Immunocytochemical studies of neurofilament antigens in the neurofibrillary pathology induced by aluminum

The Involvement of Post-Translational Modifications in Regulating the Development and Progression of Alzheimer's Disease

Post-translational modifications (PTMs) have been recently reported to be involved in the development and progression of Alzheimer's disease (AD). In detail, PTMs include phosphorylation, glycation, acetylation, sumoylation, ubiquitination, methylation, nitration, and truncation, which are associated with pathological functions of AD-related proteins, such as β-amyloid (Aβ), β-site APP-cleavage enzyme 1 (BACE1), and tau protein. In particular, the roles of aberrant PTMs in the trafficking, cleavage, and degradation of AD-associated proteins, leading to the cognitive decline of the disease, are summarized under AD conditions. By summarizing these research progress, the gaps will be filled between PMTs and AD, which will facilitate the discovery of potential biomarkers, leading to the establishment of novel clinical intervention methods against AD.

Cytoskeletal abnormalities in long-term embryonic CNS transplants isolated within peripheral nerve

Cells from the fetal central nervous system (CNS) of rat embryos survive and differentiate when transplanted into the peripheral nervous system (PNS) of adult rats. The experiments described here were aimed at investigating selected molecular and ultrastructural features of dissociated CNS cells from the telencephalon of 12-day-old embryos isolated for long periods of time within PNS segments. Neurons and glia of grafts examined 6-12 months after transplantation into the PNS developed several cytoskeletal abnormalities. In neurons, these changes included Hirano bodies within dendrites and a marked perikaryal immunoreactivity to RT97, a monoclonal antibody that normally recognizes in neuronal processes the phosphorylated 200 kDa protein subunit of neurofilaments. Rosenthal fibres were seen within the glial cells. Similar-looking abnormalities have been described in certain human and animal neurodegenerative diseases and in ageing. Although a relationship between the changes in these long-term neural transplants and such diseases is unknown, these observations provide an opportunity for studying their pathogenesis within laboratory conditions.

Neurotoxic effects of dietary aluminium

Neurochemical responses to chronic oral aluminium administration have been studied in rats. Aluminium (0.3%) was added to drinking water of adult rats for four weeks or longer and weanling rats were given aluminium for eight weeks. Selective cognitive impairment was demonstrated in the adult rats. Aluminium inhibited calcium flux and phosphoinositide metabolism, one product of which (inositol 1,4,5-trisphosphate) modulates intracellular calcium levels. In weanling rats aluminium decreased the in vivo concentration of inositol 1,4,5-trisphosphate in the hippocampus. An increase in cyclic AMP concentrations by 30-70% in various brain regions in adult and weanling rats was found. Aluminium enhanced agonist-stimulated but not basal cyclic AMP production in vitro. It was postulated that aluminium inhibits the GTPase activity of the stimulatory G protein, Gs, leading to prolonged activation of Gs after receptor stimulation and increased cyclic AMP production. Aluminium treatment also increased the phosphorylation of microtubule-associated protein 2 (MAP-2) and the 200 kDa neurofilament protein (NF-H) but several other phosphoproteins were unaffected. Concentrations of seven structural proteins--MAP-2, tau, NF-H, NF-M (150 kDa), NF-L (68 kDa), tubulin and spectrin--were measured in rat brain regions by immunoblot methods. MAP-2 was most consistently decreased. These studies show that chronic oral aluminium administration to rats has significant neurochemical consequences. Three sites of action are implicated: altered calcium homeostasis, enhanced cyclic AMP production, and changes in cytoskeletal protein phosphorylation states and concentrations.

Aluminum in hippocampal neurons from humans with Alzheimer's disease

Using a staining technique developed in 2004, we examined hippocampal tissue from autopsy-confirmed cases of Alzheimer's disease (AD) and controls. The stain disclosed aluminum in cells and subcellular structure. All pyramidal neurons in these aged specimens appeared to exhibit at least some degree of aluminum staining. Many displayed visible aluminum only in their nucleolus. At the other extreme were neurons that stained for aluminum throughout their nucleus and cytoplasm. The remainder exhibited intermediate degrees of staining. On the basis of their aluminum staining patterns, all pyramidal neurons could be classified into stages that indicated two distinct neuropathological processes, either (1) progressive increase of nuclear aluminum (often accompanied by granulovacuolar degeneration with granules that stain for aluminum) or (2) formation of neurofibrillary tangles (NFTs) in regions of aluminum-rich cytoplasm, especially in AD brain tissue. In the latter process, intraneuronal NFTs appeared to displace nuclei and then enucleate the affected neurons during the course of their transformation into extracellular NFTs. Given that the NFTs we observed in human neurons always developed in conjunction with cytoplasmic aluminum, we hypothesize that aluminum plays an important role in their formation and should therefore be reconsidered as a causative factor for AD.

Cannabinoid-receptor 1 null mice are susceptible to neurofilament damage and caspase 3 activation

Administered cannabinoids have been shown to ameliorate signs of CNS inflammatory disease in a number of animal models, including allergic encephalomyelitis. More recently, neuroprotective actions have been attributed to activation of the cannabinoid 1 receptor in a number of in vitro and in vivo models. One of these, chronic relapsing experimental allergic encephalomyelitis, is considered a robust analog of multiple sclerosis. In this study, spinal cord tissue from cannabinoid receptor 1 knockout mice was analyzed for neurofilament H and myelin basic protein content, as markers of neurons/axons and myelin respectively, during the course of chronic relapsing experimental allergic encephalomyelitis. Dephosphorylation of a neurofilament H epitope, immunoreactive to the SMI32 antibody, was assessed as a marker of axonal damage and levels of the endpoint cell death mediator caspase 3 were evaluated. It was found that both neurofilament and myelin basic protein levels decrease over the course of disease, indicating concomitant neuronal/axonal loss and demyelination. Loss of each marker was more severe in cannabinoid receptor 1 knockout animals. Increased SMI32 reactivity was observed as disease progressed. SMI32 reactivity was significantly increased in knockout animals over wildtype counterparts, an indication of greater axonal dephosphorylation and injury. Active caspase 3 levels were increased in all animals during disease, with knockout animals displaying highest levels, even in knockout animals prior to disease induction. These results indicate that lack of the cannabinoid receptor 1 is associated with increased caspase activation and greater loss and/or compromise of myelin and axonal/neuronal proteins. The increase of caspase 3 in knockout mice prior to disease induction indicates a latent physiological effect of the missing receptor. The data presented further strengthen the hypothesis of neuroprotection elicited via cannabinoid receptor 1 signaling.

