G-CSF activation of AKT is not sufficient to prolong neutrophil survival

Hereditary chronic neutrophilic leukemia in a four-generation family without transformation to acute leukemia

Chronic neutrophilic leukemia (CNL) is a rare myeloproliferative neoplasm (MPN) characterized by peripheral blood neutrophilia, marrow granulocyte hyperplasia, hepatosplenomegaly, and driver mutations in the colony-stimulating factor 3 receptor (CSF3R). Designation of activating CSF3R mutations as a defining genomic abnormality for CNL has led to increased recognition of the disease. However, the natural history of CNL remains poorly understood with most patients reported being of older age, lacking germline data, and having poor survival, in part due to transformation to acute leukemia. CSF3R driver mutations in most patients with CNL have been reported to be acquired, although rare cases of germline mutations have been described. Here, we report the largest pedigree to date with familial CNL, spanning four generations with affected family members ranging in age from 4 to 53 years, none of whom have transformed to acute leukemia. A heterozygous T618I CSF3R mutation was identified in peripheral blood and mesenchymal stromal cells from the proband and in all affected living family members, while the unaffected family members tested were homozygous wild type. We show that the T618I mutation also confers a survival advantage to neutrophils in an MCL1-dependent manner. Collectively, these data provide additional insights into the natural history of familial CNL arising from T618I CSF3R mutations and suggest that enhanced neutrophil survival also contributes to the high neutrophil count observed in patients with CNL.

CD11c regulates neutrophil maturation

Sepsis continues to be associated with high morbidity and mortality. Currently, sepsis is managed only conservatively. In sepsis, a substantial number of neutrophils is required, leading to accelerated neutrophil production. Immature neutrophils are released into the circulation to meet a demand, despite their less effective functioning in microbial eradication. Although an intervention to provide more mature neutrophils may serve as a potential sepsis treatment, the mechanism of neutrophil differentiation and maturation remains poorly understood. We discovered that CD11c, traditionally known as a dendritic cell marker, was expressed in neutrophils and regulated neutrophil maturation and effector functions. In the absence of CD11c, neutrophil maturation was impaired in the bone marrow, concomitant with a significant increase in the proliferation and apoptosis of preneutrophils, associated with less effector functions. Under lipopolysaccharide challenge, inducing an emergent neutrophil production in the bone marrow, CD11c deficiency exaggerated the release of immature neutrophils into the circulation, associated with a significant proliferation and apoptosis of preneutrophils. In contrast, constitutively active CD11c knock-in mice showed accelerated neutrophil maturation associated with enhanced effector functions, which further supports the notion that CD11c regulates neutrophil maturation. Furthermore, the constitutively active CD11c knock-in mice offered enhanced bacterial eradication. Taken together, we discovered that CD11c was critical for the regulation of neutrophil maturation, and CD11c activation could serve as a potential target for sepsis treatment.

MST1 controls murine neutrophil homeostasis via the G-CSFR/STAT3 axis

The release of neutrophils from the bone marrow into the blood circulation is essential for neutrophil homeostasis and the protection of the organism from invading microorganisms. Granulocyte colony-stimulating factor (G-CSF) plays a pivotal role in this process and guides granulopoiesis as well as the release of bone marrow neutrophils into the blood stream both during homeostasis and in case of infection through activation of the G-CSF receptor/signal transduction and activation of transcription 3 (STAT3) signaling pathway. Here, we investigated the role of the mammalian sterile 20-like kinase 1 (MST1) for neutrophil homeostasis and neutrophil mobilization. We found increased plasma levels of G-CSF in Mst1 ^-/- mice compared to wild type mice both under homeostatic conditions as well as after stimulation with the proinflammatory cytokine TNF-α. In addition, G-CSF-induced mobilization of neutrophils from the bone marrow into the blood circulation in vivo was markedly reduced in the absence of MST1. Interestingly, this was not accompanied by differences in the number of blood neutrophils. Addressing the underlying molecular mechanism of MST1-regulated neutrophil mobilization, we found reduced STAT3 phosphorylation and impaired upregulation of CXCR2 in Mst1 ^-/- bone marrow neutrophils compared to wild type cells, while JAK2 phosphorylation was not altered. Taken together, we identify MST1 as a critical modulator of neutrophil homeostasis and neutrophil mobilization from the bone marrow, which adds another important aspect to the complex role of MST1 in regulating innate immunity.

