Biomedical subjects

C W Cotman

Publications and source records attributed to C W Cotman.

At least 109 records · Page 6Linked to original sources

PubMed1996

DNA damage and apoptosis in Alzheimer's disease: colocalization with c-Jun immunoreactivity, relationship to brain area, and effect of postmortem delay.

Many neurons in Alzheimer's disease (AD) exhibit terminal deoxynucleotidyl transferase (TdT) labeling for DNA strand breaks with a distribution suggestive of apoptosis. We have shown previously that immunoreactivity for c-Jun is elevated in AD and found in association with neuronal pathology. In addition, cultured neurons undergoing beta-amyloid-mediated apoptosis exhibit a selective and prolonged induction of c-Jun. Consequently, we conducted double-labeling experiments to examine whether c-Jun is associated with DNA strand breaks in AD tissue; we observed a strong colocalization between these markers. As would be predicted based on the distribution of AD pathology, we also found that TdT labeling was prominent in the entorhinal cortex, but absent or at very low levels in cerebellum. Furthermore, we confirmed that postmortem delay (PMD) does not affect TdT labeling within the limits used for tissue used in this study. However, in contrast to previous studies, we report an increase in TdT labeling with more extended PMDs. Finally, gel electrophoresis of genomic DNA isolated from AD and control cases failed to reveal evidence for either an apoptotic or a necrotic mechanism of cell death in AD, possibly because of a low number of cells actually undergoing cell death at any given time. Our findings support the hypothesis that DNA damage labeled using TdT reflects neuronal vulnerability and cell loss associated with AD pathology, and that at least a portion of the cells labeled with this technique is undergoing apoptosis. Furthermore, in agreement with in vitro findings, these results suggest a relationship between the expression of c-Jun and neuronal risk and/or cell death in AD.

Aged↗

PubMed1996

Up-regulation of Bcl-2 is associated with neuronal DNA damage in Alzheimer's disease.

Cell death and neurofibrillary tangle formation are prominent features of Alzheimer's disease (AD). It has been suggested that DNA damage may reflect neuronal vulnerability. In this context, the Ced homologue Bcl-2 is able to repress a number of cell death programs. Recently we found both numerous nuclei exhibiting DNA damage within neurons in the AD brain and increases in Bcl-2 immunoreactivity. In this study, we examined the relationship between Bcl-2 expression and nuclear DNA damage or tangle formation. Nuclei exhibiting DNA damage were associated with an up-regulation of Bcl-2 expression, whereas tangle-bearing neurons were associated with a down-regulation of Bcl-2 expression.

Aged↗

PubMed1996

Localization and cell association of C1q in Alzheimer's disease brain.

The complement protein, C1q, has been shown to bind to fibrillar beta-amyloid, resulting in the activation of the classical complement pathway. C1q has also been found associated with most but not all amyloid deposits in brain. To determine whether C1q is exclusively associated with plaques containing the fibrillar form of beta-amyloid, normal and Alzheimer brain were immunohistochemically double labeled using thioflavine, which specifically stains beta-amyloid in a beta-sheet conformation, and an affinity- purified antibody to human C1q. C1q immunostaining was colocalized with nearly all thioflavine-positive plaques, while C1q was not detected in beta-amyloid immunopositive plaques which were thioflavine-negative. Beta-amyloid plaques in nondemented controls (which are typically thioflavine-negative) were also negative for C1q. Microglia and astrocytes of reactive morphology were also associated with C1q-positive plaques and neurons. Interestingly, many neuronal cells in the AD brain, but not microglia or astrocytes, stained prominently with anti-C1q. Neurons in control brain were not C1q positive. Our data suggest that some of these C1q-positive structures were neurofibrillary tangles immunoreactive for hyperphosphorylated tau, which may be binding extracellular C1q. However, a large number of the C1q-positive neurons had intact cell morphology; suggesting that these cells may be synthesizing this critical complement component. Since the presence of C1q suggests the activation of complement and/or the activation of proinflammatory events, and the specific class of plaques that contain C1q are the type that corresponds to observed clinical dementia, these findings further support the hypothesis that complement plays a role in the pathogenesis of AD.

