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

Shabala L, Howells C, West AK, Chung RS - Mol Neurodegener (2010)

Bottom Line: This decrease in survival correlated with increased K+ efflux from the cells.Ca2+ uptake was significantly higher only after prolonged Abeta treatment with 2.5-fold increase in total Ca2+ uptake over 20 min post glutamate application after six days of Abeta treatment or longer (P < 0.05).Our data suggest that long term exposure to Abeta 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.

View Article: PubMed Central - HTML - PubMed

Affiliation: NeuroRepair Group, Menzies Research Institute, University of Tasmania, Private Bag 23, Hobart, Tasmania, 7001, Australia. L.Shabala@utas.edu.au.

ABSTRACT

Background: Alzheimer's disease (AD) is a progressive neurodegenerative disease, characterised by the formation of insoluble amyloidogenic plaques and neurofibrillary tangles. Beta amyloid (Abeta) peptide is one of the main constituents in Abeta plaques, and is thought to be a primary causative agent in AD. Neurons are likely to be exposed to chronic, sublethal doses of Abeta 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 muM of Abeta1-40 over 7 days and compared their survival with age-similar untreated cells. We also investigated whether chronic Abeta exposure affects neuronal susceptibility to the subsequent acute excitotoxicity induced by 10 muM glutamate and assessed how Ca2+ and K+ homeostasis were affected by either treatment.

Results: We show that continuous exposure to 1 muM Abeta1-40 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 muM Abeta 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 Abeta 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 Abeta treatment with 2.5-fold increase in total Ca2+ uptake over 20 min post glutamate application after six days of Abeta treatment or longer (P < 0.05).

Conclusions: Our data suggest that long term exposure to Abeta 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 Abeta.

No MeSH data available.


Related in: MedlinePlus

Effect of glutamate application on K+ fluxes. Glutamate (10 μM) was applied to cortical neurons following daily treatment with 1 μM Aβ1-40, and to age-matched un-treated control cells. Peak values of K+ fluxes (A) and steady-state K+ fluxes recorded 20 min after glutamate application (B) are shown for one, three, six, and eight days of treatment with Aβ. Peak K+ efflux was substantially (1.6-fold) higher after one day of treatment with soluble Aβ1-40 than in age-similar control cells and further increased to 5.7-fold difference after six days of treatment. The capacity of cortical neurons to retain K+ flux at pre-stress levels after glutamate challenge was assessed by comparing steady-state values of K+ fluxes 20 min post-treatment. K+ efflux in Aβ treated cells was significantly higher than in age-similar controls after treatment with Aβ suggesting that Aβ accumulation by neurons reduces their ability to maintain K+ homeostasis. * - P < 0.05, ** - P < 0.02, t-test. Error bars represent SEM (n = 4-7).
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Figure 6: Effect of glutamate application on K+ fluxes. Glutamate (10 μM) was applied to cortical neurons following daily treatment with 1 μM Aβ1-40, and to age-matched un-treated control cells. Peak values of K+ fluxes (A) and steady-state K+ fluxes recorded 20 min after glutamate application (B) are shown for one, three, six, and eight days of treatment with Aβ. Peak K+ efflux was substantially (1.6-fold) higher after one day of treatment with soluble Aβ1-40 than in age-similar control cells and further increased to 5.7-fold difference after six days of treatment. The capacity of cortical neurons to retain K+ flux at pre-stress levels after glutamate challenge was assessed by comparing steady-state values of K+ fluxes 20 min post-treatment. K+ efflux in Aβ treated cells was significantly higher than in age-similar controls after treatment with Aβ suggesting that Aβ accumulation by neurons reduces their ability to maintain K+ homeostasis. * - P < 0.05, ** - P < 0.02, t-test. Error bars represent SEM (n = 4-7).

Mentions: Acute treatment of cortical neurons with 10 μM glutamate led to a dramatic K+ efflux from neurons that returned to pre-stress conditions within 20 min after the challenge (Figures 4A, B). Notably, the magnitude of K+ efflux was higher in cells treated with Aβ for six days or longer (peak values in the graphs). We therefore compared the magnitudes of the peak K+ efflux from neurons treated with Aβ with age-similar controls and found that K+ efflux was substantially (1.6-fold) higher even after one day of treatment with soluble Aβ1-40 (Figure 6A). This difference was more pronounced with increase of duration of the treatment with Aβ leading to more than 3.5-fold increase in the peak K+ efflux after six and eight days of treatment with soluble monomeric Aβ1-40 (1 μM), (Figure 6A).


