Molecular Regulation of DNA Damage-Induced Apoptosis in Neurons of Cerebral Cortex

Abstract

Cerebral cortical neuron degeneration occurs in brain disorders manifesting throughout life, but the mechanisms are understood poorly. We used cultured embryonic mouse cortical neurons and an in vivo mouse model to study mechanisms of DNA damaged-induced apoptosis in immature and differentiated neurons. p53 drives apoptosis of immature and differentiated cortical neurons through its rapid and prominent activation stimulated by DNA strand breaks induced by topoisomerase-I and -II inhibition. Blocking p53-DNA transactivation with alpha-pifithrin protects immature neurons; blocking p53-mitochondrial functions with mu-pifithrin protects differentiated neurons. Mitochondrial death proteins are upregulated in apoptotic immature and differentiated neurons and have nonredundant proapoptotic functions; Bak is more dominant than Bax in differentiated neurons. p53 phosphorylation is mediated by ataxia telangiectasia mutated (ATM) kinase. ATM inactivation is antiapoptotic, particularly in differentiated neurons, whereas inhibition of c-Abl protects immature neurons but not differentiated neurons. Cell death protein expression patterns in mouse forebrain are mostly similar to cultured neurons. DNA damage induces prominent p53 activation and apoptosis in cerebral cortex in vivo. Thus, DNA strand breaks in cortical neurons induce rapid p53-mediated apoptosis through actions of upstream ATM and c-Abl kinases and downstream mitochondrial death proteins. This molecular network operates through variations depending on neuron maturity.

DNA Damage Response and DNA Repair in Skeletal Myocytes From a Mouse Model of Spinal Muscular Atrophy

“…This hypothesis was based on the evidence that SMN and some of its binding partners function in DNA repair (17,18) and that human SMA fibroblasts show increased sensitivity to the DNA topoisomerase-I inhibitor camptothecin (78), which induces DNA-SSBs and apoptosis (51). Moreover, our experiments demonstrating DNA damage accumulation in SMA mouse skeletal muscles very early in the disease suggested that muscle-specific DNA damage repair defects could be a pathological mechanism in SMA (14).…”

“…Etoposide (Sigma, St Louis, MO, E1383) was dissolved at 10 mM in 1:1 medium:DMSO, and further diluted to 10 lM in myotube differentiation medium for exposure to differentiated myotubes. This dosage was shown to induce reliable DNA damage in cultured differentiated mouse neurons (51). For the control condition, 1:1 medium:DMSO was diluted in differentiation medium at an equivalent volume.…”

Age-related hearing loss in C57BL/6J mice is mediated by Bak-dependent mitochondrial apoptosis

“…However, recent studies suggest that Bak acts upstream of Bax in promoting mitochondrial apoptosis (25,45), and that Bak plays the central role in apoptosis of differentiated neurons (24). Moreover, Bak may play an exclusive role in oxidative stress-mediated apoptosis in the brain (25), and also in mitochondrial fragmentation (45).…”

“…S3 A and B). To confirm that age-related cochlear cell death was apoptotic, we conducted TUNEL staining to measure nuclear DNA fragmentation, a key feature of apoptosis (16,24), in 5-and 15-month-old Bak Ϫ/Ϫ and WT mice. Consistent with the SG neuron and OH cell counts, aging resulted in increased levels of TUNEL-positive cells in the WT cochlea, whereas levels of TUNEL-positive cells in the Bak Ϫ/Ϫ cochlea did not increase with age (Fig.…”

Cell Cycle and DNA Damage Response in Postmitotic Neurons

“…The signal transduction mechanisms in neurons that link DNA damage to apoptosis are not well characterized, and the sensors of DNA damage in neurons are largely unknown (Martin et al, 2009). However, some observations suggest that DDR in postmitotic neurons may have survival checkpoint that serves to eliminate neurons with excessive DNA damage.…”