Single-Cell Transcriptome Analysis of Acute Myeloid Leukemia Cells Using Methanol Fixation and Cryopreservation
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ABSTRACT: Introduction: The application of single-cell RNA sequencing has greatly improved our under-standing of various cellular and molecular mechanisms involved in physiological and pathophysi-ological processes. However, obtaining living cells for this technique can be difficult under certain conditions. To solve this problem, the methanol fixation method appeared as a promising alternative for routine clinical use. Materials and Methods: In this study, we selected two AML samples that had been fixed in methanol for 12–18 months. Once the cells were rehydrated, these samples were subjected to single-cell RNA sequencing. We then compared the results obtained from these samples with those obtained from the same samples cryopreserved in DMSO. Results: We used a previously validated methanol fixation protocol to perform scRNA-seq on DMSO cryopreserved cells and cells fixed in methanol for more than one year. Preliminary results show that methanol fixation induces some genetic and transcriptional modification compared with DMSO cryopreservation but remains a valuable method for single-cell analysis of primary human leukemia cells. Conclusions: The initial findings from this study highlight certain resemblances in methanol fixation over a 12-month period and cryopreservation with DMSO, along with associated transcriptional level modifications. However, we observed genetic degradation in the fixation condition when extending beyond one year. Despite certain study limitations, it is evident that short-term methanol fixation can be effec-tively used for leukemia blast samples. Its ease of implementation holds the potential to simplify the integration of this technique into routine clinical practice.
Project description:Recently, combining single-cell RNA sequencing (scRNA-seq) with upstream cell preservation procedures such as cryopreservation or methanol fixation has become more common. By separating cell handling and preparation, from downstream library generation, scRNA-seq workflows are more flexible and manageable. However, the inherent transcriptomics changes associated with cell preservation and how they may bias further downstream analysis remain unknown. Here, we present a side-by-side droplet-based scRNA-seq analysis, comparing the gold standard – fresh cells – to three different cell preservation workflows: dimethyl sulfoxide based cryopreservation, methanol fixation and CellCover reagent. Cryopreservation proved to be the most robust protocol, maximizing both cell integrity and low background ambient RNA. Importantly, gene expression profiles from fresh cells correlated most with those of cryopreserved cells. Such similarities were consistently observed across the tested cell lines (R ≥ 0.97), monocyte-derived macrophages (R = 0.97) and immune cells (R = 0.99). In contrast, both methanol fixation and CellCover preservation showed an increased ambient RNA background and an overall lower gene expression correlation to fresh cells. Thus, our results demonstrate the superiority of cryopreservation over other cell preservation methods. We expect our comparative study to provide single cell omics researchers invaluable support when integrating cell preservation into their scRNA-seq studies.
Project description:Recently, combining single-cell RNA sequencing (scRNA-seq) with upstream cell preservation procedures such as cryopreservation or methanol fixation has become more common. By separating cell handling and preparation, from downstream library generation, scRNA-seq workflows are more flexible and manageable. However, the inherent transcriptomics changes associated with cell preservation and how they may bias further downstream analysis remain unknown. Here, we present a side-by-side droplet-based scRNA-seq analysis, comparing the gold standard – fresh cells – to three different cell preservation workflows: dimethyl sulfoxide based cryopreservation, methanol fixation and CellCover reagent. Cryopreservation proved to be the most robust protocol, maximizing both cell integrity and low background ambient RNA. Importantly, gene expression profiles from fresh cells correlated most with those of cryopreserved cells. Such similarities were consistently observed across the tested cell lines (R ≥ 0.97), monocyte-derived macrophages (R = 0.97) and immune cells (R = 0.99). In contrast, both methanol fixation and CellCover preservation showed an increased ambient RNA background and an overall lower gene expression correlation to fresh cells. Thus, our results demonstrate the superiority of cryopreservation over other cell preservation methods. We expect our comparative study to provide single cell omics researchers invaluable support when integrating cell preservation into their scRNA-seq studies.
