Transmission Electron Microscopy Reveals Propionic Acid-induced Alterations to Mitochondrial Morphology in SH-SY5Y Cells

Mitochondrial dysregulation is implicated in numerous neurological disorders. Mitochondrial dynamics, including biogenesis, fusion and fission, are essential components of mitostasis which is modulated by complex regulatory mechanisms. Although expression studies are often used to investigate mitochondrial dynamics, these studies may be limited by the interdependent and temporal nature of mitostasis. Transmission electron microscopy (TEM) and cryogenic preparation methods provide a direct approach to examine mitochondrial ultrastructure in neurons. We investigated the utility of TEM to visualize mitochondrial morphological changes in SH-SY5Y cells treated with propionic acid (PPA). We examined whether morphological alterations were associated with differences in membrane potential or expression of biogenesis, fusion and fission genes. PPA induced a significant decrease in mitochondrial area (p<0.01 5mM), Feret's diameter and perimeter (p<0.05 5mM), and in area2 (p<0.05 3mM, p<0.01 5mM) – consistent with a shift towards fission. Morphological changes were not associated with significant differences in mitochondrial membrane potential. However, we observed decreased gene expression of NRF1 (p<0.01), TFAM (p<0.05), and STOML2 (p<0.0001). These data support a disruption of the balance in dynamics to preserve function under stress. This demonstrates the utility of TEM to provide insight into mitochondrial dynamics and function which can inform targeted mechanistic investigations into neuropathology.