Wound healing is a coordinated process that initially relies on pro-inflammatory macrophages, followed by a pro-resolution function of these cells. Changes in cellular metabolism likely dictate these ...distinct activities, but the nature of these changes has been unclear. Here, we profiled early- versus late-stage skin wound macrophages in mice at both the transcriptional and functional levels. We found that glycolytic metabolism in the early phase is not sufficient to ensure productive repair. Instead, by combining conditional disruption of the electron transport chain with deletion of mitochondrial aspartyl-tRNA synthetase, followed by single-cell sequencing analysis, we found that a subpopulation of early-stage wound macrophages are marked by mitochondrial ROS (mtROS) production and HIF1α stabilization, which ultimately drives a pro-angiogenic program essential for timely healing. In contrast, late-phase, pro-resolving wound macrophages are marked by IL-4Rα-mediated mitochondrial respiration and mitohormesis. Collectively, we identify changes in mitochondrial metabolism as a critical control mechanism for macrophage effector functions during wound healing.
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•Early-stage, inflammatory versus late-stage, pro-resolving wound macrophages are profiled•Pro-inflammatory wound macrophages are marked by mtROS production and HIF1α stabilization•This molecular process is required for proper vascularization during wound repair•Pro-resolving macrophages are marked by mitochondrial respiration and mitohormesis
How mitochondrial metabolism contributes to the early-stage, pro-inflammatory versus late-stage, pro-resolution functions of macrophages during wound healing requires further investigation. Here, Willenborg et al. show that effective wound healing requires the production of mtROS in early-stage wound macrophages to promote proper vascularization, while late-stage wound macrophages are dependent on OXPHOS and mitohormesis.
Mast cells (MCs) are tissue-resident hematopoietic cells intensely studied for their role as effectors in allergic immune responses. Yolk sac–derived embryonic MCs first populate tissues and are ...later replaced by definitive MCs. We show that definitive MC progenitors expand locally in skin and form clonal colonies that cover stable territories. In MC-deficient skin, colonies grow by proliferation of MCs at the border of the clonal territory. Clonal growth ceases at common borders of neighboring colonies. In steady state, colony self-renewal is independent of bone marrow contribution, and the clonal architecture remains fixed if not disturbed by skin inflammation. Inflammatory cues increase MC density setpoint, stimulating the influx of new progenitors from the bone marrow as well as proliferation of skin-resident cells. The expanding new arrivals disrespect territories of preexisting MC clones. We conclude that during a limited window early in development, definitive MC precursors efficiently enter the skin, expand, and self-maintain, occupying stable territories. In adulthood, circulating progenitors, excluded from steady-state skin, are recruited only into inflamed skin where they clonally expand alongside proliferating skin-resident MCs, disorganizing the original architecture of clonal territories.
Hematopoietic stem cells (HSCs) are the ultimate source of blood and immune cells and transplantation reveals their unique potential to regenerate all blood lineages lifelong. HSCs are considered a ...quiescent reserve population under homeostatic conditions, which can be rapidly activated by perturbations to fuel blood regeneration. In accordance with this concept, inflammation and loss of blood cells were reported to stimulate proliferation of HSCs, which is associated with a decline in their transplantation potential. To investigate the contribution of primitive HSC to the hematopoietic stress response in the native environment, we use Fgd5-driven fate mapping and H2B-GFP proliferation tracking mouse models. While primitive HSCs were robustly activated by severe myeloablation, they did not contribute to the regeneration of mature blood cells in response to prototypic hematopoietic emergencies such as acute inflammation or blood loss. Even chronic inflammatory stimulation, which triggered vigorous HSC proliferation, only resulted in weak contribution of HSCs to mature blood cell production. Thus, our data demonstrates that primitive HSCs do not participate in the hematopoietic recovery from common perturbations and calls for the re-evaluation of the concept of HSC-driven stress responses.
