In vivo expression of the intermediate filament peripherin in rat motoneurons: modulation by inhibitory and stimulatory signals

The Efficiency of Direct Maturation: the Comparison of Two hiPSC Differentiation Approaches into Motor Neurons

Motor neurons (MNs) derived from human-induced pluripotent stem cells (hiPSC) hold great potential for the treatment of various motor neurodegenerative diseases as transplantations with a low-risk of rejection are made possible. There are many hiPSC differentiation protocols that pursue to imitate the multistep process of motor neurogenesis in vivo. However, these often apply viral vectors, feeder cells, or antibiotics to generate hiPSC and MNs, limiting their translational potential. In this study, a virus-, feeder-, and antibiotic-free method was used for reprogramming hiPSC, which were maintained in culture medium produced under clinical good manufacturing practice. Differentiation into MNs was performed with standardized, chemically defined, and antibiotic-free culture media. The identity of hiPSC, neuronal progenitors, and mature MNs was continuously verified by the detection of specific markers at the genetic and protein level via qRT-PCR, flow cytometry, Western Blot, and immunofluorescence. MNX1- and ChAT-positive motoneuronal progenitor cells were formed after neural induction via dual-SMAD inhibition and expansion. For maturation, an approach aiming to directly mature these progenitors was compared to an approach that included an additional differentiation step for further specification. Although both approaches generated mature MNs expressing characteristic postmitotic markers, the direct maturation approach appeared to be more efficient. These results provide new insights into the suitability of two standardized differentiation approaches for generating mature MNs, which might pave the way for future clinical applications.

Evaluation of peripherin in biofluids of patients with motor neuron diseases

Peripherin (PRPH), a type III intermediate filament, assembles with neurofilaments in neurons of the peripheral nervous system, including lower motor neurons (LMN). To evaluate the role of PRPH in LMN degeneration, we assessed PRPH and neurofilament light chain (NfL) in cerebrospinal fluid (CSF) and serum of 91 patients with motor neuron diseases (MND) and 69 controls. Overall, we found PRPH to be more concentrated in serum than in CSF. Serum PRPH resulted significantly increased in MND patients but it was unrelated to CSF‐NfL or survival in the amyotrophic lateral sclerosis (ALS) subset. PRPH might represent a marker of LMN involvement.

α-Internexin and Peripherin: Expression, Assembly, Functions, and Roles in Disease

α-Internexin and peripherin are neuronal-specific intermediate filament (IF) proteins. α-Internexin is a type IV IF protein like the neurofilament triplet proteins (NFTPs, which include neurofilament light chain, neurofilament medium chain, and neurofilament high chain) that are generally considered to be the primary components of the neuronal IFs. However, α-internexin is often expressed together with the NFTPs and has been proposed as the fourth subunit of the neurofilaments in the central nervous system. α-Internexin is also expressed earlier in the development than the NFTPs and is a maker for neuronal IF inclusion disease. α-Internexin can self-polymerize in vitro and in transfected cells and it is present in the absence of the NFTP in development and in granule cells in the cerebellum. In contrast, peripherin is a type III IF protein. Like α-internexin, peripherin is specific to the nervous system, but it is expressed predominantly in the peripheral nervous system (PNS). Peripherin can also self-assemble both in vitro and in transfected cells. It is as abundant as the NFTPs in the sciatic nerve and can be considered a fourth subunit of the neurofilaments in the PNS. Peripherin has multiple isoforms that arise from intron retention, cryptic intron receptor site or alternative translation initiation. The functional significance of these isoforms is not clear. Peripherin is a major component found in inclusions of patients with amyotrophic lateral sclerosis (ALS) and peripherin expression is upregulated in ALS patients.

Mitochondrial dynamics in peripheral neuropathies

SIGNIFICANCE

Mitochondrial dynamics describes the continuous change in the position, size, and shape of mitochondria within cells. The morphological and functional complexity of neurons, the remarkable length of their processes, and the rapid changes in metabolic requirements arising from their intrinsic excitability render these cells particularly dependent on effective mitochondrial function and positioning. The rules that govern these changes and their functional significance are not fully understood, yet the dysfunction of mitochondrial dynamics has been implicated as a pathogenetic factor in a number of diseases, including disorders of the central and peripheral nervous systems.

