The WNT antagonist Dickkopf2 promotes angiogenesis in rodent and human endothelial cells

Abstract

Neovessel formation is a complex process governed by the orchestrated action of multiple factors that regulate EC specification and dynamics within a growing vascular tree. These factors have been widely exploited to develop therapies for angiogenesis-related diseases such as diabetic retinopathy and tumor growth and metastasis. WNT signaling has been implicated in the regulation and development of the vascular system, but the detailed mechanism of this process remains unclear. Here, we report that Dickkopf1 (DKK1) and Dickkopf2 (DKK2), originally known as WNT antagonists, play opposite functional roles in regulating angiogenesis. DKK2 induced during EC morphogenesis promoted angiogenesis in cultured human endothelial cells and in in vivo assays using mice. Its structural homolog, DKK1, suppressed angiogenesis and was repressed upon induction of morphogenesis. Importantly, local injection of DKK2 protein significantly improved tissue repair, with enhanced neovascularization in animal models of both hind limb ischemia and myocardial infarction. We further showed that DKK2 stimulated filopodial dynamics and angiogenic sprouting of ECs via a signaling cascade involving LRP6-mediated APC/Asef2/Cdc42 activation. Thus, our findings demonstrate the distinct functions of DKK1 and DKK2 in controlling angiogenesis and suggest that DKK2 may be a viable therapeutic target in the treatment of ischemic vascular diseases.

The Wnt pathway and the roles for its antagonists, DKKS, in angiogenesis

“…Interestingly, Dkk-1 expression is upregulated during endothelial cell differentiation in vitro. Upon plating on Matrigel, Dkk-1 is rapidly downregulated during tubular network formation of endothelial cells (65). These data suggest a Dkk-1 role in endothelial cell function during neovascularization.…”

“…In support of this, recent findings that Dkks play important roles in angiogenesis provide further insight into the potential of secreted Wnt antagonists in angiogenesis. In particular, Dkk-2 shows profound therapeutic effects in two ischemic disease models (65). Furthermore, neovessels induced by Dkk-2 are more functional and normal compared to VEGFinduced neovessels (65), demonstrating an advantage over other angiogenic factors.…”

“…During embryogenesis in mice, Dkk-1 expression is temporally and spatially regulated, which gives Dkk-1 the potential to regulate anterior-posterior axial pattern formation, including head induction. At later stages of development and after birth, Dkk-1 expression is detected in the aorta and retinal vasculature, respectively (64,65). Dkk-1 expression is also observed in human endothelial cells cultured in vitro.…”

“…Recently, we demonstrated that endothelial cell-specific expression of Dkk-2 leads to a retinal vascular phenotype opposite that of Dkk-1. Dkk-2 overexpression in endothelial cells increases vessel density, number of tip cells, and filopodia extension in mouse retina (65). Furthermore, Dkk-2 treatment promotes angiogenesis in ischemic animal models, including hindlimb ischemia and myocardial infarction models.…”

“…Wnt signaling is overactivated and retinal neovascularization develops in the oxygen-induced retinopathy mouse model, also, which is attenuated by Dkk-1 (66). Recently, we showed that endothelial cell-specific overexpression of Dkk-1 in mice results in significant vessel defects, including reduction of radial vessel expansion and the number of tip cells and filopodia in the retina (65). Conflicting results regarding the role of Dkk-1 in angiogenesis have been reported.…”