Vascular endothelial growth factor-c regulates hematopoietic stem cell fate in the dorsal aorta

Hematopoietic stem and progenitor cells (HSPCs) are multipotent cells that self-renew or differentiate to establish the entire blood hierarchy. HSPCs arise from the hemogenic endothelium of the dorsal aorta (DA) during development in a process called endothelial-to-hematopoietic transition. The factors and signals that control HSPC fate decisions from the hemogenic endothelium are not fully understood. We found that vegfc has a role in HSPC emergence from the zebrafish DA. Using time-lapse live imaging, we show that some HSPCs in the DA of vegfc loss-of-function embryos display altered cellular behavior. Instead of typical budding from the DA, emergent HSPCs exhibit crawling behavior similar to myeloid cells. This was confirmed by increased myeloid cell marker expression in the ventral wall of the DA and the caudal hematopoietic tissue. This increase in myeloid cells corresponded with a decrease in HSPCs that persisted into larval stages. Together, our data suggests vegfc regulates HSPC emergence in the hemogenic endothelium, in part by suppressing a myeloid cell fate. Our study provides a potential signal for modulation of HSPC fate in stem cell differentiation protocols.

Low blood levels of high-density lipoprotein (HDL) cholesterol are positively associated with cancer

Purpose There is a growing body of evidence suggesting a decisive involvement of the human lipid metabolism in cancer development. However, clinical data on the association between blood triglyceride or cholesterol levels including the cholesterol transporters high-density and low-density lipoproteins (LDL, HDL) and cancer incidence have remained inconclusive. Here, we investigated the association between blood triglyceride as well as total, LDL and HDL cholesterol levels and cancer among outpatients from Germany. Methods 61,936 patients with available blood lipid values were identified from the IQVIA Disease Analyzer database and followed up between 2005 and 2019. Multivariable logistic regression models were used to study the association between lipid values and cancer. Results The probability of cancer was significantly lower among patients with elevated total cholesterol concentrations and higher in patients with decreased HDL serum levels. In contrast, serum concentrations of LDL and triglycerides had no impact on cancer risk. In cancer site-stratified analyses, we observed a trend towards higher rates of cancers from digestive organs, breast, skin cancer, urinary tract and cancers from lymphoid and hematopoietic tissue in patients with HDL values < 35 mg/dl, while a negative association between total cholesterol > 250 mg/dl and respiratory organ as well as urinary tract cancers was observed. Conclusion Our data strongly support the hypothesis that serum-specific lipid profiles are positively associated with cancer.

Susceptibility and Pathology in Juvenile Atlantic Cod Gadus morhua to a Marine Viral Haemorrhagic Septicaemia Virus Isolated from Diseased Rainbow Trout Oncorhynchus mykiss

The first known outbreak caused by a viral haemorrhagic septicaemia virus (VHSV) strain of genotype III in rainbow trout occurred in 2007 at a marine farm in Storfjorden, Norway. The source of the virus is unknown, and cod and other marine fish around the farms are suspected as a possible reservoir. The main objective of this study was to test the susceptibility of juvenile Atlantic cod to the VHSV isolate from Storfjorden. As the pathology of VHS in cod is sparsely described, an additional aim of the study was to give a histopathological description of the disease. Two separate challenge experiments were carried out, using both intra peritoneal (ip) injection and cohabitation as challenge methods. Mortality in the ip injection experiment leveled at approximately 50% three weeks post challenge. Both immunohistochemical and rRT-PCR analysis of organs sampled from diseased and surviving fish confirmed VHSV infection. No VHSV was detected in the cohabitants. The results indicate that Atlantic cod has a low natural susceptibility to this VHSV genotype III strain. One of the most extensive pathological changes was degeneration of cardiac myocytes. Immunohistochemistry confirmed that the lesions were related to VHSV. In some fish, the hematopoietic tissue of spleen and kidney showed degeneration and immunostaining, classical signs of VHS, as described in rainbow trout. Positive immunostaining of the capillaries of the gills, suggests this organ as a useful alternative when screening for VHSV.

CHIP: is clonal hematopoiesis a surrogate for aging and other disease?

