Intraneuronal accumulation of amyloid-β peptides as the pathomechanism linking autism and its co-morbidities: epilepsy and self-injurious behavior - the hypothesis

Autism spectrum disorder (ASD) is associated with enhanced processing of amyloid-β precursor protein (APP) by secretase-α, higher blood levels of sAPPα and intraneuronal accumulation of N-terminally truncated Aβ peptides in the brain cortex - mainly in the GABAergic neurons expressing parvalbumin - and subcortical structures. Brain Aβ accumulation has been also described in epilepsy-the frequent ASD co-morbidity. Furthermore, Aβ peptides have been shown to induce electroconvulsive episodes. Enhanced production and altered processing of APP, as well as accumulation of Aβ in the brain are also frequent consequences of traumatic brain injuries which result from self-injurious behaviors, another ASD co-morbidity. We discuss distinct consequences of accumulation of Aβ in the neurons and synapses depending on the Aβ species, their posttranslational modifications, concentration, level of aggregation and oligomerization, as well as brain structures, cell types and subcellular structures where it occurs. The biological effects of Aβ species which are discussed in the context of the pathomechanisms of ASD, epilepsy, and self-injurious behavior include modulation of transcription-both activation and repression; induction of oxidative stress; activation and alteration of membrane receptors' signaling; formation of calcium channels causing hyper-activation of neurons; reduction of GABAergic signaling - all of which lead to disruption of functions of synapses and neuronal networks. We conclude that ASD, epilepsy, and self-injurious behaviors all contribute to the enhanced production and accumulation of Aβ peptides which in turn cause and enhance dysfunctions of the neuronal networks that manifest as autism clinical symptoms, epilepsy, and self-injurious behaviors.

Enhanced accumulation of N-terminally truncated Aβ with and without pyroglutamate-11 modification in parvalbumin-expressing GABAergic neurons in idiopathic and dup15q11.2-q13 autism

Autism, the most frequent neurodevelopmental disorder of a very complex etiopathology, is associated with dysregulation of cellular homeostatic mechanisms, including processing of amyloid-β precursor protein (APP). Products of APP processing — N-terminally truncated amyloid-β peptide (N-tr-Aβ) species — are accumulated in autism in neurons and glia in the cortex, cerebellum, and subcortical structures of the brain. This process in neurons is correlated with increased oxidative stress. Because abnormally high levels of N-tr-Aβ are detected in only a fraction of neurons in the prefrontal cortex, we applied immunocytochemical staining and confocal microscopy in autopsy brain material from idiopathic and chromosome 15q11.2-q13 duplication (dup-15) autism to measure the load of N-tr-Aβ in the cells and synapses and to identify the subpopulation of neurons affected by these pathophysiological processes. The peptides accumulated in autism are N-terminally truncated; therefore, we produced a new antibody against Aβ truncated at N-terminal amino acid 11 modified to pyroglutamate to evaluate the presence and distribution of this peptide species in autism. We also quantified and characterized the oligomerization patterns of the Aβ-immunoreactive peptides in autism and control frozen brain samples. We provide morphological evidence, that in idiopathic and dup-15 autism, accumulation of N-tr-Aβ with and without pyroglutamate-11 modified N-terminus affects mainly the parvalbumin-expressing subpopulation of GABAergic neurons. N-tr-Aβ peptides are accumulated in neurons’ cytoplasm and nucleus as well as in GABAergic synapses. Aβ peptides with both C-terminus 40 and 42 were detected by immunoblotting in frozen cortex samples, in the form of dimers and complexes of the molecular sizes of 18-24kD and 32-34kD. We propose that deposition of N-tr-Aβ specifically affects the functions of the parvalbumin-expressing GABAergic neurons and results in a dysregulation of brain excitatory–inhibitory homeostasis in autism. This process may be the target of new therapies.

Generation and Partial Characterization of Rabbit Monoclonal Antibody to Amyloid-β Peptide 1-37 (Aβ37)

Secreted soluble amyloid-β 1-37 (Aβ37) peptide is one of the prominent Aβ forms next to Aβ40, and is found in cerebrospinal fluid (CSF) and blood. Recent studies have shown the importance of quantitation of CSF Aβ37 levels in combination with Aβ38, Aβ40, and Aβ42 to support the diagnosis of patients with probable Alzheimer's disease (AD), and the value of antibody to Aβ37 to facilitate drug discovery studies. However, the availability of reliable and specific monoclonal antibody to Aβ37 is very limited. Our aims were: 1) to generate and partially characterize rabbit monoclonal antibody (RabmAb) to Aβ37, and 2) to determine whether the antibody detects changes in Aβ37 levels produced by a γ-secretase modulator (GSM). Our generated RabmAb to Aβ37 was found to be specific to Aβ37, since it did not react with Aβ36, Aβ38, Aβ39, Aβ40, and Aβ42 in an ELISA or immunoblotting. The epitope of the antibody was contained in the seven C-terminal residues of Aβ37. The antibody was sensitive enough to measure CSF and plasma Aβ37 levels in ELISA. Immunohistological studies showed the presence of Aβ37-positive deposits in the brain of AD, and Down syndrome persons diagnosed with AD. Our studies also showed that the antibody detected Aβ37 increases in CSF and brains of rodents following treatment with a GSM. Thus, our antibody can be widely applied to AD research, and in a panel based approach it may have potential to support the diagnosis of probable AD, and in testing the effect of GSMs to target AD.

Generation of Rabbit Monoclonal Antibody to Amyloid-β38 (Aβ38): Increased Plasma Aβ38 Levels in Down Syndrome

Secreted soluble amyloid-β (Aβ)38 is the second most prominent Aβ form next to Aβ40, and is found in cerebrospinal fluid (CSF) and blood. Recent studies have shown the importance of quantitation of CSF Aβ38 levels in combination with those of Aβ40 and Aβ42 to support the diagnosis of Alzheimer's disease (AD), and other neurodegenerative diseases, and to facilitate drug discovery studies. However, the availability of reliable and specific Aβ38 monoclonal antibody is limited. Our first aim was to generate and partially characterize rabbit monoclonal antibody (RabmAb) to Aβ38. The antibody was specific to Aβ38, since it did not react with Aβ37, Aβ39, Aβ40, or Aβ42 in ELISA or immunoblotting. The antibody was sensitive enough to measure Aβ38 levels in plasma. Our second aim was to quantitate Aβ38 levels in plasma from older Down syndrome (DS) persons and age-matched controls. Persons with DS (35 years and older) have neuropathological changes characteristic of AD. Studies have shown that plasma Aβ40 and Aβ42 levels are higher in older persons with DS than in controls. However, none examined Aβ38 levels in DS. Our quantitation data showed that, like Aβ40 and Aβ42 plasma levels, Aβ38 plasma levels were higher in DS than in controls. Longitudinal studies will determine whether plasma Aβ38 levels in combination with levels of Aβ40 and Aβ42 are useful to predict early signs of AD in DS.

