Presenilin mutations and calcium signaling defects in the nervous and immune systems

Hepatic transcript profiling in beef cattle: Effects of rumen-protected niacin supplementation

The objective of our study was to assess the effect of rumen-protected niacin supplementation on the transcriptome of liver tissue in growing Angus × Simmental steers and heifers through RNA-seq analysis. Consequently, we wanted to assess the known role of niacin in the physiological processes of vasodilation, detoxification, and immune function in beef hepatic tissue. Normal weaned calves (~8 months old) were provided either a control diet or a diet supplemented with rumen-protected niacin (6 g/hd/d) for a 30-day period, followed by a liver biopsy. We observed a significant list of changes at the transcriptome level due to rumen-protected niacin supplementation. Several metabolic pathways revealed potential positive effects to the animal's liver metabolism due to administration of rumen-protected niacin; for example, a decrease in lipolysis, apoptosis, inflammatory responses, atherosclerosis, oxidative stress, fibrosis, and vasodilation-related pathways. Therefore, results from our study showed that the liver transcriptional machinery switched several metabolic pathways to a condition that could potentially benefit the health status of animals supplemented with rumen-protected niacin. In conclusion, based on the results of our study, we can suggest the utilization of rumen-protected niacin supplementation as a nutritional strategy could improve the health status of growing beef cattle in different beef production stages, such as backgrounding operations or new arrivals to a feedlot.

Cardiovascular-Specific PSEN1 Deletion Leads to Abnormalities in Calcium homeostasis

Mutations of PSEN1 have been reported in dilated cardiomyopathy pedigrees. Understanding the effects and mechanisms of PSEN1 in cardiomyocytes might have important implications for treatment of heart diseases. Here, we showed that PSEN1 was down-regulated in ischemia-induced failing hearts. Functionally, cardiovascular specific PSEN1 deletion led to spontaneous death of the mice due to cardiomyopathy. At the age of 11 months, the ratio of the heart weight/body weight was slightly lower in the Sm22a-PSEN1-KO mice compared with that of the WT mice. Echocardiography showed that the percentage of ejection fraction and fractional shortening was significantly reduced in the Sm22a-PSEN1-KO group compared with the percent of these measures in the WT group, indicating that PSEN1-KO resulted in heart failure. The abnormally regulated genes resulted from PSEN1-KO were detected to be enriched in muscle development and dilated cardiomyopathy. Among them, several genes encode Ca²⁺ ion channels, promoting us to investigate the effects of PSEN1 KO on regulation of Ca²⁺ in isolated adult cardiomyocytes. Consistently, in isolated adult cardiomyocytes, PSEN1-KO increased the concentration of cytosolic Ca²⁺ and reduced Ca²⁺ concentration inside the sarcoplasmic reticulum (SR) lumen at the resting stage. Additionally, SR Ca²⁺ was decreased in the failing hearts of WT mice, but with the lowest levels observed in the failing hearts of PSEN1 knockout mice. These results indicate that the process of Ca²⁺ release from SR into cytoplasm was affected by PSEN1 KO. Therefore, the abnormalities in Ca²⁺ homeostasis resulted from downregulation of PSEN1 in failing hearts might contribute to aging-related cardiomyopathy, which might had important implications for the treatment of aging-related heart diseases. This article is protected by copyright. All rights reserved.

Acetylcholine suppresses phagocytosis via binding to muscarinic- and nicotinic-acetylcholine receptors and subsequently interfering Ca2+- and NFκB-signaling pathways in blood clam

Though immunomodulation via cholinergic neurotransmitter acetylcholine (ACh), an important part of neuroendocrine-immune (NEI) regulatory network, has been well established in vertebrate species, the mechanisms remain poorly understood in invertebrates. In the present study, the immunomodulatory effect of ACh on haemocyte phagocytosis was investigated in an invertebrate bivalve species, Tegillarca granosa. Data obtained showed that in vitro ACh incubation suppressed phagocytic activity of haemocytes along with a significant elevation in intracellular Ca²⁺. In addition, the expressions of genes from Ca²⁺ signaling pathway were significantly induced whereas those from NF-κB signaling pathway were significantly down-regulated by ACh incubation. Furthermore, these adverse impacts of ACh were significantly relieved by the blocking of muscarinic acetylcholine receptors (mAChRs) or nicotinic acetylcholine receptors (nAChRs) using corresponding antagonists. Our study suggests that ACh suppresses phagocytosis via binding to both mAChRs and nAChRs, which disrupts intracellular Ca²⁺ homeostasis and subsequently interferes with downstream Ca²⁺ and NF-κB signaling pathways.

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.

Role of GPCR signaling and calcium dysregulation in Alzheimer's disease

Alzheimer's disease (AD), a late onset neurodegenerative disorder is characterized by the loss of memory, disordered cognitive function, caused by accumulation of amyloid-β (Aβ) peptide and neurofibrillary tangles (NFTs) in the neocortex and hippocampal brain area. Extensive research has been done on the findings of the disease etiology or pathological causes of aggregation of Aβ and hyperphosphorylation of tau protein without much promising results. Recently, calcium dysregulation has been reported to play an important role in the pathophysiology of AD. Calcium ion acts as one of the major secondary messengers, regulates many signaling pathways involved in cell survival, proliferation, differentiation, transcription and apoptosis. Calcium signaling is one of the major signaling pathways involved in the formation of memory, generation of energy and other physiological functions. It also can modulate function of many proteins upon binding. Dysregulation in calcium homeostasis leads to many physiological changes leading to neurodegenerative diseases including AD. In AD, GPCRs generate secondary messengers which regulate calcium homeostasis inside the cell and is reported to be disturbed in the pathological condition. Calcium channels and receptors present on the plasma membrane and intracellular organelle maintain calcium homeostasis through different signaling mechanisms. In this review, we have summarized the different calcium channels and receptors involved in calcium dysregulation which in turn play a critical role in the pathogenesis of AD. Understanding the role of calcium channels and GPCRs to maintain calcium homeostasis is an attempt to develop effective AD treatments.

