Charles Duyckaerts

Classification and basic pathology of Alzheimer disease

The lesions of Alzheimer disease include accumulation of proteins, losses of neurons and synapses, and alterations related to reactive processes. Extracellular Aβ accumulation occurs in the parenchyma as diffuse, focal or stellate deposits. It may involve the vessel walls of arteries, veins and capillaries. The cases in which the capillary vessel walls are affected have a higher probability of having one or two apoε 4 alleles. Parenchymal as well as vascular Aβ deposition follows a stepwise progression. Tau accumulation, probably the best histopathological correlate of the clinical symptoms, takes three aspects: in the cell body of the neuron as neurofibrillary tangle, in the dendrites as neuropil threads, and in the axons forming the senile plaque neuritic corona. The progression of tau pathology is stepwise and stereotyped from the entorhinal cortex, through the hippocampus, to the isocortex. The neuronal loss is heterogeneous and area-specific. Its mechanism is still discussed. The timing of the synaptic loss, probably linked to Aβ peptide itself, maybe as oligomers, is also controversial. Various clinico-pathological types of Alzheimer disease have been described, according to the type of the lesions (plaque only and tangle predominant), the type of onset (focal onset), the cause (genetic or sporadic) and the associated lesions (Lewy bodies, vascular lesions, hippocampal sclerosis, TDP-43 inclusions and argyrophilic grain disease).

A Multicenter Study of Glucocerebrosidase Mutations in Dementia With Lewy Bodies

IMPORTANCEnWhile mutations in glucocerebrosidase (GBA1) are associated with an increased risk for Parkinson disease (PD), it is important to establish whether such mutations are also a common risk factor for other Lewy body disorders.nnnOBJECTIVEnTo establish whether GBA1 mutations are a risk factor for dementia with Lewy bodies (DLB). DESIGN We compared genotype data on patients and controls from 11 centers. Data concerning demographics, age at onset, disease duration, and clinical and pathological features were collected when available. We conducted pooled analyses using logistic regression to investigate GBA1 mutation carrier status as predicting DLB or PD with dementia status, using common control subjects as a reference group. Random-effects meta-analyses were conducted to account for additional heterogeneity.nnnSETTINGnEleven centers from sites around the world performing genotyping.nnnPARTICIPANTSnSeven hundred twenty-one cases met diagnostic criteria for DLB and 151 had PD with dementia. We compared these cases with 1962 controls from the same centers matched for age, sex, and ethnicity.nnnMAIN OUTCOME MEASURESnFrequency of GBA1 mutations in cases and controls. RESULTS We found a significant association between GBA1 mutation carrier status and DLB, with an odds ratio of 8.28 (95% CI, 4.78-14.88). The odds ratio for PD with dementia was 6.48 (95% CI, 2.53-15.37). The mean age at diagnosis of DLB was earlier in GBA1 mutation carriers than in noncarriers (63.5 vs 68.9 years; P < .001), with higher disease severity scores.nnnCONCLUSIONS AND RELEVANCEnMutations in GBA1 are a significant risk factor for DLB. GBA1 mutations likely play an even larger role in the genetic etiology of DLB than in PD, providing insight into the role of glucocerebrosidase in Lewy body disease.

Subcellular topography of neuronal Aβ peptide in APPxPS1 transgenic mice

In transgenic mice expressing human mutant beta-amyloid precursor protein (APP) and mutant presenilin-1 (PS1), Abeta antibodies labeled granules, about 1 microm in diameter, in the perikaryon of neurons clustered in the isocortex, hippocampus, amygdala, thalamus, and brainstem. The granules were present before the onset of Abeta deposits; their number increased up to 9 months and decreased in 15-month-old animals. They were immunostained by antibodies against Abeta 40, Abeta 42, and APP C-terminal region. In double immunofluorescence experiments, the intracellular Abeta co-localized with lysosome markers and less frequently with MG160, a Golgi marker. Abeta accumulation correlated with an increased volume of lysosomes and Golgi apparatus, while the volume of endoplasmic reticulum and early endosomes did not change. Some granules were immunolabeled with an antibody against flotillin-1, a raft marker. At electron microscopy, Abeta, APP-C terminal, cathepsin D, and flotillin-1 epitopes were found in the lumen of multivesicular bodies. This study shows that Abeta peptide and APP C-terminal region accumulate in multivesicular bodies containing lysosomal enzymes, while APP N-terminus is excluded from them. Multivesicular bodies could secondarily liberate their content in the extracellular space as suggested by the association of cathepsin D with Abeta peptide in the extracellular space.

