In vitro evaluation of cell-seeded chitosan films for peripheral nerve tissue engineering

Natural biomaterials have attracted an increasing interest in the field of tissue-engineered nerve grafts, representing a possible alternative to autologous nerve transplantation. With the prospect of developing a novel entubulation strategy for transected nerves with cell-seeded chitosan films, we examined the biocompatibility of such films in vitro. Different types of rat Schwann cells (SCs)--immortalized, neonatal, and adult-of the chitosan substrate. Both cell types were viable on the biomaterial and showed different metabolic activities and proliferation behavior, indicating cell-type-specific cell-biomaterial interaction. Moreover, the cell types also displayed their typical morphology. In cocultures adult SCs used the BMSCs as a feeder layer and no negative interactions between both cell types were detected. Further, the chitosan films allow neurite outgrowth from dissociated sensory neurons, which is additionally supported on film preseeded with SC-BMSC cocultures. The presented chitosan films therefore demonstrate high potential for their use in tissue-engineered nerve grafts.

Morphometric parameters of peripheral nerves in calves correlated with conduction velocity

BACKGROUND

Peripheral nerve injuries are the most frequent neurologic disorder in cattle. So far, no physiologic values have been established for the motor nerve conduction velocity (mNCV) in this precocial species.

OBJECTIVES

The electrophysiologic and morphometric reference values of peripheral nerves in calves were determined. It was hypothesized that these parameters would correlate to the high degree of maturity in the first days of life in this species compared to other species.

ANIMALS

Twenty-six healthy calves were used in this study.

METHODS

The mNCV of the radial and the sciatic/common peroneal nerve was measured in all 26 calves. Nerve biopsies from a group of 6 calves were taken to correlate the obtained electrophysiologic data with morphological parameters.

RESULTS

The mean mNCV of the radial nerve was 48.3 ± 10.6 m/s, whereas the mean mNCV of the sciatic/peroneal nerve was with 83.8 ± 5.9 m/s significantly faster (P < .0001). The average fiber diameter was 8.40 ± 2.80 μm (range, 1.98-17.90 μm) and the average g-ratio was 0.61 ± 0.04 SD.

CONCLUSION AND CLINICAL IMPORTANCE

The established reference values for mNCV in calves correlate well with the evaluated morphometric parameters. Attributable to their comparably fast mNCV and high fiber diameters, juvenile calves appear to be much more mature individuals than other mammals. Electrophysiologic characterization of peripheral nerve injury now is feasible in this species.

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.

Bilateral crosstalk of rho- and extracellular-signal-regulated-kinase (ERK) pathways is confined to an unidirectional mode in spinal muscular atrophy (SMA)

Rho-kinase (ROCK) as well as extracellular signal regulated kinase (ERK) control actin cytoskeletal organization thereby regulating dynamic changes of cellular morphology. In neurons, motility processes such as axonal guidance and neurite outgrowth demand a fine regulation of upstream pathways. Here we demonstrate a bilateral ROCK-ERK information flow in neurons. This process is shifted towards an unidirectional crosstalk in a model of the neurodegenerative disease Spinal Muscular Atrophy (SMA), ultimately leading to neurite outgrowth dysregulations. As both pathways are of therapeutic relevance for SMA, our results argue for a combinatorial ROCK/ERK-targeting as a future treatment strategy.

Immobile survival of motoneuron (SMN) protein stored in Cajal bodies can be mobilized by protein interactions

Reduced levels of survival of motoneuron (SMN) protein lead to spinal muscular atrophy, but it is still unknown how SMN protects motoneurons in the spinal cord against degeneration. In the nucleus, SMN is associated with two types of nuclear bodies denoted as gems and Cajal bodies (CBs). The 23 kDa isoform of fibroblast growth factor-2 (FGF-2(23)) is a nuclear protein that binds to SMN and destabilizes the SMN-Gemin2 complex. In the present study, we show that FGF-2(23) depletes SMN from CBs without affecting their general structure. FRAP analysis of SMN-EGFP in CBs demonstrated that the majority of SMN in CBs remained mobile and allowed quantification of fast, slow and immobile nuclear SMN populations. The potential for SMN release was confirmed by in vivo photoconversion of SMN-Dendra2, indicating that CBs concentrate immobile SMN that could have a specialized function in CBs. FGF-2(23) accelerated SMN release from CBs, accompanied by a conversion of immobile SMN into a mobile population. Furthermore, FGF-2(23) caused snRNP accumulation in CBs. We propose a model in which Cajal bodies store immobile SMN that can be mobilized by its nuclear interaction partner FGF-2(23), leading to U4 snRNP accumulation in CBs, indicating a role for immobile SMN in tri-snRNP assembly.

