Lipocalin-2, a member of the lipocalin family of proteins, was originally identified as a gelatinase-associated component of neutrophil secretory granules (1). Lipocalin-2 is involved in innate immunity, iron homeostasis, and apoptosis. Lipocalin-2 limits bacterial growth by binding to bacterial siderophores and sequestering iron (2-4). In mammalian cells, iron-loaded lipocalin-2 binds to its receptor, 24p3R, and is internalized, thereby releasing iron and increasing the intracellular iron concentration (5). Conversely, iron-free lipocalin-2 promotes apoptosis (5). Lipocalin-2 is also expressed in adipose tissue and promotes insulin resistance in cultured mouse adipocytes (6).
