Participation of presenilin 2 in apoptosis: enhanced basal activity conferred by an Alzheimer mutation

Ascorbic acid attenuates gasoline-induced testicular toxicity, sperm quality deterioration, and testosterone imbalance in rats

The present study evaluated the protective effect of ascorbic acid (ASCB) against gasoline fumes (PET) induced testicular oxidative stress, sperm toxicity, and testosterone imbalance in Wistar rats. Twenty-four (24) male albino rats (75 ± 16 g) were randomized into three experimental groups (N = 8). The control group: received normal saline, PET group: exposed to PET 6 h daily by inhalation in an exposure chamber and PET + 200 mg ASCB/kg body weight group: exposed to PET 6 h daily by inhalation and administered ASCB per os. Treatment of ASCB and PET exposure was done thrice and five times weekly for a period of 10 weeks respectively. ASCB co-treatment prevented PET-induced increases in the oxidative stress markers (glutathione, glutathione S-transferase, superoxide dismutase, catalase, hydrogen peroxide generation, nitric oxide, and lipid peroxidation) and serum testosterone concentration (p < .05). Sperm quality was low and those with damaged heads and tails increased alongside histological injuries in the PET-exposed rats, which were also minimized with ASCB administration. ASCB protected against PET-induced oxidative stress, sperm, and testis damage in rats.

Combined Protective Effects of Quercetin, Rutin, and Gallic Acid against Cadmium-Induced Testicular Damages in Young-Adult Rats

Cadmium (Cd) is a toxic metal that damages several tissues of animals and humans including the testis. The ameliorative effects of quercetin (QUE), rutin (RUT), and gallic acid (GAL) at 20 mg kg-1 body weight alone or in combination against testicular injury induced by Cd (24 mg kg-1 body weight) in male Wistar rats were evaluated in this study. Forty-two (42) rats were randomly grouped into six (6) groups: (1) vehicle control group, (2) Cd group, (3) RUT+Cd group, (4) GAL+Cd group, (5) QUE+Cd group, and (6) RUT+GAL+QUE+Cd group. At the end of the oral gavage of the tested chemicals, the rats were sacrificed, blood samples were collected, and testes were harvested and processed for biochemical assays. Cd exposure damaged the testis (smaller epithelium thickness and spermatogenesis index and sloughing of the epithelium); increased lipid peroxidation, glutathione S-transferase activity, and DNA fragmentation; and diminished glutathione reductase activity and serum testosterone level 40 days posttreatment. Treatment with the phenolics separately or in combination attenuated the effect of Cd on serum testosterone, glutathione reductase and glutathione S-transferase activities, lipid peroxidation, and percent fragmented DNA. The increased nitric oxide concentration in the QUE+Cd group was attenuated to control values in the combined (RUT+GAL+QUE+Cd) exposure group. Coadministration of the phenolics appears to have more substantial protective effects than their single effects against Cd-induced testicular DNA damage, glutathione S-transferase activity, and the recovery of testosterone levels and spermatogenesis index. Overall, the tested phenolics can reduce testicular damage more efficiently in their combined form than individual administration.

PSEN2 and ABCA7 variants causing early-onset preclinical pathological changes in Alzheimer's disease: a case report and literature review

BACKGROUND

Alzheimer's disease (AD) is a debilitating and highly heritable neurodegenerative disease. Early-onset AD (EOAD) was defined as AD occurring before age 65. Although it has a high genetic risk, EOAD due to PSEN2 variation is very rare. ABCA7 is an important risk gene for AD. Previously reported cases mainly carried variations in a single pathogenic or risk gene. METHODS AND RESULTS: In this study, we report a 35-year-old female carrying variants in both the PSEN2 gene (c.640G > T p.V214L) and ABCA7 gene (c.2848G > A p.V950M). Four previously reported cases carried PSEN2 V214L, and no reported cases carried ABCA7 V950M. She had a history of migraine, patent foramen ovale, spontaneous subarachnoid hemorrhage without aneurysm, and multiple cerebral microhemorrhages. Her MMSE score was 24/30, and her MoCA score was 22/30. The concentration of Aβ42 and the ratio of Aβ42 to Aβ40 in cerebral spinal fluid were obviously decreased. Published variants of PSEN2 and ABCA7 in PubMed were reviewed, and the patients' characteristics were summarized and compared to provide information for the clinical diagnosis of AD.

CONCLUSIONS

It is necessary to conduct genetic screening in cases with atypical manifestations.

The cellular model for Alzheimer's disease research: PC12 cells

Alzheimer's disease (AD) is a common age-related neurodegenerative disease characterized by progressive cognitive decline and irreversible memory impairment. Currently, several studies have failed to fully elucidate AD's cellular and molecular mechanisms. For this purpose, research on related cellular models may propose potential predictive models for the drug development of AD. Therefore, many cells characterized by neuronal properties are widely used to mimic the pathological process of AD, such as PC12, SH-SY5Y, and N2a, especially the PC12 pheochromocytoma cell line. Thus, this review covers the most systematic essay that used PC12 cells to study AD. We depict the cellular source, culture condition, differentiation methods, transfection methods, drugs inducing AD, general approaches (evaluation methods and metrics), and in vitro cellular models used in parallel with PC12 cells.

The dark side of Alzheimer's disease: unstructured biology of proteins from the amyloid cascade signaling pathway

Alzheimer's disease (AD) is a leading cause of age-related dementia worldwide. Despite more than a century of intensive research, we are not anywhere near the discovery of a cure for this disease or a way to prevent its progression. Among the various molecular mechanisms proposed for the description of the pathogenesis and progression of AD, the amyloid cascade hypothesis, according to which accumulation of a product of amyloid precursor protein (APP) cleavage, amyloid β (Aβ) peptide, induces pathological changes in the brain observed in AD, occupies a unique niche. Although multiple proteins have been implicated in this amyloid cascade signaling pathway, their structure-function relationships are mostly unexplored. However, it is known that two major proteins related to AD pathology, Aβ peptide, and microtubule-associated protein tau belong to the category of intrinsically disordered proteins (IDPs), which are the functionally important proteins characterized by a lack of fixed, ordered three-dimensional structure. IDPs and intrinsically disordered protein regions (IDPRs) play numerous vital roles in various cellular processes, such as signaling, cell cycle regulation, macromolecular recognition, and promiscuous binding. However, the deregulation and misfolding of IDPs may lead to disturbed signaling, interactions, and disease pathogenesis. Often, molecular recognition-related IDPs/IDPRs undergo disorder-to-order transition upon binding to their biological partners and contain specific disorder-based binding motifs, known as molecular recognition features (MoRFs). Knowing the intrinsic disorder status and disorder-based functionality of proteins associated with amyloid cascade signaling pathway may help to untangle the mechanisms of AD pathogenesis and help identify therapeutic targets. In this paper, we have used multiple computational tools to evaluate the presence of intrinsic disorder and MoRFs in 27 proteins potentially relevant to the amyloid cascade signaling pathway. Among these, BIN1, APP, APOE, PICALM, PSEN1 and CD33 were found to be highly disordered. Furthermore, their disorder-based binding regions and associated short linear motifs have also been identified. These findings represent important foundation for the future research, and experimental characterization of disordered regions in these proteins is required to better understand their roles in AD pathogenesis.

