Immunohistochemical distribution of amyloid precursor protein during normal rat development

Amyloid precursor protein and its interacting proteins in neurodevelopment

Amyloid precursor protein (APP) is a key molecule in the pathogenesis of Alzheimer's disease (AD) as the pathogenic amyloid-β peptide is derived from it. Two closely related APP family proteins (APPs) have also been identified in mammals. Current knowledge, including genetic analyses of gain- and loss-of-function mutants, highlights the importance of APPs in various physiological functions. Notably, APPs consist of multiple extracellular and intracellular protein-binding regions/domains. Protein-protein interactions are crucial for many cellular processes. In past decades, many APPs interactors have been identified which assist the revelation of the putative roles of APPs. Importantly, some of these interactors have been shown to influence several APPs-mediated neuronal processes which are found defective in AD and other neurodegenerative disorders. Studying APPs-interactor complexes would not only advance our understanding of the physiological roles of APPs but also provide further insights into the association of these processes to neurodegeneration, which may lead to the development of novel therapies. In this mini-review, we summarize the roles of APPs-interactor complexes in neurodevelopmental processes including neurogenesis, neurite outgrowth, axonal guidance and synaptogenesis.

The localization of amyloid precursor protein to ependymal cilia in vertebrates and its role in ciliogenesis and brain development in zebrafish

Amyloid precursor protein (APP) is expressed in many tissues in human, mice and in zebrafish. In zebrafish, there are two orthologues, Appa and Appb. Interestingly, some cellular processes associated with APP overlap with cilia-mediated functions. Whereas the localization of APP to primary cilia of in vitro-cultured cells has been reported, we addressed the presence of APP in motile and in non-motile sensory cilia and its potential implication for ciliogenesis using zebrafish, mouse, and human samples. We report that Appa and Appb are expressed by ciliated cells and become localized at the membrane of cilia in the olfactory epithelium, otic vesicle and in the brain ventricles of zebrafish embryos. App in ependymal cilia persisted in adult zebrafish and was also detected in mouse and human brain. Finally, we found morphologically abnormal ependymal cilia and smaller brain ventricles in appa^−/−appb^−/− mutant zebrafish. Our findings demonstrate an evolutionary conserved localisation of APP to cilia and suggest a role of App in ciliogenesis and cilia-related functions.

Cerebellar alterations in a model of Down syndrome: The role of the Dyrk1A gene

Down syndrome (DS) is characterized by a marked reduction in the size of the brain and cerebellum. These changes play an important role in the motor alterations and cognitive disabilities observed in this condition. The Ts65Dn (TS) mouse, the most commonly used model of DS, reflects many DS phenotypes, including alterations in cerebellar morphology. One of the genes that is overexpressed in both individuals with DS and TS mice is DYRK1A/Dyrk1A (dual-specificity tyrosine-(Y)-phosphorylation regulated kinase 1A), which has been implicated in the altered cerebellar structural and functional phenotypes observed in both populations. The aim of this study was to evaluate the effect of Dyrk1A on different alterations observed in the cerebellum of TS animals. TS mice were crossed with Dyrk1A +/- KO mice to obtain mice with a triplicate segment of Mmu16 that included Dyrk1A (TS +/+/+), mice with triplicate copies of the same genes that carried only two copies of Dyrk1A (TS +/+/-), euploid mice that expressed a normal dose of Dyrk1A (CO +/+) and CO animals with a single copy of Dyrk1A (CO +/-). Male mice were used for all experiments. The normalization of the Dyrk1A gene dosage did not rescue the reduced cerebellar volume. However, it increased the size of the granular and molecular layers, the densities of granular and Purkinje cells, and dendritic arborization. Furthermore, it improved the excitatory/inhibitory balance and walking pattern of TS +/+/- mice. These results support the hypothesis that Dyrk1A is involved in some of the structural and functional cerebellar phenotypes observed in the TS mouse model.

Amyloid Precursor-Like Protein 2 deletion-induced retinal synaptopathy related to congenital stationary night blindness: structural, functional and molecular characteristics

Background

Amyloid precursor protein knockout mice (APP-KO) have impaired differentiation of amacrine and horizontal cells. APP is part of a gene family and its paralogue amyloid precursor-like protein 2 (APLP2) has both shared as well as distinct expression patterns to APP, including in the retina. Given the impact of APP in the retina we investigated how APLP2 expression affected the retina using APLP2 knockout mice (APLP2-KO).

Results

Using histology, morphometric analysis with noninvasive imaging technique and electron microscopy, we showed that APLP2-KO retina displayed abnormal formation of the outer synaptic layer, accompanied with greatly impaired photoreceptor ribbon synapses in adults. Moreover, APLP2-KO displayed a significant decease in ON-bipolar, rod bipolar and type 2 OFF-cone bipolar cells (36, 21 and 63 %, respectively). Reduction of the number of bipolar cells was accompanied with disrupted dendrites, reduced expression of metabotropic glutamate receptor 6 at the dendritic tips and alteration of axon terminals in the OFF laminae of the inner plexiform layer. In contrast, the APP-KO photoreceptor ribbon synapses and bipolar cells were intact. The APLP2-KO retina displayed numerous phenotypic similarities with the congenital stationary night blindness, a non-progressive retinal degeneration disease characterized by the loss of night vision. The pathological phenotypes in the APLP2-KO mouse correlated to altered transcription of genes involved in pre- and postsynatic structure/function, including CACNA1F, GRM6, TRMP1 and Gα0, and a normal scotopic a-wave electroretinogram amplitude, markedly reduced scotopic electroretinogram b-wave and modestly reduced photopic cone response. This confirmed the impaired function of the photoreceptor ribbon synapses and retinal bipolar cells, as is also observed in congenital stationary night blindness. Since congenital stationary night blindness present at birth, we extended our analysis to retinal differentiation and showed impaired differentiation of different bipolar cell subtypes and an altered temporal sequence of development from OFF to ON laminae in the inner plexiform layer. This was associated with the altered expression patterns of bipolar cell generation and differentiation factors, including MATH3, CHX10, VSX1 and OTX2.

Conclusions

These findings demonstrate that APLP2 couples retina development and synaptic genes and present the first evidence that APLP2 expression may be linked to synaptic disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s13041-016-0245-z) contains supplementary material, which is available to authorized users.

Pudendal nerve stretch reduces external urethral sphincter activity in rats

PURPOSE

Most animal models of stress urinary incontinence simulate maternal injuries of childbirth since delivery is a major risk factor but they do not reproduce the nerve stretch known to occur during human childbirth. We hypothesized that pudendal nerve stretch produces reversible dysfunction of the external urethral sphincter.

MATERIALS AND METHODS

Female virgin Sprague-Dawley® rats were anesthetized with urethane. Bilateral pudendal nerve stretch or sham injury was performed for 5 minutes. External urethral sphincter electromyography and leak point pressure were recorded immediately before and after, and 10, 30, 60 and 120 minutes after pudendal nerve stretch. Post-pudendal nerve stretch results were compared to prestretch values and to values in sham injured animals. The pudendal nerves underwent qualitative histological assessment. The nucleus of Onuf was evaluated by immunohistochemistry and polymerase chain reaction for β-APP and c-Fos expression as markers of neuronal activity and injury.

