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Entorhinal Cortex dysfunction can be rescued by inhibition of microglial RAGE in an Alzheimer ’ s disease mouse model

View Article: PubMed Central - PubMed

ABSTRACT

The Entorhinal cortex (EC) has been implicated in the early stages of Alzheimer’s disease (AD). In particular, spreading of neuronal dysfunction within the EC-Hippocampal network has been suggested. We have investigated the time course of EC dysfunction in the AD mouse model carrying human mutation of amyloid precursor protein (mhAPP) expressing human Aβ. We found that in mhAPP mice plasticity impairment is first observed in EC superficial layer and further affected with time. A selective impairment of LTP was observed in layer II horizontal connections of EC slices from 2 month old mhAPP mice, whereas at later stage of neurodegeneration (6 month) basal synaptic transmission and LTD were also affected. Accordingly, early synaptic deficit in the mhAPP mice were associated with a selective impairment in EC-dependent associative memory tasks. The introduction of the dominant-negative form of RAGE lacking RAGE signalling targeted to microglia (DNMSR) in mhAPP mice prevented synaptic and behavioural deficit, reducing the activation of stress related kinases (p38MAPK and JNK). Our results support the involvement of the EC in the development and progression of the synaptic and behavioural deficit during amyloid-dependent neurodegeneration and demonstrate that microglial RAGE activation in presence of Aβ-enriched environment contributes to the EC vulnerability.

No MeSH data available.


Related in: MedlinePlus

Inhibition of microglial RAGE prevents EC synaptic impairment in mhAPP mice at different stages of neurodegeneration.In 2 month old mice (A) deficiency of RAGE did not alter LTP expression in DNMSR EC slices (grey circles) and was sufficient to prevent LTP impairment in double mhAPPxDNMSR transgenic EC slices (open circles), with respect to single mhAPP transgenic slices (black diamonds); insert shows representative FPs recorded during baseline (a) or after HFS stimulation (b). The protective effect provided by RAGE signaling inhibition was confirmed in older animals (6 months of age); in (B) the LTP was normally expressed in either DNMSR (grey circles) or mhAPPxDNMSR slices (open circles) with respect to mhAPP slices (black diamonds); insert shows representative FPs recorded during baseline (a) or after HFS stimulation (b). Similarly, LTD was inducible by LFS in EC slices from 6 month old DNMSR (grey circles) and mhAPPxDNMSR (open circles) mice with respect to slices from age-matched mhAPP mice (black diamonds); insert shows representative FPs recorded during baseline (a) or after LFS stimulation (b). In (A–C) scale bars correspond to 0.5 mV and 5 ms. Error bars indicate SEM.
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f3: Inhibition of microglial RAGE prevents EC synaptic impairment in mhAPP mice at different stages of neurodegeneration.In 2 month old mice (A) deficiency of RAGE did not alter LTP expression in DNMSR EC slices (grey circles) and was sufficient to prevent LTP impairment in double mhAPPxDNMSR transgenic EC slices (open circles), with respect to single mhAPP transgenic slices (black diamonds); insert shows representative FPs recorded during baseline (a) or after HFS stimulation (b). The protective effect provided by RAGE signaling inhibition was confirmed in older animals (6 months of age); in (B) the LTP was normally expressed in either DNMSR (grey circles) or mhAPPxDNMSR slices (open circles) with respect to mhAPP slices (black diamonds); insert shows representative FPs recorded during baseline (a) or after HFS stimulation (b). Similarly, LTD was inducible by LFS in EC slices from 6 month old DNMSR (grey circles) and mhAPPxDNMSR (open circles) mice with respect to slices from age-matched mhAPP mice (black diamonds); insert shows representative FPs recorded during baseline (a) or after LFS stimulation (b). In (A–C) scale bars correspond to 0.5 mV and 5 ms. Error bars indicate SEM.