Exogenous Ca2+ mitigates the toxic effects of TiO2 nanoparticles on phagocytosis, cell viability, and apoptosis in haemocytes of a marine bivalve mollusk, Tegillarca granosa

Phagocytosis suppression induced by nanoparticles (NPs) exposure is increasingly reported in marine species. However, the mechanisms underlying this impact remain poorly understood. In order to improve our present understanding of the immunotoxicity of NPs, acute (96 h) TiO₂ NP exposure and rescue trials via exogenous supply of Ca²⁺ were performed in the blood clam, Tegillarca granosa. The results show that the phagocytosis rate, cell viability, and intracellular Ca²⁺ concentration of haemocytes were significantly suppressed, whereas the intracellular ROS concentration of haemocytes significantly increased upon nTiO₂ exposure. Exposure to nTiO₂ also led to the significant downregulation of Caspase-3, Caspase-6, apoptosis regulator Bcl-2, Bcl-2-associated X, calmodulin kinase II, and calmodulin kinase kinase II. Furthermore, the toxic impacts of nTiO₂ were partially mitigated by the addition of exogenous Ca²⁺, as indicated by the recovery tendency in almost all the measured parameters. The present study indicates that Ca²⁺ signaling could be one of the key pathways through which nTiO₂ attacks phagocytosis.

Waterborne Cd2+ weakens the immune responses of blood clam through impacting Ca2+ signaling and Ca2+ related apoptosis pathways

Exposure to heavy metals such as Cadmium (Cd) may exert detrimental impacts on the immune responses of marine bivalve species. However, the immunotoxicity of Cd on blood clams remains unknown to date. Furthermore, though Cd²⁺ is known to compete with calcium (Ca²⁺) ions for their binding sites in cells and inhibit Ca²⁺ influx, whether Cd²⁺ weakens the immune responses of marine bivalves through inducing intracellular Ca²⁺ disorders still remains unclear. Therefore, the immunotoxicity of Cd²⁺ at different waterborne Ca²⁺ concentrations on blood clam, Tegillarca granosa, were investigated in the present study. Results obtained demonstrated that the total number, phagocytic activity, and red granulocytes ratio of the haemocytes were all significantly reduced after 10 days exposure of individuals to 25 μg/L Cd²⁺. However, when the waterborne Ca²⁺ concentrations were elevated by 10% and 20% (approximately 370 and 410 mg/L, respectively), mitigation effects on the immune responses of individuals were detected. In addition, though the expressions of genes from the Ca²⁺ signaling and Ca²⁺-related apoptosis pathways were significantly altered by Cd²⁺ exposure, the expression patterns of these genes were similar to that of the control when the waterborne Ca²⁺ concentrations were elevated, suggesting a relieving effect of waterborne Ca²⁺ on Cd²⁺ induced toxicity to haemocytes. The results obtained in the present study revealed that waterborne Cd²⁺ may hamper the immune responses of T. granosa through influencing Ca²⁺ signaling and Ca²⁺-related apoptosis pathways, which can be partially mitigated by elevating the waterborne Ca²⁺ concentrations.

Phlorotannin-rich Ecklonia cava reduces the production of beta-amyloid by modulating alpha- and gamma-secretase expression and activity

Beta-amyloid (Aβ) is a major pathogenic peptide in Alzheimer's disease (AD) and is generated by the processing of amyloid precursor protein (APP). We have previously reported that the brown algae Ecklonia cava, which has anti-oxidant and anti-inflammatory functions, decreased Aβ production and further aggregation in HEK293 cells expressing the APP Swedish mutation. Here, we show the reduction mechanism of Aβ production using the butanol extract of Ecklonia cava through the examination of expression and activity of alpha-, beta-, and gamma-secretase. Treatment with the extract resulted in the activation of alpha-secretase with a contrasting decrease in its mRNA and protein expression. This activation was consistent with the translocation of the extract into the plasma membrane of the secretase. Gamma-secretase activity was lowered by E. cava, and this effect may be due to the decreased expression of PSEN1 mRNA and protein. In addition, the basal nuclear location of PSEN1, which may affect chromosome missegregation in neurodegenerative disease, was reduced by the extract, despite the significance of this finding remains unclear. Taken together, these results led us to conclude that E. cava regulated the expression and activity of gamma-secretase and alpha-secretase, leading to a reduction in Aβ production by the stable cells. Our data indicate that E. cava is a novel natural-product candidate for AD treatment, although further in vivo studies are needed.

Modulation of transient receptor potential melastatin related 7 channel by presenilins

Presenilins (PS1 and PS2) are multifunctional proteins involved in a diverse array of molecular and cellular functions, including proteolysis, development, neurogenesis, synaptic plasticity, ion channel regulation and phospholipid metabolism. Mutations in presenilin genes are responsible for the majority of Familial Alzheimer disease (FAD). Consequently, FAD-associated mutations in genes encoding PS1 or PS2 lead to several key cellular phenotypes, including alterations in proteolysis of β-amyloid precursor protein (APP) and Ca(2+) entry. The mechanism underlying presenilin (PS)-mediated modulation of Ca(2+) entry remains to be determined. Our previous studies showed that the PS-dependent down-regulation of phosphatidylinositol-4,5-bisphosphate (PIP2) is attributable to the observed Ca(2+) deficits. In this study, we attempted to identify the ion channel that is subject to the PIP2 and PS-dependent modulation. We found that Ca(2+) or Zn(2+) entry via the transient receptor potential melastatin 7 (TRPM7) channel was attenuated by the presence of FAD-associated PS1 mutants, such as ΔE9 and L286V. TRPM7 has been implicated in Mg(2+) homeostasis and embryonic development. The intracellular delivery of PIP2 restored TRPM7-mediated Ca(2+) influx, indicating that the observed deficits in Ca(2+) entry are due to downregulation of PIP2. Conversely, PS1 and PS2 deficiency, previously shown to upregulate PIP2 levels, potentiated TRPM7-mediated Ca(2+) influx. PS-dependent changes in Ca(2+) influx could be neutralized by a TRPM7 channel blocker. Collectively, these results indicate that TRPM7 may underlie the Ca(2+) entry deficits observed in FAD-associated PS mutants and suggest that the normal function of PS involves regulation of TRPM7 through a PIP2-dependent mechanism.

AlzPathway: a comprehensive map of signaling pathways of Alzheimer's disease

Background

Alzheimer’s disease (AD) is the most common cause of dementia among the elderly. To clarify pathogenesis of AD, thousands of reports have been accumulating. However, knowledge of signaling pathways in the field of AD has not been compiled as a database before.

Description

Here, we have constructed a publicly available pathway map called “AlzPathway” that comprehensively catalogs signaling pathways in the field of AD. We have collected and manually curated over 100 review articles related to AD, and have built an AD pathway map using CellDesigner. AlzPathway is currently composed of 1347 molecules and 1070 reactions in neuron, brain blood barrier, presynaptic, postsynaptic, astrocyte, and microglial cells and their cellular localizations. AlzPathway is available as both the SBML (Systems Biology Markup Language) map for CellDesigner and the high resolution image map. AlzPathway is also available as a web service (online map) based on Payao system, a community-based, collaborative web service platform for pathway model curation, enabling continuous updates by AD researchers.

