Mutant presenilins disturb neuronal calcium homeostasis in the brain of transgenic mice, decreasing the threshold for excitotoxicity and facilitating long-term potentiation

Rodent Models of Alzheimer's Disease: Past Misconceptions and Future Prospects

Alzheimer's disease (AD) is a progressive neurodegenerative disease with no effective treatments, not least due to the lack of authentic animal models. Typically, rodent models recapitulate the effects but not causes of AD, such as cholinergic neuron loss: lesioning of cholinergic neurons mimics the cognitive decline reminiscent of AD but not its neuropathology. Alternative models rely on the overexpression of genes associated with familial AD, such as amyloid precursor protein, or have genetically amplified expression of mutant tau. Yet transgenic rodent models poorly replicate the neuropathogenesis and protein overexpression patterns of sporadic AD. Seeding rodents with amyloid or tau facilitates the formation of these pathologies but cannot account for their initial accumulation. Intracerebral infusion of proinflammatory agents offer an alternative model, but these fail to replicate the cause of AD. A novel model is therefore needed, perhaps similar to those used for Parkinson's disease, namely adult wildtype rodents with neuron-specific (dopaminergic) lesions within the same vulnerable brainstem nuclei, 'the isodendritic core', which are the first to degenerate in AD. Site-selective targeting of these nuclei in adult rodents may recapitulate the initial neurodegenerative processes in AD to faithfully mimic its pathogenesis and progression, ultimately leading to presymptomatic biomarkers and preventative therapies.

Critical thinking of Alzheimer's transgenic mouse model: current research and future perspective

Transgenic models are useful tools for studying the pathogenesis of and drug development for Alzheimer's Disease (AD). AD models are constructed usually using overexpression or knock-in of multiple pathogenic gene mutations from familial AD. Each transgenic model has its unique behavioral and pathological features. This review summarizes the research progress of transgenic mouse models, and their progress in the unique mechanism of amyloid-β oligomers, including the first transgenic mouse model built in China based on a single gene mutation (PSEN1 V97L) found in Chinese familial AD. We further summarized the preclinical findings of drugs using the models, and their future application in exploring the upstream mechanisms and multitarget drug development in AD.

Amyloid β-based therapy for Alzheimer's disease: challenges, successes and future

Amyloid β protein (Aβ) is the main component of neuritic plaques in Alzheimer's disease (AD), and its accumulation has been considered as the molecular driver of Alzheimer's pathogenesis and progression. Aβ has been the prime target for the development of AD therapy. However, the repeated failures of Aβ-targeted clinical trials have cast considerable doubt on the amyloid cascade hypothesis and whether the development of Alzheimer's drug has followed the correct course. However, the recent successes of Aβ targeted trials have assuaged those doubts. In this review, we discussed the evolution of the amyloid cascade hypothesis over the last 30 years and summarized its application in Alzheimer's diagnosis and modification. In particular, we extensively discussed the pitfalls, promises and important unanswered questions regarding the current anti-Aβ therapy, as well as strategies for further study and development of more feasible Aβ-targeted approaches in the optimization of AD prevention and treatment.

Mitochondrial Ca2+ signaling and Alzheimer's disease: Too much or too little?

Alzheimer's disease (AD) is a neurodegenerative disease, caused by poorly known pathogenic mechanisms and aggravated by delayed therapeutic intervention, that still lacks an effective cure. However, it is clear that some important neurophysiological processes are altered years before the onset of clinical symptoms, offering the possibility of identifying biological targets useful for implementation of new therapies. Of note, evidence has been provided suggesting that mitochondria, pivotal organelles in sustaining neuronal energy demand and modulating synaptic activity, are dysfunctional in AD samples. In particular, alterations in mitochondrial Ca²⁺ signaling have been proposed as causal events for neurodegeneration, although the exact outcomes and molecular mechanisms of these defects, as well as their longitudinal progression, are not always clear. Here, we discuss the importance of a correct mitochondrial Ca²⁺ handling for neuronal physiology and summarize the latest findings on dysfunctional mitochondrial Ca²⁺ pathways in AD, analysing possible consequences contributing to the neurodegeneration that characterizes the disease.

The Path to Progress Preclinical Studies of Age-Related Neurodegenerative Diseases: A Perspective on Rodent and hiPSC-Derived Models

Alzheimer's disease (AD) and Parkinson's disease (PD) are the two most prevalent age-related neurodegenerative diseases, and currently no effective clinical treatments exist for either, despite decades of clinical trials. The failure to translate preclinical findings into effective treatments is indicative of a problem in the current evaluation pipeline for potential therapeutics. At present, there are no useful animal models for AD and PD research that reflect the entire biology of the diseases, specifically, the more common non-Mendelian forms. Whereas the field continues to seek suitable rodent models for investigating potential therapeutics for these diseases, rodent models have still been used primarily for preclinical studies. Here, we advocate for a paradigm shift toward the application of human-induced pluripotent stem cell (hiPSC)-derived systems for PD and AD modeling and the development of improved human-based models in a dish for drug discovery and preclinical assessment of therapeutic targets.

Presenilin-2 and Calcium Handling: Molecules, Organelles, Cells and Brain Networks

Presenilin-2 (PS2) is one of the three proteins that are dominantly mutated in familial Alzheimer's disease (FAD). It forms the catalytic core of the γ-secretase complex-a function shared with its homolog presenilin-1 (PS1)-the enzyme ultimately responsible of amyloid-β (Aβ) formation. Besides its enzymatic activity, PS2 is a multifunctional protein, being specifically involved, independently of γ-secretase activity, in the modulation of several cellular processes, such as Ca2+ signalling, mitochondrial function, inter-organelle communication, and autophagy. As for the former, evidence has accumulated that supports the involvement of PS2 at different levels, ranging from organelle Ca2+ handling to Ca2+ entry through plasma membrane channels. Thus FAD-linked PS2 mutations impact on multiple aspects of cell and tissue physiology, including bioenergetics and brain network excitability. In this contribution, we summarize the main findings on PS2, primarily as a modulator of Ca2+ homeostasis, with particular emphasis on the role of its mutations in the pathogenesis of FAD. Identification of cell pathways and molecules that are specifically targeted by PS2 mutants, as well as of common targets shared with PS1 mutants, will be fundamental to disentangle the complexity of memory loss and brain degeneration that occurs in Alzheimer's disease (AD).

