Abstract
Purpose: :
The iron carrier transferrin is expressed at remarkably high levels in the normal retina, and its expression is further up-regulated in Age Related Macular Degeneration (AMD). The role of transferrin in AMD and other retinal degenerations is still unclear. A point mutation in the transferrin gene of HPX mice results in less than 1% of normal transferrin protein production. We aimed to characterize the retinal phenotype of HPX mice in order to gain additional insight into the role of transferrin in retinal function.
Methods: :
To ensure their survival, HPX-/- mice were treated weekly with intraperitoneal injections of transferrin. Electroretinograms (ERGs) were recorded at one and two months of age in HPX-/-, HPX-/+, and wild type (WT) mice. At the two months time point ophthalmoscopy was performed, retinal structure was evaluated by histology, and transferrin content was estimated by semi-quantitative immunohistochemistry (IHC). mRNA levels of transferrin, ceruloplasmin, and transferrin receptor were measured by quantitative PCR (QPCR).
Results: :
At one and two months of age WT and HPX+/- mice had similar dark- and light-adapted full-field ERG responses whereas in HPX-/- mice ERG amplitudes were significantly reduced. For example, at two months of age, mean dark-adapted mixed cone-rod b-wave amplitude at maximal stimulus intensity was 357±123µV in HPX-/-, versus 624±134µV in WT mice (p=0.01). Ophthalmoscopy revealed retinal pallor in HPX-/- mice. However, histological examination demonstrated preserved retinal structure and total retinal thickness did not differ between the three groups of animals (WT: 192±8.5µm, HPX+/-: 200±7µm, HPX-/-: 197±15µm, p=0.63). IHC for transferrin demonstrated reduced staining intensity by a mean of 17% (p=0.3) and 37% (p=0.03) in HPX+/- retinas and HPX-/- retinas, respectively, as compared with WT retinas. QPCR demonstrated decreased mRNA levels of transferrin (by 2.7 folds; p =0.03), ceruloplasmin (by 1.6-fold; p=0.05), and transferrin receptor (by 2.2-fold; p=0.003) in HPX-/- mice compared with WT mice.
Conclusions: :
Despite the lack of retinal transferrin protein production, systemic transferrin supplementation enables postnatal retinal development in HPX-/- mice. Yet, ERG responses and retinal transferrin protein levels are altered in HPX-/- mice, suggesting that transferrin may be required for normal retinal function.
Keywords: retina • oxidation/oxidative or free radical damage • gene/expression