Recent findings suggest that hypercholesterolemia may contribute to the onset of Alzheimer’s disease (AD)-like dementia but the underlying mechanisms remain unknown. In this study, we evaluated the cognitive performance in rodent models of hypercholesterolemia in relation to neuroinflammatory changes and amyloid precursor protein (APP) processing, the two key parameters of AD pathogenesis. Groups of normal C57BL/6 and low density lipoprotein receptor (LDLR)-deficient mice were fed a high fat/cholesterol diet for an 8-week period and tested for memory in a radial arm maze. It was found that the C57BL/6 mice receiving a high fat diet were deficient in handling an increasing working memory (WM) load compared to counterparts receiving a control diet while the hypercholesterolemic LDLR−/− mice showed impaired WM regardless of diet. Immunohistochemical analysis revealed the presence of activated microglia and astrocytes in the hippocampi from high fat-fed C57BL/6 mice and LDLR−/− mice. Consistent with a neuroinflammatory response, the hyperlipidemic mice showed increased expression of cytokines/mediators including TNFα, IL-1β, IL-6, NOS2 and COX2. There was also an induced expression of the key APP processing enzyme i.e., BACE1 in both high fat/cholesterol-fed C57BL/6 and LDLR−/− mice accompanied by an increased generation of C-terminal fragments (CTFs) of APP. Although ELISA for Aβ failed to record significant changes in the non-transgenic mice, a 3-fold increase in Aβ-40 accumulation was apparent in a strain of transgenic mice expressing wt hAPP on high fat/cholesterol diet. The findings link hypercholesterolemia with cognitive dysfunction potentially mediated by increased neuroinflammation and APP processing in a non-transgenic mouse model.

Down syndrome (DS) individuals develop several neuropathological hallmarks seen in Alzheimer's disease, including cognitive decline and the early loss of cholinergic markers in the basal forebrain. These deficits are replicated in the Ts65Dn mouse, which contains a partial trisomy of murine chromosome 16, the orthologous genetic segment to human chromosome 21. Oxidative stress levels are elevated early in DS, and may contribute to the neurodegeneration seen in these individuals. We evaluated oxidative stress in Ts65Dn mice, and assessed the efficacy of long-term antioxidant supplementation on memory and basal forebrain pathology. We report that oxidative stress was elevated in the adult Ts65Dn brain, and that supplementation with the antioxidant vitamin E effectively reduced these markers. Also, Ts65Dn mice receiving vitamin E exhibited improved performance on a spatial working memory task and showed an attenuation of cholinergic neuron pathology in the basal forebrain. This study provides evidence that vitamin E delays onset of cognitive and morphological abnormalities in a mouse model of DS, and may represent a safe and effective treatment early in the progression of DS neuropathology.

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The amyloid hypothesis has dominated the thinking in our attempts to understand, diagnose and develop drugs for Alzheimer's disease (AD). This article presents a new hypothesis that takes into account the numerous familial AD (FAD) mutations in the amyloid precursor protein (APP) and its processing pathways, but suggests a new perspective beyond toxicity of forms of the amyloid beta-peptide (Abeta). Clearly, amyloid deposits are an invariable feature of AD. Moreover, although APP is normally processed to secreted and membrane-bound fragments, sAPPbeta and CTFbeta, by BACE, and the latter is subsequently processed by gamma-secretase to Abeta and CTFgamma, this pathway mostly yields Abeta of 40 residues, and increases in the levels of the amyloidogenic 42-residue Abeta (Abeta42) are seen in the majority of the mutations linked to the disease. The resulting theory is that the disease is caused by amyloid toxicity, which impairs memory and triggers deposition of the microtubule associated protein, Tau, as neurofibrillary tangles. Nevertheless, a few exceptional FAD mutations and the presence of large amounts of amyloid deposits in a group of cognitively normal elderly patients suggest that the disease process is more complex. Indeed, it has been hard to demonstrate the toxicity of Abeta42 and the actual target has been shifted to small oligomers of the peptide, named Abeta derived diffusible ligands (ADDLs). Our hypothesis is that the disease is more complex and caused by a failure of APP metabolism or clearance, which simultaneously affects several other membrane proteins. Thus, a traffic jam is created by failure of important pathways such as gamma-secretase processing of residual intramembrane domains released from the metabolism of multiple membrane proteins, which ultimately leads to a multiple system failure. In this theory, toxicity of Abeta42 will only contribute partially, if at all, to neurodegeneration in AD. More significantly, this theory would predict that focussing on specific reagents such as gamma-secretase inhibitors that hamper metabolism of APP, may initially show some beneficial effects on cognitive performance by elimination of acutely toxic ADDLs, but over the longer term may exacerbate the disease process by reducing membrane protein turnover.

