Exosomes: Methods for Isolation and Characterization in Biological Samples.

Exosomes are small lipid bilayer-encapsulated nanosized extracellular vesicles of endosomal origin. Exosomes are secreted by almost all cell types and are a crucial player in intercellular communication. Exosomes transmit cellular information from donor to recipient cells in the form of proteins, lipids, and nucleic acids and influence several physiological and pathological responses. Due to their capacity to carry a variety of cellular cargo, low immunogenicity and cytotoxicity, biocompatibility, and ability to cross the blood-brain barrier, these nanosized vesicles are considered excellent diagnostic tools and drug-delivery vehicles. Despite their tremendous potential, the progress in therapeutic applications of exosomes is hindered by inadequate isolation techniques, poor characterization, and scarcity of specific biomarkers. The current research in the field is focused on overcoming these limitations. In this chapter, we have reviewed conventional exosome isolation and characterization methods and recent advancements, their advantages and limitations, persistent challenges in exosome research, and future directions.

Isolation and Characterization of Extracellular Vesicles from Cell Culture Media.

Extracellular vesicles (EVs) were once believed to serve as a means of disposing of cellular waste. However, recent discoveries have identified their crucial roles in intercellular communication between neighboring and distant cells. Almost all cell types have now been identified to produce EVs, which play a vital role in transporting cellular cargo. The functional roles of EVs, along with their implications in (patho)physiology of various diseases, are still being explored. In the last decade, the identification of EV roles in pathophysiology, pharmacology, and diagnostics has gained significant interest, albeit the development of universal methods for the isolation and characterization of EVs has been the limiting factor. A further challenge is ensuring that EVs of various size categories, which are thought to be produced via independent cellular mechanisms and often differ in their cargo and physiological purpose, can be separated and studied in isolation.This protocol provides an efficient and accessible method for isolating and characterizing EV samples from conditioned cell culture media. The combination of differential centrifugation and the use of a commercial EV-precipitation kit allows for the rapid isolation of a highly pure sample of EVs separated by size. A microfluidic resistive pulse sensing (MRPS)-based method is then used to quantify the particles, as well as to assess the size distribution of the EV sample. As a result, this protocol provides a reproducible means to isolate and characterize EVs of a variety of sizes from nearly any cultured cells.

Exosomes Isolation, Purification, and Characterization.

Exosomes are double-layered lipid membranous nanovesicles that are endosomal in origin and secreted by almost all cells. They are 30-130 nm in size and contain various molecular signatures such as miRNAs, mRNAs, DNA, lipids, and proteins. Due to their highly heterogeneous content, exosomes have a major role in influencing cellular physiology and pathology. Although exosome research has been in progress for a long time, its biomedical applications have recently been expanding due to its bio-friendly nature. However, the most challenging part is its isolation to obtain quality exosomes with good yield. Therefore, in this chapter, we have described appropriate protocols for exosome isolation and characterization along with alternative purification methods.

Isolation of Mitochondria from Murine Skeletal Muscle.

Skeletal muscle is one of the largest tissues in human body. Besides enabling voluntary movements and maintaining body's metabolic homeostasis, skeletal muscle is also a target of many pathological conditions. Mitochondria occupy 10-15% volume of a muscle myofiber and regulate many cellular processes, which often determine the fate of the cell. Isolation of mitochondria from skeletal muscle provides opportunities for various multi-omics studies with a focus on mitochondria in biomedical research field. Here we describe a protocol to efficiently isolate mitochondria with high quality and purity from skeletal muscle of mice using Nycodenz density gradient ultracentrifugation.

Chloroplast Isolation in Agavaceas.

Chloroplast isolation protocols have been extensively developed for various species of plants, particularly model organisms with easily manipulable physical characteristics. However, succulent plants, such as Agave angustifolia Haw., which possess adaptations for arid environments like the Crassulacean acid metabolism (CAM) and a thicker cuticle, have received less attention, resulting in a potential knowledge gap. This chapter presents a specialized protocol focusing on isolating chloroplast from A. angustifolia, a species exhibiting adaptations to arid conditions and holding ecological and economic significance due to its role in producing bacanora and mezcal beverages. By successfully isolating chloroplast from A. angustifolia plant growth in ex vitro and in vitro conditions, this protocol enables comprehensive future analyses to elucidate metabolic processes and explore potential applications in related species. Consequently, this research aims to bridge this knowledge gap in chloroplast isolation for succulent plants, providing new insights for future investigations in the field.

