Iron Deficiency Impairs Mitochondrial Energetics and Early Axonal Growth and Branching in Developing Hippocampal Neurons

Background: Energy deficits underlie many neurodevelopmental, neuropsychiatric, and neurodegenerative diseases implicating mitochondria as a potential therapeutic target. Iron is necessary for neuronal energy output through its direct role in mitochondrial oxidative phosphorylation. Iron deficiency (ID) reduces mitochondrial energetic capacity in developing hippocampal neurons and causes simplified dendritic arbors and impaired learning and memory. Objectives: This study aimed to determine the effect of ID on axonogenesis, which has not been previously explored. Methods: We used an embryonic mouse mixed-sex primary hippocampal neuron culture model of developmental ID, using iron chelation with low micromolar deferoxamine (DFO) from 3 d in vitro (DIV) to 7 DIV compared with untreated control cultures. Mitochondrial respiration and dynamics, cytoskeletal and metabolic gene expression, and axonal and synaptic morphology were quantified and compared using t-test, analysis of variance, and multivariate statistical analyses. Results: Seven DIV DFO-treated neuron cultures (n = 4–17) demonstrated moderate ID with significantly decreased mRNA levels for genes involved in axon cytoskeletal development (Gda, Pfn2, and Nuak1; ∼20%–40% lower) and metabolic homeostasis (Ndufs1, Ddit4, and Slc2a3; ∼20%–25% lower). DFO significantly reduced total adenosine-5′-triphosphate production rate and measures of mitochondrial oxidative phosphorylation by ∼25% to 50% compared with control cultures (n = 11–14). DFO significantly reduced the length of the primary axon and axonal branches by ∼20%, without affecting branch number (n = 100 neurons). Axonal mitochondrial motility was not altered by ID (n = 11–12 neurons), suggesting that impaired mitochondrial energetics, and not trafficking, is the predominate mitochondrial contribution to axon morphological deficits. Ultimately, at 18 DIV, DFO significantly reduced the density of postsynaptic density puncta, a measure of neuronal capacity for synapse formation, by 30% (n = 26–32 neurons). Conclusions: These findings provide the first link between iron-dependent neuronal energy production and early axon structural development and highlight the importance of maintaining sufficient iron during the embryonic period of rapid axonal growth to prevent the persistent negative consequences of ID on neuronal structure.