Increased levels of the Kunitz protease inhibitor-containing beta APP mRNAs in rat brain following neurotoxic damage

Amyloid precursor protein induces reactive astrogliosis

AIM

Astrocytes respond to stressors by acquiring a reactive state characterized by changes in their morphology and function. Molecules underlying reactive astrogliosis, however, remain largely unknown. Given that several studies observed increase in the Amyloid Precursor Protein (APP) in reactive astrocytes, we here test whether APP plays a role in reactive astrogliosis.

METHODS

We investigated whether APP instigates reactive astroglios by examining in vitro and in vivo the morphology and function of naive and APP-deficient astrocytes in response to APP and well-established stressors.

RESULTS

Overexpression of APP in cultured astrocytes led to remodeling of the intermediate filament network, enhancement of cytokine production, and activation of cellular programs centered around the interferon (IFN) pathway, all signs of reactive astrogliosis. Conversely, APP deletion abrogated remodeling of the intermediate filament network and blunted expression of IFN-stimulated gene products in response to lipopolysaccharide. Following traumatic brain injury (TBI), mouse reactive astrocytes also exhibited an association between APP and IFN, while APP deletion curbed the increase in glial fibrillary acidic protein observed canonically in astrocytes in response to TBI.

CONCLUSIONS

The APP thus represents a candidate molecular inducer and regulator of reactive astrogliosis. This finding has implications for understanding pathophysiology of neurodegenerative and other diseases of the nervous system characterized by reactive astrogliosis and opens potential new therapeutic avenues targeting APP and its pathways to modulate reactive astrogliosis.

Amyloid precursor protein induces reactive astrogliosis

We present in vitro and in vivo evidence demonstrating that Amyloid Precursor Protein (APP) acts as an essential instigator of reactive astrogliosis. Cell-specific overexpression of APP in cultured astrocytes led to remodelling of the intermediate filament network, enhancement of cytokine production and activation of cellular programs centred around the interferon (IFN) pathway, all signs of reactive astrogliosis. Conversely, APP deletion in cultured astrocytes abrogated remodelling of the intermediate filament network and blunted expression of IFN stimulated gene (ISG) products in response to lipopolysaccharide (LPS). Following traumatic brain injury (TBI), mouse reactive astrocytes also exhibited an association between APP and IFN, while APP deletion curbed the increase in glial fibrillary acidic protein (GFAP) observed canonically in astrocytes in response to TBI. Thus, APP represents a molecular inducer and regulator of reactive astrogliosis.

Investigating HIV-Human Interaction Networks to Unravel Pathogenic Mechanism for Drug Discovery: A Systems Biology Approach

BACKGROUND

Two big issues in the study of pathogens are determining how pathogens infect hosts and how the host defends itself against infection. Therefore, investigating host-pathogen interactions is important for understanding pathogenicity and host defensive mechanisms and treating infections.

METHODS

In this study, we used omics data, including time-course data from high-throughput sequencing, real-time polymerase chain reaction, and human microRNA (miRNA) and protein-protein interaction to construct an interspecies protein-protein and miRNA interaction (PPMI) network of human CD4+ T cells during HIV-1 infection through system modeling and identification.

RESULTS

By applying a functional annotation tool to the identified PPMI network at each stage of HIV infection, we found that repressions of three miRNAs, miR-140-5p, miR-320a, and miR-941, are involved in the development of autoimmune disorders, tumor proliferation, and the pathogenesis of T cells at the reverse transcription stage. Repressions of miR-331-3p and miR-320a are involved in HIV-1 replication, replicative spread, anti-apoptosis, cell proliferation, and dysregulation of cell cycle control at the integration/replication stage. Repression of miR-341-5p is involved in carcinogenesis at the late stage of HIV-1 infection.

CONCLUSION

By investigating the common core proteins and changes in specific proteins in the PPMI network between the stages of HIV-1 infection, we obtained pathogenic insights into the functional core modules and identified potential drug combinations for treating patients with HIV-1 infection, including thalidomide, oxaprozin, and metformin, at the reverse transcription stage; quercetin, nifedipine, and fenbendazole, at the integration/replication stage; and staurosporine, quercetin, prednisolone, and flufenamic acid, at the late stage.

Role of prostacyclin signaling in endothelial production of soluble amyloid precursor protein-α in cerebral microvessels

We tested hypothesis that activation of the prostacyclin (PGI2) receptor (IP receptor) signaling pathway in cerebral microvessels plays an important role in the metabolism of amyloid precursor protein (APP). In human brain microvascular endothelial cells activation of IP receptor with the stable analogue of PGI2, iloprost, stimulated expression of amyloid precursor protein and a disintegrin and metalloprotease 10 (ADAM10), resulting in an increased production of the neuroprotective and anticoagulant molecule, soluble APPα (sAPPα). Selective agonist of IP receptor, cicaprost, and adenylyl cyclase activator, forskolin, also enhanced expression of amyloid precursor protein and ADAM10. Notably, in cerebral microvessels of IP receptor knockout mice, protein levels of APP and ADAM10 were reduced. In addition, iloprost increased protein levels of peroxisome proliferator-activated receptor δ (PPARδ) in human brain microvascular endothelial cells. PPARδ-siRNA abolished iloprost-augmented protein expression of ADAM10. In contrast, GW501516 (a selective agonist of PPARδ) upregulated ADAM10 and increased production of sAPPα. Genetic deletion of endothelial PPARδ (ePPARδ-/-) in mice significantly reduced cerebral microvascular expression of ADAM10 and production of sAPPα. In vivo treatment with GW501516 increased sAPPα content in hippocampus of wild type mice but not in hippocampus of ePPARδ-/- mice. Our findings identified previously unrecognized role of IP-PPARδ signal transduction pathway in the production of sAPPα in cerebral microvasculature.

Amyloid precursor protein and proinflammatory changes are regulated in brain and adipose tissue in a murine model of high fat diet-induced obesity

Background

Middle age obesity is recognized as a risk factor for Alzheimer's disease (AD) although a mechanistic linkage remains unclear. Based upon the fact that obese adipose tissue and AD brains are both areas of proinflammatory change, a possible common event is chronic inflammation. Since an autosomal dominant form of AD is associated with mutations in the gene coding for the ubiquitously expressed transmembrane protein, amyloid precursor protein (APP) and recent evidence demonstrates increased APP levels in adipose tissue during obesity it is feasible that APP serves some function in both disease conditions.

Methodology/Principal Findings

To determine whether diet-induced obesity produced proinflammatory changes and altered APP expression in brain versus adipose tissue, 6 week old C57BL6/J mice were maintained on a control or high fat diet for 22 weeks. Protein levels and cell-specific APP expression along with markers of inflammation and immune cell activation were compared between hippocampus, abdominal subcutaneous fat and visceral pericardial fat. APP stimulation-dependent changes in macrophage and adipocyte culture phenotype were examined for comparison to the in vivo changes.

Conclusions/Significance

Adipose tissue and brain from high fat diet fed animals demonstrated increased TNF-α and microglial and macrophage activation. Both brains and adipose tissue also had elevated APP levels localizing to neurons and macrophage/adipocytes, respectively. APP agonist antibody stimulation of macrophage cultures increased specific cytokine secretion with no obvious effects on adipocyte culture phenotype. These data support the hypothesis that high fat diet-dependent obesity results in concomitant pro-inflammatory changes in brain and adipose tissue that is characterized, in part, by increased levels of APP that may be contributing specifically to inflammatory changes that occur.

Amyloid precursor protein revisited: neuron-specific expression and highly stable nature of soluble derivatives

APP processing and amyloid-β production play a central role in Alzheimer disease pathogenesis. APP has been considered a ubiquitously expressed protein. In addition to amyloid-β, α- or β-secretase-dependent cleavage of APP also generates soluble secreted APP (APPsα or APPsβ, respectively). Interestingly, APPsβ has been shown to be subject to further cleavage to create an N-APP fragment that binds to the DR6 death receptor and mediates axon pruning and degeneration under trophic factor withdrawal conditions. By performing APP immunocytochemical staining, we found that, unexpectedly, many antibodies yielded nonspecific staining in APP-null samples. Screening of a series of antibodies allowed us to identify a rabbit monoclonal antibody Y188 that is highly specific for APP and prompted us to re-examine the expression, localization, and stability of endogenous APP and APPsβ in wild-type and in APPsβ knock-in mice, respectively. In contrast to earlier studies, we found that APP is specifically expressed in neurons and that its expression cannot be detected in major types of glial cells under basal or neuroinflammatory conditions. Both APPsα and APPsβ are highly stable in the central nervous system (CNS) and do not undergo further cleavage with or without trophic factor support. Our results clarify several key questions with regard to the fundamental properties of APP and offer critical cellular insights into the pathophysiology of APP.