With the ever‐increasing population of aged individuals at risk of developing Alzheimer’s disease (AD), there is an urgent need for a sensitive, specific, non‐invasive, and diagnostic standard. The majority of efforts have focused on auto‐antibodies against amyloid‐β (Aβ) protein, both as a potential treatment, and a reliable biomarker of AD pathology. Naturally occurring antibodies against Aβ are found in the CSF and plasma of patients with AD as well as healthy control subjects. To date, differences between diseased and control subjects have been highly variable. However, some of the antibody will be in preformed antigen–antibody complexes and the extent and nature of such complexes may provide a potential explanation for the variable results reported in human studies. Thus, measuring total amounts of antigen or antibody following unmasking is critical. Here, using a technique for dissociating antibody–antigen complexes, we found significant differences in serum antibodies to Aβ between AD and aged‐matched control subjects. While the current study demonstrates the relevance of measuring total antibody, bound and unbound, against Aβ in AD, this technique may be applicable to diseases such as acquired immune deficiency syndrome and hepatitis B where determination of antigen and antibody levels are important for disease diagnosis and assessing disease progression.

The Alzheimer amyloid-β (Aβ) accumulates in several types of retinal degeneration and in Alzheimer disease (AD), but its source has been unclear. We detected the neuronal 695 amino acid form of Aβ-precursor protein (AβPP) in the normal retina and AβPP751 in the retinal pigment epithelium (RPE) and anterior eye tissues. Similar to the brain, α- and β-secretases cleaved AβPP to soluble derivatives (sAPP) α or β and membrane-bound C-terminal fragments (CTF) α or β in the retina and RPE. Levels of sAPP were particularly high in the vitreous and low in aqueous humor revealing a molecular barrier for AβPP. In contrast, Aβ40 and Aβ42 levels were only 50% lower in the aqueous than the vitreous humor, indicating relatively barrier-free movement of Aβ. These studies demonstrated a relatively high yield of AβPP and Aβ in the ocular fluids, which may serve as a trackable marker for AD. In addition, failure of free clearance from the eye may trigger retina degeneration in a manner similar to Aβ-related neurodegeneration in AD.

Wet age-related macular degeneration (AMD) attacks the integrity of the retinal pigment epithelium (RPE) barrier system. The pathogenic process was hypothesized to be mediated by vascular endothelial growth factor (VEGF) and antagonized by pigment epithelium-derived factor (PEDF). To dissect these functional interactions, monolayer cultures of RPE cells were established, and changes in transepithelial resistance were evaluated after administration of PEDF, placenta growth factor (VEGF-R1 agonist), and VEGF-E (VEGF-R2 agonist). A recently described mechanism of VEGF inhibition in endothelia required the release of VEGF-R1 intracellular domain by ␥-secretase. To evaluate this pathway in the RPE, cells were pretreated with inhibitors DAPT or LY411575. Processing of VEGF receptors was assessed by Western blot analysis. Administration of VEGF-E rapidly increased RPE permeability, and PEDF inhibited the VEGF-E response dose-dependently. Both ␥-secretase antagonists prevented the inhibitory effects of PEDF. The co-administration of PEDF and VEGF-E depleted the amount of VEGF-R2 in the membrane and increased the amount of VEGF-R2 ectodomain in the media. Therefore, the inhibitory effect of PEDF appears to be mediated via the processing of VEGF-R2 by ␥-secretase. ␥-Secretase generates the amyloid-␤ (A␤) peptide of Alzheimer disease from its precursor (amyloid precursor protein). This peptide is also a component of drusen in dry AMD. The results support the hypothesis that misregulation of ␥-secretase may not only lead to A␤ deposits in dry AMD but can also be damaging to RPE function by blocking the protective effects of PEDF to prevent VEGF from driving the dry to wet AMD transition. Age-related macular degeneration (AMD)2 is often diagnosed by the appearance of subretinal fluid. This fluid causes a local detachment of the retina in the macular area resulting in decreased visual acuity in the center of the visual field (1). The resulting macular edema can lead to complete vision loss (2). Although the excessive fluid mainly comes from capillaries in the inner retina, the removal of subretinal fluid is dependent on the RPE. The maintenance of RPE barrier function is essential for the efficient removal of the fluid (3), and the disruption of the RPE barrier can eventually lead to choroidal neovascularization.Recent clinical studies have shown that intravitreally administered anti-VEGF compounds are effective therapies for choroidal neovascularization (4 -6). Originally, VEGF was described as an endothelial angiogenic and vasopermeability factor. The leakage through the vessels of the inner retina increases in response to VEGF (7,8). However, the release of VEGF also affects RPE function (9 -11). We have recently shown that RPE barrier integrity is modulated by VEGF through apically oriented VEGF-R2 receptors (12). Thus, there is a growing body of evidence that intraocular VEGF can increase the permeability of both the inner and outer bloodretina barriers, contributing to the accumulation of subretinal fluid and macular ed...