Sox17-mediated expression of adherent molecules is required for the maintenance of undifferentiated hematopoietic cluster formation in midgestation mouse embryos

Light at the ENDothelium-role of Sox17 and Runx1 in endothelial dysfunction and pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease that is characterized by an obliterative vasculopathy of the distal pulmonary circulation. Despite significant progress in our understanding of the pathophysiology, currently approved medical therapies for PAH act primarily as pulmonary vasodilators and fail to address the underlying processes that lead to the development and progression of the disease. Endothelial dysregulation in response to stress, injury or physiologic stimuli followed by perivascular infiltration of immune cells plays a prominent role in the pulmonary vascular remodeling of PAH. Over the last few decades, our understanding of endothelial cell dysregulation has evolved and brought to light a number of transcription factors that play important roles in vascular homeostasis and angiogenesis. In this review, we examine two such factors, SOX17 and one of its downstream targets, RUNX1 and the emerging data that implicate their roles in the pathogenesis of PAH. We review their discovery and discuss their function in angiogenesis and lung vascular development including their roles in endothelial to hematopoietic transition (EHT) and their ability to drive progenitor stem cells toward an endothelial or myeloid fate. We also summarize the data from studies that link mutations in Sox17 with an increased risk of developing PAH and studies that implicate Sox17 and Runx1 in the pathogenesis of PAH. Finally, we review the results of recent studies from our lab demonstrating the efficacy of preventing and reversing pulmonary hypertension in animal models of PAH by deleting RUNX1 expression in endothelial or myeloid cells or by the use of RUNX1 inhibitors. By investigating PAH through the lens of SOX17 and RUNX1 we hope to shed light on the role of these transcription factors in vascular homeostasis and endothelial dysregulation, their contribution to pulmonary vascular remodeling in PAH, and their potential as novel therapeutic targets for treating this devastating disease.

A Sox17 downstream gene Rasip1 is involved in the hematopoietic activity of intra-aortic hematopoietic clusters in the midgestation mouse embryo

BACKGROUND

During mouse embryonic development, definitive hematopoiesis is first detected around embryonic day (E) 10.5 in the aorta-gonad-mesonephros (AGM) region. Hematopoietic stem cells (HSCs) arise in the dorsal aorta's intra-aortic hematopoietic cell clusters (IAHCs). We have previously reported that a transcription factor Sox17 is expressed in IAHCs, and that, among them, CD45lowc-Kithigh cells have high hematopoietic activity. Furthermore, forced expression of Sox17 in this population of cells can maintain the formation of hematopoietic cell clusters. However, how Sox17 does so, particularly downstream signaling involved, remains poorly understood. The purpose of this study is to search for new Sox17 targets which contribute to cluster formation with hematopoietic activity.

METHODS

RNA-sequencing (RNA-seq) analysis was done to identify genes that are upregulated in Sox17-expressing IAHCs as compared with Sox17-negative ones. Among the top 7 highly expressed genes, Rasip1 which had been reported to be a vascular-specific regulator was focused on in this study, and firstly, the whole-mount immunostaining was done. We conducted luciferase reporter assay and chromatin immunoprecipitation (ChIP) assay to examine whether Sox17 regulates Rasip1 gene expression via binding to its enhancer element. We also analyzed the cluster formation and the multilineage colony-forming ability of Rasip1-transduced cells and Rasip1-knockdown Sox17-transduced cells.

RESULTS

The increase of the Rasip1 expression level was observed in Sox17-positive CD45lowc-Kithigh cells as compared with the Sox17-nonexpressing control. Also, the expression level of the Rasip1 gene was increased by the Sox17-nuclear translocation. Rasip1 was expressed on the membrane of IAHCs, overlapping with the endothelial cell marker, CD31, and hematopoietic stem/progenitor marker (HSPC), c-Kit. Rasip1 expression was observed in most part of c-Kit+Sox17+ cells in IAHCs. Luciferase reporter assay and ChIP assay indicated that one of the five putative Sox17-binding sites in the Rasip1 enhancer region was important for Rasip1 expression via Sox17 binding. Rasip1 knockdown in Sox17-transduced cells decreased the cluster formation and diminished the colony-forming ability, while overexpression of Rasip1 in CD45lowc-Kithigh cells led to a significant but transient increase in hematopoietic activity.