A Review of the Familial Alzheimer's Disease Locus PRESENILIN 2 and Its Relationship to PRESENILIN 1

PRESENILIN 1 (PSEN1) and PRESENILIN 2 (PSEN2) genes are loci for mutations causing familial Alzheimer's disease (fAD). However, the function of these genes and how they contribute to fAD pathogenesis has not been fully determined. This review provides a summary of the overlapping and independent functions of the PRESENILINS with a focus on the lesser studied PSEN2. As a core component of the γ-secretase complex, the PSEN2 protein is involved in many γ-secretase-related physiological activities, including innate immunity, Notch signaling, autophagy, and mitochondrial function. These physiological activities have all been associated with AD progression, indicating that PSEN2 plays a particular role in AD pathogenesis.

Bax inhibitor 1 is a γ-secretase-independent presenilin-binding protein

β-amyloid is regarded by some scientists to be the cause of Alzheimer’s disease (AD). One of the strongest arguments against this hypothesis is the presence of hundreds of AD-causing mutations in presenilin, but none in the other three components of γ-secretase. This observation implies a γ-secretase–independent function of presenilin. To understand such a putative function, discovery of presenilin-binding proteins represents an important first step. In this study, we report the identification of Bax-inhibitor 1 (BI1) as a stable interacting partner of presenilin 1 (PS1), but not the intact γ-secretase. Our results link PS1 to BI1, a protein thought to play a role in apoptosis and calcium channel regulation. This finding opens a range of possibilities for the investigation of PS1 function and AD genesis.

Presenilin is the catalytic subunit of γ-secretase, a four-component intramembrane protease responsible for the generation of β-amyloid (Aβ) peptides. Over 200 Alzheimer’s disease-related mutations have been identified in presenilin 1 (PS1) and PS2. Here, we report that Bax-inhibitor 1 (BI1), an evolutionarily conserved transmembrane protein, stably associates with PS1. BI1 specifically interacts with PS1 in isolation, but not with PS1 in the context of an assembled γ-secretase. The PS1–BI1 complex exhibits no apparent proteolytic activity, as judged by the inability to produce Aβ40 and Aβ42 from the substrate APP-C99. At an equimolar concentration, BI1 has no impact on the proteolytic activity of γ-secretase; at a 200-fold molar excess, BI1 reduces γ-secretase activity nearly by half. Our biochemical study identified BI1 as a PS1-interacting protein, suggesting additional functions of PS1 beyond its involvement in γ-secretase.

Role of APP Interactions with Heterotrimeric G Proteins: Physiological Functions and Pathological Consequences

Following the discovery that the amyloid precursor protein (APP) is the source of β-amyloid peptides (Aβ) that accumulate in Alzheimer’s disease (AD), structural analyses suggested that the holoprotein resembles a transmembrane receptor. Initial studies using reconstituted membranes demonstrated that APP can directly interact with the heterotrimeric G protein Gαo (but not other G proteins) via an evolutionarily G protein-binding motif in its cytoplasmic domain. Subsequent investigations in cell culture showed that antibodies against the extracellular domain of APP could stimulate Gαo activity, presumably mimicking endogenous APP ligands. In addition, chronically activating wild type APP or overexpressing mutant APP isoforms linked with familial AD could provoke Go-dependent neurotoxic responses, while biochemical assays using human brain samples suggested that the endogenous APP-Go interactions are perturbed in AD patients. More recently, several G protein-dependent pathways have been implicated in the physiological roles of APP, coupled with evidence that APP interacts both physically and functionally with Gαo in a variety of contexts. Work in insect models has demonstrated that the APP ortholog APPL directly interacts with Gαo in motile neurons, whereby APPL-Gαo signaling regulates the response of migratory neurons to ligands encountered in the developing nervous system. Concurrent studies using cultured mammalian neurons and organotypic hippocampal slice preparations have shown that APP signaling transduces the neuroprotective effects of soluble sAPPα fragments via modulation of the PI3K/Akt pathway, providing a mechanism for integrating the stress and survival responses regulated by APP. Notably, this effect was also inhibited by pertussis toxin, indicating an essential role for Gαo/i proteins. Unexpectedly, C-terminal fragments (CTFs) derived from APP have also been found to interact with Gαs, whereby CTF-Gαs signaling can promote neurite outgrowth via adenylyl cyclase/PKA-dependent pathways. These reports offer the intriguing perspective that G protein switching might modulate APP-dependent responses in a context-dependent manner. In this review, we provide an up-to-date perspective on the model that APP plays a variety of roles as an atypical G protein-coupled receptor in both the developing and adult nervous system, and we discuss the hypothesis that disruption of these normal functions might contribute to the progressive neuropathologies that typify AD.

Presenilin 2 overexpression is associated with apoptosis in Neuro2a cells

Presenilin 1 (PS1) and PS2 are evolutionarily conserved transmembrane proteins of the aspartyl protease family. Initially, they were reported to be associated with the early onset of familial, early-onset Alzheimer’s disease. PS1 has been implicated in several crucial brain functions including developmental processes, synaptic plasticity, and processing of various molecules, while PS2 has been poorly studied and is considered to be a compensatory partner of PS1. Certain controversial reports have suggested that PS2 has a role in apoptosis, though the underlying mechanism is not clear. To ascertain the role of PS2 in apoptosis, mouse neuroblastoma cells (Neuro2a) were transfected with a cDNA construct encoding full length mouse PS2 and analyzed for viability, expression of PS1, PS2, Bax and p53, Bax protein, and status of chromatin condensation. Our results showed reduced viability, condensed chromatin and higher expression of Bax at mRNA and protein levels, but no change in the expression of p53 and PS1 in PS2-overexpressing Neuro2a cells. Thus, it is evident that PS2, independent of PS1, is associated with apoptosis via a Bax-mediated pathway. These findings might help in the understanding of the involvement of PS2 in apoptosis and its associated brain disorders.

■ REVIEW : The Presenilins

Presenilin-1 and presenilin-2 are highly homologous genes located on chromosomes 14 and 1, respectively, that have recently been linked to some cases of early-onset autosomal dominant inherited forms of Alzhei mer's disease (AD). Presenilins are integral membrane proteins localized in the endoplasmic reticulum of neurons throughout the nervous system. Studies of presenilin-1 knockout mice, and of invertebrate homo logues of presenilins and their interacting proteins, suggest major roles for presenilins in normal develop ment. Presenilin-1 mutant knockin mice do not exhibit developmental abnormalities, which indicates that the pathogenic mechanism of presenilin mutations involves gain of an adverse property of the mutant protein. Expression of presenilin mutations in cultured neurons and transgenic mice results in increased sensitivity to apoptosis induced by trophic factor withdrawal and exposure to oxidative and metabolic insults, and also alters gene expression. The pathogenic mechanism of presenilin mutations may involve perturbed endo plasmic reticulum calcium homeostasis resulting in enhanced oxidative stress, altered proteolytic processing of the amyloid precursor protein (APP), and increased neuronal vulnerability to excitotoxicity. Studies of presenilins are rapidly increasing our understanding the molecular and cellular underpinnings of AD and are also elucidating novel roles of the endoplasmic reticulum in neuronal plasticity and cell death. NEURO SCIENTIST 5:112-124, 1999

