Interleukin-6 protects retinal ganglion cells from pressure-induced death.
OBJECTIVE
The response of retinal ganglion cells (RGCs) to ocular pressure in glaucoma likely involves signals from astrocytes and microglia. How glia-derived factors influence RGC survival at ambient and elevated pressure and whether the inflammatory cytokine interleukin-6 (IL-6) is a contributing factor were investigated.


METHODS
Primary cultures of retinal astrocytes, microglia, and RGCs were prepared using immunomagnetic separation. Comparisons were made of RGC survival at ambient and elevated pressure (+70 mm Hg) and with pressure-conditioned medium from glia with, and depleted of, IL-6.


RESULTS
Pressure elevated for 24 to 48 hours reduced RGC density, increased TUNEL labeling, and upregulated several apoptotic genes, including the early immediate genes c-jun and jun-B. Pressure-conditioned medium from astrocytes reduced RGC survival another 38%, while microglia medium returned RGC survival to ambient levels. These effects were unrelated to IL-6 in microglia medium. Neither astrocyte- nor microglia-conditioned medium affected ambient RGC survival unless depleted of IL-6, which induced a 63% and a 18% decrease in RGCs, respectively. Recombinant IL-6 equivalent to levels in glia-conditioned medium doubled RGC survival at elevated pressure.


CONCLUSIONS
For RGCs at ambient pressure, IL-6 secreted from astrocytes and microglia under pressure is adequate to abate other proapoptotic signals from these glia. For RGCs challenged by elevated pressure, decreased IL-6 in astrocyte medium is insufficient to counteract these signals. Increased IL-6 in microglia medium counters not only proapoptotic signals from these cells but also the pressure-induced apoptotic cascade intrinsic to RGCs.
Sappington
Rebecca M
RM
Vanderbilt Eye Institute, Vanderbilt University Medical Center, Nashville, Tennessee 37232-0654, USA.
Chan
Matilda
M
Calkins
David J
DJ
D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D002469:Cell Separation; D019610:Cytoprotection / Q000187:drug effects; D004797:Enzyme-Linked Immunosorbent Assay; D006874:Hydrostatic Pressure; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D015850:Interleukin-6 / Q000494:pharmacology* / Q000502:physiology; D017628:Microglia / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000494:pharmacology; D012165:Retinal Ganglion Cells / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015854:Up-Regulation; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000378:metabolism
D015850:Interleukin-6; D019253:Proto-Oncogene Proteins c-bcl-2; D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D011994:Recombinant Proteins; D051028:bcl-2-Associated X Protein