Regulation of myofibroblast differentiation by cardiac glycosides

Myofibroblast differentiation is a key process in pathogenesis of fibrotic diseases. Cardiac glycosides (ouabain, digoxin) inhibit Na(+)-K(+)-ATPase, resulting in increased intracellular [Na(+)]-to-[K(+)] ratio in cells. Microarray analysis suggested that increased intracellular [Na(+)]/[K(+)] ratio...

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Published in:American journal of physiology. Lung cellular and molecular physiology 2016-05, Vol.310 (9), p.L815-L823
Main Authors: La, Jennifer, Reed, Eleanor B, Koltsova, Svetlana, Akimova, Olga, Hamanaka, Robert B, Mutlu, Gökhan M, Orlov, Sergei N, Dulin, Nickolai O
Format: Article
Language:English
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Cardiac Glycosides - pharmacology
Cell Differentiation
Cells, Cultured
Cyclic AMP-Dependent Protein Kinases - metabolism
Cyclooxygenase 2 - genetics
Cyclooxygenase 2 - metabolism
Digoxin - pharmacology
Enzyme Activation
Enzymes
Fibroblasts
Gene Expression
Humans
Idiopathic Pulmonary Fibrosis - pathology
Lung - pathology
Molecules
Myofibroblasts - drug effects
Myofibroblasts - physiology
Organic chemicals
Ouabain - pharmacology
Pathogenesis
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Summary:Myofibroblast differentiation is a key process in pathogenesis of fibrotic diseases. Cardiac glycosides (ouabain, digoxin) inhibit Na(+)-K(+)-ATPase, resulting in increased intracellular [Na(+)]-to-[K(+)] ratio in cells. Microarray analysis suggested that increased intracellular [Na(+)]/[K(+)] ratio may promote the expression of cyclooxygenase-2 (COX-2), a critical enzyme in the synthesis of prostaglandins. Given antifibrotic effects of prostaglandins through activation of protein kinase A (PKA), we examined if cardiac glycosides stimulate COX-2 expression in human lung fibroblasts and how they affect myofibroblast differentiation. Ouabain stimulated a profound COX-2 expression and a sustained PKA activation, which was blocked by COX-2 inhibitor or by COX-2 knockdown. Ouabain-induced COX-2 expression and PKA activation were abolished by the inhibitor of the Na(+)/Ca(2+) exchanger, KB-R4943. Ouabain inhibited transforming growth factor-β (TGF-β)-induced Rho activation, stress fiber formation, serum response factor activation, and the expression of smooth muscle α-actin, collagen-1, and fibronectin. These effects were recapitulated by an increase in intracellular [Na(+)]/[K(+)] ratio through the treatment of cells with K(+)-free medium or with digoxin. Although inhibition of COX-2 or of the Na(+)/Ca(2+) exchanger blocked ouabain-induced PKA activation, this failed to reverse the inhibition of TGF-β-induced Rho activation or myofibroblast differentiation by ouabain. Together, these data demonstrate that ouabain, through the increase in intracellular [Na(+)]/[K(+)] ratio, drives the induction of COX-2 expression and PKA activation, which is accompanied by a decreased Rho activation and myofibroblast differentiation in response to TGF-β. However, COX-2 expression and PKA activation are not sufficient for inhibition of the fibrotic effects of TGF-β by ouabain, suggesting that additional mechanisms must exist.
ISSN:1040-0605
1522-1504
DOI:10.1152/ajplung.00322.2015