IGF-I enhances neurite regeneration but is not required for its survival in adult DRG explant

Insulin-Like Growth Factor-1: A Promising Therapeutic Target for Peripheral Nerve Injury

Patients who sustain peripheral nerve injuries (PNIs) are often left with debilitating sensory and motor loss. Presently, there is a lack of clinically available therapeutics that can be given as an adjunct to surgical repair to enhance the regenerative process. Insulin-like growth factor-1 (IGF-1) represents a promising therapeutic target to meet this need, given its well-described trophic and anti-apoptotic effects on neurons, Schwann cells (SCs), and myocytes. Here, we review the literature regarding the therapeutic potential of IGF-1 in PNI. We appraised the literature for the various approaches of IGF-1 administration with the aim of identifying which are the most promising in offering a pathway toward clinical application. We also sought to determine the optimal reported dosage ranges for the various delivery approaches that have been investigated.

IGF-1 and Chondroitinase ABC Augment Nerve Regeneration after Vascularized Composite Limb Allotransplantation

Impaired nerve regeneration and inadequate recovery of motor and sensory function following peripheral nerve repair remain the most significant hurdles to optimal functional and quality of life outcomes in vascularized tissue allotransplantation (VCA). Neurotherapeutics such as Insulin-like Growth Factor-1 (IGF-1) and chondroitinase ABC (CH) have shown promise in augmenting or accelerating nerve regeneration in experimental models and may have potential in VCA. The aim of this study was to evaluate the efficacy of low dose IGF-1, CH or their combination (IGF-1+CH) on nerve regeneration following VCA. We used an allogeneic rat hind limb VCA model maintained on low-dose FK506 (tacrolimus) therapy to prevent rejection. Experimental animals received neurotherapeutics administered intra-operatively as multiple intraneural injections. The IGF-1 and IGF-1+CH groups received daily IGF-1 (intramuscular and intraneural injections). Histomorphometry and immunohistochemistry were used to evaluate outcomes at five weeks. Overall, compared to controls, all experimental groups showed improvements in nerve and muscle (gastrocnemius) histomorphometry. The IGF-1 group demonstrated superior distal regeneration as confirmed by Schwann cell (SC) immunohistochemistry as well as some degree of extrafascicular regeneration. IGF-1 and CH effectively promote nerve regeneration after VCA as confirmed by histomorphometric and immunohistochemical outcomes.

Neurotrophic and neuroprotective properties of exendin-4 in adult rat dorsal root ganglion neurons: involvement of insulin and RhoA

Glucagon-like peptide-1 (GLP-1) is thought to preserve neurons and glia following axonal injury and neurodegenerative disorders. We investigated the neurotrophic and neuroprotective properties of exendin (Ex)-4, a synthetic GLP-1 receptor (GLP-1R) agonist, on adult rat dorsal root ganglion (DRG) neurons and PC12 cells. GLP-1R was predominantly localized on large and small peptidergic neurons in vivo and in vitro, suggesting the involvement of GLP-1 in both the large and small sensory fiber functions. Ex-4 dose-dependently (1 ≤ 10 ≤ 100 nM) promoted neurite outgrowth and neuronal survival at 2 and 7 days in culture, respectively. Treatment with 100 nM Ex-4 restored the reduced neurite outgrowth and viability of DRG neurons caused by the insulin removal from the medium and suppressed the activity of RhoA, an inhibitory regulator for peripheral nerve regeneration, in PC12 cells. Furthermore, these effects were attenuated by co-treatment with phosphatidylinositol-3'-phosphate kinase (PI3K) inhibitor, LY294002. These findings imply that Ex-4 enhances neurite outgrowth and neuronal survival through the activation of PI3K signaling pathway, which negatively regulates RhoA activity. Ex-4 and other GLP-1R agonists may compensate for the reduced insulin effects on neurons, thereby being beneficial for the treatment of diabetic neuropathy.

