Expression patterns of beta-amyloid precursor protein (beta-APP) in neural and nonneural human tissues from Alzheimer's disease and control subjects

Postmortem brains reveal similar but not identical amyloid precursor protein-like immunoreactivity in Alzheimer compared with other dementias

Concentrations of amyloid precursor protein (APP)-like immunoreactivity (APPLIR) have been determined by Western blotting in a soluble fraction and two membrane fractions of two areas of brain cortex from patients with Alzheimer's disease (AD) and other dementias. There were no significant differences between AD and other cases in species with the Kunitz protease inhibitor domain. However, the total soluble APPLIR was higher in AD and it was hypothesized that this relates to cholinergic hypoactivity.

Elderly patients with schizophrenia exhibit infrequent neurodegenerative lesions

Immunohistochemistry and conventional stains were used to examine the brains of 10 elderly patients with both schizophrenia and dementia to characterize the neuropathology of their cognitive deterioration. Control cases included five nondemented elderly patients with schizophrenia, five age-compatible Alzheimer's disease (AD) patients, and five neurologically normal elderly patients. Only one of the patients with schizophrenia and dementia had AD, another was diagnosed with adult polyglucosan body disease, and the others were devoid of neuropathology that could account for dementia. Quantitation of immunohistochemically detected neurofibrillary tangles and senile plaques revealed similarly low counts for the normal control group and both schizophrenia groups. Typically, the neuropathological causes of dementia can be identified in up to 95% of cases, with AD accounting for 50-60%. The unexpected lack of neuropathological findings to explain the cognitive deterioration in this group of elderly patients with schizophrenia prompts speculation about alternative etiologies.

Expression of beta-amyloid precursor protein in the developing human spinal cord

Human fetal spinal cords and other non-neural tissues from cases with gestational age from 6 to 21 weeks were examined with a panel of antibodies to different domains of beta-amyloid precursor proteins (beta-APPs). In the early developmental stages, the beta-APPs were expressed in three distinct layers, i.e., primitive neuroepithelial cell layer, mantle layer and marginal layer. beta-APP immunoreactivity was most prominent in cell bodies of putative neuroblasts located in the outer ventral part of the mantle layer. beta-APP expression diminished as the spinal cord matured and a weak residual immunoreactivity was detected exclusively in a subset of the anterior horn cells by 21 weeks gestational age. Throughout the gestational ages examined, no convincing beta/A4 immunostaining was seen in any of the spinal cord regions. Outside the spinal cord, beta-APP immunostaining was consistently present in (1) cell bodies and proximal nerves of immature neurons of dorsal root ganglia and in (2) myotubules, although these cells were devoid of beta/A4 immunoreactivity. Western blot analysis of fetal spinal cord revealed immunoreactive bands with apparent molecular weight between 100 and 140 kDa in the membrane-associated fraction, while soluble proteins with a molecular mass centered on 115 kDa were detected in the cytosolic fraction. Our results indicate that: (1) one or more isoforms of full length beta-APPs are expressed at very early gestational ages in the developing human spinal cord; (2) the normal metabolism of beta-APPs does not result in accumulations of beta/A4 fragments.

Amyloid plaques in cerebellar cortex and the integrity of Purkinje cell dendrites

We probed serial and near serial sections of cerebellum from 13 Alzheimer's disease (AD), 10 older Down's syndrome (DS) patients, and 9 age-matched, non-AD controls, using single and double labeling immunohistochemistry to investigate the pathologic consequences of beta-amyloid or A4 (A beta) deposits in cerebellum and their relationship to Purkinje cells (PCs). Our data showed that A beta deposits in cerebellum of AD and older DS adults only form diffuse or preamyloid plaques and the density of A beta lesions per unit area of molecular layer correlated with the number of PCs per unit length of the subjacent PC layer in double immunostained sections (r = 0.85; p < 0.001). About 65% of these cerebellar A beta deposits were in physical contact with PC dendrites. No A beta plaques were found in the cerebellum of controls. Despite the abundance of A beta deposits in the cerebellar cortex of AD and older DS patients, neither PC bodies nor PC dendrites in physical contact with A beta lesions showed evidence of structural abnormalities.

An aspect of Alzheimer neuropathology after suicide transport damage

Concentrations of APP-like immunoreactivity have been determined by western blotting in a soluble fraction and two membrane fractions of brain cortex from demented patients (14 with Alzheimer's disease and 8 with other diagnoses). The concentration of APP in the soluble fraction correlated with the number of pyramidal neurones but not astrocytes or indices of interneurones. Experimental lesions in rats and quantitative autoradiography were used to investigate the cellular localisation of receptors. Lesions were produced by intrastriatal or intracortical injections of volkensin to destroy corticofugal and corticortical pyramidal neurons respectively. Volkensin treatment caused significant loss of pyramidal neurones which was accompanied by reduced binding to muscarinic cholinergic m1 receptors. [3H] 8-OH-DPAT (serotonin 1A receptors) binding was reduced only following intrastriatal volkensin. Results from the human and rat investigations are discussed in terms of the biology of cortical pyramidal neurones and drugs for the treatment of Alzheimer's disease.

