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Original Contribution |

Caspase Gene Expression in the Brain as a Function of the Clinical Progression of Alzheimer Disease FREE

Patrick N. Pompl, MS; Shrishailam Yemul, PhD; Zhongmin Xiang, PhD; Lap Ho, PhD; Varham Haroutunian, PhD; Dushyant Purohit, MD; Richard Mohs, MD; Giulio Maria Pasinetti, MD, PhD
[+] Author Affiliations

From the Neuroinflammation Research Laboratories, Department of Psychiatry (Mr Pompl and Drs Yemul, Xiang, Ho, and Pasinetti), and the Departments of Pathology (Dr Purohit) and Psychiatry (Dr Mohs), Mount Sinai School of Medicine, New York, NY; and the Department of Psychiatry, Bronx Veteran Affairs Medical Center, Bronx, NY (Dr Haroutunian).


Arch Neurol. 2003;60(3):369-376. doi:10.1001/archneur.60.3.369.
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Background  Caspase gene expression has previously been reported in terminal Alzheimer disease (AD) brain, but, currently, little is known about the temporal pattern of caspase gene expression relative to the onset and clinical progression of AD.

Objective  To derive a profile of caspase gene expression and proapoptotic indexes as a function of the clinical and neuropathologic progression of AD dementia.

Setting and Patients  Postmortem survey of nursing home patients characterized clinically by Clinical Dementia Rating (CDR) and neuropathologically by Consortium to Establish a Registry for Alzheimer's Disease criteria.

Design and Outcome Measures  To assess messenger RNA expression of caspase-1, -2L, -2S, -3, -5, -6, -7, -8, and -9; apoptotic cell death by TUNEL assay; and poly (ADP-ribose) polymerase cleavage in postmortem brain tissue samples from cognitively normal (CDR 0), high risk of developing AD dementia (CDR 0.5), and severe dementia (CDR 5) cases.

Results  Compared with CDR 0 cases, elevated messenger RNA expression of caspase-1 and caspase-7 in the entorhinal cortex of CDR 0.5 cases coincided with increased poly (ADP-ribose) polymerase cleavage but not apoptotic cell injury. In the entorhinal cortex of CDR 5 cases, we found elevation of caspase-1, -2L, -3, -5, -6, -7, -8, and -9 and a greater than 4-fold increase in TUNEL-positive cells. Caspase messenger RNA expression was closely associated with neurofibrillary tangle and, to a lesser extent, neuritic plaque density.

Conclusions  Proapoptotic mechanisms may be at play early in the onset of AD (before overt signs of apoptosis) and may be a conditional factor for later apoptotic cell injury or death. These data have relevance to potential therapeutic interventions for AD using selective caspase inhibitors.

Figures in this Article

THE CLINICAL progression of Alzheimer disease (AD) is characterized by the subtle onset of cognitive impairment followed by increasing functional deficits in multiple cognitive and noncognitive domains. Neuropathologically, the clinical progression of AD is marked by the formation of neuritic plaques (NPs) and neurofibrillary tangles (NFTs) and neuronal loss in select brain regions.17 Although definitive neuronal loss is a consistent feature of severe AD dementia, growing evidence indicates that select neuronal loss, assessed stereologically, is detectable in regions of the hippocampal formation and entorhinal cortex (EC) in very mild AD.8,9

Currently, the mechanisms responsible for cell death in AD are not well understood. However, recent evidence10,11 suggests that apoptotic cell injury and, eventually, cell death is a major contributor to the AD neurodegenerative process. Apoptosis is regulated by the cysteine protease family of genes known as caspases.12 Through a cascade of upstream "initiator" caspases (caspase-2L, -2S, -5, -8, and -9), cells become committed to the apoptotic process, then, after activation of downstream "executioner" caspases (caspase-3, -6, and -7), cells subsequently undergo dramatic morphologic changes that result in cell death.11 In vitro1318 and in vivo19,20 studies report elevated expression and activation of several caspases in models of AD and suggest a role for these proteases in the disease process. Consistent with these data, accumulating evidence suggests elevation of caspase levels in the brain of severe definitive AD cases10,2123 and elevation of apoptotic cell injury indicated by TUNEL (terminal deoxynucleotidyl transferase deoxyuridine triphosphate–mediated nick end labeling) assay and DNA fragmentation.5,7,2435

However, much of the available information on proapoptotic caspase expression in AD comes from studies of cases of severe AD dementia and includes relatively few of the known caspases. To clarify the potential role of caspase activation with respect to proapoptotic events in AD onset and progression, we assessed the expression of initiator and executioner caspases in the EC (Brodmann area [BM] 36/38), a region highly affected in AD, and in the occipital cortex (OC) (BM17), an unaffected region in AD, as a function of AD dementia progression. All samples were obtained from patients characterized by Clinical Dementia Rating (CDR) and include cognitively normal (CDR 0), at high risk to develop AD (CDR 0.5), and late-stage AD (CDR 5) cases.

We report an early and select induction of proapoptotic caspases in the EC-BM36/38 of CDR 0.5 cases that coincided with increased cleavage of the DNA repair molecule poly (ADP-ribose) polymerase (PARP). Furthermore, whereas the disease progressed from CDR 0.5 to severe terminal CDR 5, comprehensive recruitment and elevation of caspase messenger RNA (mRNA) expression was associated with TUNEL-positive apoptotic cells in the EC-BM36/38 and density of NFTs. The studies suggest that induction of caspase expression may be an early event in AD dementia and may play an important role in the clinical and neuropathologic progression of this disease.

