Vascular Notch Signaling in Stress Hematopoiesis

The lncRNA DUBR is regulated by CTCF and coordinates chromatin landscape and gene expression in hematopoietic cells

Master hematopoietic transcription factors (TFs) and long noncoding RNAs (lncRNAs) coordinate shaping lineage-specific gene expression programs during hematopoietic differentiation. The architectural protein CCCTC-binding factor (CTCF) has emerged as a pivotal regulator of gene expression in cell differentiation. However, the relationship and its regulatory effect of CTCF on lncRNA genes in hematopoiesis remain elusive. We demonstrated that CTCF constrains the lncRNA DUBRtranscription throughout erythroid differentiation. DUBR is highly expressed in human hematopoietic stem and progenitor cells (HSPCs) but depleted in erythroblasts. DUBR perturbation dysregulates hematopoietic-erythroid cell differentiation genes and facilitates genome-wide activation of regulatory elements. A genomic map of RNA occupancy revealed that DUBR associates with a set of genes involved in regulating hematopoietic differentiation, including the erythroid repressor HES1, which targets a subset of regulatory elements of DUBR-dysregulated genes. Our results support the role of DUBR as a regulator of a hematopoietic differentiation gene program by coordinating the expression of genes and influencing their chromatin regulatory landscape.

Red Blood Cell-Related Phenotype-Genotype Correlations in Chronic and Acute Critical Illnesses (Traumatic Brain Injury Cohort and COVID-19 Cohort)

Changes in red blood cell (RBC)-related parameters and anemia are common in both severe chronic and acute diseases. RBC-related phenotypes have a heritable component. However, it is unclear whether the contribution of genetic variability is pronounced when hematological parameters are affected by physiological stress. In this study, we analyzed RBC-related phenotypes and phenotype-genotype correlations in two exome-sequenced patient cohorts with or at a high risk for a critical illness: chronic TBI patients admitted for rehabilitation and patients with acute COVID-19. In the analysis of exome data, we focused on the cumulative effects of rare high-impact variants (qualifying variants, QVs) in specific gene sets, represented by Notch signaling pathway genes, based on the results of enrichment analysis in anemic TBI patients and three predefined gene sets for phenotypes of interest derived from GO, GWAS, and HPO resources. In both patient cohorts, anemia was associated with the cumulative effects of QVs in the GO (TBI: p = 0.0003, OR = 2.47 (1.54-4.88); COVID-19: p = 0.0004, OR = 2.12 (1.39-3.25)) and Notch pathway-derived (TBI: p = 0.0017, OR = 2.33 (1.35-4.02); COVID-19: p = 0.0012, OR =8.00 (1.79-35.74)) gene sets. In the multiple linear regression analysis, genetic variables contributed to RBC indices in patients with TBI. In COVID-19 patients, QVs in Notch pathway genes influenced RBC, HGB, and HCT levels, whereas genes from other sets influenced MCHC levels. Thus, in this exploratory study, exome data analysis yielded similar and different results in the two patient cohorts, supporting the view that genetic factors may contribute to RBC-related phenotypic performance in both severe chronic and acute health conditions.

Adipose-Derived Mesenchymal Stem Cell Facilitate Hematopoietic Stem Cell Proliferation via the Jagged-1/Notch-1/Hes Signaling Pathway

Background

Poor graft function (PGF) is a life-threatening complication following hematopoietic stem cell transplantation (HSCT). Current therapies, such as CD34+ cell infusion, have shown limited effectiveness. Conversely, mesenchymal stem cells (MSCs) show potential in addressing PGF. Adipose-derived mesenchymal stem cells (ADSCs) effectively support long-term hematopoietic stem cell proliferation. Therefore, this study aimed to investigate the mechanisms underlying the long-term hematopoietic support provided by ADSCs.

