Phosphodiesterase III inhibitor promotes drainage of cerebrovascular ß-amyloid.

OBJECTIVE: Brain amyloidosis is a key feature of Alzheimer's disease (AD). It also incorporates cerebrovascular amyloid ß (Aß) in the form of cerebral amyloid angiopathy (CAA) involving neurovascular dysfunction. We have recently shown by retrospective analysis that patients with mild cognitive impairment receiving a vasoactive drug cilostazol, a selective inhibitor of phosphodiesterase (PDE) III, exhibit significantly reduced cognitive decline. Here, we tested whether cilostazol protects against the disruption of the neurovascular unit and facilitates the arterial pulsation-driven perivascular drainage of Aß in AD/CAA. METHODS: We explored the expression of PDE III in postmortem human brain tissue followed by a series of experiments examining the effects of cilostazol on Aß metabolism in transgenic mice (Tg-SwDI mice) as a model of cerebrovascular ß-amyloidosis, as well as cultured neurons. RESULTS: We established that PDE III is abnormally upregulated in cerebral blood vessels of AD and CAA subjects and closely correlates with vascular amyloid burden. Furthermore, we demonstrated that cilostazol treatment maintained cerebral hyperemic and vasodilative responses to hypercapnia and acetylcholine, suppressed degeneration of pericytes and vascular smooth muscle cells, promoted perivascular drainage of soluble fluorescent Aß1-40, and rescued cognitive deficits in Tg-SwDI mice. Although cilostazol decreased endogenous Aß production in cultured neurons, C-terminal fragment of amyloid precursor protein expression was not altered in cilostazol-treated Tg-SwDI mice. INTERPRETATION: The predominant action of cilostazol on Aß metabolism is likely to facilitate Aß clearance due to the sustained cerebrovascular function in vivo. Our findings mechanistically demonstrate that cilostazol is a promising therapeutic approach for AD and CAA.

Vascular pathology in Alzheimer's disease.

Histopathologically, numerous senile plaques and neurofibrillary tangles were remarkably observed in the brain with Alzheimer's disease. At the same time, so much simple atrophy of nerve cells was evident under light microscopy.Electron microscopical observations of serial sections revealed that small blood vessels, including capillaries, had a deep relationship to the amyloid fibrils which formed the senile plaques and they had fallen into degenerative states. The vascular feet of the astroglial cells surrounding small blood vessels showed degenerative features, and many nerve cells in this area either showed various degrees of degeneration or apparently were destroyed. The atrophy of the brain with Alzheimer's disease is considered to be caused by the amyloid angiopathy of small blood vessels and the degeneration of capillaries and vascular feet. These findings strongly suggest that the major causal mechanism of Alzheimer's disease is an alteration of the blood-brain barrier. Morphology is an expression of both the structure and the function of organs in the living body. Based on this viewpoint, this review article emphasizes that the morphological changes to small blood vessels in the brain with Alzheimer's disease convey crucial information and clues for solving the underlying mechanism that causes the disease.

Impaired expression of importin/karyopherin beta1 leads to post-implantation lethality.

Importin beta1 (Impbeta)/karyopherin beta1 (Kpnb1) mediates the nuclear import of a large variety of substrates. This study aimed to investigate the requirement for the Kpnb1 gene in mouse development, using a gene trap line, B6-CB-Ayu8108(GtgeoIMEG) (Ayu8108(geo)), in which the trap vector was inserted into the promoter region of the Kpnb1 gene, but in reverse orientation of the Kpnb1 gene. Ayu8108(geo/geo) homozygous embryos could develop to the blastocyst stage, but died before embryonic day 5.5, and expression of the Kpnb1 gene in homozygous blastocysts was undetectable. We also replaced the betageo gene with Impbeta cDNA through Cre-mediated recombination to rescue Impbeta expression. Homozygous mice for the rescued allele Ayu8108(Impbeta/Impbeta) were born and developed normally. These results demonstrated that the cause of post-implantation lethality of Ayu8108(geo/geo) homozygous embryos was impaired expression of the Kpnb1 gene, indicating indispensable roles of Impbeta1 in early development of mice.

Vascular pathology in Alzheimer's disease.

This report briefly describes the morphological examination in several types of senile plaques made by using serial sections for both light and electron microscopy in order to observe the relationship between senile plaques and cerebral microvessels.

Identification of an aging-related spherical inclusion in the human brain.

Inclusions, such as corpora amylacea, axonal spheroids and ubiquitin-positive granular structures, are present in aged brains. We found a phosphorylated tau-positive inclusion in brain tissues obtained from 13 non-demented subjects and five patients with Alzheimer's disease. This inclusion was spherical and 3-20 microm in size. It was most frequently detected in the hippocampal CA1 region and in the prosubiculum but was not present in the white matter. The density of this inclusion increased significantly with aging and decreased after the occurrence of neurofibrillary tangles. The presence of the inclusion was confirmed using immunoelectron microscopy. These findings show a possibility that the inclusion is a novel aging-related structure in the human brain.

Disulfide-bond formation in the transthyretin mutant Y114C prevents amyloid fibril formation in vivo and in vitro.

The Y114C mutation in human transthyretin (TTR) is associated with a particular form of familial amyloidotic polyneuropathy. We show that vitreous aggregates ex vivo consist of either regular amyloid fibrils or disordered disulfide-linked precipitates that maintain the ability to bind Congo red. Furthermore, we demonstrate in vitro that the ATTR Y114C mutant exists in three forms: one unstable but nativelike tetrameric form, one highly aggregated form in which a network of disulfide bonds is formed, and one fibrillar form. The disulfide-linked aggregates and the fibrillar form of the mutant can be induced by heat induction under nonreduced and reduced conditions, respectively. Both forms are recognized by the amyloid specific antibody MAB(39-44). In a previous study, we have linked exposure of this epitope in TTR to a three-residue shift in beta-strand D. The X-ray crystallographic structure of reduced tetrameric ATTR Y114C shows a structure similar to that of the wild type but with a more buried position of Cys10 and with beta-mercaptoethanol associated with Cys114, verifying the strong tendency for this residue to form disulfide bonds. Combined with the ex vivo data, our in vitro findings suggest that ATTR Y114C can lead to disease either by forming regular unbranched amyloid fibrils or by forming disulfide-linked aggregates that maintain amyloid-like properties but are unable to form regular amyloid fibrils.