Oligodendrocytes are a novel source of amyloid peptide generation

Alzheimer’s disease is characterised by regional neuronal degeneration, synaptic loss, and the progressive deposition of the 4 kDa β-amyloid peptide (Aβ) in senile plaques and accumulation of tau protein as neurofibrillary tangles. Aβ derives from the larger precursor molecule, amyloid precursor protein (APP) by proteolytic processing via β- and γ-secretases. While APP expression is well documented in neurons and astrocytes, the case for oligodendrocytes is less clear. The latter cell type is reported to express different isoforms of APP, and we have confirmed this observation by immunocytochemistry in cultures of differentiated rat cortical oligodendrocytes. Moreover, by means of a sensitive electrochemiluminescent immunoassay employing Aβ C-terminal specific antibodies, mature oligodendrocytes are shown to secrete the 40 and 42 amino acid Aβ species (Aβ40 and Aβ42). Secretion of Aβ peptides was reduced by incubating oligodendrocytes with α- and β-secretase inhibitors, or a γ-secretase inhibitor. Disturbances of APP processing and/ or synthesis in oligodendrocytes may account for some myelin disorders observed in Alzheimer's disease and other senile dementias.

Expression of APP pathway mRNAs and proteins in Alzheimer's disease

In both trisomy 21 and rare cases of triplication of amyloid precursor protein (APP) Alzheimer's disease (AD) pathological changes are believed to be secondary to increased expression of APP. We hypothesized that sporadic AD may also be associated with changes in transcription of APP or its metabolic partners. To address this issue, temporal neocortex of 27 AD and 21 non-demented control brains was examined to assess mRNA levels of APP isoforms (total APP, APP containing the Kunitz protease inhibitor domain [APP-KPI] and APP770) and APP metabolic enzymatic partners (the APP cleaving enzymes beta-secretase [BACE] and presenilin-1 [PS-1], and putative clearance molecules, low-density lipoprotein receptor protein [LRP] and apolipoprotein E [apoE]). Furthermore, we evaluated how changes in APP at the mRNA level affect the amount of Tris buffer extractable APP protein and Abeta40 and 42 peptides in AD and control brains. As assessed by quantitative PCR, APP-KPI (p=0.007), APP770 (p=0.004), PS-1 (p=0.004), LRP (p=0.003), apoE (p=0.0002) and GFAP (p<0.0001) mRNA levels all increased in AD, and there was a shift from APP695 (a neuronal isoform) towards KPI containing isoforms that are present in glia as well. APP-KPI mRNA levels correlated with soluble APPalpha-KPI protein (sAPPalpha-KPI) levels measured by ELISA (tau=0.33, p=0.015 by Kendall's rank correlation); in turn, soluble APPalpha-KPI protein levels positively correlated with Tris-extractable, soluble Abeta40 (p=0.046) and 42 levels (p=0.007). The ratio of soluble APPalpha-KPI protein levels to total APP protein increased in AD, and also correlated with GFAP protein levels in AD. These results suggest that altered transcription of APP in AD is proportionately associated with Abeta peptide, may occur in the context of gliosis, and may contribute to Abeta deposition in sporadic AD.

Promoter mutations that increase amyloid precursor-protein expression are associated with Alzheimer disease

Genetic variations in promoter sequences that alter gene expression play a prominent role in increasing susceptibility to complex diseases. Also, expression levels of APP are essentially regulated by its core promoter and 5' upstream regulatory region and correlate with amyloid beta levels in Alzheimer disease (AD) brains. Here, we systematically sequenced the proximal promoter (-766/+204) and two functional distal regions (-2634/-2159 and -2096/-1563) of APP in two independent AD series with onset ages < or =70 years (Belgian sample, n=180; Dutch sample, n=111) and identified eight novel sequence variants. Three mutations (-118C-->A, -369C-->G, and -534G-->A) identified only in patients with AD showed, in vitro, a nearly twofold neuron-specific increase in APP transcriptional activity, similar to what is expected from triplication of APP in Down syndrome. These mutations either abolished (AP-2 and HES-1) or created (Oct1) transcription-factor binding sites involved in the development and differentiation of neuronal systems. Also, two of these clustered in the 200-bp region (-540/-340) of the APP promoter that showed the highest degree of species conservation. The present study provides evidence that APP-promoter mutations that significantly increase APP expression levels are associated with AD.

Human apoB overexpression and a high-cholesterol diet differently modify the brain APP metabolism in the transgenic mouse model of atherosclerosis

Epidemiological and biochemical data suggest a link between the cholesterol metabolism, the amyloid precursor protein (APP) processing and the increased cerebral beta-amyloid (Abeta) deposition in Alzheimer's disease (AD). The individual and combined effects of a high-cholesterol (HC) diet and the overexpression of the human apoB-100 gene were therefore examined on the cerebral expression and processing of APP in homozygous apoB-100 transgenic mice [Tg (apoB(+/+))], a validated model of atherosclerosis. When fed with 2% cholesterol for 17 weeks, only the wild-type mice exhibited significantly increased APP695 (123%) and APP770 (138%) mRNA levels in the cortex. The HC diet-induced hypercholesterolemia significantly increased the APP isoform levels in the membrane-bound fraction, not only in the wild-type animals (114%), but also in the Tg apoB(+/+) group (171%). The overexpression of human apoB-100 gene by the liver alone reduced the brain APP isoform levels in the membrane-bound fraction (78%), whereas the levels were increased by the combined effect of HC and the overexpression of the human apoB-100 gene (134%). The protein kinase C and beta-secretase protein levels were not altered by the individual or combined effects of these two factors. Our data indicate that the two atherogenic factors, the HC diet and the overexpression of the human apoB-100 gene by the liver, could exert different effects on the processing and expression of APP in the mice brain.

Restraint stress induces beta-amyloid precursor protein mRNA expression in the rat basolateral amygdala

Several studies have shown the involvement of beta-amyloid precursor proteins (APP) isoforms in physiological process like development of the central nervous system (CNS), functional roles in mature brain, and in pathological process like Alzheimer's disease, neuronal experimental damage, and stress, among others. However, the APP functions are still not clear. In the brain, APP(695) isoform is predominantly found in neurons while APP(751/770) isoforms are predominantly found in astroglial cells and have been associated to neurodegenerative processes. Acute or chronic stress in rats may trigger specific response mechanisms in several brain areas such as amygdala, hippocampus and cortex with the involvement of multiple neurotransmitters. Chronic stress may also induce neuronal injury in rat hippocampus. In situ hybridization (ISH) was used to investigate the expression of APP(695) and APP(751/770) mRNA in amygdala and hippocampus of male Wistar rats (n=4-6 per group) after acute (2 or 6h) or chronic (2h daily/7 days or 6h daily/21 days) restraint stress. Only the APP(695) mRNA expression was significantly increased in the basolateral amygdaloid nuclei following acute or chronic restraint. No APP isoform changed in hippocampus after any stress condition. These results suggest that restraint stress induces changes in gene expression of APP(695) in basolateral amygdaloid nucleus, an area related to stress response.

