Heart disease and cancer represent the number one and number two killer diseases in developed countries. Identifying biomarkers to detect these and other diseases at early stages remains an important research goal and researchers are scrambling for ways to identify contributing factors to the pathogenesis of diseased cells in the body. In recent years, research has turned to the study of microRNA (miRNA) as possible biomarkers due to their extensive role in biological processes and cell functionality in normal vs. diseased cells. Microarrays combined with quantitative real-time PCR (qRT-PCR) validation are proving to be valuable tools for miRNA expression profiling and are predicted to play a crucial role in biomarker discovery and detection.
An important but challenging part of combating tough diseases like cancer and heart disease is the identification of key biomarkers at early stages of the disease from samples that are easily obtained by the least invasive methods. miRNAs are showing great potential as biomarkers as their control over cellular biological processes and contributions to the pathogenesis of diseases is slowly elucidated. It is now known that they influence cellular functionality by key regulation of gene expression, causing either translational inhibition or mRNA degradation. It is this regulation and deregulation that has been shown to influence the development of normal cells into diseased cells. Understanding exactly when and how miRNA expression is influencing this development will undoubtedly help lead to improved diagnosis and possibly treatment for certain disease types. Microarray detection is proving to be an important tool in this endeavor as it enables global expression profiling of miRNA, creating an expression signature for cells at particular stages of development or disease progression and so offers numerous possibilities for the study of biomarkers on a cellular level. First in the discovery of distinct miRNA sequences’ roles in the formation and regulation of cells, and second, as a tool for the detection of biomarkers that may ultimately prove to be indicators of disease stage, potential new therapeutic targets, and/or predictors of treatment efficacy.
In a recent study conducted by the Department of Laboratory Medicine at St. Michael’s Hospital, Toronto, researchers used miRNA microarray analysis (LC Sciences, Houston, TX) to discover unique human miRNA sequences which may serve as biomarkers in renal carcinoma cells1. To carry out this study, the researchers performed miRNA analysis on both normal kidney cells and histologically confirmed cancerous cells obtained from patients who had undergone a nephrectomy. Thirty-three deregulated miRNAs were found and qRT-PCR was then used to validate three of the top deregulated miRNA sequences on multiple matching pairs or cancerous and normal tissues. Extensive bioinformatics and pathway analysis found that five of the thirty-three miRNA sequences were not deregulated in other cancers. The authors suggest that these miRNAs have the potential to be biomarkers and that there may be tissue specific miRNA expression signatures which can distinguish different types of cancers.
In another study, conducted by a team at the University of Medicine and Dentistry of New Jersey, researchers employed miRNA microarray analysis (LC Sciences, Houston, TX) to generate miRNA expression signatures of different areas of infarcted rat hearts in the early phase of acute myocardial infarction (AMI) and compared them with noninfarcted areas2. They found miRNAs differentially expressed in both the infarcted areas (33 miRs) and the border areas (injured cells near the infracted zone, 33 miRs) at six hours after AMI by microarray. Some of the differentially expressed miRNAs were further analyzed by qRT-PCR to verify the microarray results. An important finding of this study was that the miRNA expression signature of the border area was very different than the infracted area, representing a possible therapeutic window for AMI. The authors suggest that miRNAs play important roles in the pathophysiology of AMI and that some miRNAs may be considered as new therapeutic targets or biomarkers for ischemic heart disease such as AMI.
The teaming of miRNA microarray analysis with qRT-PCR validation is proving to be a very powerful tool in the identification and detection of biomarkers. In one study potential biomarkers were identified that may be able to distinguish disease types, and thus be valuable as predictors of the efficacy of a particular treatment, and in other, potential biomarkers were identified at an early stage of the disease, which may prove to be therapeutic targets. While microarray provides a global expression profile, qRT-PCR continues to be the high standard for validating expression of unique miRNA sequences. Combining these two analysis approaches allows for a broad and reliable analysis of miRNA expression.
- Chow TF, Youssef YM, Lianidou E, Romaschin AD, Honey RJ, Stewart R, Pace KT, Yousef GM. (2009) Differential expression profiling of microRNAs and their potential involvement in renal cell carcinoma pathogenesis. Clin Biochem [Epub ahead of print]. [abstract]
- Dong S, Cheng Y, Yang J, Li J, Liu X, Wang X, Wang D, Krall TJ, Delphin ES, Zhang C. (2009) MicroRNA expression signature and the role of microRNA-21 in the early phase of acute myocardial infarction. J Biol Chem 284(43), 29514-25. [abstract]