TRP Channels Role in Pain Associated With Neurodegenerative Diseases

Transient receptor potential (TRP) are cation channels expressed in both non-excitable and excitable cells from diverse tissues, including heart, lung, and brain. The TRP channel family includes 28 isoforms activated by physical and chemical stimuli, such as temperature, pH, osmotic pressure, and noxious stimuli. Recently, it has been shown that TRP channels are also directly or indirectly activated by reactive oxygen species. Oxidative stress plays an essential role in neurodegenerative disorders, such as Alzheimer's and Parkinson's diseases, and TRP channels are involved in the progression of those diseases by mechanisms involving changes in the crosstalk between Ca2+ regulation, oxidative stress, and production of inflammatory mediators. TRP channels involved in nociception include members of the TRPV, TRPM, TRPA, and TRPC subfamilies that transduce physical and chemical noxious stimuli. It has also been reported that pain is a complex issue in patients with Alzheimer's and Parkinson's diseases, and adequate management of pain in those conditions is still in discussion. TRPV1 has a role in neuroinflammation, a critical mechanism involved in neurodegeneration. Therefore, some studies have considered TRPV1 as a target for both pain treatment and neurodegenerative disorders. Thus, this review aimed to describe the TRP-dependent mechanism that can mediate pain sensation in neurodegenerative diseases and the therapeutic approach available to palliate pain and neurodegenerative symptoms throughout the regulation of these channels.

Intracellular Calcium Dysregulation by the Alzheimer's Disease-Linked Protein Presenilin 2

Alzheimer's disease (AD) is the most common form of dementia. Even though most AD cases are sporadic, a small percentage is familial due to autosomal dominant mutations in amyloid precursor protein (APP), presenilin-1 (PSEN1), and presenilin-2 (PSEN2) genes. AD mutations contribute to the generation of toxic amyloid β (Aβ) peptides and the formation of cerebral plaques, leading to the formulation of the amyloid cascade hypothesis for AD pathogenesis. Many drugs have been developed to inhibit this pathway but all these approaches currently failed, raising the need to find additional pathogenic mechanisms. Alterations in cellular calcium (Ca2+) signaling have also been reported as causative of neurodegeneration. Interestingly, Aβ peptides, mutated presenilin-1 (PS1), and presenilin-2 (PS2) variously lead to modifications in Ca2+ homeostasis. In this contribution, we focus on PS2, summarizing how AD-linked PS2 mutants alter multiple Ca2+ pathways and the functional consequences of this Ca2+ dysregulation in AD pathogenesis.

Targeting Synaptic Plasticity in Experimental Models of Alzheimer's Disease

Long-term potentiation (LTP) and long-term depression (LTD) of hippocampal synaptic transmission represent the principal experimental models underlying learning and memory. Alterations of synaptic plasticity are observed in several neurodegenerative disorders, including Alzheimer’s disease (AD). Indeed, synaptic dysfunction is an early event in AD, making it an attractive therapeutic target for pharmaceutical intervention. To date, intensive investigations have characterized hippocampal synaptic transmission, LTP, and LTD in in vitro and in murine models of AD. In this review, we describe the synaptic alterations across the main AD models generated so far. We then examine the clinical perspective of LTP/LTD studies and discuss the limitations of non-clinical models and how to improve their predictive validity in the drug discovery process.

Ca2+ homeostasis dysregulation in Alzheimer's disease: a focus on plasma membrane and cell organelles

Emerging evidence indicates that Ca²⁺ is a vital factor in modulating the pathogenesis of Alzheimer's disease (AD). In healthy neurons, Ca²⁺ concentration is balanced to maintain a lower level in the cytosol than in the extracellular space or certain intracellular compartments such as endoplasmic reticulum (ER) and the lysosome, whereas this homeostasis is broken in AD. On the plasma membrane, the AD hallmarks amyloid-β (Aβ) and tau interact with ligand-gated or voltage-gated Ca²⁺-influx channels and inhibit the Ca²⁺-efflux ATPase or exchangers, leading to an elevated intracellular Ca²⁺ level and disrupted Ca²⁺ signal. In the ER, the disabled presenilin "Ca²⁺ leak" function and the direct implications of Aβ and presenilin mutants contribute to Ca²⁺-signal disorder. The enhanced ryanodine receptor (RyR)-mediated and inositol 1,4,5-trisphosphate receptor (IP₃R)-mediated Ca²⁺ release from the ER aggravates cytosolic Ca²⁺ disorder and triggers apoptosis; the down-regulated ER Ca²⁺ sensor, stromal interaction molecule (STIM), alleviates store-operated Ca²⁺ entry in plasma membrane, leading to spine loss. The increased transfer of Ca²⁺ from ER to mitochondria through mitochondria-associated ER membrane (MAM) causes Ca²⁺ overload in the mitochondrial matrix and consequently opens the cellular damage-related channel, mitochondrial permeability transition pore (mPTP). In this review, we discuss the effects of Aβ, tau and presenilin on neuronal Ca²⁺ signal, focusing on the receptors and regulators in plasma membrane and ER; we briefly introduce the involvement of MAM-mediated Ca²⁺ transfer and mPTP opening in AD pathogenesis.-Wang, X., Zheng, W. Ca²⁺ homeostasis dysregulation in Alzheimer's disease: a focus on plasma membrane and cell organelles.

Preclinical Models of Alzheimer's Disease: Relevance and Translational Validity

The only drugs currently approved for the treatment of Alzheimer's Disease (AD) are four acetylcholinesterase inhibitors and the NMDA antagonist memantine. Apart from these drugs, which have minimal to no clinical benefit, the 40-year search for effective therapeutics to treat AD has resulted in a clinical failure rate of 100% not only for compounds that prevent brain amyloid deposition or remove existing amyloid plaques but also those acting by a variety of other putative disease-associated mechanisms. This indicates that the preclinical data generated from current AD targets to support the selection, optimization, and translation of new chemical entities (NCEs) and biologics to clinical trials is seriously compromised. While many of these failures reflect flawed hypotheses or a lack of adequate characterization of the preclinical pharmacodynamic and pharmacokinetic (PD/PK) properties of lead NCEs-including their bioavailability and toxicity-the conceptualization, validation, and interrogation of the current animal models of AD represent key limitations. The overwhelming majority of these AD models are transgenic, based on aspects of the amyloid hypothesis and the genetics of the familial form of the disease. As a result, these generally lack construct and predictive validity for the sporadic form of the human disease. The 170 or so transgenic models, perhaps the largest number ever focused on a single disease, use rodents, mainly mice, and in addition to amyloid also address aspects of tau causality with more complex multigene models including other presumed causative factors together with amyloid. This overview discusses the current animal models of AD in the context of both the controversies surrounding the causative role of amyloid in the disease and the need to develop validated models of cognitive function/dysfunction that more appropriately reflect the phenotype(s) of human aged-related dementias. © 2019 by John Wiley & Sons, Inc.

