Microarrayed human bone marrow organoids for modeling blood stem cell dynamics

In many leukemia patients, a poor prognosis is attributed either to the development of chemotherapy resistance by leukemic stem cells (LSCs) or to the inefficient engraftment of transplanted hematopoietic stem/progenitor cells (HSPCs) into the bone marrow (BM). Here, we build a 3D in vitro model system of bone marrow organoids (BMOs) that recapitulate several structural and cellular components of native BM. These organoids are formed in a high-throughput manner from the aggregation of endothelial and mesenchymal cells within hydrogel microwells. Accordingly, the mesenchymal compartment shows partial maintenance of its self-renewal and multilineage potential, while endothelial cells self-organize into an interconnected vessel-like network. Intriguingly, such an endothelial compartment enhances the recruitment of HSPCs in a chemokine ligand/receptor-dependent manner, reminiscent of HSPC homing behavior in vivo. Additionally, we also model LSC migration and nesting in BMOs, thus highlighting the potential of this system as a well accessible and scalable preclinical model for candidate drug screening and patient-specific assays.

Gastruloids as in vitro models of embryonic blood development with spatial and temporal resolution

Gastruloids are three-dimensional embryonic organoids that reproduce key features of early mammalian development in vitro with unique scalability, accessibility, and spatiotemporal similarity to real embryos. Recently, we adapted the gastruloid culture conditions to promote cardiovascular development. In this work, we extended these conditions to capture features of embryonic blood development through a combination of immunophenotyping, detailed transcriptomics analysis, and identification of blood stem/progenitor cell potency. We uncovered the emergence of blood progenitor and erythroid-like cell populations in late gastruloids and showed the multipotent clonogenic capacity of these cells, both in vitro and after transplantation into irradiated mice. We also identified the spatial localization near a vessel-like plexus in the anterior portion of gastruloids with similarities to the emergence of blood stem cells in the mouse embryo. These results highlight the potential and applicability of gastruloids to the in vitro study of complex processes in embryonic blood development with spatiotemporal fidelity.

A Single Metabolite which Modulates Lipid Metabolism Alters Hematopoietic Stem/Progenitor Cell Behavior and Promotes Lymphoid Reconstitution

Fatty acid β-oxidation (FAO), the breakdown of lipids, is a metabolic pathway used by various stem cells. FAO levels are generally high during quiescence and downregulated with proliferation. The endogenous metabolite malonyl-CoA modulates lipid metabolism as a reversible FAO inhibitor and as a substrate for de novo lipogenesis. Here we assessed whether malonyl-CoA can be exploited to steer the behavior of hematopoietic stem/progenitor cells (HSPCs), quiescent stem cells of clinical relevance. Treatment of mouse HSPCs in vitro with malonyl-CoA increases HSPC numbers compared with nontreated controls and ameliorates blood reconstitution capacity when transplanted in vivo, mainly through enhanced lymphoid reconstitution. Similarly, human HSPC numbers also increase upon malonyl-CoA treatment in vitro. These data corroborate that lipid metabolism can be targeted to direct cell fate and stem cell proliferation. Physiological modulation of metabolic pathways, rather than genetic or pharmacological inhibition, provides unique perspectives for stem cell manipulations in health and disease.

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Modulating lipid metabolism with malonyl-CoA increases murine HSPCs in vitro

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Malonyl-CoA promotes lymphoid cell fate of HSPCs in vitro and in vivo

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The myeloid bias in aged HSPCs is partially recovered with malonyl-CoA exposure

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Malonyl-CoA increases the numbers of human HSPCs in vitro

The NAD-Booster Nicotinamide Riboside Potently Stimulates Hematopoiesis through Increased Mitochondrial Clearance

It has been recently shown that increased oxidative phosphorylation, as reflected by increased mitochondrial activity, together with impairment of the mitochondrial stress response, can severely compromise hematopoietic stem cell (HSC) regeneration. Here we show that the NAD⁺-boosting agent nicotinamide riboside (NR) reduces mitochondrial activity within HSCs through increased mitochondrial clearance, leading to increased asymmetric HSC divisions. NR dietary supplementation results in a significantly enlarged pool of progenitors, without concurrent HSC exhaustion, improves survival by 80%, and accelerates blood recovery after murine lethal irradiation and limiting-HSC transplantation. In immune-deficient mice, NR increased the production of human leucocytes from hCD34+ progenitors. Our work demonstrates for the first time a positive effect of NAD⁺-boosting strategies on the most primitive blood stem cells, establishing a link between HSC mitochondrial stress, mitophagy, and stem-cell fate decision, and unveiling the potential of NR to improve recovery of patients suffering from hematological failure including post chemo- and radiotherapy.

