(22) Neuronal Iron Status and Mitochondria Regulate Axon Development During Early Periods of Dynamic Growth

Timothy Monko, University of Minnesota Medical School, Minneapolis, MN, United States; Jordan Treder, University of Minnesota, United States; Lorene Lanier, University of Minnesota Medical School, United States; Michael Georgieff, University of Minnesota Medical School, United States; Thomas Bastian, University of Minnesota Medical School, United States

Background: The developing brain requires coordination of axon outgrowth and guidance molecules to enable growth cone pathfinding towards targets. The growth cone has high metabolic requirements in order to continually produce energy, dynamically rearrange the cytoskeleton, and traffic proteins. To meet these local energy demands mitochondria are trafficked to and accumulate in the growth cone and at nascent branch points; mitochondrial function and iron homeostasis are intimately linked as iron is metabolized in mitochondria and is required for aerobic ATP production. Iron is required for anterograde mitochondrial trafficking to support dendritic arborization and thus proper regulation of iron homeostasis is necessary for the functional development of neurons. Consequently, iron deficiency—the most common gestational-neonatal micronutrient disorder in the world—affects learning and memory, psychosocial behaviors, and motor skills even after repletion of iron.

Objectives: The neurological changes observed with iron deficiency are linked to dysregulation of axon growth, branching, and synapse formation in other disease states. This led us to hypothesize that iron-dependent mitochondrial function is necessary for proper regulation of axonal growth dynamics.

Design/Methods: Cultured hippocampal neurons obtained from embryonic day 16.5 mice were treated with 9μm Deferoxamine (DFO) starting at 3 days in vitro (DIV) to generate iron deficient neurons. At 7 DIV, iron deficient (DFO+) and iron sufficient (control; DFO-) neurons were live imaged to observe axon morphology and mitochondrial motility.

Results: Iron sufficient neurons supported both lengthening of the primary growth cone-led axon and branching along the axon shaft compared to iron deficient neurons which had a negative relationship between primary axon growth and branching (p = .024; see Figure). Live imaging of mitochondria in the terminal region of the axon showed that iron deficient neurons have a trend towards decreased mitochondrial velocity (p = .100), increased pausing (p = .070), and decreased density (p = .065) compared to iron-sufficient neurons.

Conclusion: Iron may be required for proper mitochondrial function to support both primary axon growth and branching. To follow up on these findings, we are developing a primary neuron culture model to investigate iron regulation in axon development using live imaging of cytoskeletal dynamics and mitochondria motility.