Nano-CuO impairs spatial cognition associated with inhibiting hippocampal long-term potentiation via affecting glutamatergic neurotransmission in rats

Manufactured metal nanoparticles and their applications are continuously expanding because of their unique characteristics while their increasing use may predispose to potential health problems. Several studies have reported the adverse effects of copper oxide nanoparticles (nano-CuO) relative to ecotoxicity and cell toxicity, whereas little is known about the neurotoxicity of nano-CuO. The present study aimed to examine its effects on spatial cognition, hippocampal function, and the possible mechanisms. Male Wistar rats were used to establish an animal model, and nano-CuO was administered at a dose of 0.5 mg/kg/day for 2 weeks. The Morris water maze (MWM) test was employed to evaluate learning and memory. The long-term potentiation (LTP) from Schaffer collaterals to the hippocampal CA1 region, and the effects of nano-CuO on synases were recorded in the hippocampal CA1 neurons of rats. MWM test showed that learning and memory abilities were impaired significantly by nano-CuO ( p < 0.05). The LTP test demonstrated that the field excitatory postsynaptic potential (fEPSP) slopes were significantly lower in nano-CuO-treated groups compared with the control group ( p < 0.01). Furthermore, the data of whole-cell patch-clamp experiments showed that nano-CuO markedly depressed the frequencies of both spontaneous excitatory postsynaptic currents (sEPSCs) and miniature EPSCs (mEPSCs), indicating an effect of nano-CuO on inhibiting the release frequency of glutamate presynapticly ( p < 0.01). Meanwhile, the amplitudes of both sEPSC and mEPSC were significantly reduced in nano-CuO-treated animals, which suggested that the effect of nano-CuO modulates postsynaptic receptor kinetics ( p < 0.01). Paired pulse facilitation (PPF) ( p < 0.05) and the expression of NR2A, but not NR2B, of N-methyl-d-aspartate (NMDA) subunits ( p < 0.05), were decreased significantly. In conclusion, nano-CuO impaired glutamate transmission presynapticly and postsynapticly, which may contribute importantly to diminished LTP and other induced cognitive deficits.

Intracellular Ca2+ stores control in vivo neuronal hyperactivity in a mouse model of Alzheimer's disease

Neuronal hyperactivity is the emerging functional hallmark of Alzheimer's disease (AD) in both humans and different mouse models, mediating an impairment of memory and cognition. The mechanisms underlying neuronal hyperactivity remain, however, elusive. In vivo Ca²⁺ imaging of somatic, dendritic, and axonal activity patterns of cortical neurons revealed that both healthy aging and AD-related mutations augment neuronal hyperactivity. The AD-related enhancement occurred even without amyloid deposition and neuroinflammation, mainly due to presenilin-mediated dysfunction of intracellular Ca²⁺ stores in presynaptic boutons, likely causing more frequent activation of synaptic NMDA receptors. In mutant but not wild-type mice, store emptying reduced both the frequency and amplitude of presynaptic Ca²⁺ transients and, most importantly, normalized neuronal network activity. Postsynaptically, the store dysfunction was minor and largely restricted to hyperactive cells. These findings identify presynaptic Ca²⁺ stores as a key element controlling AD-related neuronal hyperactivity and as a target for disease-modifying treatments.

Alzheimer's disease: experimental models and reality

Experimental models of Alzheimer's disease (AD) are critical to gaining a better understanding of pathogenesis and to assess the potential of novel therapeutic approaches. The most commonly used experimental animal models are transgenic mice that overexpress human genes associated with familial AD (FAD) that result in the formation of amyloid plaques. However, AD is defined by the presence and interplay of both amyloid plaques and neurofibrillary tangle pathology. The track record of success in AD clinical trials thus far has been very poor. In part, this high failure rate has been related to the premature translation of highly successful results in animal models that mirror only limited aspects of AD pathology to humans. A greater understanding of the strengths and weakness of each of the various models and the use of more than one model to evaluate potential therapies would help enhance the success of therapy translation from preclinical studies to patients. In this review, we summarize the pathological features and limitations of the major experimental models of AD, including transgenic mice, transgenic rats, various physiological models of sporadic AD and in vitro human cell culture models.

Central role for NMDA receptors in redox mediated impairment of synaptic function during aging and Alzheimer's disease

Increased human longevity has magnified the negative impact that aging can have on cognitive integrity of older individuals experiencing some decline in cognitive function. Approximately 30% of the elderly will have cognitive problems that influence their independence. Impaired executive function and memory performance are observed in normal aging and yet can be an early sign of a progressive cognitive impairment of Alzheimer's disease (AD), the most common form of dementia. Brain regions that are vulnerable to aging exhibit the earliest pathology of AD. Senescent synaptic function is observed as a shift in Ca²⁺-dependent synaptic plasticity and similar mechanisms are thought to contribute to the early cognitive deficits associated with AD. In the case of aging, intracellular redox state mediates a shift in Ca²⁺ regulation including N-methyl-d-aspartate (NMDA) receptor hypofunction and increased Ca²⁺ release from intracellular stores to alter synaptic plasticity. AD can interact with these aging processes such that molecules linked to AD, β-amyloid (Aβ) and mutated presenilin 1 (PS1), can also degrade NMDA receptor function, promote Ca²⁺ release from intracellular stores, and may increase oxidative stress. Thus, age is one of the most important predictors of AD and brain aging likely contributes to the onset of AD. The focus of this review article is to provide an update on mechanisms that contribute to the senescent synapse and possible interactions with AD-related molecules, with special emphasis on regulation of NMDA receptors.

Dendritic Spine Pathology in Neurodegenerative Diseases

Substantial progress has been made toward understanding the neuropathology, genetic origins, and epidemiology of neurodegenerative diseases, including Alzheimer's disease; tauopathies, such as frontotemporal dementia; α-synucleinopathies, such as Parkinson's disease or dementia with Lewy bodies; Huntington's disease; and amyotrophic lateral sclerosis with dementia, as well as prion diseases. Recent evidence has implicated dendritic spine dysfunction as an important substrate of the pathogenesis of dementia in these disorders. Dendritic spines are specialized structures, extending from the neuronal processes, on which excitatory synaptic contacts are formed, and the loss of dendritic spines correlates with the loss of synaptic function. We review the literature that has implicated direct or indirect structural alterations at dendritic spines in the pathogenesis of major neurodegenerative diseases, focusing on those that lead to dementias such as Alzheimer's, Parkinson's, and Huntington's diseases, as well as frontotemporal dementia and prion diseases. We stress the importance of in vivo studies in animal models.