Impairment of anterograde and retrograde neurofilament transport after anti-kinesin and anti-dynein antibody microinjection in chicken dorsal root ganglia

The purpose of the present study was to investigate the participation of the motor proteins kinesin and dynein in axonal transport of neurofilaments (NF) in cultured dorsal root ganglia neurons. Therefore, we performed live-recording studies of the green fluorescent protein-tagged neurofilament M (GFP-NF-M) to assay transport processes in neurons. Co-localization studies revealed that GFP-NF-M was capable to build a functional NF network with other NF subunits, including phosphorylated heavy neurofilaments (NF-H-PH). Time-lapse recordings using confocal laser scanning microscopy exhibited fast transport of NF dots in anterograde and retrograde direction through a photobleached gap. Following microinjection of anti-kinesin antibodies or colchicine treatment an impairment of anterograde as well as retrograde NF transport was observed during live-recording experiments. In contrast, microinjection of anti-dynein antibodies only impaired retrograde transport of NF whereas the anterograde movement of GFP-NF-M was unaffected. Treatment of the cells with unspecific antibodies had no effect.

Inorganics and hormesis

The article is a comprehensive review of the occurrence of hormetic dose-response relationships induced by inorganic agents, including toxic agents, of significant environmental and public health interest (e.g., arsenic, cadmium, lead, mercury, selenium, and zinc). Hormetic responses occurred in a wide range of biological models (i.e., plants, invertebrate and vertebrate animals) for a large and diverse array of endpoints. Particular attention was given to providing an assessment of the quantitative features of the dose-response relationships and underlying mechanisms that could account for the biphasic nature of the hormetic response. These findings indicate that hormetic responses commonly occur in appropriately designed experiments and are highly generalizeable with respect to biological model responses. The hormetic dose response should be seen as a reliable feature of the dose response for inorganic agents and will have an important impact on the estimated effects of such agents on environmental and human receptors.

Axonal and perikaryal involvement in chronic inflammatory demyelinating polyneuropathy

OBJECTIVES

To assess the extent of loss of myelinated nerve fibres and spinal motor neuron loss in chronic inflammatory demyelinating polyneuropathy (CIDP), a clinicopathological study was conducted on biopsied sural nerves and necropsied spinal cords from patients with CIDP.

METHODS

The myelinated fibre pathology of 71 biopsied sural nerves and motor neuron pathology of nine necropsied spinal cords at L4 levels in patients with CIDP were quantitatively and immunohistochemically assessed.

RESULTS

Myelinated nerve fibre density was significantly diminished to 65.4% of the control values (p <0.0001), correlating inversely with the extent of segmental demyelination and remyelination (r = -0.43, p < 0.0005) and duration of illness (r = -0.31, p < 0.01). Numbers of large spinal motor neurons in CIDP were variably but significantly diminished (range from 46.0 to 97.6% of the age matched control value (p < 0.005)), and reactive astrogliosis was evident in the ventral horn in CIDP. The frequency of ventral horn neurons exhibiting central chromatolysis and the accumulation of phosphorylated high molecular weight neurofilament protein was significantly higher in CIDP than in controls (p<0.01 and p<0.05).

CONCLUSIONS

The loss of nerve axons and spinal motor neurons is common in CIDP, and extensive in some cases. These neuronal and axonal losses may influence the functional prognosis in CIDP.

Aluminum enhances iron uptake and expression of neurofibrillary tangle protein in neuroblastoma cells

Aluminum (Al) and iron (Fe) have been implicated as playing a toxic role in the pathologic lesions of Alzheimer's disease. In the following report we describe the uptake and toxicity of Al, the effect of Al on Fe uptake, and the expression of neurofibrillary tangle (NFT) protein in murine neuroblastoma cells (Neuro 2A). Significant cell Al uptake and inhibition of cell growth were seen in Neuro 2A cells at 24, 48, 72, and 96 h after plating in medium containing Al transferrin (Al-Tf) and Al citrate. Al-loaded Neuro 2A cells showed increased rates of 59Fe and 125I-Tf uptake and total cellular Fe content at 24, 48, 72, and 96 h after plating compared with control cultures. Significant increases in NFT protein staining were detected in Al-exposed cells at 72 and 96 h in culture compared with controls. The intensity of NFT staining in Al-loaded cells was directly proportional to the time in culture. There was no difference in malonyldialdehyde levels measured in control versus Al-loaded Neuro 2A cells. These results suggest that the accumulation of Al in Neuro 2A cells resulted in increased uptake of Fe, inhibition of cell growth, and expression of NFT protein, partially mimicking the pathological hallmarks of Alzheimer's disease. This model system may also be applicable for Al-induced dialysis dementia, because the Al concentrations at which cell toxicity occurred can be found in dialysis patients.

What are the facts and artifacts of the pathogenesis and etiology of Alzheimer disease?

Over the past decade, an increased clinical awareness, together with advances in biochemical, cellular, and molecular analyses, have catapulted the study of Alzheimer disease to the forefront of biomedical research. During this time, a great number of theories, regarding disease pathogenesis, have come and gone but several have persisted. Here, we critically evaluate these theories in an attempt to delineate the facts from the artifacts.

Cisplatin induced intermediate filament reorganization and altered mitochondrial function in 3T3 cells and drug-sensitive and -resistant Walker 256 cells

Cisplatin has acute but reversible effects on the organization of the intermediate filament component of the cytoskeleton as well as the mitochondrial function of cultured 3T3 cells. These effects do not involve major changes in total cell or cytoskeletal protein synthesis and appear to be distinct from the long-term cytotoxicity produced by the drug. Cells treated with similar concentrations of second-generation platinum compounds, which have reduced nephrotoxic effects in vivo, do not exhibit alterations in intermediate filament organization nor mitochondrial rhodamine 123 fluorescence. Similar studies with cisplatin-sensitive and -resistant lines of rat Walker 256 cells indicated that the drug-induced intermediate filament collapse and decreased mitochondrial rhodamine 123 fluorescence correlated with the susceptibility of these cells to the lethal effects of cisplatin.

Neurofilament proteins in Y-cells of the cat lateral geniculate nucleus: normal expression and alteration with visual deprivation

We examined neurofilament staining in the normal and visually deprived lateral geniculate nucleus (LGN), using the SMI-32 antibody. This antibody preferentially stains LGN cells that display the morphological characteristics of Y-cells. The soma sizes of SMI-32-stained cells were consistent with those of the overall population of Y-cells, and the Golgi-like staining of their dendrites revealed a radial distribution that often crossed laminar boundaries. Labeled cells were distributed within the A laminae (primarily near laminar borders), the magnocellular portion of the C laminae, and the medial intralaminar nucleus, but they were absent in the parvocellular C laminae. Electron microscopic examination of SMI-32-stained tissue revealed that staining was confined to somata, dendrites, and large myelinated axons. Retinal synapses on SMI-32-labeled dendrites were primarily simple axodendritic contacts; few triadic arrangements were observed. In the LGN of cats reared with monocular lid suture, SMI-32 staining was decreased significantly in the A laminae that received input from the deprived eye. Dephosphorylation of the tissue did not alter the cellular SMI-32 staining patterns. Analysis of staining patterns in the C laminae and monocular zone of the A laminae suggests that changes in the cytoskeleton after lid suture reflect cell class and not binocular competition. Taken together, the results from normal and lid-sutured animals suggest that the cat LGN offers a unique model system in which the cytoskeleton of one class of cells can be manipulated by altering neuronal activity.

