Aggregation of amyloidogenic proteins into insoluble amyloid fibrils is implicated in various neurodegenerative diseases. This process involves protein assembly into oligomeric intermediates and fibrils with highly polymorphic molecular structures. These structural differences may be responsible for different disease presentations. For this reason, elucidation of the structural features and assembly kinetics of amyloidogenic proteins has been an area of intense study. We report here the results of high-speed atomic force microscopy (HS-AFM) studies of fibril formation and elongation by the 42-residue form of the amyloid β-protein (Aβ1–42), a key pathogenetic agent of Alzheimer's disease. Our data demonstrate two different growth modes of Aβ1–42, one producing straight fibrils and the other producing spiral fibrils. Each mode depends on initial fibril nucleus structure, but switching from one growth mode to another was occasionally observed, suggesting that fibril end structure fluctuated between the two growth modes. This switching phenomenon was affected by buffer salt composition. Our findings indicate that polymorphism in fibril structure can occur after fibril nucleation and is affected by relatively modest changes in environmental conditions.

Amyloid b-protein (Ab) and a-synuclein (aS) are the primary components of amyloid plaques and Lewy bodies (LBs), respectively. Aggregations of Ab and aS are considered to be a critical step during neurodegeneration associated with Alzheimer's disease (AD) and Lewy body diseases (LBD), respectively. The AD is characterized by the accumulation of Ab plaques and neurofibrillary tangles. Interestingly, up to 50% of AD cases exhibit significant LB pathology in addition to plaques and tangles (Hamilton 2000). Likewise, patients with dementia with LBs (DLB) frequently exhibit AD pathology, particularly senile plaques (Armstrong et al. 1997).Recent studies suggest that accumulations of oligomers might be the neurotoxic species, rather than fibrils. The progressive accumulation of Ab oligomers has been identified as a central toxic event during AD that leads to synaptic dysfunction (Ono and Yamada 2011), whereas the formation of aS oligomers that disrupt membrane and mitochondrial activity has been linked to LBD (Kim et al. 2009).It was previously shown that Ab enhances aS accumulation and neuronal deficits using transgenic mice with neuronal expression of Ab and aS (Masliah et al. 2001). Nuclear magnetic resonance study showed that Ab and aS might interact directly at a few sites (Mandal et al. 2006). A recent in vitro study reported that Ab and aS might interact directly to form hybrid pore-like oligomers that contribute to neurodegeneration (Tsigelny et al. 2008). These studies suggest that interactions between Ab and aS are involved in the pathogenesis of AD and LBD, but the seeding effects of their aggregates on aggregation pathways have not been elucidated. Thus, we determined whether fibrils or crosslinked oligomers of Ab40, Ab42, and aS have cross-seeding effects on each other's aggregation pathways in vitro. Abbreviations used: Ab, amyloid b-protein; AD, Alzheimer's disease; APP, amyloid precursor protein; APS, ammonium persulfate; aS, a-synuclein; DLB, dementia with Lewy bodies; EM, electron microscopy; fAb, Ab fibrils; faS, aS fibrils; LBD, Lewy body diseases; LBs, Lewy bodies; NAC, non-amyloid component; oligo, cross-linked oligomers; PD, Parkinson's disease; PICUP, photo-induced cross-linking of unmodified proteins; Ru(bpy), tris(2,2¢-bipyridyl)dichlororuthenium(II) hexahydrate; SDS-PAGE, sodium dodecyl sulfate-polyacrylamide gel electrophoresis; ThS, Thioflavin S; ThT, Thioflavin T. However, the seeding effects of their aggregates on their aggregation pathways are not completely clear. To investigate the cross-seeding effects of Ab and aS, we examined how sonicated fibrils or cross-linked oligomers of Ab40, Ab42, and aS affected their aggregation pathways using thioflavin T(S) assay and electron microscopy. Fibrils and oligomers of Ab40, Ab42, and aS acted as seeds, and affected the aggregation pathways within and among species. The seeding effects of aS fibrils were higher than those of Ab40 and Ab42 fibrils in the Ab40 and Ab42 aggregation pathways, respectively. We showed that Ab and aS acted as seeds an...

