Endothelial TGF-β signaling instructs smooth muscle development in the cardiac outflow tract

Abstract

19The development of the cardiac outflow tract (OFT), which connects the heart to the great 20 arteries, relies on a complex crosstalk between endothelial (ECs) and smooth muscle (SMCs) 21 cells. Defects in OFT development can lead to severe malformations, including aortic 22 aneurysms, which have often been associated with impaired TGF-β signaling. To further 23 investigate the role of TGF-β signaling in OFT formation, we generated zebrafish lacking the 24 type I TGF-β receptor Alk5 and found a strikingly specific dilation of the OFT. alk5 mutants 25 also exhibit increased EC numbers, extracellular matrix (ECM) and SMC disorganization. 26 Surprisingly, endothelial-specific alk5 overexpression in alk5 mutants rescues both 27 endothelial and SMC defects. Furthermore, modulation of the ECM gene fibulin-5, a TGF-β 28 target, partially restores OFT morphology and function. These findings reveal a new 29 requirement for endothelial TGF-β signaling in OFT morphogenesis and suggest an important 30 role for the endothelium in the etiology of aortic malformations.31 32

Integration of multiple imaging platforms to uncover cardiac defects in adult zebrafish

“…Overall, our data indicate that while the loss of alk5a alone does not cause embryonic defects (Boezio et al, 2020), it can cause a cardiac defect symptomatic only at later stages. Our data also identify the OFT (orthologous to the mammalian aortic root) as the main compartment affected in alk5a mutants.…”

“…We elected to investigate alk5a mutants ( Figure 1A), a third type of mutant, i.e., one that does not exhibit embryonic phenotypes or pericardial edema at adult stages but can potentially develop cardiac phenotypes. alk5a; alk5b double mutants exhibit severe pericardial edema at early developmental stages, due to a defective outflow tract (OFT) (Boezio et al, 2020). In contrast, alk5a single mutant larvae do not exhibit any obvious defects ( Figure 1 -figure supplement 1 A, B), including in the cardiovascular system (Figure 1 -figure supplement 1 C-D'), and survive to adulthood.…”

“…All the fish used in the study were in the Tg(kdrl:eGFP) s843 (Jin et al, 2005) background. The tgfbr1a bns329 fish (Boezio et al, 2020) carry a 2 bp insertion and a 6 bp deletion in exon 1. For all the experiments, maternal zygotic tgfbr1a -/fish were analyzed and compared to WT fish.…”

Transcriptional drifts associated with environmental changes in endothelial cells

“…It can be postulated that loss of architecture in-vitro could induce the loss of expression of acute phase transcripts, as seen with injury of the aorta in vivo (54). These endothelial-heterotypic crosstalks have been shown essential during development and vascular pathologies such as aneurysms (55).…”

A zebrafish forward genetic screen identifies an indispensable threonine residue in the kinase domain of PRKD2

“…Pathways that play crucial role in atrioventricular development are emerging to be involved also in shaping the outflow tract. These include the Yap1 klf2a/Notch axis (Duchemin et al, 2019) as well as Tgfβ (Boezio et al, 2020). Based on that, it is not surprising that prkd2 mutants show defects both in the bulbus arteriosus (initially) and the atrioventricular valve.…”