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Arterioscler Thromb Vasc Biol. 2017 Aug;37(8):1462-1469. doi: 10.1161/ATVBAHA.117.309444. Epub 2017 Jun 15.

Cardiotonic Steroids Stimulate Macrophage Inflammatory Responses Through a Pathway Involving CD36, TLR4, and Na/K-ATPase.

Author information

1
From the Blood Research Institute, Blood Center of Wisconsin, Milwaukee (Y.C., W.H., M.Y., G.X., W.C., R.L.S.); Department of Cell Biology, Neurobiology and Anatomy (M.Y., R.L.S.) and Department of Medicine (R.L.S.), Medical College of Wisconsin, Milwaukee; and Departments of Medicine, Pharmacology and Surgery, Joan C. Edwards School of Medicine, Marshall University, Huntington, WV (Z.X.).
2
From the Blood Research Institute, Blood Center of Wisconsin, Milwaukee (Y.C., W.H., M.Y., G.X., W.C., R.L.S.); Department of Cell Biology, Neurobiology and Anatomy (M.Y., R.L.S.) and Department of Medicine (R.L.S.), Medical College of Wisconsin, Milwaukee; and Departments of Medicine, Pharmacology and Surgery, Joan C. Edwards School of Medicine, Marshall University, Huntington, WV (Z.X.). rsilverstein@mcw.edu.

Abstract

OBJECTIVE:

Circulating levels of cardiotonic steroids (CTS) are elevated in various chronic inflammatory conditions, but the role of CTS in inflammation remains largely unknown. We have previously shown that the CTS ouabain stimulates proinflammatory responses in murine macrophages. In this study, we aim to explore the mechanism how CTS induce proinflammatory responses in primary murine and human macrophages.

APPROACH AND RESULTS:

Using both murine peritoneal macrophages and human monocyte-derived macrophages, we demonstrated that ouabain activated NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells), leading to proinflammatory cytokine (eg, MCP-1 [monocyte chemotactic protein 1], TNF-α [tumor necrosis factor-α], IL-1β [interleukin-1β], and IL-6) production. By applying siRNA techniques and murine peritoneal macrophages isolated from genetically modified mice, we showed that macrophages partially deficient in Na/K-ATPase, the receptor for CTS, or fully deficient in the scavenger receptor CD36 or TLR4 (Toll-like receptor) were resistant to ouabain-induced NF-κB activation, suggesting an indispensable role of these 3 receptors in this pathway. Mechanistically, this effect of ouabain was independent of the ion transport function of the Na/K-ATPase. Instead, ouabain stimulated a signaling complex, including Na/K-ATPase, CD36, and TLR4. Subsequently, TLR4 recruited MyD88 adaptor protein for NF-κB activation. Furthermore, intraperitoneal injection of ouabain into mice specifically recruited Ly6C+CCR2+ monocyte subtypes to the peritoneal cavities, indicating that the CTS ouabain triggers inflammation in vivo.

CONCLUSIONS:

CTS activate NF-κB leading to proinflammatory cytokine production in primary macrophages through a signaling complex, including CD36, TLR4, and Na/K-ATPase. These findings warrant further studies on endogenous CTS in chronic inflammatory diseases, such as atherosclerosis.

KEYWORDS:

atherosclerosis; cytokines; inflammation; ion pumps; macrophages

PMID:
28619997
PMCID:
PMC5532064
DOI:
10.1161/ATVBAHA.117.309444
[Indexed for MEDLINE]
Free PMC Article

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