Conditional Muller Cell Ablation Leads to Retinal Iron Accumulation

PURPOSE. Retinal iron accumulation is observed in a wide range of retinal degenerative diseases, including AMD. Previous work suggests that Muller glial cells may be important mediators of retinal iron transport, distribution, and regulation. A transgenic model of Muller cell loss recently demonstrated that primary Muller cell ablation leads to blood-retinal barrier leakage and photoreceptor degeneration, and it recapitulates clinical features observed in macular telangiectasia type 2 (MacTel2), a rare human disease that features Muller cell loss. We used this mouse model to determine the effect of Muller cell loss on retinal iron homeostasis. METHODS. Changes in total retinal iron levels after Muller cell ablation were measured using inductively coupled plasma mass spectrometry. Corresponding changes in the expression of iron flux and iron storage proteins were determined using quantitative PCR, Western analysis, and immunohistochemistry. RESULTS. Muller cell loss led to blood-retinal barrier breakdown and increased iron levels throughout the neurosensory retina. There were corresponding changes in mRNA and/or protein levels of ferritin, transferrin receptor, ferroportin, Zip8, and Zip14. There were also increased iron levels within the RPE of retinal sections from a patient with MacTel2 and both RPE and neurosensory retina of a patient with diabetic retinopathy, which, like MacTel2, causes retinal vascular leakage. CONCLUSION. This study shows that Muller cells and the blood-retinal barrier play pivotal roles in the regulation of retinal iron homeostasis. The retinal iron accumulation resulting from blood-retinal barrier dysfunction may contribute to retinal degeneration in this model and in diseases such as MacTel2 and diabetic retinopathy.