Neuronal nucleus and cytoplasm volume deficit in children with autism and volume increase in adolescents and adults

Introduction

Characterization of the type and topography of structural changes and their alterations throughout the lifespan of individuals with autism is essential for understanding the mechanisms contributing to the autistic phenotype. The aim of this stereological study of neurons in 16 brain structures of 14 autistic and 14 control subjects from 4 to 64 years of age was to establish the course of neuronal nuclear and cytoplasmic volume changes throughout the lifespan of individuals with autism.

Results

Our data indicate that a deficit of neuronal soma volume in children with autism is associated with deficits in the volume of the neuronal nucleus and cytoplasm. The significant deficits of neuronal nuclear and cytoplasmic volumes in 13 of 16 examined subcortical structures, archicortex, cerebellum, and brainstem in 4- to 8-year-old autistic children suggest a global nature of brain developmental abnormalities, but with region-specific differences in the severity of neuronal pathology. The observed increase in nuclear volumes in 8 of 16 structures in the autistic teenagers/young adults and decrease in nuclear volumes in 14 of 16 regions in the age-matched control subjects reveal opposite trajectories throughout the lifespan. The deficit in neuronal nuclear volumes, ranging from 7% to 42% in the 16 examined regions in children with autism, and in neuronal cytoplasmic volumes from 1% to 31%, as well as the broader range of interindividual differences for the nuclear than the cytoplasmic volume deficits, suggest a partial distinction between nuclear and cytoplasmic pathology.

Conclusions

The most severe deficit of both neuronal nucleus and cytoplasm volume in 4-to 8-year-old autistic children appears to be a reflection of early developmental alterations that may have a major contribution to the autistic phenotype. The broad range of functions of the affected structures implies that their developmental and age-associated abnormalities contribute not only to the diagnostic features of autism but also to the broad spectrum of clinical alterations associated with autism. Lack of clinical improvement in autistic teenagers and adults indicates that the observed increase in neuron nucleus and cytoplasm volume close to control level does not normalize brain function.

Autoantibodies against neuronal progenitors in sera from children with autism

The pathological role of autoantibodies in development of CNS disorders is a new idea with growing interest among neuroscientists. The involvement of autoimmune response in the pathogenesis of autism spectrum disorders (ASD) has been suggested by the presence of multiple brain-specific autoantibodies in children with ASD and in their mothers. The possibility of the effect of autoimmunity on neurogenesis and postnatal brain plasticity has not been determined. The presence of autoantibodies against human neuronal progenitor cells (NPCs) stimulated for neuronal differentiation in culture was tested in sera from children with autism (n=20) and age-matched controls (n=18) by immunoblotting and immunocytochemistry. Immunoreactivity against multiple NPCs proteins of molecular sizes of approximately 55 kDa, 105 kDa, 150 kDa, and 210 kDa in sera from individuals with autism had a higher incidence and was stronger than in control sera which immunoreacted mainly with a 150 kDa protein. The sera from children with autism immunoreacted the strongest with NPCs expressing neuronal markers Tuj1 and doublecortin, but not astrocyte marker GFAP. The epitopes recognized by antibodies from sera were not human-specific because they detected also NPCs in situ in murine hippocampus. The autoimmune reactions against NPCs suggest an impaired tolerance to neural antigens in autism. These autoantibodies may be symptomatic for autism and furthermore, their presence suggests that autoimmunity may affect postnatal neuronal plasticity particularly after impairment of blood-brain barrier. Future studies will determine the diagnostic value of the presence of autoantibodies in autism and the therapeutic value of prevention of autoimmunity in autism.

Intracellular distribution of differentially phosphorylated dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A)

The gene encoding dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) is located within the Down syndrome (DS) critical region of chromosome 21. DYRK1A interacts with a plethora of substrates in the cytosol, cytoskeleton, and nucleus. Its overexpression is a contributing factor to the developmental alterations and age-associated pathology observed in DS. We hypothesized that the intracellular distribution of DYRK1A and cell-compartment-specific functions are associated with DYRK1A posttranslational modifications. Fractionation showed that, in both human and mouse brain, almost 80% of DYRK1A was associated with the cytoskeleton, and the remaining DYRK1A was present in the cytosolic and nuclear fractions. Coimmunoprecipitation revealed that DYRK1A in the brain cytoskeleton fraction forms complexes with filamentous actin, neurofilaments, and tubulin. Two-dimensional gel analysis of the fractions revealed DYRK1A with distinct isoelectric points: 5.5-6.5 in the nucleus, 7.2-8.2 in the cytoskeleton, and 8.7 in the cytosol. Phosphate-affinity gel electrophoresis demonstrated several bands of DYRK1A with different mobility shifts for nuclear, cytoskeletal, and cytosolic DYRK1A, indicating modification by phosphorylation. Mass spectrometry analysis disclosed one phosphorylated site in the cytosolic DYRK1A and multiple phosphorylated residues in the cytoskeletal DYRK1A, including two not previously described. This study supports the hypothesis that intracellular distribution and compartment-specific functions of DYRK1A may depend on its phosphorylation pattern.

The link between intraneuronal N-truncated amyloid-β peptide and oxidatively modified lipids in idiopathic autism and dup(15q11.2-q13)/autism

BACKGROUND

Autism is a neurodevelopmental disorder of unknown etiopathogenesis associated with structural and functional abnormalities of neurons and increased formation of reactive oxygen species. Our previous study revealed enhanced accumulation of amino-terminally truncated amyloid-β (Aβ) in brain neurons and glia in children and adults with autism. Verification of the hypothesis that intraneuronal Aβ may cause oxidative stress was the aim of this study.

RESULTS

The relationships between neuronal Aβ and oxidative stress markers-4-hydroxy-2-nonenal (HNE) and malondialdehyde (MDA)-were examined in the frontal cortex from individuals aged 7-32 years with idiopathic autism or with chromosome 15q11.2-q13 duplications (dup(15)) with autism, and age-matched controls. Quantification of confocal microscopy images revealed significantly higher levels of neuronal N-truncated Aβ and HNE and MDA in idiopathic autism and dup(15)/autism than in controls. Lipid peroxidation products were detected in all mitochondria and lipofuscin deposits, in numerous autophagic vacuoles and lysosomes, and in less than 5% of synapses. Neuronal Aβ was co-localized with HNE and MDA, and increased Aβ levels correlated with higher levels of HNE and MDA.

