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Accumulation of neurotoxic amyloid-β (Aβ) is central to the pathology of Alzheimer’s disease (AD). Elucidating the mechanisms of Aβ accumulation will therefore expedite the development of Aβ-targeting AD therapeutics. We examined activity of an Aβ-degrading protease (matrix metalloprotease 2) to investigate whether biochemical factors consistent with conditions in the AD brain contribute to Aβ accumulation by altering Aβ sensitivity to proteolytic degradation. An Aβ amino acid mutation found in familial AD, Aβ interactions with zinc (Zn), and increased Aβ hydrophobicity all strongly prevented Aβ degradation. Consistent to all of these factors is the promotion of specific Aβ aggregates where the protease cleavage site, confirmed by mass spectrometry, is inaccessible within an amyloid structure. These data indicate decreased degradation due to amyloid formation initiates Aβ accumulation by preventing normal protease activity. Zn also prevented Aβ degradation by the proteases neprilysin and insulin degrading enzyme. Treating Zn-induced Aβ amyloid with the metal-protein attenuating compound clioquinol reversed amyloid formation and restored the peptide’s sensitivity to degradation by matrix metalloprotease 2. This provides new data indicating that therapeutic compounds designed to modulate Aβ-metal interactions can inhibit Aβ accumulation by restoring the catalytic potential of Aβ-degrading proteases. [ABSTRACT FROM AUTHOR]

Findings that antioxidant treatment may be beneficial in Alzheimer's disease indicate that oxidative stress is an important factor in its pathogenesis. Studies have also suggested that cholesterol imbalance in the brain might be related to the development of neurological disorders. Previously, we have reported that U18666A, a cholesterol transport-inhibiting agent, leads to apoptosis and intracellular cholesterol accumulation in primary cortical neurons. In this study, we found that neuronal apoptosis mediated by U18666A is associated with oxidative stress in the treated cortical neurons. Cortical neurons treated with U18666A also showed decreased secretion and increased intraneuronal accumulation of β-amyloid. The association of neuronal apoptosis with oxidative stress and Aβ accumulation may provide clues to the pathogenesis of Alzheimer's disease, as well as the role oxidative stress plays in other neurodegenerative diseases. [ABSTRACT FROM AUTHOR]

Transgenic mice carrying mutant Cu/Zn superoxide dismutase (SOD1) recapitulate the motor impairment of human amyotrophic lateral sclerosis (ALS). The amyloid-β (Aβ) peptide associated with Alzheimer's disease is neurotoxic. To investigate the potential role of Aβ in ALS development, we generated a double transgenic mouse line that overexpresses SOD1G93A and amyloid precursor protein (APP)-C100. The transgenic mouse C100.SOD1G93A overexpresses Aβ and shows earlier onset of motor impairment but has the same lifespan as the single transgenic SOD1G93A mouse. To determine the mechanism associated with this early-onset phenotype, we measured copper and zinc levels in brain and spinal cord and found both significantly elevated in the single and double transgenic mice compared with their littermate control mice. Increased glial fibrillary acidic protein and decreased APP levels in the spinal cord of C100.SOD1G93A mice compared with the SOD1G93A mice agree with the neuronal damage observed by immunohistochemical analysis. In the spinal cords of C100.SOD1G93A double transgenic mice, soluble Aβ was elevated in mice at end-stage disease compared with the pre-symptomatic stage. Buffer-insoluble SOD1 aggregates were significantly elevated in the pre-symptomatic mice of C100.SOD1G93A compared with the age-matched SOD1G93A mice, correlating with the earlier onset of motor impairment in the C100.SOD1G93A mice. This study supports abnormal SOD1 protein aggregation as the pathogenic mechanism in ALS, and implicates a potential role for Aβ in the development of ALS by exacerbating SOD1G93A aggregation. [ABSTRACT FROM AUTHOR]

Mounting evidence is demonstrating roles for the amyloid precursor protein (APP) and its proteolytic product Aβ in metal homeostasis. Furthermore, aberrant metal homeostasis is observed in patients with Alzheimer's disease (AD), and this may contribute to AD pathogenesis, by enhancing the formation of reactive oxygen species and toxic Aβ oligomers and facilitating the formation of the hallmark amyloid deposits in AD brain. Indeed, zinc released from synaptic activity has been shown to induce parenchymal and cerebrovascular amyloid in transgenic mice. On the other hand, abnormal metabolism of APP and Aβ may impair brain metal homeostasis as part of the AD pathogenic process. Aβ and APP expression have both been shown to decrease brain copper (Cu) levels, whereas increasing brain Cu availability results in decreased levels of Aβ and amyloid plaque formation in transgenic mice. Lowering Cu concentrations can downregulate the transcription of APP,strengthening the hypothesis that APP and Aβ form part of the Cu homeostatic machinery in the brain. This is a complex pathway, and it appears that when the sensitive metal balance in the brain is sufficiently disrupted, it can lead to the self-perpetuating pathogenesis of AD. Clinical trials are currently studying agents that can remedy abnormal Aβ–metal interactions. [ABSTRACT FROM AUTHOR]