Amyloid Precursor Protein sAPP Research Articles

Lack of APLP1 leads to subtle alterations in neuronal morphology but does not affect learning and memory.

The amyloid precursor protein APP plays a crucial role in Alzheimer pathogenesis. Its physiological functions, however, are only beginning to be unraveled. APP belongs to a small gene family, including besides APP the closely related amyloid precursor-like proteins APLP1 and APLP2, that all constitute synaptic adhesion proteins. While APP and APLP2 are ubiquitously expressed, APLP1 is specific for the nervous system. Previous genetic studies, including combined knockouts of several family members, pointed towards a unique role for APLP1, as only APP/APLP1 double knockouts were viable. We now examined brain and neuronal morphology in APLP1 single knockout (KO) animals, that have to date not been studied in detail. Here, we report that APLP1-KO mice show normal spine density in hippocampal CA1 pyramidal cells and subtle alterations in dendritic complexity. Extracellular field recordings revealed normal basal synaptic transmission and no alterations in synaptic plasticity (LTP). Further, behavioral studies revealed in APLP1-KO mice a small deficit in motor function and reduced diurnal locomotor activity, while learning and memory were not affected by the loss of APLP1. In summary, our study indicates that APP family members serve both distinct and overlapping functions that need to be considered for therapeutic treatments of Alzheimer's disease.

A proof of concept for targeting the PrPC - Amyloid β peptide interaction in basal prostate cancer and mesenchymal colon cancer

The cellular prion protein PrPC partners with caveolin-1 (CAV1) in neurodegenerative diseases but whether this interplay occurs in cancer has never been investigated. By leveraging patient and cell line datasets, we uncover a molecular link between PrPC and CAV1 across cancer. Using cell-based assays, we show that PrPC regulates the expression of and interacts with CAV1. PrPC additionally controls the expression of the amyloid precursor protein APP and of the Aβ generating enzyme BACE1, and regulates the levels of Aβ, whose accumulation is a central event in Alzheimer’s disease. We further identify DKK1 and DKK3, involved in both Alzheimer’s disease and cancer progression, as targets of the PrPC-dependent axis. Finally, we establish that antibody-mediated blocking of the Aβ-PrPC interaction delays the growth of prostate cancer cell line-derived xenografts and prevents the development of metastases. Our data additionally support an enrichment of the Aβ-PrPC-dependent pathway in the basal subtype of prostate cancer, associated with anti-hormonal therapy resistance, and in mesenchymal colon cancer, associated with poor prognosis. Thus, based on a parallel with neurodegenerative diseases, our results bring to light an Aβ-PrPC axis and support the potential of targeting this pathway in patients with selected subtypes of prostate and colon cancer.

Titanium dioxide and carbon black nanoparticles disrupt neuronal homeostasis via excessive activation of cellular prion protein signaling

BackgroundEpidemiological emerging evidence shows that human exposure to some nanosized materials present in the environment would contribute to the onset and/or progression of Alzheimer’s disease (AD). The cellular and molecular mechanisms whereby nanoparticles would exert some adverse effects towards neurons and take part in AD pathology are nevertheless unknown.ResultsHere, we provide the prime evidence that titanium dioxide (TiO2) and carbon black (CB) nanoparticles (NPs) bind the cellular form of the prion protein (PrPC), a plasma membrane protein well known for its implication in prion diseases and prion-like diseases, such as AD. The interaction between TiO2- or CB-NPs and PrPC at the surface of neuronal cells grown in culture corrupts PrPC signaling function. This triggers PrPC-dependent activation of NADPH oxidase and subsequent production of reactive oxygen species (ROS) that alters redox equilibrium. Through PrPC interaction, NPs also promote the activation of 3-phosphoinositide-dependent kinase 1 (PDK1), which in turn provokes the internalization of the neuroprotective TACE α-secretase. This diverts TACE cleavage activity away from (i) TNFα receptors (TNFR), whose accumulation at the plasma membrane augments the vulnerability of NP-exposed neuronal cells to TNFα -associated inflammation, and (ii) the amyloid precursor protein APP, leading to overproduction of neurotoxic amyloid Aβ40/42 peptides. The silencing of PrPC or the pharmacological inhibition of PDK1 protects neuronal cells from TiO2- and CB-NPs effects regarding ROS production, TNFα hypersensitivity, and Aβ rise. Finally, we show that dysregulation of the PrPC-PDK1-TACE pathway likely occurs in the brain of mice injected with TiO2-NPs by the intra-cerebro-ventricular route as we monitor a rise of TNFR at the cell surface of several groups of neurons located in distinct brain areas.ConclusionOur in vitro and in vivo study thus posits for the first time normal cellular prion protein PrPC as being a neuronal receptor of TiO2- and CB-NPs and identifies PrPC-coupled signaling pathways by which those nanoparticles alter redox equilibrium, augment the intrinsic sensitivity of neurons to neuroinflammation, and provoke a rise of Aβ peptides. By identifying signaling cascades dysregulated by TiO2- and CB-NPs in neurons, our data shed light on how human exposure to some NPs might be related to AD.

