Fast near-whole-brain imaging in adult Drosophila during responses to stimuli and behavior

Whole-brain recordings give us a global perspective of the brain in action. In this study, we describe a method using light field microscopy to record near-whole brain calcium and voltage activity at high speed in behaving adult flies. We first obtained global activity maps for various stimuli and behaviors. Notably, we found that brain activity increased on a global scale when the fly walked but not when it groomed. This global increase with walking was particularly strong in dopamine neurons. Second, we extracted maps of spatially distinct sources of activity as well as their time series using principal component analysis and independent component analysis. The characteristic shapes in the maps matched the anatomy of subneuropil regions and, in some cases, a specific neuron type. Brain structures that responded to light and odor were consistent with previous reports, confirming the new technique's validity. We also observed previously uncharacterized behavior-related activity as well as patterns of spontaneous voltage activity.

Activation of caspase-6 in aging and mild cognitive impairment

Active caspase-6 (Csp6) and Tau cleaved by Csp6 (TauDeltaCsp6) are abundant in neuritic plaques (NPs), neuropil threads (NPTs), and neurofibrillary tangles (NFTs) in end-stage Alzheimer's disease (AD) (Guo H, Albrecht S, Bourdeau M, Petzke T, Bergeron C, LeBlanc AC: Active caspase-6 and caspase-6 cleaved Tau in neuropil threads, neuritic plaques and neurofibrillary tangles of Alzheimer's disease. Am J Pathol 2004, 165:523-531). The goal of this study was to determine whether active Csp6 is present in young and aged noncognitively impaired (NCI); aged mild cognitively impaired (MCI); and aged mild, moderate, severe, and very severe AD individuals. Csp6 activity was assessed with anti-p20Csp6 and TauDeltaCsp6 immunoreactivity. Active Csp6 is present in NFTs, NPTs, and NPs at all stages of AD. Active Csp6 is present in NFTs of all MCI cases and present in NPTs and NPs of some MCI cases. Active Csp6 is present in NFTs and NPTs of all NCI cases but is absent in younger cases. The level of TauDeltaCsp6-positive NFTs and NPTs correlates inversely with global cognitive scores in NCI individuals. Therefore, Csp6 activity can occur with aging in the absence of AD and is always associated with clinical and pathological features of confirmed AD cases. Given the ability of active Csp6 to increase amyloid-beta peptide production and cleave Tau and several synaptic proteins (LeBlanc AC, Liu H, Goodyer C, Bergeron C, Hammond J: Caspase-6 role in apoptosis of human neurons, amyloidogenesis and Alzheimer's disease. J Biol Chem 1999, 274:23426-23436; Petzke TL, Rousselet E, Goodyer C, LeBlanc AC: Substrates of caspase-6 in human primary neurons: a proteomic study. Program No. 80.9. 2005 Abstract Viewer/Itinerary Planner. Washington, DC: Society for Neuroscience. Online), we suggest that active Csp6 could be an early instigator of neuronal dysfunction.

Visual association pathology in preclinical Alzheimer disease

The transition from normal aging to mild cognitive impairment to Alzheimer disease (AD) is often indistinct. Imaging studies suggest early changes in posterior brain regions, including posterior temporoparietal and occipital cortex, but pathologic studies show initial changes in the medial temporal lobe with progressive neocortical involvement as cognition deteriorates. We evaluated the regional distribution of AD pathology in 41 elderly brain donors from the Framingham Heart Study who were cognitively intact, mildly impaired, or demented on the basis of probable AD. We found that 52% of the cognitively intact subjects, and all subjects with mild cognitive impairment or dementia, had dense neurofibrillary tangles (NFTs), neuropil threads, and tau-immunoreactive neurites surrounding neuritic plaques (NPs) in visual association cortex Brodmann area 19. All cognitively intact subjects with area 19 NFTs also had dense core NP and beta amyloid (Abeta) angiopathy in area 19. Area 19 pathology was occasionally present in the absence of substantial pathology in the hippocampus or entorhinal cortex and was not correlated with medial temporal lobe pathology. Dense AD pathology in area 19 is present in some cognitively intact subjects with preclinical AD. The unique metabolic, connectional, and vascular features of this region may confer enhanced vulnerability to neurodegeneration.

The history of the paired helical filaments

The original recognition of the paired helical filaments is discussed and amplified. The original description of what are now the neuropil threads is mentioned. The ensuing importance of both these structures is emphasised and a morphology-based hypothesis of the development of the disease from the original stimuli is offered.

