Neurofilament mRNA is reduced in Parkinson's disease substantia nigra pars compacta neurons

Parkinson mice show functional and molecular changes in the gut long before motoric disease onset

BACKGROUND

There is increasing evidence that Parkinson's disease (PD) might start in the gut, thus involving and compromising also the enteric nervous system (ENS). At the clinical onset of the disease the majority of dopaminergic neurons in the midbrain is already destroyed, so that the lack of early biomarkers for the disease represents a major challenge for developing timely treatment interventions. Here, we use a transgenic A30P-α-synuclein-overexpressing PD mouse model to identify appropriate candidate markers in the gut before hallmark symptoms begin to manifest.

METHODS

Based on a gait analysis and striatal dopamine levels, we defined 2-month-old A30P mice as pre-symptomatic (psA30P), since they are not showing any motoric impairments of the skeletal neuromuscular system and no reduced dopamine levels, but an intestinal α-synuclein pathology. Mice at this particular age were further used to analyze functional and molecular alterations in both, the gastrointestinal tract and the ENS, to identify early pathological changes. We examined the gastrointestinal motility, the molecular composition of the ENS, as well as the expression of regulating miRNAs. Moreover, we applied A30P-α-synuclein challenges in vitro to simulate PD in the ENS.

RESULTS

A retarded gut motility and early molecular dysregulations were found in the myenteric plexus of psA30P mice. We found that i.e. neurofilament light chain, vesicle-associated membrane protein 2 and calbindin 2, together with the miRNAs that regulate them, are significantly altered in the psA30P, thus representing potential biomarkers for early PD. Many of the dysregulated miRNAs found in the psA30P mice are reported to be changed in PD patients as well, either in blood, cerebrospinal fluid or brain tissue. Interestingly, the in vitro approaches delivered similar changes in the ENS cultures as seen in the transgenic animals, thus confirming the data from the mouse model.

CONCLUSIONS

These findings provide an interesting and novel approach for the identification of appropriate biomarkers in men.

The Cytoskeleton as a Modulator of Aging and Neurodegeneration

The cytoskeleton consists of filamentous protein polymers that form organized structures, contributing to a multitude of cell life aspects. It includes three types of polymers: the actin microfilaments, the microtubules and the intermediate filaments. Decades of research have implicated the cytoskeleton in processes that regulate cellular and organismal aging, as well as neurodegeneration associated with injury or neurodegenerative disease, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, Amyotrophic Lateral Sclerosis, or Charcot Marie Tooth disease. Here, we provide a brief overview of cytoskeletal structure and function, and discuss experimental evidence linking cytoskeletal function and dynamics with aging and neurodegeneration.

Altered neurofilament protein expression in the lateral vestibular nucleus in Parkinson's disease

A major cause of morbidity in Parkinson's disease (PD) is postural instability. The neuropathology underlying postural instability is unknown. Postural control is mediated by Deiters' neurons of the lateral vestibular nucleus (LVN), which are the brainstem origin of descending vestibulospinal reflexes. Deiters' neurons express the cytostructural protein, non-phosphorylated neurofilament protein (NPNFP). In PD, reduced expression of NPNFP in substantia nigra (SN) neurons is believed to contribute to dysfunction. It was the aim of this study to determine if there is altered expression of NPNFP in the LVN in PD. We immunolabeled NPNFP in brainstem sections of six aged controls (mean age 92 yo) and six PD donors (mean age 83 yo). Our results show there was a ~ 50% reduction in NPNFP-positive Deiters' neurons compared to controls (13 ± 2.0/section vs 25.7 ± 3.0/section; p < 0.01, repeated measures ANOVA). In contrast, there was no difference in NPNFP-positive counts in the facial nucleus between control and PD. The normalized intensity of NPNFP labeling in LVN was also reduced in PD (0.87 ± 0.05 vs 1.09 ± 0.03; p < 0.01). There was a 35% concurrent reduction in NPNFP-positive neuropil in PD relative to controls (p < 0.01). We also show there was an 84% increase (p < 0.05) in somatic lipofuscin in PD patients compared to control. Lipofuscin aggregation has been shown to increase not only with age but also with neurodegeneration. Furthermore, decreased NPNFP intensity was strongly correlated with increasing lipofuscin autofluorescence across all cases (R ² = 0.81, p < 0.01). These results show two alterations in cellular content with PD, reduced expression and intensity of NPNFP and increased lipofuscin aggregation in Deiter's neurons. These changes may contribute to degeneration of postural reflexes observed in PD.

NF-L in cerebrospinal fluid and serum is a biomarker of neuronal damage in an inducible mouse model of neurodegeneration

Accumulation of neurofilaments (NFs), the major constituents of the neuronal cytoskeleton, is a distinctive feature of neurological diseases and several studies have shown that soluble NFs can be detected in the cerebrospinal fluid (CSF) of patients with neurological diseases, such as multiple sclerosis and frontotemporal dementia. Here we have used an inducible transgenic mouse model of neurodegeneration, CamKII-TetOp25 mice, to evaluate whether NF-L levels in CSF or blood can be used as a biochemical biomarker of neurodegeneration. Induction of p25 transgene brain expression led to increase in CSF and serum NF-L levels that correlated with ongoing neurodegeneration. Switching off p25 prevented further increases in both CSF and serum NF-L levels and concomitantly stopped the progression of neurodegeneration. The levels of CSF NF-L detected in p25 mice are about 4-fold higher than the CSF levels detected in patients with chronic neurodegenerative diseases, such as symptomatic FTD (bvFTD). In addition, our data indicate that the NF-L detected in CSF is most likely a cleaved form of NF-L. These results suggest that CSF and serum NF-L are of interest to be further explored as potential translational dynamic biomarkers of neurodegeneration or as pharmacodynamics biomarkers at least in preclinical animal studies.

Quantitative expression proteomics and phosphoproteomics profile of brain from PINK1 knockout mice: insights into mechanisms of familial Parkinson's disease

Parkinson's disease (PD) is an age-related, neurodegenerative motor disorder characterized by progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta and presence of α-synuclein-containing protein aggregates. Mutations in the mitochondrial Ser/Thr kinase PTEN-induced kinase 1 (PINK1) are associated with an autosomal recessive familial form of early-onset PD. Recent studies have suggested that PINK1 plays important neuroprotective roles against mitochondrial dysfunction by phosphorylating and recruiting Parkin, a cytosolic E3 ubiquitin ligase, to facilitate elimination of damaged mitochondria via autophagy-lysosomal pathways. Loss of PINK1 in cells and animals leads to various mitochondrial impairments and oxidative stress, culminating in dopaminergic neuronal death in humans. Using a 2-D polyacrylamide gel electrophoresis proteomics approach, the differences in expressed brain proteome and phosphoproteome between 6-month-old PINK1-deficient mice and wild-type mice were identified. The observed changes in the brain proteome and phosphoproteome of mice lacking PINK1 suggest that defects in signaling networks, energy metabolism, cellular proteostasis, and neuronal structure and plasticity are involved in the pathogenesis of familial PD. Mutations in PINK1 are associated with an early-onset form of Parkinson's disease (PD). This study examines changes in the proteome and phosphoproteome of the PINK1 knockout mouse brain. Alterations were noted in several key proteins associated with: increased oxidative stress, aberrant cellular signaling, altered neuronal structure, decreased synaptic plasticity, reduced neurotransmission, diminished proteostasis networks, and altered metabolism. 14-3-3ε, 14-3-3 protein epsilon; 3-PGDH, phosphoglycerate dehydrogenase; ALDOA, aldolase A; APT1, acyl-protein thioesterase 1; CaM, calmodulin; CBR3, carbonyl reductase [NADPH] 3; ENO2, gamma-enolase; HPRT, hypoxanthine-guanine phosphoribosyltransferase; HSP70, heat-shock-related 70 kDa protein 2; IDHc, cytoplasmic isocitrate dehydrogenase [NADP+]; MAPK1, mitogen-activated protein kinase 1; MEK1, MAP kinase kinase 1; MDHc, cytoplasmic malate dehydrogenase; NFM, neurofilament medium polypeptide; NSF, N-ethylmaleimide-sensitive fusion protein; PHB, prohibitin; PINK1, PTEN-induced putative kinase 1; PPIaseA, peptidyl-prolyl cis-trans isomerase A; PSA2, proteasome subunit alpha type-2; TK, transketolase; VDAC-2, voltage-dependent anion-selective channel protein 2.

