Cellular-specific role of toll-like receptor 4 in hepatic ischemia-reperfusion injury in mice

Abstract

Ischemia-reperfusion (I/R) injury is a process whereby an initial hypoxic insult and subsequent return of blood flow leads to the propagation of innate immune responses and organ injury. The necessity of the pattern recognition receptor, toll-like receptor (TLR)-4, for this innate immune response has been previously shown. However, TLR4 is present on various cell types of the liver, both immune and non-immune cells. Therefore, we sought to determine the role of TLR4 in individual cell populations, specifically parenchymal hepatocytes, myeloid cells including Kupffer cells, and dendritic cells following hepatic I/R. When hepatocyte specific (Alb-TLR4-/-) and myeloid cell specific (Lyz-TLR4-/-) TLR4 knockout mice were subjected to warm hepatic ischemia there was significant protection in these mice compared to wild-type (WT). However, the protection afforded in these two strains was significantly less than global TLR4 specific TLR4 knockout (TLR4-/-) mice. Dendritic cell specific TLR4-/- (CD11c-TLR4-/-) mice had significantly increased hepatocellular damage compared to WT mice. Circulating levels of high mobility group box-1 (HMGB1) were significantly reduced in the Alb-TLR4-/- mice compared to WT, Lyz-TLR4-/-, CD11c-TLR4-/- mice and equivalent to global TLR4-/- mice, suggesting that TLR4 mediated HMGB1 release from hepatocytes may be a source of HMGB1 after I/R. Hepatocytes exposed to hypoxia responded by rapidly phosphorylating the mitogen-activated protein kinases JNK and p38 in a TLR4-dependent manner; inhibition of JNK decreased the release of HMGB1 after both hypoxia in vitro and I/R in vivo. Conclusion These results provide insight into the individual cellular response of TLR4. It was found that the parenchymal hepatocyte is an active participant in the sterile inflammatory response after I/R through TLR4-mediated activation of pro-inflammatory signaling and release of danger signals such as HMGB1.

Emerging Role of High-Mobility Group Box 1 (HMGB1) in Liver Diseases

“…Injection of recombinant HMGB1 exacerbates, whereas treatment with HMGB1-neutralizing antibody protects hepatic I/R damage in TLR4 wildtype mice, but not TLR4-deficient mice (38). In addition, TLR4 from parenchymal cells but not myeloid cells and DCs also regulates hepatic I/R-induced HMGB1 release by activation of reactive oxygen species and calcium/calmodulin-dependent protein kinase (CaMK) signaling pathway (38,40). Treatment with CaMK inhibitor (KN93) and antioxidant Nacetylcysteine inhibit HMGB1 release and protect against liver I/R injury in animal models.…”

Ischemia-Reperfusion Injury in Fatty Liver Is Mediated by Activated NADPH Oxidase 2 in Rats

“…9 The sterile immune response is the main cause of toxicity and cell death during warm ischemia, where ROS signaling is sustained during reperfusion. 10 In contrast, other studies have shown that ROS derived from Kupffer cells are essential for I/R liver injury. Activated Kupffer cells significantly increase their release of ROS and proinflammatory cytokines, including TNF-α, IL-1, INFγ, and IL-12.…”

Role of miR-148a in Mitigating Hepatic Ischemia-Reperfusion Injury by Repressing the TLR4 Signaling Pathway via Targeting CaMKIIα in Vivo and in Vitro

“…Liver I/R injury can activate TLR4 through ATP generation, cellular ion (especially calcium [Ca 2+ ]) homeostasis, and generation of reactive oxygen species [9]. Ca 2+ plays as a major second messenger role in regulating a broad range of important cellular processes.…”