Deposition of amyloid fibrils promotes cell-surface accumulation of amyloid β precursor protein

Amyloid beta protein (Abeta) deposition and neuronal degeneration are characteristic pathological features of Alzheimer's disease (AD). In vitro, Abeta fibrils (fAbeta) induce neuronal degeneration reminiscent to AD, but the mechanism of neurotoxicity is unknown. Here we show that amyloid fibrils increase the level of cell-surface full-length amyloid beta precursor protein (h-AbetaPP) and secreted AbetaPP (s-AbetaPP). Pulse-chase analysis indicated that fAbeta selectively inhibited the turnover of cell-surface AbetaPP, without altering its intracellular levels. FAbeta-induced AbetaPP accumulation was not abrogated by cycloheximide, suggesting that increased protein synthesis is not critically required. Abeta fibrils sequester s-AbetaPP from the culture medium and promote its accumulation at the cell surface, indicating that binding of Abeta fibrils mediates AbetaPP accumulation. A time course analysis of Abeta treatment showed that AbetaPP level is elevated before significant cell death can be detected, while other toxic insults do not augment AbetaPP level, suggesting that AbetaPP may be specifically involved in early stages of Abeta-induced neurodegeneration. Finally, Abeta fibrils promote clustering of h-AbetaPP in abnormal focal adhesion-like (FA-like) structures that mediate neuronal dystrophy, increasing its association with the cytoskeleton. These results indicate that the interaction of Abeta fibrils with AbetaPP is an early event in the mechanism of Abeta-induced neurodegeneration that may play a significant role in AD pathogenesis.

Prostaglandin E2 regulates amyloid precursor protein expression via the EP2 receptor in cultured rat microglia

We investigated the effects of prostaglandin E2 (PGE2) on amyloid precursor protein (APP) expression in cultured rat microglia. PGE2 treatment significantly increased the expression of APP holoprotein and was associated with an elevation in cyclic AMP (cAMP). Direct activation of adenylate cyclase with forskolin also increased APP expression. Co-treatment of microglia with PGE2 and the PKA inhibitor H-89 suppressed the overexpression of APP caused by PGE2 alone. The prostaglandin EP2 receptor is known to be positively coupled to cAMP production. Stimulation of the EP2 receptor with butaprost increased APP holoprotein, whereas co-incubation of the cells with PGE(2) and the EP2 receptor antagonist AH-6809 blocked the effect of PGE2 on APP expression. These data suggest that PGE2 is able to regulate the expression of APP, and that this effect may be mediated by the EP2 receptor and the cAMP signaling cascade.

Amyloid precursor protein mRNA levels in Alzheimer's disease brain

Insoluble beta-amyloid deposits in Alzheimer's disease (AD) brain are proteolytically derived from the membrane bound amyloid precursor protein (APP). The APP gene is differentially spliced to produce isoforms that can be classified into those containing a Kunitz-type serine protease inhibitor domain (K(+), APP(751), APP(770), APRP(365) and APRP(563)), and those without (K(-), APP(695) and APP(714)). Given the hypothesis that Abeta is a result of aberrant catabolism of APP, differential expression of mRNA isoforms containing protease inhibitors might play an active role in the pathology of AD. We took 513 cerebral cortex samples from 90 AD and 81 control brains and quantified the mRNA isoforms of APP with TaqMan real-time RT-PCR. After adjustment for age at death, brain pH and gender we found a change in the ratio of KPI(+) to KPI(-) mRNA isoforms of APP. Three separate probes, designed to recognise only KPI(+) mRNA species, gave increases of between 28% and 50% in AD brains relative to controls (p=0.002). There was no change in the mRNA levels of KPI-(APP 695) (p=0.898). Therefore, whilst KPI-mRNA levels remained stable the KPI(+) species increased specifically in the AD brains.

Transforming growth factor-beta 1 potentiates amyloid-beta generation in astrocytes and in transgenic mice

Accumulation of the amyloid-beta peptide (Abeta) in the brain is crucial for development of Alzheimer's disease. Expression of transforming growth factor-beta1 (TGF-beta1), an immunosuppressive cytokine, has been correlated in vivo with Abeta accumulation in transgenic mice and recently with Abeta clearance by activated microglia. Here, we demonstrate that TGF-beta1 drives the production of Abeta40/42 by astrocytes leading to Abeta production in TGF-beta1 transgenic mice. First, TGF-beta1 induces the overexpression of the amyloid precursor protein (APP) in astrocytes but not in neurons, involving a highly conserved TGF-beta1-responsive element in the 5'-untranslated region (+54/+74) of the APP promoter. Second, we demonstrated an increased release of soluble APP-beta which led to TGF-beta1-induced Abeta generation in both murine and human astrocytes. These results demonstrate that TGF-beta1 potentiates Abeta production in human astrocytes and may enhance the formation of plaques burden in the brain of Alzheimer's disease patients.

Long-term accumulation of amyloid-beta in axons following brain trauma without persistent upregulation of amyloid precursor protein genes

Brain trauma has been shown to be a risk factor for developing Alzheimer disease (AD), and AD-like plaques containing amyloid-beta (Abeta) peptides have been found in the brain shortly following trauma. Here, we evaluated the effects of brain trauma on the accumulation of Abeta and expression of amyloid precursor protein (APP) genes (APP695 and APP751/ 770) over 1 yr in a non-transgenic rodent model. Anesthetized male Sprague-Dawley rats were subjected to parasagittal fluid percussion brain injury of moderate severity (2.5-2.9 atm) or sham treatment and their brains were evaluated at 2, 4, 7, 14 days, and 1, 2, 6, 12 months following injury. Immunohistochemical analysis detected only weak Abeta staining by 2 wk following injury. However, by 1 month to 1 yr following injury, strong immunoreactivity for Abeta was found in damaged axons throughout the thalamus and white matter. Western blot analysis confirmed the accumulation of Abeta peptides in tissue from injured brains. Although in situ hybridization demonstrated an increased gene expression of APP751/770 surrounding the cortical lesion at 2 to 7 days following injury, this expression returned to baseline levels at all subsequent time points and no increase in the expression of APP695 was detected at any time point. These results demonstrate that long-termAbeta accumulation in damaged axons can be induced in a non-transgenic rodent model of brain trauma. Surprisingly, the extent of this Abeta production appeared to be dependent on the maturity of the injury, but uncoupled from the gene expression of APP. Together, these data suggest a mechanism that may contribute to long-term neurodegeneration following brain trauma.

Abeta as a bioflocculant: implications for the amyloid hypothesis of Alzheimer's disease

Research into Alzheimer's disease (AD) has been guided by the view that deposits of fibrillar amyloid-beta peptide (Abeta) are neurotoxic and are largely responsible for the neurodegeneration that accompanies the disease. This 'amyloid hypothesis' has claimed support from a wide range of molecular, genetic and animal studies. We critically review these observations and highlight inconsistencies between the predictions of the amyloid hypothesis and the published data. We show that the data provide equal support for a 'bioflocculant hypothesis', which posits that Abeta is normally produced to bind neurotoxic solutes (such as metal ions), while the precipitation of Abeta into plaques may be an efficient means of presenting these toxins to phagocytes. We conclude that if the deposition of Abeta represents a physiological response to injury then therapeutic treatments aimed at reducing the availability of Abeta may hasten the disease process and associated cognitive decline in AD.

Age-dependent differential regulation of genes encoding APP and alpha-synuclein in hippocampal synaptic plasticity

We investigated the modulation of the messenger RNA encoding the amyloid precursor protein (APP) and alpha-synuclein following induction of long-term potentiation (LTP) in the dentate gyrus of young and aged rats. Three hours after tetanic stimulation, LTP induced in the young rats was maintained; the aged rats, however, fell into two subgroups: those in which LTP was maintained, and those in which LTP had declined to basal levels. In young rats, the global expression of mRNAs of all isoforms of APP and in particular that of the isoform lacking the KPI domain were significantly upregulated. In aged rats, the global expression of mRNAs of all isoforms of APP was not modified, regardless of whether LTP was maintained or not. The level of mRNA encoding the Kunitz protease-inhibitory (KPI)-minus isoform of APP, however, was increased in aged rats in which LTP was maintained, suggesting that the gene of this isoform may be more specifically regulated by synaptic plasticity. In contrast, we found that the gene encoding alpha-synuclein showed a trend towards being downregulated at the mRNA level in young rats following LTP, and significantly so in aged rats in which LTP was maintained, whereas it was not downregulated in aged rats with decremental LTP. These data suggest that the regulated expression of APP isoforms is part of the tanscriptional response associated with the enduring forms of synaptic plasticity and is altered with age. Whereas the level of alpha-synuclein mRNA is not apparently modified in normal LTP, it may reflect a mechanism of apoptotic cell death in aging that is in part responsible for decremental synaptic plasticity.

