An update on the toxicity of Abeta in Alzheimer's disease

Genetic Phenotypes of Alzheimer's Disease: Mechanisms and Potential Therapy

Years of intensive research has brought us extensive knowledge on the genetic and molecular factors involved in Alzheimer's disease (AD). In addition to the mutations in the three main causative genes of familial AD (FAD) including presenilins and amyloid precursor protein genes, studies have identified several genes as the most plausible genes for the onset and progression of FAD, such as triggering receptor expressed on myeloid cells 2, sortilin-related receptor 1, and adenosine triphosphate-binding cassette transporter subfamily A member 7. The apolipoprotein E ε4 allele is reported to be the strongest genetic risk factor for sporadic AD (SAD), and it also plays an important role in FAD. Here, we reviewed recent developments in genetic and molecular studies that contributed to the understanding of the genetic phenotypes of FAD and compared them with SAD. We further reviewed the advancements in AD gene therapy and discussed the future perspectives based on the genetic phenotypes.

Receptors for Advanced Glycation End Products (RAGE): Promising Targets Aiming at the Treatment of Neurodegenerative Conditions

Advanced glycation end products (AGEs) are compounds formed after the non-enzymatic addition of reducing sugars to lipids, proteins, and nucleic acids. They are associated with the development of various clinical complications observed in diabetes and cardiovascular diseases, such as retinopathy, nephropathy, diabetic neuropathy, and others. In addition, compelling evidence indicates that these molecules participate in the progression of neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Multiple cellular and molecular alterations triggered by AGEs that could alter homeostasis have been identified. One of the main targets for AGE signaling is the receptor for advanced glycation end-products (RAGE). Importantly, this receptor is the target of not only AGEs, but also amyloid β peptides, HMGB1 (high-mobility group box-1), members of the S100 protein family, and glycosaminoglycans. The activation of this receptor induces intracellular signaling cascades that are involved in pathological processes and cell death. Therefore, RAGE represents a key target for pharmacological interventions in neurodegenerative diseases. This review will discuss the various effects of AGEs and RAGE activation in the pathophysiology of neurodegenerative diseases, as well as the currently available pharmacological tools and promising drug candidates.

Cannabinoids for Agitation in Alzheimer's Disease

Agitation is a common neuropsychiatric symptom of Alzheimer's disease (AD) that greatly impacts quality of life and amplifies caregiver burden. Agitation in AD may be associated with volume loss in the anterior cingulate cortex, posterior cingulate cortex, insula, amygdala, and frontal cortex, as well as with degeneration of monoaminergic neurotransmission, disrupted circadian rhythms, and frailty. Current pharmacologic options have troubling safety concerns and only modest efficacy. There is increasing interest in cannabinoids as promising agents due to preclinical and early clinical research that suggest cannabinoids can elicit anxiolytic, antidepressant, and/or anti-inflammatory effects. Cannabinoids may relieve agitation by regulating neurotransmitters, improving comorbidities and circadian rhythms, and increasing cerebral circulation. Here we discuss the possible contributory mechanisms for agitation in AD and the therapeutic relevance of cannabinoids, including CBD and THC.

Lindera glauca Blume ameliorates amyloid-β1-42-induced memory impairment in mice with neuroprotection and activation of the CREB-BDNF pathway

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disorder presenting cognitive decline accompanied by deposits of amyloid-β (Aβ) and tau hyperphosphorylation. Without current treatment to AD, many studies suggested diverse approaches, one of which was herbal medicine and its active compounds. Very few studies have examined the effect of Lindera glauca Blume (L. glauca) in models of degenerative disease despite the attention that it received as a novel potential treatment source. We examined the efficacy of L. glauca in a mouse model of AD, which was induced by intrahippocampal injection of Aβ1-42.

METHODS

Mice were intrahippocampally infused with Aβ1-42 and were orally administered ethanolic extract of L.glauca before and after infusion for 21 days. Y-maze test and Morris water maze was conducted to assess memory impairment. Immunohistochemistry and western blot analysis were performed to assess the effect of L. glauca administration on pathological changes in mice.