PI3K Isoforms in Cell Signalling and Innate Immune Cell Responses

Phosphoinositide-3-kinases (PI3Ks) are enzymes involved in signalling and modification of the function of all mammalian cells. These enzymes phosphorylate the 3-hydroxyl group of the inositol ring of phosphatidylinositol, resulting in lipid products that act as second messengers responsible for coordinating many cellular functions, including activation, chemotaxis, proliferation and survival. The identification of the functions that are mediated by a specific PI3K isoform is complex and depends on the specific cell type and inflammatory context. In this chapter we will focus on the role of PI3K isoforms in the context of innate immunity, focusing on the mechanisms by which PI3K signalling regulates phagocytosis, the activation of immunoglobulin, chemokine and cytokines receptors, production of ROS and cell migration, and how PI3K signalling plays a central role in host defence against infections and tissue injury.

Recent Developments in Extracellular Matrix Remodeling for Fat Grafting

Remodeling of the extracellular matrix (ECM), which provides structural and biochemical support for surrounding cells, is vital for adipose tissue regeneration after autologous fat grafting. Rapid and high-quality ECM remodeling can improve the retention rate after fat grafting by promoting neovascularization, regulating stem cells differentiation, and suppressing chronic inflammation. The degradation and deposition of ECM are regulated by various factors, including hypoxia, blood supply, inflammation, and stem cells. By contrast, ECM remodeling alters these regulatory factors, resulting in a dynamic relationship between them. Although researchers have attempted to identify the cellular sources of factors associated with tissue regeneration and regulation of the microenvironment, the factors and mechanisms that affect adipose tissue ECM remodeling remain incompletely understood. This review describes the process of adipose ECM remodeling after grafting and summarizes the factors that affect ECM reconstruction. Also, this review provides an overview of the clinical methods to avoid poor ECM remodeling. These findings may provide new ideas for improving the retention of adipose tissue after fat transplantation.

G-CSF, the guardian of granulopoiesis

A considerable amount of continuous proliferation and differentiation is required to produce daily a billion new neutrophils in an adult human. Of the few cytokines and factors known to control neutrophil production, G-CSF is the guardian of granulopoiesis. G-CSF/CSF3R signaling involves the recruitment of non-receptor protein tyrosine kinases and their dependent signaling pathways of serine/threonine kinases, tyrosine phosphatases, and lipid second messengers. These pathways converge to activate the families of STAT and C/EBP transcription factors. CSF3R mutations are associated with human disorders of neutrophil production, including severe congenital neutropenia, neutrophilia, and myeloid malignancies. More than three decades after their identification, cloning, and characterization of G-CSF and G-CSF receptor, fundamental questions remain about their physiology.

New insight into the mechanism of granulocyte colony-stimulating factor (G-CSF) that induces the mobilization of neutrophils

Over the past 20 years, granulocyte colony-stimulating factor (G-CSF) has driven the attention of researchers as a therapeutic agent for curing patients suffering from neutropenia. Despite the successful use of G-CSF, it currently requires daily injections, which are inconvenient, expensive, and distressing for children. Therefore, an alternative strategy for using G-CSF for treatment is needed. Understanding the G-CSF structure, expression, mechanism of action, and how it induces neutrophils mobilization is crucial to producing promising cancer therapy. The ability of G-CSF to mobilize hematopoietic stem cells from the bone marrow into the blood circulation was consequently exploited and altered the practice of hematopoietic stem cell transplantation. This is the motivation for the current review, which sheds light on the history of G-CSF and then focuses on the mechanism of action upon binding to its receptor (G-CSFR) and how that had led to the stimulation of neutrophils mobilization. The findings of this review show new insight into the mechanism of G-CSF that induces neutrophils mobilization. Thus, Understanding the G-CSF will provide a more effective treatment for all neutropenia patients.

