Bis(monoacylglycero)phosphate lipids in the retinal pigment epithelium implicate lysosomal/endosomal dysfunction in a model of Stargardt disease and human retinas

David M G Anderson,M Wade Calcutt,Rosalie K Crouch,Zsolt Ablonczy,Richard M Caprioli,Jeffrey M Spraggins,Anne M Hanneken,Kevin L Schey,Yiannis Koutalos

doi:10.1038/s41598-017-17402-1

Abstract

Stargardt disease is a juvenile onset retinal degeneration, associated with elevated levels of lipofuscin and its bis-retinoid components, such as N-retinylidene-N-retinylethanolamine (A2E). However, the pathogenesis of Stargardt is still poorly understood and targeted treatments are not available. Utilizing high spatial and high mass resolution matrix assisted laser desorption ionization (MALDI) imaging mass spectrometry (IMS), we determined alterations of lipid profiles specifically localized to the retinal pigment epithelium (RPE) in Abca4−/− Stargardt model mice compared to their relevant background strain. Extensive analysis by LC-MS/MS in both positive and negative ion mode was required to accurately confirm the identity of one highly expressed lipid class, bis(monoacylgylercoro)phosphate (BMP) lipids, and to distinguish them from isobaric species. The same BMP lipids were also detected in the RPE of healthy human retina. BMP lipids have been previously associated with the endosomal/lysosomal storage diseases Niemann-Pick and neuronal ceroid lipofuscinosis and have been reported to regulate cholesterol levels in endosomes. These results suggest that perturbations in lipid metabolism associated with late endosomal/lysosomal dysfunction may play a role in the pathogenesis of Stargardt disease and is evidenced in human retinas.

Highlights

Retinal degeneration is a complex multifactorial process resulting in death of the light sensitive photoreceptors present in the outer retina[1]
High mass resolution matrix assisted laser desorption ionization (MALDI) imaging mass spectrometry (IMS) of animal model tissue provided the localization of 3 signals that were uniquely present in the retinal pigment epithelium (RPE) layer of Abca4−/− mouse tissue when compared to Sv129 control
The signals observed with high abundance in the Abca4−/− mouse model in these data were distinguished from potential isobaric species and identified using LC-MS/MS analysis in both positive and negative ionization mode

Summary

Introduction

Retinal degeneration is a complex multifactorial process resulting in death of the light sensitive photoreceptors present in the outer retina[1]. Subsequent targeted liquid chromatography tandem mass spectrometry (LC-MS/MS) enabled identification of multiple bis(monoacylglycero)phosphate lipids species (BMP), a structurally unique family of lipids that have been observed in a number of endosomal/lysosomal storage diseases[46,47,48]. These results provide evidence of lipid disturbances and potential endosomal/lysosomal defects in the RPE spatially resolved across the tissues in an animal model of Stargardt disease. The presence of the same lipids in human donor tissue is consistent with the concept that lipid disturbances and potential endosomal/lysosomal defects in the RPE are likely to play a role in the pathogenesis of Stargardt disease and possibly other retinal disorders

Methods

Results

Conclusion