Characterization and CRISPR/Cas9-mediated genetic manipulation of neutrophils derived from Hoxb8-ER-immortalized myeloid progenitors

Neutrophils represent a first line of defense against a wide variety of microbial pathogens. Transduction with an estrogen receptor-Hoxb8 transcription factor fusion construct conditionally immortalizes myeloid progenitor cells (NeutPro) capable of differentiation into neutrophils. This system has been very useful for generating large numbers of murine neutrophils for in vitro and in vivo studies. However, some questions remain as to how closely neutrophils derived from these immortalized progenitors reflect primary neutrophils. Here we describe our experience with NeutPro-derived neutrophils as it relates to our studies of Yersinia pestis pathogenesis. NeutPro neutrophils have circular or multilobed nuclei, similar to primary bone marrow neutrophils. Differentiation of neutrophils from NeutPro cells leads to increased expression of CD11b, GR1, CD62L, and Ly6G. However, the NeutPro neutrophils expressed lower levels of Ly6G than bone marrow neutrophils. NeutPro neutrophils produced reactive oxygen species at slightly lower levels than bone marrow neutrophils, and the 2 cell types phagocytosed and killed Y. pestis in vitro to a similar degree. To further demonstrate their utility, we used a nonviral method for nuclear delivery of CRISPR/Cas9 guide RNA complexes to delete genes of interest in NeutPro cells. In summary, we have found these cells to be morphologically and functionally equivalent to primary neutrophils and useful for in vitro assays related to studies of bacterial pathogenesis.

Hox-driven conditional immortalization of myeloid and lymphoid progenitors: Uses, advantages, and future potential

Those who study macrophage biology struggle with the decision whether to utilize primary macrophages derived directly from mice or opt for the convenience and genetic tractability of immortalized macrophage-like cell lines in in vitro studies. Particularly when it comes to studying phagocytosis and phagosomal maturation-a signature cellular process of the macrophage-many commonly used cell lines are not representative of what occurs in primary macrophages. A system developed by Mark Kamps' group, that utilizes conditionally constitutive activity of Hox transcription factors (Hoxb8 and Hoxa9) to immortalize differentiation-competent myeloid cell progenitors of mice, offers an alternative to the macrophage/macrophage-like dichotomy. In this resource, we will review the use of Hoxb8 and Hoxa9 as hematopoietic regulators to conditionally immortalize murine hematopoietic progenitor cells which retain their ability to differentiate into many functional immune cell types including macrophages, neutrophils, basophils, osteoclasts, eosinophils, dendritic cells, as well as limited potential for the generation of lymphocytes. We further demonstrate that the use of macrophages derived from Hoxb8/Hoxa9 immortalized progenitors and their similarities to bone marrow-derived macrophages. To supplement the existing data, mass spectrometry-based proteomics, flow cytometry, cytology, and in vitro phagosomal assays were conducted on macrophages derived from Hoxb8 immortalized progenitors and compared to bone marrow-derived macrophages and the macrophage-like cell line J774. We additionally propose the use of a standardized nomenclature to describe cells derived from the Hoxb8/Hoxa9 system in anticipation of their expanded use in the study of leukocyte cell biology.

Production of Murine Macrophages from Hoxb8-Immortalized Myeloblasts: Utility and Use in the Context of Salmonella Infection

Salmonella enterica is a Gram-negative intracellular pathogen that causes a range of life-threatening diseases in humans and animals worldwide. In a systemic infection, the ability of Salmonella to survive/replicate in macrophages, particularly in the liver and spleen, is crucial for virulence. Transformed macrophage cell lines and primary macrophages prepared from mouse bone marrow are commonly used models for the study of Salmonella infection. However, these models raise technical or ethical issues that highlight the need for alternative methods. This chapter describes a technique for immortalizing early hematopoietic progenitor cells derived from wild-type or transgenic mice and using them to produce macrophages. It validates, through a specific example, the interest of this cellular approach for the study of Salmonella infection.

SKAP2 is required for defense against K. pneumoniae infection and neutrophil respiratory burst

Klebsiella pneumoniae is a respiratory, blood, liver, and bladder pathogen of significant clinical concern. We show that the adaptor protein, SKAP2, is required for protection against K. pneumoniae (ATCC 43816) pulmonary infections. Skap2-/- mice had 100-fold higher bacterial burden when compared to wild-type and burden was controlled by SKAP2 expression in innate immune cells. Skap2-/- neutrophils and monocytes were present in infected lungs, and the neutrophils degranulated normally in response to K. pneumoniae infection in mice; however, K. pneumoniae-stimulated reactive oxygen species (ROS) production in vitro was abolished. K. pneumoniae-induced neutrophil ROS response required the activity of SFKs, Syk, Btk, PLCγ2, and PKC. The loss of SKAP2 significantly hindered the K. pneumoniae-induced phosphorylation of SFKs, Syk, and Pyk2 implicating SKAP2 as proximal to their activation in pathogen-signaling pathways. In conclusion, SKAP2-dependent signaling in neutrophils is essential for K. pneumoniae-activated ROS production and for promoting bacterial clearance during infection.

