Clinical value of plasma ALZpath pTau217 immunoassay for assessing mild cognitive impairment.

BACKGROUND: Among plasma biomarkers for Alzheimer's disease (AD), pTau181 and pTau217 are the most promising. However, transition from research to routine clinical use will require confirmation of clinical performance in prospective cohorts and evaluation of cofounding factors. METHOD: pTau181 and pTau217 were quantified using, Quanterix and ALZpath, SIMOA assays in the well-characterised prospective multicentre BALTAZAR (Biomarker of AmyLoid pepTide and AlZheimer's diseAse Risk) cohort of participants with mild cognitive impairment (MCI). RESULTS: Among participants with MCI, 55% were Aß+ and 29% developed dementia due to AD. pTau181 and pTau217 were higher in the Aß+ population with fold change of 1.5 and 2.7, respectively. MCI that converted to AD also had higher levels than non-converters, with HRs of 1.38 (1.26 to 1.51) for pTau181 compared with 8.22 (5.45 to 12.39) for pTau217. The area under the curve for predicting Aß+ was 0.783 (95% CI 0.721 to 0.836; cut-point 2.75 pg/mL) for pTau181 and 0.914 (95% CI 0.868 to 0.948; cut-point 0.44 pg/mL) for pTau217. The high predictive power of pTau217 was not improved by adding age, sex and apolipoprotein E ε4 (APOEε4) status, in a logistic model. Age, APOEε4 and renal dysfunction were associated with pTau levels, but the clinical performance of pTau217 was only marginally altered by these factors. Using a two cut-point approach, a 95% positive predictive value for Aß+ corresponded to pTau217 >0.8 pg/mL and a 95% negative predictive value at <0.23 pg/mL. At these two cut-points, the percentages of MCI conversion were 56.8% and 9.7%, respectively, while the annual rates of decline in Mini-Mental State Examination were -2.32 versus -0.65. CONCLUSIONS: Plasma pTau217 and pTau181 both correlate with AD, but the fold change in pTau217 makes it better to diagnose cerebral amyloidosis, and predict cognitive decline and conversion to AD dementia.

Head-to-Head Comparison of Two Plasma Phospho-tau Assays in Predicting Conversion of Mild Cognitive Impairment to Dementia.

BACKGROUND: Among blood biomarkers, phospho-tau181 (pTau181) is one of the most efficient in detecting Alzheimer disease across its continuum. However, transition from research to routine clinical use will require confirmation of clinical performance in prospective cohorts and evaluation of cofounding factors. METHODS: Here we tested the Lumipulse assay for plasma pTau181 in mild cognitive impairment (MCI) participants from the Baltazar prospective cohort. We compared the performance of this assay to the corresponding Simoa assay for the prediction of conversion to dementia. We also evaluated the association with various routine blood parameters indicative of comorbidities. RESULTS: Lumipulse and Simoa gave similar results overall, with hazard ratios for conversion to dementia of 3.48 (95% CI, 2.23-5.45) and 3.70 (95%CI, 2.39-5.87), respectively. However, the 2 tests differ somewhat in terms of the patients identified, suggesting that their use may be complementary. When combined with age, sex, and apolipoprotein E (APOE)ε4 status, areas under the curves for conversion detection were 0.736 (95% CI, 0.682-0.791) for Lumipulse and 0.733 (95% CI, 0.679-0.788) for Simoa. Plasma pTau181 was independently associated with renal dysfunction (assessed by creatinine and glomerular filtration) for both assays. Cardiovascular factors (adiponectin and cholesterol), nutritional, and inflammatory markers (total protein content, C-reactive protein) also impacted plasma pTau181 concentration, although more so with the Simoa than with the Lumipulse assay. CONCLUSIONS: Plasma pTau181 measured using the fully automated Lumipulse assay performs as well as the Simoa assay for detecting conversion to dementia of MCI patients within 3 years and Lumipulse is less affected by comorbidities. This study suggests a pathway to routine noninvasive in vitro diagnosis-approved testing to contribute to the management of Alzheimer disease. CLINICALTRIALS.GOV REGISTRATION NUMBER: NCT01315639.