The functions of the amyloid precursor protein gene

The amyloid precursor protein (APP) gene and its protein products have multiple functions in the central nervous system and fulfil criteria as neuractive peptides: presence, release and identity of action. There is increased understanding of the role of secretases (proteases) in the metabolism of APP and the production of its peptide fragments. The APP gene and its products have physiological roles in synaptic action, development of the brain, and in the response to stress and injury. These functions reveal the strategic importance of APP in the workings of the brain and point to its evolutionary significance.

Expression of amyloid precursor protein in human astrocytes in vitro: isoform-specific increases following heat shock

The beta-amyloid protein deposited in senile plaques and cerebral blood vessels in the Alzheimer's disease brain is derived from the larger transmembrane spanning amyloid precursor protein. The present study investigates the effects of heat shock on the expression and processing of amyloid precursor protein in a normal human fetal astrocytic cell line CC2565 using reverse transcription-polymerase chain reaction, in situ hybridization histochemistry and western blot analysis. Heat shock led to an increase in the messenger RNA encoding Kunitz protease inhibitor isoforms of amyloid precursor protein, which peaked at 4h post-heat shock. This increase was confined to the messenger RNA encoding amyloid precursor protein-751, with a decrease in amyloid precursor protein-770 and no change in amyloid precursor protein-695. This shift in splicing was accompanied by a significant decrease in secreted amyloid precursor protein and an increase in beta-secretase processing within the cell. These findings demonstrate that astrocytes in vitro demonstrate a striking response to heat shock. This is unlikely to be due to a direct action on the promoter region of the gene, since the response is specific for one splice variant; amyloid precursor protein-751 messenger RNA. This increase in expression is further accompanied by a decrease in secretion of amyloid precursor protein, implying a shift in processing towards an intracellular route, possibly via the actions of the beta-secretase enzyme, which is known to be potentially amyloidogenic. Such a mechanism may contribute to amyloidosis in the intact brain in response to cellular stress, such as head injury.

Expression of beta-amyloid precursor and Bcl-2 proto-oncogene proteins in rat retinas after intravitreal injection of aminoadipic acid

In order to investigate the role of glia in relation to factors that affect the expression of beta-amyloid precursor protein (betaAPP) and B cell lymphoma oncogene protein (Bcl-2) in the central nervous tissue, the patterns of expression of betaAPP and Bcl-2 in developing and mature rat retinas were studied immunocytochemically after intravitreal injection of alpha-aminoadipic acid (alpha-AAA), a glutamate analogue and gliotoxin that is known to cause injury of retinal Müller glial cells. In normal developing retinas, betaAPP and Bcl-2 were expressed primarily but transiently in a small number of neurons in the ganglion cell layer during the first postnatal week. Immunoreactivity of betaAPP and Bcl-2 appeared in the endfeet and proximal part of the radial processes of Müller glial cells from the second postnatal week onwards. In rats that received intravitreal injection of alpha-AAA at birth, there was a loss of immunoreactivity to vimentin, and a delayed expressed on betaAPP or Bcl-2 in Muller glial cells until 3-5 weeks post-injection. Immunoreactive neurons were also observed in the inner retina especially in the ganglion cell layer from 5 to 35 days after injection. A significant reduction in numerical density of cells with large somata in the ganglion cell layer was observed in the neonatally injected retinas at P56, which was accompanied by an increased immunostaining in radial processes of Müller glial cells. In contrast, no detectable changes in the expression of betaAPP and Bcl-2 were observed in retina that received alpha-AAA as adults. These results indicate that the gliotoxin alpha-AAA has long lasting effects on the expression of betaAPP and Bcl-2 in Müller glial cells as well as neurons in the developing but not mature retinas. The loss of vimentin and delayed expression of betaAPP and Bcl-2 in developing Müller glial cells suggests that the metabolic integrity of Müller cells was temporarily compromised, which may have adverse effects on developing neurons that are vulnerable or dependent on trophic support from the Müller glial cells.

Regional distribution of presenilin-1 messenger RNA in the embryonic rat brain: comparison with beta-amyloid precursor protein messenger RNA localization

The messenger RNA expression of presenilin-1, an important gene responsible for early-onset familial Alzheimer's disease, was investigated in the embryonic rat brain with in situ hybridization histochemistry using an oligonucleotide probe specific to the messenger RNA. It was also compared with that of beta-amyloid precursor protein messenger RNA. Presenilin-1 and beta-amyloid precursor protein messenger RNA were abundantly expressed throughout the central nervous system in the embryonic day 13, 17 and 20 rat brain. Presenilin-1 messenger RNA was strongly expressed in both neuroepithelium and differentiating fields. In contrast, beta-amyloid precursor protein messenger RNA was preferentially expressed in differentiating fields, while low expression of beta-amyloid precursor protein messenger RNA was seen in neuroepithelium. Although the expression patterns of these two messenger RNAs were basically similar, there seemed to be a tendency that presenilin-1 messenger RNA was preferentially expressed in immature neurons, while beta-amyloid precursor protein messenger RNA was preferentially expressed in mature neurons, suggesting that presenilin-1 is expressed earlier than beta-amyloid precursor protein and that presenilin-1 is involved in beta-amyloid precursor protein processing. These data raise the possibility that presenilin-1 and beta-amyloid precursor protein co-operatively play pivotal roles in rat neurogenesis.

Prostaglandin E2 stimulates amyloid precursor protein gene expression: inhibition by immunosuppressants

Amyloid plaques that accumulate in the brains of patients with Alzheimer's disease (AD) are primarily composed of aggregates of amyloid peptides that are derived from the amyloid precursor protein (APP). Overexpression of APP in cell cultures increases the formation of amyloidogenic peptides and causes neurodegeneration and cognitive dysfunction in transgenic mice. We now report that activation of prostaglandin E2 (PGE2) receptors increases cAMP formation and stimulates overexpression of APP mRNA and holoprotein in primary cultures of cortical astrocytes. Levels of glial fibrillary acidic protein were also increased by PGE2 treatment, suggesting that these cultured astrocytes resemble reactive astrocytes found in vivo. The stimulation by PGE2 of APP synthesis was mimicked or blocked by activators or inhibitors, respectively, of protein kinase A. Actinomycin D or cycloheximide also inhibited the increase in APP holoprotein stimulated by PGE2. Treatment of astrocytes with 8-Bromo-cAMP or forskolin for 24 hr also stimulated APP overexpression in cultured astrocytes. The immunosuppressants cyclosporin A and FK-506 inhibited the increase in APP mRNA and holoprotein levels caused by PGE2 or by other treatments that elevated cellular cAMP levels; the inhibitory effect of FK-506 but not of cyclosporin A was attenuated by rapamycin. These results suggest that prostaglandins produced by brain injury or inflammation can activate APP transcription in astrocytes and that immunosuppressants may be used to prevent APP overexpression and possibly the pathophysiological processes underlying AD.

Indicators of glial activation and brain oxidative stress after intraventricular infusion of endotoxin

Glial activation and oxidative stress are both consequences of brain aging. To investigate whether glial activation causes oxidative stress or not, the immune activator, lipopolysaccharide (LPS), was intraventricularly injected into the rat brain. The expression of candidate genes were examined by in situ hybridization histochemistry (ISHH) combined with immunohistochemistry for glial markers over a period of time up to 24 h after the LPS injection. The mRNA for glial fibrillary acidic protein (GFAP) was elevated around the injection site by 2 h, and the volume of elevated expression spread to the entire brain after 6 h, with higher levels present in the injected hemisphere. The level of inducible isoform of nitric oxide synthase (i-NOS) mRNA increased in a punctate-like pattern in the region of the injection by 6 h and this response spread to the entire brain after 12 h. These results indicate that the glia are activated for at least 24 h after a single LPS injection. The mRNAs for a heat-shock protein (HSP70) and for the manganese-dependent superoxide dismutase (Mn-SOD) were elevated in the ipsilateral hemisphere as early as 2 h post-injection, but these responses subsided nearly to basal levels by 4 h. These levels of mRNAs for these genes increased again after 6 h of the LPS injection; thus, the earlier increases of the messages appeared to be associated with the survival surgery procedure. With microautoradiographic analysis, scattered OX-42 positive cells expressed i-NOS mRNA after 6 h post-injection, but elevation of Mn-SOD mRNA was not detected in either microglia or astrocytes at any time point examined. The level for Cu/Zn-SOD mRNA did not alter at any time point. The beta-amyloid precursor protein (betaAPP) mRNAs were elevated beginning at 6 h. These results indicate that chronic glial activation leads to a condition of oxidative stress in the brain. The data also suggest that LPS injection could be used to study the effects of chronic glial activation on the survival of neuronal populations that could be at risk from oxidative stress.