A new and reliable guide for studies of neuronal loss based on focal lesions and combinations of in vivo and in vitro approaches

In this study, we describe a simple and reliable method to study neuroprotective effects in living and organized neural tissue. This method, which was based on retinal explants for in vivo focal lesions, was conceived as a collection of modular procedures, which can be customized for particular demands. With this model, it is possible to combine immunohistochemistry with image data analysis to track the two- or three-dimensional redistribution of proteins as a time/space function of primary cell loss. At the same time, it is possible to finely control the exposure of the tissue to specific drugs and molecules. In order to illustrate the use of the proposed method, we tested the effects of two different nanotube compounds on retinal explant viability. Transcriptome analyses can be separately performed in the lesion focus and penumbra with laser capture microdissection followed by polymerase chain reaction analyses. In addition, other common experimental drawbacks, such as high individual variance, are eliminated. With intraocular injections, treatments can be verified in vivo, with one eye serving as the experimental tissue and the other serving as the control tissue. In summary, we describe a flexible and easy method, which can be useful in combination with a broad variety of recently developed neuroprotective strategies, to study neurodegeneration.

The insulin-like growth factor 1 receptor is essential for axonal regeneration in adult central nervous system neurons

Axonal regeneration is an essential condition to re-establish functional neuronal connections in the injured adult central nervous system (CNS), but efficient regrowth of severed axons has proven to be very difficult to achieve. Although significant progress has been made in identifying the intrinsic and extrinsic mechanisms involved, many aspects remain unresolved. Axonal development in embryonic CNS (hippocampus) requires the obligate activation of the insulin-like growth factor 1 receptor (IGF-1R). Based on known similarities between axonal growth in fetal compared to mature CNS, we decided to examine the expression of the IGF-1R, using an antibody to the βgc subunit or a polyclonal anti-peptide antibody directed to the IGF-R (C20), in an in vitro model of adult CNS axonal regeneration, namely retinal ganglion cells (RGC) derived from adult rat retinas. Expression of both βgc and the β subunit recognized by C20 antibody were low in freshly isolated adult RGC, but increased significantly after 4 days in vitro. As in embryonic axons, βgc was localised to distal regions and leading growth cones in RGC. IGF-1R-βgc co-localised with activated p85 involved in the phosphatidylinositol-3 kinase (PI3K) signaling pathway, upon stimulation with IGF-1. Blocking experiments using either an antibody which neutralises IGF-1R activation, shRNA designed against the IGF-1R sequence, or the PI3K pathway inhibitor LY294002, all significantly reduced axon regeneration from adult RGC in vitro (∼40% RGC possessed axons in controls vs 2-8% in the different blocking studies). Finally, co-transfection of RGC with shRNA to silence IGF-1R together with a vector containing a constitutively active form of downstream PI3K (p110), fully restored axonal outgrowth in vitro. Hence these data demonstrate that axonal regeneration in adult CNS neurons requires re-expression and activation of IGF-1R, and targeting this system may offer new therapeutic approaches to enhancing axonal regeneration following trauma.

Activation of ERK1/2 and PI3K/Akt by IGF-1 on GAP-43 expression in DRG neurons with excitotoxicity induced by glutamate in vitro