RECENT ADVANCES

In recent years, a number of mutations of genes encoding proteins that play important roles in mitochondrial dynamics and function have been discovered in patients with Charcot-Marie-Tooth (CMT) disease, a hereditary peripheral neuropathy. These findings have directly linked mitochondrial pathology to the pathology of peripheral nerve and have identified certain aspects of mitochondrial dynamics as potential early events in the pathogenesis of CMT. In addition, mitochondrial dysfunction has now been implicated in the pathogenesis of noninherited neuropathies, including diabetic and inflammatory neuropathies.

CRITICAL ISSUES

The role of mitochondria in peripheral nerve diseases has been mostly examined in vitro, and less so in animal models.

FUTURE DIRECTIONS

This review examines available evidence for the role of mitochondrial dynamics in the pathogenesis of peripheral neuropathies, their relevance in human diseases, and future challenges for research in this field.

Enhancement of cultured adult motor neuron survival with cold pre-incubation

The aim of the study was to extend the survival of adult spinal motor neurons in serum free culture. Anterior half of the spinal cord was removed from young adult mice and dissociated. Cultured cells attempted to extend neurites within hours of incubation at 37 °C and died within 24 h. To prevent this early regenerative activity, thus to decrease the metabolic requirements of the neurons, cultures were transferred to 4 °C immediately after they were set and kept there for 3 days. Preparations were then taken to 37 °C where they lived up to 8 days. Some neurons continued to extend neurites until the day they died. To understand whether the enhancement of survival involves new protein synthesis, transcription and translation were blocked during cold pre-incubation, which shortened the half life of neurons but not changed the maximum survival period. In conclusion this study has shown that, in the serum-free cultures, the survival of adult spinal motor neurons can be significantly enhanced by cold pre-incubation whose effect seems to depend largely on a reduction in the metabolic activity and less on new protein synthesis.

Synaptic profiles during neurite extension, refinement and retraction in the developing cochlea

Background

During development, excess synapses form between the central and peripheral nervous systems that are then eliminated to achieve correct connectivity. In the peripheral auditory system, the developing type I spiral ganglion afferent fibres undergo a dramatic re-organisation, initially forming connections with both sensory inner hair cells (IHCs) and outer hair cells (OHCs). The OHC connections are then selectively eliminated, leaving sparse innervation by type II afferent fibres, whilst the type I afferent synapses with IHCs are consolidated.

Results

We examined the molecular makeup of the synaptic contacts formed onto the IHCs and OHCs during this period of afferent fibre remodelling. We observed that presynaptic ribbons initially form at all the afferent neurite contacts, i.e. not only at the expected developing IHC-type I fibre synapses but also at OHCs where type I fibres temporarily contact. Moreover, the transient contacts forming onto OHCs possess a broad set of pre- and postsynaptic proteins, suggesting that functional synaptic connections are formed prior to the removal of type I fibre innervation. AMPA-type glutamate receptor subunits were transiently observed at the base of the OHCs, with their downregulation occurring in parallel with the withdrawal of type I fibres, dispersal of presynaptic ribbons, and downregulation of the anchoring proteins Bassoon and Shank. Conversely, at developing type I afferent IHC synapses, the presence of pre- and postsynaptic scaffold proteins was maintained, with differential plasticity in AMPA receptor subunits observed and AMPA receptor subunit composition changing around hearing onset.

Conclusions

Overall our data show a differential balance in the patterns of synaptic proteins at developing afferent IHC versus OHC synapses that likely reflect their stable versus transient fates.

The nuclear events guiding successful nerve regeneration

Peripheral nervous system (PNS) neurons survive and regenerate after nerve injury, whereas central nervous system (CNS) neurons lack the capacity to do so. The inability of the CNS to regenerate presumably results from a lack of intrinsic growth activity and a permissive environment. To achieve CNS regeneration, we can learn from successful nerve regeneration in the PNS. Neurons in the PNS elicit dynamic changes in gene expression in response to permissive environmental cues following nerve injury. To switch gene expression on and off in injured neurons, transcription factors and their networks should be carefully orchestrated according to the regeneration program. This is the so-called "intrinsic power of axonal growth." There is an increasing repertoire of candidate transcription factors induced by nerve injury. Some of them potentiate the survival and axonal regeneration of damaged neurons in vivo; however, our knowledge of transcriptional events in injured neurons is still limited. How do these transcription factors communicate with each other? How does the transcriptional machinery regulate the wide variety of regeneration-associated genes (RAGs) in the properly coordinated manner? In this review, we describe our current understanding of the injury-inducible transcriptional factors that enhance the intrinsic growth capacity, and propose a potential role for specificity protein 1 (Sp1), which provides a platform to recruit injury-inducible transcription factors, in simultaneous gene regulation. Finally, we discuss an additional mechanism that is involved in epigenetic modifications in damaged neurons. A comprehensive understanding of the nuclear events in injured neurons will provide clues to clinical interventions for successful nerve regeneration.