A pathological role of the Hsp40 protein Ydj1/DnaJA1 in models of Alzheimer's disease.

Alzheimer's disease (AD) is the most common form of dementia with millions of people affected worldwide. Pathophysiological manifestations of AD include the extracellular accumulation of amyloid beta (Abeta) pep-tides, products of the proteolytic cleavage of the amy-loid precursor protein APP. Increasing evidence sug-gests that Abeta peptides also accumulate intracellular-ly, triggering neurotoxic events such as mitochondrial dysfunction. However, the molecular factors driving formation and toxicity of intracellular Abeta are poorly understood. In our recent study [EMBO Mol Med 2022 - e13952], we used different eukaryotic model systems to identify such factors. Based on a genetic screen in yeast and subsequent molecular analyses, we found that both the yeast chaperone Ydj1 and its human ortholog DnaJA1 physically interact with Abeta, facili-tate the aggregation of Abeta peptides into small oli-gomers and promote their translocation to mitochon-dria. Deletion or downregulation of this chaperone pro-tected from Abeta-mediated toxicity in yeast and Dro-sophila AD models, respectively. Most importantly, the identified chaperone is found to be dysregulated in post-mortem human samples of AD patients. Here, we aim to outline our key findings, highlighting pathological functions of a heat shock protein (Hsp) family member, which are generally considered protective rather than toxic during neurodegeneration. Our results thus chal-lenge the concept of developing generalized chaperone activation-based therapies and call for carefully consid-ering also maladaptive functions of specific heat shock proteins.

New Insights into the Molecular Bases of Familial Alzheimer's Disease.

Like several neurodegenerative disorders, such as Prion and Parkinson diseases, Alzheimer’s disease (AD) is characterized by spreading mechanism of aggregated proteins in the brain in a typical “prion-like” manner. Recent genetic studies have identified in four genes associated with inherited AD (amyloid precursor protein-APP, Presenilin-1, Presenilin-2 and Apolipoprotein E), rare mutations which cause dysregulation of APP processing and alterations of folding of the derived amyloid beta peptide (Aβ). Accumulation and aggregation of Aβ in the brain can trigger a series of intracellular events, including hyperphosphorylation of tau protein, leading to the pathological features of AD. However, mutations in these four genes account for a small of the total genetic risk for familial AD (FAD). Genome-wide association studies have recently led to the identification of additional AD candidate genes. Here, we review an update of well-established, highly penetrant FAD-causing genes with correlation to the protein misfolding pathway, and novel emerging candidate FAD genes, as well as inherited risk factors. Knowledge of these genes and of their correlated biochemical cascade will provide several potential targets for treatment of AD and aging-related disorders.