CONCLUSIONS

The results suggest a self-enhancing pathological process in autism that is initiated by intraneuronal deposition of N-truncated Aβ in childhood. The cascade of events includes altered APP metabolism and abnormal intracellular accumulation of N-terminally truncated Aβ which is a source of reactive oxygen species, which in turn increase the formation of lipid peroxidation products. The latter enhance Aβ deposition and sustain the cascade of changes contributing to metabolic and functional impairments of neurons in autism of an unknown etiology and caused by chromosome 15q11.2-q13 duplication.

Effect of DYRK1A activity inhibition on development of neuronal progenitors isolated from Ts65Dn mice

Overexpression of dual-specificity tyrosine-(Y)-phosphorylation-regulated kinase 1A (DYRK1A), encoded by a gene located in the Down syndrome (DS) critical region, is considered a major contributor to developmental abnormalities in DS. DYRK1A regulates numerous genes involved in neuronal commitment, differentiation, maturation, and apoptosis. Because alterations of neurogenesis could lead to impaired brain development and mental retardation in individuals with DS, pharmacological normalization of DYRK1A activity has been postulated as DS therapy. We tested the effect of harmine, a specific DYRK1A inhibitor, on the development of neuronal progenitor cells (NPCs) isolated from the periventricular zone of newborn mice with segmental trisomy 16 (Ts65Dn mice), a mouse model for DS that overexpresses Dyrk1A by 1.5-fold. Trisomy did not affect the ability of NPCs to expand in culture. Twenty-four hours after stimulation of migration and neuronal differentiation, NPCs showed increased expression of Dyrk1A, particularly in the trisomic cultures. After 7 days, NPCs developed into a heterogeneous population of differentiating neurons and astrocytes that expressed Dyrk1A in the nuclei. In comparison with disomic cells, NPCs with trisomy showed premature neuronal differentiation and enhanced γ-aminobutyric acid (GABA)-ergic differentiation, but astrocyte development was unchanged. Harmine prevented premature neuronal maturation of trisomic NPCs but not acceleration of GABA-ergic development. In control NPCs, harmine treatment caused altered neuronal development of NPCs, similar to that in trisomic NPCs with Dyrk1A overexpression. This study suggests that pharmacological normalization of DYRK1A activity may have a potential role in DS therapy.

Link between DYRK1A overexpression and several-fold enhancement of neurofibrillary degeneration with 3-repeat tau protein in Down syndrome

Triplication of chromosome 21 in Down syndrome (DS) results in overexpression of the minibrain kinase/dual-specificity tyrosine phosphorylated and regulated kinase 1A gene (DYRK1A). DYRK1A phosphorylates cytoplasmic tau protein and appears in intraneuronal neurofibrillary tangles (NFTs). We have previously shown significantly more DYRK1A-positive NFTs in DS brains than in sporadic Alzheimer disease (AD) brains. This study demonstrates a gene dosage-proportional increase in the level of DYRK1A in DS in the cytoplasm and the cell nucleus, and enhanced cytoplasmic and nuclear immunoreactivity of DYRK1A in DS. The results suggest that overexpressed DYRK1A may alter both phosphorylation of tau and alternative splicing factor (ASF). Two-dimensional electrophoresis revealed modification of ASF phosphorylation in DS/AD and AD in comparison to controls. Altered phosphorylation of ASF by overexpressed nuclear DYRK1A may contribute to the alternative splicing of the tau gene and an increase by 2.68 × of the 3R/4R ratio in DS/AD, and a several-fold increase in the number of 3R tau-positive NFTs in DS/AD subjects compared with that in sporadic AD subjects. These data support the hypothesis that phosphorylation of ASF by overexpressed DYRK1A may contribute to alternative splicing of exon 10, increased expression of 3R tau, and early onset of neurofibrillary degeneration in DS.

Sera from children with autism alter proliferation of human neuronal progenitor cells exposed to oxidation

Altered brain development during embryogenesis and early postnatal life has been hypothesized to be responsible for the abnormal behaviors of people with autism. The specific genetic background that alters vulnerability to some environmental insults has been suggested in the etiology of autism; however, the specific pathomechanisms have not been identified. Recently, we showed that sera from children with autism alter the maturation of human neuronal progenitor cells (NPCs) in culture. Results suggest that pre-programmed neurogenesis, i.e., neuronal proliferation, migration, differentiation, growth, and circuit organization, can be affected differently by factors present in autistic sera. In this report, we tested the effect of autistic sera on the vulnerability of NPCs to oxidative stress-a recognized risk factor of autism. We found that mild oxidative stress reduced proliferation of differentiating NPCs but not immature NPCs. This decrease of proliferation was less prominent in cultures treated with sera from children with autism than from age-matched controls. These results suggest that altered response of NPCs to oxidative stress may play a role in the etiology of autism.

The role of overexpressed DYRK1A protein in the early onset of neurofibrillary degeneration in Down syndrome

The gene encoding the minibrain kinase/dual-specificity tyrosine phosphorylated and regulated kinase 1A (DYRK1A) is located in the Down syndrome (DS) critical region of chromosome 21. The third copy of DYRK1A is believed to contribute to abnormal brain development in patients with DS. In vitro studies showing that DYRK1A phosphorylates tau protein suggest that this kinase is also involved in tau protein phosphorylation in the human brain and contributes to neurofibrillary degeneration, and that this contribution might be enhanced in patients with DS. To explore this hypothesis, the brain tissue from 57 subjects including 16 control subjects, 21 patients with DS, and 20 patients with sporadic Alzheimer's disease (AD) was examined with two antibodies to the amino-terminus of DYRK1A (7F3 and G-19), as well as two polyclonal antibodies to its carboxy-terminus (X1079 and 324446). Western blots demonstrated higher levels of full-length DYRK1A in the brains of patients with DS when compared to control brains. Immunocytochemistry revealed that DYRK1A accumulates in neurofibrillary tangles (NFTs) in subjects with sporadic AD and in subjects with DS/AD. Overexpression of DYRK1A in patients with DS was associated with an increase in DYRK1A-positive NFTs in a gene dosage-dependent manner. Results support the hypothesis that overexpressed DYRK1A contributes to neurofibrillary degeneration in DS more significantly than in subjects with two copies of the DYRK1A gene and sporadic AD. Immunoreactivity with antibodies against DYRK1A not only in NFTs but also in granules in granulovacuolar degeneration and in corpora amylacea suggests that DYRK1A is involved in all three forms of degeneration and that overexpression of this kinase may contribute to the early onset of these pathologies in DS.

