X-ray fluorescence microscopic measurement of elemental distribution in the mouse retina with age

The biologically important metals such as zinc, copper and iron play key roles in retinal function, yet no study has mapped the spatio-temporal distribution of retinal biometals in healthy or diseased retina. We investigated a natural mouse model of retinal degeneration, the Cln6^nclf mouse. As dysfunctional metabolism of biometals is observed in the brains of these animals and deregulated metal homeostasis has been linked to retinal degeneration, we focused on mapping the elemental distribution in the healthy and Cln6^nclf mouse retina with age. Retinal and RPE elemental homeostasis was mapped in Cln6^nclf and C57BL6/J mice from 1 to 8 months of age using X-ray Fluorescence Microscopy at the Australian Synchrotron. In the healthy retina, we detected a progressive loss of phosphorus in the outer nuclear layer and significant reduction in iron in the inner segments of the photoreceptors. Further investigation revealed a unique elemental signature for each retinal layer, with high areal concentrations of iron and sulfur in the photoreceptor segments and calcium, phosphorus, zinc and potassium enrichment predominantly in the nuclear layers. The analysis of retinae from Cln6^nclf mice did not show significant temporal changes in elemental distributions compared to age matched controls, despite significant photoreceptor cell loss. Our data therefore demonstrates that retinal layers have unique elemental composition. Elemental distribution is, with few exceptions, stably maintained over time in healthy and Cln6^nclf mouse retina, suggesting conservation of elemental distribution is critical for basic retinal function with age and is not modulated by processes underlying retinal degeneration.