Project description:Background: The cryopreservation of semen is crucial for conserving genetic diversity and reproductive success in endangered species like the Siberian sturgeon. However, this process can cause cryodamage, affecting quality and protein profile of spermatozoa. While cryoprotectants like dimethyl sulfoxide (DMSO) and methanol (MeOH) facilitate post-thaw motility recovery, DMSO-preserved spermatozoa exhibit reduced fertilizing ability. This study investigates how DMSO and MeOH impact the proteome of Siberian sturgeon spermatozoa and examines semen quality parameters. Two complementary approaches of quantitative proteomics, liquid chromatography-mass spectrometry (LC-MS) and two-dimensional difference in gel electrophoresis (2D-DIGE), were used to analyze the proteomic profiles of fresh and cryopreserved spermatozoa, as well as the extracellular medium (EM; n=7 for each group). Results: Cryopreservation led to a decline in motility parameters (MOT, VCL, PROG) and viability, along with an increase in ROS levels, membrane fluidity, and acrosome damage. Despite similar quality parameters between DMSO and MeOH-preserved sperm, DMSO-preserved sperm showed dramatically lower fertilization success (6.2% vs 51.2%). A total of 224 and 118 differentially abundant proteins in spermatozoa cryopreserved with MeOH and DMSO, respectively, were identified compared to fresh samples, with 342 and 363 proteins released into the EM. The most affected proteins by cryopreservation included H2A, CABYR, PYGM, ENO3, DBI and LTA4H. Additionally, 36 and 39 uniquely altered sperm-leakage proteins were identified for MeOH and DMSO cryopreserved samples, respectively. Bioinformatic analysis showed that MeOH-specific proteins were related to chromosomal structure and mitochondrial functionality, while DMSO-specific proteins were mainly involved in acrosome reaction, zona pellucida binding, flagella structure, and nuclear pore organization. These proteins are potentially involved in sturgeon sperm fertilizing ability. The expression of six proteins was verified by western blot analysis. Conclusions: This study provides the first comprehensive proteomic characterization of Siberian sturgeon spermatozoa after cryopreservation with DMSO and MeOH, revealing insights into proteomic changes that affect fertilizing ability and aiding conservation efforts for this endangered species.
Project description:Single-cell transcriptomics methods have become very popular to study the cellular composition of organs and tissues and characterize the expression profiles of the individual cells that compose them. The main critical step for single-cell transcriptomics methods is sample preparation. Several methods have been developed to preserve cells after sample dissociation to uncouple sample handling from library preparation. Yet, the suitability of these methods depends on the types of cells to be processed. In this project, we perform a systematic comparison of preservation methods for droplet-based single-cell RNA-seq (scRNA-seq) on human neural progenitor cell populations derived from induced pluripotent stem cells (iPSCs) and highlight their strengths and weaknesses. We compared the cellular composition and expression profile of single-cell suspensions from fresh NPCs with that of NPCs preserved with Dimethyl Sulfoxide (DMSO), Methanol, vivoPHIX and Acetil-methanol (ACME). Our results show that while DMSO provides the highest cell quality in terms of RNA molecules and genes detected per cell. Yet, it strongly affects the cellular composition and the expression profile of the resulting datasets. In contrast, methanol fixed samples display a cellular composition like that of fresh samples while providing a good cell quality and smaller expression biases. Taken together, our results show that methanol fixation is the method of choice for performing droplet-based single-cell transcriptomics experiments on neural cell populations.
