Concordance of Alzheimer's Disease-Related Biomarkers Between Intraventricular and Lumbar Cerebrospinal Fluid in Idiopathic Normal Pressure Hydrocephalus.

BACKGROUND: Alzheimer's disease cerebrospinal fluid (CSF) biomarkers amyloid-ß 1-42 (Aß42), total tau (T-tau), and phosphorylated tau 181 (P-tau181) are widely used. However, concentration gradient of these biomarkers between intraventricular (V-CSF) and lumbar CSF (L-CSF) has been demonstrated in idiopathic normal pressure hydrocephalus (iNPH), potentially affecting clinical utility. OBJECTIVE: Here we aim to provide conversion factors for clinical and research use between V-CSF and L-CSF. METHODS: Altogether 138 iNPH patients participated. L-CSF samples were obtained prior to shunt surgery. Intraoperative V-CSF samples were obtained from 97 patients. Post-operative follow-up L- and V-CSF (shunt reservoir) samples of 41 patients were obtained 1-73 months after surgery and then after 3, 6, and 18 months. CSF concentrations of Aß42, T-tau, and P-tau181 were analyzed using commercial ELISA assays. RESULTS: Preoperative L-CSF Aß42, T-tau, and P-tau181 correlated to intraoperative V-CSF (ρ= 0.34-0.55, p < 0.001). Strong correlations were seen between postoperative L- and V-CSF for all biomarkers in every follow-up sampling point (ρs Aß42: 0.77-0.88, T-tau: 0.91-0.94, P-tau181: 0.94-0.96, p < 0.0001). Regression equations were determined for intraoperative V- and preoperative L-CSF (Aß42: V-CSF = 185+0.34*L-CSF, T-tau: Ln(V-CSF) = 3.11+0.49*Ln(L-CSF), P-tau181: V-CSF = 8.2+0.51*L-CSF), and for postoperative V- and L-CSF (Aß42: V-CSF = 86.7+0.75*L-CSF, T-tau: V-CSF = 86.9+0.62*L-CSF, P-tau181: V-CSF = 2.6+0.74*L-CSF). CONCLUSION: Aß42, T-tau, and P-tau181 correlate linearly in-between V- and L-CSF, even stronger after CSF shunt surgery. Equations presented here, provide a novel tool to use V-CSF for diagnostic and prognostic entities relying on the L-CSF concentrations and can be applicable to clinical use when L-CSF samples are not available or less invasively obtained shunt reservoir samples should be interpreted.

Time Trends of Cerebrospinal Fluid Biomarkers of Neurodegeneration in Idiopathic Normal Pressure Hydrocephalus.

BACKGROUND: Longitudinal changes in cerebrospinal fluid (CSF) biomarkers are seldom studied. Furthermore, data on biomarker gradient between lumbar (L-) and ventricular (V-) compartments seems to be discordant. OBJECTIVE: To examine alteration of CSF biomarkers reflecting Alzheimer's disease (AD)-related amyloid-ß (Aß) aggregation, tau pathology, neurodegeneration, and early synaptic degeneration by CSF shunt surgery in idiopathic normal pressure hydrocephalus (iNPH) in relation to AD-related changes in brain biopsy. In addition, biomarker levels in L- and V-CSF were compared. METHODS: L-CSF was collected prior to shunt placement and, together with V-CSF, 3-73 months after surgery. Thereafter, additional CSF sampling took place at 3, 6, and 18 months after the baseline sample from 26 iNPH patients with confirmed Aß plaques in frontal cortical brain biopsy and 13 iNPH patients without Aß pathology. CSF Amyloid-ß42 (Aß42), total tau (T-tau), phosphorylated tau (P-tau181), neurofilament light (NFL), and neurogranin (NRGN) were analyzed with customized ELISAs. RESULTS: All biomarkers but Aß42 increased notably by 140-810% in L-CSF after CSF diversion and then stabilized. Aß42 instead showed divergent longitudinal decrease between Aß-positive and -negative patients in L-CSF, and thereafter increase in Aß-negative iNPH patients in both L- and V-CSF. All five biomarkers correlated highly between V-CSF and L-CSF (Aß42 R = 0.87, T-tau R = 0.83, P-tau R = 0.92, NFL R = 0.94, NRGN R = 0.9; all p < 0.0001) but were systematically lower in V-CSF (Aß42 14 %, T-tau 22%, P-tau 20%, NFL 32%, NRGN 19%). With APOE genotype-grouping, only Aß42 showed higher concentration in non-carriers of allele ɛ4. CONCLUSION: Longitudinal follow up shows that after an initial post-surgery increase, T-tau, P-tau, and NRGN are stable in iNPH patients regardless of brain biopsy Aß pathology, while NFL normalized toward its pre-shunt levels. Aß42 as biomarker seems to be the least affected by the surgical procedure or shunt and may be the best predictor of AD risk in iNPH patients. All biomarker concentrations were lower in V- than L-CSF yet showing strong correlations.

