Lipocalin-2 production by astrocytes in response to high concentrations of glutamate

Abstract

Aims: Glutamate-induced excitotoxicity is mainly mediated by neuronal NMDA receptors; however, it is unclear how astrocytes are involved in this phenomenon. This study aimed to explore the effects of excess glutamate on astrocytes both in vitro and in vivo.

Methods: We used astrocyte-enriched cultures (AECs), in which microglia were removed from mixed glial cultures, to investigate the effects of extracellular glutamate on these cells by microarray, quantitative PCR, ELISA, and immunostaining. We also examined the production of lipocalin-2 (Lcn2) by immunohistochemistry in the brains of mice after status epilepticus induced by pilocarpine and by ELISA in the cerebrospinal fluid (CSF) of patients characterised by status epilepticus.

Results: Microarray analysis identified Lcn2 as a factor upregulated in AECs by excess glutamate; glutamate addition increased Lcn2 in the cytoplasm of astrocytes and AECs released Lcn2 in a concentration-dependent manner. Lcn2 production was reduced by chemical inhibition of metabotropic glutamate receptor or siRNA knockdown of metabotropic glutamate receptor 3. Furthermore, Lcn2 was increased in the astrocytes of a status epilepticus mouse model and in the CSF of human patients.

Conclusion: These results indicate that astrocytes stimulate Lcn2 production via metabotropic glutamate receptor 3 in response to high concentrations of glutamate.

Keywords: Astrocyte; FIRES; GRM3; Glutamate; Lcn2; NGAL; Status epilepticus.