Published online Aug 21, 2017. doi: 10.3748/wjg.v23.i31.5692
Peer-review started: January 9, 2017
First decision: March 16, 2017
Revised: May 9, 2017
Accepted: July 4, 2017
Article in press: July 4, 2017
Published online: August 21, 2017
Processing time: 224 Days and 22.1 Hours
To evaluate the role of tissue factor (TF) and protease activated receptor (PAR)-2 in liver fibrosis.
Using CCl4 administration for eight weeks, we induced hepatic fibrosis in wild-type C57BL/6 mice and in mice with deletion of the cytoplasmic signalling domain of TF (TF§CT/§CT), deletion of PAR-2 (PAR-2-/-) and combined deletion of TF signalling domain and PAR-2 (TF§CT/§CT/PAR-2-/-). Hepatic fibrosis area was assessed by quantitative imaging of picrosirius red staining. Hepatic collagen content was assessed by hydroxyproline levels. Hepatic stellate cells (αSMA positive) and hepatic macrophages (CD68 positive) were identified by immunohistochemistry. Hepatic gene expression was determined by PCR and liver TGFβ1 content by ELISA.
CCl4 treated mice with deletion of the PAR-2 gene (PAR-2-/-) and the cytoplasmic domain of TF (TF§CT/§CT) developed significantly less hepatic fibrosis, characterised by reduced liver fibrosis area and hydroxyproline content, compared to control wildtype mice treated with CCl4. The observed reduction in histological fibrosis was accompanied by a significant decrease in the hepatic content of TGFβ, the prototypic fibrogenic cytokine, as well as fewer activated hepatic stellate cells and hepatic macrophages. Deletion of the TF cytoplasmic signalling domain reduced hepatic fibrosis to levels similar to those observed in mice lacking PAR-2 signalling but combined deletion provided no added protection against fibrosis indicating a lack of mutual modulating effects that have been observed in other contexts such as angiogenic responses.
Tissue factor cytoplasmic domain is involved in TF-PAR-2 signalling initiating hepatic fibrosis and is a potential therapeutic target, as its deletion would not impact coagulation.
Core tip: No effective anti-fibrotic therapies are available for patients with cirrhosis. PAR-2, a receptor that activates coagulation and inflammation, promotes hepatic fibrosis; whether tissue factor (TF), the primary initiator of the coagulation cascade, affects hepatic fibrosis is unknown. We found that deletion of the TF cytoplasmic domain reduces fibrosis through an effect on hepatic stellate cell activation, possibly mediated through reduced hepatic macrophage activation. Currently available direct thrombin inhibitors may be useful in preventing hepatic fibrosis while therapeutic targeting of the cytoplasmic domain of TF may be useful in patients with advanced liver disease, as its deletion does not alter coagulation.