Prolonged Aβ treatment leads to impairment in the ability of primary cortical neurons to maintain K+ and Ca2+ homeostasis

Abstract

BackgroundAlzheimer's disease (AD) is a progressive neurodegenerative disease, characterised by the formation of insoluble amyloidogenic plaques and neurofibrillary tangles. Beta amyloid (Aβ) peptide is one of the main constituents in Aβ plaques, and is thought to be a primary causative agent in AD. Neurons are likely to be exposed to chronic, sublethal doses of Aβ over an extended time during the pathogenesis of AD, however most studies published to date using in vitro models have focussed on acute studies. To experimentally model the progressive pathogenesis of AD, we exposed primary cortical neurons daily to 1 μM of Aβ1-40 over 7 days and compared their survival with age-similar untreated cells. We also investigated whether chronic Aβ exposure affects neuronal susceptibility to the subsequent acute excitotoxicity induced by 10 μM glutamate and assessed how Ca2+ and K+ homeostasis were affected by either treatment.ResultsWe show that continuous exposure to 1 μM Aβ1-40 for seven days decreased survival of cultured cortical neurons by 20%. This decrease in survival correlated with increased K+ efflux from the cells. One day treatment with 1 μM Aβ followed by glutamate led to a substantially higher K+ efflux than in the age-similar untreated control. This difference further increased with the duration of the treatment. K+ efflux also remained higher in Aβ treated cells 20 min after glutamate application leading to 2.8-fold higher total K+ effluxed from the cells compared to controls. Ca2+ uptake was significantly higher only after prolonged Aβ treatment with 2.5-fold increase in total Ca2+ uptake over 20 min post glutamate application after six days of Aβ treatment or longer (P < 0.05).ConclusionsOur data suggest that long term exposure to Aβ is detrimental because it reduces the ability of cortical neurons to maintain K+ and Ca2+ homeostasis in response to glutamate challenge, a response that might underlie the early symptoms of AD. The observed inability to maintain K+ homeostasis might furthermore be useful in future studies as an early indicator of pathological changes in response to Aβ.

G-Protein-Coupled Inwardly Rectifying Potassium (GIRK) Channel Activation by the p75 Neurotrophin Receptor Is Required for Amyloid β Toxicity

“…Although, it is possible that the baclofen treatment masked the toxic effect of Aβ by an unrelated mechanism, taken together with our other data, the correlation between baclofen-induced down-regulation of GIRK channel activity and reduced Aβ-toxicity is consistent with a causal relationship. Potassium dysregulation is a feature of Alzheimer's disease brain tissue (Roberts et al, 2016 ), and similar to our findings, others have shown that potassium efflux from cortical neurons can be promoted by Aβ, and that this efflux is required to cause subsequent degeneration, although the mechanism remains unclear (Yu et al, 1998 ; Shabala et al, 2010 ). Our data indicate that Aβ 42 treatment causes sufficient potassium to leave the cell to reduce the intracellular potassium concentration to approximately half (80 mM), which in turn is permissive for the apoptosome to assemble and caspases to be activated, a finding that is consistent with previous reports (Cain et al, 2001 ; Coulson et al, 2008 ).…”

The role of choroid plexus in IVIG-induced beta-amyloid clearance

“…This dose regimen was shown to produce a significant accumulation of Aβ in Z310 cells in our previous studies (Behl et al, 2009a, Behl et al, 2009b) and in vitro toxicity studies (Shabala et al, 2010). Aβ concentrations in outer chamber were gradually increased from 0 into 0.28±0.06 ng/ml at 1 hr and 4.2±0.96 ng/ml at 3 hrs following treatments.…”

Electroacupuncture at Governor Vessel improves neurobehavioral function via reduction of complexin1

“…Complete experimental procedure of microelectrode ion flux estimation (MIFF) has been processed by a modified procedures according to the previously reports (Shabala et al, 2010). Cortical neurons for the MIFE detections were cultured for 6 days at 5× 10 5 cells/well on coverslips coated with poly-L-lysine.…”