Partial loss of endothelial nitric oxide leads to increased cerebrovascular beta amyloid

Cerebral amyloid angiopathy (CAA) is present in over half of the elderly population and in 80–90% of Alzheimer’s disease (AD) patients. CAA is defined by the deposition of beta amyloid (Aβ) in small cerebral arteries and capillaries. Cardiovascular risk factors are associated with an increased incidence of CAA. We utilized 18-month-old endothelial nitric oxide synthase (eNOS) heterozygous knockout (+/−) mice, a clinically relevant model of endothelial dysfunction, to examine the role of endothelial nitric oxide (NO) in vascular Aβ accumulation. eNOS+/− mice had significantly higher vascular levels of Aβ40 (P < 0.05). Aβ42 was not detected. There was no difference in Aβ in brain tissue. Amyloid precursor protein and β-site APP cleavage enzyme 1 protein levels were unaltered, while levels of the α-secretase enzyme, a disintegrin and metalloproteinase 10, were significantly lower in eNOS + /− microvascular tissue (P < 0.05). Insulin degrading enzyme and low-density lipoprotein receptor-related protein 1 were significantly increased in eNOS+/− microvascular tissue, most likely an adaptive response to locally higher Aβ concentrations. Lastly, catalase and CuZn superoxide dismutase were significantly elevated in eNOS+/− microvascular tissue (P < 0.05). These data demonstrate decreased availability of endothelial NO leads to increased cerebrovascular concentration of Aβ along with compensatory mechanisms to protect the vasculature.

Lipid bilayer position and orientation of novel carprofens, modulators of γ-secretase in Alzheimer's disease

γ-Secretase is an integral membrane protein complex and is involved in the cleavage of the amyloid precursor protein APP to produce amyloid-β peptides. Amyloid-β peptides are considered causative agents for Alzheimer's disease and drugs targeted at γ-secretase are investigated as therapeutic treatments. We synthesized new carprofen derivatives, which showed γ-secretase modulating activity and determined their precise position, orientation, and dynamics in lipid membranes by combining neutron diffraction, solid-state NMR spectroscopy, and molecular dynamics simulations. Our data indicate that the carprofen derivatives are inserted into the membrane interface, where the exact position and orientation depends on the lipid phase. This knowledge will help to understand the docking of carprofen derivatives to γ-secretase and in the design of new potent drugs. The approach presented here promises to serve as a general guideline how drug/target interactions in membranes can be analyzed in a comprehensive manner.

Quantifying the Proteolytic Cleavage of Plasma Membrane Proteins in Living Cells.

The standard approach to study the activity of proteases consists of lysing cells and measuring the changes in the fluorescence properties of a synthetic substrate after cleavage in vitro. Here, a general protocol that uses a bi-fluorescent chimeric construct of a known substrate protein that follows the proteolytic processing in living cells is described. This approach is useful, in particular, to search for pharmacological conditions altering the cleavage rate of a certain protease, or to investigate the biological factors influencing a certain proteolytic mechanism. Three different methods (microscopy, flow cytometry, and spectroscopy) to detect fluorescence changes due to alteration in the processing are described. This approach was originally developed for studying conditions affecting the proteolytic activity of the β-secretase Bace1 on the amyloid precursor protein APP, but can in principle be applied to investigate any membrane protein undergoing ectodomain shedding by proteolytic cleavage. © 2018 by John Wiley & Sons, Inc.

Effect of ten-eleven translocation protein on the expression of amyloid precursor protein and β-site APP cleaving enzyme-1 in SH-SY5Y and IMR-32 cells in folic acid deficiency and the underlying mechanisms