Klebsiella pneumoniae is a type of bacteria that can cause life-threatening infections – including pneumonia, blood stream infections, and urinary tract infections – in hospitalized patients. These infections can be difficult to treat because some K. pneumoniae are resistant to antibiotics. The bacteria are normally found in the human intestine, and they do not usually cause infections in healthy people. This implies that healthy people’s immune systems are better able to fend off K. pneumoniae infections; learning how could help scientists develop new ways to treat or prevent infections in hospitalized patients.

In healthy people, a type of immune cell called neutrophils are the first line of defense against bacterial infections. Several different proteins are needed to activate neutrophils, including a protein called SKAP2. But the role of this protein in fighting K. pneumoniae infections is not clear.

To find out what role SKAP2 plays in the defense against pneumonia caused by K. pneumoniae, Nguyen et al. compared infections in mice with and without the protein. Mice lacking SKAP2 in their white blood cells had more bacteria in their lungs than normal mice. The experiments showed that neutrophils from mice with SKAP2 produce a burst of chemicals called “reactive oxygen species”, which can kill bacteria. But neutrophils without the protein do not. Without SKAP2, several proteins that help produce reactive oxygen species do not work.

Understanding the role of SKAP2 in fighting infections may help scientists better understand the immune system. This could help clinicians to treat conditions that cause it to be hyperactive or ineffective. More studies are needed to determine if SKAP2 works the same way in human neutrophils and if it works against all types of K. pneumoniae. If it does, then scientists might be able use this information to develop therapies that help the immune system fight infections.

CRISPR/Cas9 Immunoengineering of Hoxb8-Immortalized Progenitor Cells for Revealing CCR7-Mediated Dendritic Cell Signaling and Migration Mechanisms in vivo

To present antigens to cognate T cells, dendritic cells (DCs) exploit the chemokine receptor CCR7 to travel from peripheral tissue via afferent lymphatic vessels to directly enter draining lymph nodes through the floor of the subcapsular sinus. Here, we combined unlimited proliferative capacity of conditionally Hoxb8-immortalized hematopoietic progenitor cells with CRISPR/Cas9 technology to create a powerful experimental system to investigate DC migration and function. Hematopoietic progenitor cells from the bone marrow of Cas9-transgenic mice were conditionally immortalized by lentiviral transduction introducing a doxycycline-regulated form of the transcription factor Hoxb8 (Cas9-Hoxb8 cells). These cells could be stably cultured for weeks in the presence of doxycycline and puromycin, allowing us to introduce additional genetic modifications applying CRISPR/Cas9 technology. Importantly, modified Cas9-Hoxb8 cells retained their potential to differentiate in vitro into myeloid cells, and GM-CSF-differentiated Cas9-Hoxb8 cells showed the classical phenotype of GM-CSF-differentiated bone marrow-derived dendritic cells. Following intralymphatic delivery Cas9-Hoxb8 DCs entered the lymph node in a CCR7-dependent manner. Finally, we used two-photon microscopy and imaged Cas9-Hoxb8 DCs that expressed the genetic Ca2+ sensor GCaMP6S to visualize in real-time chemokine-induced Ca2+ signaling of lymph-derived DCs entering the LN parenchyma. Altogether, our study not only allows mechanistic insights in DC migration in vivo, but also provides a platform for the immunoengineering of DCs that, in combination with two-photon imaging, can be exploited to further dissect DC dynamics in vivo.

Formyl-peptide receptor 2 governs leukocyte influx in local Staphylococcus aureus infections

