B. De Strooper

Destabilization of beta-catenin by mutations in presenilin-1 potentiates neuronal apoptosis.

Mutations of the presenilin-1 gene are a major cause of familial early-onset Alzheimers disease. Presenilin-1 can associate with members of the catenin family of signalling proteins, but the significance of this association is unknown,. Here we show that presenilin-1 forms a complex with β-catenin in vivo that increases β-catenin stability. Pathogenic mutations in the presenilin-1 gene reduce the ability of presenilin-1 to stabilize β-catenin, and lead to increased degradation of β-catenin in the brains of transgenic mice. Moreover, β-catenin levels are markedly reduced in the brains of Alzheimers disease patients with presenilin-1 mutations. Loss of β-catenin signalling increases neuronal vulnerability to apoptosis induced by amyloid-β protein. Thus, mutations in presenilin-1 may increase neuronal apoptosis by altering the stability of β-catenin, predisposing individuals to early-onset Alzheimers disease.

Expression in mouse embryos and in adult mouse brain of three members of the amyloid precursor protein family, of the alpha-2-macroglobulin receptor/low density lipoprotein receptor-related protein and of its ligands apolipoprotein E, lipoprotein lipase, alpha-2-macroglobulin and the 40,000 molecular weight receptor-associated protein

We have analysed by northern blotting and by in situ hybridization the expression patterns of eight different genes during the second half of mouse embryonic development and in adult mouse brain: we compared the messenger RNA levels of amyloid precursor protein and of the two amyloid precursor protein-like proteins 1 and 2 and we have analysed expression of apolipoprotein E and of its main receptor in brain, the alpha-2-macroglobulin/low density lipoprotein receptor-related protein and three other ligands: the proteinase inhibitor alpha-2-macroglobulin, the modifying enzyme lipoprotein lipase and the 44,000 molecular weight heparin binding protein, a ligand of unknown function. During embryogenesis the temporal expression pattern differs considerably for the three members of the amyloid precursor proteins. Total embryo messenger RNA levels of amyloid precursor protein and amyloid precursor protein-like protein 2 increased progressively, while amyloid precursor protein-like protein 1 messenger RNA showed a burst of synthesis between days 10 and 13 post-coitum. Significantly, expression of the alpha-2-macroglobulin/low density lipoprotein receptor-related protein and of its associated protein, the 44,000 molecular weight heparin binding protein, exhibited their most important increase very similar to that of amyloid precursor protein-like protein 1, between days 10 and 13 post-coitum. Apolipoprotein E, lipoprotein lipase and alpha-2-macroglobulin messenger RNA levels in total embryos increased progressively, beginning most pronounced at days 13, 15 and 17, respectively. In mouse embryos, in situ hybridization established amyloid precursor protein, amyloid precursor protein-like protein 2 and alpha-2-macroglobulin/low density lipoprotein receptor-related protein messenger RNA to be expressed in most organs, with the notable exception of the liver, while expression of the other studied proteins was much more restricted. Among adult mouse tissues, the genes investigated were expressed very prominently in brain, except for lipoprotein lipase and for the complete absence of alpha-2-macroglobulin messenger RNA. In adult mouse brain, the cortex and hippocampus exhibited strong signals for most genes analysed. Exceptions are lipoprotein lipase and apolipoprotein E messenger RNAs, and the absent alpha-2-macroglobulin messenger RNA. Several interesting features, similarities as well as differences, between brain tissue sections hybridized with probes for amyloid precursor protein, amyloid precursor protein-like proteins 1 and 2 and between alpha-2-macroglobulin/low density lipoprotein receptor-related protein and heparin binding protein-44 were observed and are described. The results are further discussed in view of the known or anticipated physiological functions of the proteins examined and of their possible role in the etiology of Alzheimers disease.

ADAM10 regulates FasL cell surface expression and modulates FasL-induced cytotoxicity and activation-induced cell death

The apoptosis-inducing Fas ligand (FasL) is a type II transmembrane protein that is involved in the downregulation of immune reactions by activation-induced cell death (AICD) as well as in T cell-mediated cytotoxicity. Proteolytic cleavage leads to the generation of membrane-bound N-terminal fragments and a soluble FasL (sFasL) ectodomain. sFasL can be detected in the serum of patients with dysregulated inflammatory diseases and is discussed to affect Fas-FasL-mediated apoptosis. Using pharmacological approaches in 293T cells, in vitro cleavage assays as well as loss and gain of function studies in murine embryonic fibroblasts (MEFs), we demonstrate that the disintegrin and metalloprotease ADAM10 is critically involved in the shedding of FasL. In primary human T cells, FasL shedding is significantly reduced after inhibition of ADAM10. The resulting elevated FasL surface expression is associated with increased killing capacity and an increase of T cells undergoing AICD. Overall, our findings suggest that ADAM10 represents an important molecular modulator of FasL-mediated cell death.

