Blockade of platelet function modifies the outcome of acute liver injury

Paracetamol toxicity is a major cause of acute liver failure. The sterile inflammatory response led by neutrophils is critical in mediating liver healing after toxic injury. We have shown that platelets sequester within... [ view full abstract ]

Paracetamol toxicity is a major cause of acute liver failure. The sterile inflammatory response led by neutrophils is critical in mediating liver healing after toxic injury. We have shown that platelets sequester within the sinusoids in liver injury and that they support adhesion of neutrophils. The platelet receptor CLEC-2 mediates powerful platelet activation through its ligand podoplanin (PDPN) which is  upregulated on a variety of hepatic cells during inflammation. Thus we aimed to investigate whether blockade of CLEC-2-dependent platelet activation reduced toxic liver injury. We demonstrated that podoplanin is unregulated in the human liver during acute injury. Thus paracetamol and carbon tetrachloride were used to induce murine liver damage, and the role of CLEC-2-mediated platelet activation was investigated using mice deficient in CLEC-2(PF4creClec1bfl/fl ), or its activating ligand podoplanin (Vav1-iCre+ PDPNfl/fl ) or by using PDPN blocking antibodies (PDPN AB). Liver damage was assessed histologically, by measuring serum ALT and by cytometric quantification of inflammatory cells within the parenchyma. WT and CLEC-2 deficient mice exhibited comparable liver injury immediately after APAP or CCl4 administration. However if CLEC-2 dependent platelet activation was blocked (CLEC-2 deficient, PDPN deficient, or anti-PDPN AB treated mice ) we observed accelerated healing compared to control mice. Blockade of CLEC-2 dependent platelet activation enhanced TNFα dependent, hepatic neutrophil recruitment  which correlated with liver recovery. Importantly neutrophil depletion reversed the protective effect induced by CLEC-2 blockade. Thus platelet activation is involved in determining the outcome of the sterile inflammatory response to toxic liver injury. We provide the first demonstration that therapeutically blocking platelet activation enhances neutrophil driven liver repair. The fact that blocking CLEC-2 mediated platelet activation enhances liver repair without causing bleeding suggests this may represent a completely novel treatment for human acute liver failure.