Calbindin D28k blocks the proapoptotic actions of mutant presenilin 1: reduced oxidative stress and preserved mitochondrial function

Melatonin-induced calbindin-D9k expression reduces hydrogen peroxide-mediated cell death in rat pituitary GH3 cells

In this study, we investigated whether calbindin-D9k (CaBP-9k) expression was regulated by melatonin during hydrogen peroxide (H(2)O(2))-induced cell death in rat pituitary GH3 cells. CaBP-9k expression was increased by melatonin in a dose- and time-dependent manner, indicating that CaBP-9k expression is regulated by melatonin. Cell survival was increased approximately 27-30% where H(2)O(2)-treated cells (0.25 or 0.5 mm) were also incubated with 1 mm melatonin, when compared with H(2)O(2) alone or H(2)O(2) plus 0.5 mm melatonin. This result was consistent with 4,6-diamidino-2-phenylindole staining. CaBP-9k expression was also augmented by co-treatment with H(2)O(2) and 1 mm melatonin, suggesting a functional relationship between increased cell death and melatonin-induced CaBP-9k expression during H(2)O(2)-mediated apoptosis. Bcl-2-associated protein expression increased following treatment with H(2)O(2) alone, whereas Bcl-2 expression was elevated following treatment with melatonin alone, or H(2)O(2) plus melatonin. The expression of p53 was depressed by treatment with melatonin alone, or co-treatment with H(2)O(2) plus melatonin. These results correlated with CaBP-9k expression levels and activation of the mitogen-activated protein kinase/extracellular signal-regulated kinase signaling pathway. Knockdown of CaBP-9k expression using a small inhibitory RNA resulted in an elevation of H(2)O(2)-induced cell death, whereas cell survival was increased in cells that overexpressed CaBP-9k, providing additional evidence that the induction of CaBP-9k expression may be associated with survival signaling during H(2)O(2)-mediated oxidative cell death. CaBP-9k appears to interact with p53, suggesting a possible role for this interaction in cell proliferation and cell cycle progression.

Melatonin-induced estrogen receptor alpha-mediated calbindin-D9k expression plays a role in H2O2-mediated cell death in rat pituitary GH3 cells

Calbindin-D9k (CaBP-9k) is a 9-kDa polypeptide possessing two calcium-binding sites that is expressed in the mammalian intestine, uterus, and pituitary gland. The factors regulating the expression of the estrogen receptor (ER) and CaBP-9k in the pituitary gland are currently unknown. In this study, we investigated whether the ER and CaBP-9k expression are regulated by melatonin during H(2)O(2)-induced cell death in rat pituitary GH3 cells. Cell survival increased by approximately 27-36% in H(2)O(2) plus melatonin compared to H(2)O(2) alone, and CaBP-9k expression was augmented by treatment with H(2)O(2) plus melatonin. These results suggest that the increase in cell survival and the melatonin-induced CaBP-9k expression may play a role in protecting cells against H(2)O(2)-mediated cell death. This result is also consistent with the increase in CaBP-9k expression leading to rises in p-ERK and p-Bad (S112). Over-expression of CaBP-9k caused an increase in p-ERK. ERalpha expression was higher in H(2)O(2) plus melatonin-treated cells compared to those treated with H(2)O(2) alone, while ERbeta expression was not. Also, ERalpha in the nuclear fraction increased in the presence of melatonin and decreased in the presence of ICI 182 780 or ICI 182 780 plus melatonin. The relative binding affinity of ERalpha for melatonin was higher than that of ERbeta, suggesting that melatonin has the potential to preferentially bind ERalpha. In conclusion, these results indicate that melatonin may increase CaBP-9k expression through ERalpha.

Calcium hypothesis of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder caused by an increase in amyloid metabolism. The calcium hypothesis of AD explores how activation of the amyloidogenic pathway may function to remodel the neuronal Ca(2+) signaling pathways responsible for cognition. Hydrolysis of the beta-amyloid precursor protein (APP) yields two products that can influence Ca(2+) signaling. Firstly, the amyloids released to the outside form oligomers that enhance the entry of Ca(2+) that is pumped into the endoplasmic reticulum (ER). An increase in the luminal level of Ca(2+) within the ER enhances the sensitivity of the ryanodine receptors (RYRs) to increase the amount of Ca(2+) being released from the internal stores. Secondly, the APP intracellular domain may alter the expression of key signaling components such as the RYR. It is proposed that this remodeling of Ca(2+) signaling will result in the learning and memory deficits that occur early during the onset of AD. In particular, the Ca(2+) signaling remodeling may erase newly acquired memories by enhancing the mechanism of long-term depression that depends on activation of the Ca(2+)-dependent protein phosphatase calcineurin. The alteration in Ca(2+) signaling will also contribute to the neurodegeneration that characterizes the later stages of dementia.

Calcium dysregulation in Alzheimer's disease: from mechanisms to therapeutic opportunities

Calcium is involved in many facets of neuronal physiology, including activity, growth and differentiation, synaptic plasticity, and learning and memory, as well as pathophysiology, including necrosis, apoptosis, and degeneration. Though disturbances in calcium homeostasis in cells from Alzheimer's disease (AD) patients have been observed for many years, much more attention was focused on amyloid-beta (Abeta) and tau as key causative factors for the disease. Nevertheless, increasing lines of evidence have recently reported that calcium dysregulation plays a central role in AD pathogenesis. Systemic calcium changes accompany almost the whole brain pathology process that is observed in AD, including synaptic dysfunction, mitochondrial dysfunction, presenilins mutation, Abeta production and Tau phosphorylation. Given the early and ubiquitous involvement of calcium dysregulation in AD pathogenesis, it logically presents a variety of potential therapeutic targets for AD prevention and treatment, such as calcium channels in the plasma membrane, calcium channels in the endoplasmic reticulum membrane, Abeta-formed calcium channels, calcium-related proteins. The review aims to provide an overview of the current understanding of the molecular mechanisms involved in calcium dysregulation in AD, and an insight on how to exploit calcium regulation as therapeutic opportunities in AD.

Numb-mediated neurite outgrowth is isoform-dependent, and requires activation of voltage-dependent calcium channels

Numb is an evolutionarily conserved protein that controls the differentiation of neuronal progenitor cells by unknown mechanisms. Here we report that the neural cells expressing Numb isoforms with short phosphotyrosine-binding (SPTB) domain undergo extensive neurite outgrowth, an effect that can be blocked by voltage-gated Ca2+ channel (VGCC) inhibitor or by Ca2+ chelator. In contrast, tyrosine kinase inhibitor, genistein, and selective receptor tyrosine kinase (TrkA) inhibitor, K252alpha did not affect SPTB Numb-mediated neurite outgrowth. MAP kinase inhibitor, PD98059 partially reduced SPTB Numb-mediated neurite outgrowth. Cells expressing SPTB Numbs exhibit increased whole-cell Ca2+ current densities (ICa) which can be prevented by preincubation of either nifedipine or PD98095. Cells expressing LPTB Numbs expressed little ICa (density) and were not able to grow neurites. Our results indicate that Ca2+ influx through VGCC may be required for SPTB Numb-mediated neurite outgrowth, suggesting that Numb promotes neuronal differentiation by a mechanism involving PTB domain-specific regulation of Ca2+ influx and MAP kinase activation.

