The zipper groups of the amyloid state of proteins.

Fibrous proteins in the amyloid state are found both associated with numerous diseases and in the normal functions of cells. Amyloid fibers contain a repetitive spine, commonly built from a pair of ß-sheets whose ß-strands run perpendicular to the fiber direction and whose side chains interdigitate, much like the teeth of a zipper. In fiber spines known as homosteric zippers, identical protein segments sharing identical packing environments make the two ß-sheets. In previous work based on atomic resolution crystal structures of homosteric zippers derived from a dozen proteins, the symmetries of homosteric zippers were categorized into eight classes. Here, it is shown through a formal derivation that each homosteric zipper class corresponds to a unique set of symmetry groups termed `zipper groups'. Furthermore, the eight previously identified classes do not account for all of the 15 possible zipper groups, which may be categorized into the complete set of ten classes. Because of their foundations in group theory, the 15 zipper groups provide a mathematically rigorous classification for homosteric zippers.

Amyloid precursor protein is required for convergent-extension movements during Zebrafish development.

Amyloid precursor protein (APP) has been a focus of intense investigation because of its role in Alzheimer's disease (AD), however, its biological function remains uncertain. Loss of APP and APP-like proteins results in postnatal lethality in mice, suggesting a role during embryogenesis. Here we show that in a zebrafish model system, knock down of APP results in the generation of fish with dramatically reduced body length and a short, curly tail. In situ examination of gene expression suggests that the APP morphant embryos have defective convergent-extension movements. We also show that wild-type human APP rescues the morphant phenotype, but the Swedish mutant APP, which causes familial AD (fAD), does not rescue the developmental defects. Collectively, this work demonstrates that the zebrafish model is a powerful system to define the role of APP during embryonic development and to evaluate the functional activity of fAD mutant APP.

Reduced brain volumes in mice expressing APP-Austrian mutation but not in mice expressing APP-Swedish-Austrian mutations.

We previously described two transgenic mouse lines expressing sub-endogenous levels of the 'Austrian' APP-T714I mutation (driven by the prenatally active PDGF-beta promoter; APP-Au mice) and showing intraneuronal Abeta pathology and reduced brain volumes on MRI at 12 and 20 months of age. To further investigate whether reduced brain sizes were caused by neurodegeneration or a neurodevelopmental defect, we now measured brain volumes as early as postnatal day 10. At this age, a distinguishable reduction in brain volumes was absent, indicating that brain volume deficits in APP-Au mice are not caused by a neurodevelopmental defect. To further study the association between intraneuronal Abeta and reduced brain volumes, we further generated and analyzed an APP transgenic mouse model expressing both Austrian and Swedish (K670N/M671L) mutations (APP-SwAu mice). APP-Swedish mutation is known to lead to altered APP processing in the secretory pathway, precluding its later processing in endosomal-lysosomal compartments, the site of intraneuronal Abeta accumulation. Also, to have higher levels of transgene expression only after birth, a murine Thy-1 promoter was utilized for APP-SwAu mouse lines. Despite having five times higher transgene APP levels compared to APP-Au mice, APP-SwAu mice showed significantly lower intraneuronal Abeta levels in the absence of reduced brain volumes, suggesting that intraneuronal Abeta accumulation is related to reduced brain volumes in APP-Au mice. These data also provide a first in vivo indication of altered processing of APP-Swedish at sub-endogenous levels, an effect not observed in mouse models expressing the APP-Swedish mutation in high amounts.

Toward a reliable distinction between patients with mild cognitive impairment and Alzheimer-type dementia versus major depression.

