Glial reactivity, an early feature of diabetic retinopathy.
OBJECTIVE
To characterize early structural gliotic reactions in retinal Müller cells, astrocytes, and microglia in experimentally induced diabetes.


METHODS
Rats were rendered diabetic by streptozotocin injection and killed after 2, 4, 12, or 20 weeks. Cell densities were determined in flatmounted retinas or transverse semithin sections. Expression of glial fibrillary acidic protein (GFAP) was localized on frozen sections or flatmounts by immunofluorescence and confocal microscopy, and GFAP content was evaluated by Western blot analysis. Microglial cells were visualized by binding of isolectin B4 or staining with antibodies to phosphotyrosine residues. The integrity of the blood-retinal barrier was assessed by intravenous injection of Evans blue.


RESULTS
The density of Müller cells and microglia was significantly increased at 4 weeks of diabetes compared with nondiabetic controls. GFAP expression in Müller cells was not detected at 4 weeks but was prominent at 12 weeks. The number of astrocytes was significantly reduced at 4 weeks in the peripapillary and far peripheral retina. Shape changes of microglial cells indicated functional activation. Leakage of the blood-retinal barrier was observed at 2 weeks of hyperglycemia, the earliest time point investigated.


CONCLUSIONS
The leakage of the blood-retinal barrier before glial reactivity suggests that glia are early targets of vascular hyperpermeability. The individual glial cell types react differentially to the diabetic state. Müller cells undergo hyperplasia preceding GFAP expression, and microglial cells are activated, whereas astrocytes regress. This glial behavior may contribute decisively to the onset and development of neuropathy in the diabetic retina.
Rungger-Brändle
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Cell Biology Laboratory, University Eye Clinic, Geneva, Switzerland. elisabeth.rungger@hcuge.ch
Dosso
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AA
Leuenberger
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PM
D000818:Animals; D001813:Blood-Retinal Barrier; D015153:Blotting, Western; D002199:Capillary Permeability; D002452:Cell Count; D003921:Diabetes Mellitus, Experimental / Q000139:chemically induced / Q000378:metabolism / Q000473:pathology*; D003930:Diabetic Retinopathy / Q000139:chemically induced / Q000378:metabolism / Q000473:pathology*; D019084:Fluorescent Antibody Technique, Indirect; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D018613:Microscopy, Confocal; D009457:Neuroglia / Q000378:metabolism / Q000473:pathology*; D051381:Rats; D011921:Rats, Inbred WKY; D012171:Retinal Vessels / Q000378:metabolism / Q000473:pathology
D005904:Glial Fibrillary Acidic Protein