Deletion of TP signaling in macrophages delays liver repair following APAP-induced liver injury by reducing accumulation of reparative macrophage and production of HGF.

Abstract

Background: Acetaminophen (APAP)-induced liver injury is the most common cause of acute liver failure. Macrophages are key players in liver restoration following APAP-induced liver injury. Thromboxane A₂ (TXA₂) and its receptor, thromboxane prostanoid (TP) receptor, have been shown to be involved in tissue repair. However, whether TP signaling plays a role in liver repair after APAP hepatotoxicity by affecting macrophage function remains unclear.

Methods: Male TP knockout (TP^-/-) and C57BL/6 wild-type (WT) mice were treated with APAP (300 mg/kg). In addition, macrophage-specific TP-knockout (TP^△mac) and control WT mice were treated with APAP. We explored changes in liver inflammation, liver repair, and macrophage accumulation in mice treated with APAP.

Results: Compared with WT mice, TP^-/- mice showed aggravated liver injury as indicated by increased levels of alanine transaminase (ALT) and necrotic area as well as delayed liver repair as indicated by decreased expression of proliferating cell nuclear antigen (PCNA). Macrophage deletion exacerbated APAP-induced liver injury and impaired liver repair. Transplantation of TP-deficient bone marrow (BM) cells to WT or TP^-/- mice aggravated APAP hepatotoxicity with suppressed accumulation of macrophages, while transplantation of WT-BM cells to WT or TP^-/- mice attenuated APAP-induced liver injury with accumulation of macrophages in the injured regions. Macrophage-specific TP^-/- mice exacerbated liver injury and delayed liver repair, which was associated with increased pro-inflammatory macrophages and decreased reparative macrophages and hepatocyte growth factor (HGF) expression. In vitro, TP signaling facilitated macrophage polarization to a reparative phenotype. Transfer of cultured BM-derived macrophages from control mice to macrophage-specific TP^-/- mice attenuated APAP-induced liver injury and promoted liver repair. HGF treatment mitigated APAP-induced inflammation and promoted liver repair after APAP-induced liver injury.

Conclusions: Deletion of TP signaling in macrophages delays liver repair following APAP-induced liver injury, which is associated with reduced accumulation of reparative macrophages and the hepatotrophic factor HGF. Specific activation of TP signaling in macrophages may be a potential therapeutic target for liver repair and regeneration after APAP hepatotoxicity.