The main goal of this grant application is to identify microRNA (miRNA) targets that protect the alveolar epithelium from excessive inflammation during acute lung injury (ALI). ALI is characterized by acute respiratory failure in the setting of non-cardiogenic pulmonary edema. It causes acute respiratory distress syndrome (ARDS) in humans. The current application is focused on identifying miRNAs that could be targeted to dampen alveolar epithelial inflammation. To identify miRNA targets that dampen alveolar inflammation, we exposed mice to ventilator-induced lung injury (VILI) and isolated alveolar epithelial cells. A microarray analysis identified miR-147 as a leading candidate. Confirmatory studies demonstrated that miR-147 is induced during ALI by mechanical ventilation in vivo or through in vitro exposure of alveolar epithelia to cyclic mechanical stretch. In vivo elevations of miR-147 levels during ALI persisted despite depletion of neutrophils or macrophages. In addition, we identified a role for hypoxia-inducible transcription factor HIF1A for miR-147 induction. miR-147-/- mice experience more severe lung injury during VILI. A search for miR-147 targets identified toll-like receptor adaptor molecule 2 (TICAM2) as pro- inflammatory target. In line with a link of miR-147 with TICAM2 expression, we found that alveolar epithelia isolated from miR-147loxp/loxp SPC Cre+ mice showed elevated Ticam2 levels. Similarly, increased pulmonary edema during VILI of miR-147loxp/loxp SPC Cre+ mice was resuscitated by concomitant genetic deletion of Ticam2. miR-147 overexpression via miR-147-containing nano-particles was protective during ALI. Finally, proof-of-principle studies in ARDS patients showed elevated miR-147 levels in their BAL fluid. Therefore, we hypothesize that HIF-dependent induction of miR-147 represents an endogenous pathway to dampen lung inflammation. We designed 3 specific aims, where we will first study the expression of miR-147 utilizing in vitro modeling systems (Aim 1).
Aim 2 is focused on in vivo studies of ALI, where we will utilize tissue-specific approaches of miR-147 deletion and examine mice with a mutation of the miR-147 binding site in the TICAM2 3' untranslated region (genetic targeting for these mice was successful). Finally, we will target miR-147 for the treatment of ARDS in Aim 3.
Our studies are designed to lay the groundwork for novel therapeutic approaches for treating patients with acute respiratory distress syndrome (ARDS). If successful, these studies will introduce microRNA-based therapy into the treatment of ARDS.