Conserved Molecular Underpinnings and Characterization of a Role for Caveolin-1 in the Tumor Microenvironment of Mature T-Cell Lymphomas

Neoplasms of extra-thymic T-cell origin represent a rare and difficult population characterized by poor clinical outcome, aggressive presentation, and poorly defined molecular characteristics. Much work has been done to gain greater insights into distinguishing features among malignant subtypes, but there also exists a need to identify unifying characteristics to assist in rapid diagnosis and subsequent potential treatment. Herein, we investigated gene expression data of five different mature T-cell lymphoma subtypes (n = 187) and found 21 genes to be up- and down-regulated across all malignancies in comparison to healthy CD4⁺ and CD8⁺ T-cell controls (n = 52). From these results, we sought to characterize a role for caveolin-1 (CAV1), a gene with previous description in the progression of both solid and hematological tumors. Caveolin-1 was upregulated, albeit with a heterogeneous nature, across all mature T-cell lymphoma subtypes, a finding confirmed using immunohistochemical staining on an independent sampling of mature T-cell lymphoma biopsies (n = 65 cases). Further, stratifying malignant samples in accordance with high and low CAV1 expression revealed that higher expression of CAV1 in mature T-cell lymphomas is analogous with an enhanced inflammatory and invasive gene expression profile. Taken together, these results demonstrate a role for CAV1 in the tumor microenvironment of mature T-cell malignancies and point toward potential prognostic implications.

Twenty Years of Presenilins--Important Proteins in Health and Disease

Alzheimer's disease (AD) is characterized by progressive decline in cognitive functions associated with depositions of aggregated proteins in the form of extracellular plaques and neurofibrillary tangles in the brain. Extracellular plaques contain characteristic fibrils of amyloid β peptides (Aβ); tangles consist of paired helical filaments of the microtubuli-associated protein tau. Although AD manifests predominantly at ages above 65 years, rare cases show a much earlier onset of disease symptoms with very similar neuropathological characteristics. In 1995, two homologous genes were identified, in which mutations are associated with dominantly inherited familial forms of early onset AD. The genes therefore were dubbed presenilins (PS) and encode polytopic transmembrane proteins. At this time the role of these proteins in the pathogenesis of AD and their biological function in general were completely unknown. However, individuals carrying PS mutations showed alterations in the composition of different length variants of Aβ peptides in blood and cerebrospinal fluid, which indicated the potential involvement of presenilins in the metabolism of Aβ. After 20 years of intense research, the roles of presenilins in Aβ generation as well as important functions in biological processes have been identified. Presenilins represent the catalytic components of protease complexes that directly cleave the amyloid precursor protein (APP) but also many other proteins with important physiological functions. Here, the progress in presenilin research from basic characterization of their cellular functions to the targeting in clinical trials for AD therapy, and potential future directions, will be discussed.

Mutations in presenilin 2 and its implications in Alzheimer's disease and other dementia-associated disorders

Alzheimer's disease (AD) is the most common form of dementia. Mutations in the genes encoding presenilin 1 (PSEN1), presenilin 2 (PSEN2), and amyloid precursor protein have been identified as the main genetic causes of familial AD. To date, more than 200 mutations have been described worldwide in PSEN1, which is highly homologous with PSEN2, while mutations in PSEN2 have been rarely reported. We performed a systematic review of studies describing the mutations identified in PSEN2. Most PSEN2 mutations were detected in European and in African populations. Only two were found in Korean populations. Interestingly, PSEN2 mutations appeared not only in AD patients but also in patients with other disorders, including frontotemporal dementia, dementia with Lewy bodies, breast cancer, dilated cardiomyopathy, and Parkinson's disease with dementia. Here, we have summarized the PSEN2 mutations and the potential implications of these mutations in dementia-associated disorders.

Loss of Presenilin 2 Function Is Associated with Defective LPS-Mediated Innate Immune Responsiveness

The importance of presenilin-dependent γ-secretase protease activities in the development, neurogenesis, and immune system is highlighted by the diversity of its substrates and characterization of Psen1- and Psen2-deficient transgenic animals. Functional differences between presenilin 1 (PS1) and presenilin 2 (PS2) are incompletely understood. In this study, we have identified a Psen2-specific function, not shared by Psen1 in Toll-like receptor signaling. We show that immortalized fibroblasts and bone marrow-derived macrophages from Psen2- but not Psen1-deficient mice display reduced responsiveness to lipopolysaccharide (LPS) with decreased nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and mitogen-activated protein kinase (MAPK) activity and diminished pro-inflammatory cytokine production. In whole animal in vivo responses, Psen2-deficient animals have abnormal systemic production of LPS-stimulated pro-inflammatory cytokines. Mechanistically, we demonstrate that Psen2 deficiency is paralleled by reduced transcription of tlr4 mRNA and loss of LPS-induced tlr4 mRNA transcription regulation. These observations illustrate a novel PS2-dependent means of modulating LPS-mediated immune responses and identify a functional distinction between PS1 and PS2 in innate immunity.

Presenilin-1 knockin mice reveal loss-of-function mechanism for familial Alzheimer's disease

Presenilins play essential roles in memory formation, synaptic function, and neuronal survival. Mutations in the Presenilin-1 (PSEN1) gene are the major cause of familial Alzheimer's disease (FAD). How PSEN1 mutations cause FAD is unclear, and pathogenic mechanisms based on gain or loss of function have been proposed. Here, we generated Psen1 knockin (KI) mice carrying the FAD mutation L435F or C410Y. Remarkably, KI mice homozygous for either mutation recapitulate the phenotypes of Psen1(-/-) mice. Neither mutation altered Psen1 mRNA expression, but both abolished γ-secretase activity. Heterozygosity for the KI mutation decreased production of Aβ40 and Aβ42, increased the Aβ42/Aβ40 ratio, and exacerbated Aβ deposition. Furthermore, the L435F mutation impairs hippocampal synaptic plasticity and memory and causes age-dependent neurodegeneration in the aging cerebral cortex. Collectively, our findings reveal that FAD mutations can cause complete loss of Presenilin-1 function in vivo, suggesting that clinical PSEN mutations produce FAD through a loss-of-function mechanism.

Cellular FLICE-like Inhibitory Protein (c-FLIP) and PS1-associated Protein (PSAP) Mediate Presenilin 1-induced γ-Secretase-dependent and -independent Apoptosis, Respectively

Presenilin 1 (PS1) has been implicated in apoptosis; however, its mechanism remains elusive. We report that PS1-induced apoptosis was associated with cellular FLICE-like inhibitory protein (c-FLIP) turnover and that γ-secretase inhibitor blocked c-FLIP turnover and also partially blocked PS1-induced apoptosis. A complete inhibition of PS1-induced apoptosis was achieved by knockdown of PS1-associated protein (PSAP), a mitochondrial proapoptotic protein that forms a complex with Bax upon induction of apoptosis, in the presence of γ-secretase inhibitor. PS1-induced apoptosis was partially inhibited by knockdown of caspase-8, Fas-associated protein with death domain (FADD), or Bid. However, knockdown of Bax or overexpression of Bcl-2 resulted in complete inhibition of PS1-induced apoptosis. These data suggest that PS1 induces apoptosis through two pathways: the γ-secretase-dependent pathway mediated by turnover of c-FLIP and the γ-secretase-independent pathway mediated by PSAP-Bax complex formation. These two pathways converge on Bax to activate mitochondria-dependent apoptosis. These findings provide new insight into the mechanisms by which PS1 is involved in apoptosis and the mechanism by which PS1 exerts its pathogenic effects. In addition, our results suggest that PS2 induces apoptosis through a pathway that is different from that of PS1.

