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

Identification of an 85-kb Heterozygous 4p Microdeletion With Full Genome Analysis in Autosomal Dominant Charcot-Marie-Tooth Disease

Background and Objectives

Charcot-Marie-Tooth disease (CMT) is a syndrome of a hereditary neurodegenerative condition affecting the peripheral nervous system and is a single gene disorder. Deep phenotyping coupled with advanced genetic techniques is critical in discovering new genetic defects of rare genetic disorders such as CMT.

Methods

We applied multidisciplinary investigations to examine the neurophysiology and nerve pathology in a family that fulfilled the diagnosis of CMT2. When phenotype-guided first-tier genetic tests and whole-exome sequencing did not yield a molecular diagnosis, we conducted full genome analysis by examining phased whole-genome sequencing and whole-genome optical mapping data to search for the causal variation. We then performed a systematic review to compare the reported patients with interstitial microdeletion in the short arm of chromosome 4.

Results

In this family with CMT2, we reported the discovery of a heterozygous 85-kb microdeletion in the short arm of chromosome 4 (4p16.3)[NC_000004.12:g.1733926_1819031del] spanning 3 genes [TACC3 (intron 6-exon 16), FGFR3 (total deletion), and LETM1 (intron 10-exon14)] that cosegregated with disease phenotypes in family members. The clinical features of peripheral nerve degeneration in our family are distinct from the well-known 4p microdeletion syndrome of Wolf-Hirschhorn syndrome, in which brain involvement is the major phenotype.

Discussion

In summary, we used the full genome analysis approach to discover a new microdeletion in a family with CMT2. The deleted segment contains 3 genes (TACC3, FGFR3, and LETM1) that likely play a role in the pathogenesis of nerve degeneration.

Autoantibodies Against Trisulfated Heparin Disaccharide and Fibroblast Growth Factor Receptor-3 May Play a Role in the Pathogenesis of Neuropathic Corneal Pain

PURPOSE

The aim of this study was to describe cases of patients with presumable dysimmune small-fiber neuropathy (SFN)-related neuropathic corneal pain (NCP), presenting with autoantibodies against trisulfated heparin disaccharide (TS-HDS) or fibroblast growth factor receptor-3 (FGFR-3).

METHODS

This study was a case series of 3 patients with NCP with positive anti-TS-HDS and/or anti-FGFR-3 autoantibodies and systemic SFN as confirmed by positive skin biopsy results.

RESULTS

All 3 patients were women with a mean age of 34.3± 6.1 years. They suffered from moderate to severe persistent chronic ocular discomfort (10/10, 10/10, and 9/10 on a visual analogue scale, respectively). Although 1 patient suffered from ocular pain and photophobia alone, the other 2 patients experienced additional non-ocular pain. One of the patients had pain on her face and head, and 1 patient reported neck and lower back pain. Two patients had high anti-TS-HDS IgM titers, whereas 1 patient had both high anti-TS-HDS IgM and anti-FGFR-3 IgG titers. Skin biopsy confirmed the presence of SFN in all patients by demonstrating decreased intraepidermal nerve fiber density.

CONCLUSIONS

The presence of anti-TS-HDS and anti-FGFR-3 autoantibodies in patients with NCP with positive skin biopsy findings for SFN highlights the potential role of dysimmune SFN in the pathogenesis of this disease.

Integrated analyses reveal evolutionarily conserved and specific injury response genes in dorsal root ganglion

Rodent dorsal root ganglion (DRG) is widely used for studying axonal injury. Extensive studies have explored genome-wide profiles on rodent DRGs under peripheral nerve insults. However, systematic integration and exploration of these data still be limited. Herein, we re-analyzed 21 RNA-seq datasets and presented a web-based resource (DRGProfile). We identified 53 evolutionarily conserved injury response genes, including well-known injury genes (Atf3, Npy and Gal) and less-studied transcriptional factors (Arid5a, Csrnp1, Zfp367). Notably, we identified species-preference injury response candidates (e.g. Gpr151, Lipn, Anxa10 in mice; Crisp3, Csrp3, Vip, Hamp in rats). Temporal profile analysis reveals expression patterns of genes related to pre-regenerative and regenerating states. Finally, we found a large sex difference in response to sciatic nerve injury, and identified four male-specific markers (Uty, Eif2s3y, Kdm5d, Ddx3y) expressed in DRG. Our study provides a comprehensive integrated landscape for expression change in DRG upon injury which will greatly contribute to the neuroscience community.

