Overdosing on iron: Elevated iron and degenerative brain disorders

All cells in organisms ranging from yeast to humans utilize iron as a cofactor or structural element of proteins that function in diverse and critical cellular functions. However, deregulation of the homeostatic mechanisms regulating iron metabolism resulting in a reduction or excess of iron within the cell or outside of it can have serious effects to the health of cells and the organism. This review provides a brief overview of the molecular and cellular mechanisms regulating iron physiology, including the molecules and processes regulating iron uptake, its storage and utilization, its recycling, and its release from the cell, such that the cellular iron levels are sufficient to meet metabolic demand but below those that cause permanent damage. The major focus of review is on the pathological consequences of dysregulation of these homeostatic mechanisms, focusing on the brain. Current advances on the role of iron accumulation to the pathogenesis of rare neurological disorders caused by genetic mutations as well as to the more prevalent and age-associated neurodegenerative diseases are described. Impact statement Brain degenerative disorders, which include some neurodevelopmental disorders and age-associated diseases, cause debilitating neurological deficits and are generally fatal. A large body of emerging evidence indicates that iron accumulation in neurons within specific regions of the brain plays an important role in the pathogenesis of many of these disorders. Iron homeostasis is a highly complex and incompletely understood process involving a large number of regulatory molecules. Our review provides a description of what is known about how iron is obtained by the body and brain and how defects in the homeostatic processes could contribute to the development of brain diseases, focusing on Alzheimer's disease and Parkinson's disease as well as four other disorders belonging to a class of inherited conditions referred to as neurodegeneration based on iron accumulation (NBIA) disorders. A description of potential therapeutic approaches being tested for each of these different disorders is provided.