RESULTS

L. glauca exhibited beneficial effects in spatial and reference learning as shown in increased time spent in the target quadrant in Morris water maze and increased spontaneous alternation in Y-maze. At the same time, decline of Aβ burden and phosphorylated tau were observed in the hippocampus of L. glauca-treated mouse under intrahippocampal injection of Aβ1-42. The results corresponded with amelioration of the decreased neuronal marker, neuronal-specific nuclear protein (NeuN) and attenuation of the increased reactive astrocyte marker, glial fibrillary acidic protein (GFAP) levels in hippocampus. Additionally, 21-day treatment with L. glauca inhibited downregulation of phosphorylated cAMP response element-binding protein (p-CREB) and brain-derived neurotrophic factor (BDNF) levels.

CONCLUSION

L. glauca improves behavioral deficits induced by Aβ1-42 and inhibits both Aβ- and tau-related pathological changes, stimulating neuroprotection mediated by CREB activation. L. glauca can be suggested as a new candidate for treatment of AD.

TREM2 function impedes tau seeding in neuritic plaques

Variants in the triggering receptor expressed on myeloid cells 2 (TREM2) have been associated with increased risk for sporadic, late-onset Alzheimer's disease. Here we show that germline knockout of Trem2 or the TREM2R47H variant reduces microgliosis around amyloid-β plaques and facilitates the seeding and spreading of neuritic plaque tau aggregates. These findings demonstrate a key role for TREM2 and microglia in limiting the development of peri-plaque tau pathologies.

Protective effect of Tenuifolin against Alzheimer's disease

Amyloid-β (Aβ) plays a critical role in the pathogenesis of Alzheimer's disease (AD), an age-related neurodegenerative ailment. Emerging evidence suggests that Tenuifolin (TEN) significantly decreases Aβ secretion and relieves cellular inflammatory responses. However, the mechanism of this activity has not been fully elucidated. In the present study, we investigate the effect of TEN on autophagy, a process that plays an important role in the generation and metabolism of Aβ, in the presence or absence of the autophagy inhibitor 3-MA. The obtained results show that TEN prevents Aβ25-35-induced inflammation and decreases Aβ1-40 and Aβ1-42 levels by decreasing BACE1 in SH-SY5Y cells. Moreover, TEN decreases the mRNA levels of BACE1 but has no impact on the gene expressions of amyloid precursor proteins (APP). 3-MA, the most widely used autophagy inhibitor, reverses the effects of TEN in Aβ25-35-induced SH-SY5Y cells. The association between TEN and autophagy was further investigated by examining the levels of autophagy markers LC3 II and Beclin 1, as well as the protein levels of mTOR, AMPK, and ULK1. The results showed that TEN increases LC3 II, Beclin 1, and mTOR, inhibits the degradation of AMPK, and increases the expression of ULK1. This suggests that TEN protects against Aβ25-35-induced cellular inflammation in an AD cell model through the regulation of autophagy, which, in part, is mediated by the activation of the AMPK/mTOR/ULK1 pathway.

The Gut-Brain Axis in Neurodegenerative Diseases and Relevance of the Canine Model: A Review

Identifying appropriate animal models is critical in developing translatable in vitro and in vivo systems for therapeutic drug development and investigating disease pathophysiology. These animal models should have direct biological and translational relevance to the underlying disease they are supposed to mimic. Aging dogs not only naturally develop a cognitive decline in many aspects including learning and memory deficits, but they also exhibit human-like individual variability in the aging process. Neurodegenerative processes that can be observed in both human and canine brains include the progressive accumulation of β-amyloid (Aβ) found as diffuse plaques in the prefrontal cortex (PFC), including the gyrus proreus (i.e., medial orbital PFC), as well as the hippocampus and the cerebral vasculature. Tau pathology, a marker of neurodegeneration and dementia progression, was also found in canine hippocampal synapses. Various epidemiological data show that human patients with neurodegenerative diseases have concurrent intestinal lesions, and histopathological changes in the gastrointestinal (GI) tract occurs decades before neurodegenerative changes. Gut microbiome alterations have also been reported in many neurodegenerative diseases including Alzheimer's (AD) and Parkinson's diseases, as well as inflammatory central nervous system (CNS) diseases. Interestingly, the dog gut microbiome more closely resembles human gut microbiome in composition and functional overlap compared to rodent models. This article reviews the physiology of the gut-brain axis (GBA) and its involvement with neurodegenerative diseases in humans. Additionally, we outline the advantages and weaknesses of current in vitro and in vivo models and discuss future research directions investigating major human neurodegenerative diseases such as AD and Parkinson's diseases using dogs.