Aluminum inhibits neurofilament assembly, cytoskeletal incorporation, and axonal transport. Dynamic nature of aluminum-induced perikaryal neurofilament accumulations as revealed by subunit turnover

The mechanism by which aluminum induces formation of perikaryal neurofilament (NF) inclusions remains unclear. Aluminum treatment inhibits: 1. The incorporation of newly synthesized NF subunits into Triton-insoluble cytoskeleton of axonal neurites; 2. Their degradation and dephosphorylation; 3. Their translocation into axonal neurites. It also fosters the accumulation of phosphorylated NFs within perikarya. In the present study, we addressed the relationship among these effects. Aluminum reduced the assembly of newly synthesized NF subunits into NFs. During examination of those subunits that did assemble in the presence of aluminum, it was revealed that aluminum also interfered with transport of newly assembled NFs into axonal neurites. Similarly, a delay in axonal transport of microinjected biotinylated NF-H was observed in aluminum-treated cells. Aluminum also inhibited the incorporation of newly synthesized and microinjected subunits into the Triton-insoluble cytoskeleton within both perikarya and neurites. Once incorporated into Triton-insoluble cytoskeletons, however, biotinylated subunits were retained within perikarya of aluminum-treated cells to a greater extent than within untreated cells. Notably, these subunits were depleted in the presence and absence of aluminum within 48 h, despite the persistence of the aluminum-induced perikaryal accumulation itself, suggesting that individual NF subunits undergo turnover even within aluminum-induced perikaryal accumulations. These findings demonstrate that aluminum interferes with multiple aspects of neurofilament dynamics and furthermore leaves open the possibility that aluminum-induced perikaryal NF whorls may not represent permanent structures, but rather may require continued recruitment of cytoskeletal constituents.

Wernicke's encephalopathy with ballooned neurons in the mamillary bodies: an immunohistochemical study

Two cases of Wernicke's encephalopathy with the rare phenomenon of ballooned neurons in the mamillary bodies are reported. Both patients suffered from acute Wernicke's symptoms starting approximately two weeks before death. The mamillary bodies contained grossly enlarged, ballooned neurons, in one case associated with focal necrosis. The affected neurons were immunoreactive for phosphorylated neurofilament (160 and 200 kDa), and synaptophysin. Ubiquitin and alpha beta-crystallin expression were not detected. The mamillo-thalamic tract appeared normal in both cases. There was a marked associated microglial reaction, as shown by the antibody Ki-MIP. It is concluded that the ballooning of mamillary neurons reflects an acute retrograde reaction to primarily axonal damage. Rather than being a rare manifestation of the disease, these cases may constitute a typical intermediate early stage (10-15 days) in the development of Wernicke's encephalopathy).

Plaque biogenesis in brain aging and Alzheimer's disease. I. Progressive changes in phosphorylation states of paired helical filaments and neurofilaments

Paired helical filament (PHF)/tau immunoreactive dystrophic neurites are a common pathological feature in the brain of patients with Alzheimer's disease. Recent studies suggest that swollen neurofilament-immunoreactive neurites are also present in senile plaques. In the present study, we investigated whether PHF/tau-positive dystrophic neurites are located in all subtypes of plaques and whether swollen neurofilament-immunoreactive neurites are hyper-phosphorylated, using a battery of antibodies to PHF/tau, neurofilament, and beta-amyloid protein. PHF/tau-positive dystrophic neurites were present in and around nearly all subtypes of plaques, including small amyloid deposits, diffuse plaques, and perivascular plaques in the hippocampal formation of Alzheimer brain. The earlier changes were detectable with AT8 antibody and later changes with PHF-1 antibody. Plaque-associated PHF/tau-positive dystrophic neurites were rare or absent in the hippocampal formation of normal aged brain. Swollen neurofilament-positive neurites appeared to be hyper-phosphorylated in Alzheimer's disease and to a lesser degree in aged control brains. Neurites that contained hyper-phosphorylated tau as well as neurofilament were strongly argentophilic because both populations of dystrophic neurites stained with silver stains. Swollen neurofilament-positive plaque-associated neurites were often present in the absence of PHF/tau-positive plaque-associated dystrophic neurites. These data suggest that PHF/tau-positive dystrophic neurites are a common component of all subtypes of plaques in Alzheimer brain and neurofilament protein in swollen neurites, like tau protein, is hyper-phosphorylated. Hyper-phosphorylated neurofilaments in plaque-associated neurites may represent one of the earliest cytoskeletal changes in vulnerable neurons in Alzheimer's disease and aged control brains.

Alterations in neural intermediate filament organization: functional implications and the induction of pathological changes related to motor neuron disease

The properties regulating the supramolecular organization of neural intermediate filament (NIF) networks have been investigated in cultured dorsal root ganglion (DRG) neurons. The studies described take advantage of the ability of endogenous NIF to incorporate purified biotinylated neurofilament triplet (NFT) proteins, NF-L, NF-M and NF-H. When injected at concentrations of 0.8-1.0 mg/ml injection buffer, each of these proteins is incorporated without perturbing the endogenous NIF network. However, at progressively higher concentrations, NF-H induces the aggregation and accumulation of NIF in the cell body. Subsequent to the induction of these aggregates, numerous alterations in the cytoarchitecture of neurons can be detected. The latter occur in a temporal sequence which appears to begin with the fragmentation of the Golgi complex. At later times, accumulation of mitochondria within the proximal region of neurites, peripheralization of the nucleus, and a significant decrease in neurite caliber become obvious. After longer time periods, the NIF aggregates are seen to react with an antibody which reveals abnormally phosphorylated NF-H. These observations demonstrate that an imbalance in the normal stoichiometric relationships among the NFT proteins rapidly alters the supramolecular organization of the NIF network. These changes most likely reflect the normal functions of neurofilaments in cell shape and the organization and cytoplasmic distribution of membranous organelles. Interestingly, virtually all of these changes closely resemble those which have been reported in motor neuron diseases such as amyotrophic lateral sclerosis (ALS). These findings suggest that cultured neurons can be used as models for more precisely defining the relationships between the formation of NIF aggregates and the sequence of cytopathological events which typify neurodegenerative diseases.