Additional confirmation of successful cell suspension fractionation of metastatic axillary node tissue.

We present herein an extension to our recently developed and published method termed "Fractionation of Nodal Cell Suspension" (FNCS). The method enables efficient subcellular fractionation into nuclear (N) and cytosolic (C) compartments of extremely fibrous and problematic metastatic axillary lymph node (mALN) tissue, using the entire nodule. For the purpose of the present study, a case of invasive lobular breast cancer (BC) patient with pT2N3aMx status and defined primary tumor markers (ERα 8, PR-B 8, and HER2 score 0) was available. Initially, the mALN tissue of this patient was analyzed by immunohistochemistry (IHC), and a positive correlation of nodal ERα, PR-B and HER2 biomarkers to those of the primary tumor was obtained. Subsequently, the mALN was FNCS fractionated into N and C, and Western blot (WB) analysis demonstrated a single band for ERα, PR-B and nuclear loading control (HDAC1) in nuclear, but not in the cytosolic compartments, confirming the efficiency of our fractionation protocol. At the same time, HER2 bands were not observed in either compartment, in accordance with HER2 negativity determined by IHC in both primary tumor and mALN tissue. In conclusion, by confirming the nuclear expression of ERα and PR-B biomarkers in metastatic loci, we demonstrate the purity of the FNCS-generated compartments - the protocol that offers a reliable tool for further analysis of nuclear versus cytosolic content in downstream analysis of novel biomarkers in the whole mALN of BC patients.

Biochemical Separation of Cytoplasmic and Nuclear Fraction for Downstream Molecular Analysis.

Biochemical fractionation is a technique used to isolate and separate distinct cellular compartments, critical for dissecting cellular mechanisms and molecular pathways. Herein we outline a biochemical fraction methodology for isolation of ultra-pure nuclei and cytoplasm. This protocol utilizes hypotonic lysis buffer to suspend cells, coupled with a calibrated centrifugation strategy, for enhanced separation of cytoplasm from the nuclear fraction. Subsequent purification steps ensure the integrity of the isolated nuclear fraction. Overall, this method facilitates accurate protein localization, essential for functional studies, demonstrating its efficacy in separating cellular compartments. © 2024 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol: Biochemical fractionation Support Protocol 1: Protein quantification using Bradford assay Support Protocol 2: SDS/PAGE and Western blotting.

Size-Selective Capturing of Exosomes Using DNA Tripods.

Fractionating and characterizing target samples are fundamental to the analysis of biomolecules. Extracellular vesicles (EVs), containing information regarding the cellular birthplace, are promising targets for biology and medicine. However, the requirement for multiple-step purification in conventional methods hinders analysis of small samples. Here, we apply a DNA origami tripod with a defined aperture of binders (e.g., antibodies against EV biomarkers), which allows us to capture the target molecule. Using exosomes as a model, we show that our tripod nanodevice can capture a specific size range of EVs with cognate biomarkers from a broad distribution of crude EV mixtures. We further demonstrate that the size of captured EVs can be controlled by changing the aperture of the tripods. This simultaneous selection with the size and biomarker approach should simplify the EV purification process and contribute to the precise analysis of target biomolecules from small samples.

Bacterial Envelope Fractionation.

Numerous bioinformatics tools allow predicting the localization of membrane proteins in the outer or inner membrane of Escherichia coli with high precision. Nevertheless, it might be desirable to experimentally verify such predictions or to assay the correct localization of recombinant or mutated variants of membrane proteins. Here we describe two methods (preferential detergent solubilization and sucrose-gradient fractionation) that allow to fractionate Gram-negative bacterial membranes and subsequently to enrich inner or outer membrane proteins.

A fractionation-based protocol to investigate RNA solubility phase transition during Xenopus oocyte maturation.

While RNAs are soluble in vitro, their solubility may be altered when incorporated into some protein complexes inside the cell. The solubility phase transition of RNAs is thus indicative of changes in the function and activity of RNAs. Here, we present a protocol for the assessment of RNA solubility phase transition during Xenopus oocyte maturation. We describe steps for sample preparation, cell fractionation, RNA extraction, real-time PCR, and analysis of the obtained results. For complete details on the use and execution of this protocol, please refer to Hwang et al. (2023).1.

