The Alzheimer's amyloid precursor is cleaved intracellularly in the trans-Golgi network or in a post-Golgi compartment.
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Alzheimer Disease↗
Biomedical subjects
M A Pappolla
Publications and source records attributed to M A Pappolla.
Evidence for intracellular cleavage of the Alzheimer's amyloid precursor in PC12 cells.
The Alzheimer's amyloid precursor (APP) is cleaved by an unidentified enzyme (APP secretase) to produce soluble APP. Fractionation of PC12 cell homogenates in a detergent-free buffer showed the presence of the Kunitz protease inhibitor (KPI)-containing soluble APP (nexin II) in the particulate fraction. Digitonin or sodium carbonate treatment of this fraction solubilized nexin II suggesting that it is contained in the lumen of vesicles. Nexin II production was not affected by lysosomotropic agents, suggesting that APP secretase is not a lysosomal enzyme. Labelling of cell surface proteins by iodination failed to detect full-length APP on the surface of PC12 cells, suggesting that most of this protein is located intracellularly. Furthermore, pulse-chase experiments showed that nexin II is detected in cell extracts before it appears in the culture medium. Cellular nexin II was detected at zero time of chase after only 5 min of pulse labelling with 35S-sulfate, indicated that APP secretase cleavage takes place immediately after APP is sulfated. Temperature block, pulse-chase, and 35S-sulfate-labelling experiments suggested that APP is cleaved by APP secretase intracellularly in the trans-Golgi network (TGN) or in a post-Golgi compartment.
Amyloid beta-Protein Precursor↗
Immunohistochemical evidence of oxidative [corrected] stress in Alzheimer's disease.
Membrane and cytoskeletal structures are known targets of oxidative injury. Brains from patients with Alzheimer's disease have cytoskeletal abnormalities and platelet and possible neuronal membrane lesions. The authors have recently demonstrated that superoxide anion is a powerful inducer of heat-shock protein synthesis, and have also shown that in response to oxidative stress or hyperthermia, intracellular levels of antioxidant enzymes increase to several folds. Whether the aforementioned mechanisms play a role in Alzheimer's disease has been suggested but is not totally established. While exploring this possibility, tissue sections from five brains with Alzheimer's disease and five neuropathologically normal age-matched controls were immunostained with polyclonal antibodies against superoxide dismutase (CuZn- and Mn- forms) and catalase. A standard avidin-biotin-peroxidase method was used for antigen detection. A subgroup of neurofibrillary tangles (15-25%) and senile plaques (50%) showed immunoreactivity for both enzymes with a staining pattern similar (but not identical) to that usually observed with antibodies against ubiquitin. Senile plaques displayed a granular pattern of immunostaining. Amyloid cores in mature classical plaques remained unstained. In addition, occasional elements with features consistent with reactive glial cells were strongly immunostained. Tangle-free neurons in both diseased and control brains showed weak to absent intracytoplasmic immunoreactivity. The immunoreactivity was totally abolished by preincubation of the primary antibodies with the corresponding purified antigens. These findings support the hypothesis that oxidative stress may be involved in the pathogenesis of Alzheimer's disease.
Alzheimer Disease↗
The genesis of the senile plaque. Further evidence in support of its neuronal origin.
Senile plaques are among the most conspicuous neuropathologic changes found in the brains of elderly individuals and patients with Alzheimer's disease (AD). The origin of the amyloid beta protein (A beta P) that accumulates in senile plaques continues to be highly controversial. Recently, using quantitative immunohistochemistry and computerized image analysis, we obtained evidence that at least a subset of early ("diffuse") senile plaques originate from neurons. In the current investigation, we employed monoclonal antibodies to A beta P and the same computerized methodology to examine in further detail the quantitative patterns of A beta P deposition in diffuse plaques in a population of intellectually intact elderly individuals. The presence of neurocentric concentration gradients of A beta P accumulation was confirmed in this study. Most significantly, this was the most predominant pattern of early amyloid deposition in the population studied. The highest concentration of A beta P was centered around neuronal cell bodies or their processes, and occasionally along neuronal plasma membranes. Computerized images showed patterns that can be interpreted as a pathogenetic sequence ranging from initial neurogenic concentration gradients centered around one single neuron to larger deposits (diffuse plaques) composed of several "anastomosing" gradients involving several adjacent neurons. It is proposed that the described very early deposits constitute the initial stage in the development of the senile plaque. Although this study does not fully prove that the accumulated A beta P is synthesized in the neuron or neuronal process it surrounds, the images herein presented suggest that neurons are the initial nidus of plaque formation.
Alzheimer Disease↗
Image analysis microspectroscopy shows that neurons participate in the genesis of a subset of early primitive (diffuse) senile plaques.
