Unexpected role of inflammatory signaling in hematopoietic stem cell development: its role beyond inflammation

DLL4 and VCAM1 enhance the emergence of T cell-competent hematopoietic progenitors from human pluripotent stem cells

T cells show tremendous efficacy as cellular therapeutics. However, obtaining primary T cells from human donors is expensive and variable. Pluripotent stem cells (PSCs) have the potential to provide a renewable source of T cells, but differentiating PSCs into hematopoietic progenitors with T cell potential remains an important challenge. Here, we report an efficient serum- and feeder-free system for differentiating human PSCs into hematopoietic progenitors and T cells. This fully defined approach allowed us to study the impact of individual proteins on blood emergence and differentiation. Providing DLL4 and VCAM1 during the endothelial-to-hematopoietic transition enhanced downstream progenitor T cell output by ~80-fold. These two proteins synergized to activate notch signaling in nascent hematopoietic stem and progenitor cells, and VCAM1 additionally promoted an inflammatory transcriptional program. We also established optimized medium formulations that enabled efficient and chemically defined maturation of functional CD8αβ+, CD4-, CD3+, TCRαβ+ T cells with a diverse TCR repertoire.

UM171 induces a homeostatic inflammatory-detoxification response supporting human HSC self-renewal

Elucidation of the molecular cues required to balance adult stem cell self-renewal and differentiation is critical for advancing cellular therapies. Herein, we report that the hematopoietic stem cell (HSC) self-renewal agonist UM171 triggers a balanced pro- and anti-inflammatory/detoxification network that relies on NFKB activation and protein C receptor-dependent ROS detoxification, respectively. We demonstrate that within this network, EPCR serves as a critical protective component as its deletion hypersensitizes primitive hematopoietic cells to pro-inflammatory signals and ROS accumulation resulting in compromised stem cell function. Conversely, abrogation of the pro-inflammatory activity of UM171 through treatment with dexamethasone, cAMP elevating agents or NFkB inhibitors abolishes EPCR upregulation and HSC expansion. Together, these results show that UM171 stimulates ex vivo HSC expansion by establishing a critical balance between key pro- and anti-inflammatory mediators of self-renewal.

Mobilized Peripheral Blood versus Cord Blood: Insight into the Distinct Role of Proinflammatory Cytokines on Survival, Clonogenic Ability, and Migration of CD34+ Cells

Inflammation may play a role in cancer. However, the contribution of cytokine-mediated crosstalk between normal hemopoietic stem/progenitor cells (HSPCs) and their (inflammatory) microenvironment is largely elusive. Here we compared survival, phenotype, and function of neonatal (umbilical cord blood (CB)) and adult (normal G-CSF-mobilized peripheral blood (mPB)) CD34⁺ cells after in vitro exposure to combined crucial inflammatory factors such as interleukin- (IL-) 1β, IL-6, tumor necrosis factor- (TNF-) α, or tissue inhibitor of metalloproteinases-1 (TIMP-1). To mimic bone marrow (BM) niche, coculture experiments with normal BM stromal cells (BMSCs) were also performed. We found that combined inflammatory cytokines increased only the in vitro survival of CB-derived CD34⁺ cells by reducing apoptosis. Conversely, selected combinations of inflammatory cytokines (IL-1β + TNF-α, IL-6 + TNF-α, and IL-1β + TNF-α + TIMP-1) mainly enhanced the in vitro CXCR4-driven migration of mPB-derived CD34⁺ cells. TNF-α, alone or in combination, upregulated CD44 and CD13 expression in both sources. Finally, BMSCs alone increased survival/migration of CB- and mPB-derived CD34⁺ cells at the same extent of the combined inflammatory cytokines; importantly, their copresence did not show additive/synergistic effect. Taken together, these data indicate that combined proinflammatory stimuli promote distinct in vitro functional activation of neonatal or adult normal HSPCs.

Hematopoietic Hierarchy - An Updated Roadmap

The classical roadmap of hematopoietic hierarchy has been proposed for nearly 20 years and has become a dogma of stem cell research for most types of adult stem cells, including hematopoietic stem cells (HSCs). However, with the development of new technologies such as omics approaches at single-cell resolution, recent studies in vitro and in vivo have suggested that heterogeneity is a common feature of HSCs and their progenies. While these findings broaden our understanding of hematopoiesis, they also challenge the well-accepted hematopoietic hierarchy roadmap. Here, we review recent advances in the hematopoiesis field and provide an updated view to incorporate these new findings as well as to reflect on the complexity of HSCs and their derivatives in development and adulthood.

Myelodysplastic syndrome patients present more severe respiratory muscle impairment and reduced forced vital capacity: Is disordered inflammatory signaling the culprit?

BACKGROUND/OBJECTIVES

The ageing process is associated with gradual decline in respiratory system performance. Anemia is highly prevalent among older adults and usually associated with adverse outcomes. Myelodysplastic syndromes (MDS) are a heterogeneous group of hematologic malignancies with increasing incidence with age and characterized by anemia and other cytopenias. The main objectives of this study were to evaluate respiratory muscle strength and lung function in elderly patients with anemia, compare data between myelodysplastic syndromes and non-clonal anemias and evaluate the influence of serum IL-8 level and NF-kB activity on deteriorate pulmonary function in this specific population.

