Expression of miR-15b-5p, miR-21-5p, and SMAD7 in Lung Tissue of Sulfur Mustard-exposed Individuals with Long-term Pulmonary Complications

Sulfur mustard (SM)-exposed individuals develop late pulmonary complications, which are associated with chronic inflammation and fibrotic changes in the lung tissue. MicroRNAs are known to act as important regulators of inflammatory responses, including inflammation and fibrosis-related cytokine signaling. In this study, we investigated the expression miR-15b-5p and miR-21-5p, two regulators of TGF-β signaling, as well as their target molecule, SMAD7, in lung tissues from SM-exposed and control individuals. Total RNA was extracted from formalin-fixed paraffin-embedded (FFPE) lung tissue biopsies obtained during surgery from SM-exposed (n=20) or control (n=20) cases. Quality of the extracted RNA was evaluated by an Agilent Bioanalyzer and RNA was quantified using a NanoDrop. MiR-21-5p, miR-15b-5p and SMAD7 expression levels were measured by real-time RT-PCR. miR-21-5p expression levels were significantly decreased (2.7 fold) in the lung tissues from SM-exposed individuals compared with tissues obtained from the control group (p=0.02). There were no significant differences in miR-15b-5p expression levels between the two groups (p=0.94). Interestingly, SMAD7 expression levels were significantly higher (5.8 fold) in SM-exposed individuals' lung tissues compared with the control group (p=0.045). Our data indicate that exposure to sulfur mustard affects the expression of miR-21-5p as well as its target, SMAD7, in lung tissues many years after exposure. Considering the role of SMAD7 in the regulation of TGF-β signaling, these changes might point to a potential mechanism by which SM-exposure regulates inflammatory/fibrotic alterations in lung tissue.