Mitochondrial complex I defects increase ubiquitin in substantia nigra

Parkinson׳s disease (PD) is the second most common neurodegenerative disorder in the developed world, and is characterized by the loss of dopaminergic (DA) neurons in the substantia nigra (SN) of midbrain. Mitochondrial complex I dysfunction has been implicated in PD pathophysiology, yet the molecular mechanism by which complex I defects may cause DA neurodegeneration remain unclear. Using Ndufs4 mouse model of mitochondrial complex I deficiency, we observed a remarkable ubiquitin protein increase in SN of Ndufs4-/- (KO) mice. By contrast, neurofilaments were significantly decreased in SN of KO mice. Furthermore, mass spectrometry and co-immunoprecipitation (Co-IP) analysis indicated an increase in ubiquitinated neurofilaments in midbrain of KO mice, whereas 20S proteasome activities were decreased, which could potentially explain the buildup of ubiquitin protein. Collectively, these data suggest that mitochondrial complex I defects cause proteasome inhibition, a consequent increase in ubiquitinated neurofilaments and other proteins, and decrease the expression of neurofilaments that could be relevant to the mechanism of DA neuronal death in PD.

Optic nerve crush induces spatial and temporal gene expression patterns in retina and optic nerve of BALB/cJ mice

Background

Central nervous system (CNS) trauma and neurodegenerative disorders trigger a cascade of cellular and molecular events resulting in neuronal apoptosis and regenerative failure. The pathogenic mechanisms and gene expression changes associated with these detrimental events can be effectively studied using a rodent optic nerve crush (ONC) model. The purpose of this study was to use a mouse ONC model to: (a) evaluate changes in retina and optic nerve (ON) gene expression, (b) identify neurodegenerative pathogenic pathways and (c) discover potential new therapeutic targets.

Results

Only 54% of total neurons survived in the ganglion cell layer (GCL) 28 days post crush. Using Bayesian Estimation of Temporal Regulation (BETR) gene expression analysis, we identified significantly altered expression of 1,723 and 2,110 genes in the retina and ON, respectively. Meta-analysis of altered gene expression (≥1.5, ≤-1.5, p < 0.05) using Partek and DAVID demonstrated 28 up and 20 down-regulated retinal gene clusters and 57 up and 41 down-regulated optic nerve clusters. Regulated gene clusters included regenerative change, synaptic plasticity, axonogenesis, neuron projection, and neuron differentiation. Expression of selected genes (Vsnl1, Syt1, Synpr and Nrn1) from retinal and ON neuronal clusters were quantitatively and qualitatively examined for their relation to axonal neurodegeneration by immunohistochemistry and qRT-PCR.

Conclusion

A number of detrimental gene expression changes occur that contribute to trauma-induced neurodegeneration after injury to ON axons. Nrn1 (synaptic plasticity gene), Synpr and Syt1 (synaptic vesicle fusion genes), and Vsnl1 (neuron differentiation associated gene) were a few of the potentially unique genes identified that were down-regulated spatially and temporally in our rodent ONC model. Bioinformatic meta-analysis identified significant tissue-specific and time-dependent gene clusters associated with regenerative changes, synaptic plasticity, axonogenesis, neuron projection, and neuron differentiation. These ONC induced neuronal loss and regenerative failure associated clusters can be extrapolated to changes occurring in other forms of CNS trauma or in clinical neurodegenerative pathological settings. In conclusion, this study identified potential therapeutic targets to address two key mechanisms of CNS trauma and neurodegeneration: neuronal loss and regenerative failure.

Functional integrity of the habenula is necessary for social play behaviour in rats

During post-weaning development, a marked increase in peer-peer interactions is observed in mammals, including humans, which is signified by the abundance of social play behaviour. Social play is highly rewarding, and known to be modulated through monoaminergic neurotransmission. Recently, the habenula has received widespread attention because of its role in the regulation of monoaminergic neurotransmission as well as in a variety of emotional and cognitive functions. Therefore, in the present study, we investigated the involvement of the habenula in social play behaviour. Using the neuronal activity maker c-fos, we showed that the habenula was activated after 24 h of social isolation in adolescent rats, and that a subsequent social play interaction reduced c-fos activity in the medial part of the lateral habenula. This suggested that habenula activity modulated the aversive properties of social isolation, which was alleviated by the positive effects of social play. Furthermore, after functional inactivation of the habenula, using a mixture of the GABA receptor agonists baclofen and muscimol, social play behaviour was markedly reduced, whereby responsiveness to play solicitation was more sensitive to habenula inactivation than play solicitation itself. Together, our data indicate an important role for the habenula in the processing of positive (i.e., social play behaviour) and negative (i.e., social isolation) social information in adolescent rats. Altered habenula function might therefore be related to the social impairments in childhood and adolescent psychiatric disorders such as autism, attention deficit/hyperactivity disorder and early-onset schizophrenia.

Critical role of calpain in spinal cord degeneration in Parkinson's disease

While multiple molecular mechanisms contribute to midbrain nigrostriatal dopaminergic degeneration in Parkinson's disease (PD), the mechanism of damage in non-dopaminergic sites within the central nervous system, including the spinal cord, is not well-understood. Thus, to understand the comprehensive pathophysiology underlying this devastating disease, postmortem spinal cord tissue samples (cervical, thoracic, and lumbar segments) from patients with PD were analyzed compared to age-matched normal subjects or Alzheimer's disease for selective molecular markers of neurodegeneration and inflammation. Distal axonal degeneration, relative abundance of both sensory and motor neuron death, selective loss of ChAT(+) motoneurons, reactive astrogliosis, microgliosis, increased cycloxygenase-2 (Cox-2) expression, and infiltration of T cells were observed in spinal cord of PD patients compared to normal subjects. Biochemical analyses of spinal cord tissues revealed associated inflammatory and proteolytic events (elevated levels of Cox-2, expression and activity of μ- and m-calpain, degradation of axonal neurofilament protein, and concomitantly low levels of endogenous inhibitor - calpastatin) in spinal cord of PD patients. Thus, pathologically upregulated calpain activity in spinal cords of patients with PD may contribute to inflammatory response-mediated neuronal death, leading to motor dysfunction. We proposed calpain over-activation and calpain-calpastatin dysregulation driving in a cascade of inflammatory responses (microglial activation and T cell infiltration) and degenerative pathways culminating in axonal degeneration and neuronal death in spinal cord of Parkinson's disease patients. This may be one of the crucial mechanisms in the degenerative process.