RESULTS

A total of 14 rats underwent bilateral pudendal nerve stretch (9) or sham injury (5). Each nerve was stretched a mean ± SEM of 74% ± 18% on the left side and 63% ± 13% on the right side. Electromyography amplitude decreased significantly immediately after stretch compared to before stretch and after sham injury (p = 0.003) but it recovered by 30 minutes after stretch. There was no significant change in leak point pressure at any time. Two hours after injury histology showed occasional neuronal degeneration. β-APP and c-Fos expression was similar in the 2 groups.

CONCLUSIONS

Acute pudendal nerve stretch produces reversible electrophysiological dysfunction but without leak point pressure impairment. Pudendal nerve stretch shows promise in modeling injury. It should be tested as part of a multi-injury, chronic, physiological model of human childbirth injury.

SC1/hevin identifies early white matter injury after ischemia and intracerebral hemorrhage in young and aged rats

The progression of white matter damage after ischemic and hemorrhagic strokes can exacerbate the initial injury, but little is known about the processes involved. We show that the antiadhesive matricellular glycoprotein SC1 is a novel early marker of white matter damage in 3 models of acute injury in the rat striatum: transient focal ischemia, intracerebral hemorrhage, and a needle penetration wound. SC1 was restricted to the damaged portions of axon bundles that bordered stroke lesions in young-adult and aged rats. SC1 peaked at 1 and 3 days after intracerebral hemorrhage and at 7 days after ischemia. The SC1-positive bundles usually expressed degraded myelin basic protein and amyloid precursor protein, a marker of axonal injury. At the hematoma edge, SC1 was seen in a few axon bundles that retained myelin basic protein staining. In these bundles, punctate SC1 staining filled individual axons, extended beyond a core of pan-axonal neurofilament and NF200 and was inside or overlapped with myelin basic protein staining when it was present. Aged rats had less SC1 (and amyloid precursor protein) after both types of stroke, suggesting a reduced axonal response. SC1 also labeled amyloid precursor protein-positive axon bundles along the needle penetration tract of saline-injected rats; thus, SC1 appears to characterize damaged striatal white matter damage after multiple types of injury.

Identification of a novel amyloid precursor protein processing pathway that generates secreted N-terminal fragments

Alzheimer's disease (AD) is a neurodegenerative disorder of the central nervous system. The proteolytic processing of the amyloid precursor protein (APP) into the β-amyloid (Aβ) peptide is a central event in AD. While the pathway that generates Aβ is well described, many questions remain concerning general APP metabolism and its metabolites. It is becoming clear that the amino-terminal region of APP can be processed to release small N-terminal fragments (NTFs). The purpose of this study was to investigate the occurrence and generation of APP NTFs in vivo and in cell culture (SH-SY5Y) in order to delineate the cellular pathways implicated in their generation. We were able to detect 17- to 28-kDa APP NTFs in human and mouse brain tissue that are distinct from N-APP fragments previously reported. We show that the 17- to 28-kDa APP NTFs were highly expressed in mice from the age of 2 wk to adulthood. SH-SY5Y studies indicate the generation of APP NTFs involves a novel APP processing pathway, regulated by protein kinase C, but independent of α-secretase or β-secretase 1 (BACE) activity. These results identify a novel, developmentally regulated APP processing pathway that may play an important role in the physiological function of APP.

APP involvement in retinogenesis of mice

Very few studies have examined expression and function of amyloid precursor protein (APP) in the retina. We showed that APP mRNA and protein are expressed according to the different waves of retinal differentiation. Depletion of App led to an absence of amacrine cells, a 50% increase in the number of horizontal cells and alteration of the synapses. The retinas of adult APP(-/-) mice showed only half as many glycinergic amacrine cells as wild-type retinas. We identified Ptf1a, which plays a role in controlling both amacrine and horizontal cell fates, as a downstream effector of APP. The observation of a similar phenotype in sorLA knockout mice, a major regulator of APP processing, suggests that regulation of APP functions via sorLA controls the determination of amacrine and horizontal cell fate. These findings provide novel insights that indicate that APP plays an important role in retinal differentiation.

Amyloid precursor protein binding protein-1 modulates cell cycle progression in fetal neural stem cells

Amyloid precursor protein binding protein-1 (APP-BP1) binds to the carboxyl terminus of the amyloid precursor protein (APP) and serves as the bipartite activation enzyme for the ubiquitin-like protein, NEDD8. In the present study, we explored the physiological role of APP-BP1 in the cell cycle progression of fetal neural stem cells. Our results show that cell cycle progression of the cells is arrested at the G1 phase by depletion of APP-BP1, which results in a marked decrease in the proliferation of the cells. This action of APP-BP1 is antagonistically regulated by the interaction with APP. Consistent with the evidence that APP-BP1 function is critical for cell cycle progression, the amount of APP-BP1 varies depending upon cell cycle phase, with culminating expression at S-phase. Furthermore, our FRET experiment revealed that phosphorylation of APP at threonine 668, known to occur during the G2/M phase, is required for the interaction between APP and APP-BP1. We also found a moderate ubiquitous level of APP-BP1 mRNA in developing embryonic and early postnatal brains; however, APP-BP1 expression is reduced by P12, and only low levels of APP-BP1 were found in the adult brain. In the cerebral cortex of E16 rats, substantial expression of both APP-BP1 and APP mRNAs was observed in the ventricular zone. Collectively, these results indicate that APP-BP1 plays an important role in the cell cycle progression of fetal neural stem cells, through the interaction with APP, which is fostered by phosphorylation of threonine 668.

Differential expression of CD44 variants among meningioma subtypes

Aims/background-CD44 is a widely distributed cell surface molecule which has numerous isoforms generated by alternative splicing. The diverse functions related to the CD44 variants (CD44v) have been reported in various physiological and pathological conditions. The pattern of expression of CD44v among meningioma subtypes was investigated to ascertain whether CD44 variants play a role in a variety of biological processes, such as epithelial differentiation and extracranial metastasis.Methods-Twenty three meningiomas were studied immunohistochemically using novel antibodies directed against CD44 isoforms. Six of the 23 samples were analysed by reverse transcription polymerase chain reaction (RT-PCR), followed by Southern blotting with CD44v specific probes.Results-In meningothelial, fibrous and anaplastic meningiomas, a standard form of CD44 was detected by RT-PCR and was homogeneously expressed in tumour cells when studied immunohistochemically. CD44v was not detected in these subtypes. In secretory meningiomas, however, CD44v isoforms were strongly expressed in the cell clusters that produce secretory granules and also accumulated in the granules. The population of tumour cells immunopositive for CD44v was similar to that which stained with antibodies directed against carcinoembryonic antigen, epithelial membrane antigen and ezrin. On RT-PCR with Southern blotting, only the secretory type showed high level expression of CD44v.Conclusions-CD44v in meningiomas is expressed in relation to tumour cell differentiation towards the epithelial type.