Altered development of neuronal progenitor cells after stimulation with autistic blood sera

Changes of brain structure and functions in people with autism may result from altered neuronal development, however, no adequate cellular or animal models are available to study neurogenesis in autism. Neuronal development can be modeled in culture of neuronal progenitor cells (NPCs) stimulated with serum to differentiate into neurons. Because sera from people with autism and age-matched controls contain different levels of numerous biologically active factors, we hypothesized that development of human NPCs induced to differentiate into neurons with sera from children with autism reflects the altered early neuronal development that leads to autism. The control and autistic sera were collected from siblings aged below 6 years that lived in the same environment. The effect of sera on differentiation of NPC neurospheres into neuronal colonies was tested in 72-h-long cultures by morphometry, immunocytochemistry and immunoblotting. We found that sera from children with autism significantly reduced NPCs' proliferation, but stimulated cell migration, development of small neurons with processes, length of processes and synaptogenesis. These results suggest that development of network of processes and synaptogenesis--the specific events in the brain during postnatal ontogenesis--are altered in autism. Further studies in this cell culture model may explain some of the cellular alterations described in autistic patients.

Intraneuronal Abeta immunoreactivity is not a predictor of brain amyloidosis-beta or neurofibrillary degeneration

Amyloid beta (Abeta) immunoreactivity in neurons was examined in brains of 32 control subjects, 31 people with Down syndrome, and 36 patients with sporadic Alzheimer's disease to determine if intraneuronal Abeta immunoreactivity is an early manifestation of Alzheimer-type pathology leading to fibrillar plaque formation and/or neurofibrillary degeneration. The appearance of Abeta immunoreactivity in neurons in infants and stable neuron-type specific Abeta immunoreactivity in a majority of brain structures during late childhood, adulthood, and normal aging does not support this hypothesis. The absence or detection of only traces of reaction with antibodies against 4-13 aa and 8-17 aa of Abeta in neurons indicated that intraneuronal Abeta was mainly a product of alpha- and gamma-secretases (Abeta(17-40/42)). The presence of N-terminally truncated Abeta(17-40) and Abeta(17-42) in the control brains was confirmed by Western blotting and the identity of Abeta(17-40) was confirmed by mass spectrometry. The prevalence of products of alpha- and gamma -secretases in neurons and beta- and gamma-secretases in plaques argues against major contribution of Abeta-immunopositive material detected in neuronal soma to amyloid deposit in plaques. The strongest intraneuronal Abeta(17-42) immunoreactivity was observed in structures with low susceptibility to fibrillar Abeta deposition, neurofibrillary degeneration, and neuronal loss compared to areas more vulnerable to Alzheimer-type pathology. These observations indicate that the intraneuronal Abeta immunoreactivity detected in this study is not a predictor of brain amyloidosis or neurofibrillary degeneration. The constant level of Abeta immunoreactivity in structures free from neuronal pathology during essentially the entire life span suggests that intraneuronal amino-terminally truncated Abeta represents a product of normal neuronal metabolism.

Neprilysin protects human neuronal progenitor cells against impaired development caused by amyloid-β peptide

Transplantation of human neuronal progenitor cells (HNPC) is being considered for neuroreplacement therapy in beta-amyloidosis associated with neuronal loss in Down's syndrome and Alzheimer's disease. However, the influence of amyloid-beta-containing brain environment on the development of HNPCs is unknown. Recently, we demonstrated that amyloid-beta peptide (Abeta) impaired differentiation of HNPCs in culture through oxidative stress. Now we studied the effect of neprilysin, an Abeta-degrading enzyme, on development of neuronal colonies from neurospheres of HNPCs in the presence of Abeta1-40. Neprilysin increased the number of neurospheres that formed colonies of neuron-like cells. This effect of neprilysin was associated with reduced amounts of the monomeric and dimeric Abeta that remained in culture supernatants as well as the Abeta uptaken by differentiating HNPCs. Phosphoramidon, a neprilysin inhibitor, attenuated these effects of neprilysin. In control cultures of HNPCs that grew without exogenous Abeta1-40, the treatment with neprilysin reduced the number of developing colonies. This effect might result from degradation by neprilysin of endogenous Abeta produced and secreted by HNPCs or other peptides that are involved in neuronal development. The results demonstrate that even a partial reduction of extracellular Abeta levels by neprilysin may facilitate development of HNPCs into neurons in an environment overloaded with Abeta. This finding suggests that neprilysin could facilitate neuroreplacement therapy with HNPCs in treatment of neurodegenerative diseases.

Induction of vascular amyloidosis-β by oxidative stress depends on APOE genotype

The reduced antioxidant defense in apolipoprotein E epsilon4/epsilon4 carriers may contribute to beta-amyloidosis. Previously we found that Fe(2+)-induced oxidative stress caused greater protein oxidation in epsilon4/epsilon4 than in epsilon3/epsilon3 human brain vascular smooth muscle cells. Moreover, Fe(2+) induced lysosomal accumulation of endogenous Abeta and APOE in cultured cells, and Abeta deposition in vascular tunica media in organotypic cultures of brain vessels. Here we demonstrated that Fe(2+) enhanced an uptake of exogenous Abeta 1-40 and its deposition together with APOE in lysosomes in myocytes. Abeta deposits were associated with lipid-peroxidation and protein ubiquitination, and were more abundant and stable in epsilon4/epsilon4 than in epsilon3/epsilon3 cells. In organotypic cultures of brain vessels Fe(2+) induced deposition of non-fibrillar and fibrillar Abeta 1-40 in vascular tunica media. We hypothesize that locally increased concentrations of iron induce accumulation of exogenous and endogenous Abeta in SMCs, triggering beta-amyloid angiopathy. The greater susceptibility of epsilon4 carriers to Fe(2+) ions may result in an increased risk of beta-amyloidosis.