Thapsigargin affects presenilin-2 but not presenilin-1 regulation in SK-N-BE cells

Presenilin-1 (PS1) and presenilin-2 (PS2) are transmembrane proteins widely expressed in the central nervous system, which function as the catalytic subunits of γ-secretase, the enzyme that releases amyloid-β protein (Aβ) from ectodomain cleaved amyloid precursor protein (APP) by intramembrane proteolysis. Mutations in PS1, PS2, and Aβ protein precursor are involved in the etiology of familial Alzheimer's disease (FAD), while the cause of the sporadic form of AD (SAD) is still not known. However, since similar neuropathological changes have been observed in both FAD and SAD, a common pathway in the etiology of the disease has been suggested. Given that age-related deranged Ca(2+) regulation has been hypothesized to play a role in SAD pathogenesis via PS gene regulation and γ-secretase activity, we studied the in vitro regulation of PS1 and PS2 in the human neuron-like SK-N-BE cell line treated with the specific endoplasmic reticulum (ER) calcium ATPase inhibitor Thapsigargin (THG), to introduce intracellular Ca(2+) perturbations and mimic the altered Ca(2+) homeostasis observed in AD. Our results showed a consistent and significant down-regulation of PS2, while PS1 appeared to be unmodulated. These events were accompanied by oxidative stress and a number of morphological alterations suggestive of the induction of apoptotic machinery. The administration of the antioxidant N-acetylcysteine (NAC) did not revert the THG-induced effects reported, while treatment with the Ca(2+)-independent ER stressor Brefeldin A did not modulate basal PS1 and PS2 expression. Collectively, these results suggest that Ca(2+) fluctuation rather than ER stress and/or oxidative imbalance seems to play an essential role in PS2 regulation and confirm that, despite their strong homology, PS1 and PS2 could play different roles in AD.

Critical role of presenilin-dependent γ-secretase activity in DNA damage-induced promyelocytic leukemia protein expression and apoptosis

Promyelocytic leukemia (PML) is a major component of macromolecular multiprotein complexes called PML nuclear-bodies (PML-NBs). These PML-NBs recruit numerous proteins including CBP, p53 and HIPK2 in response to DNA damage, senescence and apoptosis. In this study, we investigated the effect of presenilin (PS), the main component of the γ-secretase complex, in PML/p53 expression and downstream consequences during DNA damage-induced cell death using camptothecin (CPT). We found that the loss of PS in PS knockout (KO) MEFs (mouse embryonic fibroblasts) results in severely blunted PML expression and attenuated cell death upon CPT exposure, a phenotype that is fully reversed by re-expression of PS1 in PS KO cells and recapitulated by γ-secretase inhibitors in hPS1 MEFs. Interestingly, the γ-secretase cleavage product, APP intracellular domain (AICD), together with Fe65-induced PML expression at the protein and transcriptional levels in PS KO cells. PML and p53 reciprocally positively regulated each other during CPT-induced DNA damage, both of which were dependent on PS. Finally, elevated levels of PML-NB, PML protein and PML mRNA were detected in the brain tissues from Alzheimer's disease (AD) patients, where γ-secretase activity is essential for pathogenesis. Our data provide for the first time, a critical role of the PS/AICD-PML/p53 pathway in DNA damage-induced apoptosis, and implicate this pathway in AD pathogenesis.

Caspase-9 mediates synaptic plasticity and memory deficits of Danish dementia knock-in mice: caspase-9 inhibition provides therapeutic protection

BACKGROUND

Mutations in either Aβ Precursor protein (APP) or genes that regulate APP processing, such as BRI2/ITM2B and PSEN1/PSEN2, cause familial dementias. Although dementias due to APP/PSEN1/PSEN2 mutations are classified as familial Alzheimer disease (FAD) and those due to mutations in BRI2/ITM2B as British and Danish dementias (FBD, FDD), data suggest that these diseases have a common pathogenesis involving toxic APP metabolites. It was previously shown that FAD mutations in APP and PSENs promote activation of caspases leading to the hypothesis that aberrant caspase activation could participate in AD pathogenesis.

RESULTS

Here, we tested whether a similar mechanism applies to the Danish BRI2/ITM2B mutation. We have generated a genetically congruous mouse model of FDD, called FDD(KI), which presents memory and synaptic plasticity deficits. We found that caspase-9 is activated in hippocampal synaptic fractions of FDD(KI) mice and inhibition of caspase-9 activity rescues both synaptic plasticity and memory deficits.

CONCLUSION

These data directly implicate caspase-9 in the pathogenesis of Danish dementia and suggest that reducing caspase-9 activity is a valid therapeutic approach to treating human dementias.

Tip60 HAT activity mediates APP induced lethality and apoptotic cell death in the CNS of a Drosophila Alzheimer's disease model

Histone acetylation of chromatin promotes dynamic transcriptional responses in neurons that influence neuroplasticity critical for cognitive ability. It has been demonstrated that Tip60 histone acetyltransferase (HAT) activity is involved in the transcriptional regulation of genes enriched for neuronal function as well as the control of synaptic plasticity. Accordingly, Tip60 has been implicated in the neurodegenerative disorder Alzheimer's disease (AD) via transcriptional regulatory complex formation with the AD linked amyloid precursor protein (APP) intracellular domain (AICD). As such, inappropriate complex formation may contribute to AD-linked neurodegeneration by misregulation of target genes involved in neurogenesis; however, a direct and causative epigenetic based role for Tip60 HAT activity in this process during neuronal development in vivo remains unclear. Here, we demonstrate that nervous system specific loss of Tip60 HAT activity enhances APP mediated lethality and neuronal apoptotic cell death in the central nervous system (CNS) of a transgenic AD fly model while remarkably, overexpression of Tip60 diminishes these defects. Notably, all of these effects are dependent upon the C-terminus of APP that is required for transcriptional regulatory complex formation with Tip60. Importantly, we show that the expression of certain AD linked Tip60 gene targets critical for regulating apoptotic pathways are modified in the presence of APP. Our results are the first to demonstrate a functional interaction between Tip60 and APP in mediating nervous system development and apoptotic neuronal cell death in the CNS of an AD fly model in vivo, and support a novel neuroprotective role for Tip60 HAT activity in AD neurodegenerative pathology.

Rhomboid proteases in mitochondria and plastids: keeping organelles in shape

Rhomboids constitute the most widespread and conserved family of intramembrane cleaving proteases. They are key regulators of critical cellular processes in bacteria and animals, and are poised to play an equally important role also in plants. Among eukaryotes, a distinct subfamily of rhomboids, prototyped by the mammalian mitochondrial protein Parl, ensures the maintenance of the structural and functional integrity of mitochondria and plastids. Here, we discuss the studies that in the past decade have unveiled the role, regulation, and structure of this unique group of rhomboid proteases. This article is part of a Special Issue entitled: Protein Import and Quality Control in Mitochondria and Plastids.

