Peripherin expression in hippocampal neurons induced by muscle soluble factor(s)

Posttranscriptional regulation of neurofilament proteins and tau in health and disease

Neurofilament and tau proteins are neuron-specific cytoskeletal proteins that are enriched in axons, regulated by many of the same protein kinases, interact physically, and are the principal constituents of neurofibrillary lesions in major adult-onset dementias. Both proteins share functions related to the modulation of stability and functions of the microtubule network in axons, axonal transport and scaffolding of organelles, long-term synaptic potentiation, and learning and memory. Expression of these proteins is regulated not only at the transcriptional level but also through posttranscriptional control of pre-mRNA splicing, mRNA stability, transport, localization, local translation and degradation. Current evidence suggests that posttranscriptional determinants of their levels are usually regulated by RNA-binding proteins and microRNAs primarily through 3'-untranslated regions of neurofilament and tau mRNAs. Dysregulations of neurofilament and tau expression caused by mutations or pathologies of RNA-binding proteins such as TDP43, FUS and microRNAs are increasingly recognized in association with varied neurological disorders. In this review, we summarize the current understanding of posttranscriptional control of neurofilament and tau by examining the posttranscriptional regulation of neurofilament and tau by RNA-binding proteins and microRNAs implicated in health and diseases.

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.

Leukaemia inhibitory factor is over-expressed by ischaemic brain tissue concomitant with reduced plasma expression following acute stroke

Leukaemia inhibitory factor (LIF) is a glycoprotein of the interleukin-6 family, which has potent pro-inflammatory properties and is involved in regulation of neuronal differentiation. We have previously identified its upregulation in gene microarrays following acute ischaemic stroke in man. LIF expression and localization was measured in human ischaemic stroke autopsy specimens, in a rat model of middle cerebral artery occlusion (MCAO) and in human foetal neural cell cultures following oxygen-glucose deprivation (OGD) by Western blotting and immunohistochemistry. Circulating LIF was determined in the plasma of patients in the hyper-acute stroke phase using a multiplex enzyme-linked-immunosorbent serologic assay system. Patients demonstrated an increase in LIF expression in peri-infarcted regions with localization in neurons and endothelial cells of microvessels surrounding the infarcted core. The rat MCAO model showed similar upregulation in neurons with a peak increase at 90 min. Circulating serum LIF expression was significantly decreased in the hyper-acute phase of stroke. Brain-derived neurons and glia cultured in vitro demonstrated an increase in gene/protein and protein expression respectively following exposure to OGD. Increased LIF expression in peri-infarcted regions and sequestration from the peripheral circulation in acute stroke patients are characteristic of the pathobiological response to ischaemia and tissue damage.

Neuronal intermediate filaments and ALS: a new look at an old question

One of the pathological hallmarks of ALS is the presence of axonal spheroids and perikaryal accumulations/aggregations comprised of the neuronal intermediate filament proteins, neurofilaments and peripherin. These abnormalities represent a point of convergence of both familial and sporadic forms of the disease and understanding their formation may reveal shared pathways in what is otherwise considered a highly heterogeneous disorder. Here we provide a review of the basic biology of neurofilaments and peripherin and the evidence linking them with ALS disease pathogenesis.

Proteomic and biochemical analyses ofin vitro carcinogen-induced lung cell transformation: Synergism between arsenic and benzo[a]pyrene

Chronic coexposures to carcinogens inorganic arsenic and benzo[a]pyrene (B[a]P) are common in the living environment. However, little is known about their effects exerted at the proteome level. Our previous study in rat lung epithelial cells showed that cell transformation frequency increased by more than 100-fold when arsenic was given in combination with B[a]P than cells either exposed to arsenic or B[a]P alone. This demonstrated a synergism between them. Here, we reported that alterations to the proteome varied and were more pronounced in the transformed cells that were exposed to a combination of arsenic and B[a]P than to B[a]P and much less to arsenic alone when compared to passage-matched control cells. In general, three proteins belonging to intermediate filaments were found to be significantly down-regulated and six proteins belonging to antioxidative stress-, chaperone-, and glycolytic proteins were up-regulated in these transformed cells. These transformed cells were also associated with an increase of proliferation and de-differentiation. Taken together, our findings suggest that although arsenic or B[a]P alone is sufficient to induce cell transformation and alter the proteome to a similar extent, the effects of coexposure are much more pronounced. This further substantiates the notion that these carcinogens act in concert during cocarcinogenesis.