Long-term safety and tolerability of atabecestat (JNJ-54861911), an oral BACE1 inhibitor, in early Alzheimer's disease spectrum patients: a randomized, double-blind, placebo-controlled study and a two-period extension study.

BACKGROUND: Atabecestat, a potent brain-penetrable inhibitor of BACE1 activity that reduces CSF amyloid beta (Aß), was developed for oral treatment for Alzheimer's disease (AD). The long-term safety and effect of atabecestat on cognitive performance in participants with predementia AD in two phase 2 studies were assessed. METHODS: In the placebo-controlled double-blind parent ALZ2002 study, participants aged 50 to 85 years were randomized (1:1:1) to placebo or atabecestat 10 or 50 mg once daily (later reduced to 5 and 25 mg) for 6 months. Participants entered ALZ2004, a 12-month treatment extension with placebo or atabecestat 10 or 25 mg, followed by an open-label phase. Safety, changes in CSF biomarker levels, brain volume, and effects on cognitive performance were assessed. RESULTS: Of 114 participants randomized in ALZ2002, 99 (87%) completed, 90 entered the ALZ2004 double-blind phase, and 77 progressed to the open-label phase. CSF Aß fragments and sAPPß were reduced dose-proportionately. Decreases in whole brain and hippocampal volumes were greater in participants with mild cognitive impairment (MCI) due to AD than in preclinical AD, but were not affected by treatment. In ALZ2004, change from baseline in RBANS trended toward worse scores for atabecestat versus placebo. Elevated liver enzyme adverse events reported in 12 participants on atabecestat resulted in dosage modification and increased frequency of safety monitoring. Treatment discontinuation normalized ALT or AST in all except one with pretreatment elevation, which remained mildly elevated. No case met ALT/AST > 3× ULN and total bilirubin > 2× ULN (Hy's law). CONCLUSION: Atabecestat was associated with trend toward declines in cognition, and elevation of liver enzymes. TRIAL REGISTRATION: ALZ2002: ClinicalTrials.gov, NCT02260674, registered October 9, 2014; ALZ2004: ClinicalTrials.gov, NCT02406027, registered April 1, 2015.

Relevance of the interplay between amyloid and tau for cognitive impairment in early Alzheimer's disease.

Amyloid ß (Aß) and tau are key hallmark features of Alzheimer's disease (AD) neuropathology. The interplay of Aß and tau for cognitive impairment in early AD was examined with cross-sectional analysis, measured by cerebrospinal fluid biomarkers (Aß1-42, total tau [t-tau], and phosphorylated tau [p-tau181P]), and on cognitive performance by the repeatable battery for assessment of neuropsychological status (RBANS). Participants (n = 246) included cognitively normal (Aß-), mild cognitively impaired (Aß-), preclinical AD (Aß+), and prodromal AD (Aß+). Overall, cognitive scores (RBANS total scale score) had a moderate negative correlation to t-tau (n = 246; r = -0.434; p < 0.001) and p-tau181P (r = -0.389; p < 0.001). When classified by Aß status, this correlation to t-tau was applicable only in Aß+ participants (n = 139; r = -0.451, p < 0.001) but not Aß- participants (n = 107; r = 0.137, p = 0.16), with identical findings for p-tau. Both tau (p < 0.0001) and interaction of Aß1-42 with tau (p = 0.006) affected RBANS, but not Aß1-42 alone. Cognitive/memory performance correlated well with cerebrospinal fluid tau levels across early stages of AD, although the correlation is Aß dependent.