Amyloid-beta impairs development of neuronal progenitor cells by oxidative mechanisms

Neuronal progenitor cells (NPCs) are being considered for treatment of neurodegenerative diseases associated with beta-amyloidosis: Alzheimer's disease (AD) and Down syndrome (DS). However, the neurotoxic properties of amyloid-beta peptide (Abeta) may impair survival and differentiation of transplanted NPCs. Hence, we studied the influence of Abeta on development of human NPCs--proliferation, migration, formation of colonies of neurons, formation processes--in culture. Pre-fibrillized human Abeta1-40 blocked development of neuronal colonies. NPC development was impaired in the presence of soluble Abeta1-40 (1.75-7 microM), and NPC differentiation into large and small neurons was altered, as demonstrated by morphometry. Antioxidant vitamin E partially abolished these effects, but not the reduced formation of neuronal processes. NPCs cultured with 7 microM Abeta1-40 accumulated Abeta monomers and oligomers and contained higher levels of protein carbonyls and lipid peroxidation products HNE and MDA. We suggest that Abeta1-40 impairs development of NPCs by oxidative damage. Hence, a prerequisite of successful neuroreplacement therapy using NPCs in AD and DS/AD may be removal of amyloid-beta and antioxidative treatment.

Extracellular Deposits of Aβ Produced in Cultures of Alzheimer Disease Brain Vascular Smooth Muscle Cells

Alzheimer disease (AD) and Down syndrome (DS) brains contain deposits of amyloid-beta peptide that are located extracellularly in the neuropil and in blood vessels walls. A small fraction of brain Abeta is detected intracellularly in neurons, smooth muscle cells, and microglia. The roles of these extracellular and intracellular pools of Abeta in pathogenesis of AD-type dementia are controversial. Cell culture models of vascular amyloidosis-beta revealed intracellular, but not extracellular deposition of Abeta. Here we demonstrate for the first time, formation of extracellular deposits of Abeta in primary cultures of vascular smooth muscle cells isolated from AD cases with cerebrovascular amyloid angiopathy. Extracellular Abeta deposition required the use of cultures that produced high quantities of Abeta, which contained at least 50% of cells forming intracellular Abeta deposits, and providing extracellular matrix proteins. During 12 days of culture in this system, we observed accumulation of nonfibrillar, granular deposits in extracellular matrix, similar to early stages of vascular amyloidogenesis in vivo. This is a valuable system to study the effects of various potential amyloidogenic factors on formation of extracellular Abeta deposits.

The effect of oxidative stress on amyloid precursor protein processing in cells engaged in beta-amyloidosis is related to apolipoprotein E genotype

The reduced antioxidative defense in allele epsilon4 carriers is suggested to contribute to beta-amyloidosis in Alzheimer's disease and Down's syndrome. We studied the effect of oxidative stress on accumulation of amyloid-beta peptide (Abeta) in vascular smooth muscle cells (SMCs) that are engaged in production of amyloid-beta in vivo. Previously, we found that oxidative stress caused by ferrous ions induced accumulation of Abeta-apolipoprotein E deposits in lysosomes and was associated with a greater oxidative protein damage in epsilon4 carriers. Here, we demonstrate that ferrous ions induce formation of Abeta deposits also in vascular tunica media in organotypic cultures of whole brain vessels, suggesting the role of oxidative stress in development of vascular beta-amyloidosis. Cellular accumulation of Abeta in SMCs treated with ferrous ions was associated with a greater accumulation of C-terminal amyloid precursor protein (APP) fragments in epsilon4/epsilon4 than in epsilon3/epsilon3 myocytes and reduced the amount of soluble APPalpha in epsilon3/epsilon3, but not epsilon4/epsilon4, cultures. Antioxidant vitamin E prevented these effects, and, when applied alone, diminished the amount of APP C-terminal fragments and increased the amount of secreted APP in epsilon3/epsilon3, but not epsilon4/epsilon4, cells. C-terminal APP-immunoreactive material was accumulated in lysosomes partly with Abeta- and N-terminal APP immunoreactivities. These results suggest that the increased accumulation of APP and its fragments in lysosomes may yield additional amounts of cellular Abeta, particularly in epsilon4 carriers. We hypothesize that the altered processing of APP in SMCs locally exposed to oxidative stress facilitates cellular deposition of Abeta and contribute to the increased risk of development of beta-amyloidosis in epsilon4/epsilon4 carriers.

Lysosomal deposition of Abeta in cultures of brain vascular smooth muscle cells is enhanced by iron

Recently, we found that brain vascular smooth muscle cells from Tg2576 mice over-expressed the APP transgene in culture, secreted amyloid-beta peptide (Abeta) and accumulated Abeta intracellularly. Now we detected this intracellular Abeta inside lysosomes, which were also rich in C-terminal domain of APP, but not in endoplasmic reticulum, Golgi apparatus, or trans-Golgi network. Treatment of cultures with ferrous ions (50-150 microM) increased the proportion of muscle cells with Abeta immunoreactive granules and the amounts of intracellular Abeta1-40 and Abeta1-42 in a dose-dependent manner. This increase of intracellular Abeta1-40 by iron was inhibited by alpha-tocopherol, but not by a water-soluble antioxidant melatonin. The increase of intracellular Abeta1-42 by iron was not inhibited by alpha-tocopherol or melatonin. Cell treatment with iron did not alter the lysosomal localization of Abeta immunoreactivity. Cell treatment with iron (II and III), copper (II), zinc (II) and aluminum (III) increased cellular levels of carbonyls. However, the effect of zinc on Abeta accumulation in cultures was weak, and there were no effects of copper and aluminum. The data suggest that iron may be the factor that triggers vascular amyloidosis. Lysosomal accumulation of APP and Abeta initiates deposition of amyloid in blood vessels in Tg2576 mice.

Cell type- and brain structure-specific patterns of distribution of minibrain kinase in human brain

The minibrain kinase (Mnb/Dyrk1A) gene is localized in the Down syndrome (DS) critical region of chromosome 21. This gene encodes a proline-directed serine/threonine protein kinase (minibrain kinase-Mnb/Dyrk1A), which is required for the proliferation of distinct neuronal cell types during postembryonic neurogenesis. To study the distribution of Mnb/Dyrk1A during human brain development and aging, we raised Mnb/Dyrk1A-specific antibody (mAb 7F3) and examined 22 brains of normal subjects from 8 months to 90 years of age. We found that neurons were the only cells showing the presence of 7F3-positive product in both cell nucleus and cytoplasm. Nuclear localization supports the concept that Mnb/Dyrk1A may be involved in control of gene expression. Synaptic localization of Mnb/Dyrk1A also supports our previous studies suggesting that Mnb/Dyrk1A is a regulator of assembly of endocytic apparatus and appears to be involved in synaptic vesicle recycling and synaptic signal transmission. Accumulation of numerous 7F3-positive corpora amylacea in the memory and motor system subdivisions in subjects older than 33 years of age indicates that Mnb/Dyrk1A is colocalized with markers of astrocyte and neuron degeneration. Differences in the topography and the amount of Mnb/Dyrk1A in neurons, astrocytes, and ependymal and endothelial cells appear to reflect cell type- and brain structure-specific patterns in trafficking and utilization of Mnb/Dyrk1A.