Amyloid precursor protein modulates beta-catenin degradation

Background

The amyloid precursor protein (APP) is genetically associated with Alzheimer's disease (AD). Elucidating the function of APP should help understand AD pathogenesis and provide insights into therapeutic designs against this devastating neurodegenerative disease.

Results

We demonstrate that APP expression in primary neurons induces β-catenin phosphorylation at Ser₃₃, Ser₃₇, and Thr₄₁ (S33/37/T41) residues, which is a prerequisite for β-catenin ubiquitinylation and proteasomal degradation. APP-induced phosphorylation of β-catenin resulted in the reduction of total β-catenin levels, suggesting that APP expression promotes β-catenin degradation. In contrast, treatment of neurons with APP siRNAs increased total β-catenin levels and decreased β-catenin phosphorylation at residues S33/37/T41. Further, β-catenin was dramatically increased in hippocampal CA1 pyramidal cells from APP knockout animals. Acute expression of wild type APP or of familial AD APP mutants in primary neurons downregulated β-catenin in membrane and cytosolic fractions, and did not appear to affect nuclear β-catenin or β-catenin-dependent transcription. Conversely, in APP knockout CA1 pyramidal cells, accumulation of β-catenin was associated with the upregulation of cyclin D1, a downstream target of β-catenin signaling. Together, these data establish that APP downregulates β-catenin and suggest a role for APP in sustaining neuronal function by preventing cell cycle reactivation and maintaining synaptic integrity.

Conclusion

We have provided strong evidence that APP modulates β-catenin degradation in vitro and in vivo. Future studies may investigate whether APP processing is necessary for β-catenin downregulation, and determine if excessive APP expression contributes to AD pathogenesis through abnormal β-catenin downregulation.

Down syndrome gene dosage imbalance on cerebellum development

Down syndrome (DS) is a chromosomal disorder whereby genes on chromosome 21 are present in three copies. This gene copy imbalance is thought to be responsible for a number of debilitating conditions experienced by individuals with DS. Amongst these is a reduced cerebellar volume, or cerebellar hypoplasia, which is believed to contribute to the perturbation of fine motor control. Mouse models of DS (such as Ts65Dn, Ts1Cje, Tc1) exhibit a cerebellar phenotype similar to that of individuals with DS and which primarily manifests as a disruption of the density of the granule cell layer. Dissecting which of the three-copy genes are responsible for this phenotype (the primary gene dosage effect) has been a task undertaken by researchers working with various segmental trisomies and transgenic mice. It is generally agreed that, when expressed, three-copy genes of trisomic mice are expressed at around 1.5 times that of the same genes in euploid (wild-type) mice. However, amongst these studies there does not appear to be a consensus on the nature and extent of differential expression of two-copy genes in trisomic mice-the secondary dosage effect. Much of this variation may have to do with the stage of development investigated and the nature and complexity of the tissue (i.e. whole brain versus the cerebellum). The recent discovery that trisomic granule cell precursors are less sensitive to sonic hedgehog-induced proliferation has opened up another avenue for the identification of three-copy genes responsible for the cerebellar phenotype. It is hoped that further investigation of this phenomenon, together with new mouse segmental trisomies and transgenics, will reveal the cause of the proliferation deficit and allow for potential treatment.

Nerve growth factor, neural stem cells and Alzheimer's disease

The protein family of the neurotrophins (NTs) comprises structurally and functionally related molecules such as nerve growth factor (NGF) which influences the proliferation, differentiation, survival and death of neuronal cells. In addition to their established functions for cell survival, NTs also mediate higher brain activities such as learning and memory. Changes in NT expression levels have thus been implicated in neurological diseases such as Alzheimer's disease (AD), an age-related neurodegenerative disorder that is characterized by progressive loss of memory and deterioration of higher cognitive functions. The present review provides an overview of the functional role of NGF in neural stem cells and AD while pointing to a potential application of this peptide for the treatment of AD.

The insect homologue of the amyloid precursor protein interacts with the heterotrimeric G protein Go alpha in an identified population of migratory neurons

The amyloid precursor protein (APP) is the source of Abeta fragments implicated in the formation of senile plaques in Alzheimer's disease (AD). APP-related proteins are also expressed at high levels in the embryonic nervous system and may serve a variety of developmental functions, including the regulation of neuronal migration. To investigate this issue, we have cloned an orthologue of APP (msAPPL) from the moth, Manduca sexta, a preparation that permits in vivo manipulations of an identified set of migratory neurons (EP cells) within the developing enteric nervous system. Previously, we found that EP cell migration is regulated by the heterotrimeric G protein Goalpha: when activated by unknown receptors, Goalpha induces the onset of Ca2+ spiking in these neurons, which in turn down-regulates neuronal motility. We have now shown that msAPPL is first expressed by the EP cells shortly before the onset of migration and that this protein undergoes a sequence of trafficking, processing, and glycosylation events that correspond to discrete phases of neuronal migration and differentiation. We also show that msAPPL interacts with Goalpha in the EP cells, suggesting that msAPPL may serve as a novel G-protein-coupled receptor capable of modulating specific aspects of migration via Goalpha-dependent signal transduction.

Expression of amyloid precursor protein-like molecule in astroglial cells of the subventricular zone and rostral migratory stream of the adult rat forebrain

In adult mammals, new neurons in the subventricular zone (SVZ) of the lateral ventricle (LV) migrate tangentially through the rostral migratory stream (RMS) to the olfactory bulb (OB), where they mature into local interneurons. Using a monoclonal antibody for the beta-amyloid precursor protein (APP) (mAb 22C11), which is specific for the amino-terminal region of the secreted form of APP and recognizes all APP isoforms and APP-related proteins, immunoreactivity was detected in specific subpopulations of cells in the SVZ and RMS of the adult rat forebrain. In the SVZ, APP-like immunoreactivity was detected in the ependymal cells lining the LV and some of the subependymal cells. The latter were regarded as astrocytes, because they were positive for the glial markers, S-100 protein (S-100) and glial fibrillary acidic protein (GFAP). APP-like immunoreactive astrocytes exhibited strong labelling of the perinuclear cytoplasm and often possessed a long, fine process similar to that found with radial glia. The process extended to an APP-like immunoreactive meshwork in the RMS that consisted of cytoplasmic processes of astrocytes forming 'glial tubes'. Double-immunofluorescent labelling with a highly polysialylated neural cell adhesion molecule (PSA-NCAM) confirmed that the APP-like immunoreactive astrocytes in the SVZ and meshwork in the RMS made close contact with PSA-NCAM-immunopositive neuroblasts, suggesting an interaction between APP-containing cells and neuroblasts. This region of the adult brain is a useful in vivo model to investigate the role of APP in neurogenesis.

