Nerve Growth Factor Molecule Research Articles

The pleiotropic molecule NGF regulates the in vitro properties of fibroblasts, keratinocytes, and endothelial cells: implications for wound healing.

Nerve growth factor (NGF) is recognized as a pleiotropic molecule, exerting a variety of biological effects on different cell types and pathophysiological conditions, and its role in tissue wound healing has been recently highlighted. However, the preferential cellular target of NGF is still elusive in the complex cellular and molecular cross talk that accompanies wound healing. Thus, to explore possible NGF cellular targets in skin wound healing, we investigated the in vitro NGF responsiveness of keratinocytes (cell line HEKa), fibroblasts (cell line BJ), and endothelial cells (cell line HUVEC), also in the presence of adverse microenvironmental conditions, e.g., hyperglycemia. The main results are summarized as follows: 1) NGF stimulates keratinocyte proliferation and HUVEC proliferation and angiogenesis in a dose-dependent manner although it has no effect on fibroblast proliferation; 2) NGF stimulates keratinocyte but not fibroblast migration in the wound healing assay; and 3) NGF completely reverts the proliferation impairment of keratinocytes and the angiogenesis impairment of HUVECs induced by high d-glucose concentration in the culture medium. These results contribute to better understanding possible targets for the therapeutic use of NGF in skin repair.

Effects of serum albumin on SPR-measured affinity of small molecule inhibitors binding to nerve growth factor

The study of the interactions between a drug and plasma serum proteins are necessary in determining pharmacological and toxicological properties for therapeutic development. Small molecule nerve growth factor (NGF) inhibitors have been investigated for their abilities to inhibit NGF binding to TrkA as a potential therapeutic option for the treatment of neuropathic and inflammatory pain. In this study, surface plasmon resonance (SPR) spectroscopy and 125I-NGF radioisotope binding assays were carried out to better understand the role of serum albumin (SA) in small molecule binding to NGF. SA has been characterized as a universal drug carrier with up to seven binding domains on its surface to transport drug molecules to target tissues. Here, we use SPR kinetic analysis to analyze the change in specificity of small molecules to immobilized NGF in the presence and absence of SA. In the presence of SA an overall increase in small molecule binding affinity for NGF was observed compared to binding in the absence of SA. Our results suggest a crucial role for SA in the pharmacokinetics of small molecule binding to NGF. This effect will require consideration when developing therapeutic agents.

Nerve growth factor signalling in pathology and regeneration of human teeth

Nerve growth factor (NGF) is a key regulator of the development and differentiation of neuronal and non-neuronal cells. In the present study we examined the distribution of NGF and its low and high-affinity receptors, p75NTR and TrkA respectively, in permanent human teeth under normal and pathological conditions. In intact functional teeth, NGF, p75NTR and TrkA are weakly expressed in dental pulp fibroblasts and odontoblasts that are responsible for dentine formation, while the NGF and p75NTR molecules are strongly expressed in nerve fibres innervating the dental pulp. In carious and injured teeth NGF and TrkA expression is upregulated in a selective manner in odontoblasts surrounding the injury sites, indicating a link between NGF signalling and dental tissue repair events. Accordingly, NGF and TrkA expression is strongly upregulated in cultured primary human dental mesenchymal cells during their differentiation into odontoblasts. Targeted release of NGF in cultured human tooth slices induced extensive axonal growth and migration of Schwann cells towards the NGF administration site. These results show that NGF signalling is strongly linked to pathological and regenerative processes in human teeth and suggest a potential role for this neurotrophic molecule in pulp regeneration.

Conformational Rigidity within Plasticity Promotes Differential Target Recognition of Nerve Growth Factor.

