Accelerated apoptosis of peripheral blood monocytes in Cebpb-deficient mice

https://doi.org/10.1016/j.bbrc.2015.07.045Get rights and content

Highlights

  • The number of peripheral blood monocytes was reduced in Cebpb−/− mice.

  • C/EBPβ was cell-intrinsically required for maintenance of peripheral blood monocytes.

  • Bone marrow monopoiesis was intact in Cebpb−/− mice.

  • Apoptosis of monocytes was enhanced in the peripheral blood of Cebpb−/− mice.

  • C/EBPβ is required for the survival of monocytes in peripheral blood.

Abstract

The CCAAT/enhancer-binding protein β (C/EBPβ) transcription factor is required for granulopoiesis under stress conditions. However, little is known about its roles in steady state hematopoiesis. Here, we analyzed the peripheral blood and bone marrow of Cebpb−/− mice at steady state by flow cytometry and unexpectedly found that the number of peripheral blood monocytes was severely reduced, while the number of bone marrow monocytes was maintained. The ability of Cebpb−/− bone marrow cells to give rise to macrophages/monocytes in vitro was comparable to that of wild-type bone marrow cells. Apoptosis of monocytes was enhanced in the peripheral blood, but not in the bone marrow of Cebpb−/− mice. These results indicate that C/EBPβ is required for the survival of monocytes in peripheral blood.

Introduction

The leucine zipper basic region-containing transcription factor CCAAT/enhancer-binding protein β (C/EBPβ) is a member of the C/EBP family [1], [2], [3], [4]. C/EBPβ regulates the proliferation, differentiation, survival, and metabolism of many cell types through the activation or repression of target genes [5], [6], [7], [8], [9], [10]. Within the hematopoietic system, C/EBPβ is involved in regulation of the development and function of macrophages [11], [12], [13], [14]. In addition, we and others previously reported that C/EBPβ is required for granulopoiesis during emergencies such as infection and cytokine stimulation, but is dispensable at steady state [15], [16]. Under stress conditions, C/EBPβ is induced or activated and elicits its activities to facilitate proliferation and differentiation of granulocyte precursors [15], [16], [17], [18], [19], [20], [21], [22]. By contrast, the role of C/EBPβ in steady state hematopoiesis is largely unknown. Therefore, we carefully analyzed the peripheral blood and bone marrow of Cebpb−/− mice by flow cytometry and unexpectedly found that the number of peripheral blood monocytes was much lower in Cebpb−/− mice than in wild-type (WT) littermate controls. We discuss the mechanisms by which C/EBPβ is involved in the regulation of monocyte homeostasis.

Section snippets

Mice

C57BL/6 mice were purchased from CLEA Japan (Tokyo, Japan). CD45.1+ mice (a kind gift from Dr. Shigekazu Nagata, Osaka University, Japan) and Cebpb−/− mice were bred and maintained under specific pathogen-free conditions in Kyoto University. Littermates were used as controls in all experiments involving Cebpb−/− mice. The animal protocols were approved by the Committee on Animal Research of Kyoto University Faculty of Medicine.

Manual differential counts of peripheral blood

Smears of mouse peripheral blood were stained using a Diff-Quik Kit

Monocytes in peripheral blood are reduced in Cebpb−/− mice

We first analyzed the complete blood cell count and differential counts of peripheral blood from WT and Cebpb−/− mice. The total white blood cell count was significantly higher in Cebpb−/− mice than in WT mice, while the numbers of red blood cells and platelets were comparable between WT and Cebpb−/− mice. In analyses of manual differential counts, the frequencies of neutrophils, eosinophils, and lymphocytes were almost the same in WT and Cebpb−/− mice (Table 1). Notably, both the frequency and

Discussion

Monocytes are bone marrow-derived phagocytes that circulate in peripheral blood and give rise to macrophages [24]. The process of monocyte production is controlled by interplay among multiple factors including transcription factors [25], [26], [27], [28], [29], [30], [31]. In the present study, we found that C/EBPβ is required for the survival of peripheral blood monocytes, while it is dispensable for the development and/or maintenance of mature cells of other lineages at steady state. Our

Conflicts of interest

The authors have no conflicts of interest.

Acknowledgments

This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology (25461615, 11068019 to H.H., 25430149 to A.Y., 15K09453 to Y.M. and 23112507, 24390244, 25112706, 11068019 to T.M.), a grant from the Project for Development of Innovative Research on Cancer Therapeutics from MEXT in Japan (to H.H. and T.M.), a Grant-in-Aid from the Ministry of Health, Labor and Welfare in Japan (to T.M.), the National Cancer Center Research

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