Distinct biochemical signatures characterize peripherin isoform expression in both traumatic neuronal injury and motor neuron disease

Peripherin is a type III intermediate filament protein that is up-regulated during neuronal injury and is a major component of pathological inclusions found within degenerating motor neurons of patients with amyotrophic lateral sclerosis (ALS). The relationship between these inclusions and their protein constituents remains largely unknown. We have previously shown that peripherin expression is characterized by tissue-specific, intra-isoform associations that contribute to filament structure; changes to the normal isoform expression pattern is associated with malformed filaments and intracellular inclusions. Here, we profile peripherin isoform expression and ratio changes in traumatic neuronal injury, transgenic mouse models of motor neuron disease, and ALS. Extensive western blot analyses of Triton X-100 soluble and insoluble fractions of neuronal tissue from these conditions revealed significant changes in peripherin isoform content which could be differentiated by electrophoretic banding patterns to produce distinct peripherin biochemical signatures. Significantly, we found that the pattern of peripherin expression in ALS most closely approximates that of peripherin over-expressing mice, but differs with regard to inter-individual variations in isoform-specific expression. Overall, these results provide important insights into complex post-transcriptional processes that may underlie a continuum between peripherin-mediated neuronal repair and its role in the pathogenesis of motor neuron disease.

Peripherin and ATF3 genes are differentially regulated in regenerating and non-regenerating primary sensory neurons

Peripheral nerve injury leads to deficient recovery of sensation and a causative factor may be that only 50-60% of primary sensory neurons succeed in regenerating axons after primary nerve repair. In this study, an in vivo rat sciatic nerve injury and regeneration model was combined with laser microdissection and quantitative real-time polymerase chain reaction with the aim of examining the gene expression of regenerative molecules in cutaneous and muscular sensory neurons. Recent studies have identified peripherin and ATF-3 molecules as crucial for neurite outgrowth propagation; our novel findings demonstrate a subpopulation of non-regenerating sensory neurons characterized by a failure to upregulate transcription of these molecules and that a greater peripherin mRNA expression in injured cutaneous neurons may potentiate this subpopulation to regenerate more axons than muscle afferent neurons following injury. The gene expression of the structural neurofilament NF-H is found to be significantly downregulated following injury in both sensory subpopulations.

Analysis of cochlear protein profiles of Wistar, Sprague-Dawley, and Fischer 344 rats with normal hearing function

Differences in the expression of cochlear proteins are likely to affect the susceptibility of different animal models to specific types of auditory pathology. However, little is currently known about proteins that are abundantly expressed in inner ear. Identification of these proteins may facilitate the search for biomarkers of susceptibility and intervention targets. To begin to address this issue, we analyzed cochlear protein profiles of three strains of rats, Wistar, Sprague-Dawley, and Fischer 344, using a broad spectrum antibody microarray. Normal hearing function of the animals was ascertained using distortion product otoacoustic emissions (DPOAE). Of 725 proteins screened in whole cochlea, more than 80% were detected in all three strains. However, there were striking differences in the levels at which they occur. Among 213 proteins expressed at levels>or=2 fold of actin, only 7.5% were detected at these levels in all three strains. Myosin light chain kinase (MLCK) was immunolocalized in cuticular plate of outer hair cells (OHC) while mitogen activated protein (MAP) kinase-extracellular-signal regulated kinase1/2 (ERK1/2) was detected as foci in OHC, pillar cells, strial marginal cells, and fibroblasts of spiral ligament. A review of literature indicated that the expression of 7 (44%) of these 16 proteins were detected for the first time in the inner ear, although there were implications of the presence of some of these proteins. One of these abundant, but unstudied, proteins, MAP kinase activated protein kinase2 (MAPKAPK2), shows strong immunolabeling in pillar cells and inner hair cells (IHC). There was moderate MAPKAPK2 labeling in OHC, supporting cells, neurons, and marginal, intermediate, and basal cells. The current study provides the first, large cochlear protein profile of multiple rat strains. The diversity in expression of abundant proteins in these strains may contribute to differences in susceptibility of these strains to aging, noise, or ototoxic drugs.

