Background

The molecular basis of the increased susceptibility of steatotic livers to warm ischemia/reperfusion (I/R) injury during transplantation remains undefined. Animal model for warm I/R injury was induced in obese Zucker rats. Lean Zucker rats provided controls. Two dimensional differential gel electrophoresis was performed with liver protein extracts. Protein features with significant abundance ratios (p < 0.01) between the two cohorts were selected and analyzed with HPLC/MS. Proteins were identified by Uniprot database. Interactive protein networks were generated using Ingenuity Pathway Analysis and GRANITE software.

Results

The relative abundance of 105 proteins was observed in warm I/R injury. Functional grouping revealed four categories of importance: molecular chaperones/endoplasmic reticulum (ER) stress, oxidative stress, metabolism, and cell structure. Hypoxia up-regulated 1, calcium binding protein 1, calreticulin, heat shock protein (HSP) 60, HSP-90, and protein disulfide isomerase 3 were chaperonins significantly (p < 0.01) down-regulated and only one chaperonin, HSP-1was significantly upregulated in steatotic liver following I/R.

Conclusion

Down-regulation of the chaperones identified in this analysis may contribute to the increased ER stress and, consequently, apoptosis and necrosis. This study provides an initial platform for future investigation of the role of chaperones and therapeutic targets for increasing the viability of steatotic liver allografts.

Hepatic steatosis continues to present a major challenge in liver transplantation. These organs have been shown to have an increased susceptibility to cold ischemia and reperfusion (CIR) injury compared to otherwise comparable lean livers; the mechanisms governing this increased susceptibility to CIR injury are not fully understood. Endoplasmic reticulum (ER) stress is an important link between hepatic steatosis, insulin resistance and the metabolic syndrome. In this study, we investigated ER stress signaling and blockade in the mediation of CIR injury in severely steatotic rodent allografts. Steatotic allografts from genetically leptin-resistant rodents had increased ER stress responses and increased markers of hepatocellular injury following liver transplantation into strain-matched lean recipients. ER stress response components were decreased by the chemical chaperone, TUDCA, resulting in improvement of the allograft injury. TUDCA treatment decreased NF-κB activation, and the pro-inflammatory cytokines IL-6 and IL-1β. However, the predominant response was decreased expression of the ER stress cell death mediator, CHOP. Further, activation of the inflammation-associated caspase 11 was decreased linking ER Stress/CHOP to pro-inflammatory cytokine production following steatotic liver transplantation. These data confirm ER stress in steatotic allografts, and implicate this as a mediating mechanism of inflammation and hepatocyte death in the steatotic liver allograft.