Abstract 2462: Progesterone Induces Human Leukocyte Antigen-G Expression in the Vascular Endothelium: A Potential Protective Strategy against Cardiac Allograft Rejection
Background: We have demonstrated an association between endomyocardial and soluble expression of human leukocyte antigen-G (HLA-G) with improved graft tolerance in heart transplant (HT) recipients; yet, the exact mechanisms of HLA-G expression post-transplant remain unclear. We assessed HLA-G expression in the human endothelium to determine if therapeutic agents can be targeted towards inducing vascular endothelial HLA-G expression as a potential strategy to protect against cardiac allograft vasculopathy (CAV) and, subsequently, reduce immunosuppressive therapy in HT patients.
Methods: Cultured human coronary artery endothelial cells (HCAECs) and aortic endothelial cells (HAECs) were incubated for 48 hours with interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α) or interleukin-10 (IL-10) at 0.1–200 ng/ml, progesterone (0–5000 ng/ml), or subjected to 24 hours of hypoxia (pO2<0.1%) followed by reoxygenation (pO2=21%) for 48 hours (H/R). All treatments have been shown to upregulate HLA-G in cell lines known to express this protein. HLA-G levels in culture supernatants were detected by ELISA and quantified according to a purified HLA-G protein standard curve.
Results: HLA-G was not expressed at baseline by HCAECs and HAECs. All doses of IFN-γ, TNF-α, and IL-10, as well as H/R, failed to induce HLA-G expression. Increasing doses of progesterone resulted in a corresponding upregulation of HLA-G by HCAECs and HAECs. Shed and soluble HLA-G levels in culture supernatants after treatment with 50, 500 and 5000 ng/mL progesterone, respectively, were 45±5.3, 162±21.9 and 332±18.7 ng/mL in HCAECs (p<0.01 for all doses vs. vehicle) and 34±7.4, 102±25.6 and 198±39.0 ng/ml in HAECs (p<0.01 for all doses vs. vehicle). Treatment with mifepristone, a progesterone receptor antagonist abolished this effect.
Conclusions: For the first time we have demonstrated HLA-G expression by vascular endothelial cells following incubation with progesterone in a dose-dependent manner. Although HLA-G expression is tightly regulated, it has been shown to protect against allograft rejection when expressed post-HT. Hence, induction of endothelial HLA-G expression may represent a promising and novel therapeutic strategy of protecting against CAV in HT patients.