CpG preconditioning reduces accumulation of lysophosphatidylcholine in ischemic brain tissue after middle cerebral artery occlusion

Leonidas Mavroudakis,Julia Laskin,Kyle D Duncan,Mary P Stenzel-Poore,Susan L Stevens,Ingela Lanekoff

doi:10.1007/s00216-020-02987-w

Abstract

Ischemic stroke is one of the major causes of death and permanent disability in the world. However, the molecular mechanisms surrounding tissue damage are complex and further studies are needed to gain insights necessary for development of treatment. Prophylactic treatment by administration of cytosine-guanine (CpG) oligodeoxynucleotides has been shown to provide neuroprotection against anticipated ischemic injury. CpG binds to Toll-like receptor 9 (TLR9) causing initialization of an inflammatory response that limits visible ischemic damages upon subsequent stroke. Here, we use nanospray desorption electrospray ionization (nano-DESI) mass spectrometry imaging (MSI) to characterize molecular effects of CpG preconditioning prior to middle cerebral artery occlusion (MCAO) and reperfusion. By doping the nano-DESI solvent with appropriate internal standards, we can study and compare distributions of phosphatidylcholine (PC) and lysophosphatidylcholine (LPC) in the ischemic hemisphere of the brain despite the large changes in alkali metal abundances. Our results show that CpG preconditioning not only reduces the infarct size but it also decreases the degradation of PC and accumulation of LPC species, which indicates reduced cell membrane breakdown and overall ischemic damage. Our findings show that molecular mechanisms of PC degradation are intact despite CpG preconditioning but that these are limited due to the initialized inflammatory response.

Highlights

Published in the topical collection Mass Spectrometry Imaging 2.0 with guest editors Shane R
The amount of accumulation is generally difficult to determine with mass spectrometry imaging (MSI) due to the significant increase in sodium and decrease in potassium concentration in this region, which results in different ion images depending on the selected adduct [3, 20]
total ion current (TIC) normalization is a typical strategy for presenting MSI data; it assumes that changes in the chemical composition in different cellular regions of the tissue do not affect ionization [42]

Summary

Introduction

Published in the topical collection Mass Spectrometry Imaging 2.0 with guest editors Shane R. Ischemic stroke, accounting for 87% of all strokes, occurs after the obstruction of blood vessels supplying blood to a region of the brain. Oxygen and nutrients, such as glucose, cannot reach the brain cells in this region, which leads to oxidative stress, ionic imbalance, inflammation, and apoptosis [2]. The depletion of adenosine triphosphate (ATP) in the ischemic area leads to disruption of the sodium-potassium pump. This results in accumulation of Na+ inside the cells and a concomitant decrease of K+ in the ischemic region [2,3,4]. While many events during ischemia are known, much remains to be learned, making it challenging but necessary to develop treatments to alleviate the negative complex biochemical mechanisms that are activated during stroke

Methods

Results

Conclusion