Synergy of NUP98-HOXA10 Fusion Gene and NrasG12D Mutation Preserves the Stemness of Hematopoietic Stem Cells on Culture Condition

Small-molecule α-lipoic acid targets ELK1 to balance human neutrophil and erythrocyte differentiation

BACKGROUND

Erythroid and myeloid differentiation disorders are commonly occurred in leukemia. Given that the relationship between erythroid and myeloid lineages is still unclear. To find the co-regulators in erythroid and myeloid differentiation might help to find new target for therapy of myeloid leukemia. In hematopoiesis, ALA (alpha lipoic acid) is reported to inhibit neutrophil lineage determination by targeting transcription factor ELK1 in granulocyte-monocyte progenitors via splicing factor SF3B1. However, further exploration is needed to determine whether ELK1 is a common regulatory factor for erythroid and myeloid differentiation.

METHODS

In vitro culture of isolated CD34+, CMPs (common myeloid progenitors) and CD34+ CD371- HSPCs (hematopoietic stem progenitor cells) were performed to assay the differentiation potential of monocytes, neutrophils, and erythrocytes. Overexpression lentivirus of long isoform (L-ELK1) or the short isoform (S-ELK1) of ELK1 transduced CD34+ HSPCs were transplanted into NSG mice to assay the human lymphocyte and myeloid differentiation differences 3 months after transplantation. Knocking down of SRSF11, which was high expressed in CD371+GMPs (granulocyte-monocyte progenitors), upregulated by ALA and binding to ELK1-RNA splicing site, was performed to analyze the function in erythroid differentiation derived from CD34+ CD123mid CD38+ CD371- HPCs (hematopoietic progenitor cells). RNA sequencing of L-ELK1 and S-ELK1 overexpressed CD34+ CD123mid CD38+ CD371- HPCs were performed to assay the signals changed by ELK1.

RESULTS

Here, we presented new evidence that ALA promoted erythroid differentiation by targeting the transcription factor ELK1 in CD34+ CD371- hematopoietic stem progenitor cells (HSPCs). Overexpression of either the long isoform (L-ELK1) or the short isoform (S-ELK1) of ELK1 inhibited erythroid-cell differentiation, but knockdown of ELK1 did not affect erythroid-cell differentiation. RNAseq analysis of CD34+ CD123mid CD38+ CD371- HPCs showed that L-ELK1 upregulated the expression of genes related to neutrophil activity, phosphorylation, and hypoxia signals, while S-ELK1 mainly regulated hypoxia-related signals. However, most of the genes that were upregulated by L-ELK1 were only moderately upregulated by S-ELK1, which might be due to a lack of serum response factor interaction and regulation domains in S-ELK1 compared to L-ELK1. In summary, the differentiation of neutrophils and erythrocytes might need to rely on the dose of L-ELK1 and S-ELK1 to achieve precise regulation via RNA splicing signals at early lineage commitment.

CONCLUSIONS

ALA and ELK1 are found to regulate both human granulopoiesis and erythropoiesis via RNA spliceosome, and ALA-ELK1 signal might be the target of human leukemia therapy.

Characterization of naked mole-rat hematopoiesis reveals unique stem and progenitor cell patterns and neotenic traits

Naked mole rats (NMRs) are the longest-lived rodents yet their stem cell characteristics remain enigmatic. Here, we comprehensively mapped the NMR hematopoietic landscape and identified unique features likely contributing to longevity. Adult NMRs form red blood cells in spleen and marrow, which comprise a myeloid bias toward granulopoiesis together with decreased B-lymphopoiesis. Remarkably, youthful blood and marrow single-cell transcriptomes and cell compositions are largely maintained until at least middle age. Similar to primates, the primitive stem and progenitor cell (HSPC) compartment is marked by CD34 and THY1. Stem cell polarity is seen for Tubulin but not CDC42, and is not lost until 12 years of age. HSPC respiration rates are as low as in purified human stem cells, in concert with a strong expression signature for fatty acid metabolism. The pool of quiescent stem cells is higher than in mice, and the cell cycle of hematopoietic cells is prolonged. By characterizing the NMR hematopoietic landscape, we identified resilience phenotypes such as an increased quiescent HSPC compartment, absence of age-related decline, and neotenic traits likely geared toward longevity.