Nerve Growth Factor (NGF), the prototype of the neurotrophin family, is essential for maintenance and growth of different neuronal populations. The X-ray crystal structure of NGF has been known since the early '90s and shows a β-sandwich fold with extensive loops that are involved in the interaction with its binding partners. Understanding the dynamical properties of these loops is thus important for molecular recognition. We present here a combined solution NMR/molecular dynamics study which addresses the question of whether and how much the long loops of NGF are flexible and describes the N-terminal intrinsic conformational tendency of the unbound NGF molecule. NMR titration experiments allowed identification of a previously undetected epitope of the anti-NGF antagonist antibody αD11 which will be of crucial importance for future drug lead discovery. The present study thus recapitulates all the available structural information and unveils the conformational versatility of the relatively rigid NGF loops upon functional ligand binding.

Nerve growth factor: role in growth, differentiation and controlling cancer cell development.

Recent progress in the Nerve Growth Factor (NGF) research has shown that this factor acts not only outside its classical domain of the peripheral and central nervous system, but also on non-neuronal and cancer cells. This latter observation has led to divergent hypothesis about the role of NGF, its specific distribution pattern within the tissues and its implication in induction as well as progression of carcinogenesis. Moreover, other recent studies have shown that NGF has direct clinical relevance in certain human brain neuron degeneration and a number of human ocular disorders. These studies, by suggesting that NGF is involved in a plethora of physiological function in health and disease, warrant further investigation regarding the true role of NGF in carcinogenesis. Based on our long-lasting experience in the physiopathology of NGF, we aimed to review previous and recent in vivo and in vitro NGF studies on tumor cell induction, progression and arrest. Overall, these studies indicate that the only presence of NGF is unable to generate cell carcinogenesis, both in normal neuronal and non-neuronal cells/tissues. However, it cannot be excluded the possibility that the co-expression of NGF and pro-carcinogenic molecules might open to different consequence. Whether NGF plays a direct or an indirect role in cell proliferation during carcinogenesis remains to demonstrate.

Neurotrophic Effects of Mu Bie Zi (Momordica cochinchinensis) Seed Elucidated by High-Throughput Screening of Natural Products for NGF Mimetic Effects in PC-12 Cells.

Post-mitotic central nervous system (CNS) neurons have limited capacity for regeneration, creating a challenge in the development of effective therapeutics for spinal cord injury or neurodegenerative diseases. Furthermore, therapeutic use of human neurotrophic agents such as nerve growth factor (NGF) are limited due to hampered transport across the blood brain barrier (BBB) and a large number of peripheral side effects (e.g. neuro-inflammatory pain/tissue degeneration etc.). Therefore, there is a continued need for discovery of small molecule NGF mimetics that can penetrate the BBB and initiate CNS neuronal outgrowth/regeneration. In the current study, we conduct an exploratory high-through-put (HTP) screening of 1144 predominantly natural/herb products (947 natural herbs/plants/spices, 29 polyphenolics and 168 synthetic drugs) for ability to induce neurite outgrowth in PC12 dopaminergic cells grown on rat tail collagen, over 7 days. The data indicate a remarkably rare event-low hit ratio with only 1/1144 tested substances (<111.25 µg/mL) being capable of inducing neurite outgrowth in a dose dependent manner, identified as; Mu Bie Zi, Momordica cochinchinensis seed extract (MCS). To quantify the neurotrophic effects of MCS, 36 images (n = 6) (average of 340 cells per image), were numerically assessed for neurite length, neurite count/cell and min/max neurite length in microns (µm) using Image J software. The data show neurite elongation from 0.07 ± 0.02 µm (controls) to 5.5 ± 0.62 µm (NGF 0.5 μg/mL) and 3.39 ± 0.45 µm (138 μg/mL) in MCS, where the average maximum length per group extended from 3.58 ± 0.42 µm (controls) to 41.93 ± 3.14 µm (NGF) and 40.20 ± 2.72 µm (MCS). Imaging analysis using immunocytochemistry (ICC) confirmed that NGF and MCS had similar influence on 3-D orientation/expression of 160/200 kD neurofilament, tubulin and F-actin. These latent changes were associated with early rise in phosphorylated extracellular signal-regulated kinase (ERK) p-Erk1 (T202/Y204)/p-Erk2 (T185/Y187) at 60 min with mild changes in pAKT peaking at 5 min, and no indication of pMEK involvement. These findings demonstrate a remarkable infrequency of natural products or polyphenolic constituents to exert neurotrophic effects at low concentrations, and elucidate a unique property of MCS extract to do so. Future research will be required to delineate in depth mechanism of action of MCS, constituents responsible and potential for therapeutic application in CNS degenerative disease or injury.

