Mechanisms of Action of Extracorporeal Photopheresis in the Control of BOS: Involvement of Circulating miRNAs

Abstract

<h3>Purpose</h3> MicroRNAs (miRNAs) are considered important modulators of the immune system and have been associated with several diseases. Available clinical evidence suggests improvement or stabilization of lung function in BOS patients treated by extracorporeal photopheresis (ECP). However, few studies have explored the epigenetic and molecular regulation of this therapy. In particular, no studies have addressed miRNAs expression during ECP treatment in BOS. The aim of the study was to evaluate whether a specific set of miRNAs, known to be involved in immune regulation, showed a significant dysregulation during ECP. <h3>Methods</h3> Total RNA was isolated from serum of BOS patients prior to start ECP treatment and after 6 months. The expression profiles of different miRNAs were obtained by qPCR. Patients whose FEV₁ declined less than 10% with respect to basal value were classified as responders. <h3>Results</h3> Twenty-six BOS patients receiving ECP and 17 healthy subjects were included in the analysis. Among the studied miRNAs, we observed a significant down-regulation of circulating hsa-miR-155-5p (p<0.0001), hsa-miR-146a-5p (p<0.0001) and hsa-miR-31-5p (p =0.015) in BOS patients at ECP start when compared to healthy subjects. In order to investigate differential miRNAs expression associated with ECP response, miRNAs levels were compared among responders and non-responders. None of the tested miRNAs was significantly different in the two subpopulations prior to ECP initiation. In responders, paired analysis showed increased expression levels of hsa-miR-155-5p after 6-months treatment (p<0.0001). ECP also induced a significant reduction in hsa-miR-23b-3p expression levels (p<0.0001), although its levels were not significantly dysregulated at baseline compared to healthy controls. <h3>Conclusion</h3> The significant down regulation of miR-155 and miR-146a in patients experiencing BOS at ECP start is in line with a low level of immunologic tolerance towards the allograft. Of note, ECP induces an increase of miR-155p among responders. Variation of miR-23b during treatment is more controversial, possibly related to a modulation of fibrogenic molecular pathways.