Abstract
Hypothermia has been proposed as a therapeutic intervention for some retinal conditions, including ischemic insults. Cold exposure elevates expression of cold-shock proteins (CSP), including RNA-binding motif protein 3 (RBM3) and cold inducible RNA-binding protein (CIRP), but their presence in mammalian retina is so far unknown. Here we show the effects of hypothermia on the expression of these CSPs in retina-derived cell lines and in the retina of newborn and adult rats. Two cell lines of retinal origin, R28 and mRPE, were exposed to 32°C for different time periods and CSP expression was measured by qRT-PCR and Western blotting. Neonatal and adult Sprague-Dawley rats were exposed to a cold environment (8°C) and expression of CSPs in their retinas was studied by Western blotting, multiple inmunofluorescence, and confocal microscopy. RBM3 expression was upregulated by cold in both R28 and mRPE cells in a time-dependent fashion. On the other hand, CIRP was upregulated in R28 cells but not in mRPE. In vivo, expression of CSPs was negligible in the retina of newborn and adult rats kept at room temperature (24°C). Exposure to a cold environment elicited a strong expression of both proteins, especially in retinal pigment epithelium cells, photoreceptors, bipolar, amacrine and horizontal cells, Müller cells, and ganglion cells. In conclusion, CSP expression rapidly rises in the mammalian retina following exposure to hypothermia in a cell type-specific pattern. This observation may be at the basis of the molecular mechanism by which hypothermia exerts its therapeutic effects in the retina.
Highlights
Hypothermia, or exposure to cold temperatures, is being used clinically as a therapeutical intervention to reduce the symptoms of several pathologies, including stroke [1,2,3,4], coronary artery bypass surgery [5], neurodegeneration after cardiopulmonary resuscitation [6], or neonatal asphyxia [7], among others
We identify the cold-induced responses of RNAbinding motif protein 3 (RBM3) and cold inducible RNA-binding protein (CIRP) in cell lines of retinal origin as well as in retinas of neonatal and adult rats using quantitative real time PCR, Western blotting, and immunofluorescence
In R28 there was a clear overexpression of CIRP at all time points when compared with cells at 37°C (Fig 1C) but there was no significant response to moderate cold exposure in mRPE cells (Fig 1D)
Summary
Hypothermia, or exposure to cold temperatures, is being used clinically as a therapeutical intervention to reduce the symptoms of several pathologies, including stroke [1,2,3,4], coronary artery bypass surgery [5], neurodegeneration after cardiopulmonary resuscitation [6], or neonatal asphyxia [7], among others. A large number of animal studies has shown that hypothermia may be very useful in protecting the retina, especially in the context of ischemia [9,10,11,12,13,14,15,16,17,18] Supporting these data, there are some in vitro and ex vivo experiments showing that exposing isolated retinas or cultured retinal cells to cold temperatures results in reducing NMDA-mediated excitotoxicity [19], reducing secretion of vascular endothelial growth factor (VEGF) [20], and increasing survival against toxicants [21]. These proteins, which belong to the heterogeneous nuclear ribonucleoprotein family, bind to cellular RNAs and regulate their half-life and their expression potential and their final functions [23,24,25,26]
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