Ferrous ion deficiency drives naphthalene-1,4-dione coated black carbon-induced mitochondrial dysfunction and phagocytic capacity depression in RAW264.7 cells.

Numerous reports indicated that particulate matter (PM) 2.5 could influence mitochondrion function and disrupt iron homeostasis. Many existing studies predominantly emphasize the role of iron overload (Fe3 +/Fe2+ accumulation) on the damage of mitochondria. But whether the PM could induce iron deficiency or not and related dysfunction remain unclear. Current related clues suggest those need to be investigated. In this study, we employed naphthalene-1,4-dione (1,4 NQ) coated black carbon (BC) as a PM2.5 surrogate to reveal the role of Fe2+ deficiency in 1,4 NQ-BC induced phagocytic capacity depression and mitochondrial dysfunction. Sprague-Dawley rats were exposed to 1,4 NQ-BC (0, 300, 600, 1200 μg/ week) through intratracheal instillation for 30 days. Alveolar macrophages (AMs) of rats and RAW264.7 cells served as in vitro models. It was found that 1,4 NQ-BC depressed the phagocytic capacity of RAW264.7 cells. Meanwhile it reduced adenosine triphosphate (ATP) level and mitochondrial membrane potential (ΔΨm) in both AMs and RAW264.7 cells. Liquid chromatography-mass spectrometry assay revealed that 1,4 NQ-BC promoted glycolysis while depressed oxidative phosphorylation process. Notably, the reduction of Fe2+ was detected simultaneously with the upregulation of FPN1 after 1,4 NQ-BC treatment. Supplementation of ferric ammonium citrate (FAC) elevated Fe2+ level in RAW264.7 cells. Furthermore, siRNA-mediated depression of ferroportin1 (FPN1) and transcription factor EB (TFEB) overexpression could rescue 1,4 NQ-BC-induced Fe2+ deficiency. Importantly, Fe²⁺ replenishment reversed 1,4-NQ-BC-induced ATP depletion and rehabilitated mitochondrion function, hence restored phagocytic capacity of RAW264.7 cells. In conclusion, our findings identified Fe²⁺ deficiency as a sensitive mediator of 1,4 NQ-BC-induced mitochondrial and phagocytic dysfunction in macrophages. The results suggested that the rescue of Fe2+ deficiency could restore 1,4 NQ-BC induced mitochondrial dysfunction and phagocytotic disability in macrophages.