Conclusions

AlzPathway is the first comprehensive map of intra, inter and extra cellular AD signaling pathways which can enable mechanistic deciphering of AD pathogenesis. The AlzPathway map is accessible at http://alzpathway.org/.

Intracellular Ca2+ storage in health and disease: a dynamic equilibrium

Homeostatic control of the endoplasmic reticulum (ER) both as the site for protein handling (synthesis, folding, trafficking, disaggregation and degradation) and as a Ca2+ store is of crucial importance for correct functioning of the cell. Disturbance of the homeostatic control mechanisms leads to a vast array of severe pathologies. The Ca2+ content of the ER is a dynamic equilibrium between active uptake via Ca2+ pumps and Ca2+ release by a number of highly regulated Ca2+-release channels. Regulation of the Ca2+-release channels is very complex and several mechanisms are still poorly understood or controversial. There is increasing evidence that a number of unrelated proteins, either by themselves or in association with other Ca2+ channels, can provide additional Ca2+-leak pathways. The ER is a dynamic organelle and changes in its size and components have been described, either as a result of (de)differentiation processes affecting the secretory capacity of cells, or as a result of adaptation mechanisms to diverse stress conditions such as the unfolded protein response and autophagy. In this review we want to give an overview of the current knowledge of the (short-term) regulatory mechanisms that affect Ca2+-release and Ca2+-leak pathways and of the (long-term) adaptations in ER size and capacity. Understanding of the consequences of these mechanisms for cellular Ca2+ signaling could provide a huge therapeutic potential.

Variations in the neuropathology of familial Alzheimer's disease

Mutations in the amyloid precursor protein (APP), presenilin 1 (PSEN1) and presenilin 2 (PSEN2) genes cause autosomal dominant familial Alzheimer's disease (AD). PSEN1 and PSEN2 are essential components of the gamma-secretase complex, which cleaves APP to affect Abeta processing. Disruptions in Abeta processing have been hypothesised to be the major cause of AD (the amyloid cascade hypothesis). These genetic cases exhibit all the classic hallmark pathologies of AD including neuritic plaques, neurofibrillary tangles (NFT), tissue atrophy, neuronal loss and inflammation, often in significantly enhanced quantities. In particular, these cases have average greater hippocampal atrophy and NFT, more significant cortical Abeta42 plaque deposition and more substantial inflammation. Enhanced cerebral Abeta40 angiopathy is a feature of many cases, but particularly those with APP mutations where it can be the dominant pathology. Additional frontotemporal neuronal loss in association with increased tau pathology appears unique to PSEN mutations, with mutations in exons 8 and 9 having enlarged cotton wool plaques throughout their cortex. The mechanisms driving these pathological differences in AD are discussed.

Neuronal cell death in neurodegenerative diseases: recurring themes around protein handling

Neuronal cell death plays a role in many chronic neurodegenerative diseases with the loss of particular subsets of neurons. The loss of the neurons occurs during a period of many years, which can make the mode(s) of cell death and the initiating factors difficult to determine. In vitro and in vivo models have proved invaluable in this regard, yielding insight into cell death pathways. This review describes the main mechanisms of neuronal cell death, particularly apoptosis, necrosis, excitotoxicity and autophagic cell death, and their role in neurodegenerative diseases such as ischaemia, Alzheimer's, Parkinson's and Huntington's diseases. Crosstalk between these death mechanisms is also discussed. The link between cell death and protein mishandling, including misfolded proteins, impairment of protein degradation, protein aggregation is described and finally, some pro-survival strategies are discussed.

Subfield and layer-specific depletion in calbindin-D28K, calretinin and parvalbumin immunoreactivity in the dentate gyrus of amyloid precursor protein/presenilin 1 transgenic mice

The depletion of neuronal calcium binding proteins deprives neurons of the capacity to buffer high levels of intracellular Ca(2+) and this leaves them vulnerable to pathological processes, such as those present in Alzheimer's disease (AD). The aim of the present study was to investigate the expression of the calcium binding proteins, calbindin-D28K, calretinin and parvalbumin in the dentate gyrus (DG) of amyloid precursor protein (APP)/presenilin 1 (PS1) transgenic (Tg) mice and their non-Tg littermates, as well as the relation with the deposition of human amyloid beta (Abeta). We measured the expression of these three proteins at seven different rostro-caudal levels, and in the molecular, granular and polymorphic layers of the DG. We found that, except in the most caudal part of the DG, there is a substantial loss of calbindin-D28K immunoreactivity in all three layers of the DG in APP/PS1 mice compared with the non-Tg mice. Significant loss of calretinin immunoreactivity is present in most of the polymorphic layer of the DG of APP/PS1 mice compared with the non-Tg mice, as well as in the rostral and intermediate part of the inner molecular layer. Compared with the non-Tg mice parvalbumin immunoreactivity is significantly reduced throughout the whole polymorphic layer as well as in the rostral and intermediate part of the granular layer of DG in APP/PS1 mice. The relatively preservation of calbindin immunoreactivity in the caudal part of molecular and granular layers as well as calretinin immunoreactivity in the caudal part of polymorphic layer of the DG is likely related to the lower Abeta expression in those parts of DG. The present data suggest an involvement of calcium-dependent pathways in the pathogenesis of AD and indicate that there exists a subfield and layer-specific decrease in immunoreactivity which is related to the type of calcium-binding protein in APP/PS1 mice. Moreover, it seems that APP expression affects more the calbindin expression then parvalbumin and calretinin expression in the DG of APP/PS1 Tg mice.

Defective signal transduction in B lymphocytes lacking presenilin proteins

The mammalian presenilin (PS) proteins mediate the posttranslational cleavage of several protein substrates, including amyloid precursor protein, Notch family members, and CD44, but they have also been suggested to function in diverse cellular processes, including calcium-dependent signaling and apoptosis. We carried out an integrative computational study of multiple genomic datasets, including RNA expression, protein interaction, and pathway analyses, which implicated PS proteins in Toll-like receptor signaling. To test these computational predictions, we analyzed mice carrying a conditional allele of PS1 and a germ line-inactivating allele of PS2, together with Cre site-specific recombinase expression under the influence of CD19 control sequences. Notably, B cells deficient in both PS1 and PS2 function have an unexpected and substantial deficit in both lipopolysaccharide and B cell antigen receptor-induced proliferation and signal transduction events, including a defect in anti-IgM-mediated calcium flux. Taken together, these results demonstrate a fundamental and unanticipated role for PS proteins in B cell function and emphasize the potency of (systems level) integrative analysis of whole-genome datasets in identifying novel biologic signal transduction relationships. Our findings also suggest that pharmacologic inhibition of PS for the treatment of conditions such as Alzheimer's disease may have potential consequences for immune system function.

