Dual specificity phosphatase MKP1 and retinal ischemic preconditioning

Abstract

INTRODUCTION: We previously described the phemenon of retinal ischemic preconditioning (1) and showed significant increases in the dual-specificity phosphatase MKP-1 with preconditioning (2). In this study we examined the role of MKP-1 in ischemic preconditioning and specifically, its role in regulating MAPK p38. METHODS: Ischemia was produced by elevation of intraocular pressure above systolic arterial blood pressure for 55 min in anesthetized adult Wistar rats. Pre-conditioning was produced by ligating the central retinal artery for 5 min using suture occlusion, 24 h prior to ischemia. Interfering RNA (siRNA) to MKP-1 or, non-silencing siRNA, was injected into the vitreous 6 h prior to ischemia. Recovery was assessed using electroretinography (ERG) and histological examination of 5-micron thick retinal paraffin embedded sections. The a and b waves, and oscillatory potentials (OPs) were measured before and 1 week after ischemia and normalized relative to pre-ischemic baseline and corrected for diurnal variation in the normal non-ischemic eye. The P2 (which reflects function of the rod bipolar cells in the inner retina) was derived using the Hood-Birch model (3). Levels of phosphorylated MAPKs p38, ERK, and JNK were measured relative to total levels of protein at 24 h after ischemic preconditioning +/- siRNA to MPK-1 or non-silencing siRNA. RESULTS: Injection of interfering RNA to to MKP-1 significantly (P < 0.05) attenuated the protective effect of ischemic preconditoning as reflected by decreased recovery of the electroretinogram a, b wave and oscillatory potentials (OPs) and the P2 (Figure).[figure1]The blockade of MKP-1 by siRNA resulted in an increase in activation of p38 at 24 h following preconditioning to 146 +/- 7 % vs that with non-silencing siRNA (108 +/ 13%, P < 0.05). MKP-1 siRNA did not alter the levels of phosphorylated JNK or ERK after preconditioning. CONCLUSIONS: The results show the involvement of dual-specificity phosphatase MKP1 in ischemic preconditioning and suggest that MKP-1 is involved in ischemic preconditioning by regulating levels of activated MAPK p38.