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Early Effects of Aβ Oligomers on Dendritic Spine Dynamics and Arborization in Hippocampal Neurons

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Early Effects of Aβ Oligomers on Dendritic Spine Dynamics and Arborization in Hippocampal Neurons

Carolina Ortiz-Sanz et al. Front Synaptic Neurosci.

Abstract

Alzheimer's disease (AD) is a neurodegenerative disorder that leads to impaired memory and cognitive deficits. Spine loss as well as changes in spine morphology correlates with cognitive impairment in this neurological disorder. Many studies in animal models and ex vivo cultures indicate that amyloid β-peptide (Aβ) oligomers induce synaptic damage early during the progression of the disease. Here, in order to determine the events that initiate synaptic alterations, we acutely applied oligomeric Aβ to primary hippocampal neurons and an ex vivo model of organotypic hippocampal cultures from a mouse after targeted expression of EGFP to allow high-resolution imaging and algorithm-based evaluation of spine changes. Dendritic spines were classified as thin, stubby or mushroom, based on morphology. In vivo, time-lapse imaging showed that the three spine types were relatively stable, although their stability significantly decreased after treatment with Aβ oligomers. Unexpectedly, we observed that the density of total dendritic spines increased in organotypic hippocampal slices treated with Aβ compared to control cultures. Specifically, the fraction of stubby spines significantly increased, while mushroom and thin spines remained unaltered. Pharmacological tools revealed that acute Aβ oligomers induced spine changes through mechanisms involving CaMKII and integrin β1 activities. Additionally, analysis of dendritic complexity based on a 3D reconstruction of the whole neuron morphology showed an increase in the apical dendrite length and branching points in CA1 organotypic hippocampal slices treated with Aβ. In contrast to spines, the morphological changes were affected by integrin β1 but not by CaMKII inhibition. Altogether, these data indicate that the Aβ oligomers exhibit early dual effects by acutely enhancing dendritic complexity and spine density.

Keywords: Alzheimer’s disease; Aβ oligomers; CaMKII; dendrites; integrin β1; spines.

Figures

Figure 1
Figure 1
Stability and dynamics of dendritic spine types during short amyloid β (Aβ) treatment. (A) Representative western blot shows the broad range of molecular weight protein markers (lane 1) and oligomeric and monomeric forms (lane 2) of Aβ(1–42) preparation probed with monoclonal antibody 6E10. (B) The bar graph illustrates the relative quantification (band intensity expressed as the percentage of band volumes of total proteins) of high molecular weight (HMW), low molecular weight (LMW) and monomeric forms of Aβ preparation (n = 4 preparations). (C) Micrographs show confocal time-lapse images of dendritic segments displaying stable spines (filled arrowheads) and dynamic spines (open arrowheads) at 10-min intervals in control and Aβ conditions. Scale bar, 2 μm. (D) Bar diagram representing the cumulative average of dendritic spine stability and dynamics at during 50 min interval. (E,F) Bar graphs represent quantification of stability (E) and dynamics (F) of control and Aβ-treated spines at the indicated 10 min interval. (G,H) Detailed analysis of the percentage (G) and density (H) of the three types of dendritic spines in the 30–40 min time interval. *p < 0.05, compared to non-treated cells; paired one-way ANOVA, n = 8 dendrites, of eight neurons (30 spines/dendrite).
Figure 2
Figure 2
Hippocampal slices treated with Aβ oligomers show an increase in the total dendritic spine density, which is reverted with CaMKII and integrin β1 inhibitors. (A) Organotypic hippocampal slices were infected with sindbis virus expressing EGFP at day 12 in vitro. Three days later, slices were treated with Aβ oligomers 1 μM or vehicle and fixed at day 15 in vitro as indicated on the timeline. (B) Micrographs obtained by confocal imaging show apical dendritic segments from CA1 hippocampal neurons in control and Aβ treatment conditions in the presence of different inhibitors, AIP (CaMKII inhibitor) and CD29 (integrin β1 inhibitor). Scale bar, 2 μm. (C,D) Bar graphs represent quantification of spine density and spine mean length in different cultures. (E) The bar graph shows quantification of stubby spine density after Aβ treatment in the presence or absence of inhibitors. *p < 0.05, **p < 0.01, ***p < 0.001, n.s. non-significant, compared to non-treated cells; paired one-way ANOVA. Data are represented as mean ± standard error of the mean (SEM), n = 35 dendrites of 5–6 neurons per condition.
Figure 3
Figure 3
CaMKII inhibitor shifts Aβ-induced spine morphology alterations on hippocampal CA1 neurons as shown by a multidimensional spine density analysis. Multidimensional spine density histograms representing equal numbers (600 random dendritic spines/condition) of spines from control and Aβ treated samples (A) or Aβ treated samples in presence or absence of CaMKII inhibitor (B). Heatmap graphs were derived by plotting spine densities as a function of spine length × head diameter for each sample. Difference plots were derived by comparing group Aβ values vs. control (A, right) or CaMKII + Aβ values vs. Aβ alone values (B, right). Note that the presence of CaMKII inhibitor shifts spine parameters back towards lower head diameter.
Figure 4
Figure 4
Aβ oligomers induce dendritic complexity at sites of Schaffer collateral input. (A) 3D reconstructions of representative CA1 neurons in untreated and Aβ-treated cells. (B–E) Quantitative analysis of dendritic complexity as determined from apical path length (B), apical branching points (C), basal path length (D) and basal branching points (E). (F,G) Sholl analysis of the dendritic tree in CA1 neurons after Aβ treatment indicates higher branching in the proximal part of the apical but not in basal dendrites. *p < 0.05, **p < 0.01, n.s. non-significant, compared to non-treated cells; paired student’s t-test (B–E) or two-way ANOVA (F,G). Data are represented as mean ± SEM, n = 7 neurons per condition.

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References

    1. Alberdi E., Sánchez-Gómez M. V., Cavaliere F., Pérez-Samartín A., Zugaza J. L., Trullas R., et al. . (2010). Amyloid β oligomers induce Ca2+ dysregulation and neuronal death through activation of ionotropic glutamate receptors. Cell Calcium 47, 264–272. 10.1016/j.ceca.2009.12.010 - DOI - PubMed
    1. Alberdi E., Sánchez-Gómez M. V., Ruiz A., Cavaliere F., Ortiz-Sanz C., Quintela-López T., et al. . (2018). Mangiferin and morin attenuate oxidative stress, mitochondrial dysfunction, and neurocytotoxicity, induced by amyloid β oligomers. Oxid. Med. Cell. Longev. 2018:2856063. 10.1155/2018/2856063 - DOI - PMC - PubMed
    1. Androuin A., Potier B., Nägerl U. V., Cattaert D., Danglot L., Thierry M., et al. . (2018). Evidence for altered dendritic spine compartmentalization in Alzheimer’s disease and functional effects in a mouse model. Acta Neuropathol. 135, 839–854. 10.1007/s00401-018-1847-6 - DOI - PubMed
    1. Bakota L., Brandt R. (2016). Tau biology and Tau-directed therapies for Alzheimer’s disease. Drugs 76, 301–313. 10.1007/s40265-015-0529-0 - DOI - PMC - PubMed
    1. Baleriola J., Walker C. A., Jean Y. Y., Crary J. F., Troy C. M., Nagy P. L., et al. . (2014). Axonally synthesized ATF4 transmits a neurodegenerative signal across brain regions. Cell 158, 1159–1172. 10.1016/j.cell.2014.07.001 - DOI - PMC - PubMed
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