Differential regulation of fibroblast growth factor (FGF)-2 and FGF receptor 1 mRNAs and FGF-2 isoforms in spinal ganglia and sciatic nerve after peripheral nerve lesion

Composite Hydrogel Conduit Incorporated with Platelet-Rich Plasma Improved the Regenerative Microenvironment for Peripheral Nerve Repair

Peripheral nerve regeneration and functional recovery remain major challenges in clinical practice. Nerve guidance conduits (NGCs) which can regulate the regenerative microenvironment are beneficial for peripheral nerve repair. Platelet-rich plasma (PRP) can secrete multiple growth factors to regulate the regenerative microenvironment. However, current administration methods of PRP are rapidly activated followed by the burst release of growth factors, causing low therapeutic efficiency in vivo. To overcome these disadvantages, a composite nerve conduit was fabricated by incorporating PRP into a gelatin methacrylate (GelMA) and sodium alginate (SA) hydrogel. The GelMA/SA-3/PRP-20 NGCs possess optimal mechanical properties, degradation rate, and superior biological performance. Importantly, GelMA/SA-3/PRP-20 NGCs achieved the sustained release of two major growth factors (VEGF-A, PDGF-BB) from PRP. Moreover, the GelMA/SA-3/PRP-20 NGCs significantly promoted the migration of Schwann cells and the neovascularization of endothelial cells in vitro. While bridging 10 mm rat sciatic nerve defects, the GelMA/SA-3/PRP-20 NGCs promoted axonal regeneration and functional recovery of peripheral nerves. Therefore, the GelMA/SA-3/PRP-20 NGCs could regulate the regenerative microenvironment by sustained release of growth factors from PRP and shed new light on the clinical application of PRP in peripheral nerve repair.

Central Facial Nervous System Biomolecules Involved in Peripheral Facial Nerve Injury Responses and Potential Therapeutic Strategies

Peripheral facial nerve injury leads to changes in the expression of various neuroactive substances that affect nerve cell damage, survival, growth, and regeneration. In the case of peripheral facial nerve damage, the injury directly affects the peripheral nerves and induces changes in the central nervous system (CNS) through various factors, but the substances involved in these changes in the CNS are not well understood. The objective of this review is to investigate the biomolecules involved in peripheral facial nerve damage so as to gain insight into the mechanisms and limitations of targeting the CNS after such damage and identify potential facial nerve treatment strategies. To this end, we searched PubMed using keywords and exclusion criteria and selected 29 eligible experimental studies. Our analysis summarizes basic experimental studies on changes in the CNS following peripheral facial nerve damage, focusing on biomolecules that increase or decrease in the CNS and/or those involved in the damage, and reviews various approaches for treating facial nerve injury. By establishing the biomolecules in the CNS that change after peripheral nerve damage, we can expect to identify factors that play an important role in functional recovery from facial nerve damage. Accordingly, this review could represent a significant step toward developing treatment strategies for peripheral facial palsy.

Multiple Nf1 Schwann cell populations reprogram the plexiform neurofibroma tumor microenvironment

To define alterations early in tumor formation, we studied nerve tumors in neurofibromatosis 1 (NF1), a tumor predisposition syndrome. Affected individuals develop neurofibromas, benign tumors driven by NF1 loss in Schwann cells (SCs). By comparing normal nerve cells to plexiform neurofibroma (PN) cells using single-cell and bulk RNA sequencing, we identified changes in 5 SC populations, including a de novo SC progenitor-like (SCP-like) population. Long after Nf1 loss, SC populations developed PN-specific expression of Dcn, Postn, and Cd74, with sustained expression of the injury response gene Postn and showed dramatic expansion of immune and stromal cell populations; in corresponding human PNs, the immune and stromal cells comprised 90% of cells. Comparisons between injury-related and tumor monocytes/macrophages support early monocyte recruitment and aberrant macrophage differentiation. Cross-species analysis verified each SC population and unique conserved patterns of predicted cell-cell communication in each SC population. This analysis identified PROS1-AXL, FGF-FGFR, and MIF-CD74 and its effector pathway NF-κB as deregulated in NF1 SC populations, including SCP-like cells predicted to influence other types of SCs, stromal cells, and/or immune cells in mouse and human. These findings highlight remarkable changes in multiple types of SCs and identify therapeutic targets for PN.

Fibroblast Growth Factors as Tools in the Management of Neuropathic Pain Disorders

Neuropathic pain is caused by a damage to or dysfunction of the somatosensory nervous system. The main mechanisms underlying neuropathic pain include ectopic activity in nociceptive nerves, peripheral and central sensitization, impaired inhibitory modulation, and microglial activation. Fibroblast growth factors (FGFs) make up a large family of growth factors that mediate neural development, metabolism, and function through three main key signaling pathways, including RAS/MAP kinase pathway, PI3 kinase/Akt pathway, and PLCγ. An association between the members of the FGF system and the improvement of neuropathic pain has become evident, recently. These signaling molecules may be expected to provide new drug targets for the treatment of neuropathic pain. To the best of our knowledge, it is the first study that reviews the relationship between some members of the FGF system and neuropathic pain.

Growth factors-based therapeutic strategies and their underlying signaling mechanisms for peripheral nerve regeneration

Peripheral nerve injury (PNI), one of the most common concerns following trauma, can result in a significant loss of sensory or motor function. Restoration of the injured nerves requires a complex cellular and molecular response to rebuild the functional axons so that they can accurately connect with their original targets. However, there is no optimized therapy for complete recovery after PNI. Supplementation with exogenous growth factors (GFs) is an emerging and versatile therapeutic strategy for promoting nerve regeneration and functional recovery. GFs activate the downstream targets of various signaling cascades through binding with their corresponding receptors to exert their multiple effects on neurorestoration and tissue regeneration. However, the simple administration of GFs is insufficient for reconstructing PNI due to their short half‑life and rapid deactivation in body fluids. To overcome these shortcomings, several nerve conduits derived from biological tissue or synthetic materials have been developed. Their good biocompatibility and biofunctionality made them a suitable vehicle for the delivery of multiple GFs to support peripheral nerve regeneration. After repairing nerve defects, the controlled release of GFs from the conduit structures is able to continuously improve axonal regeneration and functional outcome. Thus, therapies with growth factor (GF) delivery systems have received increasing attention in recent years. Here, we mainly review the therapeutic capacity of GFs and their incorporation into nerve guides for repairing PNI. In addition, the possible receptors and signaling mechanisms of the GF family exerting their biological effects are also emphasized.

FGF5 Regulates Schwann Cell Migration and Adhesion

The fibroblast growth factor (FGF) family polypeptides play key roles in promoting tissue regeneration and repair. FGF5 is strongly up-regulated in Schwann cells of the peripheral nervous system following injury; however, a role for FGF5 in peripheral nerve regeneration has not been shown up to now. In this report, we examined the expression of FGF5 and its receptors FGFR1-4 in Schwann cells of the mouse sciatic nerve following injury, and then measured the effects of FGF5 treatment upon cultured primary rat Schwann cells. By microarray and mRNA sequencing data analysis, RT-PCR, qPCR, western blotting and immunostaining, we show that FGF5 is highly up-regulated in Schwann cells of the mouse distal sciatic nerve following injury, and FGFR1 and FGFR2 are highly expressed in Schwann cells of the peripheral nerve both before and following injury. Using cultured primary rat Schwann cells, we show that FGF5 inhibits ERK1/2 MAP kinase activity but promotes rapid Schwann cell migration and adhesion via the upregulation of N-cadherin. Thus, FGF5 is an autocrine regulator of Schwann cells to regulate Schwann cell migration and adhesion.

