Fig. 3: Myelin dysfunction alters APP processing.
From: Myelin dysfunction drives amyloid-β deposition in models of Alzheimer’s disease
a, High-pressure freezing EM of optic nerves from 6-month-old WT and Cnp−/− mice. Nerves from Cnp−/− mice show (plaque-independent) axonal swellings with accumulation of endosomal and lysosomal structures and multivesicular bodies. The same observations were made in three independent samples per mice per group. b, Schematic representation of APP cleavage and binding sites of anti-APP and anti-Aβ antibodies used. c, Fluorescent and chromogenic immunostaining images of APP and APP cleavage enzymes BACE1 (β-secretase) and PSEN2 (as part of the γ-secretase complex) in white matter (fimbria) from Cnp−/−;5×FAD mice. Grey arrowheads mark plaque-associated axonal swellings typically forming a corona. Black and white arrowheads indicate plaque-independent axonal swellings as observed in Cnp−/− mice. d, Fluorescent and chromogenic immunostainings of Aβ peptides in white matter (fimbria) of Cnp−/−;5×FAD mice and 5×FAD mice. Grey arrowheads indicate proper amyloid plaques, typically stained intensely. White arrows indicate swellings stained positive by the respective Aβ-antibody, but typically stained less intensely and more round in structure. e, Quantification of axonal swellings positive for APP, BACE1, PSEN2 and Aβ (6C3) in white matter (fimbria) of 5×FAD control mice and Cnp−/−;5xFAD mice. For BACE1 and APP quantification, n = 5 for 5×FAD and Cnp−/−;5×FAD. For PSEN2 quantification, n = 3 for 5×FAD and n = 5 for Cnp−/−;5×FAD. For 6C3, n = 3 for 5×FAD and Cnp−/−;5×FAD. f, Fluorescent immunoblot analysis of BACE1 levels in microdissected cortex of Cnp−/−;5×FAD mice and 5×FAD mice. g, Fluorescent immunoblot analysis of APP fragmentation in the membrane-bound fraction of microdissected cortical tissue of Cnp−/−;5×FAD mice and 5×FAD control mice. (p)C99, phospho-C99. For f and g, the molecular weight marker (in kDa) is indicated on the left. For quantifications in f and g, full-length APP (fAPP) and BACE1 levels were normalized to total protein stain. CTF levels were normalized to fAPP. n = 3 per group. For e–g, statistical analysis: two-sided, unpaired Student’s t-test (P values are indicated in the graphs). Bars represent means, dots represent biological replicates/mice/lanes/n. Source data are given in Supplementary Fig. 1.
