Let It Flow: Morpholino Knockdown in Zebrafish Embryos Reveals a Pro-Angiogenic Effect of the Metalloprotease Meprin α2

Abstract

BackgroundMeprin metalloproteases are thought to be involved in basic physiological functions such as cell proliferation and tissue differentiation. However, the specific functions of these enzymes are still ambiguous, although a variety of growth factors and structural proteins have been identified as meprin substrates. The discovery of meprins α1, α2 and β in teleost fish provided the basis for uncovering their physiological functions by gene silencing in vivo.Methodology/Principal FindingsA Morpholino knockdown in zebrafish embryos targeting meprin α1 and β mRNA caused defects in general tissue differentiation. But meprin α2 morphants were affected more specifically and showed severe failures in the formation of the vascular system provoking the hypothesis of a pro-angiogenic effect. The blood circulation was largely diminished resulting in erythrocyte accumulation. These phenotypes mimic a previously described VEGF-A morphant, revealing a possible role of meprin α in VEGF-A activation. Indeed, human recombinant meprin α processed the vascular endothelial growth factor-A (VEGF-A) specifically, revealing the same cleavage products detectable for VEGF from zebrafish whole lysate.Conclusions/SignificanceOur results demonstrate that meprin metalloproteases are important for cell differentiation and proliferation already during embryogenesis, predominantly by the activation of growth factors. Thus, we conclude that meprins play a significant role in VEGF-A processing, subsequently regulating angiogenesis. Therefore, meprin α might be a new therapeutic target in cardiovascular diseases or in tumor growth inhibition.