Expression of the protooncogene bcl-2 in Alzheimer's disease brain

The Connection between Chronic Liver Damage and Sporadic Alzheimer's Disease: Evidence and Insights from a Rat Model

Junk foods are typically low in essential nutrients, such as vitamins, minerals, and antioxidants. They are also loaded with trans fats and saturated fats, which can increase the level of triglycerides in the blood. High triglyceride levels can contribute to the development of non-alcoholic fatty liver disease (NAFLD), a condition where excess fat accumulates in the liver. A high intake of junk foods can lead to insulin resistance, a condition where the body's cells become less responsive to insulin. A diet lacking in nutrients and loaded with unwanted toxins can impair the liver's ability to detoxify harmful substances and damage its overall function. It is known that the regular consumption of junk food can be linked to memory impairment and cognitive decline. Several studies have shown that diets high in unhealthy fats, sugars, and processed foods can negatively impact brain health, including memory function. In this study, Wistar rats were used to model Late-Onset Alzheimer's Disease (LOAD), which was inspired by knowledge of the liver-brain axis's role in causing dementia. The model mimicked junk-food-induced liver-brain damage, and was developed by using the toxins d-galactosamine, ethanol and d-galactose. To begin with, the model rats demonstrated insulin resistance, a characteristic of LOAD patients. Glucose levels in both the brain and liver tissues were significantly elevated in the model, paralleling clinical findings in LOAD patients. High glucose levels in the brain lead to the increased production of advanced glycation end-products (AGEs), which, along with amyloid beta, harm neighbouring neurons. Histopathological analysis revealed deformed glial nodules, apoptotic neurons, and amyloid plaques in the brain section in the later stages of the disease. Simultaneously, the liver section displayed features of cirrhosis, including an effaced lobular architecture and the extravasation of red blood cells. Liver enzymes ALT, AST and ALP were consistently elevated with disease progression. Furthermore, immunohistochemistry confirmed the presence of amyloid precursor protein (APP) in the diseased brain. The positive expression of Hypoxia-Inducible Factor 3-Alpha (HIF3A) in the brain indicated hypoxic conditions, which is consistent with other LOAD studies. This model also exhibited damaged intestinal villi and excessive bowel and urinary incontinence, indicating malnutrition and a disturbed gut microbiome, which is also consistent with LOAD patients. Bioinformatics analysis on serum protein suggests a few affected molecular pathways, like the amyloid secretase pathway, androgen/oestrogen/progesterone biosynthesis, the apoptosis signalling pathway, the insulin/IGF pathway-protein kinase B signalling cascade, the Metabotropic glutamate receptor group I pathway, the Wnt signalling pathway, etc. Behavioural analysis confirmed memory decline and the loss of muscle strength with disease progression. Overall, this rat model of LOAD sheds valuable light on LOAD pathology and highlights the potential link between liver dysfunction, particularly induced by the excessive consumption of junk food, and LOAD. This study contributes to a deeper understanding of the complex molecular mechanisms involved in LOAD, paving the way for new possibilities in therapeutic interventions.

Posttreatment with Ospemifene Attenuates Hypoxia- and Ischemia-Induced Apoptosis in Primary Neuronal Cells via Selective Modulation of Estrogen Receptors

Stroke and perinatal asphyxia have detrimental effects on neuronal cells, causing millions of deaths worldwide each year. Since currently available therapies are insufficient, there is an urgent need for novel neuroprotective strategies to address the effects of cerebrovascular accidents. One such recent approach is based on the neuroprotective properties of estrogen receptors (ERs). However, activation of ERs by estrogens may contribute to the development of endometriosis or hormone-dependent cancers. Therefore, in this study, we utilized ospemifene, a novel selective estrogen receptor modulator (SERM) already used in dyspareunia treatment. Here, we demonstrated that posttreatment with ospemifene in primary neocortical cell cultures subjected to 18 h of hypoxia and/or ischemia followed by 6 h of reoxygenation has robust neuroprotective potential. Ospemifene partially reverses hypoxia- and ischemia-induced changes in LDH release, the degree of neurodegeneration, and metabolic activity. The mechanism of the neuroprotective actions of ospemifene involves the inhibition of apoptosis since the compound decreases caspase-3 overactivity during hypoxia and enhances mitochondrial membrane potential during ischemia. Moreover, in both models, ospemifene decreased the levels of the proapoptotic proteins BAX, FAS, FASL, and GSK3β while increasing the level of the antiapoptotic protein BCL2. Silencing of specific ERs showed that the neuroprotective actions of ospemifene are mediated mainly via ESR1 (during hypoxia and ischemia) and GPER1 (during hypoxia), which is supported by ospemifene-evoked increases in ESR1 protein levels in hypoxic and ischemic neurons. The results identify ospemifene as a promising neuroprotectant, which in the future may be used to treat injuries due to brain hypoxia/ischemia.

