Hippocampal interneuron loss in an APP/PS1 double mutant mouse and in Alzheimer's disease

Abstract

Hippocampal atrophy and neuron loss are commonly found in Alzheimer's disease (AD). However, the underlying molecular mechanisms and the fate in the AD hippocampus of subpopulations of interneurons that express the calcium-binding proteins parvalbumin (PV) and calretinin (CR) has not yet been properly assessed. Using quantitative stereologic methods, we analyzed the regional pattern of age-related loss of PV- and CR-immunoreactive (ir) neurons in the hippocampus of mice that carry M233T/L235P knocked-in mutations in presenilin-1 (PS1) and overexpress a mutated human beta-amyloid precursor protein (APP), namely, the APP(SL)/PS1 KI mice, as well as in APP(SL) mice and PS1 KI mice. We found a loss of PV-ir neurons (40-50%) in the CA1-2, and a loss of CR-ir neurons (37-52%) in the dentate gyrus and hilus of APP(SL)/PS1 KI mice. Interestingly, comparable PV- and CR-ir neuron losses were observed in the dentate gyrus of postmortem brain specimens obtained from patients with AD. The loss of these interneurons in AD may have substantial functional repercussions on local inhibitory processes in the hippocampus.

Fig. 1

Mean and standard error of the mean (SEM) of estimated numbers of PV-ir neurons (a–c; NN-PV) and numbers of CR-ir neurons (d–f; NN-CR) in the dentate gyrus and hilus (DG; a, d), CA3 (b, e), and CA1-2 (stratum pyramidale) (c, f) in the hippocampus of either 2-month-old (M2) or 10-month-old (M10) PS1ho KI mice (light gray bars) and APP^SL/PS1ho KI mice (open bars). Results of general linear model univariate analysis of variance are summarized in Table 2; results of post hoc Bonferroni tests for pairwise comparisons between animals in groups M2 and M10, of the same genotype are indicated in the graphs. *p < 0.05, **p < 0.01

Fig. 2

Representative high-power photomicrographs showing region-specific immunofluorescence detection of Aβ (yellow fluorescence) and GFAP (green fluorescence) within the dentate gyrus in the hippocampus of APP^SL mice at 2 month of age (M2; a) and 10 months of age (M10; c) as well as of APP^SL/PS1ho KI mice at M2 (b) and M10 (d) (sections counterstained with Hoechst 33342, pseudocolored in red for better contrast). Note the age-related aggregation of extracellular Aβ, the strong increase in GFAP immunoreactivity and particularly the neuron loss in the APP^SL/PS1ho KI mice. Scale bar 33 μm

Fig. 3

Immunohistochemical detection of parvalbumin (PV) in the area CA1-2 (red fluorescence in a–d and a′–d′) and calretinin (CR) in the DG (red fluorescence in e–h and e′–h′) in the hippocampus of 2-month-old (a–h) and 10-month-old (a′–h′) APP^SL mice (a, a′, e, e′), PS1he KI mice (b, b′, f, f′), PS1ho KI mice (c, c′, g, g′) and APP^SL/PS1ho KI mice (d, d′, h, h′). Sections were counterstained with Hoechst (pseudocolored in green for better contrast). Note the substantial age-related loss of PV-ir neurons in the CA1-2 of the PS1he KI mice, PS1ho KI mice and APP^SL/PS1ho KI mice (arrows in b′, c′ and d′), as well as of CR-ir neurons in the dentate gyrus and hilus of the PS1ho KI mice and APP^SL/PS1ho KI mice (arrows in g′ and h′). Scale bar 100 μm

Fig. 4

Immunohistochemical detection of parvalbumin (PV) (red fluorescence in a–h and a′–h′) and calretinin (CR) (red fluorescence in i–q and i′–q′) within the DG (a–d′), the CA3 (e–m′) and the CA1-2 (n–q′) regions of the hippocampus of 2-month-old (a–h and i–q) and 10-month-old (a′–h′ and i′–q′) APP^SL mice (a, a′, e, e′, i, i′, n, n′), PS1he KI mice (b, b′, f, f′, k, k′, o, o′), PS1ho KI mice (c, c′, g, g′, l, l′, p, p′) and APP^SL/PS1ho KI mice (d, d′, h, h′, m, m′, q, q′). Sections were counterstained with Hoechst (pseudocolored in green for better contrast). Scale bar 100 μm

Fig. 5

Densities of PV-ir neurons (a–c) and CR-ir neurons (d–f) (means ± SEM) in the dentate gyrus (DG; a, d), CA3 (b, e), and CA1-2 (c, f) in the hippocampus of 2-month-old (M2) and 10-month-old (M10) PS1ho KI mice (light gray bars) and APP^SL/PS1ho KI mice (open bars). Results of general linear model univariate analysis of variance are summarized in Table 2; results of post hoc Bonferroni tests for pairwise comparisons between animals in groups M2 and M10 of the same genotype are indicated in the graphs. **p < 0.01

Fig. 6

Representative photomicrographs of sections from human postmortem brains of a control (a, c) and an AD patient (b, d) showing neurons immunoreactive for CR (a, b) and PV (c, d) (arrows) within the dentate gyrus (DG) and hilus (H) of the hippocampus. The rectangles show the positions at which the high-power photomicrographs (insets) were taken. Note the loss of CR-immunoreactive neurons in the brain from the AD patient and the substantial gliosis within the hilus of this brain (inset in b). Scale bar 200 μm (50 μm for the insets)

Fig. 7

Mean and standard error of the mean (SEM) of densities of PV-ir neurons (a; ND-PV-H) or CR-ir neurons (b; ND-CR-H) in the dentate gyrus and hilus in postmortem brains from either control subjects (black bars) or AD subjects (open bars). Results of general linear model univariate analysis of variance are summarized in Table 2 and indicated in the graph. *p <0.01