Alzheimer Disease↗

PubMed1996

beta-Amyloid increases enzyme activity and protein levels of glutamine synthetase in cultured astrocytes.

Previous studies have reported that beta-amyloid peptides induce properties of reactivity in cultured astrocytes. We report here that aggregated A beta peptides increase expression of the enzyme glutamine synthetase in cultured astrocytes, as assessed by enzyme assay, Western blot analysis, and immunocytochemistry. The enhanced enzyme levels occur gradually over a period of 4 days after A beta exposure and maintain peak values for at least several days thereafter. These data suggest that A beta-related reactive astrocytosis in Alzheimer's disease brain may benefit local neurons by enhancing glial capacity to regulate levels of the excitotoxin glutamate.

Amyloid beta-Peptides↗

PubMed1996

Beta-amyloid accumulation correlates with cognitive dysfunction in the aged canine.

It is well known that beta-amyloid accumulates abnormally in Alzheimer's disease; however, beta-amyloid's relationship to cognitive dysfunction has not been clearly established and is often confounded by the presence of neurofibrillary tangles. We used canines to investigate the relationship between beta-amyloid accumulation and cognitive function in an animal model of aging lacking neurofibrillary tangles. The performance of 20 canines (11 purebred beagles and 9 mongrels) on a battery of six cognitive tasks was measured. These tasks included Reward Approach and Object Approach learning, as well as Discrimination, Reversal, Object Recognition, and Spatial learning and memory. Aged canines were impaired on some tasks but not others. beta-Amyloid-immunopositive plaques were found in many of the older animals. Plaques were all of the diffuse subtype and many contained intact neurons detected with double-labeling for neurofilaments. No neurofibrillary tangles were detected. beta-Amyloid was also associated with the processes of many neurons and with blood vessels. Using computerized image analysis, we quantified the area occupied by beta-amyloid in entorhinal cortex, frontal cortex, and cerebellum. Controlling for age-related increases in beta-amyloid, we observed that increased beta-amyloid deposition is strongly associated with deficits on Discrimination learning (r = .80), Reversal learning (r = .65), and Spatial learning (r = .54) but not the other tasks. There were a few differences between breeds which are discussed in the text. Overall, these data suggest that beta-amyloid deposition may be a contributing factor to age-related cognitive dysfunction prior to the onset of neurofibrillary tangle formation.

Alzheimer Disease↗

PubMed1996

Cross-linking of concanavalin A receptors on cortical neurons induces programmed cell death.

The loss of neurons by programmed cell death is a normal feature of the nervous system during development and has recently been implicated as a major mechanism of cell death in neurodegenerative diseases. In some cases, programmed cell death is induced by the activation of membrane receptors and is referred to as activation-induced programmed cell death. Activation-induced programmed cell death has been previously described in cells from the immune system, in which the activation of receptors by receptor clustering leads to programmed cell death. To determine whether activation-induced programmed cell death occurs in neurons, Concanavalin A was used to cross-link membrane receptors on cortical neurons. Concanavalin A-induced neuronal death was dose dependent and effective at concentrations previously shown to induce activation-induced programmed cell death in lymphocytes. Programmed cell death was attenuated when Concanavalin A-specific binding to neurons was blocked with methyl alpha-D-mannopyranoside. Succinyl Concanavalin A, which bound to Concanavalin A receptors but was ineffective at cross-linking them, did not induce programmed cell death. Concanavalin A-induced neuronal death exhibited many of the hallmarks associated with programmed cell death, such as membrane blebbing, nuclear condensation and margination, and internucleosomal DNA cleavage. In addition, neurons exposed to Concanavalin A displayed a rapid, robust, and persistent increase in the immediate early gene protein c-Jun. A similar increase in c-Jun precedes programmed cell death induced by beta-amyloid in neurons, and under some conditions an increase in c-Jun has been shown to be required for programmed cell death to occur in neurons. Increased expression of c-jun and other immediate early genes has also been correlated with activation-induced programmed cell death in lymphocytes. These observations suggest that Concanavalin A induces activation-induced programmed cell death in neurons via signals produced from the cross-linking of receptors on neuronal membranes. These results also raise the possibility that beta-amyloid induces programmed cell death in a similar manner, by causing the cross-linking of receptors on neuronal membranes. This mechanism may be relevant to neuronal programmed cell death that occurs during development and neurodegeneration.

