Dysregulation of Neuroprotective Lipoxin Pathway in Astrocytes in Response to Cytokines and Ocular Hypertension.

PURPOSE: Glaucoma leads to vision loss due to retinal ganglion cell death. Astrocyte reactivity contributes to its neurodegeneration. Our recent study found that lipoxin B 4 (LXB 4 ), produced by retinal astrocytes, has direct neuroprotective actions on retinal ganglion cells. However, regulation of lipoxin formation and cellular targets for their neuroprotective activity in glaucoma remain to be defined. We investigated if ocular hypertension and inflammatory cytokines regulate astrocyte lipoxin pathway and if LXB 4 can regulate astrocyte reactivity.

DESIGN: Experimental study.

SUBJECTS/PARTICIPANTS/CONTROLS: C57BL/6J mice were administered silicon oil into the anterior chamber to induce ocular hypertension (n=40). Age and gender-matched mice served as control subjects (n=40).

METHODS: RNAscope in-situ hybridization, RNA-seq, and qPCR to analyze gene expression. LC/MS/MS lipidomics to assess functional expression of the lipoxin pathway. Retinal flat mounts and immunohistochemistry (IHC) to assess macroglia reactivity. OCT quantified the retinal layer thickness in vivo, and ERG assessed retinal function. Primary human brain astrocytes were used for in vitro reactivity experiments. Non-human primate optic nerves were used to assess gene and functional expression of the lipoxin pathway.

MAIN OUTCOME MEASURES: Intraocular pressure, RGC function, OCT measurements, gene expression, in situ hybridization, lipidomic analysis, and IHC.

RESULTS: Gene expression and lipidomic analysis established functional expression of the lipoxin pathway in the mouse retina, optic nerve of mice and primates, as well as human brain astrocytes. Ocular hypertension caused significant dysregulation of this pathway, with an increase in 5-lipoxygenase (5-LOX) activity and a decrease in 15-lipoxygenase activity. This dysregulation was coincident with a marked upregulation of astrocyte reactivity in the mouse retina. Reactive human brain astrocytes also showed a marked increase in 5-LOX. Administration of LXB 4 regulated the lipoxin pathway, restored and amplified LXA 4 generation, and mitigated astrocyte reactivity in mouse retinas and human brain astrocytes.

CONCLUSIONS: The lipoxin pathway is functionally expressed in retina and brain astrocytes, optic nerves of rodents and primates, a resident neuroprotective pathway that is downregulated in reactive astrocytes. Novel cellular targets for LXB 4 's neuroprotective action is inhibition of astrocyte reactivity and restoration of lipoxin generation. Amplifying the lipoxin pathway is a potential target to disrupt or prevent astrocyte reactivity in neurodegenerative diseases.