ABSTRACT: The generation of A?, the main component of senile plaques in Alzheimer's disease (AD), is precluded by ?-secretase cleavage within the A? domain of the amyloid precursor protein (APP). We identified two rare mutations (Q170H and R181G) in the prodomain of the metalloprotease, ADAM10, that cosegregate with late-onset AD (LOAD). Here, we addressed the pathogenicity of these mutations in transgenic mice expressing human ADAM10 in brain. In Tg2576 AD mice, both mutations attenuated ?-secretase activity of ADAM10 and shifted APP processing toward ?-secretase-mediated cleavage, while enhancing A? plaque load and reactive gliosis. We also demonstrated ADAM10 expression potentiates adult hippocampal neurogenesis, which is reduced by the LOAD mutations. Mechanistically, both LOAD mutations impaired the molecular chaperone activity of ADAM10 prodomain. Collectively, these findings suggest that diminished ?-secretase activity, owing to LOAD ADAM10 prodomain mutations, leads to AD-related pathology, strongly supporting ADAM10 as a promising therapeutic target for this devastating disease.
Project description:Proteolytic cleavage of the amyloid precursor protein (APP) by the two proteases ?- and ?-secretases controls the generation of the amyloid ? peptide (A?), a key player in Alzheimer's disease pathogenesis. The ?-secretase ADAM10 and the ?-secretase BACE1 have opposite effects on A? generation and are assumed to compete for APP as a substrate, such that their cleavages are inversely coupled. This concept was mainly demonstrated in studies using activation or overexpression of ?- and ?-secretases. Here, we report that this inverse coupling is not seen to the same extent upon inhibition of the endogenous proteases. Genetic and pharmacological inhibition of ADAM10 and BACE1 revealed that the endogenous, constitutive ?-secretase cleavage of APP is largely uncoupled from ?-secretase cleavage and A? generation in neuroglioma H4 cells and in neuronally differentiated SH-SY5Y cells. In contrast, inverse coupling was observed in primary cortical neurons. However, this coupling was not bidirectional. Inhibition of BACE1 increased ADAM10 cleavage of APP, but a reduction of ADAM10 activity did not increase the BACE1 cleavage of APP in the neurons. Our analysis shows that the inverse coupling of the endogenous ?- and ?-secretase cleavages depends on the cellular model and suggests that a reduction of ADAM10 activity is unlikely to increase the AD risk through increased ?-secretase cleavage.
Project description:ADAM10, a member of a disintegrin and metalloprotease family, is an alpha-secretase capable of anti-amyloidogenic proteolysis of the amyloid precursor protein. Here, we present evidence for genetic association of ADAM10 with Alzheimer's disease (AD) as well as two rare potentially disease-associated non-synonymous mutations, Q170H and R181G, in the ADAM10 prodomain. These mutations were found in 11 of 16 affected individuals (average onset age 69.5 years) from seven late-onset AD families. Each mutation was also found in one unaffected subject implying incomplete penetrance. Functionally, both mutations significantly attenuated alpha-secretase activity of ADAM10 (>70% decrease), and elevated Abeta levels (1.5-3.5-fold) in cell-based studies. In summary, we provide the first evidence of ADAM10 as a candidate AD susceptibility gene, and report two potentially pathogenic mutations with incomplete penetrance for late-onset familial AD.
Project description:A disintegrin and metalloprotease 10 (ADAM10) is the α-secretase for amyloid precursor protein (APP). ADAM10 cleaves APP to generate neuroprotective soluble APPα (sAPPα), which precludes the generation of Aβ, a defining feature of Alzheimer's disease (AD) pathophysiology. Reduced ADAM10 activity is implicated in AD, but the mechanisms mediating ADAM10 modulation are unclear. We find that the plasma membrane enzyme glycerophosphodiester phosphodiesterase 2 (GDE2) stimulates ADAM10 APP cleavage by shedding and inactivating reversion-inducing cysteine-rich protein with Kazal motifs (RECK), a glycosylphosphatidylinositol (GPI)-anchored inhibitor of ADAM10. In AD, membrane-tethered RECK is highly elevated and GDE2 is abnormally sequestered inside neurons. Genetic ablation of GDE2 phenocopies increased membrane RECK in AD, which is causal for reduced sAPPα, increased Aβ, and synaptic protein loss. RECK reduction restores the balance of APP processing and rescues synaptic protein deficits. These studies identify GDE2 control of RECK surface activity as essential for ADAM10 α-secretase function and physiological APP processing. Moreover, our results suggest the involvement of the GDE2-RECK-ADAM10 pathway in AD pathophysiology and highlight RECK as a potential target for therapeutic development.