Regulating Axonal Responses to Injury: The Intersection between Signaling Pathways Involved in Axon Myelination and The Inhibition of Axon Regeneration

Following spinal cord injury (SCI), a multitude of intrinsic and extrinsic factors adversely affect the gene programs that govern the expression of regeneration-associated genes (RAGs) and the production of a diversity of extracellular matrix molecules (ECM). Insufficient RAG expression in the injured neuron and the presence of inhibitory ECM at the lesion, leads to structural alterations in the axon that perturb the growth machinery, or form an extraneous barrier to axonal regeneration, respectively. Here, the role of myelin, both intact and debris, in antagonizing axon regeneration has been the focus of numerous investigations. These studies have employed antagonizing antibodies and knockout animals to examine how the growth cone of the re-growing axon responds to the presence of myelin and myelin-associated inhibitors (MAIs) within the lesion environment and caudal spinal cord. However, less attention has been placed on how the myelination of the axon after SCI, whether by endogenous glia or exogenously implanted glia, may alter axon regeneration. Here, we examine the intersection between intracellular signaling pathways in neurons and glia that are involved in axon myelination and axon growth, to provide greater insight into how interrogating this complex network of molecular interactions may lead to new therapeutics targeting SCI.

Peripheral Nerve Regeneration through Hydrogel-Enriched Chitosan Conduits Containing Engineered Schwann Cells for Drug Delivery

Critical length nerve defects in the rat sciatic nerve model were reconstructed with chitosan nerve guides filled with Schwann cells (SCs) containing hydrogel. The transplanted SCs were naive or had been genetically modified to overexpress neurotrophic factors, thus providing a cellular neurotrophic factor delivery system. Prior to the assessment in vivo, in vitro studies evaluating the properties of engineered SCs overexpressing glial cell line-derived neurotrophic factor (GDNF) or fibroblast growth factor 2 (FGF-218kDa) demonstrated their neurite outgrowth inductive bioactivity for sympathetic PC-12 cells as well as for dissociated dorsal root ganglion cell drop cultures. SCs within NVR-hydrogel, which is mainly composed of hyaluronic acid and laminin, were delivered into the lumen of chitosan hollow conduits with a 5% degree of acetylation. The viability and neurotrophic factor production by engineered SCs within NVR-Gel inside the chitosan nerve guides was further demonstrated in vitro. In vivo we studied the outcome of peripheral nerve regeneration after reconstruction of 15-mm nerve gaps with either chitosan/NVR-Gel/SCs composite nerve guides or autologous nerve grafts (ANGs). While ANGs did guarantee for functional sensory and motor regeneration in 100% of the animals, delivery of NVR-Gel into the chitosan nerve guides obviously impaired sufficient axonal outgrowth. This obstacle was overcome to a remarkable extent when the NVR-Gel was enriched with FGF-218kDa overexpressing SCs.

Neurotrophic factor-α1 prevents stress-induced depression through enhancement of neurogenesis and is activated by rosiglitazone

Major depressive disorder is often linked to stress. Although short-term stress is without effect in mice, prolonged stress leads to depressive-like behavior, indicating that an allostatic mechanism exists in this difference. Here we demonstrate that mice after short-term (1 h per day for 7 days) chronic restraint stress (CRS), do not display depressive-like behavior. Analysis of the hippocampus of these mice showed increased levels of neurotrophic factor-α1 (NF-α1; also known as carboxypeptidase E, CPE), concomitant with enhanced fibroblast growth factor 2 (FGF2) expression, and an increase in neurogenesis in the dentate gyrus. In contrast, after prolonged (6 h per day for 21 days) CRS, mice show decreased hippocampal NF-α1 and FGF2 levels and depressive-like responses. In NF-α1-knockout mice, hippocampal FGF2 levels and neurogenesis are reduced. These mice exhibit depressive-like behavior that is reversed by FGF2 administration. Indeed, studies in cultured hippocampal neurons reveal that NF-α1 treatment directly upregulates FGF2 expression through extracellular signal-regulated kinase-Sp1 signaling. Thus, during short-term CRS, hippocampal NF-α1 expression is upregulated and has a key role in preventing the onset of depressive-like behavior through enhanced FGF2-mediated neurogenesis. To evaluate the therapeutic potential of this pathway, we examined, rosiglitazone (Rosi), a PPARγ agonist, which has been shown to have antidepressant activity in rodents and humans. Rosi upregulates FGF2 expression in a NF-α1-dependent manner in hippocampal neurons. Mice fed Rosi show increased hippocampal NF-α1 levels and neurogenesis compared with controls, thereby indicating the antidepressant action of this drug. Development of drugs that activate the NF-α1/FGF2/neurogenesis pathway can offer a new approach to depression therapy.

Nerve injury induces the expression of syndecan-1 heparan sulfate proteoglycan in primary sensory neurons

Heparan sulfate proteoglycans (HSPGs) have important functions in development of the central nervous system; however, their functions in nerve injury are not yet fully understood. We previously reported the expression of syndecan-1, a type of HSPG, in cranial motor neurons after nerve injury, suggesting the importance of syndecan-1 in the pathology of motor nerve injury. In this study, we examined the expression of syndecan-1, a type of HSPG, in primary sensory neurons after nerve injury in mice. Sciatic nerve axotomy strongly induced the expression of syndecan-1 in a subpopulation of injured dorsal root ganglion (DRG) neurons, which were small in size and had CGRP- or isolectin B4-positive fibers. Syndecan-1 was also distributed in the dorsal horn of the spinal cord ipsilateral to the axotomy, and located on the membrane of axons in lamina II of the dorsal horn. Not only sciatic nerve axotomy, infraorbital nerve axotomy also induced the expression of syndecan-1 in trigeminal ganglion neurons. Moreover, syndecan-1 knockdown in cultured DRG neurons induced a shorter neurite extension. These results suggest that syndecan-1 expression in injured primary sensory neurons may have functional roles in nerve regeneration and synaptic plasticity, resulting in the development of neuropathic pain.

A nuclear odyssey: fibroblast growth factor-2 (FGF-2) as a regulator of nuclear homeostasis in the nervous system

Nuclear localization of classical growth factors is a well-known phenomenon but still remains a molecular and cellular conundrum. Fibroblast growth factor-2 (FGF-2) is an excellent example of a protein which functions as an extracellular molecule involved in canonical receptor tyrosine kinase signaling as well as displaying intracellular functions. Paracrine and nuclear functions are two important sides of the same protein. FGF-2 is expressed in isoforms with different molecular weights from one mRNA species. In rodents, all of these isoforms become imported to the nucleus. In this review, we discuss structural and functional aspects of FGF-2 isoforms in the nervous system. The nuclear odyssey of FGF-2 is reflected by nuclear dynamics, localization to nuclear bodies such as nucleoli, binding to chromatin and engagement in various protein interactions. Recently discovered molecular partnerships of the isoforms shed light on their nuclear functions, thereby greatly extending our knowledge of the multifaceted functions of FGF-2.