Review on intermediate filaments of the nervous system and their pathological alterations

Intermediate filaments (IFs) of the nervous system, including neurofilaments, α-internexin, glial fibrillary acidic protein, synemin, nestin, peripherin and vimentin, are finely expressed following elaborated cell, tissue and developmental specific patterns. A common characteristic of several neurodegenerative diseases is the abnormal accumulation of neuronal IFs in cell bodies or along the axon, often associated with impairment of the axonal transport and degeneration of neurons. In this review, we also present several perturbations of IF metabolism and organization associated with neurodegenerative disorders. Such modifications could represent strong markers of neuronal damages. Moreover, recent data suggest that IFs represent potential biomarkers to determine the disease progression or the differential stages of a neuronal disorder. Finally, recent investigations on IF expression and function in cancer provide evidence that they may be useful as markers, or targets of brain tumours, especially high-grade glioma. A better knowledge of the molecular mechanisms of IF alterations, combined to neuroimaging, is essential to improve diagnosis and therapeutic strategies of such neurodegenerative diseases and glioma.

Cellular activation in limbic brain systems during social play behaviour in rats

Positive social interactions during the juvenile and adolescent phases of life are essential for proper social and cognitive development in mammals, including humans. During this developmental period, there is a marked increase in peer-peer interactions, signified by the abundance of social play behaviour. Despite its importance for behavioural development, our knowledge of the neural underpinnings of social play behaviour is limited. Therefore, the purpose of this study was to map the neural circuits involved in social play behaviour in rats. This was achieved by examining cellular activity after social play using the immediate early gene c-Fos as a marker. After a session of social play behaviour, pronounced increases in c-Fos expression were observed in the medial prefrontal cortex, medial and ventral orbitofrontal cortex, dorsal striatum, nucleus accumbens core and shell, lateral amygdala, several thalamic nuclei, dorsal raphe and the pedunculopontine tegmental nucleus. Importantly, the cellular activity patterns after social play were topographically organized in this network, as indicated by play-specific correlations in c-Fos activity between regions with known direct connections. These correlations suggest involvement in social play behaviour of the projections from the medial prefrontal cortex to the striatum, and of amygdala and monoaminergic inputs to frontal cortex and striatum. The analyses presented here outline a topographically organized neural network implicated in processes such as reward, motivation and cognitive control over behaviour, which mediates social play behaviour in rats.

Correlational study of the serum levels of the glial fibrillary acidic protein and neurofilament proteins in Parkinson's disease patients

OBJECTIVE

To investigate changes in the serum levels of the glial fibrillary acidic protein (GFAP) and neurofilament proteins (NFs) in patients with Parkinson's disease (PD) and to determine their clinical significance.

METHODS

In this study, 82 subjects were divided into 3 groups: the PD group, the acute cerebral infarction (ACI) group, and a normal control group. The serum levels of GFAP and NFs were measured using a sandwich ELISA assay.

RESULTS

The serum levels of GFAP and NFs were significantly higher in the PD and the ACI groups than in the normal control group (P<0.05). There was no significant difference between the PD group and the ACI group (P>0.05). The serum level of GFAP in the PD group had no significant correlation with duration of the disease or age (P>0.05). The serum level of NFs in the PD group was significantly correlated with duration of the disease and age (P<0.05).

CONCLUSIONS

The serum levels of GFAP and NFs were significantly higher in the PD group than in the normal group, indicating that astrocytic activity may remain elevated during the axonal degeneration that occurs over duration of the disease, although this activity is not specific to the disease.

Neurofilamentopathy in neurodegenerative diseases

Neurofilament protein alterations are found in many neurodegenerative diseases, such as amyotrophic lateral sclerosis, Parkinson, Alzheimer, and Charcot-Marie-Tooth. Abnormal modifications of neurofilament, such as mutation, oxidation and phosphorylation, are linked to the disease-related alteration. In this review, the most recent discovery and central arguments about functions, pathological modifications, and genetic mutations related to neurofilaments in neurodegenerative diseases is presented.

Live cell imaging of cytoskeletal dynamics in neurons using fluorescence photoactivation

Alzheimer's disease and other neurodegenerative disorders share some common features at the cellular level, which are often associated with a change in cytoskeletal dynamics. Live cell imaging has been applied to study various aspects of cell physiology including cytoskeletal dynamics. Recently, fluorescence photoactivation (FPA) has been developed as a novel approach to analyze protein dynamics in living cells with high sensitivity. Here, we describe the application of FPA to determine interactions and mobility of the microtubule-associated protein tau in neurons as an example for a disease-related cytoskeletal protein and discuss further applications of FPA to study cytoskeletal dynamics in neurodegenerative diseases.

Neuronal intermediate filaments and neurodegenerative disorders

Intermediate filaments represent the most abundant cytoskeletal element in mature neurons. Mutations and/or accumulations of neuronal intermediate filament proteins are frequently observed in several human neurodegenerative disorders. Although it is now admitted that disorganization of the neurofilament network may be directly involved in neurodegeneration, certain type of perikaryal intermediate filament aggregates confer protection in motor neuron disease. The use of various mouse models provided a better knowledge of the role played by the disorganization of intermediate filaments in the pathogenesis of neurodegenerative disorders, but the mechanisms leading to the formation of these aggregates remain elusive. Here, we will review some neurodegenerative diseases involving intermediate filaments abnormalities and possible mechanisms susceptible to provoke them.

Mice with targeted disruption of neurofilament light subunit display formation of protein aggregation in motoneurons and downregulation of complement receptor type 3 alpha subunit in microglia in the spinal cord at their earlier age: a possible feature in pre-clinical development of neurodegenerative diseases

The pathogenesis of neurodegenerative diseases prior to the onset of symptoms is generally not clear. The present study has employed a mouse model with a lack of the low-molecular-weight neurofilament subunit (NFL-/-), in which formation of protein aggregates occurs in neurons, to investigate glial cellular reactions in the lumbar cord segments of NFL-/- mice at ages from 1 to 6 months. Age-matched C57BL/6 mice serve as the control. Apparent neurofilament positive aggregates in the cytoplasm of motoneurons have been observed in NFL-/- mice. However, there were no noticeable changes in microglial numbers and GFAP staining of astrocytes. Unexpectedly, a downregulation in expression of complement receptor type 3 alpha subunit (CD11b) was detected in the spinal cord of NFL-/- mice, while there was no obvious difference between NFL-/- and C57BL/6 mice in the CD11b staining intensity of macrophages from livers and spleens. In addition, retardation in morphological transformation from activated to amoeboid microglia in response to sciatic nerve injury, differential expressions of some cytokines in the lumbar cord segments and induction of Iba-1 (ionized calcium-binding adaptor molecule-1) expression in microglia were observed in NFL-/- mice. Our results suggest not only the existence of an inhibitory niche for CD11b expression in microglia in the lumbar cord segments of NFL-/- mice but also differential microglial reactions between earlier and later stages of neuropathogenesis. Although the real cause for such inhibition is still unknown, this effect might play a particular role in the survival of the abnormal protein aggregate-bearing motoneurons in the early development stage of neurodegeneration in the NFL-/- mice.

