Cytokine combinations for human blood stem cell expansion induce cell type- and cytokine-specific signaling dynamics

Signaling proteins in HSC fate determination are unequally segregated during asymmetric cell division

Hematopoietic stem cells (HSCs) continuously replenish mature blood cells with limited lifespans. To maintain the HSC compartment while ensuring output of differentiated cells, HSCs undergo asymmetric cell division (ACD), generating two daughter cells with different fates: one will proliferate and give rise to the differentiated cells' progeny, and one will return to quiescence to maintain the HSC compartment. A balance between MEK/ERK and mTORC1 pathways is needed to ensure HSC homeostasis. Here, we show that activation of these pathways is spatially segregated in premitotic HSCs and unequally inherited during ACD. A combination of genetic and chemical perturbations shows that an ERK-dependent mechanism determines the balance between pathways affecting polarity, proliferation, and metabolism, and thus determines the frequency of asymmetrically dividing HSCs. Our data identify druggable targets that modulate HSC fate determination at the level of asymmetric division.

Advances in hematopoietic stem cells ex vivo expansion associated with bone marrow niche

Hematopoietic stem cells (HSCs) are an ideal source for the treatment of many hematological diseases and malignancies, as well as diseases of other systems, because of their two important features, self-renewal and multipotential differentiation, which have the ability to rebuild the blood system and immune system of the body. However, so far, the insufficient number of available HSCs, whether from bone marrow (BM), mobilized peripheral blood or umbilical cord blood, is still the main restricting factor for the clinical application. Therefore, strategies to expand HSCs numbers and maintain HSCs functions through ex vivo culture are urgently required. In this review, we outline the basic biology characteristics of HSCs, and focus on the regulatory factors in BM niche affecting the functions of HSCs. Then, we introduce several representative strategies used for HSCs from these three sources ex vivo expansion associated with BM niche. These findings have deepened our understanding of the mechanisms by which HSCs balance self-renewal and differentiation and provided a theoretical basis for the efficient clinical HSCs expansion.

Against all odds: The road to success in the development of human immune reconstitution mice

The mouse genome has a high degree of homology with the human genome, and its physiological, biochemical, and developmental regulation mechanisms are similar to those of humans; therefore, mice are widely used as experimental animals. However, it is undeniable that interspecies differences between humans and mice can lead to experimental errors. The differences in the immune system have become an important factor limiting current immunological research. The application of immunodeficient mice provides a possible solution to these problems. By transplanting human immune cells or tissues, such as peripheral blood mononuclear cells or hematopoietic stem cells, into immunodeficient mice, a human immune system can be reconstituted in the mouse body, and the engrafted immune cells can elicit human-specific immune responses. Researchers have been actively exploring the development and differentiation conditions of host recipient animals and grafts in order to achieve better immune reconstitution. Through genetic engineering methods, immunodeficient mice can be further modified to provide a favorable developmental and differentiation microenvironment for the grafts. From initially only being able to reconstruct single T lymphocyte lineages, it is now possible to reconstruct lymphoid and myeloid cells, providing important research tools for immunology-related studies. In this review, we compare the differences in immune systems of humans and mice, describe the development history of human immune reconstitution from the perspectives of immunodeficient mice and grafts, and discuss the latest advances in enhancing the efficiency of human immune cell reconstitution, aiming to provide important references for immunological related researches.

A guide to ERK dynamics, part 2: downstream decoding

Signaling by the extracellular signal-regulated kinase (ERK) pathway controls many cellular processes, including cell division, death, and differentiation. In this second installment of a two-part review, we address the question of how the ERK pathway exerts distinct and context-specific effects on multiple processes. We discuss how the dynamics of ERK activity induce selective changes in gene expression programs, with insights from both experiments and computational models. With a focus on single-cell biosensor-based studies, we summarize four major functional modes for ERK signaling in tissues: adjusting the size of cell populations, gradient-based patterning, wave propagation of morphological changes, and diversification of cellular gene expression states. These modes of operation are disrupted in cancer and other related diseases and represent potential targets for therapeutic intervention. By understanding the dynamic mechanisms involved in ERK signaling, there is potential for pharmacological strategies that not only simply inhibit ERK, but also restore functional activity patterns and improve disease outcomes.