Plasma phosphorylated tau 181 predicts amyloid status and conversion to dementia stage dependent on renal function.

OBJECTIVES: Plasma P-tau181 is an increasingly established diagnostic marker for Alzheimer's disease (AD). Further validation in prospective cohorts is still needed, as well as the study of confounding factors that could influence its blood level. METHODS: This study is ancillary to the prospective multicentre Biomarker of AmyLoid pepTide and AlZheimer's diseAse Risk cohort that enrolled participants with mild cognitive impairment (MCI) who were examined for conversion to dementia for up to 3 years. Plasma Ptau-181 was measured using the ultrasensitive Quanterix HD-X assay. RESULTS: Among 476 MCI participants, 67% were amyloid positive (Aß+) at baseline and 30% developed dementia. Plasma P-tau181 was higher in the Aß+ population (3.9 (SD 1.4) vs 2.6 (SD 1.4) pg/mL) and in MCI that converted to dementia (3.8 (SD 1.5) vs 2.9 (SD 1.4) pg/mL). The addition of plasma P-tau181 to a logistic regression model combining age, sex, APOEε4 status and Mini Mental State Examination improved predictive performance (areas under the curve 0.691-0.744 for conversion and 0.786-0.849 for Aß+). The Kaplan-Meier curve of conversion to dementia, according to the tertiles of plasma P-tau181, revealed a significant predictive value (Log rank p<0.0001) with an HR of 3.8 (95% CI 2.5 to 5.8). In addition, patients with plasma P-Tau(181) ≤2.32 pg/mL had a conversion rate of less than 20% over a 3-year period. Using a linear regression approach, chronic kidney disease, creatinine and estimated glomerular filtration rate were independently associated with plasma P-tau181 concentrations. CONCLUSIONS: Plasma P-tau181 effectively detects Aß+ status and conversion to dementia, confirming the value of this blood biomarker for the management of AD. However, renal function significantly modifies its levels and may thus induce diagnostic errors if not taken into account.

Blood Neurofilament Levels Predict Cognitive Decline across the Alzheimer's Disease Continuum.

Neurofilament light chain (NfL) is a potential diagnostic and prognostic plasma biomarker for numerous neurological diseases including Alzheimer's disease (AD). In this study, we investigated the relationship between baseline plasma concentration of Nfl and Mild Cognitive Impairment in participants who did and did not have a clinically determined diagnosis of dementia by the end of the three-year study. Additionally, we explored the connection between baseline plasma concentration of NfL and AD dementia patients, considering their demographics, clinical features, and cognitive profiles. A total of 350 participants from the Biomarker of AmyLoid pepTide and AlZheimer's diseAse Risk (BALTAZAR) multicenter prospective study were investigated: 161 AD dementia participants and 189 MCI participants (of which 141 had amnestic MCI and 48 non-amnestic MCI). Plasma biomarkers were measured at baseline and the progression of clinical and cognitive profiles was followed over the three years of follow-up. Baseline plasma NfL concentration increased across the Alzheimer's disease continuum with a mean NfL value of 17.1 ng/mL [SD = 6.1] in non-amnestic MCI, 20.7 ng/mL [SD = 12.0] in amnestic MCI, and 23.1 ng/mL [SD = 22.7] in AD dementia patients. Plasma NfL concentration correlated with age, body mass index (BMI), and global cognitive performance and decline, as measured by the Mini-Mental State Examination (MMSE). MMSE scores decreased in parallel with increasing plasma NfL concentration, independently of age and BMI. However, NfL concentration did not predict MCI participants' conversion to dementia within three years. Discussion: Baseline plasma NfL concentration is associated with cognitive status along the AD continuum, suggesting its usefulness as a potential informative biomarker for cognitive decline follow-up in patients.

