Constitutive androstane receptor in macrophages regulates Toll-like receptor 4-mediated innate immune responses during endotoxemic liver injury

Macrophage proinflammatory hyperactivation drives the pathogenesis of acute liver injury, a common complication of severe sepsis. The nuclear receptor constitutive androstane receptor (CAR) modulates xenobiotic and endobiotic metabolism, but its role in endotoxin-induced liver injury remains unclear. Our study aims to reveal the regulatory effect of CAR on macrophages under LPS stimulation and uncover the underlying mechanism. Here, we report that CAR is highly expressed in human and murine macrophages. Dexamethasone and CITCO, human CAR agonists, triggered CAR nuclear translocation, attenuating inflammation in primary hMDMs from healthy donors. CAR agonists markedly attenuated endotoxin-induced liver damage in mice, alleviating hepatocyte death and hepatic inflammation. Macrophage-hepatocyte coculture confirmed that CAR inhibited inflammation through macrophage crosstalk. CAR-mediated hepatoprotection and anti-inflammatory effects were absent in AAV8-F4/80-Car-treated mice, confirming the essential role of CAR in macrophages. Mechanistically, CAR interacts with Tlr4 and influences its mRNA stability, and the suppressive effects of CAR on TLR4 were proven in Tlr4-KO mice. Furthermore, CAR activation reduced LPS-induced inflammation in BMDMs, Raw264.7 cells, and THP-1 cells, and Car or Tlr4 knockdown abolished CAR-mediated immunosuppression. Overall, macrophage CAR activation attenuated endotoxin-induced liver injury and hepatic inflammation through the TLR4 signaling pathway, providing insights for treating inflammatory liver diseases.