Fibroblast growth factor 2 regulates adequate nigrostriatal pathway formation in mice

Fibroblast growth factor 2 (FGF-2) is an important neurotrophic factor that promotes survival of adult mesencephalic dopaminergic (mDA) neurons and regulates their adequate development. Since mDA neurons degenerate in Parkinson's disease, a comprehensive understanding of their development and maintenance might contribute to the development of causative therapeutic approaches. The current analysis addressed the role of FGF-2 in mDA axonal outgrowth, pathway formation, and innervation of respective forebrain targets using organotypic explant cocultures of ventral midbrain (VM) and forebrain (FB). An enhanced green fluorescent protein (EGFP) transgenic mouse strain was used for the VM explants, which allowed combining and distinguishing of individual VM and FB tissue from wildtype and FGF-2-deficient embryonic day (E)14.5 embryos, respectively. These cocultures provided a suitable model to study the role of target-derived FB and intrinsic VM-derived FGF-2. In fact, we show that loss of FGF-2 in both FB and VM results in significantly increased mDA fiber outgrowth compared to wildtype cocultures, proving a regulatory role of FGF-2 during nigrostriatal wiring. Further, we found in heterogeneous cocultures deficient for FGF-2 in FB and VM, respectively, similar phenotypes with wider fiber tracts compared to wildtype cocultures and shorter fiber outgrowth distance than cocultures completely deficient for FGF-2. Additionally, the loss of target-derived FGF-2 in FB explants resulted in decreased caudorostral glial migration. Together these findings imply an intricate interplay of target-derived and VM-derived FGF signaling, which assures an adequate nigrostriatal pathway formation and target innervation.

The use of chitosan-based scaffolds to enhance regeneration in the nervous system

Various biomaterials have been proposed to build up scaffolds for promoting neural repair. Among them, chitosan, a derivative of chitin, has been raising more and more interest among basic and clinical scientists. A number of studies with neuronal and glial cell cultures have shown that this biomaterial has biomimetic properties, which make it a good candidate for developing innovative devices for neural repair. Yet, in vivo experimental studies have shown that chitosan can be successfully used to create scaffolds that promote regeneration both in the central and in the peripheral nervous system. In this review, the relevant literature on the use of chitosan in the nervous tissue, either alone or in combination with other components, is overviewed. Altogether, the promising in vitro and in vivo experimental results make it possible to foresee that time for clinical trials with chitosan-based nerve regeneration-promoting devices is approaching quickly.

Cooperation of nuclear fibroblast growth factor receptor 1 and Nurr1 offers new interactive mechanism in postmitotic development of mesencephalic dopaminergic neurons

Experiments in mice deficient for Nurr1 or expressing the dominant-negative FGF receptor (FGFR) identified orphan nuclear receptor Nurr1 and FGFR1 as essential factors in development of mesencephalic dopaminergic (mDA) neurons. FGFR1 affects brain cell development by two distinct mechanisms. Activation of cell surface FGFR1 by secreted FGFs stimulates proliferation of neural progenitor cells, whereas direct integrative nuclear FGFR1 signaling (INFS) is associated with an exit from the cell cycle and neuronal differentiation. Both Nurr1 and INFS activate expression of neuronal genes, such as tyrosine hydroxylase (TH), which is the rate-limiting enzyme in dopamine synthesis. Here, we show that nuclear FGFR1 and Nurr1 are expressed in the nuclei of developing TH-positive cells in the embryonic ventral midbrain. Both nuclear receptors were effectively co-immunoprecipitated from the ventral midbrain of FGF-2-deficient embryonic mice, which previously showed an increase of mDA neurons and enhanced nuclear FGFR1 accumulation. Immunoprecipitation and co-localization experiments showed the presence of Nurr1 and FGFR1 in common nuclear protein complexes. Fluorescence recovery after photobleaching and chromatin immunoprecipitation experiments demonstrated the Nurr1-mediated shift of nuclear FGFR1-EGFP mobility toward a transcriptionally active population and that both Nurr1 and FGFR1 bind to a common region in the TH gene promoter. Furthermore, nuclear FGFR1 or its 23-kDa FGF-2 ligand (FGF-2(23)) enhances Nurr1-dependent activation of the TH gene promoter. Transcriptional cooperation of FGFR1 with Nurr1 was confirmed on isolated Nurr1-binding elements. The proposed INFS/Nurr1 nuclear partnership provides a novel mechanism for TH gene regulation in mDA neurons and a potential therapeutic target in neurodevelopmental and neurodegenerative disorders.