Tau protein aggregation in the frontal and entorhinal cortices as a function of aging

OBJECTIVES

The abnormal accumulation of tau protein is increasingly recognized as the neuropathological hallmark of a number of dementing illness in which frontotemporal lobar degeneration occurs. In this paper we examined the age-dependant deposition of tau protein in the frontal and entorhinal neocortices.

METHODS

We examined autopsy records from 1997 to 2002 and selected 87 cases (10 in each decade from 0 to 79 years of age, 7 in 80-89 decade) with no history of dementia or other neurodegenerative diseases, and for which neurodegenerative diseases were excluded neuropathologically. Archival paraffin-embedded frontal and entorhinal cortices were examined by both Gallyas-Braak silver staining and a panel of antibodies recognizing tau protein accumulation.

RESULTS

Tau neuronal aggregates were observed in both frontal and entorhinal cortices in the third decade. While the frontal neuronal tau aggregates remained infrequent in the remaining decades, the number and extent ofneuronal tau aggregates in the entorhinal cortex increased such that by the 7th decade the majority of cases showed extensive tau aggregate formation. The most consistent morphological observation was of dense, perikaryal neuronal tau-immunoreactive aggregates, similar to the total tau distribution, firstly presenting in cortical layers II and III and subsequently involving in layers IV-VI. Neuropil threads became maximal in the 9th decade in both frontal and entorhinal cortices. Astrocytic tau accumulation was first observed in both frontal and entorhinal cortices in the 6th decade, predominantly in layer I and subcortical white matter, and increased in number with aging. Extraneuronal tau reactive aggregates and coiled bodies were rarely observed in the entorhinal cortex, and when present, were scattered through layer II to VI.

CONCLUSIONS

We have observed an age-dependant pattern of neuronal, extraneuronal and glial tau protein accumulation in the entorhinal cortex in individuals without neurodegenerative diseases. In contrast, tau protein aggregation is infrequently observed in the frontal cortex as a function of aging.

14-3-3 proteins and zeta isoform containing neurofibrillary tangles in patients with Alzheimer's disease

Immunolocalization of 14-3-3 proteins in Alzheimer's disease (AD) brains was investigated using isoform-specific antibodies. Weak granular immunoreactivity of 14-3-3 proteins was found in neuronal cytoplasm in control subjects and AD brains. Both intracellular and extracellular neurofibrillary tangles (NFTs), as well as neuropil thread-like structures, were immunopositive for 14-3-3 proteins. This was corroborated by triple-fluorolabeling method visualizing paired helical filament (PHF) tau and 14-3-3 epitopes in relation to fibrillary state detected by thiazin red. Pretangle neurons (positive for PHF-tau without fibrillary structure detected by thiazin red) only contained fine granular immunoreactivity (IR) of 14-3-3, which was similarly found in unaffected neurons. Granular cytoplasmic IR of 14-3-3 proteins in pretangle neurons was not colocalized to granular tau-like IR, which suggests that participation of 14-3-3 proteins in NFT formation was restricted to its later stages. Its zeta isoform was most prominent in these NFTs, suggesting that this isoform is a major component involved in the formation of NFTs. In contrast, IR of epsilon isoform was found in the neuropil of the hippocampus and that of sigma isoform was localized to granule cells of the dentate gyrus in AD brains, as seen in the age-matched controls. Expression of 14-3-3 proteins were found to be highly variable and dependent on their isoforms, regions and cell types. Molecular, as well as topographical, dissection of 14-3-3 proteins will provide us with an improved understanding of this molecule in normal and pathological conditions.

Active caspase-6 and caspase-6-cleaved tau in neuropil threads, neuritic plaques, and neurofibrillary tangles of Alzheimer's disease