Alzheimer's disease-like APP processing in wild-type mice identifies synaptic defects as initial steps of disease progression

Background

Alzheimer’s disease (AD) is the most frequent form of dementia in the elderly and no effective treatment is currently available. The mechanisms triggering AD onset and progression are still imperfectly dissected. We aimed at deciphering the modifications occurring in vivo during the very early stages of AD, before the development of amyloid deposits, neurofibrillary tangles, neuronal death and inflammation. Most current AD models based on Amyloid Precursor Protein (APP) overproduction beginning from in utero, to rapidly reproduce the histological and behavioral features of the disease within a few months, are not appropriate to study the early steps of AD development. As a means to mimic in vivo amyloid APP processing closer to the human situation in AD, we used an adeno-associated virus (AAV)-based transfer of human mutant APP and Presenilin 1 (PS1) genes to the hippocampi of two-month-old C57Bl/6 J mice to express human APP, without significant overexpression and to specifically induce its amyloid processing.

Results

The human APP, βCTF and Aβ42/40 ratio were similar to those in hippocampal tissues from AD patients. Three months after injection the murine Tau protein was hyperphosphorylated and rapid synaptic failure occurred characterized by decreased levels of both PSD-95 and metabolites related to neuromodulation, on proton magnetic resonance spectroscopy (¹H-MRS). Astrocytic GLT-1 transporter levels were lower and the tonic glutamatergic current was stronger on electrophysiological recordings of CA1 hippocampal region, revealing the overstimulation of extrasynaptic N-methyl D-aspartate receptor (NMDAR) which precedes the loss of long-term potentiation (LTP). These modifications were associated with early behavioral impairments in the Open-field, Y-maze and Morris Mater Maze tasks.

Conclusions

Altogether, this demonstrates that an AD-like APP processing, yielding to levels of APP, βCTF and Aβ42/Aβ40 ratio similar to those observed in AD patients, are sufficient to rapidly trigger early steps of the amyloidogenic and Tau pathways in vivo. With this strategy, we identified a sequence of early events likely to account for disease onset and described a model that may facilitate efforts to decipher the factors triggering AD and to evaluate early neuroprotective strategies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-016-0070-y) contains supplementary material, which is available to authorized users.

Analyzing dendritic spine pathology in Alzheimer's disease: problems and opportunities

Synaptic failure is an immediate cause of cognitive decline and memory dysfunction in Alzheimer’s disease. Dendritic spines are specialized structures on neuronal processes, on which excitatory synaptic contacts take place and the loss of dendritic spines directly correlates with the loss of synaptic function. Dendritic spines are readily accessible for both in vitro and in vivo experiments and have, therefore, been studied in great detail in Alzheimer’s disease mouse models. To date, a large number of different mechanisms have been proposed to cause dendritic spine dysfunction and loss in Alzheimer’s disease. For instance, amyloid beta fibrils, diffusible oligomers or the intracellular accumulation of amyloid beta have been found to alter the function and structure of dendritic spines by distinct mechanisms. Furthermore, tau hyperphosphorylation and microglia activation, which are thought to be consequences of amyloidosis in Alzheimer’s disease, may also contribute to spine loss. Lastly, genetic and therapeutic interventions employed to model the disease and elucidate its pathogenetic mechanisms in experimental animals may cause alterations of dendritic spines on their own. However, to date none of these mechanisms have been translated into successful therapeutic approaches for the human disease. Here, we critically review the most intensely studied mechanisms of spine loss in Alzheimer’s disease as well as the possible pitfalls inherent in the animal models of such a complex neurodegenerative disorder.

G206D Mutation of Presenilin-1 Reduces Pen2 Interaction, Increases Aβ42/Aβ40 Ratio and Elevates ER Ca(2+) Accumulation

Early-onset familial Alzheimer's disease (AD) is most commonly associated with the mutations in presenilin-1 (PS1). PS1 is the catalytic component of the γ-secretase complex, which cleaves amyloid precursor protein to produce amyloid-β (Aβ), the major cause of AD. Presenilin enhancer 2 (Pen2) is critical for activating γ-secretase and exporting PS1 from endoplasmic reticulum (ER). Among all the familial AD-linked PS1 mutations, mutations at the G206 amino acid are the most adjacent position to the Pen2 binding site. Here, we characterized the effect of a familial AD-linked PS1 G206D mutation on the PS1-Pen2 interaction and the accompanied alteration in γ-secretase-dependent and -independent functions. We found that the G206D mutation reduced PS1-Pen2 interaction, but did not abolish γ-secretase formation and PS1 endoproteolysis. For γ-secretase-dependent function, the G206D mutation increased Aβ42 production but not Notch cleavage. For γ-secretase-independent function, this mutation disrupted the ER calcium homeostasis but not lysosomal calcium homeostasis and autophagosome maturation. Impaired ER calcium homeostasis may due to the reduced mutant PS1 level in the ER. Although this mutation did not alter the cell survival under stress, both increased Aβ42 ratio and disturbed ER calcium regulation could be the mechanisms underlying the pathogenesis of the familial AD-linked PS1 G206D mutation.

Suppression of InsP3 receptor-mediated Ca2+ signaling alleviates mutant presenilin-linked familial Alzheimer's disease pathogenesis

Exaggerated intracellular Ca(2+) signaling is a robust proximal phenotype observed in cells expressing familial Alzheimer's disease (FAD)-causing mutant presenilins (PSs). The mechanisms that underlie this phenotype are controversial and their in vivo relevance for AD pathogenesis is unknown. Here, we used a genetic approach to identify the mechanisms involved and to evaluate their role in the etiology of AD in two FAD mouse models. Genetic reduction of the type 1 inositol trisphosphate receptor (InsP3R1) by 50% normalized exaggerated Ca(2+) signaling observed in cortical and hippocampal neurons in both animal models. In PS1M146V knock-in mice, reduced InsP3R1 expression restored normal ryanodine receptor and cAMP response element-binding protein (CREB)-dependent gene expression and rescued aberrant hippocampal long-term potentiation (LTP). In 3xTg mice, reduced InsP3R1 expression profoundly attenuated amyloid β accumulation and tau hyperphosphorylation and rescued hippocampal LTP and memory deficits. These results indicate that exaggerated Ca(2+) signaling, which is associated with FAD PS, is mediated by InsP3R and contributes to disease pathogenesis in vivo. Targeting the InsP3 signaling pathway could be considered a potential therapeutic strategy for patients harboring mutations in PS linked to AD.

