Hepatic recruitment of the inflammatory Gr1+ monocyte... : Hepatology (original) (raw)

Liver Biology/Pathobiology

Hepatic recruitment of the inflammatory Gr1+ monocyte subset upon liver injury promotes hepatic fibrosis#

Karlmark, Karlin Raja1; Weiskirchen, Ralf2; Zimmermann, Henning W.1; Gassler, Nikolaus3; Ginhoux, Florent5; Weber, Christian4; Merad, Miriam5; Luedde, Tom1; Trautwein, Christian1; Tacke, Frank1*†

1 Department of Medicine III, RWTH University Hospital Aachen, Aachen, Germany

2 Institute of Clinical Chemistry and Pathobiochemistry, RWTH University Hospital Aachen, Aachen, Germany

3 Institute of Pathology, RWTH University Hospital Aachen, Aachen, Germany

4 Institute for Molecular Cardiovascular Research, RWTH University Hospital Aachen, Aachen, Germany

5 Department of Gene and Cell Medicine, Mount Sinai School of Medicine, New York, NY

* Department of Medicine III, RWTH-University Hospital Aachen, Pauwelsstraße 30, 52074 Aachen, Germany

Email:[email protected]

Received January 2, 2009; accepted February 23, 2009.

Published online 16 March 2009 in Wiley InterScience (www.interscience.wiley.com).

Grant sponsor: German Research Foundation; Grant Numbers: DFG Ta434/2-1 SFB-TRR57; Grant sponsor: Interdisciplinary Centre for Clinical Research BIOMAT within the Faculty of Medicine at RWTH Aachen University.

# Potential conflict of interest: Nothing to report.

† fax: (49)-241-80-82455

Additional Supporting Information may be found in the online version of this article.

Abstract

In addition to liver-resident Kupffer cells, infiltrating immune cells have recently been linked to the development of liver fibrosis. Blood monocytes are circulating precursors of tissue macrophages and can be divided into two functionally distinct subpopulations in mice: Gr1hi (Ly6Chi) and Gr1lo (Ly6Clo) monocytes. The role of these monocyte subsets in hepatic fibrosis and the mechanisms of their differential recruitment into the injured liver are unknown. We therefore characterized subpopulations of infiltrating monocytes in acute and chronic carbon tetrachloride (CCl4)-induced liver injury in mice using flow cytometry and immunohistochemistry. Inflammatory Gr1hi but not Gr1lo monocytes are massively recruited into the liver upon toxic injury constituting an up to 10-fold increase in CD11b+F4/80+ intrahepatic macrophages. Comparing wild-type with C-C chemokine receptor (CCR2)-deficient and CCR2/CCR6–deficient mice revealed that CCR2 critically controls intrahepatic Gr1hi monocyte accumulation by mediating their egress from bone marrow. During chronic liver damage, intrahepatic CD11b+F4/80+Gr1+ monocyte-derived cells differentiate preferentially into inducible nitric oxide synthase–producing macrophages exerting proinflammatory and profibrogenic actions, such as promoting hepatic stellate cell (HSC) activation, T helper 1–T cell differentiation and transforming growth factor β (TGF-β) release. Impaired monocyte subset recruitment in _Ccr2_−/− and _Ccr2_−/−_Ccr6_−/− mice results in reduced HSC activation and diminished liver fibrosis. Moreover, adoptively transferred Gr1hi monocytes traffic into the injured liver and promote fibrosis progression in wild-type and _Ccr2_−/−_Ccr6_−/− mice, which are otherwise protected from hepatic fibrosis. Intrahepatic CD11b+F4/80+Gr1+ monocyte-derived macrophages purified from CCl4-treated animals, but not naïve bone marrow monocytes or control lymphocytes, directly activate HSCs in a TGF-β–dependent manner in vitro. Conclusion: Inflammatory Gr1+ monocytes, recruited into the injured liver via CCR2-dependent bone marrow egress, promote the progression of liver fibrosis. Thus, they may represent an interesting novel target for antifibrotic strategies. (Hepatology 2009;50:261–274.)