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

Shabala L, Howells C, West AK, Chung RS - Mol Neurodegener (2010)

Effect of glutamate application on K+ fluxes. Glutamate (10 μM) was applied to cortical neurons following daily treatment with 1 μM Aβ1-40, and to age-matched un-treated control cells. Peak values of K+ fluxes (A) and steady-state K+ fluxes recorded 20 min after glutamate application (B) are shown for one, three, six, and eight days of treatment with Aβ. Peak K+ efflux was substantially (1.6-fold) higher after one day of treatment with soluble Aβ1-40 than in age-similar control cells and further increased to 5.7-fold difference after six days of treatment. The capacity of cortical neurons to retain K+ flux at pre-stress levels after glutamate challenge was assessed by comparing steady-state values of K+ fluxes 20 min post-treatment. K+ efflux in Aβ treated cells was significantly higher than in age-similar controls after treatment with Aβ suggesting that Aβ accumulation by neurons reduces their ability to maintain K+ homeostasis. * - P < 0.05, ** - P < 0.02, t-test. Error bars represent SEM (n = 4-7).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC2927593&req=5

Figure 6: Effect of glutamate application on K+ fluxes. Glutamate (10 μM) was applied to cortical neurons following daily treatment with 1 μM Aβ1-40, and to age-matched un-treated control cells. Peak values of K+ fluxes (A) and steady-state K+ fluxes recorded 20 min after glutamate application (B) are shown for one, three, six, and eight days of treatment with Aβ. Peak K+ efflux was substantially (1.6-fold) higher after one day of treatment with soluble Aβ1-40 than in age-similar control cells and further increased to 5.7-fold difference after six days of treatment. The capacity of cortical neurons to retain K+ flux at pre-stress levels after glutamate challenge was assessed by comparing steady-state values of K+ fluxes 20 min post-treatment. K+ efflux in Aβ treated cells was significantly higher than in age-similar controls after treatment with Aβ suggesting that Aβ accumulation by neurons reduces their ability to maintain K+ homeostasis. * - P < 0.05, ** - P < 0.02, t-test. Error bars represent SEM (n = 4-7).
Mentions: Acute treatment of cortical neurons with 10 μM glutamate led to a dramatic K+ efflux from neurons that returned to pre-stress conditions within 20 min after the challenge (Figures 4A, B). Notably, the magnitude of K+ efflux was higher in cells treated with Aβ for six days or longer (peak values in the graphs). We therefore compared the magnitudes of the peak K+ efflux from neurons treated with Aβ with age-similar controls and found that K+ efflux was substantially (1.6-fold) higher even after one day of treatment with soluble Aβ1-40 (Figure 6A). This difference was more pronounced with increase of duration of the treatment with Aβ leading to more than 3.5-fold increase in the peak K+ efflux after six and eight days of treatment with soluble monomeric Aβ1-40 (1 μM), (Figure 6A).

Bottom Line: This decrease in survival correlated with increased K+ efflux from the cells.Ca2+ uptake was significantly higher only after prolonged Abeta treatment with 2.5-fold increase in total Ca2+ uptake over 20 min post glutamate application after six days of Abeta treatment or longer (P < 0.05).Our data suggest that long term exposure to Abeta 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.

View Article: PubMed Central - HTML - PubMed

Affiliation: NeuroRepair Group, Menzies Research Institute, University of Tasmania, Private Bag 23, Hobart, Tasmania, 7001, Australia. L.Shabala@utas.edu.au.

ABSTRACT

Background: Alzheimer's disease (AD) is a progressive neurodegenerative disease, characterised by the formation of insoluble amyloidogenic plaques and neurofibrillary tangles. Beta amyloid (Abeta) peptide is one of the main constituents in Abeta plaques, and is thought to be a primary causative agent in AD. Neurons are likely to be exposed to chronic, sublethal doses of Abeta 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 muM of Abeta1-40 over 7 days and compared their survival with age-similar untreated cells. We also investigated whether chronic Abeta exposure affects neuronal susceptibility to the subsequent acute excitotoxicity induced by 10 muM glutamate and assessed how Ca2+ and K+ homeostasis were affected by either treatment.

Results: We show that continuous exposure to 1 muM Abeta1-40 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 muM Abeta 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 Abeta 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 Abeta treatment with 2.5-fold increase in total Ca2+ uptake over 20 min post glutamate application after six days of Abeta treatment or longer (P < 0.05).

Conclusions: Our data suggest that long term exposure to Abeta 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 Abeta.

No MeSH data available.


Related in: MedlinePlus