Extracellular vesicles released from blood-brain barrier endothelial cells mediate brain iron accumulation during...

Brain inflammation leads to an increase in the amount of iron in brain tissue, but the source of the iron that could lead to accumulation remains unclear. Our recent in vitro study discovered that, in addition to the traditional pathway, iron can be released from the blood-brain barrier via extracellular vesicles (EVs). Herein, we investigated the impact of brain inflammation on iron release via EVs from the brain microvasculature (BMV). For this study, we induced brain inflammation in three-month-old C57BL/6 by intracerebroventricular injection of lipopolysaccharide (LPS, 12 μg/mice). For in vitro, we used human blood-brain barrier endothelial cells derived from human-induced pluripotent stem cells (hiPSCs). The LPS injection activated microglia and astrocytes as well as increased brain proinflammatory cytokines compared to the control mice. Furthermore, brain inflammation increased the iron levels in the brain parenchyma but decreased the iron levels in BMV. Brain inflammation was associated with the degradation of ferroportin (FPN1), an iron exporter, in the BMV. CD63, an EVs membrane protein, was increased in the BMV and associated with increased FTH1 release via EVs from BMVs to the brain. Moreover, brain inflammation decreased iron in BMV as evidenced by an increase in the transferrin receptor and decreased FTH1, suggestive of increased iron uptake. Pharmacological reduction of EVs by GW4869 reduced iron accumulation in the inflamed brain parenchyma compared to control mice. In summary, we have discovered a novel mechanism by which BMV-released EVs enriched with FTH1 and reveal a significant mechanism for brain iron accumulation during inflammation.