Plasma amyloid beta predicts conversion to dementia in subjects with mild cognitive impairment: The BALTAZAR study.

INTRODUCTION: Blood-based biomarkers are the next challenge for Alzheimer's disease (AD) diagnosis and prognosis. METHODS: Mild cognitive impairment (MCI) participants (N = 485) of the BALTAZAR study, a large-scale longitudinal multicenter cohort, were followed-up for 3 years. A total of 165 of them converted to dementia (95% AD). Associations of conversion and plasma amyloid beta (Aß)1-42 , Aß1-40 , Aß1-42 /Aß1-40 ratio were analyzed with logistic and Cox models. RESULTS: Converters to dementia had lower level of plasma Aß1-42 (37.1 pg/mL [12.5] vs. 39.2 [11.1] , P value = .03) and lower Aß1-42 /Aß1-40 ratio than non-converters (0.148 [0.125] vs. 0.154 [0.076], P value = .02). MCI participants in the highest quartile of Aß1-42 /Aß1-40 ratio (>0.169) had a significant lower risk of conversion (hazard ratio adjusted for age, sex, education, apolipoprotein E ε4, hippocampus atrophy = 0.52 (95% confidence interval [0.31-0.86], P value = .01). DISCUSSION: In this large cohort of MCI subjects we identified a threshold for plasma Aß1-42 /Aß1-40 ratio that may detect patients with a low risk of conversion to dementia within 3 years.

Protein interacting with Amyloid Precursor Protein tail-1 (PAT1) is involved in early endocytosis.

Protein interacting with Amyloid Precursor Protein (APP) tail 1 (PAT1) also called APPBP2 or Ara 67 has different targets such as APP or androgen receptor and is expressed in several tissues. PAT1 is known to be involved in the subcellular trafficking of its targets. We previously observed in primary neurons that PAT1 is poorly associated with APP at the cell surface. Here we show that PAT1 colocalizes with vesicles close to the cell surface labeled with Rab5, Rab4, EEA1 and Rabaptin-5 but not with Rab11 and Rab7. Moreover, PAT1 expression regulates the number of EEA1 and Rab5 vesicles, and endocytosis/recycling of the transferrin receptor. In addition, low levels of PAT1 decrease the size of transferrin-colocalized EEA1 vesicles with time following transferrin uptake. Finally, overexpression of the APP binding domain to PAT1 is sufficient to compromise endocytosis. Altogether, these data suggest that PAT1 is a new actor in transferrin early endocytosis. Whether this new function of PAT1 may have consequences in pathology remains to be determined.

Targeting demyelination via α-secretases promoting sAPPα release to enhance remyelination in central nervous system.

Remyelination is an endogenous regenerative process of myelin repair in the central nervous system (CNS) with limited efficacy in demyelinating disorders. As strategies enhancing endogenous remyelination become a therapeutic challenge, we have focused our study on α-secretase-induced sAPPα release, a soluble endogenous protein with neuroprotective and neurotrophic properties. However, the role of sAPPα in remyelination is not known. Therefore, we investigated the remyelination potential of α-secretase-induced sAPPα release following CNS demyelination in mice. Acute demyelination was induced by feeding mice with cuprizone (CPZ) for 5weeks. To test the protective effect and the remyelination potential of etazolate, an α-secretase activator, we designed two treatment protocols. Etazolate was administrated either during the last two weeks or at the end of the CPZ intoxication. In both protocols, etazolate restored the number of myelinated axons in corpus callosum with a corresponding increase in the amount of MBP, one of the major myelin proteins in the brain. We also performed ex vivo studies to decipher etazolate's mechanism of action in a lysolecithin-induced demyelination model using organotypic culture of cerebellar slices. Etazolate treatment was able to i) enhance the release of sAPPα in the culture media of demyelinated slices, ii) protect myelinated axons from demyelination, iii) increase the number of mature oligodendrocytes, iv) promote the reappearance of the paired Caspr+ adjacent to the nodes of Ranvier and v) increase the percentage of myelinated axons with short internodes, an indicator of remyelination. Etazolate failed to promote all the aforementioned effects in the presence of GI254023X, an α-secretase inhibitor. Moreover, the protective effects of etazolate in demyelinated slices were mimicked by sAPPα treatment in a dose-dependent manner. In conclusion, etazolate-induced sAPPα release protects myelinated axons from demyelination while also promoting remyelination. This work, thus, highlights the therapeutic potential of strategies that enhance sAPPα release in demyelinating disorders.