Amyloidogenic Processing of Human Amyloid Precursor Protein in Hippocampal Neurons Devoid of Cathepsin D

βA4-Amyloid peptide, the main component of the amyloid plaques in the brain of Alzheimers disease patients is produced from amyloid precursor protein (APP) by proteolytical processing. Several lines of evidence suggest a direct role for cathepsin D, the major endosomal/lysosomal aspartic endopeptidase, in βA4-amyloid peptide generation. Here we tested this hypothesis using primary cultures of hippocampal neurons derived from cathepsin D-deficient (knock out) mice and expressing wild-type human APP and two clinical APP variants via recombinant Semliki Forest virus. We demonstrate APP secretory processing, production of carboxyl-terminal amyloid fragments, and secretion of the βA4-amyloid peptide in the complete absence of cathepsin D. The results rule out cathepsin D as a critical component of α-, β-, or γ-secretase and therefore as a primary target for drugs aimed at decreasing the βA4-amyloid peptide burden in Alzheimers disease.

Deletion of Adam10 in endothelial cells leads to defects in organ-specific vascular structures

During vertebrate angiogenesis, Notch regulates the cell-fate decision between vascular tip cells versus stalk cells. Canonical Notch signaling depends on sequential proteolytic events, whereby interaction of Notch with membrane-anchored ligands triggers proteolytic processing, first by Adam10 and then presenilins. This liberates the Notch intracellular domain, allowing it to enter the nucleus and activate Notch-dependent genes. Here we report that conditional inactivation of Adam10 in endothelial cells (A10ΔEC) recapitulates the increased branching and density of the retinal vasculature that is also caused by interfering with Notch signaling. Moreover, A10ΔEC mice have additional vascular abnormalities, including aberrant subcapsular hepatic veins, enlarged glomeruli, intestinal polyps containing endothelial cell masses, abnormal endochondral ossification, leading to stunted long bone growth and increased pathologic neovascularization following oxygen-induced retinopathy. Our findings support a model in which Adam10 is a crucial regulator of endothelial cell-fate decisions, most likely because of its essential role in canonical Notch signaling.

Alzheimer's disease. A firm base for drug development.

Alzheimers disease is a progressive dementia in which massive protein deposits accumulate as either amyloid plaques or neurofibrillary tangles. The plaques are composed of a peptide called Aβ, which is liberated from its precursor, the amyloid precursor protein, by cleavage at two sites. The enzyme that cleaves at one of these sites, the β site, has now been identified, and it is likely to be a good target for drugs.

Co-regulation of intragenic microRNA miR-153 and its host gene Ia-2 β: identification of miR-153 target genes with functions related to IA-2β in pancreas and brain

Aims/hypothesisWe analysed the genomic organisation of miR-153, a microRNA embedded in genes that encode two of the major type 1 diabetes autoantigens, islet-associated protein (IA)-2 and IA-2β. We also identified miR-153 target genes that correlated with IA-2β localisation and function.MethodsA bioinformatics approach was used to identify miR-153’s genomic organisation. To analyse the co-regulation of miR-153 and IA-2β, quantitative PCR analysis of miR-153 and Ia-2β (also known as Ptprn2) was performed after a glucose stimulation assay in MIN6B cells and isolated murine pancreatic islets, and also in wild-type Ia-2 (also known as Ptprn), Ia-2β single knockout and Ia-2/Ia-2β double knockout mouse brain and pancreatic islets. Bioinformatics identification of miR-153 target genes and validation via luciferase reporter assays, western blotting and quantitative PCR were also carried out.ResultsTwo copies of miR-153, miR-153-1 and miR-153-2, are localised in intron 19 of Ia-2 and Ia-2β, respectively. In rodents, only miR-153-2 is conserved. We demonstrated that expression of miR-153-2 and Ia-2β in rodents is partially co-regulated as demonstrated by a strong reduction of miR-153 expression levels in Ia-2β knockout and Ia-2/Ia-2β double knockout mice. miR-153 levels were unaffected in Ia-2 knockout mice. In addition, glucose stimulation, which increases Ia-2 and Ia-2β expression, also significantly increased expression of miR-153. Several predicted targets of miR-153 were reduced after glucose stimulation in vitro, correlating with the increase in miR-153 levels.Conclusions/interpretationThis study suggests the involvement of miR-153, IA-2β and miR-153 target genes in a regulatory network, which is potentially relevant to insulin and neurotransmitter release.