Prolonged survival and milder impairment of motor function in the SOD1 ALS mouse model devoid of fibroblast growth factor 2

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by selective motoneuron loss in brain and spinal cord. Mutations in the superoxide dismutase (SOD) 1 gene account for 10-20% of familial ALS patients. The ALS-mouse model over-expressing a mutant human SOD1 (G93A) gene closely mimics human ALS disease. The cause for the selective death of motoneurons is still unclear, but among several pathomechanisms discussed, loss of neurotrophic factors is one possibility. Basic fibroblast growth factor 2 (FGF-2) plays a prominent role in the motor system. In order to evaluate a role of FGF-2 in ALS pathogenesis, double mouse mutants transgenic for the human SOD1 mutation and lacking the endogenous FGF-2 gene were generated. Both heterozygous and homozygous FGF-2 deficient mutant SOD1 mice showed a significant delay in disease onset and less impaired motor performance in comparison to mutant SOD1 mice with normal FGF-2 levels. Survival of the double mouse mutants was significantly prolonged for two weeks. Motoneuron numbers were significantly higher in the double mutants and astrocytosis was diminished at disease endstage. While one would initially have expected that FGF-2 deficiency deteriorates the phenotype of mutant SOD1 animals, our results revealed a protective effect of FGF-2 reduction. In search of the underlying mechanisms, we could show up-regulation of other neurotrophic factors with proven protective effects in the ALS mouse model, ciliary neurotrophic factor (CNTF) and glial derived neurotrophic factor (GDNF) in muscle and spinal cord tissue of double mutant animals.

Analysis of the fibroblast growth factor system reveals alterations in a mouse model of spinal muscular atrophy

The monogenetic disease Spinal Muscular Atrophy (SMA) is characterized by a progressive loss of motoneurons leading to muscle weakness and atrophy due to severe reduction of the Survival of Motoneuron (SMN) protein. Several models of SMA show deficits in neurite outgrowth and maintenance of neuromuscular junction (NMJ) structure. Survival of motoneurons, axonal outgrowth and formation of NMJ is controlled by neurotrophic factors such as the Fibroblast Growth Factor (FGF) system. Besides their classical role as extracellular ligands, some FGFs exert also intracellular functions controlling neuronal differentiation. We have previously shown that intracellular FGF-2 binds to SMN and regulates the number of a subtype of nuclear bodies which are reduced in SMA patients. In the light of these findings, we systematically analyzed the FGF-system comprising five canonical receptors and 22 ligands in a severe mouse model of SMA. In this study, we demonstrate widespread alterations of the FGF-system in both muscle and spinal cord. Importantly, FGF-receptor 1 is upregulated in spinal cord at a pre-symptomatic stage as well as in a mouse motoneuron-like cell-line NSC34 based model of SMA. Consistent with that, phosphorylations of FGFR-downstream targets Akt and ERK are increased. Moreover, ERK hyper-phosphorylation is functionally linked to FGFR-1 as revealed by receptor inhibition experiments. Our study shows that the FGF system is dysregulated at an early stage in SMA and may contribute to the SMA pathogenesis.

C3 peptide promotes axonal regeneration and functional motor recovery after peripheral nerve injury

Peripheral nerve injuries are frequently seen in trauma patients and due to delayed nerve repair, lifelong disabilities often follow this type of injury. Innovative therapies are needed to facilitate and expedite peripheral nerve regeneration. The purpose of this study was to determine the effects of a 1-time topical application of a 26-amino-acid fragment (C3(156-181)), derived from the Clostridium botulinum C3-exoenzyme, on peripheral nerve regeneration in 2 models of nerve injury and repair in adult rats. After sciatic nerve crush, different dosages of C3(156-181) dissolved in buffer or reference solutions (nerve growth factor or C3(bot)-wild-type protein) or vehicle-only were injected through an epineurial opening into the lesion sites. After 10-mm nerve autotransplantation, either 8.0 nmol/kg C3(156-181) or vehicle were injected into the proximal and distal suture sites. For a period of 3 to 10 postoperative weeks, C3(156-181)-treated animals showed a faster motor recovery than control animals. After crush injury, axonal outgrowth and elongation were activated and consequently resulted in faster motor recovery. The nerve autotransplantation model further elucidated that C3(156-181) treatment accounts for better axonal elongation into motor targets and reduced axonal sprouting, which are followed by enhanced axonal maturation and better axonal functionality. The effects of C3(156-181) are likely caused by a nonenzymatic down-regulation of active RhoA. Our results indicate the potential of C3(156-181) as a therapeutic agent for the topical treatment of peripheral nerve repair sites.

