Annexin A3 is associated with cell death in lactacystin-mediated neuronal injury.

Massive neuronal apoptosis and accumulation of protein aggregates in the cortex and hippocampus of the brain are hallmarks of several neurodegenerative disorders, indicating ubiquitin proteasome system (UPS) dysfunction. Lactacystin, a classical proteasome inhibitor, is used to simulate ubiquitin proteasome system dysfunction in neurons to mimic pathological features of neurodegenerative disorders. Based on Western blot analyses, we reported for the first time that annexin A3 (AnxA3) is not only endogenously expressed in mouse cortical neurons but also more importantly, by gene expression microarray and real-time RT-PCR that it is greatly transcriptional up-regulated to approximately 11- and 15-fold, respectively in murine primary cortical neurons with 1μM lactacystin for 24h. Up-regulation of AnxA3 expression occurred after 12-15h post-lactacystin treatment, which corresponded with the onset of neuronal injury, with approximately 25% of the neurons being non-viable by that time interval. Western blot analysis with anti-AnxA3 antibodies further validated that up-regulation of AnxA3 only occurs with onset of neuronal death, and not with the onset of proteasome inhibition, which occurs at 4.5h post-lactacystin treatment. Over-expression studies suggested AnxA3 might be involved in death promotion during lactacystin-mediated neuronal death, since caspase-3 activation was significantly stronger upon neuronal AnxA3 over-expression. We propose AnxA3 up-regulation may have significant relevance in the elucidation of neurodegenerative pathophysiology.