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Absence of amyloid β oligomers at the postsynapse and regulated synaptic Zn2+ in cognitively intact aged individuals with Alzheimer's disease neuropathology.

Bjorklund NL, Reese LC, Sadagoparamanujam VM, Ghirardi V, Woltjer RL, Taglialatela G - Mol Neurodegener (2012)

Bottom Line: Early cognitive impairment in Alzheimer Disease (AD) is thought to result from the dysfunctional effect of amyloid beta (Aβ) oligomers targeting the synapses.Notably, however, we also found that while present in soluble fractions, Aβ oligomers are absent from hippocampal postsynapses in NDAN cases.Taken together, these data illustrate that despite substantial AD neuropathology, Aβ oligomers, and increased synaptic vesicle Zn2+, susceptible brain tissue in these aged NDAN individuals features, as compared to symptomatic AD subjects, significantly lower total Zn2+ levels and no association of Aβ oligomers with the postsynapse, which collectively may promote the maintenance of intact cognitive function.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Neuroscience and Cell Biology, Galveston, TX 77555, USA.

ABSTRACT

Background: Early cognitive impairment in Alzheimer Disease (AD) is thought to result from the dysfunctional effect of amyloid beta (Aβ) oligomers targeting the synapses. Some individuals, however, escape cognitive decline despite the presence of the neuropathologic features of AD (Aβ plaques and neurofibrillary tangles). We term this group Non-Demented with AD Neuropathology or NDAN. The present study illustrates one putative resistance mechanism involved in NDAN cases which may suggest targets for the effective treatment of AD.

Results: Here we describe the localization of Aβ oligomers at the postsynapse in hippocampi from AD cases. Notably, however, we also found that while present in soluble fractions, Aβ oligomers are absent from hippocampal postsynapses in NDAN cases. In addition, levels of phosphorylated (active) CREB, a transcription factor important for synaptic plasticity, are normal in NDAN individuals, suggesting that their synapses are functionally intact. Analysis of Zn2+ showed that levels were increased in both soluble fractions and synaptic vesicles in AD hippocampi, paralleled by a decrease of expression of the synaptic vesicle Zn2+ transporter, ZnT3. Conversely, in NDAN individuals, levels of Zn2+ in soluble fractions were significantly lower than in AD, whereas in synaptic vesicles the levels of Zn2+ were similar to AD, but accompanied by preserved expression of the ZnT3.

Conclusions: Taken together, these data illustrate that despite substantial AD neuropathology, Aβ oligomers, and increased synaptic vesicle Zn2+, susceptible brain tissue in these aged NDAN individuals features, as compared to symptomatic AD subjects, significantly lower total Zn2+ levels and no association of Aβ oligomers with the postsynapse, which collectively may promote the maintenance of intact cognitive function.

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Synaptic fractionation demonstrates that low molecular weight Aβ oligomers associate with the PSD in AD but not NDAN hippocampal specimens. (A) PSD95, a postsynaptic marker, and synaptophysin (Synphys), a presynaptic marker, were probed in the total homogenate (Hom), synaptosomal (Syn), synaptic vesicles (SV), and postsynaptic density (PSD) fractions isolated from a frozen human hippocampal specimen from a control, non-demented aged individual. Enrichment of the different fractions is shown by the presence/absence of synaptic markers. The fractionation was successful for all case types (control, AD and NDAN) as shown by the purity of PSD fractions in (B). The isolated PSD fraction from hippocampal samples from different cases from each group (aged matched controls, AD, and NDAN) were immunoblotted together (representative blot shown; 40 μg protein each lane of a 10-20% tris-glycine gradient gel) and probed using 6e10 (C) showing LMW Aβ only associates with AD samples. (D) Densitometric analyses of each of the Aβ species (monomer/dimer = 4–8.5 kD band, trimer = 12 kD, and tetramer = 16 kD) demonstrates that all Aβ species are increased in AD. The results are expressed as the mean ± SEM using propagation of error and normalized with AD = 100%. The asterisk denotes the values significantly higher than control (monomer/dimer, p = 0.012, trimer, p = < 0.001, and tetramer, p = 0.014; ANOVA; a Bonferroni correction was required for the monomer/dimer and trimer density values). Hippocampus PSD fractions (80 μg) from age-matched controls, AD, and NDAN samples were immunoblotted and probed using NU4 (E). A lane is included at the end showing synthetic (Synt) Aβ oligomers probed by NU4 for comparison. The densitometric analysis (F) of the dimer/trimer band shows that AD cases are significantly higher than control and NDAN (both groups are essentially the same as background), while the tetrameric species was not found to be significantly different across the groups (p = 0.67). The asterisk denotes significance compared to control, p < 0.05, ANOVA. All Western blots shown are representative of 9–10 individual cases assayed in each group and experiments were repeated 3 – 4 times
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Figure 2: Synaptic fractionation demonstrates that low molecular weight Aβ oligomers associate with the PSD in AD but not NDAN hippocampal specimens. (A) PSD95, a postsynaptic marker, and synaptophysin (Synphys), a presynaptic marker, were probed in the total homogenate (Hom), synaptosomal (Syn), synaptic vesicles (SV), and postsynaptic density (PSD) fractions isolated from a frozen human hippocampal specimen from a control, non-demented aged individual. Enrichment of the different fractions is shown by the presence/absence of synaptic markers. The fractionation was successful for all case types (control, AD and NDAN) as shown by the purity of PSD fractions in (B). The isolated PSD fraction from hippocampal samples from different cases from each group (aged matched controls, AD, and NDAN) were immunoblotted together (representative blot shown; 40 μg protein each lane of a 10-20% tris-glycine gradient gel) and probed using 6e10 (C) showing LMW Aβ only associates with AD samples. (D) Densitometric analyses of each of the Aβ species (monomer/dimer = 4–8.5 kD band, trimer = 12 kD, and tetramer = 16 kD) demonstrates that all Aβ species are increased in AD. The results are expressed as the mean ± SEM using propagation of error and normalized with AD = 100%. The asterisk denotes the values significantly higher than control (monomer/dimer, p = 0.012, trimer, p = < 0.001, and tetramer, p = 0.014; ANOVA; a Bonferroni correction was required for the monomer/dimer and trimer density values). Hippocampus PSD fractions (80 μg) from age-matched controls, AD, and NDAN samples were immunoblotted and probed using NU4 (E). A lane is included at the end showing synthetic (Synt) Aβ oligomers probed by NU4 for comparison. The densitometric analysis (F) of the dimer/trimer band shows that AD cases are significantly higher than control and NDAN (both groups are essentially the same as background), while the tetrameric species was not found to be significantly different across the groups (p = 0.67). The asterisk denotes significance compared to control, p < 0.05, ANOVA. All Western blots shown are representative of 9–10 individual cases assayed in each group and experiments were repeated 3 – 4 times