Yin Yang 1 sustains biosynthetic demands during brain development in a stage-specific manner

The transcription factor Yin Yang 1 (YY1) plays an important role in human disease. It is often overexpressed in cancers and mutations can lead to a congenital haploinsufficiency syndrome characterized by craniofacial dysmorphisms and neurological dysfunctions, consistent with a role in brain development. Here, we show that Yy1 controls murine cerebral cortex development in a stage-dependent manner. By regulating a wide range of metabolic pathways and protein translation, Yy1 maintains proliferation and survival of neural progenitor cells (NPCs) at early stages of brain development. Despite its constitutive expression, however, the dependence on Yy1 declines over the course of corticogenesis. This is associated with decreasing importance of processes controlled by Yy1 during development, as reflected by diminished protein synthesis rates at later developmental stages. Thus, our study unravels a novel role for Yy1 as a stage-dependent regulator of brain development and shows that biosynthetic demands of NPCs dynamically change throughout development.

The transcription factor Yin Yang 1 (YY1) plays an important role in human disease, yet little is known about its role in brain development. This study shows that YY1 controls cerebral cortex development by maintaining proliferation and survival of neural progenitor cells via transcriptional regulation of genes involved in metabolism and protein translation.

Single-cell analyses identify bioengineered niches for enhanced maintenance of hematopoietic stem cells

The in vitro expansion of long-term hematopoietic stem cells (HSCs) remains a substantial challenge, largely because of our limited understanding of the mechanisms that control HSC fate choices. Using single-cell multigene expression analysis and time-lapse microscopy, here we define gene expression signatures and cell cycle hallmarks of murine HSCs and the earliest multipotent progenitors (MPPs), and analyze systematically single HSC fate choices in culture. Our analysis revealed twelve differentially expressed genes marking the quiescent HSC state, including four genes encoding cell–cell interaction signals in the niche. Under basal culture conditions, most HSCs rapidly commit to become early MPPs. In contrast, when we present ligands of the identified niche components such as JamC or Esam within artificial niches, HSC cycling is reduced and long-term multipotency in vivo is maintained. Our approach to bioengineer artificial niches should be useful in other stem cell systems.

Haematopoietic stem cell (HSC) self-renewal is not sufficiently understood to recapitulate in vitro. Here, the authors generate gene signature and cell cycle hallmarks of single murine HSCs, and use identified endothelial receptors Esam and JamC as substrates to enhance HSC growth in engineered niches.

Designer matrices for intestinal stem cell and organoid culture

Epithelial organoids recapitulate multiple aspects of real organs, making them promising models of organ development, function and disease. However, the full potential of organoids in research and therapy has remained unrealized, owing to the poorly defined animal-derived matrices in which they are grown. Here we used modular synthetic hydrogel networks to define the key extracellular matrix (ECM) parameters that govern intestinal stem cell (ISC) expansion and organoid formation, and show that separate stages of the process require different mechanical environments and ECM components. In particular, fibronectin-based adhesion was sufficient for ISC survival and proliferation. High matrix stiffness significantly enhanced ISC expansion through a yes-associated protein 1 (YAP)-dependent mechanism. ISC differentiation and organoid formation, on the other hand, required a soft matrix and laminin-based adhesion. We used these insights to build a fully defined culture system for the expansion of mouse and human ISCs. We also produced mechanically dynamic matrices that were initially optimal for ISC expansion and subsequently permissive to differentiation and intestinal organoid formation, thus creating well-defined alternatives to animal-derived matrices for the culture of mouse and human stem-cell-derived organoids. Our approach overcomes multiple limitations of current organoid cultures and greatly expands their applicability in basic and clinical research. The principles presented here can be extended to identify designer matrices that are optimal for long-term culture of other types of stem cells and organoids.

Associative effects between two fibre sources on ileal and overall digestibilities of amino acids, energy and cell-wall components in growing pigs

1. The associative effects of two fibre sources on ileal and overall digestibility of amino acids, energy and cell-wall components were studied by comparing wheat bran and soya-bean hulls in semi-purified diets given to growing pigs. 2. Castrated male pigs were prepared with ileo-rectal anastomosis to measure ileal digestibility, and overall digestibility was measured in pigs without anastomosis. 3. The three diets contained 190 g total fibre/kg dry matter (DM), derived from each fibre source or from a mixture of both fibre sources, so that each source provided half the amount of total fibre, and 170 g crude protein (nitrogen x 6.25)/kg DM by additions of casein. 4. The effects of fibre sources on the ileal digestibility of amino acids were additive for most amino acids; the only significant interactions were found for threonine, methionine and aspartic acid. In contrast with ileal digestibility, systematic negative interactions between fibre sources on overall digestibility of amino acids were noted. 5. There was no interaction between fibre sources in their effects on the digestibility of energy or of cell-wall components, irrespective of the site of digestion. The digestibility values were higher with soya-bean hulls than with wheat bran, especially at the faecal level. 6. It is concluded that ileal digestibility of amino acids provides a better estimate of amino acid availability, as ileal measurements allow a better discrimination between diets than faecal measurements when distinct fibre sources are used alone or in combination at the same total fibre content. In contrast, for energy, the measurement of digestibility at both faecal and ileal levels permits the estimation of the partition of available nutrients between the small and large intestines.