Mechanisms Underlying H 2 O 2 -Evoked Carbonyl Modification of Cytoskeletal Protein and Axon Injury in PC-12 Cells

Background/Aims: To investigate the mechanism that enables oxidative stress and cytoskeleton protein carbonylation to contribute to axonal dysfunction in traumatic brain injury (TBI). Methods: We created an in vitro model of neuronal oxidative damage by exposing a neuron-like cell line (PC-12) to different concentrations (100 μM, 200 μM, and 300 μM) of H2O2 for 24 h or 48 h. Carbonyl modification of cytoskeletal proteins (β-actin and β-tubulin) and its impact on β-actin/β-tubulin filament dynamics were determined by enzyme-linked immunosorbent assay, immunostaining, and western blotting. Depolymerization of β-actin/β-tubulin filaments was evaluated using the monomer/polymer ratio of each protein via western blotting. Phosphorylation of the neurofilament heavy chain (P-NFH) was used as an axonal injury marker and detected by immunostaining. Results: Our results showed that H2O2 treatment led to increased oxidative stress in PC-12 cells, as indicated by the increased generation of malondialdehyde and 8-hydroxydeoxyguanosine and decreased intracellular glutathione levels. H2O2 treatment also increased carbonyl modification of total proteins and cytoskeleton proteins β-actin/β-tubulin, which occurred concurrently with the suppression of proteasome activity. Moreover, H2O2 treatment increased the generation of the axonal injury marker P-NFH, and depolymerization of the β-actin/β-tubulin filaments was indicated by increased monomer/polymer ratios of each protein. Lastly, overexpression of the proteasome β5 subunit in PC-12 cells significantly reduced the H2O2-induced accumulation of carbonylated β-actin/ β-tubulin, P-NFH, and β-actin/β-tubulin depolymerization. Conclusions: We concluded that carbonylation of cytoskeleton proteins could lead to depolymerization of their filaments and axonal injury, and proteasome suppression contributes to the accumulation of carbonylated proteins under oxidative conditions.