Pharmacodynamics of atabecestat (JNJ-54861911), an oral BACE1 inhibitor in patients with early Alzheimer's disease: randomized, double-blind, placebo-controlled study.

BACKGROUND: ß-Secretase enzyme (BACE) inhibition has been proposed as a priority treatment mechanism for Alzheimer's disease (AD), but treatment initiation may need to be very early. We present proof of mechanism of atabecestat (also known as JNJ-54861911), an oral BACE inhibitor for the treatment of AD, in Caucasian and Japanese populations with early AD who do not show signs of dementia. METHODS: In two similarly designed phase I studies, a sample of amyloid-positive elderly patients comprising 45 Caucasian patients with early AD diagnosed as preclinical AD (n = 15, Clinical Dementia Rating [CDR] = 0) or with mild cognitive impairment due to AD (n = 30, CDR = 0.5) and 18 Japanese patients diagnosed as preclinical AD (CDR-J = 0) were randomized 1:1:1 to atabecestat 10 or 50 mg or placebo (n = 6-8/treatment) daily for 4 weeks. Safety, pharmacokinetics (PK), and pharmacodynamics (PD) (i.e., reduction of cerebrospinal fluid [CSF] amyloid beta 1-40 [Aß1-40] levels [primary endpoint] and effect on other AD biomarkers) of atabecestat were evaluated. RESULTS: In both populations, atabecestat was well tolerated and characterized by linear PK and high central nervous system penetrance of unbound drug. Atabecestat significantly reduced CSF Aß1-40 levels from baseline at day 28 in both the 10-mg (67-68%) and 50-mg (87-90%) dose groups compared with placebo. For Caucasians with early AD, the least squares mean differences (95% CI) were - 69.37 (- 72.25; - 61.50) and - 92.74 (- 100.08; - 85.39), and for Japanese with preclinical AD, they were - 62.48 (- 78.32; - 46.64) and - 80.81 (- 96.13; - 65.49), respectively. PK/PD model simulations confirmed that once-daily 10 mg and 50 mg atabecestat can attain 60-70% and 90% Aß1-40 reductions, respectively. The trend of the reduction was similar across the Aß1-37, Aß1-38, and Aß1-42 fragments in both atabecestat dose groups, consistent with Aß1-40. CSF amyloid precursor protein fragment (sAPPß) levels declined from baseline, regardless of patient population, whereas CSF sAPPα levels increased compared with placebo. There were no relevant changes in either CSF total tau or phosphorylated tau 181P over a 4-week treatment period. CONCLUSIONS: JNJ-54861911 at 10 and 50 mg daily doses after 4 weeks resulted in mean CSF Aß1-40 reductions of 67% and up to 90% in both Caucasian and Japanese patients with early stage AD, confirming results in healthy elderly adults. TRIAL REGISTRATION: ALZ1005: ClinicalTrials.gov, NCT01978548. Registered on 7 November 2013. ALZ1008: ClinicalTrials.gov, NCT02360657. Registered on 10 February 2015.

S-[18F]THK-5117-PET and [11C]PIB-PET Imaging in Idiopathic Normal Pressure Hydrocephalus in Relation to Confirmed Amyloid-ß Plaques and Tau in Brain Biopsies.