Anti-FGFR3 antibody epitopes are functional sites and correlate with the neuropathy pattern

Antibodies against FGFR3 define a subgroup of sensory neuropathy (SN). The aim of this study was to identify the epitope(s) of anti-FGFR3 autoantibodies and potential epitope-dependent clinical subtypes. Using SPOT methodology, five specific candidate epitopes, three in the juxtamembrane domain (JMD) and two in the tyrosine kinase domain (TKD), were screened with 68 anti-FGFR3-positive patients and 35 healthy controls. The identified epitopes cover 6/15 functionally relevant sites of the protein. Four patients reacted with the JMD and 11 with the TKD, partly even in a phosphorylation-state dependent manner. The epitope could not be identified in the others. Patients with antibodies recognizing TKD exhibited a more severe clinical and electrophysiological impairment than others.

Fibroblast Growth Factor Signalling in the Diseased Nervous System

Fibroblast growth factors (FGFs) act as key signalling molecules in brain development, maintenance, and repair. They influence the intricate relationship between myelinating cells and axons as well as the association of astrocytic and microglial processes with neuronal perikarya and synapses. Advances in molecular genetics and imaging techniques have allowed novel insights into FGF signalling in recent years. Conditional mouse mutants have revealed the functional significance of neuronal and glial FGF receptors, not only in tissue protection, axon regeneration, and glial proliferation but also in instant behavioural changes. This review provides a summary of recent findings regarding the role of FGFs and their receptors in the nervous system and in the pathogenesis of major neurological and psychiatric disorders.

Clinical features with anti fibroblast growth factor receptor 3 (FGFR3) antibody-related polyneuropathy: a retrospective study

Background

Despite its initial association with sensory neuropathies, anti-fibroblast growth factor receptor 3 (FGFR3) antibodies have been since reported with a broad range of neuropathies and clinical features. The aim of the study is to report the clinical and electro diagnostic findings in a cohort of patients with sensory or sensorimotor polyneuropathy and anti-FGFR3 antibodies.

Methods

We performed a retrospective chart review to assess the clinical characteristics of patients with sensory or sensorimotor neuropathy related to FGFR3 antibodies. Descriptive statistics were reported using frequencies and percentages for categorical variables and median and interquartile range (IQR) for continuous variables.

Results

This study included 14 patients (9 women) with a median age of 51.9 years (IQR 48–57). The most common presenting symptoms were painful paresthesia (100%), gait instability (42.9%), constitutional symptoms (42.9%), and autonomic symptoms (28.6%). Onset of symptoms was chronic (≥12 weeks) in eight patients (57.1%). Examination showed a distal loss of sensation to pin prick (100%), as well as impaired vibration sensation (78.6%) and proprioception (35.7%), in the distal extremities. We also observed mild weakness in the distal lower-extremities (42.9%). Three patients (21.4%) had trigeminal neuralgia, three patients (21.4%) had co-existing autoimmune disease, and one patient (7.1%) had a history of renal cell carcinoma. The mean titer of FGFR3 antibody was 14,285.71 (IQR 5000–16,750). All 14 patients produced normal results in the neuropathy workup. Nerve conduction study and electromyography showed sensory axonal neuropathy in four patients (28.6%), sensorimotor axonal neuropathy in seven patients (50%), and a normal result in three patients (21.4%). For those with a normal NCS/EMG, a skin biopsy showed a non-length-dependent small fiber neuropathy.

Conclusions

Neuropathy related to FGFR3 antibodies can potentially involve small and large fibers, sensory and motor fibers, and even the trigeminal nerve, which contributes to a highly variable clinical presentation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-021-02090-2.

