Methionine 35 oxidation reduces toxic and pro-apoptotic effects of the amyloid β-protein fragment (31–35) on isolated brain mitochondria

Abstract

Amyloid β-peptide (AβP), the central constituent of senile plaques in Alzheimer's disease (AD) brain, has been shown to be a source of free radical oxidative stress that may lead to neurodegeneration. In particular, it is well known that oxidation of methionine 35, is strongly related to the pathogenesis of AD, since it represents the residue in AβP most susceptible to oxidation in vivo. In the present study, we used the fragment 31–35 of AβP, which has a single methionine at residue 35, in order to investigate the influence of the oxidation state of methionine-35 on the toxic and pro-apoptotic effects induced by Aβ(31–35) on isolated brain mitochondria. The obtained results show that exposure of isolated mitochondria from rat brain to AβP(31–35) determines (i) a large release of cytochrome c (ii) a significant reduction in mitochondrial respiration and (iii) a slight drop in the mitochondrial membrane potential (ΔΨ). In contrast, the amplitude of these events resulted attenuated or completely abrogated in isolated brain mitochondria exposed to the AβP(31–35)Met35 OX, in which methionine 35 was oxidized to methionine sulfoxide. We have further characterized the action of AβP(31–35) and Aβ(31–35)Met35 OX peptide on PC12 cells. Although these two peptides, compromised mitochondrial function at a different extent as assessed by MTT reduction, neither one of them decreased cell viability as measured by Trypan Blue exclusion assay. The results obtained in this study support the hypothesis that the oxidative state of Met-35 may play a critical role in the mechanisms responsible of neurotoxicity exerted by this peptide.