Leukocytes express formyl-peptide receptors (FPRs), which sense microbe-associated molecular pattern (MAMP) molecules, leading to leukocyte chemotaxis and activation. We recently demonstrated that phenol-soluble modulin (PSM) peptides from highly pathogenic Staphylococcus aureus are efficient ligands for the human FPR2. How PSM detection by FPR2 impacts on the course of S. aureus infections has remained unknown. We characterized the specificity of mouse FPR2 (mFpr2) using a receptor-transfected cell line, homeobox b8 (Hoxb8), and primary neutrophils isolated from wild-type (WT) or mFpr2^-/- mice. The influx of leukocytes into the peritoneum of WT and mFpr2^-/- mice was analyzed. We demonstrate that mFpr2 is specifically activated by PSMs in mice, and they represent the first secreted pathogen-derived ligands for the mFpr2. Intraperitoneal infection with S. aureus led to lower numbers of immigrated leukocytes in mFpr2^-/- compared with WT mice at 3 h after infection, and this difference was not observed when mice were infected with an S. aureus PSM mutant. Our data support the hypothesis that the mFpr2 is the functional homolog of the human FPR2 and that a mouse infection model represents a suitable model for analyzing the role of PSMs during infection. PSM recognition by mFpr2 shapes leukocyte influx in local infections, the typical infections caused by S. aureus-Weiss, E., Hanzelmann, D., Fehlhaber, B., Klos, A., von Loewenich, F. D., Liese, J., Peschel, A., Kretschmer, D. Formyl-peptide receptor 2 governs leukocyte influx in local Staphylococcus aureus infections.

Interferon-γ-dependent control of Anaplasma phagocytophilum by murine neutrophil granulocytes

Background

Anaplasma phagocytophilum is a Gram-negative obligate intracellular bacterium that is transmitted by ticks of the Ixodes ricinus complex. It replicates in neutrophils and elicits febrile disease in humans and animals. Because of its striking tropism for neutrophils, A. phagocytophilum has been used as a model organism to study the immune response against obligate intracellular pathogens. In mice, the control of A. phagocytophilum in the early phase of infection is dependent on natural killer cell-derived interferon-γ (IFN-γ). In contrast, the final elimination strictly requires CD4⁺ T-cells. It is a matter of debate, whether neutrophils serve only as host cells or as killer cells as well.

Results

To study this, we used in vitro generated murine neutrophils with defects in major antimicrobial molecules such as NADPH-oxidase (gp91^phox−/−), myeloperoxidase (MPO^−/−) and inducible nitric oxide synthase (iNOS^−/−). However, bacterial growth in gene-deficient neutrophils was comparable to that in wild-type cells. Whereas gp91^phox and MPO expression remained unchanged, the infection led to an induction of iNOS. In neutrophils stimulated with IFN-γ, bacterial growth was significantly impaired, and iNOS was induced. However, the antibacterial effect of IFN-γ was still seen in iNOS^−/− neutrophils.

Conclusion

Thus, murine in vitro generated neutrophils stimulated with IFN-γ seem to act as killer cells by an iNOS-independent mechanism.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2274-6) contains supplementary material, which is available to authorized users.

Zfp462 deficiency causes anxiety-like behaviors with excessive self-grooming in mice

Zfp462 is a newly identified vertebrate-specific zinc finger protein that contains nearly 2500 amino acids and 23 putative C2H2-type zinc finger domains. So far, the functions of Zfp462 remain unclear. In our study, we showed that Zfp462 is expressed predominantly in the developing brain, especially in the cerebral cortex and hippocampus regions from embryonic day 7.5 to early postnatal stage. By using a piggyBac transposon-generated Zfp462 knockout (KO) mouse model, we found that Zfp462 KO mice exhibited prenatal lethality with normal neural tube patterning, whereas heterozygous (Het) Zfp462 KO (Zfp462^+/- ) mice showed developmental delay with low body weight and brain weight. Behavioral studies showed that Zfp462^+/- mice presented anxiety-like behaviors with excessive self-grooming and hair loss, which were similar to the pathological grooming behaviors in Hoxb8 KO mice. Further analysis of grooming microstructure showed the impairment of grooming patterning in Zfp462^+/- mice. In addition, the mRNA levels of Pbx1 (pre-B-cell leukemia homeobox 1, an interacting protein of Zfp462) and Hoxb8 decreased in the brains of Zfp462^+/- mice, which may be the cause of anxiety-like behaviors. Finally, imipramine, a widely used and effective anti-anxiety medicine, rescued anxiety-like behaviors and excessive self-grooming in Zfp462^+/- mice. In conclusion, Zfp462 deficiency causes anxiety-like behaviors with excessive self-grooming in mice. This provides a novel genetic mouse model for anxiety disorders and a useful tool to determine potential therapeutic targets for anxiety disorders and screen anti-anxiety drugs.

In Vitro Differentiation of Mouse Granulocytes

Granulocytes are central players of the immune system and, once activated, a tightly controlled balance between effector functions and cell removal by apoptosis guarantees maximal host benefit with least possible collateral damage to healthy tissue.Granulocytes are terminally differentiated cells that cannot be maintained in culture for prolonged times. Isolating primary granulocytes is inefficient and challenging when working with mice, and especially so for the lowly abundant eosinophil and basophil subtypes. Here we describe an in vitro protocol to massively expand mouse derived myeloid progenitors and to differentiate them "on demand" and in large numbers into mature neutrophils or basophils.