacological inhibition of BACE1. These data suggest BACE1 inhibition as a therapeutic approach to accelerate regeneration and recovery after peripheral nerve damage.

Adhesion molecule L1 overexpressed under the control of the neuronal Thy-1 promoter improves myelination after peripheral nerve injury in adult mice

L1 is an adhesion molecule favorably influencing the functional and anatomical recoveries after central nervous system (CNS) injuries. Its roles in peripheral nervous system (PNS) regeneration are less well understood. Studies using knockout mice have surprisingly revealed that L1 has a negative impact on functional nerve regeneration by inhibiting Schwann cell proliferation. To further elucidate the roles of L1 in PNS regeneration, here we used a novel transgenic mouse overexpressing L1 in neurons, but not in PNS or CNS glial cells, under the control of a neuron-specific Thy-1 promoter. Without nerve injury, the transgene expression, as compared to wild-type mice, had no effect on femoral nerve function, numbers of quadriceps motoneurons and myelinated axons in the femoral nerve but resulted in slightly reduced myelination in the sensory saphenous nerve and increased neurofilament density in myelinated axons of the quadriceps motor nerve branch. After femoral nerve injury, L1 overexpression had no impact on the time course and degree of functional recovery. Unaffected were also numbers of regenerated quadriceps motoneurons, precision of muscle reinnervation, axon numbers and internodal lengths in the regenerated nerves. Despite the lack of functional effects, myelination in the motor and sensory femoral nerve branches was significantly improved and loss of perisomatic inhibitory terminals on motoneurons was attenuated in the transgenic mice. Our results indicate that L1 is a regulator of myelination in the injured PNS and warrant studies aiming to improve function in demyelinating PNS and CNS disorders using exogenous L1.

Extrinsic and intrinsic determinants of nerve regeneration

After central nervous system (CNS) injury axons fail to regenerate often leading to persistent neurologic deficit although injured peripheral nervous system (PNS) axons mount a robust regenerative response that may lead to functional recovery. Some of the failures of CNS regeneration arise from the many glial-based inhibitory molecules found in the injured CNS, whereas the intrinsic regenerative potential of some CNS neurons is actively curtailed during CNS maturation and limited after injury. In this review, the molecular basis for extrinsic and intrinsic modulation of axon regeneration within the nervous system is evaluated. A more complete understanding of the factors limiting axonal regeneration will provide a rational basis, which is used to develop improved treatments for nervous system injury.

Secretion of EGF-like domain of heregulinβ promotes axonal growth and functional recovery of injured sciatic nerve.

Neuregulin 1 (NRG1) and epidermal growth factor receptor (ErbB) signaling pathways control Schwann cells during axonal regeneration in an injured peripheral nervous system. We investigated whether a persistent supply of recombinant NRG1 to the injury site could improve axonal growth and recovery of sensory and motor functions in rats during nerve regeneration. We generated a recombinant adenovirus expressing a secreted form of EGF-like domain from Heregulinβ (sHRGβE-Ad). This virus, sHRGβE-Ad allowed for the secretion of 30-50 ng of small sHRGβE peptides per 10(7-8) virus particle outside cells and was able to phosphorylate ErbB receptors. Transduction of the concentrated sHRGβE-Ad into an axotomy model of sciatic nerve damage caused an effective promotion of nerve regeneration, as shown by histological features of the axons and Schwann cells, as well as increased expression of neurofilaments, GAP43 and S100 in the distal stump of the injury site. This result is consistent with longer axon lengths and thicker calibers observed in the sHRGβE-Ad treated animals. Furthermore, sensory and motor functions were significantly improved in sHRGβE-Ad treated animals when evaluated by a behavioral test. These results suggest a therapeutic potential for sHRGβE-Ad in treatment of peripheral nerve injury.

Glial cell line‐derived neurotrophic factor is expressed by inflammatory cells in the sciatic nerves of Lewis rats with experimental autoimmune neuritis

Neurotrophic factors, including glial cell line-derived neurotrophic factor (GDNF), have been known to play a role in neuroprotection in the injured peripheral nervous system (PNS). To evaluate the involvement of GDNF in experimental autoimmune neuritis (EAN) pathogenesis, the expression of GDNF in rat sciatic nerves with EAN was studied. Western blot analysis showed that the level of GDNF protein significantly increased 1.8-fold at the paralytic stage of EAN at day 12 post-immunization (PI) (p < 0.01), and its level further increased approximately 2.5-fold at day 21 PI (p < 0.001) in the sciatic nerves of EAN-affected rats compared with those of control rats, and then declined thereafter at day 28 PI. Immunohistochemical analysis showed that axons and Schwann cells constitutively contained GDNF in normal controls. In sciatic nerves with EAN at day 12 PI, GDNF was immunostained in infiltrating inflammatory cells including macrophages and T cells. Collectively, we postulate that GDNF plays a regulatory role in EAN paralysis. A paradoxical role of inflammatory cells to ameliorate PNS inflammation remains to be further studied in EAN, an animal model of human demyelinating disease.

Low Density Lipoprotein Receptor-related Protein (LRP1) Regulates Rac1 and RhoA Reciprocally to Control Schwann Cell Adhesion and Migration

LDL receptor-related protein (LRP1) is expressed by Schwann cells in vivo mainly after injury to the peripheral nervous system (PNS). Schwann cells in primary culture, which provide a model of Schwann cells in the injured PNS, also express abundant LRP1. Herein, we show that LRP1 gene-silencing or treatment with receptor-associated protein (RAP) promotes Schwann cell adhesion and inhibits cell migration on fibronectin. LRP1 gene-silencing also resulted in the formation of prominent focal adhesions and actin stress fibers. These changes, which were induced by loss of LRP1 expression or activity, were explained mechanistically by an increase in activated RhoA, coupled with a decrease in activated Rac1. Known LRP1 ligands, including matrix metalloprotease-9, tissue-type plasminogen activator, and alpha(2)-macroglobulin activated Rac1 in LRP1-expressing Schwann cells. An inhibitor of Rac1 activation promoted Schwann cell adhesion. Conversely, in cells in which LRP1 was silenced, a Rho kinase inhibitor promoted migration and inhibited adhesion. These results demonstrate that direct binding of ligands to LRP1 controls activation of small Rho family GTPases. The effects of LRP1 gene-silencing and RAP implicate autocrine pathways involving endogenously produced LRP1 ligands. Regulation of Schwann cell migration by LRP1 may be important in PNS injury.