Selective inhibition of cyclooxygenase-2 protects porcine aortic endothelial cells from human antibody-mediated complement-dependent cytotoxicity

Background: Cyclooxygenase-2 (COX-2) is an inducible Enzyme with catalytic activity for biosynthesis of prostaglandins which are the key mediators of inflammation. COX-2 is also the therapeutic target for widely used non-steroidal anti-inflammatory drugs (NSAIDs). However, the involvement of COX-2 in xenotransplantation (eg, pig-to-non-human primate) remains poorly recognized.

Methods: We investigated the mechanisms that regulate COX-2 expression and the effects of COX-2 on porcine aortic endothelial cell (PAEC) viability using in vitro pig-to-primate xenotransplantation model and in vivo pig-to-mouse cellular transplant model. Regulation of COX-2 expression was assessed by real-time quantitative polymerase chain reaction (qPCR) and Western blotting. The effects of inhibition or downregulation of COX-2 on PAEC viability were assessed by propidium iodide (PI)-Annexin V staining and Cell Counting Kit-8 assay.

Results: Human serum triggered robust COX-2 expression in PAECs in a dose- and time-dependent manner. Induction of COX-2 expression by human serum was partially through activation of both canonical and non-canonical nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling and increasing intracellular calcium. Cytokines like tumor necrosis factor alpha (TNF-α), interleukin 1 beta (IL-1β), IL-17, were able to induce COX-2 expression. Selective inhibition of COX-2 by celecoxib dramatically decreased PAEC death in vitro and in vivo as defined by propidium iodide (PI)-Annexin V staining. Consistently, downregulation of COX-2 expression by NF-κB inhibitors or calcium chelator BAPTA decreased human serum-induced PAEC death as well. Silencing of COX-2 expression by small interfering RNA (siRNA) protected PAEC viability when transplanted under kidney capsule of C57BL/6 mice.

Conclusions: Taken together, our data suggest that COX-2 is highly induced in PAECs by xenogenic serum and associated with human antibody-mediated complement-dependent cytotoxicity. COX-2 might be a potential therapeutic target to improve xenotransplantation.