PATIENT SELECTION CRITERIA

Human postmortem brain samples from AD and age-matched non-AD cases were obtained from the Alzheimer's Disease Brain Bank of the Mount Sinai School of Medicine. The cases selected had either no significant neuropathological features or only neuropathological features associated with AD.36,37 A multistep approach based on cognitive and functional status during the last 6 months of life was applied to the assignment of CDRs38 as previously reported.36,37 Samples of OC and EC were divided into groups on the basis of their CDRs as follows (OC/EC): CDR 0, nondemented (n = 9/9); CDR 0.5, at high risk of developing AD dementia (n = 14/9); and CDR 5, severe dementia (n = 9/9).

The extent of NFT and β-amyloid NP staining in the EC was assessed in accord with the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) neuropathologic battery.1 Multiple (˜5) high-power (×200, 0.5-mm2) fields were examined in each histologic slide from multiple regions according to the CERAD regional sampling scheme. The density of NFTs and NPs was rated on a 4-point scale as follows: 0, absent; 1, sparse; 3, moderate; and 5, severe. Plaques were visualized after either Bielschowsky silver or thioflavin-S staining.39 Three of us (P.N.P., S.Y., and Z.X.) were masked to the clinical diagnosis of each case until all histochemical and mRNA quantitative analyses were completed and values were assigned to each specimen.

RIBONUCLEASE PROTECTION ASSAY

Total RNA was prepared using an RNA isolation system (Ultraspec; BIOTECX Laboratories Inc, Houston, Tex), based on the acid guanidinium thiocyanate-phenol-chloroform method.40,41 RNA was assayed using a multiprobe ribonuclease protection assay system (BD RiboQuant; BD PharMingen, San Diego, Calif). A custom probe set containing complementary DNA templates for the following human caspase genes was used: caspase-1, -2L, -2S, -3, -5, -6, -7, -8, and -9. The probe set also included the housekeeping gene products L32 and glyceraldehyde phosphate dehydrogenase as internal controls for normalization of assay conditions. Details on the generation of (α-32P) uridine-5′-triphosphate antisense RNA probes and conditions of the ribonuclease protection assay were in accord with the manufacturer's instructions. The radioactively labeled ribonuclease protection fragments were quantitated using a Storm 860 Phosphor Screen Scanner with the ImageQuant software package (Molecular Dynamics, Piscataway, NJ). Each ribonuclease protection assay analysis was conducted with 10 µg of total RNA, according to 260 nm absorbance values. Data are expressed as a ratio of the specific mRNA of interest normalized to the constitutively expressed glyceraldehyde phosphate dehydrogenase mRNA. Normalization of caspase mRNA signals to L32 did not change the outcome of the results (data not shown). The validity of the RNA assay (BD PharMingen) for assessing changes in caspase gene expression throughout a variety of independent experiments was recently reported.42 For information regarding RNA sample quality and exclusion criteria, see Figure 1.

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Figure 1. Baseline ribonuclease protection assay (RPA) profile of mean caspase messenger RNA (mRNA) expression in the entorhinal cortex (EC) (Brodmann area 36/38) and the occipital cortex (OC) (BM17) of cognitively normal cases (Clinical Dementia Rating [CDR] 0). Caspase mRNA levels are expressed as a ratio to the housekeeping gene glyceraldehyde phosphate dehydrogenase (GAPDH). In these studies, an initial RNA quality control for RNA sample quality assessment consisted of agarose gel assessment of ethidium bromide staining of 18S and 28S ribosomal RNA integrity and detection of low-molecular-weight "smearing" of degraded mRNA. All samples were subjected to RPA, regardless of initial quality control assessment. Only samples with nondegraded RNA verified by ethidium bromide and RPA analyses were included in the study. In each brain region examined, RNA exclusion was similarly distributed among the different CDR categories. Error bars represent SEM.

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TUNEL APOPTOTIC ASSAY

The TUNEL method was used to identify apoptotic cell injury according to the protocol of an apoptosis detection kit (ApopTag; Intergen, Purchase, NY). Paraffin brain tissue sections (10µM) encompassing the dorsoventral extent of the EC-BM36/38 (n = 5-6 cases for each CDR group, tissue from the contralateral hemisphere of that used for mRNA extraction) were deparaffinized in a clearing agent (Histoclear; National Diagnostics, Atlanta, Ga), rehydrated in descending concentrations of ethanol, and rinsed in phosphate-buffered saline solution. After pretreatment with protease K (20 µg/mL) for 15 minutes, the sections were incubated with terminal deoxynucleotidyl transferase enzyme in a humidified chamber at 37°C for 1 hour and then incubated with antidigoxigenin conjugate for 30 minutes. The TUNEL-labeled cells were then visualized using a DAB substrate kit (Vector Laboratories, Burlingame, Calif). The slides were counterstained with methyl green and mounted for microscopy. Control tissue sections incubated in the absence of terminal deoxynucleotidyl transferase enzyme had negative findings from staining.

For quantification of the number of TUNEL-positive cells, images were digitized using a high-resolution charged-coupled device camera (Sony, Tokyo, Japan) and quantified using image analysis software (Bioquant; R&M Biometrics Inc, Nashville, Tenn) as previously described.43

