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Here, using two-photon phosphorescence lifetime microscopy, the local oxygen tension in the bone marrow of live mice is found to be quite low, with spatiotemporal variations depending on the blood vessel type, distance to the endosteum, and changes in cellularity after stress. Oxygen tension in live bone marrow Low oxygen tension (hypoxia) is commonly thought to be a shared niche characteristic in maintaining quiescence in many stem cell types. However, local oxygen concentration, for example in the bone marrow, has never been measured directly. Charles Lin and colleagues have now developed a method based on two-photon microscopy to measure the absolute local oxygen tension ( p O 2 ) in the marrow of live animals. Using this method, they found that while vascular density is high throughout the bone marrow, overall oxygenation is quite low and there is heterogeneity in local p O 2 with respect to vessel type and location. For example, surprisingly, the endosteal region is not the region of the lowest p O 2 . After radiation or chemotherapy, bone marrow p O 2 becomes elevated and transplanted haematopoietic stem/progenitor cells do not seek out regions with the lowest p O 2 for homing. Characterization of how the microenvironment, or niche, regulates stem cell activity is central to understanding stem cell biology and to developing strategies for the therapeutic manipulation of stem cells 1 . Low oxygen tension (hypoxia) is commonly thought to be a shared niche characteristic in maintaining quiescence in multiple stem cell types 2 , 3 , 4 . However, support for the existence of a hypoxic niche has largely come from indirect evidence such as proteomic analysis 5 , expression of hypoxia inducible factor-1α ( Hif-1 α) and related genes 6 , and staining with surrogate hypoxic markers (for example, pimonidazole) 6 , 7 , 8 . Here we perform direct in vivo measurements of local oxygen tension ( p O 2 ) in the bone marrow of live mice. Using two-photon phosphorescence lifetime microscopy, we determined the absolute p O 2 of the bone marrow to be quite low (<32 mm Hg) despite very high vascular density. We further uncovered heterogeneities in local p O 2 , with the lowest p O 2 (∼9.9 mm Hg, or 1.3%) found in deeper peri-sinusoidal regions. The endosteal region, by contrast, is less hypoxic as it is perfused with small arteries that are often positive for the marker nestin. These p O 2 values change markedly after radiation and chemotherapy, pointing to the role of stress in altering the stem cell metabolic microenvironment.

The cellular constituents forming the haematopoietic stem cell (HSC) niche in the bone marrow are unclear, with studies implicating osteoblasts, endothelial and perivascular cells. Here we demonstrate that mesenchymal stem cells (MSCs), identified using nestin expression, constitute an essential HSC niche component. Nestin + MSCs contain all the bone-marrow colony-forming-unit fibroblastic activity and can be propagated as non-adherent ‘mesenspheres’ that can self-renew and expand in serial transplantations. Nestin + MSCs are spatially associated with HSCs and adrenergic nerve fibres, and highly express HSC maintenance genes. These genes, and others triggering osteoblastic differentiation, are selectively downregulated during enforced HSC mobilization or β3 adrenoreceptor activation. Whereas parathormone administration doubles the number of bone marrow nestin + cells and favours their osteoblastic differentiation, in vivo nestin + cell depletion rapidly reduces HSC content in the bone marrow. Purified HSCs home near nestin + MSCs in the bone marrow of lethally irradiated mice, whereas in vivo nestin + cell depletion significantly reduces bone marrow homing of haematopoietic progenitors. These results uncover an unprecedented partnership between two distinct somatic stem-cell types and are indicative of a unique niche in the bone marrow made of heterotypic stem-cell pairs. A stem-cell niche made for two The identity of the cells that form the haematopoietic stem-cell niche in the bone marrow has been unclear. Paul Frenette and colleagues have now identified nestin-expressing mesenchymal stem cells as niche-forming cells. These cells show a close physical association with haematopoietic stem cells, express high levels of genes involved in stem-cell maintenance, and their depletion reduces bone-marrow homing of haematopoietic progenitors. This work reveals the stem-cell niche in the bone marrow as a partnership between two distinct somatic stem-cell types. The identity of the cells that form the haematopoietic stem cell (HSC) niche in bone marrow has been unclear. These authors identify nestin-expressing mesenchymal stem cells as niche-forming cells. These nestin-expressing cells show a close physical association with HSCs and express high levels of genes involved in HSC maintenance, and their depletion reduces bone marrow homing of haematopoietic progenitors.

