A small population of liver endothelial cells undergoes endothelial-to-mesenchymal transition in response to chronic liver injury

Abstract

Rising evidence points to endothelial-to-mesenchymal transition (EndMT) as a significant source of the mesenchymal cell population in fibrotic diseases. In this context, we hypothesized that liver endothelial cells undergo EndMT during fibrosis progression. Cirrhosis in mice was induced by CCl A transgenic mouse expressing a red fluorescent protein reporter under the control of Tie2 promoter (Tie2-tdTomato) was used to trace the acquisition of EndMT. Sinusoidal vascular connectivity was evaluated by intravital microscopy and high-resolution three-dimensional confocal microscopy. A modest but significant fraction of liver endothelial cells from both cirrhotic patients and CCl-treated Tie2-tdTomato mice acquired an EndMT phenotype characterized by the coexpression of CD31 and α-smooth muscle actin, compared with noncirrhotic livers. Bone morphogenetic protein-7 (BMP-7) inhibited the acquisition of EndMT induced by transforming growth factor-β1 (TGF-β1) treatment in cultured primary mouse liver endothelial cells from control mice. EndMT was also reduced significantly in vivo in cirrhotic Tie2-tdTomato mice treated intraperitoneally with BMP-7 compared with untreated mice (1.9 ± 0.2 vs. 3.8 ± 0.3%, respectively; < 0.05). The decrease of EndMT in cirrhotic livers correlated with a significant decrease in liver fibrosis ( < 0.05) and an improvement in the vascular disorganization rate ( < 0.05). We demonstrated the acquisition of the EndMT phenotype by a subpopulation of endothelial cells from cirrhotic livers in both animal models and patients. BMP-7 treatment decreases the occurrence of the EndMT phenotype and has a positive impact on the severity of disease by reducing fibrosis and sinusoidal vascular disorganization. A subpopulation of liver endothelial cells from cirrhotic patients and mice with liver fibrosis undergoes endothelial-to-mesenchymal transition. Liver endothelial cells from healthy mice could transition into a mesenchymal phenotype in culture in response to TGF-β1 treatment. Fibrotic livers treated chronically with BMP-7 showed lower EndMT acquisition, reduced fibrosis, and improved vascular organization.

The Endothelium as a Driver of Liver Fibrosis and Regeneration

“…Their direct contribution is due to the synthesis of laminin and collagen in response to TGFβ1 after sustained injury [159]. Whether endothelial cells generated from endothelial-to-mesenchymal transition [160] may contribute to ECM deposition remains a field of research.…”

Single-cell transcriptomics reveals zone-specific alterations of liver sinusoidal endothelial cells in cirrhosis

“…Even if liver ECs underwent EndMT in vivo, their population would be very small, as also indicated by Ribera et al (30) results and ours may come from the difference of the study subjects, i.e., humans and mice. It should be mentioned that the same group of researchers recently showed the zonation pattern of hepatic stellate cells (HSCs), which was conserved between healthy and fibrotic mouse livers (3) .…”

“…Several studies reported that LSECs undergo EndMT in response to chronic liver injury (30)(31)(32) . In contrast, we did not find notable increases in mesenchymal markers, such as Figure 6).…”

“…Several studies on fibrotic diseases, including cardiac fibrosis (61) , renal fibrosis (62) and pulmonary fibrosis (60 63) , indicated that ECs could give rise to myofibroblasts through EndMT. In liver fibrosis too, some studies indicated EndMT in LSECs (30)(31)(32) . In contrast, we did not find evidence of EndMT in LSECs in cirrhotic livers in our scRNA-seq data as well as immunostaining of liver sections from two models of liver fibrosis/cirrhosis [CCl 4 inhalation and bile duct ligation (BDL) models] using EC-GFP reporter mice (Figure 8), although LSECs underwent EndMT in a cultured condition in a time dependent manner (Supplemental Figure 6).…”

The Vascular Involvement in Soft Tissue Fibrosis—Lessons Learned from Pathological Scarring

“…Regarding liver fibrosis, patients and mice with liver cirrhosis bear a modest but still noticeable subpopulation of liver endothelial cells that express both CD31 and α-SMA. Moreover, when mice with liver cirrhosis were treated with BMP-7 (which prevents cultured murine liver endothelial cells from undergoing TGF-β1-induced EndoMT), their liver fibrosis improved [62].…”