Inhibition of lipid metabolism by targeting delivery to liver macrophages for the prevention of pro-inflammatory phenotype

Coordinator: E. Fattal (Partner 16)
Starting date: January 2014

Non alcoholic fatty liver disease (NAFLD) is known to be associated with obesity, insulin resistance, diabetes, hypertriglyceridemia and arterial hypertension in the metabolic syndrome. With the increasing incidence of obesity, NAFLD becomes probably the most common cause of chronic liver disease in Western countries. NAFLD can progress from steatosis to steatohepatitis (NASH, non-alcoholic steatohepatitis), fibrosis, cirrhosis and hepatocellular carcinoma. NASH is characterized by steatosis associated with liver inflammation and associated to a liver immune dysregulation. Recruitment of inflammatory cells into the liver and their subsequent activation are the key steps in the progression of liver disease. NAFLD is associated with changes in hepatic lymphocyte subsets including reduced numbers of hepatic NKT and T regulatory lymphocytes. Correcting these NKT or T regulatory lymphocyte deficiencies by adoptive transfer in murine models of NASH reduces liver damage. In addition to the redistribution of hepatic lymphocyte subsets, we have shown that liver inflammation in obese mice results not only from steatosis but also from lymphocyte hyper-responsiveness to chemotactic agents. Although weight loss and correction of insulin resistance are relevant therapeutic targets to improve NASH, there is currently no treatment for advanced NAFLD. In this regard, understanding mechanisms responsible for the immune dysregulation leading to NASH remains a significant challenge.

Innate immunity and in particular resident macrophages in the liver, Kupffer cells (KC) play a key role in the onset of NASH. KC are potential antigen presenting cells but also participate to the ability of dendritic cells to stimulate the T cell response by producing prostaglandins. Therefore, modifications of the KC phenotype could induce an abnormal immune response of the liver. We recently proved that KC of obese mice had a pro-inflammatory phenotype. We demonstrated that the KC from fatty livers were loaded with lipid droplets named “fat-laden” KC. Lipidomic analysis showed that toxic lipids such as free cholesterol, cholesterol esters, diacylglycerols or ceramides were accumulated in these fat-laden KC. Analysis of mRNA expression demonstrated that toxic lipid accumulation is associated with a disturbance of lipid metabolism encompassing lipid synthesis, oxidation, uptake and secretion in fat-laden KC. We have shown that fat-laden KC produce higher level of pro-inflammatory cytokines and chemokines inducing a higher recruitment of T-CD4+ and B lymphocytes following a LPS challenge. We specifically inhibited in situ lipogenesis, via the chemically acetyl-CoA carboxylase inhibition by TOFA, and proved, in this condition, that KC were able to reverse the pro-inflammatory phenotype. We proved that accumulated lipids directly orient KCs towards a pro-inflammatory phenotype and participate to the development of an abnormal immune response in the liver.

Restoration of a non-inflammatory phenotype of the KC by modulating the lipid metabolism is considered as a new potential target to treat NAFLD. This could be nicely achieved using nanotechnologies. Indeed, since colloidal carriers have a high affinity for KC after intravenous administration, the delivery of siRNA or other chemicals such as TOFA or derivatives will be administered by means of lipids carriers (lipoplexes for siRNA or liposomes for chemicals).

The aim of this project, which involves three main partners (Partner 3, 15 & 16) including one team outside the LERMIT, consists in proving that in vivo targeting to Kupffer cells of siRNA or inhibitors allow a specific modulation of their pro-inflammatory phenotype and then the liver immune response. Several bottlenecks must be overcome as high specific delivery of siRNA or drugs to KC especially in obese mice, persistence of the in vivo inhibition, absence (or low) activation of KC by liposomes or lipoplexes as side effects.