Regulation of neuronal differentiation by proteins associated with nuclear bodies

Nuclear bodies are large sub-nuclear structures composed of RNA and protein molecules. The Survival of Motor Neuron (SMN) protein localizes to Cajal bodies (CBs) and nuclear gems. Diminished cellular concentration of SMN is associated with the neurodegenerative disease Spinal Muscular Atrophy (SMA). How nuclear body architecture and its structural components influence neuronal differentiation remains elusive. In this study, we analyzed the effects of SMN and two of its interaction partners in cellular models of neuronal differentiation. The nuclear 23 kDa isoform of Fibroblast Growth Factor - 2 (FGF-2(23)) is one of these interacting proteins - and was previously observed to influence nuclear bodies by destabilizing nuclear gems and mobilizing SMN from Cajal bodies (CBs). Here we demonstrate that FGF-2(23) blocks SMN-promoted neurite outgrowth, and also show that SMN disrupts FGF-2(23)-dependent transcription. Our results indicate that FGF-2(23) and SMN form an inactive complex that interferes with neuronal differentiation by mutually antagonizing nuclear functions. Coilin is another nuclear SMN binding partner and a marker protein for Cajal bodies (CBs). In addition, coilin is essential for CB function in maturation of small nuclear ribonucleoprotein particles (snRNPs). The role of coilin outside of Cajal bodies and its putative impacts in tissue differentiation are poorly defined. The present study shows that protein levels of nucleoplasmic coilin outside of CBs decrease during neuronal differentiation. Overexpression of coilin has an inhibitory effect on neurite outgrowth. Furthermore, we find that nucleoplasmic coilin inhibits neurite outgrowth independent of SMN binding revealing a new function for coilin in neuronal differentiation.

Repair of the Peripheral Nerve-Remyelination that Works

In this review we summarize the events known to occur after an injury in the peripheral nervous system. We have focused on the Schwann cells, as they are the most important cells for the repair process and facilitate axonal outgrowth. The environment created by this cell type is essential for the outcome of the repair process. The review starts with a description of the current state of knowledge about the initial events after injury, followed by Wallerian degeneration, and subsequent regeneration. The importance of surgical repair, carried out as soon as possible to increase the chances of a good outcome, is emphasized throughout the review. The review concludes by describing the target re-innervation, which today is one of the most serious problems for nerve regeneration. It is clear, compiling this data, that even though regeneration of the peripheral nervous system is possible, more research in this area is needed in order to perfect the outcome.

The pros and cons of growth factors and cytokines in peripheral axon regeneration

Injury to a peripheral nerve induces a complex cellular and molecular response required for successful axon regeneration. Proliferating Schwann cells organize into chains of cells bridging the lesion site, which is invaded by macrophages. Approximately half of the injured neuron population sends out axons that enter the glial guidance channels in response to secreted neurotrophic factors and neuropoietic cytokines. These lesion-associated polypeptides create an environment that is highly supportive for axon regrowth, particularly after acute injury, and ensure that the vast majority of regenerating axons are directed toward the distal nerve stump. Unfortunately, most neurotrophic factors and neuropoietic cytokines are also strong stimulators of axonal sprouting. Although some of the axonal branches will withdraw at later stages, the sprouting effect contributes to the misdirection of reinnervation that results in the lack of functional recovery observed in many patients with peripheral nerve injuries. Here, we critically review the role of neuronal growth factors and cytokines during axon regeneration in the peripheral nervous system. Their differential effects on axon elongation and sprouting were elucidated in various studies on intraneuronal signaling mechanisms following nerve lesion. The present data define a goal for future therapeutic strategies, namely, to selectively stimulate a Ras/Raf/ERK-mediated axon elongation program over an intrinsic PI3K-dependent axonal sprouting program in lesioned motor and sensory neurons. Instead of modulating growth factor or cytokine levels at the lesion site, targeting specific intraneuronal molecules, such as the negative feedback inhibitors of ERK signaling, has been shown to promote long-distance regeneration while avoiding sprouting of regenerating axons until they have reached their target areas.

Spatiotemporal expression profiling of proteins in rat sciatic nerve regeneration using reverse phase protein arrays

Background

Protein expression profiles throughout 28 days of peripheral nerve regeneration were characterized using an established rat sciatic nerve transection injury model. Reverse phase protein microarrays were used to identify the spatial and temporal expression profile of multiple proteins implicated in peripheral nerve regeneration including growth factors, extracellular matrix proteins, and proteins involved in adhesion and migration. This high-throughput approach enabled the simultaneous analysis of 3,360 samples on a nitrocellulose-coated slide.

Results

The extracellular matrix proteins collagen I and III, laminin gamma-1, fibronectin, nidogen and versican displayed an early increase in protein levels in the guide and proximal sections of the regenerating nerve with levels at or above the baseline expression of intact nerve by the end of the 28 day experimental course. The 28 day protein levels were also at or above baseline in the distal segment however an early increase was only noted for laminin, nidogen, and fibronectin. While the level of epidermal growth factor, ciliary neurotrophic factor and fibroblast growth factor-1 and -2 increased throughout the experimental course in the proximal and distal segments, nerve growth factor only increased in the distal segment and fibroblast growth factor-1 and -2 and nerve growth factor were the only proteins in that group to show an early increase in the guide contents. As expected, several proteins involved in cell adhesion and motility; namely focal adhesion kinase, N-cadherin and β-catenin increased earlier in the proximal and distal segments than in the guide contents reflecting the relatively acellular matrix of the early regenerate.

Conclusions

In this study we identified changes in expression of multiple proteins over time linked to regeneration of the rat sciatic nerve both demonstrating the utility of reverse phase protein arrays in nerve regeneration research and revealing a detailed, composite spatiotemporal expression profile of peripheral nerve regeneration.

S100beta and fibroblast growth factor-2 are present in cultured Schwann cells and may exert paracrine actions on the peripheral nerve injury

PURPOSE

The neurotrophic factor fibroblast growth factor-2 (FGF-2, bFGF) and Ca++ binding protein S100beta are expressed by the Schwann cells of the peripheral nerves and by the satellite cells of the dorsal root ganglia (DRG). Recent studies have pointed out the importance of the molecules in the paracrine mechanisms related to neuronal maintenance and plasticity of lesioned motor and sensory peripheral neurons. Moreover, cultured Schwann cells have been employed experimentally in the treatment of central nervous system lesions, in special the spinal cord injury, a procedure that triggers an enhanced sensorymotor function. Those cells have been proposed to repair long gap nerve injury.

METHODS

Here we used double labeling immunohistochemistry and Western blot to better characterize in vitro and in vivo the presence of the proteins in the Schwann cells and in the satellite cells of the DRG as well as their regulation in those cells after a crush of the rat sciatic nerve.

RESULTS

FGF-2 and S100beta are present in the Schwann cells of the sciatic nerve and in the satellite cells of the DRG. S100beta positive satellite cells showed increased size of the axotomized DRG and possessed elevated amount of FGF-2 immunoreactivity. Reactive satellite cells with increased FGF-2 labeling formed a ring-like structure surrounding DRG neuronal cell bodies.Reactive S100beta positive Schwann cells of proximal stump of axotomized sciatic nerve also expressed higher amounts of FGF-2.

CONCLUSION

Reactive peripheral glial cells synthesizing FGF-2 and S100beta may be important in wound repair and restorative events in the lesioned peripheral nerves.