Protein aggregation in the pathogenesis of familial and sporadic Parkinson's disease

Parkinson's disease (PD) is a slowly progressive, age-related, neurodegenerative disorder. The cause and mechanism of neuronal death have been elusive. However, recent genetic, postmortem and experimental evidence show that protein accumulation and aggregation are prominent occurrences in both sporadic and familial PD. The relevance of these events to other cellular and biochemical changes, and to the neurodegenerative process, is being unraveled. It is increasingly evident that one or a combination of defects, including mutations, oxidative stress, mitochondrial impairment and dysfunction of the ubiquitin-proteasome system, lead to an excess production and aggregation of abnormal proteins in PD. In this respect, altered protein handling appears to be a central factor in the pathogenic process occurring in the various hereditary and sporadic forms of PD. This suggests that manipulation of proteolytic systems is a rational approach in the development of neuroprotective therapies that could modify the pathological course of PD.

A NUDEL-dependent mechanism of neurofilament assembly regulates the integrity of CNS neurons

The cytoskeleton controls the architecture and survival of central nervous system (CNS) neurons by maintaining the stability of axons and dendrites. Although neurofilaments (NFs) constitute the main cytoskeletal network in these structures, the mechanism that underlies subunit incorporation into filaments remains a mystery. Here we report that NUDEL, a mammalian homologue of the Aspergillus nidulans nuclear distribution molecule NudE, is important for NF assembly, transport and neuronal integrity. NUDEL facilitates the polymerization of NFs through a direct interaction with the NF light subunit (NF-L). Knockdown of NUDEL by RNA interference (RNAi) in a neuroblastoma cell line, primary cortical neurons or post-natal mouse brain destabilizes NF-L and alters the homeostasis of NFs. This results in NF abnormalities and morphological changes reminiscent of neurodegeneration. Furthermore, variations in levels of NUDEL correlate with disease progression and NF defects in a mouse model of neurodegeneration. Thus, NUDEL contributes to the integrity of CNS neurons by regulating NF assembly.

The amount of neurofilaments aggregated in the cell body is controlled by their increased sensitivity to trypsin-like proteases

Neurofilaments are synthesised and assembled in neuronal cell bodies, transported along axons and degraded at the synapse. However, in several pathological situations they aggregate in cell bodies or axons. To investigate their turnover when separated from their normal site of degradation, we used a previously described transgenic model characterised by perikaryal retention of neurofilaments, and compared the basic features of both neurofilament synthesis and degradation with that observed in normal mice. Despite the massive perikaryal aggregates, neurofilament transcript levels were found to be unchanged, whereas the total accumulation of neurofilament proteins was markedly reduced. Neurofilaments isolated from transgenic samples are more sensitive to both trypsin and α-chymotrypsin mediated proteolysis. Consistent with their greater in vitro sensitivity, trypsin immunolabeling of cell bodies was stronger in transgenic mice. These results show a novel mechanism to regulate the amount of neurofilaments when they abnormally aggregate.

Alteration in α-synuclein mRNA expression in Parkinson's disease

The presynaptic protein alpha-synuclein is considered to play an important role in the pathophysiology of Parkinson's disease (PD). Point mutations in the alpha-synuclein gene have been demonstrated in familial PD and alpha-synuclein is a major component of Lewy bodies, the pathological hallmark of the sporadic disease. It is not clear whether abnormal accumulation of alpha-synuclein is the result of abnormal levels of expression of the gene in neurodegenerative conditions. Expression of alpha-synuclein mRNA was therefore studied in control and PD brain using semiquantitative in situ hybridization. alpha-synuclein was expressed widely and hybridization signal was seen in most cortical regions, hippocampus, cerebellum, and brain stem. There was little mRNA in the striatum and no hybridization signal was detected in glia. High levels of alpha-synuclein mRNA expression in neurons did not seem to be a marker for Lewy body formation. Abundant signal was seen both in regions in which Lewy body deposition occurs commonly in idiopathic PD (PD), such as substantia nigra and frontal and temporal cortex, as well as in less susceptible regions, e.g. visual cortex. Quantitative comparison of mRNA expression in regions of predilection for Lewy body formation showed that mRNA expression was reduced significantly in melanized substantia nigra neurons and frontal cortex neurons in Parkinson's disease. In substantia nigra neurons there seemed to be a negative correlation between cellular mRNA expression and disease duration. These findings are in broad agreement with other studies of the expression of alpha-synuclein mRNA in human brain and suggest that Lewy body formation is unlikely to be the result of overexpression of alpha-synuclein.

Increased expression of multiple neurofilament mRNAs during regeneration of vertebrate central nervous system axons

Characteristic changes in the expression of neuronal intermediate filaments (nIFs), an abundant cytoskeletal component of vertebrate axons, accompany successful axon regeneration. In mammalian regenerating PNS, expression of nIFs that are characteristic of mature neurons becomes suppressed throughout regeneration, whereas that of peripherin, which is abundant in developing axons, increases. Comparable changes are absent from mammalian injured CNS; but in goldfish and lamprey CNS, expression of several nIFs increases during axon regrowth. To obtain a broader view of the nIF response of successfully regenerating vertebrate CNS, in situ hybridization and video densitometry were used to track multiple nIF mRNAs during optic axon regeneration in Xenopus laevis. As in other successfully regenerating systems, peripherin expression increased rapidly after injury and expression of those nIFs characteristic of mature retinal ganglion cells decreased. Unlike the decrease in nIF mRNAs of regenerating PNS, that of Xenopus retinal ganglion cells was transient, with most nIF mRNAs increasing above normal during axon regrowth. At the peak of regeneration, increases in each nIF mRNA resulted in a doubling of the total amount of nIF mRNA, as well as a shift in the relative proportions contributed by each nIF. The relative proportions of peripherin and NF-M increased above normal, whereas proportions of xefiltin and NF-L decreased and that of XNIF remained the same. The increases in peripherin and NF-M mRNAs were accompanied by increases in protein. These results are consistent with the hypothesis that successful axon regeneration involves changes in nIF subunit composition conducive to growth and argue that a successful injury response differs between CNS and PNS.

Neurofilament L gene is not a genetic factor of sporadic and familial Parkinson's disease

Mutations in two genes, alpha-synuclein and parkin, have been identified as some rare causes for familial Parkinson's disease (PD). alpha-Synuclein and parkin protein have subsequently been identified in Lewy bodies (LB). To gain further insight into the pathogenesis of PD we investigated the role of neurofilament light (NF-L), another component of LB aggregation. A detailed mutation search of the NF-L gene in 328 sporadic and familial PD patients of German ancestry revealed three silent DNA changes (G163A, C224T, C487T) in three unrelated patients. Analysis of the promoter region of the NF-L gene identified a total of three base pair substitutions defining five haplotypes. Association studies based on these haplotypes revealed no significant differences between PD patients and 344 control individuals. Therefore, NF-L is unlikely to play a major role in the pathogenesis of PD.