Mentions: Activation of RAGE in neurons was involved in synaptic dysfunction induced by exogenous application of Aβ in the EC2425; in particular increasing synthetic Aβ concentration up to a micromolar level induces RAGE activation in microglial cells that progressively affects basal synaptic transmission and LTD, in addition to LTP24. These results prompted us to verify the hypothesis that inhibition of RAGE signalling in microglia would represent the best strategy to prevent the synaptic effects of Aβ accumulation in mhAPP mice. First, we recorded EC slices prepared from either DNMSR or double transgenic mhAPPxDNMSR 2 month old mice. As previously reported, deficiency of RAGE in microglia does not affect basal synaptic transmission and LTD in EC slices24. As reported in Fig. 3A, LTP induction and maintenance were also not affected in DNMSR slices (139 ± 12% of baseline, mice n = 4; slices n = 8; p < 0.05 vs. baseline) and were comparable to WT controls. Remarkably, deficiency of RAGE in microglia was able to prevent synaptic plasticity impairment induced by mutant APP overexpression. The mean LTP in slices from mhAPPxDNMSR mice was significantly higher respect to slices from single mhAPP transgenic mice (130 ± 5%, mice n = 4, slices n = 6, vs. 99 ± 6% of baseline mice n = 3, slices n = 6 respectively, p < 0.001; Fig. 3A) and was comparable to that recorded in slices from DNMSR mice (p = 0.716). As reported above at a later stage of neurodegeneration, corresponding to 6 months of age, synaptic impairment in mhAPP slices involved basic synaptic transmission and LTD expression. According to what reported in younger animals, no significant differences were found in synaptic transmission between DNMSR and WT slices obtained from 6 month old mice (Supplemental Fig. S2); in addition HFS was capable of inducing a stable LTP in DNMSR slices (138 ± 7% of baseline ampl., mice n = 4, slices n = 6, p < 0.001 vs. baseline; Fig. 3B). More importantly, at this later stage, deficiency of RAGE in microglia rescued basal synaptic transmission (Supplemental Fig. S2) and LTP expression in double transgenic mhAPPxDNMSR slices compared to single mhAPP slices (137 ± 11%, mice n = 3, slices n = 6, vs. 97 ± 3% of baseline mice n = 3, slices n = 6 respectively, p < 0.05; Fig. 3B). Moreover, RAGE signalling inhibition protected mhAPP slices from LTD impairment. According to what reported above, LTD was completely abolished in 6 month old mhAPP slices (100 ± 7%, mice n = 3, slices n = 6; p = 0.160 vs. baseline; Fig. 3C); in contrast, after LFS stimulation a statistically significant LTD was induced in mhAPPxDNMSR slices (76 ± 8%, mice n = 3, slices n = 6; p < 0.001 vs. baseline; Fig. 3C) that was comparable to that obtained in either DNMSR (78 ± 6%, mice n = 3, slices n = 6; p < 0.001 vs. baseline; p = 0.359 vs. mhAPPxDNMSR; Fig. 3C) or WT controls slices (80 ± 5% of baseline, mice n = 4; slices n = 7; Fig. 2C; p = 0.294 vs. mhAPPxDNMSR). Therefore, microglial RAGE activation in presence of APP overexpression is relevant to induce progressive synaptic alteration in the EC superficial Layer II.