Cancer and Alzheimer's Inverse Correlation: an Immunogenetic Analysis

Numerous studies have demonstrated an inverse link between cancer and Alzheimer's disease (AD), with data suggesting that people with Alzheimer's have a decreased risk of cancer and vice versa. Although other studies have investigated mechanisms to explain this relationship, the connection between these two diseases remains largely unexplained. Processes seen in cancer, such as decreased apoptosis and increased cell proliferation, seem to be reversed in AD. Given the need for effective therapeutic strategies for AD, comparisons with cancer could yield valuable insights into the disease process and perhaps result in new treatments. Here, through a review of existing literature, we compared the expressions of genes involved in cell proliferation and apoptosis to establish a genetic basis for the reciprocal association between AD and cancer. We discuss an array of genes involved in the aforementioned processes, their relevance to both diseases, and how changes in those genes produce varying effects in either disease.

Amorfrutin B Protects Mouse Brain Neurons from Hypoxia/Ischemia by Inhibiting Apoptosis and Autophagy Processes Through Gene Methylation- and miRNA-Dependent Regulation

Amorfrutin B is a selective modulator of the PPARγ receptor, which has recently been identified as an effective neuroprotective compound that protects brain neurons from hypoxic and ischemic damage. Our study demonstrated for the first time that a 6-h delayed post-treatment with amorfrutin B prevented hypoxia/ischemia-induced neuronal apoptosis in terms of the loss of mitochondrial membrane potential, heterochromatin foci formation, and expression of specific genes and proteins. The expression of all studied apoptosis-related factors was decreased in response to amorfrutin B, both during hypoxia and ischemia, except for the expression of anti-apoptotic BCL2, which was increased. After post-treatment with amorfrutin B, the methylation rate of the pro-apoptotic Bax gene was inversely correlated with the protein level, which explained the decrease in the BAX/BCL2 ratio as a result of Bax hypermethylation. The mechanisms of the protective action of amorfrutin B also involved the inhibition of autophagy, as evidenced by diminished autophagolysosome formation and the loss of neuroprotective properties of amorfrutin B after the silencing of Becn1 and/or Atg7. Although post-treatment with amorfrutin B reduced the expression levels of Becn1, Nup62, and Ambra1 during hypoxia, it stimulated Atg5 and the protein levels of MAP1LC3B and AMBRA1 during ischemia, supporting the ambiguous role of autophagy in the development of brain pathologies. Furthermore, amorfrutin B affected the expression levels of apoptosis-focused and autophagy-related miRNAs, and many of these miRNAs were oppositely regulated by amorfrutin B and hypoxia/ischemia. The results strongly support the position of amorfrutin B among the most promising anti-stroke and wide-window therapeutics.

Systematic review of human post-mortem immunohistochemical studies and bioinformatics analyses unveil the complexity of astrocyte reaction in Alzheimer's disease

AIMS

Reactive astrocytes in Alzheimer's disease (AD) have traditionally been demonstrated by increased glial fibrillary acidic protein (GFAP) immunoreactivity; however, astrocyte reaction is a complex and heterogeneous phenomenon involving multiple astrocyte functions beyond cytoskeletal remodelling. To better understand astrocyte reaction in AD, we conducted a systematic review of astrocyte immunohistochemical studies in post-mortem AD brains followed by bioinformatics analyses on the extracted reactive astrocyte markers.

METHODS

NCBI PubMed, APA PsycInfo and WoS-SCIE databases were interrogated for original English research articles with the search terms 'Alzheimer's disease' AND 'astrocytes.' Bioinformatics analyses included protein-protein interaction network analysis, pathway enrichment, and transcription factor enrichment, as well as comparison with public human -omics datasets.