BACKGROUND: Cerebrospinal fluid (CSF) levels of soluble amyloid precursor protein (sAPP) and its alpha-secreted form (alpha-sAPP) were investigated as a means to distinguish between individuals with mild cognitive impairment (MCI) and Alzheimer-type dementia (DAT) and those with major depressive episode (MDE) showing secondary memory deficits. METHODS: Twenty-seven patients with MCI, 32 with probable DAT, and 24 with MDE attending a memory clinic were studied. Cerebrospinal fluid levels of sAPP/amyloid precursor-like protein 2 (APLP2) and alpha-sAPP were detected by Western blotting. RESULTS: Patients with MDE had the highest CSF levels of total sAPP/APLP2 as compared with MCI and DAT patients (p < .001); sAPP/APLP2 levels were higher in MCI than in DAT subjects. Whereas alpha-sAPP levels did not differ between the MCI and DAT groups, median levels of this peptide were significantly lower in MCI and DAT versus MDE patients. CONCLUSIONS: Soluble amyloid precursor protein/APLP2 and alpha-sAPP concentrations in CSF can differentiate between DAT and MCI versus MDE, facilitating early ameliorative interventions and appropriate treatment regimens.

Cortical dysplasia resembling human type 2 lissencephaly in mice lacking all three APP family members.

The Alzheimer's disease beta-amyloid precursor protein (APP) is a member of a larger gene family that includes the amyloid precursor-like proteins, termed APLP1 and APLP2. We previously documented that APLP2-/-APLP1-/- and APLP2-/-APP-/- mice die postnatally, while APLP1-/-APP-/- mice and single mutants were viable. We now report that mice lacking all three APP/APLP family members survive through embryonic development, and die shortly after birth. In contrast to double-mutant animals with perinatal lethality, 81% of triple mutants showed cranial abnormalities. In 68% of triple mutants, we observed cortical dysplasias characterized by focal ectopic neuroblasts that had migrated through the basal lamina and pial membrane, a phenotype that resembles human type II lissencephaly. Moreover, at E18.5 triple mutants showed a partial loss of cortical Cajal Retzius (CR) cells, suggesting that APP/APLPs play a crucial role in the survival of CR cells and neuronal adhesion. Collectively, our data reveal an essential role for APP family members in normal brain development and early postnatal survival.

Amyloid precursor protein mRNA levels in Alzheimer's disease brain.

Insoluble beta-amyloid deposits in Alzheimer's disease (AD) brain are proteolytically derived from the membrane bound amyloid precursor protein (APP). The APP gene is differentially spliced to produce isoforms that can be classified into those containing a Kunitz-type serine protease inhibitor domain (K(+), APP(751), APP(770), APRP(365) and APRP(563)), and those without (K(-), APP(695) and APP(714)). Given the hypothesis that Abeta is a result of aberrant catabolism of APP, differential expression of mRNA isoforms containing protease inhibitors might play an active role in the pathology of AD. We took 513 cerebral cortex samples from 90 AD and 81 control brains and quantified the mRNA isoforms of APP with TaqMan real-time RT-PCR. After adjustment for age at death, brain pH and gender we found a change in the ratio of KPI(+) to KPI(-) mRNA isoforms of APP. Three separate probes, designed to recognise only KPI(+) mRNA species, gave increases of between 28% and 50% in AD brains relative to controls (p=0.002). There was no change in the mRNA levels of KPI-(APP 695) (p=0.898). Therefore, whilst KPI-mRNA levels remained stable the KPI(+) species increased specifically in the AD brains.

Early stages of probable Alzheimer disease are associated with changes in platelet amyloid precursor protein forms.

Previous findings demonstrated an altered pattern of amyloid precursor protein (APP) forms in platelets of Alzheimer disease (AD) patients, compared both with healthy control subjects or patients with non-Alzheimer-type dementia. The present study aims to evaluate whether platelet APP form ratio (APPr) is altered in patients with early stage AD. We selected 40 patients with early stage AD and 40 age-matched healthy controls. Compared with controls (mean+/-SD=0.91+/-0.3), mean APPr was decreased in AD (mean+/-SD=0.46+/-0.26, p<0.0001). Sixteen very mild AD patients (clinical dementia rating=0.5), identified among the AD group, showed a significant decrease of APPr values (mean+/-SD=0.50+/-0.3, p<0.0001). These findings indicate that alteration of APP processing in platelets is an early event and suggest that this assay might be of diagnostic value in differentiating mild AD from normal ageing.

Amyloid precursor protein in guinea pigs--complete cDNA sequence and alternative splicing.

