Fig. 3.

Neurodegeneration is accelerated in cTAP mice, and degenerating nuclei are TUNEL+ and caspase-3 negative, while adaptive activation of caspase-3 is observed locally at synapses of the CA1. a Breeding strategy for generating CaMKIIα-Cre^ER;Tdp-43^F/F;APP_swe/PS1ΔE9 mice and littermate controls. (#) Indicates the Mendelian frequency of pups from each litter expected to carry the genotype of interest. b: a–f TUNEL staining for DNA fragmentation (hatched arrows) is absent from AP (b: a, d), detectable in cT (b: b, e), and most prominent in cTAP mice (b: c, f) in degenerating regions of the hippocampus (CA3) and frontal cortex (layer V) at 3 months of age. TUNEL positive cells (hatched arrows) show brown nuclear labeling and attritional morphology. Neurons in the CA3 and cortex of AP mice were devoid of labeling (open arrows) and appeared morphologically healthy. b: g–i Cleaved caspase-3 immunoreactivity (brown–red) was accumulated in the striatum radiatum (sr) of CA1 but not in the stratum pyramidal layer (sp) of cTAP mice (b: i) at 8 months of age. Immunoreactivity was less conspicuous in cT mice (b: h) and was not detected in AP mice (b: g). Cleaved caspase-3 immunoreactivity appeared as punctate synaptic terminal-like staining (hatched arrows in b: h, i). All sections were counterstained with cresyl violet. Scale bars 135 μm. c The number of TUNEL stained neurons/mm² increased significantly in cT and cTAP mice compared to AP littermates [F(1,14) = 27.23, p < 0.001; Gabriel AP vs. cT **p = 0.002, AP vs. cTAP ***p < 0.001, cT vs. cTAP NS p = 0.131]. d Left representative images of neurodegeneration in each genotype by H + E stain at 8 months (N = 6/group). Numerous CA1 pyramidal neurons show pale staining cytoplasm in cTAP mice (left, boxed), in contrast to normal cytoplasm of AP and most cT neurons. Occasional darkly stained pyknotic cells (arrow) are also visible in cTAP mice. Scale bars 100 μm. Middle and Right electron micrographs from CA1 pyramidal neurons at 6 months show sparsely populated and discontinuous cytoplasm with loss of electron dense ribosomes (right, boxed areas) in cTAP mice, compared to cT and AP littermates. Dystrophic organelles, including mitochondria (middle, red; right, arrowheads), and Golgi/smooth ER (middle, green) are most severe in the cTAP mouse. Dystrophic neurites (pink) only occasionally contain lysosomes (black). Scale bars 2 μm. N 1/group