Effects of tetrabrominated diphenyl ether and hexabromocyclododecanes in single and complex exposure to hepatoma HepG2 cells

This study was designed to determine cytotoxic effects of PBDE-47 and HBCDs individually or with a mixture of both compounds exposure to Hep G2 cells. The results showed PBDE-47 and HBCDs induced increase of nitric oxide synthase (NOS) activity, release of NO, dissipation of mitochondria membrane potential and cell apoptosis. Exposure to HBCDs induced ROS formation. Moreover, preincubation with PTIO (NO scavanger) and N-acetylcysteine (ROS scavanger) partially reversed cytotoxic effects of these compounds. The possible mechanism is that PBDE-47 and HBCDs could boost generation of NO and/or ROS, impact mitochondria, and result in start-ups of apoptosis program. Cells exposed to mixture of both compounds and each of them showed non-apoptotic rate significant difference, but the combination of them caused more adverse effects on cells. These results suggest that PBDE-47 and HBCDs in single and complex exposure have the cytotoxic activity of anti-proliferation and induction of apoptosis in tumor cells in vitro.

The molecular programme of tumour reversion: the steps beyond malignant transformation

How cells become malignant has preoccupied scientists for over a century. However, the converse question is also valid: are tumour cells capable of reverting from their malignant state? Askanazy's studies in 1907 indicated that teratoma cells could differentiate into normal somatic tissues and current evidence indicates that some tumour cells have acquired the molecular circuitry that results in the negation of chromosomal instability, translocations, oncogene activation and loss of tumour suppressor genes. Studying these extremely rare events of tumour reversion and deciphering these pathways, which involve SIAH1, presenilin 1, TSAP6 and translationally controlled tumour protein (TCTP), could lead to new avenues in cancer treatment.

Cholinergic degeneration and memory loss delayed by vitamin E in a Down syndrome mouse model

Down syndrome (DS) individuals develop several neuropathological hallmarks seen in Alzheimer's disease, including cognitive decline and the early loss of cholinergic markers in the basal forebrain. These deficits are replicated in the Ts65Dn mouse, which contains a partial trisomy of murine chromosome 16, the orthologous genetic segment to human chromosome 21. Oxidative stress levels are elevated early in DS, and may contribute to the neurodegeneration seen in these individuals. We evaluated oxidative stress in Ts65Dn mice, and assessed the efficacy of long-term antioxidant supplementation on memory and basal forebrain pathology. We report that oxidative stress was elevated in the adult Ts65Dn brain, and that supplementation with the antioxidant vitamin E effectively reduced these markers. Also, Ts65Dn mice receiving vitamin E exhibited improved performance on a spatial working memory task and showed an attenuation of cholinergic neuron pathology in the basal forebrain. This study provides evidence that vitamin E delays onset of cognitive and morphological abnormalities in a mouse model of DS, and may represent a safe and effective treatment early in the progression of DS neuropathology.

Mitochondrial Ca2+ overload underlies Abeta oligomers neurotoxicity providing an unexpected mechanism of neuroprotection by NSAIDs

Dysregulation of intracellular Ca²⁺ homeostasis may underlie amyloid β peptide (Aβ) toxicity in Alzheimer's Disease (AD) but the mechanism is unknown. In search for this mechanism we found that Aβ_1–42 oligomers, the assembly state correlating best with cognitive decline in AD, but not Aβ fibrils, induce a massive entry of Ca²⁺ in neurons and promote mitochondrial Ca²⁺ overload as shown by bioluminescence imaging of targeted aequorin in individual neurons. Aβ oligomers induce also mitochondrial permeability transition, cytochrome c release, apoptosis and cell death. Mitochondrial depolarization prevents mitochondrial Ca²⁺ overload, cytochrome c release and cell death. In addition, we found that a series of non-steroidal anti-inflammatory drugs (NSAIDs) including salicylate, sulindac sulfide, indomethacin, ibuprofen and R-flurbiprofen depolarize mitochondria and inhibit mitochondrial Ca²⁺ overload, cytochrome c release and cell death induced by Aβ oligomers. Our results indicate that i) mitochondrial Ca²⁺ overload underlies the neurotoxicity induced by Aβ oligomers and ii) inhibition of mitochondrial Ca²⁺ overload provides a novel mechanism of neuroprotection by NSAIDs against Aβ oligomers and AD.

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.

Apoptosis induction on human hepatoma cells Hep G2 of decabrominated diphenyl ether (PBDE-209)

Polybrominated diphenyl ethers (PBDEs) are an important class of halogenated organic brominated flame retardants. Because of their presence in abiotic and biotic environments widely and their structural similarity to polychlorinated biphenyls (PCBs), concern has been raised on their possible adverse health effects to humans. This study was designed to determine the anti-proliferative, apoptotic properties of decabrominated diphenyl ether (PBDE-209), using a human hepatoma Hep G2 line as a model system. Hep G2 cells were cultured in the presence of PBDE-209 at various concentrations (1.0-100.0 micromol/L) for 72 h and the percentage of cell viability was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. The results showed that PBDE-209 inhibited the cells viability in time and concentration-dependent characteristics at concentrations (10.0-100.0 micromol/L). We found that anti-proliferative effect of PBDE-209 was associated with apoptosis on Hep G2 cells by determinations of morphological changes, cell cycle and apoptosis. Mechanism study showed that PBDE-209 could increase the generation of intracellular reactive oxygen species (ROS) concentration-dependently. Antioxidant N-acetylcyteine partially inhibited the increase of ROS. The mechanism for its hepatoma-inhibitory effects was the induction of cellular apoptosis through ROS generation. In addition, activity of lactate dehydrogenase (LDH) release increased when the cells incubated with PBDE-209 at various concentrations and times. These results suggested that PBDE-209 had the toxicity activity of anti-proliferation and induction of apoptosis in tumor cells in vitro.

Pretreatment with PTD-calbindin D 28k alleviates rat brain injury induced by ischemia and reperfusion

Calcium toxicity remains the central focus of ischemic brain injury. Calcium channel antagonists have been reported to be neuroprotective in ischemic animal models but have failed in clinical trials. Rather than block the calcium channels, calbindin proteins can buffer excessive intracellular Ca2+, and as a result, maintain the calcium homeostasis. In the present study, we investigated the effect of calbindin D 28k (CaBD) in ischemic brain using the novel technique protein transduction domain (PTD)-mediated protein transduction. We generated PTD-CaBD in Escherichia coli, tested its biologic activity in N-methyl-D-aspartate (NMDA)- and oxygen-glucose deprivation (OGD)-induced hippocampal injury models, and examined the protection of the fusion protein using a rat brain focal ischemia model. Infarct volume was determined using 2,3,5-triphenyl-tetrazolium chloride staining; neuronal injury was examined using terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate-biotin nick end labeling (TUNEL) staining and cleaved caspase-3 assay. The results showed that the PTD-CaBD was efficiently delivered into Cos7 cells, hippocampal slice cells, and brain tissue. Pretreatment with PTD-CaBD decreased intracellular free calcium concentration and reduced cell death in NMDA- or OGD-exposed hippocampal slices (P<0.05). Intraperitoneal administration of PTD-CaBD before transient middle cerebral artery occlusion decreased brain infarct volume (280+/-47 versus 166+/-70 mm3, P<0.05), and improved neurologic outcomes compared with the control. Further studies showed that, compared with the control animals, PTD-CaBD decreased TUNEL (58%+/-7% versus 29%+/-3%, P<0.05)- and cleaved caspase-3 (62+/-4/field versus 31+/-6/field, P<0.05)-positive cells in the ischemic boundary zone. These results indicate that systemic administration of PTD-CaBD could attenuate ischemic brain injury, suggesting that PTD-mediated protein transduction might provide a promising and effective approach for the therapies of brain diseases, including cerebral ischemia.