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.

The endo-lysosomal sorting machinery interacts with the intermediate filament cytoskeleton

Cytoskeletal networks control organelle subcellular distribution and function. Herein, we describe a previously unsuspected association between intermediate filament proteins and the adaptor complex AP-3. AP-3 and intermediate filament proteins cosedimented and coimmunoprecipitated as a complex free of microtubule and actin binding proteins. Genetic perturbation of the intermediate filament cytoskeleton triggered changes in the subcellular distribution of the adaptor AP-3 and late endocytic/lysosome compartments. Concomitant with these architectural changes, and similarly to AP-3-null mocha cells, fibroblasts lacking vimentin were compromised in their vesicular zinc uptake, their organellar pH, and their total and surface content of AP-3 cargoes. However, the total content and surface levels, as well as the distribution of the transferrin receptor, a membrane protein whose sorting is AP-3 independent, remained unaltered in both AP-3- and vimentin-null cells. Based on the phenotypic convergence between AP-3 and vimentin deficiencies, we predicted and documented a reduced autophagosome content in mocha cells, a phenotype previously reported in cells with disrupted intermediate filament cytoskeletons. Our results reveal a novel role of the intermediate filament cytoskeleton in organelle/adaptor positioning and in regulation of the adaptor complex AP-3.

Late onset of motor neurons in mice overexpressing wild-type peripherin

Peripherin, a type III intermediate filament (IF) protein, upregulated by injury and inflammatory cytokines, is a component of IF inclusion bodies associated with degenerating motor neurons in sporadic amyotrophic lateral sclerosis (ALS). We report here that sustained overexpression of wild-type peripherin in mice provokes massive and selective degeneration of motor axons during aging. Remarkably, the onset of peripherin-mediated disease was precipitated by a deficiency of neurofilament light (NF-L) protein, a phenomenon associated with sporadic ALS. In NF-L null mice, the overexpression of peripherin led to early- onset formation of IF inclusions and to the selective death of spinal motor neurons at 6 mo of age. We also report the formation of similar peripherin inclusions in presymptomatic transgenic mice expressing a mutant form of superoxide dismutase linked to ALS. Taken together, these results suggest that IF inclusions containing peripherin may play a contributory role in motor neuron disease.

Peripherin is not a contributing factor to motor neuron disease in a mouse model of amyotrophic lateral sclerosis caused by mutant superoxide dismutase

Peripherin is a type III intermediate filament protein detected in axonal spheroids associated with amyotrophic lateral sclerosis (ALS). The overexpression of peripherin induces degeneration of spinal motor neurons during aging in transgenic mice and in cultured neuronal cells derived from peripherin transgenic embryos. Here, we investigated whether peripherin is a contributor of pathogenesis in mice overexpressing a mutant superoxide dismutase 1 (SOD1(G37R)) gene linked to familial ALS. This was done by the generation and analysis of SOD1(G37R) mice that either overexpress a peripherin transgene (G37R;TgPer mice) or lack the endogenous peripherin gene (G37R;Per-/- mice). Surprisingly, upregulation or suppression of peripherin expression had no effects on disease onset, mortality, and loss of motor neurons in SOD1(G37R) mice. These results provide compelling evidence that peripherin is not a key contributor of motor neuron degeneration associated with toxicity of mutant SOD1.

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.