Deficits in the mitochondrial enzyme α-ketoglutarate dehydrogenase lead to Alzheimer's disease-like calcium dysregulation

Understanding the molecular sequence of events that culminate in multiple abnormalities in brains from patients that died with Alzheimer's disease (AD) will help to reveal the mechanisms of the disease and identify upstream events as therapeutic targets. The activity of the mitochondrial α-ketoglutarate dehydrogenase complex (KGDHC) in homogenates from autopsy brain declines with AD. Experimental reductions in KGDHC in mouse models of AD promote plaque and tangle formation, the hallmark pathologies of AD. We hypothesize that deficits in KGDHC also lead to the abnormalities in endoplasmic reticulum (ER) calcium stores and cytosolic calcium following K(+) depolarization that occurs in cells from AD patients and transgenic models of AD. The activity of the mitochondrial enzyme KGDHC was diminished acutely (minutes), long-term (days), or chronically (weeks). Acute inhibition of KGDHC produced effects on calcium opposite to those in AD, while the chronic or long-term inhibition of KGDHC mimicked the AD-related changes in calcium. Divergent changes in proteins released from the mitochondria that affect endoplasmic reticulum calcium channels may underlie the selective cellular consequences of acute versus longer term inhibition of KGDHC. The results suggest that the mitochondrial abnormalities in AD can be upstream of those in calcium.

The role of neuronal calcium sensors in balancing synaptic plasticity and synaptic dysfunction

Neuronal calcium sensors (NCS) readily bind calcium and undergo conformational changes enabling them to interact and regulate specific target molecules. These interactions lead to dynamic alterations in protein trafficking that significantly impact upon synaptic function. Emerging evidence suggests that NCS and alterations in Ca(2+) mobilization modulate glutamate receptor trafficking, subsequently determining the expression of different forms of synaptic plasticity. In this review, we aim to discuss the functional relevance of NCS in protein trafficking and their emerging role in synaptic plasticity. Their significance within the concept of "translational neuroscience" will also be highlighted, by assessing their potential as key molecules in neurodegeneration.

Dantrolene is neuroprotective in Huntington's disease transgenic mouse model

Background

Huntington's disease (HD) is a progressive neurodegenerative disorder caused by a polyglutamine expansion in the Huntingtin protein which results in the selective degeneration of striatal medium spiny neurons (MSNs). Our group has previously demonstrated that calcium (Ca²⁺) signaling is abnormal in MSNs from the yeast artificial chromosome transgenic mouse model of HD (YAC128). Moreover, we demonstrated that deranged intracellular Ca²⁺ signaling sensitizes YAC128 MSNs to glutamate-induced excitotoxicity when compared to wild type (WT) MSNs. In previous studies we also observed abnormal neuronal Ca²⁺ signaling in neurons from spinocerebellar ataxia 2 (SCA2) and spinocerebellar ataxia 3 (SCA3) mouse models and demonstrated that treatment with dantrolene, a ryanodine receptor antagonist and clinically relevant Ca²⁺ signaling stabilizer, was neuroprotective in experiments with these mouse models. The aim of the current study was to evaluate potential beneficial effects of dantrolene in experiments with YAC128 HD mouse model.

Results

The application of caffeine and glutamate resulted in increased Ca²⁺ release from intracellular stores in YAC128 MSN cultures when compared to WT MSN cultures. Pre-treatment with dantrolene protected YAC128 MSNs from glutamate excitotoxicty, with an effective concentration of 100 nM and above. Feeding dantrolene (5 mg/kg) twice a week to YAC128 mice between 2 months and 11.5 months of age resulted in significantly improved performance in the beam-walking and gait-walking assays. Neuropathological analysis revealed that long-term dantrolene feeding to YAC128 mice significantly reduced the loss of NeuN-positive striatal neurons and reduced formation of Htt^exp nuclear aggregates.

Conclusions

Our results support the hypothesis that deranged Ca²⁺ signaling plays an important role in HD pathology. Our data also implicate the RyanRs as a potential therapeutic target for the treatment of HD and demonstrate that RyanR inhibitors and Ca²⁺ signaling stabilizers such as dantrolene should be considered as potential therapeutics for the treatment of HD and other polyQ-expansion disorders.

Alzheimer disease-related presenilin-1 variants exert distinct effects on monoamine oxidase-A activity in vitro

Monoamine oxidase-A (MAO-A) has been associated with both depression and Alzheimer disease (AD). Recently, carriers of AD-related presenilin-1 (PS-1) alleles have been found to be at higher risk for developing clinical depression. We chose to examine whether PS-1 could influence MAO-A function in vitro. Overexpression of selected AD-related PS-1 variants (wildtype, Y115H, ΔEx9 and M146V) in mouse hippocampal HT-22 cells affects MAO-A catalytic activity in a variant-specific manner. The ability of the PS-1 substrate-competitor DAPT to induce MAO-A activity in cells expressing either PS-1 wildtype or PS-1(M146V) suggests the potential for a direct influence of PS-1 on MAO-A function. In support of this, we were able to co-immunoprecipitate MAO-A with FLAG-tagged PS-1 wildtype and M146V proteins. This potential for a direct protein-protein interaction between PS-1 and MAO-A is not specific for HT-22 cells as we were also able to co-immunoprecipitate MAO-A with FLAG-PS-1 variants in N2a mouse neuroblastoma cells and in HEK293 human embryonic kidney cells. Finally, we demonstrate that the two PS-1 variants reported to be associated with an increased incidence of clinical depression [e.g., A431E and L235V] both induce MAO-A activity in HT-22 cells. A direct influence of PS-1 variants on MAO-A function could provide an explanation for the changes in monoaminergic tone observed in several neurodegenerative processes including AD. The ability to induce MAO-A catalytic activity with a PS-1/γ-secretase inhibitor should also be considered when designing secretase inhibitor-based therapeutics.

Presenilin mouse and zebrafish models for dementia: focus on neurogenesis

Autosomal dominant mutations in the presenilin gene PSEN cause familial Alzheimer's disease (AD), a neurological disorder pathologically characterized by intraneuronal accumulation and extracellular deposition of amyloid-β in plaques and intraneuronal, hyperphosphorylated tau aggregation in neurofibrillary tangles. Presenilins (PS/PSENs) are part of the proteolytic γ-secretase complex, which cleaves substrate proteins within the membrane. Cleavage of the amyloid precursor protein (APP) by γ-secretase releases amyloid-β peptides. Besides its role in the processing of APP and other transmembrane proteins, presenilin plays an important role in neural progenitor cell maintenance and neurogenesis. In this review, we discuss the role of presenilin in relation to neurogenesis and neurodegeneration and review the currently available presenilin animal models. In addition to established mouse models, zebrafish are emerging as an attractive vertebrate model organism to study the role of presenilin during the development of the nervous system and in neurodegenerative disorders involving presenilin. Zebrafish is a suitable model organism for large-scale drug screening, making this a valuable model to identify novel therapeutic targets for AD.

