An optimized procedure for exosome isolation and analysis using serum samples: Application to cancer biomarker discovery.

Exosomes are RNA and protein-containing nanovesicles secreted by all cell types and found in abundance in body fluids, including blood, urine and cerebrospinal fluid. These vesicles seem to be a perfect source of biomarkers, as their cargo largely reflects the content of parental cells, and exosomes originating from all organs can be obtained from circulation through minimally invasive or non-invasive means. Here we describe an optimized procedure for exosome isolation and analysis using clinical samples, starting from quick and robust extraction of exosomes with Total exosome isolation reagent, then isolation of RNA followed by qRT-PCR. Effectiveness of this workflow is exemplified by analysis of the miRNA content of exosomes derived from serum samples - obtained from the patients with metastatic prostate cancer, treated prostate cancer patients who have undergone prostatectomy, and control patients without prostate cancer. Three promising exosomal microRNA biomarkers were identified, discriminating these groups: hsa-miR375, hsa-miR21, hsa-miR574.

Dissecting childhood asthma with nasal transcriptomics distinguishes subphenotypes of disease.

BACKGROUND: Bronchial airway expression profiling has identified inflammatory subphenotypes of asthma, but the invasiveness of this technique has limited its application to childhood asthma. OBJECTIVES: We sought to determine whether the nasal transcriptome can proxy expression changes in the lung airway transcriptome in asthmatic patients. We also sought to determine whether the nasal transcriptome can distinguish subphenotypes of asthma. METHODS: Whole-transcriptome RNA sequencing was performed on nasal airway brushings from 10 control subjects and 10 asthmatic subjects, which were compared with established bronchial and small-airway transcriptomes. Targeted RNA sequencing nasal expression analysis was used to profile 105 genes in 50 asthmatic subjects and 50 control subjects for differential expression and clustering analyses. RESULTS: We found 90.2% overlap in expressed genes and strong correlation in gene expression (ρ = .87) between the nasal and bronchial transcriptomes. Previously observed asthmatic bronchial differential expression was strongly correlated with asthmatic nasal differential expression (ρ = 0.77, P = 5.6 × 10(-9)). Clustering analysis identified TH2-high and TH2-low subjects differentiated by expression of 70 genes, including IL13, IL5, periostin (POSTN), calcium-activated chloride channel regulator 1 (CLCA1), and serpin peptidase inhibitor, clade B (SERPINB2). TH2-high subjects were more likely to have atopy (odds ratio, 10.3; P = 3.5 × 10(-6)), atopic asthma (odds ratio, 32.6; P = 6.9 × 10(-7)), high blood eosinophil counts (odds ratio, 9.1; P = 2.6 × 10(-6)), and rhinitis (odds ratio, 8.3; P = 4.1 × 10(-6)) compared with TH2-low subjects. Nasal IL13 expression levels were 3.9-fold higher in asthmatic participants who experienced an asthma exacerbation in the past year (P = .01). Several differentially expressed nasal genes were specific to asthma and independent of atopic status. CONCLUSION: Nasal airway gene expression profiles largely recapitulate expression profiles in the lung airways. Nasal expression profiling can be used to identify subjects with IL13-driven asthma and a TH2-skewed systemic immune response.

Exosomes: current knowledge of their composition, biological functions, and diagnostic and therapeutic potentials.

