We previously showed that prolonged cold ischemic storage (CIS) of donor B6 hearts results in complement dependent, CTLA4Ig-resistant rejection in BALB/c recipients. In this system, donor IRI causes complement-dependent TNFa release. As TNFa can induce apoptosis/necroptosis, we hypothesized that graft rejection is linked to IRI via complement-initiated intragraft apoptosis and/or necroptosis. To test this, we exploited SHARPIN deficient mice. SHARPIN is a physiological cellular death inhibitor; its absence lifts restraint on cell death. Sharpin^-/- B6 hearts exposed to 8h CIS and transplanted into CTLA4Ig-treated BALB/c mice were rejected with median survival time (MST) of (17±4 d), faster than 8h CIS WT hearts (42±8 d, p<0.05 n=7-9). IHC staining of grafts harvested prior to rejection confirmed increased intragraft cell death in the Sharpin^-/-. When transplanted into SCID recipients, CIS Sharpin^-/- grafts survived indefinitely, indicating that unregulated intragraft cell death does not directly lead to graft failure in Sharpin^-/- hearts. Donor hearts that lack CYLD, a cell death initiating molecule and SHARPIN i.e. Cyld^-/-Sharpin^-/- exposed to 8 h CIS rescued the shortened survival of Sharpin^-/- hearts to MST 32.5 ±4 d (n=6, p<0.05 vs. Sharpin^-/-), further implicating intragraft apoptosis/necroptosis. To formally link recipient complement activation to IRI-induced intragraft cell death, we transplanted 8h CIS B6 Sharpin^-/- hearts into CTLA4Ig-treated C3^-/- or to C3^-/-C5^-/- BALB/c recipients. Survival is >D30 (ongoing), n=6, p<0.05 vs Sharpin^-/- into WT supporting the conclusion that recipient complement activation causes graft rejection through activating intragraft cell death. RIPK3 is required for necroptosis but not apoptosis. To test whether necroptosis mediates rejection in this system, we transplanted 8h CIS B6 RIPK3^-/- hearts into CTLA4-Ig treated BALB/c recipients. The allografts survived with MST >80 days, n=, p<0.05 vs WT, supporting a pathogenic role for necroptosis. Together our results provide new insights by uniquely demonstrating that IR injury initiates recipient complement activation that in turn drives intragraft necroptosis to cause costimulatory blockade-resistant, T cell-mediated, allograft rejection. The findings provide a foundation for testing whether peritransplant inhibition of necroptosis positively impacts transplant outcomes in humans.

CITATION INFORMATION: Ang R., Chun N., Ting A., Heeger P. Linking Donor Ischemia Reperfusion Injury (IRI) to Costimulatory Blockade Resistant Murine Heart Graft Rejection through Complement-Initiated Necroptosis Am J Transplant. 2017;17 (suppl 3).

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