Project description:Background: Interest in single-cell whole transcriptome analysis is growing rapidly, especially for profiling rare or heterogeneous populations of cells. In almost all reported works, investigators have used live cells which represent several inconveniences and limitations. Some recent cell fixation methods did not work with most primary cells including immune cells. Methods: The methanol-fixation and new processing method was introduced to preserve PBMCs for single-cell RNA sequencing (scRNA-Seq) analysis on 10X Chromium platform. Results: When methanol fixation protocol was broken up into three steps, we found that PBMC RNA was degraded during rehydration with PBS, not at cell fixation and up to three-month storage steps. Resuspension but not rehydration in 3X saline sodium citrate (SSC) buffer instead of PBS preserved PBMC RNA integrity and prevented RNA leakage. Diluted SSC buffer did not interfere with full-length cDNA synthesis. The methanol-fixed PBMCs resuspended in 3X SSC were successfully implemented into 10X Chromium standard scRNA-seq workflows with no elevated low quality cells and cell doublets. The fixation process did not alter the single-cell transcriptional profiles and gene expression levels. Major subpopulations classified by marker genes could be identified in fixed PBMCs at a similar proportion as in live PBMCs. This new fixation processing protocol was validated in CD8+ T cell and several other cell types. Conclusions: We expect that the methanol-based cell fixation procedure presented here will substantially enable complex experimental design with primary cells at single cell resolution.
Project description:We have developed a methodology for isolation of high-quality RNA from cells that are fixed, stained and sorted by flow cytometry that allows routine transcriptomic analysis of highly purified cell populations and single cells. This method, essentially developed by modifying existing staining and sorting protocols, involves fixation of cells with glyoxal, an alternative fixative to commonly used formaldehyde, followed by methanol permeabilization, a 2-step primary and secondary antibody staining and sorting by flow cytometry. The advantage of using glyoxal is that it does not crosslink RNA to proteins nor form stable RNA adducts, ensuring that RNA remains accessible and amenable to enzymatic manipulation after glyoxal fixation. The dataset comprising mRNA seq libraries from unprocessed or fixed and stained human cancer cells demonstrate that RNA recovered from glyoxal-fixed cells does not retain sufficient glyoxal adducts to impair reverse transcription, and also reveal very few differentially expressed genes between the 2 groups. The dataset derived from fixed and stained cells that were sorted into CCNB1 positive or negative fractions show the applicability of this method for sorting highly purified cell fractions as the CCNB1 positive fractions show strong enrichment for G2-phase cells according to the GO analysis.
Project description:We report how methanol fixation influences transcriptome profile in single cell RNA-seq. We generatad Smart-seq2 data from two cell lines, and both live and fixed cells from each cell line were processed and analyzed to illustrate fixaiton effect.
Project description:Background: Recent developments in droplet-based microfluidics allow the transcriptional profiling of thousands of individual cells, in a quantitative, highly parallel and cost-effective way. A critical, often limiting step is the preparation of cells in an unperturbed state, not compromised by stress or ageing. Another challenge are rare cells that need to be collected over several days, or samples prepared at different times or locations. Results: Here, we used chemical fixation to overcome these problems. Methanol fixation allowed us to stabilize and preserve dissociated cells for weeks. By using mixtures of fixed human and mouse cells, we showed that individual transcriptomes could be confidently assigned to one of the two species. Single-cell gene expression from live and fixed samples correlated well with bulk mRNA-seq data. We then applied methanol fixation to transcriptionally profile primary single cells from dissociated complex tissues. Low RNA content cells from Drosophila embryos, as well as mouse hindbrain and cerebellum cells sorted by FACS, were successfully analysed after fixation, storage and single-cell droplet RNA-seq. We were able to identify diverse cell populations, including neuronal subtypes. As an additional resource, we provide 'dropbead', an R package for exploratory data analysis, visualization and filtering of Drop-seq data. Conclusions: We expect that the availability of a simple cell fixation method will open up many new opportunities in diverse biological contexts to analyse transcriptional dynamics at single cell resolution.
Project description:Cryopreservation is a routinely used methodology for prolonged storage of viable cells. The use of cryo-protective agents (CPAs) such as dimethylsulfoxide (DMSO), glycerol or trehalose is paramount to reduce cellular cryo-injury but their effectiveness is still limited. The current study focuses on establishing and modulating the proteomic and the corresponding biological profiles associated with the cryo-injury of human leukaemia (HL-60) cells cryopreserved in DMSO alone or DMSO +/- novel CPAs [e.g. nigerose (Nig) or salidroside (Sal)].