Proteomic analysis of peripheral leukocytes in Alzheimer's disease patients treated with divalproex sodium

The molecular profiling of peripheral tissues, including circulating leukocytes, may hold promise in the discovery of biomarkers for diagnosing and treating neurodegenerative diseases, including Alzheimer's disease (AD). As a proof-of-concept, we performed a proteomics study on peripheral leukocytes from patients with AD both before and during treatment with divalproex sodium. Using two-dimensional gel electrophoresis and MALDI-TOF mass spectrometry, we identified 10 differentially expressed proteins: two up-regulated proteins, 14-3-3 protein epsilon and peroxiredoxin 2; and eight down-regulated proteins, actin-interacting protein, mitogen activated protein kinase 1, beta actin, annexin A1, glyceraldehyde 3-phosphate dehydrogenase, transforming protein RhoA, acidic leucine-rich nuclear phosphoprotein 32 family member B, and a currently unidentified protein. A subset was validated on both the transcript and protein levels in normal human peripheral blood mononuclear cell cultures treated with valproic acid. These proteins comprise a number of functional classes that may be important to the biology of AD and to the therapeutic action of valproate. These data also suggest the potential of using peripheral leukocytes to monitor pharmaceutical action for neurodegenerative diseases.

A role for presenilin in post-stress regulation: effects of presenilin mutations on Ca2+ currents in Drosophila

It has been shown that presenilin is involved in maintaining Ca2+ homeostasis in neurons, including regulating endoplasmic reticulum (ER) Ca2+ storage. From studies of primary cultures and cell lines, however, its role in stress-induced responses is still controversial. In the present study we analyzed the effects of presenilin mutations on membrane currents and synaptic functions in response to stress using an in vivo preparation. We examined voltage-gated K+ and Ca2+ currents at the Drosophila larval neuromuscular junction (NMJ) with voltage-clamp recordings. Our data showed that both currents were generally unaffected by loss-of-function or Alzheimer's disease (AD) -associated presenilin mutations under normal or stress conditions induced by heat shock (HS) or ER stress. In larvae expressing the mutant presenilins, prolonged Ca2+ tail current, reflecting slower deactivation kinetics of Ca2+ channels, was observed 1 day after stress treatments were terminated. It was further demonstrated that the L-type Ca2+ channel was specifically affected under these conditions. Moreover, synaptic plasticity at the NMJ was reduced in larvae expressing the mutant presenilins. At the behavioral level, memory in adult flies was impaired in the presenilin mutants 1 day after HS. The results show that presenilin function is important during the poststress period and its impairment contributes to memory dysfunction observed during adaptation to normal conditions after stress. Our findings suggest a new stress-related mechanism by which presenilin may be implicated in the neuropathology of AD.

Mitochondrial membrane permeabilization in cell death

Irrespective of the morphological features of end-stage cell death (that may be apoptotic, necrotic, autophagic, or mitotic), mitochondrial membrane permeabilization (MMP) is frequently the decisive event that delimits the frontier between survival and death. Thus mitochondrial membranes constitute the battleground on which opposing signals combat to seal the cell's fate. Local players that determine the propensity to MMP include the pro- and antiapoptotic members of the Bcl-2 family, proteins from the mitochondrialpermeability transition pore complex, as well as a plethora of interacting partners including mitochondrial lipids. Intermediate metabolites, redox processes, sphingolipids, ion gradients, transcription factors, as well as kinases and phosphatases link lethal and vital signals emanating from distinct subcellular compartments to mitochondria. Thus mitochondria integrate a variety of proapoptotic signals. Once MMP has been induced, it causes the release of catabolic hydrolases and activators of such enzymes (including those of caspases) from mitochondria. These catabolic enzymes as well as the cessation of the bioenergetic and redox functions of mitochondria finally lead to cell death, meaning that mitochondria coordinate the late stage of cellular demise. Pathological cell death induced by ischemia/reperfusion, intoxication with xenobiotics, neurodegenerative diseases, or viral infection also relies on MMP as a critical event. The inhibition of MMP constitutes an important strategy for the pharmaceutical prevention of unwarranted cell death. Conversely, induction of MMP in tumor cells constitutes the goal of anticancer chemotherapy.

Expression of a familial Alzheimer's disease-linked presenilin-1 variant enhances perforant pathway lesion-induced neuronal loss in the entorhinal cortex

Alzheimer's disease (AD) is characterized by neuronal loss in the hippocampus and entorhinal cortex that is manifested by progressive memory impairment and cognitive decline. Autosomal-dominant, familial forms of AD (FAD) are caused by mutations in genes encoding amyloid precursor protein, presenilin-1 (PS1), and presenilin 2. Although it is established that expression of mutant PS1 variants leads to increased production of highly fibrillogenic amyloidbeta42 (Abeta42) peptides that deposit in the brains of patients with AD, the mechanism(s) by which Abeta deposition and expression of mutant genes induce lamina- and region-specific vulnerability of neuronal populations is not known. We have examined the hypothesis that expression of transgene-encoded FAD-linked mutant PS1 variants in entorhinal cortex neurons exacerbates the vulnerability of these cells to lesion-induced neuronal loss. To test this notion, we transected the perforant pathway (PP) of transgenic mice harboring either wild-type human PS1 (PS1HWT) or the FAD-linked mutant PS1DeltaE9 variant and examined neuronal survival in layer II of the entorhinal cortex (ECL2). Remarkably, PP transections lead to marked reductions in the numbers of ECL2 neurons in the ECL2 of mice expressing mutant PS1, compared with ECL2 neurons in PP-lesioned PS1HWT mice. Finally, and in contrast to studies in nontransgenic mice and in mice expressing PS1HWT, ECL2 neurons that express mutant PS1 and the calcium binding protein calbindin-D28k in ECL2 are also susceptible to lesion-induced neuronal loss. We conclude that expression of FAD-linked mutant PS1 variants enhances the vulnerability of neurons in the entorhinal cortex to PP lesion-induced cytotoxicity.