Transient receptor potential channels in Alzheimer's disease

Cognitive impairment and emotional disturbances in Alzheimer's disease (AD) result from the degeneration of synapses and neuronal death 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 can render neurons vulnerable to excitotoxicity and apoptosis by disruption of cellular Ca(2+) homeostasis and neurotoxic factors including reactive oxygen species (ROS), nitric oxide (NO), and cytokines. Many lines of evidence have suggested that transient receptor potential (TRP) channels consisting of six main subfamilies termed the TRPC (canonical), TRPV (vanilloid), TRPM (melastatin), TRPP (polycystin), TRPML (mucolipin), and TRPA (ankyrin) are involved in Ca(2+) homeostasis disruption. Thus, emerging evidence of the pathophysiological role of TRP channels has yielded promising candidates for molecular entities mediating Ca(2+) homeostasis disruption in AD. In this review, we focus on the TRP channels in AD and highlight some TRP "suspects" for which a role in AD can be anticipated. An understanding of the involvement of TRP channels in AD may lead to the development of new target therapies.

Critical Role of the Epithelial Ca2+Channel TRPV5 in Active Ca2+Reabsorption as Revealed by TRPV5/Calbindin-D28KKnockout Mice

The epithelial Ca(2+) channel TRPV5 facilitates apical Ca(2+) entry during active Ca(2+) reabsorption in the distal convoluted tubule. In this process, cytosolic Ca(2+) remains at low nontoxic concentrations because the Ca(2+) influx is buffered rapidly by calbindin-D(28K). Subsequently, Ca(2+) that is bound to calbindin-D(28K) is shuttled toward the basolateral Ca(2+) extrusion systems. For addressing the in vivo role of TRPV5 and calbindin-D(28K) in the maintenance of the Ca(2+) balance, single- and double-knockout mice of TRPV5 and calbindin-D(28K) (TRPV5(-/-), calbindin-D(28K)(-/-), and TRPV5(-/-)/calbindin-D(28K)(-/-)) were characterized. These mice strains were fed two Ca(2+) diets (0.02 and 2% wt/wt) to investigate the influence of dietary Ca(2+) content on the Ca(2+) balance. Urine analysis indicated that TRPV5(-/-)/calbindin-D(28K)(-/-) mice exhibit on both diets hypercalciuria compared with wild-type mice. Ca(2+) excretion in TRPV5(-/-)/calbindin-D(28K)(-/-) mice was not significantly different from TRPV5(-/-) mice, whereas calbindin-D(28K)(-/-) mice did not show hypercalciuria. The similarity between TRPV5(-/-)/calbindin-D(28K)(-/-) and TRPV5(-/-) mice was supported further by an equivalent increase in renal calbindin-D(9K) expression and in intestinal Ca(2+) hyperabsorption as a result of upregulation of calbindin-D(9K) and TRPV6 expression in the duodenum. Elevated serum parathyroid hormone and 1,25-dihydroxyvitamin D(3) levels accompanied the enhanced expression of the Ca(2+) transporters. Intestinal Ca(2+) absorption and expression of calbindin-D(9K) and TRPV6, as well as serum parameters of the calbindin-D(28K)(-/-) mice, did not differ from those of wild-type mice. These results underline the gatekeeper function of TRPV5 being the rate-limiting step in active Ca(2+) reabsorption, unlike calbindin-D(28K), which possibly is compensated by calbindin-D(9K).

Calbindin-D28K dynamically controls TRPV5-mediated Ca2+ transport

In Ca(2+)-transporting epithelia, calbindin-D(28K) (CaBP(28K)) facilitates Ca(2+) diffusion from the luminal Ca(2+) entry side of the cell to the basolateral side, where Ca(2+) is extruded into the extracellular compartment. Simultaneously, CaBP(28K) provides protection against toxic high Ca(2+) levels by buffering the cytosolic Ca(2+) concentration ([Ca(2+)](i)) during high Ca(2+) influx. CaBP(28K) consistently colocalizes with the epithelial Ca(2+) channel TRPV5, which constitutes the apical entry step in renal Ca(2+)-transporting epithelial cells. Here, we demonstrate using protein-binding analysis, subcellular fractionation and evanescent-field microscopy that CaBP(28K) translocates towards the plasma membrane and directly associates with TRPV5 at a low [Ca(2+)](i). (45)Ca(2+) uptake measurements, electrophysiological recordings and transcellular Ca(2+) transport assays of lentivirus-infected primary rabbit connecting tubule/distal convolute tubule cells revealed that associated CaBP(28K) tightly buffers the flux of Ca(2+) entering the cell via TRPV5, facilitating high Ca(2+) transport rates by preventing channel inactivation. In summary, CaBP(28K) acts in Ca(2+)-transporting epithelia as a dynamic Ca(2+) buffer, regulating [Ca(2+)] in close vicinity to the TRPV5 pore by direct association with the channel.

Decreased susceptibility to oxidative stress underlies the resistance of specific dopaminergic cell populations to paraquat-induced degeneration

The vulnerability of different dopaminergic cell populations to damage caused by the herbicide paraquat was assessed by stereological counts of tyrosine hydroxylase-positive and calbindin-D28k-immunoreactive neurons in A9 (substantia nigra pars compacta) and A10 (ventral tegmental area and other cell groups). In saline-treated control mice, tyrosine hydroxylase-immunoreactive neurons represented 80% and 45% of the total neuronal population in A9 and A10, respectively, and the number of calbindin-D28k-positive neurons was five times greater in A10 than A9. Sequential injections with paraquat resulted in a significant loss of dopaminergic neurons in A9. In contrast, tyrosine hydroxylase-positive cells in A10 were spared from paraquat-induced degeneration. Furthermore, expression of calbindin-D28k was consistently associated with neuronal resistance to the herbicide in both A9 and A10. Paraquat exposure also induced oxidative stress as indicated by an increase in the number of midbrain cells positive for 4-hydroxy-2-nonenal, a marker of lipid peroxidation. Co-localization studies revealed that calbindin-D28k immunoreactivity overlapped with tyrosine hydroxylase labeling and that, after paraquat administration, (i) the vast majority of midbrain 4-hydroxy-2-nonenal-immunoreactive cells were dopaminergic (tyrosine hydroxylase-immunoreactive), (ii) tyrosine hydroxylase/4-hydroxy-2-nonenal-positive neurons were much more prevalent in A9 than A10, and (iii) all calbindin-D28k-containing neurons were characterized by lack of lipid peroxidation (4-hydroxy-2-nonenal immunoreactivity). Results in this paraquat model emphasize that, despite sharing a similar dopaminergic phenotype, different groups of midbrain neurons vary dramatically in their vulnerability to injury. Data also indicate that these differences are attributable, at least in part, to a varying susceptibility of dopaminergic cell populations to oxidative stress.

