Sub-lethal levels of amyloid β-peptide oligomers decrease non-transferrin-bound iron uptake and do not potentiate iron toxicity in primary hippocampal neurons

Abstract

Two major lesions are pathological hallmarks in Alzheimer's disease (AD): the presence of neurofibrillary tangles formed by intracellular aggregates of the hyperphosphorylated form of the cytoskeletal tau protein, and of senile plaques composed of extracellular aggregates of amyloid beta (Aβ) peptide. Current hypotheses regard soluble amyloid beta oligomers (AβOs) as pathological causative agents in AD. These aggregates cause significant calcium deregulation and mediate neurotoxicity by disrupting synaptic activity. Additionally, the presence of high concentrations of metal ions such as copper, zinc, aluminum and iron in neurofibrillary tangles and senile plaques, plus the fact that they accelerate the rate of formation of Aβ fibrils and AβOs in vitro, suggests that accumulation of these metals in the brain is relevant to AD pathology. A common cellular response to AβOs and transition metals such as copper and iron is the generation of oxidative stress, with the ensuing damage to cellular components. Using hippocampal neurons in primary culture, we report here the effects of treatment with AβOs on the (+)IRE and (-)IRE mRNA levels of the divalent metal transporter DMT1. We found that non-lethal AβOs concentrations decreased DMT1 (-)IRE without affecting DMT1 (+)IRE mRNA levels, and inhibited non-transferrin bound iron uptake. In addition, since both iron and AβOs induce oxidative damage, we studied whether their neurotoxic effects are synergistic. In the range of concentrations and times used in this study, AβOs did not potentiate iron-induced cell death while iron chelation did not decrease AβOs-induced cell death. The lack of synergism between iron and AβOs suggests that these two neurotoxic agents converge in a common target, which initiates signaling processes that promote neurodegeneration.

RyR2-Mediated Ca2+ Release and Mitochondrial ROS Generation Partake in the Synaptic Dysfunction Caused by Amyloid β Peptide Oligomers

“…We used the sub-lethal AβOs concentration of 500 nM, which is deleterious to neuronal function because it inhibits long term potentiation (Wang et al, 2002; Schlenzig et al, 2012) and produces aberrations in synapse composition, shape and density (Lacor et al, 2007). Furthermore, treatment with 500 nM AβOs increases reactive oxygen species (ROS) levels (De Felice et al, 2007; Lobos et al, 2016), decreases non-transferrin-bound iron uptake (SanMartín et al, 2012b) and induces differential gene expression (Sebollela et al, 2012). Addition of 500 nM AβOs increases cytoplasmic calcium in primary hippocampal (Paula-Lima et al, 2011) and cortical neurons (Ferreira et al, 2014) and cerebellar granule cells (Sanz-Blasco et al, 2008), and results in depolarization of mitochondrial membrane potential in primary cortical neurons (Ferreira et al, 2014) and cerebellar granule cells (Sanz-Blasco et al, 2008), among other effects.…”

“…The Aβ 1-42 peptide was prepared as previously described, as a HFIP film (De Felice et al, 2007; Paula-Lima et al, 2011; SanMartín et al, 2012a,b; Lobos et al, 2016). This film is dissolved next in DMSO to obtain a 5 mM stock solution, which is subsequently diluted with cold phosphate buffered saline (PBS) to 100 μM and incubated overnight at 4°C.…”

“…Eighteen-day-old embryos from Sprague-Dawley rats were used to obtain primary hippocampal cultures, as we previously described (Paula-Lima et al, 2005, 2011; SanMartín et al, 2012a,b, 2014, Lobos et al, 2016). Concisely, after meninges removal from brains, hippocampi were dissected and hippocampal cells were dissociated softly in HANKS-glucose solution.…”

A delicate balance: Iron metabolism and diseases of the brain

“…It was proposed by the authors that the observed iron change is due to the increased amount of Aβ (Wan et al, 2011), however, it can be alternatively explained by loss-of-APP function. Aβ oligomers were shown to decrease NTBI uptake, however, the disease relevance was unclear (SanMartin et al, 2012). Recently, tau protein was found to mediate APP trafficking, and reduction of tau blocked iron export, leading to intracellular iron accumulation (Lei et al, 2012).…”

Systematic review of potential health risks posed by pharmaceutical, occupational and consumer exposures to metallic and nanoscale aluminum, aluminum oxides, aluminum hydroxide and its soluble salts

“…Zinc +2 and Cu +2 accelerate amorphous Aβ aggregation whereas Al +3 and Fe +3 tend to promote Aβ fibril and oligomer formation (Kawahara 2005, Kawahara and Kato-Negishi 2011, Ricchelli et al 2005). SanMartín et al (2012) interpreted the elevated concentrations of Al, Cu, Fe, and Zn in human neurofibrillary tangles and senile plaques along with their in vitro acceleration of Aβ fibril and amyloid β oligomer formation as consequences of oxidative stress.…”