The molecular landscape and associated clinical experience in infant medulloblastoma: prognostic significance of second-generation subtypes.

AIMS: Biomarker-driven therapies have not been developed for infant medulloblastoma (iMB). We sought to robustly sub-classify iMB, and proffer strategies for personalized, risk-adapted therapies. METHODS: We characterized the iMB molecular landscape, including second-generation subtyping, and the associated retrospective clinical experience, using large independent discovery/validation cohorts (n = 387). RESULTS: iMBGrp3 (42%) and iMBSHH (40%) subgroups predominated. iMBGrp3 harboured second-generation subtypes II/III/IV. Subtype II strongly associated with large-cell/anaplastic pathology (LCA; 23%) and MYC amplification (19%), defining a very-high-risk group (0% 10yr overall survival (OS)), which progressed rapidly on all therapies; novel approaches are urgently required. Subtype VII (predominant within iMBGrp4 ) and subtype IV tumours were standard risk (80% OS) using upfront CSI-based therapies; randomized-controlled trials of upfront radiation-sparing and/or second-line radiotherapy should be considered. Seventy-five per cent of iMBSHH showed DN/MBEN histopathology in discovery and validation cohorts (P < 0.0001); central pathology review determined diagnosis of histological variants to WHO standards. In multivariable models, non-DN/MBEN pathology was associated significantly with worse outcomes within iMBSHH . iMBSHH harboured two distinct subtypes (iMBSHH-I/II ). Within the discriminated favourable-risk iMBSHH DN/MBEN patient group, iMBSHH-II had significantly better progression-free survival than iMBSHH-I , offering opportunities for risk-adapted stratification of upfront therapies. Both iMBSHH-I and iMBSHH-II showed notable rescue rates (56% combined post-relapse survival), further supporting delay of irradiation. Survival models and risk factors described were reproducible in independent cohorts, strongly supporting their further investigation and development. CONCLUSIONS: Investigations of large, retrospective cohorts have enabled the comprehensive and robust characterization of molecular heterogeneity within iMB. Novel subtypes are clinically significant and subgroup-dependent survival models highlight opportunities for biomarker-directed therapies.

Expression of p16 and p21 in the frontal association cortex of ALS/MND brains suggests neuronal cell cycle dysregulation and astrocyte senescence in early stages of the disease.

AIMS: Cellular senescence plays a role in organismal ageing and has been linked to persistent DNA damage in age-related diseases. Brain senescence has been described in astrocytes and microglia, but it is less well understood in neurones. Evidence suggests that neurones activate a senescence-like mechanism that could contribute to neurodegeneration. We aimed to determine whether a persistent DNA damage response (DDR) and senescence activation are features of motor neurone disease (amyotrophic lateral sclerosis, ALS/MND). METHODS: We examined expression of senescence (p16 and p21) and DNA damage markers (8-OHdG and γH2AX) in motor cortex (MCx), frontal association cortex (FACx) and occipital cortex (OCx) in post-mortem tissue donated by patients with ALS/MND and controls. RESULTS: Nuclear expression of p16 and p21 was detected in glial cells; double immunofluorescence for p16/p21 and glial fibrillary acidic protein (GFAP) suggested that some of these cells were GFAP+ astrocytes. p21 nuclear expression was also found in neurones. Higher levels of p16+ (glia, P = 0.028) and p21+ (glia, P = 0.003; neurones, P = 0.008) cells were found in the FACx of ALS/MND donors but not in the MCx or OCx. Expression of p16 and p21 did not correlate with 8-OHdG or γH2AX. CONCLUSIONS: Expression of p16 and p21 in glia, mainly in astrocytes, suggests senescence induction in these cells; however, neuronal p21 expression might reflect a more general mechanism of age-related cell cycle dysregulation. The significantly higher proportion of cells expressing either p16 or p21 in the FACx of ALS/MND donors could indicate senescence activation and cell cycle dysregulation in early stages of the disease.

Epidemiological pathology of Aß deposition in the ageing brain in CFAS: addition of multiple Aß-derived measures does not improve dementia assessment using logistic regression and machine learning approaches.