Methods

ADSCs were isolated from mice and subsequently identified. In vitro experiments involved coculturing ADSCs as feeders with Lin-Sca-1+c-kit+ (LSK) cells from mice for 2 and 5 weeks. The number of LSK cells was quantified after coculture. Scanning electron microscopy was utilized to observe the interaction between ADSCs and LSK cells. Hes-1 expression was assessed using western blot and real-time quantitative PCR. An γ-secretase inhibitor (GSI) was used to confirm the involvement of the Jagged-1/Notch-1/Hes-1 pathway in LSK cell expansion. Additionally, Jagged-1 was knocked down in ADSCs to demonstrate its significance in ADSC-mediated hematopoietic support. In vivo experiments were conducted to study the hematopoietic support provided by ADSCs through the infusion of LSK, LSK + fibroblasts, and LSK + ADSCs, respectively. Mouse survival, platelet count, leukocyte count, and hemoglobin levels were monitored.

Results

ADSCs showed high-Jagged-1 expression and promoted LSK cell proliferation. There was a direct interaction between ADSCs and LSK cells. After coculture, Hes-1 expression increased in LSK cells. Moreover, GSI-reduced LSK cell proliferation and Hes-1 expression. Knockdown of Jagged-1 attenuated ADSCs-mediated promotion of LSK cell proliferation. Furthermore, ADSCs facilitated hematopoietic recovery and promoted the survival of NOD/SCID mice.

Conclusion

The hematopoietic support provided by ADSCs both in vivo and in vitro may be mediated, at least in part, through the Jagged-1/Notch-1 signaling pathway. These findings provide valuable insights into the mechanisms underlying ADSCs-mediated hematopoietic support and may have implications for improving the treatment of PGF following HSCT.

Identification and single-base gene-editing functional validation of a cis-EPO variant as a genetic predictor for EPO-increasing therapies

Hypoxia-inducible factor prolyl hydroxylase inhibitors (HIF-PHIs) are currently under clinical development for treating anemia in chronic kidney disease (CKD), but it is important to monitor their cardiovascular safety. Genetic variants can be used as predictors to help inform the potential risk of adverse effects associated with drug treatments. We therefore aimed to use human genetics to help assess the risk of adverse cardiovascular events associated with therapeutically altered EPO levels to help inform clinical trials studying the safety of HIF-PHIs. By performing a genome-wide association meta-analysis of EPO (n = 6,127), we identified a cis-EPO variant (rs1617640) lying in the EPO promoter region. We validated this variant as most likely causal in controlling EPO levels by using genetic and functional approaches, including single-base gene editing. Using this variant as a partial predictor for therapeutic modulation of EPO and large genome-wide association data in Mendelian randomization tests, we found no evidence (at p < 0.05) that genetically predicted long-term rises in endogenous EPO, equivalent to a 2.2-unit increase, increased risk of coronary artery disease (CAD, OR [95% CI] = 1.01 [0.93, 1.07]), myocardial infarction (MI, OR [95% CI] = 0.99 [0.87, 1.15]), or stroke (OR [95% CI] = 0.97 [0.87, 1.07]). We could exclude increased odds of 1.15 for cardiovascular disease for a 2.2-unit EPO increase. A combination of genetic and functional studies provides a powerful approach to investigate the potential therapeutic profile of EPO-increasing therapies for treating anemia in CKD.

Notch Signaling in the Bone Marrow Lymphopoietic Niche

Lifelong mammalian hematopoiesis requires continuous generation of mature blood cells that originate from Hematopoietic Stem and Progenitor Cells (HSPCs) situated in the post-natal Bone Marrow (BM). The BM microenvironment is inherently complex and extensive studies have been devoted to identifying the niche that maintains HSPC homeostasis and supports hematopoietic potential. The Notch signaling pathway is required for the emergence of the definitive Hematopoietic Stem Cell (HSC) during embryonic development, but its role in BM HSC homeostasis is convoluted. Recent work has begun to explore novel roles for the Notch signaling pathway in downstream progenitor populations. In this review, we will focus an important role for Notch signaling in the establishment of a T cell primed sub-population of Common Lymphoid Progenitors (CLPs). Given that its activation mechanism relies primarily on cell-to-cell contact, Notch signaling is an ideal means to investigate and define a novel BM lymphopoietic niche. We will discuss how new genetic model systems indicate a pre-thymic, BM-specific role for Notch activation in early T cell development and what this means to the paradigm of lymphoid lineage commitment. Lastly, we will examine how leukemic T-cell acute lymphoblastic leukemia (T-ALL) blasts take advantage of Notch and downstream lymphoid signals in the pathological BM niche.