The Role of Iron in Neuronal Homeostasis: A Double-Edged Sword.

Iron is an essential micronutrient that plays a central role in numerous biological processes. Despite its relatively low abundance in the human body, iron is particularly critical for brain function. Systemic and cerebral iron homeostasis is tightly regulated through coordinated mechanisms involving absorption, transport, storage, and recycling. Within the brain, iron metabolism is further controlled by the blood-brain barrier and specialized neural cell populations, including neurons, astrocytes, oligodendrocytes, and microglia. Iron is indispensable for neurodevelopment, supporting neurogenesis, myelination, and neurotransmitter synthesis. However, both iron deficiency and iron overload have detrimental consequences. Early-life iron deficiency disrupts neural development and leads to long-lasting cognitive, motor, and behavioral impairments, whereas excessive iron accumulation promotes oxidative stress, ferroptosis, and neuroinflammation. These mechanisms have been described to contribute to the pathogenesis of major neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, neurodegeneration with brain iron accumulation, and amyotrophic lateral sclerosis. This review first outlines systemic and brain iron metabolism, highlighting how neural cells regulate homeostasis. Next, it examines iron's physiological roles, particularly in neurogenesis and neurodevelopment. Finally, it explores iron's involvement in neurodegenerative diseases, emphasizing neuroinflammation as a primary mechanism of iron toxicity.