Animals↗

PubMed1996

Thrombin attenuates neuronal cell death and modulates astrocyte reactivity induced by beta-amyloid in vitro.

beta-Amyloid protein has been implicated as a potential causative agent in the neuropathology associated with Alzheimer's disease. This possibility is supported by observations that beta-amyloid induces neuronal degeneration and astrocyte reactivity in vitro by as yet undefined mechanism(s). In this report, we present data demonstrating that the pathological effects of beta-amyloid on cultured cells are modulated by activation of the thrombin receptor. At concentrations between 50 and 500 nM, thrombin pretreatment significantly attenuates neurotoxicity mediated by fibrillar aggregates of beta 1-42 and beta 25-35 peptides. In cultured astrocytes, the stellate morphology induced by beta 1-42 and beta 25-35 aggregates can be prevented and reversed by thrombin exposures between 10 pM and 1 microM. In contrast, thrombin potentiates rather than attenuates the beta-amyloid-induced increased expression of basic fibroblast growth factor, suggesting that thrombin differentially modulates the effects of beta-amyloid on astrocytes. Thrombin's effects on both neurons and astrocytes are mimicked by thrombin receptor-activating peptide and inhibited by two potent thrombin inhibitors, hirudin and protease nexin-1. These data provide both new insight into the signaling pathways underlying the cellular effects of beta-amyloid and additional support for the role of thrombin as an important mediator of neuropathological events.

Amyloid beta-Peptides↗

PubMed1996

Exposure of astrocytes to thrombin reduces levels of the metabotropic glutamate receptor mGluR5.

Thrombin is one of the first regulatory molecules present at sites of CNS trauma or injury. Exposure of neuronal and glial cells to thrombin produces potent morphological as well as cytoprotective and cytotoxic effects, but little is known about how this important modulator affects neurotransmitter signaling. In astrocyte cultures that have been morphologically differentiated by exposure to transforming growth factor-alpha, addition of thrombin induced a retraction of astrocytic processes and suppressed the stimulation of phosphoinositide hydrolysis by the selective metabotropic glutamate receptor (mGluR) agonist 1-aminocyclopentane-1S,3R-dicarboxylic acid. In addition to the suppression of phosphoinositide hydrolysis, thrombin treatment produced a corresponding reduction in level of mGluR5 mRNA as demonstrated with ribonuclease protection assay and reduced content of mGluR5 receptor protein as seen with western blotting. In contrast, thrombin exposure up-regulated astrocyte beta-actin mRNA levels. A synthetic hexapeptide with a sequence corresponding to the amino-terminus of the thrombin receptor's tethered ligand also mimicked the ability of thrombin to suppress mGluR5 levels and to increase beta-actin mRNA content, suggesting that these effects of thrombin are mediated by proteolytically activated cell surface thrombin receptors. Thrombin's suppressive effect on mGluR5 was resistant to pretreatment with pertussis toxin or various protein kinase and protein phosphatase inhibitors. However, the serine/threonine protein kinase inhibitor H-7 did prevent thrombin-induced reversal of astrocyte stellation and induction of beta-actin mRNA levels, indicating that these effects of thrombin involve a signaling pathway distinct from the one that mediates the suppressive effects of thrombin on mGluR5.

Animals↗

PubMed1996

Attenuation of beta-amyloid neurotoxicity in vitro by potassium-induced depolarization.

The cell death of cultured neurons triggered by beta-amyloid peptides has been theorized to model, at least in part, the neurodegeneration associated with Alzheimer's disease. To investigate potential strategies to interrupt beta-amyloid neurotoxicity in vitro, we examined the effects of potassium-induced membrane depolarization, a treatment previously demonstrated to reduce development-related apoptosis in cultured neurons. We report here that cultured rat hippocampal neurons pretreated for several hours with 30 mM KCl exhibit significantly reduced vulnerability to aggregated beta-amyloid peptides. The potassium-mediated neuroprotection was mimicked by activation of voltage-sensitive calcium channels using S(-)-Bay K8644 and was attenuated by R(+)-Bay K 8644, a blocker of voltage-dependent calcium channels, and KN-82, an inhibitor of calcium/calmodulin-dependent protein kinase II. The protein synthesis inhibitor cycloheximide also attenuated beta-amyloid neurotoxicity. Addition of cycloheximide following 30 mM KCl significantly increased protection offered by membrane depolarization, whereas cycloheximide addition during membrane depolarization blocked the protective effect. These data suggest that one cellular pathway that can inhibit neuronal death induced by beta-amyloid involves calcium influx through voltage-sensitive channels followed by stimulation of calcium/calmodulin-dependent protein kinase activity and synthesis of new protein(s).

