Loss of Smad4 drives vascular malformations via c-KIT–dependent high–fluid shear stress mimicry
Johannes Gahn, Fan Wu, Qing Zhang, Yuxi Di, Tanmaya Behera, Yonggang Ren, Zohrah Hashemi, Kuheli Banerjee, Julio Cordero, Claudia Gherman, Kornelia Andorfer, Caroline T. Seebauer, Fatemeh Mirzapour-Shafiyi, Gergana Dobreva, Martin A. Schwartz, Roxana Ola
Johannes Gahn, Fan Wu, Qing Zhang, Yuxi Di, Tanmaya Behera, Yonggang Ren, Zohrah Hashemi, Kuheli Banerjee, Julio Cordero, Claudia Gherman, Kornelia Andorfer, Caroline T. Seebauer, Fatemeh Mirzapour-Shafiyi, Gergana Dobreva, Martin A. Schwartz, Roxana Ola
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Research Article Cell biology Genetics Vascular biology

Loss of Smad4 drives vascular malformations via c-KIT–dependent high–fluid shear stress mimicry

Abstract

Vascular endothelial cells (ECs) encode a homeostatic fluid shear stress (FSS) set point that is essential for vascular stability. Deviations above or below this threshold trigger adaptive remodeling to restore physiological shear levels. Disruption of this control mechanism leads to enlarged arteriovenous malformations (AVMs) in hereditary hemorrhagic telangiectasia, a vascular disorder caused by heterozygous loss-of-function (LOF) mutation in ALK1, ENG, or SMAD4. Mechanistically, Smad4-deficient ECs are reset to a lower FSS set point value, resulting in AVMs that show characteristics of high-FSS remodeling with elevated KLF4 and high activation of the downstream Akt. Here, we investigated the KLF4/Akt upstream mechanisms by which SMAD4 sets the physiological FSS set point. We identified the receptor tyrosine kinase c-KIT as a component and regulator of the junctional mechanosensory receptor complex, which is highly upregulated in murine and human AVMs. SMAD4 restrains flow signaling by limiting c-KIT–dependent ERK5 activation and KLF4 induction. Thus, SMAD4 LOF leads to sustained c-KIT engagement in the sensory junctional apparatus, driving enhanced and prolonged activation of the ERK5/KLF4/Akt signaling axis. These results show that Smad4-LOF mutations induce malformations by disabling a key homeostatic mechanism and identify c-KIT as a potentially previously unrecognized therapeutic target.

Authors

Johannes Gahn, Fan Wu, Qing Zhang, Yuxi Di, Tanmaya Behera, Yonggang Ren, Zohrah Hashemi, Kuheli Banerjee, Julio Cordero, Claudia Gherman, Kornelia Andorfer, Caroline T. Seebauer, Fatemeh Mirzapour-Shafiyi, Gergana Dobreva, Martin A. Schwartz, Roxana Ola

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Figure 2

SMAD4 restricts junctional signals upstream of MEKK3/ERK5/KLF4/Akt activation.

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SMAD4 restricts junctional signals upstream of MEKK3/ERK5/KLF4/Akt activ...
(A, D, and G) WB for the indicated proteins in HUVECs transfected with CTRL or SMAD4 siRNAs subjected to 12 dynes/cm2 for 2 h and treated with DMSO or PP2 inhibitor (A) or transfected additionally with CD31, CDH5, and KDR/FLT4 siRNAs (D) or with MEKK3 siRNA (G). (B, E, and H) Quantification of ERK5 gel shift (upper band, quantified by densitometry) and of p-Akt normalized to total Akt, respectively (n = 4/group in B and H; n = 3/group in E). (C, F, and I) KLF4 fold-change in the indicated genotypes and treatment conditions; n = 6/group in C and F; n = 4/group in I. (J) Colabeling of Smad4fl/fl and Smad4iΔEC P6 retinas with p-ERK5 (green, upper panel), KLF4 (green, middle panel), pS6 (green, lower panel), and Isolectin B4 (IB4, white). Red, blue, and yellow arrowheads indicate arteries (a), veins (v), and capillaries, respectively. Scale bar: 50 μm. (K) Quantification of pERK5, KLF4, and pS6 in retina vascular plexus was calculated by normalizing fluorescence intensity threshold value per IB4+ vascular plexus capillary area (%) in Smad4fl/fl and Smad4iΔEC neonates (n = 3 retinas per genotype). Data are represented as mean ± SEM. Two-way ANOVA (B, C, E, F, H, and I) and Student’s t test (K) were used to determine statistical significance. *P < 0.05, **P < 0.01, ***P < 0.005, ****P < 0.001.