Abstract
Purpose :
Lipoxins (LXA4 and LXB4) are neuroprotective lipid mediators in the inner retina and their formation is regulated by retinal stress. Muller glia are among the earliest glial cells to react following ocular hypertension (OHT) and contribute to glaucomatous neuropathy. The goal of this study was to determine if Muller glia contribute to the retinal lipoxin pathway.
Methods :
Primary mouse Muller cells [Aldh1l1] (passage 3-5) and an immortalized rat Muller cell line were used to investigate expression and function of the lipoxin pathway. Cell type and purity were validated by qPCR and immunocytochemistry using established macroglia, microglia, and retinal ganglion cell (RGC) markers. RNA and functional expression of the lipoxin pathway were assessed by qPCR and LC/MS/MS-based lipidomic analysis. Muller glia reactivity was induced in vitro by treatment with a cytokine cocktail (TNF-alpha, IL1-alpha, and C1q) or a TRPV4 agonist (GSK101), for 24 hours. Muller glia reactivity was validated through qPCR expression of standard macroglia activation genes: LCN2, GFAP, Nestin, and Vimentin. Muller cell reactivity was investigated in vivo using the mouse silicon oil model of chronic ocular hypertension.
Results :
Muller glia reactivity was one of the earliest retinal cell responses to ocular hypertension in mice. qPCR analysis of primary and immortalized Muller glia established expression of the full lipoxin pathway (Alox5, Alox15, and Fpr2) in Muller glia. Lipidomic analysis established functional activity of the lipoxin pathway (formation of 5-HETE, 12-HETE and 15-HETE). More importantly, Muller cells generated neuroprotective LXB4 (500 pg/106 cells). Induction of a reactive Muller glia phenotype by both cytokine treatment or TRPV4 activation significantly changed expression of the lipoxin pathway and LXB4 release compared to homeostatic Muller glia.
Conclusions :
Muller glia, the most abundant macroglia in the retina, functionally express the lipoxin pathway and generate neuroprotective LXB4. A key feature of reactive Muller glia was a marked shift in the expression of the lipoxin pathway and LXB4 formation. These findings identify a new cell type that generates neuroprotective lipoxins in the retina. Muller glia are the predominant synaptic macroglia in the retina essential for maintaining RGCs. The role and regulation of the Muller glial neuroprotective lipoxin pathway is of great interest and warrants further investigation.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.