WESTERN BLOT ANALYSIS OF DEATH SUBSTRATE PARP CLEAVAGE

Human brain tissue lysates were prepared by sonicating 20 mg of tissue powder suspended in lysis buffer (50mM HEPES, pH 7.4, 0.1% CHAPS, 1mM dithiothreitol (DTT), 0.1mM EDTA, and 0.1% Triton X-100) for 20 seconds. The lysates were then taken through 1 cycle of freezing and thawing and were centrifuged at 10 000g for 10 minutes. The supernatants were collected and the protein concentrations were determined using a protein assay (Bio-Rad Laboratories, Hercules, Calif). Samples were electrophoresed (20 µg per lane) in 8% polyacrylamide and sodium dodecyl sulfate gels in reducing conditions and then transferred onto a nitrocellulose membrane. After blocking with 5% nonfat milk (Bio-Rad Laboratories) in 20mM Tris hydrochloride, pH 7.6, 140mM sodium chloride, and 0.1% Tween 20 (TBST), the membrane was incubated with the mouse monoclonal anti-PARP antibody (Zymed, San Francisco, Calif) (1:1000 in 1% bovine serum albumin–TBST) for 16 hours at 4°C. The membrane was then washed 3 times with TBST and incubated with peroxidase-conjugated goat anti–mouse IgG (Santa Cruz Biotech, Santa Cruz, Calif) (1:2500 in 1% bovine serum albumin–TBST) for 1 hour at room temperature. After the washing step, the protein bands were detected using a chemiluminescent substrate (West Femto; Pierce Biotechnology, Rockland, Ill). Band quantification was performed using quantitation software (Quantity-One; Bio-Rad Laboratories); PARP cleavage was expressed as a ratio of intact 116-kd PARP, and the cleaved 85-kd fragment as a percentage of CDR 0 values.

STATISTICAL ANALYSIS

Statistical analysis was performed using a software package (StatSoft; StatSoft, Tulsa, Okla). Analysis of variance was used to evaluate differences in mean values among 3 or more groups, and a 2-tailed t test was used to test the significance between differences in mean values. For all analyses, the null hypothesis was rejected at P<.05.

PATIENT POPULATION

Patient information for samples of the EC-BM36/38 included in this study is summarized in Table 1. Analysis of variance indicated that there were no significant differences among the different CDR groups with respect to postmortem interval and age at death. Cause of death was reviewed for all the patients to rule out the possibility that intercurrent infection or other events would affect study measures. Of 25 patients included in the study, 21 died of acute cardiac failure (including cardiorespiratory failure or arrest, ventricular fibrillation, cardiopulmonary arrest, myocardial infarct, and congestive heart failure), 1 of cancer, 1 of pneumonia, and 2 of unknown causes.

Table Graphic Jump LocationTable 1 Patient Demographics and Neuropathologic Data
REGIONAL DISTRIBUTION OF CASPASE mRNA EXPRESSION IN THE BRAIN OF COGNITIVELY NORMAL CASES

Caspase mRNA expression in the EC-BM36/38 and the OC-BM17 was first determined by ribonuclease protection assay analysis of cognitively normal cases (CDR 0) and was expressed as a ratio to the housekeeping gene glyceraldehyde phosphate dehydrogenase (Figure 1). The mean levels of mRNA expression of individual caspases (caspase-1, -2L, -2S, -3, -5, -6, -7, -8, and -9) were consistent between the EC-BM36/38 and the OC-BM17 (Figure 1). However, among the caspases, differences in baseline mRNA expression levels were evident. Caspase-8 had the lowest level of expression in the EC and the OC.

CASPASE mRNA EXPRESSION AS A FUNCTION OF THE CDR

Caspase mRNA expression was measured in the EC-BM36/38 and the OC-BM17 of normal cognitive control cases (CDR 0), cases at high risk of developing AD (CDR 0.5), and late-stage AD dementia cases (CDR 5). Evaluation of CDR 0.5 cases indicated a greater than 1.5-fold elevation of mRNA expression of caspase-1 and -7 in the EC-BM36/38 at this early CDR stage relative to the CDR 0 control group (Figure 2). When CDR 5 cases were examined, we found that in addition to elevated caspase-1 and caspase-7 mRNA expression, caspase-2S, -3, -5, -8, and -9 levels exhibited greater than 1.5- to 2-fold increases in expression relative to the CDR 0 control group (Figure 2).

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Figure 2.

Ribonuclease protection assay profile of mean caspase messenger RNA (mRNA) expression (expressed as a ratio to the housekeeping gene glyceraldehyde phosphate dehydrogenase [GAPDH]) in the entorhinal cortex (Brodmann area 36/38) as a function of Clinical Dementia Rating (CDR) (CDR 0 = cognitively normal, CDR 0.5 = questionable dementia, and CDR 5 = severe dementia); caspase/GAPDH mRNA levels are expressed as percentages of the CDR 0 group. Asterisk indicates P<.05; dagger, P<.001 vs CDR 0 by 2-tailed t test. Error bars represent SEM.

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no significant difference in any caspase mRNA expression was observed in the OC-BM17 at any of the CDRs examined (Table 2). However, although not statistically significant, we observed a trend for decreased caspase expression in the OC-BM17 of cases at high risk of developing AD dementia (CDR 0.5).

Table Graphic Jump LocationTable 2 Caspase Expression in the Occipital Cortex (BM17)*
CASPASE mRNA EXPRESSION AS A FUNCTION OF NEUROPATHOLOGICAL FEATURES OF AD ASSESSED BY CERAD CRITERIA

Next we explored caspase expression as a function of NFT and NP density. We found that caspase mRNA expression is elevated in the EC-BM36/38 as a function of NFT staining (Figure 3). No apparent elevation of caspase mRNA expression was found as a function of NP staining (Figure 4). Compared with cases with absent or sparse NFTs (CERAD 0-1), those with moderate NFT staining (CERAD 3) had significantly elevated mRNA expression of caspase-1, -2L, -3, -5, -6, -7, and -8, and those with severe NFT staining (CERAD 5) had elevated expression of caspase-1, -2L, -3, -5, -6, -7, -8 and -9. Compared with cases with absent or sparse NP staining (CERAD 0-1), those with severe NP staining (CERAD 5) exhibited a select increase in mRNA expression of caspase-5 and caspase-6 only. No significant difference in caspase mRNA expression was observed in the OC of any of the CDRs examined (data not shown).

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Figure 3.