PARTICIPANTS

Individuals aged 60 and older with anemia secondary to MDS, non-clonal anemia and healthy elderly individuals.

MEASUREMENTS

Forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), and FEV1/ FVC ratio were measured by spirometry. Respiratory muscle strength was evaluated by maximal static respiratory pressures measurement. IL-8 analysis was performed by ELISA and activity of NF-kB by chemiluminescent assay.

RESULTS

Mean Hb concentration was comparable between patients with anemia. Significant differences were detected between all patients with anemia and controls for maximum-effort inspiratory mouth pressure (PImax) and also for maximum-effort expiratory mouth pressure (PEmax). The MDS group recorded a significantly lower PImax and PEmax percent predicted when compared to non-clonal anemia group. For FVC and FEV1, a significant difference was found in anemic patients, with even significantly lower values for FVC and FEV1 in MDS group. No significant differences were detected for PImax and PEmax and spirometry parameters when anemic patients were stratified according to the degree of anemia. A significant negative impact in FVC (% pred), PImax (% pred) and PEmax (% pred) was observed in patients with MDS and higher levels of IL-8 or increased activity of NF-kB.

CONCLUSION

A negative impact of anemia, independent of its degree, was demonstrated in respiratory muscle strength and lung function particularly in MDS. The well known elevated proinflammatory cytokines in MDS patients were proposed to play a role as was demonstrated by detrimental effect of higher IL-8 and NF-kB in pulmonary function tests in this population.

Inflammation: a key regulator of hematopoietic stem cell fate in health and disease

Hematopoietic stem cells (HSCs) are responsible for lifelong production of blood cells. At the same time, they must respond rapidly to acute needs such as infection or injury. Significant interest has emerged in how inflammation regulates HSC fate and how it affects the long-term functionality of HSCs and the blood system as a whole. Here we detail recent advances and unanswered questions at the intersection between inflammation and HSC biology in the contexts of development, aging, and hematological malignancy.

Proinflammatory Signals as Fuel for the Fire of Hematopoietic Stem Cell Emergence

Hematopoietic stem cells (HSCs) have the extraordinary ability to both self-renew and generate all mature blood cell lineages. The ability to produce or expand patient-derived HSCs in vitro would greatly improve the outcome for patients with blood disorders that are currently treated with allogeneic HSC transplantation. Many laboratories have been working to identify the signals required for HSC emergence in their native environments to apply this knowledge in vitro. Recently, several signals traditionally known to underlie classical inflammation have emerged as essential regulators of HSC development. In this review we synthesize the findings that have established inflammatory cues as key regulators of HSC development.

Interleukin-8 and nuclear factor kappa B are increased and positively correlated in myelodysplastic syndrome

The pathogenesis of myelodysplastic syndromes (MDS) is complex and depends on the interaction between aberrant hematopoietic cells and their microenvironment, probably including aberrations in cytokines and their signaling pathways. To evaluate interleukin-8 (IL-8) plasma levels and nuclear factor kappa B (NF-kB) in patients with MDS and to test possible correlation between IL-8 and NF-Kb, a total of 45 individuals were analyzed: 25 consecutive adult de novo MDS patients and 20 sex and age-matched healthy elderly volunteers. IL-8 analysis was performed by ELISA and activity of NF-kB by chemiluminescent assay. MDS patients showed higher level of IL-8 when compared to controls (p = 0.006). Patients aged 75 and above showed even higher levels (p = 0.035). NF-kB activity was significantly elevated in MDS patients when compared to controls (p < 0.0001) and higher in patients older than 75 years (p = 0.047). NF-kB activity was associated with higher serum ferritin (p = 0.042) and higher percentage of blasts (p = 0.028). A significant positive correlation between IL-8 and NF-kB was demonstrated (r = 0.480; p = 0.015). Many pathways involved in pathophysiology of MDS have been recently described, suggesting that an inflammatory process may act as a pathogenic driver. In this study, significantly elevated levels of IL-8 and NF-kB were demonstrated in MDS patients, with positive association of NF-kB with some markers of poor prognosis. A positive correlation between IL-8 and NF-kB suggests they cooperate as part of a complex networking of immune and inflammatory factors involved in MDS.

Stress and Non-Stress Roles of Inflammatory Signals during HSC Emergence and Maintenance

Hematopoietic stem cells (HSCs) are a rare population that gives rise to almost all cells of the hematopoietic system, including immune cells. Until recently, it was thought that immune cells sense inflammatory signaling and HSCs respond only secondarily to these signals. However, it was later shown that adult HSCs could directly sense and respond to inflammatory signals, resulting in a higher output of immune cells. Recent studies demonstrated that inflammatory signaling is also vital for HSC ontogeny. These signals are thought to arise in the absence of pathogens, are active during development, and indispensable for HSC formation. In contrast, during times of stress and disease, inflammatory responses can be activated and can have devastating effects on HSCs. In this review, we summarize the current knowledge about inflammatory signaling in HSC development and maintenance, as well as the endogenous molecular cues that can trigger inflammatory pathway activation. Finally, we comment of the role of inflammatory signaling in hematopoietic diseases.