sphingosine-1-phosphate and Pulmonary-Fibrosis

Aberrant wound healing responses to lung injury are believed to contribute to fibrotic lung diseases, such as idiopathic pulmonary fibrosis (IPF). The lysophospholipids lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P), by virtue of their ability to mediate many basic cellular functions, including survival, proliferation, migration, and contraction, can influence many of the biological processes involved in wound healing. Accordingly, recent investigations indicate that LPA and S1P may play critical roles in regulating the development of lung fibrosis. Here we review the evidence indicating that LPA and S1P regulate pulmonary fibrosis and the potential mechanisms through which these lysophospholipids may influence fibrogenesis induced by lung injury.

Topics: Capillary Permeability; Cell Physiological Phenomena; Epithelial Cells; Fibroblasts; Humans; Lysophospholipids; Pulmonary Alveoli; Pulmonary Fibrosis; Receptors, Lysophosphatidic Acid; Receptors, Lysosphingolipid; Signal Transduction; Sphingosine; Wound Healing

Synthetic sphingosine 1-phosphate receptor 1 modulators constitute a new class of drugs for the treatment of autoimmune diseases. Sphingosine 1-phosphate (S1P) signaling, however, is also involved in the development of fibrosis. Using normal human lung fibroblasts, we investigated the induction of fibrotic responses by the S1P receptor (S1PR) agonists S1P, FTY720-P, ponesimod, and SEW2871 and compared them with the responses induced by the known fibrotic mediator TGF-β1. In contrast to TGF-β1, S1PR agonists did not induce expression of the myofibroblast marker α-smooth muscle actin. However, TGF-β1, S1P, and FTY720-P caused robust stimulation of extracellular matrix (ECM) synthesis and increased pro-fibrotic marker gene expression including connective tissue growth factor. Ponesimod showed limited and SEW2871 showed no pro-fibrotic potential in these readouts. Analysis of pro-fibrotic signaling pathways showed that in contrast to TGF-β1, S1PR agonists did not activate Smad2/3 signaling but rather activated PI3K/Akt and ERK1/2 signaling to induce ECM synthesis. The strong induction of ECM synthesis by the nonselective agonists S1P and FTY720-P was due to the stimulation of S1P2 and S1P3 receptors, whereas the weaker induction of ECM synthesis at high concentrations of ponesimod was due to a low potency activation of S1P3 receptors. Finally, in normal human lung fibroblast-derived myofibroblasts that were generated by TGF-β1 pretreatment, S1P and FTY720-P were effective stimulators of ECM synthesis, whereas ponesimod was inactive, because of the down-regulation of S1P3R expression in myofibroblasts. These data demonstrate that S1PR agonists are pro-fibrotic via S1P2R and S1P3R stimulation using Smad-independent pathways.

Topics: Actins; Animals; CHO Cells; Cricetinae; Cricetulus; Down-Regulation; Extracellular Matrix; Humans; Lung; Lysophospholipids; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Myofibroblasts; Organophosphates; Oxadiazoles; Phosphatidylinositol 3-Kinases; Proto-Oncogene Proteins c-akt; Pulmonary Fibrosis; Receptors, Lysosphingolipid; Signal Transduction; Smad2 Protein; Smad3 Protein; Sphingosine; Thiazoles; Thiophenes; Transforming Growth Factor beta1

The sphingomyelin/ceramide signaling pathway is an important component of many cellular processes implicated in the pathogenesis of lung disease. Acid sphingomyelinase (ASM) is a key mediator of this pathway, but its specific role in pulmonary fibrosis has not been previously investigated. Here we used the bleomycin model of pulmonary fibrosis to investigate fibrotic responses in normal and ASM knockout (ASM(-/-)) mice, and in NIH3T3 fibroblasts with and without ASM siRNA treatment.. Mice and cells with and without ASM activity were treated with bleomycin, and the effects on lung inflammation, formation of collagen producing myofibroblasts, and apoptosis were assessed.. The development of bleomycin-induced inflammation and fibrosis in wildtype mice correlated with the rapid activation of ASM, and was markedly attenuated in the absence of ASM activity. Along with the elevated ASM activity, there also was an elevation of acid ceramidase (AC) activity, which was sustained for up to 14 days post-bleomycin treatment. Studies in NIH3T3 fibroblasts confirmed these findings, and revealed a direct effect of ASM/AC activation on the formation of myofibroblasts. Cell studies also showed that a downstream effect of bleomycin treatment was the production of sphingosine-1-phosphate.. These data demonstrate that the sphingomyelin/ceramide signaling pathway is involved in the pathogenesis of bleomycin-induced pulmonary fibrosis, and suggest that inhibition of ASM may potentially slow the fibrotic process in the lung.

Topics: Actins; Animals; Antibiotics, Antineoplastic; Bleomycin; Lysophospholipids; Mice; Mice, Inbred C57BL; Mice, Knockout; NIH 3T3 Cells; Pneumonia; Pulmonary Fibrosis; RNA Interference; RNA, Small Interfering; Signal Transduction; Sphingomyelin Phosphodiesterase; Sphingosine