Teresa Gomez-Isla

Use of structural magnetic resonance imaging to predict who will get Alzheimer's disease

We used magnetic resonance imaging (MRI) measurements to determine whether persons in the prodromal phase of Alzheimers disease (AD) could be accurately identified before they developed clinically diagnosed dementia. Normal subjects (n = 24) and those with mild memory difficulty (n = 79) received an MRI scan at baseline and were then followed annually for 3 years to determine which individuals subsequently met clinical criteria for AD. Patients with mild AD at baseline were also evaluated (n = 16). Nineteen of the 79 subjects with mild memory difficulty “converted” to a diagnosis of probable AD after 3 years of follow‐up. Baseline MRI measures of the entorhinal cortex, the banks of the superior temporal sulcus, and the anterior cingulate were most useful in discriminating the status of the subjects on follow‐up examination. The accuracy of discrimination was related to the clinical similarity between groups. One hundred percent (100%) of normal subjects and patients with mild AD could be discriminated from one another based on these MRI measures. When the normals were compared with the individuals with memory impairments who ultimately developed AD (the converters), the accuracy of discrimination was 93%, based on the MRI measures at baseline (sensitivity = 0.95; specificity = 0.90). The discrimination of the normal subjects and the individuals with mild memory problems who did not progress to the point where they met clinical criteria for probable AD over the 3 years of follow‐up (the “questionables”) was 85% and the discrimination of the questionables and converters was 75%. The apolipoprotein E genotype did not improve the accuracy of discrimination. The specific regions selected for each of these discriminations provides information concerning the hierarchical fashion in which the pathology of AD may affect the brain during its prodromal phase. Ann Neurol 2000;47:430–439.

Attenuation of Delayed Neuronal Death After Mild Focal Ischemia in Mice by Inhibition of the Caspase Family

Inhibitors of apoptosis and of excitotoxic cell death reduce brain damage after transient and permanent middle cerebral artery occlusion. We compared the neuroprotective effects of two caspase family inhibitors with the N-methyl-d-aspartate receptor antagonist (+)-MK-801 hydrogen maleate (MK-801) in a newly characterized cycloheximidesensitive murine model of transient middle cerebral artery occlusion (30 minutes) in which apoptotic cell death is prominent. Ischemic infarction, undetected by 2,3,5-triphenyltetrazolium chloride staining at 24-hour reperfusion, featured prominently in the striatum at 72 hours and 7 days on hematoxylin-eosin—stained sections. Markers of apoptosis, such as oligonucleosomal DNA damage (laddering) and terminal deoxynucleotidyl transferase—mediated dUTP-biotin nick-end labeling (TUNEL)–positive cells first appeared at 24 hours and increased significantly at 72 hours and 7 days after reperfusion. The TUNEL-labeled cells were mostly neurons and stained negative for glial (GFAP, glial fibrillary acid protein) and leukocyte specific markers (CD-45). The caspase inhibitors, N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (z-VAD.FMK; 120 ng intracerebroventricularly) or N-benzyloxycarbonyl-Asp-Glu-Val-Asp-fluoromethyl ketone (z-DEVD.FMK; 480 ng intracerebroventricularly) decreased infarct size and neurologic deficits when administered 6 hours after reperfusion. The extent of protection was greater than in models of more prolonged ischemia or after permanent occlusion, and the therapeutic window was extended from 0 to 1 hours after 2-hour middle cerebral artery occlusion to at least 6 hours after brief ischemia. Also, z-VAD.FMK and z-DEVD.FMK treatment decreased oligonucleosomal DNA damage (DNA laddering) as assessed by quantitative autoradiography after gel electrophoresis. By contrast, MK-801 protected brain tissue only when given before ischemia (3 mg/kg intraperitoneally), but not at 3 or 6 hours after reperfusion. Despite a decrease in infarct size after MK-801 pretreatment, the amount of DNA laddering did not decrease 72 hours after reperfusion, thereby suggesting a mechanism distinct from inhibition of apoptosis. Hence, 30 minutes of reversible ischemia augments apoptotic cell death, which can be attenuated by delayed z-VADPMK and z-DEVD.FMK administration with preservation of neurologic function. By contrast, the therapeutic window for MK-801 does not extend beyond the time of occlusion, probably because its primary mechanism of action does not block the development of apoptotic cell death.