Inhibition of proteolysis enhances aluminum-induced perikaryal neurofilament accumulation but does not enhance tau accumulation

As observed for neurons in situ, phosphorylated neurofilament (NF) epitopes are normally segregated within the axonal cytoskeleton of NB2a/d1 cells. However, accumulations of phosphorylated NFs develop in NB2a/d1 perikarya following exposure to aluminum salts and following inhibition of proteolysis. In the present study, we observed that perikarya of cells exposed to both aluminum and the protease inhibitor C1 (also known as "AllNal") were more intensely labeled by monoclonal antibodies directed against both nonphosphorylated and phosphorylated epitopes than were cells treated with either aluminum or protease inhibitor alone. Since these monoclonal antibodies crossreact with tau, we also immunostained cells treated under these conditions with monoclonal antibodies directed against phosphate-insensitive (5E2) and phosphorylated (PHF-1) epitopes of tau. Aluminum treatment, but not C1 treatment, induced accumulation of total tau isoforms as judged by an increase in 5E2 immunoreactivity. Neither treatment, either separately or in combination, induced an increase in PHF-1 immunoreactivity. These findings suggest that alterations in immunoreactivity with SMI antibodies reflected increases in NF epitopes. This was confirmed by immunoblot analyses. Since proteolysis is apparently instrumental in maintaining the normal distribution patterns of phosphorylated NF epitopes, these findings implicate deficiencies in proteolytic mechanisms in the development of neurofibrillary pathology, and underscore the possibility of a multiple etiology in human neuropathological conditions.

Brief potassium depolarization decreases levels of neurofilament proteins in CNS culture

Little is known about the effects of brief potassium depolarization that occurs concurrently with transient ischemia, epilepsy and head trauma. To investigate the effect of short-term depolarization on light (NF-L), middle (NF-M), and heavy (NF-H) neurofilament proteins and determine the role played by calcium in that effect, mixed septo-hippocampal cultures were exposed to 60 mM K+ for 6 min, in the presence of 0 to 11.8 mM Ca2+. Twenty-four hours later, neurofilament immunoreactivity in Western blots of depolarized cultures was decreased to 60% or less of control levels. Decreases were Ca2+-dependent, not due to cell loss, and affected both phosphorylated and nonphosphorylated proteins. The phosphorylation state of NF-M and NF-H influenced the degree of loss observed. Changes in the pattern of immunolabelling of neuritic processes were also associated with depolarization. Thus, brief potassium depolarization may contribute to cytoskeletal disruption following brain injury.

Time course of neurofilament protein loss following depolarization-induced injury in CNS culture

In septo-hippocampal cell cultures, brief potassium depolarization produces calcium-dependent decreases in neurofilament proteins and loss of fine neuritic processes within 24 h. It is not known whether neurons later exhibit delayed degeneration and die, live with enduring neurofilament loss, or restore neurofilament protein levels. Therefore, we exposed septohippocampal cultures to 6 min potassium depolarization (60 mM) with 2.8-11.8 mM extracellular Ca2+ and evaluated immunoreactivity for low, medium and heavy neurofilament proteins, neuronal number, and neuronal morphology for 10 days. Neuronal number remained unchanged; neurofilament protein levels recovered to between 31% and 99% of control levels, and fine neuritic processes reappeared.

Aluminum treatment of intact neuroblastoma cells alters neurofilament subunit phosphorylation, solubility, and proteolysis

Addition of 400 microM AlCl3 to the culture medium for 72 h has been previously shown to induce perikaryal whorls of intermediate-sized filaments in intact mouse NB2a/d1 neuroblastoma cells. Immunoblot analyses demonstrated that in vivo treatment of cells with aluminum induced the de novo appearance of extensively phosphorylated NF-H isoforms in cytoskeletons of undifferentiated cells and increased levels of these isoforms in differentiated cells. Neurofilament subunits isolated from intact cells treated with aluminum were resistant to dephosphorylation in vitro by alkaline phosphatase and to in vitro degradation by endogenous calcium-dependent protease(s). These alterations were accompanied by a greater tendency of neurofilaments to form insoluble aggregates after isolation. These findings demonstrate direct effects of aluminum on neurofilament subunits within intact neuronal cells similar to those previously demonstrated following in vitro exposure of isolated neurofilaments to aluminum.

Brain mRNA from infants of aluminium-exposed lactating rabbits

The neurotoxicity of aluminium (Al) involves bundling of neurofilaments, increased chromatin binding and decreased protein synthesis in Al injected rabbits. Thus, using an amphipathic Al ligand, maltol, experiments were carried out to examine whether or not administration of Al to lactating mother rabbits reduces brain protein synthesis in their offspring. Lactating mother rabbits received s.c. injections 3 times weekly of aluminium (Al) maltolate (1 mg Al/kg body wt) or an equivalent weight of maltol, for 4 weeks post-partum. Polysome preparations were obtained from the brain of their infants in order to assess mRNA translation in cell-free protein synthesizing systems. The brain polysomes showed a statistically significant reduction in the incorporation of [14C]leucine into protein. The poly (A)+ and poly (A)- fractions obtained from these polysomes showed reductions of 44% or more in the incorporation of [35S]methionine into protein. A variety of products separated by SDS-polyacrylamide gel electrophoresis all exhibited decreased labelling. These experiments suggest that infant rabbits exposed to a highly neurotoxic form of Al in milk exhibit changes in brain protein synthesis which resemble those in infants injected directly with Al.

Aluminum binds to the hyperphosphorylated tau in Alzheimer's disease: a hypothesis

The hypterphosphorylation of tau proteins is a well-established step in the expression of the pathological features in Alzheimer's disease (AD). While a primary event that links aluminum and AD, the so-called 'aluminum hypotheses', is far from being demonstrated, however, the metal ion could be an important etiological factor, most likely not the only one, of AD etiopathogenesis acting as an aggregating agent of the cytoskeletal elements forming very stable bridges between phosphate groups of the hyperphosphorylated tau elements.

Calcium modulates aluminum neurotoxicity and interaction with neurofilaments

We examined the influence of calcium on neurotoxicity of AlCl3 and Al-lactate toward differentiated NB2a/d1 cells. Apart from induction of perikaryal neurofibrillary inclusions, AlCl3 at 1 mM induced no obvious additional signs of toxicity when added to culture medium in the presence of the normal medium CaCl2 content of 1.8 mM, nor when extracellular calcium was decreased by the addition to the medium of 0.9 mM EDTA. Increasing the extracellular CaCl2 concentration by fivefold was only marginally toxic, but in the presence of AlCl3, reduced viable cell numbers by well over 50% as compared to control cultures, and by approximately 50% vs fivefold CaCl2 alone. A twofold increase in extracellular CaCl2 did not increase the percentage of cells exhibiting Bielschowsky-positive perikarya, but induced a near doubling in the percentage of cells exhibiting accumulations in the presence of 1 mM Al-lactate. AlCl3 (1 mM) retards the electrophoretic migration of NF subunits on SDS-gels. This effect was eliminated by withholding CaCl2 from the incubation mixture and including 5 mM EDTA during incubation of cytoskeletons with AlCl3. The presence of CaCl2 alone did not alter NF migration. These findings underscore the possibility that multiple factors, including those that compromise general neuronal homeostasis, may contribute to neurofibrillary pathology.

