Expression and localization of the iron-siderophore binding protein lipocalin 2 in the normal rat brain and after kainate-induced excitotoxicity

Lipocalin 2 (LCN2) is produced by mammalian hosts to bind bacterial siderophore and sequester free iron as part of an innate immune response, and could also play a role in tissue iron homeostasis, but thus far, little is known about its expression in the CNS. The present study was carried out to study the expression of the lipocalin in the normal rat brain and after neuronal injury induced by kainate (KA). Low levels of LCN2 mRNA and protein expression were detected in most regions of the normal brain except the olfactory bulb, brainstem and cerebellum. KA lesions resulted in damage to the hippocampus, leading to an early increase at three days and a sustained elevation in LCN2 mRNA level of 16-fold, and protein expression at 80-fold in the lesioned tissue compared to controls at 2 weeks post-KA injection. The sustained elevation in mRNA expression was not detected among other lipocalins surveyed using real-time RT-PCR - apoD, PGDS, Rbp4 and LCN5. Single and double immunostaining confirmed that LCN2 is present in astrocytes in the olfactory bulb, brainstem and cerebellum of the normal brain, and reactive astrocytes in the KA-lesioned hippocampus. In conclusion, the present study showed LCN2 to be present in select brain regions, and is upregulated in astrocytes after neuronal injury induced by kainate. We postulate that, as in the periphery, LCN2 may have a role in iron transport or trafficking in the CNS.