Alzheimer Disease↗

PubMed1996

Acquisition and long-term retention of a gross motor skill in Alzheimer's disease patients under constant and varied practice conditions.

This study examined the acquisition and long-term retention of a gross motor skill, namely, tossing, in 23 moderately to severely demented Alzheimer's disease (AD) patients and 22 health older adults. To identify optimal learning strategies, subjects received 10 weeks of training under either constant or variable practice conditions. Accuracy at the tossing task was assessed immediately, one week, and one month following training. AD patients given constant practice were able to learn and retain the tossing task as well as healthy adults. Although controls performed equally well in both conditions, AD patients showed significantly less improvement when practiced at various distances from the target. By the one-month post-test, these patients had lost any minimal gains achieved through practice. In comparison, AD patients receiving constant practice showed essentially no forgetting across post-tests. The inability to benefit from varied practice suggests that AD patients may have difficulty accessing and/or forming motor schemas.

Aged↗

PubMed1996

Apolipoprotein-E genotyping of diabetic dementia patients: is diabetes rare in Alzheimer's disease?

OBJECTIVES: To determine whether diabetes is rare in Alzheimer disease (AD) relative to other types of dementia and whether diabetics with dementia have a low frequency of the Apolipoprotein-E E4 genotype. DESIGN: Observational survey study. SETTING: An Irvine, California, outpatient dementia assessment center. PARTICIPANTS: A total of 123 patients with AD, 51 with vascular dementia, 57 with "mixed" vascular dementia and AD, and 34 with "other" dementias (non-vascular non-AD). MEASUREMENTS: Demographic data; histories and evidence of diabetes, hypertension, heart disease, stroke; and Apolipoprotein-E genotype for 95 cases distributed across the groups. RESULTS: There were 15 diabetics in the sample (5.7%), all of whom had extensive vascular disease. Diabetes was rare in AD patients (0.8%) relative to vascular dementia (11.8%), mixed vascular/AD dementia (8.8%), and "other" dementia patients (8.8%). In addition, the E4 allele of apolipoprotein-E, associated with high risk for AD, was frequent in the AD group (71.4%), but in the diabetic group it was only as frequent as in the general population (38.5%). In the diabetics with E4, 60% (3/5) had mixed dementia. CONCLUSIONS: Diabetics with dementia rarely have AD except as a component of mixed dementia. Apo-E genotyping showed only average E4 allele frequency in diabetics compared with the high E4 frequency found in AD patients. However, mixed dementia in diabetics may be associated with the E4 allele, suggesting that close control of diabetes may be particularly important for those with E4 since they may be more likely than others to develop both diseases.

Aged↗

PubMed1996

Mechanisms of neuronal death in Alzheimer's disease.

Recent data in cell culture has shown that brain neurons are particularly vulnerable to degeneration by apoptosis. Further the inducers that activate the program (e.g. beta-amyloid, oxidatative damage, low energy metabolism) correspond to conditions present in the Alzheimer's disease (AD) brain. This suggests the possibility that apoptosis may be one of the mechanisms contributing to neuronal loss in this disease. Indeed, some neurons in vulnerable regions of the AD brain show evidence of DNA damage, nuclear apoptotic bodies, chromatin condensation, and the induction of select genes characteristic of apoptosis in cell culture and animal models. This suggests the existence of apoptosis in the AD brain, a hypothesis also consistent with evolving research in one of the regulatory functions of the presenilin genes. On the other hand, DNA damage is present in the majority of neurons in vulnerable regions in early and mild cases. In most tissues, cells in fully activated apoptosis degenerate and are removed within hours to days and thus it seems all DNA damage is unlikely to signify terminal apoptosis. The presence of extensive DNA damage suggests an acceleration of damage, faulty repair process, loss of protective mechanisms, or an activation and arrest of aspects of the apoptotic program. DNA damage is unlikely to be an artifact of postmortem delay or agonal state. The existence of protective mechanisms for neurons may exist as these cells are nondividing and essential. In this context it is interesting that Bcl-2 is upregulated in most neurons with DNA damage. Further, at least one DNA repair enzyme is also upregulated. Thus it appears as if neurons are in a struggle between degeneration and repair. As research advances it is critical to reduce the stimuli that cause the neuronal damage and discover the key intervention points to assist neurons in the repair processes.

