α5 and αv integrins cooperate to regulate vascular smooth muscle and neural crest functions in vivo

Abstract

The RGD-binding α5 and αv integrins have been shown to be key regulators of vascular smooth muscle cell (vSMC) function in vitro. However, their role on vSMCs during vascular development in vivo remains unclear. To address this issue, we have generated mice that lack α5, αv or both α5 and αv integrins on their vSMCs, using the SM22α-Cre transgenic mouse line. To our surprise, neither α5 nor αv mutants displayed any obvious vascular defects during embryonic development. By contrast, mice lacking both α5 and αv integrins developed interrupted aortic arches, large brachiocephalic/ carotid artery aneurysms and cardiac septation defects, but developed extensive and apparently normal vasculature in the skin. Cardiovascular defects were also found, along with cleft palates and ectopically located thymi, in Wnt1-Cre α5/αv mutants, suggesting that α5 and αv cooperate on neural crest-derived cells to control the remodelling of the pharyngeal arches and the septation of the heart and outflow tract. Analysis of cultured α5/αv-deficient vSMCs suggests that this is achieved, at least in part, through proper assembly of RGD-containing extracellular matrix proteins and the correct incorporation and activation of latent TGF-β.

Neural crest cell-autonomous roles of fibronectin in cardiovascular development

“…Similarly, Turlo et al (2012) used the SM22α-Cre transgenic line to ablate integrin β1 and showed that the expression of β1-containing integrin heterodimers, which include α5β1, in smooth muscle cells was important for maintaining AAA VSMCs and AAA integrity. Taken together with the studies by Turlo et al (2012) and Turner et al (2015), our work demonstrates that signaling by Fn1 and integrin α5β1 is essential for both the morphogenesis and maintenance of the AAAs: our studies establish the requisite role of Fn1 and integrin α5β1 in the differentiation of NC cells into VSMCs, thereby regulating the remodeling of symmetrical PAAs into the AAAs. The work of Turlo et al (2012) and Turner et al (2015) demonstrated that following the differentiation of NC cells into VSMCs, signaling by α5-, αv-and β1-containing integrin heterodimers is essential for maintaining VSMCs and the architecture of the AAA vessel wall.…”

“…Known embryonic sources of VSMCs include the lateral and paraxial mesoderm, mesothelia and the NC (Jiang et al, 2000;Le Lievre and Le Douarin, 1975;Que et al, 2008;Rinkevich et al, 2012;Wasteson et al, 2008;Wilm et al, 2005). Studies by others and our lab indicated that integrin α5 is not required for the differentiation of mesodermal cells into VSMCs Turner et al, 2014Turner et al, , 2015. Furthermore, addition of Fn1 to mesodermal VSMC precursors stimulated their proliferation and the synthetic phenotype and opposed their differentiation into smooth muscle cells (Bae et al, 2014;Hedin et al, 1988;Shi et al, 2014).…”

“…Thus, our studies specifically address the role of Fn1 and integrin α5 in the differentiation of multi-potent NC cells into VSMCs. By contrast, Turner et al (2015) used the SM22α-Cre transgenic line to ablate integrins α5 and αv in smooth muscle lineages, including those derived from the NC. SM22α is a marker of early smooth muscle differentiation.…”

“…SM22α is a marker of early smooth muscle differentiation. Thus, the downregulation of integrins α5 and αv in Itga5/Itgav SM22-Cre double mutants has most likely occurred after the onset of VSMC differentiation in the NC, explaining the lack of VSMC differentiation defect in these mutants (Turner et al, 2015). Similarly, Turlo et al (2012) used the SM22α-Cre transgenic line to ablate integrin β1 and showed that the expression of β1-containing integrin heterodimers, which include α5β1, in smooth muscle cells was important for maintaining AAA VSMCs and AAA integrity.…”

Development of Mural Cells: From In Vivo Understanding to In Vitro Recapitulation

“…Typically, VSMC-specific knockout of integrin receptor subunits such as b1 [156], a4 [157], a7 [158], a5, and av [159], but not a5 alone [160], yields similar phenotypes with disturbed mural recruitment and vessel organization. However, these defects are not the result of ablated mural differentiation, but rather impaired migration, proliferation, and association with maturing vessels.…”