Visualizing spatial lipid distribution in porcine lens by MALDI imaging high-resolution mass spectrometry

Veronika Vidová,Jaroslav Pól,Michael Volný,Petr Novák,Vladimír Havlíček,Susanne K Wiedmer,Juha M Holopainen

doi:10.1194/jlr.m005488

Abstract

The intraocular lens contains high levels of both cholesterol and sphingolipids, which are believed to be functionally important for normal lens physiology. The aim of this study was to explore the spatial distribution of sphingolipids in the ocular lens using mass spectrometry imaging (MSI). Matrix-assisted laser desorption/ionization (MALDI) imaging with ultra high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was used to visualize the lipid spatial distribution. Equatorially-cryosectioned, 12 microm thick slices of tissue were thaw-mounted to an indium-tin oxide (ITO) glass slide by soft-landing to an ethanol layer. This procedure maintained the tissue integrity. After the automated MALDI matrix deposition, the entire lens section was examined by MALDI MSI in a 150 microm raster. We obtained spatial- and concentration-dependent distributions of seven lens sphingomyelins (SM) and two ceramide-1-phosphates (CerP), which are important lipid second messengers. Glycosylated sphingolipids or sphingolipid breakdown products were not observed. Owing to ultra high resolution MS, all lipids were identified with high confidence, and distinct distribution patterns for each of them are presented. The distribution patterns of SMs provide an understanding of the physiological functioning of these lipids in clear lenses and offer a novel pathophysiological means for understanding diseases of the lens.

Highlights

The intraocular lens contains high levels of both cholesterol and sphingolipids, which are believed to be functionally important for normal lens physiology
It seems that protein modifications, such as Abbreviations: CerP, ceramide-1-phosphate; FT-ICR MS, Fourier transform ion cyclotron resonance mass spectrometry; ITO, indium-tin oxide; Matrix-assisted laser desorption/ionization (MALDI), matrix-assisted laser desorption/ionization; MSI, mass spectrometry imaging
We have extended our previous studies to provide spatial organization of SMs and other identified sphingolipid species in clear porcine lenses using ultra high resolution MALDI imaging coupled with Fourier transform ion-cyclotron resonance mass spectrometry (FT-ICR MS)

Summary

Introduction

The intraocular lens contains high levels of both cholesterol and sphingolipids, which are believed to be functionally important for normal lens physiology. Matrix-assisted laser desorption/ionization (MALDI) imaging with ultra high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was used to visualize the lipid spatial distribution. Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) has been developed and successfully used for spatial localizations of proteins, peptides, and lipids [1, 2]. To the best of our knowledge, only a few studies discuss the spatial distribution of lens proteins, namely, the integral lens protein aquaporin and its truncation products [10, 11] and ␣-crystallin [1, 12] It seems that protein modifications, such as Abbreviations: CerP, ceramide-1-phosphate; FT-ICR MS, Fourier transform ion cyclotron resonance mass spectrometry; ITO, indium-tin oxide; MALDI, matrix-assisted laser desorption/ionization; MSI, mass spectrometry imaging. Rujoi et al [13], performed MALDItime of flight (TOF) MS analysis of neutral phospholipids in selected spots of the lens tissue

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