A Close Look at BACE1 Inhibitors for Alzheimer's Disease Treatment

Alzheimer's disease (AD), the most common cause of age-dependent dementia, is one of the most significant healthcare problems worldwide. Aggravating this situation, drugs that are currently US Food and Drug Administration (FDA)-approved for AD treatment do not prevent or delay disease progression. Therefore, developing effective therapies for AD patients is of critical urgency. Human genetic and clinical studies over the past three decades have indicated that abnormal generation or accumulation of amyloid-β (Aβ) peptides is a likely culprit in AD pathogenesis. Aβ is generated from amyloid precursor protein (APP) via proteolytic cleavage by β-site APP cleaving enzyme 1 (BACE1) (memapsin 2, β-secretase, Asp 2 protease) and γ-secretase. Mice deficient in BACE1 show abrogated production of Aβ. Therefore, pharmacological inhibition of BACE1 is being intensively pursued as a therapeutic approach to treat AD patients. Recent setbacks in clinical trials with BACE1 inhibitors have highlighted the critical importance of understanding how to properly inhibit BACE1 to treat AD patients. This review summarizes the recent studies on the role of BACE1 in synaptic functions as well as our views on BACE1 inhibition as an effective AD treatment.

PI3K/AKT/mTOR/p70S6K Pathway Is Involved in Aβ25-35-Induced Autophagy

Disruption or deregulation of the autophagy system has been implicated in neurodegenerative disorders such as Alzheimer's disease (AD). Aβ plays an important role in this autophagic system. In many cases, autophagy is regulated by the phosphatidylinositol 3-phosphate kinase/AKT/mammalian target of rapamycin/p70 ribosomal protein S6 kinase (PI3K/AKT/mTOR/p70S6K) signaling pathway. However, whether this signaling pathway is involved in Aβ-induced autophagy in neuronal cells is not known. Here, we studied whether Aβ25-35 induces autophagy in HT22 cells and C57 mice and investigated whether PI3K is involved in the autophagy induction. We found that Aβ25-35 inhibited HT22 cell viability in a dose- and time-dependent manner. Aβ25-35 induced autophagosome formation, the conversion of microtubule-associated protein light chain 3 (LC3), and the suppression of the mTOR pathway both in vitro and in vivo. Furthermore, Aβ25-35 impaired the learning abilities of C57 mice. Our study suggests that Aβ25-35 induces autophagy and the PI3K/AKT/mTOR/p70S6K pathway is involved in the process, which improves our understanding of the pathogenesis of AD and provides an additional model for AD research.

Altered synaptic structure in the hippocampus in a mouse model of Alzheimer's disease with soluble amyloid-β oligomers and no plaque pathology

Background

Mounting evidence suggests that soluble oligomers of amyloid-β (oAβ) represent the pertinent synaptotoxic form of Aβ in sporadic Alzheimer’s disease (AD); however, the mechanistic links between oAβ and synaptic degeneration remain elusive. Most in vivo experiments to date have been limited to examining the toxicity of oAβ in mouse models that also possess insoluble fibrillar Aβ (fAβ), and data generated from these models can lead to ambiguous interpretations. Our goal in the present study was to examine the effects of soluble oAβ on neuronal and synaptic structure in the amyloid precursor protein (APP) E693Q (“Dutch”) mouse model of AD, which develops intraneuronal accumulation of soluble oAβ with no detectable plaques in AD-relevant brain regions. We performed quantitative analyses of neuronal pathology, including dendrite morphology, spine density, and synapse ultrastructure in individual hippocampal CA1 neurons.