We present the cDNA sequence of the guinea pig amyloid precursor protein comprising the complete coding sequence of 770 amino-acid residues. By alternative splicing of three exons transcripts encoding for 695, 714 and 751 amino acids and all forms previously denoted as L-APP are also generated. Guinea pig amyloid precursor protein was shown to exhibit extensive sequence similarity to its human and murine homologues of approx. 97% at the protein level which implies an evolutionary conserved but yet not fully understood physiological function.

Purification and spectroscopic characterization of beta-amyloid precursor protein from porcine brains.

Soluble and membrane-bound isoforms of beta-amyloid protein precursor (APP) of Alzheimer's disease were extracted and purified from porcine brains. At least three types of soluble APP and membrane-bound APP with different molecular masses, ranging from 86 kDa to 116 kDa, were obtained. CD and infrared spectroscopies were used to determine the overall secondary-structure content of APP. The infrared spectra of soluble and membrane-bound APP (in dry and hydrated states) were similar in the amide-I and amide-II regions, suggesting that the overall secondary structures of the soluble and membrane isoforms were roughly identical. The amide-I band is composed of at least five component bands, located at 1694, 1674, 1652, 1637 and 1618 cm(-1) for soluble APP, and located at 1687, 1674, 1651, 1637 and 1614-1606 cm(-1) for membrane-bound APP, as evidenced by their respective second-derivative infrared spectra. The 1651-1652-cm(-1) band was associated with alpha-helix structures, while two types of beta-sheet structures are evidenced by two characteristic pairs of component bands. The 1674-cm(-1) and 1637-cm(-1) bands for soluble APP and membrane-bound APP were tentatively associated to beta-sheet structures. The second pair of bands, located at 1694 cm(-1) and at 1618 cm(-1) for soluble APP and at 1687 cm(-1) and 1614-1606 cm(-1) for membrane-bound APP, were associated with intermolecular beta-sheet structures or aggregated strands, as confirmed by heat denaturation. CD spectra indicated the presence of alpha-helix structures in soluble and membrane-bound APP. The secondary-structure content, estimated from CD spectra, was about 40-45% alpha-helix and 15-20% beta-sheet structures for soluble and membrane-bound APP.

The Alzheimer amyloid precursor proteoglycan (appican) is present in brain and is produced by astrocytes but not by neurons in primary neural cultures.

Recent studies showed that the Alzheimer amyloid precursor (APP) occurs as the core protein of a chondroitin sulfate proteoglycan (appican) in C6 glioma cells. In the present study we show that appican is present in both human and rat brain tissue. Cortical rat brain cell cultures were used to identify appican-producing cells. Soluble secreted and cell-associated appican was produced by mixed glial cultures but not by primary neuronal cultures. Among the three major glial cell types, astrocytes produced high levels of appican, while oligodendrocytes failed to produce any. Only low levels of this molecule were occasionally detected in microglial cultures. Expression of appican in astrocyte cultures was regulated by the composition of the growth media. N2a neuroblastoma cells also produced appican; however, treatment with dibutyryl cAMP which promotes neuronal differentiation in these cells inhibited its production without inhibiting synthesis of APP. In contrast to the restricted expression of appican, APP was present in all cultures, and its production was independent of appican synthesis. Neuronal cultures produced mainly APP695 while glial cultures produced the Kunitz type protease inhibitor containing APP. The astrocyte-specific expression of appican suggests a function distinct from the function of APP. Brain appicans may play a role in the development of Alzheimer disease neuropathology.

Alzheimer's disease beta-amyloid precursor protein in rat neural cells in culture.

Immunochemical studies were performed on Alzheimer's beta-amyloid precursor protein (APP) in rat brain and cultured rat neural cells. Multiple APP subtypes were detected on immunoblots of brain homogenate with several antisera specific for subsequences of APP. In rat neural cell cultures, it was demonstrated that the composition of APP subtypes differed among cell types and subcellular fractions, and that APP subtypes in PC12h cells varied in their heparin binding affinity, suggesting distinct functional roles for different APP subtypes. Compatible with the possible role of APP in cell-matrix interaction, an increase in oligodendroglial APP was observed following their attachment onto poly-L-lysine substratum.