Mean caspase messenger RNA (mRNA) expression (expressed as a ratio to the housekeeping gene glyceraldehyde phosphate dehydrogenase [GAPDH]) in the entorhinal cortex (Brodmann area 36/38) as a function of neurofibrillary tangle (NFT) density (assessed by the Consortium to Establish a Registry for Alzheimer's Disease 4-point scale). Expression of caspase-1, -3, -5, -6, -7, and -8 was significantly increased as a function of NFT density; elevation of caspase-9 expression was seen only in cases exhibiting severe NFT density. Error bars represent SEM. Asterisk indicates P<.05; dagger, P<.001; and double dagger, P<.005 by 2-tailed t test (caspase-2S data omitted).

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Figure 4.

Mean caspase messenger RNA (mRNA) expression (expressed as a ratio to the housekeeping gene glyceraldehyde phosphate dehydrogenase [GAPDH]) in the entorhinal cortex (Brodmann area 36/38) as a function of neuritic plaque (NP) density (assessed by the Consortium to Establish a Registry for Alzheimer's Disease 4-point scale). Significant increases in caspase-5 and caspase-6 were observed in cases exhibiting severe NP density. Error bars represent SEM. Asterisk indicates P<.05 by 2-tailed t test (caspase-2S data omitted).

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PARP CLEAVAGE AND APOPTOSIS AS A FUNCTION OF CDR

Because the DNA repair enzyme PARP is a preferential substrate for caspase-1 and caspase-7 (and caspase-3), we next explored the potential functional relationship between elevated caspase-1 and caspase-7 mRNA expression and PARP cleavage in the EC-BM36/38. As assessed by Western blot immunoreactivity, we found a greater than 1.5-fold decrease in the ratio of the intact 116-kd native PARP to cleaved 85-kd processed PARP in CDR 0.5 cases relative to CDR 0 controls, suggesting increased processing of PARP in these cases. No change in the PARP ratio was found in the EC-BM36/38 of CDR 5 cases.

To evaluate the relationship between caspase expression and apoptosis, we next measured apoptotic cell injury in the EC-BM36/38 using the TUNEL technique. In contrast to the PARP evidence, we found no differences in the number of TUNEL-positive cells in the EC-BM36/38 of cases at high risk of developing AD dementia (CDR 0.5) compared with CDR 0 control cases. However, a greater than 5-fold elevation in TUNEL-positive apoptotic injured cells was found in the EC-BM36/38 of cases characterized by severe dementia (CDR 5) (Figure 5B). No differences in TUNEL-positive cell counts were observed in the OC of any of the CDR stages examined (data not shown).

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Figure 5.

A, Mean poly (ADP-ribose) polymerase (PARP) cleavage in the entorhinal cortex (Brodmann area 36/38) of cognitively normal (Clinical Dementia Rating [CDR] 0), high risk of developing Alzheimer disease dementia (CDR 0.5), and severe dementia (CDR 5) cases. Mean PARP cleavage is given as a ratio of intact 116-kd PARP, and the cleaved 85-kd fragment is expressed as a percentage of CDR 0 values. Asterisk indicates P<.05 vs CDR 0; n = 5 or 6 per group. The inset shows Western blot analysis detailing the levels of intact 116-kd and cleaved/processed 85-kd PARP immunoreactivity as a function of CDR. B, The number of TUNEL-positive cells, counted automatically from 10 random fields from 5 to 7 tissue sections encompassing the rostrocaudal extent of the entorhinal cortex (Brodmann area 36/38) (n = 5-6 per CDR group). The inset shows representative micrographs of TUNEL-positive cells from CDR 0, 0.5, and 5 cases (original magnification ×20). Error bars represent SEM.

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The mRNA expression of caspase-1, -2L, -2S, -3, -5, -6, -7, -8, and -9 was assessed as a function of the progression of AD clinical dementia in samples of the EC-BM36/38 and OC-BM17 of patients characterized by CDR and CERAD criteria. Caspase expression was then compared with PARP cleavage activity, apoptotic cell counts by TUNEL assay, and the degree of NP and NFT staining (assessed by CERAD criteria). We found an early select up-regulation of caspase-1 (also known as interleukin 1β converting enzyme) and caspase-7 expression and increased PARP cleavage in the EC-BM36/38 of cases at high risk of developing AD (CDR 0.5) in the absence of apoptotic cell injury assessed by TUNEL. In the EC-BM36/38 of severe or terminal clinical dementia cases (CDR 5), we found that in addition to the elevated expression of caspase-1 and caspase-7, there was also an elevation in caspase-2S, -3, -5, -8, and -9 expression and a 5-fold increase in TUNEL-positive cells. The overall up-regulation of caspases was positively associated with CERAD-rated NFT and, to a lesser extent, NP staining. No changes in caspase mRNA expression were observed in the OC-BM17 at any of the CDRs examined, further confirming the specificity and selectivity of changes in caspase mRNA expression found in EC-BM36/38. This study demonstrates that in AD there is a broad and evolving expression of proapoptotic caspases in a brain region integral to memory function (EC-BM36/38) as the disease progresses.

The reported elevation of caspase-1 and caspase-7 expression in cases at high risk of developing AD dementia suggests that these caspases may be risk factors for AD dementia. This evidence of elevated caspase-1 expression is consistent with previous studies4446 showing increased levels of the caspase-1 cleavage product interleukin 1β in the plasma of probable AD cases. However, we note that our recent survey of cytokine expression in AD brain did not find interleukin 1β to be elevated at any CDR stage of AD dementia investigated.45 Thus, alternative cellular pathways, independent of available pro–interleukin 1β, may be related to or associated with caspase-1 elevation, as reflected by increased mRNA expression.

Cleavage of the DNA excision repair molecule PARP was elevated in CDR 0.5 cases. Caspase-1 and caspase-7 have been demonstrated to potently cleave PARP4749 and thus may be involved in this early propagation of DNA damage. However, our parallel histologic analyses of (the same) CDR 0.5 cases revealed no change in TUNEL-positive cell counts compared with CDR 0 cases. Thus, it may be that caspase-mediated DNA damage and PARP cleavage in early AD are insufficient for successful induction of apoptosis and may require the recruitment of additional caspases to do so.

