T-Cell Derived Lipocalin-2 Upregulates TNF-α in Optic Nerve Head Astrocytes

Abstract

The purpose of this study was to investigate lipocalin-2 (Lcn2) as a potential reactive astrocyte marker in the glaucomatous optic nerve. Glaucoma is a disease of the optic nerve that results in irreversible vision loss secondary to retinal ganglion cell damage and astrocyte reactivity in response to glaucomatous injury. Due to the role of Lcn2 in reactive astrocytes of glaucomatous optic nerves being poorly elucidated, we studied Lcn2 in the setting of optic nerve crush (ONC), DBA/2J, and microbead injection (ocular hypertension) models. In situ hybridization and immunohistochemistry (IHC) were used to detect and localize Lcn2 in tissue samples. Quantification was performed using qPCR. We found that Lcn2 expression is upregulated in the ONC and DBA/2J models, but not in the microbead injection model. IHC revealed Lcn2+ cells starting 4 h following ONC. However, in contrast to what was expected, these cells were not astrocytes or microglia. Instead, the co-labeling of Lcn2+ cells with CD3 indicates a T-cell population. qPCR screening of ONH astrocytes cultured in Lcn2 revealed that neither the neurotoxic A1 nor neuroprotective A2 reactive astrocyte phenotype was acquired. Instead, Lcn2 differentially upregulated the inflammatory marker TNF-α in astrocytes, thus demonstrating that Lcn2 is not a marker for reactive astrocytes. These findings propose a link between Lcn2 and TNF-α that may be key in decreasing ON inflammatory degeneration.