Relative susceptibility of cytoskeleton-associated and soluble neurofilament subunits to aluminum exposure in intact cells. A possible mechanism for reduction of neurofilament axonal transport during aluminum neurotoxicity

Previous studies have demonstrated the appearance of phosphorylated neurofilament (NF) subunits within perikaryal cytoskeletons following aluminum exposure. In order to examine the mechanisms leading to this altered distribution of NF subunits, we carried out biochemical analyses of NF subunits in Triton-insoluble and -soluble fractions derived from aluminum-treated NB2a/d1 cells. In addition to increases in the Triton-insoluble cytoskeleton, increases in all three NF subunits were also detected within the Triton-soluble fraction of aluminum-treated cells. To address the nature of this increase in Triton-soluble subunits, aluminum-treated and untreated cultures were harvested in the absence of Triton and fractionated by established procedures to yield fractions greatly enriched for perikarya and neurites, respectively. Each of these subcellular fractions was then subjected to further homogenization in the presence of 1% Triton and centrifugation to yield Triton-insoluble cytoskeletons and Triton-soluble material derived from perikarya and axonal neurites, respectively. Resulting Triton-soluble fractions were "clarified" by high-speed centrifugation to eliminate oligomeric assemblies or soluble neurofilaments. Immunoblot analysis demonstrated quantitative recovery of the aluminum-induced increase in Triton-soluble NF subunits in the perikaryal fraction. Additional aluminum-treated and untreated cultures were pulse-chase radiolabeled with [35S]methionine and fractionated into Triton-insoluble and soluble fractions from isolated perikarya and axonal neurites. Autoradiographic analysis of immunoprecipitated NF subunits revealed that aluminum treatment delayed the translocation of newly synthesized subunits into neurites and resulted in the accumulation of radiolabeled subunits within the Triton-soluble fraction of perikarya. These findings suggest that aluminum may exert a relatively greater effect on NF subunits that have not yet undergone axonal transport and/or incorporation into Triton-insoluble structures vs those that have already deposited into axons. This possibility was supported by the observation that a higher concentration of aluminum was required to alter the electrophoretic migration of in vitro reassembled neurofilaments vs that required for unassembled NF subunits. These findings provide possible mechanisms for the accumulation of NF subunits in perikarya during aluminum intoxication.

The organization of neurofilaments accumulated in perikaryon following aluminum administration: relationship between structure and phosphorylation of neurofilaments

Neurofilaments accumulated in perikarya and dendrites of anterior horn cells and Purkinje cells of rabbit treated by aluminum chloride were analysed with a variety of techniques. Four different monoclonal antibodies against phosphorylated and nonphosphorylated epitopes on neurofilament H subunit were used to compare phosphorylation state of these accumulated neurofilaments with that of axonal neurofilaments. Although immunoblotting revealed no significant difference in phosphorylation between control and aluminum-treated brains, accumulated neurofilaments were immunocytochemically more phosphorylated than control perikaryal or dendritic neurofilaments. With detailed analysis of cryothin-section immunogold labeling, accumulated neurofilaments were, however, significantly less phosphorylated than axonal neurofilaments. With quick-freeze deep etching, core filaments of accumulated neurofilaments are as dense as axonal neurofilaments but much less regularly aligned. Cross-bridges of accumulated neurofilaments were less frequent and more branched than those of axonal neurofilaments, and when examined with combined immunocytochemistry and deep etching, were less phosphorylated. These results suggest that there is a relationship between the phosphorylation and the structural organization of neurofilaments. The phosphorylation of neurofilament H subunit may be necessary for formation of frequent and straight cross-bridges and resulting regular alignment of core filaments.

Retardation of neuritic outgrowth and cytoskeletal changes accompany acetylcholinesterase inhibitor treatment in cultured rat dorsal root ganglion neurons

Over the past two decades acetylcholinesterase (AChE) has been shown to be present in numerous non-cholinergic and non-cholinoceptive tissues. Interestingly, transient expression of AChE in developing nervous tissue corresponds temporally with neuronal migration and neuritic outgrowth. This observation has led our laboratory to investigate a possible novel, non-cholinergic role for AChE in the development of the nervous system. In a previous study, we demonstrated that the activity of AChE in cultured dorsal root ganglion neurons (DRGN) can be modulated by the substratum. In our current study, we have examined the effects of AChE inhibitor treatment on neuritic outgrowth on the highly permissive substratum Matrigel and the less permissive substratum Collagen Type I. DRGN received serial dilutions of the AChE-specific inhibitor 1,5-bis-(4-allyldimethylammoniumphenyl) pentan-3-one dibromide (BW284c51) ranging from 10(-4) to 10(-7) M. Results showed that neuritic outgrowth was significantly reduced in DRGN grown on Matrigel at 10(-5) and 10(-4) M BW284c51, while outgrowth on Collagen Type I was significantly reduced at 10(-6), 10(-5), and 10(-4) M concentrations of BW284c51. Inhibitor treatment did not affect cell survival and neuritic outgrowth from BW284c51-treated cells recovered to control levels after removal of the inhibitor from the medium. In addition, massive spiraling accumulations of 10 nm filaments were observed in the cell bodies of treated neurons, which resemble neurofibrillary inclusions observed in neuropathological diseases such as Pick's disease. This study demonstrates that AChE inhibitor treatment retards neuritic outgrowth and neuronal migration of cultured DRGN which is accompanied by cytoskeletal abnormalities in the cell body.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurotoxic effects of aluminium on embryonic chick brain cultures

Toxic damage of brain cells by aluminium (Al) is discussed as a possible factor in the development of neurodegenerative disorders in humans. To investigate neurotoxic effects of Al, serum-free cultures of mechanically dissociated embryonic chick (stage 28-29) forebrain, brain stem and optic tectum, and for comparison meningeal cells, were treated with Al (0-1000 microM) for 7 days. Effects of Al on cell viability (lysosomal and mitochondrial activity) and differentiation (synthesis of cell-specific proteins) were found to the brain area specific with the highest sensitivity observed in optic tectum. No inhibiting effects on cell viability could be observed in cultures of forebrain and meninges in the concentration range tested. In all three brain tissue cultures, threshold levels for the reduction of cell differentiation parameters were found at lower concentrations [concentration resulting in a 50% decrease (IC50) > 180 microM] than for the inhibition of cell viability (IC50 > 280 microM), indicating a specific toxic potential of Al for cytoskeletal alterations. The culture levels of nerve cell-specific markers microtubule-associated protein type 2 (the most sensitive parameter) and the 68-kDa neurofilament were inhibited at lower concentrations (IC50 180-630 microM) than the astrocyte-specific glial fibrillary acidic protein (IC50 700-approximately 1000 microM), demonstrating a particularly high sensitivity of neurons in comparison to astrocytes. Based on these differences in Al sensitivity observed for different cell markers in the various brain tissue cultures, the in vitro system used in the present study proved to be a suitable model to assess brain area and cell type-specific neurotoxic effects of Al.