In support of this theory, in the EC-BM36/38 of CDR 5 cases we found an induction of the full spectrum of caspases assayed (caspase-1, -2L, -3, -5, -6, -7, -8, and -9), except caspase 2S (an antagonist of apoptosis).50,51 This massive recruitment of caspases in terminal dementia coincided with a 5-fold increase in TUNEL-positive cells and a decrease in the overall level of PARP protein, with a shift toward decreased PARP cleavage. In view of recent evidence52 that PARP expression and activity are down-regulated during apoptotic cell death in vitro, our data suggest that caspase expression in terminal AD may sufficiently overcome antiapoptotic mechanisms and cause DNA damage sufficient enough to induce actual apoptotic cell injury and, eventually, cell death.

However, the evidence supporting definitive apoptotic cell death in AD is equivocal.10,34,5356 For example, we note that the TUNEL technique is limited to identifying only proapoptotic changes and not definitive apoptotic cell death (eg, chromatin condensation and apoptotic bodies). Thus, it remains to be determined whether apoptosis is indeed a pathologic end point in AD and whether perhaps other nonapoptotic features of caspases may promote neurodegeneration and the progression of AD clinical dementia.

For example, caspases15,57,58 have been shown to cleave the amyloid precursor protein in vitro.49,59 As previously reported by Raina et al,10 mRNA expression of caspase-6 and caspase-5 coincided well with severe plaque staining. Also consistent with earlier studies,10,60 we report a strong positive association of caspase-1, -3, -5, -6, -7, -8, and, to a lesser extent, -9 with NFT staining. Thus, it may be the case that in addition to proapoptotic activity, caspase expression involves a pathologic interplay with cytoskeletal components during the clinical progression of AD dementia and impacts neuropathological features of AD.

Currently, it is difficult to offer a definitive resolution to the questions of caspase-related neurodegeneration in AD, but our data underscore the need for further characterization of proapoptotic and antiapoptotic cascades in AD. Cotman61 suggests that there is stringent competition between proapoptotic and antiapoptotic signals before commitment to apoptosis. Further understanding of the mechanisms related to caspase induction under normal and pathologic conditions will yield significant insight about the relevance of these events to the onset or progression of neuropathological features and will potentially provide a rationale for the therapeutic regulation of caspases in AD and similar neurodegenerative disorders.

Corresponding author and reprints: Giulio Maria Pasinetti, MD, PhD, Neuroinflammation Research Laboratories, Department of Psychiatry, Mount Sinai School of Medicine, One Gustave L. Levy Place, New York, NY 10029 (e-mail: giulio.pasinetti@mssm.edu).

Accepted for publication October 1, 2002.

This study was supported by the National Institutes of Health (Bethesda, Md) grant AG 02219 (Drs Mohs and Pasinetti).

Author contributions: Study concept and design (Mr Pompl and Drs Ho, Mohs, and Pasinetti); acquisition of data (Drs Yemul, Xiang, Haroutunian, Purohit, and Mohs); analysis and interpretation of data (Mr Pompl and Dr Pasinetti); drafting of the manuscript (Mr Pompl and Dr Pasinetti); critical revision of the manuscript for important intellectual content (Mr Pompl and Drs Yemul, Xiang, Ho, Haroutunian, Purohit, Mohs, and Pasinetti); statistical expertise (Dr Yemul); obtained funding (Drs Mohs and Pasinetti); administrative, technical, and material support (Mr Pompl and Drs Xiang, Haroutunian, Purohit, Mohs, and Pasinetti); study supervision (Drs Ho and Pasinetti).