Ageing and neuronal vulnerability

Everyone ages, but only some will develop a neurodegenerative disorder in the process. Disease might occur when cells fail to respond adaptively to age-related increases in oxidative, metabolic and ionic stress, thereby resulting in the accumulation of damaged proteins, DNA and membranes. Determinants of neuronal vulnerability might include cell size and location, metabolism of disease-specific proteins and a repertoire of signal transduction pathways and stress resistance mechanisms. Emerging evidence on protein interaction networks that monitor and respond to the normal ageing process suggests that successful neural ageing is possible for most people, but also cautions that cures for neurodegenerative disorders are unlikely in the near future.

Carboxymethyl-chitosan protects rabbit chondrocytes from interleukin-1beta-induced apoptosis

Chondrocyte apoptosis is important in pathogenesis of osteoarthritis. Chitosan is a non-toxic, biodegradable and biocompatible glycosaminoglycan. In this study, the effects of carboxymethyl-chitosan (CM-chitosan), a soluble derivative of chitosan, on chondrocyte apoptosis were investigated. Primary rabbit chondrocytes were cultured and induced to apoptosis by 10 ng/ml interleukin-1beta (IL-1beta). After treatment with various concentrations of CM-chitosan (50, 100, 200 microg/ml), the apoptotic rate, mitochondrial function, nitric oxide production, and the levels of inducible nitric oxide synthase (iNOS) mRNA and reactive oxygen species in IL-1beta-induced chondrocytes were examined. The results showed that CM-chitosan could inhibit chondrocyte apoptosis in a dose-dependent manner. Furthermore, it could partly restore the levels of mitochondrial membrane potential and ATP, decrease nitric oxide production by down-regulation of iNOS mRNA expression, and scavenge reactive oxygen species in chondrocytes induced by IL-1beta. The results suggested that the inhibitory effects of CM-chitosan on IL-1beta-induced chondrocyte apoptosis were possibly due to the protection of mitochondrial function, the decline in the levels of nitric oxide and reactive oxygen species.

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.

Effects of amino acids from selenium-rich silkworm pupas on human hepatoma cells

Selenium (Se) plays an important role in cancer-prevention. Silkworm pupas have been used as a Chinese traditional medicine since ancient time. In order to find effective carcinostatic agents, Se-rich amino acids were extracted from Ziyang silkworm pupas. The Se content of Ziyang pupas was measured to be 215 times higher than that of Luoyang normal ones, and the majority of Se was stored in proteins. Composition analysis showed that Se-rich amino acids from Ziyang pupas had higher amounts of selenomethionine, methionine, cystine, and tyrosine than normal amino acids from Luoyang pupas which were rich in amino acids containing alkyl side chains. When cultured with human hepatoma cells SMMC-7721, Se-rich amino acids at concentrations of 0.5, 1.5, and 2.5 micromol L(-1) Se significantly and dose-dependently inhibited cell viability, induced changes in cell morphology and cycle, and caused cell apoptosis. On the contrary, normal amino acids did not show any inhibitory effect on SMMC-7721 cells. Sodium selenite or selenomethionine at the same Se concentrations only slightly inhibited the hepatoma cells. Mechanism study showed that selenium-rich amino acids could increase the generation of intracellular reactive oxygen species (ROS) concentration-dependently. Antioxidant N-acetylcyteine partially inhibited the increase of ROS. Those results suggested that Se-rich amino acids were effective carcinostatic agents compared with sodium selenite and selenomethionine. The mechanism for their hepatoma-inhibitory effects was the induction of cellular apoptosis through ROS generation.

Calcium dysregulation in Alzheimer's disease: Recent advances gained from genetically modified animals

Alzheimer's disease is a progressive and irreversible neurodegenerative disorder that leads to cognitive, memory and behavioural impairments. Two decades of research have implicated disturbances of intracellular calcium homeostasis as playing a proximal pathological role in the neurodegeneration associated with Alzheimer's disease. A large preponderance of evidence has been gained from the use of a diverse range of cell lines. Whilst useful in understanding the principal mechanism of neurotoxicity associated with Alzheimer's disease, technical differences, such as cell type or even the form of amyloid-beta used often underlie conflicting results. In this review, we discuss recent contributions that transgenic technology has brought to this field. For example, the triple transgenic mouse model of Alzheimer's disease has implicated intraneuronal accumulation of the amyloid-beta peptide as an initiating factor in synaptic dysfunction and behavioural deficits. Importantly, this synaptic dysfunction occurs prior to cell loss or extracellular amyloid plaque accumulation. The cause of synaptic dysfunction is unknown but it is likely that amyloid-beta and its ability to disrupt intracellular calcium homeostasis plays a key role in this process.

NF-κB in the Survival and Plasticity of Neurons

The transcription factor nuclear factor kappa-B (NF-kappaB) is involved in regulating responses of neurons to activation of several different signaling pathways in a variety of physiological and pathological settings. During development of the nervous system NF-kappaB is activated in growing neurons by neurotrophic factors and can induce the expression of genes involved in cell differentiation and survival. In the mature nervous system NF-kappaB is activated in synapses in response to excitatory synaptic transmission and may play a pivotal role in processes such as learning and memory. NF-kappaB is activated in neurons and glial cells in acute neurodegenerative conditions such as stroke and traumatic injury, as well as in chronic neurodegenerative conditions such as Alzheimer's disease. Activation of NF-kappaB in neurons can promote their survival by inducing the expression of genes encoding anti-apoptotic proteins such as Bcl-2 and the antioxidant enzyme Mn-superoxide dismutase. On the other hand, by inducing the production and release of inflammatory cytokines, reactive oxygen molecules and excitotoxins, activation of NF-kappaB in microglia and astrocytes may contribute to neuronal degeneration. Emerging findings suggest roles for NF-kappaB as a mediator of effects of behavioral and dietary factors on neuronal plasticity. NF-kappaB provides an attractive target for the development of novel therapeutic approaches for a range of neurological disorders.

Annexin 7-immunoreactive microglia in the hippocampus of control and adrenalectomized rats

Annexin 7 (ANX7), also termed synexin, is a member of the annexin family of calcium-binding proteins. In the present study, we examined the distribution and cellular localization of ANX7-immunoreactivity in the rat hippocampus and its response to adrenalectomy (ADX). ANX7 was co-localized with OX42 in microglia distributed throughout the hippocampus of both control and ADX animals. ANX7-immunoreactivity was not detected in GFAP-positive astrocytes or in hippocampal neurons. At 1-week and 4-weeks following ADX, we observed a population of large, ameboid, ANX7-immunopositive microglia ("reactive microglia") which were largely confined to the granule cell layer of the dentate gyrus throughout its rostrocaudal extent. No reactive microglia were present in the hippocampus of sham-ADX or ADX + corticosterone treated animals. In 4-weeks ADX animals but not 1-week ADX, ANX7-immunostaining was significantly increased in the mossy fiber layer of CA3, due to the presence of many small, dark-staining "activated microglia". Our results show that ANX7 is abundantly expressed in the rat hippocampus by different microglial forms (e.g., ramified, activated and reactive microglia), suggesting an important role for this calcium-binding protein in microglial Ca2+-dependent processes.