Clinical characteristics of fibroblast growth factor receptor 3 antibody-related polyneuropathy: a retrospective study

BACKGROUND AND PURPOSE

Autoantibodies are increasingly being used as a diagnostic biomarker of chronic inflammatory neuropathies. However, their role and associated clinical syndrome are not well defined.

METHODS

This retrospective chart review evaluated the clinical presentation, diagnostic workup and therapeutic responses in fibroblast growth factor receptor 3 (FGFR3) antibody-associated neuropathy.

RESULTS

A total of 27 patients [14 men, aged 29-87 (65 ± 14) years] with positive FGFR3 antibody were included. Distal lower-extremity paresthesia (66%), unsteady gait (26%) and foot drop (11%) were common presenting symptoms. Symptom onset was acute in four (15%) cases. Distal lower-extremity weakness (mild in eight and severe in three patients) was the most frequent motor finding. Decreased distal sensation to pinprick (59%) and loss of vibration sensation (37%) were observed. Titer of FGFR3 ranged between 3100 and 30 000 (normal < 3000) with a mean of 10 688 ± 7284. Apart from the occasional association of other neuropathy-related autoantibodies, comprehensive neuropathy workup was otherwise unrevealing. Six patients had other autoimmune disease and seven patients had a history of cancer. Electromyography reflected sensorimotor neuropathy with mixed axonal and demyelinating features in 11 cases. Pure sensory neuropathy was noted in three patients. Demyelination was found in five of six nerve biopsies. Intravenous immunoglobulin response was observed in 8/10 treated patients.

CONCLUSIONS

The FGFR3 antibody appears not to be restricted to sensory neuropathy only. Its role in the pathogenicity of chronic inflammatory neuropathies is not yet well established and, although there may be a role for immunotherapy, larger studies are warranted.

A Phase Ib Study of the FGFR/VEGFR Inhibitor Dovitinib With Gemcitabine and Capecitabine in Advanced Solid Tumor and Pancreatic Cancer Patients

OBJECTIVES

Preclinical studies demonstrated antitumor activity of dovitinib in pancreatic cancer models. This phase Ib study aimed to determine the maximum tolerated dose (MTD) of dovitinib in combination with gemcitabine and capecitabine and to characterize the safety and pharmacokinetic profile in patients with advanced pancreatic and biliary tract cancers and solid malignancies.

MATERIALS AND METHODS

Patients received gemcitabine 1000 mg/m² intravenously on days 1 and 8, capecitabine 1300 mg/m² oral daily from day 1 to 14, and dovitinib oral daily 5 days on and 2 days off, every 21-day cycle. The standard 3+3 dose escalation design was utilized and the study expanded to treat an additional 20 advanced pancreatic and biliary tract cancers patients at MTD.

RESULTS

A total of 29 patients were enrolled. One patient experienced dose-limiting grade 3 colitis. Two patients developed clinically significant neuropathy after the first cycle requiring dose reduction. The MTD was not reached and dovitinib 300 mg was declared the recommended dose for expansion. The most frequent grade 2 or worse adverse events were fatigue (45%), neutropenia (41%), thrombocytopenia (34%), anemia (24%), nausea (24%), and palmer-plantar erythrodysaesthesia syndrome (21%). Partial responses were observed in 5 patients. Pharmacokinetic studies showed no drug-drug interaction between dovitinib, capecitabine and gemcitabine. Fibroblast growth factor 23 plasma level increased in 4 of 5 patients during the first cycle of treatment.

CONCLUSIONS

Dovitinib 300 mg daily is the recommended dose when combined with gemcitabine and capecitabine, achieving clinically relevant plasma concentrations. The study combination demonstrated encouraging efficacy signals in advanced pancreatic cancer.

FGFR3 Antibodies in Neuropathy: What to Do With Them?

OBJECTIVES

To describe the variability of fibroblast growth factor receptor 3 (FGFR3) antibody titers in a small series of patients.

METHODS

We performed a retrospective review of patients with neuropathy and positive FGFR3 antibodies.