RESULTS

A total of 306 articles meeting eligibility criteria rendered 196 proteins, most of which were reported to be upregulated in AD vs control brains. Besides cytoskeletal remodelling (e.g., GFAP), bioinformatics analyses revealed a wide range of functional alterations including neuroinflammation (e.g., IL6, MAPK1/3/8 and TNF), oxidative stress and antioxidant defence (e.g., MT1A/2A, NFE2L2, NOS1/2/3, PRDX6 and SOD1/2), lipid metabolism (e.g., APOE, CLU and LRP1), proteostasis (e.g., cathepsins, CRYAB and HSPB1/2/6/8), extracellular matrix organisation (e.g., CD44, MMP1/3 and SERPINA3), and neurotransmission (e.g., CHRNA7, GABA, GLUL, GRM5, MAOB and SLC1A2), among others. CTCF and ESR1 emerged as potential transcription factors driving these changes. Comparison with published -omics datasets validated our results, demonstrating a significant overlap with reported transcriptomic and proteomic changes in AD brains and/or CSF.

CONCLUSIONS

Our systematic review of the neuropathological literature reveals the complexity of AD reactive astrogliosis. We have shared these findings as an online resource available at www.astrocyteatlas.org.

The role of Bcl-2 proteins in modulating neuronal Ca2+ signaling in health and in Alzheimer's disease

The family of B-cell lymphoma-2 (Bcl-2) proteins exerts key functions in cellular health. Bcl-2 primarily acts in mitochondria where it controls the initiation of apoptosis. However, during the last decades, it has become clear that this family of proteins is also involved in controlling intracellular Ca²⁺ signaling, a critical process for the function of most cell types, including neurons. Several anti- and pro-apoptotic Bcl-2 family members are expressed in neurons and impact neuronal function. Importantly, expression levels of neuronal Bcl-2 proteins are affected by age. In this review, we focus on the emerging roles of Bcl-2 proteins in neuronal cells. Specifically, we discuss how their dysregulation contributes to the onset, development, and progression of neurodegeneration in the context of Alzheimer's disease (AD). Aberrant Ca²⁺ signaling plays an important role in the pathogenesis of AD, and we propose that dysregulation of the Bcl-2-Ca²⁺ signaling axis may contribute to the progression of AD and that herein, Bcl-2 may constitute a potential therapeutic target for the treatment of AD.

Selective Targeting of Non-nuclear Estrogen Receptors with PaPE-1 as a New Treatment Strategy for Alzheimer's Disease

Alzheimer’s disease (AD) is a multifactorial and severe neurodegenerative disorder characterized by progressive memory decline, the presence of Aβ plaques and tau tangles, brain atrophy, and neuronal loss. Available therapies provide moderate symptomatic relief but do not alter disease progression. This study demonstrated that PaPE-1, which has been designed to selectively activate non-nuclear estrogen receptors (ERs), has anti-AD capacity, as evidenced in a cellular model of the disease. In this model, the treatment of mouse neocortical neurons with Aβ (5 and 10 μM) induced apoptosis (loss of mitochondrial membrane potential, activation of caspase-3, induction of apoptosis-related genes and proteins) accompanied by increases in levels of reactive oxygen species (ROS) and lactate dehydrogenase (LDH) as well as reduced cell viability. Following 24 h of exposure, PaPE-1 inhibited Aβ-evoked effects, as shown by reduced parameters of neurotoxicity, oxidative stress, and apoptosis. Because PaPE-1 downregulated Aβ-induced Fas/FAS expression but upregulated that of Aβ-induced FasL, the role of PaPE-1 in controlling the external apoptotic pathway is controversial. However, PaPE-1 normalized Aβ-induced loss of mitochondrial membrane potential and restored the BAX/BCL2 ratio, suggesting that the anti-AD capacity of PaPE-1 particularly relies on inhibition of the mitochondrial apoptotic pathway. These data provide new evidence for an anti-AD strategy that utilizes the selective targeting of non-nuclear ERs with PaPE-1.

Mitochondria and cell bioenergetics: increasingly recognized components and a possible etiologic cause of Alzheimer's disease

SIGNIFICANCE

Mitochondria and brain bioenergetics are increasingly thought to play an important role in Alzheimer's disease (AD).

RECENT ADVANCES

Data that support this view are discussed from the perspective of the amyloid cascade hypothesis, which assumes beta-amyloid perturbs mitochondrial function, and from an opposite perspective that assumes mitochondrial dysfunction promotes brain amyloidosis. A detailed review of cytoplasmic hybrid (cybrid) studies, which argue mitochondrial DNA (mtDNA) contributes to sporadic AD, is provided. Recent AD endophenotype data that further suggest an mtDNA contribution are also summarized.