Emergence of highly neurofilament-immunoreactive zipper-like axon segments at the transection site in scalpel-cordotomized adult rats

Following transection of the spinal cord, severed axonal ends retract from the lesion site and attempt regeneration within 24 h of injury. Molecular mechanisms underlying such rapid axonal reactions after severance are not fully characterized so far. To better understand the early axonal degenerating and regenerating processes, we examined the immunohistological expression of axonal cytoskeletal proteins from 5 min to 48 h after scalpel-transection of adult rat spinal cord white matter. Within 30 min of transection, expression of neurofilament (NF)- and peripherin-like immunoreactivity (-IR) was enhanced in severed axonal ends, which conversely lost beta-III-tubulin-IR expression, indicating differential expression of beta-III-tubulin-IR and NF/peripherin-IR. During the next few hours, the strongly-NF/peripherin-IR-positive severed axonal ends adhered to each other and these cytoskeletal alterations expanded bi-directionally (rostro-caudally) 100-300 microm away from the transection point. Within 6 h of transection, secondary axotomy occurred at about 300 microm-rostral and -caudal to the primary transection point, which finally formed strongly-NF/peripherin-IR-positive zipper-like axon segments at the transection site. Notably, sprouting of secondarily severed axons was observed within 6 h of injury. The regenerative axons, which extended toward the transection site, could not traverse the transection site where the zipper-like axon segments resided. The zipper-like axon segments showed abnormal axolemmal permeability through the leakage of an axonal tracer. Western blot analysis revealed a slight increase in peripherin content in transected spinal cord. Local treatment with cycloheximide suppressed the axotomy-induced peripherin-IR-enhancement in severed ends, suggesting the occurrence of intra-axonal peripherin synthesis in vivo. Treatment with calpain inhibitors frequently formed abnormally swollen microtubule-free ends, which suggests that calpain-activation is critical for functional growth cone formation in adult rat spinal cord. These observations indicate that adult rat cordotomy with a scalpel results in the rapid formation of intensely NF-IR-positive zipper-like axon segments at the transection site, which are similar to "preserved fibers" reported by Ramon y Cajal [Ramon y Cajal S (1928) Degeneration and regeneration in the nervous system. New York: Hafner]. On the other hand, axonal regenerative responses start within 6 h of injury, which may be supported by calpain-activation and intra-axonal protein synthesis.

Neuronal expression of peripherin, a type III intermediate filament protein, in the mouse hindbrain

Peripherin is a 57 kDa Type III intermediate filament protein associated with neurite extension, neuropathies such as amyotrophic lateral sclerosis, and cranial nerve and dorsal root projections. However, knowledge of peripherin expression in the CNS is limited. We have used immunoperoxidase histochemistry to characterise peripherin expression in the mouse hindbrain, including the inferior colliculus, pons, medulla and cerebellum. Peripherin immunolabelling was observed in the nerve fibres and nuclei that are associated with all cranial nerves [(CN) V-XII] in the hindbrain. Peripherin expression was prominent in the cell bodies and axons of the mesenchephalic trigeminal nucleus and the pars compacta region of nucleus ambiguus, and in the fibres that comprise the solitary tract, the descending spinal trigeminal tract and the trigeminal and facial nerves. A small proportion of peripherin positive fibres in CN VIII likely arise from cochlear type II spiral ganglion neurons. Peripherin positive fibres were also observed in the inferior cerebellar peduncle and folia in the intermediate zone of the cerebellum. Antibody specificity was confirmed by absence of labelling in hindbrain tissue from peripherin knockout mice. This study shows that in the adult mouse hindbrain, peripherin is expressed in discrete neuronal subpopulations that have sensory, motor and autonomic functions.

