Abstract Body (Do not enter title and authors here): Background: Idiopathic pulmonary fibrosis (IPF) is a progressive lung disease with a median survival period of 3-5 years from the onset of respiratory symptoms. The hallmark of IPF is an accumulation of extracellular matrix proteins in the pulmonary interstitium, stiffening the tissue and ultimately disrupting respiratory mechanics. Given the debilitating nature of IPF and the need for more accessible therapeutics, there is increasing interest in identifying new molecular targets.
Hypothesis: Given the demonstrated anti-fibrotic potential of extracellular-cyclic AMP (e-cAMP) in cardiopulmonary pathology, we hypothesized that manipulation of this pathway would improve outcomes with respect to disease progression using experimental models of IPF.
Methods: Primary human lung fibroblasts were isolated from pulmonary tissue obtained from healthy control donors (NHLF) and patients diagnosed with IPF. Cell proliferation and fibroblast-to-myofibroblast differentiation were evaluated by BrdU incorporation assay and real-time qPCR, respectively. For in vivo experimental modeling of pulmonary fibrosis, we used the bleomycin model of IPF in mice.
Results: Real-time qPCR and western blot analyses demonstrated increased levels of inhibitory PDEs and decreased intracellular cAMP levels in IPF. We found Protein Kinase A (PKA) and cAMP-response element binding protein (CREB) activities (readouts of e-cAMP signaling) to be decreased in lungs from PF-diseased mice and in lung fibroblasts from IPF patients. Exogenous e-cAMP induced an increase in intracellular cAMP levels and inhibited proliferation and differentiation of lung fibroblasts in vitro. Importantly, treatment e-cAMP decreased collagen deposition, restored lung function and improved survival in bleomycin-treated mice.
Conclusion: Taken together, we demonstrate the presence of an extracellular cAMP pathway in mouse and human lung fibroblasts. Our study demonstrate that the intracellular cAMP pathway is dysregulated in the setting of IPF. Of interest, activation of the e-cAMP pathway can overcome this dysregulation and provide a therapeutic effect.