Neuroglobin and Histoglobin (cytoglobin) – New hexacoordinate globins in the human eye

Abstract

Abstract: : Purpose: To determine the presence and distribution of neuroglobin and histoglobin (cytoglobin) in human retinas. Methods: Specific polyclonal antibodies to human neuroglobin and histoglobin were generated and used to determine expression and localization by immunofluorescence microscopy in human retinal sections. Results: Neuroglobin immunoreactivity appeared to be present in the photoreceptor layer (predominantly in the inner segments of the photoreceptors), in some cells of the inner nuclear layer and was very abundant in the retinal ganglion cell layer. The retinal pigment epithelium did not show positive immunoreactivity for neuroglobin. Histoglobin immunoreactivity appeared to be predominantly localized to the ganglion cell layer and inner nuclear layer. Some immunoreactivity was present in the outer plexiform layer. Histoglobin immunoreactivity was not detected in the photoreceptors or retinal pigment epithelium. Conclusions: Neuroglobin and histoglobin are widely distributed globins in human retinal tissue. High affinity for the binding of oxygen molecules and relatively slow release rate constants do not support the role of these molecules as classical oxygen transporting molecules as is the case for hemoglobin and myoglobin. However, the specific kinetics of these hexacoordinate globins may be supportive of their role as temporary oxygen reservoirs, which might provide minimal, but continuous supply of intracellular oxygen during ischemic and anoxic conditions. Specific localization of neuroglobin (outer and inner retina layers) and histoglobin (inner retina and RGCs) might be suggestive of a potential important role in oxygen homeostasis and ischemia–induced cell signaling in human retinas and optic nerves.

Keywords: ganglion cells • immunohistochemistry • oxidation/oxidative or free radical damage