Characterizing the Morphological Changes and Dynamic of Mitochondria in Neurons after Exposure to ß-amyloid Peptide

Abstract

Objectives: Mitochondria are the energy plant producing ATP to neurons. It has been known that mitochondria have active dynamic fission and fusion to maintain the integrity of this organelle. Many laboratories are able to measure the length of mitochondria. Many reports show the shortening of mitochondria, leading the authors to draw a conclusion of mitochondrial dysfunctions. As our laboratory focuses on how autophagy is initiated from intracellular organelle in Alzheimer's disease, we aim to re-evaluate morphology of mitochondria. Our hypothesis is that there is no significant fragmentation of mitochondria, but just morphological changes. Methods: Primary cultures of hippocampal neurons were employed in our study. We used different fluorescent protein-tagged RFP-mito, photoactivable-mito, pKillerRed-mito constructs to allow us to visualize and trace the dynamic of mitochondria in neurons under 2-photon confocal microscopy. We also used mitoSOX, Rhod-2 and TMRE to monitor the changes of oxidative stress, calcium and membrane potential of mitochondria. Results: Mitochondria displayed a change of their morphology from longitudinal to granule-shape in neurons shortly after exposure to oligomeric Aß peptide. However, there was no change of their volume, indicating no fragmentation. There was no significant reduction on membrane potential or ADP/ATP ratio. Change of their morphology was induced by oxidative stress. Conclusions: Our study reveals that mitochondria in hippocampal neurons are functional and display intact morphology. The results revise the current concept that shortening of mitochondria does not indicate any dysfunction or fragmentation of mitochondria. Our study provides indirect evidence by showing that autophagy is not initiated from mitochondria.