Previously, we have shown that caspase-6 but not caspase-3 is activated by serum deprivation and induces a protracted cell death in primary cultures of human neurons (LeBlanc AC, Liu H, Goodyer C, Bergeron C, Hammond J: Caspase-6 role in apoptosis of human neurons, amyloidogenesis and Alzheimer's disease. J Biol Chem 1999, 274:23426-23436 and Zhang Y, Goodyer C, LeBlanc A: Selective and protracted apoptosis in human primary neurons microinjected with active caspase-3, -6, -7, and -8. J Neurosci 2000, 20:8384-8389). Here, we show with neoepitope antibodies that the p20 subunit of active caspase-6 increases twofold to threefold in the affected temporal and frontal cortex but not in the unaffected cerebellum of Alzheimer's disease brains and is present in neurofibrillary tangles, neuropil threads, and the neuritic plaques. Furthermore, a neoepitope antibody to caspase-6-cleaved Tau strongly detects intracellular tangles, extracellular tangles, pretangles, neuropil threads, and neuritic plaques. Immunoreactivity with both antibodies in pretangles indicates that the caspase-6 is active early in the pathogenesis of Alzheimer's disease. In contrast to the nuclear and cytosolic localization of active caspase-6 in apoptotic neurons of fetal and adult ischemic brains, the active caspase-6 in Alzheimer's disease brains is sequestered into the tangles or neurites. The localization of active caspase-6 may strongly jeopardize the structural integrity of the neuronal cytoskeletal system leading to inescapable neuronal dysfunction and eventual cell death in Alzheimer's disease neurons. Our results suggest that active caspase-6 is strongly implicated in human neuronal degeneration and apoptosis.

Tau immunohistochemistry in acute brain injury

Epidemiological studies have identified a history of head injury as a risk factor for Alzheimer's disease. However, the neuropathological mechanism underlying this relationship is as yet unclear. Neuronal cytoskeletal changes in the form of neurofibrillary tangles and neuropil threads have recently been demonstrated in young men who had sustained repetitive head injury and subsequently died in their 20s. In addition, recent experimental studies have found accumulation of tau within neuronal somata and damaged axons following diffuse brain injury. We hypothesized that tau-immunoreactive tangles may be present in the brains of patients who died after a single acute blunt head injury. A total of 45 cases of fatal head injury were immunostained for tau. They comprised nine groups (n=5 for each group) separated by age (0-19 years, 20-50 years, 50+ years) and survival time (<24 h, 24 h-1 week, 1 week-1 month) and were compared with age-matched controls. Subtle alterations in tau immunoreactivity, for example, in oligodendrocytes, were present in some head injury cases but not controls. However, neurofibrillary tangles did not appear more prevalent after traumatic brain injury (TBI) when compared with age-matched controls. Although alterations in tau immunoreactivity may occur which warrant further study, neurofibrillary tangles were not more prevalent after a single fatal episode of TBI.

4-repeat tauopathy sharing pathological and biochemical features of corticobasal degeneration and progressive supranuclear palsy

We report a 67-year-old man with 4-repeat (4R) tauopathy sharing both features of corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP). Although CBD and PSP have a common pathological feature that 4R tau accumulates in neurons and glia, recent pathological studies have confirmed differences between the two disorders. Clinical features of the present case were asymmetrical apraxia, parkinsonism, memory disturbance, disorientation and left limb myoclonus with a 5-year history. Pathological features were the widespread occurrence of 4R tau-positive structures including pre-tangles, neurofibrillary tangles, astrocytic plaques, tufted astrocytes, coiled bodies and argyrophilic threads. Biochemically, immunoblotting of insoluble tau demonstrated the low molecular fragments of 37 kDa and 33 kDa observed in typical CBD and PSP, respectively, in addition to the presence of 4R tau isoforms. The present case shared tau-related pathological and biochemical features of CBD and PSP. These findings support that CBD and PSP are closely associated disorders having a pathogenesis common to 4R tauopathy.

Cholesterol storage and tau pathology in Niemann-Pick type C disease in the brain

Niemann-Pick type C disease is an inherited neurovisceral storage disorder with intracellular accumulation of cholesterol. In affected brains, many ballooned neurons are seen. Considerable nerve cell loss of unknown pathogenesis leads to neurological deterioration and dementia. Chemical examination of brains has failed to demonstrate increased levels of cholesterol. Using filipin fluorometry of neuronal cells in tissue slices, we found massive accumulation of cholesterol in neurons in four out of five human Niemann-Pick type C cases including adult patients. Neurofibrillary tangles composed of aggregates of the otherwise highly soluble protein tau were present in three Niemann-Pick type C cases and were also immunologically identical to those associated with Alzheimer's disease. However, only a thin slab of spinal cord or a tiny piece of isocortex was available for examination in the two cases without tangles. In a further semi-quantitative analysis of 576 neurons, we determined higher cholesterol content in tangle-bearing neurons than in adjacent tangle-free neurons. The association of cholesterol accumulation with neurofibrillary degeneration in Niemann-Pick type C disease and Alzheimer's disease awakens interest in the role of impaired cholesterol metabolism in the development of neurofibrillary tangles in both diseases.