Hypothyroidism in the developing rat brain is associated with marked oxidative stress and aberrant intraneuronal accumulation of neurofilaments

The effects of hypothyroidism on parameters of oxidative stress and on intraneuronal distribution of neurofilaments have been investigated in the developing rat brain. Progressive hypothyroidism during the first 4 weeks of postnatal development led to an increase in superoxide dismutase and catalase activity, decline in the level of glutathione and mitochondrial cytochrome c oxidase activity and increase in the level of .OH radical along with enhanced protein carbonylation and lipid peroxidation. Immunocytochemical staining of cryostat sections of normal and hypothyroid cerebella from 25 day postnatal rats with anti neurofilament (NF) light chain (L) antibody showed aberrant accumulation of neurofilaments in the perikaryon of the hypothyroid Purkinje neurons in contrast to relatively uniform distribution in the controls. The morphological and biochemical alterations in the neurons of the developing hypothyroid brain are comparable to those seen in several neurodegenerative diseases.

Neurofilament-rich intraneuronal inclusions exacerbate neurodegenerative sequelae of brain trauma in NFH/LacZ transgenic mice

Several neurodegenerative disorders are characterized by filamentous inclusions in neurons that selectively degenerate. The role these inclusions play in neuron degeneration is unclear, but this issue can be investigated experimentally in relevant animal models. The NFH/LacZ transgenic (TG) mice overexpress the high-molecular-weight neurofilament (NF) subunit (NFH) fused to beta-galactosidase, and these hybrid proteins aggregate into NF-rich, filamentous neuronal cytoplasmic inclusions (NCIs) that have been implicated in the progressive, age-dependent degeneration in subsets of affected neurons. Thus, these TG mice recapitulate some of the key pathology of neurodegenerative disorders with intraneuronal inclusions. To determine if the NCIs compromise neuron survival following traumatic brain injury (TBI), 3- to 6-month old TG and wild-type (WT) mice were subjected to TBI or sham injury. At 2 weeks post-TBI, the TG group showed increased TUNEL staining and activated caspase-3 immunoreactivity in cells of cerebral cortex, adjacent white matter, and hippocampus underlying the injury site, relative to control mice, but this labeling decreased at 4 weeks and was minimal thereafter. Compared to control mice, by 8 weeks postinjury, the TG mice showed a marked decrease in neuron density and increased gliosis in the hippocampal dentate gyrus and CA3 region as well as in the lateral thalamus, while the few remaining CA3 neurons exhibited cytoskeletal alterations, decreased synaptic protein immunoreactivity, and dissolution of NCIs. The more profound long-term neurodegenerative sequelae of TBI in the NFH/LacZ mice compared to WT mice suggest that the presence of intraneuronal inclusions may impair the recovery and long-term viability of injured neurons.

Reduced expression and altered distribution of neurofilaments in neurons cultured in thyroid hormone-deficient medium

The effect of thyroid hormone (TH) deficiency on the expression of neurofilament (NF) proteins and their intracellular distribution has been examined in primary cultures of neurons from embryonic rat cerebra. Northern blot analysis showed that in TH-deficient (THdef) neurons, the expression of all three NF mRNAs (NF-L, NF-M and NF-H) are retarded by 50-70% at days 7, 15 and 25 of culture compared with their TH-supplemented (THsup) counterparts. Western blot analysis also showed a decline of 60-80% in the expression of all the NF-proteins at all time points. Immunofluorescent staining of neurons from THdef and THsup cultures at days 7, 15, and 25 with monoclonal anti NF-L antibody showed that with age, TH deficiency reduced the localization of NF-L in the cell body with a corresponding increase in the hillock and proximal axon region. The present neuronal culture system offers an excellent experimental model for studying the biochemical events responsible for the altered NF pathology in degenerating neurons.

Regulation of neurofilament gene expression by thyroid hormone in the developing rat brain

The role of thyroid hormone (TH) in the expression of neurofilament (NF) genes during the first 3-4 postnatal weeks of rat brain development has been examined. I.p. administration of TH to 2-day-old hypothyroid rats resulted in a 2-fold increase in cerebral NF-M and NF-L mRNAs, while administration to 15-day-old hypothyroid rats led to a 1.5- to 3-fold increase in NF-H mRNA within 2-4 h of hormone injection. Comparison of the level of these mRNAs in cerebra from 5, 10, 15 and 20-day-old normal and hypothyroid rats by Northern blot analysis revealed that hypothyroidism declined the expression of all three mRNAs by 50-70% at all ages examined. Western blot analysis of total protein and cytoskeletal proteins isolated from cerebras of 5, 10, 15, 20 and 25-day-old normal and hypothyroid rats demonstrated an even greater reduction (60-90%) in the expression of NF proteins in the hypothyroid cerebra during the period examined. The overall results show that TH plays an important role in regulating the expression of all three NF genes during rat brain development.

Post mortem studies in Parkinson's disease--is it possible to detect brain areas for specific symptoms?

Parkinson's disease (PD) is characterized by progressive neuronal loss associated with Lewy bodies in many subcortical nuclei leading to multiple biochemical and pathophysiological changes of clinical relevance. Loss of nigral neurons causing striatal dopamine deficiency is related to both the duration and clinical stages (severity) of the disease. The clinical subtypes of PD have different morphological lesion patterns: a) The akinetic-rigid type shows more severe cell loss in the ventrolateral part of substantia nigra zona compacta (SNZC) that projects to the dorsal putamen than the medial part projecting to caudate nucleus and anterior putamen, with negative correlation between SNZC cell counts, severity of akinesia-rigidity, and dopamine loss in the posterior putamen. Reduced dopaminergic input causes overactivity of the GABA ergic inhibitory striatal neurons projecting via the "indirect loop" to SN zona reticulata (SNZR) and medial pallidum (GPI) leading to inhibition of the glutamatergic thalamo-cortical motor loop and reduced cortical activation. b) The tremor-dominant type shows more severe neuron loss in medial than in lateral SNZC and damage to the retrorubral field A8 containing only few tyrosine hydroxylase and dopamine transporter immunoreactive (IR) neurons but mainly calretinin-IR cells. A8 that is rather preserved in rigid-akinetic PD (protective role of calcium-binding protein?) projects to the matrix of dorsolateral striatum and ventromedial thalamus. Together with area A10 it influences the strial efflux via SNZR to thalamus and from there to prefrontal cortex. Rest tremor in PD is associated with increased metabolism in the thalamus, subthalamus, pons, and premotor-cortical network suggesting an increased functional activity of thalamo-motor projections. In essential tremor, no significant pathomorphological changes but overactivity of cerebello-thalamic loop have been observed. c) In the akinetic-rigid forms of multisystem atrophy, degeneration is more severe in the lateral SNZC with severe loss of calbindin-IR cells reflecting initial degeneration of the striatal matrix in the caudal putamen with transsynaptic degeneration of striatonigral efferences that remain intact in PD. This fact and loss of striatal D2 receptors--as in advanced stages of PD--are reasons for negative response to L-dopa substitution. These data suggest different pathophysiological mechanisms of the clinical subtypes of PD that have important therapeutic implications. d) Involvement of extranigral structures in PD includes the mesocortical dopaminergic system, the noradrenergic locus coeruleus, dorsal vagal nucleus and medullary nuclei, serotonergic dorsal raphe, nucleus basalis of Meynert and other cholinergic brainstem nuclei, e.g. Westphal-Edinger nucleus (controlling pupillomotor function), posterolateral hypothalamus and the limbic system, e.g. amygdaloid nucleus, part of hippocampal formation, limbic thalamic nuclei with prefrontal projections, etc. Damage to multiple neuronal systems by the progressing degenerative process causing complex biochemical changes may explain the variable clinical picture of PD including vegetative, behavioural and cognitive dysfunctions, depression, pharmacotoxic psychoses, etc. Future comparative clinico-morphological and pathobiochemical studies will further elucidate the pathophysiological basis of specific clinical symptoms of PD and related disorders providing a broader basis for effective treatment strategies. Parkinson's disease (PD) is characterized by progressive degeneration of the nigrostriatal dopaminergic system and other subcortical neuronal systems leading to striatal dopamine deficiency and other biochemical deficits related to the variable clinical signs and symptoms of the disorder. (ABSTRACT TRUNCATED)