CONCLUSIONS

Rasip1 knockdown in Sox17-transduced CD45lowc-Kithigh cells displayed a significant decrease in the multilineage colony-forming ability and the cluster size. Rasip1 overexpression in Sox17-untransduced CD45lowc-Kithigh cells led to a significant but transient increase in the multilineage colony-forming ability, suggesting the presence of a cooperating factor for sustained hematopoietic activity.

Assessment of the Hematopoietic Differentiation Potential of Human Pluripotent Stem Cells in 2D and 3D Culture Systems

BACKGROUND

In vitro methods for hematopoietic differentiation of human pluripotent stem cells (hPSC) are a matter of priority for the in-depth research into the mechanisms of early embryogenesis. So-far, published results regarding the generation of hematopoietic cells come from studies using either 2D or 3D culture formats, hence, it is difficult to discern their particular contribution to the development of the concept of a unique in vitro model in close resemblance to in vivo hematopoiesis.

AIM OF THE STUDY

To assess using the same culture conditions and the same time course, the potential of each of these two formats to support differentiation of human pluripotent stem cells to primitive hematopoiesis without exogenous activation of Wnt signaling.

METHODS

We used in parallel 2D and 3D formats, the same culture environment and assay methods (flow cytometry, IF, qPCR) to investigate stages of commitment and specification of mesodermal, and hemogenic endothelial cells to CD34 hematopoietic cells and evaluated their clonogenic capacity in a CFU system.

RESULTS

We show an adequate formation of mesoderm, an efficient commitment to hemogenic endothelium, a higher number of CD34 hematopoietic cells, and colony-forming capacity potential only in the 3D format-supported differentiation.

CONCLUSIONS

This study shows that the 3D but not the 2D format ensures the induction and realization by endogenous mechanisms of human pluripotent stem cells' intrinsic differentiation program to primitive hematopoietic cells. We propose that the 3D format provides an adequate level of upregulation of the endogenous Wnt/β-catenin signaling.

The pathophysiological role of novel pulmonary arterial hypertension gene SOX17

Pulmonary arterial hypertension (PAH) is a progressive disease predominantly targeting pre-capillary blood vessels. Adverse structural remodelling and increased pulmonary vascular resistance result in cardiac hypertrophy and ultimately failure of the right ventricle. Recent whole-genome and whole-exome sequencing studies have identified SOX17 as a novel risk gene in PAH, with a dominant mode of inheritance and incomplete penetrance. Rare deleterious variants in the gene and more common variants in upstream enhancer sites have both been associated with the disease, and a deficiency of SOX17 expression may predispose to PAH. This review aims to consolidate the evidence linking genetic variants in SOX17 to PAH, and explores the numerous targets and effects of the transcription factor, focusing on the pulmonary vasculature and the pathobiology of PAH.

Sry-related High Mobility Group Box 17 Functions as a Tumor Suppressor by Antagonizing the Wingless-related Integration Site Pathway

A transcription factor Sry-related high mobility group box (Sox) 17 is involved in developmental processes including spermatogenesis, cardiovascular system, endoderm formation, and so on. In this article, we firstly review the studies on the relation between the Sox17 expression and tumor malignancy. Although Sox17 positively promotes various tissue development, most of the cancers associated with Sox17 show decreased expression levels of Sox17, and an inverse correlation between Sox17 expression and malignancy is revealed. We briefly discuss the mechanism of such Sox17 down-regulation by focusing on DNA methylation of CpG sites located in the Sox17 gene promoter. Next, we overview the function of Sox17 in the fetal hematopoiesis, particularly in the dorsal aorta in midgestation mouse embryos. The Sox17 expression in hematopoietic stem cell (HSC)-containing intra-aortic hematopoietic cell cluster (IAHCs) is important for the cluster formation with the hematopoietic ability. The sustained expression of Sox17 in adult bone marrow HSCs and the cells in IAHCs of the dorsal aorta indicate abnormalities that are low lymphocyte chimerism and the aberrant proliferation of common myeloid progenitors in transplantation experiments. We then summarize the perspectives of Sox17 research in cancer control.