Role of Adiponectin in Preventing Chronic Rejection and the Underlying Molecular Immunoregulatory Signaling Pathway

This dissertation, "Role of Adiponectin in Preventing Chronic Rejection and the Underlying Molecular Immunoregulatory Signaling Pathway" by Daxu, Li, 李大旭, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Chronic rejection is a major obstacle to long-term survival of organ transplants. PPAR-γ agonist rosiglitazone has been shown to reduce graft rejection but the underlying mechanisms remain unclear. Combined treatment of rosiglitazone and anti-IL-5 antibody prevented MHC class II histoincompatiblecardiac graft rejection with a reduction of cellular infiltration, vasculopathy and interstitial fibrosis in a heterotopic heart transplantation model. In particularly, rosiglitazone decreased CD8 T cells infiltration and luminal occlusion, while anti-IL-5 antibody reduced eosinophil infiltration and collagen deposition. Adiponectin gene (APN) is a PPAR-γ target gene, and the expression of APN receptor AdipoRII in grafts, dendritic cells (DCs) and T cells are increased by rosiglitazone. These findings prompted me to further examine the immunomodulatory role of APN in graft rejection. APN is an anti-inflammatory adipocytokine, and has been shown to inhibitimmunostimulatory function of monocytes and macrophages. Rosiglitazone suppresses DCs maturation, activation and proliferation;hence, it is possible that APN could protect graft rejection through immunoregulation of DCs. Here, using in vitro culture systems, I found that APN has only moderate effect on the differentiation of bone marrow derived DCs but itcould alter DC phenotypes. APN-treated DCs showed an increased expression of PD-L1, which is consistent with the increased PD-L1 expression in rosiglitazone treated cardiac allografts. APN-treated DCs led to a decreased proliferation and reduction of IL-2production of T cell. Moreover, APN-treated DCs increased the expansion of Tregs (regulatory T cells) which could be inhibited by the blockage of PD-1/PD-L1 pathway, suggesting that PD-1/PD-L1 pathway and expansion of Tregs played important roles in APN-treated DCs mediated immunomodulation. Further, I employed APN-/-mice for functional and mechanistic studies, and found that cardiac allografts were not rejected by APN-/-recipient mice even after 120 days post-transplantation. Histological analyses revealed very little eosinophils, CD4 and CD8 T cells infiltration; no collagen deposit and no vessel occlusion in the cardiac allografts. Furthermore, Th2 cytokines such as IL-4 and IL-5 were lower in cardiac allografts and in the serum of APN-/-recipient. Inhibition of AMPK signaling, a major APN mediated pathway, reduced the eosinophils infiltration in wild type recipient. In contrast, AMPK activation increased eosinophils infiltration in APN-null recipient. APN enhanced T cell proliferation. AMPK and P38MAPK inhibitors as well as anti-IL-4 antibody inhibited APN-induced T cell proliferation. P38 MAPK inhibitors reduced IL-4 production in mature DCs but enhanced IL-4 expression in immature DCs. In EL-4 T cells, APN increased nuclear expressions of GATA-3 and p-STAT6 and augmented IL-4 expression, and the phenomenon was suppressed by target specific knockdown of AdipoR I and II. In summary, current study provides new mechanistic insights of PPAR-γ activation and APN signaling in the modulation of adaptive and transplantation immunity, establishing a link between metabolism and immune regulation. DOI: 10.5353/th_b4715596 Subjects: Adipose tissues Graft rejection - Prevention Heart - Transplantation - Immunological aspects