REAP+: A single preparation for rapid isolation of nuclei, cytoplasm, and mitochondria.

REAP+ is an enhanced version of the rapid, efficient, and practical (REAP) method designed for the isolation of nuclear fractions. This improved version, REAP+, enables fast and effective extraction of mitochondria, cytoplasm, and nuclei. The mechanical cell disruption process has been optimized to cerebral tissues, snap-frozen liver, and HT22 cells with remarkable fraction enrichment. REAP+ is well-suited for samples containing minimal protein quantities, such as mouse hippocampal slices. The method was validated by Western blot and marker enzyme activities, such as LDH and G6PDH for the cytoplasmic fraction and succinate dehydrogenase and cytochrome c oxidase for the mitochondrial fraction. One of the outstanding features of this method is its rapid execution, yielding fractions within 15 min, allowing for simultaneous preparation of multiple samples. In essence, REAP+ emerges as a swift, efficient, and practical technique for the concurrent isolation of nuclei, cytoplasm, and mitochondria from various cell types and tissues. The method would be suitable to study the multicompartment translocation of proteins, such as metabolic enzymes and transcription factors migrating from cytosol to the mitochondria and nuclei. Moreover, its compatibility with small samples, such as hippocampal slices, and its potential applicability to human biopsies, highlights the potential application in medical research.

Density-Based Fractionation of Cell-Conditioned Medium to Prepare Proteomics Grade Extracellular Vesicles.

The identification of the molecular composition of extracellular vesicles (EV) by omics approaches, including proteomics, requires the separation of EV from non-EV confounding factors present in the source biofluid. In this protocol, we present the sequential implementation of density gradient ultracentrifugation and size-exclusion chromatography to prepare EV from cell-conditioned medium with high specificity and repeatability. This approach enables the recovery of intact purified EV suited for downstream functional assays and biomarker discovery by omics approaches.

Deep and fast label-free Dynamic Organellar Mapping.

The Dynamic Organellar Maps (DOMs) approach combines cell fractionation and shotgun-proteomics for global profiling analysis of protein subcellular localization. Here, we enhance the performance of DOMs through data-independent acquisition (DIA) mass spectrometry. DIA-DOMs achieve twice the depth of our previous workflow in the same mass spectrometry runtime, and substantially improve profiling precision and reproducibility. We leverage this gain to establish flexible map formats scaling from high-throughput analyses to extra-deep coverage. Furthermore, we introduce DOM-ABC, a powerful and user-friendly open-source software tool for analyzing profiling data. We apply DIA-DOMs to capture subcellular localization changes in response to starvation and disruption of lysosomal pH in HeLa cells, which identifies a subset of Golgi proteins that cycle through endosomes. An imaging time-course reveals different cycling patterns and confirms the quantitative predictive power of our translocation analysis. DIA-DOMs offer a superior workflow for label-free spatial proteomics as a systematic phenotype discovery tool.

Separation of Single Core and Multicore Lytic Granules by Subcellular Fractionation and Immunoisolation.

Subcellular fractionation is an important tool used to separate intracellular organelles, structures or proteins. Here, we describe a stepwise protocol to isolate two types of lytic granules, multicore (MCG), and single core (SCG), from primary murine CTLs. We used cell disruption by nitrogen cavitation followed by separation of organelles via discontinuous sucrose density gradient centrifugation. Immunoisolation with a Synaptobrevin 2 antibody attached to magnetic beads was then used to harvest Synaptobrevin 2 positive granules for immunoblotting, mass spectrometry, electron, and light microscopy.

A general method for quantitative fractionation of mammalian cells.

Subcellular fractionation in combination with mass spectrometry-based proteomics is a powerful tool to study localization of key proteins in health and disease. Here we offered a reliable and rapid method for mammalian cell fractionation, tuned for such proteomic analyses. This method proves readily applicable to different cell lines in which all the cellular contents are accounted for, while maintaining nuclear and nuclear envelope integrity. We demonstrated the method's utility by quantifying the effects of a nuclear export inhibitor on nucleoplasmic and cytoplasmic proteomes.

The proteome and transcriptome of stress granules and P bodies during human T lymphocyte activation.