Modeling presenilin-dependent familial Alzheimer's disease: emphasis on presenilin substrate-mediated signaling and synaptic function

Mutations in PSEN genes, which encode presenilin proteins, cause familial early-onset Alzheimer's disease (AD). Transgenic mouse models based on coexpression of familial AD-associated presenilin and amyloid precursor protein variants successfully mimic characteristic pathological features of AD, including plaque formation, synaptic dysfunction, and loss of memory. Presenilins function as the catalytic subunit of gamma-secretase, the enzyme that catalyzes intramembraneous proteolysis of amyloid precursor protein to release beta-amyloid peptides. Familial AD-associated mutations in presenilins alter the site of gamma-secretase cleavage in a manner that increases the generation of longer and highly fibrillogenic beta-amyloid peptides. In addition to amyloid precursor protein, gamma-secretase catalyzes intramembrane proteolysis of many other substrates known to be important for synaptic function. This paper focuses on how various animal models have enabled us to elucidate the physiological importance of diverse gamma-secretase substrates, including amyloid precursor protein and discusses their roles in the context of cellular signaling and synaptic function.

Role of presenilins in neuronal calcium homeostasis

Alzheimer's disease (AD) is a progressive and irreversible neurodegenerative disorder. Familial AD (FAD) mutations in presenilins have been linked to calcium (Ca(2+)) signaling abnormalities. To explain these results, we previously proposed that presenilins function as endoplasmic reticulum (ER) passive Ca(2+) leak channels. To directly investigate the role of presenilins in neuronal ER Ca(2+) homeostasis, we here performed a series of Ca(2+) imaging experiments with primary neuronal cultures from conditional presenilin double-knock-out mice (PS1(dTAG/dTAG), PS2(-/-)) and from triple-transgenic AD mice (KI-PS1(M146V), Thy1-APP(KM670/671NL), Thy1-tau(P301L)). Obtained results provided additional support to the hypothesis that presenilins function as ER Ca(2+) leak channels in neurons. Interestingly, we discovered that presenilins play a major role in ER Ca(2+) leak function in hippocampal but not in striatal neurons. We further discovered that, in hippocampal neurons, loss of presenilin-mediated ER Ca(2+) leak function was compensated by an increase in expression and function of ryanodine receptors (RyanRs). Long-term feeding of the RyanR inhibitor dantrolene to amyloid precursor protein-presenilin-1 mice (Thy1-APP(KM670/671NL), Thy1-PS1(L166P)) resulted in an increased amyloid load, loss of synaptic markers, and neuronal atrophy in hippocampal and cortical regions. These results indicate that disruption of ER Ca(2+) leak function of presenilins may play an important role in AD pathogenesis.

Enhanced dentate gyrus synaptic plasticity but reduced neurogenesis in a mouse model of amyloidosis

Long-term potentiation (LTP) and neurogenesis in the dentate gyrus (DG) are correlated forms of hippocampal plasticity which share, under physiological conditions, common regulatory mechanisms. In Alzheimer's disease (AD), their alterations are potentially associated with the early cellular pathology and cognitive decline. We analyzed DG LTP and neurogenesis in B6.152H mice, an amyloid precursor protein and presenilin 2 double-transgenic mouse model of amyloidosis and observed that DG LTP was strongly enhanced before and after amyloid plaque formation. Whereas proliferation of DG neuronal progenitor cells was unchanged, survival of newborn neurons was strongly decreased already before plaque formation. As similar alteration of neurogenesis was observed in PS2APP mice without changes in DG LTP (Richards et al. 2003), this study suggests that enhanced synaptic plasticity did not rescue impaired neurogenesis, and supports decreased survival of newborn neurons as an early event associated with AD detectable even before plaque formation.

Mitochondria: the calcium connection

Calcium handling by mitochondria is a key feature in cell life. It is involved in energy production for cell activity, in buffering and shaping cytosolic calcium rises and also in determining cell fate by triggering or preventing apoptosis. Both mitochondria and the mechanisms involved in the control of calcium homeostasis have been extensively studied, but they still provide researchers with long-standing or even new challenges. Technical improvements in the tools employed for the investigation of calcium dynamics have been-and are still-opening new perspectives in this field, and more prominently for mitochondria. In this review we present a state-of-the-art toolkit for calcium measurements, with major emphasis on the advantages of genetically encoded indicators. These indicators can be efficiently and selectively targeted to specific cellular sub-compartments, allowing previously unavailable high-definition calcium dynamic studies. We also summarize the main features of cellular and, in more detail, mitochondrial calcium handling, especially focusing on the latest breakthroughs in the field, such as the recent direct characterization of the calcium microdomains that occur on the mitochondrial surface upon cellular stimulation. Additionally, we provide a major example of the key role played by calcium in patho-physiology by briefly describing the extensively reported-albeit highly controversial-alterations of calcium homeostasis in Alzheimer's disease, casting lights on the possible alterations in mitochondrial calcium handling in this pathology.

Transgenic mouse models of Alzheimer's disease

Alzheimer's disease is the most common cause of senile dementia in the United States and Europe. At present, there is no effective treatment. Given the disease's prevalence and poor prognosis, the development of animal models has been a high research priority. Transgenic modeling has been pursued on the basis of the amyloid hypothesis and has taken advantage of mutations in the amyloid precursor protein and the presenilins that cause familial forms of Alzheimer's disease. Modeling has been most aggressively pursued in mice, for which the techniques of genetic modification are well developed. Transgenic mouse models now exist that mimic a range of Alzheimer's disease-related pathologies. Although none of the models fully replicates the human disease, the models have contributed significant insights into the pathophysiology of beta-amyloid toxicity, particularly with respect to the effects of different beta-amyloid species and the possible pathogenic role of beta-amyloid oligomers. They have also been widely used in the preclinical testing of potential therapeutic modalities and have played a pivotal role in the development of immunotherapies for Alzheimer's disease that are currently in clinical trials. These models will, without a doubt, continue to play central roles in preclinical testing and be used as tools for developing insights into the biological basis of Alzheimer's disease.