Aß-amyloid deposition is a key feature of Alzheimer's disease, but Consortium to Establish a Registry for Alzheimer's Disease (CERAD) assessment, based on neuritic plaque density, shows a limited relationships to dementia. Thal phase is based on a neuroanatomical hierarchy of Aß-deposition, and in combination with Braak neurofibrillary tangle staging also allows derivation of primary age-related tauopathy (PART). We sought to determine whether Thal Aß phase predicts dementia better than CERAD in a population-representative cohort (n = 186) derived from the Cognitive Function and Ageing Study (CFAS). Cerebral amyloid angiopathy (CAA) was quantitied as the number of neuroanatomical areas involved and cases meeting criteria for PART were defined to determine if they are a distinct pathological group within the ageing population. Agreement with the Thal scheme was excellent. In univariate analysis Thal phase performed less well as a predictor of dementia than CERAD, Braak or CAA. Logistic regression, decision tree and linear discriminant analysis were performed for multivariable analysis, with similar results. Thal phase did not provide a better explanation of dementia than CERAD, and there was no additional benefit to including more than one assessment of Aß in the model. Number of areas involved by CAA was highly correlated with assessment based on a severity score (p < 0.001). The presence of capillary involvement (CAA type I) was associated with higher Thal phase and Braak stage (p < 0.001). CAA was not associated with microinfarcts (p = 0.1). Cases satisfying pathological criteria for PART were present at a frequency of 10.2% but were not older and did not have a higher likelihood of dementia than a comparison group of individuals with similar Braak stage but with more Aß. They also did not have higher hippocampal-tau stage, although PART was weakly associated with increased presence of thorn-shaped astrocytes (p = 0.048), suggesting common age-related mechanisms. Thal phase is highly applicable in a population-representative setting and allows definition of pathological subgroups, such as PART. Thal phase, plaque density, and extent and type of CAA measure different aspects of Aß pathology, but addition of more than one Aß measure does not improve dementia prediction, probably because these variables are highly correlated. Machine learning predictions reveal the importance of combining neuropathological measurements for the assessment of dementia.

Combined fused in sarcoma-positive (FUS+) basophilic inclusion body disease and atypical tauopathy presenting with an amyotrophic lateral sclerosis/motor neurone disease (ALS/MND)-plus phenotype.

AIMS: Amyotrophic lateral sclerosis/motor neurone disease (ALS/MND) is characterized by the presence of inclusions containing TDP-43 within motor neurones. In rare cases, ALS/MND may be associated with inclusions containing other proteins, such as fused in sarcoma (FUS), while motor system pathology may rarely be a feature of other neurodegenerative disorders. We here have investigated the association of FUS and tau pathology. METHODS: We report a case with an ALS/MND-plus clinical syndrome which pathologically demonstrated both FUS pathology and an atypical tauopathy. RESULTS: Clinical motor involvement was predominantly present in the upper motor neurone, and was accompanied by extrapyramidal features and sensory involvement, but with only minimal cognitive impairment. The presentation was sporadic and gene mutation screening was negative. Post mortem study demonstrated inclusions positive for FUS, including basophilic inclusion bodies. This was associated with 4R-tauopathy, largely as non-fibrillary diffuse phospho-tau in neurones, with granulovacuolar degeneration in a more restricted distribution. Double-staining revealed that neurones contained both types of protein pathology. CONCLUSION: FUS-positive basophilic inclusion body disease is a rare cause of ALS/MND, but in this case was associated with an unusual atypical tauopathy. The coexistence of two such rare neuropathologies raises the question of a pathogenic interaction.

Age-associated changes in the blood-brain barrier: comparative studies in human and mouse.

AIMS: While vascular pathology is a common feature of a range of neurodegenerative diseases, we hypothesized that vascular changes occur in association with normal ageing. Therefore, we aimed to characterize age-associated changes in the blood-brain barrier (BBB) in human and mouse cohorts. METHODS: Immunohistochemistry and Evans blue assays were used to characterize BBB dysfunction (tight junction protein expression and serum plasma protein accumulation), vascular pathology (pericyte loss and vascular density) and glial pathology (astrocyte and microglial density) in ageing neurological control human prefrontal cortex (a total of 23 cases from 5 age groups representing the spectrum of young adult to old age: 20-30 years, 31-45 years, 46-60 years, 61-75 years and 75+) and C57BL/6 mice (3 months, 12 months, 18 months and 24 months, n = 5/6 per group). RESULTS: Quantification of the tight junction protein ZO-1 within the cortex and cerebellum of the mouse cohort showed a significant trend to both increased number (cortex P < 0.001, cerebellum P < 0.001) and length (cortex P < 0.001, cerebellum P < 0.001) of junctional breaks associated with increasing age. GFAP expression significantly correlated with ageing in the mice (P = 0.037). In the human cohort, assessment of human protein accumulation (albumin, fibrinogen and human IgG) demonstrated cells morphologically resembling clasmatodendritic astrocytes, indicative of BBB dysfunction. Semiquantitative assessment of astrogliosis in the cortex expression revealed an association with age (P = 0.003), while no age-associated changes in microglial pathology, microvascular density or pericyte coverage were detected. CONCLUSIONS: This study demonstrates BBB dysfunction in normal brain ageing, both in human and mouse cohorts.