Plasma amyloid levels within the Alzheimer's process and correlations with central biomarkers.

INTRODUCTION: Diagnostic relevance of plasma amyloid ß (Aß) for Alzheimer's disease (AD) process yields conflicting results. The objective of the study was to assess plasma levels of Aß42 and Aß40 in amnestic mild cognitive impairment (MCI), nonamnestic MCI, and AD patients and to investigate relationships between peripheral and central biomarkers. METHODS: One thousand forty participants (417 amnestic MCI, 122 nonamnestic MCI, and 501 AD) from the Biomarker of AmyLoïd pepTide and AlZheimer's diseAse Risk multicenter prospective study with cognition, plasma, cerebrospinal fluid (CSF), and magnetic resonance imaging assessments were included. RESULTS: Plasma Aß1-42 and Aß1-40 were lower in AD (36.9 [11.7] and 263 [80] pg/mL) than in amnestic MCI (38.2 [11.9] and 269 [68] pg/mL) than in nonamnestic MCI (39.7 [10.5] and 272 [52] pg/mL), respectively (P = .01 for overall difference between groups for Aß1-42 and P = .04 for Aß1-40). Globally, plasma Aß1-42 correlated with age, Mini-Mental State Examination, and APOE Îµ4 allele. Plasma Aß1-42 correlated with all CSF biomarkers in MCI but only with CSF Aß42 in AD. DISCUSSION: Plasma Aß was associated with cognitive status and CSF biomarkers, suggesting the interest of plasma amyloid biomarkers for diagnosis purpose.

PAT1 inversely regulates the surface Amyloid Precursor Protein level in mouse primary neurons.

BACKGROUND: The amyloid precursor protein (APP) is a key molecule in Alzheimer disease. Its localization at the cell surface can trigger downstream signaling and APP cleavages. APP trafficking to the cell surface in neurons is not clearly understood and may be related to the interactions with its partners. In this respect, by having homologies with kinesin light chain domains and because of its capacity to bind APP, PAT1 represents a good candidate. RESULTS: We observed that PAT1 binds poorly APP at the cell surface of primary cortical neurons contrary to cytoplasmic APP. Using down and up-regulation of PAT1, we observed respectively an increase and decrease of APP at the cell surface. The increase of APP at the cell surface induced by low levels of PAT1 did not trigger cell death signaling. CONCLUSIONS: These data suggest that PAT1 slows down APP trafficking to the cell surface in primary cortical neurons. Our results contribute to the elucidation of mechanisms involved in APP trafficking in Alzheimer disease.

Cytoplasmic SET induces tau hyperphosphorylation through a decrease of methylated phosphatase 2A.

