Alternative splicing of toll-like receptor pathway mRNAs in lung immune cells from patients with ARDS

Acute respiratory distress syndrome (ARDS) is characterized by robust inflammation in the lungs and systemic circulation. In this context, the toll-like receptor (TLR) signaling pathway plays a major role, driving inflammation that promotes host defense but also causing pathological tissue damage. To limit excessive inflammation, TLR signaling must be tightly controlled. One mechanism that modulates TLR signaling is alternative splicing of TLR pathway pre-mRNAs, which balances production of positively acting inflammatory mediators with alternative splice forms that terminate inflammation. To determine whether altered TLR pathway splicing contributes to pathological inflammation in ARDS, we evaluated two central mediators of the TLR signaling pathway, the MyD88 signaling adapter and the IRAK1 signaling kinase, in leukocytes isolated from bronchoalveolar lavage (BAL) of patients with ARDS. We found that MyD88 gene expression was decreased in BAL immune cells, whereas IRAK1 gene expression was increased. In parallel, we monitored long proinflammatory (MyD88-L and IRAK1) and shorter anti-inflammatory (MyD88-S and IRAK1c) splice forms and determined that IRAK1 splicing was shifted in a proinflammatory direction in patients with ARDS. Finally, we evaluated relationships between MyD88 isoform levels in BAL leukocytes and clinical outcomes. We conclude that pre-mRNA splicing of TLR pathway genes is altered in lung immune cells in patients with ARDS, that monitoring splicing of these genes may provide important prognostic information, and that manipulating splicing of these genes may be a useful novel therapeutic approach that needs further investigation.NEW & NOTEWORTHY We found that MyD88 expression is decreased, that IRAK1 expression is increased, and that IRAK1 splicing is shifted in a proinflammatory direction, in lung immune cells in patients with ARDS. We also find that MyD88 expression levels may correlate with survival in patients with ARDS. Thus, changes in expression and splicing of these two genes offer potential novel prognostic and therapeutic targets for ARDS.