*Purpose: Hepatic ischemia-reperfusion injury (IRI) plays a governing role in orthotopic liver transplantation, significantly impairing early graft function and increasing organ susceptibility to rejection. Neutrophil activation is a major, but still incompletely characterized, event driving the progression of hepatic IRI. A previously performed multi-omic analysis on post reperfusion liver tissue from a mouse model of hepatic IRI, and human orthotopic liver transplants, identified SYK as a potential mediator of neutrophil activation IRI. Therefore, this study was designed to address the underlying mechanism of Syk signaling pathways that are active and their inflammatory process occurring during hepatic IRI.

*Methods: Adult 10-12 week old mice were split in to two groups: treatment with a) Syk inhibitor R788 every day for 5 days prior to IRI, and b) Vehicle everyday for 5 days prior to IRI. Mice in each group were then subdivided in to mice that underwent a 70% partial warm ischemia for 60 minutes, followed by 6 and 24 hours of reperfusion (n=5/group), or mice that were subject only to a sham midline laparotomy (n=3/group). All mice were then euthanized for blood and hepatic tissue collection at each time point. Standard flow cytometry of whole blood was performed with cell specific target markers to identify specific subpopulations.

*Results: Specific Syk inhibition depressed neutrophil activation and recruitment in hepatic IRI. Flow cytometric analysis of the circulating CD11b+/Ly6G+ neutrophil cell subset in whole blood retrieved at 6h and 24h post-IRI showed a significantly lower relative % of CD11b+/Ly6G+ neutrophils in mice treated with R788, when compared to those treated solely with vehicle. Inhibiting neutrophil activation was also associated to a significant decrease in the number of liver infiltrating Ly6G+ neutrophils at 6h and 24h post-reperfusion, when compared to vehicle treated control mice. Syk inhibition led to reduced expression of pro-inflammatory iNOS and increased expression of TGF-β at 6h of reperfusion. As a result, mice treated with R788 had significantly reduced serum ALT levels and ameliorated histological hepatic injury at both 6h and 24h of hepatic reperfusion.

*Conclusions: This study demonstrates that preconditioning mice with SYK specific inhibition protects livers from hepatic IRI via the downregulation of neutrophil infiltration. Moreover, it demonstrates the potential of multi-omics analysis approach for the identification of novel therapeutic targets in hepatic IRI.

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