Acute lung injury is a devastating illness with an annual world-wide incidence in the hundreds of thousands. It occurs in the context of severe pneumonia, sepsis, trauma or other life-threatening illnesses, and is among the most feared manifestations of emerging infections and bioterrorist attacks. Pathologically, there is a transmural insult to the gas exchange apparatus that manifests clinically as respiratory failure. In the course of the disease process, the injured airspace fills with proliferating fibroblasts resulting in stiff lungs and profound hypoxemia. When patients die, fibroblasts and their connective tissue products persist in the alveolar airspace. In contrast, when patients survive, timely fibroblast apoptosis leads to restoration of the gas exchange surface. To improve patient outcome, we sought to identify an apoptotic regulatory pathway amenable to the drug discovery process. In studies providing the first evidence that apoptosis was subject to translational control, we discovered that fibroblast viability is regulated by the level and activity of the mRNA cap-binding apparatus, eukaryotic translation initiation factor 4F (eIF4F). Ectopic over expression of eIF4E, the rate limiting component of eIF4F, blocks fibroblast apoptosis; whereas over expression of the eIF4E repressor protein, 4E-BP1, triggers fibroblast apoptosis in vitro and in vivo. We therefore propose that pathological persistence of fibroblasts in the healing lung may result from aberrant translational activation of mRNAs encoding critical antiapoptotic proteins and hypothesize that therapies capable of titrating cap-dependent translation to physiological levels have the potential to restore sensitivity of lung fibroblasts in the healing lung to apoptosis. To provide proof of concept for this approach, we will present preliminary data in the murine bleomycin model of lung injury showing that: 1) mice lacking translational repressor 4E-BP1 develop more fibrosis than wild type mice after lung injury; and 2) targeted elimination of fibroblasts after lung injury leads to decreased fibrosis and increased survival. We plan to test our hypothesis through 2 specific aims.
Aim 1 : Synthesize and evaluate hydantoin-based compounds hitting the 7-methyl guanosine mRNA cap-binding pocket of eukaryotic translation initiation factor 4E (eIF4E), a bona fide molecular target controlling the translation of mRNA encoding key regulators of fibroblast apoptosis.
Aim 2. Apply a novel gone expression microarray-based molecular target discovery system to primary cultures of lung fibroblasts from patients with acute lung injury to identify apoptotic regulatory proteins that are candidate molecular targets for antifibrotic drug discovery. If successful, our work will confirm or refute eIF4E as an antifibrotic therapeutic target, and may lead to the identification of new acute lung injury-specific molecular targets for antifibrotic drug discovery.
