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Matrix Selection for the Visualization of Small Molecules and Lipids in Brain Tumors Using Untargeted MALDI-TOF Mass Spectrometry Imaging

ABSTRACT: Matrix-assisted laser desorption/ionization mass spectrometry imaging allows for the study of metabolic activity in the tumor microenvironment of brain cancers. The detectable metabolites within these tumors are contingent upon the choice of matrix, deposition technique, and polarity setting. In this study, we compared the performance of three different matrices, two deposition techniques, and the use of positive and negative polarity in two different brain cancer types and across two species. Optimal combinations were confirmed by a comparative analysis of lipid and small-molecule abundance by using liquid chromatography-mass spectrometry and RNA sequencing to assess differential metabolites and enzymes between normal and tumor regions. Our findings indicate that in the tumor-bearing brain, the recrystallized α-cyano-4-hydroxycinnamic acid matrix with positive polarity offered superior performance for both detected metabolites and consistency with other techniques. Beyond these implications for brain cancer, our work establishes a workflow to identify optimal matrices for spatial metabolomics studies.

ORGANISM(S): Mus musculus

PROVIDER: GSE279139 | GEO | 2024/10/09

REPOSITORIES: GEO

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Project description:<p>Human brain organoids are emerging models to study human brain development and pathology as they recapitulate the development and characteristics of major neural cell types, and enable manipulation through an <em>in vitro</em> system. Over the past decade, with the advent of spatial technologies, mass spectrometry imaging (MSI) has become a prominent tool for metabolic microscopy, providing label-free, non-targeted molecular and spatial distribution information of the metabolites within tissue, including lipids. This technology has never been used for studies of brain organoids and here, we set out to develop a standardized protocol for preparation and mass spectrometry imaging of human brain organoids. We present an optimized and validated sample preparation protocol, including sample fixation, optimal embedding solution, homogenous deposition of matrices, data acquisition and processing to maximize the molecular information derived from mass spectrometry imaging. We focus on lipids in organoids, as they play critical roles during cellular and brain development. Using high spatial and mass resolution in positive- and negative-ion modes, we detected 260 lipids in the organoids. Seven of them were uniquely localized within the neurogenic niches or rosettes as confirmed by histology, suggesting their importance for neuroprogenitor proliferation. We observed a particularly striking distribution of ceramide-phosphoethanolamine CerPE 36:1; O2 restricted within rosettes and of phosphatidyl-ethanolamine PE 38:3, which was distributed throughout the organoid tissue but not in rosettes. This suggests that ceramide in this particular lipid species might be important for neuroprogenitor biology, while its removal may be important for terminal differentiation of their progeny. Overall, our study establishes the first optimized experimental pipeline and data processing strategy for mass spectrometry imaging of human brain organoids, allowing direct comparison of lipid signal intensities and distributions in these tissues. Further, our data shed new light on the complex processes that govern brain development by identifying specific lipid signatures that may play a role in metabolic cell fate trajectories. mass spectrometry imaging thus has great potential in advancing our understanding of early brain development as well as disease modeling and drug discovery.</p>

Project description:The fibroblast-populated 3D collagen matrix has been used to study the effect of mechanical stress on cell fate; this process is relevant to the fields of wound healing and tissue engineering. Gene array data was generated from mechanically stressed vs. stress-released matrices. The parameters of the collagen matrix model were: collagen type = bovine type I; collagen concentration = 1.5 mg/mL; initial matrix volume = 0.2 mL; initial matrix diameter = 11 mm (cultured in 24-well plates); cell type = human foreskin fibroblast, passage <10; initial matrix cell concentration = 1,000,000 cell/mL (200,000 cell/matrix); culture medium = 5% FBS in DMEM with 1 M-BM-5g/mL ascorbate. Matrices (n = 6 per experimental group) were incubated for 24 hr in the attached state; the released groups then underwent matrix detachment from the culture plate (defined as t = 0), while the attached groups were left undisturbed. RNA was isolated from attached and released matrices 6 and 24 hr after t = 0. Gene expression in the attached vs. released condition at 6 or 24 hr then was analyzed by hybridizing the anti-sense RNA derived from attached and released matrices at a given time point onto a single chip. Refer to the attached Figure 1 for the experimental design. The index experiment was defined as the comparison of gene expression in attached vs. released collagen matrices in a single strain of human foreskin fibroblasts at 6 and 24 hr after stress-release (i.e., after t = 0). Each experiment utilized two mechanical conditions (attached and released) at two time points (6 and 24 hr). So with each condition utilizing 6 matrices, each index experiment required a total of 24 matrices. In each index experiment, the chip hybridizations were: (i) 6 hr attached vs. 6 hr released, and (ii) 24 hr attached vs. 24 hr released (i.e., two gene chips per index experiment). Each hybridization was done using a 10K spotted gene chip manufactured in the UNMC Microarray Core Facility. The index experiment was performed on three fibroblast strains, meaning that expressional data was derived from three foreskin donors (nonpooled samples). Dye-swap was not performed; dye assigned to attached vs. released remained constant among all chips. Since the index experiment was performed three times, the total number of gene chips used for this entire dataset was six.

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Matrix Selection for the Visualization of Small Molecules and Lipids in Brain Tumors Using Untargeted MALDI-TOF Mass Spectrometry Imaging

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