CRITICAL ISSUES AND FUTURE DIRECTIONS

Biochemical, molecular, cybrid, biomarker, and clinical data pertinent to the mitochondria-bioenergetics-AD nexus are synthesized and the mitochondrial cascade hypothesis, which represents a mitochondria-centric attempt to conceptualize sporadic AD, is discussed.

Alzheimer's disease: pathological mechanisms and the beneficial role of melatonin

Alzheimer's disease (AD) is a highly complex neurodegenerative disorder of the aged that has multiple factors which contribute to its etiology in terms of initiation and progression. This review summarizes these diverse aspects of this form of dementia. Several hypotheses, often with overlapping features, have been formulated to explain this debilitating condition. Perhaps the best-known hypothesis to explain AD is that which involves the role of the accumulation of amyloid-β peptide in the brain. Other theories that have been invoked to explain AD and summarized in this review include the cholinergic hypothesis, the role of neuroinflammation, the calcium hypothesis, the insulin resistance hypothesis, and the association of AD with peroxidation of brain lipids. In addition to summarizing each of the theories that have been used to explain the structural neural changes and the pathophysiology of AD, the potential role of melatonin in influencing each of the theoretical processes involved is discussed. Melatonin is an endogenously produced and multifunctioning molecule that could theoretically intervene at any of a number of sites to abate the changes associated with the development of AD. Production of this indoleamine diminishes with increasing age, coincident with the onset of AD. In addition to its potent antioxidant and anti-inflammatory activities, melatonin has a multitude of other functions that could assist in explaining each of the hypotheses summarized above. The intent of this review is to stimulate interest in melatonin as a potentially useful agent in attenuating and/or delaying AD.

Differential response of apoptosis-regulatory Bcl-2 and Bax proteins to an inflammatory challenge in the cerebral cortex and hippocampus of aging mice

Apoptosis plays a key role in normal aging and neurodegeneration. It is now known that normal aging implies low-grade inflammation and increases susceptibility to neurodegenerative diseases, which, in turn, include a neuroinflammatory component. We here investigated, using mice of 2-3 months, 10-11 months, or 18-21 months of age, the expression of apoptosis-regulatory proteins in cortical brain regions in response to intracerebroventricular administration of pro-inflammatory cytokines. A mixture of interferon-gamma and tumor necrosis factor-alpha was injected, using vehicle (phosphate-buffered saline) as control. At 4 days, levels of the anti-apoptotic Bcl-2 and pro-apoptotic Bax proteins in the cerebral cortex and hippocampus, examined with Western blotting, were markedly upregulated by cytokine exposure in mice of all age groups with respect to controls. Interestingly, cytokine-elicited Bcl-2 upregulation was aging-dependent, with significant enhancement paralleling the animals' age. Cytokine-elicited Bax expression did not exhibit instead significant aging-related variation. Using the same paradigm and 1 or 2 day survival, Bcl-2 immunoreactivity was observed mainly in neurons of cortex and hippocampus of both control and cytokine-treated mice of all age groups. Furthermore, immunohistochemistry confirmed the enhancement of cytokine-elicited Bcl-2 expression in the cerebral cortex and hippocampus of old mice, and showed that this finding was already evident in the second day after cytokine exposure. The data point out the novel finding that Bcl-2 and Bax expression in cortical brain regions is differentially regulated during senescence in response to an acute inflammatory challenge. Aging-related Bcl-2 increases in neurons after cytokine exposure could contribute to amplify neuroprotective mechanisms in the old brain.

Up-regulation of Bcl-2 in APP transgenic mice is associated with neuroprotection

Abeta-induced neurodegeneration is limited in APP and APP+PS1 transgenic mice. In middle-aged APP + PS1 transgenic mice, we found significantly increased Bcl-2 expression. The increase in Bcl-2 is restricted to amyloid-containing brain regions and is not found at young ages, suggesting that Abeta deposition is the stimulus for increased Bcl-2. Western blot results were confirmed with immunohistochemistry and qRT-PCR. In addition, we found that APP transgenic mice were protected from neurotoxicity caused by an injection of bak BH3 fusion peptides, known to induce apoptosis by antagonizing bcl protein activity. Nissl and fluorojade-stained slides showed that the active bak BH3 peptide caused substantial neuronal loss in the dentate gyrus and CA3 regions of nontransgenic, but not APP mice. The inactive mutant bak BH3 peptide did not cause degeneration in any mice. These data demonstrate that the increased Bcl-2 expression in brain regions containing Abeta deposits is associated with neuroprotection.