Alzheimer Disease↗

PubMed1995

Image analysis of beta-amyloid load in Alzheimer's disease and relation to dementia severity.

The protein beta-amyloid is said to be central to the disease process of Alzheimer's disease (AD). Several groups have developed transgenic models that overexpress the amyloid precursor protein or beta-amyloid and then develop AD-like neuropathology. Another report suggests that beta-amyloid accumulation in old dogs correlates with cognitive impairment. However, many other researchers argue that beta-amyloid deposition in senile plaques is a secondary event because plaque numbers in man do not correlate well with cognition. We set out to analyse this conumdrum in man. We selected 16 mild to severely demented AD cases on the basis of mini-mental state exam scores (MMSE; n = 16). We also included 4 controls who represented the upper range of cognitive ability. We used a computer-based image analysis of cross-sectional area of the brain occupied by beta-amyloid immunopositive deposition. We used this technique in preference to conventional methods of manual plaque counts and found a strong relation between beta-amyloid load in entorhinal cortex and cognition measured on various scales (r = -0.93 versus the Blessed IMC). Our study suggests that the size of cortical area affected by beta-amyloid deposition is an important factor in the clinical manifestation of dementia, and lends support to the possibility that beta-amyloid is central to the aetiology of AD.

Aged↗

PubMed1995

Immunoreactivity for Bcl-2 protein within neurons in the Alzheimer's disease brain increases with disease severity.

Bcl-2 protein has been suggested to be one of the proteins preventing apoptosis in a variety of cell types. Recently, apoptosis has been suggested to have an important role in the pathogenesis of Alzheimer's disease (AD). We have utilized Bcl-2 immunohistochemical methods to examine Bcl-2 in the hippocampus and entorhinal cortex of AD patients ranging in clinical and neuropathological severity from mild to severe and compared these results to those obtained from age-matched controls. Immunoreactivity for Bcl-2 was predominantly found within neurons. Bcl-2 immunostaining within AD tissue was increased relative to controls in most neurons of the entorhinal cortex, subiculum, CA1, CA2, CA3, hilus and dentate gyrus. Relative Bcl-2 staining increased in parallel with increasing disease severity. However, neurons exhibiting immunoreactivity for markers of neurofibrillary tangle formation (AT8 and PHF-1) showed reduced Bcl-2 staining, suggesting that Bcl-2 may be down regulated in these degenerating neurons. Bcl-2 immunoreactivity within astrocytes and the vasculature was also increased in AD. These results suggest that Bcl-2 protein may have a role in compensation responses to AD pathology, perhaps affording to the remaining neurons a margin of protection from apoptosis.

Aged↗

PubMed1995

Heparan sulfate and chondroitin sulfate glycosaminoglycan attenuate beta-amyloid(25-35) induced neurodegeneration in cultured hippocampal neurons.

beta-Amyloid peptide has been reported to be toxic to neurons in vitro and in vivo. The fragment of the beta 1-42 peptide believed to be responsible for this toxicity consists of amino acids 25 to 35. beta-amyloid protein, heparan sulfate (HS) glycosaminoglycan (GAG), and proteoglycan (PG) are all localized throughout the senile plaques found in Alzheimer's disease. Chondroitin sulfate (CS) and dermatan sulfate have also been found at the periphery of senile plaques. We have found that both HS and CS prevented neurite fragmentation and toxicity normally induced by beta 25-35. HS and CS by themselves did not have a significant influence on cell viability, indicating that their protective actions were not due to a general trophic effect. In contrast, cultures treated with HS and beta 1-42 did not show significantly reduced toxicity compared to cultures treated with beta 1-42 alone despite specific binding interactions. These data indicate that one function of GAGs in the brain may be to protect neurons from select toxic insults and injury, and additionally suggest that HS interacts differently with different beta-amyloid fragments. These data further suggest that different beta-amyloid fragments may induce distinct mechanisms of toxicity in vitro.

