Implanted microvessels progress through distinct neovascularization phenotypes

Abstract

We have previously demonstrated that implanted microvessels form a new microcirculation with minimal host-derived vessel investment. Our objective was to define the vascular phenotypes present during neovascularization in these implants and identify post-angiogenesis events. Morphological, functional and transcriptional assessments identified three distinct vascular phenotypes in the implants: sprouting angiogenesis, neovascular remodeling, and network maturation. A sprouting angiogenic phenotype appeared first, characterized by high proliferation and low mural cell coverage. This was followed by a neovascular remodeling phenotype characterized by a perfused, poorly organized neovascular network, reduced proliferation, and re-associated mural cells. The last phenotype included a vascular network organized into a stereotypical tree structure containing vessels with normal perivascular cell associations. In addition, proliferation was low and was restricted to the walls of larger microvessels. The transition from angiogenesis to neovascular remodeling coincided with the appearance of blood flow in the implant neovasculature. Analysis of vascularspecific and global gene expression indicates that the intermediate, neovascular remodeling phenotype is transcriptionally distinct from the other two phenotypes. Therefore, this vascular phenotype likely is not simply a transitional phenotype but a distinct vascular phenotype involving unique cellular and vascular processes. Furthermore, this neovascular remodeling phase may be a normal aspect of the general neovascularization process. Given that this phenotype is arguably dysfunctional, many of the microvasculatures present within compromised or diseased tissues may not represent a failure to progress appropriately through a normally occurring neovascularization phenotype.

Large-scale time series microscopy of neovessel growth during angiogenesis

“…In this system, neovessels spontaneously sprout from the intact, parent microvessel in a manner analogous to what is thought to occur in-vivo [20]. Furthermore, the neovasculature that arises from the parent microvessels in this model recapitulates all of the post-angiogenesis vascular activities necessary to form a mature, stable and functional microcirculation when implanted [13,21,20,22].…”

Vascularization strategies of engineered tissues and their application in cardiac regeneration

“…This was followed by a neovascular remodeling phenotype by 14 days characterized by a perfused, poorly organized neovascular network, reduced proliferation, and recruitment of mural cells. The last phenotype, present by days 21-28, included a vascular network organized into a stereotypical tree structure containing vessels with normal perivascular cell associations [60]. In addition, after in vivo implantation, MF-based constructs were able to generate vessels with specific arterio-venous phenotypes, as characterised by the presence of either EphrinB2 or EphB4 positive vessels (arterial and venous identity, respectively) (Fig.…”

“…Page 16 of 42 embedded in 3D collagen gels, MFs from mouse [60], rat [21,61] and human sources [61] can form a microvascular bed, without the addition of exogenous growth factors, forming vascularized constructs in vitro. When vascular constructs were implanted subcutaneously in severe combined-immunodeficient (SCID) mice, the vasculature inosculated with the host circulation and expanded into a microvascular bed containing perfused, mature heterogeneous vessel elements [61].…”

“…This system also reproduces important aspects of vascularization, angiogenesis, inosculation, and network remodelling [61]. When the vascular characteristics present during neovascularization in these implants were analyzed on the aspects of morphology, function and transcription, three distinct vascular phenotypes in the implants were identified: sprouting angiogenesis, neovascular remodeling, and network maturation [60]. A sprouting angiogenic phenotype appeared by 7 days post-implantation, characterized by high proliferation and low mural cell coverage.…”

Biofabrication of Vascular Networks

“…In the adult, microvascular beds are expanded primarily via angiogenesis coupled with those subsequent vascular processes leading to interconnected, mature vessels (postangiogenesis) [25]. For purposes of fabricating vascular networks, angiogenesis is an effective means to generate the vessel segments of the new tree.…”