High molecular weight FGF2: the biology of a nuclear growth factor

Fibroblast growth factor 2 (FGF2) is one of the most studied growth factors to date. Most attention has been dedicated to the smallest, 18 kDa FGF2 variant that is released by cells and acts through activation of cell-surface FGF-receptor tyrosine kinases. There are, however, several higher molecular weight (HMW) variants of FGF2 that rarely leave their producing cells, are retained in the nucleus and act independently of FGF-receptors (FGFR). Despite significant evidence documenting the expression and intracellular trafficking of HMW FGF2, many important questions remain about the physiological roles and mechanisms of action of HMW FGF2. In this review, we summarize the current knowledge about the biology of HMW FGF2, its role in disease and areas for future investigation.

Physiological role of basic FGF in peripheral nerve development and regeneration: potential for reconstruction approaches

According to expression studies and functional analyses in mutant mice and in rats, FGF-2 appears to be specifically involved during development of peripheral nerves and in de-/re-generating processes at the lesion site and in spinal ganglia. In the absence of FGF receptor (FGFR)3, axonal and myelin diameters of peripheral nerves are significantly reduced, suggesting that FGFR3 physiologically regulates axonal development. The normally occurring neuronal cell death in spinal ganglia after peripheral nerve axotomy does not take place in FGF-2 and FGFR3-deleted mice, respectively, suggesting that injury-induced apoptosis is mediated via FGF-2 binding to FGFR3. According to a bimodal function of FGF-2, lesion-induced neuron death in rat spinal ganglia can be prevented by application of FGF-2 to the proximal nerve stump, which could be mediated via FGFR1/2. At the lesion site, FGF-2 appears to be involved in stimulating Schwann cell proliferation, promoting neurite outgrowth, especially of sensory nerve fibers, and regulating remyelination.

Expression and regulation of Sef, a novel signaling inhibitor of receptor tyrosine kinases-mediated signaling in the nervous system

Fibroblast growth factors (FGFs) signal via four distinct high affinity cell surface tyrosine kinase receptors, termed FGFR1-FGFR4 (FGFR-FGF-receptor). Recently, a new modulator of the FGF signaling pathway, the transmembrane protein 'similar expression to FGF genes' (Sef), has been identified in zebrafish and subsequently in mammals. Sef from mouse and human inhibits FGF mitogenic activity. In the present study, we analyzed the expression of Sef in distinct rat brain areas, in the spinal cord and in peripheral nerves and spinal ganglia using semi-quantitative RT-PCR. Furthermore, we studied the cellular expression pattern of Sef in intact spinal ganglia and sciatic nerves and, in addition, after crush lesion, using in situ hybridization and immunohistochemistry. Sef transcripts were expressed in all brain areas evaluated and in the spinal cord. A neuronal expression was found in both intact and injured spinal ganglia. Intact sciatic nerves, however, showed little or no Sef expression. Seven days after injury, high Sef expression was concentrated to the crush site, and Schwann cells seemed to be the source of Sef. The labeling pattern of up-regulated Sef was complementary to the patterns of FGF-2 and FGFR1-3, which were localized proximal and distal to the crush site. These results suggest an involvement of Sef during the nerve regeneration process, possibly by fine-tuning the effects of FGF signaling.

Cellular analysis of S100Beta and fibroblast growth factor-2 in the dorsal root ganglia and sciatic nerve of rodents. focus on paracrine actions of activated satellite cells after axotomy

The role of satellite cells, a type of peripheral glia, in the paracrine mechanisms related to neuronal maintenance and plasticity in the dorsal root ganglia (DRG) needs to be further investigated. This study employed immunohistochemistry and image analysis to investigate basic fibroblast growth factor (bFGF, FGF-2) and S100Beta immunoreactivities in the DRG and sciatic nerve of the rat and mouse. Well-characterized antibodies against bovine (residues 1-24) and rat (residues 1-23) FGF-2 were employed. Furthermore, the state of satellite cell reaction and changes in the FGF-2/S100Beta immunoreactivity were analyzed after axotomy of rat sciatic nerve. Scattered neurons and the majority of the satellite cells of the rat DRG and also Schwann cells of the rat sciatic nerve stained for S100Beta. In the mouse, strong S100Beta was encountered in the majority of sensory neurons and Schwann cells. Moderate FGF-2 (residues 1-24) immunoreactivity was found in scattered small size neurons of the rat DRG. A strong FGF-2 (residues 1-23) immunoreactivity was achieved in the satellite cells of rat DRG. Both FGF-2 antisera showed strong labeling in the mouse DRG sensory neurons. Activated satellite cells of the axotomized DRG possessed increased amount of FGF-2 and S100Beta immunoreactivity as demonstrated by quantitative image analysis. The proximal stump of the lesioned rat sciatic nerve showed increased FGF-2 (residues 1-24 and 1-23) in the Schwann cells, myelin sheaths, and neuronal fibers, without changes in the level of S100Beta immunoreactivity. Results suggested a possible interaction between FGF-2 and S100Beta in activated satellite cells of the DRG, which might trigger paracrine actions in the axotomized sensory neurons.

Activation of fibroblast growth factor receptor by axotomy, through downstream p38 in dorsal root ganglion, contributes to neuropathic pain

The possible involvement of fibroblast growth factor receptor (FGFR) activation in the dorsal root ganglion (DRG) was examined following peripheral nerve injury in the rat. Ligation of the sciatic nerve down-regulated FGFR2, -3 and -4 mRNA; however, the expression of FGFR1 mRNA showed no change. Activation of FGFR was examined by immunohistochemistry using an antibody of the phosphorylated form of FGFR1-4. Ligation of the sciatic nerve produced phosphorylation of FGFR in the L4 and 5 DRG ipsilateral to the injury, starting at 3 days after the lesion and persisting for more than 30 days. Substantial activation of FGFR was observed, mainly in unmyelinated small DRG neurons that co-expressed phosphorylated p38 mitogen-activated protein kinase (MAPK). Continuous intrathecal infusion of the FGFR1 inhibitor, 3-[3-(2-carboxyethyl)-4-methylpyrrol-2-methylidenyl]-2-indolinone, reduced p38 MAPK phosphorylation in the DRG and pain-related behaviors in the partial sciatic nerve model rat without affecting on the activation of spinal glia cells (microglia and astrocyte). In the injured small DRG neurons, activation of FGFR1 may contribute to the generation of neuropathic pain by activating p38 MAPK.

Possible joint origin of restless leg syndrome (RLS) and migraine

Sleep disorders have been described in migraine patients. Among sleep disorders RLS has been reported in up to one-third of migraineurs. Adverse effects of anti migraine therapy by dopamine antagonists can not fully explain this association. Therefore we present the hypothesis that RLS and migraine may have a joint origin. The hypothesis is supported by: (1) the same genetic origin for migraine without aura and RLS in single Italian family on chromosome 14q21; this gene codes survival motor neuron-interacting protein 1 (SIP1) which can play role in both diseases. (2) Correlation of both RLS and migraine with fibromyalgia. (3) Alteration of cortical excitability in both migraine and RLS.