Cerebral amyloid angiopathy plays a direct role in the pathogenesis of Alzheimer’s disease

For the purposes of this debate here we argue the case that cerebral amyloid angiopathy (CAA) has a direct role in the pathogenesis of Alzheimer's disease (AD). Firstly, there is a very close relationship between CAA and AD and they share genetic risk factors. Secondly, we propose a specific mechanism which puts age-related cerebrovascular degeneration at a crucial point in the pathogenesis of AD as follows. Amyloid beta-protein (Abeta) is normally eliminated from the brain along with extracellular fluid by bulk flow along the perivascular pathway. Age-related fibrosis of cerebral cortical and meningeal arteries leads to impaired drainage of Abeta along the perivascular pathway and, together with the production of Abeta by smooth muscle cells and perivascular cells, is responsible for accumulation of Abeta as CAA. Reduced elimination leads to increased concentration of soluble Abeta in the extracellular fluid of the brain parenchyma. Increased concentration of soluble Abeta leads to the formation of insoluble Abeta plaques, other features of AD pathology, and dementia.

The effect of oxidative stress on accumulation of apolipoprotein E3 and E4 in a cell culture model of beta-amyloid angiopathy (CAA)

Apolipoprotein E (apoE) is a multifunctional molecule that is active during brain development, maintenance, and injury. Allele epsilon 4 of apoE is recognized as a risk factor for beta-amyloidosis, but the responsible mechanisms are not clear. Recently, we showed that vascular smooth muscle cells (SMCs) from epsilon 4/ epsilon 4 carriers are the most susceptible to oxidative protein damage that was associated with the appearance of apoE-Abeta-immunoreactive granules in cells. Here, we demonstrate that apoE4 is more readily accumulated in SMCs treated with ferrous ions than is apoE3. ApoE accumulated in lysosomes in the form of monomers, dimers, apoE-containing complexes, and apoE fragments. ApoE4 and apoE4-containing complexes persisted in SMCs longer than apoE3 and its complexes. Both isoforms of apoE stimulated formation of apoE-Abeta deposits and increased immobilization of iron in cultures treated with ferrous ions. The accumulation of apoE-Abeta deposits in lysosomes was associated with the appearance of lipid peroxidation products such as malondialdehyde and 4-hydroxynonenal-2-nonenal. The higher cellular accumulation of apoE4 than apoE3 in SMCs exposed to oxidative stress may facilitate development of beta-amyloid angiopathy that is more frequent in epsilon 4/ epsilon 4 carriers.

Secretion and accumulation of Abeta by brain vascular smooth muscle cells from AbetaPP-Swedish transgenic mice

Alzheimer amyloid-beta is deposited in the neuropil and in brain blood vessels in transgenic Tg2576 mice that overexpress human amyloid-beta precursor protein (AbetaPP) containing the Swedish mutation (AbetaPP-Swe). Because the AbetaPP transgene in Tg2576 mice is placed behind the PrP promoter, all amyloid-beta, including vascular amyloid, is considered to be of neuronal origin. We studied the expression of the transgenic AbetaPP in smooth muscle cells cultured from brain blood vessels from Tg2576 mice. We found that brain vascular smooth muscle cells overexpressed human AbetaPP-Swe approximately 4 times the physiological levels of mouse AbetaPP. The cultured cells secreted abundant Abeta1-40 and Abeta1-42 and formed intracellular Abeta-immunoreactive granules. The percentage of cells containing intracellular Abeta and the amount of intracellular Abeta were significantly higher in cultures obtained from 14-month-old than from 4-month-old mice, as tested on first or second passages. During cell senescence in culture, intracellular accumulation of Abeta and C-terminal fragments of AbetaPP increased in cells derived from both 4- and 14-month-old mice. Vascular muscle cells from Tg2576 mice appear to be a valuable model of the intracellular accumulation of Abeta. We suggest that vascular muscle cells may be involved in the production of cerebrovascular amyloid in Tg2576 mice.

TGFbeta1 enhances formation of cellular Abeta/apoE deposits in vascular myocytes

Brain injury increases the risk of Alzheimer's disease (AD) through unknown mechanisms. We studied deposition of amyloid-beta protein (Abeta) in cells exposed to transforming growth factor beta1 (TGFbeta1), a cytokine that regulates cell metabolism during brain injury, and apolipoproteinE (apoE), the major lipid transporter in the brain. The studies were conducted by using brain vascular smooth muscle cells that are engaged in beta-amyloidosis in vivo and produce Abeta in cell culture. We found that cell treatment with TGFbeta1 together with apoE4 strongly increased the amount of cellular Abeta. The intracellular Abeta co-localized with apoE but not with TGFbeta, similarly as in vascular beta-amyloid. Some cellular Abeta/apoE deposits increased in size and persisted in culture even after the TGFbeta1 and apoE4 were removed. The appearance of cellular deposits of Abeta was associated with increased production of the amyloid-beta precursor protein and cellular retention of its mature form. The results suggest that the concomitant presence of apoE and TGFbeta1 can trigger vascular beta-amyloidosis by inducing intracellular formation of stable Abeta/apoE deposits.

Oxidative protein damage in cells engaged in beta-amyloidosis is related to apoE genotype

The epsilon4 allele of apolipoprotein E (apoE) is a risk factor for Alzheimer's disease. The reduced antioxidant defense in epsilon4 carriers is suggested to contribute to beta-amyloidosis. We found that oxidative stress induced by treatment with Fe2+ ions raised more protein carbonyls in vascular smooth muscle cells isolated from human brains with apoE genotype epsilon4/epsilon4 than with 3epsilon/epsilon3 and epsilon3/epsilon4. Antioxidant vitamin E prevented formation of carbonyls but not in cells with genotype epsilon4/epsilon4. Treatment with Fe2+ ions induced cellular accumulation of amyloid-beta protein (Abeta)-immunoreactive material that co-localized with heme oxygenase, a marker of oxidative stress, and apoE. We hypothesize that the damage caused by oxidation in epsilon4/epsilon4 carriers facilitates development of beta-amyloidosis.