Adsorption of NGF and BDNF derived peptides on gold surfaces

This study tackles the interaction between gold surfaces and two peptide fragments named NGF(1-14) and BDNF(1-12), able to mimic the proliferative activity of the nerve growth factor (NGF) and the brain derived neurotrophic factor (BDNF), respectively. The physical adsorption processes on the solid surface from both single and binary peptide solutions, at physiological and acid pH, were investigated by QCM-D and CD experiments, as well as by molecular dynamics calculations. The relevant physicochemical properties at the hybrid bio-interface, including peptide-surface interaction, conformational changes, hydrodynamic thickness, viscoelastic parameters, and competitive vs. synergic behaviour of the two peptide fragments towards the surface, were scrutinized. Biological assays with neuronal cells pointed to the maintenance of the biological activity of NGF(1-14) and BDNF(1-12) peptide molecules within the adlayers on the gold surface.

Effects of High Salt-Exposure on the Development of Retina and Lens in 5.5-Day Chick Embryo

Background/Aims: Excess maternal salt intake during pregnancy may alter fetal development. However, our knowledge on how an increased salt intake during pregnancy influences fetal eye development is limited. In this study, we investigated the effects of high-salt treatment on the developing eyes in chick embryos, especially focusing on the development of the retina and the lens. Methods: 5.5-day chick embryos were exposed to 280mosm/l (n=17), or 300mosm/l (n=16) NaCl. The treated embryos were then incubated for 96 hours before they were fixed with 4% paraformaldehyde for H&E staining, whole-mount embryo immunostaining and TUNEL staining. BrdU and PH3 incorporation experiments were performed on the chick embryos after high-salt treatment. RT-PCR analyses were conducted from chick retina tissues. Results: We demonstrated that high-salt treatment altered the size of eyes in chick embryos, induced malformation of the eyes and impaired the development of the lens and the retina. We found an impaired expression of Paired box 6 (PAX6) and neuronal cells in the developing retina as revealed by neurofilament immunofluorescent staining. There was a reduction in the number of BrdU-positive cells and PH3-positive cells in the retina, indicating an impaired cell proliferation with high-salt treatment. High-salt treatment also resulted in an increased number of TUNEL-positive cells in the retina, indicating a higher amount of cell death. RT-PCR data displayed that the expression of the pro-apoptotic molecule nerve growth factor (NGF) in chick retina was increased and CyclinD1 was reduced with high-salt treatment. The size of the lens was reduced and Pax6 expression in the lens was significantly inhibited. High salt-treatment was detrimental to the migration of neural crest cells. Conclusion: Taken together, our study demonstrated that high-salt exposure of 5.5-day chick embryos led to an impairment of retina and lens development, possibly through interfering with Pax6 expression.

A Novel Dimeric Dipeptide Mimetic of the Nerve Growth Factor Exhibits Pharmacological Effects upon Systemic Administration and Has No Side Effects Accompanying the Neurotrophin Treatment

The development of small molecule nerve growth factor (NGF) mimetics is a promising approach to overcome limitations in the use of the neurotrophin as a drug, which are poor pharmacokinetics and undesirable side effects. We designed dimeric dipeptide called GK-2 (bis(N-succinyl-L-glutamyl-L-lysine)hexametylendiamide) on the base of beta-turn sequence of NGF loop4 which most exposed to solvent and hence can play the major role in the interaction of NGF with the receptor. It was shown, that GK-2 stimulates phosphorylation of TrkA receptor, selectively activates PI3K/Akt signaling cascade that is important for cell survival, and does not activate MAPK/Erk pathway, associated not only with cell survival but also with cell differentiation. According to these data, GK-2 in vitro prevented H2O2- or MPTP- or glutamate-induced neuronal cell death at nanomolar concentrations, but did not provoke neurite outgrowth in PC12 cells. In vivo GK-2 exhibits therapeutic effects in models of Parkinson’s disease, Alzheimer’s disease, brain ischemia and diabetes mellitus. GK-2 shows activity in doses 0.01 - 5 mg/kg intraperitoneally and retains the activity after oral administration in dose 10 mg/kg. GK-2 has no side effects accompanying NGF treatment namely hyperalgesia and weight loss. Thus, the designed dimeric substituted dipeptide provides promising drug candidate and a molecular tool for investigating the possibility of divergence in NGF therapeutic and adverse effects.