Project description:The membrane bound metalloprotease meprin ? is important for collagen fibril assembly in connective tissue formation and for the detachment of the intestinal mucus layer for proper barrier function. Recent proteomic studies revealed dozens of putative new substrates of meprin ?, including the amyloid precursor protein (APP). It was shown that APP is cleaved by meprin ? in distinct ways, either at the ?-secretase site resulting in increased levels of A? peptides, or at the N-terminus releasing 11 kDa, and 20 kDa peptide fragments. The latter event was discussed to be rather neuroprotective, whereas the ectodomain shedding of APP by meprin ? reminiscent to BACE-1 is in line with the amyloid hypothesis of Alzheimer's disease, promoting neurodegeneration. The N-terminal 11 kDa and 20 kDa peptide fragments represent physiological cleavage products, since they are found in human brains under different diseased or non-diseased states, whereas these fragments are completely missing in brains of meprin ? knock-out animals. Meprin ? is not only a sheddase of adhesion molecules, such as APP, but was additionally demonstrated to cleave within the prodomain of ADAM10. Activated ADAM10, the ?-secretase of APP, is then able to shed meprin ? from the cell surface thereby abolishing the ?-secretase activity. All together meprin ? seems to be a novel player in APP processing events, even influencing other enzymes involved in APP cleavage.
Project description:In a transgenic mouse model of Alzheimer disease (AD), cleavage of the amyloid precursor protein (APP) by the α-secretase ADAM10 prevented amyloid plaque formation and alleviated cognitive deficits. Furthermore, there was a positive influence of ADAM10 over-expression on neurotransmitter-specific formation of synapses and on synaptic plasticity. To assess the influence of ADAM10 on the gene expression profile in the brain we performed microarray analysis using RNA isolated from brains of five month old mice over-expressing either the α-secretase ADAM10 or a dominant-negative mutant (dn) of this enzyme. As compared to non-transgenic wild-type mice, 355 genes were found to be differentially expressed in ADAM10 transgenic mice and 143 genes in dnADAM10 mice. A higher number of genes was found to be differentially regulated in double-transgenic mouse strains additionally expressing the human APP V717I mutant (APP[V717I]). Thus, α-secretase cleavage of over-expressed APP[V717I] alters CNS gene expression additionally. Keywords: genetic modification
Project description:The amyloid precursor protein (APP) undergoes constitutive shedding by a protease activity called alpha-secretase. This is considered an important mechanism preventing the generation of the Alzheimer's disease amyloid-beta peptide (Abeta). alpha-Secretase appears to be a metalloprotease of the ADAM family, but its identity remains to be established. Using a novel alpha-secretase-cleavage site-specific antibody, we found that RNAi-mediated knockdown of ADAM10, but surprisingly not of ADAM9 or 17, completely suppressed APP alpha-secretase cleavage in different cell lines and in primary murine neurons. Other proteases were not able to compensate for this loss of alpha-cleavage. This finding was further confirmed by mass-spectrometric detection of APP-cleavage fragments. Surprisingly, in different cell lines, the reduction of alpha-secretase cleavage was not paralleled by a corresponding increase in the Abeta-generating beta-secretase cleavage, revealing that both proteases do not always compete for APP as a substrate. Instead, our data suggest a novel pathway for APP processing, in which ADAM10 can partially compete with gamma-secretase for the cleavage of a C-terminal APP fragment generated by beta-secretase. We conclude that ADAM10 is the physiologically relevant, constitutive alpha-secretase of APP.
Project description:<h4>Background</h4>Amyloid precursor protein (APP), best known for its association with Alzheimer disease, has recently been implicated in breast cancer progression. However, the precise mechanism involved remains unclear. Here, we investigated the role of APP proteolytic cleavage in breast cancer functions.<h4>Methods</h4>The presence of APP proteolytic cleavage products was examined in breast cancer cell lines. The functional roles of APP in breast cancer were studied in vitro and tumor xenograft model using siRNA. The effects of full length APP and the ?-secretase cleaved ectodomain fragment, soluble APP? (sAPP?) were further investigated for their overexpression in breast cancers. The ?-secretase involved was identified. The ?-secretase expression together with APP was examined in clinical breast cancers.<h4>Results</h4>We showed that APP underwent proteolytic cleavage in breast cancer cells to generate sAPP?. The sAPP? and full length protein mediated breast cancer migration and proliferation, but in different functional extent. This proteolytic cleavage was mediated by ADAM10. Downregulation of APP and ADAM10 brought about similar functional effects. Overexpression of sAPP? reversed the effects of ADAM10 downregulation. Interestingly, in patients with non-luminal breast cancers, APP and ADAM10 expression correlated with each other and their co-expression was associated with the worst outcome.<h4>Conclusions</h4>These results demonstrated the contributory role of APP cleavage on its oncogenic roles in breast cancer. ADAM10 was the key ?-secretase. APP and ADAM10 co-expression was associated with worse survival in non-luminal breast cancers. Targeting of APP or its processing by ADAM10 might be a promising treatment option in these cancers.