MOCA is an integrator of the neuronal death signals that are activated by familial Alzheimer's disease-related mutants of amyloid β precursor protein and presenilins

The death of cholinergic neurons in the cerebral cortex and certain subcortical regions is linked to irreversible dementia relevant to AD (Alzheimer's disease). Although multiple studies have shown that expression of a FAD (familial AD)-linked APP (amyloid β precursor protein) or a PS (presenilin) mutant, but not that of wild-type APP or PS, induced neuronal death by activating intracellular death signals, it remains to be addressed how these signals are interrelated and what the key molecule involved in this process is. In the present study, we show that the PS1-mediated (or possibly the PS2-mediated) signal is essential for the APP-mediated death in a γ-secretase-independent manner and vice versa. MOCA (modifier of cell adhesion), which was originally identified as being a PS- and Rac1-binding protein, is a common downstream constituent of these neuronal death signals. Detailed molecular analysis indicates that MOCA is a key molecule of the AD-relevant neuronal death signals that links the PS-mediated death signal with the APP-mediated death signal at a point between Rac1 [or Cdc42 (cell division cycle 42)] and ASK1 (apoptosis signal-regulating kinase 1).

γ-Secretase complexes containing caspase-cleaved presenilin-1 increase intracellular Aβ(42) /Aβ(40) ratio

Markers for caspase activation and apoptosis have been shown in brains of Alzheimer's disease (AD) patients and AD-mouse models. In neurons, caspase activation is associated with elevated amyloid β-peptide (Aβ) production. Caspases cleave numerous substrates including presenilin-1 (PS1). The cleavage takes place in the large cytosolic loop of PS1-C-terminal fragment (PS1CTF), generating a truncated PS1CTF lacking half of the loop domain (caspCTF). The loop has been shown to possess important regulatory functions with regard to Aβ(40) and Aβ(42) production. Previously, we have demonstrated that γ-secretase complexes are active during apoptosis regardless of caspase cleavage in the PS1CTF-loop. Here, a PS1/PS2-knockout mouse blastocyst-derived cell line was used to establish stable or transient cell lines expressing either caspCTF or full-length CTF (wtCTF). We show that caspCTF restores γ-secretase activity and forms active γ-secretase complexes together with Nicastrin, Pen-2, Aph-1 and PS1-N-terminal fragment. Further, caspCTF containing γ-secretase complexes have a sustained capacity to cleave amyloid precursor protein (APP) and Notch, generating APP and Notch intracellular domain, respectively. However, when compared to wtCTF cells, caspCTF cells exhibit increased intracellular production of Aβ(42) accompanied by increased intracellular Aβ(42) /Aβ(40) ratio without changing the Aβ secretion pattern. Similarly, induction of apoptosis in wtCTF cells generate a similar shift in intracellular Aβ pattern with increased Aβ(42) /Aβ(40) ratio. In summary, we show that caspase cleavage of PS1 generates a γ-secretase complex that increases the intracellular Aβ(42) /Aβ(40) ratio. This can have implications for AD pathogenesis and suggests caspase inhibitors as potential therapeutic agents.

The mitochondrial pathways of apoptosis

Apoptosis is a process of programmed cell death that serves as a major mechanism for the precise regulation of cell numbers, and as a defense mechanism to remove unwanted and potentially dangerous cells. Studies in nematode, Drosophila and mammals have shown that, although regulation of the cell death machinery is somehow different from one species to another, it is controlled by homologous proteins and involves mitochondria. In mammals, activation of caspases (cysteine proteases that are the main executioners of apoptosis) is under the tight control of the Bcl-2 family proteins, named in reference to the first discovered mammalian cell death regulator. These proteins mainly act by regulating the release of caspases activators from mitochondria. Although for a long time the absence of mitochondrial changes was considered as a hallmark of apoptosis, mitochondria appear today as the central executioner of apoptosis. In this chapter, we present the current view on the mitochondrial pathway of apoptosis with a particular attention to new aspects of the regulation of the Bcl-2 proteins family control of mitochondrial membrane permeabilization: the mechanisms implicated in their mitochondrial targeting and activation during apoptosis, the function(s) of the oncosuppressive protein p53 at the mitochondria and the role of the processes of mitochondrial fusion and fission.

Neurodegenerative processes in Alzheimer’s disease: an overview of pathogenesis with strategic biomarker potential

Since Alzheimer’s disease (AD) is the leading cause of senile dementia in the USA, affecting 15% of people over the age of 65 years and almost 50% of those aged over 85 years, the need for an adequate and early diagnosis as well as preventative measure against disease onset and progression is increasing. Epidemiological and molecular studies suggest that AD has multiple etiologies, including genetic mutations, genetic variations affecting susceptibility and environmental factors. All these aspects can promote the formation and the accumulation of insoluble amyloid-β and hyperphosphorylated tau. Since the disease is multifactorial and clinical diagnosis is highly exclusive, the need for a sensitive, specific and reliable biomarker for the disease is crucial. While amyloid and amyloid-related compounds may be useful biomarkers in the early diagnosis of AD, the multitude of other characteristic features of AD presented in this article may be similarly appropriate. For example, genetic mutations play a role in a subset of AD patients (often with early disease onset and more severe disease progression), and genetic analysis could thus play a role in disease diagnosis. Similarly, oxidative damage to various proteins, nucleic acids and other cellular compounds, probably arising from mitochondrial abnormalities, is found early in the disease and may provide certain biochemical signatures of disease. Ultimately, specific assays for genetic, protein and oxidative profiles and mitochondrial abnormalities, as well as those for amyloid-β and its immunological response, may serve as a relevant group of biomarkers that could be informative to individuals regarding risk of disease, as well as for indicators of the progression of disease. Correspondingly, new developments in treatment options will probably be available.

Presenilin 2 is the predominant γ-secretase in microglia and modulates cytokine release

Presenilin 1 (PS1) and Presenilin 2 (PS2) are the enzymatic component of the γ-secretase complex that cleaves amyloid precursor protein (APP) to release amyloid beta (Aβ) peptide. PS deficiency in mice results in neuroinflammation and neurodegeneration in the absence of accumulated Aβ. We hypothesize that PS influences neuroinflammation through its γ-secretase action in CNS innate immune cells. We exposed primary murine microglia to a pharmacological γ-secretase inhibitor which resulted in exaggerated release of TNFα and IL-6 in response to lipopolysaccharide. To determine if this response was mediated by PS1, PS2 or both we used shRNA to knockdown each PS in a murine microglia cell line. Knockdown of PS1 did not lead to decreased γ-secretase activity while PS2 knockdown caused markedly decreased γ-secretase activity. Augmented proinflammatory cytokine release was observed after knockdown of PS2 but not PS1. Proinflammatory stimuli increased microglial PS2 gene transcription and protein in vitro. This is the first demonstration that PS2 regulates CNS innate immunity. Taken together, our findings suggest that PS2 is the predominant γ-secretase in microglia and modulates release of proinflammatory cytokines. We propose PS2 may participate in a negative feedback loop regulating inflammatory behavior in microglia.