Regionally specific changes in levels of cortical S100beta in bipolar 1 disorder but not schizophrenia

OBJECTIVE

To determine if levels of the glial-derived proteins S100beta and glial acidic fibrillary protein (GFAP) and the pro- and antiapoptotic proteins p53 and Bcl-2 were altered in the cortex of subjects with schizophrenia or bipolar 1 disorder.

METHOD

Levels of S100beta, GFAP, p53 and Bcl-2 were measured in cortex (Brodmann's Areas (BAs) 9, 10, 46 and 40) of control subjects and subjects with schizophrenia, bipolar 1 disorder and in the cortex of rats treated with haloperidol or lithium using protein-specific antibodies and western blot analysis.

RESULTS

Levels of S100beta were decreased in BA 9 and increased in BA 40 from subjects with bipolar 1 disorder. Levels of this protein were not altered in other CNS regions, in schizophrenia or in the cortex of rats treated with haloperidol or lithium. No changes in levels of the other three proteins were detected across diagnoses.

CONCLUSIONS

Regionally selective changes in cortical S100beta may be associated with the pathology of bipolar 1 disorder and may reflect derangements in neuronal death or survival.

Reactive astrocytes express bis, a bcl-2-binding protein, after transient forebrain ischemia

Bis (also called Bag-3), identified as a novel Bcl-2-interacting protein, has been shown to enhance anti-cell death activity of Bcl-2. Because ischemia/reperfusion induces expression of Bcl-2, we examined the changes in the pattern of Bis expression in the adult rat hippocampus after transient forebrain ischemia. Western blot analysis with protein extracts from the hippocampus showed that, compared with controls, levels of Bis were markedly increased seven days after ischemia. An immunohistochemical study showed that the expression of Bis increased preferentially in the CA1 and the dentate hilar regions, and peaked at 3-7 days after reperfusion. The temporal and spatial patterns of expression for both Bis and glial fibrillary acidic protein (GFAP) were very similar, and double immunofluorescence histochemistry showed that Bis was expressed in reactive astrocytes, which express GFAP. Immunolabeling of adjacent sections with anti-Bcl-2 and anti-Hsp70 antibodies revealed that the pattern of Bis expression closely correlates with that of Bcl-2, but clearly differs from that of Hsp70. Coexpression of Bis and Bcl-2 in reactive astrocytes was confirmed by double immunofluorescence histochemistry. Our results demonstrate that reactive astrocytes transiently up-regulate Bis after ischemia/reperfusion in the adult rat hippocampus. However, the precise role of Bis in the astrocytic response to ischemia/reperfusion in relation to Bcl-2 remains to be determined.

Neuronal cell death in Down's syndrome

Down's syndrome (DS), occurring in 0.8 out of 1,000 live births, is a genetic disorder in which an extra portion of chromosome 21 leads to several abnormalities. With respect to the nervous system, it causes mental retardation. It is conceived that abnormal neuronal cell death in development is involved, but there is no direct evidence yet. In addition to developmental brain abnormalities, almost all DS brains over 40 years old manifest a similar pathology to Alzheimer's disease (AD), including the presence of senile plaques (SP) and neurofibrillary tangles (NFT). Although there was a debate to segregate dementia from underlying mental retardation, at least some portion of DS patients exhibit deteriorated mental status with aging. The mechanism underlying these abnormalities at the molecular level remains to be elucidated. Recently there have been several reports suggesting abnormalities reflecting increased risk to apoptosis in DS brains. Increased expression of several apoptosis-related genes (p53, fas, ratio of bax to bcl-2, GAPDH) in DS brains has been reported. Cultured neurons from both patients and model animals are reportedly more vulnerable to apoptosis. Overproduction of reactive oxygen species and its causative roles for increased apoptosis in DS tissues are suggested. One possible hypothesis is an increased susceptibility to apoptosis due to p53 overactivation in DS brains. A beta 42, a critical peptide for AD pathology from amyloid precursor protein (APP), can be detected in DS brains. A beta 42 is deposited in SP from an early stage, suggesting common molecular mechanisms in DS and AD. Animal models for DS are important in the search of molecular mechanisms. Several types of models are now available. Future DS studies are expected to integrate information from animal models and human tissues.

