CCR2 and CD44 Promote Inflammatory Cell Recruitment during Fatty Liver Formation in a Lithogenic Diet Fed Mouse Model

Charlotte E. Egan,Arlin B. Rogers,Eric Y. Denkers,Delbert S. Abi Abdallah,Kirk J. Maurer,Erin K. Daugherity,Muriel Moser

doi:10.1371/journal.pone.0065247

Abstract

Non-alcoholic fatty liver disease (NAFLD) is a common disease with a spectrum of presentations. The current study utilized a lithogenic diet model of NAFLD. The diet was fed to mice that are either resistant (AKR) or susceptible (BALB/c and C57BL/6) to hepatitis followed by molecular and flow cytometric analysis. Following this, a similar approach was taken in congenic mice with specific mutations in immunological genes. The initial study identified a significant and profound increase in multiple ligands for the chemokine receptor CCR2 and an increase in CD44 expression in susceptible C57BL/6 (B6) but not resistant AKR mice. Ccr2−/− mice were completely protected from hepatitis and Cd44−/− mice were partially protected. Despite protection from inflammation, both strains displayed similar histological steatosis scores and significant increases in serum liver enzymes. CD45+CD44+ cells bound to hyaluronic acid (HA) in diet fed B6 mice but not Cd44−/− or Ccr2−/− mice. Ccr2−/− mice displayed a diminished HA binding phenotype most notably in monocytes, and CD8+ T-cells. In conclusion, this study demonstrates that absence of CCR2 completely and CD44 partially reduces hepatic leukocyte recruitment. These data also provide evidence that there are multiple redundant CCR2 ligands produced during hepatic lipid accumulation and describes the induction of a strong HA binding phenotype in response to LD feeding in some subsets of leukocytes from susceptible strains.

Highlights

Non-alcoholic fatty liver disease (NAFLD) is an increasingly common disease of humans affecting approximately 30–40% of individuals in the United States depending on the study population [1,2]
hyaluronic acid (HA) Binding Occurs Primarily on Monocytes, CD8+ T-cells and Dendritic Cells The lack of HA binding by hepatic leukocytes from Ccr22/2 mice during lithogenic diet (LD) feeding was an unexpected finding so we examined if this was the result of altered CD44 expression or a difference in the binding capacity of the CD44 molecules
Our findings reinforce studies in humans that have identified CCR2 and CD44 as being increased in nonalcoholic steatohepatitis (NASH) patients and they establish a possible link between these two molecules in lipid mediated hepatitis progression in so far as Ccr22/2 mice are largely protected from CD44 mediated HA binding [6,7,20]

Summary

Introduction

Non-alcoholic fatty liver disease (NAFLD) is an increasingly common disease of humans affecting approximately 30–40% of individuals in the United States depending on the study population [1,2]. The roles of chemokine ligands and their associated receptors are well established in the recruitment of immune cells during inflammation. Ovariectomized mice fed high fat diets display worse hepatitis than their intact counterparts and this exacerbation of disease is associated with increased liver expression of CCL2 [5]. Human patients with NASH display hepatic upregulation of many chemokines and other leukocyte adhesion molecules [6]. Consistent with the findings in human patients, CCR2 inhibition in obese prone mice fed a ‘‘Western’’ diet reduced adipose tissue inflammation and associated comorbidities including hepatic macrophage recruitment [8,9]

Objectives

Methods

Results

Conclusion