Using Spatial Transcriptomics to Reveal Fetal Liver Hematopoietic Stem Cell-Niche Interactions

The hematopoietic stem cell (HSC) microenvironment, termed the niche, supports the proliferation, self-renewal, and differentiation abilities of HSCs. The definitive HSCs emerge from the hemogenic endothelium in the aorta-gonad-mesonephros (AGM) region after E11.5, and then migrate to the fetal liver after E12.5 for expansion. After E17.5, HSCs migrate to the bone marrow and reside in the bone marrow for the postnatal stage and adulthood. Because the fetal liver is thought to be a harbor for the rapid expansion of HSCs, numerous studies have focused on the fetal liver HSC niche in the search for novel niche factors and niche cells that support HSC expansion. However, to our knowledge, there are no successes in translating the niche factors to a clinical application for the expansion of HSCs ex vivo. In this study, we are using cutting-edge spatial transcriptomics to comprehensively study the transcriptomics and interactions between HSCs and the niche cells in the fetal liver, and in search of the niche cells and factors for HSC expansion. To understand the spatial distribution and interactions between HSCs and niche cells in the fetal liver, we introduced 2 spatial transcriptomic methods, slide-seq, and 10x Visium, in our study on E14.5 mouse fetal liver. By integrating with a parallel single-cell sequencing analysis, we revealed the spatial transcriptomics of HSCs and potential niche cells, including hepatoblasts, endothelium cells, macrophages, megakaryocytes, and hepatic stellate cells/perivascular mesenchymal cells (PMCs) in E14.5 mouse fetal liver. Interestingly, we found that the PMCs were characterized by enriched N-cadherin expression. Both slide-seq and 10x Visium showed that the N-cadherin-expressing PMCs are enriched in the portal vessel area. Importantly, the majority of fetal liver HSCs are in close proximity to N-cadherin-expressing PMCs, indicating a supportive role of N-cadherin-expressing PMCs in HSC maintenance. Subsequent CellPhoneDB (CPDB) analysis demonstrated that the N-cadherin-expressing PMCs are major niche-signaling senders with an enriched expression of niche factors, such as CXCL12 and KITL, and stemness pathway-related ligands, such as IGF1, IGF2, TGFβ2, TGFβ3, JAG2, and DLK1, indicating N-cadherin-expressing PMCs could be the major niche cells in supporting HSCs in the fetal liver. This finding was consistent with our previous finding that N-cadherin-expressing bone and marrow stromal progenitor cells can maintain reserve HSCs in the adult bone marrow. Moreover, CPDB analysis indicated that other potential niche cells, such as endothelium cells, macrophages, and megakaryocytes, may support HSCs in different signal transduction pathways. For example, endothelium cells have an enriched expression of KITL, IGF2, DLL1, TGFβ1, and TGFβ2; macrophages have enriched expression of KITL, IFNγ, and TGFβ1; megakaryocytes have enriched expression of PF4, JAG2 and TGFβ1. Intriguingly, our previous studies showed that megakaryocytes could promote HSC expansion under stress conditions in the bone marrow. To investigate the potential role of N-cadherin-expressing cells in supporting fetal liver HSCs, we generated an N-cad CreER;Cxcl12 and an N-cad CreER;Scf mouse model to conditionally knockout the well-studied niche factors, CXCL12 and SCF, in N-cadherin-expressing cells. Conditional knockout of either Cxcl12 or Scf in N-cadherin-expressing cells resulted in an increase in the number of HSCs. Moreover, conditional knockout of Cxcxl12 in N-cadherin-expressing cells also resulted in a myeloid-biased differentiation. We postulate that the knockout of Cxcl12 or Scf in N-cadherin-expressing cells leads to the migration of HSCs towards other potential niche cells, such as macrophages and megakaryocytes, which may induce HSC expansion and biased differentiation. In summary, by using cutting-edge spatial transcriptomics, we revealed a comprehensive spatial transcriptomics of HSCs and niche cells in E14.5 mouse fetal liver. The N-cadherin-expressing cells in the fetal liver is a major niche in maintaining HSCs, while other potential niches may be responsible for the expansion of HSCs. In the future, we will use multiple approaches, such as spatial transcriptomics and fluorescence in situ hybridization (FISH), to verify the distribution changes of HSCs in N-cad CreER;Cxcl12 mouse, and to reveal the niches in support of the expansion of HSCs. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