Alpha-synuclein expression in the developing human brain

Alpha (alpha)-synuclein is a presynaptic protein, abnormal expression of which has been associated with neurodegenerative and neoplastic diseases. It is abundant in the developing vertebrate central nervous system (CNS), but less is known about its developmental expression in the human CNS. Immunohistochemical expression of alpha-synuclein was studied in 39 fetal, perinatal, pediatric, and adolescent brains. Perikaryal expression of alpha-synuclein is observed as early as 11-wk gestation in the cortical plate. Several discrete neuronal groups in the hippocampus, basal ganglia, and brain stem express perikaryal alpha-synuclein by 20-wk gestation, persisting through the first few years of life. In the cerebellum, alpha-synuclein is present by 21-wk gestation and persists into adult life as a coarse granular neuropil reaction product in the internal granular layer, and as a diffuse neuropil "blush" in the molecular layer. The germinal matrix, glia, endothelial cells, external granular layer, Pukinje cells, and dentate neurons are consistently negative for alpha-synuclein. We conclude that alpha-synuclein is expressed very early in human gestation, and that its distribution and temporal sequence of expression varies in discrete neuronal groups. Perikaryal alpha-synuclein starts disappearing from the neuronal cytosol in early childhood, and only the neuropil retains immunoreactivity into adulthood. The reappearance of alpha-synuclein in the adult neuronal cytosol in certain disease processes may represent reemergence of cues from an earlier developmental stage as part of a stress response.

Nicotinic acetylcholine receptor distribution in relation to spinal neurotransmission pathways

Neuronal nicotinic receptors (nAChR) are pentameric assemblies of subunits of a gene family where specified combinations of alpha and beta subunits form functional receptors. To extend our understanding of the role of spinal nAChR in the processing of sensory stimuli and regulation of autonomic and motor responses, we initiated investigations to localize nAChR subunit expression within discrete spinal regions and cell types. High-affinity epibatidine binding was present in the superficial dorsal and ventral horns, the mediolateral and central canal regions. RT-PCR identified transcripts for alpha3, alpha4, alpha5, beta2, and beta4 in both spinal cord parenchyma and dorsal root ganglia (DRG). Our affinity-purified antibodies against alpha3, alpha4, alpha5, beta2, and beta4 subunits identified specific protein bands of appropriate molecular mass (preadsorbed with the respective antigens) in specific tissues and cells that express nicotinic receptors, including the spinal cord and DRG neurons. Having established the absence of crossreactivity with related subunits, specific fluorescence labeling of nerve terminals and cell bodies was achieved and correlated with the distribution of defined marker proteins and nicotinic receptor binding sites determined autoradiographically. Our findings indicate that alpha3, alpha4, alpha5, beta2, and beta4 subunits are all expressed on primary afferents (IB4-positive terminals) in the spinal cord. The predominant presynaptic (synaptophysin colocalization) labeling is in the superficial layer of the dorsal horn. These receptor subunits, except for beta4, are also present in postsynaptic autonomic (anti-bNOS-positive) and somatic motor neurons (anti-VAChT-positive). The alpha3, alpha5, and beta2 subunits showed additional staining in glial (anti-GFAP-positive) cells. These studies reveal a dense and distinguishable distribution of nAChR subunits in the spinal cord and point toward future therapeutic targeting for specific spinal actions.

Alzheimer's disease proteins in cerebellar and hippocampal synapses during postnatal development and aging of the rat

Alzheimer's dementia may be considered a synaptic disease of central neurons: the loss of synapses, reflected by early cognitive impairments, precedes the appearance of extra cellular focal deposits of beta-amyloid peptide in the brain of patients. Distinct immunocytochemical patterns of amyloid precursor proteins (APPs) have previously been demonstrated in the synapses by ultrastructural analysis in the cerebellum and hippocampus of adult rats and mice. Now we show that during postnatal development and during aging in these structures, the immunocytochemical expression of APPs increases in the synapses in parallel with the known up-regulation of total APPs brain levels. Interestingly, as shown previously in the adult rodents, the presenilins (PSs) 1 and 2, which intervene in APPs metabolism, exhibit a synaptic distribution pattern similar to that of APPs with parallel quantitative changes throughout life. In the brain tissue, single and double immunocytochemistry at the ultrastructural level shows co-localisation of APPs and PSs in axonal and dendritic synaptic compartments during postnatal synaptogenesis, adulthood and aging. In addition, double-labelling immunocytofluorescence detects these proteins close to synaptophysin at the growth cones of developing cultured neurons. Thusly, the brain expression of APPs and PSs appears to be regulated synchronously during lifespan in the synaptic compartments where the proteins are colocated. This suggests that PS-dependent processing of important synaptic proteins such as APPs could intervene in age-induced adjustments of synaptic relationships between specific types of neurons.

Beta-amyloid precursor protein staining in nonhomicidal pediatric medicolegal autopsies

Immunohistochemical staining for beta-amyloid precursor protein (betaAPP) has been validated as a marker for axonal injury in adults surviving > or = 2 hours after white matter damage. The significance of betaAPP staining in pediatric brains and spinal cords is not as well established. We evaluated the white matter immunoreactivity for betaAPP from a variety of pediatric medicolegal autopsies: natural disease (non-Sudden Infant Death Syndrome [SIDS]), SIDS, motor vehicle accidents, drowning, near-drowning, overlay, carbon monoxide toxicity, miscellaneous trauma, and mechanical asphyxia. The cases of carbon monoxide toxicity, motor vehicle accidents (death at scene), drowning (with resuscitation), and a natural (non-SIDS) death had no significant white matter staining. The traumatic deaths with a significant survival interval, a variety of natural deaths, the near-drowning case, and surprisingly, all SIDS had detectable betaAPP white matter immunostaining. These results demonstrate that features other than traumatic axonal injury, such as metabolic insults and hypoxic-ischemic injury secondary to vascular compromise, must contribute to betaAPP immunostaining. In addition, we describe a variety of betaAPP-immunoreactive structures not previously reported in the pediatric population. This study illustrates that betaAPP immunostaining enhances detection of a variety of white matter changes, and provides a basis for interpretation of these results.

Neuroplasticity in Alzheimer's disease

Ramon y Cajal proclaimed in 1928 that "once development was ended, the founts of growth and regeneration of the axons and dendrites dried up irrevocably. In the adult centers the nerve paths are something fixed, ended and immutable. Everything must die, nothing may be regenerated. It is for the science of the future to change, if possible, this harsh decree." (Ramon y Cajal, 1928). In large part, despite the extensive knowledge gained since then, the latter directive has not yet been achieved by 'modern' science. Although we know now that Ramon y Cajal's observation on CNS plasticity is largely true (for lower brain and primary cortical structures), there are mechanisms for recovery from CNS injury. These mechanisms, however, may contribute to the vulnerability to neurodegenerative disease. They may also be exploited therapeutically to help alleviate the suffering from neurodegenerative conditions.