RESULTS

We report 7 patients (3 women) with an age range 44-81 years. Symptoms were acute onset in 3 and subacute onset in 4 patients. Five had neuropathic pain. Examination revealed normal large fiber function to mild/moderate predominantly sensory neuropathy and ataxia in one patient. Electrodiagnostic studies revealed normal large fiber function (3), demyelinating neuropathy (1), and mild/moderate axonal neuropathy (3). Four patients had high and 3 patients had low FGFR3 titers. Repeat testing revealed absence of antibodies in 2 patients and a significant reduction in one patient without any intervening immunotherapy.

CONCLUSIONS

Our case series highlights the variability and inconsistency in FGFR3 antibody titers through enzyme-linked immunosorbent assay testing. These antibody titers should always be interpreted with caution in clinical context.

The neurochemistry of peripheral nerve regeneration

Peripheral nerve injuries (PNIs) can be most disabling, resulting in the loss of sensitivity, motor function and autonomic control in the involved anatomical segment. Although injured peripheral nerves are capable of regeneration, sub-optimal recovery of function is seen even with the best reconstruction. Distal axonal degeneration is an unavoidable consequence of PNI. There are currently few strategies aimed to maintain the distal pathway and/or target fidelity during regeneration across the zone of injury. The current state of the art approaches have been focussed on the site of nerve injury and not on their distal muscular targets or representative proximal cell bodies or central cortical regions. This is a comprehensive literature review of the neurochemistry of peripheral nerve regeneration and a state of the art analysis of experimental compounds (inorganic and organic agents) with demonstrated neurotherapeutic efficacy in improving cell body and neuron survival, reducing scar formation and maximising overall nerve regeneration.

The transcriptional landscape of dorsal root ganglia after sciatic nerve transection

Following peripheral nerve injury, transcriptional responses are orchestrated to regulate the expression of numerous genes in the lesioned nerve, thus activating the intrinsic regeneration program. To better understand the molecular regulation of peripheral nerve regeneration, we aimed at investigating the transcriptional landscape of dorsal root ganglia (DRGs) after sciatic nerve transection in rats. The cDNA microarray analysis was used to identify thousands of genes that were differentially expressed at different time points post nerve injury (PNI). The results from Euclidean distance matrix, principal component analysis, and hierarchical clustering indicated that 2 nodal transitions in temporal gene expressions could segregate 3 distinct transcriptional phases within the period of 14 d PNI. The 3 phases were designated as “a stress response phase”, “a pre-regeneration phase”, and “a regeneration phase”, respectively, by referring to morphological observation of post-nerve-injury changes. The gene ontology (GO) analysis revealed the distinct features of biological process, cellular component, and molecular function at each transcriptional phase. Moreover, Ingenuity Pathway Analysis suggested that differentially expressed genes, mainly transcription factors and genes associated with neurite/axon growth, might be integrated into regulatory networks to mediate the regulation of peripheral nerve regeneration in a highly cooperative manner.

Current status and future directions of botulinum neurotoxins for targeting pain processing

Current evidence suggests that botulinum neurotoxins (BoNTs) A1 and B1, given locally into peripheral tissues such as skin, muscles, and joints, alter nociceptive processing otherwise initiated by inflammation or nerve injury in animal models and humans. Recent data indicate that such locally delivered BoNTs exert not only local action on sensory afferent terminals but undergo transport to central afferent cell bodies (dorsal root ganglia) and spinal dorsal horn terminals, where they cleave SNAREs and block transmitter release. Increasing evidence supports the possibility of a trans-synaptic movement to alter postsynaptic function in neuronal and possibly non-neuronal (glial) cells. The vast majority of these studies have been conducted on BoNT/A1 and BoNT/B1, the only two pharmaceutically developed variants. However, now over 40 different subtypes of botulinum neurotoxins (BoNTs) have been identified. By combining our existing and rapidly growing understanding of BoNT/A1 and /B1 in altering nociceptive processing with explorations of the specific characteristics of the various toxins from this family, we may be able to discover or design novel, effective, and long-lasting pain therapeutics. This review will focus on our current understanding of the molecular mechanisms whereby BoNTs alter pain processing, and future directions in the development of these agents as pain therapeutics.

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.