Long-term repopulating (LT) hematopoietic stem cells (HSCs) are the most undifferentiated cells at the top of the hematopoietic hierarchy. The regulation of HSC pool size and its contribution to ...hematopoiesis are incompletely understood. We depleted hematopoietic stem and progenitor cells (HSPCs) in adult mice in situ and found that LT-HSCs recovered from initially very low levels (<1%) to below 10% of normal numbers but not more, whereas progenitor cells substantially recovered shortly after depletion. In spite of the persistent and massive reduction of LT-HSCs, steady-state hematopoiesis was unaffected and residual HSCs remained quiescent. Hematopoietic stress, although reported to recruit quiescent HSCs into cycle, was well tolerated by HSPC-depleted mice and did not induce expansion of the small LT-HSC compartment. Only upon 5-fluorouracil treatment was HSPC-depleted bone marrow compromised in reconstituting hematopoiesis, demonstrating that HSCs and early progenitors are crucial to compensate myeloablation. Hence, a contracted HSC compartment cannot recover in situ to its original size, and normal steady-state blood cell generation is sustained with <10% of normal LT-HSC numbers without increased contribution of the few residual cells.
•After induced HSPC depletion, HSC numbers remain at low levels whereas progenitors show robust recovery.•Despite low HSC numbers, hematopoiesis proceeds normally without increased proliferation of the few residual HSCs.
Hematopoietic stem cells (HSCs) continuously replenish all blood cell types through a series of differentiation steps and repeated cell divisions that involve the generation of lineage-committed ...progenitors. However, whether cell division in HSCs precedes differentiation is unclear. To this end, we used an HSC cell-tracing approach and Ki67
knock-in mice, in a non-conditioned transplantation model, to assess divisional history, cell cycle progression, and differentiation of adult HSCs. Our results reveal that HSCs are able to differentiate into restricted progenitors, especially common myeloid, megakaryocyte-erythroid and pre-megakaryocyte progenitors, without undergoing cell division and even before entering the S phase of the cell cycle. Additionally, the phenotype of the undivided but differentiated progenitors correlated with the expression of lineage-specific genes and loss of multipotency. Thus HSC fate decisions can be uncoupled from physical cell division. These results facilitate a better understanding of the mechanisms that control fate decisions in hematopoietic cells.
The prevailing view on murine hematopoiesis and on hematopoietic stem cells (HSCs) in particular derives from experiments that are related to regeneration after irradiation and HSC transplantation. ...However, over the past years, different experimental techniques have been developed to investigate hematopoiesis under homeostatic conditions, thereby providing access to proliferation and differentiation rates of hematopoietic stem and progenitor cells in the unperturbed situation. Moreover, it has become clear that hematopoiesis undergoes distinct changes during aging with large effects on HSC abundance, lineage contribution, asymmetry of division, and self‐renewal potential. However, it is currently not fully resolved how stem and progenitor cells interact to respond to varying demands and how this balance is altered by an aging‐induced shift in HSC polarity. Aiming toward a conceptual understanding, we introduce a novel in silico model to investigate the dynamics of HSC response to varying demand. By introducing an internal feedback within a heterogeneous HSC population, the model is suited to consistently describe both hematopoietic homeostasis and regeneration, including the limited regulation of HSCs in the homeostatic situation. The model further explains the age‐dependent increase in phenotypic HSCs as a consequence of the cells' inability to preserve divisional asymmetry. Our model suggests a dynamically regulated population of intrinsically asymmetrically dividing HSCs as suitable control mechanism that adheres with many qualitative and quantitative findings on hematopoietic recovery after stress and aging. The modeling approach thereby illustrates how a mathematical formalism can support both the conceptual and the quantitative understanding of regulatory principles in HSC biology.
We present a simple mathematical model for the regulation of populations of murine hematopoietic stem cells (consisting of repopulating hematopoietic stem cells and maintaining hematopoietic stem cells) and progenitors. By assuming that repopulating hematopoietic stem cell proliferation is driven by downstream demand and by incorporating the ability of repopulating hematopoietic stem cells to divide asymmetrically, we are able to explain the observed aging‐related increase in repopulating hematopoietic stem cell numbers due to a decline in their capability to divide asymmetrically as well as recent experimental findings on specific depletion of hematopoietic stem and progenitor cells and their recovery. We further investigate the system reaction, if similar experiments are conducted in old mice.