BACKGROUND: The neuronal cytoplasmic localization of SET, an inhibitor of the phosphatase 2A (PP2A), results in tau hyperphosphorylation in the brains of Alzheimer patients through mechanisms that are still not well defined. RESULTS: We used primary neurons and mouse brain slices to show that SET is translocated to the cytoplasm in a manner independent of both its cleavage and over-expression. The localization of SET in the cytoplasm, either by the translocation of endogenous SET or by internalization of the recombinant full-length SET protein, induced tau hyperphosphorylation. Cytoplasmic recombinant full-length SET in mouse brain slices induced a decrease of PP2A activity through a decrease of methylated PP2A levels. The levels of methylated PP2A were negatively correlated with tau hyperphosphorylation at Ser-202 but not with the abnormal phosphorylation of tau at Ser-422. CONCLUSIONS: The presence of full-length SET in the neuronal cytoplasm is sufficient to impair PP2A methylation and activity, leading to tau hyperphosphorylation. In addition, our data suggest that tau hyperphosphorylation is regulated by different mechanisms at distinct sites. The translocation of SET to the neuronal cytoplasm, the low activity of PP2A, and tau hyperphosphorylation are associated in the brains of Alzheimer patients. Our data show a link between the translocation of SET in the cytoplasm and the decrease of methylated PP2A levels leading to a decrease of PP2A activity and tau hyperphosphorylation. This chain of events may contribute to the pathogenesis of Alzheimer disease.

Role of cholesterol metabolism in the pathogenesis of Alzheimer's disease.

PURPOSE OF REVIEW: Cholesterol has been shown to stimulate the cleavage of amyloid precursor protein (APP) into amyloid peptides involved in Alzheimer's disease. However, high level of peripheral cholesterol as a risk factor for Alzheimer's disease is still debated. This current review provides an update of the recent literature on cholesterol and APP metabolisms in the brain. RECENT FINDINGS: First, a new relationship between neuronal APP and cholesterol has been shown in which this protein controls cholesterol turnover required for neuronal activity. Second, oxysterols are able to stimulate the synthesis of ATP-binding cassette transporters involved in the exchange of amyloid peptides between the blood and the brain. Third, changes in APP targeting to lipid rafts and/or their composition in cholesterol regulate amyloid peptide production. SUMMARY: These recent findings open new areas of investigations to control the neuronal activity and to decrease the amyloid peptide levels in brain, opening on new preventive and therapeutic strategies for Alzheimer's disease.

Functions of Aß, sAPPα and sAPPß : similarities and differences.

Amyloid peptide (Aß) is derived from the cleavage of amyloid precursor protein (APP), which also generates the soluble peptide APPß (sAPPß). An antagonist and major APP metabolic pathway involves cleavage by alpha secretase, which releases sAPPα. Although soluble Aß oligomers are neurotoxic, Aß monomers share similar properties with sAPPα. These include neurotrophic and neuroprotective effects, as well as stimulation of neural-progenitor proliferation. The properties of Aß monomers and the neurotrophic capacity of sAPPß to stimulate axonal outgrowth suggest that Aß production is not deleterious per se. Consequently, therapeutic strategies for Alzheimer's disease that are targeted at Aß-cleaving enzymes should modulate rather than inhibit Aß generation. These strategies should focus on the factors that induce the conversion of Aß monomers into toxic soluble oligomers. Another interesting therapeutic approach is to focus on the mechanisms of the different properties of sAPPα. Indeed, increasing sAPPα levels could shift proliferating cells towards tumorigenesis. In contrast to its neuroprotective effects, sAPPα is also able to activate microglia, leading to neurotoxicity. Understanding the mechanisms that underlie the different properties of sAPPα could therefore lead to the development of therapeutic strategies against Alzheimer's disease, which could be curative as well as preventive.

New highly sensitive rodent and human tests for soluble amyloid precursor protein alpha quantification: preclinical and clinical applications in Alzheimer's disease.