Stress granules (SGs) and processing bodies (PBs) are membraneless cytoplasmic assemblies regulating mRNAs under environmental stress such as viral infections, neurological disorders, or cancer. Upon antigen stimulation, T lymphocytes mediate their immune functions under regulatory mechanisms involving SGs and PBs. However, the impact of T cell activation on such complexes in terms of formation, constitution, and relationship remains unknown. Here, by combining proteomic, transcriptomic, and immunofluorescence approaches, we simultaneously characterized the SGs and PBs from primary human T lymphocytes pre and post stimulation. The identification of the proteomes and transcriptomes of SGs and PBs indicate an unanticipated molecular and functional complementarity. Notwithstanding, these granules keep distinct spatial organizations and abilities to interact with mRNAs. This comprehensive characterization of the RNP granule proteomic and transcriptomic landscapes provides a unique resource for future investigations on SGs and PBs in T lymphocytes.

Isolation of Mammalian Peroxisomes by Density Gradient Centrifugation.

Sophisticated organelle fractionation strategies were the workhorse of early peroxisome research and led to the characterization of the principal functions of the organelle. However, even in the era of molecular biology and "omics" technologies, they are still of importance to unravel peroxisome-specific proteomes, confirm the localization of still uncharacterized proteins, analyze peroxisome metabolism or lipid composition, or study their protein import mechanism. To isolate and analyze peroxisomes for these purposes, density gradient centrifugation still represents a highly reliable and reproducible technique. This article describes two protocols to purify peroxisomes from either liver tissue or the HepG2 hepatoma cell line. The protocol for liver enables purification of peroxisome fractions with high purity (95%) and is therefore suitable to study low-abundant peroxisomal proteins or analyze their lipid composition, for example. The protocol presented for HepG2 cells is not suitable to gain highly pure peroxisomal fractions but is intended to be used for gradient profiling experiments and allows easier manipulation of the peroxisomal compartment, e.g., by gene knockdown or protein overexpression for functional studies. Both purification methods therefore represent complementary tools to be used to analyze different aspects of peroxisome physiology. Please note that this is an updated version of a protocol, which has been published in a former volume of Methods in Molecular Biology.

Analysis of Yeast Peroxisomes via Spatial Proteomics.

Peroxisomes are ubiquitous organelles with essential functions in numerous cellular processes such as lipid metabolism, detoxification of reactive oxygen species, and signaling. Knowledge of the peroxisomal proteome including multi-localized proteins and, most importantly, changes of its composition induced by altering cellular conditions or impaired peroxisome biogenesis and function is of paramount importance for a holistic view on peroxisomes and their diverse functions in a cellular context. In this chapter, we provide a spatial proteomics protocol specifically tailored to the analysis of the peroxisomal proteome of baker's yeast that enables the definition of the peroxisomal proteome under distinct conditions and to monitor dynamic changes of the proteome including the relocation of individual proteins to a different cellular compartment. The protocol comprises subcellular fractionation by differential centrifugation followed by Nycodenz density gradient centrifugation of a crude peroxisomal fraction, quantitative mass spectrometric measurements of subcellular and density gradient fractions, and advanced computational data analysis, resulting in the establishment of organellar maps on a global scale.

Characterization of Yeast Peroxisomes: Enrichment of Peroxisomal Fractions and Analysis of ß-Oxidation Activity.

Subcellular fractionation approaches have allowed for the identification of various functionally distinct organelles including peroxisomes. The methods enable enrichment of organelles and combined with downstream assays allow for the identification of biochemical functions, composition, and structural characteristics of these compartments. In this chapter, we describe the methods for differential centrifugation and Nycodenz gradients in the yeast Saccharomyces cerevisiae and describe assays for fatty acid ß-oxidation in intact cells and in peroxisomal fractions.

Isolation of Functional Mitochondria and Pure mtDNA from Murine Tissues.

Detailed analysis of mitochondrial function cannot be achieved without good quality preparations of isolated mitochondria. Ideally, the isolation protocol should be quick, while producing a reasonably pure pool of mitochondria that are still intact and coupled. Here, we describe a fast and simple method for the purification of mammalian mitochondria relying on isopycnic density gradient centrifugation. We describe specific steps that should be taken into consideration when functional mitochondria from different tissues should be isolated. This protocol is suitable for the analysis of many aspects of the organelle's structure and function.