Objective To investigate the effect of ten-eleven translocation protein on the proliferation of human neuroblastoma cell lines SH-SY5Y and IMR-32 and the expression of amyloid precursor protein, PS1, and β-site APP cleaving enzyme-1 in the absence of folic acid and possible mechanisms involved. Methods SH-SY5Y and IMR-32 cells were cultured in vitro and divided into the folic acid deficiency group (0 mg/L), the low folic acid group (1mg/L), and the normal control group (4mg/L). The MTT method was used to observe cell proliferation, and RT-PCR was adopted to detect the mRNA expression of APP, PS1, BACE1, DNMTs and TETs in the cells in real-time. Besides, we generated a stable low-level TET1 expression cell line, and compared the expression with that in a negative control group. Furthermore, the expression of fluorescent protein was observed by fluorescence inverted microscope, cell proliferation was measured by the MTT assay, and mRNA levels of TET1, APP, PS1, and BACE1 were detected by RT-PCR. Results (1) In the folic acid deficiency group and the low folic acid group, cell proliferation of SH-SY5Y after 120 h and of IMR-32 cell after 144 h significantly decreased (P<0.001) .The mRNA levels of APP, PS1, BACE1, DNMT1, DNMT3a, DNMT3b, TET1, TET2, and TET3 in SH-SY5Y cells increased (F=80.315, 35.386, 101.979, 786.407, 80.331, 131.545, 28.000, 9.165, and 102.167, all P<0.05); the mRNA levels of APP, PS1, BACE1, DNMT1, DNMT3b, TET1, TET2, and TET3 in IMR-32 cells also rose (F=12.283, 93.669, 40.815, 157.234, 24.835, 147.594, 54.794, and 73.068, all P<0.05). (2) Generation of a stable low-level TET1 expression cell line: The mRNA level of TET1 in the low expression group (SH-SY5Y-shTET1) was 0.25±0.02, which was significantly lower than that in the negative control group (1.00±0.09) (P=0.007); the mRNA level of TET1 in the low expression group (IMR-32-shTET1) was 0.28±0.07, significantly lower than that in the negative control group (1.00±0.01) (P=0.003). (3)The proliferative ability of the low expression groups (SH-SY5Y-shTET1 and IMR-32-shTET1) was significantly higher than that in the negative control group (P<0.01). The mRNA levels of APP and BACE1 decreased (P<0.01 or P<0.05). Conclusion In the human neuroblastoma cell lines SH-SY5Y and IMR-32, folic acid deficiency up-regulates the expression of TETs, increases the expression of APP and BACE1 in the cells by TET protein demethylation, and inhibits cell growth. Key words: Folic acid; DNA methyhransferases; Fen-eleven; Amyloid protein; β-site App-cleavingenzyme

SIRT3 activator Honokiol attenuates β-Amyloid by modulating amyloidogenic pathway.

Honokiol (poly-phenolic lignan from Magnolia grandiflora) is a Sirtuin-3 (SIRT3) activator which exhibit antioxidant activity and augment mitochondrial functions in several experimental models. Modern evidence suggests the critical role of SIRT3 in the progression of several metabolic and neurodegenerative diseases. Amyloid beta (Aβ), the precursor to extracellular senile plaques, accumulates in the brains of patients with Alzheimer’s disease (AD) and is related to the development of cognitive impairment and neuronal cell death. Aβ is generated from amyloid-β precursor protein (APP) through sequential cleavages, first by β-secretase and then by γ-secretase. Drugs modulating this pathway are believed to be one of the most promising strategies for AD treatment. In the present study, we found that Honokiol significantly enhanced SIRT3 expression, reduced reactive oxygen species generation and lipid peroxidation, enhanced antioxidant activities, and mitochondrial function thereby reducing Aβ and sAPPβ levels in Chinese Hamster Ovarian (CHO) cells (carrying the amyloid precursor protein-APP and Presenilin PS1 mutation). Mechanistic studies revealed that Honokiol affects neither protein levels of APP nor α-secretase activity. In contrast, Honokiol increased the expression of AMPK, CREB, and PGC-1α, thereby inhibiting β-secretase activity leading to reduced Aβ levels. These results suggest that Honokiol is an activator of SIRT3 capable of improving antioxidant activity, mitochondrial energy regulation, while decreasing Aβ, thereby indicating it to be a lead compound for AD drug development.