BACKGROUND: Amyloid precursor protein (APP), a key molecule in Alzheimer's disease (AD), is metabolized in two alternative cleavages, generating either the amyloidogenic peptides involved in AD pathology or the soluble form of APP (sAPPα). The level of amyloidogenic peptides in human cerebrospinal fluid (CSF) is considered to be a biomarker of AD, whereas the level of sAPPα in CSF as a biomarker has not been clearly established. sAPPα has neurotrophic and neuroprotective properties. Stimulating its formation and secretion is a promising therapeutic target in AD research. To this end, very sensitive tests for preclinical and clinical research are required. METHODS: The tests are based on homogenous time-resolved fluorescence and require no washing steps. RESULTS: We describe two new rapid and sensitive tests for quantifying mouse and human sAPPα. These 20 µl-volume tests quantify the levels of: i) endogenous mouse sAPPα in the conditioned medium of mouse neuron primary cultures, as well as in the CSF of wild-type mice, ii) human sAPPα in the CSF of AD mouse models, and iii) human sAPPα in the CSF of AD and non-AD patients. These tests require only 5 µl of conditioned medium from 5 × 10(4) mouse primary neurons, 1 µl of CSF from wild-type and transgenic mice, and 0.5 µl of human CSF. CONCLUSIONS: The high sensitivity of the mouse sAPPα test will allow high-throughput investigations of molecules capable of increasing the secretion of endogenous sAPPα in primary neurons, as well as the in vivo validation of molecules of interest through the quantification of sAPPα in the CSF of treated wild-type mice. Active molecules could then be tested in the AD mouse models by quantifying human sAPPα in the CSF through the progression of the disease. Finally, the human sAPPα test could strengthen the biological diagnosis of AD in large clinical investigations. Taken together, these new tests have a wide field of applications in preclinical and clinical studies.

Citrulline prevents age-related LTP decline in old rats.

The prevalence of cognitive decline is increasing as the ageing population is considerably growing. Restricting this age-associated process has become a challenging public health issue. The age-related increase in oxidative stress plays a major role in cognitive decline, because of its harmful effect on functional plasticity of the brain, such as long-term potentiation (LTP). Here, we show that citrulline (Cit) has powerful antioxidant properties that can limit ex vivo oxidative stress-induced LTP impairment in the hippocampus. We also illustrate that a three-month Cit supplementation has a protective effect on LTP in aged rats in vivo. The identification of a Cit oxidation byproduct in vitro suggests that the antioxidant properties of Cit could result from its own oxidation. Cit supplementation may be a promising preventive nutritional approach to limit age-related cognitive decline.

Corrigendum: Somatostatin and Neuropeptide Y in Cerebrospinal Fluid: Correlations With Amyloid Peptides Aß1-42, and Tau Proteins in Elderly Patients With Mild Cognitive Impairment.

[This corrects the article DOI: 10.3389/fnagi.2018.00297.].

Activity requires soluble amyloid precursor protein alpha to promote neurite outgrowth in neural stem cell-derived neurons via activation of the MAPK pathway.

It is known that activity modulates neuronal differentiation in the adult brain but the signalling mechanisms underlying this process remain to be identified. We show here that activity requires soluble amyloid precursor protein (sAPP) to enhance neurite outgrowth of young neurons differentiating from neural stem cells. Inhibition of sAPP secretion and anti-APP antibodies both abolished the effect of depolarization on neurite outgrowth, whereas exogenous sAPPalpha, similar to depolarization, induced neurite elongation. Depolarization and sAPPalpha both required active N-methyl-D-aspartic acid receptor (NMDAR) and mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) recruitment to induce neurite outgrowth. However, depolarization and sAPPalpha played different roles in modulating this signalling cascade. Depolarization induced ERK phosphorylation with fast kinetics via activation of NMDAR. By contrast, acute application of sAPPalpha did not lead to ERK activation. However, continuous generation of sAPPalpha was necessary for depolarization-induced ERK phosphorylation, indicating that sAPPalpha promotes MAPK/ERK recruitment by an indirect mechanism. In addition, we found that blockade of NMDAR down-regulated APP expression, whereas depolarization increased sAPPalpha, suggesting that activity may also act upstream of sAPP signalling by regulating the amount of cellular APP and extracellular sAPPalpha. Finally, we show that soluble amyloid precursor-like protein 2 (sAPLP2), but not sAPLP1, is functionally redundant to sAPP in promoting neurite outgrowth and that soluble members of the APP family require membrane-bound APP to enhance neurite outgrowth. In summary, these experiments indicate a novel role of APP family members in activity-dependent neuronal differentiation.

