Transplant recipients developing anti-donor HLA antibodies after transplantation demonstrate increased risk of antibody-mediated rejection, transplant associated vasculopathies and graft loss. HLA class I signaling pathways have been implicated in these processes because ligation of class I molecules by anti-HLA antibodies initiates intracellular signals in endothelial cells that synergize with growth factor receptors to elicit survival and proliferation. We found that anti-HLA antibodies elicit different signal transduction outcomes, survival vs. proliferation, depending upon their specificity, titer and the degree of HLA antigen expression on the endothelial cell. These studies provide a paradigm for further elucidating the molecular mechanisms underlying how the concentration of antibody mediates survival and proliferation events in endothelium and their relationship to transplant outcome. Activation of anti-apoptotic and cell survival machinery in endothelial cells is augmented when cells are exposed to low concentrations of anti-HLA antibodies. In contrast, treatment of endothelial cells with high concentrations of HLA antibodies stimulates cell proliferation. This suggests that low levels of antibody binding to HLA may be beneficial to transplant survival by activating survival pathways that promote graft accommodation. On the other hand, high levels of antibody binding may have a detrimental effect on graft survival by upregulating FGFR expression, stimulating cell proliferation and increasing risk for development of transplant vasculopathy. We believe these findings are clinically relevant and may explain differences in transplant outcome in recipients producing anti-donor HLA antibodies. The overall goals of this proposal are to elucidate whether the intracellular signaling events initiated by antibody ligation of class I molecules are influenced by the specificity and concentration of the antibody and to determine the clinical relevance of class I signaling pathways in transplantation.
Aim 1 will focus on HLA interactions with 2 integrins and survival and proliferation phosphorylation cascades induced by different titers of anti-HLA antibody on primary human endothelial cells. These studies will permit us to dissect the class I signaling pathways and explore the cause-effect relationships between proteins in the pathway.
Aim 2 will test whether the antibody induced phosphorylation cascades identified in cultured EC are also operational in vivo. We will study the effect of different titers and specificities of anti-MHC antibody on induction of cell survival and proliferation signal transduction pathways in a RAG1 knock out murine heterotopic cardiac transplant model.
Aim 3 will explore whether anti-MHC class I induced phosphorylation of proteins in cardiac transplant biopsies correlate with the presence and titer of circulating anti-donor-HLA antibodies, diagnosis of antibody-mediated acute and chronic rejection and transplant outcome. These experiments will confirm the biological relevance of class I mediated signaling in human transplantation.

Public Health Relevance

Studying anti-HLA antibody mediated signal transduction in the proposed in vitro and in vivo models will permit us to establish the importance of the class I signaling pathways in solid organ transplant outcome. These studies will identify key signaling proteins mediating acute and chronic antibody-mediated rejection and may permit the development of new treatment strategies. Using samples from transplant recipients, this study will develop and test class I antibody mediated signal transduction as reliable indicators of transplant outcome and provide insight into mechanisms underlying antibody mediated graft injury.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
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Atherosclerosis and Inflammation of the Cardiovascular System Study Section (AICS)
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Nabavi, Nasrin N
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University of California Los Angeles
Schools of Medicine
Los Angeles
United States
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Salehi, Sahar; Sosa, Rebecca A; Jin, Yi-Ping et al. (2018) Outside-in HLA class I signaling regulates ICAM-1 clustering and endothelial cell-monocyte interactions via mTOR in transplant antibody-mediated rejection. Am J Transplant 18:1096-1109
Pearl, Meghan H; Zhang, Qiuheng; Palma Diaz, Miguel Fernando et al. (2018) Angiotensin II Type 1 receptor antibodies are associated with inflammatory cytokines and poor clinical outcomes in pediatric kidney transplantation. Kidney Int 93:260-269
Jin, Yi-Ping; Valenzuela, Nicole M; Zhang, Xiaohai et al. (2018) HLA Class II-Triggered Signaling Cascades Cause Endothelial Cell Proliferation and Migration: Relevance to Antibody-Mediated Transplant Rejection. J Immunol 200:2372-2390
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Valenzuela, Nicole M; Thomas, Kimberly A; Mulder, Arend et al. (2017) Complement-Mediated Enhancement of Monocyte Adhesion to Endothelial Cells by HLA Antibodies, and Blockade by a Specific Inhibitor of the Classical Complement Cascade, TNT003. Transplantation 101:1559-1572
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Wallace, William Dean; Li, Ning; Andersen, Claus B et al. (2016) Banff study of pathologic changes in lung allograft biopsy specimens with donor-specific antibodies. J Heart Lung Transplant 35:40-8
Pizzo, Helen P; Ettenger, Robert B; Gjertson, David W et al. (2016) Sirolimus and tacrolimus coefficient of variation is associated with rejection, donor-specific antibodies, and nonadherence. Pediatr Nephrol 31:2345-2352
Zhang, Qiuheng; Reed, Elaine F (2016) The importance of non-HLA antibodies in transplantation. Nat Rev Nephrol 12:484-95

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