Survival of patients after acute lung injury requires restoration of anatomic integrity to damaged alveolar units. In the acute respiratory distress syndrome (ARDS), the entire alveolar wall is injured resulting in loss of the epithelium and microcirculatory endothelium. In response to peptide growth factors, and provisional matrix macromolecules, interstitial fibroblasts migrate into the airspace where they proliferate, effacing the gas exchange surface resulting in shunt physiology. We previously found that myofibroblasts apoptosis occurs in the alveolar airspace is patients recover from acute lung injury. During the current funding period, we discovered that translational control is of fundamental importance in regulating fibroblast viability. We have shown that the level and activity of translation initiation factor 4E (eIF4E), the mRNA cap binding protein, controls a pathway necessary for survival for proliferating fibroblasts. Translation factor 4E is activated by growth factor signaling pathways that phosphorylate eIF4E, as well as pathways which lead to phosphorylation of the three defined eIF4E inhibitory binding proteins, 4E-BP1, 2 and 3. Phosphorylation of 4E-BPs decreases their affinity for eIF4E freeing it to initiate translation. eIF4E is one of three components of the mRNA cap binding complex, termed eIF4F, which also includes eIF4G and eIF4A. For this competing renewal, our objective is to define which steps in the translation initiation process are responsible for regulating fibroblast viability, and to examine the biological relevance of our results using preclinical lung injury models and available lung tissue from patients with ARDS:
Aim 1 - In vitro, develop fibroblast lines with increased or decreased function of each protein component of eIF4F, and quantify viability after induction of apoptosis;
Aim 2 - Utilize preclinical models to examine proof of principle: modulate the activity of eIF4E pharmacologically in fibrogenic (BHT+O2) murine models of lung injury. Quantify resultant fibrosis biochemically as total lung hydroxyproline;
Aim 3 - Compare the tissue distribution of eIF4E, 4E-BPs and fibroblast apoptosis in our model systems with that observed in available lung tissue from patients with ARDS to evaluate the plausibility of extending our concept to the clinical setting. If we identify steps in the translation initiation process that regulate fibroblast viability, then it is plausible that modulating translational control mechanisms in patients with ARDS may speed repair by promoting elimination of intraalveolar fibrosis.
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