Pro-domain in precursor nerve growth factor mediates cell death

Nerve growth factor (NGF) is synthesized as a precursor, proNGF that undergoes post-translational processing to generate the biologically active mature NGF. While the neurotrophic function of NGF is well established, the activity of the proNGF precursor is still unclear. In this study, we have cloned the pro-domain of the precursor NGF molecule and have elucidated its function. We have used both mature and the furin resistant pro(R/G)NGF as controls in our experiments. Both pro(R/G)NGF and mature NGF (NGF) exhibited neurotrophic activity on PC12 cells while the pro-domain itself promoted cell death. The pro-domain, has been found to mediate apoptosis possibly by promoting the formation of a signaling complex comprising of endogenous p75NTR receptor, Bim/Bcl2 group of proteins and JNK and MEK1/2 signaling pathways.

Cortical peroxynitration of nerve growth factor in aged and cognitively impaired rats

Basal forebrain cholinergic neurons (BFCN), a system involved in learning and memory processes, are highly dependent on a continuous supply of biologically active nerve growth factor (NGF). Age-related cholinergic atrophy and cell loss in normal brains is apparently not complemented by reductions in the levels of NGF as could be expected. In the present work, cortical proNGF/NGF were immunoprecipitated from cortical brain homogenates from young and aged and behaviorally characterized rats and resolved with antinitrotyrosine antibodies to reveal nitration of tyrosine residues in proteins. Cortical proNGF in aged and cognitively impaired rats was found to be a target for peroxynitrite-mediated oxidative damage with correlative impact on decrease in choline acetyltransferase activity. These studies provide evidence for oxidative stress damage of NGF molecules in the cerebral cortex of cognitively impaired aged rats as previously shown in AD human brains.

An NGF mimetic, MIM-D3, stimulates conjunctival cell glycoconjugate secretion and demonstrates therapeutic efficacy in a rat model of dry eye

The aim of this study was to evaluate the efficacy of MIM-D3, a small molecule nerve growth factor (NGF) peptidomimetic, as a therapeutic agent in rats with scopolamine induced dry eye. NGF plays an important role in ocular surface maintenance and corneal wound healing and was recently shown to have mucin secretagogue activity in conjunctival cells. We investigated whether MIM-D3 increased glycoconjugate secretion in conjunctival cells in vitro and in rat tear fluids in vivo. Primary rat conjunctival cell cultures were treated with increasing concentrations of MIM-D3 and evaluated for glycoconjugate secretion, proliferation and MAPK1/2 activation. Glycoconjugates were quantitated in tear fluids from normal rats treated topically with increasing doses of MIM-D3 (0.4%, 1% and 2.5%). Dry eye was induced in rats by subcutaneous scopolamine treatment, administered by surgically implanted osmotic pumps for 14 or 28 days. Aqueous tear production, tear clearance, fluorescein corneal staining and tear break-up time (tBUT) were evaluated. Glycoconjugates and NGF were quantitated in the tear fluids by enzyme-linked lectin assay (ELLA) and enzyme-linked immunosorbant assay (ELISA), respectively. We found that 50 μM MIM-D3 statistically significantly induced a 1.3-fold increase in glycoconjugate secretion and a 2.3-fold increase in MAPK1/2 activation without increasing proliferation from conjunctival cell cultures. Application of 2.5% MIM-D3 in normal rat eyes statistically significantly increased tear glycoconjugate concentration by 2.3-fold. In the experimental dry eye model, application of 1% MIM-D3 to rat eyes for either 1 or 17 consecutive days, followed by 1 week of no dosing produced a statistically significant decrease in corneal staining ( p < 0.001), a slight increase in tBUT, and increases in tear glycoconjugates ( p < 0.05) compared to vehicle. Scopolamine treatment also caused a statistically significant increase of endogenous NGF in tears ( p < 0.005). We concluded that the increase in glycoconjugate concentration by the 1% MIM-D3 dose may have improved the quality and stability of the tear film, and thereby improved healing on the ocular surface in dry eye. Therefore, MIM-D3 may have therapeutic potential as a topical agent for the treatment of dry eye.