Investigating the amyloid-beta enhancing effect of cGMP in neuro2a cells

Long-term potentiation (LTP) and the process of memory formation require activation of cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP) pathways. Notably, recent evidence indicated that both cyclic nucleotides boost the production of amyloid-beta (Aβ) peptides. In particular, cAMP was shown to favor hippocampal LTP by stimulating the synthesis of the amyloid precursor protein APP, whereas cGMP was found to enhance LTP and to improve memory by increasing Aβ levels without affecting the expression of APP. The results of the present study substantiate that cGMP has a role in the endocytic pathway of APP and suggest a scenario where the cyclic nucleotide enhances the production of Aβ by favoring the trafficking of APP from the cell cortex to the endolysosomal compartment.

Pathogenic Aβ A2V versus protective Aβ A2T mutation: Early stage aggregation and membrane interaction

We investigated the effects of punctual A-to-V and A-to-T mutations in the amyloid precursor protein APP, corresponding to position 2 of Aβ1–42. Those mutations had opposite effects on the onset and progression of Alzheimer disease, the former inducing early AD pathology and the latter protecting against the onset of the disease. We applied Static and Dynamic Light Scattering and Circular Dichroism, to study the different mutants in the early stages of the aggregation process, essential for the disease. Comparative results showed that the aggregation pathways differ in the kinetics and extent of the process, in the size of the aggregates and in the evolution of the secondary structure, resulting in fibrils of different morphology, as seen by AFM. Mutated peptides had comparable toxic effects on N2a cells. Moreover, as assessed by X-ray scattering, all of them displayed disordering effects on the internal structure of mixed phospholipids-gangliosides model membranes.

Increased Acetylation of Histone H4 at Lysine 12 (H4K12) in Monocytes of Transgenic Alzheimer’s Mice and in Human Patients

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by amyloid-β (Aβ) plaque formation, tau pathology, neurodegeneration and inflammatory processes. Monocytes are involved in inflammation in AD and are recruited to the diseased brain. Recently it has been shown that aberrant epigenetic processes including acetylation are associated with the development of AD. The aim of the present study was to examine acetylation of histone H4 at lysine 12 (H4K12) in monocytes in two transgenic AD mouse models (the triple transgenic 3xTg and a model overexpressing amyloid-precursor protein APP with the Swedish-Dutch-Iowa mutations), and to compare with monocytes isolated from human patients with mild cognitive impairment (MCI) and AD. Mouse and human monocytes were selectively isolated with a positive (PluriSelect) respectively with a negative selection method (Miltenyi). Histones were extracted and acetylation of H4K12 was analyzed by a quantification fluorometric kit. Moreover, monocyte cytokine release was measured and cell death analyzed by FACS using incorporation of 7-AAD. Our data show a significant increase of monocytic H4K12 acetylation in both transgenic AD mouse models early during development of the plaque deposition in the brain. In line with these data we found significantly elevated acetylation of H4K12 in human patients with MCI but not in patients with AD. Further we observed that the monocytes of AD mice and of AD patients were significantly more vulnerable to cell damage (as seen by 7-AAD incorporation in FACS analysis) and displayed an enhanced release of pro-inflammatory cytokines (MIP2 and TNFα). Our findings indicate that epigenetic changes in peripheral monocytes are an early event in AD-pathology. Thus H4K12 acetylation may be considered as a novel biomarker for early changes in AD development.