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Love  SBarber  RWilcock  GK Increased poly(ADP-ribosyl)ation of nuclear proteins in Alzheimer's disease. Brain.1999;122(pt 2):247-253.
Arends  MJWyllie  AH Apoptosis: mechanisms and roles in pathology. Int Rev Exp Pathol.1991;32:223-254.
Dragunow  MFaull  RLLawlor  P  et al In situ evidence for DNA fragmentation in Huntington's disease striatum and Alzheimer's disease temporal lobes. Neuroreport.1995;6:1053-1057.
Lassmann  HBancher  CBreitschopf  H  et al Cell death in Alzheimer's disease evaluated by DNA fragmentation in situ. Acta Neuropathol (Berl).1995;89:35-41.
Lucassen  PJChung  WCKamphorst  WSwaab  DF DNA damage distribution in the human brain as shown by in situ end labeling: area-specific differences in aging and Alzheimer disease in the absence of apoptotic morphology. J Neuropathol Exp Neurol.1997;56:887-900.
Smale  GNichols  NRBrady  DRFinch  CEHorton Jr  WE Evidence for apoptotic cell death in Alzheimer's disease. Exp Neurol.1995;133:225-230.
Troncoso  JCSukhov  RRKawas  CHKoliatsos  VE In situ labeling of dying cortical neurons in normal aging and in Alzheimer's disease: correlations with senile plaques and disease progression. J Neuropathol Exp Neurol.1996;55:1134-1142.
Lassmann  HBancher  CBreitschopf  H  et al Cell death in Alzheimer's disease evaluated by DNA fragmentation in situ. Acta Neuropathol (Berl).1995;89:35-41.
Su  JHAnderson  AJCummings  BJCotman  CW Immunohistochemical evidence for apoptosis in Alzheimer's disease. Neuroreport.1994;5:2529-2533.
Perry  GNunomura  ASmith  MA A suicide note from Alzheimer disease neurons? Nat Med.1998;4:897-898.
Perry  GNunomura  ALucassen  PLassmann  HSmith  MA Apoptosis and Alzheimer's disease. Science.1998;282:1268-1269.
Cotman  CWSu  JH Mechanisms of neuronal death in Alzheimer's disease. Brain Pathol.1996;6:493-506.
Haroutunian  VPerl  DPPurohit  DP  et al Regional distribution of neuritic plaques in the nondemented elderly and subjects with very mild Alzheimer disease. Arch Neurol.1998;55:1185-1191.
Haroutunian  VPurohit  DPPerl  DP  et al Neurofibrillary tangles in nondemented elderly subjects and mild Alzheimer disease. Arch Neurol.1999;56:713-718.
Berg  L Clinical Dementia Rating (CDR). Psychopharmacol Bull.1988;24:637-639.
Yamamoto  THirano  A A comparative study of modified Bielschowsky, Bodian and thioflavin S stains on Alzheimer's neurofibrillary tangles. Neuropathol Appl Neurobiol.1986;12:3-9.
Chomczynski  PSacchi  N Single-step method of RNA isolation by acid guanidinium thiocyanate-phenol-chloroform extraction. Anal Biochem.1987;162:156-159.
Luterman  JDHaroutunian  VYemul  S  et al Cytokine gene expression as a function of the clinical progression of Alzheimer disease dementia. Arch Neurol.2000;57:1153-1160.
Wotawa  ASolier  SLogette  ESolary  ECorcos  L Differential influence of etoposide on two caspase-2 mRNA isoforms in leukemic cells. Cancer Lett.2002;185:181-189.
Ho  LPieroni  CWinger  DPurohit  DPAisen  PSPasinetti  GM Regional distribution of cyclooxygenase-2 in the hippocampal formation in Alzheimer's disease. J Neurosci Res.1999;57:295-303.
Licastro  FPedrini  SCaputo  L  et al Increased plasma levels of interleukin-1, interleukin-6 and α-1-antichymotrypsin in patients with Alzheimer's disease: peripheral inflammation or signals from the brain? J Neuroimmunol.2000;103:97-102.
Licastro  FPedrini  SFerri  C  et al Gene polymorphism affecting α1-antichymotrypsin and interleukin-1 plasma levels increases Alzheimer's disease risk. Ann Neurol.2000;48:388-391.
Paganelli  RDi Iorio  APatricelli  L  et al Proinflammatory cytokines in sera of elderly patients with dementia: levels in vascular injury are higher than those of mild-moderate Alzheimer's disease patients. Exp Gerontol.2002;37:257-263.
Salvesen  GSDixit  VM Caspases: intracellular signaling by proteolysis. Cell.1997;91:443-446.
Margolin  NRaybuck  SAWilson  KP  et al Substrate and inhibitor specificity of interleukin-1 β–converting enzyme and related caspases. J Biol Chem.1997;272:7223-7228.
Germain  MAffar  EBD'Amours  DDixit  VMSalvesen  GSPoirier  GG Cleavage of automodified poly(ADP-ribose) polymerase during apoptosis: evidence for involvement of caspase-7. J Biol Chem.1999;274:28379-28384.
Ito  AUehara  TNomura  Y Isolation of Ich-1S (caspase-2S)–binding protein that partially inhibits caspase activity. FEBS Lett.2000;470:360-364.
Solary  EDroin  NBettaieb  ACorcos  LDimanche-Boitrel  MTGarrido  C Positive and negative regulation of apoptotic pathways by cytotoxic agents in hematological malignancies. Leukemia.2000;14:1833-1849.
Alexandre  SRast  CNguyen-Ba  GPoirier  GGVasseur  P PARP degradation in apoptotic Syrian hamster embryo (SHE) cells compared to HL60 cell line. Biochimie.2000;82:1115-1122.
Perry  GNunomura  ASmith  MA A suicide note from Alzheimer disease neurons? Nat Med.1998;4:897-898.
Nagy  ZSEsiri  MM Apoptosis-related protein expression in the hippocampus in Alzheimer's disease. Neurobiol Aging.1997;18:565-571.
de la Monte  SMSohn  YKWands  JR Correlates of p53- and Fas (CD95)-mediated apoptosis in Alzheimer's disease. J Neurol Sci.1997;152:73-83.
Engidawork  EGulesserian  TSeidl  RCairns  NLubec  G Expression of apoptosis related proteins in brains of patients with Alzheimer's disease. Neurosci Lett.2001;303:79-82.
Lu  DCRabizadeh  SChandra  S  et al A second cytotoxic proteolytic peptide derived from amyloid β-protein precursor. Nat Med.2000;6:397-404.
LeBlanc  ALiu  HGoodyer  CBergeron  CHammond  J Caspase-6 role in apoptosis of human neurons, amyloidogenesis, and Alzheimer's disease. J Biol Chem.1999;274:23426-23436.
Barnes  NYLi  LYoshikawa  KSchwartz  LMOppenheim  RWMilligan  CE Increased production of amyloid precursor protein provides a substrate for caspase-3 in dying motoneurons. J Neurosci.1998;18:5869-5880.
Rohn  TTHead  ESu  JH  et al Correlation between caspase activation and neurofibrillary tangle formation in Alzheimer's disease. Am J Pathol.2001;158:189-198.
Cotman  CW Apoptosis decision cascades and neuronal degeneration in Alzheimer's disease. Neurobiol Aging.1998;19:S29-S32.

