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Hemopexin in the human retina: Protection of the retina against heme‐mediated toxicity
Author(s) -
Hunt Richard C.,
Hunt D. Margaret,
Gaur Nand,
Smith Ann
Publication year - 1996
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/(sici)1097-4652(199607)168:1<71::aid-jcp9>3.0.co;2-5
Subject(s) - hemopexin , heme , retina , microbiology and biotechnology , retinal , endocytic cycle , chemistry , ferritin , biochemistry , protoporphyrin , biology , receptor , enzyme , endocytosis , neuroscience , porphyrin
The existence of the blood‐retinal barrier means that proteins that protect the retina from damage by reactive oxygen species must either be made locally or specifically transported across the barrier cells; however, such transepithelial transport does not seem to occur. Among the circulatory proteins that protect against iron‐catalyzed production of free radicals are apo‐transferrin, which binds ferric iron and has previously been shown to be made by cells of the neural retina (Davis and Hunt, 1993, J. Cell Physiol., 156 :280–285), and the extracellular antioxidant, apo‐hemopexin, which binds free heme (iron‐protoporphyrin IX). Since hemorrhage and heme release can be important contributing factors in retinal disease, evidence of a hemopexin‐based retinal protection system was sought. The human retina has been shown to contain apo‐hemopexin which is probably synthesized locally since its mRNA can be detected in retinal tissue dissected from human donor eyes. It is likely that the retina contains a mechanism for the degradation of hemopexin‐bound heme since the blood‐retinal barrier also precludes the exit of heme‐hemopexin from the retina. Retinal pigment epithelial cells have been found to bind and internalize heme‐hemopexin in a temperature‐dependent, saturable, and specific manner, analogous to the receptor‐mediated endocytic system of hepatoma cells. Moreover, the binding of heme‐hemopexin to the cells stimulates the expression of heme oxygenase‐1, metallothionein‐1, and ferritin. © 1996 Wiley‐Liss, Inc.