Downstream effector molecules in successful peripheral nerve regeneration

The robust axon regeneration that occurs following peripheral nerve injury is driven by transcriptional activation of the regeneration program and by the expression of a wide range of downstream effector molecules from neuropeptides and neurotrophic factors to adhesion molecules and cytoskeletal adaptor proteins. These regeneration-associated effector molecules regulate the actin-tubulin machinery of growth-cones, integrate intracellular signalling and stimulatory and inhibitory signals from the local environment and translate them into axon elongation. In addition to the neuronally derived molecules, an important transcriptional component is found in locally activated Schwann cells and macrophages, which release a number of cytokines, growth factors and neurotrophins that support neuronal survival and axonal regeneration and that might provide directional guidance cues towards appropriate peripheral targets. This review aims to provide a comprehensive up-to-date account of the transcriptional regulation and functional role of these effector molecules and of the information that they can give us with regard to the organisation of the regeneration program.

Functional role of the interaction between polysialic acid and extracellular histone H1

Polysialic acid (PSA) is a large and highly negatively charged glycan that plays crucial roles in nervous system development and function in the adult. It has been suggested to facilitate cell migration, neurite outgrowth, and synaptic plasticity because its hydration volume could enhance flexibility of cell interactions. Evidence for receptors of PSA has so far been elusive. We now identified histone H1 as binding partner of PSA via a single-chain variable fragment antibody using an anti-idiotypic approach. Histone H1 directly binds to PSA as shown by ELISA. Surface biotinylation of cultured cerebellar neurons indicated an extracellular localization of histone H1. Immunostaining of live cerebellar neurons and Schwann cells confirmed that an extracellular pool of histone H1 colocalizes with PSA at the cell surface. Histone H1 was also detected in detergent-insoluble synaptosomal membrane subfractions and postsynaptic densities. When applied in vitro, histone H1 stimulated neuritogenesis, process formation and proliferation of Schwann cells, and migration of neural precursor cells via a PSA-dependent mechanism, further indicating that histone H1 is active extracellularly. These in vitro observations suggested an important functional role for the interaction between histone H1 and PSA not only for nervous system development but also for regeneration in the adult. Indeed, histone H1 improved functional recovery, axon regrowth, and precision of reinnervation of the motor branch in adult mice with femoral nerve injury. Our findings encourage investigations on the therapeutic potential of histone H1 in humans.

Biocompatibility and bioactivity of designer self-assembling nanofiber scaffold containing FGL motif for rat dorsal root ganglion neurons

We report here a designer self-assembling peptide nanofiber scaffold developed specifically for nerve tissue engineering. We synthesized a peptide FGL-RADA containing FGL (EVYVVAENQQGKSKA), the motif of neural cell adhesion molecule (NCAM), and then attended to make a FGL nanofiber scaffold (FGL-NS) by assembling FGL-RADA with the peptide RADA-16 (AcN-RADARADARADARADA-CONH2). The microstructures of the scaffolds were tested using atomic force microscopy (AFM), and rheological properties of materials were accessed. Then we demonstrated the biocompatibility and bioactivity of FGL-NS for rat dorsal root ganglion neurons (DRGn). We found that the designer self-assembling peptide scaffold was noncytotoxic to neurons and able to promote adhesion and neurite sprouting of neurons. Our results indicate that the designer peptide scaffold containing FGL had excellent biocompatibility and bioactivity with adult sensory neurons and could be used for neuronal regeneration.

Directing traffic in neural cells: determinants of receptor tyrosine kinase localization and cellular responses

The trafficking of receptor tyrosine kinases (RTKs) to distinct subcellular locations is essential for the specificity and fidelity of signal transduction and biological responses. This is particularly important in the PNS and CNS in which RTKs mediate key events in the development and maintenance of neurons and glia through a wide range of neural processes, including survival, proliferation, differentiation, neurite outgrowth, and synaptogenesis. The mechanisms that regulate the targeting of RTKs to their subcellular destinations for appropriate signal transduction, however, are still elusive. In this review, we discuss evidence for the spatial organization of signaling machinery into distinct subcellular compartments, as well as the role for ligand specificity, receptor sorting signals, and lipid raft microdomains in RTK targeting and the resultant cellular responses in neural cells.