Neuronal cell death in Alzheimer's disease and a neuroprotective factor, humanin

Brain atrophy caused by neuronal loss is a prominent pathological feature of Alzheimer's disease (AD). Amyloid beta (Abeta), the major component of senile plaques, is considered to play a central role in neuronal cell death. In addition to removal of the toxic Abeta, direct suppression of neuronal loss is an essential part of AD treatment; however, no such neuroprotective therapies have been developed. Excess amount of Abeta evokes multiple cytotoxic mechanisms, involving increase of the intracellular Ca(2+) level, oxidative stress, and receptor-mediated activation of cell-death cascades. Such diversity in cytotoxic mechanisms induced by Abeta clearly indicates a complex nature of the AD-related neuronal cell death. We have identified a 24-residue peptide, Humanin (HN), which suppresses in vitro neuronal cell death caused by all AD-related insults, including Abeta, so far tested. The anti-AD effect of HN has been further confirmed in vivo using mice with Abeta-induced amnesia. Altogether, such potent neuroprotective activity of HN against AD-relevant cytotoxicity both in vitro and in vivo suggests the potential clinical applications of HN in novel AD therapies aimed at controlling neuronal death.

Biomarkers in Alzheimer's disease: past, present and future

Epidemiological and molecular studies suggest that Alzheimer's disease (AD) has multiple etiologies including genetic mutations, genetic variations affecting susceptibility and environmental factors. These aspects can promote the formation and accumulation of insoluble amyloid-beta and hyperphosphorylated tau. Since the disease is multifactorial and clinical diagnosis is highly exclusive, the need for a sensitive, specific and reliable biomarker is crucial. The concept of a biomarker implies sensitivity and specificity relative to the condition being considered. For clinical practice, AD diagnosis has been based on adherence to clinical criteria such as the NINCDS/ADRDA and DSM-IV. A more recent set of diagnostic criteria proposed incorporates imaging findings into the diagnosis of AD. In this article, we consider the most studied candidates or group of candidates for AD biomarkers, including pathological processes and proteins (amyloid-beta, tau, oxidative stress, mitochondrial/metabolic changes and cell-cycle processes), or autoantibodies thereto, as well as genetic factors.

The PARL family of mitochondrial rhomboid proteases

Rhomboids are an ancient and conserved family of intramembrane-cleaving proteases, a small group of proteolytic enzymes capable of hydrolyzing a peptide bond within a transmembrane helix that anchors a substrate protein to the membrane. Mitochondrial rhomboids evolved in eukaryotes to coordinate a critical aspect of cell biology, the regulation of mitochondrial membranes dynamics. This function appears to have required the emergence of a structural feature that is unique among all other rhomboids: an additional transmembrane helix (TMH) positioned at the N-terminus of six TMHs that form the core proteolytic domain of all prokaryotic and eukaryotic rhomboids. This "1+6" structure, which is shared only among mitochondrial rhomboids, defines a subfamily of rhomboids with the prototypical family member being mammalian Parl. Here, we present the findings that in 11 years have elevated mitochondrial rhomboids as the gatekeepers of mitochondrial dynamics and apoptosis; further, we discuss the aspects of their biology that are bound to introduce new paradigm shifts in our understanding of how the organelle uses this unique type of protease to govern stress, signaling to the nucleus, and other key mitochondrial activities in health and disease.

Alzheimer Abeta peptide induces chromosome mis-segregation and aneuploidy, including trisomy 21: requirement for tau and APP

Chromosome aneuploidy, especially trisomy 21, arises in both familial and sporadic Alzheimer's disease. Expression of FAD genes or exposure to Aβ peptide induces aneuploidy in tg-mice and cultured cells. The requirement for GSK-3β, calpain, and Tau in Aβ-induced chromosome mis-segregation points to MT dysfunction as contributing to AD pathogenesis.

Both sporadic and familial Alzheimer's disease (AD) patients exhibit increased chromosome aneuploidy, particularly trisomy 21, in neurons and other cells. Significantly, trisomy 21/Down syndrome patients develop early onset AD pathology. We investigated the mechanism underlying mosaic chromosome aneuploidy in AD and report that FAD mutations in the Alzheimer Amyloid Precursor Protein gene, APP, induce chromosome mis-segregation and aneuploidy in transgenic mice and in transfected cells. Furthermore, adding synthetic Aβ peptide, the pathogenic product of APP, to cultured cells causes rapid and robust chromosome mis-segregation leading to aneuploid, including trisomy 21, daughters, which is prevented by LiCl addition or Ca²⁺ chelation and is replicated in tau KO cells, implicating GSK-3β, calpain, and Tau-dependent microtubule transport in the aneugenic activity of Aβ. Furthermore, APP KO cells are resistant to the aneugenic activity of Aβ, as they have been shown previously to be resistant to Aβ-induced tau phosphorylation and cell toxicity. These results indicate that Aβ-induced microtubule dysfunction leads to aneuploid neurons and may thereby contribute to the pathogenesis of AD.

CD 4+ T cells in the pathobiology of neurodegenerative disorders

CD4+ T cells orchestrate innate and adaptive immunity. In the central nervous system they modulate immune responses including cell trafficking and glial neuroregulatory functions through an array of soluble molecules cell-cell interactions affecting tissue homeostasis. During disease their roles evolve to an auto-aggressive or, alternatively, protective phenotype. How such a balance is struck in the setting of neurodegenerative disorders may reflect a dichotomy between regulatory T cell, anti-inflammatory and neuroprotective activities versus effector T cell inflammation and neurodegeneration. Interestingly, such roles may show commonalities amongst neurodegenerative diseases. Herein we focus on strategies to modulate such CD4+ T cell responses for therapeutic gain.

Heterotrimeric G proteins and apoptosis: intersecting signaling pathways leading to context dependent phenotypes

Apoptosis, a programmed cell death mechanism, is a fundamental process during the normal development and somatic maintenance of all multicellular organisms and thus is highly conserved and tightly regulated through numerous signaling pathways. Apoptosis is of particular clinical importance as its dysregulation contributes significantly to numerous human diseases, primarily through changes in the expression and activation of key apoptotic regulators. Each of the four families of heterotrimeric G proteins (G(s), G(i/o), G(q/11) and G(12/13)) has been implicated in numerous cellular signaling processes, including proliferation, transformation, migration, differentiation, and apoptosis. Heterotrimeric G protein signaling is an important but not widely studied mechanism regulating apoptosis. G protein Signaling and Apoptosis broadly cover two large bodies of literature and share numerous signaling pathways. Examination of the intersection between these two areas is the focus of this review. Several studies have implicated signaling through each of the four heterotrimeric G protein families to regulate apoptosis within numerous disease contexts, but the mechanism(s) are not well defined. Each G protein family has been shown to stimulate and/or inhibit apoptosis in a context-dependent fashion through regulating numerous downstream effectors including the Bcl-2 family, NF-kappaB, PI3 Kinase, MAP Kinases, and small GTPases. These cell-type specific and G protein coupled receptor dependent effects have led to a complex body of literature of G protein regulation of apoptosis. Here, we review the literature and summarize apoptotic signaling through each of the four heterotrimeric G protein families (and the relevant G protein coupled receptors), and discuss limitations and future directions for research on regulating apoptosis through G protein coupled mechanisms. Continued investigation in this field is essential for the identification of important targets for pharmacological intervention in numerous diseases.

