*Purpose: We and others have reported on benefits of endoplasmic reticulum (ER) stress modulation against hepatic ischemia-reperfusion injury (IRI) in orthotopic liver transplantation (OLT). Although activation of Sirtuin 1 (SIRT1), an enzymatic stressor regulator, mitigated experimental liver IRI, its clinical relevance as well as hepatocyte-specific SIRT1 function remain unknown. We employed a mouse OLT model and analyzed clinical OLT biopsies (Bx) to determine as to whether and how hepatocyte SIRT1 – ER stress (ATF4/CHOP) axis may affect OLT outcomes.

*Methods: WT or hepatocyte-specific SIRT1 deficient (hSIRT1-KO) mouse livers, subjected to extended (18h) cold storage (4C in UW solution), were transplanted to WT mice; liver/serum samples were collected at 6h post-reperfusion. Human liver Bx collected from 60 OLT patients (2h after reperfusion; prior to abdominal closure) were analyzed by Western blots/RT-PCR.

*Results: Compared with WT liver grafts (WT>WT), hepatocyte SIRT1 disruption in the donor liver (hSIRT1-KO>WT) aggravated IRI, as evidenced by: 1/ sALT/sAST levels (ALT: 7321±6104 vs 3875±1869 IU/L, n=12/12, p=0.037; AST: 3671±2678 vs 1853±532 IU/L, n=12/12, p=0.015); 2/ Suzuki’s histological grading (p<0.05); 3/ frequency of TUNEL+ cells (p<0.05); 4/ augmented neutrophil/macrophage infiltration (IHC, p<0.05); 5/ enhanced mRNA levels coding for CXCL10/MCP1/IL1β (p<0.05); 6/ increased hepatic ATF4/CHOP expression (WB, p<0.05); and 7/ impaired survival of IR-stressed OLTs (2-weeks: 11 vs 44%, n=9/9, p=0.036). Primary mouse hepatocyte cultures from hSIRT1-KO mice showed enhanced ATF4/CHOP expression, as compared to WT counterparts, while SIRT1 silencing (siRNA) increased ATF4/CHOP levels in WT hepatocytes in vitro (WB, p<0.05). Post-reperfusion graft SIRT1 levels in human Bx negatively correlated with protein expression of ATF4 (r=-0.313, p=0.015), CHOP (r=-0.342, p=0.007); CXCL10 mRNA levels (r=-0.444, p<0.001); sALT levels (r=-0.452, p<0.001) at POD1. Indeed, human OLTs with high-SIRT1 expression (n=30) showed: 1/ suppressed ATF4 (p=0.004) and CHOP (p=0.003) protein levels; 2/ depressed mRNA levels coding for CD80 (p=0.018), CD86 (p=0.017) and CXCL10 (p=0.009); 3/ improved hepatocellular function (sALT=242±27 vs 488±65 IU/L, p= 0.005); 4/ shorter post-OLT hospital stay (37±5 vs 48±8 days); and 5/ superior post-OLT survival (3-years: 91.0 vs 75.7%, p=0.088) and rejection-free survival (3-years: 84.7 vs 69.5%), as compared to low-SIRT1 expression clinical cohort (n=30).

*Conclusions: This translational study documents a novel hepatocyte SIRT1/ATF4/CHOP signaling axis in OLT cytoprotection against IR-stress, providing the basis for SIRT1-inducing therapeutic strategies in transplant recipients.

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