RETINAL GFAP AND BFGF EXPRESSION AFTER MULTIPLE ARGON-LASER PHOTOCOAGULATION INJURIES ASSESSED BY BOTH IMMUNOREACTIVITY AND MESSENGER-RNA LEVELS

The expression of GFAP and bFGF after retinal photocoagulation injury in the rat was assessed by immunocytochemistry and reverse transcripta se PCR. Beta-actin mRNA expression was unaltered after injury and was therefore a good control for the quality of the RNA samples and the PC R reaction. GFAP mRNA increased from undetectable levels in normal ret ina to relatively high levels at 24 and 48 hr after injury, returning to barely detectable levels at 3 and 7 days. Muller cell GFAP immunore activity was elevated by 24 hr, stronger by 48 hr and persisted for 30 -45 days. Thus, the expression of GFAP immunoreactivity after photocoa gulation was due to new protein synthesis but the mRNA, and therefore the stimulus, was only present for a few days. This indicates that the GFAP protein in Muller cells has a long lifetime similar to that of a strocytes despite different gene control elements. bFGF is a possible stimulus for Muller GFAP expression because Muller cells have bFGF rec eptors. bFGF mRNA was detectable in normal, 24 and 48 hr retinas but d ecreased to undetectable levels (even after 35 cycles of PCR) at three days after injury and had only partly recovered by 7 days. Immunocyto chemistry demonstrated a rapid change in localization of bFGF at the l esion sites early after lesion. At 2-3 days bFGF in blood vessels was markedly increased while at 7 days there was an increase around the ph otoreceptors flanking each lesion. These shifts in bFGF localization w ere too late to be a stimulus for the widespread upregulation of GFAP expression by Muller cells. The reduction in bFGF mRNA at three days w as unexpected as studies of brain injury generally show a longer lasti ng elevation of bFGF expression. Therefore it is likely that bFGF expr ession is controlled by different mechanisms in the retina compared to the brain. However, a reduction in bFGF synthesis after photocoagulat ion is consistent with the anti-angiogenic effect of laser photocoagul ation in diabetic retinopathy (C) 1997 Academic Press Limited.