BACKGROUND: Detection of pathological tau aggregates could facilitate clinical diagnosis of Alzheimer's disease (AD) and monitor drug effects in clinical trials. S-[18F]THK-5117 could be a potential tracer to detect pathological tau deposits in brain. However, no previous study have correlated S-[18F]THK-5117 uptake in PET with brain biopsy verified tau pathology in vivo. OBJECTIVE: Here we aim to evaluate the association between cerebrospinal fluid (CSF) AD biomarkers, S-[18F]THK-5117, and [11C]PIB PET against tau and amyloid lesions in brain biopsy. METHODS: Fourteen patients with idiopathic normal pressure hydrocephalus (iNPH) with previous shunt surgery including right frontal cortical brain biopsy and CSF Aß1 - 42, total tau, and P-tau181 measures, underwent brain MRI, [11C]PIB PET, and S-[18F]THK-5117 PET imaging. RESULTS: Seven patients had amyloid-ß (Aß, 4G8) plaques, two both Aß and phosphorylated tau (Pτ, AT8) and one only Pτ in biopsy. As expected, increased brain biopsy Aß was well associated with higher [11C]PIB uptake in PET. However, S-[18F]THK-5117 uptake did not show any statistically significant correlation with either brain biopsy Pτ or CSF P-tau181 or total tau. CONCLUSIONS: S-[18F]THK-5117 lacked clear association with neuropathologically verified tau pathology in brain biopsy probably, at least partially, due to off-target binding. Further studies with larger samples of patients with different tau tracers are urgently needed. The detection of simultaneous Aß and tau pathology in iNPH is important since that may indicate poorer and especially shorter response for CSF shunt surgery compared with no pathology.

Deficiency in Neuronal TGF-ß Signaling Leads to Nigrostriatal Degeneration and Activation of TGF-ß Signaling Protects against MPTP Neurotoxicity in Mice.

Transforming growth factor-ß (TGF-ß) plays an important role in the development and maintenance of embryonic dopaminergic (DA) neurons in the midbrain. To study the function of TGF-ß signaling in the adult nigrostriatal system, we generated transgenic mice with reduced TGF-ß signaling in mature neurons. These mice display age-related motor deficits and degeneration of the nigrostriatal system. Increasing TGF-ß signaling in the substantia nigra through adeno-associated virus expressing a constitutively active type I receptor significantly reduces 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced dopaminergic neurodegeneration and motor deficits. These results suggest that TGF-ß signaling is critical for adult DA neuron survival and that modulating this signaling pathway has therapeutic potential in Parkinson disease.SIGNIFICANCE STATEMENT We show that reducing Transforming growth factor-ß (TGF-ß) signaling promotes Parkinson disease-related pathologies and motor deficits, and increasing TGF-ß signaling reduces neurotoxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, a parkinsonism-inducing agent. Our results provide a rationale to pursue a means of increasing TGF-ß signaling as a potential therapy for Parkinson's disease.

Hallmarks of Alzheimer's Disease in Stem-Cell-Derived Human Neurons Transplanted into Mouse Brain.

Human pluripotent stem cells (PSCs) provide a unique entry to study species-specific aspects of human disorders such as Alzheimer's disease (AD). However, in vitro culture of neurons deprives them of their natural environment. Here we transplanted human PSC-derived cortical neuronal precursors into the brain of a murine AD model. Human neurons differentiate and integrate into the brain, express 3R/4R Tau splice forms, show abnormal phosphorylation and conformational Tau changes, and undergo neurodegeneration. Remarkably, cell death was dissociated from tangle formation in this natural 3D model of AD. Using genome-wide expression analysis, we observed upregulation of genes involved in myelination and downregulation of genes related to memory and cognition, synaptic transmission, and neuron projection. This novel chimeric model for AD displays human-specific pathological features and allows the analysis of different genetic backgrounds and mutations during the course of the disease.

BACE1 Dynamics Upon Inhibition with a BACE Inhibitor and Correlation to Downstream Alzheimer's Disease Markers in Elderly Healthy Participants.

The ß-site amyloid-ß protein precursor (AßPP) cleaving enzyme-1 (BACE1) is the rate limiting enzyme in the generation of amyloid-ß peptide (Aß) from AßPP, one of the major pathways in Alzheimer's disease (AD) pathology. Increased BACE1 levels and activity have been reported in the brain of patients with sporadic AD. Therefore, changes of BACE1 levels in the cerebrospinal fluid (CSF) have also been investigated as a possible biomarker of the disease. We analyzed BACE1 levels in CSF of elderly healthy participants before and after chronic treatment with a BACE inhibitor (BACEi) and evaluated the correlation between BACE1 levels and downstream AD markers. Overall, BACE1 CSF levels showed strong correlations to all downstream AD markers investigated. This is the first reported finding that shows BACE1 levels in CSF were well correlated to its end product Aß1 - 42. As previously described, BACE1 levels were strongly correlated to total-tau and phosphorylated tau levels in CSF. Generally, chronic BACE inhibition did not influence BACE1 CSF protein levels. Follow-up studies including early-stage AD pathophysiology and prodromal AD patients will help to understand the importance of measuring BACE1 routinely in daily clinical practice and AD clinical trials.