Presenilin-1 mRNA and beta-amyloid precursor protein mRNA are expressed in the developing rat olfactory and vestibulocochlear systems

The mRNA expression of presenilin-1 (PS1) and beta-amyloid precursor protein (betaAPP) was investigated in the embryonic day 20 rat olfactory bulb, nasal cavity, and inner ear using in situ hybridization histochemistry. In the olfactory bulb, PS1 mRNA was strongly expressed in both olfactory bulb neuroepithelium and the differentiating olfactory bulb. In contrast, betaAPP mRNA was preferentially expressed in differentiating fields. In the nasal cavity, PS1 mRNA was strongly expressed throughout the olfactory epithelium, while betaAPP mRNA expression was concentrated in the middle part of the epithelium. In the membrane labyrinth of the inner ear, although PS1 mRNA was evenly distributed in both sensory epithelium and supporting cells, betaAPP mRNA was exclusively expressed in the sensory epithelium. These data suggest that PS1 is expressed earlier than betaAPP, and that PS1 and betaAPP co-operatively play pivotal roles in the development of the olfactory and vestibulocochlear systems.

Increased expression of amyloid precursor protein and amyloid precursor-like protein 2 during trophic factor withdrawal-induced death of neuronal PC12 cells

Programmed cell death (PCD) (apoptosis) is implicated in the neuronal cell death of Alzheimer's disease (AD). We investigated expression of amyloid precursor protein (APP) and amyloid precursor-like protein 2 (APLP2) during trophic factor deprivation-induced PCD of neuronally differentiated PC12 cells. Neuronal PC12 cells underwent PCD within two days following withdrawal of nerve growth factor (NGF) from the culture medium. Total APP mRNA levels increased gradually after 24 h, reaching levels 250% higher than those in control cells at 48 h after NGF withdrawal, and total APLP2 mRNA levels also increased similarly at 48 h. Analysis of the three major APP mRNA isoforms APP695, APP751, and APP770 by reverse transcription polymerase chain reaction showed a substantial increase in the proportion of APP770 at 48 h after NGF withdrawal. Basic fibroblast growth factor, which prevented the appearance of PCD after NGF withdrawal, inhibited the increases in APP and APLP2 mRNA levels as well as the increase in the proportion of APP770. Cellular holoprotein levels of total APP, APP containing the Kunitz protease inhibitor domain, and APLP2 also increased by approximately 60%, 100%, and 30%, respectively, at 48 h after NGF withdrawal. These data indicate that in neuronal PC12 cells undergoing PCD following trophic factor withdrawal, the syntheses of both APP and APLP2 are upregulated, and the alternative splicing of the APP gene is modified. This implies a linkage between APP and APLP2 expression and neuronal PCD.

Enhancement of beta-amyloid precursor protein transcription and expression by the soluble interleukin-6 receptor/interleukin-6 complex

We investigated a potential role for the soluble interleukin-6 receptor (sIL-6R) in modulating interleukin-6 (IL-6) function in the central nervous system by assessing IL-6 and sIL-6R effects on beta-amyloid precursor protein (beta-APP) transcription and expression in cells of human neuronal origin. Cells transfected with a luciferase reporter plasmid containing a 3.8 kb DNA fragment of the beta-APP promoter were shown to have inducible promoter activity when treated with phorbol ester or basic fibroblast growth factor, but not when treated with lipopolysaccharide or Il-6. PCR amplification analysis revealed the presence of mRNA encoding the signaling subunit of the Il-6 receptor complex, the gp130 subunit, at levels approximating that found in human cortical tissue. The mRNA encoding the IL-6 receptor, however, was poorly expressed and was detectable only at high amplification cycles. When purified sIL-6R protein was added together with IL-6, there was a rapid induction of promoter activity within 2 h of stimulation followed by elevations in protein levels of both cell-associated and secreted beta-APP. Analysis of mRNA transcripts from human cortical brain tissue and cell cultures derived from fetal human brain demonstrated the presence of an alternatively spliced secreted form of the IL-6 receptor mRNA, suggesting that cells of the central nervous system may themselves be a source of sIL-6R protein. The capacity for sIL-6R to enhance IL-6 function and broaden the IL-6 target cell population in the brain has implications for the regulation of beta-APP expression in disease states such as Alzheimer's disease where elevations in brain IL-6 levels have been reported.

Relative increase in Alzheimer's disease of soluble forms of cerebral Abeta amyloid protein precursor containing the Kunitz protease inhibitory domain

Although a number of studies have examined amyloid precursor protein (APP) mRNA levels in Alzheimer's disease (AD), no clear consensus has emerged as to whether the levels of transcripts for isoforms containing a Kunitz protease inhibitory (KPI)-encoded region are increased or decreased in AD. Here we compare AD and control brain for the relative amounts of APP protein containing KPI to APP protein lacking this domain. APP protein was purified from the soluble subcellular fraction and Triton X-100 membrane pellet extract of one hemisphere of AD (n = 10), normal (n = 7), and neurological control (n = 5) brains. The amount of KPI-containing APP in the purified protein samples was determined using two independent assay methods. The first assay exploited the inhibitory action of KPI-containing APP on trypsin. The second assay employed reflectance analysis of Western blots. The proportion of KPI-containing forms of APP in the soluble subcellular fraction of AD brains is significantly elevated (p < 0.01) compared with controls. Species containing a KPI domain comprise 32-41 and 76-77% of purified soluble APP from control and AD brains, respectively. For purified membrane-associated APP, 72-77 and 65-82% of control and AD samples, respectively, contain a KPI domain. Since KPI-containing species of APP may be more amyloidogenic (Ho, L., Fukuchi, K., and Yonkin, S. G. (1996) J. Biol. Chem. 271, 30929-30934), our findings support an imbalance of isoforms as one possible mechanism for amyloid deposition in sporadic AD.

The neuroprotective effects of the recombinant interleukin-1 receptor antagonist rhIL-1ra after excitotoxic stimulation with kainic acid and its relationship to the amyloid precursor protein gene

The cytokine interleukin-1 (IL-1) and its endogenous antagonist (IL-1ra) have important functions in the central nervous system. Recent experimental observations have suggested that recombinant IL-1RA (rhIL-1ra) has neuroprotective properties in ischaemia, excitotoxicity, and trauma. We wished to see what effect rhIL-1ra had on kainic acid-induced neuronal death and to investigate how this might relate to changes in expression of the amyloid precursor protein gene (APP) and glial fibrillary acid protein (GFAP) using in situ hybridization. Wistar rats were treated by intracerebroventricular administration with rhIL-1ra at doses of 10, 20 and 40 microg given 10 min before and 10 min after intraperitoneal kainic acid 10 mg/kg. Behaviour was measured and, after 10 days, the brains were removed for histology and in situ hybridization. There were no anticonvulsant effects on kainic acid-induced wet dog shakes or limbic motor seizures. There were no differences in the effects of rhIL-1ra at all doses tested on hippocampal temperature, blood pressure, blood gases, pH, and glucose in comparison to control. With rhIL-1ra 10 microg given twice, there was significant protection of neurons in the CA1 and CA3 field of the hippocampus and dorsal thalamus, but not in the primary olfactory cortex-amygdaloid region. Small, but insignificant, neuroprotective effects were observed in the same anatomical regions with a dose of 20 microg given twice, and no neuroprotective effects were observed with 40 microg. The enhanced neuronal survival in CA1, CA3 and the dorsal thalamus was associated with preservation of APP 695 mRNA (neuronal form) and lack of stimulation of APP 770 (glial form) and GFAP messages. Where there was no neuroprotection APP 695 mRNA was reduced and stimulation of both APP 770 and GFAP mRNAs was observed. In conclusion, rhIL-1ra has dose- and region-dependent effects on neuronal survival after kainic acid and prevents damage-induced changes in APP and GFAP mRNAs.

