Essential role for autophagy during invariant NKT cell development

Abstract

Autophagy is an evolutionarily conserved cellular homeostatic pathway essential for development, immunity, and cell death. Although autophagy modulates MHC antigen presentation, it remains unclear whether autophagy defects impact on CD1d lipid loading and presentation to invariant natural killer T (iNKT) cells and on iNKT cell differentiation in the thymus. Furthermore, it remains unclear whether iNKT and conventional T cells have similar autophagy requirements for differentiation, survival, and/or activation. We report that, in mice with a conditional deletion of the essential autophagy gene Atg7 in the T-cell compartment (CD4 Cre-Atg7), thymic iNKT cell development-unlike conventional T-cell development-is blocked at an early stage and mature iNKT cells are absent in peripheral lymphoid organs. The defect is not due to altered loading of intracellular iNKT cell agonists; rather, it is T-cell-intrinsic, resulting in enhanced susceptibility of iNKT cells to apoptosis. We show that autophagy increases during iNKT cell thymic differentiation and that it developmentally regulates mitochondrial content through mitophagy in the thymus of mice and humans. Autophagy defects result in the intracellular accumulation of mitochondrial superoxide species and subsequent apoptotic cell death. Although autophagy-deficient conventional T cells develop normally, they show impaired peripheral survival, particularly memory CD8 + T cells. Because iNKT cells, unlike conventional T cells, differentiate into memory cells while in the thymus, our results highlight a unique autophagy-dependent metabolic regulation of adaptive and innate T cells, which is required for transition to a quiescent state after population expansion.utophagy is an evolutionarily conserved catabolic process that, by facilitating the breakdown and recycling of damaged organelles and long-lived proteins, is essential to maintaining cellular homeostasis (1). The autophagy pathway is highly regulated during development and also by environmental factors such as nutrient availability/starvation, hypoxia, and reactive oxygen species (ROS). The process is controlled by a number of autophagy-related genes (Atg) and starts with the formation of a double-membraned vesicle (the autophagosome) engulfing the cytoplasmic components to be delivered to the lysosome for degradation. Formation of the autophagosome requires the concerted action of two ubiquitin-like conjugation systems in which Atg12 is covalently linked to Atg5 and Atg8 is conjugated to phosphatidylethanolamine (2, 3). Atg7 is a necessary catalyst in both conjugation systems and is therefore essential for autophagy (3).Due to its important role in cellular homeostasis, dysregulation of autophagy has been implicated in several pathological processes, including neurodegeneration, autoimmunity, cancer, and infection (4). Furthermore, autophagy plays an important role during immune responses by regulating pathogen handling and antigen presentation (5, 6). It is well established that different populations of αβ T lymph...

Invariant NKT Cells Require Autophagy To Coordinate Proliferation and Survival Signals during Differentiation

“…However, inhibition of mTOR was not able to rescue the defect in i NKT cells, indicating Fnip1 is required for i NKT cell development in both an mTOR-dependent and -independent manner (75), and a connection to decreased autophagy was not established in this study. While this manuscript was in revision, a study was published indicating that mice with a Atg7 deficiency driven by CD4 Cre have a reduction in i NKT cells in the thymus and periphery, consistent with the results here (76). …”

Autophagy regulates T lymphocyte proliferation through selective degradation of the cell-cycle inhibitor CDKN1B/p27Kip1

“…5,6 Autophagy plays an essential role in the development and function of T lymphocytes. Autophagy regulates the calcium mobilization and energy metabolism in T cells, [7][8][9] is critical for effector CD8 + T cell survival and memory formation, 10,11 promotes the proliferation and survival of invariant NKT cells 12,13 and tunes down TCR signaling by degrading BCL10. 14 Autophagy starts with a membrane precursor called the phagophore.…”

The autophagy machinery restrains iNKT cell activation through CD1D1 internalization

“…20,56 Mice with T lymphocyte-specific deletion of Atg5 or Atg7 show reduced progression of thymic iNKT cells through the cell cycle and lower frequencies of both thymic and peripheral iNKT cell populations due to increased apoptosis and impaired survival. 20,56 Frequencies of thymic and peripheral iNKT cells were unchanged in Atg5-DC CKO mice, supporting the notion that the reported deficit in iNKT cell differentiation is cell-autonomous. Our data indicate that while autophagy proteins regulate iNKT cell development via T cell-intrinsic effects, they attenuate peripheral iNKT activation through their function in DC-mediated antigen processing and presentation.…”

“…20 To investigate this discrepancy we generated BMDCs from Atg5-deficient mice and also found that they elicit IL2 production by iNKT cells following uptake of glycolipid antigens to the same level as BMDCs from wild-type mice (Fig. S2).…”