Physiological function and putative therapeutic impact of the FGF-2 system in peripheral nerve regeneration—Lessons from in vivo studies in mice and rats

Diffusible and substratum-bound molecules regulate development and regeneration of the peripheral nervous system. The understanding of physiological function of these factors could have an impact on the development of new therapeutic strategies to stimulate nerve regeneration across long gaps. Within the group of trophic factors, basic fibroblast growth factor (FGF-2) and its high-affinity receptors are expressed in the intact peripheral nervous system and regulated following nerve injury. After exogenous application, FGF-2 promotes neuronal survival and neurite outgrowth in vitro and in vivo. In this review, animal studies on the physiological role of the endogenous FGF-2 system and the regenerative capacity after exogenous FGF-2 administration are summarized. The concept of FGF-2 function is discussed in context with other growth factors that are also physiologically relevant in the peripheral nervous system. Studies of sciatic nerve axotomy in FGF-2- and FGF receptor (R) 3-deleted mice, respectively, strongly suggested that FGF-2 binding to FGFR3 is involved in injury-induced neuronal apoptosis. At the lesion site, inhibition of myelination and stimulation of Schwann cell proliferation by FGF-2 via FGFR1/2 is suggested from rat and mouse studies, whereas neurite formation is very likely enhanced via FGFR3 activation. Additionally to these demonstrated physiological functions of endogenous FGF-2, administration of FGF-2 isoforms in the rat model of nerve regeneration across long gaps revealed a role of the high molecular weight isoforms of FGF-2 on sensory recovery. Within the group of physiologically relevant trophic factors, the FGF-2 system seems to be crucially involved in the scenario of peripheral nerve development and regeneration.

Faster nerve regeneration after sciatic nerve injury in mice over-expressing basic fibroblast growth factor

Basic fibroblast growth factor (FGF-2) is expressed in the peripheral nervous system and is up-regulated after nerve lesion. It has been demonstrated that administration of FGF-2 protects neurons from injury-induced cell death and promotes axonal regrowth. Using transgenic mice over-expressing FGF-2 (TgFGF-2), we addressed the importance of endogenously generated FGF-2 on sensory neuron loss and sciatic nerve regeneration. After sciatic nerve transection, wild-type and transgenic mice showed the same degree of cell death in L5 spinal ganglia. Also, the number of chromatolytic, eccentric, and pyknotic sensory neurons was not changed under elevated levels of FGF-2. Morphometric evaluation of intact nerves from TgFGF-2 mice revealed no difference in number and size of myelinated fibers compared to wild-type mice. One week after crush injury, the number of regenerated axons was doubled and the myelin thickness was significantly smaller in transgenic mice. After 2 and 4 weeks, morphometric analysis and functional tests revealed no differences in recovery of sensory and motor nerve fibers. To study the role of FGF-2 over-expression on Schwann cell proliferation during the early regeneration process, we used BrdU-labeling to mark dividing cells. In transgenic mice, the number of proliferating cells was significantly increased distal to the crush site compared to wild-types. We propose that endogenously synthesized FGF-2 influences early peripheral nerve regeneration by regulating Schwann cell proliferation, axonal regrowth, and remyelination.

Differentially promoted peripheral nerve regeneration by grafted Schwann cells over-expressing different FGF-2 isoforms

Artificial nerve grafts are needed to reconstruct massive defects in the peripheral nervous system when autologous nerve grafts are not available in sufficient amounts. Nerve grafts containing Schwann cells display a suitable substrate for long-distance regeneration. We present here a comprehensive analysis of the in vivo effects of different isoforms of fibroblast growth factor-2 (FGF-2) on peripheral nerve regeneration across long gaps. FGF-2 isoforms were provided by grafted, genetically modified Schwann cells over-expressing 18-kDa-FGF-2 and 21-/23-kDa-FGF-2, respectively. Functional tests evaluated motor and sensory recovery. Additionally, morphometrical analyses of regenerated nerves were performed 3 and 6 months after grafting. Distinct regeneration promoting effects of the different FGF-2 isoforms were found. 18-kDa-FGF-2 mediated inhibitory effects on the grade of myelination of regenerating axons, whereas 21-/23-kDa-FGF-2 mediated early recovery of sensory functions and stimulation of long-distance myelination of regenerating axons. The results contribute to the development of new therapeutic strategies in peripheral nerve repair.

Regulation of neuronal death and calcitonin gene-related peptide by fibroblast growth factor-2 and FGFR3 after peripheral nerve injury: Evidence from mouse mutants

The presence and regulation of basic fibroblast growth factor and its high-affinity tyrosine kinase receptor FGFR3 in sensory neurons during development and after peripheral nerve injury suggest a physiological role of the fibroblast growth factor-2 system for survival and maintenance of sensory neurons. Here we investigated L5 spinal ganglia of intact and lesioned fibroblast growth factor-2 knock-out and FGFR3 knock-out mice. Quantification of sensory neurons in intact L5 spinal ganglia revealed no differences between wild-types and mutant mice. After sciatic nerve axotomy, the normally occurring neuron loss in wild-type mice was significantly reduced in both knock-out strains suggesting that fibroblast growth factor-2 is involved in neuronal death mediated via FGFR3. In addition, the number of chromatolytic and eccentric cells was significantly increased in fibroblast growth factor-2 knock-out mice indicating a transient protection of injured spinal ganglia neurons in the absence of fibroblast growth factor-2. The expression of the neuropeptide calcitonin gene-related peptide in sensory neurons of intact fibroblast growth factor-2 knock-out and FGFR3 knock-out mice was not changed in comparison to adequate wild-types. Fibroblast growth factor-2 wild-type and FGFR3 wild-type mice showed a lesion-induced decrease of calcitonin gene-related peptide-positive neurons in ipsilateral L5 spinal ganglia whereas the loss of calcitonin gene-related peptide-immunoreactive sensory neurons is reduced in the absence of fibroblast growth factor-2 or FGFR3, respectively. In addition, FGFR3 wild-type and knock-out mice displayed a contralateral reduction of the neuropeptide after axotomy. These results suggest that endogenous fibroblast growth factor-2 and FGFR3 are crucially involved in the regulation of survival and calcitonin gene-related peptide expression of lumbar sensory neurons after lesion, but not during development.

The effects of axotomy on neurons and satellite glial cells in mouse trigeminal ganglion

Damage to peripheral nerves induces ectopic firing in sensory neurons, which can contribute to neuropathic pain. As most of the information on this topic is on dorsal root ganglia we decided to examine the influence of infra-orbital nerve section on cells of murine trigeminal ganglia. We characterized the electrophysiological properties of neurons with intracellular electrodes. Changes in the coupling of satellite glial cells (SGCs) were monitored by intracelluar injection of the fluorescent dye Lucifer yellow. Electrophysiology of SGCs was studied with the patch-clamp technique. Six to eight days after axotomy, the percentage of neurons that fire spontaneously increased from 1.6 to 12.8%, the membrane depolarized from -51.1 to -45.5 mV, the percentage of cells with spontaneous potential oscillations increased from 19 to 37%, the membrane input resistance decreased from 44.4 to 39.5 MOmega, and the threshold for firing an action potential decreased from 0.61 to 0.42 nA. These changes are consistent with increased neuronal excitability. SGCs were mutually coupled around a given neuron in 21% of the cases, and to SGCs around neighboring neurons in only 4.8% of the cases. After axotomy these values increased to 37.1 and 25.8%, respectively. After axotomy the membrane resistance of SGCs decreased from 101 MOmega in controls to 40 MOmega, possibly due to increased coupling among these cells. We conclude that axotomy affects both neurons and SGCs in the trigeminal ganglion. The increased neuronal excitability and ectopic firing may play a major role in neuropathic pain.

