Anne-Sofie Johansson

Leukotriene B ₄ (LTB ₄ ), a potent chemotactic and immune‐modulating eicosanoid, signals via two receptors (BLT ₁ and BLT ₂ ), leading to rapid but transient migratory, adhesive and secretory responses in phagocytes. Previously, we reported that BLT ₁ is the predominating BLT in human umbilical vein endothelial cells (HUVEC). However, little is known about how ligation of these receptors affects adhesive and secretory endothelial responses over time. Here, we demonstrate that in HUVEC, LTB ₄ dose‐dependently and stereospecifically causes a biphasic tethering of neutrophils, where the second phase is robust, similar to that induced by lipopolysaccharide, and persists for 3–8 h. LTB ₄ also causes up‐regulation of E‐selectin, ICAM‐1 and VCAM‐1 and release of MCP‐1 and nitric oxide (but not of IL‐8 or HMGB1). These responses appeared to be mediated via BLT ₁ and BLT ₂ as judged by BLT ₁ shRNA gene silencing and/or treatment with BLT ₁ and BLT ₂ specific antagonists prior to LTB ₄ activation of HUVEC. Moreover, LTB ₄ responses used primarily the MAP kinase/Erk pathway. Our findings suggest a new role for LTB ₄ not only in early but also in late vascular inflammatory responses.

Age is a risk factor for hematologic malignancies. Attributes of the aging hematopoietic system include increased myelopoiesis, impaired adaptive immunity, and a functional decline of the hematopoietic stem cells (HSCs) that maintain hematopoiesis. Changes in the composition of diverse HSC subsets have been suggested to be responsible for age-related alterations, however, the underlying regulatory mechanisms are incompletely understood in the context of HSC heterogeneity. In this study, we investigated how distinct HSC subsets, separated by CD49b, functionally and molecularly change their behavior with age. We demonstrate that the lineage differentiation of both lymphoid-biased and myeloid-biased HSC subsets progressively shifts to a higher myeloid cellular output during aging. In parallel, we show that HSCs selectively undergo age-dependent gene expression and gene regulatory changes in a progressive manner, which is initiated already in the juvenile stage. Overall, our studies suggest that aging intrinsically alters both cellular and molecular properties of HSCs.

Hematopoiesis is maintained by hematopoietic stem cells (HSCs) that replenish all blood lineages throughout life. It is well-established that the HSC pool is functionally heterogeneous consisting of cells differing in longevity, self-renewal ability, cell proliferation, and lineage differentiation. Although HSCs can be identified through the Lineage^–Sca-1⁺c-Kit⁺CD48^–CD34^–CD150⁺ immunophenotype, the cell surface marker combination does not permit absolute purification of functional HSCs with long-term reconstituting ability. Therefore, prospective isolation of long-term HSCs is crucial for mechanistic understanding of the biological functions of HSCs and for resolving functional heterogeneity within the HSC population. Here, we show that the combination of CD229 and CD49b cell surface markers within the phenotypic HSC compartment identifies a subset of multipotent progenitor (MPP) cells with high proliferative activity and short-term reconstituting ability. Thus, the addition of CD229 and CD49b to conventional HSC markers permits prospective isolation of functional HSCs by distinguishing MPPs in the HSC compartment.

Age is a risk factor for hematologic malignancies. Attributes of the aging hematopoietic system include increased myelopoiesis, impaired adaptive immunity, and a functional decline of the hematopoietic stem cells (HSCs) that maintain hematopoiesis. Changes in the composition of diverse HSC subsets have been suggested to be responsible for age-related alterations, however, the underlying regulatory mechanisms are incompletely understood in the context of HSC heterogeneity. In this study, we investigated how distinct HSC subsets, separated by CD49b, functionally and molecularly change their behavior with age. We demonstrate that blood lineage differentiation progressively shifts to a higher myeloid cellular output in both lymphoid-biased and myeloid-biased HSC subsets during aging. In parallel, we show that HSCs selectively undergo age-dependent gene expression and gene regulatory molecular changes in a progressive manner, which is initiated already in the pre-adult stage. Overall, our studies suggest that aging intrinsically alters both cellular and molecular properties of HSCs. Highlights: With age a gradual shift towards myeloid differentiation occurs in both myeloid-biased and lymphoid-biased enriched HSC subsets. Age-related molecular changes preferentially occur in HSCs. Functionally distinct HSC subsets with high transcriptional similarity can be distinguished on the epigenetic level. HSC aging is associated with a progressive increase in chromatin accessibility.

Leukemia cutis or leukemic cell infiltration in skin is one of the common extramedullary manifestations of acute myeloid leukemia (AML) and signifies a poorer prognosis. However, its pathogenesis and maintenance remain understudied. Here, we report massive AML cell infiltration in the skin in a transplantation-induced MLL-AF9 AML mouse model. These AML cells could regenerate AML after transplantation. Prospective niche characterization revealed that skin harbored mesenchymal progenitor cells (MPCs) with a similar phenotype as BM mesenchymal stem cells. These skin MPCs protected AML-initiating stem cells (LSCs) from chemotherapy in vitro partially via mitochondrial transfer. Furthermore, Lama4 deletion in skin MPCs promoted AML LSC proliferation and chemoresistance. Importantly, more chemoresistant AML LSCs appeared to be retained in Lama4−/− mouse skin after cytarabine treatment. Our study reveals the characteristics and previously unrecognized roles of skin mesenchymal niches in maintaining and protecting AML LSCs during chemotherapy, meriting future exploration of their impact on AML relapse.

The development of B cells relies on an intricate network of transcription factors critical for developmental progression and lineage commitment. In the B cell developmental trajectory, a temporal switch from predominant Foxo3 to Foxo1 expression occurs at the CLP stage. Utilizing VAV-iCre mediated conditional deletion, we found that the loss of FOXO3 impaired B cell development from LMPP down to B cell precursors, while the loss of FOXO1 impaired B cell commitment and resulted in a complete developmental block at the CD25 negative proB cell stage. Strikingly, the combined loss of FOXO1 and FOXO3 resulted in the failure to restrict the myeloid potential of CLPs and the complete loss of the B cell lineage. This is underpinned by the failure to enforce the early B-lineage gene regulatory circuitry upon a predominantly pre-established open chromatin landscape. Altogether, this demonstrates that FOXO3 and FOXO1 cooperatively govern early lineage restriction and initiation of B-lineage commitment in CLPs. SUMMARY: Common lymphoid progenitors co-express the transcription factors FOXO1 and FOXO3. Removing FOXO1 and FOXO3 at this developmental stage results in regained myeloid potential, failed establishment of the early B cell gene regulatory program, and the complete loss of the B cell lineage.

1 Alveolar macrophages efficiently phagocytize particles deposited in the alveolar part of the lung. Phagolysosomal pH in alveolar macrophages from rabbits, dogs, baboons and guinea pigs is around 5 pH units. A low pH is of importance for clearance of inorganic particles and probably also for defence against bacteria and fungi. 2 Phagolysosomal pH in alveolar macrophages from smokers and non-smokers was measured using fluorescein-conjugated amorphous silica particles as a probe. pH was the same in both groups and similar to earlier studies on alveolar macrophages from animals. 3 The morphological picture between alveolar macrophages from smokers and non-smokers differed clearly with a high number of dense inclusions of great variation in size and shape in macrophages from smokers. Ingested test particles were located in all types of inclusions. 4 We conclude that phagolysosomal pH in human alveolar macrophages is similar to that in several animal species and that it is rather insensitive to influence from the environment.