Introduction: The mammalian Target of Rapamycin (mTOR) is targeted clinically with rapamycin (RAPA) to prevent allograft rejection. mTOR functions in two mTOR-containing complexes, mTOR complex (mTORC) 1 and 2. RAPA only inhibits mTORC1, but novel ATP-competitive mTOR inhibitors now allow study of RAPA-resistant mTOR by inhibiting both complexes. Dendritic cells (DC) are the most potent antigen-presenting cells and are crucial regulators of alloimmunity, thus we sought to determine the function of RAPA-resistant mTOR in these cells.
Methods: Conventional CD11c+ DC were generated from C57BL/6 or B7-H1-/- bone marrow cells cultured with GM-CSF and IL-4 for 8d. On d2, RAPA or ATP-competitive mTORC1/2 inhibitors were added. mTORC2-deficient DC were generated from the bone marrow of rictor-/- mice. DC were used as stimulators of BALB/c CD4+CD25– T cells in mixed leukocyte reaction (MLR) or stimulated with LPS and assessed for STAT3 phosphorylation by immunoblot.
Results: DC B7-H1 expression was reduced by RAPA and genetic deletion of rictor, but augmented by mTORC1/2 inhibition, suggesting that B7-H1 is negatively regulated by RAPA-resistant mTORC1. mTORC1/2-inhibited DC showed increased STAT3 phosphorylation, and B7-H1 upregulation by mTORC1/2 inhibition was dependent on STAT3. These findings correlated with specific reduction in the expression of SOCS3, a negative regulator of STAT3. mTORC1/2-inhibited DC increased regulatory T cell (Treg) induction compared to control and RAPA-exposed DC. Although mTORC1/2-inhibited DC expressed elevated levels of IL-10, their enhanced ability to induce Treg was only dependent on B7-H1. Neutralization of IL-1Β in MLR further reduced the ability of B7-H1-/- mTORC1/2-inhibited DC to induce Treg.
Conclusions: We identify a novel pathway regulating the key DC immune regulatory molecules B7-H1 and IL-10 that is RAPA-resistant and mTORC2-independent. While RAPA paradoxically reduces expression of these anti-inflammatory molecules, ATP-competitive mTOR inhibitors augment their expression. These data suggest that targeting RAPA-resistant mTOR may be beneficial in the therapy of allograft rejection.
To cite this abstract in AMA style:Rosborough B, Raich-Regue D, Matta B, Lee K, Boothby M, Turnquist H, Thomson A. Rapamycin-Resistant mTORC1 Regulates Dendritic Cell B7-H1 Expression That Acts in Synergy with IL-1β To Promote Regulatory T Cell Induction [abstract]. Am J Transplant. 2013; 13 (suppl 5). https://atcmeetingabstracts.com/abstract/rapamycin-resistant-mtorc1-regulates-dendritic-cell-b7-h1-expression-that-acts-in-synergy-with-il-1-to-promote-regulatory-t-cell-induction/. Accessed April 22, 2021.
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