Microglial Cx3cr1 knockout prevents neuron loss in a mouse model of Alzheimer's disease

Abstract

Microglia, the immune cells of the brain, can have a beneficial effect in Alzheimer's disease by phagocytosing amyloid-beta. Two-photon in vivo imaging of neuron loss in the intact brain of living Alzheimer's disease mice revealed an involvement of microglia in neuron elimination, indicated by locally increased number and migration velocity of microglia around lost neurons. Knockout of the microglial chemokine receptor Cx3cr1, which is critical in neuron-microglia communication, prevented neuron loss.

Figure 1

Microglial CX₃CR1-dependent neuron loss in 5xTg mice. (a) Fluorescence two-photon in vivo images of neurons (yellow), microglia (green) and blood vessels (red) before (day 0), at (day 7) and after (day 14) neuron loss. Circles indicate lost neurons and arrows indicate present neurons. (b) Neuron loss per volume over a 28-d imaging interval (n = 4–9 mice per genotype, aged 4–6 months). (c–f) High-magnification time-lapse images (c) of a lost neuron in a and a neuron from a 5xTg-Cx3cr1^−/− mouse (e). Traces of individual microglia in c and e are shown in d and f. (g) Microglia density of different genotypes (n = 4 per group) over time in a volume of 7.5 × 10⁵ µm³ around neurons as in c and e and more than 100 µm distant. Note that microglia density increased before neuron loss. (h) Mean migration velocity of microglia somata over 28 d (n = 4 per group). (i) Soluble (S) and insoluble (P) Aβ40 content in brain homogenates of 5xTg-Cx3cr1^+/− and 5xTg-Cx3cr1^−/− mice (n = 5 per group). (j) Subsequent time points (0 min, 5 min) were superimposed (dt = 5 min) to measure gained (green arrow), lost (red arrow) and stable (yellow area) processes. (k,l) Microglia TOR (k) and TOR per cell (l) of various genotypes (n = 4 mice per group) and at more than 100 µm from neuron loss. Scale bars represent 20 µm (a), 10 µm (c,e) and 5 µm (j). **P < 0.01, ***P < 0.001. Error bars indicate s.e.m.