Quantitative miRNA Expression Analysis Using Fluidigm Microfluidics Dynamic Arrays

MicroRNA (miRNA) is a small non-coding RNA that can regulate gene expression in both plants and animals. Studies showed that miRNAs play a critical role in human cancer by targeting messenger RNAs that are positive or negative regulators of cell proliferation and apoptosis. Here, we evaluated miRNA expression in formalin fixed, paraffin embedded (FFPE) samples and fresh frozen (FF) samples using a high throughput qPCR-based microfluidic dynamic array technology (Fluidigm). We compared the results to hybridization-based microarray platforms using the same samples. We obtained a highly correlated Ct values between multiplex and single-plex RT reactions using standard qPCR assays for miRNA expression. For the same samples, the microfluidic technology (Fluidigm 48.48 dynamic array systems) resulted in a left shift towards lower Ct values compared to those observed by standard TaqMan (ABI 7900HT, mean difference, 3.79). In addition, as little as 10ng total RNA was sufficient to reproducibly detect up to 96 miRNAs at a wide range of expression values using a single 96-multiplexing RT reaction in either FFPE or FF samples. Comparison of miRNAs expression values measured by microfluidic technology with those obtained by other array and Next Generation sequencing platforms showed positive concordance using the same samples but revealed significant differences for a large fraction of miRNA targets. The qPCRarray based microfluidic technology can be used in conjunction with multiplexed RT reactions for miRNA gene expression profiling. This approach is highly reproducible and the results correlate closely with the existing singleplex qPCR platform while achieving much higher throughput at lower sample input and reagent usage. It is a rapid, cost effective, customizable array platform for miRNA expression profiling and validation. However, comparison of miRNA expression using different platforms requires caution and the use of multiple platforms

Multi-Platform Analysis of MicroRNA Expression Measurements in RNA from Fresh Frozen and FFPE Tissues

<div><p>MicroRNAs play a role in regulating diverse biological processes and have considerable utility as molecular markers for diagnosis and monitoring of human disease. Several technologies are available commercially for measuring microRNA expression. However, cross-platform comparisons do not necessarily correlate well, making it difficult to determine which platform most closely represents the true microRNA expression level in a tissue. To address this issue, we have analyzed RNA derived from cell lines, as well as fresh frozen and formalin-fixed paraffin embedded tissues, using Affymetrix, Agilent, and Illumina microRNA arrays, NanoString counting, and Illumina Next Generation Sequencing. We compared the performance within- and between the different platforms, and then verified these results with those of quantitative PCR data. Our results demonstrate that the within-platform reproducibility for each method is consistently high and although the gene expression profiles from each platform show unique traits, comparison of genes that were commonly detectable showed that detection of microRNA transcripts was similar across multiple platforms.</p> </div

Expression correlations of data derived from fresh frozen (FF) and paraffin-embedded (FFPE) samples.

<p>Correlations of log2 transformed signal counts for each platform are shown (A–F) along with the respective Pearson correlation (r) coefficients. The average expression values of two replicates were used except for miRNA-Seq, where individual samples were directly compared as indicated.</p

Replicate performance of tested miRNA platforms.

*<p>The miRNA transcripts interrogated by each platform were assessed based on platform-specific metrics. n =  number of interrogated transcripts by each platform and were used to calculate the Pearson Correlations(r).</p

Experimental design of the miRNA expression platform comparison.

<p>RNA from replicate samples derived from normal lung, lung tumor, and a cell line were extracted by methods as indicated. All samples were subsequently analyzed by Illumina, Affymetrix, Agilent, NanoString, Illumina miRNA-Seq, and Fluidigm qPCR.</p

Correlation of miRNA expression fold-change in Fluidigm-based qPCR compared to five other miRNA gene profiling platforms.

*<p>The number of miRNA transcripts shared among all platforms and detected by qPCR in the fresh frozen and formalin-fixed paraffin embedded samples as indicated. Spearman correlation coefficient (r_s) and its associated p-value are indicated.</p