Enriched early experiences of mice underexpressing the beta-amyloid precursor protein restore spatial learning capabilities but not normal openfield behavior of adult animals

We have previously reported severely impaired spatial learning in mutant mice underexpressing a shortened variant of the beta-amyloid precursor protein (beta-APPtheta/theta). This targeted mutation is functionally equivalent to a null mutation. It also disturbs behavioral and neurological maturation with deficits emerging mainly between postnatal day (pd) 11 and 19. Such early tested mice exhibited almost no genotype-related difference in Morris water maze learning, raising the possibility that early handling might have compensated for genetic deficits. To verify this effect, we compared watermaze learning and open field behavior of 66 adult mutant and wildtype mice having been handled during pd 3-27 with that of 70 non-handled mutant and wildtype mice. Neurological testing during pd 3-27 markedly reduced time near wall and improved spatial retention of adult mutants, restoring their learning capabilities to wildtype levels. Early handling did not cure the mutation associated activity deficit in the open field, but mainly increased center field exploration in both mutants and wildtypes. In a follow-up experiment we analyzed whether an early (pd 3-10, n = 22) or middle (pd 11-19, n = 24) period of handling in form of neurological testing had differential effects on adult behavior. Mice handled during pd 11-19 had slightly shorter escape times than mice handled during pd 3-10 but were not significantly different in other behavioral measures. There were no sex related differences. Correlational and factor analysis showed that both the mutation and early handling had pleiotropic behavioral effects, resulting in differentially impaired mutants depending on the test situation. Likewise, early handling affected not only thigmotactic tendencies but also, more subtly, other behavioral components underlying water maze learning. We conclude that early postnatal stimulation can prevent mutation induced learning deficits in adult mice, but probably through other developmental mechanisms than those affected by the mutation. This implies that some behavioral impairments related to beta-APP malfunction may be corrected through simple treatments.

Developmental expression of the beta-amyloid precursor protein and heat-shock protein 70 in the cerebral hemisphere region of the rat brain

Alzheimer's disease (AD) is characterized by depositions of the amyloid beta protein (A beta) in the brain in the form of extracellular plaques and cerebrovascular amyloid. A beta (approximately 4 kDa) is derived from a family of large (approximately 110 kDa) beta-amyloid precursor proteins (APP), which are integral membrane glycoproteins. Although a connection between AD and alcoholism has recently been suggested, this relationship has not been explored at the molecular level. Our hypothesis is that APP has a role in brain development and that abnormal APP levels may be involved in dementia associated with AD and alcoholism. We compared the profile of total APP levels between ethanol naïve alcohol-preferring (P) and alcohol-nonpreferring (NP) rats. We also investigated the possibility that APP levels can be regulated in an age-dependent manner in young rats. We studied the distribution of two proteins in the cerebral hemisphere region of the rat brain at various developmental periods. Six groups composed of the following different ages of rats were used: 7, 14, 21, 36, 43, and 78 (postnatal) days. Cell extracts from different regions of the brain were subjected to Western immunoblotting using mAb22C11. Our results suggest that levels of high-molecular-weight APP bands were greater in brain extracts from 7-day-old P rats than in other samples tested, and that the distribution of APP levels was more uneven in brain extracts from different ages of P than from NP rats. These initial results suggest that APP may play an important role in the early development of the rat brain and the alcohol-preferring trait may influence APP processing in the developing brain.

Reduced corpus callosum, fornix and hippocampus in PDAPP transgenic mouse model of Alzheimer's disease

Persons with Alzheimer's disease (AD) have progressive reductions in the relative sizes of the corpus callosum and hippocampus. Homozygotic PDAPP transgenic mice over-expressing a mutant form of the human amyloid precursor protein have more pronounced reductions in these regions, which are apparent prior to the deposition of amyloid plaques and do not progress with advancing age. The length of the corpus callosum was reduced by two-thirds, the fornix commissure was negligible, and the hippocampal volume was reduced by one-third, suggesting a massive disconnection between the cerebral hemispheres and the hippocampi in PDAPP mice. These findings, which might account for the early, nonprogressive behavioral abnormalities observed in these animals, have implications for the study of AD.

Ontogenetic changes in protein level of amyloid precursor protein (APP) in growth cones and synaptosomes from rat brain and prenatal expression pattern of APP mRNA isoforms in developing rat embryo

To elucidate the functional role of the amyloid precursor protein (APP) during brain ontogeny, developmental changes of APP levels in growth cones and synaptosomes were studied from embryonic day 14 up to postnatal day (PD) 400 using Western analysis. APP level in growth cones was low during prenatal stages of development, but demonstrating a continuous increase from PD 3 up to PD 10. Highest concentration of APP in synaptosomes was found between PD 7 and 10, followed by a considerable decrease up to PD 30 and persisting at this level up to PD 400. In situ hybridization to differentiate between APP695 mRNA, APP751 mRNA and APP770 mRNA revealed distinct age-related expression pattern of various APP isoforms. During prenatal brain development APP695 mRNA is maximally expressed in brain structures, containing differentiating nerve cells. APP751 and APP770 mRNA isoforms are diffusely distributed in the embryo throughout the prenatal period examined and their expression is higher in peripheral organs such as skin, lung, liver and bones as compared to the brain. The increase of APP level during synaptogenesis suggests a functional role of APP in the processes of neurite outgrowth and cell targeting as well as in the maintenance of the functional integrity of synapses in the mature brain. The APP695 isoform seems to be the major form involved in embryonic brain maturation.

Alzheimer's disease as a disorder of mechanisms underlying structural brain self-organization

Mental function has as its cerebral basis a specific dynamic structure. In particular, cortical and limbic areas involved in "higher brain functions" such as learning, memory, perception, self-awareness and consciousness continuously need to be self-adjusted even after development is completed. By this lifelong self-optimization process, the cognitive, behavioural and emotional reactivity of an individual is stepwise remodelled to meet the environmental demands. While the presence of rigid synaptic connections ensures the stability of the principal characteristics of function, the variable configuration of the flexible synaptic connections determines the unique, non-repeatable character of an experienced mental act. With the increasing need during evolution to organize brain structures of increasing complexity, this process of selective dynamic stabilization and destabilization of synaptic connections becomes more and more important. These mechanisms of structural stabilization and labilization underlying a lifelong synaptic remodelling according to experience, are accompanied, however, by increasing inherent possibilities of failure and may, thus, not only allow for the evolutionary acquisition of "higher brain function" but at the same time provide the basis for a variety of neuropsychiatric disorders. It is the objective of the present paper to outline the hypothesis that it might be the disturbance of structural brain self-organization which, based on both genetic and epigenetic information, constantly "creates" and "re-creates" the brain throughout life, that is the defect that underlies Alzheimer's disease (AD). This hypothesis is, in particular, based on the following lines of evidence. (1) AD is a synaptic disorder. (2) AD is associated with aberrant sprouting at both the presynaptic (axonal) and postsynaptic (dendritic) site. (3) The spatial and temporal distribution of AD pathology follows the pattern of structural neuroplasticity in adulthood, which is a developmental pattern. (4) AD pathology preferentially involves molecules critical for the regulation of modifications of synaptic connections, i.e. "morphoregulatory" molecules that are developmentally controlled, such as growth-inducing and growth-associated molecules, synaptic molecules, adhesion molecules, molecules involved in membrane turnover, cytoskeletal proteins, etc. (5) Life events that place an additional burden on the plastic capacity of the brain or that require a particularly high plastic capacity of the brain might trigger the onset of the disease or might stimulate a more rapid progression of the disease. In other words, they might increase the risk for AD in the sense that they determine when, not whether, one gets AD. (6) AD is associated with a reactivation of developmental programmes that are incompatible with a differentiated cellular background and, therefore, lead to neuronal death. From this hypothesis, it can be predicted that a therapeutic intervention into these pathogenetic mechanisms is a particular challenge as it potentially interferes with those mechanisms that at the same time provide the basis for "higher brain function".

