Identificação dos mecanismos de regulação das células Natural Killer pelo fator de transcrição C/EBPG (CCAAT/enhancer binding protein gamma)

Lopes, IA. Identification of Natural Killer cells regulation mechanisms by the transcription factor C/EBPG (CCAAT/enhancer binding protein gamma) 2018. 90f. Dissertation (Master's degree in Science). Medical School of Ribeirão Preto, University of São Paulo, Ribeirão Preto, 2018. C/EBP (CCAAT/enhance-binding proteins) are a family of transcription factors involved in a variety of hematopoietic processes, regulating both terminal differentiation and cellular proliferation. Among these, it is known that C/EBP gamma (C/EBPG) is involved in the functional maturation of Natural Killer (NK) cells. However, the mediators of this regulation are unknown. NK cells are lymphocytes with effector functions of cytotoxicity and production of cytokines, both dependent on a dynamic equilibrium between the expression of activating and inhibitory receptors as well as cytokine receptors. The two functions (cytotoxic and secretory) make NK cells important components of hematopoiesis, able to eliminate susceptible targets as well as recruit other cells to amplify inflammatory responses. In face of incompatibility between target cells and NK effector cells, cytotoxic effects predominate; while in the absence of incompatibility, cytokine-mediated effects that influence other hematopoietic cells prevail. For example, cytokines such as IFNγ, TNFα, TGFβ, GMCSF and IL-10, produced by NK cells, are potential regulators of hematopoietic stem cells (HSC). With the aim of studying the regulation of NK cells by C/EBPG, we isolated NK cells from transgenic C/ebpg knockout (KO) animals and controls to analyze their differential gene expression and function, with a special focus on hematopoiesis regulation. In order to identify potential C/EBPG target genes, we isolated C/ebpg-deficient and control NK cells by the use of sorting by flow cytometry and isolated RNA for gene expression analysis. Differential expression of C/ebpg target genes was performed by Real-time PCR for eight genes differentially expressed in the microarray analysis: Il-10, Gmcsf, Ifng, Tnfa, Tgfb, Tlr4, Myd88 e Irak4. When compared to controls, non-activated and IL-2-stimulated C/ebpg KO NK cells presented a tendency to have higher expression of Myd88. Cytokine levels of IL-2, IL-4, IL-6, IL-10, IL-17α, TNFα and IFNγ, obtained from NK culture supernatants, were verified by flow cytometry, after IL-2 activation. Among these cytokines, the production of IFNγ by C/ebpg-deficient NK cells was found to be reduced. To further characterize NK cells, we analyzed their frequency (Lineage /CD3/NK1.1 cells) and the expression of the receptors NKG2D, Ly49D and NKG2A, and both analyses presented similar expression between control or C/epbg KO NK cells. The functional subtypes of these cells were characterized according to the expression of CD27 and CD11b, which allow the identification of NK subpopulations as immature secretory, mature secretory, cytotoxic or tolerant. The KO animals showed higher percentage of secretory cells and percentual and numerical reduction of cytotoxic cells when compared to the NK control cells. In agreement, CD107a expression was 5-times lower in C/ebpg KO splenocytes than in control splenocytes after co-incubation with YAC-1 cells. In addition, a cytotoxicity assay by flow cytometry was performed. The fluorescent probe CTO (Cell Tracker Orange) was incorporated to YAC-1 cells, used as target cells. As a result, in the 10:1 NK:target cells ratio, C/ebp KO cells were less cytotoxic than NK control cells. We concluded that C/ebpg-deficient cells are dysfunctional, have a greater secretory potential and an altered expression of genes and cytokines as compared to their controls. The potential mediators revealed by our study, in particular, IFNγ, may be important targets for the regulation of NK secretory function.