Alzheimer's disease phenotypes and genotypes associated with mutations in presenilin 2

Mutations in presenilin 2 are rare causes of early onset familial Alzheimer's disease. Eighteen presenilin 2 mutations have been reported, although not all have been confirmed pathogenic. Much remains to be learned about the range of phenotypes associated with these mutations. We have analysed our unique collection of 146 affected cases in 11 Volga German families, 101 who are likely to have the same N141I mutation in presenilin 2 (54 genotyped confirmed). We have also assessed the detailed neuropathologic findings in 18 autopsies from these families and reviewed the world's literature on other presenilin 2 mutations; presenting a novel mutation that is predicted to lead to a premature truncation codon. Seven presenilin 2 mutations reported in the literature have strong evidence for pathogenicity whereas others may be benign polymorphisms. One hundred and one affected persons, with sufficient historical information from the Volga German pedigrees (N141I mutation), had a mean onset age of 53.7 years+/-7.8 (range 39-75) and mean age at death of 64.2 years+/-9.8 (range 43-88). These figures overlap with and generally fall between the results from the subjects in our centre who have late onset familial Alzheimer's disease or mutations in presenilin 1. Seizures were noted in 20 (30%) of 64 subjects with detailed medical records. Two mutation carriers lived beyond age 80 without developing dementia, representing uncommon examples of decreased penetrance. Two persons had severe amyloid angiopathy and haemorrhagic stroke. Eighteen cases had detailed histopathology available and analysed at our institution. Braak stage was five or six, amyloid angiopathy and neuritic plaques were common and more than 75% had Lewy bodies in the amygdala. TAR DNA-binding protein-43 inclusions were uncommon. In addition, a 58-year-old female with a 2 year course of cognitive decline and no family history of dementia has abnormal fludeoxyglucose-positron emission tomography imaging and a novel 2 base pair deletion in presenilin 2 at nucleotide 342/343, predicted to produce a frame-shift and premature termination. We conclude that mutations in presenilin 2 are rare with only seven being well documented in the literature. The best studied N141I mutation produces an Alzheimer's disease phenotype with a wide range of onset ages overlapping both early and late onset Alzheimer's disease, often associated with seizures, high penetrance and typical Alzheimer's disease neuropathology. A novel premature termination mutation supports loss of function or haploinsufficiency as pathogenic mechanisms in presenilin 2 associated Alzheimer's disease.

Hippocampal interneuron loss in an APP/PS1 double mutant mouse and in Alzheimer's disease

Hippocampal atrophy and neuron loss are commonly found in Alzheimer's disease (AD). However, the underlying molecular mechanisms and the fate in the AD hippocampus of subpopulations of interneurons that express the calcium-binding proteins parvalbumin (PV) and calretinin (CR) has not yet been properly assessed. Using quantitative stereologic methods, we analyzed the regional pattern of age-related loss of PV- and CR-immunoreactive (ir) neurons in the hippocampus of mice that carry M233T/L235P knocked-in mutations in presenilin-1 (PS1) and overexpress a mutated human beta-amyloid precursor protein (APP), namely, the APP(SL)/PS1 KI mice, as well as in APP(SL) mice and PS1 KI mice. We found a loss of PV-ir neurons (40-50%) in the CA1-2, and a loss of CR-ir neurons (37-52%) in the dentate gyrus and hilus of APP(SL)/PS1 KI mice. Interestingly, comparable PV- and CR-ir neuron losses were observed in the dentate gyrus of postmortem brain specimens obtained from patients with AD. The loss of these interneurons in AD may have substantial functional repercussions on local inhibitory processes in the hippocampus.

The functional neurophysiology of the amyloid precursor protein (APP) processing pathway

Amyloid beta (Abeta) peptides derived from proteolytic cleavage of amyloid precursor protein (APP) are thought to be a pivotal toxic species in the pathogenesis of Alzheimer's disease (AD). Furthermore, evidence has been accumulating that components of APP processing pathway are involved in non-pathological normal function of the CNS. In this review we aim to cover the extensive body of research aimed at understanding how components of this pathway contribute to neurophysiological function of the CNS in health and disease. We briefly outline changes to clinical neurophysiology seen in AD patients before discussing functional changes in mouse models of AD which range from changes to basal synaptic transmission and synaptic plasticity through to abnormal synchronous network activity. We then describe the various neurophysiological actions that are produced by application of exogenous Abeta in various forms, and finally discuss a number or other neurophysiological aspects of the APP pathway, including functional activities of components of secretase complexes other than Abeta production.

Presenilin transgenic mice as models of Alzheimer's disease

Mutations in presenilin-1 (PS1) and presenilin-2 (PS2) cause familial Alzheimer's disease (FAD). Presenilins influence multiple molecular pathways and are best known for their role in the gamma-secretase cleavage of type I transmembrane proteins including the amyloid precursor protein (APP). PS1 and PS2 FAD mutant transgenic mice have been generated using a variety of promoters. PS1-associated FAD mutations have also been knocked into the endogenous mouse gene. PS FAD mutant mice consistently show elevations of Abeta42 with little if any effect on Abeta40. When crossed with plaque forming APP FAD mutant lines, the PS1 FAD mutants cause earlier and more extensive plaque deposition. Although single transgenic PS1 or PS2 mice do not form plaques, they exhibit a number of pathological features including age-related neuronal and synaptic loss as well as vascular pathology. They also exhibit increased susceptibility to excitotoxic injury most likely on the basis of exaggerated calcium release from the endoplasmic reticulum. Electrophysiologically long-term potentiation in the hippocampus is increased in young PS1 FAD mutant mice but this effect appears to be lost with aging. In most studies neurogenesis in the adult hippocampus is also impaired by PS1 FAD mutants. Mice in which PS1 has been conditionally knocked out in adult forebrain on a PS2 null background (PS1/2 cDKO) develop a striking neurodegeneration that mimics AD neuropathology in being associated with neuronal and synaptic loss, astrogliosis and hyperphosphorylation of tau, although it is not accompanied by plaque deposits. The relevance of PS transgenic mice as models of AD is discussed.

Deranged calcium signaling and neurodegeneration in spinocerebellar ataxia type 2

Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominantly inherited, neurodegenerative disease caused by an expansion of polyglutamine tracts in the cytosolic protein ataxin-2 (Atx2). Cerebellar Purkinje cells (PCs) are predominantly affected in SCA2. The cause of PC degeneration in SCA2 is unknown. Here we demonstrate that mutant Atx2-58Q, but not wild-type (WT) Atx2-22Q, specifically associates with the cytosolic C-terminal region of type 1 inositol 1,4,5-trisphosphate receptor (InsP(3)R1), an intracellular calcium (Ca(2+)) release channel. Association with Atx2-58Q increased the sensitivity of InsP(3)R1 to activation by InsP(3) in planar lipid bilayer reconstitution experiments. To validate physiological significance of these findings, we performed a series of experiments with an SCA2-58Q transgenic mouse model that expresses human full-length Atx2-58Q protein under the control of a PC-specific promoter. In Ca(2+) imaging experiments, we demonstrated that stimulation with 3,5-dihydroxyphenylglycine (DHPG) resulted in higher Ca(2+) responses in 58Q PC cultures than in WT PC cultures. DHPG-induced Ca(2+) responses in 58Q PC cultures were blocked by the addition of ryanodine, an inhibitor of the ryanodine receptor (RyanR). We further demonstrated that application of glutamate induced more pronounced cell death in 58Q PC cultures than in WT PC cultures. Glutamate-induced cell death of 58Q PC cultures was attenuated by dantrolene, a clinically relevant RyanR inhibitor and Ca(2+) stabilizer. In whole animal experiments, we demonstrated that long-term feeding of SCA1-58Q mice with dantrolene alleviated age-dependent motor deficits (quantified in beam-walk and rotarod assays) and reduced PC loss observed in untreated SCA2-58Q mice by 12 months of age (quantified by stereology). Results of our studies indicate that disturbed neuronal Ca(2+) signaling may play an important role in SCA2 pathology and also suggest that the RyanR constitutes a potential therapeutic target for treatment of SCA2 patients.