Phosphorylation of tau, Abeta-formation, and apoptosis after in vivo inhibition of PP-1 and PP-2A

Chronic inhibition of protein phosphatases 1 and 2A in vivo was induced by infusion of okadaic acid into lateral ventricles of rat brain for up to 4 months. Cytoskeletal pathology, alterations of the amyloid precursor protein, and apoptotic cell death induced by this treatment followed a certain sequence and spatial distribution. Changes in the expression, phosphorylation, and subcellular distribution of neurofilament proteins and tau, as well as first signs of apoptotic cell death, occurred already after about 2 weeks. The distribution of apoptotic cells, however, was different from those revealing a high accumulation of hyperphosphorylated tau, indicating that those cytoskeletal pathology had no obvious sequelae for the viability of these neurones. A continuation of treatment for longer than 2 weeks induced diffuse deposits of both hyperphosphorylated tau and A beta-amyloid-immunoreactive material in white matter areas that increased in size and number over time. Because tau-phosphorylation is a regulator of the dynamic stability of microtubules, the pathology observed in the present experimental paradigm in the white matter might be viewed as an indication of a disturbed axonal transport. It is hypothesized that perturbations of the axonal transport might also be critically involved in the formation of paired helical filaments and amyloid deposits in Alzheimer's disease.

The amyloid precursor protein gene: a neuropeptide gene with diverse functions in the central nervous system

The amyloid precursor protein (APP) is a member of a family of proteins found in the central nervous system with a fundamental role in the pathogenesis of Alzheimer's disease. This review describes the experimental evidence that has provided functional insights into this protein and emphasizes the importance of APP in many neurobiological processes.

Reversible ischemia increases levels of Alzheimer amyloid protein precursor without increasing levels of mRNA in the rabbit spinal cord

In a rabbit spinal cord ischemia model (RSCIM), the time courses of neuropathological damage of the spinal cord and neurological impairment of the motor functions are well established, demonstrating that the extent of neuropathological damage and the severity of neurological impairment are closely correlated. We used the RSCIM to elucidate the effects of reversible (15 min) and irreversible (60 min) ischemia on the endogenous levels of amyloid protein precursors (APPs) at both the mRNA and protein levels in the caudolumbar/sacral region of the spinal cord. We speculate that endogenous APPs are induced by ischemia as either trophic factors or stress-induced proteins in the RSCIM. A 15-min occlusion transiently increased the APP protein levels in neurons, which returned to the original levels by the end of 60 min occlusion. The increase in APP protein levels during 15-min ischemic insult does not appear to involve regulation at the mRNA level. The increased level of APPs, particularly of the soluble form, could support the possibility that APPs play a neuroprotective role in the RSCIM as stress-induced proteins. In contrast, failure to maintain the increased APP protein levels or to increase the mRNA, as seen in the 60-min ischemia samples, may be one of the causal factors that induce necrosis and neuronal cell death leading to irreversible neurological impairment.

Oligodendrocytes express different isoforms of beta-amyloid precursor protein in chemically defined cell culture conditions: in situ hybridization and immunocytochemical detection

The expression of beta-amyloid precursor protein (betaAPP) by astrocytes is well documented; however, data concerning oligodendrocytes remain controversial. The main goal of the present study was to determine whether or not oligodendrocytes in culture constitutively express the different betaAPP isoforms. Oligodendrocytes were cultured in a chemically defined medium that avoids putative effects of unknown serum factors on oligodendrocyte development. We have employed immunocytochemistry and in situ hybridization with antibodies and synthetic oligonucleotides recognizing, respectively, specific protein epitopes and mRNA transcripts of rat betaAPP isoforms. Oligodendrocytes, in both mixed primary cultures in the presence of serum or in secondary cultures in defined medium, were clearly labeled by antibodies directed to different betaAPP sequences. Antibodies against the serine protease inhibitor domain of betaAPP, also strongly labelled oligodendrocytes. Immunohistochemistry and in situ hybridization were combined to determine precisely the expression of different isoforms of betaAPP. In situ hybridization revealed the presence in oligodendrocytes of mRNA transcripts coding not only for betaAPP695 but also for betaAPP770 and betaAPP751. This indicates that betaAPP immunoreactivity found in oligodendrocytes corresponds to constitutive expression of betaAPP. Oligodendrocyte cultured in chemically defined medium are able to express not only betaAPP695 but also betaAPP770, betaAPP751 isoforms containing the Kunitz protease inhibitor domain. Although the role of betaAPP in the pathological processes of Alzheimer's disease (AD) remains unknown, possible disturbances of betaAPP processing and/or synthesis in oligodendrocytes may account for some myelin disorders observed in AD and other senile dementias.

mRNAs encoding urokinase-type plasminogen activator and plasminogen activator inhibitor-1 are elevated in the mouse brain following kainate-mediated excitation

Urokinase-type plasminogen activator (uPA) is an inducible extracellular serine protease implicated in fibrinolysis and in tissue remodeling. Recently, we have localized uPA mRNA strictly in limbic structures and the parietal cortex of the adult mouse brain. Here, we tested whether the systemic treatment of mice with kainic acid (KA), an amino acid inducing limbic seizures, could elevate in the brain mRNAs encoding uPA and its specific inhibitor, plasminogen activator inhibitor-1 (PAI-1), a major antifibrinolytic agent. Brain sections encompassing the hippocampus were tested through in situ hybridization using radiolabeled riboprobes specific for the two mRNA species. The results showed that KA greatly enhanced both mRNA species in sites of limbic structures and cortex. However, in the hypothalamus and brain blood vessels only PAI-1 mRNA was elevated. Those were also the only two locations where PAI-1 mRNA was detected in the non-treated control brain, although at a low level. For both mRNAs, KA enhancement was first evident 2-4 h after treatment, and it was most prolonged in the hippocampal area, where prominent hybridization signals persisted for three days. Here, both mRNAs were initially elevated in the hilar region of the dentate gyrus and in the molecular and oriens layers; however, PAI-1 mRNA became evident throughout the area, while uPA mRNA became especially pronounced in the CA3/CA4 subfield. In the cortex both mRNA types were induced, but only uPA mRNA was elevated in the retrosplenial cortex, and also in the subiculum. In the amygdaloid complex, uPA mRNA was restricted to the basolateral nucleus, whereas PAI-1 mRNA was seen throughout the structure, however, excluding this nucleus. These data show that seizure activity enhances the expression of uPA and PAI-1 genes in the brain; the patterns of enhancement suggest that the protease and its inhibitor may act in brain plasticity in synchrony, however, also independently of each other. Furthermore, the results suggest that by elevating PAI-1 mRNA in brain blood vessels, limbic seizures generate a risk for stroke.

