Expression of peripherin, NADPH-diaphorase and NOS in the adult rat neocortex

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.

Inflammation, plasticity and real-time imaging after cerebral ischemia

With an incidence of approximately 350 in 100,000, stroke is the third leading cause of death and a major cause of disability in industrialized countries. At present, although progress has been made in understanding the molecular pathways that lead to ischemic cell death, the current clinical treatments remain poorly effective. There is mounting evidence that inflammation plays an important role in cerebral ischemia. Experimentally and clinically, brain response to ischemic injury is associated with an acute and prolonged inflammatory process characterized by the activation of resident glial cells, production of inflammatory cytokines as well as leukocyte and monocyte infiltration in the brain, events that may contribute to ischemic brain injury and affect brain recovery and plasticity. However, whether the post-ischemic inflammatory response is deleterious or beneficial to brain recovery is presently a matter of debate and controversies. Here, we summarize the current knowledge on the molecular mechanisms underlying post-ischemic neuronal plasticity and the potential role of inflammation in regenerative processes and functional recovery after stroke. Furthermore, because of the dynamic nature of the brain inflammatory response, we highlight the importance of the development of novel experimental approaches such as real-time imaging. Finally, we discuss the novel transgenic reporter mice models that have allowed us to visualize and to analyze the processes such as neuroinflammation and neuronal repair from the ischemic brains of live animals.

Abnormal cellular translocation of alpha-internexin in spinal motor neurons of Dystonia musculorum mice

Dystonia musculorum (dt) is a mutant mouse with hereditary neuropathy where the dysfunction is mainly found in the dorsal root ganglia (DRG) neurons but not in the spinal motor neurons. However, the accumulation of intermediate filament (IF) proteins in the swelling axons of spinal motor neurons could be found in dt/dt mice. In order to understand the pathological role of neuronal IFs in the swelling axons of spinal motor neurons from dt/dt mice, we extensively examined the distribution of neuronal IF proteins. By immunofluorescence staining, our results indicated that alpha-internexin was a major component in the swelling axon and showed abnormal translocation in the nuclei of spinal motor neurons in dt/dt mice. This abnormal translocation of alpha-internexin in the nuclei of spinal motor neurons was also confirmed by Western blotting and immunoelectron microscopy. Instead of the 10-nm filamentous structure, a diffuse immunopositive pattern of alpha-internexin was observed in the nucleus of spinal motor neurons in dt/dt mutants. We further examined the cell death of spinal motor neurons by TUNEL assay, and no TUNEL-positive cells could be identified from spinal motor neurons in dt/dt mice. From these observations we suggest that abnormal accumulation of neuronal IFs in the swelling axons and abnormal translocation of alpha-internexin in the nuclei of the spinal motor neurons from dt/dt mice may not directly cause cell death of the spinal motor neurons.

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.

Tau is Endogenously Nitrated in Mouse Brain: Identification of a Tyrosine Residue Modified In vivo by NO

Nitration of tau protein is normally linked to neurodegeneration but, until now, no comprehensive information is available regarding tau nitration in healthy subjects. It has been previously reported that in differentiated PC12 cells, tau co-immunoprecipitated with alpha-tubulin is nitrated at tyrosine residues and that this post-translation modification doesn't impair the association of tau with the cytoskeleton. The present paper is focused on the identification of tyrosine residues endogenously modified in tau from PC12 cells and reports for the first time that tau is also nitrated in vivo in normal mouse brain and that one tyrosine is endogenously modified.

Tyrosine nitration is a novel post-translational modification occurring on the neural intermediate filament protein peripherin

The biological implication of protein tyrosine nitration in signaling pathways triggered by nitric oxide is recently emerging. Here we report for the first time that nitrotyrosination occurs in the neural intermediate filament protein peripherin. In neuron-like PC12 cells, nitrated peripherin is associated with the cytoskeleton fraction, its level increases during the progression of NGF-induced differentiation and the nitrated protein remains closely associated with stable microtubules. Tyr 17 and Tyr 376 were identified by MALDI-TOF analyses as two specific residues endogenously nitrated. Finally, peripherin nitration is not restricted to PC12 cells but it is also present in vivo in rat brain.

A Possible Cellular Mechanism of Neuronal Loss in the Dorsal Root Ganglia of Dystonia musculorum (dt) Mice

Dystonia musculorum (dt) is a mutant mouse with hereditary sensory neuropathy. A defective bullous pemphigoid antigen 1 (BPAG1) gene is responsible for this mutation. In the present study, we examined the distribution of neuronal intermediate filament proteins in the central and peripheral processes of the dorsal root ganglia (DRG) in adult dt mice using different approaches. We found that not only BPAG1, but also alpha-internexin was absent in the DRG neurons in adult dt mice. To study the relationship between the absence of alpha-internexin and the progressive neuronal loss in the DRG of dt mice, we further cultured DRG neurons from embryonic dt mutants. Immunocytochemical assay of cultured DRG neurons from dt embryos revealed that alpha-internexin was aggregated in the proximal region of axons and juxtanuclear region of the cytoplasma, yet the other intermediate filament proteins were widely distributed in all processes. The active caspase-3 activity was observed in the dt neuron with massive accumulation of alpha-internexin. From our observations, we suggest that the interaction between BPAG1 and alpha-internexin may be one of the key factors involved in neuronal degeneration, and abnormal accumulation of alpha-internexin may impair the axonal transport and subsequently turns on the cascade of neuronal apoptosis in dt mice.