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.

Alterations in excitotoxicity and prostaglandin metabolism in a transgenic mouse model of Alzheimer's disease

To address the potential impact of presenilin mutations on the prostaglandin metabolism in a neurodegenerative model of glutamatergic excitotoxicity, we injected kainic acid intraperitoneally (30mg/kg body weight) into mice over-expressing the human N141I mutation of presenilin-2, which is known to cause an early-onset form of Alzheimer's disease. We compared the seizure activity as well as seizure lethality in 2- and 6-month-old mice, transgenic for the above-mentioned point mutation, and their wildtype littermates and found that mice harboring the hN141I mutation showed a relative resistance to excitotoxic treatment. This was associated with a constituitively reduced expression of the cyclooxygenases COX-1 and COX-2 in the hippocampus of N141I presenilin-2 mice and a reduced induction of COX-2 expression post-kainate injection. In the past, clinical trials have suggested that both non-steroidal anti-inflammatory drugs, which impact upon a cell's prostaglandin metabolism, and glutamatergic antagonists might be of benefit to patients suffering from Alzheimer's-type dementias. Yet, the exact mechanism by which these drugs are beneficial remains unclear, although it seems possible that presenilins might be implicated in the process, at least in the case of early-onset forms. The data presented here strongly support the notion of an implication of presenilins in the alterations in the prostaglandin system, which have been observed in Alzheimer's disease and may contribute to the underlying pathogenesis of the disease.

APP/PS1KI bigenic mice develop early synaptic deficits and hippocampus atrophy

Abeta accumulation has an important function in the etiology of Alzheimer's disease (AD) with its typical clinical symptoms, like memory impairment and changes in personality. However, the mode of this toxic activity is still a matter of scientific debate. We used the APP/PS1KI mouse model for AD, because it is the only model so far which develops 50% hippocampal CA1 neuron loss at the age of 1 year. Previously, we have shown that this model develops severe learning deficits occurring much earlier at the age of 6 months. This observation prompted us to study the anatomical and cellular basis at this time point in more detail. In the current report, we observed that at 6 months of age there is already a 33% CA1 neuron loss and an 18% atrophy of the hippocampus, together with a drastic reduction of long-term potentiation and disrupted paired pulse facilitation. Interestingly, at 4 months of age, there was no long-term potentiation deficit in CA1. This was accompanied by reduced levels of pre- and post-synaptic markers. We also observed that intraneuronal and total amount of different Abeta peptides including N-modified, fibrillar and oligomeric Abeta species increased and coincided well with CA1 neuron loss. Overall, these data provide the basis for the observed robust working memory deficits in this mouse model for AD at 6 months of age.

Presenilin-2 dampens intracellular Ca2+ stores by increasing Ca2+ leakage and reducing Ca2+ uptake

We have previously shown that familial Alzheimer’s disease mutants of presenilin-2 (PS2) and, to a lesser extent, of presenilin-1 (PS1) lower the Ca²⁺ concentration of intracellular stores. We here examined the mechanism by which wild-type and mutant PS2 affect store Ca²⁺ handling. By using HeLa, SH-SY5Y and MEFs as model cells, and recombinant aequorins as Ca²⁺ probes, we show evidence that transient expression of either wild-type or mutant PS2 increases the passive Ca²⁺ leakage: both ryanodine- and IP₃-receptors contribute to Ca²⁺ exit out of the ER, whereas the ribosome translocon complex is not involved. In SH-SY5Y cells and MEFs, wild-type and mutant PS2 potently reduce the uptake of Ca²⁺ inside the stores, an effect that can be counteracted by over-expression of SERCA-2B. On this line, in wild-type MEFs, lowering the endogenous level of PS2 by RNA interference, increases the Ca²⁺-loading capability of intracellular stores. Furthermore, we show that in PS double knockout MEFs, reduction of Ca²⁺ stores is mimicked by the expression of PS2-D366A, a loss-of-function mutant, uncleaved because also devoid of presenilinase activity but not by co-expression of the two catalytic active fragments of PS2. In summary, both physiological and increased levels of wild-type and mutant PS2 reduce the Ca²⁺ uptake by intracellular stores. To exert this newly described function, PS2 needs to be in its full-length form, even if it can subsequently be cleaved.

Quantitative proteomic analysis of mitochondria in aging PS-1 transgenic mice

Accumulating evidence suggests mitochondrial alterations are intimately associated with the pathogenesis of Alzheimer's disease (AD). In order to determine if mutations of presenilin-1 (PS-1) affect levels of mitochondrial proteins at different ages we enriched mitochondrial fractions from 3-, 6-, 12-month-old knock-in mice expressing the M146V PS-1 mutation and identified, and quantified proteins using cleavable isotope-coded affinity tag labeling and two-dimensional liquid chromatography/tandem mass spectrometry (2D-LC/MS/MS). Using this approach, 165 non-redundant proteins were identified with 80 of them present in all three age groups. Specifically, at young ages (3 and 6 months), Na(+)/K(+) ATPase and several signal transduction proteins exhibited elevated levels, but dropped dramatically at 12 months. In contrast, components of the oxidative phosporylation pathway (OXPHOS), the mitochondrial permeability transition pore (MPTP), and energy metabolism proteins remained unchanged at 3 months but significantly increased with age. We propose that alterations in calcium homeostasis induced by the PS-1 mutation have a major impact in young animals by inhibiting the function of relevant proteins and inducing compensatory changes. However, in older mice combination of the PS-1 mutation and accumulated oxidative damage results in a functional suppression of OXPHOS and MPTP proteins requiring a compensatory increase in expression levels. In contrast, signal transduction proteins showed decreased levels due to a break down in the compensatory mechanisms. The dysfunction of Na(+)/K(+) ATPase and signal transduction proteins may induce impaired cognition and memory before neurodegeneration occurs.