Role of CLEC-2-driven platelet activation in the pathogenesis of toxic liver damage. (23rd February 2017) - Chauhan, Abhishek
Abstract: Background: Toxic liver injury from drugs including paracetamol is the main cause of acute liver failure in developed countries. The mechanisms that drive irreversible liver failure are poorly understood; platelets could have an important role in this process given their roles beyond haemostasis, including liver regeneration. Ligation of the platelet receptor CLEC-2 with its cognate ligand podoplanin (PDPN) powerfully activates platelets; we sought to investigate the role of CLEC-2 in the pathogenesis of acute liver failure. Methods: Paracetamol or carbon tetrachloride (CCl4 ) were used to induce acute liver damage in mice. The role of CLEC-2-mediated platelet activation was investigated in mice with conditional deletions for either the platelet CLEC-2 receptor (PF4cre CLEC1b fl/fl ) or PDPN (Vav1-iCre + PDPN fl/fl ), or with specific function blocking antibodies. Liver necrosis, and the subsequent inflammatory response, was gauged by assessment of hepatic leucocyte infiltration and measurement of liver histological and serum markers. Findings: Initial liver injury after CCl4 and paracetamol administration was similar in both wild-type (WT) and CLEC-2-deficient mice. Abrogating CLEC-2-driven platelet activation accelerated liver healing from both toxic insults: mean serum alanine aminotransferase [ALT] after paracetamol administration was 1264 IU/L (SE 296·5) in WT mice versus 52·00 (5·00) in CLEC-2-deficient mice (n=5–8, p=0·0078); and after CCl4 4451 (886·3) versus 367 (99·35) (n=4–8, p=0·0015). Targeting this pathway therapeutically with a specific PDPN function blocking antibody in WT mice also enhanced liver healing: after CCl4 administration mean ALT in control antibody treated mice was 5482 (SE 785·4) versus 598·8 (102·4) in anti-PDPN antibody treated mice (n=6, p=0·0001), and after paracetamol 2850 (1128) versus 194·5 (61·26) (p=0·0176). In-vitro experiments showed that CLEC-2-deficient platelets interacted with Kupffer cells to enhance production of tumour necrosis factor α (TNFα) and increase accumulation of hepatic neutrophils. Healing was prevented by either blocking TNFα or depleting neutrophils in mice. Upregulation of PDPN on Kupffer cells in human acute liver failure suggests that this pathway is also activated in human beings. Interpretation: Platelets are involved in determining the outcome of the sterile inflammatory response to toxic liver injury. Platelet activation via CLEC-2 in the context of an acute liver injury inhibits TNFα-driven reparative inflammation mediated by neutrophils. The fact that blocking CLEC-2-mediated platelet activation enhances neutrophil-driven liver repair without causing bleeding, suggests that this could be a completely novel treatment for human acute liver failure. Funding: Wellcome Trust.