Review: Neuropathology and behavioural features of transgenic murine models of Alzheimer's disease.

Our understanding of the underlying biology of Alzheimer's disease (AD) has been steadily progressing; however, this is yet to translate into a successful treatment in humans. The use of transgenic mouse models has helped to develop our understanding of AD, not only in terms of disease pathology, but also with the associated cognitive impairments typical of AD. Plaques and neurofibrillary tangles are often among the last pathological changes in AD mouse models, after neuronal loss and gliosis. There is a general consensus that successful treatments need to be applied before the onset of these pathologies and associated cognitive symptoms. This review discusses the different types of AD mouse models in terms of the temporal progression of the disease, how well they replicate the pathological changes seen in human AD and their cognitive defects. We provide a critical assessment of the behavioural tests used with AD mice to assess cognitive changes and decline, and discuss how successfully they correlate with cognitive impairments in humans with AD. This information is an important tool for AD researchers when deciding on appropriate mouse models, and when selecting measures to assess behavioural and cognitive change.

Review: Astrocytes in Alzheimer's disease and other age-associated dementias: a supporting player with a central role.

Astrocytes have essential roles in the central nervous system and are also implicated in the pathogenesis of neurodegenerative disease. Forming non-overlapping domains, astrocytes are highly complex cells. Immunohistochemistry to a variety of proteins can be used to study astrocytes in tissue, labelling different cellular components and sub-populations, including glial fibrillary acidic protein, ALDH1L1, CD44, NDRG2 and amino acid transporters, but none of these labels the entire astrocyte population. Increasing heterogeneity is recognized in the astrocyte population, a complexity that is relevant both to their normal function and pathogenic roles. They are involved in neuronal support, as active components of the tripartite synapse and in cell interactions within the neurovascular unit (NVU), where they are essential for blood-brain barrier maintenance and neurovascular coupling. Astrocytes change with age, and their responses may modulate the cellular effects of neurodegenerative pathologies, which alone do not explain all of the variance in statistical models of neurodegenerative dementias. Astrocytes respond to both the neurofibrillary tangles and plaques of Alzheimer's disease, to hyperphosphorylated tau and Aß, eliciting an effect which may be neuroprotective or deleterious. Not only astrocyte hypertrophy, in the form of gliosis, occurs, but also astrocyte injury and atrophy. Loss of normal astrocyte functions may contribute to reduced support for neurones and dysfunction of the NVU. Understanding how astrocytes contribute to dementia requires an understanding of the underlying heterogeneity of astrocyte populations, and the complexity of their responses to pathology. Enhancing the supportive and neuroprotective components of the astrocyte response has potential translational applications in therapeutic approaches to dementia.

Microinfarcts in an older population-representative brain donor cohort (MRC CFAS): Prevalence, relation to dementia and mobility, and implications for the evaluation of cerebral Small Vessel Disease.

INTRODUCTION: Microinfarcts, small ischaemic foci common in ageing brain, are associated with dementia and gait dysfunction. We determined their relationship with dementia, mobility and cerebrovascular disease in an older population-representative brain donor cohort. These data on microinfarcts were evaluated in relation to pathological assessments of clinically significant cerebral small vessel disease (SVD). METHODS: Microinfarcts were assessed in the MRC Cognitive Function and Ageing Study (n = 331). Nine brain areas were staged according to the number of areas affected. RESULTS: 36% of brains showed at least 1 microinfarct. Higher cortical microinfarct stage was associated with dementia at death (OR 1.41, 95% CI 1.02; 1.96, P = 0.038), whilst cortical and subcortical microinfarct stages were associated with impaired mobility (OR 1.36, 95% CI 1.05-1.74; P 0.018) and falls (OR 1.96, 95% CI 1.11-3.43; P = 0.02). Adding data on microinfarcts to a definition of SVD, based on white matter lesions (WMLs), lacunes and significant arteriosclerosis, were assessed by comparing area under ROC curve (AUC) with and without microinfarcts. SVD was significantly related to dementia status with or without inclusion of microinfarcts. Modelling potential pathological definitions of SVD to predict dementia or impaired mobility indicated optimal prediction using combined assessment of WMLs, lacunes and microinfarcts. CONCLUSION: Cortical (dementia) and subcortical microinfarcts (impaired mobility) are related to diverse clinical outcomes. Optimal pathological assessment of significant SVD in brain ageing is achieved based on WMLs, lacunes and microinfarcts and may not require subjective assessment of the extent and severity of arteriosclerosis.