Misfolded proteins, endoplasmic reticulum stress and neurodegeneration

The accumulation of misfolded proteins (e.g. mutant or damaged proteins) triggers cellular stress responses that protect cells against the toxic buildup of such proteins. However, prolonged stress due to the buildup of these toxic proteins induces specific death pathways. Dissecting these pathways should be valuable in understanding the pathogenesis of, and ultimately in designing therapy for, neurodegenerative diseases that feature misfolded proteins.

Suppression of calcium release from inositol 1,4,5-trisphosphate-sensitive stores mediates the anti-apoptotic function of nuclear factor-kappaB

The activation of the transcription factor nuclear factor-kappaB (NF-kappaB) by growth factors, cytokines, and cellular stress can prevent apoptosis, but the underlying mechanism is unknown. Here we provide evidence for an action of NF-kappaB on calcium signaling that accounts for its anti-apoptotic function. Embryonic fibroblasts lacking the transactivating subunit of NF-kappaB RelA (p65) exhibit enhanced inositol 1,4,5-trisphosphate (IP(3)) receptor-mediated calcium release and increased sensitivity to apoptosis, which are restored upon re-expression of RelA. The size of the endoplasmic reticulum (ER) calcium pool and the number of IP(3) receptors per cell are decreased in response to stimuli that activate NF-kappaB and are increased when NF-kappaB activity is suppressed. The selective antagonism of IP(3) receptors blocks apoptosis in RelA-deficient cells, whereas activation of NF-kappaB in normal cells leads to decreased levels of the type 1 IP(3) receptor and decreased calcium release. Overexpression of Bcl-2 normalizes ER calcium homeostasis and prevents calcium-mediated apoptosis in RelA-deficient cells. These findings establish an ER calcium channel as a pivotal target for NF-kappaB-mediated cell survival signaling.

Overexpression of calsenilin enhances γ-secretase activity

Presenilin/gamma-secretase is a membrane-associated protease that cleaves within the transmembrane region of the amyloid precursor protein (APP) to generate amyloid-beta peptide (Abeta) whose deposition in the brain is a characteristic of Alzheimer's disease (AD). Calsenilin, a calcium binding protein that has been shown to interact with the C-termini of both presenilin 1 (PS1) and presenilin 2 (PS2), appears to play a role in transcriptional regulation and apoptosis and to bind to A-type voltage-gated potassium channels. Here, we report that overexpression of calsenilin enhanced gamma-secretase activity in cells. The effect of calsenilin on the gamma-cleavage of substrates was blocked by the selective gamma-secretase inhibitor L-685,458. We also employed a cellular gamma-cleavage GFP-reporter assay to demonstrate the effect of calsenilin on gamma-secretase activity. To establish a direct role for calsenilin in regulating gamma-secretase activity, we incubated purified calsenilin with isolated membrane fractions and found increased Abeta production in a cell free system. These data suggest that calsenilin may be one of the regulatory factors for gamma-secretase.

Calcium binding sequences in calmyrin regulates interaction with presenilin-2

Calmyrin is a myristoylated calcium binding protein that contains four putative EF-hands. Calmyrin interacts with a number of proteins, including presenilin-2 (PS2). However, the biophysical properties of calmyrin, and the molecular mechanisms that regulate its binding to different partners, are not well understood. By site-directed mutagenesis and Ca2+ binding studies, we found that calmyrin binds two Ca2+ ions with a dissociation constant of approximately 53 microM, and that the two C-terminal EF-hands 3 and 4 bind calcium. Using ultraviolet spectroscopy, circular dichroism (CD), and NMR, we found that Ca(2+)-free and -bound calmyrin have substantially different protein conformations. By yeast two-hybrid assays, we found that both EF-hands 3 and 4 of calmyrin must be intact for calmyrin to interact with PS2-loop sequences. Pulse-chase studies of HeLa cells transfected with calmyrin expression constructs indicated that wild-type (Wt) calmyrin has a half-life of approximately 75 min, whereas a mutant defective in myristoylation turns over more rapidly (half-life of 35 min). By contrast, the half-lives of calmyrin mutants with a disrupted EF-hand 3 or EF-hand 4 were 52 and 170 min, respectively. Using immunofluorescence staining of HeLa cells transfected with Wt and mutant calmyrin cDNAs, we found that both calcium binding and myristoylation are important for dynamic intracellular targeting of calmyrin. Double immunofluorescence microscopy indicated that Wt and myristoylation-defective calmyrin proteins colocalize efficiently and to the same extent with PS2, whereas calmyrin mutants defective in calcium binding display less colocalization with PS2. Our results suggest that calmyrin functions as a calcium sensor and that calcium binding sequences in calmyrin are important for interaction with the PS2 loop.

Coupling endoplasmic reticulum stress to the cell death program

The endoplasmic reticulum (ER) regulates protein synthesis, protein folding and trafficking, cellular responses to stress and intracellular calcium (Ca(2+)) levels. Alterations in Ca(2+) homeostasis and accumulation of misfolded proteins in the ER cause ER stress that ultimately leads to apoptosis. Prolonged ER stress is linked to the pathogenesis of several different neurodegenerative disorders. Apoptosis is a form of cell death that involves the concerted action of a number of intracellular signaling pathways including members of the caspase family of cysteine proteases. The two main apoptotic pathways, the death receptor ('extrinsic') and mitochondrial ('intrinsic') pathways, are activated by caspase-8 and -9, respectively, both of which are found in the cytoplasm. Recent studies point to the ER as a third subcellular compartment implicated in apoptotic execution. Here, we review evidence for the contribution of various cellular molecules that contribute to ER stress and subsequent cellular death. It is hoped that dissection of the molecular components and pathways that alter ER structure and function and ultimately promote cellular death will provide a framework for understanding degenerative disorders that feature misfolded proteins.

Potential role of presenilin-regulated signaling pathways in sporadic neurodegeneration

Neurodegenerative diseases can be genetic or sporadic in origin. Genetic analysis has changed the study of the pathogenesis of these disorders by showing the causative functions of rare mutations. Yet, in the most common age-associated neurodegenerative diseases such as Alzheimer's and Parkinson's diseases, the causes of neurodegeneration remain to be clarified. The observations that presenilin modulates proteolysis and turnover of several signaling molecules have led to speculations that pathways that are important in development may contribute to neurodegeneration. In this article, the possibility that these presenilin-regulated molecules may contribute to neurodegeneration is reviewed.