C-Terminal Threonine Reduces Aβ43 Amyloidogenicity Compared with Aβ42

Aβ43, a product of the proteolysis of the amyloid precursor protein APP, is related to Aβ42 by an additional Thr residue at the C-terminus. Aβ43 is typically generated at low levels compared with the predominant Aβ42 and Aβ40 forms, but it has been suggested that this longer peptide might have an impact on amyloid-β aggregation and Alzheimer's disease that is out of proportion to its brain content. Here, we report that both Aβ42 and Aβ43 spontaneously aggregate into mature amyloid fibrils via sequential appearance of the same series of oligomeric and protofibrillar intermediates, the earliest of which appears to lack β-structure. In spite of the additional β-branched amino acid at the C-terminus, Aβ43 fibrils have fewer strong backbone H-bonds than Aβ42 fibrils, some of which are lost at the C-terminus. In contrast to previous reports, we found that Aβ43 spontaneously aggregates more slowly than Aβ42. In addition, Aβ43 fibrils are very inefficient at seeding Aβ42 amyloid formation, even though Aβ42 fibrils efficiently seed amyloid formation by Aβ43 monomers. Finally, mixtures of Aβ42 and Aβ43 aggregate more slowly than Aβ42 alone. Both in this Aβ42/Aβ43 co-aggregation reaction and in cross-seeding by Aβ42 fibrils, the structure of the Aβ43 in the product fibrils is influenced by the presence of Aβ42. The results provide new details of amyloid structure and assembly pathways, an example of structural plasticity in prion-like replication, and data showing that low levels of Aβ43 in the brain are unlikely to favorably impact the aggregation of Aβ42.

Epigenetic Induction of EGR-1 Expression by the Amyloid Precursor Protein during Exposure to Novelty

Following transcriptome comparison of primary cultures isolated from brain of mice expressing or not the amyloid precursor protein APP, we found transcription of the EGR-1 gene to be regulated by APP. In primary cultures of cortical neurons, APP significantly down regulated EGR-1 expression at both mRNA and protein levels in a γ-secretase independent manner. The intracellular domain of APP did not interact with EGR-1 gene promoter, but enrichment of acetylated histone H4 at the EGR-1 promoter region was measured in APP-/- neurons, as well as in brain of APP-/- mice, in which increase in EGR-1 expression was also measured. These results argue for an important function of APP in the epigenetic regulation of EGR-1 gene transcription both in vitro and in vivo. In APP-/- mice, constitutive overexpression of EGR-1 in brain impaired epigenetic induction of this early transcriptional regulator during exposure to novelty. Altogether, these results indicate an important function of APP in the epigenetic regulation of the transcription of EGR-1, known to be important for memory formation.

New flurbiprofen derivatives: synthesis, membrane affinity and evaluation of in vitro effect on β-amyloid levels.

Alzheimer’s disease (AD) is characterized by irreversible and progressive loss of memory and cognition and profound neuronal loss. Current therapeutic strategies for the treatment of AD have been directed to a variety of targets with the aim of reversing or preventing the disease but, unfortunately, the available treatments often produce no significant clinical benefits. During the last decades compounds that inhibit or modulate γ-secretase, reducing β amyloid (Aβ) levels, have been considered as potential therapeutics for AD. Among these the (R)-enantiomer of flurbiprofen (FLU) seems to be very promising, but it shows low brain penetration. In this study, in order to improve the properties of FLU against Alzheimer’s pathogenesis we synthesized some novel FLU lipophilic analogues. Lipophilicity of the new molecules has been characterized in terms of clogP, log KC18/W and log K IAM/W values. Permeability has been determined in both gastrointestinal PAMPA (PAMPA-GI) at different pH values and in brain blood barrier PAMPA (PAMPA-BBB) models. They were also tested for their ability to inhibit in vitro γ-secretase activity using rat CTXTNA2 astrocytes. Interestingly, the investigated molecules demonstrated to reduce Aβ 42 levels without affecting the amyloid precursor protein APP level in a clear concentrations-dependent manner.

Early hippocampal synaptic plasticity and episodic like-memory deficits in a transgenic mouse model of Alzheimer disease - involvment of corticosterone

Background The etiology of Alzheimer’s disease (AD) is unclear and no cure is yet available. The function of the hippocampus, a key structure responsible for memory encoding and consolidation, is affected early in AD leading to progressive irreversible memory loss. There is strong evidence that AD onset is, at least partly, due to accumulation within the hippocampus of peptides processed from the amyloid precursor protein APP, such as amyloid-beta (A?). Also, several studies demonstrated an abnormal elevation in the main stress hormone, cortisol (CORT in mice), in the initial phase of AD in patients and in mouse models. Here, we investigated if early co-accumulation of CORT and APP-derived peptides could be a main trigger driving the onset of memory deficits in AD.