Assay to probe proteolytic processing of Notch by γ-secretase.

With the increasing appreciation of the role of Notch in development and disease, measuring its cleavage and signaling activity in cellular systems has become important. Here we describe a cell-based method to analyze the cleavage of Notch at the S3 site by γ-secretase. HEK cells are transfected with an N-terminal truncated and myc-labeled mNotchΔE construct which can be easily and quantitatively detected by western blotting.

Regulation of amyloid precursor protein processing by serotonin signaling.

Proteolytic processing of the amyloid precursor protein (APP) by the ß- and γ-secretases releases the amyloid-ß peptide (Aß), which deposits in senile plaques and contributes to the etiology of Alzheimer's disease (AD). The α-secretase cleaves APP in the Aß peptide sequence to generate soluble APPα (sAPPα). Upregulation of α-secretase activity through the 5-hydroxytryptamine 4 (5-HT4) receptor has been shown to reduce Aß production, amyloid plaque load and to improve cognitive impairment in transgenic mouse models of AD. Consequently, activation of 5-HT4 receptors following agonist stimulation is considered to be a therapeutic strategy for AD treatment; however, the signaling cascade involved in 5-HT4 receptor-stimulated proteolysis of APP remains to be determined. Here we used chemical and siRNA inhibition to identify the proteins which mediate 5-HT4d receptor-stimulated α-secretase activity in the SH-SY5Y human neuronal cell line. We show that G protein and Src dependent activation of phospholipase C are required for α-secretase activity, while, unexpectedly, adenylyl cyclase and cAMP are not involved. Further elucidation of the signaling pathway indicates that inositol triphosphate phosphorylation and casein kinase 2 activation is also a prerequisite for α-secretase activity. Our findings provide a novel route to explore the treatment of AD through 5-HT4 receptor-induced α-secretase activation.

When the dust settles: what did we learn from the bexarotene discussion?

With 27 million people affected by Alzheimer's disease (AD), any proposal of a novel avenue for drug development is hot news. When Cramer and colleagues proposed last year that they could tackle AD pathology in an AD mouse model with bexarotene, a drug already in use in the clinic for other diseases, the news was covered worldwide by the popular press. Apolipoprotein E4 is the strongest genetic risk factor for AD and bexarotene appeared to exert spectacular effects on AD pathology when tested in APP/PS1 transgenic mice. One year later the slumbering discussion on the use of bexarotene in AD exploded in a flurry of papers. Four papers question the initial optimistic claims, while two others can only partially support the original work. We summarize here the available data and try to make sense out of the controversy. The major question is what we can learn from the experiments and what these studies imply for the further development of bexarotene in the clinic.

Dose-dependent improvements in learning and memory deficits in APPPS1-21 transgenic mice treated with the orally active Aß toxicity inhibitor SEN1500.

In the Alzheimer's disease (AD) brain, accumulation of Aß1-42 peptides is suggested to initiate a cascade of pathological events. To date, no treatments are available that can reverse or delay AD-related symptoms in patients. In the current study, we introduce a new Aß toxicity inhibitor, SEN1500, which in addition to its block effect on Aß1-42 toxicity in synaptophysin assays, can be administered orally and cross the blood-brain barrier without adverse effects in mice. In a different set of animals, APPPS1-21 mice were fed with three different doses of SEN1500 (1 mg/kg, 5 mg/kg and 20 mg/kg) for a period of 5 months. Cognition was assessed in a variety of behavioral tests (Morris water maze, social recognition, conditioned taste aversion and passive avoidance). Results suggest a positive effect on cognition with 20 mg/kg SEN1500 compared to control APPPS1-21 mice. However, no changes in soluble or insoluble Aß1-40 and Aß1-42 were detected in the brains of SEN1500-fed mice. SEN1500 also attenuated the effect of Aß1-42 on synaptophysin levels in mouse cortical neurons, which indicated that the compound blocked the synaptic toxicity of Aß1-42. In vitro and in vivo effects presented here suggest that SEN1500 could be an interesting AD therapeutic.

