T‐cell immunoglobulin and mucin domain 4 (TIM‐4) signaling in innate immune‐mediated liver ischemia‐reperfusion injury

Hepatic ischemia‐reperfusion injury (IRI), an innate immunity‐driven inflammation response, occurs in multiple clinical settings including liver resection, transplantation, trauma, and shock. T‐cell immunoglobulin and mucin (TIM)‐4, the only TIM protein not expressed on T cells, is found on macrophages and dendritic cells. The regulatory function of macrophage TIM‐4 in the engulfment of apoptotic/necrotic bodies in innate immunity‐mediated disease states remains unknown. This study focuses on the putative role of TIM‐4 signaling in a model of liver warm ischemia (90 minutes) and reperfusion. The ischemia insult triggered TIM‐4 expression by stressed hepatocellular phosphatidylserine (PS) presentation, peaking at 6 hours of reperfusion, and coinciding with the maximal hepatocellular damage. TIM‐4‐deficient or wild‐type WT mice treated with antagonistic TIM‐4 monoclonal antibody (mAb) were resistant against liver IRI, evidenced by diminished serum alanine aminotransferase (sALT) levels and well‐preserved hepatic architecture. Liver hepatoprotection rendered by TIM‐4 deficiency was accompanied by diminished macrophage infiltration/chemoattraction, phagocytosis, and activation of Toll‐like receptor (TLR)2/4/9‐dependent signaling. Correlating with in vivo kinetics, the peak of TIM‐4 induction in lipopolysaccharide (LPS)‐activated bone marrow derived‐macrophages (BMM) was detected in 6‐hour cultures. To mimic liver IRI, we employed hydrogen peroxide‐necrotic hepatocytes, which readily present PS. Indeed, necrotic hepatocytes were efficiently captured/engulfed by WT (TIM‐4+) but not by TIM‐4‐deficient BMM. Finally, in a newly established model of liver IRI, adoptive transfer of WT but not TIM‐4‐deficient BMM readily recreated local inflammation response/hepatocellular damage in the CD11b‐DTR mouse system. Conclusion: These findings document the importance of macrophage‐specific TIM‐4 activation in the mechanism of hepatic IRI. Macrophage TIM‐4 may represent a therapeutic target to minimize innate inflammatory responses in IR‐stressed organs. (Hepatology 2014;60:2051–2063)