Insulin-like growth factor-1 (IGF-1) is a neurotrophic factor and plays an important role in promoting axonal growth from dorsal root ganglion (DRG) neurons. Whether IGF-1 influences growth-associated protein 43 (GAP-43) expression and activates the extracellular signal-regulated protein kinase (ERK1/2) and the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathways in DRG neurons with excitotoxicity induced by glutamate (Glu) remains unknown. In this study, embryonic 15-day-old rat DRG explants were cultured for 48 h and then exposed to IGF-1, Glu, Glu + IGF-1, Glu + IGF-1 + PD98059, Glu + IGF-1 + LY294002, Glu + IGF-1 + PD98059 + LY294002 for additional 12 h. The DRG explants were continuously exposed to growth media as control. The levels of GAP-43 mRNA were detected by real time-PCR analysis. The protein levels of GAP-43, phosphorylated ERK1/2, phosphorylated Akt, total ERK1/2, and total Akt were detected by Western blot assay. GAP-43 expression in situ was determined by immunofluorescent labeling. Apoptotic cell death was monitored by Hoechst 33342 staining. IGF-1 alone increased GAP-43 and its mRNA levels in the absence of Glu. The decreased GAP-43 and its mRNA levels caused by Glu could be partially reversed by the presence of IGF-1. IGF-1 rescued neuronal cell death caused by Glu. Neither the ERK1/2 inhibitor PD98059 nor the PI3K inhibitor LY294002 blocked the effect of IGF-1, but both inhibitors together were effective. To validate the impact of GAP-43 expression by IGF-1, GAP-43 induction was blocked by administration of dexamethasone (DEX). IGF-1 partially rescued the decrease of GAP-43 and its mRNA levels induced by DEX. DEX induced an increase of cell apoptosis. IGF-1 may play an important role in neuroprotective effects on DRG neurons through regulating GAP-43 expression with excitotoxicity induced by Glu and the process was involved in both ERK1/2 and PI3K/Akt signaling pathways.

Effects of insulin-like growth factor-1 on expression of sensory neuropeptides in cultured dorsal root ganglion neurons in the absence or presence of glutamate

Insulin-like growth factor-1 (IGF-1) is a neurotrophic factor and plays an important role in promoting axonal growth from dorsal root ganglion (DRG) neurons. Whether IGF-1 could influence expression of sensory neuropeptides substance P (SP) and calcitonin gene-related peptide (CGRP) of the cultured DRG neurons with excitotoxicity induced by glutamate (Glu) remains unknown. In the present study, primary cultured DRG neurons were used to determine the effects of IGF-1 on expression of SP and CGRP of the neurons with Glu-induced excitotoxicity. The DRG neurons were dissociated and cultured for 48 hr and then exposed to Glu (0.2 mmol/L), IGF-1 (20 nmol/L), and Glu (0.2 mmol/L) plus IGF-1 (20 nmol/L) for additional 12 hr. The DRG neurons were continuously exposed to growth media as control. After that, all the above cultured DRG neurons were processed for detecting SP and CGRP expression by Western blot analysis. The expression of SP and CGRP increased significantly in primary cultured DRG neurons in the presence of IGF-1. The ability of IGF-1 on SP and CGRP expression may play a role in neurogenic inflammation or nociception.

Localization and function of insulin-like growth factor 1 in dorsal root ganglia in a rat disc herniation model

STUDY DESIGN

we investigated the localization of insulin-like growth factor 1 (IGF-1) using immunohistochemistry and the effects of small interfering RNA (siRNA) on IGF-1 in dorsal root ganglions (DRG) in a rat lumbar disc herniation (LDH) model.

OBJECTIVE

to determine the localization and function of IGF-1 in DRG of an experimental model of LDH.

SUMMARY OF BACKGROUND DATA

mechanical compression and chemical irritation are 2 major causative factors of radiculopathy in LDH. IGF-1, Ccnd1, Cdc2a, and CyclinA2 genes have been shown to be significantly upregulated in the mechanical model, but not in the chemical model. However, the localization and function of IGF-1 in DRG remain unknown in the mechanical compression animals.

METHODS

twenty-six adult female Sprague-Dawley rats were used in this study. A mechanical compression model was prepared by inserting a stainless rod. The rod was not inserted in the sham model. Expression of IGF-1 and Neuronal Nucli (NeuN) or glial fibrillary acidic protein was determined using double-fluorescence 7 days after mechanical compression (n = 5). Rats were randomly separated into 3 groups for the siRNA study (n = 7 in each group): (1) vehicle group; (2) siRNA group; and (3) sham group. The mechanical withdrawal threshold of the plantar food pad was examined using von Frey filaments for 35 days.

RESULTS

IGF-1 was localized particularly in the neuronal cell body, and revealed that it colocalized with NeuN but not with glial fibrillary acidic protein. The threshold was reduced in the vehicle and siRNA groups compared with the sham group. The threshold of the siRNA group significantly recovered from reduction compared with the vehicle group at 5 days after surgery, and this effect persisted throughout the experimental period. CONCLUSION.: IGF-1 was localized with neuronal cell bodies in DRG. IGF-1 knockdown caused a reduction in mechanical allodynia. The upregulation of IGF-1 might be a key factor in painful radiculopathy induced by mechanical factors.

