LSC - 2019 - Post-transcriptional dysregulation as a novel mechanism underlying non-responsive severe asthma

Background: Severe asthmatics (SA) are asthma patients who show poor response to therapy including high-dose glucocorticoids (GC). SA (5-10% of asthmatics) have frequent exacerbations leading to lung function decline over time. The mechanisms underlying SA non-responsiveness are poorly understood. Aim: To investigate the role of microRNAs (miRNAs) and RNA binding proteins (RBPs) in SA non-responsiveness. Method: We applied Frac-seq (subcellular fractionation and RNA-seq) in bronchial epithelial cells (BECs) from healthy controls and SA and small RNA-seq to determine miRNA expression. Frac-seq determines total (transcribed) and polyribosome-bound (translated) mRNA levels. Over/knock-down experiments assessed the role of miRNA and RBPs in GC response. Results: 6 miRNAs potentially regulate ~50% of differentially translated mRNAs in SA, rendering cells non-responsive to GCs when transfected into BECs. We found RBPs ZFP36L1(L1) and ZFP36L2(L2) down-regulated in SA. L1 and L2 levels correlate positively with FEV1 and inversely with airway reversibility. U-BIOPRED data confirmed lower levels of L1/L2 in SA patients on oral GCs compared to SA on inhaled therapy. L1/L2 are potentially inhibited by miRNAs up-regulated in SA according to miRNA target predictions and preliminary results. Frac-seq on primary BECs depleted of L1/L2 and treated with GCs demonstrated a major level of genome-wide post-transcriptional regulation by GCs mediated by L1/L2. Conclusion: Our results demonstrate that GCs act post-transcriptionally in an L1/L2-dependent manner. We propose a novel post-transcriptional mechanism that may underlie impaired GC responses in SA, opening new avenues in the understanding and management of SA.