Results

When assessing neuronal morphology and complexity we observed significant alterations in apical but not in basal dendritic arbor length in Dutch mice compared to wild type. Moreover, Dutch mice exhibited a significant decrease in dendritic arborization with a decrease in dendritic length and number of intersections at 120 μm and 150 μm from the soma, respectively. We next examined synaptic parameters and found that while there were no differences in overall synaptic structure, Dutch mice displayed a significant reduction in the post-synaptic density (PSD) length of synapses on mushroom spines, in comparison to wild type littermates.

Conclusion

The structural alterations to individual neurons in Dutch mice along with the changes in larger dendritic spines support the Aβ oligomer hypothesis, which postulates that the early cognitive impairments that occur in AD are attributed to the accumulation of soluble oAβ first affecting at the synaptic level with subsequent structural disturbances and cellular degeneration.

Electronic supplementary material

The online version of this article (doi:10.1186/1750-1326-9-41) contains supplementary material, which is available to authorized users.

Lessons from two prevalent amyloidoses-what amylin and Aβ have in common

The amyloidogenic peptide Aβ plays a key role in Alzheimer's disease (AD) forming insoluble aggregates in the brain. The peptide shares its amyloidogenic properties with amylin that forms aggregates in the pancreas of patients with Type 2 Diabetes mellitus (T2DM). While epidemiological studies establish a link between these two diseases, it is becoming increasingly clear that they also share biochemical features suggesting common pathogenic mechanisms. We discuss commonalities as to how Aβ and amylin deregulate the cellular proteome, how they impair mitochondrial functions, to which receptors they bind, aspects of their clearance and how therapeutic strategies exploit the commonalities between Aβ and amylin. We conclude that research into these two molecules is mutually beneficial for the treatment of AD and T2DM.

PAK inactivation impairs social recognition in 3xTg-AD Mice without increasing brain deposition of tau and Aβ

Defects in p21-activated kinase (PAK) are suspected to play a role in cognitive symptoms of Alzheimer's disease (AD). Dysfunction in PAK leads to cofilin activation, drebrin displacement from its actin-binding site, actin depolymerization/severing, and, ultimately, defects in spine dynamics and cognitive impairment in mice. To determine the role of PAK in AD, we first quantified PAK by immunoblotting in homogenates from the parietal neocortex of subjects with a clinical diagnosis of no cognitive impairment (n = 12), mild cognitive impairment (n = 12), or AD (n = 12). A loss of total PAK, detected in the cortex of AD patients (-39% versus controls), was correlated with cognitive impairment (r(2) = 0.148, p = 0.027) and deposition of total and phosphorylated tau (r(2) = 0.235 and r(2) = 0.206, respectively), but not with Aβ42 (r(2) = 0.056). Accordingly, we found a decrease of total PAK in the cortex of 12- and 20-month-old 3xTg-AD mice, an animal model of AD-like Aβ and tau neuropathologies. To determine whether PAK dysfunction aggravates AD phenotype, 3xTg-AD mice were crossed with dominant-negative PAK mice. PAK inactivation led to obliteration of social recognition in old 3xTg-AD mice, which was associated with a decrease in cortical drebrin (-25%), but without enhancement of Aβ/tau pathology or any clear electrophysiological signature. Overall, our data suggest that PAK decrease is a consequence of AD neuropathology and that therapeutic activation of PAK may exert symptomatic benefits on high brain function.