Fibroblast growth factor receptor 3 signaling regulates injury-related effects in the peripheral nervous system

Fibroblast growth factor receptor (FGFR) signaling is crucial for neural development and regeneration. Here we investigated the L5 spinal ganglion and the sciatic nerve of intact Fgfr3-deficient mice after nerve injury. Quantification of sensory neurons in the L5 spinal ganglion revealed no significant differences between wild-type and Fgfr3-deficient mice. Seven days after nerve lesion, the normally occurring neuron loss in wild-type mice was not found in Fgfr3-deficient animals, suggesting that FGFR3 signaling is involved in the cell death process. Morphometric analysis of the sciatic nerve showed similar numbers of myelinated axons, but the axonal and myelin diameter was significantly smaller in Fgfr3-deficient mice compared to the wild types. Evaluation of regenerating myelinated axons of the sciatic nerve revealed no differences between both mouse strains 7 days after crush injury. Our results suggest that FGFR3 signaling seems to be involved in processes of damage-induced neuron death and axonal development.

Enhanced survival, reinnervation, and functional recovery of intrastriatal dopamine grafts co-transplanted with Schwann cells overexpressing high molecular weight FGF-2 isoforms

Dopaminergic (DA) micrografts were co-transplanted with Schwann cells (SC) overexpressing 18 kDa and 21/23 kDa FGF-2 into the caudate-putamen unit (CPu) of unilaterally 6-hydroxydopamine-lesioned rats. We report here that SC engineered to overexpress FGF-2 promoted DA-graft-induced restoration, whether co-transplanted at the same site or grafted at a second more distant site within the CPu. In addition, the 21/23 kDa FGF-2 isoforms resulted in a significantly better reinnervation and survival of dopaminergic micrografts when compared to the 18-kDa FGF-2 isoform. However, this effect was not that distinct on functional recovery due to, for example, ceiling effects. One main finding of this study was the influence of the gene promotor on DA survival, respectively, vector-mediated trophism. Therefore, comparisons in terms of survival between 18 kDa and higher molecular weight (HMW) FGF-2 are complicated in the mixed grafted experiments. Furthermore, the first demonstration of the presence of the 21/23 kDa FGF-2 isoforms in the nigrostriatal system and their potent neurotrophic in vivo activities, as shown in the present study, suggest (I) a physiological role of these proteins for dopaminergic neurons and (II) a restorative potential under normal as well as regenerative processes. However, FGF-2-mediated effects are more pronounced after co-transplantation with SC/DA cells mixed in one suspension at the same implantation side than in the side-by-side approach with a spatially and temporally separated transplantation of SC (day 1) and DA-cells (day 3). These findings indicate the necessity of direct contact between FGF-2 and DA-neurons, further elucidate the neurotrophic role of FGF-2 for DA-neurons and highlight the differential restorative potentials of its respective isoforms. We propose that administration of HMW FGF-2 may be used to improve function in the rat Parkinson's disease model.

Axonal regeneration across long gaps in silicone chambers filled with Schwann cells overexpressing high molecular weight FGF-2

Basic fibroblast growth factor (FGF-2) has been shown to enhance the survival and neurite extension of various types of neurons including spinal ganglion neurons. In addition, endogenous FGF-2 and FGF receptors are upregulated following peripheral nerve lesion in ganglia and at the lesion site. FGF-2 protein is expressed in different isoforms (18 kDa, 21 kDa, 23 kDa) and differentially regulated after nerve injury. In the rat we analyzed the regenerative capacity of the high molecular weight (HMW) FGF-2 isoforms (21/23 kDa) to support the regeneration of the axotomized adult sciatic nerve across long gaps. The nerve stumps were inserted into the opposite ends of a silicone chamber resulting in an interstump gap of 15 mm. Silicone tubes were filled with Matrigel or a mixture of Schwann cells (SC) and Matrigel. SC were prepared from newborn rats and transfected to overexpress HMW FGF-2. Four weeks after the operation procedure, channels were analyzed with regard to tissue cables bridging both nerve stumps and myelinated axons distal to the original proximal nerve stump. Peripheral nerves interposed with HMW Schwann cells displayed significantly enhanced nerve regeneration, with the greatest number of tissue cables containing myelinated axons and the highest number of myelinated axons. These results suggest that a cellular substrate together with a source of a trophic factor could be a promising tool to promote nerve regeneration and, therefore, become useful also for a clinical approach to repair long gaps.

Expression of the fibroblast growth factor-2 isoforms and the FGF receptor 1–4 transcripts in the rat model system of Parkinson's disease

Basic fibroblast growth factor (FGF)-2 occurs in different isoforms representing different translation products of a single mRNA. We have previously shown that the high molecular weight FGF-2 isoforms (21, 23 kD) stimulated survival- and neurite-promoting activities and protective effects on cultured embryonic dopaminergic (DA) neurons of the substantia nigra (Neuroscience 100 (2000) 73). In this study the expression of FGF-2 isoforms in the striatum and substantia nigra was analyzed by Western blot in adult intact rats and following complete unilateral 6-hydroxydopamine (6-OHDA) lesion. In intact rats, all three FGF-2 isoforms (18, 21, 23 kD) are expressed. Neurotoxin-mediated lesion of nigral DA neurons revealed no change of the FGF-2 isoform expression pattern in the nigrostriatal system. Additionally, the FGF receptors 1, 2 and 3 are expressed in these tissues and displayed no alterations after 6-OHDA injection as demonstrated by RT-PCR. The presence of all three FGF-2 isoforms and the FGFR 1-3, together with the previous demonstrated neurotrophic effects of FGF-2 on dopaminergic neurons, suggest a physiological function of the FGF-2 isoforms in the nigrostriatal system.

Targeted disruption of the FGF-2 gene affects the response to peripheral nerve injury

Basic fibroblast growth factor (FGF-2) is involved in the development, maintenance, and survival of the nervous system. To study the physiological role of endogenous FGF-2 during peripheral nerve regeneration, we analyzed sciatic nerves of FGF-2-deleted mice by using morphometric, morphological, and immunocytochemical methods. Quantification of number and size of myelinated axons in intact sciatic nerves revealed no difference between wild-type and FGF-2 knock-out (ko) animals. One week after nerve crush, FGF-2 ko mice showed about five times more regenerated myelinated axons with increased myelin and axon diameter in comparison to wild-types close to the injury site. In addition, quantitative distribution of macrophages and collapsed myelin profiles suggested faster Wallerian degeneration in FGF-2-deleted mice close to the lesion site. Our results suggest that endogenous FGF-2 is crucially involved in the early phase of peripheral nerve regeneration possibly by regulation of Schwann cell differentiation.

Basic fibroblast growth factor isoforms promote axonal elongation and branching of adult sensory neurons in vitro

Synthesis of the multifunctional cytokine basic fibroblast growth factor (FGF-2) is up-regulated after sciatic nerve lesion. In this study, the effects of low and high molecular weight FGF-2 isoforms on axonal elongation and branching of dissociated rat sensory neurons derived from adult lumbar dorsal root ganglia were investigated. These neurons express FGF receptor (FGFR) type I in the cytoplasmic/membrane compartment and in nuclear speckles. FGF-2 isoforms increase the number of axonal branches in cultures obtained from control rats, but do not promote axonal elongation. In response to a preconditioning lesion, i.e. transection of the sciatic nerve 1 week before culture, the axonal length of ipsilateral lumbar sensory neurons increases two-fold when compared with non-lesioned control rats, and this response is significantly enhanced by FGF-2 isoforms but not by nerve growth factor (NGF). Neurons dissociated from ganglia located contralaterally to the lesion exhibit a smaller increase in axon elongation (30%). The stimulating effects of FGF-2 isoforms on axon growth are fully blocked, and the enhanced regeneration of prelesioned neurons is reduced by the FGFR inhibitor SU5402 suggesting an involvement of endogenous FGF signaling in response to a lesion. The present data support a direct neurotrophic role of the 18 kD and 23 kD FGF-2 isoforms on adult axonal regeneration which may be of therapeutic value in the treatment of peripheral nerve lesions. Furthermore, evidence is provided for an enhanced regenerative capacity not only of preaxotomized neurons but also of homonymous non-axotomized neurons.