Amyloid beta-Peptides↗

PubMed1995

Amino-terminal deletions enhance aggregation of beta-amyloid peptides in vitro.

beta-Amyloid protein, which assembles into pathological aggregates deposited in Alzheimer's disease brain tissue, exhibits N-terminal heterogeneity both in vitro and in vivo. To investigate the effects of this N-terminal heterogeneity on the assembly characteristics and biophysical properties of beta-amyloid, we synthesized a series of peptides with progressively shortened N termini (initial residues at positions beta 1, beta 4, beta 8, beta 12, and beta 17) and C termini extending to residue beta 40 or beta 42. We report that peptides with N-terminal deletions exhibit enhanced peptide aggregation relative to full-length species, as quantitatively assessed by sedimentation analyses. Overall, sedimentation levels were greater for peptides terminating at residue beta 42 than for those terminating at residue beta 40. To determine if established biophysical features of the full-length protein were maintained in the truncated peptides, structural and bioactive properties of these peptides were examined and compared. Full-length and truncated peptides exhibiting aggregation showed circular dichroism spectra consistent with predominant beta-sheet conformation, fibrillar morphology under transmission electron microscopy, and significant toxicity in cultures of rat hippocampal neurons. These data demonstrate that N-terminal deletions enhance aggregation of beta-amyloid into neurotoxic, beta-sheet fibrils and suggest that such peptides may initiate and/or nucleate the pathological deposition of beta-amyloid.

Alzheimer Disease↗

PubMed1995

Differentiation of serum-free mouse embryo cells into astrocytes is accompanied by induction of glutamine synthetase activity.

Serum-free mouse embryo (SFME) cells derived in a defined serum-free medium have been cultured for more than 200 generations and display properties of neural progenitor cells. SFME cells express the neuroepithelial stem cell marker nestin in defined serum-free medium. Exposure of SFME cells to transforming growth factor beta (TGF-beta) or serum decreases nestin expression and induces the astrocyte marker glial fibrillary acidic protein, suggesting that SFME cells differentiate into astrocytes upon exposure to TGF-beta or serum. We examined the expression by SFME cells of the functional central nervous system (CNS) astrocyte marker glutamine synthetase (GS). GS activity is induced in SFME cells upon exposure to TFG-beta or serum. The induction of GS activity was dose- and time-dependent and was reversible. Retinoic acid, hydrocortisone, and dibutyryl cyclic AMP also induced GS expression. The induction of GS activity was accompanied by an increase in the level of GS mRNA and protein. This work provides further evidence that SFME cells represent neural progenitor cells which differentiate into functional astrocytes upon exposure to TGF-beta or serum.

Animals↗

PubMed1995

Neural-network-based classification of cognitively normal, demented, Alzheimer disease and vascular dementia from single photon emission with computed tomography image data from brain.

Single photon emission with computed tomography (SPECT) hexamethylphenylethyleneamineoxime technetium-99 images were analyzed by an optimal interpolative neural network (OINN) algorithm to determine whether the network could discriminate among clinically diagnosed groups of elderly normal, Alzheimer disease (AD), and vascular dementia (VD) subjects. After initial image preprocessing and registration, image features were obtained that were representative of the mean regional tissue uptake. These features were extracted from a given image by averaging the intensities over various regions defined by suitable masks. After training, the network classified independent trials of patients whose clinical diagnoses conformed to published criteria for probable AD or probable/possible VD. For the SPECT data used in the current tests, the OINN agreement was 80 and 86% for probable AD and probable/possible VD, respectively. These results suggest that artificial neural network methods offer potential in diagnoses from brain images and possibly in other areas of scientific research where complex patterns of data may have scientifically meaningful groupings that are not easily identifiable by the researcher.

Aged↗