Setagin and secretagogin-R22: Posttranscriptional modification products of the secretagogin gene

We describe two new variants of the recently identified hexa-EF-hand calcium binding protein secretagogin. The first variant (secretagogin-R22) is characterized by one single amino acid exchange (Q/R) at codon 22, most likely due to RNA editing. The second variant of secretagogin (setagin) consists of 49 amino acids. Due to a frame shift, only the first 27 amino acids are identical to secretagogin. We demonstrate that this protein truncation results in complete loss of the calcium binding capacity. Setagin expression was found in considerable amounts in the pancreas whereas secretagogin and secretagogin-R22 were also found in the central nervous system and organs containing neurendocrine cells.

Anti-oxidant gene expression imbalance, aging and Down syndrome

The expression of copper zinc superoxide dismutase (SOD1), manganese superoxide dismutase (SOD2), glutathione peroxidase (GPx), and catalase (CAT) genes have been detected in human skin fibroblast cells for 2 year normal child (control), 50 year old normal male and female and a 1 year old Down Syndrome (DS) male and female with established trisomy karyotype using the RT-PCR technique. Differential expression of these genes is quantified individually against a beta-Actin gene that has been employed as an internal control. The immunoblotting of cell lysate proteins with polyclonal antibodies exhibit SOD1 (16 kD), SOD2 (40 kD), GPx (23 and 92 kD), CAT (64 kD), and Actin (43 kD) as translational products. The results demonstrate that the enhancement in the level of mRNAs encoding SOD1 in DS male and female, as well as aged male and female are 51, 21, 31 and 50% respectively compared to the normal child (control). In SOD2, DS male and female display higher (176%) and lower (26%) levels of expression whereas aged male and female exhibit enhanced levels of expression (66 and 119%) respectively compared to the control. This study demonstrates that DS affects the female less than the male whereas in the aging process, the female is more prone to oxidative damage than the male. These results not only indicate that the level of GPx mRNA is constant except in DS male, which shows a downward regulation but that even CAT mRNA is upward regulated in aged as well as in DS males and females. These disproportionate changes in anti-oxidant genes, which are incapable of coping with over expressed genes, may contribute towards the aging process, dementia and Down syndrome.

Suppression of calbindin D28K in estrogen-induced hamster renal tumors

It has been hypothesized that generation of reactive estrogen-quinone species and oxidative stress, both of which result from the metabolic activation of estrogens, plays an important role in estrogen-induced carcinogenesis. In the present investigation, we used an estrogen-induced hamster renal tumor model to identify gene(s) associated with oxidative stress that may be differentially expressed in estrogen-induced tumors compared with untreated controls. Hamsters were implanted with 17beta-estradiol (E2) for 7 months. This treatment resulted in the development of target organ specific kidney tumors. Delta differential PCR technique on RNA isolated from estrogen-induced hamster renal tumors and untreated control kidneys identified a number of cDNA fragments that were differentially expressed in tumor RNA compared with untreated controls. We report the cloning of one of the differentially expressed cDNA fragments, the hamster calbindin-D28k (Cb28k) cDNA, and present a finding that both Cb28k mRNA and protein are suppressed in estrogen-induced hamster renal tumors compared with untreated controls. Cb28k is a Vitamin D3-dependent calcium binding protein that acts as a buffer to maintain intracellular calcium homeostasis, although its exact role is still not clear. Since Cb28k gene has been shown to be associated with providing cells resistance against oxidative stress, Cb28k may be an important biomarker in estrogen-mediated carcinogenesis and oxidative stress.

Intracellularly generated amyloid-β peptide counteracts the antiapoptotic function of its precursor protein and primes proapoptotic pathways for activation by other insults in neuroblastoma cells

Most mutations in amyloid precursor proteins (APPs) linked to early onset familial Alzheimer's disease (FAD) increase the production of amyloid-beta peptides ending at residue 42 (Abeta42), which are released from APP by beta- and gamma-secretase cleavage. Stably transfected cells expressing wild-type human APP (APP(WT)) were more resistant to apoptosis-inducing treatments than cells expressing FAD-mutant human APP (APP(FAD)). Preventing Abeta42 production with an M596I mutation (beta-), which blocks beta-secretase cleavage of APP, or by treatment with a gamma-secretase inhibitor increased the resistance of APP(FAD)-expressing cells to apoptosis. Exposing hAPP(FAD/beta-) cells to exogenous Abeta42 or conditioned medium from Abeta42-producing APP(FAD) cells did not diminish their resistance to apoptosis. Preventing APP from entering the distal secretory pathway, where most Abeta peptides are generated, by retaining APP in the endoplasmic reticulum (ER)/intermediate compartment (IC) increased the resistance of APP(FAD)-expressing cells to apoptosis and did not alter the resistance of APP(WT)-expressing cells. p53-mediated gene transactivation after apoptosis-inducing treatments was much stronger in APP(FAD) cells than in hAPP(WT) or hAPP(FAD/beta-) cells. In contrast, upon induction of ER stress, cells expressing APP(FAD), hAPP(FAD/beta-), or APP(WT) had comparable levels of glucose-regulated protein-78 mRNA, an unfolded protein response indicator. We conclude that Abeta, especially intracellular Abeta, counteracts the antiapoptotic function of its precursor protein and predisposes cells to p53-mediated, and possibly other, proapoptotic pathways.

The C-terminal Tail of Presenilin Regulates Omi/HtrA2 Protease Activity

Presenilin mutations are responsible for most cases of autosomal dominant inherited forms of early onset Alzheimer disease. Presenilins play an important role in amyloid beta-precursor processing, NOTCH receptor signaling, and apoptosis. However, the molecular mechanisms by which presenilins regulate apoptosis are not fully understood. Here, we report that presenilin-1 (PS1) regulates the proteolytic activity of the serine protease Omi/HtrA2 through direct interaction with its regulatory PDZ domain. We show that a peptide corresponding to the cytoplasmic C-terminal tail of PS1 dramatically increases the proteolytic activity of Omi/HtrA2 toward the inhibitor of apoptosis proteins and beta-casein and induces cell death in an Omi/HtrA2-dependent manner. Consistent with these results, ectopic expression of full-length PS1, but not PS1 lacking the C-terminal PDZ binding motif, potentiated Omi/HtrA2-induced cell death. Our results suggest that the C terminus of PS1 is an activation peptide ligand for the PDZ domain of Omi/HtrA2 and may regulate the protease activity of Omi/HtrA2 after its release from the mitochondria during apoptosis. This mechanism of Omi/HtrA2 activation is similar to the mechanism of activation of the related bacterial DegS protease by the outer-membrane porins.

Proteome Analysis Associated with Cadmium Adaptation in U937 Cells

Cadmium is a well known environmental toxicant and carcinogen. To identify proteins involved in cellular adaptive responses to cadmium, we established cadmium-adapted U937 cells that exhibit resistance to cadmium-induced apoptosis, and we performed comparative proteome analysis of these cells with parental cells that were either untreated or treated with cadmium. Newly identified proteins that were changed in expression level in both adapted cells and cadmium-treated parental cells included proteins implicated in cell proliferation and malignant transformation. Most interesting, a calcium-binding protein calbindin-D(28k) was increased only in the adapted cells but not in cadmium-exposed parental cells. The level of calbindin-D(28k) increased by the degree of cadmium adaptation and was stably maintained without selective pressure of cadmium. Cadmium-adapted U937 cells were resistant to the toxic effects of cytosolic calcium rise by cadmium treatment and by depletion of intracellular calcium stores, suggesting that enhanced calcium buffering by up-regulated calbindin-D(28k) may be responsible for acquiring resistance to cadmium-induced apoptosis. We demonstrated that overexpression of calbindin-D(28k) in MN9D neuronal cells resulted in reduced cadmium-induced apoptosis. Our study documents for the first time that cells respond to long term cadmium exposure by increasing calbindin-D(28k) expression, thereby attenuating cadmium-induced apoptosis.