Single-Molecule Imaging of NGF Axonal Transport in Microfluidic Devices

Nerve growth factor (NGF) plays a critical role in neuron survival and functioning. NGF binds and activates membrane receptors TrkA, endocytosed NGF-TrkA complex then recruits various motor proteins to transport along cytoskeletal tracks towards cell body, where downstream signaling processes are regulated. Our recent study revealed that the majority of endosomes contain a single NGF molecule, which makes single-molecule imaging an essential tool for NGF studies. However single-molecule imaging in live cells is often limited by the intrinsic background fluorescence. Here, we efficiently reduced the background by employing a microfluidic culture platform, which can guide the growth of neurons and allow separately controlled microenvironment for cell bodies or axon termini. Single-molecule imaging of Qdot-labeled NGF in live axons shows exclusive retrograde transport of cargoes toward cell body with a stop-and-go pattern. Measurements at various temperatures show that the rate of NGF retrograde transport decreased exponentially over the range of 36-14 degree Celsius. A 10-degree decrease in temperature resulted in a threefold decrease in the rate of NGF retrograde transport. Our successful measurements of NGF transport suggest that the microfluidic device can serve as a unique platform for single-molecule imaging of molecular processes in live neurons.

Long-term Delivery of Nerve Growth Factor by Encapsulated Cell Biodelivery in the Göttingen Minipig Basal Forebrain

Nerve growth factor (NGF) prevents cholinergic degeneration in Alzheimer's disease (AD) and improves memory in AD animal models. In humans, the safe delivery of therapeutic doses of NGF is challenging. For clinical use, we have therefore developed an encapsulated cell (EC) biodelivery device, capable of local delivery of NGF. The clinical device, named NsG0202, houses an NGF-secreting cell line (NGC-0295), which is derived from a human retinal pigment epithelial (RPE) cell line, stably genetically modified to secrete NGF. Bioactivity and correct processing of NGF was confirmed in vitro. NsG0202 devices were implanted in the basal forebrain of Göttingen minipigs and the function and retrievability were evaluated after 7 weeks, 6 and 12 months. All devices were implanted and retrieved without associated complications. They were physically intact and contained a high number of viable and NGF-producing NGC-0295 cells after explantation. Increased NGF levels were detected in tissue surrounding the devices. The implants were well tolerated as determined by histopathological brain tissue analysis, blood analysis, and general health status of the pigs. The NsG0202 device represents a promising approach for treating the cognitive decline in AD patients.

Cistanches Herba enhances learning and memory by inducing nerve growth factor

Nerve growth factor (NGF) has potent biological activities such as preventing neuronal death, promoting neurite outgrowth, supporting synapse formation, and enhancing memory function. NGF and NGF-like molecules can potentially be used to treat neurodegenerative disorders, such as dementia. This study investigated the effects of Cistanches Herba, a widely used medicinal herb, on NGF regulation and its neuronal actions, including neurite outgrowth, synapse formation, and learning and memory enhancement. Cistanches Herba extract (CHE; 250 μg/ml) increased NGF induction in C6 cells and led to neurite extension in PC12 cells. It also stimulated NGF secretion in the cortex and hippocampus of the mouse brain at 5 and 20 mg/kg/day (3 days, p.o.). Furthermore, CHE increased neuronal cell differentiation, neurite length, and synapse formation in the mouse hippocampus. CHE significantly enhanced learning and memory, as demonstrated by passive avoidance test and novel object recognition test. These results suggest that CHE is useful for improving memory function via its action in upregulating NGF.