Amyloid and tau neuropathology differentially affect prefrontal synaptic plasticity and cognitive performance in mouse models of Alzheimer's disease.

Alzheimer's disease (AD) is a consequence of degenerative brain pathology with amyloid plaque deposition and neurofibrillary tangle formation. These distinct aspects of AD neuropathology have been suggested to induce a cascade of pathological events ultimately leading to neurodegeneration as well as cognitive and behavioral decline. Amyloid and tau neuropathology is known to develop along distinct stages and affect parts of the brain differentially. In this study, we examined two mouse AD lines (AßPPPS1-21 and Tau22 mice), which mimic different partial aspects of AD pathology, at comparable stages of their pathology. Since prefrontal cortex (PFC) is one of the first regions to be affected in clinical AD, we compared long-term potentiation (LTP) of synaptic responses in medial PFC of AßPPPS1-21 and Tau22 mice. Frontal LTP was impaired in AßPPPS1-21 mice, but not in Tau22 mice. Consequently, we observed different behavioral defects between AßPPPS1-21 and Tau22 animals. Apart from spatial learning deficits, AßPPPS1-21 transgenic mice were impaired in fear learning, aversion learning, and extinction learning, whereas THY-Tau22 were impaired in appetitive responding. Discriminant function analysis identified critical behavioral variables that differentiated AßPPPS1-21 and THY-Tau22 mice from wild type littermates, and further confirmed that amyloid- versus tau-pathology differentially affects brain function.

Comment on "ApoE-directed therapeutics rapidly clear ß-amyloid and reverse deficits in AD mouse models".

Cramer et al. (Reports, 23 March 2012, p. 1503; published online 9 February 2012) tested bexarotene as a potential ß-amyloid-lowering drug for Alzheimer's disease (AD). We were not able to reproduce the described effects in several animal models. Drug formulation appears very critical. Our data call for extreme caution when considering this compound for use in AD patients.

Chronic 5-HT4 receptor activation decreases Aß production and deposition in hAPP/PS1 mice.

Lowering the production and accumulation of Aß has been explored as treatment for Alzheimer's disease (AD), because Aß is postulated to play an important role in the pathogenesis of AD. 5-HT4 receptors are an interesting drug target in this regard, as their activation might stimulate α-secretase processing, which increases sAPPα and reduces Aß, at least according to the central dogma in APP processing. Here we describe a novel high-affinity 5-HT4 receptor agonist SSP-002392 that, in cultured human neuroblastoma cells, potently increases the levels of cAMP and sAPPα at 100-fold lower concentrations than the effective concentrations of prucalopride, a known selective 5-HT4 receptor agonist. Chronic administration of this compound in a hAPP/PS1 mouse model of Alzheimer's disease decreased soluble and insoluble Aß in hippocampus, but the potential mechanisms underlying these observations seem to be complex. We found no evidence for direct α-secretase stimulation in the brain in vivo, but observed decreased APP and BACE-1 expression and elevated astroglia and microglia responses. Taken together these results provide support for a potential disease-modifying aspect when stimulating central 5-HT4 receptors; however, the complexity of the phenomena warrants further research.

ADAM9 inhibition increases membrane activity of ADAM10 and controls α-secretase processing of amyloid precursor protein.

