Ding L., et al., A Lung Tissue Bank for Gene Expression Studies in Chronic Obstructive Pulmonary Disease, COPD, 1(2): pp 191–204 highlight an important issue in their study, namely, the applicability of using archival tissue in diseases such as chronic obstructive pulmonary disease (COPD) for RNA extraction and gene expression studies. Importantly, their study compares different archival samples—initially prepared either by rapid freezing of the tissue or formalin fixation followed by paraffin embedding—for RNA quantity as well as quality. As an additional step, they also compare RNA in laser capture microdissected cells from both the frozen and paraffin‐embedded tissue. These techniques have not previously utilized banked tissue from patients with COPD. The results of this study confirm findings from studies of other tissue types that have demonstrated paraffin‐embedded tissue can yield RNA, although the purity and degradation are worse than in other tissues, and that laser capture microdissection (LCM) can be used to assess RNA species. The authors' lung tissue bank spans 24 years and thus has important implications for current and future tissue banks in terms of the value of stored lung tissue for gene expression studies.
COPD is a major cause of death and disability among Americans, is very common, estimated to affect over 20 million people in this country and is now the fourth leading cause of death; however, until recently, the study of COPD has been limited to physiology and imaging of patients diagnosed with advanced disease. COPD pathogenesis is now being evaluated by obtaining blood and secretions from patients. Newer animal models are actively being investigated. Heretofore, study of the actual diseased human lung tissue has played a minor role in the search for disease‐specific pathogenesis. Yet, it is quite clear that animal models and cells can only approximate the human disease and that the gold standard of disease investigation will be direct interrogation of human tissue. The ability to characterize cellular and molecular abnormalities and correlate them with disease severity and outcome is a powerful tool in the research arsenal. Human lung tissue banks, particularly of nonneoplastic diseases, are not widely available, and how to capture and maintain this limited tissue in a meaningful manner is critical. This study provides good evidence that tissue banked for up to 20 years may still provide quality RNA for gene expression studies in human lung.
A tantalizing finding in this study is that oligo‐dT primed RNA is less likely to provide amplified products than random hexamers. The authors hypothesize that this may be because the site of priming by oligo‐dT (the polyA tail of the mRNA) is likely to be absent or physically separated from the sites of subsequent PCR priming. This is an important finding, if confirmed, as oligo‐dT primed RNA is currently more commonly used than the random hexamer approach.
This study represents a well‐organized attempt by a very good group of investigators to determine the applicability of different types of tissues for RNA analysis. The authors raise important issues in their analyses. It is clear that archival tissue will remain an important source for future disease‐specific studies. The chance to unite human tissue with the potential of genomics will undoubtedly allow new opportunities for disease mechanism exploration and development of novel therapeutic approaches.