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

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.

Roles for Chemokines in Liver Disease

“…91,92 However, the contribution of this system has recently been confirmed in mice receiving a lithogenic diet, because strains susceptible to fat accumulation had a marked reduction in leukocyte recruitment in the absence of CCL2. 93 Similar evidence, although not as consistent as for CCL2, has been provided for the receptor CCR5 and its ligands, including CCL5, which was found to be overexpressed in a dietary model of steatosis. 94 An additional mechanism that has been suggested to contribute to liver inflammation is the excessive responsiveness of immune cells to chemokines, in particular CXCL12 and CXCL13, as indicated by studies in obese mice in which adoptive transfer of different leukocyte populations was used.…”

The receptor CD44 is associated with systemic insulin resistance and proinflammatory macrophages in human adipose tissue

“…We previously demonstrated an 11-fold increase in adipose tissue expression of Cd44 in obese as compared with lean mice [4]. Furthermore, knockout of Cd44 prevented the development of obesity-induced insulin resistance and glucose intolerance [4,7], as well as inflammation in adipose tissue and liver [15,16]. Recently, we also found that CD44 is strongly expressed on ATMs in dietinduced obese mice, and antibody neutralisation of CD44 suppressed visceral adipose tissue inflammation and reduced hyperglycaemia and insulin resistance as effectively as metformin and pioglitazone [7].…”

Interactions between CD44 and Hyaluronan in Leukocyte Trafficking

“…A number of recent studies have described a critical role for CD44–HA interactions in the pathogenesis of fatty-liver disease, the leading cause of chronic liver disease in United States and a growing problem worldwide ( 38 ). CD44-deficient mice have markedly attenuated hepatitis in a mouse model of non-alcoholic steatohepatitis (NASH), induced by administration of a lithogenic diet ( 39 , 40 ). Leukocytes harvested from lithogenic diet-fed mice display significant upregulation of their HA-binding capacity ( 39 ).…”