Syntaxin-binding protein STXBP5 inhibits endothelial exocytosis and promotes platelet secretion
Qiuyu Zhu, … , Craig N. Morrell, Charles J. Lowenstein
Qiuyu Zhu, … , Craig N. Morrell, Charles J. Lowenstein
Published October 1, 2014; First published September 17, 2014
Citation Information: J Clin Invest. 2014;124(10):4503-4516. https://doi.org/10.1172/JCI71245.
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Research Article

Syntaxin-binding protein STXBP5 inhibits endothelial exocytosis and promotes platelet secretion

Abstract

In humans, vWF levels predict the risk of myocardial infarction and thrombosis; however, the factors that influence vWF levels are not completely understood. Recent genome-wide association studies (GWAS) have identified syntaxin-binding protein 5 (STXBP5) as a candidate gene linked to changes in vWF plasma levels, though the functional relationship between STXBP5 and vWF is unknown. We hypothesized that STXBP5 inhibits endothelial cell exocytosis. We found that STXBP5 is expressed in human endothelial cells and colocalizes with and interacts with syntaxin 4. In human endothelial cells reduction of STXBP5 increased exocytosis of vWF and P-selectin. Mice lacking Stxbp5 had higher levels of vWF in the plasma, increased P-selectin translocation, and more platelet-endothelial interactions, which suggests that STXBP5 inhibits endothelial exocytosis. However, Stxbp5 KO mice also displayed hemostasis defects, including prolonged tail bleeding times and impaired mesenteric arteriole and carotid artery thrombosis. Furthermore, platelets from Stxbp5 KO mice had defects in platelet secretion and activation; thus, STXBP5 inhibits endothelial exocytosis but promotes platelet secretion. Our study reveals a vascular function for STXBP5, validates the functional relevance of a candidate gene identified by GWAS, and suggests that variation within STXBP5 is a genetic risk for venous thromboembolic disease.

Authors

Qiuyu Zhu, Munekazu Yamakuchi, Sara Ture, Maria de la Luz Garcia-Hernandez, Kyung Ae Ko, Kristina L. Modjeski, Michael B. LoMonaco, Andrew D. Johnson, Christopher J. O’Donnell, Yoshimi Takai, Craig N. Morrell, Charles J. Lowenstein

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Figure 1

STXBP5 expression and transcript variants.

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STXBP5 expression and transcript variants. (A) STXBP5 expression in huma...
(A) STXBP5 expression in human ECs. Lysates of cultured HAECs, HUVECs, and HDMVECs were probed by IB with antibody against STXBP5. Blotting to β-actin was used as a loading control. Representative of 3 separate experiments. (B) Stxbp5 expression in murine tissue. RNA was isolated from WT mouse tissues, and Stxbp5 mRNA expression was measured by qPCR and normalized to mRNA level in brain (n = 3). (C) Human STXBP5 transcript variants. STXBP5 transcript variants were detected by RT-PCR using primers flanking splice region in human brain, HUVECs, human platelets, and HEK293 cells. The products were separated by agarose gel, sequenced, and compared with NCBI reference sequences (STXBP5-X1, PCR product 370 bp in length, 99% similarity to NCBI entry; STXBP5-X2, 322 bp, 95% similarity; STXBP5-2, 307 bp, 100% similarity; STXBP5-X3, 262 bp, 100% similarity; STXBP5-1, 199 bp, 100% similarity). (D) Relative abundance of STXBP5 transcript variants in human brain, HUVECs, and human platelets, measured by qPCR using variant-specific Taqman probes and expressed relative to brain STXBP5-1 (assigned as 100%) (n = 3). All data are mean ± SD.