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

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

Temporal profile of apoptotic-like changes in neurons and astrocytes following controlled cortical impact injury in the rat

Apoptotic cell death has been observed in both neurodegenerative diseases and acute neurological traumas such as ischemia, spinal cord injury, and traumatic brain injury (TBI). Recent studies employing different models of TBI have described morphological and biochemical changes characteristic of apoptosis following injury. However, no study has examined the temporal profile of apoptosis following controlled cortical impact (CCI) injury in the rat. In addition, the relative frequency of apoptotic profiles in different cell types (neurons versus glia) following CCI has yet to be investigated. In the present experiments, injured cortex was subjected to DNA electrophoresis, and serial sections from the contusion area were stained with hematoxylin and eosin or Hoechst 33258 or double-labeled with TUNEL and neuronal or glial markers. The results of the present study indicate that CCI produces a substantial amount of DNA damage associated with both apoptotic-like and necrotic-like cell death phenotypes primarily at the site of cortical impact and focal contusion. DNA damage, as measured by TUNEL and DNA electrophoresis, was most apparent 1 day following injury and absent by 14 days post-TBI. However, quantitative analysis showed that the majority of TUNEL-positive cells failed to exhibit apoptotic-like morphology and were probably undergoing necrosis. In addition, apoptotic-like morphology was predominantly observed in neurons compared to astrocytes. The present study provides further evidence that apoptosis is involved in the pathology of TBI and could contribute to some of the ensuing cell death following injury.

Bcl-2 and Bax protein expression in neurofibrillary tangles in progressive supranuclear palsy

Double-labeling immunohistochemistry to Bcl-2 and Bax and to tau protein was examined in the brains of patients with progressive supranuclear palsy (PSP) to study the possible relationship between the expression of Bax and Bcl-2 proteins and neurofibrillary tangle formation. No differences between Bcl-2 and Bax immunoreactivity in neurons of the brain stem were observed in PSP patients and controls. Moreover, the intensity of Bcl-2 and Bax immunoreactivity was similar in tangle-bearing and non-tangle-bearing neurons in PSP patients. These results suggest that Bcl-2 and Bax are probably not implicated in neurofibrillary tangle formation in PSP.

Alzheimer's disease and brain development: common molecular pathways

Research on the causes and treatments of Alzheimer's disease (AD) has led investigators down numerous avenues. Although many models have been proposed, no single model of AD satisfactorily accounts for all neuropathologic findings as well as the requirement of aging for disease onset. The mechanisms of disease progression are equally unclear. We hypothesize that alternative gene expression during AD plays a critical role in disease progression. Numerous developmentally regulated genes and cell cycle proteins have been shown to be re-expressed or activated during AD. These proteins include transcription factors, members of the cell cycle regulatory machinery, and programmed cell death genes. Such proteins play an important role during brain development and would likely exert powerful effects if re-expressed in the adult brain. We propose that the re-expression or activation of developmentally regulated genes define molecular mechanisms active both during brain development and in AD.

Alteration of proteins regulating apoptosis, Bcl-2, Bcl-x, Bax, Bak, Bad, ICH-1 and CPP32, in Alzheimer's disease

Recently, apoptosis has been implicated in the selective neuronal loss of Alzheimer's disease (AD). Apoptosis is regulated by the B cell leukemia-2 gene product (Bcl-2) family (Bcl-2, Bcl-x, Bax, Bak and Bad) and the caspase family (ICH-1 and CPP32), with apoptosis being prevented by Bcl-2 and Bcl-x, and promoted by Bax, Bak, Bad, ICH-1 and CPP32. In the present study, we examined the levels of these proteins in the membranous and cytosolic fractions of temporal cortex in AD and control brain. In the membranous fraction, the levels of Bcl-2 alpha, Bcl-xL, Bcl-x beta, Bak and Bad were increased in AD. In the cytosolic fractions, the level of Bcl-x beta was increased, while Bcl-xL, Bax, Bak, and Bad and ICH-1L were unchanged. CPP32 was not detected in AD or control brain. These findings demonstrate a differential involvement of cell death-regulatory proteins in AD and suggest that Bak, Bad, Bcl-2 and Bcl-x are upregulated in AD brains.