Single-molecule imaging of NGF axonal transport in microfluidic devices

Nerve growth factor (NGF) signaling begins at the nerve terminal, where it binds and activates membrane receptors and subsequently carries the cell-survival signal to the cell body through the axon. A recent study revealed that the majority of endosomes contain a single NGF molecule, which makes single-molecule imaging an essential tool for NGF studies. Despite being an increasingly popular technique, single-molecule imaging in live cells is often limited by background fluorescence. Here, we employed a microfluidic culture platform to achieve background reduction for single-molecule imaging in live neurons. Microfluidic devices guide the growth of neurons and allow separately controlled microenvironment for cell bodies or axon termini. Designs of microfluidic devices were optimized and a three-compartment device successfully achieved direct observation of axonal transport of single NGF when quantum dot labeled NGF (Qdot-NGF) was applied only to the distal-axon compartment while imaging was carried out exclusively in the cell-body compartment. Qdot-NGF was shown to move exclusively toward the cell body with a characteristic stop-and-go pattern of movements. Measurements at various temperatures show that the rate of NGF retrograde transport decreased exponentially over the range of 36-14 degrees C. A 10 degrees C decrease in temperature resulted in a threefold decrease in the rate of NGF retrograde transport. Our successful measurements of NGF transport suggest that the microfluidic device can serve as a unique platform for single-molecule imaging of molecular processes in neurons.

Surfactant-free Formulation of Poly(Lactic/Glycolic) Acid Nanoparticles Encapsulating Functional Polypeptide: A Technical Note

Therapeutic proteins or polypeptides can be formulated into various particulate delivery systems including the polymeric carriers to avoid rapid degradation and to maintain the sustained release for better therapeutic effects (1). Poly(lactic/glycolic) acid (PLGA) micro/nanoparticle is a widely used formulation agent because of its good biodegradability, biocompatibility, and approved clinical usage, which have been available in the market to treat prostate cancer, acromegaly, periodontal disease, and pediatric growth hormone deficiency (2). The sustaining and complete release of proteins in their native or active forms from the PLGA micro/nanoparticles is often a challenging task (3). Proteins are generally formulated into PLGA nanoparticles by water/oil/water double-emulsion–solvent evaporation method, which generates hydrophilic/hydrophobic interface that may result in the unfolding or denaturing of protein molecules (4). Thus, polymeric surfactants are usually used to lower surface tension of protein solutions and to prevent aggregation of protein molecules at hydrophobic surface (1). Polyvinyl alcohol (PVA) is a widely used polymeric surfactant in the exterior aqueous phase as an emulsifier. However, the safety of PVA still appears to be a concern from the previous literature reports (5,6). Following repeated subcutaneous or intravenous administrations of PVA, various organ lesions and hypertension have been reported in rats, and central nervous system depression and anemia followed by renal damage have also been reported in beagle dogs; whereas, orally administered PVA is relatively harmless in mice or rat (5,6). Therefore, residual PVA was always removed by washing procedures such as repetitive centrifugation (7) or filtration (8), which removes not only the PVA but also the unencapsulated proteins or polypeptides, which might be often valuable or hard to collect. Hence, a few substituting emulsifiers have been studied. For example, poly(ethylene glycol) (PEG) was used successfully as the stabilizer to prepare enzyme-loaded PLGA microparticles (9). Besides, surfactant-free formulation was achieved by nanoprecipitation/solvent-displacement method that would not alter surface properties of PLGA nanoparticles, but this method may suffer the low encapsulation efficiency when low protein concentration solution is to be used (10). In the present study, we introduced another surfactant-free method to prepare PLGA nanoparticles encapsulating polypeptides by double-emulsion–solvent evaporation method. We used sucrose as the stabilizer of the exterior aqueous phase to prevent aggregation of PLGA nanoparticles during formulation process. Nerve growth factor (NGF), a small secreted protein which can induce the differentiation and survival of particular target neurons, was used as the model protein. As sucrose is a nontoxic material, additional washing procedures are not necessarily needed for NGF-loaded PLGA nanoparticles, and thus, the valuable NGF loss can be minimized. The release of functional NGF molecules from these nanoparticles was verified by either the antibody recognition in enzyme-linked immunosorbent assay (ELISA) method or the induction on the neurite outgrowth of PC-12 cells.