Amyloid is a component of the senile plaques that characterize one of the major neuropathologic changes in patients with Alzheimer's disease (AD). The sequence of events leading to the accumulation of amyloid precursors in senile plaques is unknown. In previous studies, the authors have shown that congophilic deposits in a subset of mature amyloid plaques are angiocentric. In this study, the authors used image analysis microspectroscopy and an antibody directed against a synthetic beta-protein (beta) or A4 sequence to examine the distribution patterns of this protein in serial sections from brains of patients with AD and in normal aged brains after quantitative immunohistochemistry. Image analysis of early primitive plaques disclosed two main patterns of early beta/A4 deposition, which consisted of neurocentric and angiocentric decreasing concentration gradients. In most instances, these gradients were not recognizable by the naked eye but appeared strikingly conspicuous after image subtraction and pseudocoloring. The described neurocentric gradients suggest that deposition of this protein, in at least some early primitive plaques, is related to neurons and possibly originates from these cells. The opposite viewpoint, i.e., that peripherally synthesized beta/A4 protein would 'sink in' toward neurons, is not supported because in very early plaques the highest immunoreactivity within the gradient was the neuronal body itself. A hypothesis is offered to reconcile the presence of both neurocentric and angiocentric depositions of these substances.
Aged↗
Two distinct types of intraneuronal neurofibrillary tangles highlighted by polarized light after silver impregnation with a modified Bielschowsky method.
Neurofibrillary tangles (NFTs) are one of the morphological hallmarks of Alzheimer's disease. The birefringency and dichroism of NFTs following congo red staining have long been known. Herein, we report the observation that a subset of NFTs show distinct birefringency induced by a modified Bielschowsky silver impregnation method. Birefringency of NFTs could not be elicited after silver impregnation with one other version of the Bielschowsky method or with the Bodian technique. To our knowledge, these properties of NFTs after metal impregnation have not been previously documented.
Alzheimer Disease↗
Bradykinin induces superoxide anion release from human endothelial cells.
The time-dependent release of superoxide anion (O2-) from bradykinin (Bk)-stimulated human umbilical vein endothelial cells (EC) was measured as the superoxide dismutase-inhibitable reduction of ferricytochrome C employing a novel application of microspectrophotometry. In the absence of Bk, O2- release by EC was not detectable. EC exposure to Bk (10(-6) to 10(-5) M) resulted in a rapid release of O2-. The release of O2- occurred within 5 minutes of exposure. O2- release was partially inhibited by indomethacin (63 +/- 6%), thus suggesting that arachidonic acid metabolism, through cyclooxygenase, contributes to EC O2- production. EC O2- release may be an important component in the pathophysiologic actions of Bk on vascular function.
Bradykinin↗
Ultrastructural evidence that insoluble microtubules are components of the neurofibrillary tangle.
The ultrastructure of Alzheimer's neurofibrillary tangles is heterogeneous and includes abnormal paired helical filaments (PHF) and various other insoluble structures. Insoluble non-PHF components isolated from neurofibrillary tangles were examined by electron microscopy. Comparison of these fractions with normal assembled neurofilaments and normal brain microtubules revealed scattered profiles which were morphologically (not chemically) identical to structures present in the microtubule, but not in the neurofilament preparations. These results support the notion that insoluble microtubules contribute to the make up of the neurofibrillary tangle. Based on these findings, preliminary experiments were conducted which suggest that non-enzymatic glycosylation may be a pathway leading to insolubility of the microtubules.
Aged↗
Permanent alterations in the hypothalamic-pituitary-thyroid axis in the rat following phenytoin exposure in utero.
Phenytoin exposure in utero results in permanent alterations of the hypothalamic-pituitary-thyroid axis in the rat. The DPH exposed animals have decreased weight gain, thyroxine and triiodothyronine concentrations. In addition, they have blunted thyroid-stimulating hormone responses to thyrotropin-releasing hormone, propylthiouracil challenge or thyroidectomy. The diminished pituitary response in these animals is similar to that reported in neonatal thyrotoxicosis in the rat. This may be due, in part, to structural similarities between phenytoin and the thyroid hormone.
Animals↗
Concurrent neuroborreliosis and Alzheimer's disease: analysis of the evidence.
Several recent reports have claimed a possible association between Borrelia burgdorferi infection and Alzheimer's disease (AD). Herein, we describe our search for additional evidence of neuroborreliosis in AD. Brain tissue from neuropathologically confirmed cases of AD was cultured for B burgdorferi using standard microbiologic methods. Material derived from culture was further examined using electron microscopy, direct immunofluorescence and acridine orange fluorescence. Previous studies have shown high titers of antiborrelia antibodies in CSF in all cases of confirmed neuroborreliosis; therefore, we tested CSF from neuropathologically confirmed cases of AD by indirect immunofluorescence and enzyme-linked immunoassay. In addition, imprint preparations from AD and control brain tissues were studied by direct immunofluorescence using a monoclonal antiborrelia antibody. Finally, a Western blot method was used to analyze protein extracts from cultures and AD brain tissue for the presence of borrelia antigen. Contrary to previous studies, our results do not support an association between infection with B burgdorferi and AD.
