Abstract
Although apoptosis has been extensively studied in developing neurons, the dynamic changes in this pathway after neuronal maturation remain largely unexplored. We show that as neurons mature, cytochrome c- mediated apoptosis progresses from inhibitor of apoptosis protein-dependent to -independent regulation because of a complete loss of Apaf-1 expression. However, after DNA damage, mature neurons resynthesize Apaf-1 through the cell cycle-related E2F1 pathway and restore their apoptotic potential. Surprisingly, we find that E2F1 is sufficient to induce Apaf-1 expression in developing but not mature neurons. Rather, Apaf-1 up-regulation in mature neurons requires both chromatin derepression and E2F1 transcriptional activity. This differential capacity of E2F1 to induce Apaf-1 transcription is because of the association of the Apaf-1 promoter with active chromatin in developing neurons and repressed chromatin in mature neurons. These data specifically illustrate how the apoptotic pathway in mature neurons becomes increasingly restricted by a novel mechanism involving the regulation of chromatin structure.