Somatic mutations are an unavoidable consequence of aging tissues. Even though most mutations are functionally silent, some may affect genes critical to proper tissue self-renewal and differentiation, resulting in the outgrowth of affected cells, also known as clonal expansion. In hematopoietic tissue such clonal dominance is known as clonal hematopoiesis (CH). Sporadic CH is frequent in aging and affects over 10% of individuals beyond the fifth decade of life. It has been associated with an increased risk of hematologic malignancies and cardiovascular disease. In addition to aging, CH has been observed in other hematologic conditions and confers an adaptation of hematopoietic stem cells (HSCs) to various environmental stressors and cell-intrinsic defects. In the presence of extrinsic stressors such as genotoxic therapies, T-cell-mediated immune attack, or inflammation, somatic mutations may result in augmentation of HSC fitness. Such attuned HSCs can evade the environmental insults and outcompete their unadapted counterparts. Similarly, in inherited bone marrow failures, somatic mutations in HSCs frequently lead to the reversion of inherited defects. This may occur via the direct correction of germline mutations or indirect compensatory mechanisms. Occasionally, such adaptation may involve oncogenes or tumor suppressors, resulting in malignant transformation. In this brief article, we focus on the mechanisms of clonal dominance in various clinical and biological contexts.

A Clinical Case of Aplastic Anemia After COVID-19 Infection

Aplastic anemia is a rare disease of the blood system characterized by suppression of hematopoiesis in all lines of hematopoiesis, replacement of hematopoietic tissue with fatty tissue and absence of other causes or diseases that can suppress hematopoiesis. The incidence is 2-3 cases per 1 million population per year in the regions of Europe and America, rates are 2-3 times higher in East Asia. The disease most often begins between the ages of 10 and 25 years and over 60 years. The etiology remains unknown in 70-80 % of cases. The frequency of acquired cases predominates over congenital cases. The triggering factors can be chemical, physical exposures, medications, and viral infections. This case report describes a case of a patient developing aplastic anemia, as a result of a coronavirus infection.

Hematological and Hematopoietic Effects of Bactericidal Doses of Trans-Cinnamaldehyde and Thyme Oil on Cyprinus carpio Juveniles

The effects of two potential antibacterial agents of plant origin: trans-cinnamaldehyde (TC) and thyme oil (TO) on the peripheral blood parameters and cellular composition of hematopoietic tissue of Cyprinus carpio were studied. Both phytochemicals were used in the doses based on the bactericidal concentrations against Aeromonas spp. developed earlier in in vitro study. The fish were fed for 2 weeks on a commercial feed supplemented with 10 μl/kg of TC or 20 μl/kg of TO. Groups TC1 and TO1 were fed diets containing phytochemicals daily, while groups TC2 and TO2 every 2 days. Control group and groups TC2 and TO2 on the remaining days were fed plain feed. Peripheral blood and head kidney hematopoietic tissue were sampled from all the fish at the end of the experiment. In all the groups, hematological values were within the reference ranges for the healthy common carp juveniles. However, blood hemoglobin (Hb) concentration and mean corpuscular hemoglobin concentration (MCHC) were significantly lower in all the groups exposed to TC and TO, while MCH in TC1, TO1, and TO2 compared to the control. TC and TO did not affect leukocyte count [white blood cell (WBC)], differential leukocyte count, the oxidative activity of phagocytes [nitroblue tetrazolium (NBT)], or thrombocyte count (Thro). No significant alterations were observed in the hematopoietic tissue. The results showed that TC and TO exhibited no considerable hematotoxic effects and trials of their use in the treatment of fish infected with Aeromonas spp. may be undertaken.

Clonal hematopoiesis in individuals with ANKRD26 or ETV6 germline mutations

Currently, there are at least a dozen recognized hereditary hematopoietic malignancies (HHMs), some of which phenocopy others. Among these, three HHMs driven by germline mutations in ANKRD26, ETV6, or RUNX1 share a phenotype of thrombocytopenia, qualitative platelet defects, and an increased lifetime risk of hematopoietic malignancies (HMs). Prior work has demonstrated that RUNX1 germline mutation carriers experience an elevated lifetime risk (66%) for developing clonal hematopoiesis (CH) prior to age 50. Germline mutations in ANKRD26 or ETV6 phenocopy RUNX1 germline mutations, but no studies have focused on the risk of CH in individuals with germline mutations in ANKRD26 or ETV6. To determine the prevalence of CH in individuals with germline mutations in ANKRD26 or ETV6, we performed next generation sequencing on hematopoietic tissue from twelve individuals with either germline ANKRD26 or germline ETV6 mutations. Each patient had thrombocytopenia but had not developed HMs. Among the seven individuals with germline ANKRD26 mutations, one patient had a CH clone driven by a somatic SF3B1 mutation (p.Lys700Glu). This mutation increased from a variant allele frequency (VAF) of 9.4% at age 56 to 17.4% at age 60. None of the germline ETV6 mutation carriers had evidence of CH at the limits of detection of the NGS assay (5% VAF). Unlike individuals with germline mutations in RUNX1, no individuals under the age of 50 with germline mutations in ANKRD26 or ETV6 had detectable CH. This work demonstrates that ANKRD26 germline mutation carriers, but not ETV6 mutation carriers, experience elevated risk for CH.

