Distinct endoplasmic reticulum stress responses are triggered during human liver transplantation.
Injury due to cold ischaemia-reperfusion (IR) represents a major cause of primary graft non-function following human liver transplantation. This major cellular response translates into a dramatic decrease in intracellular ATP concentration during the ischaemic phase, thus sensitizing cells to reperfusion shock. We postulated that IR-induced cellular damage might cause alterations of the secretory pathway, particularly at the level of endoplasmic reticulum (ER) function. Under these circumstances, the ER triggers an adaptive response named the 'unfolded protein response' (UPR). In this study, we show that the expression of BiP, CHOP/GADD153 and GADD34, known to be induced specifically upon ER stress, are differentially affected upon IR, thus suggesting that distinct ER stress responses are activated during each phase of transplantation. With an approach combining semi-quantitative RT-PCR and immunoblotting using phospho-specific antibodies, we show that the IRE-1 pathway is activated upon early ischaemia and, in a second phase, upon early reperfusion. This occurs through the atypical splicing of XBP-1 mRNA, its translation into a transcriptionally active XBP-1 protein and the subsequent increase in EDEM mRNA expression, and may also contribute to the observed reperfusion-induced activation of MAPK/SAPK. In contrast, we demonstrate that the PERK pathway, leading to inhibition of cap-dependent translation, is mainly activated upon reperfusion, as shown by PERK and eIF2alpha phosphorylation. PERK activation is detected restrictively in sinusoidal endothelial cells and could contribute to the exaggerated sensivity of this liver cell type to IR injury. These results correlate well with the observed defect in protein secretion and suggest that the biphasic ER stress response may influence liver secretory functions and, as a consequence, condition liver transplantation outcomes.
Emadali
Anouk
A
Organelle Signaling Laboratory, Department of Surgery, McGill University, Montreal, PQ, H3A 1A1 Canada.
Nguyên
Duc Thang
DT
Rochon
Caroline
C
Tzimas
Georges N
GN
Metrakos
Peter P
PP
Chevet
Eric
E
D004721:Endoplasmic Reticulum / Q000502:physiology*; D004722:Endoribonucleases; D042783:Endothelial Cells / Q000201:enzymology; D006801:Humans; D008099:Liver / Q000201:enzymology; D016031:Liver Transplantation; D008565:Membrane Proteins / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D048055:Mitogen-Activated Protein Kinase 8 / Q000378:metabolism; D018384:Oxidative Stress; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D015427:Reperfusion Injury / Q000201:enzymology / Q000503:physiopathology*; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D015398:Signal Transduction; D019892:eIF-2 Kinase / Q000502:physiology; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D004722:Endoribonucleases; D008565:Membrane Proteins; D048052:Mitogen-Activated Protein Kinase 3; D048055:Mitogen-Activated Protein Kinase 8; D017346:Protein Serine-Threonine Kinases; D011506:Proteins; D019892:eIF-2 Kinase; D048051:p38 Mitogen-Activated Protein Kinases; C403982:ERN2 protein, human