SSR180575 (7-chloro-N,N,5-trimethyl-4-oxo-3-phenyl-3,5-dihydro-4H-pyridazino[4,5-b]indole-1-acetamide), a peripheral benzodiazepine receptor ligand, promotes neuronal survival and repair

In the present study, we have investigated the potential neuroprotective effects of a novel peripheral benzodiazepine binding site (PBR) ligand, 7-chloro-N,N,5-trimethyl-4-oxo-3-phenyl-3,5-dihydro-4H-pyridazino[4,5-b]indole-1-acetamide (SSR180575), in models of central and peripheral neurodegeneration in vivo and its effect on steroid concentrations in plasma and nervous tissue. SSR180575 shows high affinity (IC(50), 2.5-3.5 nM) and selectivity for the rat and human PBR and potently inhibits the in vivo binding of [(3)H]alpidem to PBR in the rat brain and spleen after oral or i.p. administration (ID(50), 0.1-0.3 mg/kg). In an experimental model of motoneuron degeneration induced by facial nerve axotomy in the immature rat, SSR180575 given i.p. or orally for 8 days rescued facial motoneurons, increasing their survival by 40 to 72% at 6 and 10 mg/kg p.o. b.i.d. Moreover, in this model, SSR180575 (10 mg/kg p.o. b.i.d.) increased by 87% the number of motoneurons immunoreactive to peripherin, a type III intermediate filament, whose expression is up-regulated during nerve regeneration. SSR180575 also improved functional recovery in acrylamide-induced neuropathy in the rat when given therapeutically at 2.5 to 10 mg/kg/day p.o. Furthermore, SSR180575 (3 mg/kg i.p. b.i.d.) accelerated functional recovery of the blink reflex after local injury of the facial nerve in the rat. SSR180575 increased pregnenolone accumulation in the brain and sciatic nerve (+100% at 3 mg/kg i.p.), suggesting that its neuroprotective effects are steroid-mediated. These results indicate that PBR ligands (e.g., SSR180575) promote neuronal survival and repair in axotomy and neuropathy models and have potential for the treatment of neurodegenerative diseases (e.g., peripheral neuropathies or amyotrophic lateral sclerosis).

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.

Cytoskeletal abnormalities in amyotrophic lateral sclerosis: beneficial or detrimental effects?

Cytoskeletal abnormalities have been reported in cases of amyotrophic lateral sclerosis (ALS) including abnormal inclusions containing neurofilaments (NFs) and/or peripherin, reduced mRNA levels for the NF light (NF-L) protein and mutations in the NF heavy (NF-H) gene. Recently, transgenic mouse approaches have been used to address whether cytoskeletal changes may contribute to motor neuron disease. Mice lacking one of the three NF subunits are viable and do not develop motor neuron disease. Nonetheless, mice with null mutations for NF-L or for both NF-M and NF-H genes developed severe atrophy of ventral and dorsal root axons. The atrophic process is associated with hind limb paralysis during aging in mice deficient for both NF-M and NF-H proteins. The overexpression in mice of transgenes coding for wild-type or mutant NF proteins can provoke abnormal NF accumulations, axonal atrophy and sometimes motor dysfunction. However, the perikaryal NF accumulations are generally well tolerated by motor neurons and, except for expression of a mutant NF-L transgene, they did not provoke massive motor neuron death. Increasing the levels of perikaryal NF proteins may even confer protection in motor neuron disease caused by ALS-linked mutations in the superoxide dismutase (SOD1). In contrast, the overexpression of wild-type peripherin, a type of IF gene upregulated by inflammatory cytokines, provoked the formation of toxic IF inclusions with the high-molecular-weight NF proteins resulting in the death of motor neurons during aging. These results together with the detection of peripherin inclusions at early stage of disease in mice expressing mutant SOD1 suggest that IF inclusions containing peripherin may play a contributory role in ALS pathogenesis.

