Stimulation of sphingosine 1-phosphate signaling as an alveolar cell survival strategy in emphysema.
BACKGROUND
Vascular endothelial growth factor receptor (VEGFR) inhibition increases ceramides in lung structural cells of the alveolus, initiating apoptosis and alveolar destruction morphologically resembling emphysema. The effects of increased endogenous ceramides could be offset by sphingosine 1-phosphate (S1P), a prosurvival by-product of ceramide metabolism.


OBJECTIVE
The aims of our work were to investigate the sphingosine-S1P-S1P receptor axis in the VEGFR inhibition model of emphysema and to determine whether stimulation of S1P signaling is sufficient to functionally antagonize alveolar space enlargement.


METHODS
Concurrent to VEGFR blockade in mice, S1P signaling augmentation was achieved via treatment with the S1P precursor sphingosine, S1P agonist FTY720, or S1P receptor-1 (S1PR1) agonist SEW2871. Outcomes included sphingosine kinase-1 RNA expression and activity, sphingolipid measurements by combined liquid chromatography-tandem mass spectrometry, immunoblotting for prosurvival signaling pathways, caspase-3 activity and terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling assays, and airspace morphometry.


RESULTS
Consistent with previously reported de novo activation of ceramide synthesis, VEGFR inhibition triggered increases in lung ceramides, dihydroceramides, and dihydrosphingosine, but did not alter sphingosine kinase activity or S1P levels. Administration of sphingosine decreased the ceramide-to-S1P ratio in the lung and inhibited alveolar space enlargement, along with activation of prosurvival signaling pathways and decreased lung parenchyma cell apoptosis. Sphingosine significantly opposed ceramide-induced apoptosis in cultured lung endothelial cells, but not epithelial cells. FTY720 or SEW2871 recapitulated the protective effects of sphingosine on airspace enlargement concomitant with attenuation of VEGFR inhibitor-induced lung apoptosis.


CONCLUSIONS
Strategies aimed at augmenting the S1P-S1PR1 signaling may be effective in ameliorating the apoptotic mechanisms of emphysema development.
Diab
Khalil J
KJ
Division of Pulmonary, Allergy, Critical Care, and Occupational Medicine, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana 46202-5120, USA.
Adamowicz
Jeremy J
JJ
Kamocki
Krzysztof
K
Rush
Natalia I
NI
Garrison
Jana
J
Gu
Yuan
Y
Schweitzer
Kelly S
KS
Skobeleva
Anastasia
A
Rajashekhar
Gangaraju
G
Hubbard
Walter C
WC
Berdyshev
Evgeny V
EV
Petrache
Irina
I
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D015153:Blotting, Western; D002478:Cells, Cultured; D002518:Ceramides / Q000096:biosynthesis; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D000068876:Fingolimod Hydrochloride; D007211:Indoles / Q000494:pharmacology; D008246:Lysophospholipids / Q000096:biosynthesis / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011409:Propylene Glycols / Q000494:pharmacology; D011650:Pulmonary Alveoli / Q000187:drug effects* / Q000503:physiopathology; D011656:Pulmonary Emphysema / Q000188:drug therapy* / Q000503:physiopathology; D011758:Pyrroles / Q000494:pharmacology; D049349:Receptors, Lysosphingolipid / Q000187:drug effects* / Q000502:physiology; D040262:Receptors, Vascular Endothelial Growth Factor / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects; D013110:Sphingosine / Q000031:analogs & derivatives / Q000096:biosynthesis / Q000494:pharmacology; D000099157:Sphingosine Kinase
D002518:Ceramides; D000068876:Fingolimod Hydrochloride; D007211:Indoles; D008246:Lysophospholipids; D017853:Phosphotransferases (Alcohol Group Acceptor); D011409:Propylene Glycols; D011758:Pyrroles; D049349:Receptors, Lysosphingolipid; D040262:Receptors, Vascular Endothelial Growth Factor; D013110:Sphingosine; D000099157:Sphingosine Kinase; C060506:sphingosine 1-phosphate; C116890:Semaxinib