Compensatory signalling induced in the yolk sac vasculature by deletion of TGFβ receptors in mice

Abstract

Vascular development depends on transforming growth factor β (TGFβ), but whether signalling of this protein is required for the development of endothelial cells (ECs), vascular smooth muscle cells (VSMCs) or both is unclear. To address this, we selectively deleted the type I (ALK5, TGFBR1) and type II (TβRII, TGFBR2) receptors in mice. Absence of either receptor in ECs resulted in vascular defects in the yolk sac, as seen in mice lacking receptors in all cells, causing embryonic lethality at embryonic day (E)10.5. Deletion of TβRII specifically in VSMCs also resulted in vascular defects in the yolk sac; however, these were observed at later stages of development, allowing the embryo to survive to E12.5. Because TGFβ can also signal in ECs via ALK1 (ACVRL1), we replaced ALK5 by a mutant defective in SMAD2 and SMAD3 (SMAD2/3) activation that retained the ability to transactivate ALK1. This again caused defects in the yolk sac vasculature with embryonic lethality at E10.5, demonstrating that TGFβ/ALK1 signalling in ECs cannot compensate for the lack of TGFβ/ALK5-induced SMAD2/3 signalling in vivo. Unexpectedly, SMAD2 phosphorylation and α-smooth muscle actin (SMAα, ACTA2) expression occurred in the yolk sacs of ALK5–/– embryos and ALK5–/– embryonic stem cells undergoing vasculogenesis, and these processes could be blocked by an ALK4 (ACVR1B)/ALK5 inhibitor. Together, the data show that ALK5 is required in ECs and VSMCs for yolk sac vasculogenesis; in the absence of ALK5, ALK4 mediates SMAD2 phosphorylation and consequently SMAα expression.

Differential Roles of Macrophages in Diverse Phases of Skin Repair

“…To identify mechanisms that might mediate endothelial cell damage, we stained wound tissue for VEGF-A and TGF-b1; both are signature mediators of vascular homeostasis and endothelial cell survival (30,31). As demonstrated earlier in Fig.…”

The TGFβ type II receptor plays a critical role in the endothelial cells during cardiac development

“…By using an inducible endothelial Cre to inactivate Tgfbr2, we were able to bypass the embryonic lethality at E10.5 to E11.5 caused by the constitutively expressed Tie2-Cre or Tie1-Cre lines (Jiao et al, 2006;Carvalho et al, 2007). We, therefore, activated Cre in ECs from E11.5, which also corresponds to the stage at which endothelial to mesenchymal transformation is almost complete.…”

Co-ordinating Notch, BMP, and TGF-β signaling during heart valve development

“…To circumvent the early lethality, tissue-specific knockout mice have been used to assess TGFβ receptor functions in heart valve development. Interestingly, loss of ALK5 in endothelium using Tyrosine kinase 1 (Tie1)-or 2-(Tie2) Cre strains results in embryonic lethality at E10.5 and E13, respectively [92,93]. More specifically, embryos lacking ALK5 in Tie1 expressing cells die at E10.5 due to vascular defects in the yolk sac, similar to the complete knockout mouse [92], while loss of ALK5 in Tie2 expressing cells leads to embryonic lethality at E13 as a result of hypoplastic cardiac cushions and abnormal myocardial trabeculation [93].…”

“…Interestingly, loss of ALK5 in endothelium using Tyrosine kinase 1 (Tie1)-or 2-(Tie2) Cre strains results in embryonic lethality at E10.5 and E13, respectively [92,93]. More specifically, embryos lacking ALK5 in Tie1 expressing cells die at E10.5 due to vascular defects in the yolk sac, similar to the complete knockout mouse [92], while loss of ALK5 in Tie2 expressing cells leads to embryonic lethality at E13 as a result of hypoplastic cardiac cushions and abnormal myocardial trabeculation [93]. Both in vitro and in vivo data show that no mesenchymal cells migrate into the cushions in Tie2 endothelialspecific ALK5 knockout mice [93].…”

“…Deletion of TβRII in endothelial cells using Tie1-Cre generates vascular defects in the yolk sac comparable to the complete loss of TβRII [92]. Loss of TβRII Tie2-Cre results in embryonic lethality by E11.5 or E12.5 [95].…”