Expression microdissection isolation of enriched cell populations from archival brain tissue.

BACKGROUND: Laser capture microdissection (LCM) is an established technique for the procurement of enriched cell populations that can undergo further downstream analysis, although it does have limitations. Expression microdissection (xMD) is a new technique that begins to address these pitfalls, such as operator dependence and contamination. NEW METHOD: xMD utilises immunohistochemistry in conjunction with a chromogen to isolate specific cell types by extending the fundamental principles of LCM to create an operator-independent method for the procurement of specific CNS cell types. RESULTS: We report how xMD enables the isolation of specific cell populations, namely neurones and astrocytes, from rat formalin fixed-paraffin embedded (FFPE) tissue. Subsequent reverse transcriptase-polymerase chain reaction (RT-PCR) analysis confirms the enrichment of these specific populations. RIN values after xMD indicate samples are sufficient to carry out further analysis. COMPARISON WITH EXISTING METHOD: xMD offers a rapid method of isolating specific CNS cell types without the need for identification by an operator, reducing the amount of unintentional contamination caused by operator error, whilst also significantly reducing the time required by the current basic LCM technique. CONCLUSIONS: xMD is a superior method for the procurement of enriched cell populations from post-mortem tissue, which can be utilised to create transcriptome profiles, aiding our understanding of the contribution of these cells to a range of neurological diseases. xMD also addresses the issues associated with LCM, such as reliance on an operator to identify target cells, which can cause contamination, as well as addressing the time consuming nature of LCM.

Brain haemosiderin in older people: pathological evidence for an ischaemic origin of magnetic resonance imaging (MRI) microbleeds.

INTRODUCTION: Magnetic resonance imaging (MRI) cerebral microbleeds (CMB) arise from ferromagnetic haemosiderin iron assumed to derive from extravasation of erythrocytes. Light microscopy of ageing brain frequently reveals foci of haemosiderin from single crystalloids to larger, predominantly perivascular, aggregates. The pathological and radiological relationship between these findings is not resolved. METHODS: Haemosiderin deposition and vascular pathology in the putamen were quantified in 200 brains donated to the population-representative Medical Research Council Cognitive Function and Ageing Study. Molecular markers of gliosis and tissue integrity were assessed by immunohistochemistry in brains with highest (n = 20) and lowest (n = 20) levels of putamen haemosiderin. The association between haemosiderin counts and degenerative and vascular brain pathology, clinical data, and the haemochromatosis (HFE) gene H63D genotype were analysed. The frequency of MRI CMB in 10 cases with highest and lowest burden of putamen haemosiderin, was compared using post mortem 3T MRI. RESULTS: Greater putamen haemosiderin was significantly associated with putaminal indices of small vessel ischaemia (microinfarcts, P < 0.05; arteriolosclerosis, P < 0.05; perivascular attenuation, P < 0.001) and with lacunes in any brain region (P < 0.023) but not large vessel disease, or whole brain measures of neurodegenerative pathology. Higher levels of putamen haemosiderin correlated with more CMB (P < 0.003). CONCLUSIONS: The MRI-CMB concept should take account of brain iron homeostasis, and small vessel ischaemic change in later life, rather than only as a marker for minor episodes of cerebrovascular extravasation. These data are of clinical relevance, suggesting that basal ganglia MRI microbleeds may be a surrogate for ischaemic small vessel disease rather than exclusively a haemorrhagic diathesis.

Calcium dysregulation in relation to Alzheimer-type pathology in the ageing brain.