Morphological and biochemical analyses of amyloid plaque core proteins purified from Alzheimer disease brain tissue

Amyloid plaque cores were purified from Alzheimer disease brain tissue. Plaque core proteins were solubilized in formic acid which upon dialysis against guanidinium hydrochloride (GuHCl) partitioned into soluble (approximately 15%) and insoluble (approximately 85%) components. The GuHCl-soluble fraction contained beta-amyloid1-40, whereas the GuHCl-insoluble fraction was fractionated into six components by size exclusion HPLC: S1 (> 200 kDa), S2 (200 kDa), S3 (45 kDa), S4 (15 kDa), S5 (10 kDa), and S6 (5 kDa). Removal of the GuHCl reconstituted 10-nm filaments composed of two intertwined 5-nm strands. Fractions S5 and S6 also yielded filamentous structures when treated similarly, whereas fractions S1-S4 yielded amorphous aggregates. Chemical analysis identified S4-S6 as multimeric and monomeric beta-amyloid. Immunochemical analyses revealed alpha 1-antichymotrypsin and non-beta-amyloid segments of the beta-amyloid precursor protein within fractions S1 and S2. Several saccharide components were identified within plaque core protein preparations by fluorescence and electron microscopy, as seen with fluorescein isothiocyanate- and colloidal gold-conjugated lectins. We have shown previously that this plaque core protein complex is more toxic to neuronal cultures than beta-amyloid. The non-beta-amyloid components likely mediate this additional toxicity, imposing a significant influence on the pathophysiology of Alzheimer disease.

Human neurons derived from a teratocarcinoma cell line express solely the 695-amino acid amyloid precursor protein and produce intracellular beta-amyloid or A4 peptides

The beta-amyloid or beta/A4 peptides that accumulate as filamentous aggregates in the extracellular space of Alzheimer disease (AD) brains are derived from one or more alternatively spliced amyloid precursor proteins (APPs). The more abundant APPs in the central nervous system are the 695-(APP695), 751- (APP751), and 770- (APP770) amino acid isoforms, and each could be the source of beta/A4 peptide that accumulates in the AD brain. It is plausible that altered metabolism of these APPs by central nervous system neurons could lead to the release and deposition of beta/A4 peptide in brain parenchyma. Thus, we examined the expression and processing of the three major brain APPs in nearly pure human neurons (NT2N cells) derived from a teratocarcinoma cell line (NTera2/c1.D1 or NT2 cells) after retinoic acid treatment. NT2N neurons expressed almost exclusively APP695, whereas NT2 cells expressed predominantly APP751/770. Furthermore, the processing of the APPs in NT2N cells was distinct from NT2 and nonneuronal cells. Most significantly, the NT2N neurons but not the NT2 cells constitutively generated intracellular beta/A4 peptide and released it into the culture medium. This work demonstrates the intracellular production of beta/A4 peptide and suggests that cultured NT2N cells may provide a unique model system for understanding the contribution of neurons and APP695 to amyloidogenesis in the AD brain.

Alzheimer disease A68 proteins injected into rat brain induce codeposits of beta-amyloid, ubiquitin, and alpha 1-antichymotrypsin

Aberrantly phosphorylated tau proteins (i.e., A68 or PHF-tau) and beta-amyloid or A4 (beta A4) peptides are major components of pathologic lesions in Alzheimer disease (AD). Although A68 and beta A4 colocalize in AD neurofibrillary tangles (NFTs) and amyloid-rich senile plaques (SPs), the mechanisms leading to the convergence of A68, beta A4, and other proteins in the same AD lesions are unknown. To probe the biological properties of A68 in vivo, and to assess interactions of A68 with endogenous proteins in the rodent brain, we injected A68, dephosphorylated A68 (DEP-A68), and normal adult human tau protein into the hippocampus and neocortex of rats. In marked contrast to DEP-A68 and tau, A68 resisted rapid proteolysis and induced codeposits of three rodent proteins--i.e., beta A4, ubiquitin, and alpha 1-antichymotrypsin (ACT)--that accumulate in AD NFTs and SPs together with A68. These findings suggest that A68 may interact with beta A4, ubiquitin, and ACT in neuronal perikarya as well as in the extracellular space after release of A68 from degenerating neurons. The model system described here will facilitate efforts to elucidate mechanisms leading to the convergence of A68, beta A4, ubiquitin, and ACT in hallmark lesions of AD.

