Genome-Wide Association Study for Circulating Tissue Plasminogen Activator Levels and Functional Follow-Up Implicates Endothelial STXBP5 and STX2

Abstract

Objective Tissue plasminogen activator (tPA), a serine protease, catalyzes the conversion of plasminogen to plasmin, the major enzyme responsible for endogenous fibrinolysis. In some populations, elevated plasma levels of tPA have been associated with myocardial infarction and other cardiovascular diseases (CVD). We conducted a meta-analysis of genome-wide association studies (GWAS) to identify novel correlates of circulating levels of tPA. Approach and Results Fourteen cohort studies with tPA measures (N=26,929) contributed to the meta-analysis. Three loci were significantly associated with circulating tPA levels (P <5.0×10−8). The first locus is on 6q24.3, with the lead SNP (rs9399599, P=2.9×10−14) within STXBP5. The second locus is on 8p11.21. The lead SNP (rs3136739, P=1.3×10−9) is intronic to POLB and less than 200kb away from the tPA encoding gene PLAT. We identified a non-synonymous SNP (rs2020921) in modest LD with rs3136739 (r2 = 0.50) within exon 5 of PLAT (P=2.0×10−8). The third locus is on 12q24.33, with the lead SNP (rs7301826, P=1.0×10−9) within intron 7 of STX2. We further found evidence for association of lead SNPs in STXBP5 and STX2 with expression levels of the respective transcripts. In in vitro cell studies, silencing STXBP5 decreased release of tPA from vascular endothelial cells, while silencing of STX2 increased tPA release. Through an in-silico lookup, we found no associations of the three lead SNPs with coronary artery disease or stroke. Conclusions We identified three loci associated with circulating tPA levels, the PLAT region, STXBP5 and STX2. Our functional studies implicate a novel role for STXBP5 and STX2 in regulating tPA release.

Platelet secretion and hemostasis require syntaxin-binding protein STXBP5

“…This requirement of STXBP5 for platelet exocytosis diverges from the protein's proposed role as a negative regulator in neuronal cell, neuroendocrine cell, and EC secretion (21,24,39,47). Our present data indicate that STXBP5 may be important for cardiovascular health, as echoed in recent GWAS in which STXBP5 has been linked to thrombosis (14)(15)(16)(17)(18)(19)(20).…”

“…GWAS have linked SNPs in STXBP5 to alterations in vWF levels (14-19) and tPA levels (18). Loss of STXBP5 increases vWF release from ECs (47), but decreases tPA release (20). These results highlight potentially conflicting roles for STXBP5 in ECs, which may relate to which granules are being released.…”

“…Deletions in the Stxbp5 gene are linked to autism (36). GWAS show genetic variations in Stxbp5 are linked with increased plasma levels of vWF (14)(15)(16)(17)(18)(19), alterations in tissue plasminogen activator (tPA) levels (20), venous thrombosis (16), and arterial thrombosis (19). Specifically, 1 SNP that produces a nonsynonymous mutation (N436S) was associated with increased bleeding (18).…”

Rare variant associations with waist-to-hip ratio in European-American and African-American women from the NHLBI-Exome Sequencing Project

“…40 Meanwhile, some rare homozygous null mutations in IKBKB have been reported in patients with severe combined immunodeficiency, which result in IKKβ loss of expression and therefore impairment of immune activation. 41 Additionally, a reported GWAS signal near IKBKB downstream for the phenotype tissue plasminogen level is in partial LD with a coding variant in the tissue plasminogen activator (PLAT) gene (MIM, 173370) nearby, 42 which suggests that central adiposity with insulin resistance may be correlated with plasminogen activator through IKBKB. Interestingly, our results showed IKBKB rare variants were associated with reduced WHRs which suggested that they are protective against abdominal obesity (Figure 1a).…”

New Pathway for Tissue-Type Plasminogen Activator Regulation

“…It still remains unknown the extent to which a common secretory pathway may contribute to the correlation between plasma levels of tPA and von Willebrand factor, which is estimated as r=≈0. 3,8 because the associations at STXBP5 and STX2 do not account for this covariation.…”