Research ArticleCD44 is a key player in non-alcoholic steatohepatitis
Graphical abstract
Introduction
Global prevalence of non-alcoholic fatty liver diseases (NAFLD) ranges from 22% to 28%.1 The spectrum of these hepatic abnormalities extends from isolated steatosis to steatohepatitis (non-alcoholic steatohepatitis, NASH) and steatofibrosis leading to cirrhosis and hepatocellular carcinoma. NAFLD is one of the main causes of cirrhosis and increases the risk of liver-related death and hepatocellular carcinoma. Despite this major public health concern, treatment of NAFLD is still elusive (apart from lifestyle changes) as there is lack of efficacious pharmacological treatment. Whereas the molecular mechanisms responsible for the progression from a “safe” state to NASH are still unclear, hepatic inflammation is a key factor involved in the progression of NAFLD. Recent findings suggest that cluster of differentiation (CD)44 could play an important role in the development and progression of NAFLD, by regulating adipose tissue and liver inflammation.[2], [3], [4], [5]
CD44 is expressed on many cell types that contribute to inflammation, such as leukocytes, neutrophils and macrophages. It has been recently reported in an animal model of obesity that CD44 plays an important role in adipose tissue inflammation by promoting macrophage recruitment, which in turn enhances insulin resistance and hepatic steatosis.[2], [3] Neutralization of CD44 by specific antibodies reduces fasting blood glucose levels, weight gain, liver steatosis and insulin resistance in a dietary mouse model of obesity.4 CD44 also promotes hepatic inflammatory cell recruitment during fatty liver formation in a lithogenic diet-fed mouse model.5 In line with these data, human adipose tissue CD44 is associated with localized inflammation and systemic insulin resistance;6 weight loss in obese patients is associated with a strong decrease in the gene expression of CD44 and the macrophage marker CD68 in subcutaneous adipose tissue.7 Since osteopontin (OPN), E-selectin and hyaluronic acid (HA) are the main ligands of CD44 and are involved in liver disease,[8], [9], [10], [11], [12] we can presume that the activation of the CD44 pathway could be involved in NAFLD progression. As previously reported in human NAFLD, hepatic osteopontin and E-selectin are strongly upregulated with fibrosis and NASH, respectively.[8], [9] Upon injury, local HA production increases and is fragmented, generating low-molecular weight HA (LMW-HA) that functions as a pro-inflammatory danger-associated molecular pattern and cleared via CD44-mediated endocytosis.11 The interaction of CD44 and HA is the dominant mechanism for neutrophil sequestration in inflamed liver sinusoids.13 HA is also a biomarker for severe fibrosis and cirrhosis in various liver diseases including NAFLD and alcoholic liver disease (ALD).[14], [15], [16] The possible contribution of the CD44 pathway to the evolution from simple steatosis to NASH and fibrosis has not been fully investigated so far. We therefore evaluated the contribution of CD44 in NASH development and liver injury in experimental mouse models and in a cohort of patients at various stages of NAFLD progression.
Section snippets
Morbidly obese patients
A total of 93 patients (30 patients for the gene expression, 64 patients for the sCD44 and 5 patients for the follow-up) were recruited through the Department of Digestive Surgery and Liver Transplantation (Nice hospital) where they underwent bariatric surgery for their morbid obesity. Bariatric surgery was indicated for these patients in accordance with French guidelines. Exclusion criteria were: presence of a hepatitis B or hepatitis C infection, excessive alcohol consumption (>20 g/d) or
Upregulation of hepatic expression of CD44 with steatohepatitis
We first evaluated the hepatic level of CD44 in wild-type (WT) mice with MCDD-induced steatohepatitis. The hepatic level of the CD44 was strongly increased after 2 weeks of MCDD at the protein (Fig. 1A) and mRNA (Fig. 1B) levels. Steatohepatitis was thus associated with the hepatic upregulation of CD44 expression.
CD44 deficiency partially prevented liver injury, hepatic steatosis and steatohepatitis induced by MCDD challenge
The role of CD44 in liver injury and steatohepatitis induced by MCDD was then investigated using mice deficient for CD44. As expected, MCDD challenge was associated with elevated
Discussion
We first described in this study that steatohepatitis was associated with the upregulation of hepatic CD44 in mice and obese patients. While this upregulation of CD44 has also been reported in steatotic livers in mouse models of NAFLD,[3], [5] hepatic CD44 is more specifically increased in NASH patients. We then reported that CD44 deficiency strongly prevented liver steatosis, inflammation, injury and fibrosis in mice challenged with MCDD. This could be independent of adipose tissue
Financial support
This work was supported by grants from INSERM (France), the University of Nice, the Programme Hospitalier de Recherche Clinique (Centre Hospitalier Universitaire of Nice), and charities (Association Française pour l’Etude du Foie (AFEF)/LFB to PG, AFEF/Aptalis to BBM, Société Francophone du Diabète (SFD) to PG, SFD/Roche Pharma to PG, SFD/MSD to BBM, European Foundation for the study of Diabetes/Lilly European Diabetes Research Programme to PG). This work was also funded by the French
Conflict of interest
The authors who have taken part in this study declared that they do not have anything to disclose regarding funding or conflict of interest with respect to this manuscript.
Authors’ contributions
PG, SP and DR conceived the research and wrote the paper. SP, DR, SB, C Lebeaupin and C Luci planned and performed the experiments. CMC, RA, AI, MCSP and JG participated in human sample and data collection. AB, BBM, AT and all the other authors corrected and approved the final submitted draft.
Acknowledgments
The authors thank i) Dr V. Corcelle and the INSERM U1065 animal facility staff for their excellent care of mice; ii) Dr D. Alcor and the C3 M Imaging CORE Facility (Microscopy and Imaging platform Côte d'Azur, MICA; and iii) Dr F Larbret and the flow cytometry platform, Archet Hospital. We also thank Dr C. Postic (INSERM U1016 Institut Cochin, Paris, France) and Dr S. Lotersztajn (INSERM UMR 1149-Center for Research on Inflammation, Paris, France) for helpful discussions. We also thank Julie
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These authors contributed equally as joint first authors.