IL-23 supports host defense against systemic Candida albicans infection by ensuring myeloid cell survival

The opportunistic fungal pathogen Candida albicans can cause invasive infections in susceptible hosts and the innate immune system, in particular myeloid cell-mediated immunity, is critical for rapid immune protection and host survival during systemic candidiasis. Using a mouse model of the human disease, we identified a novel role of IL-23 in antifungal defense. IL-23-deficient mice are highly susceptible to systemic infection with C. albicans. We found that this results from a drastic reduction in all subsets of myeloid cells in the infected kidney, which in turn leads to rapid fungal overgrowth and renal tissue injury. The loss in myeloid cells is not due to a defect in emergency myelopoiesis or the recruitment of newly generated cells to the site of infection but, rather, is a consequence of impaired survival of myeloid cells at the site of infection. In fact, the absence of a functional IL-23 pathway causes massive myeloid cell apoptosis upon C. albicans infection. Importantly, IL-23 protects myeloid cells from apoptosis independently of the IL-23-IL-17 immune axis and independently of lymphocytes and innate lymphoid cells. Instead, our results suggest that IL-23 acts in a partially autocrine but not cell-intrinsic manner within the myeloid compartment to promote host protection from systemic candidiasis. Collectively, our data highlight an unprecedented and non-canonical role of IL-23 in securing survival of myeloid cells, which is key for maintaining sufficient numbers of cells at the site of infection to ensure efficient host protection.

Linked to advances in medical technology and the resulting increase in the number of intensive care patients, nosocomial infections with Candida albicans are on the rise. In patients suffering from invasive candidiasis the innate immune response is typically severely impaired. Strengthening the innate immune system has become a promising approach complementing the use of antifungal drugs. Our findings identify an unexpected and IL-17-independent role of IL-23 that prevents rapid death of myeloid cells during systemic candidiasis and thereby promotes optimal protection from disease. As such, IL-23 represents an important new piece in the puzzle of the finely tuned network of cytokines that regulates the innate immune response to fungal infection. Our results contribute to a better understanding of myeloid cell regulation during infection and thereby open new perspectives for future immunotherapeutic applications that may improve patient outcome.

Sphingolipid-mediated inflammatory signaling leading to autophagy inhibition converts erythropoiesis to myelopoiesis in human hematopoietic stem/progenitor cells

Elevated levels of the pro-inflammatory cytokine tumor necrosis factor-α (TNFα) inhibit erythropoiesis and cause anemia in patients with cancer and chronic inflammatory diseases. TNFα is also a potent activator of the sphingomyelinase (SMase)/ceramide pathway leading to ceramide synthesis and regulating cell differentiation, proliferation, apoptosis, senescence, and autophagy. Here we evaluated the implication of the TNFα/SMase/ceramide pathway on inhibition of erythropoiesis in human CD34⁺ hematopoietic stem/progenitor cells (CD34/HSPCs) from healthy donors. Exogenous synthetic C2- and C6-ceramide as well as bacterial SMase inhibited erythroid differentiation in erythropoietin-induced (Epo)CD34/HSPCs shown by the analysis of various erythroid markers. The neutral SMase inhibitor GW4869 as well as the genetic inhibition of nSMase with small interfering RNA (siRNA) against sphingomyelin phosphodiesterase 3 (SMPD3) prevented the inhibition by TNFα, but not the acid SMase inhibitor desipramine. Moreover, sphingosine-1-phosphate (S1P), a ceramide metabolite, restored erythroid differentiation, whereas TNFα inhibited sphingosine kinase-1, required for S1P synthesis. Analysis of cell morphology and colony formation demonstrated that erythropoiesis impairment was concomitant with a granulomonocytic differentiation in TNFα- and ceramide-treated EpoCD34/HSPCs. Inhibition of erythropoiesis and induction of granulomonocytic differentiation were correlated to modulation of hematopoietic transcription factors (TFs) GATA-1, GATA-2, and PU.1. Moreover, the expression of microRNAs (miR)-144/451, miR-146a, miR-155, and miR-223 was also modulated by TNFα and ceramide treatments, in line with cellular observations. Autophagy plays an essential role during erythropoiesis and our results demonstrate that the TNFα/neutral SMase/ceramide pathway inhibits autophagy in EpoCD34/HSPCs. TNFα- and ceramide-induced phosphorylation of mTOR^S2448 and ULK1^S758, inhibited Atg13^S355 phosphorylation, and blocked autophagosome formation as shown by transmission electron microscopy and GFP-LC3 punctae formation. Moreover, rapamycin prevented the inhibitory effect of TNFα and ceramides on erythropoiesis while inhibiting induction of myelopoiesis. In contrast, bafilomycin A1, but not siRNA against Atg5, induced myeloid differentiation, while both impaired erythropoiesis. We demonstrate here that the TNFα/neutral SMase/ceramide pathway inhibits erythropoiesis to induce myelopoiesis via modulation of a hematopoietic TF/miR network and inhibition of late steps of autophagy. Altogether, our results reveal an essential role of autophagy in erythroid vs. myeloid differentiation.

