Glucosylceramide Synthase Is Involved in Development of Invariant Natural Killer T Cells.

Zoran V Popovic,Mariona Rabionet,Roger Sandhoff,Damir Krunic,Hermann-Josef Gröne,Stefan Porubsky,Richard Jennemann

doi:10.3389/fimmu.2017.00848

Abstract

Invariant natural killer T (iNKT) cells represent a unique population of CD1d-restricted T lymphocytes expressing an invariant T cell receptor encoded by Vα14-Jα18 and Vα24-Jα18 gene segments in mice and humans, respectively. Recognition of CD1d-loaded endogenous lipid antigen(s) on CD4/CD8-double positive (DP) thymocytes is essential for the development of iNKT cells. The lipid repertoire of DP thymocytes and the identity of the decisive endogenous lipid ligands have not yet been fully elucidated. Glycosphingolipids (GSL) were implicated to serve as endogenous ligands. However, further in vivo investigations were hampered by early embryonal lethality of mice deficient for the key GSL-synthesizing enzyme glucosylceramide (GlcCer) synthase [GlcCer synthase (GCS), EC 2.4.1.80]. We have now analyzed the GSL composition of DP thymocytes and shown that GlcCer represented the sole neutral GSL and the acidic fraction was composed of gangliosides. Furthermore, we report on a mouse model that by combination of Vav-promoter-driven iCre and floxed GCS alleles (VavCreGCSf/f) enabled an efficient depletion of GCS-derived GSL very early in the T cell development, reaching a reduction by 99.6% in DP thymocytes. Although the general T cell population remained unaffected by this depletion, iNKT cells were reduced by approximately 50% in thymus, spleen, and liver and showed a reduced proliferation and an increased apoptosis rate. The Vβ-chains repertoire and development of iNKT cells remained unaltered. The GSL-depletion neither interfered with expression of CD1d, SLAM, and Ly108 molecules nor impeded the antigen presentation on DP thymocytes. These results indicate that GlcCer-derived GSL, in particular GlcCer, contribute to the homeostatic development of iNKT cells.

Highlights

Natural killer T (NKT) cells represent a unique T cell population co-expressing NK cell markers such as NK1.1 (CD161) [1, 2]
Lysosomal proteases and sphingolipid activator proteins, known as saposins, are indispensable for normal thymic invariant natural killer T (iNKT) cell development suggesting that loading of lipid antigens onto CD1 molecules plays a crucial role in this process [23,24,25,26]
Because the development of iNKT cells depends on presentation of lipid antigens on double positive (DP) thymocytes, we analyzed the latter cell population for its GSL composition in WT mice

Summary

Introduction

Natural killer T (NKT) cells represent a unique T cell population co-expressing NK cell markers such as NK1.1 (CD161) [1, 2]. In contrast to conventional T cells, iNKT cells recognize lipid antigens presented by non-polymorphic MHC class I-like CD1 molecules [16, 17]. Whereas presentation of peptide antigens on MHC molecules of thymic cortical epithelial cells is a prerequisite for the development of conventional T cells, positive selection of iNKT cells requires presentation of lipid antigens by CD1 molecules of double positive (CD4+/CD8+) thymocytes [20,21,22]. Lysosomal proteases and sphingolipid activator proteins, known as saposins, are indispensable for normal thymic iNKT cell development suggesting that loading of lipid antigens onto CD1 molecules plays a crucial role in this process [23,24,25,26]

Methods

Results

Conclusion