Diverse functional roles of lipocalin-2 in the central nervous system

Lipocalin-2 (LCN2) is an acute phase protein with multiple functions that has garnered a great deal of interest over the last decade. However, its precise role in the pathophysiology of the central nervous system (CNS) remains to be outlined. Emerging evidence indicates that LCN2 is synthesized and secreted as an inducible factor from activated microglia, reactive astrocytes, neurons, and endothelial cells in response to inflammatory, infectious, or injurious insults. More recently, it has been recognized as a modulatory factor for diverse cellular phenotypes in the CNS, such as cell death, survival, morphology, migration, invasion, differentiation, and functional polarization. LCN2 induces chemokine production in the CNS in response to inflammatory challenges, and actively participates in the innate immune response, cellular influx of iron, and regulation of neuroinflammation and neurodegeneration. LCN2 also modulates several biobehavioral responses including pain hypersensitivity, cognitive functions, emotional behaviors, depression, neuronal excitability, and anxiety. This review covers recent advances in our knowledge regarding functional roles of LCN2 in the CNS, and discusses how LCN2 acts as an autocrine mediator of astrocytosis, a chemokine inducer, and a modulator of various cellular phenotypes in the CNS. We finally explore the possibilities and challenges of employing LCN2 as a signature of several CNS anomalies.