Mentions: Aβ oligomers have been shown to accumulate at the synapses where they induce dysfunctional changes that impair synaptic integrity [18,20,49]. Therefore, to further assess the localization of the LMW Aβ species detected in the AD and NDAN brains, we performed a synaptic fractionation that separates presynaptic and postsynaptic fractions [50] and probed the postsynaptic fractions for the presence of Aβ by Western blotting. Successful synaptic fractionation of the brain tissues was confirmed by probing the Western blots of the different fractions with antibodies directed against pre- and postsynaptic markers as illustrated in Figure 2A. The fractionation was successful for each group (age-matched control, AD, and NDAN) as shown by the enrichment of PSD95 in the PSD fraction (Figure 2B).


Absence of amyloid β oligomers at the postsynapse and regulated synaptic Zn2+ in cognitively intact aged individuals with Alzheimer's disease neuropathology.

Bjorklund NL, Reese LC, Sadagoparamanujam VM, Ghirardi V, Woltjer RL, Taglialatela G - Mol Neurodegener (2012)

Synaptic fractionation demonstrates that low molecular weight Aβ oligomers associate with the PSD in AD but not NDAN hippocampal specimens. (A) PSD95, a postsynaptic marker, and synaptophysin (Synphys), a presynaptic marker, were probed in the total homogenate (Hom), synaptosomal (Syn), synaptic vesicles (SV), and postsynaptic density (PSD) fractions isolated from a frozen human hippocampal specimen from a control, non-demented aged individual. Enrichment of the different fractions is shown by the presence/absence of synaptic markers. The fractionation was successful for all case types (control, AD and NDAN) as shown by the purity of PSD fractions in (B). The isolated PSD fraction from hippocampal samples from different cases from each group (aged matched controls, AD, and NDAN) were immunoblotted together (representative blot shown; 40 μg protein each lane of a 10-20% tris-glycine gradient gel) and probed using 6e10 (C) showing LMW Aβ only associates with AD samples. (D) Densitometric analyses of each of the Aβ species (monomer/dimer = 4–8.5 kD band, trimer = 12 kD, and tetramer = 16 kD) demonstrates that all Aβ species are increased in AD. The results are expressed as the mean ± SEM using propagation of error and normalized with AD = 100%. The asterisk denotes the values significantly higher than control (monomer/dimer, p = 0.012, trimer, p = < 0.001, and tetramer, p = 0.014; ANOVA; a Bonferroni correction was required for the monomer/dimer and trimer density values). Hippocampus PSD fractions (80 μg) from age-matched controls, AD, and NDAN samples were immunoblotted and probed using NU4 (E). A lane is included at the end showing synthetic (Synt) Aβ oligomers probed by NU4 for comparison. The densitometric analysis (F) of the dimer/trimer band shows that AD cases are significantly higher than control and NDAN (both groups are essentially the same as background), while the tetrameric species was not found to be significantly different across the groups (p = 0.67). The asterisk denotes significance compared to control, p < 0.05, ANOVA. All Western blots shown are representative of 9–10 individual cases assayed in each group and experiments were repeated 3 – 4 times
© Copyright Policy - open-access
Related In: Results  -  Collection

