Reduction of Brain β-Amyloid (Aβ) by Fluvastatin, a Hydroxymethylglutaryl-CoA Reductase Inhibitor, through Increase in Degradation of Amyloid Precursor Protein C-terminal Fragments (APP-CTFs) and Aβ Clearance

Abstract

Epidemiological studies suggest that statins (hydroxymethylglutaryl-CoA reductase inhibitors) could reduce the risk of Alzheimer disease. Although one possible explanation is through an effect on ␤-amyloid (A␤) metabolism, its effect remains to be elucidated. Here, we explored the molecular mechanisms of how statins influence A␤ metabolism. Fluvastatin at clinical doses significantly reduced A␤ and amyloid precursor protein C-terminal fragment (APP-CTF) levels among APP metabolites in the brain of C57BL/6 mice. Chronic intracerebroventricular infusion of lysosomal inhibitors blocked these effects, indicating that up-regulation of the lysosomal degradation of endogenous APP-CTFs is involved in reduced A␤ production. Biochemical analysis suggested that this was mediated by enhanced trafficking of APP-CTFs from endosomes to lysosomes, associated with marked changes of Rab proteins, which regulate endosomal function. In primary neurons, fluvastatin enhanced the degradation of APP-CTFs through an isoprenoid-dependent mechanism. Because our previous study suggests additive effects of fluvastatin on A␤ metabolism, we examined A␤ clearance rates by using the brain efflux index method and found its increased rates at high A␤ levels from brain. As LRP1 in brain microvessels was increased, up-regulation of LRP1-mediated A␤ clearance at the blood-brain barrier might be involved. In cultured brain microvessel endothelial cells, fluvastatin increased LRP1 and the uptake of A␤, which was blocked by LRP1 antagonists, through an isoprenoid-dependent mechanism. Overall, the present study demonstrated that fluvastatin reduced A␤ level by an isoprenoid-dependent mechanism. These results have important implications for the development of disease-modifying therapy for Alzheimer disease as well as understanding of A␤ metabolism. Alzheimer disease (AD)2 is a progressive neurodegenerative disease, being the most prevalent disorder among dementia. The discoveries that the genes of familial AD-linked mutation up-regulate A␤ production and the increased rate of A␤42 production is associated with the age of onset provide conclusive evidence for the amyloid hypothesis in the pathogenesis of AD (1). Several therapies based on the amyloid hypothesis are being examined, including ␥-secretase inhibitors and A␤ vaccine therapy, as disease-modifying therapy. However, there are still many unresolved issues with their clinical application (2, 3). Furthermore, recent failures of clinical trials of these therapies raise questions on delayed timing of intervention and the efficacy of targeting only one pathway of A␤ metabolism (4, 5). More efficient treatment with higher safety is needed to treat AD.On the other hand, from basic and clinical reports, statins (hydroxymethylglutaryl-CoA reductase inhibitors), which are widely used for the treatment of hypercholesterolemic patients, might be beneficial in AD. Clinically, many case control studies support the protective effect of statins (6 -8), whereas the results of prospective studies and randomized cli...

Reduction of A by fluvastatin associates with altered levels of APP and of BACE1 and ADAM10 mRNA, independent of brain total cholesterol in rats

“…Studies have shown fluvastatin unable to cross BBB (Guillot et al, 1993) but effective in protecting BBB integrity (Kuhlmann et al, 2008) in nontransgenic mice. Consistent with these results, it was reported that fluvastatin decreased endogenous A levels through an increase in A clearance at BBB in nontransgenic mice (Shinohara et al, 2010). In addition, thus far, there was no report that fluvastatin reduces brain cholesterol levels.…”

“…However, it is still unclear by which mechanism fluvastatin regulated the expression of A PP and A PP-cleaving enzymes, ultimately resulted in the reduction of brain A levels without entering into the brain. It was reported that fluvastatin decreased endogenous A levels through an increase in A clearance at BBB in nontransgenic mice (Shinohara et al, 2010). Besides, reduction of NO levels by inhibiting the enzyme catalyzed NO biosynthesis, endothelial nitric oxide synthase (eNOS), or by knocking eNOS gene out led to increased A PP and BACE1 protein levels, as well as increased secretion of A in brain microvascular endothelial cells (Austin et al, 2010).…”

“…Although there are two types of statins, lipophilic ones able to pass through BBB and hydrophilic ones which are not, the epidemiological studies showed both kinds of statins no difference in AD risk-reduction (Wolozin et al, 2000;Rockwood and Darvesh, 2003). Lipophilic simvastatin and lovastatin, and hydrophilic atorvastatin and fluvastatin were all reported to reduce endogenous A in brain of nontransgenic mice (Burns et al, 2006;Shinohara et al, 2010) as occurred in the brain of AD patients. Despite the recognized role for statins in A reduction, the accurate mechanisms are still not completely understood.…”

Análise da expressão das proteínas Rab anterior à agregação proteica associada a neurodegeneração

“…A produção de beta-amiloide pode acontecer em uma ampla gama de compartimentos celulares como na superfície celular, rede trans-Golgi e nos endossomos (De Strooper, 2000), bem como pode ser consequência de um processo inflamatório característico da doença de Alzheimer, com a participação da prostaglandina E2 e seu receptor EP4 (Shinohara et al, 2010).…”

“…Logo o processo inflamatório favorece a formação de beta-amiloide, mas na presença de Rab 5 esse quadro é revertido nos neurônios (Shinohara et al, 2010), pois a prostaglandina é inibida, diminuindo a atividade da gamasecretase, e consequentemente a produção de beta-amiloide (Hoshino et al, 2009). Nesse trabalho os níveis de Rab 5 parecem não favorecer a possível recaptura da beta-amiloide, e ao mesmo tempo esses baixos níveis podem contribuir para produção do peptídeo beta-amiloide intracelularmente, além de também contribuírem para prejudicar a manutenção de endossomos gerais que estão ligados a outras funções neuronais como reciclagem de vesículas sinápticas Postula-se a hipótese de que as vesículas sinápticas devem sofrer um processo de maturação para tornarem-se funcionais no terminal sináptico (Bonanomi et al, 2006).…”