Imaging Mass Spectrometry Reveals Acyl-Chain- and Region-Specific Sphingolipid Metabolism in the Kidneys of Sphingomyelin Synthase 2-Deficient Mice.

Masayuki Sugimoto,Tomohiko Okuda,Yasuyuki Igarashi,Yoshito Numata,Songji Zhao,Shota Sakai,Kenichi Higashino,Yuji Kuge,Masato Wakabayashi,Yoichi Shimizu,Takeshi Yoshioka,Maurizio Del Poeta

doi:10.1371/journal.pone.0152191

Masayuki Sugimoto, Tomohiko Okuda + Show 10 more

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https://doi.org/10.1371/journal.pone.0152191

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Abstract

Obesity was reported to cause kidney injury by excessive accumulation of sphingolipids such as sphingomyelin and ceramide. Sphingomyelin synthase 2 (SMS2) is an important enzyme for hepatic sphingolipid homeostasis and its dysfunction is considered to result in fatty liver disease. The expression of SMS2 is also high in the kidneys. However, the contribution of SMS2 on renal sphingolipid metabolism remains unclear. Imaging mass spectrometry is a powerful tool to visualize the distribution and provide quantitative data on lipids in tissue sections. Thus, in this study, we analyzed the effects of SMS2 deficiency on the distribution and concentration of sphingomyelins in the liver and kidneys of mice fed with a normal-diet or a high-fat-diet using imaging mass spectrometry and liquid chromatography/electrospray ionization-tandem mass spectrometry. Our study revealed that high-fat-diet increased C18–C22 sphingomyelins, but decreased C24-sphingomyelins, in the liver and kidneys of wild-type mice. By contrast, SMS2 deficiency decreased C18–C24 sphingomyelins in the liver. Although a similar trend was observed in the whole-kidneys, the effects were minor. Interestingly, imaging mass spectrometry revealed that sphingomyelin localization was specific to each acyl-chain length in the kidneys. Further, SMS2 deficiency mainly decreased C22-sphingomyelin in the renal medulla and C24-sphingomyelins in the renal cortex. Thus, imaging mass spectrometry can provide visual assessment of the contribution of SMS2 on acyl-chain- and region-specific sphingomyelin metabolism in the kidneys.

Highlights

Imaging mass spectrometry (IMS) using matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) is a powerful tool for visualizing the distribution of various molecules in tissue sections [1,2,3,4,5]
We investigated the relationship between the intensity and concentration of each SM standard on Indium tin oxide (ITO) glass slides using the positive ion detection mode of MALDI-FTICR-IMS
We focused on the border of the renal Cx and Med, there were no observed changes in SM (d18:1/16:0) by HFDfeeding and Sphingomyelin synthase 2 (SMS2) deficiency (Fig 4B)

Summary

Introduction

Imaging mass spectrometry (IMS) using matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) is a powerful tool for visualizing the distribution of various molecules in tissue sections [1,2,3,4,5]. The major advantage of IMS is its ability to simultaneously detect a number of molecules without the use of imaging probes. Visualizing lipids using conventional histology is difficult because of their simple structure and variety of molecular species. Fourier transform ion cyclotron resonance-mass spectrometry (FTICR-MS) was used to identify the exact mass and isotopic distribution of target molecules using ultra-high-mass resolution (>500,000) and structural analysis with an MS/MS approach [10, 11]. MALDI-FTICR-IMS can clearly visualize several target molecules as independent images [10, 12]

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