Graft-versus-leukemia (GvL) reactions are responsible for the effectiveness of allogeneic hematopoietic cell transplantation as a treatment modality for myeloid neoplasia, whereby donor T- effector cells recognize leukemia neoantigens. However, a substantial fraction of patients experiences relapses because of the failure of the immunological responses to control leukemic outgrowth. Here, through a broad immunogenetic study, we demonstrate that germline and somatic reduction of human leucocyte antigen (HLA) heterogeneity enhances the risk of leukemic recurrence. We show that preexistent germline-encoded low evolutionary divergence of class II HLA genotypes constitutes an independent factor associated with disease relapse and that acquisition of clonal somatic defects in HLA alleles may lead to escape from GvL control. Both class I and II HLA genes are targeted by somatic mutations as clonal selection factors potentially impairing cellular immune responses and response to immunomodulatory strategies. These findings define key molecular modes of post-transplant leukemia escape contributing to relapse. Graft-versus-leukemia reactions are required for the eradication of myeloid malignancies after allogeneic hematopoietic cell transplantation. However, treatment efficacy is variable, depending on the immunological response. Here the authors show that dysfunction of HLA heterogeneity is associated with post-transplant leukemia relapse.

Germline pathogenic variants in DNMT3A were recently described in patients with overgrowth, obesity, behavioral, and learning difficulties ( D NMT3A O vergrowth S yndrome/DOS). Somatic mutations in the DNMT3A gene are also the most common cause of clonal hematopoiesis, and can initiate acute myeloid leukemia (AML). Using whole genome bisulfite sequencing, we studied DNA methylation in peripheral blood cells of 11 DOS patients and found a focal, canonical hypomethylation phenotype, which is most severe with the dominant negative DNMT3A R882H mutation. A germline mouse model expressing the homologous Dnmt3a R878H mutation phenocopies most aspects of the human DOS syndrome, including the methylation phenotype and an increased incidence of spontaneous hematopoietic malignancies, suggesting that all aspects of this syndrome are caused by this mutation. Germline mutations in the DNMT3A gene can cause an overgrowth syndrome associated with behavioural and hematopoietic phenotypes. Here the authors describe a mouse model of this syndrome that recapitulates many of these features, including conserved alterations in DNA methylation in the blood cells of both species.

This review examines the physiological and molecular bone marrow abnormalities associated with diabetes and discusses how bone marrow dysfunction represents a potential root for the development of the multiorgan failure characteristic of advanced diabetes. The notion of diabetes as a bone marrow and stem cell disease opens new avenues for therapeutic interventions ultimately aimed at improving the outcome of diabetic patients. Diabetes mellitus is a global health problem that results in multiorgan complications leading to high morbidity and mortality. Until recently, the effects of diabetes and hyperglycemia on the bone marrow microenvironment—a site where multiple organ systems converge and communicate—have been underappreciated. However, several new studies in mice, rats, and humans reveal that diabetes leads to multiple bone marrow microenvironmental defects, such as small vessel disease (microangiopathy), nerve terminal pauperization (neuropathy), and impaired stem cell mobilization (mobilopathy). The discovery that diabetes involves bone marrow‐derived progenitors implicated in maintaining cardiovascular homeostasis has been proposed as a bridging mechanism between micro‐ and macroangiopathy in distant organs. Herein, we review the physiological and molecular bone marrow abnormalities associated with diabetes and discuss how bone marrow dysfunction represents a potential root for the development of the multiorgan failure characteristic of advanced diabetes. The notion of diabetes as a bone marrow and stem cell disease opens new avenues for therapeutic interventions ultimately aimed at improving the outcome of diabetic patients.

Oleacein (Olea) and Oleocanthal (Oleo) are two phenolic compounds found in olive oil. Cell and animal studies have shown these two compounds can modulate inflammation, cancer, and neurodegenerative diseases. Unfortunately, the study of the pharmacokinetics of these two compounds appears difficult due to their high reactivity with primary amines. Indeed, the presence of primary amines in culture media and biological fluids raises the question as to whether the observed biological effects are attributable to the parent compounds or to their amine derivatives. In the present work, we investigated the adduct formation between Olea or Oleo and tris(hydroxymethyl)aminomethane (Tris), a well-known primary amine used primarily as a buffer system, showing that the reaction kinetics were extremely rapid. In addition, we assessed whether the newly formed Tris adducts, i.e., Olea-Tris and Oleo-Tris, retained their antioxidant capacity by means of the ABTS and DPPH radical scavenging assays, showing that their activity was partially maintained. Finally, we evaluated the anti-inflammatory activity of these adducts on murine BV-2 microglial cells stimulated with lipopolysaccharide (LPS) and kept in an amine-free culture medium, showing how the biological response varied as the compound was degraded. Taken together, these data demonstrate that the biological effects reported in the literature are mainly due to the amino-derivatives of Olea and Oleo rather than the polyphenols derived from their breakdown (tyrosol and hydroxytyrosol).