Antisperm antibodies associated with infertility: properties and encoding genes of target antigens

Infertility among couples of reproductive age is a perplexing condition when the cause is indeterminate. These cases are classified as unexplained infertility. In a subset of subjects, antisperm antibodies with sperm agglutinating and/or immobilizing activities have been detected in the blood or fluids of the reproductive tract. These cases are designated as immunologic infertility although a cause and effect relationship of the antibodies to infertility has not been established. In this review, seven target sperm antigens to antibodies associated with infertility and their encoding genes are described. The antisperm antibodies (ASAs) examined were obtained from infertile women or were monoclonal antibodies (mAb) raised against human sperm proteins. All the ASAs studied possessed potent sperm agglutinating and/or immobilizing activities. The target antigens were isolated from human and other mammalian sperm, and the encoding genes identified. The seven antigens are YWK-II, BE-20, rSMP-B, BS-63 (nucleoporin-related), BS-17 (calpastatin), HED-2 (zyxin), and 75- kDa. Each antigen is a distinct and separate entity and is produced by different cells of the reproductive tract, (e.g., germ cells, epididymal epithelial cells, and Sertoli cells). No single predominant target component has been found to interact with the ASAs. It is proposed that immunologic infertility is the consequence of the combined actions of multiple ASAs in immobilizing and/or agglutinating spermatozoa, blocking spermegg interaction, preventing implantation, and/or arresting embryo development.

The beta-amyloid precursor protein and its derivatives: from biology to learning and memory processes

Intensive investigation towards the understanding of the biology and physiological functions of the beta-amyloid precursor protein (APP) have been supported since it is known that a 39-43 amino acid fragment of APP, called the beta-amyloid protein (Abeta), accumulates in the brain parenchyma to form the typical lesions associated with Alzheimer's disease (AD). It emerges from extensive data that APP and its derivatives show a wide range of contrasting physiological properties and therefore might be involved in distinct physiological functions. Abeta has been shown to disrupt neuronal activity and to demonstrate neurotoxic properties in a wide range of experimental procedures. In contrast, both in vitro and in vivo studies suggest that APP and/or its secreted forms are important factors involved in the viability, growth and morphological and functional plasticity of nerve cells. Furthermore, several recent studies suggest that APP and its derivatives have an important role in learning and memory processes. Memory impairments can be induced in animals by intracerebral treatment with Abeta. Altered expression of the APP gene in aged animals or in genetically-modified animals also leads to memory deficits. By contrast, secreted forms of APP have recently been shown to facilitate learning and memory processes in mice. These interesting findings open novel perspectives to understand the involvement of APP in the development of cognitive deficits associated with AD. In this review, we summarize the current data concerning the biology and the behavioral effects of APP and its derivatives which may be relevant to the roles of these proteins in memory and in AD pathology.

Neuroanatomical abnormalities in behaviorally characterized APP(V717F) transgenic mice

Histological analyses were performed on the brains of APP(V717F) transgenic (Tg)mice previously studied in a battery of behavioral tests. We describe here the regional and age-dependent deposition of amyloid in both heterozygous and homozygous Tg mice. We also report that Tg mice show significant and age-dependent changes in synaptic density measured by synaptophysin immunoreactivity. Surprisingly, a rather marked hippocampal atrophy is observed as early as 3 months of age in Tg mice (20-40%). Statistical analyses revealed that the deficits in object recognition memory are related to the number of amyloid deposits in specific brain regions, whereas deficits in spatial reference and working memory are related to the changes in synaptic density and hippocampal atrophy. Our study suggests that the behavioral deficits observed in Tg mice are only in part related to amyloid deposition, but are also related to neuroanatomical alterations secondary to overexpression of the APP(V717F) transgene and independent of amyloid deposition.

Expressions of amyloid precursor protein, synaptophysin and presenilin-1 in the different areas of the developing cerebellum of rat

This study reveals the expressions of Alzheimer's disease-related amyloid precursor protein, presenilin-1, and a presynaptic marker protein, synaptophysin, in the archi-, paleo- and neocerebellum during the postnatal development of the rat. The Western blot results demonstrate a gradual increase in the soluble amyloid precursor protein level in the archicerebellum during the first 3 weeks, while in the neo- and paleocerebellum the levels reach a plateau as early as the 1st week. Immunohistochemically, the protein is present in the deep part of the external granule cell layer and the internal granule cell layer in the newborn animal, while in 3-week-old animals the staining appears mainly in the perikarya and dendrites of the Purkinje cells. The level of synaptophysin increases progressively from postnatal day 7 up to 3 weeks in the archi- and paleocerebellum, and up to 6 weeks in the neocerebellum. Immunohistochemically, the amyloid precursor protein staining appears first in the inner part of the molecular layer and in the internal granule cell layer. In a 3-week-old animal, synaptophysin staining is present in all areas of the cerebellar molecular layer and in the internal granule cell layer. The presenilin-1 immunohistochemical reaction appeared equally in the archi-, paleo- and neocerebellum. Much of the staining is present in the glial cells and Purkinje cells. Less immunoreactivity is observed in the Golgi cells and granule cells. It is concluded that the postnatal expressions of soluble and membrane-bound amyloid precursor protein, synaptophysin and presenilin-1 are regulated differently during the ontogenetical development of the archi-, paleo- and neocerebellum of rat. Further, the amyloid precursor protein and presenilin-1 may be present in cells which do not degenerate in Alzheimer's disease.

A new model of white matter injury in neonatal rats with bilateral carotid artery occlusion

Periventricular leukomalacia is an important cause of cerebral palsy and characterized by cysts and coagulation necrosis in the periventricular white matter. Since no model of periventricular leukomalacia has been established in small animals, it is expected to establish a new model of white matter injury in immature rodents. Bilateral carotid arteries were occluded in neonatal rats at 5 days of age, and the brain neuropathologically examined at 7 days of age. Among 22 brains histologically examined, 20 (90.9%) had white matter changes including coagulation necrosis and cystic lesions in and around the internal capsule, while only two had small cerebral infarction and five showed some ischemic neurons in the cerebral cortex. Cerebral blood flow (CBF) decreased to about 25% of controls in the subcortical white matter in the animals with bilateral carotid artery occlusion (BCAO). Amyloid precursor protein (APP) immunohistochemistry demonstrated various APP-immunoreactive axonal profiles in the internal capsule and the subcortical white matter, and stronger expression of APP in pyramidal neurons in the cerebral cortex of BCAO brains. These results indicated that the white matter is more vulnerable than the cerebral cortex in 5-day-old rats when CBF decreases to about 25% and suggested that this model is useful for investigating the white matter changes induced by cerebral hypoperfusion in the neonatal brain, since previous models of hypoxic-ischemic brain injury in neonatal mice and rats revealed preferential susceptibility of the gray matter. It was also indicated that APP is a sensitive marker for mild axonal disruption in the white matter of the immature brain.