Construction of a self-assembled supramolecular macroring that has distances and orientations of porphyrin dimer units in close analogy to those of the natural light-harvesting complexes was achieved. In natural light-harvesting complexes, bacteriochlorophyll-a's are arranged in macroring structures by coordination from imidazolyl side chains. A structural determination of a light-harvesting antenna complex (LH2) elucidated the arrangement of 18 bacteriochlorophyll-a's in a slipped-cofacial way with C9 symmetry in B850 in 1995. To obtain such an elegant macroring architecture as an artificial light-harvesting complex, we connected slipped-cofacial dimers of imidazolylporphyrins in a gable-porphyrin orientation. The introduction of zinc assembled by coordination porphyrins with originally a broad molecular weight distribution (MWD). When coordination bonds were cleaved and reorganized under high dilution conditions using chloroform/methanol solution, the MWD was perfectly converged. This crop gave particle images of a uniform height by atomic force microscopy measurements. Further purification was successfully achieved by gel permeation chromatography, and the first eluting component gave a diameter corresponding to the cyclic hexamer of gable-porphyrins from a small-angle X-ray scattering measurement with synchrotron radiation. In summary, porphyrin assemblies in a macroring arrangement were constructed using the gable-porphyrin motif, and their photophysical properties are highly interesting.

Lewy bodies, mainly composed of a-synuclein (aS), are pathological hallmarks of Parkinson's disease and dementia with Lewy bodies. Epidemiological studies showed that green tea consumption or habitual intake of phenolic compounds reduced Parkinson's disease risk. We previously reported that phenolic compounds inhibited aS fibrillation and destabilized preformed aS fibrils. Cumulative evidence suggests that loworder aS oligomers are neurotoxic and critical species in the pathogenesis of a-synucleinopathies. To develop disease modifying therapies for a-synucleinopathies, we examined effects of phenolic compounds (myricetin (Myr), curcumin, rosmarinic acid (RA), nordihydroguaiaretic acid, and ferulic acid) on aS oligomerization. Using methods such as photoinduced cross-linking of unmodified proteins, circular dichroism spectroscopy, the electron microscope, and the atomic force microscope, we showed that Myr and RA inhibited aS oligomerization and secondary structure conversion. The nuclear magnetic resonance analysis revealed that Myr directly bound to the N-terminal region of aS, whereas direct binding of RA to monomeric aS was not detected. Electrophysiological assays for long-term potentiation in mouse hippocampal slices revealed that Myr and RA ameliorated aS synaptic toxicity by inhibition of aS oligomerization. These results suggest that Myr and RA prevent the aS aggregation process, reducing the neurotoxicity of aS oligomers.

B‐cell lymphoma associated with haemophagocytic syndrome (HPS) is extremely rare in Western countries but has recently been increasingly reported in Asian countries. We describe seven patients with B‐cell lymphoma associated with HPS, six males and one female, age range 41–82 years (median 63 years). All patients had fever and splenomegaly, and six of the seven patients had hepatomegaly with no associated lymphadenopathy. The bone marrow showed haemophagocytosis and an infiltration of lymphoma cells. All patients showed increased levels of lactate dehydrogenase, C‐reactive protein, ferritin and soluble interleukin‐2 receptor. Lymphoma cells were positive for CD19, CD20 and surface immunoglobulin in all patients examined, and positive for CD5 in four of seven patients. Cytogenetic analyses of bone marrow cells showed a complex structural abnormality including chromosome 14q32 in two patients, 19q13 in three patients and deletion of the terminal part of 8p21 in six patients. The prognosis was poor; only two of the seven patients have survived in complete remission with a median survival of 11 months. These data suggested that B‐cell lymphoma associated with HPS might constitute a distinct biological and clinical disease entity. Abnormality of chromosome 19q13 and loss of 8p21 might be involved in the pathogenesis of this disease.