Entorhinal Cortex dysfunction can be rescued by inhibition of microglial RAGE in an Alzheimer ’ s disease mouse model
Inhibition of microglial RAGE prevents EC synaptic impairment in mhAPP mice at different stages of neurodegeneration.In 2 month old mice (A) deficiency of RAGE did not alter LTP expression in DNMSR EC slices (grey circles) and was sufficient to prevent LTP impairment in double mhAPPxDNMSR transgenic EC slices (open circles), with respect to single mhAPP transgenic slices (black diamonds); insert shows representative FPs recorded during baseline (a) or after HFS stimulation (b). The protective effect provided by RAGE signaling inhibition was confirmed in older animals (6 months of age); in (B) the LTP was normally expressed in either DNMSR (grey circles) or mhAPPxDNMSR slices (open circles) with respect to mhAPP slices (black diamonds); insert shows representative FPs recorded during baseline (a) or after HFS stimulation (b). Similarly, LTD was inducible by LFS in EC slices from 6 month old DNMSR (grey circles) and mhAPPxDNMSR (open circles) mice with respect to slices from age-matched mhAPP mice (black diamonds); insert shows representative FPs recorded during baseline (a) or after LFS stimulation (b). In (A–C) scale bars correspond to 0.5 mV and 5 ms. Error bars indicate SEM.
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f3: Inhibition of microglial RAGE prevents EC synaptic impairment in mhAPP mice at different stages of neurodegeneration.In 2 month old mice (A) deficiency of RAGE did not alter LTP expression in DNMSR EC slices (grey circles) and was sufficient to prevent LTP impairment in double mhAPPxDNMSR transgenic EC slices (open circles), with respect to single mhAPP transgenic slices (black diamonds); insert shows representative FPs recorded during baseline (a) or after HFS stimulation (b). The protective effect provided by RAGE signaling inhibition was confirmed in older animals (6 months of age); in (B) the LTP was normally expressed in either DNMSR (grey circles) or mhAPPxDNMSR slices (open circles) with respect to mhAPP slices (black diamonds); insert shows representative FPs recorded during baseline (a) or after HFS stimulation (b). Similarly, LTD was inducible by LFS in EC slices from 6 month old DNMSR (grey circles) and mhAPPxDNMSR (open circles) mice with respect to slices from age-matched mhAPP mice (black diamonds); insert shows representative FPs recorded during baseline (a) or after LFS stimulation (b). In (A–C) scale bars correspond to 0.5 mV and 5 ms. Error bars indicate SEM.
Mentions: Activation of RAGE in neurons was involved in synaptic dysfunction induced by exogenous application of Aβ in the EC2425; in particular increasing synthetic Aβ concentration up to a micromolar level induces RAGE activation in microglial cells that progressively affects basal synaptic transmission and LTD, in addition to LTP24. These results prompted us to verify the hypothesis that inhibition of RAGE signalling in microglia would represent the best strategy to prevent the synaptic effects of Aβ accumulation in mhAPP mice. First, we recorded EC slices prepared from either DNMSR or double transgenic mhAPPxDNMSR 2 month old mice. As previously reported, deficiency of RAGE in microglia does not affect basal synaptic transmission and LTD in EC slices24. As reported in Fig. 3A, LTP induction and maintenance were also not affected in DNMSR slices (139 ± 12% of baseline, mice n = 4; slices n = 8; p < 0.05 vs. baseline) and were comparable to WT controls. Remarkably, deficiency of RAGE in microglia was able to prevent synaptic plasticity impairment induced by mutant APP overexpression. The mean LTP in slices from mhAPPxDNMSR mice was significantly higher respect to slices from single mhAPP transgenic mice (130 ± 5%, mice n = 4, slices n = 6, vs. 99 ± 6% of baseline mice n = 3, slices n = 6 respectively, p < 0.001; Fig. 3A) and was comparable to that recorded in slices from DNMSR mice (p = 0.716). As reported above at a later stage of neurodegeneration, corresponding to 6 months of age, synaptic impairment in mhAPP slices involved basic synaptic transmission and LTD expression. According to what reported in younger animals, no significant differences were found in synaptic transmission between DNMSR and WT slices obtained from 6 month old mice (Supplemental Fig. S2); in addition HFS was capable of inducing a stable LTP in DNMSR slices (138 ± 7% of baseline ampl., mice n = 4, slices n = 6, p < 0.001 vs. baseline; Fig. 3B). More importantly, at this later stage, deficiency of RAGE in microglia rescued basal synaptic transmission (Supplemental Fig. S2) and LTP expression in double transgenic mhAPPxDNMSR slices compared to single mhAPP slices (137 ± 11%, mice n = 3, slices n = 6, vs. 97 ± 3% of baseline mice n = 3, slices n = 6 respectively, p < 0.05; Fig. 3B). Moreover, RAGE signalling inhibition protected mhAPP slices from LTD impairment. According to what reported above, LTD was completely abolished in 6 month old mhAPP slices (100 ± 7%, mice n = 3, slices n = 6; p = 0.160 vs. baseline; Fig. 3C); in contrast, after LFS stimulation a statistically significant LTD was induced in mhAPPxDNMSR slices (76 ± 8%, mice n = 3, slices n = 6; p < 0.001 vs. baseline; Fig. 3C) that was comparable to that obtained in either DNMSR (78 ± 6%, mice n = 3, slices n = 6; p < 0.001 vs. baseline; p = 0.359 vs. mhAPPxDNMSR; Fig. 3C) or WT controls slices (80 ± 5% of baseline, mice n = 4; slices n = 7; Fig. 2C; p = 0.294 vs. mhAPPxDNMSR). Therefore, microglial RAGE activation in presence of APP overexpression is relevant to induce progressive synaptic alteration in the EC superficial Layer II.

View Article: PubMed Central - PubMed

ABSTRACT

The Entorhinal cortex (EC) has been implicated in the early stages of Alzheimer&rsquo;s disease (AD). In particular, spreading of neuronal dysfunction within the EC-Hippocampal network has been suggested. We have investigated the time course of EC dysfunction in the AD mouse model carrying human mutation of amyloid precursor protein (mhAPP) expressing human A&beta;. We found that in mhAPP mice plasticity impairment is first observed in EC superficial layer and further affected with time. A selective impairment of LTP was observed in layer II horizontal connections of EC slices from 2 month old mhAPP mice, whereas at later stage of neurodegeneration (6 month) basal synaptic transmission and LTD were also affected. Accordingly, early synaptic deficit in the mhAPP mice were associated with a selective impairment in EC-dependent associative memory tasks. The introduction of the dominant-negative form of RAGE lacking RAGE signalling targeted to microglia (DNMSR) in mhAPP mice prevented synaptic and behavioural deficit, reducing the activation of stress related kinases (p38MAPK and JNK). Our results support the involvement of the EC in the development and progression of the synaptic and behavioural deficit during amyloid-dependent neurodegeneration and demonstrate that microglial RAGE activation in presence of A&beta;-enriched environment contributes to the EC vulnerability.

No MeSH data available.


Related in: MedlinePlus