Neurodegenerative diseases: Quantitative predictions of protein–RNA interactions

Increasing evidence indicates that RNA plays an active role in a number of neurodegenerative diseases. We recently introduced a theoretical framework, catRAPID, to predict the binding ability of protein and RNA molecules. Here, we use catRAPID to investigate ribonucleoprotein interactions linked to inherited intellectual disability, amyotrophic lateral sclerosis, Creutzfeuld-Jakob, Alzheimer's, and Parkinson's diseases. We specifically focus on (1) RNA interactions with fragile X mental retardation protein FMRP; (2) protein sequestration caused by CGG repeats; (3) noncoding transcripts regulated by TAR DNA-binding protein 43 TDP-43; (4) autogenous regulation of TDP-43 and FMRP; (5) iron-mediated expression of amyloid precursor protein APP and α-synuclein; (6) interactions between prions and RNA aptamers. Our results are in striking agreement with experimental evidence and provide new insights in processes associated with neuronal function and misfunction.

Adaptor Protein Complexes AP‐4 and AP‐5: New Players in Endosomal Trafficking and Progressive Spastic Paraplegia

The adaptor proteins (APs) are a family of five heterotetrameric complexes with important functions in vesicle trafficking. While the roles of APs 1-3 are broadly established, comparatively little is known about AP-4 and AP-5. Current evidence suggests that AP-4 mediates TGN to endosome transport of specific cargo proteins, such as the amyloid precursor protein APP, and that it is involved in basolateral sorting in polarized cells. Furthermore, several independent studies have reported human patients with mutations in AP-4 genes. AP-4 deficiency causes severe intellectual disability and progressive spastic para- or tetraplegia, supporting an important role for AP-4 in brain function and development. The newly discovered AP-5 complex appears to be involved in endosomal dynamics; its precise localization and function are still unclear. Intriguingly, AP-5 deficiency is also associated with progressive spastic paraplegia, suggesting that AP-5, like AP-4, plays a fundamental role in neuronal development and homeostasis. The unexpected phenotypic parallels between AP-4 and AP-5 patients may in turn suggest a functional relationship of the two APs in vesicle trafficking.

P2‐077: Early mitochondrial dysfunction in the etiology of Alzheimer's disease

The identification of early mechanisms underlying Alzheimer's disease (AD) and associated biomarkers could advance development of new therapies, and improve monitoring and predicting of AD progression. Mitochondrial dysfunction has been suggested to underlie early mechanisms of AD. However, no comprehensive study exists that evaluate the effect of different familial AD (FAD) mutations on mitochondrial function, dynamics, and brain metabolomics. We characterized early mitochondrial dysfunction and metabolomic signatures of energetic stress in three commonly used transgenic mouse models of FAD. Mitochondrial trafficking was examined in live neurons form embryonic FAD mice. Mitochondrial distribution, fission and fusion were examined using electron microscopy and western blot analysis in the brain tissue of AD mice at different ages. Metabolomic profiling in brain and plasma of FAD mice was done using gas-chromatograph/mass-spectrometry and HPLC analysis. Assessment of mitochondrial motility, distribution, dynamics, morphology, and metabolomic profiling revealed the specific effect of each FAD mutation on the development of mitochondrial stress and dysfunction. Inhibition of mitochondrial trafficking was characteristic for embryonic neurons from mice expressing mutant human presenilin 1, PS1(M146L) and the double mutation of human amyloid precursor protein APP(Tg2576) and PS1(M146L) contributing to the increased susceptibility of neurons to excitotoxic cell death. Significant changes in mitochondrial morphology were detected in APP and APP/PS1 mice. All three FAD models have shown a loss of the integrity of synaptic mitochondria and energy production. Metabolomic profiling revealed mutation-specific changes in the levels of metabolites reflecting altered energy metabolism and mitochondrial dysfunction in brain of FAD mice. Metabolic biomarkers adequately reflected gender differences similar to that reported for AD patients and correlated well with the biomarkers currently used for diagnosis in humans.