FIGURE 1.

DNA damage and neuronal degeneration in human amyotrophic lateral sclerosis (ALS) and mouse models of motor neuron degeneration. (A) DNA damage in the form of 8-hydroxy-2-deoxyguanosine (OHdG) immunoreactivity (blue-green crystals) and p53 immunoreactivity (brown) colocalize in the nucleus of subsets of upper motor neurons (cell at right) in human ALS cerebral cortex. Other neurons (cell at left) have accumulated OHdG immunoreactivity within the cytoplasm, possibly corresponding to DNA damage within mitochondria, but are not positive for p53. Scale bar = 10 μm. (B) Activated p53, seen as phosphoserine³⁹²-p53 immunoreactivity (brown labeling), accumulates in subsets of cortical motor neurons (arrow) in human ALS. Other neurons in the field seen by the cresyl violet counterstain show no immunoreactivity. Scale bar = 10 μm. (C) In human ALS spinal motor neurons, nuclear OHdG-DNA damage (brown) and active caspase 3 (blue-green labeling) colocalize. Scale bar = 5 μm. (D) Mitochondrial accumulation identified by cytochrome c oxidase subunit 1 immunoreactivity (brown labeling) occurs in the perikaryon of human ALS spinal motor neurons with active caspase 3 (green in cytoplasm and nucleus). Many mitochondria are positive for active caspase 3. Scale bar = 5 μm. (E, F) Comet assay on isolated lumbar spinal cord motor neurons from G93A/mutant superoxide dismutase 1 mice at 6 (F) and 8 weeks (G) of age reveals the accumulation of DNA single-strand breaks (SSBs) in subsets of cells (arrows; see original publications for assay details; 19–21). Scale bars = (F) 60 and (G) 40 mm. (G, H) Spinal motor neurons with avulsed axons accumulate DNA-SSBs (detected by comet assay, note the short tails in G) very early in response to injury and coinciding with nuclear accumulation of p53 (brown nuclear labeling in H). Note that the p53 accumulation within the nucleus can be seen at chromatin strands. Scale bars = (G, H) 6 μm. mSOD-1, mutant superoxide dismutase 1.