Endocytic Pathway Abnormalities Precede Amyloid β Deposition in Sporadic Alzheimer’s Disease and Down Syndrome: Differential Effects of APOE Genotype and Presenilin Mutations

Endocytosis is critical to the function and fate of molecules important to Alzheimers disease (AD) etiology, including the beta protein precursor (betaPP), amyloid beta (Abeta) peptide, and apolipoprotein E (ApoE). Early endosomes, a major site of Abeta peptide generation, are markedly enlarged within neurons in the Alzheimer brain, suggesting altered endocytic pathway (EP) activity. Here, we show that neuronal EP activation is a specific and very early response in AD. To evaluate endocytic activation, we used markers of internalization (rab5, rabaptin 5) and recycling (rab4), and found that enlargement of rab5-positive early endosomes in the AD brain was associated with elevated levels of rab4 immunoreactive protein and translocation of rabaptin 5 to endosomes, implying that both endocytic uptake and recycling are activated. These abnormalities were evident in pyramidal neurons of the neocortex at preclinical stages of disease when Alzheimer-like neuropathology, such as Abeta deposition, was restricted to the entorhinal region. In Down syndrome, early endosomes were significantly enlarged in some pyramidal neurons as early as 28 weeks of gestation, decades before classical AD neuropathology develops. Markers of EP activity were only minimally influenced by normal aging and other neurodegenerative diseases studied. Inheritance of the epsilon4 allele of APOE, however, accentuated early endosome enlargement at preclinical stages of AD. By contrast, endosomes were normal in size at advanced stages of familial AD caused by mutations of presenilin 1 or 2, indicating that altered endocytosis is not a consequence of Abeta deposition. These results identify EP activation as the earliest known intraneuronal change to occur in sporadic AD, the most common form of AD. Given the important role of the EP in Abeta peptide generation and ApoE function, early endosomal abnormalities provide a mechanistic link between EP alterations, genetic susceptibility factors, and Abeta generation and suggest differences that may be involved in Abeta generation and beta amyloidogenesis in subtypes of AD.

Nigral and cortical Lewy bodies and dystrophic nigral neurites in Parkinson's disease and cortical Lewy body disease contain alpha-synuclein immunoreactivity.

A mutation in the α-synuclein gene has recently been linked to some cases of familial Parkinsons disease (PD). We characterized the expression of this presynaptic protein in the midbrain, striatum, and temporal cortex of control, PD, and dementia with Lewy bodies (DLB) brain. Control brain showed punctate pericellular immunostaining. PD brain demonstrated α-synuclein immunoreactivity in nigral Lewy bodies, pale bodies and abnormal aeurites. Rare neuronal soma in PD brain were immunoreactive for α-synuclein. DLB cases demonstrated these findings as well as α-synuclein immunoreactivity in cortical Lewy bodies and CA2-3 neurites. These results suggest that, even in sporadic cases, there is an early and direct role for α-synuclein in the pathogenesis of PD and the neuropathologically related disorder DLB.

Tau positron emission tomographic imaging in aging and early Alzheimer disease

Detection of focal brain tau deposition during life could greatly facilitate accurate diagnosis of Alzheimer disease (AD), staging and monitoring of disease progression, and development of disease‐modifying therapies.

Current Advances on Different Kinases Involved in Tau Phosphorylation, and Implications in Alzheimers Disease and Tauopathies

Hyperphosphorylation and accumulation of tau in neurons (and glial cells) is one the main pathologic hallmarks in Alzheimers disease (AD) and other tauopathies, including Picks disease (PiD), progressive supranuclear palsy, corticobasal degeneration, argyrophilic grain disease and familial frontotemporal dementia and parkinsonism linked to chromosome 17 due to mutations in the tau gene (FTDP-17-tau). Hyperphosphorylation of tau is regulated by several kinases that phosphorylate specific sites of tau in vitro. GSK-3-immunoprecipitated sarcosyl-insoluble fractions in AD have the capacity to phosphorylate recombinant tau. In addition, GSK-3 phosphorylated at Ser9, that inactivates GSK-3, is found in the majority of neurons with neurofibrillary tangles and dystrophic neurites of senile plaques in AD, and in Pick bodies and other phospho-tau-containing neurons and glial cells in other tauopathies. Increased expression of active kinases, including stress-activated kinase, c-Jun N-terminal kinase (SAPK/JNK) and kinase p38 has been found in brain homogenates in all the tauopathies. Strong active SAPK/JNK and p38 immunoreactivity has been observed restricted to neurons and glial cells containing hyperphosphorylated tau, as well as in dystrophic neurites of senile plaques in AD. Moreover, SAPK/JNK- and p38-immunoprecipitated sub-cellular fractions enriched in abnormal hyperphosphorylated tau have the capacity to phosphorylate recombinant tau and c-Jun and ATF-2 which are specific substrates of SAPK/JNK and p38 in AD and PiD. Interestingly, increased expression of phosphorylated (active) SAPK/JNK and p38 and hyperphosphorylated tau containing neurites have been observed around betaA4 amyloid deposits in the brain of transgenic mice (Tg 2576) carrying the double APP Swedish mutation. These findings suggest that betaA4 amyloid has the capacity to trigger the activation of stress kinases which, in turn, phosphorylate tau in neurites surrounding amyloid deposits. Complementary findings have been reported from the autopsy of two AD patients who participated in an amyloid-beta immunization trial and died during the course of immunization-induced encephalitis. The neuropathological examination of the brain showed massive focal reduction of amyloid plaques but not of neurofibrillary degeneration. Activation of SAPK/JNK and p38 were reduced together with decreased tau hyperphosphorylation of aberrant neurites in association with decreased amyloid plaques in both Tg2576 mice and human brains. These findings support the amyloid cascade hypothesis of tau phosphorylation mediated by stress kinases in dystrophic neurites of senile plaques but not that of neurofibrillary tangles and neuropil threads in AD.