Preventing expression of the nicotinic receptor subunit α7 in SH-SY5Y cells with interference RNA indicates that this receptor may protect against the neurotoxicity of Aβ

The present aim was to characterize the influence of the α7 nicotinic acetylcholine receptor (nAChR) on BACE, the enzyme that cleaves the amyloid precursor protein (APP) at the β-site, as well as on the oxidative stress induced by amyloid-β peptide (Aβ). To this end, human neuroblastoma SH-SY5Y cells were transfected with siRNAs targeting the α7 nAChR subunit and/or exposed to Aβ1-42. For α7 nAChR, BACE1 (cleaving at the β-site of APP) and BACE2 (cleaving within the Aβ domain), α-secretase (ADAM10), and the two components of γ-secretase, PS and NCT, the mRNA and protein levels were determined by real-time PCR and Western blotting, respectively. The level of Aβ1-42 in the cell culture medium was determined by an ELISA procedure. The extent of lipid peroxidation and activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were assayed spectrophotometrically. In the transfected SH-SY5Y cells, expression of α7 nAChR was reduced; the level of BACE1 increased and that of BACE2 decreased; the amount of ADAM10 lowered; and the level of PS raised. Moreover, the level of Aβ1-42 in the culture medium was elevated. Treatment of non-transfected cells with Aβ elevated the level of malondialdehyde (MDA) and lowered the activities of SOD and GSH-Px and these changes were potentiated by inhibiting expression of α7 nAChR. These results indicate that α7 nAChR plays a significant role in amyloidogenic metabolism of APP and the oxidative stress evoked by Aβ, suggesting that this receptor might help protect against the neurotoxicity of Aβ.

Alzheimer's disease models and functional genomics-How many needles are there in the haystack?

Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD) are complex human brain disorders that affect an increasing number of people worldwide. With the identification first of the proteins that aggregate in AD and FTLD brains and subsequently of pathogenic gene mutations that cause their formation in the familial cases, the foundation was laid for the generation of animal models. These recapitulate essential aspects of the human conditions; expression of mutant forms of the amyloid-β protein-encoding APP gene in mice reproduces amyloid-β (Aβ) plaque formation in AD, while that of mutant forms of the tau-encoding microtubule-associated protein tau (MAPT) gene reproduces tau-containing neurofibrillary tangle formation, a lesion that is also prevalent in FTLD-Tau. The mouse models have been complemented by those in lower species such as C. elegans or Drosophila, highlighting the crucial role for Aβ and tau in human neurodegenerative disease. In this review, we will introduce selected AD/FTLD models and discuss how they were instrumental, by identifying deregulated mRNAs, miRNAs and proteins, in dissecting pathogenic mechanisms in neurodegenerative disease. We will discuss some recent examples, which includes miRNA species that are specifically deregulated by Aβ, mitochondrial proteins that are targets of both Aβ and tau, and the nuclear splicing factor SFPQ that accumulates in the cytoplasm in a tau-dependent manner. These examples illustrate how a functional genomics approach followed by a careful validation in experimental models and human tissue leads to a deeper understanding of the pathogenesis of AD and FTLD and ultimately, may help in finding a cure.

MicroRNAs in Neurotoxicity

MicroRNAs are gaining importance as regulators of gene expression with the capability to fine-tune and modulate cellular events. The complex network with their selective targets (mRNAs/genes) pave way for regulation of many physiological processes. Dysregulation of normal neuronal activities could result in accumulation of substances that are detrimental to neuronal functions and subsequently result in neurotoxicity. Neurotoxicity-mediated pathophysiological conditions could then manifest as diseases or disabilities like Parkinson's and Alzheimer's which have debilitating implications. Such toxicity can be a result of individuals predisposed due to genetic inheritance or from other sources such as brain tumours. Neurotoxicity can also be brought about by external agents like drugs and alcohol as well as brain injury with miRNAs playing a pivotal role in diseases. It is therefore vital to understand the expression of these microRNAs and their impact on neuronal activities. In this paper, we discuss some of the neuronal pathophysiological conditions that could be caused by dysregulated microRNAs.