The mitochondrial complex I inhibitor rotenone triggers a cerebral tauopathy

Reduced activity of the mitochondrial respiratory chain – particularly complexu2003I – may be implicated in the etiology of both Parkinsons disease and progressive supranuclear palsy, although these neurodegenerative diseases differ substantially as to their distinctive pattern of neuronal cell loss and the predominance of cerebral α‐synuclein or tau protein pathology. To determine experimentally whether chronic generalized complexu2003I inhibition has an effect on the distribution of α‐synuclein or tau, we infused rats systemically with the plant‐derived isoflavonoid rotenone. Rotenone‐treated rats with a pronounced metabolic impairment had reduced locomotor activity, dystonic limb posture and postural instability. They lost neurons in the substantia nigra and in the striatum. Spherical deposits of α‐synuclein were observed in a few cells, but cells with abnormal cytoplasmic accumulations of tau immunoreactivity were significantly more numerous in the striatum of severely lesioned rats. Abnormally high levels of tau immunoreactivity were found in the cytoplasm of neurons, oligodendrocytes and astrocytes. Ultrastructurally, tau‐immunoreactive material consisted of straight 15‐nm filaments decorated by antibodies against phosphorylated tau. Many tau+ cell bodies also stained positive for thioflavinu2003S, nitrotyrosine and ubiquitin. Some cells with abnormal tau immunoreactivity contained activated caspaseu20033. Our data suggest that chronic respiratory chain dysfunction might trigger a form of neurodegeneration in which accumulation of hyperphosphorylated tau protein predominates over deposits of α‐synuclein.

Modeling the Relation Between Neurofibrillary Tangles and Intellectual Status

The relationship between the neurofibrillary tangles and the intellectual deficit observed in senile dementia of the Alzheimer type was studied in 27 patients over the age of 75. The presence and density of tau positive tangles were assessed in six areas including limbic, paralimbic, and isocortical cortices. In the isocortical areas, the presence [1] or absence [0] of neurofibrillary tangles was better correlated with the Blessed test score than the density of the neurofibrillary tangles profiles. Multivariate analysis showed that the number of areas containing at least one neurofibrillary tangle was the best explanatory variable of the intellectual status. The cortical areas were ranked according to the prevalence of their involvement. The presence of tangles in an area of a given rank took place only if the areas of lower ranks were also involved. It is proposed that the presence of tangles in a given area is a more significant information than the value of their density. These data may lead to new diagnostic procedures.

Microglia, amyloid and dementia in Alzheimer disease A correlative study

To elucidate the role of microglia in Alzheimers disease, a clinicopathological study was performed involving 26 cases, the mental status of which had been studied pre mortem by the Blessed test score (BTS). We measured the volume density of CD 68 immunoreactive (IR) microglia, congophilic plaques and Abeta deposits, and the numerical density of neurofibrillary tangles (NFT) in a sample of Area 9 (middle frontal gyrus). Dementia was significantly correlated only with the volume density of Abeta deposits and the numerical density of NFT. The volume densities of microglia and congophilic plaques were strongly correlated. With the intellectual status used as a time scale, IR microglia and amyloid deposits appeared almost simultaneously at an early stage in the pathological cascade and decreased, whereas Abeta and NFT were still accumulating. The intellectual deficit seemed to be more significantly related to the latter two lesions than to the microglia-amyloid complex, that was visible at an earlier stage (around BTS = 15).

Local cholesterol increase triggers amyloid precursor protein-Bace1 clustering in lipid rafts and rapid endocytosis

Amyloid peptide (Aβ) is generated by sequential cleavage of the amyloid precursor protein (APP) by β‐secretase (Bacel) and γ‐secretase. Aβ production increases after plasma membrane cholesterol loading through unknown mechanisms. To determine how APP‐Bacel proximity affects this phenomenon, we developed a fluorescence lifetime imaging microscopy‐Förster resonance energy transfer (FLIM‐FRET) technique for visualization of these molecules either by epifluorescence or at the plasma membrane only using total internal reflection fluorescence. Further, we used fluorescence correlation spectroscopy to determine the lipid rafts partition of APP‐yellow fluorescent protein (YFP) and Bacel‐green fluorescent protein (GFP) molecules at the plasma membrane of neurons. We show that less than 10 min after cholesterol exposure’ Bacel‐GFP/APP‐mCherry proximity increases selectively at the membrane and APP relocalizes to raft domains’ preceded by rapid endocytosis. After longer cholesterol exposures, APP and Bacel are found in proximity intracellularly. We demonstrate that cholesterol loading does not increase Aβ production by having a direct impact on Bacel catalytic activity but rather by altering the accessibility of Bacel to its substrate’ APP. This change in accessibility is mediated by clustering in lipid rafts’ followed by rapid endocytosis.—Marquer, C., Devauges, V., CossecJ.‐C., Liot, G., Lecart, S., Saudou F., Duyckaerts, C., Leveque‐Fort, S., Potier, M.‐C. Local cholesterol increase triggers amyloid precursor protein‐Bacel clustering in lipid rafts and rapid endocytosis. FASEB J. 25, 1295–1305 (2011). www.fasebj.org