New insights into peripherin expression in cochlear neurons

Peripherin is an intermediate filament protein that is expressed in peripheral and enteric neurons. In the cochlear nervous system, peripherin expression has been extensively used as a differentiation marker by preferentially labeling the type II neuronal population at adulthood, but yet without knowing its function. Since the expression of peripherin has been associated in time with the process of axonal extension and during regeneration of nerve fibers in other systems, it was of interest to determine whether peripherin expression in cochlear neurons was a static phenotypic trait or rather prone to modifications following nerve injury. In the present study, we first compared the expression pattern of peripherin and beta III-tubulin from late embryonic stages to the adult in rat cochlea. The staining for both proteins was seen before birth within all cochlear neurons. By birth, and for 2 or 3 days, peripherin expression was gradually restricted to the type II neuronal population and their projections. In contrast, from postnatal day (P) 10 onwards, while the expression of beta III-tubulin was still found in projections of all cochlear neurons, only the type I population had beta III-tubulin immunoreactivity in their cell bodies. We next investigated the expression of peripherin in axotomized cochlear neurons using an organotypic explant model. Peripherin expression was surprisingly re-expressed in a vast majority of neurons after axotomy. In parallel, the expression and localization of beta III-tubulin and peripherin in dissociated cultures of cochlear neurons were studied. Both proteins were distributed along the entire neuronal length but exhibited complementary distribution, especially within the projections. Moreover, peripherin immunoreactivity was still abundant in the growth cone, whereas that of beta III-tubulin was decreasing at this compartment. Our findings are consistent with a model in which peripherin plays an important structural role in cochlear neurons and their projections during both development and regenerative processes and which is compatible with the assumption that frequently developmentally regulated factors are reactivated during neuronal regeneration.

Spatiotemporal definition of neurite outgrowth, refinement and retraction in the developing mouse cochlea

The adult mammalian cochlea receives dual afferent innervation: the inner sensory hair cells are innervated exclusively by type I spiral ganglion neurons (SGN), whereas the sensory outer hair cells are innervated by type II SGN. We have characterized the spatiotemporal reorganization of the dual afferent innervation pattern as it is established in the developing mouse cochlea. This reorganization occurs during the first postnatal week just before the onset of hearing. Our data reveal three distinct phases in the development of the afferent innervation of the organ of Corti: (1) neurite growth and extension of both classes of afferents to all hair cells (E18-P0); (2) neurite refinement, with formation of the outer spiral bundles innervating outer hair cells (P0-P3); (3) neurite retraction and synaptic pruning to eliminate type I SGN innervation of outer hair cells, while retaining their innervation of inner hair cells (P3-P6). The characterization of this developmental innervation pattern was made possible by the finding that tetramethylrhodamine-conjugated dextran (TMRD) specifically labeled type I SGN. Peripherin and choline-acetyltransferase immunofluorescence confirmed the type II and efferent innervation patterns, respectively, and verified the specificity of the type I SGN neurites labeled by TMRD. These findings define the precise spatiotemporal neurite reorganization of the two afferent nerve fiber populations in the cochlea, which is crucial for auditory neurotransmission. This reorganization also establishes the cochlea as a model system for studying CNS synapse development, plasticity and elimination.

Identification of peripherin as a Akt substrate in neurons

Activation of Akt-mediated signaling pathways is crucial for survival and regeneration of injured neurons. In this study, we attempted to identify novel Akt substrates by using an antibody that recognized a consensus motif phosphorylated by Akt. PC12 cells that overexpressed constitutively active Akt were used. Using two-dimensional PAGE, we identified protein spots that exhibited increased immunostaining of the antibody. Mass spectrometry revealed several major spots as the neuronal intermediate filament protein, peripherin. Using several peripherin fragments, the phosphorylation site was determined as Ser(66) in its head domain in vitro. Furthermore, a co-immunoprecipitation experiment revealed that Akt interacted with the head domain of peripherin in HEK 293T cells. An antibody against phosphorylated peripherin was raised, and induction of phosphorylated peripherin was observed not only in Akt-activated cultured cells but also in nerve-injured hypoglossal motor neurons. These results suggest that peripherin is a novel substrate for Akt in vivo and that its phosphorylation may play a role in motor nerve regeneration.

Modelo experimental comportamental e histológico da regeneração do nervo facial em ratos

O estabelecimento de modelos experimentais é o passo inicial para estudos de regeneração neural. OBJETIVO: Estabelecer modelo experimental de regeneração do nervo facial. MATERIAIS E MÉTODOS: Ratos Wistar com secção completa e sutura do tronco do nervo facial extratemporal, com análise comportamental e histológica até 9 semanas. FORMA DE ESTUDO: Estudo prospectivo experimental. RESULTADOS: Progressiva recuperação clínica e histológica dos animais. CONCLUSÃO: Estabelecemos um método aceitável para o estudo de regeneração do nervo facial em ratos.

