Toll-like receptor 4 is a key mediator of murine steatotic liver warm ischemia/reperfusion injury

Abstract

Steatotic donors are routinely rejected for transplantation because of their increased rate of primary nonfunction. These grafts are more sensitive to ischemia/reperfusion (I/R) during transplantation. Removal of endotoxin before reperfusion improves liver performance post-I/R. We hypothesize that the main modality of injury in steatotic livers is toll-like receptor 4 (TLR4) signaling. We fed 4-week-old control and TLR4-deficient (TLR4KO) mice a normal diet (ND) or a 60% high-fat diet (HFD) for 4 weeks to induce steatosis. Mice were subjected to total hepatic ischemia (35 minutes) and reperfusion (1 or 24 hours). Survival improved and liver pathology decreased at 24 hours in TLR4KO HFD animals compared to control HFD animals. An investigation of infiltrates showed that neutrophils and CD4ϩ cells were increased at 24 hours in control HFD animals, whereas TLR4KO HFD animals were similar to ND controls. Messenger RNA levels of interleukin 6 (IL-6), IL-12, and interferon gamma were elevated at 1 hour in control HFD animals, whereas TLR4KO HFD animals were similar to ND controls. IL-10 levels at 1 hour of reperfusion in control HFD and TLR4KO animals were decreased versus control ND animals. In conclusion, these improvements in liver function in TLR4KO HFD animals implicate TLR4 as a mediator of steatotic graft failure after I/R. Liver Exacerbating the already short supply of donor livers for transplantation is the usability of steatotic donor organs. Livers, whose parenchyma contains more than 30% of fat, have a dramatically increased chance of primary nonfunction, 1 and the vast majority of these organs are discarded. Furthermore, it has been shown that the degree of steatosis correlates with higher postoperative liver enzymes and increased long-term mortality.2 These livers are more sensitive to the stresses of ischemia/reperfusion (I/R) injury, especially the stresses of endotoxin exposure, than normal, lean livers. 3,4 Endotoxin from intestinal microflora is translocated across the intestinal barrier during periods of gut hypoperfusion and during periods of mesenteric congestion associated with the anhepatic phase of liver transplantation. 5 Research has shown that steatotic animals are much more sensitive to the hepatic effects of endotoxin than their lean counterparts. 6 In addition, previous research in our laboratory has shown that neutralization of translocated endotoxin with a monoclonal antibody, when administered intravenously before I/R, dramatically improves the survival and liver function of overtly steatotic animals after a period of warm I/R. The main signaling receptor for endotoxin is toll-like receptor 4 (TLR4).So far, 13 TLRs have been identified in rodents, and each of these recognizes a specific pathogen-associated molecular pattern. 8 In addition to several endogenous ligands, TLR4 specifically recognizes bacterial cell wall

Critical Role of Regulatory T Cells in Th17-Mediated Minor Antigen-Disparate Rejection

“…Indeed, the results in IL-6 2/2 mice demonstrated the regulatory role of this cytokine in the Treg/Th17 balance during antidonor immune response. High amounts of IL-6 are released in response to the surgical procedure, after TLR activation in the context of bacterial contamination and/or ischemiareperfusion injury (29,(46)(47)(48)(49). IL-6 can also be produced by dendritic cells in an Ag-specific manner through a dendritic/T cell cross-talk via the CD40-CD154 interactions (50,51).…”

Suppression of Mitochondrial Biogenesis through Toll-Like Receptor 4–Dependent Mitogen-Activated Protein Kinase Kinase/Extracellular Signal-Regulated Kinase Signaling in Endotoxin-Induced Acute Kidney Injury

“…Mice were euthanized by isoflurane asphyxiation and cervical dislocation at 1, 3, and 18 hours after LPS exposure, and kidneys and serum were collected for molecular analysis. For experiments using TLR4-deficient animals, TLR4 knockout (TLR4KO) mice were generated by crossing C57BL/10ScN mice with the tlr4 LPS-d mutation onto the C57BL/6 background for at least five generations (Ellett et al, 2009). All studies were conducted in accordance with the recommendations in the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health.…”

Interferon Regulatory Factor Signalings in Cardiometabolic Diseases

“…249 An investigation of the relevance of other TLR family members to stroke indicated that the expression of TLR7 and TLR8 were associated with poor outcome and enhanced inflammation in acute ischemic stroke 252 but that mice carrying a TLR3 or TLR9 ablation exhibited comparable brain damage after cerebral I/R injury with WT controls. 253 As in stroke insults, posthepatic ischemia, the chronic pharmacological or genetic inhibition of TLR4 accounts for the improved survival and decreased liver pathology via suppression of the inflammatory response, 254 apoptosis, 255 oxidative stress, 256 and endothelial overactivation. 257 The TLR2 mRNA level was increased in the ischemic lobes of mice that underwent partial hepatic I/R, and this increase was associated with an increase in TNF-α expression but was reversely accompanied with the alleviation of liver damage.…”