Neurofilament mRNA is reduced in Parkinson's disease substantia nigra pars compacta neurons

Lewy bodies are filamentous neuronal inclusions characteristic of Parkinson's disease, and neurofilament triplet proteins are the major components of the filaments in Lewy bodies. Since the neurofilament proteins found in Lewy bodies are abnormally phosphorylated and partially degraded, the formation of Lewy bodies may be due to the defective metabolism of these proteins, and this could lead to impairments in the structure and function of neurofilament rich neuronal processes (i.e., large caliber axons). To gain further insights into the metabolism of neurofilaments in Parkinson's disease, we evaluated neurofilament mRNA levels by semi-quantitative in situ hybridization histochemistry in postmortem tissues from Parkinson's disease and control subjects. Substantia nigra pars compacta neurons were examined with digoxigenin-UTP labeled cRNA probes to the heavy and light neurofilament mRNAs. The relative abundance of these mRNAs was measured by videodensitometric image analysis of chromogenic reaction product. Using this approach, we demonstrated that the levels of both heavy and light neurofilament mRNAs were reduced in Parkinson's disease substantia nigra pars compacta neurons. Additionally, the levels of heavy neurofilament mRNA were lowest in Lewy body containing neurons in the Parkinson's disease cases. These results suggest that the formation of neurofilament-rich Lewy bodies in substantia nigra pars compacta neurons is associated with reduced levels of the heavy and light neurofilament mRNAs in Parkinson's disease. Thus, it is possible that the accumulation of abnormal neurofilament proteins in Lewy bodies and diminished neurofilament mRNAs contribute to the degeneration of substantia nigra pars compacta neurons in Parkinson's disease.

Rimmed vacuoles of inclusion body myositis and oculopharyngeal muscular dystrophy contain amyloid precursor protein and lysosomal markers

Rimmed vacuoles are small areas of focal destruction of muscle fibres, found in inclusion body myositis, oculopharyngeal muscular dystrophy and other muscle disorders. They are known to contain amyloid proteins, probably of beta-amyloid type. We examined rimmed vacuoles immunohistochemically in 12 patients with inclusion body myositis and two patients with oculopharyngeal muscular dystrophy with antibodies to beta-amyloid precursor protein and cathepsin B and D. We found evidence for the presence of all these markers in rimmed vacuoles. These results confirm the presence of beta-amyloid in rimmed vacuoles, and provide additional support for the hypotheses that rimmed vacuoles are of lysosomal origin and that lysosomes are probably important in the metabolism of amyloid precursor protein.

Potential role of protease nexin-2/amyloid beta-protein precursor as a cerebral anticoagulant

The amyloid beta-protein precursor (APP) is the parent molecule to the amyloid beta-protein which is a major constituent of neuritic plaques and cerebrovascular deposits in Alzheimer's disease (AD). The protease inhibitor, protease nexin-2 (PN-2), is the secreted form of APP that contains the Kunitz protease inhibitor (KPI) domain. We reported that the predominant isoform of APP in human brain contains the KPI domain and is thus PN-2. Quantitation of PN-2/APP in various tissues revealed that it is primarily found in brain. Circulating blood platelets are another rich source of PN-2/APP. Platelet PN-2/APP is contained in platelet alpha granules and is secreted upon activation of platelets by physiological agonists. Protease inhibition measurements demonstrated that PN-2/APP is a potent inhibitor of intrinsic blood coagulation factor XIa. These findings suggest that PN-2/APP may play a role in the regulation of blood coagulation and platelets may serve as a systemic vehicle to deliver large amounts of this protein to sites of vascular injury. In addition, we propose that the rich, and relatively exclusive, investment of PN-2/APP in brain suggests that it may function locally as an intracerebral anticoagulant.

Amyloidogenesis in Alzheimer's disease: basic biology and animal models

A principal neuropathological hallmark of Alzheimer's disease is deposition of beta-amyloid, composed primarily of a 4 kD peptide, A beta. This peptide is derived from larger amyloid precursor proteins. The mechanisms that are responsible for A beta formation in vivo are unknown. Recently, transgenic strategies have been employed to test several hypothetical mechanisms in order to reproduce Alzheimer's disease-specific pathology in rodents.

Lewy bodies contain beta-amyloid precursor proteins of Alzheimer's disease

To assess the contribution of Alzheimer's disease amyloid proteins to cortical and substantia nigra Lewy bodies (LBs), regions of postmortem brain rich in intraneuronal LBs were examined immunohistochemically. Antibodies to epitopes in domains outside the amyloidogenic beta-amyloid peptide (BAP) in BAP precursor proteins (BAPPs) as well as to the BAP itself were used as probes. These studies showed that only BAPP epitopes outside the BAP were present in substantia nigral and cortical LBs. Thus, non-amyloidogenic domains of BAPPs may be associated with intraneuronal inclusions comprised of neurofilament proteins.