Hematopoietic-Specific Deletion of Foxo1 Promotes NK Cell Specification and Proliferation.

Pei Huang,Shuting Wu,Hongyan Peng,Fangjie Wang,Wenjing Lai,Xiaohui Li,Saber Imani,Meng Meng,Lili Wang,Yao Yang,Rixing Zhan,Jianhua Yu,Bingbo Chen,Youcai Deng

doi:10.3389/fimmu.2019.01016

Abstract

We previously reported that deletion of Foxo1, via Ncr1-iCre mice from the expression of NKp46 onward, led to enhanced natural killer (NK) cell maturation and effector function. In this model, however, the role of Foxo1 in regulating NK cell specification and early development remains exclusive. Herein, we utilized a murine model of hematopoietic-specific deletion of Foxo1 before lymphoid specification, by crossing mice carrying floxed Foxo1 alleles (Foxo1fl/fl) with Vav1-iCre mice, to revisit the role of Foxo1 on NK cell specification and early development. The data showed that hematopoietic-specific deletion of Foxo1 resulted in increased proportion and numbers of common lymphoid progenitors (CLP) (Lin−CD127+c-Kit+Sca-1+), pre-pro NK b cells (Lin−Sca-1+c-Kit−CD135−CD127+), as well as committed Lin−CD122+ cells and CD3−CD19−NKp46+ NK cells in bone marrow. Hematopoietic-specific deletion of Foxo1 also promoted NK cells proliferation in a cell-intrinsic manner, indicated by increased Ki-67 expression and more expansion of NK cell after ex vivo stimulation with IL-15. The reason for Foxo1 suppressing NK cell proliferation might be its direct transcription of the cell-cycle inhibitory genes, such as p21cip1, p27kip1, p130, Gadd45a, and Ccng2 (cyclin G2) in NK cells, supported by the evidence of decreased mRNA expression of p21cip1, p27kip1, p130, Gadd45a, and Ccng2 in Foxo1-deficient NK cells and direct binding of Foxo1 on their promoter region. Furthermore, hematopoietic-specific deletion of Foxo1 resulted in increased ratio of mature NK subsets, such as CD11b+CD27− and CD43+KLRG1+ NK cells, but decreased ratio of immature NK subsets, such as CD27+CD11b− and CD27+CD11b+ NK cells, consistent with the findings in the murine model of Ncr1-iCre mediated Foxo1 deletion. Conclusively, Foxo1 not only acts as a negative checkpoint on NK cell maturation, but also represses NK cell specification and proliferation. The relative higher expression of Foxo1 in CLP and early NK precursors may also contribute to the later NK cell proliferation and responsiveness, which warranties another separate study in the future.

Highlights

Natural killer (NK) cells are a distinct subset of group 1 innate lymphoid cells with a crucial role in innate immunity [1]
Intracellular flow cytometry analysis exhibited the efficient deletion of Foxo1 in splenic CD3−CD19−NKp46+ total natural killer (NK) cells, as well as each subset based on the expression of CD27 and CD11b [15, 16] (Figure 1A)
To find more evidence to support our finding of increased NK cells by hematopoietic-specific deletion of Foxo1, we explored the proliferation potential and cell survival of NK cells by in vivo and ex vivo experimental models

Summary

Introduction

Natural killer (NK) cells are a distinct subset of group 1 innate lymphoid cells with a crucial role in innate immunity [1]. Cytokine secretion and granule-mediated cytotoxicity are the two main effector functions of NK cells [2]. Their cytotoxic function is critical to many immune responses, including tumor immunosurveillance and elimination of viral infection [3]. During the late stage of maturation, NK cells gradually upregulate CD11b expression, downregulate CD27 expression, and obtain co-expression of CD43 and KLRG1 [5,6,7,8]. Previous studies have revealed several transcriptional factors that are positive required for each stage of NK cell development, with little known about the negative ones [9]

Methods

Results

Conclusion