Homeobox gene expression in adult dorsal root ganglia during sciatic nerve regeneration: is regeneration a recapitulation of development?

After damage of the sciatic nerve, a regeneration process is initiated. Neurons in the dorsal root ganglion regrow their axons and functional connections. The molecular mechanisms of this neuronal regenerative process have remained elusive, but a relationship with developmental processes has been conceived. This chapter discusses the applicability of the developmental hypothesis of regeneration to the dorsal root ganglion; this hypothesis states that regeneration of dorsal root ganglion neurons is a recapitulation of development. We present data on changes in gene expression upon sciatic nerve damage, and the expression and function of homeobox genes. This class of transcription factors plays a role in neuronal development. Based on these data, it is concluded that the hypothesis does not hold for dorsal root ganglion neurons, and that regeneration-specific mechanisms exist. Cytokines and the associated Jak/STAT (janus kinase/signal transducer and activator of transcription) signal transduction pathway emerge as constituents of a regeneration-specific mechanism. This mechanism may be the basis of pharmacological strategies to stimulate regeneration.

Functional regeneration of chronically injured sensory afferents into adult spinal cord after neurotrophin gene therapy

Lesioned axons within the dorsal roots fail to regenerate through the peripheral nerve transition zone and into the spinal cord. This regenerative failure leads to a persistent loss of sensory function. To induce axonal growth across this barrier, we used recombinant adenovirus to express fibroblast growth factor-2 (FGF2), nerve growth factor (NGF), L1 cell adhesion molecule (L1), or beta-galactosidase (LacZ) within the endogenous glia of the dorsal spinal cord 16 d after injury. Expression of either FGF2 or NGF, but not L1 or LacZ, induced robust axonal regeneration into normal as well as ectopic locations within the dorsal spinal cord. This regeneration led to near-normal recovery of thermal sensory function. Functional recovery and the majority of regenerating axons within the dorsal horn disappeared with recutting of the sensory roots. Injections of adenovirus encoding NGF, but not FGF2, also resulted in extensive sprouting of noninjured sensory axons, which we previously demonstrated could cause hyperalgesia and chronic pain. Thus, neurotrophic factor gene therapy administered as late as 16 d after injury may serve as a useful treatment to elicit recovery after dorsal root avulsion; however, the choice of neurotrophin is important to induce selective regeneration of damaged axons.

Axon-Schwann cell interactions regulate the expression of fibroblast growth factor-5 (FGF-5)

We screened for genes whose expression is significantly up- or downregulated during Wallerian degeneration in adult rat sciatic nerve with cDNA arrays. Fibroblast growth factor-5 (FGF-5) mRNA seemed to be induced. This was confirmed by northern blotting and in situ hybridization, as well as Western blotting for FGF-5 in axotomized nerve. Axon-Schwann cell interactions decreased the steady-state level of FGF-5 mRNA in regenerating sciatic nerves, and forskolin diminished its expression in cultured Schwann cells. We conclude that denervated Schwann cells synthesize FGF-5, which is a secreted, neuronotrophic member of the FGF family.

In vivo expression and localization of the fibroblast growth factor system in the intact and lesioned rat peripheral nerve and spinal ganglia

Basic fibroblast growth factor (FGF-2) is involved in several cellular processes of the nervous system during development, maintenance, and regeneration. In the central nervous system, FGF-2 has been shown to be expressed in neurons and glial cells, depending on the developmental stage and brain area. In the present study, a comprehensive analysis was performed of the cellular distribution of the transcripts of FGF-2 and of the FGF high-affinity receptors (R) 1-4 in intact and lesioned sciatic nerve and spinal ganglia. In the adult rat sciatic nerve FGF-2, FGFR1-3 were expressed at low levels as revealed by reverse transcriptase-polymerase chain reaction (RT-PCR). Sciatic nerve crush resulted in an increase of these transcript levels. FGFR4 expression was not detected in the intact and crushed nerve as revealed by RT-PCR and RNase protection assay. In situ hybridization using riboprobes for FGF-2, FGFR1-3 displayed staining in diverse cell types. Immunocytochemical staining of consecutive sections with cell markers for myelin, macrophages, and neurons revealed colocalization of the transcripts with Schwann cells and macrophages. In addition to FGF-2 and FGFR1, the transcripts of FGFR2-4 were expressed in neurons of spinal ganglia. Crush lesion of the sciatic nerve resulted in no alterations of the FGFR1-4 transcripts, whereas FGF-2 and FGFR3 mRNAs were up-regulated in spinal ganglia. The expression of FGFRs and FGF-2 in Schwann cells and macrophages at the lesion site of the sciatic nerve and in sensory neurons suggests that FGF-2 is involved in specific functions of these cells during regeneration.

The high molecular weight fibroblast growth factor-2 isoforms (21,000 mol. wt and 23,000 mol. wt) mediate neurotrophic activity on rat embryonic mesencephalic dopaminergic neurons in vitro

Basic fibroblast growth factor is expressed in different isoforms which display tissue and species specificity and are differentially regulated during development and after experimental interventions. The differential regulation of the fibroblast growth factor-2 isoforms may indicate specific activities and functions of these molecules. The characterization of fibroblast growth factor-2 effects, however, is almost exclusively based on studies including the 18,000 mol. wt isoform. It is not yet known whether the high molecular weight fibroblast growth factor-2 isoforms (21,000 mol. wt, 23,000 mol. wt) exert similar or distinct activities in the nervous system. In the present study, we investigated the effects of the high molecular weight isoforms on dissociated rat mesencephalic dopaminergic neurons. For this purpose, recombinant fibroblast growth factor-2 isoforms, prepared in a histidine expression system, were administered on dopaminergic neurons in vitro, and Schwann cells over-expressing the high molecular weight isoforms were co-cultured with dopaminergic neurons. This is the first demonstration to show that the high molecular weight isoforms mediate a neurotrophic activity. Exogenous high molecular weight fibroblast growth factor-2 isoforms stimulated the survival of embryonic mesencephalic dopaminergic neurons and protected them from 6-hydroxydopamine neurotoxicity. In addition, co-culture of dopaminergic neurons with high molecular weight fibroblast growth factor-2 over-expressing Schwann cells revealed an increased survival and neurite formation of the mesencephalic dopaminergic neurons. These results suggest that the high molecular weight fibroblast growth factor-2 isoforms may serve as a new tool for the treatment of Parkinson's disease.