Several canonical translocations produce oncofusion genes that can initiate acute myeloid leukemia (AML). Although each translocation is associated with unique features, the mechanisms responsible remain unclear. While proteins interacting with each oncofusion are known to be relevant for how they act, these interactions have not yet been systematically defined. To address this issue in an unbiased fashion, we fused a promiscuous biotin ligase (TurboID) in-frame with 3 favorable-risk AML oncofusion cDNAs (PML::RARA, RUNX1::RUNX1T1, and CBFB::MYH11) and identified their interacting proteins in primary murine hematopoietic cells. The PML::RARA- and RUNX1::RUNX1T1-TurboID fusion proteins labeled common and unique nuclear repressor complexes, implying their nuclear localization. However, CBFB::MYH11-TurboID-interacting proteins were largely cytoplasmic, probably because of an interaction of the MYH11 domain with several cytoplasmic myosin-related proteins. Using a variety of methods, we showed that the CBFB domain of CBFB::MYH11 sequesters RUNX1 in cytoplasmic aggregates; these findings were confirmed in primary human AML cells. Paradoxically, CBFB::MYH11 expression was associated with increased RUNX1/2 expression, suggesting the presence of a sensor for reduced functional RUNX1 protein, and a feedback loop that may attempt to compensate by increasing RUNX1/2 transcription. These findings may have broad implications for AML pathogenesis.

TNBC represents the most aggressive breast cancer subtype. Although cancer stem cells (CSCs) are a minor fraction of all cancer cells, they are highly cancerous when compared to their non-stem counterparts, playing a major role in tumor recurrence and metastasis. Angiogenic stimuli and the tumor environment response are vital factors in cancer metastasis. However, the causes and effects of tumor angiogenesis are still poorly understood. In this study, we demonstrate TNFα effects on primary triple-negative breast cancer stem cells (BCSCs). TNFα stimulation increased the mesenchymality of BCSCs in an intermediate epithelial-to-mesenchymal transition (EMT) state, enhanced proliferation, self-renewal, and invasive capacity. TNFα-treatment elicited BCSC signaling on endothelial networks in vitro and increased the network forming capacity of the endothelial cells. Our findings further demonstrate that TNFα stimulation in BCSCs has the ability to instigate distinct cellular communication within the tumor microenvironment, inducing intra-tumoral stromal invasion. Further, TNFα-treatment in BCSCs induced a pre-metastatic niche through breast-liver organ crosstalk by inducing vascular cell adhesion molecule-1 (VCAM-1) enriched neovasculogenesis in the liver of tumor-bearing mice. Overall, TNFα is an important angiogenic target to be considered in breast cancer progression to attenuate any angiogenic response in the tumor environment that could lead to secondary organ metastasis.

Objective Electroencephalography (EEG) plays a fundamental role in the diagnosis and classification of epilepsy, and inducing sleep during EEG can improve patient cooperation and enhance the detection of epileptiform activity. Despite its importance, there is currently no standardized approach for sleep induction in pediatric EEG recordings. Consequently, practices such as melatonin administration and sleep deprivation are commonly utilized. This study aimed to compare the effectiveness of 5 mg melatonin versus partial sleep deprivation in inducing sleep during nap‐time EEGs in children with epilepsy. Methods A randomized crossover trial was conducted involving 33 participants (mean age 14.5 years), each undergoing EEG following either melatonin administration or partial sleep deprivation. In the melatonin arm, participants received an oral dose 30 min before the recording, while in the sleep deprivation arm, sleep was restricted the previous night. The primary outcome was sleep onset latency, defined as the time from relaxation to non‐REM stage 2 sleep on EEG. Additionally, melatonin and its metabolite, 6‐hydroxy‐melatonin, were measured using liquid chromatography coupled with tandem mass spectrometry (LC–MS/MS). Results The study showed a mean sleep onset latency of 8.5 min after sleep deprivation and 10.1 min after melatonin administration, with a mean difference of 1.5 min. The analysis of covariance conducted with stratification based on sleep onset latency (five classes) and considering all patients confirmed that melatonin is non‐inferior to sleep deprivation in sleep onset latency, with 97.5% lower confidence limits of −0.37. Melatonin levels in the treated group confirmed adequate absorption, while they were undetectable in the sleep‐deprived group. Significance Melatonin is non‐inferior to partial sleep deprivation in reducing sleep onset latency, with comparable diagnostic yield and a favorable tolerability profile. The study demonstrates that 5 mg of melatonin is a safe, effective, and well‐tolerated alternative to partial sleep deprivation for sleep induction in pediatric EEG evaluations. Given its ease of use and consistent results, melatonin may be recommended as a practical standard for facilitating EEG recordings in children, particularly those with neurodevelopmental disorders. Plain Language Summary This randomized crossover trial evaluated the effectiveness and tolerability of melatonin administered before an EEG recording to induce sleep, compared with partial sleep deprivation. The results showed that melatonin helped children achieve sleep and was non‐inferior to sleep deprivation. Moreover, melatonin demonstrated a favorable tolerability profile, representing a safe and easier alternative to support sleep during EEG, particularly in children with neurodevelopmental disorders, and could enhance the efficiency and quality of pediatric EEG recordings.