Target gene repression mediated by miRNAs miR-181c and miR-9 both of which are down-regulated by amyloid-β

MicroRNAs (miRNAs) are small non-coding RNA regulators of protein synthesis that are essential for normal brain development and function. Their profiles are significantly altered in neurodegenerative diseases such as Alzheimer's disease (AD) that is characterized by amyloid-β (Aβ) and tau deposition in brain. How deregulated miRNAs contribute to AD is not understood, as their dysfunction could be both a cause and a consequence of disease. To address this question we had previously profiled miRNAs in models of AD. This identified miR-9 and -181c as being down-regulated by Aβ in hippocampal cultures. Interestingly, there was a remarkable overlap with those miRNAs that are deregulated in Aβ-depositing APP23 transgenic mice and in human AD tissue. While the Aβ precursor protein APP itself is a target of miRNA regulation, the challenge resides in identifying further targets. Here, we expand the repertoire of miRNA target genes by identifying the 3' untranslated regions (3' UTRs) of TGFBI, TRIM2, SIRT1 and BTBD3 as being repressed by miR-9 and -181c, either alone or in combination. Taken together, our study identifies putative target genes of miRNAs miR-9 and 181c, which may function in brain homeostasis and disease pathogenesis.

Inhibition of the mitochondrial enzyme ABAD restores the amyloid-β-mediated deregulation of estradiol

Alzheimer's disease (AD) is a conformational disease that is characterized by amyloid-β (Aβ) deposition in the brain. Aβ exerts its toxicity in part by receptor-mediated interactions that cause down-stream protein misfolding and aggregation, as well as mitochondrial dysfunction. Recent reports indicate that Aβ may also interact directly with intracellular proteins such as the mitochondrial enzyme ABAD (Aβ binding alcohol dehydrogenase) in executing its toxic effects. Mitochondrial dysfunction occurs early in AD, and Aβ's toxicity is in part mediated by inhibition of ABAD as shown previously with an ABAD decoy peptide. Here, we employed AG18051, a novel small ABAD-specific compound inhibitor, to investigate the role of ABAD in Aβ toxicity. Using SH-SY5Y neuroblastoma cells, we found that AG18051 partially blocked the Aβ-ABAD interaction in a pull-down assay while it also prevented the Aβ42-induced down-regulation of ABAD activity, as measured by levels of estradiol, a known hormone and product of ABAD activity. Furthermore, AG18051 is protective against Aβ42 toxicity, as measured by LDH release and MTT absorbance. Specifically, AG18051 reduced Aβ42-induced impairment of mitochondrial respiration and oxidative stress as shown by reduced ROS (reactive oxygen species) levels. Guided by our previous finding of shared aspects of the toxicity of Aβ and human amylin (HA), with the latter forming aggregates in Type 2 diabetes mellitus (T2DM) pancreas, we determined whether AG18051 would also confer protection from HA toxicity. We found that the inhibitor conferred only partial protection from HA toxicity indicating distinct pathomechanisms of the two amyloidogenic agents. Taken together, our results present the inhibition of ABAD by compounds such as AG18051 as a promising therapeutic strategy for the prevention and treatment of AD, and suggest levels of estradiol as a suitable read-out.

MicroRNA networks surrounding APP and amyloid-β metabolism--implications for Alzheimer's disease

MicroRNAs (miRNAs) are small non-coding RNA regulators of protein synthesis that function as "fine-tuning" tools of gene expression in development and tissue homeostasis. Their profiles are significantly altered in neurodegenerative diseases such as Alzheimer's disease (AD) that is characterized by both amyloid-β (Aβ) and tau deposition in brain. A key challenge remains in determining how changes in miRNA profiles translate into biological function in a physiological and pathological context. The key lies in identifying specific target genes for deregulated miRNAs and understanding which pathogenic factors trigger their deregulation. Here we review the literature about the intricate network of miRNAs surrounding the regulation of the amyloid precursor protein (APP) from which Aβ is derived by proteolytic cleavage. Normal brain function is highly sensitive to any changes in APP metabolism and miRNAs function at several steps to ensure that the correct APP end product is produced and in the right form and abundance. Disruptions in this miRNA regulatory network may therefore alter Aβ production, which in turn can affect miRNA expression.