Alzheimer Disease↗
The "normal" brain. "Abnormal" ubiquitinilated deposits highlight an age-related protein change.
Known morphologic changes that characterize "normal" brain senescence are insufficient to explain the widespread, age-related decline of psychomotor functions. We report that the heavily ubiquitinilated deposits can be consistently detected by immunohistochemistry in the normal senescent brain. Immunostaining of hippocampal sections from aged brains with an anti-ubiquitin antibody was unrelated to neurofibrillary degeneration or senile plaque formation. In contrast, ubiquitin deposits were not detectable in brain sections from neurologically and neuropathologically normal young individuals who had died of nonneurological causes. This finding shows an unrecognized protein change in the normal aged brain.
Adult↗
Serum protein interactions with neurotransmitter receptors: implications for Alzheimer's disease.
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Adult↗
Image analysis microspectroscopy of senile plaque capillary amyloid in Alzheimer's disease. A preliminary study.
The relationship between cerebral amyloid and the microvasculature in senile plaques was studied with image analysis microspectroscopy. This imaging technique permitted topographic quantification of amyloid concentration within microscopic subregions of single senile plaques. The highest concentration of amyloid was measured at the walls of intraplaque capillaries. Spectroscopic images revealed a decreasing gradient of amyloid concentration with increasing distance from intraplaque capillaries. The concentration of amyloid in nonplaque capillaries was lower than that measured in capillaries within well-developed amyloid plaques. These findings support the premise that plaque amyloid deposition starts at the level of the capillary.
Alzheimer Disease↗
Colloid (hyaline) inclusion bodies in the central nervous system: their presence in the substantia nigra is diagnostic of Parkinson's disease.
Intracytoplasmic "colloid" inclusions have been described within neurons of several discrete central nervous system nuclei in a variety of entities. Although they lack specificity for any particular disease, they are believed to represent one of the morphologic changes of neuronal aging. Because premature aging of the substantia nigra has been one of the claimed mechanisms occurring in Parkinson's disease, the prevalence of colloid inclusions was studied within the substantia nigra in 15 patients with Parkinson's disease, 15 age-matched controls, 50 "normal" individuals, 10 patients with dementia of Alzheimer's type, and two patients with amyotrophic lateral sclerosis. Colloid bodies were found in the substantia nigra of all patients with Parkinson's disease and were virtually absent in the other populations. Histochemical and ultrastructural analyses showed that colloid bodies differ from early and mature Lewy bodies. They may represent the "pale" inclusions rarely mentioned in the literature and often mistaken for early Lewy bodies. "Colloid" bodies in the substantia nigra are diagnostic of Parkinson's disease. These findings support the theory of "premature" aging of the substantia nigra in this disease.
Adult↗
Computerized image-analysis microspectroscopy of tissue sections.
A simple technique using monochromatic light was applied to computer-assisted image analysis of tissue sections. The method consists of the determination of the spectral characteristics of different elements of interest and selective monochromatic illumination of a microscopic field followed by image analysis. Results show a dramatic increase in resolution and contrast. By means of an image subtraction technique at two wavelengths, it was possible to achieve specific optical isolation and quantification of image components.
Animals↗
Serum protein leakage in aged human brain and inhibition of ligand binding at alpha 2-adrenergic and cholinergic binding sites.
Serum proteins are known to extravasate into the brain parenchyma in senile and presenile dementia (Glenner: Hum. Pathol. 16:433-435, 1986; Wisniewski and Kozlowski: Ann. NY Acad. Sci. 396:119-129, 1982). We have recently demonstrated that human serum Cohn fraction IV (alpha-globulin enriched) inhibits ligand binding at putative dopamine and serotonin2 receptors labeled by [3H]spiroperidol in human brain (Andorn, Pappolla, Fox, Klemens, and Martello: Proc. Natl. Acad. Sci. USA 83:4572-4575, 1986). We now demonstrate that serum proteins can be identified in the neuropil and in neuronal cell bodies in normal aged brain, that alpha-globulin-enriched fractions inhibit ligand binding at alpha 2-adrenergic and muscarinic binding sites in human brain as well, and that serum proteins can be identified within neuronal cytoplasm and axons.
Adult↗
Human serum Cohn fraction IV (alpha-globulin [correction of globin] enriched) inhibits ligand binding at neurotransmitter receptors in human brain.
Human serum proteins are found in significant density in the neuropil in brains of demented individuals. The functional significance of these abnormally distributed proteins has been unknown. We now report that alpha-globulin-enriched fractions of human serum decrease the specific binding of [3H]spiroperidol at its binding sites in postmortem human frontal cortex and caudate. The substances in this serum fraction apparently exert their effect by a direct action on the binding site. Since [3H]spiroperidol labels serotoninergic and dopaminergic among other neurotransmitter receptors, these results suggest that components of human serum inhibit the binding of ligands at neurotransmitter receptors.
Animals↗