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Lipoapoptosis induced by saturated free fatty acids stimulates monocyte migration: a novel role for Pannexin1 in liver cells

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Abstract

Recruitment of monocytes in the liver is a key pathogenic feature of hepatic inflammation in nonalcoholic steatohepatitis (NASH), but the mechanisms involved are poorly understood. Here, we studied migration of human monocytes in response to supernatants obtained from liver cells after inducing lipoapoptosis with saturated free fatty acids (FFA). Lipoapoptotic supernatants stimulated monocyte migration with the magnitude similar to a monocyte chemoattractant protein, CCL2 (MCP-1). Inhibition of c-Jun NH2-terminal kinase (JNK) in liver cells with SP600125 blocked migration of monocytes in a dose-dependent manner, indicating that JNK stimulates release of chemoattractants in lipoapoptosis. Notably, treatment of supernatants with Apyrase to remove ATP potently inhibited migration of THP-1 monocytes and partially blocked migration of primary human monocytes. Inhibition of the CCL2 receptor (CCR2) on THP-1 monocytes with RS102895, a specific CCR2 inhibitor, did not block migration induced by lipoapoptotic supernatants. Consistent with these findings, lipoapoptosis stimulated pathophysiological extracellular ATP (eATP) release that increased supernatant eATP concentration from 5 to ~60 nM. Importantly, inhibition of Panx1 expression in liver cells with short hairpin RNA (shRNA) decreased supernatant eATP concentration and inhibited monocyte migration, indicating that monocyte migration is mediated in part by Panx1-dependent eATP release. Moreover, JNK inhibition decreased supernatant eATP concentration and inhibited Pannexin1 activation, as determined by YoPro-1 uptake in liver cells in a dose-dependent manner. These results suggest that JNK regulates activation of Panx1 channels, and provide evidence that Pannexin1-dependent pathophysiological eATP release in lipoapoptosis is capable of stimulating migration of human monocytes, and may participate in the recruitment of monocytes in chronic liver injury induced by saturated FFA.

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Grants

Dr Xiao and Dr. Kilic were supported in part by the National Institutes of Health (NIH) grants R37 DK-46082 (PI, JG Fitz), R01 DK-41876 (PI, GJ Gores). Dr. Davis was supported by NIH grants P50-AR055503 (PI, C Mohan), R01DK081872 (PI, C Mohan), the Alliance for Lupus Research, and the Rheumatic Diseases Division Biomarker Core.

Conflicts of interest

No conflicts of interest, financial or otherwise, are declared by the authors.

Author contributions

FX, SLW, LD, and SFB performed the experiments. GJG assisted in manuscript preparation. GK designed the experiments; GK, FX, and LD prepared and approved the manuscript for submission.

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Authors and Affiliations

  1. Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, 75390-8884, USA

    Feng Xiao, Shar L. Waldrop, Laurie S. Davis & Gordan Kilic

  2. College of Medicine, Mayo Clinic, 200 First St. SW, Rochester, MN, 55905, USA

    Steve F. Bronk & Gregory J. Gores

  3. Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX, 75390-8884, USA

    Laurie S. Davis

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  1. Feng Xiao
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  2. Shar L. Waldrop
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Correspondence to Laurie S. Davis.

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Fig. S1

Leukocyte migration induced by ATP. Migration of human monocytes in freshly isolated peripheral blood mononuclear cells as detailed in figure 3, was measured in response to eATP using Transwell plates (GIF 17 kb)

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Xiao, F., Waldrop, S.L., Bronk, S.F. et al. Lipoapoptosis induced by saturated free fatty acids stimulates monocyte migration: a novel role for Pannexin1 in liver cells. Purinergic Signalling 11, 347–359 (2015). https://doi.org/10.1007/s11302-015-9456-5

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