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Figure 2: Synaptic fractionation demonstrates that low molecular weight Aβ oligomers associate with the PSD in AD but not NDAN hippocampal specimens. (A) PSD95, a postsynaptic marker, and synaptophysin (Synphys), a presynaptic marker, were probed in the total homogenate (Hom), synaptosomal (Syn), synaptic vesicles (SV), and postsynaptic density (PSD) fractions isolated from a frozen human hippocampal specimen from a control, non-demented aged individual. Enrichment of the different fractions is shown by the presence/absence of synaptic markers. The fractionation was successful for all case types (control, AD and NDAN) as shown by the purity of PSD fractions in (B). The isolated PSD fraction from hippocampal samples from different cases from each group (aged matched controls, AD, and NDAN) were immunoblotted together (representative blot shown; 40 μg protein each lane of a 10-20% tris-glycine gradient gel) and probed using 6e10 (C) showing LMW Aβ only associates with AD samples. (D) Densitometric analyses of each of the Aβ species (monomer/dimer = 4–8.5 kD band, trimer = 12 kD, and tetramer = 16 kD) demonstrates that all Aβ species are increased in AD. The results are expressed as the mean ± SEM using propagation of error and normalized with AD = 100%. The asterisk denotes the values significantly higher than control (monomer/dimer, p = 0.012, trimer, p = < 0.001, and tetramer, p = 0.014; ANOVA; a Bonferroni correction was required for the monomer/dimer and trimer density values). Hippocampus PSD fractions (80 μg) from age-matched controls, AD, and NDAN samples were immunoblotted and probed using NU4 (E). A lane is included at the end showing synthetic (Synt) Aβ oligomers probed by NU4 for comparison. The densitometric analysis (F) of the dimer/trimer band shows that AD cases are significantly higher than control and NDAN (both groups are essentially the same as background), while the tetrameric species was not found to be significantly different across the groups (p = 0.67). The asterisk denotes significance compared to control, p < 0.05, ANOVA. All Western blots shown are representative of 9–10 individual cases assayed in each group and experiments were repeated 3 – 4 times
Mentions: Aβ oligomers have been shown to accumulate at the synapses where they induce dysfunctional changes that impair synaptic integrity [18,20,49]. Therefore, to further assess the localization of the LMW Aβ species detected in the AD and NDAN brains, we performed a synaptic fractionation that separates presynaptic and postsynaptic fractions [50] and probed the postsynaptic fractions for the presence of Aβ by Western blotting. Successful synaptic fractionation of the brain tissues was confirmed by probing the Western blots of the different fractions with antibodies directed against pre- and postsynaptic markers as illustrated in Figure 2A. The fractionation was successful for each group (age-matched control, AD, and NDAN) as shown by the enrichment of PSD95 in the PSD fraction (Figure 2B).

Bottom Line: Early cognitive impairment in Alzheimer Disease (AD) is thought to result from the dysfunctional effect of amyloid beta (Aβ) oligomers targeting the synapses.Notably, however, we also found that while present in soluble fractions, Aβ oligomers are absent from hippocampal postsynapses in NDAN cases.Taken together, these data illustrate that despite substantial AD neuropathology, Aβ oligomers, and increased synaptic vesicle Zn2+, susceptible brain tissue in these aged NDAN individuals features, as compared to symptomatic AD subjects, significantly lower total Zn2+ levels and no association of Aβ oligomers with the postsynapse, which collectively may promote the maintenance of intact cognitive function.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Neuroscience and Cell Biology, Galveston, TX 77555, USA.

ABSTRACT

Background: Early cognitive impairment in Alzheimer Disease (AD) is thought to result from the dysfunctional effect of amyloid beta (Aβ) oligomers targeting the synapses. Some individuals, however, escape cognitive decline despite the presence of the neuropathologic features of AD (Aβ plaques and neurofibrillary tangles). We term this group Non-Demented with AD Neuropathology or NDAN. The present study illustrates one putative resistance mechanism involved in NDAN cases which may suggest targets for the effective treatment of AD.

Results: Here we describe the localization of Aβ oligomers at the postsynapse in hippocampi from AD cases. Notably, however, we also found that while present in soluble fractions, Aβ oligomers are absent from hippocampal postsynapses in NDAN cases. In addition, levels of phosphorylated (active) CREB, a transcription factor important for synaptic plasticity, are normal in NDAN individuals, suggesting that their synapses are functionally intact. Analysis of Zn2+ showed that levels were increased in both soluble fractions and synaptic vesicles in AD hippocampi, paralleled by a decrease of expression of the synaptic vesicle Zn2+ transporter, ZnT3. Conversely, in NDAN individuals, levels of Zn2+ in soluble fractions were significantly lower than in AD, whereas in synaptic vesicles the levels of Zn2+ were similar to AD, but accompanied by preserved expression of the ZnT3.

Conclusions: Taken together, these data illustrate that despite substantial AD neuropathology, Aβ oligomers, and increased synaptic vesicle Zn2+, susceptible brain tissue in these aged NDAN individuals features, as compared to symptomatic AD subjects, significantly lower total Zn2+ levels and no association of Aβ oligomers with the postsynapse, which collectively may promote the maintenance of intact cognitive function.

Show MeSH
Related in: MedlinePlus