Light-Induced Changes in the Expression of Several Calcium-Binding Proteins in the Retina of Pigmented Rabbits

Abstract

Purpose:: Calcium ion (Ca²⁺) plays several key roles for the physiology of cells, including photoreceptors and neurons in the vertebrate retina. Among the mechanisms involved in the maintenance of intracellular Ca²⁺ homeostasis, there are a series of proteins collectively known as Ca²⁺-binding proteins. Changes in the expression of some of these proteins are at the basis of some degenerative diseases.To check whether this also occurs in retinopathy associated to light exposure or not, we have analyzed immunohistochemically the occurrence of calretinin, parvalbumin, calbindin-D 28k, neurocalcin and S100 protein in the retina of pigmented rabbits exposed to circadian light.

Methods:: In order to analyze the type of light responsible for the retinal light-induced changes, we implanted intraocular lens to filter the blue segments of the visual spectrum. All the investigated Ca²⁺-binding proteins were found in the retina of control and experimental animals with a heterogeous pattern of expression in neurons and non-neuronal cells, especially photoreceptors.

Results:: Light exposure resulted in a decrease in the expression of calretinin, parvalbumin and calbindin-D 28 k, but not in variations in the expression of neurocalcin or S100 protein. Interestingly, intraocular filters for the blue component of the light spectrum partially improved the decreased expression of those proteins.

Conclusions:: As a whole, the present results suggest that an alteration in the Ca²⁺ homeostatic mechanism, involving Ca²⁺-binding proteins, might account for cell light-induced retinal pathologies.

Keywords: age-related macular degeneration • calcium • protein structure/function