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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 daily treatment with Aβ1-40 on K+ and Ca2+ fluxes. After 6DIV, cortical neurons were treated daily with 1 μM Aβ1-40 for up to eight days. Net ion fluxes were recorded daily from monolayers of cells grown on glass cover slips treated with poly-L-lysine for cell adherence. Data was acquired non-invasively using the microelectrode MIFE technique. Steady-state fluxes of K+ (A) and Ca2+ (B) are shown for one, three, six, and eight day treatment with Aβ1-40. The sign convention is 'influx positive'. While K+ flux remained similar in control and cells treated with Aβ for one and three days, an increase in duration of the treatment to six days or longer led to a four-fold increase in K+ efflux from the neural cells (**P < 0.02). No difference in the levels of Ca2+ fluxes between control and Aβ treated cells was observed. Error bars are SEM (n = 4-7).
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Figure 2: Effect of daily treatment with Aβ1-40 on K+ and Ca2+ fluxes. After 6DIV, cortical neurons were treated daily with 1 μM Aβ1-40 for up to eight days. Net ion fluxes were recorded daily from monolayers of cells grown on glass cover slips treated with poly-L-lysine for cell adherence. Data was acquired non-invasively using the microelectrode MIFE technique. Steady-state fluxes of K+ (A) and Ca2+ (B) are shown for one, three, six, and eight day treatment with Aβ1-40. The sign convention is 'influx positive'. While K+ flux remained similar in control and cells treated with Aβ for one and three days, an increase in duration of the treatment to six days or longer led to a four-fold increase in K+ efflux from the neural cells (**P < 0.02). No difference in the levels of Ca2+ fluxes between control and Aβ treated cells was observed. Error bars are SEM (n = 4-7).

Mentions: Under physiological conditions neurons are continuously exposed to low doses of Aβ. To simulate those conditions we treated neurons with 1 μM Aβ over a prolonged period of time measuring ion fluxes of interest. Therefore, we investigated whether chronic treatment with soluble Aβ1-40 can affect the ability of cortical neurons to maintain Ca2+ homeostasis (Figure 2). We also tested whether K+ homeostasis would be affected by Aβ treatments since fluxes of this ion are pivotal to neuronal activity. No difference was observed in the level of Ca2+ fluxes between untreated cells, and cells treated with Aβ1-40 for up to eight days (Figure 2A). At the same time significant differences were observed in K+ fluxes (Figure 2B). While the K+ flux was similar in control cultures and those treated with Aβ1-40 for one and three days, treatment with a soluble monomeric Aβ1-40 (1 μM) daily for a period of six days or longer led to a significantly higher K+ efflux from the neural cells. Specifically, six and eight day Aβ treatment resulted in four- and three-fold increase in K+ efflux from the cells, respectively (P < 0.02)suggesting that chronic treatment with Aβ1-40 leads to a reduced capacity of neurons to maintain K+ homeostasis.


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 daily treatment with Aβ1-40 on K+ and Ca2+ fluxes. After 6DIV, cortical neurons were treated daily with 1 μM Aβ1-40 for up to eight days. Net ion fluxes were recorded daily from monolayers of cells grown on glass cover slips treated with poly-L-lysine for cell adherence. Data was acquired non-invasively using the microelectrode MIFE technique. Steady-state fluxes of K+ (A) and Ca2+ (B) are shown for one, three, six, and eight day treatment with Aβ1-40. The sign convention is 'influx positive'. While K+ flux remained similar in control and cells treated with Aβ for one and three days, an increase in duration of the treatment to six days or longer led to a four-fold increase in K+ efflux from the neural cells (**P < 0.02). No difference in the levels of Ca2+ fluxes between control and Aβ treated cells was observed. Error bars are SEM (n = 4-7).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: Effect of daily treatment with Aβ1-40 on K+ and Ca2+ fluxes. After 6DIV, cortical neurons were treated daily with 1 μM Aβ1-40 for up to eight days. Net ion fluxes were recorded daily from monolayers of cells grown on glass cover slips treated with poly-L-lysine for cell adherence. Data was acquired non-invasively using the microelectrode MIFE technique. Steady-state fluxes of K+ (A) and Ca2+ (B) are shown for one, three, six, and eight day treatment with Aβ1-40. The sign convention is 'influx positive'. While K+ flux remained similar in control and cells treated with Aβ for one and three days, an increase in duration of the treatment to six days or longer led to a four-fold increase in K+ efflux from the neural cells (**P < 0.02). No difference in the levels of Ca2+ fluxes between control and Aβ treated cells was observed. Error bars are SEM (n = 4-7).
Mentions: Under physiological conditions neurons are continuously exposed to low doses of Aβ. To simulate those conditions we treated neurons with 1 μM Aβ over a prolonged period of time measuring ion fluxes of interest. Therefore, we investigated whether chronic treatment with soluble Aβ1-40 can affect the ability of cortical neurons to maintain Ca2+ homeostasis (Figure 2). We also tested whether K+ homeostasis would be affected by Aβ treatments since fluxes of this ion are pivotal to neuronal activity. No difference was observed in the level of Ca2+ fluxes between untreated cells, and cells treated with Aβ1-40 for up to eight days (Figure 2A). At the same time significant differences were observed in K+ fluxes (Figure 2B). While the K+ flux was similar in control cultures and those treated with Aβ1-40 for one and three days, treatment with a soluble monomeric Aβ1-40 (1 μM) daily for a period of six days or longer led to a significantly higher K+ efflux from the neural cells. Specifically, six and eight day Aβ treatment resulted in four- and three-fold increase in K+ efflux from the cells, respectively (P < 0.02)suggesting that chronic treatment with Aβ1-40 leads to a reduced capacity of neurons to maintain K+ homeostasis.

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