Both calcium and ROS as common signals mediate Na(2)SeO(3)-induced apoptosis in SW480 human colonic carcinoma cells

Recent studies have shown that reactive oxygen species (ROS) play a crucial role in Se-induced cell apoptosis. A number of studies have demonstrated that perturbed cellular calcium homeostasis has been implicated in apoptosis. The main objective of this study was to evaluate the role of Ca(2+) in Na(2)SeO(3)-induced apoptosis and the relationship between Ca(2+) and ROS in human colonic carcinoma cells SW480. When SW480 cells were exposed to 25-100 microM Na(2)SeO(3), both cell apoptosis and growth inhibition were observed by flow cytometric analysis and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay. Na(2)SeO(3) was able to induce increase of [Ca(2+)](i) and ROS production and disrupt mitochondrial membrane potential (Delta Psi m) in SW480 cells monitored by using a confocal laser scanning microscope. Ca(2+) channel inhibitor CoCl(2) and an intracellular Ca(2+) chelator o-phtalaldehyde, 1,2-bis(2-aminophenoxy)-ethane-N,N,N',N'-tetra-acetic acid acetoxymethyl ester (BAPTA) completely inhibited [Ca(2+)](i) increase, but catalase had no effect on Na(2)SeO(3)-induced increase of [Ca(2+)](i). BAPTA-AM, CoCl(2), and mitochondrial Ca(2+) uptake inhibitor ruthenium red blocked Delta Psi m dissipation. The increase of ROS was also suppressed by CoCl(2), BAPTA, ruthenium red, N-acetylcysteine and catalase, respectively. The mitochondrial uncoupler carbonyl cyanide p-(trifluoromethoxy) phenylhydrazone (FCCP) completely inhibited Na(2)SeO(3)-induced ROS increase. This showed that ROS increase is due to mitochondrial Ca(2+) overload. The Na(2)SeO(3)-induced apoptosis of SW480 cells was also inhibited by CoCl(2), BAPTA, ruthenium red, N-acetylcysteine, and catalase, respectively. The results mentioned above imply that both calcium and Ca(2+)-dependent ROS as a signal molecule mediate apoptosis induced by Na(2)SeO(3) in SW480 cells.

Biological actions and mechanism of action of calbindin in the process of apoptosis

Although it was originally proposed that the major role of calbindin is to facilitate the vitamin D dependent movement of calcium through the cytosolic compartment of the intestinal or renal cell, we found that calbindin also has a major role in different cell types in protecting against apoptotic cell death. Calbindin, which buffers calcium, can inhibit apoptosis induced by different proapoptotic stimuli. Expression of calbindin-D(28k) in neural cell suppressed the proapoptotic actions of presenilin-1, which is causally linked to familial Alzheimer's disease, by preventing calcium mediated mitochondrial damage and the subsequent release of cytochrome c. Calbindin, by buffering intracellular calcium can also protect HEK 293 kidney cells from parathyroid hormone induced apoptosis that was found to be mediated by a phospholipase C dependent increase in intracellular calcium. In addition, cytokine mediated destruction of pancreatic beta cells can be prevented by calbindin. Induction by cytokines of nitric oxide, peroxynitrite and lipid hydroperoxide production was significantly decreased in calbindin expressing beta cells. Thus, calbindin-D(28k), by inhibiting free radical formation, can protect islet beta cells from autoimmune destruction in type 1 diabetes. Calbindin-D(28k) can also protect against apoptosis in bone cells. Calbindin was found to block apoptosis in osteocytic and osteoblastic cells. Our findings suggest that calbindin is capable of directly inhibiting the activity of caspase-3, a common downstream effector of multiple apoptotic signaling pathways, and that this inhibition results in an inhibition of tumor necrosis factor (TNFalpha) and glucocorticoid induced apoptosis in bone cells. Thus, while part of calbindin's protective effect may result from buffering rises in intracellular calcium, other mechanisms of action, such as inhibition of caspase activity, also play a significant role in the prevention of apoptosis by calbindin-D(28k). These findings have implications for the prevention of degeneration in different cell types and therefore could prove important for the therapeutic intervention of many diseases, including diabetes and osteoporosis.

Prevention of glucocorticoid-induced apoptosis in osteocytes and osteoblasts by calbindin-D28k

This study show for the first time that calbindin-D28k can prevent glucocorticoid-induced bone cell death. The anti-apoptotic effect of calbindin-D28k involves inhibition of glucocorticoid induced caspase 3 activation as well as ERK activation.

INTRODUCTION

Recent studies have indicated that deleterious effects of glucocorticoids on bone involve increased apoptosis of osteocytes and osteoblasts. Because the calcium-binding protein calbindin-D28k has been reported to be anti-apoptotic in different cell types and in response to a variety of insults, we investigated whether calbindin-D28k could protect against glucocorticoid-induced cell death in bone cells.

MATERIALS AND METHODS

Apoptosis was induced by addition of dexamethasone (dex; 10-6 M) for 6 h to MLO-Y4 osteocytic cells as well as to osteoblastic cells. Apoptosis percentage was determined by examining the nuclear morphology of transfected cells. Caspase 3 activity was evaluated in bone cells and in vitro. SELDI mass spectrometry (MS) was used to examine calbindin-D28k-caspase 3 interaction. Phosphorylation of calbindin-D28k was examined by 32P incorporation as well as by MALDI-TOF MS. ERK activation was determined by Western blot.

RESULTS

The pro-apoptotic effect of dex in MLO-Y4 cells was completely inhibited in cells transfected with calbindin-D28k cDNA (5.6% apoptosis in calbindin-D28k transfected cells compared with 16.2% apoptosis in vector-transfected cells, p < 0.05). Similar results were observed in osteoblastic cells. We found that dex-induced apoptosis in bone cells was accompanied by an increase in caspase 3 activity. This increase in caspase 3 activity was inhibited in the presence of calbindin-D28k. In vitro assays indicated a concentration-dependent inhibition of caspase 3 by calbindin-D28k (Ki = 0.22 microM). Calbindin-D28k was found to inhibit caspase 3 specifically because the activity of other caspases was unaffected by calbindin-D28k. The anti-apoptotic effect of calbindin-D28k in response to dex was also reproducibly associated with an increase in the phosphorylation of ERK 1 and 2, suggesting that calbindin-D28k affects more than one signal in the glucocorticoid-induced apoptotic pathway.

CONCLUSION

Calbindin-D28k, a natural non-oncogenic protein, could be an important target in the therapeutic intervention of glucocorticoid-induced osteoporosis.