Involvement of Notch signaling in hippocampal synaptic plasticity

During development of the nervous system, the fate of stem cells is regulated by a cell surface receptor called Notch. Notch is also present in the adult mammalian brain; however, because Notch null mice die during embryonic development, it has proven difficult to determine the functions of Notch. Here, we used Notch antisense transgenic mice that develop and reproduce normally, but exhibit reduced levels of Notch, to demonstrate a role for Notch signaling in synaptic plasticity. Mice with reduced Notch levels exhibit impaired long-term potentiation (LTP) at hippocampal CA1 synapses. A Notch ligand enhances LTP in normal mice and corrects the defect in LTP in Notch antisense transgenic mice. Levels of basal and stimulation-induced NF-kappa B activity were significantly decreased in mice with reduced Notch levels. These findings suggest an important role for Notch signaling in a form of synaptic plasticity known to be associated with learning and memory processes.

Protective role of Bcl-2 on β-amyloid-induced cell death of differentiated PC12 cells: reduction of NF-κB and p38 MAP kinase activation

Activation of the apoptosis program by an increased production of beta-amyloid peptides (Abeta) has been implicated in the neuronal cell death of Alzheimer's disease (AD). Bcl-2 is a well-demonstrated anti-apoptotic protein, however, the mechanisms of anti-apoptotic action of Bcl-2 in Abeta-induced neuronal cell death are not fully understood. In the present study, we therefore have investigated the possibility that overexpression of Bcl-2 may prevent Abeta-induced cell death through inhibition of pro-apoptotic activation of p38 MAP kinase and the transcription factor NF-kappaB in nerve growth factor (NGF)-induced differentiated PC12 cells. Treatment of Abeta into differentiated PC12 cells transfected with plasmid alone resulted in increase of cell death determined by measurement of cytotoxicity and apoptosis in a dose dependent manner. Consistent with the increase of cell death, treatment of Abeta resulted in increase of p38 MAP kinase and NF-kappaB activation. However, overexpression of Bcl-2 reduced Abeta-induced apoptosis, and suppressed the activation of p38 MAP kinase and NF-kappaB. In addition, a p38 MAP kinase specific inhibitor SB 203580 attenuated Abeta-induced apoptosis. This inhibitory effect was correlated well with the inhibition of p38 MAP kniase and NF-kappaB activation. Moreover, inhibition of NF-kappaB activation by sodium salicylates reduced Abeta-induced apoptosis and activation of p38 MAP kinase, and up regulated Bcl-2 expression. These results suggest that Bcl-2 overexpression protects against Abeta-induced cell death of differentiated PC12, and its protective effect may be related to the reduction of Abeta-induced activation of p38 MAP kinase and NF-kappaB.

Impairment of phosphatase 2A contributes to the prolonged MAP kinase phosphorylation in Alzheimer's disease fibroblasts

The serine/threonine phosphatase 2A (PP2A) has been implicated in the pathogenesis of Alzheimer's disease (AD) due to its important role in regulating dephosphorylation of the microtubule-associated protein tau and mitogen-activated protein (MAP) kinase. In the present study, we show that PP2A was responsible for dephosphorylation of the extracellular signal-regulated kinase 1/2 (Erk1/2) following its activation by BK stimulation. Abnormal gene and protein expressions of PP2A, as well as its activity, were found to contribute to the abnormally prolonged Erk1/2 phosphorylation in the AD fibroblasts. Inhibition of PP2A with okadiac acid produced enhanced and more lasting Erk1/2 phosphorylation after BK stimulation, whereas FK506, an inhibitor of PP2B and FK-binding protein, inhibited the BK-stimulated Erk1/2 phosphorylation. Furthermore, while the phosphorylated Erk1/2 was concentrated in the nucleus of AC cells, it was mainly distributed in the extranuclear compartments of AD cells. These results suggest that the delayed dephosphorylation of Erk1/2 in AD cells following its BK-stimulated activation may be due to deficits of PP2A activity and impaired nuclear translocation of phosphorylated Erk1/2.

Infectious agents and age-related neurodegenerative disorders

chlamdAs with other organ systems, the vulnerability of the nervous system to infectious agents increases with aging. Several different infectious agents can cause neurodegenerative conditions, with prominent examples being human immunodeficiency virus (HIV-1) dementia and prion disorders. Such infections of the central nervous system (CNS) typically have a relatively long incubation period and a chronic progressive course, and are therefore increasing in frequency as more people live longer. Infectious agents may enter the central nervous system in infected migratory macrophages, by transcytosis across blood-brain barrier cells or by intraneuronal transfer from peripheral nerves. Synapses and lipid rafts are important sites at which infectious agents may enter neurons and/or exert their cytotoxic effects. Recent findings suggest the possibility that infectious agents may increase the risk of common age-related neurodegenerative disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS) and stroke. While scenarios can be envisioned whereby viruses such as Chlamydia pneumoniae, herpes simplex and influenza promote damage to neurons during aging, there is no conclusive evidence for a major role of these pathogens in neurodegenerative disorders. In the case of stroke, blood vessels may be adversely affected by bacteria or viruses resulting in atherosclerosis.

Regulation of apoptosis by endoplasmic reticulum pathways

Apoptotic programmed cell death pathways are activated by a diverse array of cell extrinsic and intrinsic signals, most of which are ultimately coupled to the activation of effector caspases. In many instances, this involves an obligate propagation through mitochondria, causing egress of critical proapoptotic regulators to the cytosol. Central to the regulation of the mitochondrial checkpoint is a complex three-way interplay between members of the BCL-2 family, which are comprised of an antiapoptotic subgroup including BCL-2 itself, and the proapoptotic BAX,BAK and BH3-domain-only subgroups. Constituents of all three of these BCL-2 classes, however, also converge on the endoplasmic reticulum (ER), an organelle whose critical contributions to apoptosis is only now becoming apparent. In addition to propagating death-inducing stress signals itself, the ER also contributes in a fundamental way to Fas-mediated apoptosis and to p53-dependent pathways resulting from DNA damage and oncogene expression. Mobilization of ER calcium stores can initiate the activation of cytoplasmic death pathways as well as sensitize mitochondria to direct proapoptotic stimuli. Additionally, the existence of BCL-2-regulated initiator procaspase activation complexes at the ER membrane has also been described. Here, we review the potential underlying mechanisms involved in these events and discuss pathways for ER-mitochondrial crosstalk pertinent to a number of cell death stimuli.