Possible factors in the etiology of Alzheimer's disease

Inherited cases of Alzheimer's disease (AD) comprise only a very small proportion of the total. The remainder are of unknown etiopathogenesis, but they are very probably multifactorial in origin. This article describes studies on four possible factors: aluminum; viruses--in particular, herpes simplex type I virus (HSV1); defective DNA repair; and head trauma. Specific problems associated with aluminum, such as inadvertent contamination and its insolubility, have led to some controversy over its usage. Nonetheless, the effects of aluminum on animals and neuronal cells in culture have been studied intensively. Changes in protein structure and location in the cell are described, including the finding in this laboratory of a change in tau resembling that in AD neurofibrillary tangles, and also the lack of appreciable binding of aluminum to DNA. As for HSV1, there has previously been uncertainty about whether HSV1 DNA is present in human brain. Work in this laboratory using polymerase chain reaction has shown that HSV1 DNA is present in many normal aged brains and AD brains, but is absent in brains from younger people. Studies on DNA damage and repair in AD and normal cells are described, and finally, the possible involvement of head trauma is discussed.

Interaction of aluminum ions with phosvitin

We studied the effects of aluminum ions on the dephosphorylation of phosvitin catalyzed by acid phosphatase, and the metachromasia resulting from the interaction of phosvitin with toluidine blue. In both cases the action of Al3+ was inhibitory and the extent of inhibition was dependent on Al3+ concentration and the length of incubation of Al3+/phosvitin mixtures. The inhibition profiles of dephosphorylation of phosvitin (50 micrograms/ml) showed IC50 values of 15 and 2 microM Al3+ at 1 and 48 hr incubation time, respectively. The effect was proved to be substrate directed, while the inhibition was not reversed by EDTA. In contrast, the action of other divalent or trivalent cations on the dephosphorylation process, when inhibitory, was completely reversible by EDTA. Exposure of fluorescein 5-isothiocyanate-labeled phosvitin to Al3+ resulted in: a) the failure of the protein to migrate into sodium dodecyl sulfate containing polyacrylamide gels and b) the decrease of the fluorescence emission of the bound fluorescein. These findings suggest that phosvitin can be used as a model for studying interactions of aluminum with multiphosphorylated proteins and other polyanionic biopolymers.

Stable intrachain and interchain complexes of neurofilament peptides: a putative link between Al3+ and Alzheimer disease

The etiologic role of Al3+ in Alzheimer disease has been controversial. Circular dichroism (CD) spectroscopic studies on two synthetic fragments of human neurofilament protein mid-sized subunit (NF-M), NF-M13 (KSPVPKSPVEEKG) and NF-M17 (EEKGKSPVPKSPVEEKG), and their alanine-substituted and/or serine-phosphorylated derivatives were carried out in an attempt to find a molecular mechanism for the effect of Al3+ to induce aggregation of neuronal proteins or their catabolic fragments. Al3+ and Ca2+ ions were found to induce beta-pleated sheet formation in the phosphorylated fragments. The cation sensitivity depended on the length and charge distribution of the sequence and site of phosphorylation. Al3+-induced conformational changes were irreversible to citric acid chelation, whereas Ca(2+)-induced conformational changes were reversible with citric acid. Studies of the alanine derivatives demonstrated which residues affected Al3+ or Ca2+ binding. Peptides containing at least one free (nonphosphorylated) serine residue were shown to form an intramolecular Al3+ complex, rather than an intermolecular one. In the intramolecular (intrachain) complex, the ligand function of the deprotonated serine hydroxyl was delineated [(Al.pepH-1)-type complex]. Ca2+ ions did not show a tendency for intramolecular complexing. The potential role of Al3+ in Alzheimer disease tangle and plaque formation is strongly suggested.

Triton-soluble phosphovariants of the high molecular weight neurofilament subunit from NB2a/d1 cells are assembly-competent. Implications for normal and abnormal neurofilament assembly

NB2a/d1 cells incorporate neurofilaments (NFs) containing extensively phosphorylated high (NF-H) molecular weight subunits into the Triton-insoluble cytoskeleton of axonal neurites elaborated during differentiation with dibutyryl cAMP. However, immunocytochemical and biochemical analyses demonstrate the constitutive expression and extensive phosphorylation of a sizeable pool of (200 kDa) NF-H. We examined by cell-free analyses whether or not this Triton-soluble NF-H pool was assembly-competent in cell-free analyses. Triton-soluble fractions from 35S-radiolabeled NB2a/d1 cells were incubated with dissociated mouse CNS Triton-insoluble cytoskeletons that had been dissociated by treatment with 6 M urea. Following overnight dialysis to remove urea, low-speed centrifugation to sediment Triton-insoluble cytoskeletons resulted in the co-sedimentation of radiolabeled NF-H, indicating that Triton-soluble NF-H was capable of association with Triton-insoluble structures. Triton-soluble, extensively phosphorylated NF-H from NB2a/d1 cells was also capable of co-assembling with purified NF-L. Following high-speed centrifugation (100,000 x g for 1 h) to sediment any oligomeric assemblies, the Triton-soluble fraction from NB2a/d1 cells was mixed with purified NF-L that had been solubilized by 6 M urea. Following overnight dialysis to remove urea, high-speed centrifugation sedimented both NF-L and Triton-soluble NF-H from NB2a/d1 cells, demonstrating that Triton-soluble NF-H variants are assembly-competent. These data suggest that NF-H variants represent precursors for NF assembly, and indicate that their assembly within NB2a/d1 cells, demonstrating that Triton-soluble NF-H variants are assembly-competent. These data suggest that NF-H variants represent precursors for NF assembly, and indicate that their assembly within NB2a/d1 cells must be under temporal and spatial regulation.

Phosphorylation of neurofilament H subunit as related to arrangement of neurofilaments

To find out what causes differences in phosphorylation states in neurofilaments (NF), we selected two types of dendrite, one provided with very few NFs (Purkinje cell) and the other with relatively many (anterior horn cell). We examined these with four monoclonal antibodies selected by the Western blot analysis, two (NE14 and SMI31) recognizing only phosphorylated, SMI32 recognizing only nonphosphorylated, and N52 recognizing phosphorylation-independent epitopes of NF-H. The immunoperoxidase labeling of dendrites, and also of perikarya, in both neurons was detectable with all four antibodies. After the tissue was treated with Triton X-100, the labeling was still detectable with SMI32 or N52, but undetectable with NE14 and SMI31. The brain homogenate Triton-extracted supernatant after centrifugation at 100,000g for 1 hr showed the staining of NE14, SMI31, and N52 but not that of SMI32. In Purkinje cell dendrite and perikaryon, NFs always appeared singly. In the immunogold labeling, they were labeled only with SMI32 or N52. Labeling by NE14 or SMI31 was distributed throughout the cytoplasm and hardly associated with NFs. In the anterior horn cell dendrite and perikaryon, NFs appeared both singly and in bundles. They were predominantly labeled with SMI32 or N52 when they were single, and with NE14, SMI31, or N52 when they were bundled. Even in one NF, portions that appeared single were labeled mostly with SMI32 or N52, while the remainder, to which other NFs approached closely, were labeled mostly with NE14, SMI31, or N52. Thus, when NFs appear singly, NF-H in their projections or cross-bridges with other organelles is not phosphorylated, while when NFs are bundled, NF-H is phosphorylated in crossbridges between NF core filaments. These data may explain why the NF-H is heavily phosphorylated in axons, where NFs are abundant, and not in dendrites and perikarya, where NFs are sparse.