AIMS: Calcium dyshomeostasis is implicated in the pathogenesis of several neurodegenerative disorders including Alzheimer's disease. However, much of the previous research has focused on changes in neuronal calcium signalling. In a recent microarray study we identified dysregulation of several key signalling pathways including the Ca(2+) signalling pathway in astrocytes as Alzheimer-type pathology developed. In this study we sought to determine the expression of calpain-10 and calcium/calmodulin-dependent kinase alpha (CamKIIα) in relation to Alzheimer-type pathology in a population-based study. METHODS: Using post mortem temporal cortex samples derived from the Medical Research Council Cognitive Function and Ageing Study (MRC-CFAS) ageing brain cohort we examined calpain-10 and CamKIIα gene and protein expression using quantitative polymerase chain reaction and immunohistochemistry. RESULTS: We demonstrate that astrocytic expression of calpain-10 is up-regulated, and CamKIIα down-regulated with increasing Braak stage. Using immunohistochemistry we confirm protein expression of calpain-10 in astrocytes throughout the temporal cortex and demonstrate that calpain-10 immunoreactivity is correlated with both local and global measures of Alzheimer-type pathology. In addition, we identify a subpopulation of calpain-10 immunoreactive interlaminar astrocytes that extend processes deep into the cortex. CamKIIα is predominantly neuronal in localization and is associated with the presence of diffuse plaques in the ageing brain. DISCUSSION: Dysregulated expression of key calcium signalling molecules occurs with progression of Alzheimer-type pathology in the ageing brain, highlighting the need for further functional studies of astrocytic calcium signalling with respect to disease progression.

Neuro-ophthalmological Complications of Chronic Inflammatory Demyelinating Polyradiculoneuropathy.

Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) can lead to prominent nerve hypertrophy, which can mimic other forms of neuropathy radiologically. Neuro-ophthalmological complications can also occur in CIDP, either at presentation or chronically in the disorder. This can also cause diagnostic difficulties. We report three cases of neuro-ophthalmological complications of CIDP: two cases of papilloedema and one case of proptosis. In all three cases cranial nerve hypertrophy was present. CIDP should be considered in neuro-ophthalmological presentations associated with cranial/spinal nerve root hypertrophy.

Mesial temporal astrocyte tau pathology in the MRC-CFAS ageing brain cohort.

BACKGROUND: Glial tau pathology is seen in certain tauopathies and in ageing. We determined its frequency in ageing mesial temporal lobe and its relationship to other tau pathologies in the MRC-CFAS population-representative neuropathology cohort. METHODS: Mesial temporal lobe, including hippocampus, amygdala, entorhinal cortex and white matter, was examined using immunohistochemistry with the AT8 antibody to phospho-tau and RD3 and RD4 antibodies to 3R and 4R tau isoforms. Gallyas silver stain was used to detect fibrillar aggregates. RESULTS: Thorn-shaped astrocytes (TSA), positive with AT8, RD4 and Gallyas, were present in 49% of cases. They were particularly prevalent in subpial, periventricular and white matter perivascular locations and were less frequent in grey matter. Coiled bodies were seen in 18.8%. TSA were not related to Braak neurofibrillary tangle or hippocampal tangle pathology stages. TSA in grey matter were associated with coiled bodies (p = 0.011) and argyrophilic grains (p = 0.048), which were identified in 11.5% of cases. They did not correlate with dementia. CONCLUSIONS: Astrocyte tau pathology is common in the ageing mesial temporal lobe. Its formation is independent of Alzheimer-type pathology. It is a 4R tauopathy, which may form part of a mesial temporal age-related 4R tauopathy that includes oligodendroglial tau and argyrophilic grains.

Isolation of enriched glial populations from post-mortem human CNS material by immuno-laser capture microdissection.

Isolating individual populations of cells from post-mortem (PM) central nervous system (CNS) tissue for transcriptomic analysis will provide important insights into the pathogenesis of neurodegenerative diseases. To date, research on individual CNS cell populations has been hindered by the availability of suitable PM material, unreliable sample preparation and difficulties obtaining individual cell populations. In this paper we report how rapid immunohistochemistry combined with laser capture microdissection (immuno-LCM) enables the isolation of specific cell populations from PM CNS tissue, thereby enabling the RNA profile of these individual cell types to be investigated. Specifically, we detail methods for isolating enriched glial populations (astrocytes, oligodendrocytes and microglia) and confirm this cell enrichment by polymerase chain reaction (PCR). In addition, the study details the numbers of each glial population required to obtain 50ng RNA, a suitable amount of starting material required to carry out microarray analysis that potentially may identify alterations of cell-specific genes and pathways associated with a range of neurodegenerative disorders.