BMP2 and FGF2 cooperate to induce neural-crest-like fates from fetal and adult CNS stem cells

CNS stem cells are best characterized by their ability to self-renew and to generate multiple differentiated derivatives, but the effect of mitogenic signals, such as fibroblast growth factor 2 (FGF2), on the positional identity of these cells is not well understood. Here, we report that bone morphogenetic protein 2 (BMP2) induces telencephalic CNS stem cells to fates characteristic of neural crest and choroid plexus mesenchyme, a cell type of undetermined lineage in rodents. This induction occurs both in dissociated cell culture and cortical explants of embryonic day 14.5 (E14.5) embryos, but only when cells have been exposed to FGF2. Neither EGF nor IGF1 can substitute for FGF2. An early step in this response is activation of β-catenin, a mediator of Wnt activity. The CNS stem cells first undergo an epithelial-to-mesenchymal transition and subsequently differentiate to smooth-muscle and non-CNS glia cells. Similar responses are seen with stem cells from E14.5 cortex, E18.5 cortex and adult subventricular zone, but with a progressive shift toward gliogenesis that is characteristic of normal development. These data indicate that FGF2 confers competence for dorsalization independently of its mitogenic action. This rapid and efficient induction of dorsal fates may allow identification of positional identity effectors that are co-regulated by FGF2 and BMP2.

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.

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.

Expression of peripherin in the brain of macaques (Macaca mulatta and Macaca fascicularis) occurs in astrocytes rather than neurones and is associated with encephalitis

Peripherin is a member of the type III intermediate filament family, expressed in neurones of the peripheral nervous system of many species and in a discrete subpopulation of neurones of the central nervous system (CNS) during early development in rodents. Previous studies on rats have shown that peripherin immunoreactivity increased significantly in cell bodies of spinal motor neurones following axonal injury. Our study examined the expression of peripherin in the cerebrum of normal macaques (Macaca mulatta and Macaca fascicularis) and those with encephalitis of viral (simian immunodeficiency virus and simian virus 40) or autoimmune (experimental allergic encephalomyelitis) aetiology. Immunohistochemistry, immunoelectronmicroscopy, immunofluorescence and confocal microscopy were performed on tissue sections using antibodies against cell-specific markers and peripherin. Peripherin-positive cells were absent in the cerebrum of normal macaques of all ages examined, whereas animals with encephalitis had peripherin-positive cells associated with inflammatory infiltrates. Further evaluation revealed that these peripherin-positive cells were not neurones, but were predominantly astrocytes expressing glial fibrillary acidic protein. Our study suggests that peripherin is not neurone-specific in the CNS of macaques; peripherin is expressed in astrocytes of animals with encephalitis.

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

Peripherin is a type III intermediate filament which, in contrast to the neurofilaments, is strongly up-regulated after nerve injury. Although peripherin expression is stimulated in vitro by neurotrophins and cytokines, little is known about its in vivo regulation. In this report, we show that the in vivo down-regulation of peripherin expression to normal levels during regeneration closely correlates with target reconnection in rat facial motoneurons. Prevention of reconnection, by transection and suture, results in the persistence of strong peripherin expression for prolonged periods of up to 11months. This contrasts with the modulation of the p75 low-affinity neurotrophin receptor, whose expression returns to normal even in the absence of reconnection. We further demonstrate that blockade of the axonal transport in non-injured motoneurons increases the expression of peripherin. Blockade of the axonal transport simultaneously to, or after injury of, facial motoneurons does not abolish the axotomy-induced peripherin up-regulation. These data demonstrate that the in vivo expression of peripherin is normally restrained by a distal retrogradely transported inhibitory signal. Thus, peripherin up-regulation results primarily from a lack of supply in this factor. Our results show that stimulatory factors released at the injury site are not required for the initial up-regulation and maintenance of high peripherin expression. However, they appear to enhance this increase during the acute post-lesion phase. Peripherin expression is thus finely tuned by both glial cell-derived stimulatory and distal inhibitory signals that reflect neuron-target interactions.

Nitrinergic neurons in the developing and adult human telencephalon: transient and permanent patterns of expression in comparison to other mammals

A subpopulation of cerebral cortical neurons constitutively express nitric oxide synthase (NOS) and, upon demand, produce a novel messenger molecule nitric oxide (NO) with a variety of proposed roles in the developing, adult, and diseased brain. With respect to the intensity of their histochemical (NADPH-diaphorase histochemistry) and immunocytochemical (nNOS and eNOS immunocytochemistry) staining, these nitrinergic neurons are generally divided in type I and type II cells. Type I cells are usually large, intensely stained interneurons, scattered throughout all cortical layers; they frequently co-express GABA, neuropeptide Y, and somatostatin, but rarely contain calcium-binding proteins. Type II cells are small and lightly to moderately stained, about 20-fold more numerous than type I cells, located exclusively in supragranular layers, and found almost exclusively in the primate and human brain. In the developing cerebral cortex, nitrinergic neurons are among the earliest differentiating neurons, mostly because the dominant population of prenatal nitrinergic neurons are specific fetal subplate and Cajal-Retzius cells, which are the earliest generated neurons of the cortical anlage. However, at least in the human brain, a subpopulation of principal (pyramidal) cortical neurons transiently express NOS proteins in a regionally specific manner. In fact, transient overexpression of NOS-activity is a well-documented phenomenon in the developing mammalian cerebral cortex, suggesting that nitric oxide plays a significant role in the establishment and refinement of the cortical synaptic circuitry. Nitrinergic neurons are also present in human fetal basal forebrain and basal ganglia from 15 weeks of gestation onwards, thus being among the first chemically differentiated neurons within these brain regions. Finally, a subpopulation of human dorsal pallidal neurons transiently express NADPH-diaphorase activity during midgestation.