Reconsidering marrow stem cell cycle status: insights into an actively cycling hematopoietic stem cell population
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Conversion of placental hemogenic endothelial cells to hematopoietic stem and progenitor cells
Hematopoietic stem and progenitor cells (HSPCs) are critical for the treatment of blood diseases in clinic. However, the limited source of HSPCs severely hinders their clinical application. In the embryo, hematopoietic stem cells (HSCs) arise from hemogenic endothelial (HE) cells lining the major arteries in vivo. In this work, by engineering vascular niche endothelial cells (VN-ECs), we generated functional HSPCs in vitro from ECs at various sites, including the aorta-gonad-mesonephros (AGM) region and the placenta. Firstly, we converted mouse embryonic HE cells from the AGM region (aHE) into induced HSPCs (iHSPCs), which have the abilities for multilineage differentiation and self-renewal. Mechanistically, we found that VN-ECs can promote the generation of iHSPCs via secretion of CX3CL1 and IL1A. Next, through VN-EC co-culture, we showed that placental HE (pHE) cells, a type of extra-embryonic HE cells, were successfully converted into iHSPCs (pHE-iHSPCs), which have multilineage differentiation capacity, but exhibit limited self-renewal ability. Furthermore, comparative transcriptome analysis of aHE-iHSPCs and pHE-iHSPCs showed that aHE-iHSPCs highly expressed HSC-specific and self-renewal-related genes. Moreover, experimental validation showed that retinoic acid (RA) treatment promoted the transformation of pHE cells into iHSPCs that have self-renewal ability. Collectively, our results suggested that pHE cells possess the potential to transform into self-renewing iHSPCs through RA treatment, which will facilitate the clinical application of placental endothelial cells in hematopoietic cell generation.
Deep imaging of LepR+ stromal cells in optically cleared murine bone hemisections
Tissue clearing combined with high-resolution confocal imaging is a cutting-edge approach for dissecting the three-dimensional (3D) architecture of tissues and deciphering cellular spatial interactions under physiological and pathological conditions. Deciphering the spatial interaction of leptin receptor-expressing (LepR+) stromal cells with other compartments in the bone marrow is crucial for a deeper understanding of the stem cell niche and the skeletal tissue. In this study, we introduce an optimized protocol for the 3D analysis of skeletal tissues, enabling the visualization of hematopoietic and stromal cells, especially LepR+ stromal cells, within optically cleared bone hemisections. Our method preserves the 3D tissue architecture and is extendable to other hematopoietic sites such as calvaria and vertebrae. The protocol entails tissue fixation, decalcification, and cryosectioning to reveal the marrow cavity. Completed within approximately 12 days, this process yields highly transparent tissues that maintain genetically encoded or antibody-stained fluorescent signals. The bone hemisections are compatible with diverse antibody labeling strategies. Confocal microscopy of these transparent samples allows for qualitative and quantitative image analysis using Aivia or Bitplane Imaris software, assessing a spectrum of parameters. With proper storage, the fluorescent signal in the stained and cleared bone hemisections remains intact for at least 2–3 months. This protocol is robust, straightforward to implement, and highly reproducible, offering a valuable tool for tissue architecture and cellular interaction studies.
GATA2 mutated allele specific expression is associated with a hyporesponsive state of HSC in GATA2 deficiency syndrome
GATA2 germline mutations lead to a syndrome characterized by immunodeficiency, vascular disorders and myeloid malignancies. To elucidate how these mutations affect hematopoietic homeostasis, we created a knock-in mouse model expressing the recurrent Gata2 R396Q missense mutation. Employing molecular and functional approaches, we investigated the mutation’s impact on hematopoiesis, revealing significant alterations in the hematopoietic stem and progenitor (HSPC) compartment in young age. These include increased LT-HSC numbers, reduced self-renewal potential, and impaired response to acute inflammatory stimuli. The mature HSPC compartment was primarily affected at the CMP sub-population level. In the mutant LT-HSC population, we identified an aberrant subpopulation strongly expressing CD150, resembling aging, but occurring prematurely. This population showed hyporesponsiveness, accumulated over time, and exhibited allele-specific expression (ASE) favoring the mutated Gata2 allele, also observed in GATA2 mutated patients. Our findings reveal the detrimental impact of a Gata2 recurrent missense mutation on the HSC compartment contributing to its functional decline. Defects in the CMP mature compartment, along with the inflammatory molecular signature, explain the loss of heterogeneity in HPC compartment observed in patients. Finally, our study provides a valuable model that recapitulates the ASE-related pathology observed in GATA2 deficiency, shedding light on the mechanisms contributing to the disease’s natural progression.
STING mediates increased self-renewal and lineage skewing in DNMT3A-mutated hematopoietic stem/progenitor cells
Somatic mutations in DNA methyltransferase 3 A (DNMT3A) are frequently observed in patients with hematological malignancies. Hematopoietic stem/progenitor cells (HSPCs) with mutated DNMT3A demonstrate increased self-renewal activity and skewed lineage differentiation. However, the molecular mechanisms underlying these changes remain largely unexplored. In this study, we show that Dnmt3a loss leads to the upregulation of endogenous retroviruses (ERVs) in HSPCs, subsequently activating the cGAS-STING pathway and triggering inflammatory responses in these cells. Both genetic and pharmacological inhibition of STING effectively corrects the increased self-renewal activity and differentiation skewing induced by Dnmt3a deficiency in mice. Notably, targeting STING showed inhibited acute myeloid leukemia (AML) development in a Dnmt3a-KO; Flt3-ITD AML model, comparable to AC220, an FDA-approved FLT3-ITD inhibitor. A patient-derived xenograft (PDX) model further demonstrated that targeting STING effectively alleviates the leukemic burden of DNMT3A-mutant AML. Collectively, our findings highlight a critical role for STING in hematopoietic disorders induced by DNMT3A mutations and propose STING as a potential therapeutic target for preventing the progression of DNMT3A mutation-associated leukemia.
Neutrophils in cancer: from biology to therapy
The view of neutrophils has shifted from simple phagocytic cells, whose main function is to kill pathogens, to very complex cells that are also involved in immune regulation and tissue repair. These cells are essential for maintaining and regaining tissue homeostasis. Neutrophils can be viewed as double-edged swords in a range of situations. The potent killing machinery necessary for immune responses to pathogens can easily lead to collateral damage to host tissues when inappropriately controlled. Furthermore, some subtypes of neutrophils are potent pathogen killers, whereas others are immunosuppressive or can aid in tissue healing. Finally, in tumor immunology, many examples of both protumorigenic and antitumorigenic properties of neutrophils have been described. This has important consequences for cancer therapy, as targeting neutrophils can lead to either suppressed or stimulated antitumor responses. This review will discuss the current knowledge regarding the pro- and antitumorigenic roles of neutrophils, leading to the concept of a confused state of neutrophil-driven pro-/antitumor responses.
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