Sensory ganglionopathy due to gluten sensitivity.

OBJECTIVES: Gluten sensitivity can engender neurologic dysfunction, one of the two commonest presentations being peripheral neuropathy. The commonest type of neuropathy seen in the context of gluten sensitivity is sensorimotor axonal. We report 17 patients with sensory ganglionopathy associated with gluten sensitivity. METHODS: This is a retrospective observational case series of 17 patients with sensory ganglionopathy and gluten sensitivity. All patients had been followed up for a number of years in dedicated gluten sensitivity/neurology and neuropathy clinics. RESULTS: Out of a total of 409 patients with different types of peripheral neuropathies, 53 (13%) had clinical and neurophysiologic evidence of sensory ganglionopathy. Out of these 53 patients, 17 (32%) had serologic evidence of gluten sensitivity. The mean age of those with gluten sensitivity was 67 years and the mean age at onset was 58 years. Seven of those with serologic evidence of gluten sensitivity had enteropathy on biopsy. Fifteen patients went on a gluten-free diet, resulting in stabilization of the neuropathy in 11. The remaining 4 had poor adherence to the diet and progressed, as did the 2 patients who did not opt for dietary treatment. Autopsy tissue from 3 patients demonstrated inflammation in the dorsal root ganglia with degeneration of the posterior columns of the spinal cord. CONCLUSIONS: Sensory ganglionopathy can be a manifestation of gluten sensitivity and may respond to a strict gluten-free diet.

Population variation in oxidative stress and astrocyte DNA damage in relation to Alzheimer-type pathology in the ageing brain.

AIMS: Increasing evidence suggests a role for oxidative damage to DNA in brain ageing and in neurodegenerative disorders, including Alzheimer's disease. Most studies have focussed on the reduced capacity for DNA repair by neurones, and have not taken into account the effect of oxidative stress on astrocytes, and their contribution to pathology. METHODS: We examined levels of oxidative stress, DNA damage and DNA repair mechanisms in astrocytes in a population-based sample derived from the Medical Research Council Cognitive Function and Ageing Neuropathology Study. RESULTS: We demonstrate wide variation in parameters for oxidative stress and DNA damage in astrocytes in the ageing population. We show that there is a significant reduction (P = 0.002) in the lipid peroxidation marker malondialdehyde with increasing Braak stage in Alzheimer's disease. Furthermore, we demonstrate that expression of the DNA damage-associated molecules H2AX and DNA-dependent protein kinase do not increase with increasing Braak stage, rather there is evidence of a nonsignificant reduction in DNA-dependent protein kinase expression by neurones and astrocytes, and in H2AX by neurones with increasing levels of Alzheimer's type pathology. CONCLUSIONS: These findings suggest that the changes in oxidative stress and the astrocyte DNA damage response are not accounted for as an accumulating effect due to established Alzheimer-type pathology. We hypothesize that astrocyte damage, leading to impaired function, may contribute to the development of ageing brain pathology in some individuals.

Astrocyte phenotype in relation to Alzheimer-type pathology in the ageing brain.

Astrocyte pathology occurs in association with Alzheimer's disease (AD) and in brain ageing, but is poorly characterised. We sought to define the detailed cellular pathology of astrocytes, the extent of population variation and the relationship to Alzheimer-type changes in a population-based cohort. Three staining patterns were associated with GFAP and excitatory amino acid transporter 2 (EAAT2): minimal, moderate or extensive immunoreactivity. GFAP and EAAT2 expression were inversely related (p=0.015), with trends to increased expression of GFAP (p=0.019) and decreased expression of EAAT2 (p=ns) with increasing Braak stage. GFAP and EAAT2 correlated incompletely with beta-amyloid and tau immunoreactivity. However, gliosis increased with increasing burden of neuritic (p=0.011), but not diffuse (p=ns), plaques. Double-staining revealed distinct subsets of astrocytes; GFAP(+)EAAT(-), GFAP(-)EAAT(+), or GFAP(+)EAAT(+). In contrast to the variation in GFAP and EAAT2, levels of EAAT1 and S100B showed consistent staining patterns. Alzheimer-type pathology only partially explains the variation in gliosis and astrocyte functional markers, suggesting that other factors contribute to the population variance in astrocyte pathology.

Population variation in glial fibrillary acidic protein levels in brain ageing: relationship to Alzheimer-type pathology and dementia.

