Pulsatile shear and Gja5 modulate arterial identity and remodeling events during flow-driven arteriogenesis

Abstract

SUMMARYIn the developing chicken embryo yolk sac vasculature, the expression of arterial identity genes requires arterial hemodynamic conditions. We hypothesize that arterial flow must provide a unique signal that is relevant for supporting arterial identity gene expression and is absent in veins. We analyzed factors related to flow, pressure and oxygenation in the chicken embryo vitelline vasculature in vivo. The best discrimination between arteries and veins was obtained by calculating the maximal pulsatile increase in shear rate relative to the time-averaged shear rate in the same vessel: the relative pulse slope index (RPSI). RPSI was significantly higher in arteries than veins. Arterial endothelial cells exposed to pulsatile shear in vitro augmented arterial marker expression as compared with exposure to constant shear. The expression of Gja5 correlated with arterial flow patterns: the redistribution of arterial flow provoked by vitelline artery ligation resulted in flow-driven collateral arterial network formation and was associated with increased expression of Gja5. In situ hybridization in normal and ligation embryos confirmed that Gja5 expression is confined to arteries and regulated by flow. In mice, Gja5 (connexin 40) was also expressed in arteries. In the adult, increased flow drives arteriogenesis and the formation of collateral arterial networks in peripheral occlusive diseases. Genetic ablation of Gja5 function in mice resulted in reduced arteriogenesis in two occlusion models. We conclude that pulsatile shear patterns may be central for supporting arterial identity, and that arterial Gja5 expression plays a functional role in flow-driven arteriogenesis.

Reduced Heart Rate and Cardiac Output Differentially Affect Angiogenesis, Growth, and Development in Early Chicken Embryos (Gallus domesticus)

“…In ∼3-d-old chicken embryos, the central aorta exhibits very modest cyclic stretch: only an approximately 3% diameter excursion between systole to diastole (Buschmann et al 2010). Vessels more peripheral to the aorta showed no measurable rhythmic distension associated with the cardiac cycle (Buschmann et al 2010). These observations of low vascular compliance in the early chicken embryo, which would create little to no windkessel effect to maintain a diastolic runoff of blood flow, are compatible with the measurements of the current study, showing central aortic blood velocity falling sharply to 0 in early diastole (fig.…”

“…Bradycardia and the associated increased diastolic duration increases pulse pressure in the heart and central arterial vessels in the chicken embryo (Buschmann et al 2010). Increased pulse pressure in turn will create greater blood vessel wall distension (circumferential tension), increasing the degree of mechanical distension on the endothelial cells lining the blood vessels and potentially stimulating angiogenesis through the paracrine effects of VEGF (Groenendijk et al 2007).…”

“…Increased pulse pressure in turn will create greater blood vessel wall distension (circumferential tension), increasing the degree of mechanical distension on the endothelial cells lining the blood vessels and potentially stimulating angiogenesis through the paracrine effects of VEGF (Groenendijk et al 2007). In ∼3-d-old chicken embryos, the central aorta exhibits very modest cyclic stretch: only an approximately 3% diameter excursion between systole to diastole (Buschmann et al 2010). Vessels more peripheral to the aorta showed no measurable rhythmic distension associated with the cardiac cycle (Buschmann et al 2010).…”

“…Angiogenesis results from a complex combination of genetically directed morphogenesis and the influence of local environmental factors, both biochemical and mechanical (e.g., Jones et al 2006;Lee et al 2009;Adams and Eichmann 2010;Buschmann et al 2010;Kaunas et al 2011;Knudsen and Kleinstreuer 2011;Heinke et al 2012;Burggren 2013). Chief among the mechanical influences are both blood pressure and flow (Isogai et al 2003;le Noble et al 2008).…”

“…New vessels and the eventual throughflow of blood occur as a result (see reviews in Groenendijk et al 2007;le Noble et al 2008;Egginton 2011). Arterial (as opposed to venous) identity then arises from the greater pulsatility and shear stresses that eventually emerge in the arterial vasculature (Buschmann et al 2010). Angiogenesis is crucial to the completion of the capillary network and the connecting of developing arteries and veins.…”