BACKGROUND: Cells continuously secrete a large number of microvesicles, macromolecular complexes, and small molecules into the extracellular space. Of the secreted microvesicles, the nanoparticles called exosomes are currently undergoing intense scrutiny. These are small vesicles (30-120 nm) containing nucleic acid and protein, perceived to be carriers of this cargo between diverse locations in the body. They are distinguished in their genesis by being budded into endosomes to form multivesicular bodies (MVBs) in the cytoplasm. The exosomes are released to extracellular fluids by fusion of these multivesicular bodies with the cell surface, resulting in secretion in bursts. Exosomes are secreted by all types of cells in culture, and also found in abundance in body fluids including blood, saliva, urine, and breast milk. SCOPE OF REVIEW: In this review, we summarize strategies for exosome isolation, our understanding to date of exosome composition, functions, and pathways, and discuss their potential for diagnostic and therapeutic applications. MAJOR CONCLUSIONS: Currently, the control of exosome formation, the makeup of the "cargo", biological pathways and resulting functions are incompletely understood. One of their most intriguing roles is intercellular communication--exosomes are thought to function as the messengers, delivering various effectors or signaling macromolecules between supposedly very specific cells. GENERAL SIGNIFICANCE: Both seasoned and newer investigators of nanovesicles have presented various viewpoints on what exosomes are, with some differences but a large common area. It would be useful to develop a codified definition of exosomes in both descriptive and practical terms. We hope this in turns leads to a consistent set of practices for their isolation, characterization and manipulation.

The human salivary RNA transcriptome revealed by massively parallel sequencing.

BACKGROUND: Evaluation of the salivary transcriptome is an emerging diagnostic technology with discriminatory power for disease detection. This study explored massively parallel sequencing for providing nucleotide-level sequence information for each RNA in saliva. METHODS: Transcriptome profiling with the SOLiD™ system was applied to RNA isolated from unstimulated cell-free saliva (CFS) and whole saliva (WS) from healthy human volunteers. Sequenced reads were aligned to human genome build 18 and the Human Oral Microbiome Database (HOMD). RESULTS: Massively parallel sequencing enabled the acquisition of complete sequence information for each nucleotide position of the human salivary transcriptome through alignment to multiple sequence databases. Approximately 20%-25% of the sequenced reads from CFS aligned to the human genome, and approximately 30% of the sequenced reads aligned to the HOMD. We detected the expression of >4000 coding and noncoding genes in CFS and WS. Gene expression at different genome loci showed that the structural integrity of the transcripts for the annotated genes was preserved in saliva. CONCLUSIONS: A single measurement provided RNA sequence information of gene transcript abundance for both coding and noncoding RNAs and identified sequences from >400 different microbial species within a single sample. Contrary to previous data suggesting that salivary RNA is highly fragmented, in our study the structural integrity of RNA was preserved. The high degree of sequence alignment to annotated exons and introns for each of the respective reference genomes, with sequence coverage spanning the full length of the genes, provides strong evidence that the salivary transcriptome is a complex RNA network.

Using RNA sample titrations to assess microarray platform performance and normalization techniques.

We have assessed the utility of RNA titration samples for evaluating microarray platform performance and the impact of different normalization methods on the results obtained. As part of the MicroArray Quality Control project, we investigated the performance of five commercial microarray platforms using two independent RNA samples and two titration mixtures of these samples. Focusing on 12,091 genes common across all platforms, we determined the ability of each platform to detect the correct titration response across the samples. Global deviations from the response predicted by the titration ratios were observed. These differences could be explained by variations in relative amounts of messenger RNA as a fraction of total RNA between the two independent samples. Overall, both the qualitative and quantitative correspondence across platforms was high. In summary, titration samples may be regarded as a valuable tool, not only for assessing microarray platform performance and different analysis methods, but also for determining some underlying biological features of the samples.

The MicroArray Quality Control (MAQC) project shows inter- and intraplatform reproducibility of gene expression measurements.

Over the last decade, the introduction of microarray technology has had a profound impact on gene expression research. The publication of studies with dissimilar or altogether contradictory results, obtained using different microarray platforms to analyze identical RNA samples, has raised concerns about the reliability of this technology. The MicroArray Quality Control (MAQC) project was initiated to address these concerns, as well as other performance and data analysis issues. Expression data on four titration pools from two distinct reference RNA samples were generated at multiple test sites using a variety of microarray-based and alternative technology platforms. Here we describe the experimental design and probe mapping efforts behind the MAQC project. We show intraplatform consistency across test sites as well as a high level of interplatform concordance in terms of genes identified as differentially expressed. This study provides a resource that represents an important first step toward establishing a framework for the use of microarrays in clinical and regulatory settings.

