Chronic energy depletion due to iron deficiency impairs dendritic mitochondrial motility during hippocampal neuron development

During development, neurons require highly integrated metabolic machinery to meet the large energy demands of growth, differentiation, and synaptic activity within their complex cellular architecture. Dendrites/axons require anterograde trafficking of mitochondria for local ATP synthesis to support these processes. Acute energy depletion impairs mitochondrial dynamics, but how chronic energy insufficiency affects mitochondrial trafficking and quality control during neuronal development is unknown. Because iron deficiency impairs mitochondrial respiration/ATP production, we treated mixed-sex embryonic mouse hippocampal neuron cultures with the iron chelator deferoxamine (DFO) to model chronic energetic insufficiency and its effects on mitochondrial dynamics during neuronal development. At 11 days in vitro (DIV), DFO reduced average mitochondrial speed by increasing the pause frequency of individual dendritic mitochondria. Time spent in anterograde motion was reduced; retrograde motion was spared. The average size of moving mitochondria was reduced, and the expression of fusion and fission genes was altered, indicating impaired mitochondrial quality control. Mitochondrial density was not altered, suggesting that respiratory capacity and not location is the key factor for mitochondrial regulation of early dendritic growth/branching. At 18 DIV, the overall density of mitochondria within terminal dendritic branches was reduced in DFO-treated neurons, which may contribute to the long-term deficits in connectivity and synaptic function following early-life iron deficiency. The study provides new insights into the cross-regulation between energy production and dendritic mitochondrial dynamics during neuronal development and may be particularly relevant to neuropsychiatric and neurodegenerative diseases, many of which are characterized by impaired brain iron homeostasis, energy metabolism and mitochondrial trafficking.