Humanin inhibits neuronal cell death by interacting with a cytokine receptor complex or complexes involving CNTF receptor alpha/WSX-1/gp130

Humanin (HN) inhibits neuronal death induced by various Alzheimer's disease (AD)-related insults via an unknown receptor on cell membranes. Our earlier study indicated that the activation of STAT3 was essential for HN-induced neuroprotection, suggesting that the HN receptor may belong to the cytokine receptor family. In this study, a series of loss-of-function tests indicated that gp130, the common subunit of receptors belonging to the IL-6 receptor family, was essential for HN-induced neuroprotection. Overexpression of ciliary neurotrophic factor receptor alpha (CNTFR) and/or the IL-27 receptor subunit, WSX-1, but not that of any other tested gp130-related receptor subunit, up-regulated HN binding to neuronal cells, whereas siRNA-mediated knockdown of endogenous CNTFR and/or WSX-1 reduced it. These results suggest that both CNTFR and WSX-1 may be also involved in HN binding to cells. Consistent with these results, loss-of-functions of CNTFR or WSX-1 in neuronal cells nullified their responsiveness to HN-mediated protection. In vitro-reconstituted binding assays showed that HN, but not the other control peptide, induced the hetero-oligomerization of CNTFR, WSX-1, and gp130. Together, these results indicate that HN protects neurons by binding to a complex or complexes involving CNTFR/WSX-1/gp130.

Molecular mechanisms of go signaling

Go is the most abundant G protein in the central nervous system, where it comprises about 1% of membrane protein in mammalian brains. It functions to couple cell surface receptors to intercellular effectors, which is a critical process for cells to receive, interpret and respond to extracellular signals. Go protein belongs to the pertussis toxin-sensitive Gi/Go subfamily of G proteins. A number of G-protein-coupled receptors transmit stimuli to intercellular effectors through Go. Go regulates several cellular effectors, including ion channels, enzymes, and even small GTPases to modulate cellular function. This review summarizes some of the advances in Go research and proposes areas to be further addressed in exploring the functional role of Go.

Protective effect of a phytocompound on oxidative stress and DNA fragmentation against paracetamol-induced liver damage

The hepatoprotective potential DTS (1.5 g/kg bw, Denshici-to-Chiusei, Kyotsu Jigyo, Tokyo, Japan) was evaluated against either toxic (1.5 g/kg bw) and sub-toxic (150 mg/kg bw) dosage of paracetamol-induced liver injury in Sprague-Dawley rat. Paracetamol intoxication caused a reduction of serum total protein and increase levels of serum alkaline phosphatase (ALP), aspartate aminotranferase (AST) and serum alanine aminotranferase (ALT) at higher extent in the toxic group. This phenomenon was paralleled by an impaired liver redox status (reduced glutathione (GSH), superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT) and increased MDA in both paracetamol-administered groups. Moreover, a marked reduction of ATPase and thiols together with DNA fragmentation occurred in liver tissue. Animals pretreated with DTS showed a marked mitigation of the severity of liver enzyme and of the impaired redox status of the liver. Moreover, DTS partly prevented the DNA fragmentation and the decline of liver tissue ATPase and protein thiol assay as compared with both groups treated with paracetamol alone. Although more detailed studies are awaited to ascertain the detailed mode of action of DTS, it wouls seem to be related to the prevention of formation of the reactive oxygen groups thereby preventing the damage on the hepatocytes and possibly modulating the genes responsible for synthesis of liver antioxidant enzymes thus providing marked DNA protection.<br />

Cell cycle re-entry mediated neurodegeneration and its treatment role in the pathogenesis of Alzheimer's disease

As one of the earliest pathologic changes, the aberrant re-expression of many cell cycle-related proteins and inappropriate cell cycle control in specific vulnerable neuronal populations in Alzheimer's disease (AD) is emerging as an important component in the pathogenesis leading to AD and other neurodegenerative diseases. These events are clearly representative of a true cell cycle, rather than epiphenomena of other processes since, in AD and other neurodegenerative diseases, there is a true mitotic alteration that leads to DNA replication. While the exact role of cell cycle re-entry is unclear, recent studies using cell culture and animal models strongly support the notion that the dysregulation of cell cycle in neurons leads to the development of AD-related pathology such as hyperphosphorylation of tau and amyloid-beta deposition and ultimately causes neuronal cell death. Importantly, cell cycle re-entry is also evident in mutant amyloid-beta precursor protein and tau transgenic mice and, as in human disease, occurs prior to the development of the pathological hallmarks, neurofibrillary tangles and amyloid-beta plaques. Therefore, the study of aberrant cell cycle regulation in model systems, both cellular and animal, may provide extremely important insights into the pathogenesis of AD and also serve as a means to test novel therapeutic approaches.

Presenilin: RIP and beyond

Over the years the presenilins (PSENs), a family of multi-transmembrane domain proteins, have been ascribed a number of diverse potential functions. Recent in vivo evidence has supported the existence of PSEN functions beyond its well-established role in regulated intramembrane proteolysis. In this review, we will briefly discuss the ability of PSEN to modulate cellular signaling pathways through gamma-secretase cleavage of transmembrane proteins. Additionally, we will critically examine the proposed roles of PSEN in the regulation of beta-catenin function, protein trafficking, calcium regulation, and apoptosis.

Parenchymal and vascular Abeta-deposition and its effects on the degeneration of neurons and cognition in Alzheimer's disease

The deposition of the amyloid beta-protein (Abeta) is one of the pathological hallmarks of Alzheimer's disease (AD). Abeta-deposits show the morphology of senile plaques and cerebral amyloid angiopathy (CAA). Senile plaques and vascular Abeta-deposits occur first in neocorti-cal areas. Then, they expand hierarchically into further brain regions. The distribution of Abeta plaques throughout the entire brain, thereby correlates with the clinical status of the patients. Imaging techniques for Abeta make use of the hierarchical distribution of Abeta to distinguish AD patients from non-AD patients. However, pathology seen in AD patients represents a late stage of a pathological process starting 10-30 years earlier in cognitively normal individuals. In addition to the fibrillar amyloid of senile plaques, oligomeric and monomeric Abeta is found in the brain. Recent studies revealed that oligomeric Abeta is presumably the most toxic Abeta-aggregate, which interacts with glutamatergic synapses. In doing so, dendrites are presumed to be the primary target for Abeta-toxicity. In addition, vascular Abeta-deposits can lead to capillary occlusion and blood flow disturbances presumably contributing to the alteration of neurons in addition to the direct neurotoxic effects of Abeta. All these findings point to an important role of Abeta and its aggregates in the neurodegenerative process of AD. Since there is already significant neuron loss in AD patients, treatment strategies aimed at reducing the amyloid load will presumably not cure the symptoms of dementia but they may stop disease progression. Therefore, it seems to be necessary to protect the brain from Abeta-toxicity already in stages of the disease with minor neuron loss before the onset of cognitive symptoms.