Defective axonal transport of neurofilament proteins in neurons overexpressing peripherin

Peripherin is a type III neuronal intermediate filament detected in motor neuron inclusions of amyotrophic lateral sclerosis (ALS) patients. We previously reported that overexpression of peripherin provokes late-onset motor neuron dysfunction in transgenic mice. Here, we show that peripherin overexpression slows down axonal transport of neurofilament (NF) proteins, and that the transport defect precedes by several months the appearance of axonal spheroids in adult mice. Defective NF transport by peripherin up-regulation was further confirmed with dorsal root ganglia (DRG) neurons cultured from peripherin transgenic embryos. Immunofluorescence microscopy and western blotting revealed that excess peripherin provokes reduction in levels of hyperphosphorylated NF-H species in DRG neurites. Similarly the transport of a green fluorescent protein (GFP)-tagged NF-M, delivered by means of a lentiviral construct, was impaired in DRG neurites overexpressing peripherin. These results demonstrate that peripherin overexpression can cause defective transport of type IV NF proteins, a phenomenon that may account for the progressive formation of ALS-like spheroids in axons.

Induced expressions of Rab24 GTPase and LC3 in nerve-injured motor neurons

Rab24 is a member of the Rab GTPase family, but its function is unclear. Here, we demonstrated increase in Rab24 mRNA in nerve-injured hypoglossal motor neurons of rats. Expression of Rab24 mRNA was also induced in differentiated PC12 cells following proteasome inhibitor (MG132) treatment. MG132 treatment further induced expression of microtubule-associated protein light chain 3 (LC3), and accumulation of LC3-II, a processed form of LC3 and the most reliable marker for autophagy. Induction of LC3 mRNA and accumulation of LC3-II were also observed in nerve-injured hypoglossal motor neurons, and partial co-localization of Rab24 and LC3 was demonstrated by immunohistochemistry. The present data suggest that nerve injury promotes autophagy-like events, and this may be an important response for degradation of unnecessary and misfolded proteins to recycle limited amino acids, and synthesize new proteins that are necessary for survival and nerve regeneration responses.

Contactin regulates the current density and axonal expression of tetrodotoxin-resistant but not tetrodotoxin-sensitive sodium channels in DRG neurons

Contactin, a glycosyl-phosphatidylinositol (GPI)-anchored predominantly neuronal cell surface glycoprotein, associates with sodium channels Nav1.2, Nav1.3 and Nav1.9, and enhances the density of these channels on the plasma membrane in mammalian expression systems. However, a detailed functional analysis of these interactions and of untested putative interactions with other sodium channel isoforms in mammalian neuronal cells has not been carried out. We examined the expression and function of sodium channels in small-diameter dorsal root ganglion (DRG) neurons from contactin-deficient (CNTN-/-) mice, compared to CNTN+/+ litter mates. Nav1.9 is preferentially expressed in isolectin B4 (IB4)-positive neurons and thus we used this marker to subdivide small-diameter DRG neurons. Using whole-cell patch-clamp recording, we observed a greater than two-fold reduction of tetrodotoxin-resistant (TTX-R) Nav1.8 and Nav1.9 current densities in IB4+ DRG neurons cultured from CNTN-/- vs. CNTN+/+ mice. Current densities for TTX-sensitive (TTX-S) sodium channels were unaffected. Contactin's effect was selective for IB4+ neurons as current densities for both TTX-R and TTX-S channels were not significantly different in IB4- DRG neurons from the two genotypes. Consistent with these results, we have demonstrated a reduction in Nav1.8 and Nav1.9 immunostaining on peripherin-positive unmyelinated axons in sciatic nerves from CNTN-/- mice but detected no changes in the expression for the two major TTX-S channels Nav1.6 and Nav1.7. These data provide evidence of a role for contactin in selectively regulating the cell surface expression and current densities of TTX-R but not TTX-S Na+ channel isoforms in nociceptive DRG neurons; this regulation could modulate the membrane properties and excitability of these neurons.

Up-regulation of peripherin is associated with alterations in synaptic plasticity in CA1 and CA3 regions of hippocampus

Peripherin is a type III intermediate filament protein normally undetectable in most brain neurons. Here, we report a similar pattern of peripherin expression in the brains of both mice treated with systemic injections of kainic acid (KA) and in peripherin transgenic mice (Per mice) over-expressing the normal peripherin gene under its own promoter. Double-immunofluorescence labeling revealed a partial co-localization of peripherin with the microtubule-associated protein MAP2, but not with neurofilament proteins. Electrophysiological studies revealed that synaptic plasticity was markedly altered in Per mice: in CA1, long-term potentiation (LTP) was decreased in Per slices (+29 +/- 2.0%, vs. +58 +/- 5.4%, in WT); while in CA3, LTP was increased in Per (+63 +/- 3.5% vs. +43 +/- 2.4.0%). In the hippocampus of Per mice, the levels of MAP2 were decreased, though synaptophysin and PSD95 remained unchanged. These intriguing findings suggest a role of peripherin in the alteration of hippocampal synaptic plasticity.