Perturbed signal transduction in neurodegenerative disorders involving aberrant protein aggregation

Aggregation of abnormal proteins, both inside and outside of cells, is a prominent feature of major neurodegenerative disorders, including Alzheimer's, Parkinson's, polyglutamine expansion, and prion diseases. Other articles in this special issue of NeuroMolecular Medicine describe the genetic and molecular factors that promote aberrant protein aggregation. In the present article, we consider how it is that pathogenic aggregation-prone proteins compromise signal transduction pathways that regulate neuronal plasticity and survival. In some cases the protein in question may have widespread and relatively nonspecific effects on signaling. For example, amyloid beta-peptide induces membrane-associated oxidative stress, which impairs the function of various receptors, ion channels and transporters, as well as downstream kinases and transcription factors. Other proteins, such as polyglutamine repeat proteins, may affect specific protein -protein interactions, including those involved in signaling pathways activated by neurotransmitters, neurotrophins, and steroid hormones. Synapses are particularly sensitive to abnormal protein aggregation and impaired synaptic signaling may trigger apoptosis and related cell death cascades. Impairment of signal transduction in protein aggregation disorders may be amenable to therapy as demonstrated by a recent study showing that dietary restriction can preserve synaptic function and protect neurons in a mouse model of Huntington's disease. Finally, emerging findings are revealing how activation of certain signaling pathways can suppress protein aggregation and/or the cytotoxicity resulting from the abnormal protein aggregation. A better understanding of how abnormal protein aggregation occurs and how it affects and is affected by specific signal transduction pathways, is leading to novel approaches for preventing and treating neurodegenerative disorders.

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.

Neuronal depletion of calcium-dependent proteins in the dentate gyrus is tightly linked to Alzheimer's disease-related cognitive deficits

Transgenic mice expressing human amyloid precursor proteins (hAPP) and amyloid-beta peptides (Abeta) in neurons develop phenotypic alterations resembling Alzheimer's disease (AD). The mechanisms underlying cognitive deficits in AD and hAPP mice are largely unknown. We have identified two molecular alterations that accurately reflect AD-related cognitive impairments. Learning deficits in mice expressing familial AD-mutant hAPP correlated strongly with decreased levels of the calcium-binding protein calbindin-D28k (CB) and the calcium-dependent immediate early gene product c-Fos in granule cells of the dentate gyrus, a brain region critically involved in learning and memory. These molecular alterations were age-dependent and correlated with the relative abundance of Abeta1-42 but not with the amount of Abeta deposited in amyloid plaques. CB reductions in the dentate gyrus primarily reflected a decrease in neuronal CB levels rather than a loss of CB-producing neurons. CB levels were also markedly reduced in granule cells of humans with AD, even though these neurons are relatively resistant to AD-related cell death. Thus, neuronal populations resisting cell death in AD and hAPP mice can still be drastically altered at the molecular level. The tight link between Abeta-induced cognitive deficits and neuronal depletion of CB and c-Fos suggests an involvement of calcium-dependent pathways in AD-related cognitive decline and could facilitate the preclinical evaluation of novel AD treatments.

Opposing effects of ethanol and nicotine on hippocampal calbindin-D28k expression

Long-term ethanol exposure produces multiple neuroadaptations that likely contribute to dysregulation of Ca(2+) balance and neurotoxicity during ethanol withdrawal. Conversely, nicotine exposure may reduce the neurotoxic consequences of Ca(2+) dysregulation, putatively through up-regulation of the Ca(2+)-buffering protein calbindin-D(28k). The current studies were designed to examine the extent to which 10-day ethanol exposure and withdrawal altered calbindin-D(28k) expression in rat hippocampus. Further, in these studies, we examined the ability of nicotine, through action at alpha(7)(*)-bearing nicotinic acetylcholine receptors (nAChRs), to antagonize the effects of ethanol exposure on calbindin-D(28k) expression. Organotypic cultures of rat hippocampus were exposed to ethanol (50-100 mM) for 10 days. Additional cultures were exposed to 500 nM (-)-nicotine with or without the addition of 50 mM ethanol, 100 nM methyllycaconitine (an alpha(7)*-bearing nAChR antagonist), or both. Prolonged exposure to ethanol (>/=50 mM) produced significant reductions of calbindin-D(28k) immunolabeling in all regions of the hippocampal formation, even at nontoxic concentrations of ethanol. Calbindin-D(28k) expression levels returned to near-control levels after 72 h of withdrawal from 10-day ethanol exposure. Extended (-)-nicotine exposure produced significant elevations in calbindin-D(28k) expression levels that were prevented by methyllycaconitine co-exposure. Co-exposure of cultures to (-)-nicotine with ethanol resulted in an attenuation of ethanol-induced reductions in calbindin-D(28k) expression levels. These findings support the suggestion that long-term ethanol exposure reduces the neuronal capacity to buffer accumulated Ca(2+) in a reversible manner, an effect that likely contributes to withdrawal-induced neurotoxicity. Further, long-term exposure to (-)-nicotine enhances calbindin-D(28k) expression in an alpha(7)* nAChR-dependent manner and antagonizes the effects of ethanol on calbindin-D(28k) expression.

Auditory peripheral influences on calcium binding protein immunoreactivity in the cochlear nucleus during aging in the C57BL/6J mouse

The C57BL/6J (C57) mouse was selected as a suitable model for early presbyacusis to determine if there were correlations between peripheral pathology (spiral ganglion loss, inner and outer hair cell loss) and calcium binding immunoreactivity in the cochlear nucleus during aging. The quantitative stereological method, the optical fractionator, was used for determining the total number of neurons and calcium binding immunopositive neurons (calbindin, parvalbumin and calretinin) during aging in the posteroventral- and dorsal cochlear nucleus (PVCN and DCN) in C57 mice. Comparing 30-month-old to 1-month-old C57 mice, a percent increase in parvalbumin and calbindin immunoreactivity was evident in both the PVCN and DCN. Correlations were made between peripheral pathology (spiral ganglion and inner and outer hair cell loss) and calcium binding protein expression. Significant correlations between cochlear pathology and the percentage of parvalbumin and calretinin immunoreactive neurons were demonstrated in the DCN. Moreover, significant correlations were found between cochlear pathology and parvalbumin and calbindin in the PVCN. In summary, the findings imply that degenerative changes in the auditory periphery can modulate neuronal homeostasis by increasing calcium binding proteins in the PVCN and DCN during aging. Taken together, these findings suggest a role for calcium binding proteins in protecting against age-induced calcium toxicity.

Enhanced long-term potentiation in the hippocampus of rats expressing mutant presenillin-1 is age related

Electrophysiological recordings were made from Fischer rats engineered to express the human presenilin 1 gene carrying the M146V mutation. Extracellular recordings of field excitatory post-synaptic potential (EPSPs) were made to investigate EPSP properties, paired pulse responses, posttetanic potentiation, and long-term potentiation in the stratum radiatum and dentate gyrus of hippocampal slices maintained in vitro. Transgenic rats aged approximately 6 months showed no differences from their wild-type littermates in any of these properties. However, at 18 months, long-term potentiation in the CA1 was facilitated in the transgenic rats with a different pattern of synaptic enhancement. No changes were observed in paired pulse facilitation (PPF) or post-tetanic potentiation (PPT) and no changes were seen in the dentate gyrus. Field potential amplitudes were significantly greater and PPF was enhanced in the CA1 of all older rats. Intracellular recordings from CA1 pyramidal cells of the older group of rats revealed no differences in the passive or active membrane properties of cells in the two groups, but intracellularly recorded EPSPs were significantly longer.

