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S. Roth, Q. Li, A.R. Shaikh, M. Hennelly, C.E. Graham, V. Bindokas; Functional Roles of Mitogen-activated Protein Kinases in Retinal Ischemia . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2931.
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Purpose: Mitogen-activated kinases (MAPKs), consisting of three major categories of enzymes, ERK, p38, and JNK, couple cell-surface receptors to critical regulatory targets and gene transcription within cells. We examined the hypothesis that MAPKs were differentially expressed and involved in distinct functional roles following retinal ischemia (1). Methods: Retinal ischemia was induced for 60 min in rats. We performed immunoblotting of whole retinal homogenates, immunostaining of retinal cryosections, and TUNEL and caspase 3 staining for apoptosis. Activated ERK, p38, and JNK proteins were localized by flourescent double-labeling digital confocal imaging (2). To examine impact of blocking activation of MAPKs, pharmacological antagonists were injected systemically or into the vitreous prior to ischemia. Enzymatic blockade was confirmed by enzymatic assay and by measurement of expression of target proteins. Outcome was assessed using electroretinography (ERG) and measurement of retinal cell layer thickness in paraffin sections. Data were analyzed using ANOVA and post-hoc t testing, with P < 0.05 considered significant. Results: Significant increases in expression of phosphorylated JNK and p38 followed a specific time course, with increased expression beginning at 1 h, and persisting up to 1 wk later. The majority of p38-positive cells were in retinal ganglion cells (RGCs), while JNK positivity was primarily in amacrine and bipolar cells. JNK and p38 positive cells were TUNEL-positive 24 h after ischemia. Phosphorylated ERK was entirely confined to Mueller cells. While at 1 and 6 h after ischemia, phosphorylated ERK was evident in the inner nuclear layer, by 24 h, dendritic processes stained in the outer nuclear layer, with little expression beyond 24 h. Blockade of p38 (using SB20380) or ERK (using UO126) resulted in a 2-fold improvement vs vehicle in recovery of the ERG b wave after ischemia (P < 0.01, n = 8 per group) and dramatically decreased thinning of the inner nuclear layers. Moreover, significantly diminished staining for TUNEL and caspase 3 after ischemia was evident in SB20380 or UO126-treated retinae. Conclusions: The three MAPKs each demonstrate a specific cellular distribution after ischemia, and are linked to apoptosis. Blockade of p38 or ERK provides significant protection from ischemic damage suggesting a novel therapeutic role for MAPK inhibition in neuroprotection. References: (1) Roth S: Invest Ophthalmol Vis Sci 39, 775, 1998 (2) Singh M: J Neurochem 77, 466, 2001
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