Role of Immuno-Inflammatory Signals in Liver Ischemia-Reperfusion Injury

Abstract

Ischemia reperfusion injury (IRI) is a major obstacle in liver resection and liver transplantation. The initial step of IRI is mediated through ischemia which promotes the production of reactive oxygen species in Kupffer cells. This furthermore promotes the activation of pro-inflammatory signaling cascades, including tumor necrosis factor-alpha, IL-6, interferon, inducible nitric oxide synthase, TLR9/nuclear-factor kappa B pathway, and the production of damage-associated molecular patterns (DAMPs), such as ATP, histone, high mobility group box 1 (HMGB1), urate, mitochondrial formyl peptides and S100 proteins. With ongoing cell death of hepatocytes during the ischemic phase, DAMPs are built up and released into the circulation upon reperfusion. This promotes a cytokines/chemokine storm that attracts neutrophils and other immune cells to the site of tissue injury. The effect of IRI is further aggravated by the release of cytokines and chemokines, such as epithelial neutrophil activating protein (CXCL5), KC (CXCL1) and MIP-2 (CXCL2), the complement proteins C3a and C5a, mitochondrial-derived formyl peptides, leukotriene B4 and neutrophil extracellular traps (NETs) from migrating neutrophils. These NETs can also activate platelets and form Neutrophil-platelet microthrombi to further worsen ischemia in the liver. In this review we aim to summarize the current knowledge of mediators that promote liver IRI, and we will discuss the role of neutrophils and neutrophil extracellular traps in mediating IRI.

Keywords: DAMPs; Kupffer cells; NETs; ROS; ischemia-reperfusion injury; miRNA; neutrophils; platelets; thrombosis.

Figure 1

Schematic illustration showing prolonged ischemia reduces hepatic tissue oxygenation resulting in increased ROS production and DAMP release by both Kupffer cells and hepatic stellate cells which can induce hepatic cell death. These DAMPs can play a role as an innate immune cell attractant and activator, especially neutrophils to undergo NETosis. NETs can further promote platelet activation and capture resulting in microthrombi.

Figure 2

Schematic illustration showing increase in the release of NET-decorated proteins such as neutrophil elastase, cathepsin G, HMGB1 and histone upon NETosis. These proteins induce platelet activation through TLR4 and p62 pathways, resulting in the formation of microthrombi within the liver and promote IR induce liver injury.