Neonatal phlebotomy-induced anemia compromises mitochondrial bioenergetics in the developing hippocampus

BackgroundAnemia is a common medical condition in preterm infants. Previous studies show that neurodevelopmental outcomes of preterm infants are dependent in part on the degree of anemia. In a developmentally appropriately-timed neonatal mouse model, phlebotomy induced anemia (PIA) of the degree commonly seen in hospitalized preterm infants results in brain iron deficiency and hypoxia and significant short-term and long-term brain dysfunction, especially in the hippocampus. Iron and oxygen are critical for mitochondrial oxidative phosphorylation-mediated ATP production and thus energetically demanding brain developmental processes (e.g., axon/dendrite growth, myelination, synaptogenesis). ObjectiveTo test the hypothesis that neonatal PIA acutely impairs mitochondrial respiratory capacity and electron transport chain (ETC) complex function in the developing hippocampus. MethodsNeonatal mice were phlebotomized daily beginning on postnatal day 3 (P3). On P14, mitochondria were isolated from the hippocampus of male and female PIA and non-bled mice. Seahorse bioenergetic analyses were performed to determine the effects of PIA on mitochondrial oxidative phosphorylation activity and ETC complex functional capacity. ResultsPIA hippocampal mitochondria demonstrated an overall reduced oxygen consumption rate (OCR) compared to non-bled controls when ETC oxygen consumption was coupled to ATP production. PIA reduced hippocampal mitochondrial OCR that was not due to the ETC in females not males. Basal respiration, proton leak, and maximal respiratory capacity were significantly reduced in PIA hippocampal mitochondria, an effect that did not differ by sex. When mitochondrial ETC oxygen consumption was uncoupled from ATP production with the protonophore FCCP, a mild reduction in OCR was observed across all ETC complexes, with only complex I-mediated OCR being significantly lower than non-bled controls. ConclusionsThese findings suggest that impaired mitochondrial energetic capacity may mechanistically contribute to the persistent neurobehavioral deficits caused by PIA, through dysregulation of energy-demanding neurodevelopmental processes (e.g., neuron structural maturation).