Amino-terminal region of secreted form of amyloid precursor protein stimulates proliferation of neural stem cells

Beta-amyloid precursor protein (APP) has been reported to be expressed in the CNS from the early stages of development. However, the functional role of APP during early development remains unclear. In the present study, we found that the secreted form of APP (sAPP) significantly enhanced proliferation of neural stem cells. Cells were prepared from 13-day embryonic rat neocortex, which was dissected with a Pasteur pipette to make cell clusters. After 12 h of cultivation in the medium without serum, cells around the centre of the cluster were still nestin-positive proliferative cells, i.e. neural stem cells. To determine whether the proliferation of cells was regulated by sAPP, cultures were treated with recombinant sAPP695, the secreted form of human APP695 produced by yeast. Both DNA synthesis and expression of proliferating cell nuclear antigen markedly increased after 5 h of sAPP695 addition. The enhancement of DNA synthesis by sAPP695 stimulation was blocked by the 22C11 monoclonal antibody specific for the amino-terminal region of sAPP. Then, we examined the effect of the amino-terminal fragment of sAPP and the epitope peptide of 22C11 antibody, and found that both of them also promoted DNA synthesis, suggesting that the amino-terminal region of sAPP is responsible for the biological activity. Our findings indicate the possibility that sAPP enhances proliferation of neural stem cells in vivo and plays an important role during the early CNS development.

Neurobehavioral development, adult openfield exploration and swimming navigation learning in mice with a modified beta-amyloid precursor protein gene

The processing of beta-amyloid precursor protein (betaAPP) and its metabolites plays an important role in the pathogenesis of Alzheimer's disease (AD) and Down's syndrome. The authors have reported elsewhere that a targeted mutation resulting in low expression of a shortened betaAPP protein (betaAPP(delta/delta)) entails reduced learning abilities. Here the authors investigate whether these effects were caused by postnatal developmental actions of the altered protein. The authors examined 35 mice carrying the betaAPP(delta/delta) mutation for somatic growth and sensorimotor development during the first 4 postnatal weeks (pw) and compared them with 31 wildtype litter-mates. Thereafter, the same mice were tested at about 10 weeks of age for openfield behavior and for swimming navigation learning. Mutant mice showed both transient and long-lasting deficits in development. Body weight deficit started to emerge at postnatal day (pd) 12, peaked with a 15.1% deficit at pd 27 and lasted until pw 33-37. Significant transient deficits in mutant mice during sensorimotor development were observed in three time windows (pd 3-10, pd 11-19 and pd 20-27), long-lasting effects, manifest at pw 8-12 and pw 33-37, emerged at any of the three periods. In the adult mice, exploratory activity of betaAPP mutants in the openfield arena was severely reduced. In the Morris water maze task, mutant mice showed moderate escape performance deficits during the acquisition period but no impairment in spatial memory. The authors conclude that a defective betaAPP gene impairs postnatal somatic development, associated with transient as well as long-lasting neurobehavioral retardation and muscular weakness. Comparison with earlier data suggests that early postnatal handling may attenuate some of the non-cognitive performance deficits in the water maze. Further, the manifestation and time course of behavioral yet not neuropathological symptoms in betaAPP mutant mice resemble in some aspects those of the human Down's syndrome.

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.

Post-translational processing and turnover kinetics of presynaptically targeted amyloid precursor superfamily proteins in the central nervous system

The amyloid precursor superfamily is composed of three highly conserved transmembrane glycoproteins, the amyloid precursor protein (APP) and amyloid precursor-like proteins 1 and 2 (APLP1, APLP2), whose functions are unknown. Proteolytic cleavage of APP yields the betaA4 peptide, the major component of cerebral amyloid in Alzheimer's disease. Here we show that five post-translationally modified, full-length species of APP and APLP2 (but not APLP1) arrive at the mature presynaptic terminal in the fastest wave of axonal transport and are subsequently rapidly cleared (mean half-life of 3.5 h). Rapid turnover of presynaptic APP and APLP2 occurs independently of visual activity. Turnover of the most rapidly arriving APP species was accompanied by a delayed accumulation of a 120-kDa, APP fragment lacking the C terminus, consistent with presynaptic APP turnover via constitutive proteolysis. Turnover of APLP2 was not accompanied by detectable APLP2 fragment peptides, suggesting either that APLP2 either is more rapidly degraded than is APP or is retrogradely transported shortly after reaching the terminus. A single 150-kDa APLP2 species containing the Kunitz protease inhibitor domain is the major amyloid precursor superfamily protein transported to the presynapse. Presynaptic APP and APLP2 are sialylated and N- and O-glycosylated, and some also carry chondroitin sulfate glycosaminoglycan and/or dermatan sulfate glycosaminoglycan. The rapid kinetics for turnover of APP and APLP2 predict a sensitive balance of synthesis, transport, and elimination rates that may be critical to normal neuronal functions and metabolic fates of these proteins.

The role of glycoproteins in neural development function, and disease

Glycoproteins play key roles in the development, structuring, and subsequent functioning of the nervous system. However, the complex glycosylation process is a critical component in the biosynthesis of CNS glycoproteins that may be susceptible to the actions of toxicological agents or may be altered by genetic defects. This review will provide an outline of the complexity of this glycosylation process and of some of the key neural glycoproteins that play particular roles in neural development and in synaptic plasticity in the mature CNS. Finally, the potential of glycoproteins as targets for CNS disorders will be discussed.

Secreted amyloid precursor protein alpha selectively suppresses N-methyl-D-aspartate currents in hippocampal neurons: involvement of cyclic GMP

The secreted form of beta-amyloid precursor protein (sAPP alpha) is released from neurons in an activity-dependent manner; data suggest sAPP alpha may play roles in regulating neuronal excitability, plasticity, and survival. In cultured hippocampal neurons sAPP alpha can suppress elevation of [Ca2+]i induced by glutamate and can protect neurons against excitotoxicity. We now report whole-cell patch-clamp data from studies of cultured embryonic rat hippocampal neurons which demonstrate that sAPP alpha selectively suppresses N-methyl-D-aspartate currents without affecting currents induced by alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate or kainate. sAPP alpha suppressed N-methyl-D-aspartate current rapidly and reversibly at concentrations of 0.011 nM. Suppression of N-methyl-D-aspartate current by sAPP alpha is apparently mediated by cyclic guanosine monophosphate because 8-bromo-cyclic guanosine monophosphate suppressed N-methyl-D-aspartate current in a manner similar to sAPP alpha, and two different inhibitors of cyclic guanosine monophosphate-dependent protein kinase prevented sAPP alpha-induced suppression of N-methyl-D-aspartate current. In addition, okadaic acid prevented suppression of N-methyl-D-aspartate-induced current suggesting the involvement of a protein phosphatase in modulation of N-methyl-D-aspartate current by sAPP alpha. These data identify a mechanism whereby sAPP alpha can modulate cellular responses to glutamate, and suggest important roles for sAPP alpha in the various physiological and pathophysiological processes in which N-methyl-D-aspartate receptors participate.

