Differential regulation of caspase-3 by pharmacological and developmental stimuli as demonstrated using humanised caspase-3 mice

Caspase-3 is a potential therapeutic target for a number of degenerative diseases. However the development of specific caspase-3 inhibitors has been hampered by inter-species differences and the high degree of homology shared by different caspases. To circumvent these issues, we have produced and characterised a humanised caspase-3 mouse line (possessing one copy of the human gene with both copies of the murine gene disrupted) by crossing human caspase-3 transgenic mice with nullizygous caspase-3 knock-out mice. Humanised mice appeared normal and survived to adulthood. Analysis of the human gene revealed that human pro-caspase-3 was expressed in the same tissues as its murine counterpart. However humanised mice retained the hypercellularity of frontal cortex seen in their knock-out parental line and there was no biochemical evidence of human protein processing during naturally occurring neuronal death taking place during brain development. In contrast, the human protein was cleaved by the mouse machinery following anti-Fas treatment of adult mice. These data suggest that there is a fundamental difference between the activation pathways leading to caspase-3 cleavage during naturally occurring cell death in development/embryogenesis and following an apoptotic stimulus in the adult.