Insulin-like growth factor-1 regulates neurite outgrowth and neuronal migration from organotypic cultured dorsal root ganglion

ABSTRACT Insulin-like growth factor-1 (IGF-1) is a neurotrophic factor and plays an important role in promoting axonal growth from neurons. Whether IGF-1 could promote neurite outgrowth and neuronal migration of dorsal root ganglion (DRG) explants in vitro remains unknown. In the present study, organotypic rat DRG explant culture model was established. Using this unique culture system, outgrowth of neurites from the peripheral nerve attached to DRG explant and migration of neurons from DRG explant to the peripheral area were quantified in the presence (5 nmol/L, 10 nmol/L, 20 nmol/L) or absence of IGF-1. The number of nerve fiber bundles extended from DRG explant increased significantly in the presence of IGF-1 (5 nmol/L, 19.25 ± 3.11, p < .05; 10 nmol/L, 20.92 ± 2.31, p < .01; 20 nmol/L, 23.00 ± 4.09, p < .001) as compared with that in the absence of IGF-1 (16.58 ± 2.94). The number of neurons migrated from DRG explant increased significantly in the presence of IGF-1 (5 nmol/L, 104.08 ± 16.70, p < .05; 10 nmol/L, 115.25 ± 13.68, p < .001; 20 nmol/L, 138.75 ± 18.05, p < .001) as compared with that in the absence of IGF-1 (90.25 ± 8.53). These data implicated that IGF-1 could promote neurite outgrowth and neuronal migration from DRG explants in vitro.

Regulatory effects of insulin-like growth factor-1 on the expression of sensory neuropeptide mRNAs in cultured dorsal root ganglion neurons with excitotoxicity induced by glutamate

OBJECTIVE

To determine the effects of insulin-like growth factor-1 (IGF-1) on the expression of preprotachykinin (PPT) mRNA encoding substance P (SP) and calcitonin gene-related peptide (CGRP) mRNA in cultured dorsal root ganglion (DRG) neurons with excitotoxicity induced by glutamate (Glu).

METHODS

DRGs were dissected from embryonic day 15 Wistar rats. DRG neurons were dissociated and cultured for 48 h and then exposed to Glu (0.2 mmol/L) or Glu (0.2 mmol/L) plus IGF-1 (5 nmol/L, 10 nmol/L and 20 nmol/L) for 12 h. The DRG neurons in control group were exposed to only growth media throughout the experiment. After that, the living DRG neurons were observed under inverted phase contrast microscope and microphotographs were taken. The expression levels of PPT and CGRP mRNAs were detected by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

IGF-1 could inhibit Glu-induced shortening of neurite. Besides, IGF-1 could significantly increase the levels of PPT mRNA and CGRP mRNA in primary cultured DRG neurons with Glu-induced excitotoxicity, in a dose-dependent manner.

CONCLUSION

IGF-1 may exert neuroprotective effects on DRG neurons against Glu-induced excitotoxicity, probably through regulating the expression levels of PPT and CGRP mRNAs.

Peripheral sensory axon growth: from receptor binding to cellular signaling

Regeneration following axonal injury of the adult peripheral sensory nervous system is heavily influenced by factors located in a neuron's extracellular environment. These factors include neurotrophins, such as Nerve Growth Factor (NGF) and the extracellular matrix, such as laminin. The presence of these molecules in the peripheral nervous system (PNS) is a major contributing factor for the dichotomy between regenerative capacities of central vs. peripheral neurons. Although PNS neurons are capable of spontaneous regeneration, this response is critically dependent on many different factors including the type, location and severity of the injury. In this article, we will focus on the plasticity of adult dorsal root ganglion (DRG) sensory neurons and how trophic factors and the extracellular environment stimulate the activation of intracellular signaling cascades that promote axonal growth in adult dorsal root ganglion neurons.