Apoptosis decision cascades and neuronal degeneration in Alzheimer's disease

An important and unique characteristic of neurons is that they are nondividing and irreplaceable. The decisions, then, to engage and execute the apoptotic program are most serious. One of the most surprising new findings in AD brain pathology to date is the large number of neurons affected by DNA damage, even early in the disease process. This may be due to the pressure of chronic apoptotic stressors and the induction of factors which protect the cells from terminal apoptosis. It is possible that Bcl-2, Ref-1, and other such factors may act as apoptotic check points. Thus, there may exist a dynamic and extended competitive decision-making process between cell death processes and compensatory responses in the AD brain, forming a type of neuronal apoptosis decision cascade.

Characterization of the AD7C-NTP cDNA expression in Alzheimer's disease and measurement of a 41-kD protein in cerebrospinal fluid

We have isolated a novel Alu sequence-containing cDNA, designated AD7c-NTP, that is expressed in neurons, and overexpressed in brains with Alzheimer's disease (AD). The 1,442-nucleotide AD7c-NTP cDNA encodes an approximately 41-kD protein. Expression of AD7c-NTP was confirmed by nucleic acid sequencing of reverse transcriptase PCR products isolated from brain. AD7c-NTP cDNA probes hybridized with 1. 4 kB mRNA transcripts by Northern blot analysis, and monoclonal antibodies generated with the recombinant protein were immunoreactive with approximately 41-45-kD and approximately 18-21-kD molecules by Western blot analysis. In situ hybridization and immunostaining studies localized AD7c-NTP gene expression in neurons. Using a quantitative enzyme-linked sandwich immunoassay (Ghanbari, K., I. Beheshti, and H. Ghanbari, manuscript submitted for publication) constructed with antibodies to the recombinant protein, AD7c-NTP levels were measured under code in 323 clinical and postmortem cerebrospinal fluid (CSF) samples from AD, age-matched control, Parkinson's disease, and neurological disease control patients. The molecular mass of the AD7c-NTP detected in CSF was approximately 41 kD. In postmortem CSF, the mean concentration of AD7c-NTP in cases of definite AD (9.2+/-8.2 ng/ml) was higher than in the aged control group (1.6+/-0.9; P < 0.0001). In CSF samples from individuals with early possible or probable AD, the mean concentration of AD7c-NTP (4.6+/-3.4) was also elevated relative to the levels in CSF from age-matched (1.2+/-0.7) and neurological disease (1.0+/-0.9) controls, and ambulatory patients with Parkinson's disease (1.8+/-1.1) (all P < 0.001). CSF levels of AD7c-NTP were correlated with Blessed dementia scale scores (r = 0. 66; P = 0.0001) rather than age (r = -0.06; P > 0.1). In vitro studies demonstrated that overexpression of AD7c-NTP in transfected neuronal cells promotes neuritic sprouting and cell death, the two principal neuroanatomical lesions correlated with dementia in AD. The results suggest that abnormal AD7c-NTP expression is associated with AD neurodegeneration, and during the early stages of disease, CSF levels correlate with the severity of dementia.

Apoptosis-related protein expression in the hippocampus in Alzheimer's disease

Recent research indicates that apoptotic mechanisms may be involved in cell death in Alzheimer's disease (AD). We studied the expression of three members of the Bcl-2 protein family, Bcl-2, Bcl-x, and Bax, in a selection of senile and DS-related AD patients as well as in controls. These proteins are all associated with apoptotic mechanisms. In contrast to previous reports, neuronal Bcl-2 labeling was not detected in our cases, although there was some weak and inconsistent glial cell labeling. Neuronal Bcl-x expression was virtually absent in controls and the presence of the protein in AD patients was neither consistent nor specific. Some reactive glial cells were strongly labeled with the Bcl-x antibody. In contrast Bax, a protein that is believed to promote apoptosis, was widely expressed by neurones but was mainly present in areas other than CA1 in the hippocampus. Neuritic elements of some senile plaques were clearly and strongly labeled with this antibody, whereas neurofibrillary tangles and neuropil threads were not. Double labeling studies indicated that AT8-positive cells and neurites were never Bax-positive and vice versa. The possible implications of the different expression patterns are discussed in relation to neurone death in AD.