The colayer method as an efficient way to genetically modify mesencephalic progenitor cells transplanted into 6-OHDA rat model of Parkinson's disease

Exogenous cell replacement represents a potent treatment option for Parkinson's disease. However, the low survival rate of transplanted dopaminergic neurons (DA) calls for methodological improvements. Here we evaluated a method to combine transient genetic modification of neuronal progenitor cells with an optimized cell culture protocol prior to intrastriatal transplantation into 6-hydroxydopamine (6-OHDA) unilateral lesioned rats. Plasmid-based delivery of brain-derived neurotrophic factor (BDNF) increases the number of DA neurons, identified by tyrosine hydroxylase immunoreactivity (TH-ir), by 25% in vitro, compared to enhanced green fluorescence protein (EGFP)-transfected controls. However, the nucleofection itself, especially the cell detachment and reseeding procedure, decreases the TH-ir neuron number to 40% compared with nontransfected control cultures. To circumvent this drawback we established the colayer method, which contains a mix of nucleofected cells reseeded on top of an adherent sister culture in a ratio 1:3. In this setup TH-ir neuron number remains high and could be further increased by 25% after BDNF transfection. Comparison of both cell culture procedures (standard and colayer) after intrastriatal transplantation revealed a similar DA neuron survival as seen in vitro. Two weeks after grafting TH-ir neuron number was strongly reduced in animals receiving the standard EGFP-transfected cells (271 ± 62) compared to 1,723 ± 199 TH-ir neurons in the colayer group. In contrast to the in vitro results, no differences in the number of grafted TH-ir neurons were observed between BDNF, EGFP, and nontransfected colayer groups, neither 2 nor 13 weeks after transplantation. Likewise, amphetamine and apomorphine-induced rotational behavior improved similarly over time in all groups. Nevertheless, the colayer protocol provides an efficient way for neurotrophic factor release by transplanted progenitor cells and will help to study the effects of candidate factors on survival and integration of transplanted DA neurons.

The spinal muscular atrophy disease protein SMN is linked to the Rho-kinase pathway via profilin

Spinal muscular atrophy (SMA), a frequent neurodegenerative disease, is caused by reduced levels of functional survival of motoneuron (SMN) protein. SMN is involved in multiple pathways, including RNA metabolism and splicing as well as motoneuron development and function. Here we provide evidence for a major contribution of the Rho-kinase (ROCK) pathway in SMA pathogenesis. Using an in vivo protein interaction system based on SUMOylation of proteins, we found that SMN is directly interacting with profilin2a. Profilin2a binds to a stretch of proline residues in SMN, which is heavily impaired by a novel SMN2 missense mutation (S230L) derived from a SMA patient. In different SMA models, we identified differential phosphorylation of the ROCK-downstream targets cofilin, myosin-light chain phosphatase and profilin2a. We suggest that hyper-phosphorylation of profilin2a is the molecular link between SMN and the ROCK pathway repressing neurite outgrowth in neuronal cells. Finally, we found a neuron-specific increase in the F-/G-actin ratio that further support the role of actin dynamics in SMA pathogenesis.

FGF-2 deficiency does not influence FGF ligand and receptor expression during development of the nigrostriatal system

Secreted proteins of the fibroblast growth factor (FGF) family play important roles during development of various organ systems. A detailed knowledge of their temporal and spatial expression profiles, especially of closely related FGF family members, are essential to further identification of specific functions in distinct tissues. In the central nervous system dopaminergic neurons of the substantia nigra and their axonal projections into the striatum progressively degenerate in Parkinson's disease. In contrast, FGF-2 deficient mice display increased numbers of dopaminergic neurons. In this study, we determined the expression profiles of all 22 FGF-ligands and 10 FGF-receptor isoforms, in order to clarify, if FGF-2 deficiency leads to compensatory up-regulation of other FGFs in the nigrostriatal system. Three tissues, ventral mesencephalon (VM), striatum (STR) and as reference tissue spinal cord (SC) of wild-type and FGF-2 deficient mice at four developmental stages E14.5, P0, P28, and adult were comparatively analyzed by quantitative RT-PCR. As no differences between the genotypes were observed, a compensatory up-regulation can be excluded. Moreover, this analysis revealed that the majority of FGF-ligands (18/22) and FGF-receptors (9/10) are expressed during normal development of the nigrostriatal system and identified dynamic changes for some family members. By comparing relative expression level changes to SC reference tissue, general alterations in all 3 tissues, such as increased expression of FGF-1, -2, -22, FgfR-2c, -3c and decreased expression of FGF-13 during postnatal development were identified. Further, specific changes affecting only one tissue, such as increased FGF-16 (STR) or decreased FGF-17 (VM) expression, or two tissues, such as decreased expression of FGF-8 (VM, STR) and FGF-15 (SC, VM) were found. Moreover, 3 developmentally down-regulated FGFs (FGF-8b, FGF-15, FGF-17a) were functionally characterized by plasmid-based over-expression in dissociated E11.5 VM cell cultures, however, such a continuous exposure had no influence on the yield of dopaminergic neurons in vitro.