Combined effects of GDNF, BDNF, and CNTF on motoneuron differentiation in vitro

We have previously shown that glial cell line-derived neurotrophic factor (GDNF), in addition to promoting the survival of dopaminergic neurons in cultures from embryonic rat ventral mesencephalon,also increases the activity of choline acetyltransferase (ChAT) in the cranial motoneurons present in these cultures (Zurn et al.: Neuroreport 6:113-118, 1994). By using the intermediate filament protein peripherin as a motoneuron marker, we report here that GDNF increases the number of motoneurons as well as the length of their neurites. Brain-derived neurotrophic factor (BDNF) and ciliary neurotrophic factor (CNTF) also promote ChAT activity, motoneuron survival, and neurite outgrowth in these cultures, but to varying degrees. Although these three molecules have similar effects on cultured motoneurons, we provide evidence for a distinct mode of action of GDNF, BDNF, and CNTF, since combinations of GDNF and BDNF, GDNF and CNTF, and BDNF and CNTF have either additive or synergistic effects on ChAT activity and motoneuron number. In addition to the previously described motoneuron-specific neurotrophic factors BDNF and CNTF, GDNF combined with the latter two factors may provide an important tool for the treatment of human motoneuron diseases such as amyotrophic lateral sclerosis and spinal muscular atrophy, both by increasing efficiency of treatment, and by decreasing the likelihood of deleterious side-effects.

Three different states of the chromatin structure of the mouse peripherin gene

The chromatin structure of the mouse peripherin gene domain was analyzed in peripherin-positive and -negative cell lines. At least nine DNase I hypersensitive sites (HSS) are present within the 20-kb peripherin domain in the mouse neuroblastoma cell lines which express peripherin. Three of them are situated in intron I and intron III, the others being distributed within the 5' flanking region up to -5.5 kb. The presence of these sites was also investigated in the peripherin chromatin domain of peripherin-negative cell lines. Two other types of HSS distribution were observed along the peripherin gene according to the category of cell considered: constantly peripherin-negative cells, or negative cells arising from transiently peripherin-expressing precursors. From comparison of HSS patterns in these cell lines with those of neuroblastoma cells, it can be predicted that HSS located in the region -1500/+800 bp participate in cell-specific expression of the mouse peripherin gene.

Compartmentation of alpha-internexin and neurofilament triplet proteins in cultured hippocampal neurons

Intermediate filaments comprise an integral part of the neuronal cytoskeleton. However, little is known about their function, and there remains some uncertainty about their precise subcellular localization. We examined the timing of expression and distribution of alpha-internexin, neurofilament triplet proteins and peripherin using immunocytochemistry in cultured hippocampal neurons. alpha-Internexin immunostaining was present in all neurons at all developmental stages. Immunostaining appeared as long filaments in axons and short fragments in dendrites which extended into dendritic spines. The presence of alpha-internexin in dendritic spines was confirmed in situ by electron microscopy of rat hippocampal tissue sections and suggests that this intermediate filament may serve as a link between cytoskeletal elements in dendritic shafts and spines. In culture, immunostaining using antibodies against individual triplet protein subunits indicated that light (NF-L) and middle (NF-M) subunits were first expressed in cells shortly after the initiation of axonal outgrowth. Expression of the heavy (NF-H) subunit occurred a few days later. Although timing and localization of expression did not correlate with the initiation of axonal or dendritic processes, it was coincident with periods of rapid outgrowth. Triplet proteins were more abundant in axons and appeared to be incorporated into lengthier filaments than in dendrites. Highly phosphorylated NFH/M immunoreactivity was polarized to axons after 6 days in culture. The distribution of one NF-H epitope was restricted to GABAergic neurons in mature cultures, suggesting a cell-type specific modification. Peripherin was not detectable at any time in hippocampal cultures. Our results show that intermediate filaments are integral components of the neuronal cytoskeleton of cultured hippocampal neurons throughout development. Furthermore, the localization of alpha-internexin suggests that it may be involved in the formation or maintenance of dendritic spines.

