How Does the Eye Breathe? Evidence for Neuroglobin-mediated Oxygen Supply in the Mammalian Retina

Abstract

Abstract: : Purpose: Visual performance of the vertebrate eye requires large amounts of oxygen and thus the retina is one of the highest oxygen-consuming tissues of the body. Neuroglobin has been recently identified as a neuron-specific respiratory protein distantly related to hemoglobin and myoglobin. The aim of our project is to determine where neuroglobin is localized in the mammalian retina. Methods: Neuroglobin expression in the retina is determined by in situ hybridization mRNA. Specific antibodies to neuroglobin are generated and used in Western blot analysis of subcellular photoreceptor fractions and immunofluorescence microscopy of the retina. Results: Our studies reveal that neuroglobin is present at high amounts in the mammalian retina (approximately 100 µM). The estimated concentration of neuroglobin in the retina is thus about 100-fold higher than in the brain, and is in the same range as that of myoglobin in the muscle. Neuroglobin is expressed in all neurons of the retina, but not in the cells of retinal pigment epithelium. Neuroglobin mRNA was detected in the perikarya of the nuclear and ganglion layers of the neuronal retina, whereas the protein was mainly localized in the plexiform layers and in the ellipsoid region of photoreceptor inner segment. Conclusions: The distribution of neuroglobin correlates with the subcellular localization of mitochondria and with the relative oxygen demands, as the plexiform layers and the inner segment consume most of the retinal oxygen. These findings suggest that neuroglobin supplies oxygen to the retina, similar to myoglobin in the myocardium and the skeletal muscle. Furthermore, neuroglobin might scavenge free radicals generated in the retina.

Keywords: retina: distal(photoreceptors, horizontal cell • oxidation/oxidative or free radical damage