Modulation of glycine receptor subunits and gephyrin expression in the rat facial nucleus after axotomy

In the last decade, numerous studies have investigated molecular changes in excitatory glutamatergic receptors in axotomized motoneurons, but few data are available concerning the modulation of inhibitory amino acid receptors. We report here the effect of axotomy on the expression of glycine receptors, gephyrin, vesicular inhibitory amino acid transporter (VIAAT) and synapsin I in rat facial motor neurons as demonstrated by in situ hybridization and immunohistochemistry. The facial nerve trunk was sectioned unilaterally and rats were killed 1, 3, 8, 30 or 60 days after surgery. We investigated the mechanisms underlying the changes in production of these proteins following axotomy by perfusing the facial nerve with colchicine or tetrodotoxin, and injecting cardiotoxin or botulinum toxin independently and unilaterally into the whisker pads of normal rats. Animals were killed 8 days later and processed for immunohistochemistry. The abundance of GlyR subunits and gephyrin fell sharply in the axotomized facial nucleus. This decrease began 1 day after axotomy and was lowest at 8 days, with protein levels returning to normal by day 60. Abnormal synapsin immunolabelling was also observed between days 8 and 60 after axotomy but we detected no change in VIAAT immunoreactivity. The effect of colchicine was similar to, but weaker than, that of axotomy. In contrast, tetrodotoxin, cardiotoxin and botulinum toxin had no significant effect. Thus, axotomy-induced changes probably resulted from a loss of trophic factor transported from the periphery or a positive injury signal, or both. They did not seem to depend on the disruption of activity.

The facial nerve axotomy model

Experimental models such as the facial nerve axotomy paradigm in rodents allow the systematic and detailed study of the response of neurones and their microenvironment to various types of challenges. Well-studied experimental examples include peripheral nerve trauma, the retrograde axonal transport of neurotoxins and locally enhanced inflammation following the induction of experimental autoimmune encephalomyelitis in combination with axotomy. These studies have led to novel insights into the regeneration programme of the motoneurone, the role of microglia and astrocytes in synaptic plasticity and the biology of glial cells. Importantly, many of the findings obtained have proven to be valid in other functional systems and even across species barriers. In particular, microglial expression of major histocompatibility complex molecules has been found to occur in response to various types of neuronal damage and is now regarded as a characteristic component of "glial inflammation". It is found in the context of numerous neurodegenerative disorders including Parkinson's and Alzheimer's disease. The detachment of afferent axonal endings from the surface membrane of regenerating motoneurones and their subsequent displacement by microglia ("synaptic stripping") and long-lasting insulation by astrocytes have also been confirmed in humans. The medical implications of these findings are significant. Also, the facial nerve system of rats and mice has become the best studied and most widely used test system for the evaluation of neurotrophic factors.

Viral delivery of NR2D subunits reduces Mg2+ block of NMDA receptor and restores NT-3-induced potentiation of AMPA-kainate responses in maturing rat motoneurons

N-methyl-D-aspartate (NMDA) responsiveness of motoneurons declines during the initial 2 postnatal weeks due to increasing Mg2+ block of NMDA receptors. Using gene chip analyses, RT-PCR, and immunochemistry, we have shown that the NR2D subunit of the NMDA receptor (NMDAR), known to confer resistance to Mg2+ block, also declines in motoneurons during this period. We injected a viral construct (HSVnr2d) into the lumbar spinal cord on postnatal day 2 in an attempt to restore NMDAR function in motoneurons during the second postnatal week. Following HSVnr2d injection, we detected elevated levels of NR2D mRNA in spinal cord samples and NR2D protein specifically in motoneurons. These molecular changes were associated with marked functional alterations whereby NMDAR-mediated responses in motoneurons associated with both dorsal root (DR) and ventrolateral funiculus (VLF) inputs returned to values observed at E18 due to decreased Mg2+ blockade. Viruses carrying the beta-galactosidase gene did not induce these effects. NT-3 is known to potentiate AMPA-kainate responses in motoneurons if the response has an NMDAR-mediated component and thus is normally ineffective during the second postnatal week. Restoration of NMDAR-mediated responsiveness in the second postnatal week was accompanied by a return of the ability of neurotrophin-3 (NT-3) to potentiate the AMPA-kainate responses produced by both DR and VLF synaptic inputs. We conclude that delivery of the gene for a specific NMDA subunit can restore properties characteristic of younger animals to spinal cord motoneurons. This approach might be useful for enhancing the function of fibers surviving in the damaged spinal cord.