Interaction between NH(2)-tau fragment and Aβ in Alzheimer's disease mitochondria contributes to the synaptic deterioration

Although amyloid beta (Aβ) peptide can promote tau pathology and its toxicity is concurrently tau-dependent, the underlying mechanisms of the in vivo interplay of these proteins remain unsolved. Structural and functional mitochondrial alterations play an early, precipitating role in synaptic failure of Alzheimer's disease (AD) pathogenesis and an aggravated mitochondrial impairment has been described in triple APP/PS/tau transgenic mice carrying both plaques and tangles, if compared with mice overexpressing tau or amyloid precursor protein (APP) alone. Here, we show that a neurotoxic aminoterminal (NH(2))-derived tau fragment mapping between 26 and 230 amino acids of the human tau40 isoform (441 amino acids)-but not the physiological full-length protein-preferentially interacts with Aβ peptide(s) in human AD synapses in association with mitochondrial adenine nucleotide translocator-1 (ANT-1) and cyclophilin D. The two peptides-Aβ 1-42 and the smaller and more potent NH(2)-26-44 peptide of the longest 20-22 kDa NH(2)-tau fragment-inhibit the ANT-1-dependent adenosine diphosphate-adenosine triphosphate (ADP/ATP) exchange in a noncompetitive and competitive manner, respectively, and together further aggravate the mitochondrial dysfunction by exacerbating the ANT-1 impairment. Taken together, these data establish a common, direct and synergistic toxicity of pathological APP and tau products on synaptic mitochondria and suggest potential, new pathway(s) and target(s) for a combined, more efficient therapeutic intervention of early synaptic dysfunction in AD.

Morphological changes in the enteric nervous system of aging and APP23 transgenic mice

Gastrointestinal motility disorders often pose a debilitating problem, especially in elderly patients. In addition, they are frequently occurring co-morbidities in dementia. Whereas a failing enteric nervous system has already been shown to be involved in gastrointestinal motility disorders and in Parkinson's disease, a relationship with the neurodegenerative process of Alzheimer's disease was not yet shown. Therefore, we sought to document quantitative changes in the distribution of βIII-tubulin (general neuronal marker), Substance P, neuronal nitric oxide synthase (NOS), glial fibrillary acidic protein (GFAP) and S-100 immunoreactivity in addition to a qualitative assessment of the presence of amyloid in the small and large intestines of 6, 12 and 18-month-old wild type and transgenic Thy-1-APP23 mice. Amyloid deposits were seen in the vasculature, the mucosal and muscle layer of both heterozygous and wild type mice. Amyloidβ₁₋₄₂ could not be detected, pointing to a different amyloid composition than that found in senile plaques in the mice's brains. The finding of an increased density of βIII-tubulin-, Substance P- and NOS-IR-nerve fibres in heterozygous mice could not undoubtedly be related to amyloid deposition or to an activation of glial cells. Therefore, the alterations at the level of the enteric nervous system and the deposition of amyloid seem not primarily involved in the pathogenesis of Alzheimer's disease. At most they are secondary related to the neurodegenerative process. Additionally, our data could not show extensive neuronal or glial cell loss associated with aging, in contrast to other reports. Instead an increase in S100-IR was observed in senescent mice.

Amyloid precursor protein gene mutated at Swedish 670/671 sites in vitro induces changed expression of nicotinic acetylcholine receptors and neurotoxicity

In order to investigate the influence of amyloid precursor protein (APP) over-expression on the levels of nicotinic acetylcholine receptors (nAChRs), the pCDNA 3.0 carrying the Swedish 670/671 APP double mutation (APP(SWE)) gene was transfected into human neuroblastoma (SH-SY5Y) cells and primary culture of rat hippocampal neurons. The mRNA level of APP, and nAChR α3, α4 and α7 subunits were detected by real-time PCR, and their corresponding proteins as well as α-secreted APP (αAPPs) by Western blotting. [3H]Epibatidine binding sites were measured by the receptor binding assay. The results showed that significantly concomitant increases in mRNA and protein levels of SH-SY5Y cells and primary cultured neurons transfected with APP(SWE) were observed. Interestingly, a decreased αAPPs level was detected in both cells treated with APP(SWE) transfection. In addition, decreases in mRNA and protein levels of α3 nAChR subunit in SH-SY5Y cells or α4 subunit in primary cultured neurons with APP(SWE) transfection were observed. For α7 nAChR, the increased protein and mRNA levels were found in SH-SY5Y cells and primary cultured neurons with APP(SWE) transfection. The number of cholinergic receptor binding site of [3H]epibatidine was decreased in the SH-SY5Y cells transfected with APP(SWE). Elevations in the activities of AChE and BuChE and in the level of lipid peroxidation were detected in both types of cultured cells transfected with APP(SWE). These results indicated that the over-expression of APP(SWE) gene can influence the expression of nAChRs and resulted in neurotoxicity, in which this process might play an important role in the pathogenesis of Alzheimer's disease.