Poor functional recovery and muscle polyinnervation after facial nerve injury in fibroblast growth factor-2-/- mice can be improved by manual stimulation of denervated vibrissal muscles

Functional recovery following facial nerve injury is poor. Adjacent neuromuscular junctions (NMJs) are "bridged" by terminal Schwann cells and numerous regenerating axonal sprouts. We have recently shown that manual stimulation (MS) restores whisking function and reduces polyinnervation of NMJs. Furthermore, MS requires both insulin-like growth factor-1 (IGF-1) and brain-derived neurotrophic factor (BDNF). Here, we investigated whether fibroblast growth factor-2 (FGF-2) was also required for the beneficial effects of MS. Following transection and suture of the facial nerve (facial-facial anastomisis, FFA) in homozygous mice lacking FGF-2 (FGF-2(-/-)), vibrissal motor performance and the percentage of poly-innervated NMJ were quantified. In intact FGF-2(-/-) mice and their wildtype (WT) counterparts, there were no differences in amplitude of vibrissal whisking (about 50°) or in the percentage of polyinnervated NMJ (0%). After 2 months FFA and handling alone (i.e. no MS), the amplitude of vibrissal whisking in WT-mice decreased to 22±3°. In the FGF-2(-/-) mice, the amplitude was reduced further to 15±4°, that is, function was significantly poorer. Functional deficits were mirrored by increased polyinnervation of NMJ in WT mice (40.33±2.16%) with polyinnervation being increased further in FGF-2(-/-) mice (50.33±4.33%). However, regardless of the genotype, MS increased vibrissal whisking amplitude (WT: 33.9°±7.7; FGF-2(-/-): 33.4°±8.1) and concomitantly reduced polyinnervation (WT: 33.9%±7.7; FGF-2(-/-): 33.4%±8.1) to a similar extent. We conclude that, whereas lack of FGF-2 leads to poor functional recovery and target reinnervation, MS can nevertheless confer some functional benefit in its absence.

Myelination in the absence of UDP-galactose:ceramide galactosyl-transferase and fatty acid 2 -hydroxylase

BACKGROUND

The sphingolipids galactosylceramide (GalCer) and sulfatide are major myelin components and are thought to play important roles in myelin function. The importance of GalCer and sulfatide has been validated using UDP-galactose:ceramide galactosyltransferase-deficient (Cgt-/-) mice, which are impaired in myelin maintenance. These mice, however, are still able to form compact myelin. Loss of GalCer and sulfatide in these mice is accompanied by up-regulation of 2-hydroxylated fatty acid containing (HFA)-glucosylceramide in myelin. This was interpreted as a partial compensation of the loss of HFA-GalCer, which may prevent a more severe myelin phenotype. In order to test this hypothesis, we have generated Cgt-/- mice with an additional deletion of the fatty acid 2-hydroxylase (Fa2h) gene.

RESULTS

Fa2h-/-/Cgt-/- double-deficient mice lack sulfatide, GalCer, and in addition HFA-GlcCer and sphingomyelin. Interestingly, compared to Cgt-/- mice the amount of GlcCer in CNS myelin was strongly reduced in Fa2h-/-/Cgt-/- mice by more than 80%. This was accompanied by a significant increase in sphingomyelin, which was the predominant sphingolipid in Fa2h-/-/Cgt-/- mice. Despite these significant changes in myelin sphingolipids, compact myelin was formed in Fa2h-/-/Cgt-/- mice, and g-ratios of myelinated axons in the spinal cord of 4-week-old Fa2h-/-/Cgt-/- mice did not differ significantly from that of Cgt-/- mice, and there was no obvious phenotypic difference between Fa2h-/-/Cgt-/- and Cgt-/- mice

CONCLUSIONS

These data show that compact myelin can be formed with non-hydroxylated sphingomyelin as the predominant sphingolipid and suggest that the presence of HFA-GlcCer and HFA-sphingomyelin in Cgt-/- mice does not functionally compensate the loss of HFA-GalCer.