Time-course of cardiac gene profiles post-acute lung injury

Abstract Patients suffering from acute lung injury (ALI) are at high risk of developing cardiac arrhythmias. In a recent study we demonstrated that bleomycin (Bleo)-induced ALI in rats exhibited significantly more spontaneous premature ventricular contractions (PVCs) from 1 to 3 weeks post induction. Although spontaneous PVCs disappeared at 4 weeks post ALI, PVCs were evoked again by electrical stimulation of the decentralized stellate ganglia in Bleo-exposed rats but not in normal rats. The molecular mechanisms underlying cardiac arrhythmia both post ALI and during the recovery of ALI remains unclear. In the current study, we aimed to utilize non-biased RNA-Seq analysis to discover the time-course changes in cardiac gene profiles both post ALI and during the recovery from ALI. We created an ALI rat model using a single tracheal instillation of bleomycin (2.5 mg/kg) with saline as a vehicle (Veh) control. Blood Troponin level was measured and compared between Veh- and Bleo-treated rats varied between W1 to Week 4 post Veh/Bleo. Cardiac tissues were harvested at W1 or W4 post Veh/Bleo for RNA-seq analysis and validation by real time RT-PCR. One week post ALI, cardiac Troponin was significantly increased in Bleo-treated rats whereas it was undetectable in Veh-treated rats. Cardiac Troponin was largely restored at W2 and was undetectable at W4 post ALI. RNA-seq analysis of the left ventricle (LV) indicated 85 downregulated and 147 upregulated genes at 1 W post ALI vs. Veh. Gene Ontology (GO) enrichment analysis demonstrated that genes related to chronic inflammatory signaling, cell adhesion signaling, and extracellular matrix (ECM) signaling pathways were upregulated at W1 post ALI, suggesting cardiac inflammation. Furthermore, genes related to oxygen carrier activity, oxygen binding and oxygen transport signaling were also significantly altered, which may be due to acute hypoxia caused by ALI. In contrast to W1, RNA-seq analysis at W4 post ALI detected a smaller number of altered genes, including 11 downregulated and 13 upregulated genes between ALI and Veh groups. Comparing these two RNA-Seq databases, 4 genes (i.e., Phactr3, Tgm1, Drd4, Selplg) were identified as changed in both the post ALI state and during the recovery from ALI. Following real time RT-PCR validation confirmed significant changes in these four gene mRNA expressions in both post ALI and during the recovery from ALI. Phactr3 was downregulated while Tgm1, Drd4 and Selplg genes were upregulated in cardiac tissues at w1 and w4 post ALI. Phactr3 gene encodes a member of the phosphatase and actin regulator protein family. Tgm1 plays an important role in stabilizing intercellular junctions in myocardial microvascular endothelial cells, by modulating β-actin filaments. Drd4 gene encodes the D4 subtype of the dopamine receptor. Selplg gene encodes a glycoprotein that regulates T lymphocytes. Future studies are needed to examine the functional roles of these genes in cardiac injury post ALI.