Tau PET imaging in aging and early Alzheimer's disease

Detection of focal brain tau deposition during life could greatly facilitate accurate diagnosis of Alzheimer disease (AD), staging and monitoring of disease progression, and development of disease‐modifying therapies.

Validating novel tau positron emission tomography tracer [F-18]-AV-1451 (T807) on postmortem brain tissue

To examine region‐ and substrate‐specific autoradiographic and in vitro binding patterns of positron emission tomography tracer [F‐18]‐AV‐1451 (previously known as T807), tailored to allow in vivo detection of paired helical filament‐tau–containing lesions, and to determine whether there is off‐target binding to other amyloid/non‐amyloid proteins.

Apolipoprotein E genotype does not influence rates of cognitive decline in Alzheimer's disease

Background: Inheritance of the apolipoprotein E (apoE) epsilon 4 allele is a risk factor for developing Alzheimers disease (AD) and is associated with a lower age of dementia onset. The purpose of this study was to determine whether apoE genotypes differentially influence the course of cognitive decline in AD dementia. Methods: We administered nine cognitive tests that assessed explicit memory, attention, language, visuospatial function, frontal-lobe function, and logical reasoning abilities to 66 probable AD patients every 6 to 24 months over a span of up to 5.5 years. We identified apoE genotype by a PCR-based method; there were 16 patients with epsilon 3/3, 34 with epsilon 3/4, and 16 with epsilon 4/4. Using regression statistical methods, we computed the change in performance for each test for each patient over time. We then analyzed the mean change in each test in patients grouped according to apoE genotype. Results: For the AD patients as a group, performance on all cognitive tests declined significantly over time, but the rate of decline did not vary significantly across apoE genotypes on any cognitive test. Specifically, the rate of cognitive decline was not faster in patients with an epsilon 4 allele than in those with epsilon 3/3. Conclusions: These results indicate that the mechanism placing individuals with an epsilon 4 allele at risk for developing AD does not influence the rate of cognitive decline. These observations imply that the influence of apoE epsilon 4 either precedes or occurs at an early point in the AD disease process. NEUROLOGY 1996;47: 444-448

Reactive Glia not only Associates with Plaques but also Parallels Tangles in Alzheimer's Disease

Senile plaques are a prominent pathological feature of Alzheimers disease (AD), but little is understood about the association of glial cells with plaques or about the dynamics of glial responses through the disease course. We investigated the progression of reactive glial cells and their relationship with AD pathological hallmarks to test whether glial cells are linked only to amyloid deposits or also to tangle deposition, thus integrating both lesions as a marker of disease severity. We conducted a quantitative stereology-based post-mortem study on the temporal neocortex of 15 control subjects without dementia and 91 patients with AD, including measures of amyloid load, neurofibrillary tangles, reactive astrocytes, and activated microglia. We also addressed the progression of glial responses in the vicinity (≤50 μm) of dense-core plaques and tangles. Although the amyloid load reached a plateau early after symptom onset, astrocytosis and microgliosis increased linearly throughout the disease course. Moreover, glial responses correlated positively with tangle burden, whereas astrocytosis correlated negatively with cortical thickness. However, neither correlated with amyloid load. Glial responses increased linearly around existing plaques and in the vicinity of tangles. These results indicate that the progression of astrocytosis and microgliosis diverges from that of amyloid deposition, arguing against a straightforward relationship between glial cells and plaques. They also suggest that reactive glia might contribute to the ongoing neurodegeneration.