Gene expression changes in dorsal root ganglion of rat experimental lumber disc herniation models

STUDY DESIGN

Comprehensive overviews of gene expression changes in dorsal root ganglion (DRG) were obtained using microarrays in 2 rat models of experimental lumbar disc herniation (LDH).

OBJECTIVE

To clarify the mechanisms of painful radiculopathy caused by LDH from the viewpoint of gene expression changes in DRG of 2 rat models of LDH.

SUMMARY AND BACKGROUND DATA

Mechanical compression and chemical irritation are considered to be the 2 major causative factors of radiculopathy associated with LDH. Several basic studies have revealed histologic and functional changes in the nerve root and DRG induced by mechanical compression or application of nucleus pulposus. However, the effects of the 2 major factors have not been investigated in detail. METHODS.: The effects of mechanical and chemical factors were assessed in 2 models and in sham-operated rats. The mechanical compression model had a stainless steel rod inserted through a drill hole in the L5 lamina; the nucleus pulposus model had autologous nucleus pulposus placed in the drill hole, and only a drill hole was made in the L5 lamina of sham-operated rats. Samples from the left L5 DRG were harvested from the models with mechanical allodynia and from sham rats and analyzed using microarrays at 3 and 7 days after surgery.

RESULTS

The gene expression profiles differed in the 2 models at 7 days, but were similar at 3 days after surgery. Expression of the growth factor gene, insulin-like growth factor 1, and of the cyclinD1, cell division cycle 2 homolog A, and cyclinA2 genes related to the cell cycle was significantly upregulated in the DRG of the mechanical compression group at 7 days after surgery.

CONCLUSION

Mechanical and chemical factors caused altered gene expression in the DRG at 7 days after surgery, suggesting that the mechanisms of nerve injury induced by these factors differ. The upregulation of IGF-1 might be a key factor in painful radiculopathy induced by mechanical factors.

Early downregulation of IGF-I decides the fate of rat retinal ganglion cells after optic nerve injury

Retinal ganglion cells (RGCs) die by apoptosis after optic nerve injury. A number of reports have separately shown changes in pro-apoptotic proteins such as the Bcl-2 family members following optic nerve injury. However, induction time of these apoptotic signals has not been identified due to different treatments of the optic nerve, and insufficient time intervals for measurements. Therefore, the stream of cell death signals is not well understood. In the present study, we systematically reinvestigated a detailed time course of these cell death/survival signals in the rat retina after optic nerve crush, to determine the signal cascade leading to RGC apoptosis. The most conspicuous changes detected in the retina were the rapid inactivation of phospho-Akt and phospho-Bad proteins 2-3 days after optic nerve damage, and the subsequent gradual activation of Bax protein and caspase-3 activity accompanied by cell loss of RGCs 6 days after nerve injury. Cellular localization of these molecular changes was limited to RGCs. Furthermore, amount of insulin-like growth factor-I (IGF-I), an activator of the phosphatidyl inositol-3-kinase (PI3K)/Akt system, was initially decreased from RGCs 1-2 days just prior to the inactivation of phospho-Akt by optic nerve crush. Conversely, supplementation with IGF-I into the rat retina induced upregulation of phospho-Akt expression and cell survival of RGCs both in vitro and in vivo. Thus, injury to the optic nerve might induce early changes in cellular homeostasis with a plausible loss of trophic support for injured RGCs. Actually, IGF-I drastically enhanced neurite outgrowth from adult rat RGCs via a wortmannin-dependent mechanism in a retinal explant culture. Our data strongly indicate that IGF-I is a key molecule that induces RGC apoptosis or RGC survival and regeneration in the retina during the early stage of optic nerve injury.