Integration of intermediate filaments into cellular organelles

The intermediate filaments represent core components of the cytoskeleton and are known to interact with several membranous organelles. Classic examples of this are the attachment of keratin filaments to the desmosomes and the association of the lamin filament meshwork with the inner nuclear membrane. At this point, the molecular mechanisms by which the filaments link to membranes are not clearly understood. However, since a substantial body of information has been amassed, the time is now ripe for comparing notes and formulating working hypotheses. With this objective in mind, we review here pioneering studies on this subject, together with work that has appeared more recently in the literature.

Transplanted human neurons derived from a teratocarcinoma cell line (NTera-2) mature, integrate, and survive for over 1 year in the nude mouse brain

Retinoic acid (RA) induces a human teratocarcinoma cell line (NTera-2 or NT2) to give rise exclusively to post-mitotic neuron-like (NT2N) cells, but NT2N cells never acquire a fully mature neuronal phenotype in vitro. To determine whether NT2N cells can mature into adult neuron-like cells in vivo, purified NT2N cells were grafted into different regions of the central nervous system (CNS) of adult and neonatal athymic mice, and the grafts were examined immunohistochemically by light, confocal, and electron microscopy using antibodies to a panel of developmentally regulated neuronal polypeptides. NT2N grafts were distinguished from endogenous mouse neurons with antibodies that recognize human or murine specific epitopes in selected neuronal polypeptides. Viable NT2N cells were identified in > 89% of graft recipients (N = 90), and some grafts survived 14 months. Within 3 weeks of implantation, grafted NT2N cells re-extended their processes, and the location of the grafts (e.g., septum versus neocortex) appeared to determine the extent to which processes were elaborated. Within the early post-transplantation period, grafted NT2N cells expressed the same neuronal polypeptides as their in vitro counterparts. However, between 6 weeks and 4-6 months post-implantation, the grafted NT2N cells progressively acquired the molecular phenotype of fully mature in vivo neurons as evidenced by dramatically increased expression of the most highly phosphorylated isoforms of the heavy neurofilament subunit, and the de novo expression of adult CNS tau. Notably, the time course for the extension of processes and the expression of neuronal polypeptides by NT2N grafts was similar in neonatal and adult mice. Although grafted NT2N cells formed synapse-like structures and elaborated dendrites and axons, these axons remained unmyelinated. Finally, none of the transplanted NT2N cells reverted to a neoplastic state. These studies demonstrate that pure populations of grafted human NT2N cells acquire a fully mature neuronal phenotype in vivo, and that these cells integrate and survive for > 1 year post-implantation in the mouse CNS. These human neuron-like cells are an attractive model system for studies of neuronal development, polarity and transplantation.

Cytoplasmic chaperonin complexes enter neurites developing in vitro and differ in subunit composition within single cells

Chaperonins containing t-complex polypeptide-1 (CCT) are cytosolic molecular chaperone particles implicated especially in the biogenesis of cytoskeletal proteins by promoting the correct folding of the major ubiquitous cytoskeletal components, tubulin and actin. We have purified cytosolic chaperonins from the ND7/23 cell line, determined their subunit composition and examined changes in the intracellular locations of their components during differentiation of ND7/23 cells to a neuronal phenotype by using immunocytochemistry and immunoblots. Chaperonins containing the CCT alpha (TCP1) subunit enter neuritic processes and are particularly noticeable at the leading edge of growth cone-like structures where they co-localise with actin. Chaperonins containing three other components (CCT beta, epsilon and gamma), however, remain predominantly restricted to perikaryal cytoplasm. These findings suggest a heterogeneous population of chaperonin particles within single differentiated ND7/23 cells and this may reflect specialisation of chaperonin function in different cytoplasmic compartments of a neurone. Further, since ribosomes do not enter neurites while CCT alpha-containing chaperonins do, the latter may play roles, subsequent to translation, which influence cytoskeletal elaboration during neuritogenesis.