Svep1 stabilises developmental vascular anastomosis in reduced flow conditions

Abstract

Molecular mechanisms controlling the formation, stabilization and maintenance of blood vessel connections remain poorly defined. Here we identify blood flow and the large extracellular protein Svep1 as co-modulators of vessel anastomosis during developmental angiogenesis in zebrafish embryos. Both loss of Svep1 and blood flow reduction contribute to defective anastomosis of intersegmental vessels. The reduced formation and lumenisation of the dorsal longitudinal anastomotic vessel (DLAV) is associated with a compensatory increase in Vegfa/Vegfr pERK signalling, concomittant expansion of apelin-positive tip cells, but reduced expression of klf2. Experimentally, further increasing Vegfa/Vegfr signalling can rescue the DLAV formation and lumenisation defects, while its inhibition dramatically exacerbates the loss of connectivity. Mechanistically, our results suggest that flow and Svep1 co-regulate the stabilization of vascular connections, in part by modulating the Vegfa/Vegfr signalling pathway.

Svep1 is a binding ligand of Tie1 and affects specific aspects of facial lymphatic development in a Vegfc-independent manner

“…While svep1 mutants were initially identified on the basis of their lymphatic phenotype ( Karpanen et al, 2017 ), Coxam et al recently showed that svep1 mutant embryos display unique vascular defects under reduced flow conditions ( Coxam et al, 2022 ). Treatment of embryos with 0.014% tricaine between 30 and 48 hpf leads to incomplete formation of the dorsal longitudinal anastomotic vessel (DLAV) with gaps and non-lumenized DLAV segments at 2 dpf in svep1 mutant embryos.…”

“…Treatment of embryos with 0.014% tricaine between 30 and 48 hpf leads to incomplete formation of the dorsal longitudinal anastomotic vessel (DLAV) with gaps and non-lumenized DLAV segments at 2 dpf in svep1 mutant embryos. This phenotype is accompanied by increased Vegfa/Vegfr signalling and increased number of Apelin positive tip cells ( Coxam et al, 2022 ). To investigate if tie1 mutants mimic this very specific and unusual vascular defect, we treated embryos from tie1 heterozygous parents with 0.014% tricaine between 30 and 48 hpf, and subsequently imaged the intersegmental vessels in the trunk.…”

svep1 and tie1 genetically interact and affect aspects of facial lymphatic development in a Vegfc-independent manner

“…Since we could observe the same specific migratory defects in both svep1 and tie1 mutants, these results further support a possible cross-talk between both proteins. signalling and increased number of Apelin positive tip cells (Coxam et al, 2022). To investigate if tie1 mutants mimic this very specific and unusual vascular defect, we treated embryos from tie1 heterozygous parents with 0.014 % tricaine between 30 hpf and 48 hpf, and subsequently imaged the intersegmental vessels in the trunk.…”

“…D') Magnification and reduced stack numbers of boxed area in D). E) Quantification of gaps in the DLAV in sibling and tie1 mutants that were either untreated or treated with 0.014 % tricaine revealed significant increase of gaps in the DLAV in tie1 mutants according toCoxam et al, 2022. F) Quantification of lumenised trunk segments of the DLAV in siblings and tie1 mutants, either untreated or treated with 0.014 % tricaine (siblings untreated: n= 16; tie1-/untreated: n= 20; siblings treated with 0.014% tricaine: n= 20; tie1-/-treated with 0.014% tricaine: n= 22), revealed significant decrease of lumenised segments in the DLAV in tie1 mutants.…”

“…G, H) apelin:eGFP and flt1:tdTomato expression in 48 hpf old embryos after tricaine treatment from 30-48 hpf and I,J) in untreated conditions. K) Maximum intensity projection of an aISV at 48 hpf, highlighting the ventral and dorsal region used for further quantifications in J) adapted from(Coxam et al, 2022). L) Quantification of ISVs with apelin expression in dorsal and ventral parts of the ISVs.…”