Stem cell heterogeneity, plasticity, and regulation

As a population of homogeneous cells with both self-renewal and differentiation potential, stem cell pools are highly compartmentalized and contain distinct subsets that exhibit stable but limited heterogeneity during homeostasis. However, their striking plasticity is showcased under natural or artificial stress, such as injury, transplantation, cancer, and aging, leading to changes in their phenotype, constitution, metabolism, and function. The complex and diverse network of cell-extrinsic niches and signaling pathways, together with cell-intrinsic genetic and epigenetic regulators, tightly regulate both the heterogeneity during homeostasis and the plasticity under perturbation. Manipulating these factors offers better control of stem cell behavior and a potential revolution in the current state of regenerative medicine. However, disruptions of normal regulation by genetic mutation or excessive plasticity acquisition may contribute to the formation of tumors. By harnessing innovative techniques that enhance our understanding of stem cell heterogeneity and employing novel approaches to maximize the utilization of stem cell plasticity, stem cell therapy holds immense promise for revolutionizing the future of medicine.

Isolation and culture of chicken bone marrow-derived CD34+ hematopoietic stem and progenitor cells and induced differentiation to myeloid cells

Hematopoietic stem and progenitor cell (HSPC) research will help elucidate the pathogenesis of hematologic diseases. The present study aimed to establish an isolation method and culture system for chicken bone marrow (BM)-derived HSPCs and test their proliferation and differentiation abilities. Mononuclear cells were collected from chicken BM, and CD34+ HSPCs were isolated. Then, the cells were cultured in media with different cytokine compositions, and the growth status, cell phenotype, and morphological appearance of the cells were analyzed at different time points. Our results showed that Iscove's Modified Dulbecco's Medium supplemented with 50 ng/mL stem cell factor, 30 ng/mL Flt-3 ligand, 10 μg/mL interleukin 3, 50 ng/mL interleukin 6%, and 10% chicken serum supported chicken CD34+ HSPC survival ex vivo for approximately 10 d. Further, 80 ng/mL granulocyte-colony stimulating factor and 30 ng/mL granulocyte macrophage-colony stimulating factor were added into the above culture system to form a myeloid cell differentiation induction culture system. After culturing in this system for 72 h, approximately 66% of chicken CD34+ HSPCs exhibited a CD11b+ phenotype, indicating that HSPCs differentiated into myeloid cells. In conclusion, chicken BM-derived CD34+ cells possess HSPC characteristics that can self-renew and differentiate into myeloid cells in a culture medium containing growth factors.

Optogenetic manipulation identifies the roles of ERK and AKT dynamics in controlling mouse embryonic stem cell exit from pluripotency

ERK and AKT signaling control pluripotent cell self-renewal versus differentiation. ERK pathway activity over time (i.e., dynamics) is heterogeneous between individual pluripotent cells, even in response to the same stimuli. To analyze potential functions of ERK and AKT dynamics in controlling mouse embryonic stem cell (ESC) fates, we developed ESC lines and experimental pipelines for the simultaneous long-term manipulation and quantification of ERK or AKT dynamics and cell fates. We show that ERK activity duration or amplitude or the type of ERK dynamics (e.g., transient, sustained, or oscillatory) alone does not influence exit from pluripotency, but the sum of activity over time does. Interestingly, cells retain memory of previous ERK pulses, with duration of memory retention dependent on duration of previous pulse length. FGF receptor/AKT dynamics counteract ERK-induced pluripotency exit. These findings improve our understanding of how cells integrate dynamics from multiple signaling pathways and translate them into cell fate cues.

Embryonic stem cell ERK, AKT, plus STAT3 response dynamics combinatorics are heterogeneous but NANOG state independent

Signaling is central in cell fate regulation, and relevant information is encoded in its activity over time (i.e., dynamics). However, simultaneous dynamics quantification of several pathways in single mammalian stem cells has not yet been accomplished. Here we generate mouse embryonic stem cell (ESC) lines simultaneously expressing fluorescent reporters for ERK, AKT, and STAT3 signaling activity, which all control pluripotency. We quantify their single-cell dynamics combinations in response to different self-renewal stimuli and find striking heterogeneity for all pathways, some dependent on cell cycle but not pluripotency states, even in ESC populations currently assumed to be highly homogeneous. Pathways are mostly independently regulated, but some context-dependent correlations exist. These quantifications reveal surprising single-cell heterogeneity in the important cell fate control layer of signaling dynamics combinations and raise fundamental questions about the role of signaling in (stem) cell fate control.

