Recent epidemiological studies show a strong reduction in the incidence of Alzheimer's disease in patients treated with cholesterol-lowering statins. Moreover, elevated A42 levels and the 4 allele of the lipid-carrier apolipoprotein E are regarded as risk factors for sporadic and familial Alzheimer's disease. Here we demonstrate that the widely used cholesterol-lowering drugs simvastatin and lovastatin reduce intracellular and extracellular levels of A42 and A40 peptides in primary cultures of hippocampal neurons and mixed cortical neurons. Likewise, guinea pigs treated with high doses of simvastatin showed a strong and reversible reduction of cerebral A42 and A40 levels in the cerebrospinal fluid and brain homogenate. These results suggest that lipids are playing an important role in the development of Alzheimer's disease. Lowered levels of A42 may provide the mechanism for the observed reduced incidence of dementia in statin-treated patients and may open up avenues for therapeutic interventions.A part from age, environmental factors have only slight influence on the incidence of Alzheimer's disease (AD). Very recently, two independent reports showed a strong decrease in the incidence of AD and dementia for patients that were treated with statins (1, 2). Both studies were retrospective, and statins were not given in any relation to dementia. Usually statins are prescribed for treatment of elevated serum cholesterol levels in patients. They reduce cholesterol levels by inhibiting the bottleneck enzyme of cholesterol synthesis, 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase. They are widely used drugs, well characterized and considered to be very safe for long-time treatment, and approved for use in elderly patients (3, 4).The 4 allele of the apolipoprotein E (apoE) is the major genetic risk factor for AD (5). Several lines of evidence indicate that apoE 4 and statins have a related influence on AD. The normal cellular function of apoE is uptake and delivery of lipids. The isoform apoE 4 correlates with an increased risk for atherosclerosis (6) and amyloid plaque formation (7). Moreover, elevated cholesterol uptake increases amyloid plaque formation or amyloid deposition (8,9). This correlation may be extended to A production, since cellular cholesterol levels affect neuronal A production in vitro (10). Initially, A has been a focus of AD research, because it was found to be the major constituent of the amyloid plaque. It is unknown whether the amyloid plaque is actively involved in the neurodegenerative process in AD or instead is a consequence of the disease process. More recently, however, A has been a focus of AD research not because of it presence in the amyloid plaque, but because an overproduction of a minor A isoform, A42, is linked to all identified inherited forms of AD (11-13).A is produced during normal cellular processing of the Alzheimer amyloid precursor protein (APP) (14) by -secretase and ␥-secretase (15). While the majority of all A isoforms produced is A40, Ϸ10% of total A ...
The major molecular risk factor for Alzheimer disease so far identified is the amyloidogenic peptide A 42 . In addition, growing evidence suggests a role of cholesterol in Alzheimer disease pathology and A generation. However, the cellular mechanism of lipid-dependent A production remains unclear. Here we describe that the two enzymatic activities responsible for A production, -secretase and ␥-secretase, are inhibited in parallel by cholesterol reduction. Importantly, our data indicate that cholesterol depletion within the cellular context inhibits both secretases additively and independently from each other. This is unexpected because the -secretase -site amyloid precursor protein cleaving enzyme and the presenilin-containing ␥-secretase complex are structurally different from each other, and these enzymes are apparently located in different subcellular compartments. The parallel and additive inhibition has obvious consequences for therapeutic research and may indicate an intrinsic cross-talk between Alzheimer disease-related amyloid precursor protein processing, amyloid precursor protein function, and lipid biology.A peptides are the main proteinaceous component of Alzheimer disease amyloid plaques. A is derived from posttranslational cleavage of the amyloid precursor protein (APP). Cleavage of APP by BACE I (1) at the N terminus of the A sequence generates a C-terminal fragment (C99) that includes the entire A sequence. In mouse cortical neurons BACE I is essential for APP -cleavage (2). A second proteolytic activity termed ␥-secretase cleaves APP at the C-terminal end of the A sequence, releasing A 40 and A 42 during normal cellular metabolism of APP (3, 4). A fraction of APP is processed by the ␣-secretase pathway in which APP is cleaved within the A region thus precluding A formation. However, neurons predominately use the -secretory pathway at the expense of the ␣-secretory pathway to process APP (5). Moreover, neurons produce significant amounts of intracellular A in vivo and in vitro (6 -8). A specific feature of ␥-secretase is that it is capable of cleaving APP only after a major part of the APP luminal domain is removed. Under normal circumstances it is therefore not possible to assay ␥-secretase activity directly.Analyses of APP-FAD mutations (9) as well as of PS-FAD mutations (10) have corroborated the assumption that a small increase in A 42 levels causes AD (11). The subcellular activities of both -and ␥-secretase have been extensively studied. Processing of APP to A differs for different intracellular compartments (12) and depends among others on the interaction of membrane composition and the APP transmembrane domain (13). Variable amounts of -secretase activity were found along the secretory pathway starting in the ER/intermediate compartment, post-Golgi vesicles, TGN, and endosomes (14, 15). In contrast, ␥-secretase activity was found to be prominent in the ER, TGN, and plasma membrane and to produce different A isoforms in different compartments (reviewed by Hartmann (...
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