Cell-specific expression of beta-amyloid precursor protein isoform mRNAs and proteins in neurons and astrocytes

The abnormal accumulation of beta-amyloid (A beta) in senile plaques appears to be a central pathological process in Alzheimer's disease. A beta is formed by proteolysis of beta-amyloid precursor protein (APP) with several isoforms generated by alternative splicing of exons 7, 8 and 15. A semi-quantitative reverse transcription (RT)-polymerase chain reaction (PCR) analysis showed that APP695 mRNA lacking exon 7 and 8 was most abundant in primary cultures of rat neurons, while APP770 and APP751 representing, respectively, the full length and exon 8 lacking isoforms predominated in cultured astroglial cells. Antisera AP-2 and AP-4 were produced by immunizing rabbits with keyhole limpet haemocyanin coupled with synthetic peptides representing KPI region APP301-316 and A beta region APP670-686 of APP770, respectively. These polyclonal antisera were purified against the corresponding peptide using affinity chromatography. Western blot analysis of homogenates of relatively enriched neuronal and astroglial cultures showed that these antibodies discretely stained bands of proteins in a cell-specific manner. Dot-blot analysis using AP-2, AP-4 and 22C11 antibodies indicated that, in comparison with neurons, cultured astrocytes contained 3-fold greater KPI-containing APP isoform proteins. The amount of total APP proteins, which include both KPI-containing and KPI-lacking APP isoforms, was approximately 90% higher in astrocytes than in neurons. Consistent with these in vitro findings in cultured astrocytes, in fimbria-fornix lesioned rat hippocampus, labelling with AP-2 antibody, which specifically reacts with KPI-containing APP proteins, was mainly observed in glial fibrillary acidic protein-positive reactive astrocytes in vivo. The results showed that APP isoforms are expressed in a cell type-specific manner in the brain and, since deposition of A beta is closely associated with the expression of KPI-containing APP isoforms, provide further evidence for the involvement of astrocytes in plaque biogenesis.

Expression of amyloid precursor protein mRNA isoforms in rat brain is differentially regulated during postnatal maturation and by cholinergic activity

Pathological processing of the amyloid precursor protein (APP) is assumed to be responsible for the amyloid deposits in Alzheimer-diseased brain tissue, but the physiological function of this protein in the brain is still unclear. The aim of this study is to reveal whether the expression of different splicing variants of APP transcripts in distinct brain regions is driven by postnatal maturation and/or regulated by cortical cholinergic transmission, applying quantitative in situ hybridization histochemistry using 35S-labeled oligonucleotides as specific probes to differentiate between APP isoforms. In cortical brain regions, the expression of both APP695 and APP751 is high at birth and exhibits nearly adult levels. The developmental expression pattern of cortical APP695 displays a peak value around postnatal day 10, while the age-related expression of APP751 demonstrates peak values on postnatal days 10 and 25, with the highest steady state levels of APP751 mRNA on day 25. During early development, the cortical laminar distribution of the APP695, but not APP751, mRNA transiently changes from a more homogeneous distribution at birth to a pronounced laminar pattern with higher mRNA levels in cortical layer III/IV detectable at the age of 4 days and persisting until postnatal day 10. The distinct age-related changes in cortical APP695 and APP751 mRNA levels reflect the functional alterations during early brain maturation and suggest that APP695 might play a role in establishing the mature connectional pattern between neurons, whereas APP751 could play a role in controlling cellular growth and synaptogenesis. Lesion of basal forebrain cholinergic system by the selective cholinergic immunotoxin 192IgG-saporin resulted in decreased levels of APP695 but not APP751 and APP770 transcripts by about 15-20% in some cortical (cingulate, frontal, parietal, piriform cortex), hippocampal regions (CA1, dentate gyrus), and basal forebrain nuclei (medial septum, vertical limb of diagonal band), detectable not earlier than 30 days after lesion and persisting until 90 days postlesion, suggesting that the nearly complete loss of cortical cholinergic input does not have any significant impact on the expression of APP mRNA isoforms in cholinoceptive cortical target regions.

The relationship of Alzheimer-type pathology to dementia in Parkinson's disease

Lewy body degeneration of the subcortical nuclei other than the substantia nigra is common in PD and may represent the substrate for a higher vulnerability to dementia in patients with PD. Cortical pathologies of Alzheimer and Lewy body type seem to be the major determinants of dementia. The prevalence of Alzheimer's disease is not increased in PD, but "early" cortical Alzheimer lesions (usually sub-clinical in normal controls) are frequently associated with dementia in PD. Furthermore, dementia in PD is heterogeneous and should always prompt the clinician to search for treatable causes.

Serum deprivation alters the expression and the splicing at exons 7, 8 and 15 of the beta-amyloid precursor protein in the C6 glioma cell line

Amyloid deposition characterizes the pathological lesions of Alzheimer's disease. We investigated the effect of serum deprivation on the regulation of beta-amyloid precursor protein (APP) mRNA expression in C6 glioma cells. Serum deprivation increased APP mRNA levels approximately 4-fold over controls. This increase was accompanied by changes in the pattern of alternative splicing, including the novel alternatively spliced site at exon 15. The proportion of isoforms containing exons 7 and 8 significantly increased from 61% to 68%, while isoforms lacking these exons decreased from 14% to 8%. The proportion of leukocyte-derived APP, which is a novel alternatively spliced isoform lacking exon 15, significantly increased from 19% to 40%. Among the six major isoforms produced by the two independent splicing sites, L-APP752 which contains exons 7 and 8, but lacks exon 15, increased the most (approximately 10-fold). Our findings provide evidence linking APP expression to alterations in alternative splicing at exon 15. These results demonstrate that in glial cells, APP mRNA regulation involves the alteration in alternative splicing at exons 7, 8 and 15, suggesting that not only increased expression but also an imbalance in the relative abundance of the six APP isoforms in stressed condition might affect the amyloidogenesis in Alzheimer's disease.

Interleukin-1beta and glutamate activate the NF-kappaB/Rel binding site from the regulatory region of the amyloid precursor protein gene in primary neuronal cultures

We originally reported that members of the family of transcription factors NF-kappaB/Rel can specifically recognize two identical sequences, referred to as APPkappaB sites, which are present in the 5'-regulatory region of the APP gene. Here we show that the APPkappaB sites interact specifically with a complex which contains one of the subunits of the family, defined as p50 protein, and that they act as positive modulators of gene transcription in cells of neural origin. Additionally, the nuclear complex specifically binding to the APPkappaB sites is constitutively expressed in primary neurons from rat cerebellum and it is up-regulated in response to both the inflammatory cytokine interleukin-1beta (IL-1beta) and the excitatory amino acid glutamate. Since IL-1, whose levels are known to be induced in brain of individuals affected by Alzheimer's disease, and glutamate, are stimuli which have been regarded as major actors on the stage of neurodegenerative processes, we believe our evidence as potentially relevant for understanding the neuropathology associated with Alzheimer's disease.

Molecular indices of neuronal and glial plasticity in the hippocampal formation in a rodent model of age-induced spatial learning impairment

Spatial learning ability was quantitated in young and aged Long-Evans rats, and molecular markers were assessed in the striatum and hippocampal formation using immunocytochemical, immunoblotting, and in situ hybridization histochemical procedures. The mRNA for beta-amyloid precursor protein (beta APP), most likely the transcript encoding the 695-amino acid form of this protein, was elevated in pyramidal and granule cells in the hippocampus of aged rats exhibiting poorer spatial learning. In immunoblots of hippocampal protein extracts, however, the level of beta APP-like immunoreactivity was depressed in the more impaired subjects. Similarly, the level in hippocampus of the mRNA for manganese-dependent superoxide dismutase (Mn-SOD), a marker of oxidative stress, was positively correlated with the degree of behavioral impairment, but immunoblotting revealed that Mn-SOD protein was depressed in the aged hippocampus compared with young. The mRNAs for the neuronal form of nitric oxide synthase and for the astrocyte marker glial fibrillary acidic protein (GFAP) were elevated in the hippocampus in correlation with the extent of learning impairment. In the striatum, the levels of mRNA and protein for several candidate genes, including GFAP, were elevated in parallel with the learning index, but these were age effects. Several hippocampal proteins were unchanged (GFAP) or depressed (beta APP and Mn-SOD) in level, despite elevations in corresponding mRNAs. In the aged cohort, hippocampal GFAP mRNA, Mn-SOD mRNA, and beta APP emerged as predictors of behavioral impairment, suggesting the involvement of these hippocampal systems in age-related cognitive impairment.

Trypsin interaction with the senile plaques of Alzheimer disease is mediated by beta-protein precursor

In this study we demonstrate by in situ binding that trypsin interacts with the senile plaques found in Alzheimer disease. Characterization of various potential trypsin binding proteins shows that trypsin binding is mediated by beta-protein precursor (beta PP)-the progenitor of amyloid-beta in senile plaques. Using specific antisera against various proteins to sterically block trypsin blocking, we found that only those antibodies raised against proteins or peptides containing the Kunitz protease inhibitor domain were able to abolish binding. By analogy with other protease/inhibitor interactions, we speculate that the binding of trypsin to beta PP could involve concomitant beta PP cleavage. Therefore, beta PP in protecting against potentially damaging proteolysis could simultaneously liberate beta PP fragments or intermediate precursors of amyloid-beta deposits.