Hemogen/BRG1 Cooperativity Is Required for Erythrocyte Maturation and Hemoglobin Production during Mammalian Erythropoiesis

Hemogen, also known as EDAG, is a hematopoietic tissue-specific gene that regulates the proliferation and differentiation of hematopoietic cells. However, the mechanism underlying hemogen function in erythropoiesis is unclear. We found that depletion of hemogen in human CD34 + erythroid progenitor cells and HUDEP2 cells significantly reduced the expression of genes associated with heme and hemoglobin synthesis, supporting a positive role of hemogen in erythroid maturation. In human K562 cells, hemogen antagonized the occupancy of co-repressors NuRD complex and facilitated LDB1 complex-mediated chromatin looping. Hemogen recruited SWI/SNF complex ATPase BRG1 as a co-activator to regulate nucleosome accessibility and H3K27ac enrichment for promoter and enhancer activity. To ask if hemogen/BRG1 cooperativity is conserved in mammalian systems, we generated hemogen KO/KI mice and investigated hemogen/BRG1 function in murine erythropoiesis. Loss of hemogen in E12.5-E16.5 impeded erythroid differentiation through reducing the production of mature erythroblasts. ChIP-seq in WT and hemogen KO animal revealed BRG1 is largely dependent on hemogen to occupy chromatin at erythroid gene promoters and enhancers. In summary, hemogen/BRG1 interaction in mammals is essential for erythroid maturation and hemoglobin production through its active role in promoter and enhancer activity and chromatin organization. Disclosures No relevant conflicts of interest to declare.

Identification of the Adult Hematopoietic Liver as the Primary Reservoir for the Recruitment of Pro-regenerative Macrophages Required for Salamander Limb Regeneration

The lack of scar-free healing and regeneration in many adult human tissues imposes severe limitations on the recovery of function after injury. In stark contrast, salamanders can functionally repair a range of clinically relevant tissues throughout adult life. The impressive ability to regenerate whole limbs after amputation, or regenerate following cardiac injury, is critically dependent on the recruitment of (myeloid) macrophage white blood cells to the site of injury. Amputation in the absence of macrophages results in regeneration failure and scar tissue induction. Identifying the exact hematopoietic source or reservoir of myeloid cells supporting regeneration is a necessary step in characterizing differences in macrophage phenotypes regulating scarring or regeneration across species. Mammalian wounds are dominated by splenic-derived monocytes that originate in the bone marrow and differentiate into macrophages within the wound. Unlike mammals, adult axolotls do not have functional bone marrow but instead utilize liver and spleen tissues as major sites for adult hematopoiesis. To interrogate leukocyte identity, tissue origins, and modes of recruitment, we established several transgenic axolotl hematopoietic tissue transplant models and flow cytometry protocols to study cell migration and identify the source of pro-regenerative macrophages. We identified that although bidirectional trafficking of leukocytes can occur between spleen and liver tissues, the liver is the major source of leukocytes recruited to regenerating limbs. Recruitment of leukocytes and limb regeneration occurs in the absence of the spleen, thus confirming the dependence of liver-derived myeloid cells in regeneration and that splenic maturation is dispensable for the education of pro-regenerative macrophages. This work provides an important foundation for understanding the hematopoietic origins and education of myeloid cells recruited to, and essential for, adult tissue regeneration.

Hapln1b, a central organizer of the extracellular matrix, modulates kit signalling to control developmental haematopoiesis

During early vertebrate development, hematopoietic stem and progenitor cells (HSPCs) are produced from hemogenic endothelium located in the dorsal aorta, before they migrate to a transient niche where they expand, the fetal liver and the caudal hematopoietic tissue (CHT), in mammals and zebrafish, respectively. In zebrafish, previous studies have shown that the extracellular matrix (ECM) around the aorta needs to be degraded to allow HSPCs to leave the aortic floor and reach blood circulation. However, the role of the ECM components in HSPC specification has never been addressed. We show here that hapln1b, a key component of the ECM is specifically expressed in hematopoietic sites in the zebrafish embryo. Gain- and loss-of-function experiments all resulted in the absence of HSPCs in the early embryo, showing that hapln1b is required, at the correct level, to specify HSPCs in the hemogenic endothelium. Furthermore, we show that the expression of hapln1b is necessary to maintain the integrity of the ECM through its link domain. By combining functional analyses and computer modelling, we show that kitlgb interacts with the ECM to specify HSPCs. We demonstrate that the ECM is an integral component of the microenvironment and mediates cytokine signalling that is required for HSPC specification.