Abstract
Purpose::
Hereditary hemochromatosis (HH) is an autosomal recessive disorder of iron overload leading to oxidative stress in various tissues, associated with clinical symptoms such as diabetes, cardiomyopathy, liver cirrhosis, and hypogonadism. Recent studies have shown that increased iron accumulation in RPE, resulting from the combined disruption of the function of two iron regulatory proteins, ceruloplasmin and hephaestin, leads to retinal degeneration with characteristics similar to those of age-related macular degeneration (AMD). We predicted that HH would also be associated with iron overload in retina. Disruption of HFE function, (a Histocompatability leukocyte antigen class I-like protein involved in iron (FE) homeostasis) due to mutations is responsible for most cases of HH. We recently demonstrated the expression of HFE in the basolateral membrane of RPE. In the present study, we used HFE null (HFE-/-) mice at various ages along with wild type littermates to evaluate the consequences of HFE gene deletion in retina.
Methods::
RT-PCR was done to confirm the absence of HFE mRNA in HFE-/- retina. Morphological changes in retina were evaluated using hematoxylin and eosin staining. RT-PCR was done to compare the expression of other iron regulatory proteins between wild type and HFE-/- mouse retinas. Apoptosis was monitored using TUNEL assay.
Results::
RT-PCR confirmed the absence of HFE mRNA in HFE-/- mouse retina. Hematoxylin and eosin staining showed atrophy in retina of the null mice. Two other iron regulatory proteins, hemojuvelin and hepcidin, were also expressed in wild type mouse retina; the expression of hepcidin decreased whereas that of hemojuvelin was unaffected in HFE-/- mouse retina. TUNEL assay revealed increased number of apoptotic cells in the RPE and ganglion cell layers in HFE-/- mice compared to wild type mice in an age-dependent manner.
Conclusions::
HFE expression in the basolateral membrane of RPE, which is in contact with choroidal blood, indicates an essential role for the protein in regulation of retinal iron homeostasis. HFE-/- mouse retina shows evidence of retinal degeneration, characterized by increased apoptosis and atrophy in various cell layers of retina. Hepcidin is also downregulated in HFE-/- mouse retina. We speculate that patients with hemochromatosis are likely to have disrupted iron homeostasis in retina, contributing to age-related RPE dysfunction and retinal degeneration.
Keywords: retina • aging • genetics