Cellular signaling roles of TGF beta, TNF alpha and beta APP in brain injury responses and Alzheimer's disease

beta-Amyloid precursor protein (beta APP), transforming growth factor beta (TGF beta), and tumor necrosis factor-alpha (TNF alpha) are remarkably pleiotropic neural cytokines/neurotrophic factors that orchestrate intricate injury-related cellular and molecular interactions. The links between these three factors include: their responses to injury; their interactive effects on astrocytes, microglia and neurons; their ability to induce cytoprotective responses in neurons; and their association with cytopathological alterations in Alzheimer's disease. Astrocytes and microglia each produce and respond to TGF beta and TNF alpha in characteristic ways when the brain is injured. TGF beta, TNF alpha and secreted forms of beta APP (sAPP) can protect neurons against excitotoxic, metabolic and oxidative insults and may thereby serve neuroprotective roles. On the other hand, under certain conditions TNF alpha and the fibrillogenic amyloid beta-peptide (A beta) derivative of beta APP can promote damage of neuronal and glial cells, and may play roles in neurodegenerative disorders. Studies of genetically manipulated mice in which TGF beta, TNF alpha or beta APP ligand or receptor levels are altered suggest important roles for each factor in cellular responses to brain injury and indicate that mediators of neural injury responses also have the potential to enhance amyloidogenesis and/or to interfere with neuroregeneration if expressed at abnormal levels or modified by strategic point mutations. Recent studies have elucidated signal transduction pathways of TGF beta (serine/threonine kinase cascades), TNF alpha (p55 receptor linked to a sphingomyelin-ceramide-NF kappa B pathway), and secreted forms of beta APP (sAPP; receptor guanylate cyclase-cGMP-cGMP-dependent kinase-K+ channel activation). Knowledge of these signaling pathways is revealing novel molecular targets on which to focus neuroprotective therapeutic strategies in disorders ranging from stroke to Alzheimer's disease.

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.

Secreted glypican binds to the amyloid precursor protein of Alzheimer's disease (APP) and inhibits APP-induced neurite outgrowth

The amyloid precursor protein (APP) of Alzheimer's disease has been shown to stimulate neurite outgrowth in vitro. The effect of APP on neurite outgrowth can be enhanced if APP is presented to neurons in substrate-bound form, in the presence of heparan sulfate proteoglycans. To identify specific heparan sulfate proteoglycans that bind to APP, conditioned medium from neonatal mouse brain cells was subjected to affinity chromatography with recombinant APP695 as a ligand. Glypican bound strongly to the APP affinity column. Purified glypican bound to APP with an equilibrium dissociation constant of 2.8 nM and inhibited APP-induced neurite outgrowth from chick sympathetic neurons. The effect of glypican was specific for APP, as glypican did not inhibit laminin-induced neurite outgrowth. Furthermore, treatment of cultures with 4-methylumbelliferyl-beta-D-xyloside, a competitive inhibitor of proteoglycan glycanation, inhibited APP-induced neurite outgrowth but did not inhibit laminin-induced neurite outgrowth. This result suggests that endogenous proteoglycans are required for substrate-bound APP to stimulate neurite outgrowth. Secreted glypican may act to inhibit APP-induced neurite outgrowth in vivo by competing with endogenous proteoglycans for binding to APP.

The ependyma: a protective barrier between brain and cerebrospinal fluid

This review summarizes the current scientific literature concerning the ependymal lining of the cerebral ventricles of the brain with an emphasis on selective barrier function and protective roles for the common ependymal cell. Topics covered include the development, morphology, protein and enzyme expression including reactive changes, and pathology. Some cells lining the neural tube are committed at an early stage to becoming ependymal cells. They serve a secretory function and perhaps act as a cellular/axonal guidance system, particularly during fetal development. In the mature mammalian brain ependymal cells possess the structural and enzymatic characteristics necessary for scavenging and detoxifying a wide variety of substances in the CSF, thus forming a metabolic barrier at the brain-CSF interface.

MIB1 staining index and scoring of histologic features in meningioma. Indicators for the prediction of biologic potential and postoperative management

BACKGROUND

The biology of brain tumors, including cell kinetics, has been studied. Recently, monoclonal antibody to Ki67 (MIB1), a nuclear protein related to cell proliferation, has been analyzed immunohistochemically using tissue prepared from paraffin embedded sections.

METHODS

The authors assessed the prognostic usefulness of various histologic indicators of the biologic potential of meningiomas in patients who underwent total resection (Simpson's Grade I and II) by evaluating the time to recurrence as an end point. Forty-three patients with a total of 36 meningiomas and 7 hemangiopericytomas were investigated by immunohistochemical analysis using MIB1.

RESULTS

MIB1 staining index (SI) and histologic score were well correlated with the recurrence-free interval (r = -0.6749, P = 0.002 and r = -0.4939, P = 0.027, respectively) and with each other (r = 0.7909, P < 0.001). The MIB1 SI and histologic score in the nonrecurrence group were significantly lower than those in the recurrence/metastasis group (P < 0.001 and P = 0.001, respectively). The values of these indicators showed that as the value increased, so did the recurrence rate.

CONCLUSIONS

Evaluation using the MIB1 SI and total histologic score of meningioma is useful in assessing the prognosis as well as postoperative management of these patients.

Expression of beta-amyloid precursor protein (APP) in human dorsal root ganglia

The present study reports the occurrence and localization of beta-amyloid precursor protein (APP) immunoreactivity (IR) in human lumbar dorsal root ganglia of healthy adult subjects (age range 25-43 years). To ascertain that ganglionic cells displayed APP IR, neurofilament (NFP) and S-100 proteins (S100P) were studied in parallel. Immunoblotting revealed four or five major proteins with apparent molecular masses between 100-125 kDa, which corresponded with the different full-length APP isoforms. Moreover, an additional protein of approximately 55 kDa was detected. Selective APP IR was observed restricted to the satellite glial cell cytoplasms whereas neuron cell bodies resulted unlabeled. Moreover, some intraganglionic nerve fibers also displayed APP IR, apparently labelling Schwann cells. No individual differences among subjects were observed neither in the pattern of APP IR distribution, nor in the intensity of APP IR. Although it remains to be demonstrated whether or not human primary sensory neurons express APP, present results strongly suggest that supporting glial cells may be a primary source of APP or any related peptide, at least in adult healthy people. The functional and clinical relevance of these findings, if any, remain to be clarified.