Activation of caspase-3 in β-amyloid-induced apoptosis of cultured rat cortical neurons

Abstract

Amyloid β protein (Aβ) has been thought to participate in the neurodegeneration associated with Alzheimer's disease. We here report on caspase-3 activation by Aβ-treatment of cultured neurons. Treatment of rat primary cortical culture with Aβ 25–35, an active fragment of Aβ, induced neuronal death as determined by a decrease in neuron-specific microtubule-associated protein 2 (MAP2)-like immunoreactivity and by the release of cellular lactate dehydrogenase (LDH). Aβ 25–35 also induced elevation of caspase-3-like Ac-DEVD-MCA cleavage activity in advance of neuronal death with similar concentration-dependency for neuronal death. Inhibitor sensitivity of the Aβ-induced proteolytic activity was similar to that of human recombinant caspase-3. Cleavage of pro-caspase-3 and cleavage of its endogenous substrates, poly (ADP-ribose) polymerase (PARP) and α-fodrin, were produced by Aβ-treatment. A caspase-3 inhibitor, Ac-DEVD-CHO, prevented Aβ-induced DNA fragmentation and cleavage of α-fodrin, but not of PARP. Caspase inhibitor of broad specificity, Z-VAD-CH 2-DCB, additionally prevented Aβ-induced cleavage of PARP and some early loss of cell membrane integrity measured by LDH release. However, Aβ-induced condensation of nuclear chromatin and most of the late disintegration of cell membranes were not prevented in the presence of these caspase inhibitors. These results suggest that activation of both caspase-3 and caspase(s) other than caspase-3 play distinct roles in Aβ-induced apoptosis of rat cortical neurons. Furthermore, in the presence of caspase inhibitors, Aβ-induced neuronal death still occurred with different morphological features.