E3 ubiquitin ligase on the biological properties of hematopoietic stem cell

Hematopoietic stem cells are a group of heterogeneity cells with the potential to differentiate into various types of mature blood cells. Their basic biological properties include quiescence, self-renewal, multilineage differentiation, and homing ability, with the homing of exogenous hematopoietic stem cells after transplantation becoming a new focus, while the first three properties share some similarity in mechanism due to connectivity. In various complex mechanisms, the role of E3 ubiquitin ligases in hematopoietic homeostasis and malignant transformation is receiving increasing attention. As a unique part, E3 ubiquitin ligases play an important role in physiological regulation mechanism of posttranslational modification. In this review, we focus on the recent progress of the crucial role of E3 ubiquitin ligases that target specific proteins for ubiquitination to regulate biological properties of hematopoietic stem cells. Additionally, this paper deals with E3 ubiquitin ligases that affect the biological properties through aging and summarizes the relevant applications of targeting E3 ligases in hematopoietic malignancies. We present some ideas on the clinical application of E3 ubiquitin ligase to regulate hematopoietic stem cells and also believe that it is meaningful to study the upstream signal of these E3 ubiquitin ligases because hematopoietic stem cell dysfunction is caused by deficiency of some E3 ligases.

Understanding How Cells Probe the World: A Preliminary Step towards Modeling Cell Behavior?

Cell biologists have long aimed at quantitatively modeling cell function. Recently, the outstanding progress of high-throughput measurement methods and data processing tools has made this a realistic goal. The aim of this paper is twofold: First, to suggest that, while much progress has been done in modeling cell states and transitions, current accounts of environmental cues driving these transitions remain insufficient. There is a need to provide an integrated view of the biochemical, topographical and mechanical information processed by cells to take decisions. It might be rewarding in the near future to try to connect cell environmental cues to physiologically relevant outcomes rather than modeling relationships between these cues and internal signaling networks. The second aim of this paper is to review exogenous signals that are sensed by living cells and significantly influence fate decisions. Indeed, in addition to the composition of the surrounding medium, cells are highly sensitive to the properties of neighboring surfaces, including the spatial organization of anchored molecules and substrate mechanical and topographical properties. These properties should thus be included in models of cell behavior. It is also suggested that attempts at cell modeling could strongly benefit from two research lines: (i) trying to decipher the way cells encode the information they retrieve from environment analysis, and (ii) developing more standardized means of assessing the quality of proposed models, as was done in other research domains such as protein structure prediction.

Hematopoietic stem cells depend on HIM and HER

After a series of pioneering experiments on hematopoietic stem cell (HSC) function, including early evidence of heterogeneous stem cell behavior, Jim Till, Ernest McCulloch, and Lou Simminovitch put forward a stochastic model for stem cell proliferation. In contrast to the alternative model, called the "hemopoietic-inductive microenvironment" ("HIM") in which specific microenvironments drove specific and consistent outcomes, they coined the term "hemopoiesis engendered randomly" ("HER"), in which HSCs have intrinsic differences in the cellular state that introduce a probability of potential outcomes. The HIM (extrinsic) and HER (intrinsic) discussion continues nearly 60 years later, but the metaphor also has relevance beyond cellular decision making if one considers the infrastructure and systems supporting the actual scientists who make these advances-a different kind of HER and HIM, but no less important to sort out. This article concludes with some thoughts on how we might achieve a better balance between the HIMs and HERs undertaking the research as well.

Combining single-cell tracking and omics improves blood stem cell fate regulator identification

Molecular programs initiating cell fate divergence (CFD) are difficult to identify. Current approaches usually compare cells long after CFD initiation, therefore missing molecular changes at its start. Ideally, single cells that differ in their CFD molecular program but are otherwise identical are compared early in CFD. This is possible in diverging sister cells, which were identical until their mother's division and thus differ mainly in CFD properties. In asymmetrically dividing cells, divergent daughter fates are prospectively committed during division, and diverging sisters can thus be identified at the start of CFD. Using asymmetrically dividing blood stem cells, we developed a pipeline (ie, trackSeq) for imaging, tracking, isolating, and transcriptome sequencing of single cells. Their identities, kinship, and histories are maintained throughout, massively improving molecular noise filtering and candidate identification. In addition to many identified blood stem CFD regulators, we offer here this pipeline for use in CFDs other than asymmetric division.

Open-source personal pipetting robots with live-cell incubation and microscopy compatibility

Liquid handling robots have the potential to automate many procedures in life sciences. However, they are not in widespread use in academic settings, where funding, space and maintenance specialists are usually limiting. In addition, current robots require lengthy programming by specialists and are incompatible with most academic laboratories with constantly changing small-scale projects. Here, we present the Pipetting Helper Imaging Lid (PHIL), an inexpensive, small, open-source personal liquid handling robot. It is designed for inexperienced users, with self-production from cheap commercial and 3D-printable components and custom control software. PHIL successfully automates pipetting (incl. aspiration) for e.g. tissue immunostainings and stimulations of live stem and progenitor cells during time-lapse microscopy using 3D printed peristaltic pumps. PHIL is cheap enough to put a personal pipetting robot within the reach of most labs and enables users without programming skills to easily automate a large range of experiments.