INGAP peptide improves nerve function and enhances regeneration in streptozotocin-induced diabetic C57BL/6 mice

INGAP peptide comprises the core active sequence of Islet Neogenesis Associated Protein (INGAP), a pancreatic cytokine that can induce new islet formation and restore euglycemia in diabetic rodents. The ability of INGAP peptide in vitro to enhance nerve growth from sensory ganglia suggests its potential utility in peripheral nerve disorders. In this study, INGAP peptide was administered alone or in combination with insulin to streptozotocin-induced diabetic mice exhibiting signs of peripheral neuropathy. Following a 2-wk treatment period, thermal hypoalgesia in diabetic mice was significantly improved in groups that received INGAP peptide, without development of hyperalgesia. Explanted dorsal root ganglia (DRG) from these groups showed enhanced nerve outgrowth and evidence of increased mitochondrial activity. Western blotting experiments revealed attenuation of neurofilament hyperphosphorylation, up-regulation of beta-tubulin and actin, and increased phosphorylation of the transcription factor STAT3 in DRG. These findings suggest that INGAP peptide can activate some of the signaling pathways implicated in nerve regeneration in sensory ganglia, thereby providing a means of improvement of nociceptive dysfunction in the peripheral nervous system.

Oxidized galectin-1 stimulates macrophages to promote axonal regeneration in peripheral nerves after axotomy

Various neurotrophic factors that promote axonal regeneration have been investigated in vivo, but the signals that prompt neurons to send out processes in peripheral nerves after axotomy are not well understood. Previously, we have shown oxidized galectin-1 (GAL-1/Ox) promotes initial axonal growth after axotomy in peripheral nerves. However, the mechanism by which GAL-1/Ox promotes axonal regeneration remains unclear and is the subject of the present study. To identify possible target cells of GAL-1/Ox, a fluorescently labeled recombinant human GAL-1/Ox (rhGAL-1/Ox) was incubated with DRG neurons, Schwann cells, and intraperitoneal macrophages from adult rats. Only the cell surfaces of intraperitoneal macrophages bound the rhGAL-1/Ox, suggesting that these cells possess a receptor for GAL-1/Ox. Experiments examining tyrosine phosphorylation revealed that rhGAL-1/Ox stimulated changes in signal transduction pathways in these macrophages. These changes caused macrophages to secrete an axonal growth-promoting factor. This was demonstrated when conditioned media of macrophages stimulated with rhGAL-1/Ox in 48 hr culture strongly enhanced axonal regeneration from transected-nerve sites of DRG explants. Furthermore, activated macrophage-conditioned media also improved Schwann cell migration from the transected-nerve sites. From these results, we propose that axonal regeneration occurs in axotomized peripheral nerves as a result of cytosolic reduced galectin-1 being released from Schwann cells and injured axons, which then becomes oxidized in the extracellular space. Oxidized galectin-1 then stimulates macrophages to secrete a factor that promotes axonal growth and Schwann cell migration, thus enhancing peripheral nerve regeneration.

Growth hormone treatment attenuates age-related changes in hippocampal short-term plasticity and spatial learning

Downregulation of the growth hormone/insulin-like growth factor-1 (IGF-1)axis is one of the most robust biomarkers of mammalian aging. Reports have suggested that age-related changes in secretion of growth hormone and IGF-1 contribute to the development of some peripheral characteristics of the aged phenotype including decreased bone density and lean body mass. Recent work has focused on the identification of a role for age-related reductions in growth hormone and IGF-1 in the development of cognitive impairments associated with aging. In the current study, we report that aged (30 month-old) Brown Norway x Fisher rats demonstrate impairments in spatial learning compared with adult (10 month-old) animals, and that 4-month treatment with growth hormone (300 microg twice daily) attenuates age-related learning impairments. After 6 months of treatment, we employed an extracellular paired-pulse protocol to investigate age-related changes in hippocampal short-term plasticity, and found that aged rats exhibit significantly increased paired-pulse ratios (PPRs) at an interpulse interval of 50 ms compared with adult rats. Long-term growth hormone administration restored PPRs in aged animals to values comparable to those observed in adult controls. Since the age-related changes observed in PPR may result from decreases in hippocampal inhibitory tone mediated by GABA(A) receptors, we assessed GABA(A) receptor subunit expression by immunoblot analysis. Data revealed significant age-related decreases in GABA(A) receptor alpha-1 subunit expression which were attenuated by growth hormone treatment. However, hippocampal levels of the gamma2 subunit, glutamic acid decarboxylase (GAD)(65), and GAD(67) protein concentrations were not significantly affected by age or growth hormone treatment. In conclusion, we suggest that age-related decreases in growth hormone and IGF-1 contribute to cognitive decline, in part, via alterations in hippocampal short-term plasticity. Changes in plasticity may reflect a shift in the balance of hippocampal inhibitory and excitatory function.