C-C Motif Chemokine 8 promotes angiogenesis in vascular endothelial cells

Objectives Angiogenesis is an important progress associated with several pathological situations. Several chemokines have been reported to act as regulators of angiogenesis. The current study aimed to find whether C-C Motif Chemokine 8 is involved in angiogenesis regulation. Methods To verify whether C-C Motif Chemokine 8 is related to angiogenesis in plaques, carotid plaques were collected from patients with severe carotid stenosis and analysed using CD31 immunohistochemistry and real-time PCR. To further clarify the relation between C-C Motif Chemokine 8 and angiogenesis, human umbilical vein endothelium cells and human dermal microvascular endothelial cells were treated with C-C Motif Chemokine 8 in the presence or absence of C-C motif chemokine receptor 2-Ab and extracellular regulated MAP kinase 1/2 inhibition (FR180204). Proliferation and migration of human umbilical vein endothelium cells and human dermal microvascular endothelial cells were examined with Cell Counting Kit-8 and Transwell chamber assay, respectively. In vitro angiogenesis stimulated by C-C Motif Chemokine 8 was examined using tube formation assay. Ex vivo and in vivo angiogenesis were assessed by mice aortic ring assay and Matrigel plug assay, respectively. C-C motif chemokine receptors of human umbilical vein endothelium cells were examined with real-time PCR, and C-C motif chemokine receptor 1, C-C motif chemokine receptor 2, extracellular regulated MAP kinase 1/2 and phosphorylation-extracellular regulated MAP kinase 1/2 were examined with western blotting assay. Results C-C Motif Chemokine 8 was increased in carotid plaques with severe angiogenesis in both RNA and protein level. C-C Motif Chemokine 8 (5 ng/ml) weakly increased human umbilical vein endothelium cell proliferation, but not on human dermal microvascular endothelial cells. Migration and tube formation could be induced by C-C Motif Chemokine 8 in both human umbilical vein endothelium cells and human dermal microvascular endothelial cells. In mice aortic ring assay and Matrigel plug assay, C-C Motif Chemokine 8 could promote angiogenesis compared to vehicle groups. Phosphorylation of extracellular regulated MAP kinase 1/2 was increased with C-C Motif Chemokine 8 stimulation. The migration and tube formation promoted by C-C Motif Chemokine 8 could be largely blocked by C-C motif chemokine receptor 2-Ab or extracellular regulated MAP kinase 1/2 inhibition (FR180204). Conclusions C-C Motif Chemokine 8 could promote both in vitro and in vivo angiogenesis. C-C motif chemokine receptor 2 played an important role in the activation of C-C Motif Chemokine 8 and extracellular regulated MAP kinase 1/2 signalling pathway was involved in this mechanism.

The Heat Shock Protein 70 Plays a Protective Role in Sepsis by Maintenance of the Endothelial Permeability

Sepsis is a severe system inflammatory response syndrome in response to infection. The vascular endothelium cells play a key role in sepsis-induced organ dysfunction. The heat shock protein 70 (HSP70) has been reported to play an anti-inflammatory role and protect from sepsis. The present study is aimed at finding the function of HSP70 against sepsis in vascular endothelium cells. Lipopolysaccharide (LPS) and HSP70 agonist and inhibitor were used to treat HUVEC. Cell permeability was measured by transepithelial electrical resistance (TEER) assay and FITC-Dextrans. Cell junction protein levels were measured by western blot. Mice were subjected to cecal ligation and puncture (CLP) to establish a sepsis model and were observed for survival. After LPS incubation, HSP70 expression was decreased in HUVEC. LPS induced the inhibition of cell viability and the increases of IL-1β, IL-6, and TNF-α. Furthermore, cell permeability was increased and cell junction proteins (E-cadherin, occludin, and ZO-1) were downregulated after treatment with LPS. However, HSP70 could reverse these effects induced by LPS in HUVEC. In addition, LPS-induced elevated phosphorylation of p38 can be blocked by HSP70. On the other hand, we found that inhibition of HSP70 had similar effects as LPS and these effects could be alleviated by the inhibitor of p38. Subsequently, HSP70 was also found to increase survival of sepsis mice in vivo. In conclusion, HSP70 plays a protective role in sepsis by maintenance of the endothelial permeability via regulating p38 signaling.

Fumonisin B1 Induces Oxidative Stress and Breaks Barrier Functions in Pig Iliac Endothelium Cells

Fumonisins (Fums) are types of mycotoxin that widely contaminante feed material crops, and can trigger potential biological toxicities to humans and various animals. However, the toxicity of Fums on porcine blood vessels has not been fully explored. Fumonisin B1 (FB1) is the main component of Fums. Therefore, the aim of this study was to explore the effects of FB1 on the oxidative stress and tight junctions of the pig iliac endothelial cells (PIECs) in vitro. The results showed that FB1 reduced the viability of PIECs, increased the contents of lipid peroxidation product malondialdehyde (MDA), decreased the activities of antioxidant enzymes superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), catalase (CAT) and thioredoxin reductase (TrxR), and decreased the level of glutathione (GSH). In addition, the barrier functions were destroyed, along with the down-regulations on Claudin 1, Occludin and ZO-1 and the increase of paracellular permeability. Thus, this research indicates that FB1 facilitates oxidative stress and breaks barrier functions to damage pig iliac endothelium cells.