Ablation of adhesion molecule L1 in mice favours Schwann cell proliferation and functional recovery after peripheral nerve injury

The adhesion molecule L1 is one of the few adhesion molecules known to be beneficial for repair processes in the adult central nervous system of vertebrates by promoting axonal growth and neuronal survival. In the peripheral nervous system, L1 is up-regulated by myelination-competent Schwann cells and regenerating axons after nerve damage but its functional role has remained unknown. Here we tested the hypothesis that L1 is, as in the central nervous system, beneficial for nerve regeneration in the peripheral nervous system by performing combined functional and histological analyses of adult L1-deficient mice (L1y/-) and wild-type (L1y/+) littermates. Contrary to our hypothesis, quantitative video-based motion analysis revealed better locomotor recovery in L1y/- than in L1y/+ mice at 4-12 weeks after transection and surgical repair of the femoral nerve. Motoneuron regeneration in L1y/- mice was also enhanced as indicated by attenuated post-traumatic loss of motoneurons, enhanced precision of motor reinnervation, larger cell bodies of regenerated motoneurons and diminished loss of inhibitory synaptic input to motoneurons. In search of mechanisms underlying the observed effects, we analysed peripheral nerves at short time-periods (3-14 days) after transection and found that Schwann cell proliferation is strongly augmented in L1y/- versus L1y/+ mice. L1-deficient Schwann cells showed increased proliferation than wild-type Schwann cells, both in vivo and in vitro. These findings suggest a novel role for L1 in nerve regeneration. We propose that L1 negatively regulates Schwann cell proliferation after nerve damage, which in turn restricts functional recovery by limiting the trophic support for regenerating motoneurons.

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.

Preparation and in vitro activity of controlled release microspheres incorporating bFGF

OBJECTIVE

To study the preparative method of controlled release microspheres incorporating basic fibroblast growth factor (bFGF) and the bioactivities of bFGF, which were released from bFGF microspheres, on the cultured Schwann cells.

METHODS

bFGF was microcapsulated with the multiple emulsion encapsulative method using polylactic-co-glycolic acid (PLGA) as coating material. Its morphology, particle size distribution, drug loading, enveloping rate and in vitro release property were studied. The cultured Schwann cells were grouped according to the different ingredients being added to the culture medium of bFGF group or bFGF-PLGA group. Then the cytometry, cytoactivity detection and mitotic cycle analysis of Schwann cells were performed.

RESULTS

The morphology and the particle size distribution of the bFGF-PLGA microspheres were even and good. The drug loading and enveloping rate of microspheres were (27.18 x 10(-3))%+/-(0.51 x 10(-3))% and 66.43%+/-1.24%. The release property of microspheres in vitro was good and the overall release rate was 72.47% in 11 days. The in vitro cellular study showed that: at the first 2 days of plate culture, the cell number and viability of the bFGF group were statistically higher than the bFGF-PLGA group; at the 3rd and 4th days of plate culture, the cell number and viability of bFGF and bFGF-PLGA groups showed no difference; at the 6th and 8th days of the plate culture, the cell number and viability of the bFGF-PLGA group were statistically higher than the bFGF group. By flow cytometry examination, at the 2nd day of plate culture, the G2/M+S percentage of bFGF group was statistically higher than the bFGF-PLGA group, at the 4th and 8th days of plate culture, the G2/M+S percentage of the bFGF-PLGA group was statistically higher than the bFGF group.

CONCLUSIONS

It is practical to prepare the bFGF-PLGA microspheres with the multiple emulsion encapsulative method. bFGF-PLGA microspheres can preserve the bioactivities of bFGF effectively and promote the proliferation of Schwann cells in a long period because of the controlled release of bFGF from the microspheres.

Peripheral regeneration

Whereas the central nervous system (CNS) usually cannot regenerate, peripheral nerves regenerate spontaneously after injury because of a permissive environment and activation of the intrinsic growth capacity of neurons. Functional regeneration requires axon regrowth and remyelination of the regenerated axons by Schwann cells. Multiple factors including neurotrophic factors, extracellular matrix (ECM) proteins, and hormones participate in Schwann cell dedifferentiation, proliferation, and remyelination. We describe the current understanding of peripheral axon regeneration and focus on the molecules and potential mechanisms involved in remyelination.