Neurofilament-deficient axons and perikaryal aggregates in viable transgenic mice expressing a neurofilament-beta-galactosidase fusion protein

Interactions between neurofilament side arms may modulate axon caliber. To investigate this hypothesis, we derived transgenic mice expressing a fusion protein in which the carboxyl terminus of the high molecular weight neurofilament protein (NFH) was replaced by beta-galactosidase. The transgene, regulated by NFH sequences, was expressed in projection neurons. However, the fusion protein remained in perikarya precipitating large filamentous aggregates. Axons were not invested with neurofilaments and developed only small calibers. Perikaryal aggregates, with similar structural features, are associated with neurodegenerative diseases, but these mice showed few ill effects and their neurons rarely degenerated. We conclude that an organized neurofilament cytoskeleton is required by axons to achieve large calibers but is not essential for neuronal function or extended survival.

Partial reversal of aluminium-induced neurofibrillary degeneration by desferrioxamine in adult male rabbits

Desferrioxamine, a chelating agent with a high affinity for aluminium, has been reported to slow the clinical progression of dementia associated with Alzheimer's disease [4]. We report here the effects of desferrioxamine treatment on aluminium-induced neurofibrillary degeneration in rabbits. Adult male New Zealand white rabbits received a single injection of aluminium-maltolate into the lateral cerebral ventricle. Three days later, one group of rabbits was treated with intramuscular injections of desferrioxamine twice daily; a second group received saline instead of desferrioxamine. Both groups were sacrificed 4 or 5 days following initiation of desferrioxamine or saline treatment. Minimal neurofibrillary degeneration was found in two of six desferrioxamine-treated rabbits, while all six rabbits treated with saline showed extensive neurofibrillary degeneration, particularly in the ventral horn of the lower spinal cord. Quantitation of the neurofibrillary degeneration in ventral horn neurons of lumbar cord revealed 30% to be affected in saline-treated animals compared to zero-affected neurons following desferrioxamine treatment. When sacrificed just 3 days after aluminium treatment, 50% of the rabbits already revealed neurofibrillary degeneration, corresponding to the time-point when desferrioxamine treatment was begun in the above animals; on quantitation, 7.5% of ventral lumbar cord neurons were involved. These findings indicate a partial reversal of aluminium-induced neurodegeneration by desferrioxamine. Delaying desferrioxamine treatment to 6 days after aluminium administration prevented any reversal of the aluminium effect; all animals had abundant neurofibrillary degeneration as well as a striking basophilic spicular deposit of calcium and argyrophilic material in the leptomeninges, lateral ventricles and brain parenchyma adjacent to these areas.(ABSTRACT TRUNCATED AT 250 WORDS)

Aggregation of tau protein by aluminum

Aluminum has been detected in Alzheimer neurofibrillary tangles, but the significance of its presence is unknown. The principal component of tangles is the paired helical filament (PHF), comprised of tau protein. We investigated whether aluminum could induce tau protein to form filaments or aggregate. When 10 microM bovine tau or non-phosphorylated recombinant human tau was combined with 400 microM or more aluminum, tau protein appeared to aggregate, observed as a dose-dependent decrease in electrophoretic mobility on SDS-PAGE. Tau appeared as a smear above the region of the expected tau bands and, at higher aluminum doses, failed to enter the gel. A tau fragment encompassing the microtubule binding domains did not show decreased mobility in the presence of aluminum, but did form aggregates that failed to electrophorese. However no fibrillar structures were observed in the aluminum-treated tau samples when observed by electron microscopy. The effect of aluminum on tau mobility was reversed by incubating with 1 mM deferoxamine. In contrast, the morphology of PHF fibrils was unaffected by deferoxamine treatment and the characteristic abnormal mobility of PHF-tau was not reduced by deferoxamine. This suggests that aluminum is not, by itself, a significant factor in maintaining the assembly of PHF-tau as fibrils or in its abnormal mobility on SDS gels. Aluminum treatment of 3T3 fibroblasts transfected with human tau resulted in toxicity, but did not change tau expression levels or induce tau aggregation. In conclusion, aluminum appears to induce isolated tau protein to aggregate in a phosphate-independent way, without the formation of fibrils.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of aberrant neurofilament phosphorylation in neuronal perikarya. IV. Evidence for the involvement of two signals

Axonal regeneration over long distances is dependent upon events occurring both in the distal stump and in the neuronal cell body. Little is known concerning how events in the distal stump influence the cell body response to injury, or the axon reaction. In the present study, we examined this relationship for one component of the axon reaction (i.e. aberrant neurofilament (NF) phosphorylation) in the C57BL/Ola (Ola) mouse mutant, a model which exhibits delayed Wallerian degeneration (up to 3 weeks) and retarded regeneration of sensory neurons. Non-axotomized normal (C57/6J/BL) and Ola mice demonstrated modest immunostaining to phosphorylated NF (pNF) epitopes (using monoclonal antibody 06-17) in some (11%) L4 dorsal root ganglion (DRG) neuronal cell bodies. In normal mice, modest to intense immunoreactivity was present in 43% of DRG neurons at 1 week following a sciatic nerve crush (axotomy). The intensity and extent of staining declined with reinnervation, being reduced slightly at 2 weeks and more notably by 3 weeks following axotomy. In Ola mice, the intensity and extent (43%) of staining were not different from normal axotomized mice at 1 week following axotomy. However, the intensity was less and the extent of staining reduced by 28% at 2 weeks following axotomy. By 3 weeks, staining levels were again increased, being similar to that observed in Ola and normal mice at 1 week following axotomy.(ABSTRACT TRUNCATED AT 250 WORDS)

Probing modifications of the neuronal cytoskeleton

The prominent death of central neurons in Alzheimer's and Parkinson's is reflected by changes in cell shape and by the formation of characteristic cytoskeletal inclusions (neurofibrillary tangles, Lewy bodies). This review focuses on the biology of neurofilaments and microtubule-associated proteins and identifies changes that can occur to these elements from basic and clinical research perspectives. Attention is directed at certain advances in neurobiology that have been especially integral to the identification of epitope domains, protein isoforms, and posttranslational (phosphorylation) events related to the composition, development, and structure of the common cytoskeletal modifications. Recently, a number of experimental strategies have emerged to simulate the aberrant changes in neurodegenerative disorders and gain insight into possible molecular events that contribute to alterations of the cytoskeleton. Descriptions of specific systems used to induce modifications are presented. In particular, unique neural transplantation methods in animals have been used to probe possible molecular and cellular conditions concerned with abnormal cytoskeletal changes in neurons.