Mechanistic insights and potential therapeutic approaches for NUP98-rearranged hematologic malignancies

Nucleoporin 98 (NUP98) fusion oncoproteins are observed in a spectrum of hematologic malignancies, particularly pediatric leukemias with poor patient outcomes. Although wild-type full-length NUP98 is a member of the nuclear pore complex, the chromosomal translocations leading to NUP98 gene fusions involve the intrinsically disordered and N-terminal region of NUP98 with over 30 partner genes. Fusion partners include several genes bearing homeodomains or having known roles in transcriptional or epigenetic regulation. Based on data in both experimental models and patient samples, NUP98 fusion oncoprotein-driven leukemogenesis is mediated by changes in chromatin structure and gene expression. Multiple cofactors associate with NUP98 fusion oncoproteins to mediate transcriptional changes possibly via phase separation, in a manner likely dependent on the fusion partner. NUP98 gene fusions co-occur with a set of additional mutations, including FLT3-internal tandem duplication and other events contributing to increased proliferation. To improve the currently dire outcomes for patients with NUP98-rearranged malignancies, therapeutic strategies have been considered that target transcriptional and epigenetic machinery, cooperating alterations, and signaling or cell-cycle pathways. With the development of more faithful experimental systems and continued study, we anticipate great strides in our understanding of the molecular mechanisms and therapeutic vulnerabilities at play in NUP98-rearranged models. Taken together, these studies should lead to improved clinical outcomes for NUP98-rearranged leukemia.

NUP98-HOXA10hd fusion protein sustains multi-lineage haematopoiesis of lineage-committed progenitors in transplant setting

Objectives

Exploring approaches of extending the haematopoiesis time window of MPPs and lineage‐committed progenitors might produce promising therapeutic effects. NUP98‐HOXA10hd (NA) fusion protein can expand long‐term haematopoietic stem cells (HSCs) and promote engraftment competitiveness without causing obvious oncogenesis. Our objectives were to investigate the roles of NA fusion protein in MPP and downstream lineage‐committed progenitor context.

Material and Methods

300 sorted MPPs (Lin⁻CD48⁻c‐kit⁺Sca1⁺CD135⁺CD150⁻) were mixed with 5 × 10⁵ total BM helper/competitor cells and injected into irradiated recipients. For secondary transplantation, 5 × 10⁶ total BM cells from primary recipient mice were injected into lethally irradiated recipients. NA‐MPP recipient mice were sacrified for flow cytometric analysis of bone marrow progenitors at indicated time points. Sorted MPPs and myeloid progenitors were used for RNA‐seq library preparation.

Results

We showed that NA‐expressing MPPs achieved significantly longer multi‐lineage haematopoiesis (>44‐week) than natural MPPs (20‐week). NA upregulated essential genes regulating long‐term haematopoiesis, cell cycle, epigenetic regulation and responses to stress in MPPs. These molecular traits are associated with the earlier appearance of a Sca1^‐c‐kit⁺ myeloid progenitor population, and more abundant cellularity of lineage‐committed progenitor as well as bone marrow nucleated cells. Further, the NA‐derived primary bone marrow cells, which lack NA‐LSK cells, successfully repopulated secondary multi‐lineage haematopoiesis over 20 weeks.

Conclusions

This study unveiled that NA fusion protein promotes MPP and lineage‐committed progenitor engraftment via extending long‐term multi‐lineage haematopoiesis.

Alpha lipoic acid promotes development of hematopoietic progenitors derived from human embryonic stem cells by antagonizing ROS signals

Antagonism of ROS signaling can inhibit cell apoptosis and autophagy, thus favoring the maintenance and expansion of hematopoietic stem cells. Alpha lipoic acid (ALA), a small antioxidant molecule, affects cell apoptosis by lowering the ROS level. In this study, we show that ALA promoted production of human pluripotent stem cells (hPSCs) derived hemogenic endothelial cells and hematopoietic stem/progenitor cells in vitro. Transcriptome analysis of hPSCs derived hemogenic endothelial cells showed that ALA promoted endothelial‐to‐hematopoietic transition by up‐regulating RUNX1, GFI1, GFI1B, MEIS2, and HIF1A and down‐regulating SOX17, TGFB1, TGFB2, TGFB3, TGFBR1, and TGFBR2. ALA also up‐regulated sensor genes of ROS signals, including HIF1A, FOXO1, FOXO3, ATM, PETEN, SIRT1, and SIRT3, during the process of hPSCs derived hemogenic endothelial cells generation. However, in more mature hPSC‐derived hematopoietic stem/progenitor cells, ALA reduced ROS levels and inhibited apoptosis. In particular, ALA enhanced development of hPSCs derived hematopoietic stem/progenitor cells by up‐regulating HIF1A in response to a hypoxic environment. Furthermore, addition of ALA in ex vivo culture greatly improved the maintenance of functional cord blood HSCs by in vivo transplantation assay. Our findings support the conjecture that ALA plays an important role in efficient regeneration of hematopoietic stem/progenitor cells from hPSCs and maintenance of functional HSCs, providing insight into understanding of regeneration of early hematopoiesis for engineering clinically useful hPSCs derived hematopoietic stem/progenitor cells transplantation. Thus, ALA can be used in the study of hPSCs derived HSCs.