Neuronal microRNA deregulation in response to Alzheimer's disease amyloid-beta

Normal brain development and function depends on microRNA (miRNA) networks to fine tune the balance between the transcriptome and proteome of the cell. These small non-coding RNA regulators are highly enriched in brain where they play key roles in neuronal development, plasticity and disease. In neurodegenerative disorders such as Alzheimer's disease (AD), brain miRNA profiles are altered; thus miRNA dysfunction could be both a cause and a consequence of disease. Our study dissects the complexity of human AD pathology, and addresses the hypothesis that amyloid-β (Aβ) itself, a known causative factor of AD, causes neuronal miRNA deregulation, which could contribute to the pathomechanisms of AD. We used sensitive TaqMan low density miRNA arrays (TLDA) on murine primary hippocampal cultures to show that about half of all miRNAs tested were down-regulated in response to Aβ peptides. Time-course assays of neuronal Aβ treatments show that Aβ is in fact a powerful regulator of miRNA levels as the response of certain mature miRNAs is extremely rapid. Bioinformatic analysis predicts that the deregulated miRNAs are likely to affect target genes present in prominent neuronal pathways known to be disrupted in AD. Remarkably, we also found that the miRNA deregulation in hippocampal cultures was paralleled in vivo by a deregulation in the hippocampus of Aβ42-depositing APP23 mice, at the onset of Aβ plaque formation. In addition, the miRNA deregulation in hippocampal cultures and APP23 hippocampus overlaps with those obtained in human AD studies. Taken together, our findings suggest that neuronal miRNA deregulation in response to an insult by Aβ may be an important factor contributing to the cascade of events leading to AD.

Animal models for Alzheimer's disease and frontotemporal dementia: a perspective

In dementia research, animal models have become indispensable tools. They not only model aspects of the human condition, but also simulate processes that occur in humans and hence provide insight into how disease is initiated and propagated. The present review discusses two prominent human neurodegenerative disorders, Alzheimer's disease and frontotemporal dementia. It discusses what we would like to model in animals and highlights some of the more recent achievements using species as diverse as mice, fish, flies and worms. Advances in imaging and therapy are explored. We also discuss some anticipated new models and developments. These will reveal how key players in the pathogenesis of Alzheimer's disease and frontotemporal dementia, such as the peptide Aβ (amyloid β) and the protein tau, cause neuronal dysfunction and eventually, neuronal demise. Understanding these processes fully will lead to early diagnosis and therapy.

Critical appraisal of the long-term impact of memantine in treatment of moderate to severe Alzheimer's disease

Alzheimer's disease is the most common cause of dementia in older adults. The clinical features include progressive memory decline as well as cognitive deficits with executive dysfunction, language, visual perceptual difficulties, apraxia and agnosia. During the moderate to severe stage of the disease, there is a major decline in memory and function, while neuropsychiatric disturbances often emerge and patients become difficult to manage. These distressing symptoms increase caregiver burden and add to the direct costs of care of the patients. Any improvements in patient function and behavioral symptoms can reduce caregiver burden. Memantine has been available for a number of years in Europe and in North America. In this article, we examine the pharmacological rationale for its use, and the current clinical evidence for its efficacy and long-term effectiveness in the management of cognitive and behavioral symptoms in moderate to severe stages of Alzheimer's disease.