Development and application of a novel reverse transcription real-time PCR method for miR-499 quantification

MicroRNAs (miRNAs) are endogenous small RNAs of 21-25 nucleotides that can pair with sites in 3' untranslated regions in mRNAs of protein-coding genes to downregulate their expression. Recently, miR-499 and other miRNAs released in circulating blood have been reported as promising biomarkers for acute myocardial infarction (AMI). In the present study, we developed a novel reverse-transcription real-time PCR assay for human miR-499 quantification.

miR-499 was reverse-transcribed with a 3' portion-specific primer into cDNAs. The cDNAs were further extended with overlap PCR. The extended cDNAs were determined by quantitative, real-time PCR. Synthetic miR-499 was put into the RT reaction over an optimal range to generate standard curves for absolute quantification of miR-499.

In the presence of 0.0001 amol/μL to 1.0×10⁶ amol/μL of synthetic miR-499, we observed a linear correlation (R²=0.999) between the logarithm of the amount of input RNA and the CT value. The miR-499 was reliably measured at a detection limit of 0.0001 amol/μL. The miR-499 measurements in spiked plasma samples indicated excellent correlation between the novel qRT PCR and classic stem loop qRT PCR. The qRT PCR analysis demonstrated that miR-499 was detected with higher levels in plasma from the patient with AMI in acute phase (AMI) compared with those from the control groups (P<0.001).

We developed a novel reverse-transcription real-time PCR assay for human miR-499 quantification. The good reproducibility and wide linearity range may permit more use of it in the quantification of other human miRNAs in future.