Protective effect of ultra low molecular weight heparin on glutamate-induced apoptosis in cortical cells

PURPOSE

To investigate the effect of ultra low molecular weight heparin (ULMWH) on glutamate induced apoptosis in rat cortical cells and to explore the possible mechanisms.

MATERIALS AND METHODS

Cell viability was measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Apoptosis was first analyzed with Hoechst 33258 and then confirmed by DNA fragmentation. The concentration of free intracellular calcium ([Ca(2+)](i)) was determined with fura-2/AM fluorometry. The expression of Bcl-2 family protein and caspase-3 were evaluated with Western blot.

RESULTS

Typical apoptotic morphological change in rat cortical cells treated with 100 micromol/L glutamate for 24h was detected by Hoechst 33258 staining, which was then confirmed by the DNA ladder of agarose gel electrophoresis. The apoptotic rate of the glutamate treated cells was up to 33.21%, and 24 h of treatment with glutamate increased [Ca(2+)](i), down-regulated Bcl-2 expression, up-regulated Bax expression, and increased caspase-3 activation in rat cortical cells. Our research demonstrated that ULMWH pretreatment can prevent the glutamate-induced apoptosis, attenuate the increase of [Ca(2+)](i) not only in medium containing Ca(2+) but also in Ca(2+)-free medium, up-regulate the expression of Bcl-2, down-regulate the expression of Bax, and decrease caspase-3 activation.

CONCLUSION

ULMWH has neuroprotective capacity to antagonize glutamate-induced apoptosis in cortical cells, through decrease of Ca(2+) release and modulation of apoptotic processes.

IP3 receptors in cell survival and apoptosis: Ca2+ release and beyond

Inositol 1,4,5-trisphosphate receptors (IP(3)Rs) serve to discharge Ca(2+) from ER stores in response to agonist stimulation. The present review summarizes the role of these receptors in models of Ca(2+)-dependent apoptosis. In particular we focus on the regulation of IP(3)Rs by caspase-3 cleavage, cytochrome c, anti-apoptotic proteins and Akt kinase. We also address the evidence that some of the effects of IP(3)Rs in apoptosis may be independent of their ion-channel function. The role of IP(3)Rs in delivering Ca(2+) to the mitochondria is discussed from the perspective of the factors determining inter-organellar dynamics and the spatial proximity of mitochondria and ER membranes.

Down’s syndrome and Alzheimer’s disease: two sides of the same coin

All Down’s syndrome individuals develop Alzheimer’s disease (AD) neuropathology by the age of 40 years. To unite the two diseases under one hypothesis, we have suggested that classical AD, both of the genetic and late-onset sporadic forms, might be promoted by small numbers of trisomy 21 cells developing during the life of the affected individual. Recent evidence from several laboratories will be presented, which strongly supports the trisomy 21 hypothesis that defects in mitosis, and particularly in chromosome segregation, may be a part of the AD process. Specifically, genetic mutations that cause familial AD disrupt the cell cycle and lead to chromosome aneuploidy, including trisomy 21, in transgenic mice and transfected cells; cells from both familial and sporadic AD patients exhibit chromosome aneuploidy, including trisomy 21. The possibility that many cases of AD are mosaic for trisomy 21 suggests novel approaches to diagnosis and therapy.

Mutagenesis by retroviral insertion in chemical mutagen-generated quasi-haploid mammalian cells

Diploidy is a major obstacle to the mutagenic analysis of function in cultured mammalian cells. Here, we show that 6–8 rounds of chemical mutagenesis generates quasi-haploid cells that can be used as targets for insertional mutagenesis using a specially designed retroviral vector that permits rapid identification of disrupted genes in each cell that bears a phenotype of interest. The utility of combined chemical and insertional mutagenesis is illustrated by the identification of novel host genes that are required for macrophage sensitivity to anthrax lethal factor.

Alterations in presenilin 1 processing by amyloid-beta peptide in the rat retina

Accumulating evidence indicates that mutations in the presenilin 1 (PS1) gene are responsible for most cases of familial Alzheimer's disease (AD). Although its biological functions are not yet fully understood, it appears that PS1 plays a role in the processing and trafficking of the amyloid precursor protein (APP). However, little is known about factors that are involved in regulating the metabolism of PS1 especially in relation to AD pathology. In this study, we have examined the effect of optic nerve crush, intravitreal injection of the inflammatory agent lipopolysaccharide (LPS) or injection of amyloid beta(1-42) (A beta(1-42)) on the expression and processing of PS1 in the rat retina. We found that 48 h after injection of A beta(1-42) there was a dramatic alteration in the banding pattern of PS1 on Western blots, as indicated by marked changes in the levels of expression of some of its C- and N-terminal fragments in retinal homogenates. These results suggest an A beta(1-42)-induced potentiation of a non-specific stress-related but inflammation-independent alteration of processing of PS1 in this in vivo model.

p53-Dependent Aph-1 and Pen-2 anti-apoptotic phenotype requires the integrity of the gamma-secretase complex but is independent of its activity

The presenilin-dependent gamma-secretase activity, which is responsible for the generation of amyloid beta-peptide, is a high molecular weight complex composed of at least four components, namely, presenilin-1 (or presenilin-2), nicastrin, Aph-1, and Pen-2. Previous data indicated that presenilins, which are thought to harbor the catalytic core of the complex, also control p53-dependent cell death. Whether the other components of the gamma-secretase complex could also modulate the cell death process in mammalian neurons remained to be established. Here, we examined the putative contribution of Aph-1 and Pen-2 in the control of apoptosis in TSM1 cells from a neuronal origin. We show by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling and DNA fragmentation analyses that the overexpression of Aph-1a, Aph-1b, or Pen-2 drastically lowered staurosporine-induced cellular toxicity. In support of an apoptosis rather than necrosis process, Aph-1 and Pen-2 also lower staurosporine- and etoposide-induced caspase-3 expression and diminished caspase-3 activity and poly(ADP-ribose) polymerase inactivation. The Aph-1 and Pen-2 anti-apoptotic phenotype was associated with a drastic reduction of p53 expression and activity and lowered p53 mRNA transcription. Furthermore, the Aph-1- and Pen-2-associated reduction of staurosporine-induced caspase-3 activation was fully abolished by p53 deficiency. Conversely, Aph-1a, Aph-1b, and Pen-2 gene inactivation increases both caspase-3 activity and p53 mRNA levels. Finally, we show that Aph-1 and Pen-2 did not trigger an anti-apoptotic response in cells devoid of presenilins or nicastrin, whereas the protective response was still observed in fibroblasts devoid of beta-amyloid precursor protein and amyloid precursor protein like-protein 2. Furthermore, Aph-1- and Pen-2-associated protection against staurosporine-induced caspase-3 activation was not affected by the gamma-secretase inhibitors N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester and difluoromethylketone. Altogether, our study indicates that Aph-1 and Pen-2 trigger an anti-apoptotic response by lowering p53-dependent control of caspase-3. Our work also demonstrates that this phenotype is strictly dependent on the molecular integrity of the gamma-secretase complex but remains independent of the gamma-secretase catalytic activity.