Iron-Dependent Mechanism of Neuronal Bdnf Suppression by Cellular Iron Deficiency

Abstract

Abstract Objectives Iron deficiency (ID) during neural development is associated with long-term neurocognitive dysfunction. In rodent models, the cognitive deficit is associated with reduced hippocampal brain-derived neurotrophic factor (Bdnf) expression in adulthood despite early iron treatment. Since a previous study suggested a role of epigenetic modifications at the Bdnf locus, we assessed whether an iron-dependent signaling pathway from ID → HIF1α → JARID1B (Fe-containing histone demethylase) → Bdnf is responsible for Bdnf suppression in iron-deficient neurons. The objective is to determine the effect of ID on the HIF1α/JARID1B/Bdnf pathway in vitro and in vivo. Methods A hippocampal neuronal cell line HT-22 (n = 3/group) was used to assess cellular changes following deferoxamine (10 μM) induced-ID. In parallel, timed pregnant Sprague-Dawley rats were fed a purified iron deficient diet (ID, 4 mg Fe/kg) from gestational day (G)2 to through postnatal day (P)7 to induce a similar degree of neuronal ID. At P7, nursing dams where switched to a purified-iron sufficient diet (IS, 200 mg Fe/kg). Control dams were fed IS diet. Hippocampi (n = 6/group) were collected from P15 ID and IS rats. Enrichment of HIF1α, JARID1B, USF1, histone H3 methylation at the Bdnf promoter in both models was determined using ChIP-qPCR. Results were analyzed using t-test for pairwise comparison and α ≤ 0.05. Results ID increased nuclear HIF1α in HT-22 cells (P = 0.03), suggesting less hydroxylated-HIF1α due to reduced Fe-dependent prolyl hydroxylase (PHD) activity. Increased nuclear HIF1α led to increased binding and transactivation at the VEGF (positive control, P = 0.03)) and JARID1B promoters (P = 0.04), which in turns reduced Bdnf expression in HT-22 cells (P = 0.02). Similar effects were observed in iron-deficient P15 hippocampus. Conclusions This is the first evidence that ID directly regulates long-term neural gene expression through the cellular PHD/HIF1α/JARID1B pathway to induce epigenetic modifications both in vitro and in vivo models. Funding Sources 1R01NS099178.