Oxidative stress and altered mitochondrial dynamics in neurodegenerative processes

Aims: Mitochondria are very dynamic organelles. Mitochondrial dynamics (alternation of fission/fusion cycles and their axonal transport) and biogenesis are crucial for neuronal homeostasis and synaptic function; moreover, alteration of the balance between fission and fusion can determine the fate of neuronal cells. Fission processes require the intervention of Fis1 and the active form of Drp1, whereas fusion is primarily regulated by Opa1 and Mfn1/2. We here focused on correlation between oxidative stress and mitochondrial dynamics and biogenesis. Materials and Methods: We compared the effect of hydrogen peroxide and Rotenone (a neurotoxin that inhibits the Complex-I of electrons transport chain), on primary cortical neurons or models of neurodegeneration based on neuroblastoma or PC12 cells. Protein levels and distribution (cytoplasm, mitochondria or nuclei) were assessed by western blots and immunofluorescence imaging. Results: Exposure of neurons or neuroblastoma to Rotenone determined a dose-dependent (200-400-800 nM) decrease of P-Drp1 and a biphasic trend of Opa1 and Mfn2 in a time-dependent manner (1-3-6-24h). In PC12 cells, alterations of mitochondrial proteins in response to hydrogen peroxide was paralleled by differential distribution (cytoplasm/nuclei) of oxidative-stress sensors (DJ-1, Nrf2) and proteins regulating mitochondrial biogenesis (mtTFAM and PGC1a), while determining a dose- and time-dependent increase of ROS and ATP depletion. Interestingly, human fibroblasts showed similar changes in response to rotenone but a different trend in response to Amyloid-beta oligomers. Discussion/Conclusions: These studies suggest 1) the existence of a complex cross-talk underlying mitochondrial dynamics and biogenesis, 2) alteration of mitochondrial dynamic proteins as biomarkers of mitochondrial dysfunction in neurodegenerative processes.