Transgenic mice in the study of ALS: the role of neurofilaments

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurological disorder of multiple etiologies that affects primarily motor neurons in the brain and spinal cord. Abnormal accumulations of neurofilaments (NFs) in motor neurons and a down-regulation of mRNA for the NF light subunit (NF-L) are associated with ALS, but it remains unclear to what extent these NF perturbations contribute to human disease. Transgenic mouse studies demonstrated that overexpression of normal and mutant NF proteins can sometimes provoke a motor neuronopathy characterized by the presence of abnormal NF accumulations resembling those found in ALS. Remarkably, the motor neuronopathy in transgenic mice overexpressing human NF heavy (NF-H) subunits was rescued by the co-expression of a human NF-L transgene at levels that restored a correct stoichiometry of NF-L to NF-H subunits. Transgenic approaches have also been used to investigate the role of NFs in disease caused by Cu/Zn superoxide dismutase (SOD1) mutations, which is responsible for approximately 2% cases of ALS. Studies with transgenic mice expressing low levels of a fusion NF-H/lacZ protein, in which NFs are withheld from the axonal compartment, suggested that axonal NFs are not toxic intermediates required for SOD1-mediated disease. On the contrary, overexpression of human NF-H proteins was found to confer an effective protection against mutant SOD1 toxicity in transgenic mice, a phenomenon that may be due to the ability of NF proteins to chelate calcium. In conclusion, transgenic studies showed that disorganized NFs can sometimes have noxious effects resulting in neuronopathy. However, in the context of motor neuron disease caused by mutant SOD1, there is emerging evidence that NF proteins rather play a protective role.

Neurofilaments in health and disease

This article reviews current knowledge of neurofilament structure, phosphorylation, and function and neurofilament involvement in disease. Neurofilaments are obligate heteropolymers requiring the NF-L subunit together with either the NF-M or the NF-H subunit for polymer formation. Neurofilaments are very dynamic structures; they contain phosphorylation sites for a large number of protein kinases, including protein kinase A (PKA), protein kinase C (PKC), cyclin-dependent kinase 5 (Cdk5), extracellular signal regulated kinase (ERK), glycogen synthase kinase-3 (GSK-3), and stress-activated protein kinase gamma (SAPK gamma). Most of the neurofilament phosphorylation sites, located in tail regions of NF-M and NF-H, consist of the repeat sequence motif, Lys-Ser-Pro (KSP). In addition to the well-established role of neurofilaments in the control of axon caliber, there is growing evidence based on transgenic mouse studies that neurofilaments can affect the dynamics and perhaps the function of other cytoskeletal elements, such as microtubules and actin filaments. Perturbations in phosphorylation or in metabolism of neurofilaments are frequently observed in neurodegenerative diseases. A down-regulation of mRNA encoding neurofilament proteins and the presence of neurofilament deposits are common features of human neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), Parkinson's disease, and Alzheimer's disease. Although the extent to which neurofilament abnormalities contribute to pathogenesis in these human diseases remains unknown, emerging evidence, based primarily on transgenic mouse studies and on the discovery of deletion mutations in the NF-H gene of some ALS eases, suggests that disorganized neurofilaments can provoke selective degeneration and death of neurons. An interference of axonal transport by disorganized neurofilaments has been proposed as one possible mechanism of neurofilament-induced pathology. Other factors that can potentially lead to the accumulation of neurofilaments will be discussed as well as the emerging evidence for neurofilaments as being possible targets of oxidative damage by mutations in the superoxide dismutase enzyme (SOD1); such mutations are responsible for approximately 20% of familial ALS cases.

Contribution of somal Lewy bodies to neuronal death

Neuronal degeneration occurs in the substantia nigra pars compacta (SNpc) of patients with Parkinson's disease and other Lewy body-associated disorders. Lewy bodies (LBs) are abnormal inclusions found in the SNpc and other neurons of these patients. It is not known what role LBs play in the disease process; they may be harmful to the neuron or simply an epiphenomenon of the disease process. We have previously shown that some of the neuronal death occurring in the SNpc of Lewy body-associated disorders resembles apoptosis. The present study was undertaken to determine whether apoptotic-like changes were more common in SNpc neurons with somal LBs compared to those without somal LBs. Substantia nigra from cases of Lewy body-associated disorders were labeled to colocalize apoptotic-like changes and LBs using in situ end-labeling and an anti-ubiquitin antibody. Three cases demonstrated that SNpc neurons with LBs in the perikarya had the same proportion of apoptotic-like changes as SNpc neurons without somal LBs. One case had no LB-containing SNpc neurons undergoing apoptotic-like cell death. The majority of SNpc neurons undergoing apoptotic-like cell death did not appear to contain somal LBs and thus may be dying before LB formation can occur. These results support the theory that the presence of a somal LB does not predispose a neuron to undergo apoptotic-like cell death.

Differential modification of dopamine transporter and tyrosine hydroxylase mRNAs in midbrain of subjects with Parkinson's, Alzheimer's with parkinsonism, and Alzheimer's disease

The molecular characteristics of midbrain dopamine (DA) neurons have been extensively studied in Parkinson's disease (PD). No such studies of the characteristics of midbrain DA neurons in Alzheimer's disease (AD) or Alzheimer's disease with parkinsonism (AD/Park) have been published. We examined the levels of tyrosine hydroxylase (TH) protein, and the expression of TH and dopamine transporter (DAT) mRNAs, in midbrain neurons of PD, AD, and AD/Park cases. In PD, the loss of TH protein in the ventral tier of the substantia nigra pars compacta (SNpc) of the PD group in accompanied by severe losses in the number of neurons that express TH mRNA and DAT mRNA (74% loss). Remaining neurons show a shift to higher concentrations of TH mRNA but a shift to lower concentrations of DAT mRNA per cell. Hence, there is evidence that compensation in the remaining neurons can elevate concentrations of TH mRNA and lower DAT mRNA. Alternatively, there may be a predilection for a loss of neurons with high levels of DAT mRNA and low TH mRNA levels within the SNpc of PD cases. There was no change in TH protein but an elevation of TH mRNA concentrations per neuron without any change in concentrations of DAT mRNA in the AD group. The AD/Park group did not exhibit changes in the level of TH protein, but showed a small loss (26%) of neurons in the SNpc and a greater loss in other regions of the midbrain (43-53%). Remaining DA neurons showed a marked shift to lower concentrations of DAT mRNA per neuron and a nonsignificant shift in cellular concentration of TH mRNA to higher levels. This is consistent with our previous work showing that with AD/Park there is a significant reduction in the number of DAT sites located on DA terminals in the striatum, but the midbrain neurons have not died. Our results indicate that the differential regulation of mRNAs encoding TH and DAT is similar in the parkinsonian disorders (PD and AD/Park) even though the degree of cell death is very different. This might suggest that compensatory events occur in these DA neurons in AD/Park that are similar to those in PD and that result in differential effects on mRNAs encoding TH and DAT proteins.

