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Nolan Robert McGrady, Dorota L Stankowska, Hayden B Jefferies, Shaoqing He, Raghu R Krishnamoorthy; Endothelin receptors are associated with MAPK signaling in a rat model of glaucoma. Invest. Ophthalmol. Vis. Sci. 2017;58(8):245.
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© ARVO (1962-2015); The Authors (2016-present)
The endothelin system has been shown to play a causative role in the neurodegenerative effects seen in animal models of glaucoma. However, the mechanisms underlying endothelin mediated neurodegeneration need to be examined further. The goal of this study was to investigate the interaction between the ETA and ETB receptors and the involvement of the MAP kinase pathways in endothelin mediated cell death.
Wild type and ETB-deficient Wistar-Kyoto rats were subjected to IOP elevation by the Morrison’s method and maintained for 2 weeks. Retinal sections obtained from the rats were subjected to immunohistochemical analysis of extracellular regulated kinase 1/2 (ERK1/2) and c-Jun N-terminal kinase (JNK) and their phosphorylation. In a separate set of experiments, primary RGCs were isolated from post-natal day 5 pups and were transduced with an AAV-2 vector encoding the ETA receptor cDNA. The cells were maintained for 11 days for optimal ETA receptor expression and were subjected to either immunocytochemical analysis for ETA and ETB receptors or treated for 24 hr with 100nM endothelin-1 (ET-1) or endothelin-3 (ET-3). Treated RGCs were then assessed for cell death using a cell viability assay.
ETB-deficient rats showed increased immunostaining for pERK1/2 in the nerve fiber layer (NFL), ganglion cell layer (GCL) and inner plexiform layer (IPL), compared to wild type rats. Following IOP elevation, ERK1/2 phosphorylation was greatly reduced in wild type rats, while ETB-deficient rats showed better preservation of pERK1/2 levels. Conversely, immunostaining for pJNK in wild type rats was increased in the NFL following IOP elevation, but was attenuated in ETB-deficient rats. Cell culture experiments showed an appreciable upregulation of ETB receptors following overexpression of the ETA receptor as well as an increase in cell death in RGCs.
There is a substantial body of evidence for the pro-survival role of ERKs, and the pro-death role of JNKs. Although the mechanisms are not completely clear, the current study points to an association of ERK1/2 and JNK signaling with endothelin receptor expression following IOP elevation. There appears an involvement of both ETA and ETB receptor mediated signal transduction pathways during ocular hypertension. In addition, there appears to be reciprocal relationship in the upregulation of ETA and ETB receptor expression which needs to be studied in detail.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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