Astrocyte-Produced Lipoxins Protect Retinal Ganglion Cells from Acute and Chronic Stress

Abstract

Purpose : Astrocytes play critical homeostatic roles in the CNS and retina. We have demonstrated that quiescent retinal astrocytes promote retinal ganglion cell (RGC) survival in vivo, and that the protective activity is present in the astrocyte-conditioned media (ACM). Here we report that astrocyte-produced lipoxins, a family of secreted small lipid mediators, provide RGC protection from acute insult and elevated intraocular pressure (IOP). This activity includes a direct neuroprotective component that alters mitochondrial membrane potential.

Methods : ACM and control media were analyzed by LC-MS/MS to determine levels of lipid mediator production.In addition, retinal expression of lipoxin producing enzymes and receptors was determined by qPCR and immunofluorescence. Protective activity of the identified lipoxins was tested in vivo by intravitreal injection, in combination with acute kainic acid (KA) injury or sustained elevated IOP through perilimbal suture. RGC survival from the KA and IOP injury was quantified using RGC specific antibodies and functional electroretinogram. RGC survival and mitochondrial membrane potential were quantified in vitro using confocal microscopy.

Results : We established that the two endogenous lipoxins LXA₄ and LXB₄ are enriched in protective ACM. Following intravitreal injection we found that each lipoxin significantly reduced RGC loss from acute injury, with LXB₄ being more potent. Furthermore, inhibition of 5-LOX, a key enzyme for lipoxin biosynthesis, compromised RGC survival, while an antagonist against FPR2, an LXA₄ receptor, also reduced survival. Direct neuroprotective activity was observed on cultured RGCs, associated with normalization of mitochondrial membrane potential. Finally, therapeutic LXB₄ treatment in a chronic, elevated IOP rat model promoted RGC function and survival.

Conclusions : These data demonstrate that the lipoxins, LXA₄ and LXB₄, are produced by retinal astrocytes. They exhibit direct neuroprotective activity and their production is reduced following retinal injury. We characterized their biosynthesis and roles in inner retinal injury and discovered higher protective activity for LXB₄ which is associated with stabilizing mitochondrial membrane potential. Finally, we demonstrated that therapeutic LXB₄ administration is functionally and pathologically efficacious in a chronic glaucoma model.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.