Prodomains of A disintegrin and metalloproteinase (ADAM) metallopeptidases can act as highly specific intra- and intermolecular inhibitors of ADAM catalytic activity. The mouse ADAM9 prodomain (proA9; amino acids 24-204), expressed and characterized from Escherichia coli, is a competitive inhibitor of human ADAM9 catalytic/disintegrin domain with an overall inhibition constant of 280 ± 34 nM and high specificity toward ADAM9. In SY5Y neuroblastoma cells overexpressing amyloid precursor protein, proA9 treatment reduces the amount of endogenous ADAM10 enzyme in the medium while increasing membrane-bound ADAM10, as shown both by Western and activity assays with selective fluorescent peptide substrates using proteolytic activity matrix analysis. An increase in membrane-bound ADAM10 generates higher levels of soluble amyloid precursor protein α in the medium, whereas soluble amyloid precursor protein ß levels are decreased, demonstrating that inhibition of ADAM9 increases α-secretase activity on the cell membrane. Quantification of physiological ADAM10 substrates by a proteomic approach revealed that substrates, such as epidermal growth factor (EGF), HER2, osteoactivin, and CD40-ligand, are increased in the medium of BT474 breast tumor cells that were incubated with proA9, demonstrating that the regulation of ADAM10 by ADAM9 applies for many ADAM10 substrates. Taken together, our results demonstrate that ADAM10 activity is regulated by inhibition of ADAM9, and this regulation may be used to control shedding of amyloid precursor protein by enhancing α-secretase activity, a key regulatory step in the etiology of Alzheimer disease.

The disintegrin/metalloproteinase ADAM10 is essential for the establishment of the brain cortex.

The metalloproteinase and major amyloid precursor protein (APP) alpha-secretase candidate ADAM10 is responsible for the shedding of proteins important for brain development, such as cadherins, ephrins, and Notch receptors. Adam10(-/-) mice die at embryonic day 9.5, due to major defects in development of somites and vasculogenesis. To investigate the function of ADAM10 in brain, we generated Adam10 conditional knock-out (cKO) mice using a Nestin-Cre promotor, limiting ADAM10 inactivation to neural progenitor cells (NPCs) and NPC-derived neurons and glial cells. The cKO mice die perinatally with a disrupted neocortex and a severely reduced ganglionic eminence, due to precocious neuronal differentiation resulting in an early depletion of progenitor cells. Premature neuronal differentiation is associated with aberrant neuronal migration and a disorganized laminar architecture in the neocortex. Neurospheres derived from Adam10 cKO mice have a disrupted sphere organization and segregated more neurons at the expense of astrocytes. We found that Notch-1 processing was affected, leading to downregulation of several Notch-regulated genes in Adam10 cKO brains, in accordance with the central role of ADAM10 in this signaling pathway and explaining the neurogenic phenotype. Finally, we found that alpha-secretase-mediated processing of APP was largely reduced in these neurons, demonstrating that ADAM10 represents the most important APP alpha-secretase in brain. Our study reveals that ADAM10 plays a central role in the developing brain by controlling mainly Notch-dependent pathways but likely also by reducing surface shedding of other neuronal membrane proteins including APP.

Bioactive TGF-beta can associate with lipoproteins and is enriched in those containing apolipoprotein E3.

Transforming growth factor-beta1 (TGF-beta1) has central functions in development, tissue maintenance, and repair and has been implicated in major diseases. We discovered that TGF-beta1 contains several amphipathic helices and hydrophobic domains similar to apolipoprotein E (apoE), a protein involved in lipoprotein metabolism. Indeed, TGF-beta1 associates with lipoproteins isolated from human plasma, cultured liver cells, or astrocytes, and its bioactivity was highest in high-density lipoprotein preparations. Importantly, lipoproteins containing the apoE3 isoform had higher TGF-beta levels and bioactivity than those containing apoE4, a major genetic risk factor for atherosclerosis and Alzheimer's disease. Because TGF-beta1 can be protective in these diseases an association with apoE3 may be beneficial. Association of TGF-beta with different types of lipoproteins may facilitate its diffusion, regulate signaling, and offer additional specificity for this important growth factor.

Collagen VI protects neurons against Abeta toxicity.

Amyloid-beta (Abeta) peptides, widely presumed to cause Alzheimer's disease, increased mouse neuronal expression of collagen VI through a mechanism involving transforming growth factor signaling. Reduction of collagen VI augmented Abeta neurotoxicity, whereas treatment of neurons with soluble collagen VI blocked the association of Abeta oligomers with neurons, enhanced Abeta aggregation and prevented neurotoxicity. These results identify collagen VI as an important component of the neuronal injury response and demonstrate its neuroprotective potential.