Deficiency of PI3-Kinase catalytic isoforms p110γ and p110δ in mice enhances the IL-17/G-CSF axis and induces neutrophilia

Background

Phosphoinositide 3-kinase γ (PI3Kγ) and PI3Kδ are second messenger-generating enzymes with key roles in proliferation, differentiation, survival, and function of leukocytes. Deficiency of the catalytic subunits p110γ and p110δ of PI3Kγ and PI3Kδ in p110γ/δ^−/− mice leads to defective B- and T-cell homeostasis. Here we examined the role of p110γ and p110δ in the homeostasis of neutrophils by analyzing p110γ^−/−, p110δ^−/− and p110γ/δ^−/− mice.

Methods

Neutrophils and T cells in leukocyte suspensions from the bone marrow (BM), blood, spleen and lung were analyzed by flow cytometry. Serum concentrations of IL-17, of the neutrophilic growth factor G-CSF, and of the neutrophil mobilizing CXC chemokines CXCL1/KC and CXCL2/MIP-2 were measured by Bio-Plex assay. Production of G-CSF and CXCL1/KC by IL-17-stimulated primary lung tissue cells were determined by ELISA, whereas IL-17-dependent signaling in lung tissue cells was analyzed by measuring Akt phosphorylation using immunoblot.

Results

We found that in contrast to single knock-out mice, p110γ/δ^−/− mice exhibited significantly elevated neutrophil counts in blood, spleen, and lung. Increased granulocytic differentiation stages in the bone marrow of p110γ/δ^−/− mice were paralleled by increased serum concentrations of G-CSF, CXCL1/KC, and CXCL2/MIP-2. As IL-17 induces neutrophilia via the induction of G-CSF and CXC chemokines, we measured IL-17 and IL-17-producing T cells. IL-17 serum concentrations and frequencies of IL-17⁺ splenic T cells were significantly increased in p110γ/δ^−/− mice. Moreover, IFN-γ⁺, IL-4⁺, and IL-5⁺ T cell subsets were drastically increased in p110γ/δ^−/− mice, suggesting that IL-17⁺ T cells were up-regulated in the context of a general percentage increase of other cytokine producing T cell subsets.

Conclusions

We found that p110γ/δ deficiency in mice induces complex immunological changes, which might in concert contribute to neutrophilia. These findings emphasize a crucial but indirect role of both p110γ and p110δ in the regulation of neutrophil homeostasis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12964-017-0185-y) contains supplementary material, which is available to authorized users.