Project description:A hallmark of Alzheimer's disease (AD) is the accumulation of plaques of Abeta 1-40 and 1-42 peptides, which result from the sequential cleavage of APP by the beta and gamma-secretases. The production of Abeta peptides is avoided by alternate cleavage of APP by the alpha and gamma-secretases. Here we show that production of beta-amyloid and plaques in a mouse model of AD are reduced by overexpressing the NAD-dependent deacetylase SIRT1 in brain, and are increased by knocking out SIRT1 in brain. SIRT1 directly activates the transcription of the gene encoding the alpha-secretase, ADAM10. SIRT1 deacetylates and coactivates the retinoic acid receptor beta, a known regulator of ADAM10 transcription. ADAM10 activation by SIRT1 also induces the Notch pathway, which is known to repair neuronal damage in the brain. Our findings indicate SIRT1 activation is a viable strategy to combat AD and perhaps other neurodegenerative diseases.
Project description:Mutations in the amyloid precursor protein (APP) gene and the aberrant cleavage of APP by ?-secretase are associated with Alzheimer's disease (AD). Here we have developed a simple and sensitive cell-based assay to detect APP cleavage by ?-secretase. Unexpectedly, most familial AD (FAD)-linked APP mutations make APP partially resistant to ?-secretase. Mutations that alter residues N terminal to the ?-secretase cleavage site A?42 have subtle effects on cleavage efficiency and cleavage-site selectivity. In contrast, mutations that alter residues C terminal to the A?42 site reduce cleavage efficiency and dramatically shift cleavage-site specificity toward the aggregation-prone A?42. Moreover, mutations that remove positive charge at residue 53 greatly reduce the APP cleavage by ?-secretase. These results suggest a model of ?-secretase substrate recognition, in which the APP region C terminal to the A?42 site and the positively charged residue at position 53 are the primary determinants for substrate binding and cleavage-site selectivity. We further demonstrate that this model can be extended to ?-secretase processing of notch receptors, a family of highly conserved cell-surface signaling proteins.
Project description:In a transgenic mouse model of Alzheimer disease (AD), cleavage of the amyloid precursor protein (APP) by the alpha-secretase ADAM10 prevented amyloid plaque formation, and alleviated cognitive deficits. Furthermore, ADAM10 overexpression increased the cortical synaptogenesis. These results suggest that upregulation of ADAM10 in the brain has beneficial effects on AD pathology.To assess the influence of ADAM10 on the gene expression profile in the brain, we performed a microarray analysis using RNA isolated from brains of five months old mice overexpressing either the alpha-secretase ADAM10, or a dominant-negative mutant (dn) of this enzyme. As compared to non-transgenic wild-type mice, in ADAM10 transgenic mice 355 genes, and in dnADAM10 mice 143 genes were found to be differentially expressed. A higher number of genes was differentially regulated in double-transgenic mouse strains additionally expressing the human APP[V717I] mutant.Overexpression of proteolytically active ADAM10 affected several physiological pathways, such as cell communication, nervous system development, neuron projection as well as synaptic transmission. Although ADAM10 has been implicated in Notch and beta-catenin signaling, no significant changes in the respective target genes were observed in adult ADAM10 transgenic mice.Real-time RT-PCR confirmed a downregulation of genes coding for the inflammation-associated proteins S100a8 and S100a9 induced by moderate ADAM10 overexpression. Overexpression of the dominant-negative form dnADAM10 led to a significant increase in the expression of the fatty acid-binding protein Fabp7, which also has been found in higher amounts in brains of Down syndrome patients.In general, there was only a moderate alteration of gene expression in ADAM10 overexpressing mice. Genes coding for pro-inflammatory or pro-apoptotic proteins were not over-represented among differentially regulated genes. Even a decrease of inflammation markers was observed. These results are further supportive for the strategy to treat AD by increasing the alpha-secretase activity.