Figures

Place holder to copy figure label and caption

Figure 1. Baseline ribonuclease protection assay (RPA) profile of mean caspase messenger RNA (mRNA) expression in the entorhinal cortex (EC) (Brodmann area 36/38) and the occipital cortex (OC) (BM17) of cognitively normal cases (Clinical Dementia Rating [CDR] 0). Caspase mRNA levels are expressed as a ratio to the housekeeping gene glyceraldehyde phosphate dehydrogenase (GAPDH). In these studies, an initial RNA quality control for RNA sample quality assessment consisted of agarose gel assessment of ethidium bromide staining of 18S and 28S ribosomal RNA integrity and detection of low-molecular-weight "smearing" of degraded mRNA. All samples were subjected to RPA, regardless of initial quality control assessment. Only samples with nondegraded RNA verified by ethidium bromide and RPA analyses were included in the study. In each brain region examined, RNA exclusion was similarly distributed among the different CDR categories. Error bars represent SEM.

Graphic Jump Location
Place holder to copy figure label and caption
Figure 2.

Ribonuclease protection assay profile of mean caspase messenger RNA (mRNA) expression (expressed as a ratio to the housekeeping gene glyceraldehyde phosphate dehydrogenase [GAPDH]) in the entorhinal cortex (Brodmann area 36/38) as a function of Clinical Dementia Rating (CDR) (CDR 0 = cognitively normal, CDR 0.5 = questionable dementia, and CDR 5 = severe dementia); caspase/GAPDH mRNA levels are expressed as percentages of the CDR 0 group. Asterisk indicates P<.05; dagger, P<.001 vs CDR 0 by 2-tailed t test. Error bars represent SEM.

Graphic Jump Location
Place holder to copy figure label and caption
Figure 3.

Mean caspase messenger RNA (mRNA) expression (expressed as a ratio to the housekeeping gene glyceraldehyde phosphate dehydrogenase [GAPDH]) in the entorhinal cortex (Brodmann area 36/38) as a function of neurofibrillary tangle (NFT) density (assessed by the Consortium to Establish a Registry for Alzheimer's Disease 4-point scale). Expression of caspase-1, -3, -5, -6, -7, and -8 was significantly increased as a function of NFT density; elevation of caspase-9 expression was seen only in cases exhibiting severe NFT density. Error bars represent SEM. Asterisk indicates P<.05; dagger, P<.001; and double dagger, P<.005 by 2-tailed t test (caspase-2S data omitted).

Graphic Jump Location
Place holder to copy figure label and caption
Figure 4.

Mean caspase messenger RNA (mRNA) expression (expressed as a ratio to the housekeeping gene glyceraldehyde phosphate dehydrogenase [GAPDH]) in the entorhinal cortex (Brodmann area 36/38) as a function of neuritic plaque (NP) density (assessed by the Consortium to Establish a Registry for Alzheimer's Disease 4-point scale). Significant increases in caspase-5 and caspase-6 were observed in cases exhibiting severe NP density. Error bars represent SEM. Asterisk indicates P<.05 by 2-tailed t test (caspase-2S data omitted).

Graphic Jump Location
Place holder to copy figure label and caption
Figure 5.

A, Mean poly (ADP-ribose) polymerase (PARP) cleavage in the entorhinal cortex (Brodmann area 36/38) of cognitively normal (Clinical Dementia Rating [CDR] 0), high risk of developing Alzheimer disease dementia (CDR 0.5), and severe dementia (CDR 5) cases. Mean PARP cleavage is given as a ratio of intact 116-kd PARP, and the cleaved 85-kd fragment is expressed as a percentage of CDR 0 values. Asterisk indicates P<.05 vs CDR 0; n = 5 or 6 per group. The inset shows Western blot analysis detailing the levels of intact 116-kd and cleaved/processed 85-kd PARP immunoreactivity as a function of CDR. B, The number of TUNEL-positive cells, counted automatically from 10 random fields from 5 to 7 tissue sections encompassing the rostrocaudal extent of the entorhinal cortex (Brodmann area 36/38) (n = 5-6 per CDR group). The inset shows representative micrographs of TUNEL-positive cells from CDR 0, 0.5, and 5 cases (original magnification ×20). Error bars represent SEM.

Graphic Jump Location

Tables

Table Graphic Jump LocationTable 1 Patient Demographics and Neuropathologic Data
Table Graphic Jump LocationTable 2 Caspase Expression in the Occipital Cortex (BM17)*