Glial involvement in diffuse Lewy body disease

Diffuse Lewy body disease (DLBD) is characterized by the presence of Lewy bodies (LB) in the neurons and neurites of cortical, subcortical, and brain stem structures. Recently, alpha-synuclein (alphaS) has been found to be a central constituent of LB. In DLBD, abnormal accumulation of alphaS has been reported in both neurons and glia, but studies on glial lesions in DLBD have been limited. We examined in detail the constituents and distribution of glial lesions in eight patients with DLBD and report the pathogenesis of the glial lesions. alphaS-positive neuronal cytoplasmic inclusions (NI), neuropil threads (NT), and coiled bodies (CB) showed similar immunostaining profiles. Without pretreatment, NI, NT, and CB were detected by all antibodies against alphaS. The immunostaining profile of star-like astrocytes (SLA) was quite different from those of NI, NT, and CB. A few SLA were stained by an antibody against the non-Abeta component portion of alphaS without pretreatment, but formic acid pretreatment dramatically enhanced SLA immunoreactivity. SLA and CB were found in all eight brains with DLBD. SLA were scarce in the brain stem, but there were hundreds of SLA per visual field at x100 magnification in the temporal cortex of most cases, while CB were found diffusely in both the cerebral cortex and brain stem, similar to NI. This suggests that the pathogenesis of SLA is different from those of NI and CB.

Immunohistochemical study of synphilin-1 in brains of patients with dementia with Lewy bodies - synphilin-1 is non-specifically implicated in the formation of different neuronal cytoskeletal inclusions

Dementia with Lewy bodies brains were immunohistochemically investigated using anti-synphilin-1 antibodies. The alpha-synuclein-positive brainstem type and well-defined cortical type Lewy bodies (LB) were positive for synphilin-1, while ill-defined LB and LB-related neurites were negative, suggesting that synphilin-1 does not directly associate with alpha-synuclein. Synphilin-1-positive LB were double-positive for phosphorylated neurofilament. In addition, tau-positive neurofibrillary tangles (NFT) were positive for synphilin-1, while neuropil threads were negative. Immunoelectron microscopically, synphilin-1 was located on filamentous components in cortical type LB and on paired helical filaments in NFT. It is likely that synphilin-1 accumulates in the cell body according to the axonal transport blockage, and associates with abnormal cytoskeltons during the formation of LB or NFT, suggesting that synphilin-1 is non-specifically implicated in the formation of different neuronal cytoskeletal inclusions.

Structure, microtubule interactions, and paired helical filament aggregation by tau mutants of frontotemporal dementias

We have studied biochemical and structural parameters of several missense and deletion mutants of tau protein (G272V, N279K, DeltaK280, P301L, V337M, R406W) found in frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17). The mutant proteins were expressed on the basis of both full-length tau (htau40) and constructs derived from the repeat domain. They were analyzed with respect to the capacity to enhance microtubule assembly, binding of tau to microtubules, secondary structure content, and aggregation into Alzheimer-like paired helical or straight filaments. We find that the mutations cause a moderate decrease in microtubule interactions and stabilization, and they show no gross structural changes compared with the natively unfolded conformation of the wild-type protein, but the aggregation into PHFs is strongly enhanced, particularly for the mutants DeltaK280 and P301L. This gain of pathological aggregation would be consistent with the autosomal dominant nature of the disease.

Evolution of Alzheimer's disease-related cytoskeletal changes in the basal nucleus of Meynert

This study examines the evolution of Alzheimer's disease (AD)-related pathology in a subcortical predilection site, the basal nucleus of Meynert (bnM), which is a major source of cortical cholinergic innervation. Brains of 51 autopsy cases were studied using silver techniques and immunostaining for tau-associated neurofibrillary pathology and for amyloid beta protein (Abeta) deposits. All cases are classified according to a procedure permitting differentiation of six stages of AD-related neurofibrillary changes in the cerebral cortex. Initial cytoskeletal abnormalities in the bnM are already noted in stage I of cortical neurofibrillary changes. The gradual development of the neurofibrillary pathology in the bnM parallels the progression of the AD-related stages in the cerebral cortex. A variety of morphologically distinguishable cytoskeletal alterations are observed in large nerve cells which predominate in the bnM. Based on these cellular alterations, a sequence of cytoskeletal deterioration is proposed. Initially, the abnormal tau protein is distributed diffusely throughout the cell body and the neuronal processes. Subsequently, it aggregates to form a neurofibrillary tangle, which appears as a spherical somatic inclusion. The cell processes gradually become fragmented. Finally the parent cell dies, leaving behind an extraneuronal "ghost tangle". With regard to the cortical stages of AD-related neurofibrillary changes, the initial forms of cytoskeletal changes in the bnM predominate in the transentorhinal AD stages (I and II), while "ghost tangles" preferentially occur in the neocortical stages (V and VI). The considerable morphological diversity of cytoskeletal alterations is typical of stages III and IV. These results indicate that individual neurons of the bnM enter the sequence of cytoskeletal deterioration at different times.