The physiological and pharmacological role of basic fibroblast growth factor in the dopaminergic nigrostriatal system

Basic fibroblast growth factor (FGF-2) is a physiological relevant neurotrophic factor in the nigrostriatal system and hence a promising candidate for the establishment of alternative therapeutic strategies in Parkinson's disease. FGF-2 and its high-affinity receptors (FGFR) display an expression in the developing, postnatal, and adult substantia nigra (SN) and in the striatum. Exogenous application promoted survival, neurite outgrowth and protection from neurotoxin-induced death of dopaminergic (DA) neurons both in vitro and in vivo. In animal models of Parkinson's disease, co-transplantation of fetal DA cells with FGF-2 expressing cells increased survival and functional integration of the grafted DA neurons resulting in improved behavioral performance. Analyzing the physiological function of the endogenous FGF-2 system during development and after neurotoxin-induced lesion revealed for the DA neurons of the SNpc a dependence on FGFR3 signaling during development. In addition, in the absence of FGF-2 an increased number of DA neurons was found, whereas enhanced levels of FGF-2 resulted in a reduced DA cell density. Following neurotoxin-induced lesion of DA neurons, FGF-2-deleted mice displayed a higher extent of DA neuron death whereas in FGF-2 overexpressing mice more DA neurons were protected. According to the data, FGF-2 seems to promote DA neuron survival via FGFR3 during development, whereas absence of this ligand could be compensated by other members of the FGF family. In contrast, in the adult organism, FGF-2 cannot be compensated by other factors under lesion conditions suggesting a central role for this molecule in the nigrostriatal system.

Fibroblast growth factor (FGF)-2 and FGF receptor 3 are required for the development of the substantia nigra, and FGF-2 plays a crucial role for the rescue of dopaminergic neurons after 6-hydroxydopamine lesion

Basic fibroblast growth factor (FGF-2) is involved in the development and maintenance of the nervous system. Exogenous administration of FGF-2 increased dopaminergic (DA) graft survival in different animal models of Parkinson's disease. To study the physiological function of the endogenous FGF-2 system, we analyzed the nigrostriatal system of mice lacking FGF-2, mice overexpressing FGF-2, and FGF-receptor-3 (FGFR3)-deficient mice both after development and after 6-hydroxydopamine lesion. FGFR3-deficient mice (+/-) displayed a reduced number of DA neurons compared with the respective wild type. Whereas absence of FGF-2 led to significantly increased numbers of DA neurons, enhanced amount of the growth factor in mice overexpressing FGF-2 resulted in less tyrosine hydroxylase expression and a reduced DA cell density. The volumes of the substantia nigra were enlarged in both FGF-2(-/-) and in FGF-2 transgenic mice, suggesting an important role of FGF-2 for the establishment of the proper number of DA neurons and a normal sized substantia nigra during development. In a second set of experiments, the putative relevance of endogenous FGF-2 after neurotoxin application was investigated regarding the number of rescued DA neurons after partial 6-OHDA lesion. Interestingly, the results after lesion were directly opposed to the results after development: significantly less DA neurons survived in FGF-2(-/-) mice compared with wild-type mice. Together, the results indicate that FGFR3 is crucially involved in regulating the number of DA neurons. The lack of FGF-2 seems to be (over)compensated during development, but, after lesion, compensation mechanisms fail. The transgenic mice showed that endogenous FGF-2 protects DA neurons from 6-OHDA neurotoxicity.

FGFR3 mutations and medial temporal lobe dysgenesis

The authors describe a child who has hypochondroplasia due to an N540K mutation and who has medial temporal lobe dysgenesis. This association has been reported only twice before. FGFR3 is expressed in the brain during development and plays a role in hippocampal formation, and FGFR3 mutations could cause cerebral malformations in hypochondroplasia. Further neuroimaging studies of patients with hypochondroplasia and epilepsy or developmental delay may clarify the proportion of patients with hypochondroplasia with this pattern of central nervous system abnormalities.

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.

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.

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.