The ischemic stress may be the cause of the onset and the progression of the pathogenesis including RGC death in diabetic retinopathy and glaucoma (Oshitari and Roy 2007). the control retinas. In addition, the cells that were positive for SEK1-, ASK1-, and JNK were also positive for Fluoro-Jade B-positive cells. These results indicate that this increased expression of ER stress-related factors was, in part, associated with the retinal neuronal abnormalities after ischemia-reperfusion injury in rat retinas. Keywords:endoplasmic reticulum, IRE1, apoptosis signal-regulating kinase 1, SAPK/ERK kinase 1, c-Jun N-terminal kinase, Fluoro-Jade B, ischemia-reperfusion injury == Introduction == The endoplasmic reticulum (ER) is an intracellular organelle that is associated with the synthesis and folding of proteins and the post-translational modification of proteins (Rao et al 2004;Lindholm et al 2006). The accumulation of unfolded proteins or upset in the Ca2+homeostasis in the ER can trigger ER stress-induced apoptosis (Rao et al 2004;Lindholm et al 2006). Recent studies have shown that this ER stress-induced apoptosis is usually associated with the pathogenesis of various human diseases, eg, Parkinsons disease (Imai and Takahashi 2004), amyotrophic lateral sclerosis (Tobisawa et al 2003;Wootz et al 2004), polyglutamine diseases (Nishitoh et al 2002), diabetes mellitus (Oshitari et al 2008a), and acute brain disorders (Larner et al 2004;Tajiri et al 2004;Hayashi et al 2005). Apoptosis of retinal neurons is Isoforskolin usually a progressive, irreversible process that occurs following ischemic injury to the retina, eg, central or branch retinal artery occlusion (Zhang et al 2005) and ischemic optic neuropathy (Levin and Louhab 1996). To rescue the retinal neurons after ischemia and to establish neuroprotective therapies for ischemic diseases, information on the precise mechanism causing the neuronal apoptosis is required. However, the precise mechanism for retinal neuronal apoptosis has not been determined yet. The results of recent studies showed that one of the ER stress-mediated pathways, the C/EBP homologous protein (CHOP)-mediated pathway, is usually involved in the death of retinal neurons followingN-methyl-D-aspartate (NMDA) treatment CD47 (Awai et al 2006,Shimazawa et al 2007). The results of Awai and colleagues study showed that CHOP-deficient mice were more resistant to the NMDA-induced retinal injury (Awai et al 2006). Another study showed that this retinal ganglion cells (RGCs) of apoptosis signal-regulating kinase 1 (ASK1)-knockout mice (Harada et al 2006) were less susceptible to ischemia-reperfusion injury. These findings suggested that ASK1 is usually associated with the RGC death in ischemia-reperfusion retinas. The ASK1-c-Jun N-terminal kinase (JNK) pathway is known to be one of the major ER stress-induced apoptotic pathways in the central nervous system (Nishitoh et al 2002). However, the earlier study in the retina did not focus on the relationship between the ER stress and the ASK1-mediated pathway but around the ASK1p38 pathway Isoforskolin (Harada et al 2006). We have reported that this electrical translocation of the heat shock protein 27 (Hsp 27) into RGCs reduced the damage Isoforskolin of RGCs after ischemia-reperfusion injury in rat retinas (Yokoyama et al 2001). It is known that chaperon Hsp 27 stabilizes the cytoskeleton and limits the accumulation of unfolded proteins by inhibiting protein synthesis. This is relevant because the accumulation of unfolded proteins in the ER can induce ER stress-mediated apoptosis, and an increase of intracellular Ca2+can activate SAPK/ERK kinase 1 (SEK1) also called the MAP kinase/extracellular signal-regulated kinase 4 (MEK4)-mediated cell death pathway (Dolmetsch et al 1997). The purpose of this study was to determine whether the increased expression of ER stress-related factor IRE1, ASK1, SEK1/MEK4, and JNK is usually associated with damaged neurons after ischemia-reperfusion injury in rat retinas. == Methods == == Animals == The experiments were conducted on adult male Wistar (200250 g) rats, which were housed three/cage in a temperature-controlled room and had free access to food and water. The procedures used on the animals were in accordance with the Isoforskolin ARVO Statement for the Use of Animals in Ophthalmic and Vision Research. The experimental protocols were approved by the Animal Use Committee of Chiba University Graduate School of Medicine. == Induction of Ischemia == The ischemia-reperfusion in the rats was.