Association of active extracellular signal-regulated protein kinase with paired helical filaments of inclusion-body myositis muscle suggests its role in inclusion-body myositis tau phosphorylation

The possible role of extracellular signal-regulated kinase (ERK) in the pathogenesis of inclusion-body myositis (IBM) was investigated by immunostaining the active phosphorylated form of ERK in muscle biopsies of six IBM and 14 control patients. Between 80% and 90% of IBM vacuolated muscle fibers contained well-defined ERK-immunoreactive inclusions, which were co-localized by light microscopy, with phosphorylated tau in 70 to 80% of those fibers. Immunoelectronmicroscopy colocalized ERK to small amorphous tufts adjacent to the muscle fiber paired-helical filaments. Strong ERK immunoreactivity was also present at the postsynaptic domain of all human neuromuscular junctions. Our study suggests 1) that ERK, a signal transducer, might play a role in IBM pathogenesis, including participation in the pathological phosphorylation of IBM tau; and 2) that signal transduction abnormalities may be a component of the IBM pathogenic cascade. Our novel immunolocalization of ERK at the postsynaptic domain of human neuromuscular junctions supports a role in transcription of junctional-protein genes. The ERK localized in nonjunctional regions of IBM fibers may underlie the known pathological up-regulation of junctional proteins there.

Paired helical filaments of inclusion-body myositis muscle contain RNA and survival motor neuron protein

Sporadic inclusion-body myositis (s-IBM) is the most common progressive muscle disease of older persons. Pathologically, the muscle biopsy manifests various degrees of inflammation and specific vacuolar degeneration of muscle fibers characterized by paired helical filaments (PHFs) composed of phosphorylated tau. IBM vacuolated fibers also contain accumulations of several other Alzheimer-characteristic proteins. Molecular mechanisms leading to formation of the PHFs and accumulations of proteins in IBM muscle are not known. We report that the abnormal muscle fibers of IBM contained (i) acridine-orange-positive RNA inclusions that colocalized with the immunoreactivity of phosphorylated tau and (ii) survival motor neuron protein immunoreactive inclusions, which by immuno-electron microscopy were confined to paired helical filaments. This study demonstrates two novel components of the IBM paired helical filaments, which may lead to better understanding of their pathogenesis.

Conformation of paired helical filaments blocks dephosphorylation of epitopes shared with fetal tau except Ser199/202 and Ser202/Thr205

To determine if the high phosphate content of paired helical filaments (PHFs) in Alzheimer's disease (AD) is a result of limited access to filament phosphorylation sites, we studied in vitro dephosphorylation of intact PHFs, PHFs with filamentous structure abolished by formic acid treatment (PHF(FA)) and fetal human tau protein. Samples were treated with alkaline phosphatase for up to 24 h at 37 degrees C and then immunoblotted with eight well characterized tau antibodies, that recognize two phosphorylation-insensitive sites and six phosphorylation-sensitive epitopes at Thr181, Ser199/202, Ser202/Thr205, Thr231, Ser262/356 and Ser396/404. Intact PHFs were effectively dephosphorylated only at the two N-terminal epitopes Ser199/202 and Ser202/Thr205, with little change in electrophoretic mobility. In contrast, PHF(FA) were dephosphorylated at all epitopes, with particular effectiveness at those in the C-terminus and with significant increase in electrophoretic mobility. The fetal tau epitopes were effectively dephosphorylated except at Thr181 and Thr231 with marked increase in mobility. The extent of dephosphorylation of PHF(FA) was equal or more effective than in fetal tau, except for Thr181 that was minimally dephosphorylated in both proteins. The results indicate that intact PHFs, but not PHF(FA) or fetal tau display differential dephosphorylation of the N- and C-terminal epitopes. The results confirm that the filamentous conformation may significantly contribute to hyperphosphorylation of PHFs in the C-terminus. The filamentous conformation, however, does not limit access to two N-terminal epitopes Ser199/202 and Ser202/Thr205. The access to these sites in AD may be limited by other factors, e.g., inhibition of phosphatase binding.