Neuronal and glial calcium signaling in Alzheimer's disease

Cognitive impairment and emotional disturbances in Alzheimer's disease (AD) result from the degeneration of synapses and death of neurons in the limbic system and associated regions of the cerebral cortex. An alteration in the proteolytic processing of the amyloid precursor protein (APP) results in increased production and accumulation of amyloid beta-peptide (Abeta) in the brain. Abeta has been shown to cause synaptic dysfunction and can render neurons vulnerable to excitotoxicity and apoptosis by a mechanism involving disruption of cellular calcium homeostasis. By inducing membrane lipid peroxidation and generation of the aldehyde 4-hydroxynonenal, Abeta impairs the function of membrane ion-motive ATPases and glucose and glutamate transporters, and can enhance calcium influx through voltage-dependent and ligand-gated calcium channels. Reduced levels of a secreted form of APP which normally regulates synaptic plasticity and cell survival may also promote disruption of synaptic calcium homeostasis in AD. Some cases of inherited AD are caused by mutations in presenilins 1 and 2 which perturb endoplasmic reticulum (ER) calcium homeostasis such that greater amounts of calcium are released upon stimulation, possibly as the result of alterations in IP(3) and ryanodine receptor channels, Ca(2+)-ATPases and the ER stress protein Herp. Abnormalities in calcium regulation in astrocytes, oligodendrocytes, and microglia have also been documented in studies of experimental models of AD, suggesting contributions of these alterations to neuronal dysfunction and cell death in AD. Collectively, the available data show that perturbed cellular calcium homeostasis plays a prominent role in the pathogenesis of AD, suggesting potential benefits of preventative and therapeutic strategies that stabilize cellular calcium homeostasis.

Mitochondrial dysfunction, apoptotic cell death, and Alzheimer’s disease

Being major sources of reactive oxygen species (ROS), mitochondrial structures are exposed to high concentrations of ROS and might therefore be particularly susceptible to oxidative injury. Mitochondrial damage may play a pivotal role in the cell death decision. Bolstered evidence indicates that mitochondrial abnormalities might be part of the spectrum of chronic oxidative stress occurring in Alzheimer's disease (AD) finally contributing to synaptic failure and neuronal degeneration. Accumulation and oligomerization of amyloid beta (Abeta) is also thought to play a central role in the pathogenesis of this disease by probably directly leading to mitochondrial dysfunction. Moreover, numerous lines of findings indicate increased susceptibility to apoptotic cell death and increased oxidative damage as common features in neurons from sporadic AD patients but also from familial AD (FAD) cases. Here we provide a summary of recent work demonstrating some key abnormalities that may initiate and promote pathological events in AD. Finally, we emphasize a hypothetical sequence of the pathogenic steps linking sporadic AD, FAD, and Abeta production with mitochondrial dysfunction, caspase pathway, and neuronal loss.

Homocysteine and folate deficiency sensitize oligodendrocytes to the cell death-promoting effects of a presenilin-1 mutation and amyloid beta-peptide

Although damage to white matter occurs in the brains of patients with Alzheimer's disease (AD), the underlying mechanisms are unknown. Recent findings suggest that individuals with elevated levels of homocysteine are at increased risk of AD. Here we show that oligodendrocytes from mice expressing a mutant form of presenilin-1 (PS1) that causes familial AD exhibit increased sensitivity to death induced by homocysteine compared to oligodendrocytes from wild-type control mice. Homocysteine also sensitized oligodendrocytes to the cytotoxicity of amyloid beta-peptide. Folate deficiency, which is known to result in elevated levels of homocysteine in vivo, also sensitized oligodendrocytes to the cell-death-promoting actions of mutant PS1 and amyloid beta-peptide. Inhibitors of poly (ADP-ribose) polymerase and p53 protected oligodendrocytes against cell death induced by homocysteine and amyloid beta-peptide, consistent with a role for a DNA-damage response in the cell death process. These findings demonstrate an adverse effect of homocysteine on oligodendrocytes, and suggest roles for homocysteine and folate deficiency in the white matter damage in AD and related neurodegenerative disorders.

Ca2+/calmodulin-dependent modulation of cell cycle elements pRb and p27kip1 involved in the enhanced proliferation of lymphoblasts from patients with Alzheimer dementia

Failure of cell cycle regulation in neurons might be critically involved in the process of neurodegeneration in Alzheimer's disease (AD). We present here evidence to support the hypothesis that cell cycle alterations occur in cells other than neurons in AD sufferers. Lymphocytes from AD patients immortalized with Epstein-Barr virus showed an enhanced rate of proliferation and increased phosphorylation of the retinoblastoma protein (pRb) and other members of the family of pocket proteins compared with cell lines derived from normal age-matched controls. The calmodulin antagonist calmidazolium, as well as W-7 and W-13, abrogated the enhanced activity of AD cells without altering the normal basal rate of proliferation. The effect of calmidazolium was accompanied by partially dephosphorylation of pRb. No changes were found in the expression levels of the G1 cyclin/Cdks complexes. However, lymphoblasts derived from AD patients showed reduced levels of the Cdk inhibitor p27(kip1), which were restored after anti-calmodulin treatment of the cultures. These observations suggest that in AD cells the enhanced rates of cell proliferation and phosphorylation of pRb and the intracellular content of p27(kip1) may be interrelated events controlled by a mechanism dependent on the Ca(2+)/calmodulin signaling pathway. The distinct functional features of lymphoblastoid cells from AD patients offer an invaluable, noninvasive tool to investigate the etiopathogenesis, and eventually, for the early diagnosis and prognosis of this devastating disease.

Expression of group I metabotropic glutamate receptors in rat hippocampal cells in culture and their characterization by intracellular calcium ion dynamics

The distribution of group I metabotropic glutamate receptors in rat hippocampal cells in culture was examined by calcium imaging and immunocytochemistry. To distinguish different cell types in the culture, the effects of t-ACPD ((1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid) and of NMDA (N-methyl-D-aspartate) were examined. About 40% of the cultured cells showed either a transient increase or a sustained or oscillatory increase in the intracellular calcium concentration ([Ca(2+)](i)) during t-ACPD administration, while about 60% of the cells showed a sustained [Ca(2+)](i) increase in response to NMDA. Cells that showed an oscillatory [Ca(2+)](i) change during t-ACPD administration did not respond to NMDA administration, while cells that showed a sustained [Ca(2+)](i) increase during NMDA administration did not show any oscillatory response to t-ACPD. After pharmacological examination using those two agonists, the cultured cells were subjected to immunocytochemistry using anti-GFAP and ant-MAP-2 antibodies to distinguish, respectively, astrocytes and neurons. All cells responding to NMDA with a sustained [Ca(2+)](i) increase were MAP-2-positive, whereas all cells showing either oscillatory or sustained [Ca(2+)](i) increase in response to t-ACPD were GFAP-positive. The present results show that, in these cultures, group I metabotropic glutamate receptors are mainly expressed on glial cells and contribute to dynamic [Ca(2+)](i) changes in astrocytes.