NfκB signaling dynamics and their target genes differ between mouse blood cell types and induce distinct cell behavior

Cells can use signaling pathway activity over time (i.e., dynamics) to control cell fates. However, little is known about the potential existence and function of signaling dynamics in primary hematopoietic stem and progenitor cells (HSPCs). Here, we use time-lapse imaging and tracking of single murine HSPCs from GFP-p65/H2BmCherry reporter mice to quantify their nuclear factor κB (NfκB) activity dynamics in response to TNFα and IL1β. We find response dynamics to be heterogeneous between individual cells, with cell type specific dynamics distributions. Transcriptome sequencing of single cells physically isolated after live dynamics quantification shows activation of different target gene programs in cells with different dynamics. Finally, artificial induction of oscillatory NfκB activity causes changes in GMP behavior. Thus, HSPC behavior can be influenced by signaling dynamics, which are tightly regulated during hematopoietic differentiation and enable cell type specific responses to the same signaling inputs.

Fibroblast growth factor receptor 2 promotes the proliferation, migration, and invasion of ectopic stromal cells via activation of extracellular-signal-regulated kinase signaling pathway in endometriosis

Endometriosis is defined as the presence of endometrial tissues with cancer-like features in extrauterine locations. Fibroblast growth factor receptor 2 (FGFR2) is a tyrosine kinase that is involved in cancer pathogenesis. This study aimed to determine the role of FGFR2 in endometriosis. A total of 29 pairs of ectopic and eutopic endometrial tissues were collected from women with endometriosis. Endometrial tissues from women with hysteromyomas were considered as normal controls. Primary ectopic stromal cells (ESCs) were isolated from the ectopic endometrium. The role of FGFR2 in ESCs was assessed using immunohistochemistry, polymerase chain reaction, cell counting kit-8 assay, EdU staining, flow cytometry, transwell assay, and western blotting. The following signaling pathways were detected using bioinformatic analysis and confirmed in vitro. By searching the GSE171154, GSE86543, and GSE77182 datasets, FGFR2 was identified as an upregulated overlapping gene in endometriosis. Compared to eutopic and normal endometria, FGFR2 was highly expressed in ectopic tissues. Transfection of primary ESCs with FGFR2 small interfering RNA (siRNA) repressed the viability and proliferation of cells and induced apoptosis. FGFR2 siRNA inhibited the migration, invasion, and transforming growth factor-β1-triggered epithelial-mesenchymal transition (EMT). Extracellular signal-regulated kinase (ERK) signaling was found to be a downstream signaling pathway for FGFR2. The ERK1/2 inhibitor PD98059 was found to reverse the promoting effects of FGFR2 on ESC proliferation and invasion. FGFR2 silencing effectively inhibited the growth, migration, invasion, and EMT of ESCs. The effects of FGFR2 on endometriosis might be mediated via the activation of ERK signaling.

Protocol to maintain single functional mouse hematopoietic stem cells in vitro without cell division

This protocol details the isolation and in vitro maintenance of single hematopoietic stem cells (HSCs) in the absence of the bone marrow niche. The HSCs do not divide over 7 days and fully retain their long-term functional capacity in transplantation assays. Following hibernation culture, HSCs can be used to study quiescence exit and can be genetically manipulated as single cells prior to division.

For complete details on the use and execution of this protocol, please refer to Oedekoven et al. (2021).

•

In vitro maintenance of single HSCs in the absence of a hematopoietic niche

•

In vitro system to study quiescence exit in single HSCs

•

Ability to manipulate HSCs via gene modification at the single-cell level

Analyzing signaling activity and function in hematopoietic cells

Cells constantly sense their environment, allowing the adaption of cell behavior to changing needs. Fine-tuned responses to complex inputs are computed by signaling pathways, which are wired in complex connected networks. Their activity is highly context-dependent, dynamic, and heterogeneous even between closely related individual cells. Despite lots of progress, our understanding of the precise implementation, relevance, and possible manipulation of cellular signaling in health and disease therefore remains limited. Here, we discuss the requirements, potential, and limitations of the different current technologies for the analysis of hematopoietic stem and progenitor cell signaling and its effect on cell fates.