SummaryEndothelial cell (EC) identity is in part genetically predetermined. Transcription factor NR2F2 (also known as chicken ovalbumin upstream promoter transcription factor II, COUP-TFII) plays a key role in EC fate decision making; however, many of the underlying mechanisms remain enigmatic. In the present study, we demonstrate that NR2F2 differentially regulates gene expression of venous versus lymphatic ECs (LECs) and document a novel paradigm whereby NR2F2 homodimers induce a venous EC fate, while heterodimers with the LEC-specific transcription factor PROX1 instruct LEC lineage specification. NR2F2 homodimers inhibit arterial differentiation in venous ECs through direct binding to the promoter regions of the Notch target genes HEY1 and HEY2 (HEY1/2), whereas NR2F2/PROX1 heterodimers lack this inhibitory effect, resulting at least in part in non-canonical HEY1/2 expression in LECs. Furthermore, NR2F2/PROX1 heterodimers actively induce or are permissive for the expression of a major subset of LEC-specific genes. In addition to NR2F2/PROX1 heterodimerisation, the expression of HEY1 and some of these LEC-specific genes is dependent on PROX1 DNA binding. Thus, NR2F2 homodimers in venous ECs and NR2F2/PROX1 heterodimers in LECs differentially regulate EC subtype-specific genes and pathways, most prominently the Notch target genes HEY1/2. This novel mechanistic insight could pave the way for new therapeutic interventions for vascular-bed-specific disorders.

Chronic liver diseases are characterized by the expansion of ductular reaction (DR) cells and the expression of liver progenitor cell (LPC) markers. In alcoholic hepatitis (AH), the degree of DR expansion correlates with disease progression and short‐term survival. However, little is known about the biological properties of DR cells, their impact on the pathogenesis of human liver disease, and their contribution to tissue repair. In this study, we have evaluated the transcriptomic profile of DR cells by laser capture microdissection in patients with AH and assessed its association with disease progression. The transcriptome analysis of cytokeratin 7‐positive (KRT7+) DR cells uncovered intrinsic gene pathways expressed in DR and genes associated with alcoholic liver disease progression. Importantly, DR presented a proinflammatory profile with expression of neutrophil recruiting C‐X‐C motif chemokine ligand (CXC) and C‐C motif chemokine ligand chemokines. Moreover, LPC markers correlated with liver expression and circulating levels of inflammatory mediators such as CXCL5. Histologically, DR was associated with neutrophil infiltration at the periportal area. In order to model the DR and to assess its functional role, we generated LPC organoids derived from patients with cirrhosis. Liver organoids mimicked the transcriptomic and proinflammatory profile of DR cells. Conditioned medium from organoids induced neutrophil migration and enhanced cytokine expression in neutrophils. Likewise, neutrophils promoted the proinflammatory profile and the expression of chemokines of liver organoids. Conclusion: Transcriptomic and functional analysis of KRT7+ cells indicate that DR has a proinflammatory profile and promote neutrophil recruitment. These results indicate that DR may be involved in the liver inflammatory response in AH, and suggest that therapeutic strategies targeting DR cells may be useful to mitigate the inflammatory cell recruitment in AH.

SummaryIn early mouse pre-implantation development, primitive endoderm (PrE) precursors are platelet-derived growth factor receptor alpha (PDGFRα) positive. Here, we demonstrated that cultured mouse embryonic stem cells (mESCs) express PDGFRα heterogeneously, fluctuating between a PDGFRα+ (PrE-primed) and a platelet endothelial cell adhesion molecule 1 (PECAM1)-positive state (epiblast-primed). The two surface markers can be co-detected on a third subpopulation, expressing epiblast and PrE determinants (double-positive). In vitro, these subpopulations differ in their self-renewal and differentiation capability, transcriptional and epigenetic states. In vivo, double-positive cells contributed to epiblast and PrE, while PrE-primed cells exclusively contributed to PrE derivatives. The transcriptome of PDGFRα+ subpopulations differs from previously described subpopulations and shows similarities with early/mid blastocyst cells. The heterogeneity did not depend on PDGFRα but on leukemia inhibitory factor and fibroblast growth factor signaling and DNA methylation. Thus, PDGFRα+ cells represent the in vitro counterpart of in vivo PrE precursors, and their selection from cultured mESCs yields pure PrE precursors.