High Resolution Imaging Mass Spectrometry of Human Donor Eyes with Drusen and Subretinal Drusenoid Deposits

Abstract

Purpose : The molecular basis of AMD is only partly understood. Photoreceptor death and vision loss has been linked to extracellular deposits on apical and basal aspects of the retinal pigment epithelium (RPE). The purpose of this study is to use high spatial and mass resolution imaging mass spectrometry (IMS) to molecularly characterize regions of pathology observed in the neural retina, drusen, subretinal drusenoid deposit (SDD), and between photoreceptors and RPE).

Methods : Human donor eyes were either frozen or fixed following ex vivo imaging to assess AMD pathology. Tissue sections of macular and peripheral regions were analyzed using a multimodal imaging strategy which includes MALDI IMS as well as DIC, autofluorescence, and stained tissue microscopy. Adjacent sections were stained with Periodic acid-Schiff-hematoxylin and hematoxylin-eosin for morphological analysis. IMS was performed at 10-15 µm spatial resolution in both positive and negative ion modes on a Bruker Solarix 9.4T FTICR instrument with a modified MALDI source designed for high spatial resolution and a Bruker timsTOF flex instrument at 10 µm spatial resolution. To enable high-precision registration of IMS and optical signals, tissue autofluorescence and reflectance images were acquired from sections before and after IMS experiments. Lipid identifications were perfomed via LC-MS/MS in negative and positive ion modes using a Q Executive HF instrument.

Results : High spatial resolution IMS combined with registration to tissue images enabled detection of distinct lipid signals in drusen and SDD. Lipid signals observed in IMS images display heterogeneity in deposits and differences betweeen drusen and large numbers of signals in SDD. Both unesterified cholesterol and esterified cholesterol, previously seen by histochemistry, were observed surrounding and within drusen while sphingomyelin species were abundant within drusen and basal laminar deposits.Autofluorescence and DIC imaging allowed for visualization of SDD while MALDI IMS displayed a high number of signals relating to lipid and high mass signals possibly indicating glycolipids accumulating in these regions. Iinner retina internal to SDD and pathology in the RPE layer were also found to have abnormal lipid signatures.

Conclusions : IMS technology provides spatially-resolved molecular analysis of retinal pathology and extracellular deposits in human donor eyes with AMD.

This is a 2021 ARVO Annual Meeting abstract.