The regulation of neurofilament protein dynamics by phosphorylation: clues to neurofibrillary pathobiology

Neurofilament proteins are continuously modified during their lifetime by a succession of protein kinases and phosphatases. Site-specific phosphorylation or dephosphorylation within different polypeptide domains of each neurofilament subunit is now believed to regulate such behaviors of neurofilaments as subunit polymerization and exchange, axonal transport, interactions with other cytoskeletal proteins and degradation. Local regulation of phosphorylation events could account for variations in the size, morphology and dynamics of the neurofilament network in different regions of the neuron. The apparent greater plasticity of the neurofilament network in regions like the perikaryon, initial segment and nodes along the axon may provide some insight into the vulnerability of these regions in neurofibrillary disease.

In vivo activation of kainate receptors induces dephosphorylation of the heavy neurofilament subunit

Injection of kainic acid (KA) into the rat hippocampus reduced the phosphorylation-related immunoreactivity of the heavy subunit of neurofilament proteins (NF-H). The effect was demonstrated quantitatively with a dot-immunobinding assay and qualitatively by immunoblotting with monoclonal antibodies against phosphorylation-dependent and nonphosphorylation-related epitopes of NF-H. The KA-induced reduction affected 50% of the phosphorylated NF-H in half of the hippocampus after 48 h. At the same time, the nonphosphorylation-related NF-H immunoreactivity increased as revealed by immunoblotting, indicating a shift from phosphorylated to nonphosphorylated NF-H. The effects on NF-H preceded a decrease in content of the neuron-specific enolase, a soluble neuronal cytoplasmic protein. No alterations of the light subunit of neurofilament proteins occurred, suggesting that KA has a preferential effect on NF-H phosphorylation. N-Methyl-D-aspartate administered similarly did not lead to a rapid dephosphorylation of NF-H. We propose that kainate receptor-mediated dephosphorylation in NF-H is involved in the signal transduction of excitatory amino acids with consequences for neuronal functions dependent on intermediary filament phosphorylation.

Aluminum inhibits neurofilament protein degradation by multiple cytoskeleton-associated proteases

The environmental neurotoxin aluminum exerts several distinct biochemical effects on neurofilament proteins, including subunit aggregation, disruption of the normal segregation of phosphorylated subunits within axons leading to abnormal perikaryal accumulation, and inhibition of in vitro degradation by the calcium-dependent neutral protease, calpain. In the present study, we demonstrate that exposure of mouse CNS cytoskeletal preparations to aluminum chloride inhibits the degradation of neurofilament proteins by both calcium-dependent and -independent proteases that co-purify with cytoskeletons. Aluminum inhibited both calcium-dependent and calcium-independent proteolysis of the high and middle molecular weight neurofilament subunits, but inhibited only calcium-dependent, and not calcium-independent proteolysis of the low molecular weight neurofilament subunit. These findings demonstrate that aluminum interferes with multiple aspects of neurofilament protein metabolism.

A molecular mechanism for the induction of neurofilament bundling by aluminum ions

A1 induces neurofibrillary tangles in the perikaryon of neurons in vivo and in culture. The effect of A1 ions complexed with maltol, a plant-derived ligand of A1, on purified neurofilament preparations was studied in vitro. The binding of A1 to the arm-like projections of the high (H)- and medium (M)-molecular-weight neurofilament subunits causes a conformational change of the molecule (intrafilamentous reaction), characterized by an altered migration on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). In addition, A1 compounds strongly stimulate the interaction between neurofilaments (interfilamentous reaction). The possibility that phosphate groups of the H and M sidearms are involved in binding A1 ions is discussed with regard to the migration on SDS-PAGE of dephosphorylated neurofilaments incubated with A1 compounds and the alteration by A1 ions of neurofilament phosphorylation in vitro by the associated kinase. Immunoblotting analysis of neurofilaments in cultivated neurons intoxicated with A1 compounds revealed a similar A1-dependent alteration of the neurofilament subunit conformation. This result suggest that the mechanism of A1-induced bundling of neurofilaments derived from in vitro studies might be involved in the formation of tangles in situ.

Phosphatase activity against neurofilament proteins from bovine spinal cord: effect of aluminium and neuropsychoactive drugs

Protein phosphatase activity associated with neurofilament (NF) rich (Triton X-100 insoluble) fraction was extracted and partially characterised by using known inhibitors of protein phosphatases such as vanadate and fluoride. Protein phosphatase activity was demonstrated with reference to the dephosphorylation of endogenous substrate, NF protein and exogenous protein substrates, casein and phosvitin. Phosphoamino acids and beta-glycerophosphate were found to be poor substrates. Further, new observations have been made regarding the in vitro inhibitory effect of aluminium and the differential effects of some of the neuropsychoactive drugs. The findings could possibly lead to studies explaining the biochemical basis of aluminium induced neurotoxicity as well as the side effects associated with the long term medication of neuropsychoactive drugs.

Aluminum alters the electrophoretic properties of neurofilament proteins: role of phosphorylation state

Exposure of each of the three neurofilament proteins (NFPs) to AlCl3 resulted in their failure to migrate into sodium dodecyl sulfate (SDS)-containing gels. This effect was dependent on length of incubation (minimum, 2 h) and AlCl3 concentrations (minimum, 50 microM) and was not reversed by 20% SDS, 6 M urea, freeze-thawing, boiling, or extensive dialysis. The migration of vimentin and glial fibrillary acidic protein was not affected by AlCl3. The high-molecular-weight neurofilament subunit (NF-H) entered SDS-containing gels after exposure to aluminum lactate but migrated aberrantly as a long high-molecular-weight streak. Migration of the 160-kDa alpha-chymotryptic cleavage product of NF-H, which contains the higher phosphorylated tail domain, was also prevented from migrating into SDS-containing gels by AlCl3. Dephosphorylation of NF-H and the middle-molecular-weight neurofilament subunit (NF-M) eliminated these effects on gel migration. EDTA, EGTA, MgCl2, CaCl2, or FeCl3 had no effect on NF-H or NF-M migration; furthermore, preincubation with, or simultaneous exposure to, CaCl2 or FeCl3 did not alter the effect of AlCl3. One interpretation of these results is that Al3+ interacts with phosphate groups on extensively phosphorylated C-terminal sidearms of NFPs, resulting in intermolecular cross-linking. These findings demonstrate a direct effect of aluminum on NFPs and provide a possible mechanism for neurofilament accumulation in perikarya during aluminum intoxication.