Improved microarray gene expression profiling of virus-infected cells after removal of viral RNA.

BACKGROUND: Sensitivity and accuracy are key points when using microarrays to detect alterations in gene expression under different conditions. Critical to the acquisition of reliable results is the preparation of the RNA. In the field of virology, when analyzing the host cell's reaction to infection, the often high representation of viral RNA (vRNA) within total RNA preparations from infected cells is likely to interfere with microarray analysis. Yet, this effect has not been investigated despite the many reports that describe gene expression profiling of virus-infected cells using microarrays. RESULTS: In this study we used coronaviruses as a model to show that vRNA indeed interferes with microarray analysis, decreasing both sensitivity and accuracy. We also demonstrate that the removal of vRNA from total RNA samples, by means of virus-specific oligonucleotide capturing, significantly reduced the number of false-positive hits and increased the sensitivity of the method as tested on different array platforms. CONCLUSION: We therefore recommend the specific removal of vRNA, or of any other abundant 'contaminating' RNAs, from total RNA samples to improve the quality and reliability of microarray analyses.

Temporal gene expression analysis of human coronary artery endothelial cells treated with Simvastatin.

Increasing evidence indicates that the beneficial "pleiotropic" effects of statins on clinical events involve nonlipid mechanisms including the modification of blood vessel endothelial cell function. However, the involved molecular events and pathways are not completely understood. In the present study, Affymetrix microarrays were used to monitor the temporal gene expression of human coronary artery endothelial cells (HCAEC) treated with simvastatin (Sim) to gain insight into statins' direct effects on the endothelial function. We isolated and labeled mRNA from HCAEC treated with Sim for 0, 3, 6, 12, 24, and 48 h and hybridized these samples to Affymetrix GeneChip HG-U95Av2 to analyze the temporal gene expression profile. Out of 12,625 genes present on the HG-U95Av2 GeneChip, expression of 5,432 genes was detected. There were 1,475 of 5,432 genes that displayed the differential expression compared to baseline (0 h). Fifty-four genes were upregulated (< or = twofold) while 61 genes were downregulated ( > or = twofold) at 24-48 h after the Sim treatment. Many new target genes and pathways modulated by Sim were uncovered. This study indicates that many aspects of the pleiotropic effect of Sim on the endothelial cell function can be mediated by transcriptional control. Physiological function of 22% of 115 differentially expressed genes in Sim-treated HCAEC are currently unknown. These newly identified genes could be useful for new mechanistic study and new therapeutic modalities. Expressions of 13 out of 18 genes (> 70%) in the cell cycle/proliferation control process were significantly inhibited by the Sim treatment. CDC25B and ITGB4 gene expressions were validated by RT-PCR and Western blotting. Sim's inhibitory effect of on HCAEC growth was confirmed by the measurement of [3H]thymidine incorporation into the DNA synthesis. Further in-depth analysis of this effect may shed light on molecular mechanisms of Sim's beneficial inhibition of neointima formation in the atherosclerotic artery stenosis.

Small RNA sequences are readily stabilized by inclusion in a carrier rRNA.

This laboratory previously showed that an RNA derived from 5S ribosomal RNA could be used as a carrier to harbor a nucleic acid "tag" for monitoring genetically engineered or naturally occurring bacteria. The prototype system expressed a specific tagged RNA that was stable and accumulated to high levels. For such a system to be useful there should, however, be little limitation on the sequence composition and length of the insert. To test these limitations, a collection of insertion sequences were created and introduced into the artificial 5S rRNA cassette. This library consisted of random 13- and 50-base oligonucleotides that were inserted into the carrier RNA. We report here that essentially all of the insert-containing RNAs are stable and accumulate to detectable levels. Tagged RNAs were produced by both plasmid-borne and chromosomally integrated expression systems in E. coli and several Pseudomonas strains without obvious effect on the host cell. It is anticipated that in addition to its intended use in environmental monitoring, this system can be used for in vivo selection of useful artificial RNAs. Because the carrier lends stability to the RNAs, the system may also be useful in RNA production.