Abstract
Hematopoietic stem cells (HSCs) produce highly diverse cell lineages. Here, we chart native lineage pathways emanating from HSCs and define their physiological regulation by computationally ...integrating experimental approaches for fate mapping, mitotic tracking, and single-cell RNA sequencing. We find that lineages begin to split when cells leave the tip HSC population, marked by high Sca-1 and CD201 expression. Downstream, HSCs either retain high Sca-1 expression and the ability to generate lymphocytes, or irreversibly reduce Sca-1 level and enter into erythro-myelopoiesis or thrombopoiesis. Thrombopoiesis is the sum of two pathways that make comparable contributions in steady state, a long route via multipotent progenitors and CD48
hi
megakaryocyte progenitors (MkPs), and a short route from HSCs to developmentally distinct CD48
−/lo
MkPs. Enhanced thrombopoietin signaling differentially accelerates the short pathway, enabling a rapid response to increasing demand. In sum, we provide a blueprint for mapping physiological differentiation fluxes from HSCs and decipher two functionally distinct pathways of native thrombopoiesis.
Biallelic mutations of three prime repair exonuclease 1 (TREX1) cause the lupus-like disease Aicardi-Goutières syndrome in which accumulation of a yet unknown endogenous DNA substrate of TREX1 ...triggers a cyclic GMP-AMP synthase-dependent type I IFN response and systemic autoimmunity. Products of reverse transcription originating from endogenous retroelements have been suggested to be a major substrate for TREX1, and reverse transcriptase inhibitors (RTIs) were proposed as a therapeutic option in autoimmunity ensuing from defects of TREX1. In this study, we treated
mice with RTIs. The serum RTI levels reached were sufficient to block retrotransposition of endogenous retroelements. However, the treatment did not reduce the spontaneous type I IFN response and did not ameliorate lethal inflammation. Furthermore, long interspersed nuclear elements 1 retrotransposition was not enhanced in the absence of Trex1. Our data do not support the concept of retroelement-derived cDNA as key triggers of systemic autoimmunity in Trex1-deficient humans and mice and motivate the continuing search for the pathogenic IFN-inducing Trex1 substrate.
A subpopulation of deeply quiescent, so-called dormant hematopoietic stem cells (dHSCs) resides at the top of the hematopoietic hierarchy and serves as a reserve pool for HSCs. The state of dormancy ...protects the HSC pool from exhaustion throughout life; however, excessive dormancy may prevent an efficient response to hematological stresses. Despite the significance of dHSCs, the mechanisms maintaining their dormancy remain elusive. Here, we identify CD38 as a novel and broadly applicable surface marker for the enrichment of murine dHSCs. We demonstrate that cyclic adenosine diphosphate ribose (cADPR), the product of CD38 cyclase activity, regulates the expression of the transcription factor c-Fos by increasing the release of Ca2+ from the endoplasmic reticulum (ER). Subsequently, we uncover that c-Fos induces the expression of the cell cycle inhibitor p57Kip2 to drive HSC dormancy. Moreover, we found that CD38 ecto-enzymatic activity at the neighboring CD38-positive cells can promote human HSC quiescence. Together, CD38/cADPR/Ca2+/c-Fos/p57Kip2 axis maintains HSC dormancy. Pharmacological manipulations of this pathway can provide new strategies to improve the success of stem cell transplantation and blood regeneration after injury or disease.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Although bone marrow niche cells are essential for hematopoietic stem cell (HSC) maintenance, their interaction in response to stress is not well defined. Here, we used a mouse model of acute ...thrombocytopenia to investigate the cross talk between HSCs and niche cells during restoration of the thrombocyte pool. This process required membrane-localized stem cell factor (m-SCF) in megakaryocytes, which was regulated, in turn, by vascular endothelial growth factor A (VEGF-A) and platelet-derived growth factor-BB (PDGF-BB). HSCs and multipotent progenitors type 2 (MPP2), but not MPP3/4, were subsequently activated by a dual-receptor tyrosine kinase (RTK)–dependent signaling event, m-SCF/c-Kit and VEGF-A/vascular endothelial growth factor receptor 2 (VEGFR-2), contributing to their selective and early proliferation. Our findings describe a dynamic network of signals in response to the acute loss of a single blood cell type and reveal the important role of 3 RTKs and their ligands in orchestrating the selective activation of hematopoietic stem and progenitor cells (HSPCs) in thrombocytopenia.
•A dual signal from c-Kit and VEGFR-2 determines selective activation of HSCs and MPP2 in response to acute immune thrombocytopenia.•VEGF-A and PDGF-BB relocalize stem cell factor in megakaryocytes, triggering proliferation of HSPCs.
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