Aberrant expression of bcl-2 gene family in Down's syndrome brains

Down's syndrome (DS) patient brains are known to develop prematurely the same degenerative changes as those seen in Alzheimer's disease (AD). On the assumption that the apoptotic mechanism is involved in the neuronal loss in DS, we have investigated the expression of the bcl-2 gene family in DS brains and found marked alterations. The most prominent changes were in the temporal lobes where neuronal loss was greatest. Our findings suggest that a apoptotic process is involved in the neuronal loss in DS.

Apoptosis, neurotrophic factors and neurodegeneration

Apoptosis is an active process of cell death characterized by distinct morphological features, and is often the end result of a genetic programme of events, i.e. programmed cell death (PCD). There is growing evidence supporting a role for apoptosis in some neurodegenerative diseases. This conclusion is based on DNA fragmentation studies and findings of increased levels of pro-apoptotic genes in human brain and in in vivo and in vitro model systems. Additionally, there is some evidence for a loss of neurotrophin support in neurodegenerative diseases. In Alzheimer's disease, in particular, there is strong evidence from human brain studies, transgenic models and in vitro models to suggest that the mode of nerve cell death is apoptotic. In this review we describe the evidence implicating apoptosis in neurodegenerative diseases with a particular emphasis on Alzheimer's disease.

Bax expression in mammalian neurons undergoing apoptosis, and in Alzheimer's disease hippocampus

Recent studies indicate that the proto-oncogene Bax, and other related proteins (eg Bcl-2) may play a major role in determining whether cells will undergo apoptosis under conditions which promote cell death. Increased expression of Bax has been found to promote apoptosis, while over-expression of Bcl-2 can inhibit apoptosis. To investigate the role of Bax in nerve cell death in the rat brain we examined the level of Bax expression in cells undergoing apoptosis, using a hypoxic-ischemic stroke model. We found that Bax was expressed at high levels in the nuclei of neurons in the hippocampus, cortex, cerebellum, and striatum on the control side, and that Bax levels increased in hippocampal neurons undergoing apoptosis on the stroke side, and then declined (correlating with cell loss). In the Alzheimer's disease hippocampi we found a concentrated localisation of Bax in senile plaques, which correlated with the localisation of beta-amyloid protein in adjacent sections from the same brains. beta-Amyloid positive plaques are thought to contribute to the Alzheimer's disease process, possibly via an apoptotic mechanism, and this may occur via an increase in Bax in these areas. Bax was also strongly stained in tau-positive tangles in Alzheimer's disease hippocampi, suggesting Bax may play a role in tangle formation. In addition, we observed a loss of Bax expression in the dentate granule cells of Alzheimer's disease hippocampi compared with moderate Bax expression in control hippocampi, and this loss may be related to the survival of these neurons in Alzheimer's disease. Finally, we observed substantially different staining patterns of Bax using three different commercially available antisera to Bax, indicating the need for caution when interpreting results in this area.

Mechanisms of cell death in Alzheimer's disease

The etiology of Alzheimer's disease (AD) as well as its exact pathogenesis are unknown. Eventhough the deposition of beta A4 and the formation of neurofibrillary tangles represent impressive morphological hallmarks of the disease, several lines of evidence suggest that both lesions are not sufficient as causes of the neurodegenerative process. On the other hand, in vitro studies have shown that beta A4 is neurotoxic and is able to induce apoptotic cell death in neuronal cell cultures. Cells dying by apoptosis (programmed cell death) can be visualized in the tissue with a molecular biologic technique detecting fragmented nuclear DNA. Using this method, we have detected 50 x more neurons and 25 x more glial cells with nuclear DNA fragmentation in the brains of patients with AD than in non-demented controls. In contrast to previous studies, most of these cells did not reveal the characteristic morphological hallmarks of apoptosis. Most dying cells were not located within amyloid deposits and most dying cells did not bear a tangle. On the other hand, being in physical contact with an amyloid deposit increased the risk of a cell to dye by factor 5.7 and carrying a neurofibrillary tangle imposed a 3 times higher risk compared to unaffected nerve cells. Taken together, these data indicate that nerve cell death in AD occurs via a mechanism of programmed cell death different from classical apoptosis. Eventhough plaques and tangles increase the risk of cells to degenerate, both lesions are not the sole responsibles of the degenerative process, suggesting the existence of other factors that trigger the initiation of the cell death program in AD.