Transcriptional changes during hepatic ischemia-reperfusion in the rat

Ischemia-reperfusion (IR) injury, a ubiquitous consequence of liver transplantation, is a cause of early graft rejection and increased morbidity. At present, there are no effective strategies to reduce hepatic IR injury. Molecular mechanisms that promote cell survival under these circumstances are largely undefined. We examined changes in global gene expression at early reperfusion times to identify potential IR-mediated protective responses. Using a rat model of 30 minutes of 70% warm ischemia followed by reperfusion, RNA for microarray analysis was extracted from the non-ischemic and the ischemic-reperfused lobes at four reperfusion times: 0 (no reperfusion), 0.5, 2, and 6 hours. Differentially expressed genes and pathway analyses were used to identify IR-induced events. The transcriptome of the reperfused lobes was unique and discrete at each reperfusion time, showing no evidence of sustained changes of the gene expression alterations seen at 30 minutes of reperfusion. At all reperfusion times, a significant portion of gene expression changes in the reperfused lobes were present in the non-ischemic lobes. However, the earliest reperfusion time, 30 minutes, showed a marked increase in the expression of a set of immediate-early genes (c-Fos, c-Jun, Atf3, Egr1) that was exclusive to the reperfused lobe. Similarities of gene expression changes in the reperfused and the non-ischemic lobes at each time suggest that hemodynamics and/or circulating factors are potent stimuli in an IR model. However, early reperfusion events appear to reflect a cell-autonomous response that may be protective, thereby representing potential targets to ameliorate IR injury. Livers were harvested from bioloigical triplicate samples at 4 reperfusion times (0hr, 0.5hr, 2hr, 6hr) after 30 minutes of 70% warm ischemia. 3 sham animals were matched to each time point. RNA was extracted from the reperfused, ischemic, and sham livers using the RNeasy Isolation Kit (Qiagen). RTA-1_0 Rat Assays (Affymetrix Rat transcriptome 1.0) were used.