Abstract
Multiple research groups have demonstrated that the outcome of patients receiving liver grafts from brain death donors (DBD) is poorer when compared with patients receiving grafts from living donors. This might be due to an increased hepatocyte apoptosis induced after brain death (BD). In this work, we found that the activity of PP2A-Akt pathway is significantly increased in clinical donor ex vivo hepatocytes after BD by iTRAQ protein quantification analysis. The same results were confirmed in animal models. A time-dependent promotion of apoptosis was also found in DBD rabbit liver, as demonstrated by the increased levels of cleaved Caspase 3 and the decreased of Bcl-2. To further investigate the roles of PP2A and Akt in regulating apoptosis of hepatocytes after BD, we cultivated human liver cell line L02 with serum deprivation and hypoxia, to simulate the ischemic and hypoxic conditions of hepatocytes in DBD. Increased apoptosis and decreased viability were observed during the time in this model. Meanwhile PP2A activity and Akt activity were respectively increased and decreased. Notably, the proportion of Akt phosphorylation at Ser473 decreased, while other known targets of PP2A (p38, JNK and ERK) were not affected in terms of protein levels or phosphorylation. These results suggested that PP2A is involved in apoptotic induction of hepatocytes after brain death by specific suppression of Akt. This discovery was further confirmed with pharmaceutical and genetic methods. Our work implied potential targets for reducing liver cell apoptosis and improving organ donor quality after BD.
Highlights
There exists a vast disparity between the number of patients on transplant waiting list and that of available organs [1,2,3,4] and the main source of donor organs are from brain death (DBD) and cardiac death (DCD)
Compared to the sham group, Bcl-2 levels were progressively downregulated in the DBD group from 2 to 8 h post brain death, while cleaved-Caspase 3 was significantly elevated with total caspase-3 remained stable
Akt, PP2A and proteins belonging to PI3K-Akt pathway are enriched in these samples (Fig. 2b, c), suggesting that both PP2A and PI3K-Akt pathways are involved in the regulation of apoptosis in the liver tissues after brain death
Summary
There exists a vast disparity between the number of patients on transplant waiting list and that of available organs [1,2,3,4] and the main source of donor organs are from brain death (DBD) and cardiac death (DCD). Several kidney-transplant studies have revealed a consistent and significant difference in the graft survival between grafts derived from brain-dead (BD) donors and the grafts from living donors. There are more incidents of primary graft non function and poor graft survival when grafts were from BD patients than that from living donors. It was hypothesized that BD has a detrimental effect on donor organ viability [8, 9].
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