Distinctive effects of rat fibroblast growth factor-2 isoforms on PC12 and Schwann cells

Fibroblast growth factor-2 (FGF-2) is an important modulator of cell growth and differentiation and stimulates cell survival of various cells including neurons. Rat FGF-2 occurs in three isoforms, a low molecular weight 18 kD and two high molecular weight forms (21, 23 kD), representing alternative translation products from a single mRNA. The 18 kD isoform shows mainly cytoplasmatic localization, whereas the 21/23 kD FGF-2 are localized in the nucleus. In addition, the FGF-2 isoforms are differentially regulated in the sensory ganglia and peripheral nerve following nerve injury and in the adrenal medulla during post-natal development and after hormonal stimuli. The distinct intracellular distribution and differential regulation of the different FGF-2 isoforms indicate that they have unique biological roles, however, little is known about the biological effects of the high molecular weight FGF-2 isoforms. Immortalized Schwann cells and PC12 cells, which stably overexpress the different FGF-2 isoforms, showed that the different endogenous-overexpressed FGF-2 isoforms lead to dramatic modifications in cell proliferation and survival, when tested in serum-free and serum-containing medium. In contrast, application of recombinant FGF-2 isoforms on normal PC12 and immortalized Schwann cells results in similar biological effects on the proliferation and survival of the cells. Furthermore, we investigated the potential regulatory effects of endogenous-overexpressed and exogenous-applied FGF-2 isoforms on the mRNA level of the FGF-2 receptors and, additionally, on the tyrosin hydroxylase mRNA expression in PC12 cells.

Expression of interleukin-6 and its receptor in the sciatic nerve and cultured Schwann cells: relation to 18-kD fibroblast growth factor-2

Expression of interleukin-6 (IL-6) and fibroblast growth factor-2 (FGF-2) in Schwann cells is modulated by external stimuli. To study possible interactions of both factors we have analyzed mutual effects of exogenous IL-6 and FGF-2 on the expression of each other and the corresponding receptor (R) molecules IL-6R and FGFR1 after peripheral nerve lesion in vivo and in vitro using cultured Schwann cells. Using rat Schwann cells we found that IL-6 did not exert any effects on the expression of FGF-2 and FGF receptor type 1 (R1) whereas exogenously applied 18-kD FGF-2 strongly increased the expression of the mRNAs of IL-6 and its receptor. In addition, immortalized Schwann cells over-expressing the 18-kD FGF-2 isoform showed elevated levels of IL-6 and IL-6R whereas immortalized Schwann cells over-expressing the high-molecular-weight isoforms (21 kD and 23 kD) displayed unaltered IL-6 and IL-6R expression levels. According to in situ hybridization studies of intact and crushed sciatic nerves in vivo, Schwann cells seems to be the main source of IL-6 and IL-6R. Following sciatic nerve crush, the FGF-2 and the IL-6 system are upregulated after the first hours. Furthermore, we showed that the early increase of the FGF-2 protein is mainly confined to the 18-kD isoform. These results are consistent with the idea of a functional coupling of FGF-2 and the IL-6 system in the early reaction of Schwann cells to nerve injury.

Central nicotinic receptors, neurotrophic factors and neuroprotection

The multiple combinations of nAChR subunits identified in central nervous structures possess distinct pharmacological and physiological properties. A growing number of data have shown that compounds interacting with neuronal nAChRs have, both in vivo and in vitro, the potential to be neuroprotective and that treatment with nAChR agonists elicit long-lasting improving of cognitive performance in a variety of behavioural tests in rats, monkeys and humans. Epidemiological and clinical studies suggested also a potential neuroprotective/trophic role of (-)-nicotine in neurodegenerative disease, such as Alzheimer's and Parkinson's disease. Taken together experimental and clinical data largely indicate a neuroprotective/trophic role of nAChR activation involving mainly alpha7 and alpha4beta2 nAChR subtypes, as evidenced using selective nAChR antagonists, and by potent nAChR agonists recently found displaying efficacy and/or larger selective affinities than (-)-nicotine for neuronal nAChR subtypes. A neurotrophic factor gene regulation by nAChR signalling has been taken into consideration as possible mechanism involved in neuroprotective/trophic effects by nAChR activation and has evidenced an involvement of the fibroblast growth factor (FGF-2) gene as a target of nAChR signalling. These findings suggested that FGF-2 could be involved, according to the FGF-2 neurotrophic functions, in nAChR mechanisms mediating the neuronal survival, trophism and plasticity.

Neurotrophic effects of central nicotinic receptor activation

A growing number of data have shown that compounds interacting with neuronal nicotinic acetylcholine receptors (nAChRs) have, both in vivo and in vitro, the potential to be neuroprotective and that treatment with nAChR agonists elicit long-lasting improvement of cognitive performance in a variety of behavioural tests in rats, monkeys and humans. Epidemiological and clinical studies suggested also a potential neuroprotective/trophic role of (-)-nicotine in neurodegenerative disease, such as Alzheimer's disease and Parkinson's disease. This neuroprotective/trophic role of nAChR activation has been mainly mediated by alpha7 and alpha4beta2 nAChR subtypes, as evidenced using selective nAChR antagonists, and by potent nAChR agonists recently found displaying efficacy and/or larger selective affinities than (-)-nicotine for neuronal nAChR subtypes. A neurotrophic factor gene regulation by nAChR signalling has been taken into consideration as a possible mechanism involved in neuroprotective/trophic effects of nAChR activation and has given evidence that the fibroblast growth factor (FGF-2) gene is a target for nAChR signalling. These findings suggested that FGF-2 could be involved, in view of its neurotrophic functions, in nAChR mechanisms mediating neuronal survival, trophism and plasticity.

Localization and regulation of basic fibroblast growth factor (FGF-2) and FGF receptor-1 in rat superior cervical ganglion after axotomy

In response to peripheral nerve lesion, synthesis of basic fibroblast growth factor (FGF-2) increases in sensory ganglia and motoneurons. Here, we investigated the axotomy-induced regulation of FGF-2 and FGF receptor-1 (FGFR-1) expression in the autonomic nervous system using the sympathetic superior cervical ganglion of the adult rat as a model. Transcripts for both proteins were detected by ribonuclease protection assay. Western blotting indicated the presence of all three FGF-2 isoforms (18, 21, and 23 kD) in the superior cervical ganglion. Immunohistochemical analysis revealed FGF-2 localization in nuclei of satellite cells surrounding postganglionic perikarya. After transection of the carotid nerves, the number of FGF-2-immunoreactive glial cells increased. FGF-2 mRNA was up-regulated within 6 h and remained elevated for 3 weeks. The 18-, 21-, and 23-kD isoforms were all increased 7 days after axotomy. FGFR-1 immunoreactivity was observed in neuronal and nonneuronal nuclei in the normal rat superior cervical ganglion. In contrast to FGF-2, expression of FGFR-1 was unchanged in ganglia after axotomy. Taken together, the present results suggest that FGF-2 participates in neuron-glial interactions of sympathetic ganglia and may be involved in sympathetic neuron survival or nerve regeneration after nerve lesion.

Over-expression of the 18 kD and 21/23 kD fibroblast growth factor-2 isoforms in PC12 cells and Schwann cells results in altered cell morphology and growth

Basic fibroblast growth factor (FGF-2) occurs in different isoforms which represent alternative translation products from a single mRNA. The question of whether the presence of multiple FGF-2 isoforms has physiological implications is compelling but unresolved so far. However, it has been shown recently that the FGF-2 isoforms are differentially regulated in sensory ganglia and peripheral nerve following nerve injury and, moreover, in the adrenal medulla during postnatal development and after hormonal stimuli suggesting that the isoforms may serve different physiological functions. To investigate isoform-specific effects we have established immortalized Schwann cells and PC12 cells stably over-expressing the 18 kD and the HMW isoforms. We found that the over-expression of the different isoforms alters morphology and growth of the Schwann cells. PC12 cells over-expressing the 18 kD FGF-2 were found to differentiate towards the neuronal phenotype whereas over-expression of the HMW isoforms resulted in a stabilization of the endocrine phenotype. Taken together, these data corroborate the idea of FGF-2 isoform-specific functions.