Peri-arterial specification of vascular mural cells from naïve mesenchyme requires Notch signaling

Abstract

Mural cells (MCs) are essential for blood vessel stability and function; however, the mechanisms that regulate MC development remain incompletely understood, in particular those involved in MC specification. Here, we investigated the first steps of MC formation in zebrafish using transgenic reporters. Using pdgfrb and abcc9 reporters, we show that the onset of expression of abcc9, a pericyte marker in adult mice and zebrafish, occurs almost coincidentally with an increment in pdgfrb expression in peri-arterial mesenchymal cells, suggesting that these transcriptional changes mark the specification of MC lineage cells from naïve pdgfrb low mesenchymal cells. The emergence of peri-arterial pdgfrb high MCs required Notch signaling. We found that pdgfrb-positive cells express notch2 in addition to notch3, and although depletion of notch2 or notch3 failed to block MC emergence, embryos depleted of both notch2 and notch3 lost mesoderm-as well as neural crest-derived pdgfrb high MCs. Using reporters that read out Notch signaling and Notch2 receptor cleavage, we show that Notch activation in the mesenchyme precedes specification into pdgfrb high MCs. Taken together, these results show that Notch signaling is necessary for peri-arterial MC specification.

Dual function of perivascular fibroblasts in vascular stabilization in zebrafish

“…Consistent with our results, vSMCs around the dorsal aorta have been traced back to cells derived from the sclerotome in zebrafish (50). In addition, mural cells in the zebrafish trunk vessels have been shown to be dependent on the mesoderm but not the neural crest lineage (57). Thus, blood vessel support cells in the zebrafish trunk, including perivascular fibroblasts and mural cells, likely originate from the sclerotome.…”

“…In the first scenario, all perivascular fibroblasts have the equal potential to differentiate into pericytes, but extrinsic cues determine which cell to switch on the pericyte fate. Notch signaling has been implicated in the regulation of pericyte formation in both mouse and zebrafish (57; 60–63). In particular, recent work in zebrafish has shown that the activation of Notch signaling in naïve mesenchymal cells (likely corresponding to perivascular fibroblasts in our study) is crucial to induce pericyte differentiation around ISVs (Ando et al, 2019).…”

Emerging links between cerebrovascular and neurodegenerative diseases—a special role for pericytes

“…Interestingly, imatinib (Gleevec) has been shown to improve BBB integrity caused by pericyte deficiency [20], and cilostazol/iloprost reduces pericyte detachment in an experimental stroke model in rat [168]. A complementary, although less high-throughput, model system for drug screening is zebrafish, where the combination of transparent embryogenesis and new fluorescent reporters to identify the various vascular cell types allows BBB function and other aspects of vascular biology to be monitored in vivo [173] (for review see ref. The study of BBB integrity in in vitro systems could clearly accelerate research and allow high-throughput screens to be conducted (for review see ref.…”

“…Such three-dimensional tissue-mimicking systems may be better approximations of the in vivo situation than their two-dimensional counterparts, and it will be interesting to learn whether these systems will accelerate the discovery of therapeutic agents and provide new insights into mechanisms affecting BBB integrity. A complementary, although less high-throughput, model system for drug screening is zebrafish, where the combination of transparent embryogenesis and new fluorescent reporters to identify the various vascular cell types allows BBB function and other aspects of vascular biology to be monitored in vivo [173] (for review see ref. [174]).…”

Notch3 in Development, Health and Disease

“…Further work has shown that Notch3 also has roles at earlier steps in the VSMC lineage, which are masked by partial redundancy with other Notch homologues. In zebrafish, Notch2 and Notch3 act together to regulate production during embryogenesis of both mesoderm-derived and neural crest-derived mural cells, the precursors of VSMCs [32]. A similar redundancy is found in mice as Notch2, Notch3 double mutants are embryo lethal with severe loss of VSMCs and vascular abnormalities [33].…”