Sensory axon targeting is increased by NGF gene therapy within the lesioned adult femoral nerve

Even though peripheral nerves regenerate well, axons are often misrouted and reinnervate inappropriate distal pathways post-injury. Misrouting most likely occurs at branch points where regenerating axons make choices. Here, we show that the accuracy of sensory axon reinnervation is enhanced by overexpression of the guidance molecule nerve growth factor (NGF) distal to the bifurcation. We used the femoral nerve as a model, which contains both sensory and motor axons that intermingle in the parent trunk and distally segregate into the saphenous (SB) and motor branches (MB). Transection of the parent trunk resulted in misrouting of axon reinnervation to SB and MB. To enhance sensory axon targeting, recombinant adenovirus encoding NGF was injected along the SB close to the bifurcation 1 week post-injury. The accuracy of axon reinnervation was assessed by retrograde tracing at 3 or 8 weeks after nerve injury. NGF overexpression significantly increased the accuracy of SB axon reinnervation to the appropriate nerve branch, in a manner independent of enhancing axon regeneration. This novel finding provides in vivo evidence that gradient expression of neurotrophin can be used to enhance targeting of distal peripheral pathways to increase axon regeneration into the appropriate nerve branch.

A New Nerve Growth Factor-Mimetic Peptide Active on Neuropathic Pain in Rats

Analysis of the structure of nerve growth factor (NGF)-tyrosine kinase receptor A (TrkA) complex, site-directed mutagenesis studies and results from chemical modification of amino acid residues have identified loop 1, loop 4, and the N-terminal region of the NGF molecule as the most relevant for its biological activity. We synthesized several peptides mimicking the two loops (1 and 4) linked together with an appropriate spacer, with or without the N-terminal region. Two peptides named NL1L4 and L1L4 demonstrated good NGF agonist activity at a concentration as low as 3 mum. They induced differentiation of chick dorsal root ganglia and stimulated tyrosine phosphorylation of TrkA, but not TrkB, receptor. In addition L1L4 was able to induce differentiation of PC12 cells. More interestingly, the peptide with the highest "in vitro" activity (L1L4) was shown to reduce neuropathic behavior and restore neuronal function in a rat model of peripheral neuropathic pain, thereby suggesting a potential therapeutic role for this NGF-mimetic peptide.

Guiding Adult Mammalian Sensory Axons During Regeneration

Misdirection of axons after nerve injury impairs successful regeneration of adult neurons. Investigations of axon guidance in development have provided an understanding of pathfinding, but their relevance to regenerating adult axons is unclear. We investigated adult mammalian axon guidance during regeneration after peripheral nerve injury and focused on the effects of the prototypic guidance molecule nerve growth factor (NGF). Adult rat sensory neurons from dorsal root ganglia that expressed the NGF receptor tropomyosin-related kinase A (trkA) were presented with a point source of NGF in vitro. Naive trkA neurons had no net turning response to NGF, but if they had been preconditioned by a peripheral nerve transection in vivo before culturing, their growth cones were attracted toward the NGF gradient. A laminin substrate was required for this behavior and an anti-trkA antibody interrupted turning. These data demonstrate that injured adult mammalian axons can be guided as they regenerate. Moreover, despite the downregulation of trkA mRNA and protein levels within the dorsal root ganglion after injury, sensory neurons retain and increase trkA protein at the injury site where the regenerating axons are found. This may enhance the axonal response to NGF and allow guidance along an NGF gradient created in vivo in the distal nerve stump.