Receptors to steroid hormones and aromatase are expressed by cultured motoneurons but not by glial cells derived from rat embryo spinal cord

The aim of this study was to examine the expression of aromatase and receptors to steroid hormones in cultured motoneurons (MNs). We first developed an original method for obtaining rat MN cultures. Dissociated E15 rat spinal cords were purified using metrizamide and bovine serum albumin density gradients, and cells were then seeded on the culture substratum. We optimized the culture parameters and found that simple addition of rat muscle extract (ME) and conditioned culture medium (CM) from glial cell lines (GCL) derived from spinal cord were sufficient to obtain almost pure MN cultures. MNs were characterized by the presence of specific MN markers and electrophysiology. MNs could be kept alive for 2 weeks. We demonstrate that ME and CM are essential for MN development and survival respectively. Immunocytochemistry and aromatase activity assay indicated the presence of androgen and estrogen receptors as well as aromatase in MNs but not in GCL. This is the first report demonstrating the presence of both female and male sex hormone receptors and a key enzyme in steroid hormone metabolism in MNs and its absence in GCL, at least in our culture conditions. This in vitro model appears to be valuable for elucidating the impact of the sex hormone circuit in neuronal maturation. The relevance of this model for the comprehension of neurodegenerative diseases is discussed.

Induction of peripherin expression in subsets of brain neurons after lesion injury or cerebral ischemia

Peripherin is a type III intermediate filament predominantly expressed in neurons having direct axonal projections toward peripheral structures. Here, we report that brain injuries can trigger expression of peripherin and the formation of peripherin accumulations in neurons that are normally silent for this gene. Stab lesions made with nitrocellulose implants induced within 4 days the formation of peripherin accumulations, devoid of neurofilament proteins, in thalamic neurites at the site of the lesion. The local administration of interleukin-6 or leukemia inhibitory factor at the site of the stab lesion extended the expression pattern of peripherin to other neuronal subsets in areas of the cortex and/or of the hippocampus adjacent to injury. We also show that transient focal ischemia in mice, a model of stroke, can trigger within 72 h the formation of neuronal peripherin accumulations in neurons of the cortex, thalamus and hippocampus. This new type of potentially noxious intermediate filament protein accumulations, composed of peripherin, may be of relevance to many brain degenerative disorders with occurrence of proinflammatory cytokines.

Axonally transported peripheral signals regulate alpha-internexin expression in regenerating motoneurons

The class IV neuronal intermediate filament (IF) family proteins includes the neurofilament (NF) triplet proteins NF-L, NF-M, and NF-H and also the more recently characterized alpha-internexin-NF66. It is well established that NF-L, -M, and -H protein and mRNA are downregulated after peripheral nerve injury. We examined alpha-internexin protein expression after three facial nerve lesion paradigms: crush, transection, and resection. Alpha-internexin immunoreactivity was absent in the perikarya of uninjured facial motoneurons but increased dramatically in all three injury paradigms, with maximum immunoreactivity observed at 7 d after injury. Twenty-eight days after nerve crush or transection, there was a dramatic decrease in the number of alpha-internexin-positive cells. In contrast, alpha-internexin remained elevated 28 d after nerve resection, an injury that hinders regeneration and target reinnervation. In situ hybridization studies showed an increase in alpha-internexin mRNA expression in the facial nucleus at 7 and 14 d after injury. Retrograde transport of fluorogold from the whisker pads to the facial nucleus was seen only in motoneurons that lacked alpha-internexin immunoreactivity, supporting the idea that target reinnervation and inhibitory signals from the periphery regulate the expression of alpha-internexin. Blockage of axonal transport through local colchicine application induced strong immunoreactivity in motoneurons. Alpha-internexin expression was also examined after central axotomy of rubrospinal neurons, which constitutively show alpha-internexin immunoreactivity. After rubrospinal tractotomy, alpha-internexin immunoreactivity transiently increased by 7 d after injury but returned to control levels by 14 d. We conclude that alpha-internexin upregulation in injured motoneurons suggests a role for this IF protein in neuronal regeneration.