Gauging the contribution of hepatic stellate cells towards the acute phase response of hepatocytes to lipopolysaccharide

Introduction: Bacterial translocation triggers a strong immunological response in the liver, which is an important defence mechanism during acute liver injury. The expression of acute phase proteins (APP) by hepatocytes and their release to surrounding cells and the blood circuit is a central aspect of this process. APPs contribute to the elimination of pathogens, at the same time providing essential parts of a feed back loop preventing an overshooting inflammatory response by antagonizing or neutralizing inflammatory cytokines in the serum. Our aim was to measure the contribution of hepatic stellate cells (HSC) and activated myofibroblasts towards the APP activation.

Methods: We exposed cultivated hepatocytes to the tissue culture supernatants of quiescent primary HSC (day 2 of tissue culture) and myofibroblasts (day 7 of tissue culture) that had been treated with LPS for 24 hours. The expression of 46 APP genes in hepatocytes following 24 hours of exposure to HSC-conditioned medium was measured by quantitative PCR (Fluidigm). Stimulation by recombinant IL6 and LPS for 6, 12 and 24 hours was used as control.

Results: Complement factor C3, haptoglobin (Hp), hemopexin (Hpx), orosomucoid (Orm1), serum amyloid A1 and A3 (Saa1, Saa3) were significantly upregulated (P < 0.01) in mouse hepatocytes with day 2 HSC supernatant. Treatment with day 7 medium (activated myofibroblast stage) resulted in significant upregulation of the same genes plus hepcidin and fibrinogen alpha. Several genes (Hepcidin, Saa1 – 3, IL33) showed an even stronger transcriptional response to HSC supernatant than to recombinant IL-6. Hepatocytes responded to pure LPS after 12 and 24 hours to some extent, which is surprising since this cell type normally does not express the LPS-receptor TLR4, which, however may be induced in the stressful situation of hepatocyte monolayer culture.

Conclusions: HSC play an active and substantial role during the initiation and orchestration of the acute phase response to bacterial infection. Induction of hepcidin, orosomucoid and serum amyloid 1 – 3 by HSC-secreted factors exceeds induction by pure IL-6. The immunological response is similar in quiescent HSC and myofibroblasts. Cultured hepatocytes show a response to LPS stimulation.