Hepatic steatosis causes induction of the chemokine RANTES in the absence of significant hepatic inflammation

Abstract

Nonalcoholic fatty liver disease (NAFLD) encompasses a spectrum ranging from simple steatosis to cirrhosis. Hepatocellular lipid accumulation is a hallmark of both nonalcoholic steatosis and steatohepatitis (NASH). The latter develops upon pro-inflammatory cell infiltration and is widely considered as the first relevant pathophysiological step in NAFLD-progression. The chemokine CCL5/RANTES plays an important role in the progression of hepatic inflammation and fibrosis. We here aimed to investigate its expression in NAFLD. Incubation of primary human hepatocytes with palmitic acid induced a dose-dependent lipid accumulation, and corresponding dose-dependent RANTES induction in vitro. Furthermore, we observed significantly elevated hepatic RANTES expression in a dietary model of NAFLD, in which mice were fed a high-fat diet for 12 weeks. This diet induced significant hepatic steatosis but only minimal inflammation. In contrast to the liver, RANTES expression was not induced in visceral adipose tissue of the group fed with high-fat diet. Finally, RANTES serum levels were elevated in patients with ultrasound-diagnosed NAFLD. In conclusion, our data indicate hepatocytes as cellular source of elevated hepatic as well as circulating RANTES levels in response to hepatic steatosis. Noteworthy, upregulation of RANTES in response to lipid accumulation occurs in the absence of relevant inflammation, which further indicates that hepatic steatosis per se has pathophysiological relevance and should not be considered as benign.

Keywords: Hepatic steatosis; RANTES; chemokine CCL5; inflammation; liver cirrhosis; nonalcoholic fatty liver disease (NAFLD); nonalcoholic steatosis; steatohepatitis.

Figure 1

RANTES expression in an in vitro model of hepatocellular lipid accumulation. Primary human hepatocytes were incubated with 0.4 μM, 0.6 μM and 0.8 μM palmitate (Palm.) for 24 h, which leads to a dose dependent intracellular lipid accumulation as shown before [20]. Subsequently, RNA was isolated, reverse transcribed and RANTES mRNA expression was analyzed by quantitative PCR. (*p<0.05 compared to control (ctr.)).

Figure 2

RANTES expression in the liver and in visceral fat in a murine model of NAFLD. Mice were fed a high fat diet leading to hepatic steatosis. Mice receiving standard chow served as control (ctr.). (A) Assessment of hepatic triglyceride content. (B) Serum GOT levels. Analysis of (C) hepatic TNF, collagen I, ?smooth muscle actin (?sma), and RANTES mRNA expression, and (D) expression of RANTES mRNA in visceral fat by quantitative PCR. (*p<0.05 compared to control).

Figure 3

Serum RANTES levels in patients with NAFLD. Serum RANTES levels in patients with ultrasound (US) diagnosed fatty liver compared to a control (ctr.) group of patients with normal sonographic liver appearance. (*p<0.05 compared to control).