Delayed maturation of regenerating myelinated axons in mice lacking neurofilaments

Using the technique of homologous recombination in embryonic stem cells, we generated mice bearing a targeted disruption of the gene encoding the neurofilament light (NF-L) protein. The absence of NF-L protein in mice resulted in dramatic declines of approximately 20-fold in the levels of neurofilament medium and heavy proteins in the brain and sciatic nerve while increases were detected for other cytoskeletal proteins such as tubulin and GAP-43. Despite a lack of neurofilaments and hypotrophy of axons, the NF-L knockout mice develop normally and do not exhibit overt phenotypes. However, in both NF-L -/- and NF-L +/- mice, the regeneration of myelinated axons following crush injury of peripheral nerves was found to be abnormal. In the second week after axotomy, the number of newly regenerated myelinated axons in the sciatic nerve and facial nerve of NF-L -/- mice corresponded to only approximately 25 and approximately 5% of the number of myelinated axons found in normal mice, respectively. At this early postaxotomy stage, electron microscopy of nerve segments distal to the crush site in NF-L -/- mice revealed abundant clusters of axonal sprouts that were indicative of retarded maturation of regenerating fibers. The analysis of the distal sciatic nerve at 2 months after crush indicated that neurofilament-deficient axons have the capacity to regrow for a long distance and to remyelinate, albeit at a slower rate. These results provide the first direct evidence for a role of neurofilaments in the maturation of regenerating myelinated axons.

Monoclonal antibodies to purified cortical Lewy bodies recognize the mid-size neurofilament subunit

Lewy bodies (LBs) are filamentous intraneuronal inclusions that are hallmark lesions of Parkinson's disease, and LBs have been shown, by immunohistochemistry, to contain cytoskeletal as well as other cellular proteins. Similar LBs also occur in the cortical neurons of a subset of patients with Alzheimer's disease (AD), and cortical LBs are the predominant or sole lesions in the brains of patients with an AD-like dementia known as diffuse Lewy-body disease (DLBD). To gain insight into the biochemical composition of LBs, we generated monoclonal antibodies (mAbs) to LBs purified from the brains of patients with DLBD. Here, we describe three of these new mAbs (LB48, LB202, and LB204) that stained LBs by immunohistochemistry and recognized the medium molecular mass neurofilament (NF) protein in western blots. These results support the hypothesis that NF subunits are integral components of LBs. Continued efforts to clarify the composition of LBs are likely to lead to novel strategies for the antemortem diagnosis of LB disorders as well as to insight into the role LBs play in the degeneration of affected neurons in these disorders.

Selective degeneration fo Purkinje cells with Lewy body-like inclusions in aged NFHLACZ transgenic mice

Transgenic (NFHLacZ) mice expressing a fusion protein composed of a truncated high-molecular-weight mouse neurofilament (NF) protein (NFH) fused to beta-galactosidase (LacZ) develop inclusions in neurons throughout the CNS. These inclusions persist from birth to advanced age and contain massive filamentous aggregates including all three endogenous NF proteins and the NFHLacZ fusion protein. Further, the levels of endogenous NF proteins are selectively reduced in NFHLacZ mice. Because these inclusions resemble NF-rich Lewy bodies (LBs) in Parkinson's disease and LB dementia, we asked whether these lesions compromised the viability of affected neurons during aging. We studied hippocampal CA1 neurons, nearly all of which harbored inclusions (type I) devoid of cellular organelles, and cerebellar Purkinje cells, nearly all of which accumulated inclusions (type II) containing numerous entrapped organelles. Purkinje cells with type II inclusions began to degenerate in the NFHLacZ mice at approximately 1 year of age, and most were eliminated by 18 months of age. In contrast, there was no significant loss of type I inclusion-bearing CA1 neurons with age. These data suggest that the sequestration of cellular organelles in type II inclusions may isolate and impair the function of these organelles, thereby rendering Purkinje cells selectively vulnerable to degeneration with age as in neurodegenerative diseases of the elderly characterized by accumulation of LBs.

A simplified and rapid procedure for in situ hybridization on human, flash-frozen, post-mortem brain and its combination with immunohistochemistry

A simplified and rapid method is described for in situ hybridization (ISHH) studies of human post-mortem brain. Brain tissue was dissected into slices and was flash-frozen at -70 degrees C for storage. ISHH was carried out on 12 microns cryostat sections, post-fixed in 4% paraformaldehyde. The histology of human brain tissue prepared by this technique rivalled that of formalin-fixed, wax-embedded tissue. In ISHH studies, flash-frozen tissue gave superior results to those obtained following long-term fixation of tissue in 10% formalin with subsequent wax-embedding, or short-term prefixation in 4% paraformaldehyde. A systematic evaluation of commonly employed preparative procedures for ISHH was carried out on flash-frozen brain and a simplified protocol, consisting only of fixation and dehydration, was developed as a result of these studies. Specific hybridization of probes to a number of mRNA species was demonstrable in neurons in different brain regions. Using 0.5% glutaraldehyde/4% paraformaldehyde post-fixation, immunohistochemical labelling of TH-positive cortical catecholaminergic neurons and striatal dopaminergic terminals was successfully demonstrated in flash-frozen tissue. The same fixation technique also allowed combination of ISHH and immunohistochemistry for the simultaneous demonstration of tyrosine hydroxylase mRNA and peptide in neurons of human brain stem and cortex. mRNA and peptides in flash-frozen tissue were found to be stable for more than 3 years. ISHH could be readily performed on relatively large brain structures. In addition to permitting excellent ISHH and immunohistochemistry, alone or in combination, flash-freezing allows the maximum versatility of tissue use and does not compromise its study by other neuroscience techniques.

Selective loss of neurofilament proteins after exposure of differentiated human IMR-32 neuroblastoma cells to oxidative stress

Millimolar concentrations of ascorbate in the presence of iron can cause neuronal cell death. This study shows that the human neuronal cell line IMR-32 is sensitive to ascorbate and that cytotoxicity can be blocked by the antioxidant enzymes Cu/Zn-superoxide dismutase and catalase. There was a selective loss of neurofilament proteins after exposure to 5 or 10 mM ascorbate, as assessed by immunostaining and by Western blotting. Loss of actin or tubulin was not seen, suggesting that loss of neurofilaments is a sensitive and selective marker for free radical damage in these cells.