BACKGROUND: The cellular pathology of astrocytes in brain ageing and their role in modulating the brain's response to neurodegenerative pathology remain incompletely understood. METHODS: Using quantitative ELISA, we have investigated glial fibrillary acidic protein (GFAP) expression in the population-based neuropathology cohort of the Medical Research Council Cognitive Function and Ageing Study to determine: (1) the population variation in the astroglial hypertrophic response, (2) its relationship to the presence of Alzheimer-type pathology, and (3) its association with cognition. RESULTS: Increasing GFAP was found with increasing Braak stage, levels increasing even at early stages. Within Braak stages, GFAP did not differ between demented and non-demented individuals, but there was greater variance in GFAP in the demented. Possession of ApoE epsilon4 was associated with slightly increased GFAP levels (not significant) for given amyloid beta protein loads. CONCLUSION: In a population-based sample, increasing gliosis precedes development of Alzheimer lesions. Population variation in GFAP with varying Alzheimer lesion burdens suggests that they are not the only driver for astrogliosis. GFAP was not independently predictive of dementia, but the variation in astrocytic responses may be a factor modulating brain responses to neurodegenerative pathology.

Hippocampal tau pathology is related to neuroanatomical connections: an ageing population-based study.

Deposits of abnormally phosphorylated tau protein are found in numerous neurodegenerative disorders; the 'tauopathies', which include Alzheimer's and Pick's diseases, but tau pathology is also found in the ageing brain. Variation in tau pathology in brain ageing and its relationship to development of tauopathies and cognitive impairment remains unclear. We aimed to determine the extent and pattern of spread of tau pathology in the hippocampus, a susceptible region important in dementia and milder states of memory impairment, using hippocampal samples from the elderly population-based Medical Research Council Cognitive Function and Ageing Study neuropathology cohort. Tau deposition was assessed in hippocampal anatomical sub-regions using the AT8 antibody to phosphorylated tau and isoform-specific antibodies to 3 and 4-repeat tau (RD3 and RD4). Abeta pathology was also assessed. In this population sample, which includes the full ageing spectrum from individuals with no cognitive impairment to those with dementia satisfying clinico-pathology criteria for Alzheimer's disease, we have demonstrated a high prevalence at death of tau pathology. AT8, Abeta, RD3 and RD4 showed similar regional distribution and increased RD3 was noted in late-stage ghost tangles. Abeta was shown to be a poor explanatory variable for tau pathology. Tau deposition progressed in a hierarchical manner. Hippocampal input regions and projection zones (such as lateral entorhinal cortex, CA1/subiculum border and outer molecular layer of dentate) were initially affected, with anterograde progression though the hippocampal circuitry. Six hippocampal tau anatomical stages were defined, each linking projectionally to their adjacent stages, suggesting spread of tau malfunction through neuroanatomical pathways in hippocampal ageing. These stages were significantly associated with dementia, and may provide a clinically useful tool in the clinico-pathological assessment of dementia and mild cognitive impairment.

Microglial activation in white matter lesions and nonlesional white matter of ageing brains.

White matter lesions (WML), a common feature in brain ageing, are classified as periventricular (PVL) or deep subcortical (DSCL), depending on their anatomical location. Microglial activation is implicated in a number of neurodegenerative diseases, but the microglial response in WML is poorly characterized and its role in pathogenesis unknown. We have characterized the microglial response in WML and control white matter using immunohistochemistry to markers of microglial activation and of proliferation. WML of brains from an unbiased population-based autopsy cohort (Medical Research Council's Cognitive Function and Ageing Study) were identified by post mortem magnetic resonance imaging and sampled for histology. PVL contain significantly more activated microglia, expressing major histocompatibility complex (MHC) class II and the costimulatory molecules B7-2 and CD40, than either control white matter (WM) or DSCL. Furthermore, we show that significantly more microglia express the replication licensing protein minichromosome maintenance protein 2 within PVL, suggesting this is a more proliferation-permissive environment than DSCL. Although microglial activation occurs in both PVL and DSCL, our findings suggest a difference in pathogenesis between these lesion-types: the ramified, activated microglia associated with PVL may reflect immune activation resulting from disruption of the blood brain barrier, while the microglia within DSCL may reflect an innate, amoeboid phagocytic phenotype. We also show that microglia in control WM from lesional cases express significantly more MHC II than control WM from nonlesional ageing brain, suggesting that WML occur in a 'field-effect' of abnormal WM.