Oxidized galectin-1 stimulates the migration of Schwann cells from both proximal and distal stumps of transected nerves and promotes axonal regeneration after peripheral nerve injury

Oxidized galectin-1 has recently been identified as a key factor that plays important roles in initial axonal growth in injured peripheral nerves. The aim of this study was to investigate the effects of oxidized galectin-1 on regeneration of rat spinal nerves using acellular autografts (containing no viable cells) and allografts (containing no cell membranes) with special attention to the relationship between axonal regeneration and Schwann cell migration. Immunohistochemically, endogenous galectin-1 was expressed in dorsal root ganglion (DRG) neurons, spinal cord motoneurons, and axons and Schwann cells in normal sciatic nerves. Administration of oxidized recombinant human galectin-1 (rh-gal-lox, 5 ng/ml) in autograft model promoted axonal regeneration from motoneurons as well as from DRG neurons; this was confirmed by a fluorogold tracer study (p < 0.05). Anti-rh-gal-1 antibody (30 microg/ml) strongly inhibited axonal regrowth (p < 0.05). Pretreatment of allografts with rh-gal-lox stimulated the migration of Schwann cells not only from proximal stumps but also from distal stumps into the grafts, resulting in accelerated axonal regeneration (p < 0.05). Moreover, Schwann cell migration preceded the axonal growth in the presence of exogenous rh-gal-lox in the grafts. These results strongly suggest that local administration of exogenous rh-gal-lox promotes the migration of Schwann cells followed by axonal regeneration from both motor and sensory neurons, resulting in acceleration of neuronal repair. This technique may also be of value in the repair of human nerves.

Neurite growth promotion by nerve growth factor and insulin-like growth factor-1 in cultured adult sensory neurons: role of phosphoinositide 3-kinase and mitogen activated protein kinase

Although neurons of the PNS no longer require neurotrophins such as Nerve Growth Factor (NGF) for their survival, such factors are involved in regulating axonal sprouting and regeneration after injury. In addition to the neurotrophin receptors, sensory neurons are reported to express IGF-1, EGF and FGF receptors. To investigate the influence of growth factors in addition to NGF, we examined the effects of IGF-1 EGF and FGF on neurite growth from adult rat dorsal root ganglion sensory neurons in both dissociated cultures and in compartmented cultures. As expected, NGF elicited robust neuritic growth in both the dissociated and compartmented cultures. The growth response to IGF-1 was similar, although there was minimal neurite growth in response to EGF or FGF. In addition, IGF-1 (but neither FGF nor EGF), when applied to cell bodies in compartmented cultures, potentiated the distal neurite growth into NGF-containing side compartments. This potentiation was not seen when these factors were provided along with NGF in the side compartments of compartmented cultures, or in the dissociated cultures. To determine the contribution of signaling intermediates downstream of receptor activation, we used inhibitors of the potential effectors and Western blotting. The PI 3-kinase inhibitor, LY294002 attenuated neurite growth evoked by NGF, IGF and EGF in dissociated cultures, although the MAP kinase kinase (MEK) inhibitor PD098059 diminished the growth in only IGF. Immunoprecipitation and Western blotting results demonstrated differential activation of MAPK, PI 3-kinase, PLCgamma1 and SNT by the different factors. Activation of PI 3-kinase and SNT by both NGF and IGF-1 correlated with their effects on neurite growth. These results support the hypothesis that the PI 3-kinase pathway plays an important role in neuritogenesis.