Association of apolipoprotein epsilon 4 allele and neuropathologic findings in patients with dementia

Apolipoprotein E (APOE) is a lipoprotein expressed in liver and brain as one of three isoforms (APOE 2, APOE 3 and APOE 4). Recent findings suggest that the presence of APOE 4 is associated with an increased risk for both familial Alzheimer's disease and late-onset Alzheimer's disease. We extended these observations by determining the frequency of APOE alleles in patients with pathologically confirmed Alzheimer's Disease (AD), Parkinson's disease (PD), diffuse Lewy Body disease (DLBD), AD with concomitant PD pathology, demented PD patients without or with concomitant AD pathology and in schizophrenics with a progressive dementia (SCHIZ+DEM). The APOE genotype was determined by restriction digestion of polymerase chain reaction-amplified DNA isolated from frozen brain samples. The frequency of the APOE epsilon 4 allele was highest among sporadic AD and DLBD patients (0.30 and 0.38, respectively) and lowest in the SCHIZ+DEM and non-demented PD patients (0.06 and 0.1, respectively). Thus, the APOE epsilon 4 allele is over-represented selectively in patients with dementias associated with plaques and tangles and/or cortical Lewy bodies, but not in demented schizophrenics or non-demented PD patients.

Alterations of intermediate filaments in various histopathological conditions

Intermediate filament proteins belong to a multigene family and constitute an important cytoskeletal component of most vertebrate cells. Their pattern of expression is tissue specific and is highly controlled during embryonic development. Numerous pathologies are known to be associated with modifications of intermediate filament organisation, although their precise role has not yet been elucidated. The present review focuses on the most recent data concerning the possible causes of intermediate filaments disorganization in specific pathologic conditions affecting the epidermis, the liver, and the nervous system. We discuss the formation of abnormal intermediate filament networks that arise as a consequence of mutations that directly affect intermediate filament structure or are induced by multifactorial causes such as modifications of post-translational processes and changes in the levels of expression.

Loss of non-phosphorylated neurofilament immunoreactivity, with preservation of tyrosine hydroxylase, in surviving substantia nigra neurons in Parkinson's disease

The distribution of neurofilament immunoreactivity in the substantia nigra was examined by immunohistochemistry in five patients dying with Parkinson's disease and six control patients dying without neurological disease. In controls, pigmented neurons in the substantia nigra were intensively labelled by SMI32, a monoclonal antibody to non-phosphorylated neurofilament protein. In the substantia nigra from patients who had Parkinson's disease, there was a pronounced reduction of SMI32 labelling intensity in surviving pigmented neurons. By contrast, tyrosine hydroxylase immunoreactivity in surviving pigmented neurons was normal. SMI32 labelling was normal in regions of the brainstem not affected by the neuropathological process of Parkinson's disease. Findings with either antibodies to phosphorylated neurofilament, or enzymatic dephosphorylation followed by SMI32 labelling, indicated that loss of SMI32 immunostaining in Parkinson's disease was not due to masking of the neurofilament epitopes by phosphorylation. Our results indicate that neurofilament proteins are particularly likely to be disrupted or destroyed by the neuropathological process of Parkinson's disease. Nevertheless, the normal appearance of tyrosine hydroxylase indicates that protein synthesising systems may be intact in surviving neurons. Loss of neurofilament immunoreactivity may prove a sensitive neuropathological marker for characterisation of degenerating neurons in Parkinson's disease.

Astrocytes modulate retinal vasculogenesis: effects on fibronectin expression

Vasculogenesis is the formation of blood-vessels by differentiation of vascular precursor cells. Experiments using retinal models were designed to test the hypothesis that astrocytes influence this process by effects on the composition of the extracellular matrix. Retinal vasculogenesis was studied in relation to the migration of astrocytes and expression of the extracellular matrix proteins laminin and fibronectin by in vivo experiments in neonatal rats. The results show that astrocytes spread into the retina just ahead of the newly formed vessels, where they probably initiate vasculogenesis. They also establish that fibronectin, but not laminin, is expressed in the zone of vasculogenesis immediately prior to vessel formation. Increased amounts of fibronectin mRNA indicate that fibronectin is synthesized by cells within this same region during this same time period. Later, as the new vessels form, differentiation of endothelial cells is correlated with the appearance of pericytes in the vessel wall and laminin in the vascular basement membrane. In vitro experiments using conditioned medium approaches showed that astrocytes stimulate endothelial cell fibronectin expression. Taken together with the in vivo observations these in vitro results suggest that fibronectin expression is an essential component in the initiation of retinal vasculogenesis. This study is the first indication that astrocytes influence the fibronectin component of the extracellular matrix during retinal vasculogenesis and that expression of fibronectin precedes that of laminin in this process.

Characterization of a shared epitope in cortical Lewy body fibrils and Alzheimer paired helical filaments

The straight fibrils of the Lewy body contain an epitope related to phosphorylation of the KSPV motif common to the C termini of the 200- and 170-kDa neurofilament subunits and tau. To further characterize this phosphorylated neurofilament/tau epitope in Lewy bodies and to analyze the constituents of isolated Lewy bodies we used a combined biochemical and immunochemical approach. In formalin-fixed paraffin-embedded tissue cortical Lewy bodies were labelled by monoclonal antibodies directed to phosphorylation-dependent KSPV epitopes in the sequences of neurofilament and phosphorylation-independent epitopes. Immunoblotting of solubilized Lewy body fibrils with the same antibodies which stained Lewy bodies in tissue sections revealed that the immunoreactive Lewy body proteins were phosphorylated neurofilament subunits. An antibody to the 68-kDa neurofilament subunit labelled Lewy bodies and Lewy body protein at 50-68 kDa. We conclude that the shared phosphorylated epitope in Lewy body fibrils and paired helical filaments is related to the common KSPV sequence in neurofilament and tau, and that all three neurofilament subunits are present in the Lewy body. This result indicates that although Lewy bodies and neurofibrillary tangles share epitopes they are comprised of distinct structural subunits.

Altered tau and neurofilament proteins in neuro-degenerative diseases: diagnostic implications for Alzheimer's disease and Lewy body dementias

The neuronal cytoskeleton is one of the most profoundly altered organelles in late life neuro-degenerative disorders that are characterized by progressive impairments in cognitive abilities. The elucidation of the protein building blocks of these organelles as well as advances in understanding how these proteins become altered in Alzheimer's disease (AD) and other less common dementing illnesses, i.e., diffuse Lewy body disease (DLBD) or the Lewy body variant of AD (LBVAD), will provide insights into the molecular basis of these disorders. Within, we review evidence that normal adult human tau is abnormally phosphorylated and converted into the subunits of AD paired helical filaments (PHFs), and that Lewy bodies (LBs) represent accumulation of altered neurofilament (NF) triplet subunits. Although the precise biological consequences of PHF and LB formation in neurons is unknown, growing evidence suggests that the formation of PHFs and LBs from normal neuronal cytoskeletal proteins could have deleterious effects on neuronal function and survival. Finally, insights into the composition of PHFs and LBs could lead to the development of novel strategies for the timely and accurate diagnosis of AD, DLBD and the LBVAD.