References

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Rohn  TTHead  ENesse  WHCotman  CWCribbs  DH Activation of caspase-8 in the Alzheimer's disease brain. Neurobiol Dis.2001;8:1006-1016.
Love  SBarber  RWilcock  GK Increased poly(ADP-ribosyl)ation of nuclear proteins in Alzheimer's disease. Brain.1999;122(pt 2):247-253.
Arends  MJWyllie  AH Apoptosis: mechanisms and roles in pathology. Int Rev Exp Pathol.1991;32:223-254.
Dragunow  MFaull  RLLawlor  P  et al In situ evidence for DNA fragmentation in Huntington's disease striatum and Alzheimer's disease temporal lobes. Neuroreport.1995;6:1053-1057.
Lassmann  HBancher  CBreitschopf  H  et al Cell death in Alzheimer's disease evaluated by DNA fragmentation in situ. Acta Neuropathol (Berl).1995;89:35-41.
Lucassen  PJChung  WCKamphorst  WSwaab  DF DNA damage distribution in the human brain as shown by in situ end labeling: area-specific differences in aging and Alzheimer disease in the absence of apoptotic morphology. J Neuropathol Exp Neurol.1997;56:887-900.
Smale  GNichols  NRBrady  DRFinch  CEHorton Jr  WE Evidence for apoptotic cell death in Alzheimer's disease. Exp Neurol.1995;133:225-230.
Troncoso  JCSukhov  RRKawas  CHKoliatsos  VE In situ labeling of dying cortical neurons in normal aging and in Alzheimer's disease: correlations with senile plaques and disease progression. J Neuropathol Exp Neurol.1996;55:1134-1142.
Lassmann  HBancher  CBreitschopf  H  et al Cell death in Alzheimer's disease evaluated by DNA fragmentation in situ. Acta Neuropathol (Berl).1995;89:35-41.
Su  JHAnderson  AJCummings  BJCotman  CW Immunohistochemical evidence for apoptosis in Alzheimer's disease. Neuroreport.1994;5:2529-2533.
Perry  GNunomura  ASmith  MA A suicide note from Alzheimer disease neurons? Nat Med.1998;4:897-898.
Perry  GNunomura  ALucassen  PLassmann  HSmith  MA Apoptosis and Alzheimer's disease. Science.1998;282:1268-1269.
Cotman  CWSu  JH Mechanisms of neuronal death in Alzheimer's disease. Brain Pathol.1996;6:493-506.
Haroutunian  VPerl  DPPurohit  DP  et al Regional distribution of neuritic plaques in the nondemented elderly and subjects with very mild Alzheimer disease. Arch Neurol.1998;55:1185-1191.
Haroutunian  VPurohit  DPPerl  DP  et al Neurofibrillary tangles in nondemented elderly subjects and mild Alzheimer disease. Arch Neurol.1999;56:713-718.
Berg  L Clinical Dementia Rating (CDR). Psychopharmacol Bull.1988;24:637-639.
Yamamoto  THirano  A A comparative study of modified Bielschowsky, Bodian and thioflavin S stains on Alzheimer's neurofibrillary tangles. Neuropathol Appl Neurobiol.1986;12:3-9.
Chomczynski  PSacchi  N Single-step method of RNA isolation by acid guanidinium thiocyanate-phenol-chloroform extraction. Anal Biochem.1987;162:156-159.
Luterman  JDHaroutunian  VYemul  S  et al Cytokine gene expression as a function of the clinical progression of Alzheimer disease dementia. Arch Neurol.2000;57:1153-1160.
Wotawa  ASolier  SLogette  ESolary  ECorcos  L Differential influence of etoposide on two caspase-2 mRNA isoforms in leukemic cells. Cancer Lett.2002;185:181-189.
Ho  LPieroni  CWinger  DPurohit  DPAisen  PSPasinetti  GM Regional distribution of cyclooxygenase-2 in the hippocampal formation in Alzheimer's disease. J Neurosci Res.1999;57:295-303.
Licastro  FPedrini  SCaputo  L  et al Increased plasma levels of interleukin-1, interleukin-6 and α-1-antichymotrypsin in patients with Alzheimer's disease: peripheral inflammation or signals from the brain? J Neuroimmunol.2000;103:97-102.
Licastro  FPedrini  SFerri  C  et al Gene polymorphism affecting α1-antichymotrypsin and interleukin-1 plasma levels increases Alzheimer's disease risk. Ann Neurol.2000;48:388-391.
Paganelli  RDi Iorio  APatricelli  L  et al Proinflammatory cytokines in sera of elderly patients with dementia: levels in vascular injury are higher than those of mild-moderate Alzheimer's disease patients. Exp Gerontol.2002;37:257-263.
Salvesen  GSDixit  VM Caspases: intracellular signaling by proteolysis. Cell.1997;91:443-446.
Margolin  NRaybuck  SAWilson  KP  et al Substrate and inhibitor specificity of interleukin-1 β–converting enzyme and related caspases. J Biol Chem.1997;272:7223-7228.
Germain  MAffar  EBD'Amours  DDixit  VMSalvesen  GSPoirier  GG Cleavage of automodified poly(ADP-ribose) polymerase during apoptosis: evidence for involvement of caspase-7. J Biol Chem.1999;274:28379-28384.
Ito  AUehara  TNomura  Y Isolation of Ich-1S (caspase-2S)–binding protein that partially inhibits caspase activity. FEBS Lett.2000;470:360-364.
Solary  EDroin  NBettaieb  ACorcos  LDimanche-Boitrel  MTGarrido  C Positive and negative regulation of apoptotic pathways by cytotoxic agents in hematological malignancies. Leukemia.2000;14:1833-1849.
Alexandre  SRast  CNguyen-Ba  GPoirier  GGVasseur  P PARP degradation in apoptotic Syrian hamster embryo (SHE) cells compared to HL60 cell line. Biochimie.2000;82:1115-1122.
Perry  GNunomura  ASmith  MA A suicide note from Alzheimer disease neurons? Nat Med.1998;4:897-898.
Nagy  ZSEsiri  MM Apoptosis-related protein expression in the hippocampus in Alzheimer's disease. Neurobiol Aging.1997;18:565-571.
de la Monte  SMSohn  YKWands  JR Correlates of p53- and Fas (CD95)-mediated apoptosis in Alzheimer's disease. J Neurol Sci.1997;152:73-83.
Engidawork  EGulesserian  TSeidl  RCairns  NLubec  G Expression of apoptosis related proteins in brains of patients with Alzheimer's disease. Neurosci Lett.2001;303:79-82.
Lu  DCRabizadeh  SChandra  S  et al A second cytotoxic proteolytic peptide derived from amyloid β-protein precursor. Nat Med.2000;6:397-404.
LeBlanc  ALiu  HGoodyer  CBergeron  CHammond  J Caspase-6 role in apoptosis of human neurons, amyloidogenesis, and Alzheimer's disease. J Biol Chem.1999;274:23426-23436.
Barnes  NYLi  LYoshikawa  KSchwartz  LMOppenheim  RWMilligan  CE Increased production of amyloid precursor protein provides a substrate for caspase-3 in dying motoneurons. J Neurosci.1998;18:5869-5880.
Rohn  TTHead  ESu  JH  et al Correlation between caspase activation and neurofibrillary tangle formation in Alzheimer's disease. Am J Pathol.2001;158:189-198.
Cotman  CW Apoptosis decision cascades and neuronal degeneration in Alzheimer's disease. Neurobiol Aging.1998;19:S29-S32.

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