Beta-amyloid precursor protein (APP) and APP-RNA are rapidly affected by glutamate in cultured neurons: selective increase of mRNAs encoding a Kunitz protease inhibitor domain

Alternative splicing of beta-amyloid precursor protein (APP) RNA generates APP isoforms with or without a Kunitz protease inhibitor (KPI) domain. Previously, we showed that KPI (+) APP RNA, but not KPI (-) APP RNA, is upregulated in response to experimental lesions in which neurotoxicity is dependent on NMDA receptor activation and in Alzheimer's disease hippocampus. Recent studies by Mucke et al. (1995) showed that neuronal expression of human KPI (+) APP, but not KPI (-) APP, in transgenic mice is neuroprotective against experimental lesions. In this study we examined the direct effects of the excitotoxic amino acid Glu on alternatively, spliced APP RNAs and the corresponding protein isoforms in cultured rat cortical neurons. Glu treatment rapidly induced (4.5 h) KPI (+) APP RNA but not KPI (-) APP RNA. Induction of KPI (+) RNA preceded Glu-induced neuronal cell death and was partially blocked by an NMDA-receptor antagonist. In contrast to the RNA, cellular levels of KPI (+) APP were not changed by 4.5 h of Glu treatment. Instead, the cellular full-length form of the protein KPI (-) APP was reduced by approximately 50% after 2 h of Glu treatment and remained depleted after 24 h of treatment. Cellular levels of KPI (+) forms of amyloid precursor-like protein 2 (APLP2) were not changed by Glu treatment. Our data are consistent with the hypothesis that sustained NMDA-receptor activation can regulate alternative splicing of the APP pre-mRNA in neurons.

Identification and characterization of a kappa B/Rel binding site in the regulatory region of the amyloid precursor protein gene

Several observations support the hypothesis that pathogenetic mechanisms of beta amyloid formation in Alzheimer's disease may involve alterations in amyloid precursor protein (APP) gene expression. In this regard, molecular dissection of the APP gene transcriptional regulation is of primary importance. We report evidence that members of the family of transcription factors NF kappa B/Rel can specifically recognize two identical sequences located in the 5'-regulatory region of APP. These sequences, which we refer to as APP kappa B sites, interact preferentially with p50-containing members of the family. In particular, p50 homodimers and p50/p65 and p50/c-Rel heterodimers act as transcriptional activators at the APP kappa B site. Finally, the nuclear complex specifically binding to the APP kappa B sites proves to be an integral part of neurons and lymphocytes.

Ischemic stress induces deposition of amyloid beta immunoreactivity in human brain

The histoblot immunostaining technique for locating and characterizing amyloidogenic proteins was used to obtain information about the relationship of cerebral ischemia/hypoxia to the accumulation of amyloid beta protein (A beta). We investigated brains of 131 subjects (ages 25-94 years, mean 72 years). Three distribution patterns of A beta immunoreactivity were identified: (1) colocalization with diffuse and neuritic plaques of Alzheimer's disease (AD) and aging; (2) diffuse punctuate deposits in the cerebral cortex in association with small vessel cerebral vascular disease ; and (3) cerebral cortical accumulation localized to arterial boundary zones and other regions susceptible to ischemic/hypoxic injury designated "stress-induced deposits" (SID). SID were not identified in tissue sections by immunohistochemical, Congo red or Bielschowsky silver techniques; no histological abnormalities were present in adjacent formalin-fixed tissue sections, SID occurred in subjects with histories of cerebral ischemia, and severe orthostatic hypotension. There was also an association with aging in general and with the incidence of neuritic plaques specifically. These latter findings are consistent with the hypothesis that brain ischemia/hypoxia plays a role in the pathogenesis of AD.

Increased beta-amyloid precursor protein expression in astrocytes in the gerbil hippocampus following ischaemia: association with proliferation of astrocytes

Increases in beta-amyloid precursor proteins (APP), which include the beta-amyloid senile plaque protein present in patients with Alzheimer's disease, have been shown to occur in models of neuronal damage and neurotoxic cell injury. This observation led us to examine the expression of these proteins after transient ischaemic episodes in the gerbil. Animals were killed 2-28 days after ischaemia and APP were detected by immunocytochemistry at the light and electron microscopic levels with an antibody raised against the C-terminal region of these proteins. The gliotic reaction was also examined using glial fibrillary acid protein (GFAP) immunoreactivity. Two days after ischaemia, neuronal cell death was observed in the hippocampal CA1 region accompanied by astrocyte hypertrophy. These hypertrophic astrocytes were found to be GFAP positive but stained weakly for APP. Seven days after ischaemia both astrocyte hypertrophia and hyperplasia, with identified mitotic figures, were observed. These hyperplasic astrocytes were intensely stained by the APP antibody, and were observed up to 28 days after ischaemia. This shows that neuronal cell death produced by transient ischaemia is followed by an increased APP expression which appears to be associated with the hyperplasic astrocytes but not with the initial hypertrophy of this cell population. These results, when taken together with those obtained in other models of neuronal damage or death, clearly suggest that APP expression follows neuronal death and is associated with astrocyte proliferation.

Increased messenger RNA expression of the 695 and 751 amino acid isoforms of the beta-amyloid protein precursor in the thalamus of 17-year-old cynomolgus (Macaca fascicularis) monkeys

The levels of expression of messenger RNAs of the 695 and 751 amino acid isoforms of the beta-amyloid protein precursor in the brains of three-year-old and 17-year-old cynomolgus monkeys (Macaca fascicularis) were visualized and quantified by in situ hybridization histochemistry using 35S-labelled oligonucleotide probes. The analysis was carried out on coronal brain sections taken through the hippocampus and thalamus at the level of the geniculate nuclei. High densities of beta-amyloid protein precursor695 and beta-amyloid protein precursor751 messenger RNAs were found in the medial aspects of the mediodorsal, centromedian and parafascicular nuclei of the 17-year-old monkeys. The messenger RNA levels of the 695 and 751 isoforms were about two- and seven-fold, respectively, those found in the same nuclei of the three-year-old animals. The levels of these messenger RNA transcripts in the 17-year-old monkeys were not significantly different from those in the three-year-old animals in other brain areas e.g. the temporal cortex, entorhinal cortex and hippocampus. No Alzheimer's disease-like neuropathology in terms of diffuse or senile beta-amyloid plaques, dystrophic neurites or neurofibrillary tangles were detectable by specific innumohistochemical procedures in the above thalamic nuclei of the 17-year-old animals. In addition no reactive gliosis was seen in the thalamus of these monkeys.(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrastructural localization of amyloid protein precursor in the normal and postischemic gerbil brain

Intracellular localization of amyloid protein precursor (APP) in the normal and postischemic gerbil brain was examined by immunoelectron microscopy. In the normal brain, APP immunoreactivity was localized to the multivesicular body, the nuclear membrane, Golgi apparatus and rough endoplasmic reticulum. After ischemia for 5 min and reperfusion for 24 h, some neurons became intensely immunoreactive for APP in the subiculum and CA3 region of the hippocampus and layers III and V/VI of the cerebral cortex. No intense labeling occurred in glial cells. Intensely labeled neurons were characterized by eccentric nuclei and accumulation of cellular organelles in the center of the neuronal perikarya, as well as a strongly immunoreactive nuclear membrane and cisternal structures, which were presumed to be dispersed Golgi apparatus and/or fragmented rough ER. APP immunoreactivity in the multivesicular body suggests re-internalization of APP and its degradation in the endosomal-lysosomal pathway. The ultrastructural features of neurons with intense APP immunoreactivity suggested mild neuronal damage, similar to those found in central chromatolysis. This indicates that accumulation of APP in these neurons is caused by disturbance of axonal transport, although the information does not allow us to exclude the possibility of an increase in APP production.