Neuroglobin And Physiology Of Retinal Ganglion Cells

Abstract

Purpose: : Neuroglobin (Ngb) is a monomeric hemoprotein of the globin family that is mainly expressed in neurons of the central and peripheral nervous systems. Several functions have been proposed: Ngb may exert a Mb-like role, enhancing O2 supply to the mitochondria, may scavenge damaging reactive oxygen or nitrogen species, which may be generated by the respiratory chain, or may be part of a redox process that is for example instrumental in preventing apoptosis via cytochrome c reduction.This project aims to show the influence of Ngb in the mitochondrial physiology of retinal ganglion cells (RGC) ex vivo and in vivo. We study the impact of protein inactivation by sh and siRNAs for RGC viability and optic nerve respiratory chain function.

Methods: : Rat RGC were treated with sh or siRNA anti-Ngb. Rats were subjected to optomotor tests for visual function evaluation. Scanning Laser Ophthalmoscope allowed an estimation of nerve fiber density. Evaluations were completed by respiratory chain function assessments in optic nerves. RGC number (on retinal cross-sections or within primary RGC cultures), microglial activation, and reactive gliosis were evaluated by immunohistochemistry.

Results: : For eyes electroporated with shRNA anti-Ngb, there was (i) a significant reduction of nerve fibers in some animals (ii) reactive gliosis, microglial cell activation and a decrease in the Ngb intensity of labeling in some retinal regions (iii) a partial respiratory chain complex I defect in optic nerves (iiii) a decrease in RGC survival after treatment with siRNA anti-Ngb both ex vivo and in vivo. These changes were irremediable and led to a partial impairment of visual function.

Conclusions: : We demonstrate that Ngb function is a reliable marker of mitochondrial activity and is intimate associated with RGC survival. The next step toward our goal for studying Ngb function will be to overexpress the protein in animal models of optic neuropathy seeking for prevention of RGC loss.

Keywords: ganglion cells • protein structure/function • mitochondria