Assessing technical performance in differential gene expression experiments with external spike-in RNA control ratio mixtures.

There is a critical need for standard approaches to assess, report and compare the technical performance of genome-scale differential gene expression experiments. Here we assess technical performance with a proposed standard 'dashboard' of metrics derived from analysis of external spike-in RNA control ratio mixtures. These control ratio mixtures with defined abundance ratios enable assessment of diagnostic performance of differentially expressed transcript lists, limit of detection of ratio (LODR) estimates and expression ratio variability and measurement bias. The performance metrics suite is applicable to analysis of a typical experiment, and here we also apply these metrics to evaluate technical performance among laboratories. An interlaboratory study using identical samples shared among 12 laboratories with three different measurement processes demonstrates generally consistent diagnostic power across 11 laboratories. Ratio measurement variability and bias are also comparable among laboratories for the same measurement process. We observe different biases for measurement processes using different mRNA-enrichment protocols.

The complete exosome workflow solution: from isolation to characterization of RNA cargo.

Exosomes are small (30-150 nm) vesicles containing unique RNA and protein cargo, secreted by all cell types in culture. They are also found in abundance in body fluids including blood, saliva, and urine. At the moment, the mechanism of exosome formation, the makeup of the cargo, biological pathways, and resulting functions are incompletely understood. One of their most intriguing roles is intercellular communication--exosomes function as the messengers, delivering various effector or signaling macromolecules between specific cells. There is an exponentially growing need to dissect structure and the function of exosomes and utilize them for development of minimally invasive diagnostics and therapeutics. Critical to further our understanding of exosomes is the development of reagents, tools, and protocols for their isolation, characterization, and analysis of their RNA and protein contents. Here we describe a complete exosome workflow solution, starting from fast and efficient extraction of exosomes from cell culture media and serum to isolation of RNA followed by characterization of exosomal RNA content using qRT-PCR and next-generation sequencing techniques. Effectiveness of this workflow is exemplified by analysis of the RNA content of exosomes derived from HeLa cell culture media and human serum, using Ion Torrent PGM as a sequencing platform.

Methods for the extraction and RNA profiling of exosomes.

AIM: To develop protocols for isolation of exosomes and characterization of their RNA content. METHODS: Exosomes were extracted from HeLa cell culture media and human blood serum using the Total exosome isolation (from cell culture media) reagent, and Total exosome isolation (from serum) reagent respectively. Identity and purity of the exosomes was confirmed by Nanosight(®) analysis, electron microscopy, and Western blots for CD63 marker. Exosomal RNA cargo was recovered with the Total exosome RNA and protein isolation kit. Finally, RNA was profiled using Bioanalyzer and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) methodology. RESULTS: Here we describe a novel approach for robust and scalable isolation of exosomes from cell culture media and serum, with subsequent isolation and analysis of RNA residing within these vesicles. The isolation procedure is completed in a fraction of the time, compared to the current standard protocols utilizing ultracentrifugation, and allows to recover fully intact exosomes in higher yields. Exosomes were found to contain a very diverse RNA cargo, primarily short sequences 20-200 nt (such as miRNA and fragments of mRNA), however longer RNA species were detected as well, including full-length 18S and 28S rRNA. CONCLUSION: We have successfully developed a set of reagents and a workflow allowing fast and efficient extraction of exosomes, followed by isolation of RNA and its analysis by qRT-PCR and other techniques.

The External RNA Controls Consortium: a progress report.

Standard controls and best practice guidelines advance acceptance of data from research, preclinical and clinical laboratories by providing a means for evaluating data quality. The External RNA Controls Consortium (ERCC) is developing commonly agreed-upon and tested controls for use in expression assays, a true industry-wide standard control.