Pathogenesis of ELANE-mutant severe neutropenia revealed by induced pluripotent stem cells

Severe congenital neutropenia (SCN) is often associated with inherited heterozygous point mutations in ELANE, which encodes neutrophil elastase (NE). However, a lack of appropriate models to recapitulate SCN has substantially hampered the understanding of the genetic etiology and pathobiology of this disease. To this end, we generated both normal and SCN patient-derived induced pluripotent stem cells (iPSCs), and performed genome editing and differentiation protocols that recapitulate the major features of granulopoiesis. Pathogenesis of ELANE point mutations was the result of promyelocyte death and differentiation arrest, and was associated with NE mislocalization and activation of the unfolded protein response/ER stress (UPR/ER stress). Similarly, high-dose G-CSF (or downstream signaling through AKT/BCL2) rescues the dysgranulopoietic defect in SCN patient-derived iPSCs through C/EBPβ-dependent emergency granulopoiesis. In contrast, sivelestat, an NE-specific small-molecule inhibitor, corrected dysgranulopoiesis by restoring normal intracellular NE localization in primary granules; ameliorating UPR/ER stress; increasing expression of CEBPA, but not CEBPB; and promoting promyelocyte survival and differentiation. Together, these data suggest that SCN disease pathogenesis includes NE mislocalization, which in turn triggers dysfunctional survival signaling and UPR/ER stress. This paradigm has the potential to be clinically exploited to achieve therapeutic responses using lower doses of G-CSF combined with targeting to correct NE mislocalization.

Molecular control of PtdIns(3,4,5)P3 signaling in neutrophils

Neutrophils play critical roles in innate immunity and host defense. However, excessive neutrophil accumulation or hyper-responsiveness of neutrophils can be detrimental to the host system. Thus, the response of neutrophils to inflammatory stimuli needs to be tightly controlled. Many cellular processes in neutrophils are mediated by localized formation of an inositol phospholipid, phosphatidylinositol (3,4,5)-trisphosphate (PtdIns(3,4,5)P3), at the plasma membrane. The PtdIns(3,4,5)P3 signaling pathway is negatively regulated by lipid phosphatases and inositol phosphates, which consequently play a critical role in controlling neutrophil function and would be expected to act as ideal therapeutic targets for enhancing or suppressing innate immune responses. Here, we comprehensively review current understanding about the action of lipid phosphatases and inositol phosphates in the control of neutrophil function in infection and inflammation.

Cellular stress pathways in pediatric bone marrow failure syndromes: many roads lead to neutropenia

The inherited bone marrow failure syndromes, like severe congenital neutropenia (SCN) and Shwachman-Diamond syndrome (SDS), provide unique insights into normal and impaired myelopoiesis. The inherited neutropenias are heterogeneous in both clinical presentation and genetic associations, and their causative mechanisms are not well established. SCN, for example, is a genetically heterogeneous syndrome associated with mutations of ELANE, HAX1, GFI1, WAS, G6PC3, or CSF3R. The genetic diversity in SCN, along with congenital neutropenias associated with other genetically defined bone marrow failure syndromes (e.g., SDS), suggests that various pathways may be involved in their pathogenesis. Alternatively, all may lead to a final common pathway of enhanced apoptosis. The pursuit for a more complete understanding of the molecular mechanisms that drive inherited neutropenias remains at the forefront of pediatric translational and basic science investigation. Advances in our understanding of these disorders have greatly increased over the last 10 years concomitant with identification of their genetic lesions. Emerging themes include induction of the unfolded protein response (UPR), defective ribosome assembly, and p53-dependent apoptosis. Additionally, defects in metabolism, disruption of mitochondrial membrane potential, and mislocalization have been found. When perturbed, each of these lead to an intracellular stress that triggers apoptosis in the vulnerable granulocytic precursor.

Kinase AKT controls innate immune cell development and function

The critical roles of kinase AKT in tumour cell proliferation, apoptosis and protein synthesis have been widely recognized. But AKT also plays an important role in immune modulation. Recent studies have confirmed that kinase AKT can regulate the development and functions of innate immune cells (neutrophil, macrophage and dendritic cell). Studies have shown that different isoforms of kinase AKT have different effects in regulating immunity-related diseases, mainly through the mammalian target of rapamycin-dependent or -independent pathways. The purpose of this review is to illustrate the immune modulating effects of kinase AKT on innate immune cell development, survival and function.