The Parkinson’s gene PINK1 regulates cell cycle progression and promotes cancer-associated phenotypes

PINK1 (phosphatase and tensin homolog deleted on chromosome 10 (PTEN)-induced kinase 1), a Parkinson’s disease-associated gene, was identified originally because of its induction by the tumor-suppressor PTEN. PINK1 promotes cell survival and potentially metastatic functions and protects against cell stressors including chemotherapeutic agents. However, the mechanisms underlying PINK1 function in cancer cell biology are unclear. Here, using several model systems, we show that PINK1 deletion significantly reduced cancer-associated phenotypes including cell proliferation, colony formation and invasiveness, which were restored by human PINK1 overexpression. Results show that PINK1 deletion causes major defects in cell cycle progression in immortalized mouse embryonic fibroblasts (MEFs) from PINK1−/− mice, and in BE(2)-M17 cells stably transduced with short hairpin RNA against PINK1. Detailed cell cycle analyses of MEF cell lines from several PINK1−/− mice demonstrate an increased proportion of cells in G2/M and decreased number of cells in G1 following release from nocodazole block. This was concomitant with increased double and multi-nucleated cells, a reduced ability to undergo cytokinesis and to re-enter G1, and significant alterations in cell cycle markers, including failure to increase cyclin D1, all indicative of mitotic arrest. PINK1−/− cells also demonstrated ineffective cell cycle exit following serum deprivation. Cell cycle defects associated with PINK1 deficiency occur at points critical for cell division, growth and stress resistance in cancer cells were rescued by ectopic expression of human PINK1 and demonstrated PINK1 kinase dependence. The importance of PINK1 for cell cycle control is further supported by results showing that cell cycle deficits induced by PINK1 deletion were linked mechanistically to aberrant mitochondrial fission and its regulation by dynamin-related protein-1 (Drp1), known to be critical for progression of mitosis. Our data indicate that PINK1 has tumor-promoting properties and demonstrates a new function for PINK1 as a regulator of the cell cycle.

Amyloid precursor protein accumulation in Lewy body dementia and Alzheimer's disease.

The presence of amyloid precursor protein (APP) and beta-amyloid protein (beta A4) was investigated in the cerebra of 4 patients with Alzheimers disease (AD), 1 patient with Downs syndrome, 4 patients with dementia of the Lewy body type (DLB) and 4 age-matched, clinically nondemented controls, of which one displayed many amyloid plaques. The different types of amyloid plaques stained strongly with antibodies against beta A4. Antibodies against the C-terminal region of APP reacted only weakly with small swollen neurites and with globular deposits in neuritic-type plaques from patients with AD. The antibody against the N-terminal region of APP stained strongly cellular elements in the neuritic type plaques of patients with AD but not dense cored plaques. In contrast, patients with DLB displayed with this antibody a homogeneous staining of dense cored amyloid plaques. Some Lewy bodies stained with the antibody against the N-terminal region of APP as well. These results indicate that the processing of APP in AD and DLB could be different, to yield different fragments deposited in AD and DLB amyloid plaques.

The function of presenilin-1 in amyloid beta-peptide generation and brain development

Abstract Several mutations in genes that cause the familial form of Alzheimer’s Disease (FAD) have been identified. All mutations in the three FAD genes, i.e., amyloid precursor protein (APP), presenilin 1 (PS-1), and presenilin 2 (PS-2) cause an increased production of a longer, more amyloidogenic form of the amyloid peptide corroborating strongly the idea that abnormal processing of APP is central to the pathogenesis. In PS-1 deficient mice, 80% less amyloid peptide was produced. Instead, membrane associated carboxyterminal fragments generated by α- and β-secretase accumulated suggesting that PS-1 is involved in the gamma-secretase activity cleaving the transmembrane domain of APP after α- and β-secretase cleavage has occured. The clinical mutations in PS-1 which increase the production of βA41-42 therefore seem to cause a “selective” gain of its normal function.During cortical plate development in PS-1-deficient mice, neurons do not terminate their movement at the outer margin of the cortical plate, but enter the marginal zone and subarachnoid space. These focal heterotopias closely resemble those occuring, e.g., in human lissencephaly type II. The extracellular matrix of the cortical plate and marginal zone was altered as a consequence of a loss of Cajal-Retzius (CR) neurons from the marginal zone. The pathogenesis of this neuronal migration disorder is associated with a reduction and redistribution of notch-1 immunoreactivity in CR- and cortical plate neurons, a cell surface receptor operative in cell fate selection, which similar to APP is cleaved in its transmembrane domain during activation by a γ-secretase like protease.