Supplementary Figure 1: Quantification of myelin fragments in the aging brain

(a) Electron microscopy on corpus callosum is shown for a 18-month-old wild type mice. Myelin fragments (arrows) were detected in extracellular space (a), attached to axon, (b) and in the cell (c). Myelin fragments were quantified in 7 and 18-month-o-ld mice (n=3 mice per group, mean +/- s.d., **P= 0.0256, t=6.019, df=2, Student's two-tailed t test). Quantification of myelin fragments attached to axons in 6, 12 and 24-month-old wild type mice (n=3 mice per group, mean +/- s.d., one-way ANOVA, **P=0.0024, F=19.47, df=8, followed by Bonferroni’s post hoc test, 6 vs 24: **P=0.0091, t=5.358, and 12 vs 24 months, **P=0.0075, t=5.448). Each dot represents the mean value of 3 brain slices of one mouse. (b) Confocal images and quantification of number of PLP immunoreactive puncta (green) co-localizing with Iba1-positive microglia (red) in 18-month-old wild-type mice (n=3 mice per group, mean +/- s.d., ***P< 0.0001, t=21.85, df=3, Student's two-tailed t test). Analysis of myelin-associated glycoprotein (MAG), which is localized at the inner, adaxonal space, is shown. MAG immunoreactive puncta show no co-localizing with Iba1-positive microglia (red) consistent with our conclusion that myelin fragments pinch off from the outside of the sheaths (n=3 mice per group, mean +/- s.d.). Scale bar: 2 µm.