Deposition of Alzheimer's vascular amyloid-beta is associated with decreased expression of brain L-3-hydroxyacyl-coenzyme A dehydrogenase (ERAB)

L-3-hydroxyacyl-coenzyme A dehydrogenase type II (HADH) was described as an endoplasmic reticulum amyloid beta-peptide-binding protein (ERAB), which enhances Abeta toxicity, and accumulates in neurons in Alzheimer's disease (AD). Hence, HADH/ERAB was suggested to mediate the amyloid-induced neurodegeneration. We estimated the in vivo interactions of HADH and Abeta in an immunocytochemical study of ten Alzheimer's disease and seven normal brains using five monoclonal HADH-specific antibodies. We found no HADH in amyloid plaques or vascular amyloid. The neuronal expression of HADH was not correlated with the severity of amyloid load in neuropil. HADH was expressed in vascular smooth muscle cells in young and old controls and in amyloid-free blood vessels in AD cases, but little or no HADH was in smooth muscle cells in arteries with amyloid deposits. The putative intracellular interaction between HADH and Abeta in amyloid-producing cells was further studied in vascular smooth muscle cells isolated from brain blood vessels with amyloid-beta angiopathy - the cells that were shown previously to accumulate Abeta intracellularly ['Research advances in Alzheimer's disease and related disorders' (1995) 747; Brain Res. 676 (1995) 225; Neurosci. Lett. 183 (1995) 120]. HADH had a mitochondrial localization and did not co-localize with an endoplasmic reticulum marker. Cells that accumulated Abeta were those with low expression of HADH and the proteins did not co-localize. Explanation of the association between low levels of HADH and deposition of Abeta by brain smooth muscle cells requires further studies.

Role of perivascular cells and myocytes in vascular amyloidosis

Amyloidogenic processing of amyloid-beta precursor protein (APP) by cells of the brain is the major pathologic component of Alzheimer's disease. Amyloid-beta (A beta) is of heterogeneous origin. Perivascular cells of monocyte-macrophage-microglial cell lineage produce fibrillar A beta in the wall of capillaries, whereas parenchymal microglial cells produce fibrillar A beta in the parenchyma of gray matter. Fibrillar A beta deposition by perivascular cells lead to endothelial cell degeneration and death, obliteration of affected capillaries, and reduction of the length of the vascular network. These changes cause local ischemia with neuronal degeneration and death. Smooth muscle cells are the source of A beta in the tunica media of parenchymal and leptomeningeal arteries and veins. Fibrillar A beta in the tunica media of leptomeningeal and parenchymal vessels causes degeneration and necrosis of smooth muscle cells and leads to multiple cortical hemorrhages. Smooth muscle cells isolated from blood vessels with amyloid deposits secrete A beta and accumulate nonfibrillar A beta intracellularly. The amyloidogenic processing of APP can be enhanced by apolipoprotein E, reduced by transthyretin, and modulated by several cytokines.

Apolipoprotein E alters metabolism of AbetaPP in cells engaged in beta-amyloidosis

Canine smooth muscle cells (SMCs), cultured from amyloid-affected brain blood vessels accumulate Alzheimer amyloid-beta peptide (Abeta) intracellularly, either spontaneously or after treatment with apolipoprotein E (apoE). ApoE is codeposited with Abeta, which suggests that apoE participates in Abeta accumulation. We tested the hypothesis that apoE-induced accumulation of Abeta in SMCs is caused by an increased production of amyloid-beta precursor protein (AbetaPP) and/or its altered metabolism. We found that 24 hours of treatment with apoE3 or apoE4 induced intracellular accumulation of Abeta-immunoreactive deposits in SMCs but did not influence AbetaPP production and processing. The treatment with apoE3 or E4 for 3 days resulted in the following: increased Abeta-accumulation; reduced levels of secreted Abeta; increased production and cellular retention of mature AbetaPP770; and reduced culture growth, cell proliferation, and viability. ApoE4, but not apoE3, increased cellular levels of mRNA AbetaPP 770 (the main form produced in SMCs) about ninefold. ApoE3 stimulated production and cellular retention of endogenous apoE. We hypothesize that Abeta accumulation is triggered by apoE, which may bind and immobilize soluble Abeta produced in SMCs. The newly formed Abeta deposits may further accelerate Abeta accumulation by altering metabolism of AbetaPP.

Factors secreted by activated microglia and monocytes reduce amyloidogenesis in vascular smooth muscle cells

Smooth muscle cells cultured from amyloid-beta-affected arteries accumulate amyloid-beta peptide A beta. We now show that accumulation of "A beta" deposits in this model can be significantly reduced by culture in conditioned media from microglia and monocytes. Reduced A beta accumulation was associated with (i) lower secretion of A beta, (ii) increased secretion, but not cellular levels of amyloid-beta-precursor protein (A beta PP), and (iii) increased cell proliferation and metabolic activity. We suggest that improper regulation of A beta PP metabolism by monokines may facilitate vascular amyloidogenesis.

Factors produced by activated macrophages reduce accumulation of Alzheimer's beta-amyloid protein in vascular smooth muscle cells

Smooth muscle cells (SMCs) isolated from amyloid-angiopathy affected brain vessels accumulate intracellularly amyloid-beta peptide (A beta). Now we demonstrate that accumulation of A beta in SMCs can be reduced by factors secreted by macrophages - IL-1alpha, IL-6, TNF-alpha, TGF-beta1 or PGE2 - probably by stimulating the non-amyloidogenic processing of A beta precursor protein (PP). It is suggested that brain macrophages may regulate A betaPP/A beta metabolism under physiological conditions and prevent beta-amyloidosis. The disturbance of this regulatory function of brain macrophages may result in excessive production and accumulation of A beta.

Accumulation of Alzheimer amyloid-beta peptide in cultured myocytes is enhanced by serum and reduced by cerebrospinal fluid

Smooth muscle cells cultured from leptomeningeal vessels from old dogs with amyloid-angiopathy accumulate intracellular deposits that are immunoreactive for amyloid-beta peptide (A beta). We used this cellular model in the present study to examine the influence of sera and cerebrospinal fluid on intracellular accumulation of A beta-immunoreactive deposits and on secretion of soluble A beta into culture media. We found that sera from old dogs significantly increased the percentage of A beta-positive smooth muscle cells in culture. The enhanced accumulation of A beta was associated with (a) lower secretion of A beta into media, (b) altered maturation of amyloid-beta-precursor protein (A betaPP) into A betaPP751-770 with faster electrophoretic mobility, (c) increased accumulation of C-terminal fragments of A betaPP (12-15 kD, 10kD and less), and (d) increased secretion of A betaPP into culture media. These findings suggest that age- or disease-related serum factors increase accumulation of A beta by affecting production and processing of A betaPP In contrast, cerebrospinal fluids reduced accumulation of A beta. Involvement of A beta-carrier proteins-apolipoprotein E and transthyretin-in accumulation of A beta is demonstrated. Accumulation of A beta in cultured smooth muscle cells-a model of beta-amyloidosis-may be regulated by factors that alter production and processing of A betaPP as well as the fate of soluble A beta in extracellular space.