Differential epitope identification of antibodies against intracellular domains of alzheimer's amyloid precursor protein using high resolution affinity-mass spectrometry.

Several polypeptides comprising the carboxy-terminal domain of the 1-amyloid precursor protein (cAPP) were prepared by solid phase peptide synthesis, and employed as antigens for the determination of the epitopes recognised by anti-cAPP antibodies. Selective proteolytic epitope-excision and -extraction on the immobilised immune complexes, in combination with high resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) were used as major methods for epitope identification. The epitope recognised by a polyclonal anti-cAPP antibody (36-BO) was identified as APP(727-737), a sequence close to the APP transmembrane region. In contrast, the epitope recognised by a monoclonal anti-cAPP antibody (Jonas-mAb) was identified at APP(740-747) to be located more remote from the transmembrane region. The two adjacent, yet distinct epitopes recognised by two different antibodies should provide efficient tools for (i), molecular diagnostic applications, and (ii), the study of intracellular processing pathways of APP relevant to Alzheimer's disease, utilising suitable mass spectrometric and molecular imaging approaches.

Soluble Amyloid Precursor Protein Alpha Interacts with alpha3-Na, K-ATPAse to Induce Axonal Outgrowth but Not Neuroprotection: Evidence for Distinct Mechanisms Underlying these Properties.

Amyloid precursor protein (APP) is cleaved not only to generate the amyloid peptide (Aß), involved in neurodegenerative processes, but can also be metabolized by alpha secretase to produce and release soluble N-terminal APP (sAPPα), which has many properties including the induction of axonal elongation and neuroprotection. The mechanisms underlying the properties of sAPPα are not known. Here, we used proteomic analysis of mouse cortico-hippocampal membranes to identify the neuronal specific alpha3 (α3)-subunit of the plasma membrane enzyme Na, K-ATPase (NKA) as a new binding partner of sAPPα. We showed that sAPPα recruits very rapidly clusters of α3-NKA at neuronal surface, and its binding triggers a cascade of events promoting sAPPα-induced axonal outgrowth. The binding of sAPPα with α3-NKA was not observed for sAPPα-induced Aß1-42 oligomers neuroprotection, neither the downstream events particularly the interaction of sAPPα with APP before endocytosis, ERK signaling, and the translocation of SET from the nucleus to the plasma membrane. These data suggest that the mechanisms of the axonal growth promoting and neuroprotective properties of sAPPα appear to be specific and independent. The signals at the cell surface specific to trigger these mechanisms require further study.

Transient increase in sAPPα secretion in response to Aß1-42 oligomers: an attempt of neuronal self-defense?

Amyloid precursor protein (APP), a key molecule of Alzheimer disease, is metabolized in 2 antagonist pathways generating the soluble APP alpha (sAPPα) having neuroprotective properties and the beta amyloid (Aß) peptide at the origin of neurotoxic oligomers, particularly Aß1-42. Whether extracellular Aß1-42 oligomers modulate the formation and secretion of sAPPα is not known. We report here that the addition of Aß1-42 oligomers to primary cortical neurons induced a transient increase in α-secretase activity and secreted sAPPα 6-9 hours later. Preventing the generation of sAPPα by using small interfering RNAs (siRNAs) for the α-secretases ADAM10 and ADAM17 or for APP led to increased Aß1-42 oligomer-induced cell death after 24 hours. Neuronal injuries due to oxidative stress or growth factor deprivation also generated sAPPα 7 hours later. Finally, acute injection of Aß1-42 oligomers into wild-type mouse hippocampi induced transient secretion of sAPPα 48-72 hours later. Altogether, these data suggest that neurons respond to stress by generating sAPPα for their survival. These data must be taken into account when interpreting sAPPα levels as a biomarker in neurological disorders.