Vitamin D target proteins: function and regulation

Recent findings have indicated that calbindin-D(28k), the first known target of vitamin D action, is present in osteoblasts and protects against TNF and glucocorticoid induced apoptosis of osteoblastic cells. Cytokine mediated destruction of pancreatic beta cells, a cause of insulin dependent diabetes, is also inhibited by calbindin-D(28k). In calbindin-D(28k) transfected pancreatic beta cells free radical formation by cytokines is inhibited by calbindin. Thus, besides its role as a facilitator of calcium diffusion, calbindin has a major role in protecting against cellular degeneration in different cell types. Besides calbindin, the other known pronounced effect of 1,25(OH)(2)D(3) in intestine and kidney is increased synthesis of 25(OH)D(3) 24-hydroxylase (24(OH)ase) which is involved in the catabolism of 1,25(OH)(2)D(3). We have noted that CCAAT enhancer binding protein beta (C/EBPbeta) is induced by 1,25(OH)(2)D(3) in kidney and osteoblastic cells and can enhance the transcriptional response of 24(OH)ase to 1,25(OH)(2)D(3). These studies establish C/EBPbeta as a novel 1,25(OH)(2)D(3) target gene and indicate a role for C/EBPbeta in 24(OH)ase transcription. These studies extend our previous studies related to factors that affect vitamin D receptor (VDR) mediated 24(OH)ase transcription (YY1, TFIIB, CBP) and the effect of signaling pathways on 24(OH)ase transcription and cofactor recruitment.

Oxidative stress, perturbed calcium homeostasis, and immune dysfunction in Alzheimer's disease

Although Alzheimer's disease (AD) may not involve a transmissible agent, it does involve a pathogenic process similar to that of transmissible prion disorders (both involve a protein that adopts an abnormal pathogenic conformation in which it self-aggregates, forming amyloid deposits in and surrounding neurons) and viral dementias such as human immunodeficiency virus (HIV) encephalitis. The clinical presentation of patients with AD is dominated by cognitive deficits and emotional disturbances that result from dysfunction and degeneration of neurons in the limbic system and cerebral cortex. The pathogenic process in the brain involves deposition of insoluble aggregates of amyloid beta-peptide, oxidative stress and calcium dysregulation in neurons, and activation of inflammatory cytokine cascades involving microglia. However, AD patients also exhibit alterations in immune function. Studies of lymphocytes and lymphoblast cell lines from AD patients and age-matched normal control patients have documented alterations in cytokine and calcium signaling and increased levels of oxidative stress in immune cells from the AD patients. Studies of the pathogenic actions of mutations in presenilins and amyloid precursor protein that cause early-onset familial AD have established central roles for perturbed cellular calcium homeostasis and oxidative stress in the neurodegenerative process. Presenilin and amyloid precursor protein (APP) mutations also increase oxidative stress and perturb calcium signaling in lymphocytes in ways that alter their production of cytokines that are critical for proper immune responses. Immune dysfunction occurs prior to clinical symptoms in mouse models of AD, and brain cytokine responses to immune challenge are altered in presenilin mutant mice, suggesting a causal role for altered immune function in the disease process. Interestingly, immunization of AD mice with amyloid beta-peptide can stimulate the immune system to remove amyloid from the brain and can ameliorate memory deficits, suggesting that it may be possible to prevent AD by bolstering immune function.

Central role of glycogen synthase kinase-3beta in endoplasmic reticulum stress-induced caspase-3 activation

Stress of the endoplasmic reticulum (ER), which is associated with many neurodegenerative conditions, can lead to the elimination of affected cells by apoptosis through only partially understood mechanisms. Thapsigargin, which causes ER stress by inhibiting the ER Ca(2+)-ATPase, was found to not only activate the apoptosis effector caspase-3 but also to cause a large and prolonged increase in the activity of glycogen synthase kinase-3beta (GSK3beta). Activation of GSK3beta was obligatory for thapsigargin-induced activation of caspase-3, because inhibition of GSK3beta by expression of dominant-negative GSK3beta or by the GSK3beta inhibitor lithium blocked caspase-3 activation. Thapsigargin treatment activated GSK3beta by inducing dephosphorylation of phospho-Ser-9 of GSK3beta, a phosphorylation that normally maintains GSK3beta inactivated. Caspase-3 activation induced by thapsigargin was blocked by increasing the phosphorylation of Ser-9-GSK3beta with insulin-like growth factor-1 or with the phosphatase inhibitors okadaic acid and calyculin A, but the calcineurin inhibitors FK506 and cyclosporin A were ineffective. Insulin-like growth factor-1, okadaic acid, calyculin A, and lithium also protected cells from two other inducers of ER stress, tunicamycin and brefeldin A. Thus, ER stress activates GSK3beta through dephosphorylation of phospho-Ser-9, a prerequisite for caspase-3 activation, and this process is amenable to pharmacological intervention.

Endoplasmic reticulum, Bcl-2 and Ca2+ handling in apoptosis

In the complex signalling interplay that allows extracellular signals to be decoded into activation of apoptotic cell death, Ca(2+) plays a significant role. This is supported not only by evidence linking alterations in Ca(2+) homeostasis to the triggering of apoptotic (and in some cases necrotic) cell death, but also by recent data indicating that a key anti-apoptotic protein, Bcl-2, has a direct effect on ER Ca(2+) handling. We will briefly summarise the first aspect, and describe in more detail these new data, demonstrating that (i) Bcl-2 reduces the state of filling of the ER Ca(2+) store and (ii) this Ca(2+) signalling alteration renders the cells less sensitive to apoptotic stimuli. Overall, these results suggest that calcium homeostasis may represent a pharmacological target in the fundamental pathological process of apoptosis.

Calretinin and calbindin D-28k, but not parvalbumin protect against glutamate-induced delayed excitotoxicity in transfected N18-RE 105 neuroblastoma-retina hybrid cells

Excitotoxic effects leading to neuronal cell degeneration are often accompanied by a prolonged increase in the intracellular level of Ca(2+) ions and L-glutamate-induced toxicity is assumed to be mediated via a Ca(2+)-dependent mechanism. Due to their buffering properties, EF-hand Ca(2+)-binding proteins (CaBPs) can affect intracellular Ca(2+) homeostasis and a neuroprotective role has been attributed to some of the family members including calretinin, calbindin D-28k and parvalbumin. We have stably transfected N18-RE 105 neuroblastoma-retina hybrid cells with the cDNAs for the three CaBPs and investigated the effect of these proteins on the L-glutamate-induced, Ca(2+)-dependent cytotoxicity. Several clones for each CaBP were selected according to immunocytochemical staining and characterization of the overexpressed proteins by Western blot analysis. In calretinin- and parvalbumin-expressing clones, expression levels were quantitatively determined by ELISA techniques. Cytotoxicity of transfected clones was quantified by measurement of the activity of lactate dehydrogenase (LDH) that was released into the medium after L-glutamate (10 mM) exposure as a result of necrotic cell death. In untransfected and parvalbumin-transfected cells, LDH released into the medium progressively increased (starting from the 20th hour) reaching maximum levels after 28-30 h of glutamate application. In contrast, LDH release in both, calretinin and calbindin D-28k-transfected clones, was not significantly different from unstimulated transfected or untransfected cells over the same period of time. The results indicate that the 'fast' Ca(2+)-buffers calretinin and calbindin D-28k, but not the 'slow' buffer parvalbumin can protect N18-RE 105 cells from this type of Ca(2+)-dependent L-glutamate-induced delayed cytotoxicity.

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.