Apolipoproteins E3 and E4 induce, and transthyretin prevents accumulation of the Alzheimer's beta-amyloid peptide in cultured vascular smooth muscle cells

Cultured brain vascular smooth muscle cells (SMCs) accumulate beta-peptide in intracytoplasmic granules [9,10,33]. We show here that apoE3 and E4 induces the intracytoplasmic beta-peptide accumulation in cultured human and canine SMCs. The induction is dose-dependent and the accumulated granules also contain apoE and some were thioflavine S-positive. The deposits induced with apoE3 were more abundant though less stable than with apoE4. Transthyretin at physiological concentrations blocked the effects of apoE3/E4. Thus, accumulation of beta-peptide appears to be regulated by beta-peptide carrier proteins.

Secretion and accumulation of Alzheimer's beta-protein by cultured vascular smooth muscle cells from old and young dogs

Cultured smooth muscle cells isolated from beta-amyloid-affected blood vessels from old dogs accumulate beta-protein at early passages [5,24]. Now, we show that smooth muscle cells derived from amyloid-free brain blood vessels and peripheral arteries from old and young animals are induced by culture conditions to deposit intracellularly fibrillar and non-fibrillar beta-protein. Accumulation of beta-protein is associated with a higher secretion of beta-protein, but not with a higher secretion of beta-amyloid precursor protein (beta APP) or higher cellular content of beta APP. Gradual cessation of proliferative activity was observed in cultures that accumulate beta-protein.

In vitro production of beta-amyloid in smooth muscle cells isolated from amyloid angiopathy-affected vessels

Our recent results indicate that in Alzheimer's disease (AD) amyloid angiopathy, smooth muscle cells are responsible for beta-amyloid deposition in the vascular wall. Aged dogs have been shown to develop beta-amyloid angiopathy similar to that in AD. Thus, we used brain and peripheral vessels from aged and young dogs to isolate cells of the vascular wall: smooth muscle cells, fibroblasts, and endothelial cells, and to study their ability to produce beta-protein. We demonstrate that only myocytes from aged animals cultured for up to 4 weeks accumulate beta-protein-immunoreactive material intracellularly, in the form of fibrillar and amorphous deposits.

Non-fibrillar beta-amyloid protein is associated with smooth muscle cells of vessel walls in Alzheimer disease

Meningeal blood vessels were studied in Alzheimer disease (AD) and control brain specimens obtained from autopsies within 16 hours after death. Serial sections were stained with thioflavine S and Congo red and immunostained for the presence of beta-amyloid precursor protein (beta PP) and beta-protein and for smooth muscle-specific proteins myosin, alpha-actin, and desmin. Isolated blood vessels were studied by immunoblotting for the presence of beta PP, fragments of beta PP, and beta-protein. The arteries that were strongly immunopositive for beta-protein in all layers of the walls were also positive for amyloid fibrils on thioflavine S and Congo red stainings. The focal immunostaining for beta-protein in less affected vessels was located in the tunica media in the cytoplasm of smooth muscle cells or formed granules between myocytes. The cytoplasmic beta-protein and some of the small deposits present between cells were negative for amyloid fibrils. The vessels isolated from specimens containing beta-protein-immunoreactive material contained 3 kD, 4.2-4.5 kD, 8.5-9 kD, and 17.5 kD beta-protein-immunoreactive bands. These bands were not found in the samples assessed as beta-protein-negative by immunocytochemistry. These data indicate that during formation of amyloid in AD vessel walls, nonfibrillar, monomeric, and oligomeric beta-protein accumulate.

Ultrastructure of the microglia that phagocytose amyloid and the microglia that produce beta-amyloid fibrils

The function of microglia associated with beta-amyloid deposits still remains a controversial issue. On the basis of recent ultrastructural data, microglia were postulated to be cells that form amyloid fibrils, not phagocytes that remove amyloid deposits. In this electron microscopic study, we examined the ability of microglia to ingest and digest exogenous amyloid fibrils in vitro. We demonstrate that amyloid fibrils are ingested by cultured microglial cells and collected and stored in phagosomes. The ingested, nondegraded amyloid remains within phagosomes for up to 20 days, suggesting a very limited effectiveness of microglia in degrading beta-amyloid fibrils. On the other hand, we showed that in microglial cells of classical plaques in brain cortex of patients with Alzheimer's disease, amyloid fibrils appear first in altered endoplasmic reticulum and deep infoldings of cell membranes. These differences in intracellular distribution of amyloid fibrils in microglial cells support our observations that microglial cells associated with amyloid plaques are engaged in production of amyloid, but not in phagocytosis.

Acid alpha-naphthyl acetate esterase assay in murine lymphocytes

Acid alpha-naphthyl acetate esterase (ANAE) activity was assayed in cell homogenates and in intact cells by an endpoint colorimetric method, in which sodium dodecyl sulfate was used to stop the reaction. Each method of cell disruption and enzyme solubilization tested here caused a partial loss of the ANAE activity in lymphocyte preparations. The majority of the ANAE activity in lymphocytes was found to be membrane bound. The ANAE activity in thymocytes was over two times lower than that obtained for lymph node and spleen lymphocytes. Macrophages were found to contain about 18 times higher ANAE activity than mature lymphocytes.

Changes of dry mass of blood lymphocytes in the course of mouse estrous cycle and their dependence on the sexual steroid hormones

The dry mass of blood lymphocytes in female mice has been found to underline the variations according to the phases of estrous cycle. Ovariectomy caused disappearance of cyclic changes and reduced the mean dry mass of lymphocytes. Whereas estradiol was effective in restoration of the lymphocyte dry mass to the values characteristic for non-operated animals, progesterone failed to produce any noticeable effect. It is concluded that estradiol is responsible for the changes of lymphocyte dry mass observed during the successive phases of estrous cycle.