Mitochondria in cell death: novel targets for neuroprotection and cardioprotection

Post-mitotic neurons and heart muscle cells undergo apoptotic cell death in a variety of acute and chronic degenerative diseases. The intrinsic pathway of apoptosis involves the permeabilization of mitochondrial membranes, which leads to the release of protease and nuclease activators, and to bioenergetic failure. Mitochondrial permeabilization is induced by a variety of pathologically relevant second messengers, including reactive oxygen species, calcium, stress kinases and pro-apoptotic members of the Bcl-2 family. Several pharmacological agents act on mitochondria to prevent the permeabilization of their membranes, thereby inhibiting apoptosis. Such agents include inhibitors of the permeability transition pore complex (in particular ligands of cyclophilin D), openers of mitochondrial ATP-sensitive or Ca(2+)-activated K(+) channels, and proteins from the Bcl-2 family engineered to cross the plasma membrane. In addition, manipulations that modulate the expression or activity of mitochondrial uncoupling proteins can prevent the death of post-mitotic cells. Such agents hold promise for use in clinical neuroprotection and cardioprotection.

Will caloric restriction and folate protect against AD and PD?

Recent epidemiologic studies of different sample populations have suggested that the risk of AD and PD may be increased in individuals with high-calorie diets and in those with increased homocysteine levels. Dietary restriction and supplementation with folic acid can reduce neuronal damage and improve behavioral outcome in mouse models of AD and PD. Animal studies have shown that the beneficial effects of dietary restriction result, in part, from increased production of neurotrophic factors and cytoprotective protein chaperones in neurons. By keeping homocysteine levels low, folic acid can protect cerebral vessels and can prevent the accumulation of DNA damage in neurons caused by oxidative stress and facilitated by homocysteine. Although further studies are required in humans, the emerging data suggest that high-calorie diets and elevated homocysteine levels may render the brain vulnerable to neurodegenerative disorders.

Disruption of neurogenesis by amyloid beta-peptide, and perturbed neural progenitor cell homeostasis, in models of Alzheimer's disease

Neurogenesis occurs in the adult mammalian brain and may play roles in learning and memory processes and recovery from injury, suggesting that abnormalities in neural progenitor cells (NPC) might contribute to the pathogenesis of disorders of learning and memory in humans. The objectives of this study were to determine whether NPC proliferation, survival and neuronal differentiation are impaired in a transgenic mouse model of Alzheimer's disease (AD), and to determine the effects of the pathogenic form of amyloid beta-peptide (Abeta) on the survival and neuronal differentiation of cultured NPC. The proliferation and survival of NPC in the dentate gyrus of the hippocampus was reduced in mice transgenic for a mutated form of amyloid precursor protein that causes early onset familial AD. Abeta impaired the proliferation and neuronal differentiation of cultured human and rodent NPC, and promoted apoptosis of neuron-restricted NPC by a mechanism involving dysregulation of cellular calcium homeostasis and the activation of calpains and caspases. Adverse effects of Abeta on NPC may contribute to the depletion of neurons and cognitive impairment in AD.

Numb isoforms containing a short PTB domain promote neurotrophic factor-induced differentiation and neurotrophic factor withdrawal-induced death of PC12 Cells

The development of the nervous system is regulated by trophic signals that control cell proliferation, differentiation, and survival. Numb is an evolutionarily conserved protein identified by its ability to control cell fate in the nervous system of Drosophila. Mammals express four isoforms of Numb that differ in the length of a phosphotyrosine-binding (PTB) domain and a proline-rich region (PRR). Using PC12 cells stably expressing each of the human isoforms, we show that Numb regulates sensitivity of the cells to neurotrophic factor-induced differentiation and neurotrophic factor withdrawal-induced death in an isoform-specific manner. Numb isoforms containing a short PTB domain enhance the differentiation response to NGF and enhance apoptosis upon NGF withdrawal; Numb isoforms containing a long PTB domain exhibit the same sensitivity to NGF as vector-transfected cells. These effects of Numb were found to be independent of the length of the PRR. In undifferentiated conditions, the levels of full-length TrkA and of phosphorylated p44/p42 mitogen-activated protein kinase (MAPK) are increased in cells expressing Numb isoforms with a short PTB domain, indicating an up-regulation of NGF signaling pathways. Furthermore, we provide evidence that the mechanism whereby short PTB domain Numb isoforms sensitize cells to trophic factor deprivation-induced apoptosis involves elevations in intracellular calcium concentrations. Our results suggest that Numb sensitizes cells to neurotrophin responses in an isoform-specific manner, an effect that may play an important role in the development and plasticity of the nervous system.

Modification of brain aging and neurodegenerative disorders by genes, diet, and behavior

Multiple molecular, cellular, structural, and functional changes occur in the brain during aging. Neural cells may respond to these changes adaptively, or they may succumb to neurodegenerative cascades that result in disorders such as Alzheimer's and Parkinson's diseases. Multiple mechanisms are employed to maintain the integrity of nerve cell circuits and to facilitate responses to environmental demands and promote recovery of function after injury. The mechanisms include production of neurotrophic factors and cytokines, expression of various cell survival-promoting proteins (e.g., protein chaperones, antioxidant enzymes, Bcl-2 and inhibitor of apoptosis proteins), preservation of genomic integrity by telomerase and DNA repair proteins, and mobilization of neural stem cells to replace damaged neurons and glia. The aging process challenges such neuroprotective and neurorestorative mechanisms. Genetic and environmental factors superimposed upon the aging process can determine whether brain aging is successful or unsuccessful. Mutations in genes that cause inherited forms of Alzheimer's disease (amyloid precursor protein and presenilins), Parkinson's disease (alpha-synuclein and Parkin), and trinucleotide repeat disorders (huntingtin, androgen receptor, ataxin, and others) overwhelm endogenous neuroprotective mechanisms; other genes, such as those encoding apolipoprotein E(4), have more subtle effects on brain aging. On the other hand, neuroprotective mechanisms can be bolstered by dietary (caloric restriction and folate and antioxidant supplementation) and behavioral (intellectual and physical activities) modifications. At the cellular and molecular levels, successful brain aging can be facilitated by activating a hormesis response in which neurons increase production of neurotrophic factors and stress proteins. Neural stem cells that reside in the adult brain are also responsive to environmental demands and appear capable of replacing lost or dysfunctional neurons and glial cells, perhaps even in the aging brain. The recent application of modern methods of molecular and cellular biology to the problem of brain aging is revealing a remarkable capacity within brain cells for adaptation to aging and resistance to disease.