Crosstalk between neovessels and mural cells directs the site-specific expression of MT1-MMP to endothelial tip cells

Abstract

The membrane-anchored matrix metalloproteinase MT1-MMP (also known as Mmp14) plays a key role in the angiogenic process, but the mechanisms underlying its spatiotemporal regulation in the in vivo setting have not been defined. Using whole-mount immunohistochemical analysis and the lacZ gene inserted into the Mmp14 gene, we demonstrate that MT1-MMP vascular expression in vivo is confined largely to the sprouting tip of neocapillary structures where endothelial cell proliferation and collagen degradation are coordinately localized. During angiogenesis in vitro, wherein endothelial cells are stimulated to undergo neovessel formation in the presence or absence of accessory mural cells, site-specific MT1-MMP expression is shown to be controlled by crosstalk between endothelial cells and vascular smooth muscle cells (VSMC). When vessel maturation induced by VSMCs is inhibited by introducing a soluble form of the receptor tyrosine kinase Tek, MT1-MMP distribution is no longer restricted to the endothelial tip cells, but instead distributes throughout the neovessel network in vitro as well as ex vivo. Taken together, these data demonstrate that vascular maturation coordinated by endothelial cell/mural cell interactions redirects MT1-MMP expression to the neovessel tip where the protease regulates matrix remodeling at the leading edge of the developing vasculature.

SIRT1 controls endothelial angiogenic functions during vascular growth

“…For example, our data show that loss of SIRT1 down-regulates the expression of genes important for early embryonic vascular development such as the transcription factors Hex and Fli1. Moreover, knockdown of SIRT1 was associated with a reduction of MMP14 (MT1-MMP) expression, a membrane-anchored matrix metalloproteinase critical for the regulation of matrix remodeling and tip cell activity during sprouting angiogenesis (Hiraoka et al 1998;Yana et al 2007). Given the defective sprout formation in response to SIRT1 knockdown observed in our study, MMP14 is a likely downstream effector in the SIRT1-dependent signaling cascade controlling endothelial angiogenic functions.…”

Experimental and theoretical modelling of blind-ended vessels within a developing angiogenic plexus

“…In addition, matrix metalloproteases are released which loosen extracellular matrix interconnections (Roy et al, 2006) permitting the invasion of new blood vessels and other cell types involved in the wound healing response. The predominant process of creating new vascular networks is via sprouting angiogenesis (Carmeliet and Jain, 2000), an invasive process involving the breakdown of the extracellular matrix by invading sprouts (Yana, 2007). Sprouts can be either solid cords composed of endothelial cells or blind-ended vessels (BEVs) which are intermediate structures in angiogenic loop formation (Rhodin and Fujita, 1989;Hashizume and Ushiki, 2002).…”

“…Sprouts can be either solid cords composed of endothelial cells or blind-ended vessels (BEVs) which are intermediate structures in angiogenic loop formation (Rhodin and Fujita, 1989;Hashizume and Ushiki, 2002). Angiogenic sprouts contain specialised tip cells, which secrete matrix-degrading enzymes (Yana, 2007) allowing their invasion into the wound. We first observed capillary sprout formation on day 3, in agreement with observations of the initiation of angiogenesis in several other experimental models of wound healing (Scholz, 2003;Phillips et al, 1991;Sephel et al, 1996;Wagatsuma, 2007).…”

Emerging roles of SIRT1 in vascular endothelial homeostasis

“…38 Although the upstream mechanisms (direct and indirect) leading to the dysregulation of most of these genes remain to be determined, they provide interesting mechanistic insights of how SIRT1 might coordinate signaling networks and affects endothelial cell behavior. As such, the SIRT1 siRNA induced reduction of MMP14 (MT1-MMP), a membrane-anchored matrix metalloproteinase essential for tip cell activity during sprouting angiogenesis, 72,73 suggests that it might contribute to the path-finding defects observed in the SIRT1-deficient zebrafish. 38 In addition, the altered expression of genes involved in TGFβ signaling suggests that SIRT1 might be a key modulator of this signaling pathway by interfering with an upstream regulator or even an TGFβ transcriptional effector such as SMAD proteins.…”