Abstract
Purpose: :
Prior work in our laboratory has elucidated a role for the leukotrienes, 5-lipoxygenase metabolites of arachidonic acid, in the pathogenesis of diabetic retinopathy. Our goal was to determine the cell types involved in leukotriene signaling in the retina. In the brain, glial cell production of leukotrienes can alter vascular endothelial cell function. We evaluated the role of leukotriene production by retinal glial cells in the pathogenesis of diabetic retinopathy.
Methods: :
Using the streptozotocin-induced diabetic mouse model, retinas from mice at 9 months diabetes duration and retinas from nondiabetic mice were analyzed for expression of proteins involved in the biosynthesis and signaling of leukotrienes. To determine the retinal cells involved in leukotriene generation, cultured mouse retinal glial cells (mRGlia) were similarly analyzed for enzymes and receptors important in leukotriene signaling. Mouse retinal vascular endothelial cells (mREC) were examined for leukotriene receptor expression and effects of leukotriene administration on cellular viability and expression of NF-kappaB.
Results: :
Diabetic mouse retinas demonstrated a significant increase in the expression of leukotriene A4 (LTA4) hydrolase, the enzyme critical in the generation of proinflammatory leukotriene B4 (LTB4), and BLT1, the principal receptor for LTB4, when compared to retinas from nondiabetic mice. mRGlia cells also expressed LTA4 hydrolase and BLT1 with increased expression of both proteins when mRGlia were cultured in media containing 25mM glucose, diabetic-like conditions, compared to 5mM glucose. mRGlia expression of BLT1 was augmented in a time-dependent manner following addition of its ligand LTB4 to the culture media with peak levels of expression reached one hour after LTB4 addition and similar to peak levels induced by 25 mM glucose. mREC also expressed BLT1. mREC cultured in media containing 100 nM LTB4 had reduced cell viability compared to LTB4-free media. The cell death induced by LTB4 was prevented by incubation of mREC with the BLT1 antagonist U75302. In other cell types, BLT1 post-receptor signaling has been linked to activation of NF-kappaB, a regulator of proinflammatory gene transcription. Immunofluoresence studies of mREC demonstrated increased nuclear expression of the p65 subunit of NF-kappaB following LTB4 addition.
Conclusions: :
Retinal glial cells express LTA4 hydrolase and are a potential source of LTB4 production in the retina. Intraretinal synthesis of LTB4 may contribute to endothelial cell dysfunction in diabetic retinopathy.
Keywords: diabetes • retina • retinal glia