A stable proportion of Lewy body bearing neurons in the substantia nigra suggests a model in which the Lewy body causes neuronal death

Lewy bodies in Parkinson disease could be innocent bystanders or active agents responsible for neuronal death. Eighteen elderly patients with a Parkinson syndrome were studied prospectively and selected postmortem on the presence of Lewy bodies (14 cases with Parkinson disease, four with dementia with Lewy bodies). Information on disease duration was available in 17 cases. While akinesia and rigidity were linked with the neuronal loss, the percentages of Lewy body bearing neurons and of alpha-synuclein immunoreactive neurons in the substantia nigra were not correlated with the symptoms or the disease duration, and appeared stable, involving 3.6% of the neurons on average. Such stability indicated that, during the whole course of the disease, the destruction of the Lewy bodies was equal to their production. In the model that is proposed here, the Lewy bodies are eliminated when the neurons that bear them die. With the hypothesis that neuronal death is directly related to Lewy bodies, it is possible to estimate their life span, which was calculated to be 6.2 months (15.9 months for any type of alpha-synuclein inclusion).

Clinical Correlations With Lewy Body Pathology in LRRK2-Related Parkinson Disease

IMPORTANCEnMutations in leucine-rich repeat kinase 2 (LRRK2) are the most common cause of genetic Parkinson disease (PD) known to date. The clinical features of manifesting LRRK2 mutation carriers are generally indistinguishable from those of patients with sporadic PD. However, some PD cases associated with LRRK2 mutations lack Lewy bodies (LBs), a neuropathological hallmark of PD. We investigated whether the presence or absence of LBs correlates with different clinical features in LRRK2-related PD.nnnOBSERVATIONSnWe describe genetic, clinical, and neuropathological findings of 37 cases of LRRK2-related PD including 33 published and 4 unpublished cases through October 2013. Among the different mutations, the LRRK2 p.G2019S mutation was most frequently associated with LB pathology. Nonmotor features of cognitive impairment/dementia, anxiety, and orthostatic hypotension were correlated with the presence of LBs. In contrast, a primarily motor phenotype was associated with a lack of LBs.nnnCONCLUSIONS AND RELEVANCEnTo our knowledge, this is the first report of clinicopathological correlations in a series of LRRK2-related PD cases. Findings from this selected group of patients with PD demonstrated that parkinsonian motor features can occur in the absence of LBs. However, LB pathology in LRRK2-related PD may be a marker for a broader parkinsonian symptom complex including cognitive impairment.

Rating of the lesions in senile dementia of the Alzheimer type: concordance between laboratories. A European multicenter study under the auspices of EURAGE.

The study reported was intended to compare the impressions and analyses of investigators from 11 different laboratories on 2 slides, each from 6 cases with varying quantities of neuropathological change of the type found in Alzheimers disease and normal ageing. The material came from 6 selected female patients over 75 years of age all of whom had been examined in detail and assessed by the Blessed Test Score. Two were severely demented, 2 mildly demented and 2 were considered to be normal. Unstained paraffin-embedded slides were sent to the investigators, the choice of the staining techniques being left to each laboratory. A quantitative evaluation of the changes was requested in 2 specified areas of the hippocampus and in the first temporal gyrus. Subjective scores of severity and a final guess about the pre mortem intellectual status (demented or not) were asked. The 11 replies were analyzed. A total of 14 different staining techniques were used. Absolute values of density differed much from one investigator to another, for senile plaques as well as for neurofibrillary tangles. Statistical analysis showed that concordance might be improved by the use of corrective factors which would standardize the scales of measurement. The ranking of the slides in increasing order of severity was in good agreement for 9 out of 11 observers concerning the neurofibrillary tangles and 3 out of 9 observers concerning the senile plaques. The correlation between the intellectual status and the density of lesions was higher for neurofibrillary tangles than for senile plaques. The subjective scores were in better agreement for the severely affected cases than for the mildly affected ones. The lowest correlation with intellectual deficit was obtained with the quantitative scores which took into account only the senile plaques or only the hippocampal lesions. The highest correlation coefficients were obtained with the subjective scores. The observers guessed correctly the intellectual status of the 2 most affected cases and often disagreed for the intermediate and normal cases. Neuropathology is mandatory for the diagnosis of definite Alzheimers disease. Quantitative assessment is useful in cases with few lesions and light dementia but the neuropathological diagnostic procedure has to be more strictly standardized before quantitative histopathological criteria can be reliably transferred from one laboratory to another, especially when mildly affected cases are involved. Concordance seems presently easier to obtain by ranking the lesions and the cases in increasing order of severity than by using quantitative values of density.(ABSTRACT TRUNCATED AT 400 WORDS)