Plasmin Overcomes Resistance to Prostaglandin E2 in Fibrotic Lung Fibroblasts by Reorganizing Protein Kinase A Signaling

Abstract

Collagen deposition by fibroblasts contributes to scarring in fibrotic diseases. Activation of protein kinase A (PKA) by cAMP represents a pivotal brake on fibroblast activation, and the lipid mediator prostaglandin E 2 (PGE 2 ) exerts its well known antifibrotic actions through cAMP signaling. However, fibrotic fibroblasts from the lungs of patients with idiopathic pulmonary fibrosis, or of mice with bleomycin-induced fibrosis, are resistant to the normal collagen-inhibiting action of PGE 2 . In this study, we demonstrate that plasminogen activation to plasmin restores PGE 2 sensitivity in fibrotic lung fibroblasts from human and mouse. This involves amplified PKA signaling resulting from the promotion of new interactions between AKAP9 and PKA regulatory subunit II in the perinuclear region as well as from the inhibition of protein phosphatase 2A. This is the first report to show that an extracellular mediator can dramatically reorganize and amplify the intracellular PKA-A-kinase anchoring protein signaling network and suggests a new strategy to control collagen deposition by fibrotic fibroblasts.

Prostaglandin E2 Inhibits α-Smooth Muscle Actin Transcription during Myofibroblast Differentiation via Distinct Mechanisms of Modulation of Serum Response Factor and Myocardin-related Transcription Factor-A

“…Although TGF-␤1-induced SRF up-regulation was also attenuated by PGE2 in IPF cells, the extent of inhibition was more modest than in nonfibrotic cells. This too is characteristic of our prior observations in fibrotic fibroblasts from both humans and mice, in which we have found decreased sensitivity to the inhibitory actions of PGE 2 on processes such as proliferation and collagen I expression (21), which reflects both epigenetic down-regulation of EP2 expression (40) as well as impaired PKA activation (22).…”

“…PKA RI and PKA RII agonists and forskolin were purchased from Biolog (Hayward, CA). We used PKA RI and RII subunit-specific agonists each at 500 M based on our previous dose-response studies (22). Unless otherwise specified, TGF-␤1 was used at a final concentration of 2 ng/ml, and cells were pretreated for 30 min with or without PGE 2 at a final concentration of 500 nM before addition of TGF-␤1.…”

“…5A), indicating that EP2/cAMP signaling is capable of this effect. Protein kinase A (PKA) is the classically recognized downstream effector of cAMP actions, and we have shown it to mediate some but not all of the inhibitory actions of PGE 2 on fibroblasts (22). To assess the involvement of PKA in the ability of PGE 2 to abrogate SRF expression, cells were pretreated for 1 h with the cell-permeable PKA inhibitory peptide PKI(14 -22)-amide, followed by PGE 2 treatment for 30 min and then TGF-␤1 for 24 h. The ability of PGE 2 to prevent TGF-␤1-induced SRF protein expression was entirely abolished by PKI, suggesting the critical role of PKA in SRF inhibition (Fig.…”

Exchange Protein Directly Activated by cAMP (epac): A Multidomain cAMP Mediator in the Regulation of Diverse Biological Functions

“…The PDE4 inhibitor rolipram also reduced epithelial-mesenchymal transition (Kolosionek et al, 2009). PGE 2 -induced cAMP elevation exerts antifibrotic properties in human and mouse lung fibroblasts, and defects in the synthesis of PGE 2 correlate with the degree of airway remodeling in mice (Bauman et al, 2010;Okunishi et al, 2011;Stumm et al, 2011). PGE 2 also inhibits collagen deposition in fibrotic lung fibroblasts through a PGE 2 -sensing AKAP450 (AKAP9)-PKA-protein phosphatase 2A multiprotein complex Fig.…”

Following the Path of CCL2 from Prostaglandins to Periostin in Lung Fibrosis

“…Now we know that EP2 promoter hypermethylation (45), or loss of protein kinase A expression, explains why IPF fibroblasts are nonresponsive to PGE 2 (44). Fortunately, stimulation of lung fibroblasts in the presence of plasmin can overcome the resistance to PGE 2 signaling by reorganizing protein kinase A signaling (46)…”